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We demonstrate adaptive phenotypic plasticity (PP) in Neochromis greenwoodi, a rock-dwelling haplochromine cichlid from Lake Victoria. Adaptive phenotypic plasticity will enhance the chance of survival and reproduction in changing or novel environments. For rock-dwelling cichlids it may contribute to the success of settlement after migration between rocky outcrops or islands, since newly colonized patches of rock may offer different food regimes and different competitors. In our experiments, we simulated such situations by raising fry on different diets and with different competitors. We chose diet treatments in such a way that we could predict the direction of anatomical changes from functional demands. We expected an indirect effect of interspecific competition: selectively removing one prey-type by the competing species would leave N. greenwoodi with the other. We found the predicted phenotypic responses to food in trophic traits of N. greenwoodi. However, in the current experimental set-up we did not find a differentiating effect of species of competitor. We discuss the possible role of PP in allopatric and sympatric speciation. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 77, 185−192.

The ability to tolerate hypoxia in some haplochromine cichlid fishes contributes to the richness of habitats occupied by the lineage and may be important in interlacustrine dispersal through swampy channels. Lacustrine members of the genus Astatotilapia tend to be ecologically plastic but are rarely encountered in the interior of dense swamps. A notable exception is seen in the swamp corridor that joins Lake Kabaleka with Lake George, Uganda, where one species (Astatotilapia ‘wrought-iron’) is abundant, and a second species, A. aeneocolor, is rare. Both species are abundant in the open waters of the main lake. In this paper, we compare physiological (oxygen consumption) and behavioral indicators of hypoxia tolerance between A. ‘wrought-iron’ from swamp and open-water habitats and between the two species of Astatotilapia. When exposed to progressive hypoxia, all fish used aquatic surface respiration (ASR); however, swamp-dwelling A. ‘wrought-iron’ showed lower gill ventilation rates prior to the initiation of ASR, higher pre-ASR aggression rates, higher swimming speed during ASR, and a higher rate of bubble exchange than both the open-water group of A. ‘wrought-iron’ and A. aeneocolor. These differences may reflect interpopulational variation in selection pressure for low-oxygen tolerance between swamp and open-water habitats. Several lines of evidence suggest that A. ‘wrought-iron’ was in general more hypoxia tolerant than A. aeneocolor. These include a lower ASR90 threshold, a drop in gill ventilation rate with the onset of ASR, and lower rate of equilibrium loss under extreme hypoxia in A. ‘wrought-iron’. The routine metabolic rate and critical oxygen tension did not differ between swamp-dwelling and open-water A. ‘wrought-iron’, or between A. ‘wrought-iron’ and A. aeneocolor. Comparative data on the ASR thresholds and critical oxygen tensions of the Astatotilapia species from Lake Kabaleka and other East African cichlids suggest intermediate hypoxia tolerance. Nevertheless, our study suggests that some generalized lacustrine haplochromines may ‘leak’ through swamp corridors even under relatively extreme conditions.

An exploratory analysis was made of the head shape of cichlid fishes. A 3-D head truss was used, which allowed approximations of the volumes of three compartments of the head. We applied the method to six species of rock-dwelling haplochromine cichlids, of which we studied 12 populations from four rocky islands in the southern part of Lake Victoria. Head shape was correlated with eight environmental variables. Truss distances and compartment volumes correlated with these variables, e.g. volumes of the compartments containing the gills correlated (negatively) with oxygen levels; truss distances, including the oral jaws and their musculature, correlated with food composition; and eye size correlated with width of the transmission spectrum. Another finding was the likely architectonic interactions between anatomical elements. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76, 39–48.

Lake Tanganyika, the oldest of the East African Great Lakes, harbors the ecologically, mor- phologically, and behaviorally most complex of all assemblages of cichlid eshes, consisting of about 200 described species. The evolutionary old age of the cichlid assemblage, its extreme degree of mor- phological differentiation, the lack of species with intermediate morphologies, and the rapidity of lineage formation have made evolutionary reconstruction difecult. The number and origin of seeding lineages, particularly the possible contribution of riverine haplochromine cichlids to endemic lacus- trine lineages, remains unclear. Our phylogenetic analyses, based on mitochondrial DNA sequences of three gene segments of 49 species (25% of all described species, up to 2,400 bp each), yield ro- bust phylogenies that provide new insights into the Lake Tanganyika adaptive radiation as well as into the origin of the Central- and East-African haplochromine faunas. Our data suggest that eight ancientAfrican lineages may haveseededthe Tanganyikan cichlid radiation.Oneof theseseeding lin- eages, probably comprising substrate spawning Lamprologus-like species, diversieed into six lineages that evolved mouthbrooding during the initial stage of the radiation. All analyzed haplochromines from surrounding rivers and lakes seem to have evolved within the radiating Tanganyikan lineages. Thus, our endingscontradictthe current hypothesis thatancestralriverinehaplochrominescolonized Lake Tanganyika to give rise to at least part of its spectacular endemic cichlid species assemblage. Instead, the early phases of the Tanganyikan radiation affected Central and East African rivers and lakes. The haplochromines may have evolved in the Tanganyikan basin before the lake became a hydrologically and ecologically closed system and then secondarily colonized surrounding rivers. Apparently, therefore, the current diversity of Central and East African haplochromines represents a relatively young and polyphyletic fauna that evolved from or in parallel to lineages now endemic to Lake Tanganyika. (Adaptive radiation; Cichlidae; Lake Tanganyika; mitochondrial DNA sequences; molecular phylogeny; species eock.)

Background The factors determining sex are diverse in vertebrates and especially so in teleost fishes. Only a handful of master sex-determining genes have been identified, however great efforts have been undertaken to characterize the subsequent genetic network of sex differentiation in various organisms. East African cichlids offer an ideal model system to study the complexity of sexual development, since many different sex-determining mechanisms occur in closely related species of this fish family. Here, we investigated the sex-determining system and gene expression profiles during male development of Astatotilapia burtoni, a member of the rapidly radiating and exceptionally species-rich haplochromine lineage. Results Crossing experiments with hormonally sex-reversed fish provided evidence for an XX-XY sex determination system in A. burtoni. Resultant all-male broods were used to assess gene expression patterns throughout development of a set of candidate genes, previously characterized in adult cichlids only. Conclusions We could identify the onset of gonad sexual differentiation at 11–12 dpf. The expression profiles identified wnt4B and wt1A as the earliest gonad markers in A. burtoni. Furthermore we identified late testis genes (cyp19a1A, gsdf, dmrt1 and gata4), and brain markers (ctnnb1A, ctnnb1B, dax1A, foxl2, foxl3, nanos1A, nanos1B, rspo1, sf-1, sox9A and sox9B). Electronic supplementary material The online version of this article (doi:10.1186/s12863-014-0140-5) contains supplementary material, which is available to authorized users.

A critical step for speciation in the face of gene flow is the origination of reproductive isolation. The evolution of assortative mating greatly facilitates this process. Assortative mating can be mediated by one or multiple cues across an array of sensory modalities. We here explore possible cues that may underlie female mate choice in a sympatric species pair of cichlid fish from Lake Victoria, Pundamilia pundamilia and Pundamilia nyererei. Previous studies identified species-specific female preferences for male coloration, but effects of other cues could not be ruled out. Therefore, we assessed female choice in a series of experiments in which we manipulated visual (color) and chemical cues. We show that the visibility of differences in nuptial hue (i.e., either blue or red) between males of the 2 species is necessary and sufficient for assortative mating by female mate choice. Such assortment mediated by a single cue may evolve relatively quickly, but could make reproductive isolation vulnerable to environmental changes. These findings confirm the important role of female mate choice for male nuptial hue in promoting the explosive speciation of African haplochromine cichlids.

To date, about 330 currently recognized species have been described from the haplochromine cichlid species flock endemic to Lake Malaŵi, Africa. Several hundred additional species await taxonomic treatment. A new species from this flock belonging to the genus Otopharynx is described from the deep waters of Lake Malaŵi. This species (known from only two demersal trawls made at different localities in water 78–135 m deep) is characterized by the presence of three distinct spots that do not extend to the dorsum and by moderately stout, bicuspid oral jaw teeth in outer series, placing it in the genus Otopharynx. It is a relatively deep-bodied member of this genus that differs from all other three-spotted cichlids by its fleshy, lobed lips. The greatly hypertrophied lips in this species may serve a sensory function by acting as an enlarged substrate for the expression of numerous taste buds in a peri-oral field. Additional characters are presented that distinguish this new species from its congeners. ...

During the 1980s, the zooplanktivorous cyprinid dagaa (Rastrineobola argentea) expanded its habitat in Lake Victoria. After the eradication of the zooplanktivorous haplochromine cichlids from the sublittoral waters of the Mwanza Gulf (Tanzania) by introduced Nile perch (Lates niloticus), adult dagaa started to explore the bottom zone during daytime. This main daytime habitat for zooplankton and macrobenthic invertebrates was formerly occupied by the haplochromines. Besides extending its range of vertical distribution, dagaa started to include macrobenthic invertebrates in its diet. In this paper, we present two rapid morphological adaptations of dagaa to its new niche. Samples from 1988, only one year after daytime bottom dwelling became a common habit in dagaa, showed a higher number of gill filaments in comparison with samples from 1983. In contrast, the same samples showed a decrease in the number of gill rakers. The observed increase in the number of gill filaments is postulated to have improved the capacity of dagaa to extract oxygen from the water, which may be crucial to survive the relatively poor oxygen conditions in the new habitat. By decreasing the number of gill rakers dagaa has probably increased its efficiency of feeding on relatively large prey in a benthic habitat.

Respiratory characters of three east African haplochromine cichlid species that differ in their use of hypoxic wetlands were examined to consider the potential of dissolved oxygen as one factor affecting habitat use. All three species had a large gill surface area, ranging from the 67th (Pseudocrenilabrus multicolor victoriae) to 98th (Astatotilapia velifer) percentile of the known gill size range for freshwater fishes. Pseudocrenilabrus multicolor victoriae was the most tolerant to hypoxia exhibiting the lowest aquatic surface respiration (R S ) thresholds and lowest critical oxygen tension of the three species. Astatotilapia velifer had the highest ASR thresholds, gill ventilation rates, and level of surface activity of the three species, indicating a relatively low tolerance to hypoxia. Prognathochromis venator was intermediate in its response to hypoxia. These findings are discussed in light of survivorship and distribution patterns of these species following Nile perch introduction into Lake Nabugabo.

Fatty acid composition in the muscle of eight endemic haplochromine cichlids and one tilapiine cichlid from Lake Malawi was studied by gas-liquid chromatography. The species studied represent a wide variety of niches: Algae combing, shell crushing, feeding on littoral and semipelagic zooplankton, detecting invertebrates hidden in the sediment using expanded lateral line canals, and fish predation in littoral and bathypelagic zones. The sampling was done during the early rainy season. The analysis of fatty acid composition suggests that, despite the reported plasticity in feeding, the niches of the species studied are established and stable. The proportion of eicosapentaenoic acid (20:5n-3) in relation to arachidonic acid (20:4n-6) illustrated the position of these species in the foodweb: equal proportions in algae feeders and clear 20: 4n-6 dominance in species feeding on benthic prey. Although the number of replicates was small, discriminant analysis with 31 fatty acids separated the specimens into dense centers according to species. These results encourage the use of chemometric methods for studying ecological relationships among freshwater fauna and ongoing evolutionary processes.

According to a widely held view, the more than 300 species of haplochromine cichlid fishes in Lake Victoria (LV), East Africa, originated from a single founder species in less than 12,000 years. This view, however, does not follow from the published geological and molecular evidence. The former does indeed suggest that the LV basin dried out less than 15,000 years ago, but it does not provide any information about the species that re-colonized the new lake or that remained in the rivers draining the area. The molecular evidence is inconclusive with respect to the origin of the LV haplochromines because cichlids from critical regions around LV were not adequately sampled; and as far as the age of the LV haplochromines is concerned, it in fact led to an estimate of 250,000-750,000 years old. In the present study, mitochondrial DNA (control region) variation was determined by heteroduplex and sequencing analyses of more than 670 specimens collected at widely distributed East African riverine and lacustrine localities. The analyses revealed the existence of seven haplogroups (I-VII) distinguishable by characteristic substitutions. All endemic LV samples tested fell into one of these haplogroups (V) which, however, was also found to be present at various other localities, both riverine and lacustrine, outside LV. Within this haplogroup, four subgroups (VA through VD) could be distinguished, two of which (VB and VC) were represented in LV and at other localities. The great majority of the LV haplochromine species could be classified as belonging to the VC subgroup, which was found only in LV and in the rivers draining into it. Hence, while the endemic haplochromine species of LV could not have originated from a single founding population, the lake does harbour a large species flock which probably arose in situ.

This study looked for evidence of trophic shifts in the diet of two predatory catfishes (Bagrus docmac and Schilbe intermedius) following the establishment of introduced Nile perch (Lates niloticus) into lakes of the Lake Victoria basin. Bagrus docmac exhibited a shift from a primarily piscivorous diet dominated by haplochromine cichlids to a broader diet that included a significant proportion of invertebrates and the cyprinid fish, Rastrineobola argentea, which became abundant following depletion of the haplochromines. Schilbe intermedius exhibited a trophic shift from a piscivorous diet dominated by haplochromines to an insectivorous diet. The flexibility in diet exhibited by these two catfishes may have permitted these species to persist, albeit in reduced numbers, subsequent to the introduction of Nile perch and may facilitate resurgence as fishing pressure reduces numbers of large Nile perch. Resume Cette etude cherchait des preuves d'une evolution dans le regime alimentaire de deux poissons-chats predateurs (Bagrus docmac et Schilbe intermedius), suite a l'installation de la perche du Nil (Lates niloticus) introduite dans les lacs du bassin du Lac Victoria. Bagrus docmac presentait une evolution d'un regime au depart piscivore, domine par les cichlides haplochromines, vers un regime plus ouvert qui comprend une proportion significative d'invertebres et du cyprin Rastrineobola argentea, qui est devenu abondant suite a la rarefaction des haplochromines. Schilbe intermedius a manifeste une evolution d'un regime piscivore domine par les haplochromines vers un regime insectivore. La flexibilite alimentaire manifestee par ces deux poissons-chats peut avoir permis a ces deux especes de survivre, encore qu’en nombre restreint, a l'introduction de la perche du Nil et pourrait faciliter leur recuperation alors que la pression de la peche reduit le nombre de grosses perches du Nil.

The nucleotide sequences of the first internal transcribed spacer (ITS-1) of the ribosomal RNA gene cluster have been determined for 11 species of closely related endemic cichlid fishes of the Lake Victoria region (LVR) and 6 related East African cichlids. The ITS-1 sequences confirmed independently derived basal phylogenies, but provide limited insight within this species flock. The line leading to Pseudocrenilabrus multicolor arose early, close to the divergence event that separated the tilapiine and haplochromine tribes of the “African Group” of the family Cichlidae. In this phylogeny, Astatoreochromis alluaudi and the riverine Astatotilapia burtoni are sister taxa, which together are a sister group to a monophyletic assemblage including both Lake Victoria and Lake Edward taxa. The ITS-1 data support the monophyly of haplochromine genera across lakes. Since Lake Victoria is believed to have been dry between 14,500 and 12,400 BPE, the modern assemblage must have been derived from reinvasion by the products of earlier cladogenesis events. Thus, although the regional superflock is monophyletic, the haplochromines of Lake Victoria itself did not evolve in situ from a single ancestor.

Nile perch Lates niloticus is an exotic predator that has had profound effects on fish communities in lakes where it has been introduced. Length–weight relationships of Nile perch in lakes Victoria, Kyoga and Nabugabo were examined to see how they had changed following the depletion of its haplochromine prey. Length–weight relationships in the new habitats were compared to those in Lake Albert and other native habitats of the Nile perch. The length to weight ratios in the new habitats were initially higher than in Lake Albert and other native habitats. After the haplochromines had been depleted, they declined to values below those of Lake Albert and most native habitats to the lowest value known. They have remained at this level for at least 15 years in Lake Kyoga, where Nile perch was introduced earliest. A similar pattern is developing in lakes Victoria and Nabugabo. Further stress on the prey population could depress the weight to length ratios to levels where it could affect the health of Nile perch stocks and make its fishery unviable. Therefore, human exploitation of Nile perch prey should be avoided. An alternative would be to heavily fish the Nile perch to increase the prey to predator ratio.

Twelve short tandem repeat markers were successfully isolated from a cichlid, Haplochromis chilotes, in Lake Victoria, and characterized in Haplochromis pyrrhocephalus. The microsatellite regions of these markers were found to have between two and 48 alleles with heterozygosity ranging from 0.07 to 0.97. No loci showed significant departures from the Hardy-Weinberg or linkage equilibrium after the Bonferroni correction (P > 0.05). Cross-species amplification in other cichlids of Lake Victoria, Haplochromis laparogramma, Lithochromis rubripinnis, L. rufus and Haplochromis sp. 'rockkribensis', was successful.

Eight tetranucleotide microsatellite loci were isolated from the haplochromine cichlid fish, Pseudocrenilabrus multicolor victoriae , an important model species for studies in respiratory ecology, conservation, and evolution. We surveyed variation at these loci in 23 individuals from western Uganda, finding four to 19 alleles per locus and an average expected heterozygosity of 0.8575. These microsatellite loci will be used to examine gene flow and population structure in Ugandan P. m. victoriae .

Mate choice may play an important role in animal speciation. The haplochromine cichlids of Lake Victoria are suitable to test this hypothesis. Diversity in ecology, coloration and anatomy evolved in these fish faster than postzygotic barriers to gene flow, and little is known about how this diversity is maintained. It was tested whether recognizable forms are selection-maintained morphs or reproductively isolated species by investigating in the field reproductive timing, location of spawning sites, and mate choice behaviour. There was a large interspecific overlap in timing of breeding and location of spawning sites, which was largest in members of the same genus. Behavioural mate choice of such closely related taxa was highly assortative, such that it is likely that they are sexually isolated species and that direct mate choice is the major force that directs gene flow and maintains form diversity. The results differ from what is known about recent radiations of other lacustrine fish groups where speciation seems to be driven by diverging microhabitat preferences or diverging timing of reproduction, but are in agreement with predictions from models of speciation by diverging mate preferences.

Phylogenetic trees for groups of closely related species often have different topologies, depending on the genes used. One explanation for the discordant topologies is the persistence of polymorphisms through the speciation phase, followed by differential fixation of alleles in the resulting species. The existence of transspecies polymorphisms has been documented for alleles maintained by balancing selection but not for neutral alleles. In the present study, transspecific persistence of neutral polymorphisms was tested in the endemic haplochromine species flock of Lake Victoria cichlid fish. Putative noncoding region polymorphisms were identified at four randomly selected nuclear loci and tested on a collection of 12 Lake Victoria species and their putative riverine ancestors. At all loci, the same polymorphism was found to be present in nearly all the tested species, both lacustrine and riverine. Different polymorphisms at these loci were found in cichlids of other East African lakes (Malawi and Tanganyika). The Lake Victoria polymorphisms must have therefore arisen after the flocks now inhabiting the three great lakes diverged from one another, but before the riverine ancestors of the Lake Victoria flock colonized the Lake. Calculations based on the mtDNA clock suggest that the polymorphisms have persisted for about 1.4 million years. To maintain neutral polymorphisms for such a long time, the population size must have remained large throughout the entire period.

— Resource partitioning was studied on four assemblages of haplochromine cichlids at rocky islands in the southern part of Lake Victoria. The emphasis was put on diet segregation, while data on microhabitat segregation were mainly used to determine potential competitors for food. Diet and microhabitat segregation were demonstrated in all four assemblages. In one of the assemblages we observed little partitioning of resources among two filamentous algae feeders. The role of competition for food is discussed on the basis of fluctuations in diet overlap in relation to seasonal changes in food supply. Diet overlap proved to be highest in periods of food abundance. This is in concordance with the hypothesis that competition decreases in case of food abundance. Furthermore, we compared fish densities between assemblages, because competition would regulate density. We found that diets were most diverse in the assemblage with lowest fish density, while interspecific differences in diet were smallest. Food seems not to be limiting in this particular assemblage, and factors other than competition for food are probably more important in regulating density here.

— The microdistribution of ten numerically dominant species in a fish community at a rocky island in Lake Victoria was studied using invasive sampling. All were haplochromine cichlids. The community was characterized by high fish densities and by a dominance of Aufwuchs feeders. Species were non-randomly distributed, showing significant associations with water depth and other topographic parameters. Species occupied unique positions in a network of recurrent species groups. Niche partitioning through differential microdistribution was even more subtle than that reported for Lake Malawi's rock-dwelling cichlids. Species-specific microdistribution fitted qualitative predictions from ideal free distribution models with asymmetrical interference competition for food. No evidence was found for interspecific contest competition for space. Temporal niche shifts have been observed between periods of high and low water levels. Owing to a combination of reduced habitat availability with niche expansion in most species, niche overlap was larger during the lowwater period.

The mechanisms responsible for the explosive radiations of haplochromine cichlid fishes in Africa's great lakes remain controversial. Since species thought to be closely related often differ most apparendy in male breeding colours, I examined patterns of male colour variation in rock-dwelling cichlids from Lake Malawi to test whether initial divergence between species is likely to have been caused by adaptation to differing habitats, by selection against hybridization (reinforcement or character displacement), or by sexual selection. I found that all significant variation in overall male colour occurs within, not between, species complexes, in contrast to variation in habitat and behavioural traits, which differed significandy between complexes. Male colour does not vary significandy with habitat characteristics such as water depth, and sympatric species differ no more in colour than allopatric ones. These results fail to provide support for adaptation or reinforcement as initial causes of colour divergence, and are consistent with the possibility that divergence may instead have been caused by sexual selection, but a direct test of sexual selection is not yet possible.

The phylogeny of the haplochromine cichlids of Lake Kivu was studied using lepidological characters. Only one species, Haplochromis astatodon was found to have a closer relationship to a group outside Lake Kivu, namely Haplochromis sensu stricto. The other 14 species form a monophyletic lineage that is part of a subdivision in the large Lake Victoria-Edward-Kivu flock. The internal phylogeny of this lineage was resolved to the species level.

Introduction of the exotic Nile perch (Lates niloticus) into Africa's Lake Victoria accelerated decline of the diverse, endemic ichthyofauna, altered food web struc- ture, and created valuable fisheries. As the Nile perch population expanded and predation rates increased, many of the endemic fish species disappeared, total fishery yield increased nearly fourfold, and fishery-related employment approximately doubled. Ecological changes in this system now occur rapidly, are due largely to human actions, and have profound socioeconomic effects. We used a bioenergetics model of Nile perch predation rates to evaluate the consequences of previous, current, and future fishery exploitation patterns and their ecological implica- tions. The analysis produced three main conclusions: (1) Development of fisheries based on large-mesh gill nets reduced total predation by Nile perch to -40% of that estimated during the late 1970s, when Nile perch densities were greatest. (2) Expansion of recent intensive beach seine and small-mesh gill net fisheries for juvenile Nile perch could reduce total predation to -25%. (3) The combination of fishing methods could reduce total pre- dation to 10% of previous levels. Reduction in estimated predatory impact corresponds with recent reports of recovery by haplochromine populations and increased fish species diversity in regions (e.g., Napoleon Gulf, Mwanza Gulf, and Winam Gulf) where fisheries are locally intense.

Stocks of the indigenous catfish species of Lake Victoria have decreased dramatically since the beginning of the 1980s. This decline coincided with the Nile perch boom and concomitant ecological changes in the lake. In deep water, where Nile perch densities were higher, the decline proceeded more quickly than in shallow water. In the former all catfishes eventually vanished. Of the two largest species, Clarias gariepinus and Bagrus docmak, juveniles disappeared faster than adults. This indicates that predation by Nile perch may have played an important role in their decline. Other possible impacts were the deoxygenation of deepwater areas and the decline of haplochromine cichlids which were an important food source for B. docmak, C. gariepinus and Schilbe intermedius. The various catfish species were not all affected to the same extent. The endemic Xenoclarias eupogon, which lived predominantly in deep water, may have become extinct. B. docmak currently seems to be mainly restricted to refugia in rocky habitats. Synodontis victoriae and S. afrofischeri are still present in small numbers in shallow littoral areas. Schilbe intermedius and C. gariepinus seem to be the least affected of the catfishes in littoral and sublittoral areas. This may be caused, among other reasons, by their smaller habitat overlap with Nile perch than the other species. S. intermedius is partly pelagic, and a considerable part of the C. gariepinus stock lives in bodies of water surrounding the lake. The patterns of decline of the catfishes are very similar to those observed for haplochromine cichlids in the lake. The importance of catfishes for the fisheries in the lake is currently negligible.

The explosive speciation and adaptive radiation of haplochromine cichlid fishes in Lake Victoria is unrivalled among vertebrates. It holds answers to many intriguing questions about the origins and maintenance of biological diversity. Unfortunately, Lake Victoria is also a case-study in anthropogenic mass extinction. Over 50 per cent of its endemic fishes disappeared between 1980 and 1986. Hundreds of species abruptly became extinct or vanished, disappearing an order of magnitude faster than they could be described. This article examines the dynamics that underlie this fauna's extraordinary volatility, and hence points the way towards its conservation.

Background The explosively radiating evolution of cichlid fishes of Lake Malawi has yielded an amazing number of haplochromine species estimated as many as 500 to 800 with a surprising degree of diversity not only in color and stripe pattern but also in the shape of jaw and body among them. As these morphological diversities have been a central subject of adaptive speciation and taxonomic classification, such high diversity could serve as a foundation for automation of species identification of cichlids. Methodology/Principal Finding Here we demonstrate a method for automatic classification of the Lake Malawi cichlids based on computer vision and geometric morphometrics. For this end we developed a pipeline that integrates multiple image processing tools to automatically extract informative features of color and stripe patterns from a large set of photographic images of wild cichlids. The extracted information was evaluated by statistical classifiers Support Vector Machine and Random Forests. Both classifiers performed better when body shape information was added to the feature of color and stripe. Besides the coloration and stripe pattern, body shape variables boosted the accuracy of classification by about 10%. The programs were able to classify 594 live cichlid individuals belonging to 12 different classes (species and sexes) with an average accuracy of 78%, contrasting to a mere 42% success rate by human eyes. The variables that contributed most to the accuracy were body height and the hue of the most frequent color. Conclusions Computer vision showed a notable performance in extracting information from the color and stripe patterns of Lake Malawi cichlids although the information was not enough for errorless species identification. Our results indicate that there appears an unavoidable difficulty in automatic species identification of cichlid fishes, which may arise from short divergence times and gene flow between closely related species.

Two new species of zooplanktivorous haplochromine cichlids from Lake Victoria, Tanzania, are described and illustrated. These species closely resemble each other. Their affinities to other zooplanktivorous haplochromines from Lake Victoria are discussed. Haplochromis argens sp. n., which featured under nicknames (mainly H. “argens”) in more than 50 papers, was caught both in the Mwanza Gulf and the Emin Pasha Gulf, whereas H. goldschmidti sp. n. was only found in the Emin Pasha Gulf. Of the latter species only males are available, but it seems unlikely that it represents a case of male colour polymorphism as several presumably unrelated characters differ in sympatry between the two species, suggesting that there is no gene flow. Statistical analysis revealed that the overall difference between the two species is greater than that between the populations from the two locations. Body depth of the two species in sympatry in the Emin Pasha Gulf was more similar than that of H. goldschmidti sp. n. and the allopatric population of H. argens sp. n. from the Mwanza Gulf, which may indicate an overall environmental effect. However, several measurements related to the width of snout and mouth differed more between the populations of the two species in sympatry than between the allopatric populations. In contrast to a group of zooplanktivorous species that recovered successfully after environmental changes in the lake, H. argens sp. n. is among a group that became extremely rare and probably is in danger of extinction; the conservation status of H. goldschmidti sp. n. is currently unknown.

Because fish heads are densely packed with muscles, ligaments, skeletal elements and other structures, transformations in one structure may influence surrounding structures. Transformations occur during phylogeny, ontogeny and as environmentally induced alterations, i.e. phenotypic plasticity. We describe differences in intra- and interspecific transformations of the pharyngeal jaw apparatus of haplochromine cichlids. Using multivariate clustering techniques we trace possible correlations in transformations of anatomical characters of the pharyngeal jaws and surrounding structures. The intraspecific transformation analysis is based on two environmentally induced morphs of Astatoreochromis alluaudi : a molluscivorous morph with a hypertrophied pharyngeal jaw apparatus and an insectivorous one with a non-hypertrophied apparatus. For the interspecific analysis five other haplochromine species from Lake Victoria with diets ranging from insects to molluscs were investigated. Although range in diet are the same, the anatomical ranges differ between A. alluaudi and the species cline. Besides similarities in anatomical changes of the pharyngeal jaw apparatus in the intra- and interspecific cline, differences were also observed. Apparently there are among haplochromines multiple pathways to achieve similar performance. In A. alluaudi architectonic and intrinsic plasticity constraints limit the adaptability of the pharyngeal jaw apparatus. In the species cline, these constraints have been overcome by genetical adaptation.

Lake Malawi, Africa. Environmental Biology of Fishes 27: 215-233. Ribbink, A. J., B. A. Marsh, A. C. Marsh, A. C. Ribbink, and B. J. Sharp. 1983. A preliminary survey of the cichlid fishes of rocky habitats in Lake Malawi. South African Journal of Zoology 18:149-310. Schoener, T. W. 1974. Resource partitioning in ecological communities. Science 185:27-39. Turner, G. F, A. S. Grimm, 0. K. Mhone, R. L. Robinson, and T. J. Pitcher. 1991. The diet of Oreochromis lidole (Trewavas) and other chambo species in Lakes Malawi and Malombe. Journal of Fish Biology 39:15-24. Van Oijen, M. J. P. 1982. Ecological differentiation among the piscivorous haplochromine cichlids of Lake Victoria (East Africa). Netherlands Journal of Zoology 32:336-363. Zohary, T., J. Erez, M. Gophen, I. Berman-Frank, and M. Stiller. 1994. Seasonality of stable carbon isotopes within the pelagic food web of Lake Kinneret. Limnology and Oceanography 39:1030-1043.

Wetlands may protect fishes from introduced predatory fishes by providing both structural and low-oxygen refugia for prey species tolerant of the conditions that prevaa in these habitats. We examined the potential of wetlands as refugia for fishes in Lake Nabugabo, Uganda, where increased numbers of an intro- duced predator, the Nile perch (Lates niloticus), coincided with the decline or disappearance of many indige- nous species in the main lake. In 1993 and 1994 we sampled fishes in three wetland habitats: the marginal wetland ecotones of the lake, wetland lagoons separated from the lake by densely vegetated marsh habitats, and a stream separated from the lake by dense papyrus swamp. Fish distributions in these wetlands were then compared to results from two earlier fish surveys: the 1962 Cambridge expedition to Lake Nabugabo, which was conducted prior to the increase in the Nile perch population; and a 1991-1992 survey of the open lake, which reported the disappearance of 16 indigenous species. In our 1993-1994 surveys 9 of the 16 spe- cies not recovered in the 1991-1992 open-lake survey were found in the wetland ecotones or beyond the mar- gins of the lake in wetland lagoons and tributaries. Three of these species were found only beyond the mar- gins of the lake in the tributaries and lagoons within extensive wetlands. Three endemic haplochromine cichlids were abundant offshore in 1962. Of these species one has disappeared and the others are now largely confined to inshore areas. Other species that were abundant in the open waters of the lake in 1962 (e.g., the lungfish Protopterus aethiopicus) are now found primarily in wetlands. Two species, the characid Brycinus jacksonii and the cyprinid Rastrineobola argentea, are still abundant in the open waters. This study highlights the need for quantitative survey work to identify wetland refugia in the Lake Victoria Basin and suggests that some species thought to have disappeared in the mass extinction of fishes in Lakes Victoria and Kyoga may still survive in refugla. Some fish populations could recover under effective ecosystem management.

The endemic, haplochromine, cichlid species flock of Lake Malaŵi represents the most diverse assemblage of fishes of any of the world's freshwater lakes. Of particular interest are the interspecific relationships that permit so many species to coexist in this unique ecosystem. We hypothesized that a detailed study of the feeding associations among three sand-dwelling species, Taeniolethrinops praeorbitalis, Cyrtocara moori, and Protomelas annectens, would provide the necessary information needed to determine if these species are effective in harvesting specific food resources. Taeniolethrinops praeorbitalis feeds by plunging its snout into the sand, engulfing a mouthful of sand, retaining prey items, and expelling the sand through its gills. Immediately after T. praeorbitalis plunges into the sand, other species, including C. moori and P. annectens, move closer and begin to forage on the invertebrates suspended in the water column by the disturbance of the substrate or expelled through the gills ...

Evolution in great lakes has often been both quantitative (many endemic species of distantly related taxa often being present) and qualitative (outstanding levels of adaptive radiation having sometimes been achieved). These situations pose many questions, such as why there are so many endemics and so many superspecialists (and at the same time often many sibling species), as well as presenting problems relating to such matters as convergent evolution in different lakes, the possible role of key innovations, the nature of isolating mechanisms, competition and co-existence in complex communities, the roles of diverse mutualistic associations, and many others. These rich faunas also provide particularly favourable opportunities for studying patterns of speciation, while attempts to elucidate phylogenies in groups such as African cichlid fishes, that have radiated in several lakes, can be pursued on both a broad scale and at the intralacustrine level using both recently developed techniques and time-honoured methods. Rates of evolution, which differ widely between ecologically equivalent taxa in different lakes, have sometimes been extremely rapid, as attested by both molecular data and evidence from field studies. Notwithstanding their evolutionary exuberance, these rich faunas are fragile as demonstrated dramatically by the appalling tragedy that has befallen the haplochromine cichlid flock of Lake Victoria.

The photopic system of two selected haplochromine species, raised under laboratory conditions, differs distinctly. The system consists of medium and long wavelength sensitive double cones and short wavelength sensitive single cones. In this study the functional significance of the morphometrical differences of the photopic system is explained by relating them to sensitivity in red or blue light using the optomotor response to determine thresholds. H. pyrrhocephalus with its larger double cones is about twice as sensitive as H. "argens" tested in red light. In blue light its sensitivity equals that of H. "argens", although H. pyrrhocephalus has smaller and fewer single cones. The resulting loss in blue sensitivity may be compensated by the broad absorbancy of its double cone pigments. The threshold differences indicate that the sensitive visual system of H. pyrrhocephalus is tuned to a dim reddish light environment, while the visual system of H. "argens" seems more suited to light of relative high intensity and broad spectral distribution. This difference correlates with the difference in habitat of wild specimens in which retinal differences are even larger. H. "argens" is a surface dweller experiencing bright light of broad spectrum; in such an environment the higher resolution of H. "argens" is advantageous. H. pyrrhocephalus lives in deeper water in which mainly dim red light penetrates; it will benefit from a red light sensitive system at the cost of resolution.

Gophen M.,. P. B. O. Ochumba, L. S. Kaufman. Aquat. Living Resour., 1995, 8, 27-41. Dramatic changes in the Lake Victoria (East Africa) environment were observed after the introduction of the Nile perch (uites niloticus) in the 1950s. An extraordinary spectrum of endemic haplochromine fishes, a result of intralacustrine adaptive radiation was reduced by massive species extinctions (ca. 65%) due in part to predation by Nile Perch. Such an abrupt destruction of natural diversity has never before been documented by scientists. Lake Victoria's haplochromine species flock comprised upwards of 400 species (5% of the world's known freshwater fishes), encompassing a remarkably wide trophic spectrum and constituting 83% of the lake's total fish biomass. The lot evolved in an isolated part of the Nile system since the formation of the lake basin about 750 x 10"ears ago, but quite possibly as recently as 14 x 103 years ago, when most of the lake dried up. More than 50% of the haplochromine species (by number) were phytoplankton-zooplankton-detritus consumers; 55% of their biomass were detritivores and 27% zooplanktivores. The piscivore Nile perch (iutes niloticus) was first introduced into Lake Victoria in 1954. It underwent rapid population expansion in the 1980s. accompanied by haplochromine decline. Consequently, phytoplankton and detritus consumption by fishes was reduced. The biomass of the endemic Cyprinidae Rastrineobola argentea increased, as did its fishery, and predation pressure on zooplankton was therefore intensified. The population of the prawn Caridina niloticus became very dense, mostly in deep waters. The fishery and fish industry were altered fundamentally. Limnological changes suggesting eutrophication have been observed since 1960: hypolirnnetic anoxia increased and the period of extensive vertical mixing was restricted to about one month per year; phytoplankton produotivity increased and shifts from diatom to blue-green dominance occurred. Increased inputs of N (from the 1920s) and P (from the 1950s), induced through precipitation and human activity in the catchment area (agricultural and urban developments, deforestation, etc.) and high water levels accompanied by decline of available silicon, have persisted. Both top-down (Nile perch piscivory) and bottom-up (nutrient changes) influences enhanced eutrophication. The concurrent system changes in nutrient dynamics may have contributed an additional impact to the extinctions of haplochromine fishes.

The megadiverse haplochromine cichlid radiations of the East African lakes, famous examples of explosive speciation and adaptive radiation, are according to recent studies, introgressed by different riverine lineages. This study is based on the first comprehensive mitochondrial and nuclear DNA dataset from extensive sampling of riverine haplochromine cichlids. It includes species from the lower River Congo and Angolan (River Kwanza) drainages. Reconstruction of phylogenetic hypotheses revealed the paradox of clearly discordant phylogenetic signals. Closely related mtDNA haplotypes are distributed thousands of kilometres apart and across major African watersheds, whereas some neighbouring species carry drastically divergent mtDNA haplotypes. At shallow and deep phylogenetic layers, strong signals of hybridization are attributed to the complex Late Miocene/Early Pliocene palaeohistory of African rivers. Hybridization of multiple lineages across changing watersheds shaped each of the major haplochromine radiations in lakes Tanganyika, Victoria, Malawi and the Kalahari Palaeolakes, as well as a miniature species flock in the Congo basin (River Fwa). On the basis of our results, introgression occurred not only on a spatially restricted scale, but massively over almost the whole range of the haplochromine distribution. This provides an alternative view on the origin and exceptional high diversity of this enigmatic vertebrate group.

In the extremely species-rich haplochromine cichlid fishes of the East African Great Lakes, prezygotic isolation between closely related species is often maintained by color-assortative mating. In 1998, local fisherman working for the ornamental fish trade released different color morphs of the cichlid genus Tropheus into a small harbor basin in the southern part of Lake Tanganyika. This artificial amalgamation of color morphs provides a unique possibility to study mating patterns in cichlids in a natural environment over time. In a precursor study, we analyzed genotypes and phenotypes of almost 500 individuals sampled between 1999 and 2001 and uncovered a marked degree of color-assortative mating, which depended on the level of color pattern dissimilarity between morphs. Twelve years after introduction of nonindigenous morphs, we again sampled Tropheus individuals from the harbor basin and an adjacent, originally pure population and analyzed phenotypes (coloration) and genotypes (mitochondrial control region and 9 microsatellite loci) to assess the current status of the admixed population. Principal component analyses of color score data and population assignment tests demonstrate an increasing level of introgressive hybridization between morphs but also some ongoing color-assortative mating within morphs. The observed mating pattern might have been influenced by fluctuating environmental conditions such as periodic algal blooms or increased sedimentation causing turbid conditions in an otherwise clear lake.

The diverse cichlid species flocks of the East African lakes provide a classical example of adaptive radiation. Territorial aggression is thought to influence the evolution of phenotypic diversity in this system. Most vertebrates mount hormonal (androgen, glucocorticoid) responses to a territorial challenge. These hormones, in turn, influence behavior and multiple aspects of physiology and morphology. Examining variation in competition-induced hormone secretion patterns is thus fundamental to an understanding of the mechanisms of phenotypic diversification. We test here the hypothesis that diversification in male aggression has been accompanied by differentiation in steroid hormone levels. We studied two pairs of sibling species from Lake Victoria belonging to the genera Pundamilia and Mbipia. The two genera are ecologically differentiated, while sibling species pairs differ mainly in male color patterns. We found that aggression directed toward conspecific males varied between species and across genera: Pundamilia nyererei males were more aggressive than Pundamilia pundamilia males, and Mbipia mbipi males were more aggressive than Mbipia lutea males. Males of both genera exhibited comparable attack rates during acute exposure to a novel conspecific intruder, while Mbipia males were more aggressive than Pundamilia males during continuous exposure to a conspecific rival, consistent with the genus difference in feeding ecology. Variation in aggressiveness between genera, but not between sibling species, was reflected in androgen levels. We further found that M. mbipi displayed lower levels of cortisol than M. lutea. Our results suggest that concerted divergence in hormones and behavior might play an important role in the rapid speciation of cichlid fishes. (C) 2012 Elsevier Inc. All rights reserved.

Background: As in any vertebrate, heads of fishes are densely packed with functions. These functions often impose conflicting mechanical demands resulting in trade-offs in the species-specific phenotype. When phenotypical traits are linked to gender-specific parental behavior, we expect sexual differences in these trade-offs. This study aims to use mouthbrooding cichlids as an example to test hypotheses on evolutionary trade-offs between intricately linked traits that affect different aspects of fitness. We focused on the oral apparatus, which is not only equipped with features used to feed and breathe, but is also used for the incubation of eggs. We used this approach to study mouthbrooding as part of an integrated functional system with diverging performance requirements and to explore gender-specific selective environments within a species. Methodology/Principal Findings: Because cichlids are morphologically very diverse, we hypothesize that the implications of the added constraint of mouthbrooding will primarily depend on the dominant mode of feeding of the studied species. To test this, we compared the trade-off for two maternal mouthbrooding cichlid species: a "suction feeder'' (Haplochromis piceatus) and a "biter'' (H. fischeri). The comparison of morphology and performance of both species revealed clear interspecific and intersex differences. Our observation that females have larger heads was interpreted as a possible consequence of the fact that in both the studied species mouthbrooding is done by females only. As hypothesized, the observed sexual dimorphism in head shape is inferred as being suboptimal for some aspects of the feeding performance in each of the studied species. Our comparison also demonstrated that the suction feeding species had smaller egg clutches and more elongated eggs. Conclusions/Significance: Our findings support the hypothesis that there is a trade-off between mouthbrooding and feeding performance in the two studied haplochromine cichlids, stressing the importance of including species-specific information at the gender level when addressing interspecific functional/morphological differences.

Made available in DSpace on 2013-08-28T14:09:01Z (GMT). No. of bitstreams: 1 WOS000279859800001.pdf: 1585783 bytes, checksum: 40da104eda2604b3c1418867be0eb08e (MD5) Made available in DSpace on 2013-09-30T18:39:35Z (GMT). No. of bitstreams: 2 WOS000279859800001.pdf: 1585783 bytes, checksum: 40da104eda2604b3c1418867be0eb08e (MD5) WOS000279859800001.pdf.txt: 51423 bytes, checksum: b6f04bba0a8455f28d6f124b8d725380 (MD5) Previous issue date: 2010-06-15 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T13:52:23Z No. of bitstreams: 2 WOS000279859800001.pdf: 1585783 bytes, checksum: 40da104eda2604b3c1418867be0eb08e (MD5) WOS000279859800001.pdf.txt: 51423 bytes, checksum: b6f04bba0a8455f28d6f124b8d725380 (MD5) Made available in DSpace on 2014-05-20T13:52:23Z (GMT). No. of bitstreams: 2 WOS000279859800001.pdf: 1585783 bytes, checksum: 40da104eda2604b3c1418867be0eb08e (MD5) WOS000279859800001.pdf.txt: 51423 bytes, checksum: b6f04bba0a8455f28d6f124b8d725380 (MD5) Previous issue date: 2010-06-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Background: Cichlid fishes have been the subject of increasing scientific interest because of their rapid adaptive radiation which has led to an extensive ecological diversity and their enormous importance to tropical and subtropical aquaculture. To increase our understanding of chromosome evolution among cichlid species, karyotypes of one Asian, 22 African, and 30 South American cichlid species were investigated, and chromosomal data of the family was reviewed.Results: Although there is extensive variation in the karyotypes of cichlid fishes (from 2n = 32 to 2n = 60 chromosomes), the modal chromosome number for South American species was 2n = 48 and the modal number for the African ones was 2n = 44. The only Asian species analyzed, Etroplus maculatus, was observed to have 46 chromosomes. The presence of one or two macro B chromosomes was detected in two African species. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene revealed a variable number of clusters among species varying from two to six.Conclusions: The karyotype diversification of cichlids seems to have occurred through several chromosomal rearrangements involving fissions, fusions and inversions. It was possible to identify karyotype markers for the subfamilies Pseudocrenilabrinae (African) and Cichlinae (American). The karyotype analyses did not clarify the phylogenetic relationship among the Cichlinae tribes. on the other hand, the two major groups of Pseudocrenilabrinae (tilapiine and haplochromine) were clearly discriminated based on the characteristics of their karyotypes. The cytogenetic mapping of 18S ribosomal RNA (18S rRNA) gene did not follow the chromosome diversification in the family. The dynamic evolution of the repeated units of rRNA genes generates patterns of chromosomal distribution that do not help follows the phylogenetic relationships among taxa. The presence of B chromosomes in cichlids is of particular interest because they may not be represented in the reference genome sequences currently being obtained. UNESP Univ Estadual Paulista, Inst Biociencias, Dept Morfol, Botucatu, SP, Brazil UFMT Univ Fed Mato Grosso, Inst Univ Araguaia, Pontal do Araguaia, MT, Brazil Univ Maryland, Dept Biol, College Pk, MD 20742 USA Univ Oriente, Escuela Ciencias Aplicadas Mar, Boca de Rio, Venezuela UNESP Univ Estadual Paulista, Inst Biociencias, Dept Morfol, Botucatu, SP, Brazil

During the past decades, major anthropogenic environmental changes occurred in Lake Victoria, including increased predation pressure due to Nile perch introduction, and decreases in water transparency and dissolved oxygen concentrations due to eutrophication. This resulted in a collapse of the haplochromine cichlids in the sub-littoral waters of the Mwanza Gulf in 1986–1990, followed by a recovery of some species in the 1990s and 2000s, when Nile perch densities declined. We studied two data sets: (1) haplochromines from sand and mud bottoms in the pre-collapse period; (2) haplochromines from sub-littoral areas during the pre-collapse, collapse and recovery periods. Water over mud is murkier and poorer in oxygen than water over sand, and differences in haplochromine communities in these natural habitats during the pre-collapse period may predict the effects of anthropogenic eutrophication during the collapse and recovery periods. In the pre-collapse period, haplochromine densities over sand and mud did not differ, but species richness over sand was 1.6 times higher than over mud bottoms. Orange- and white-blotched colour morphs were most common at the shallowest sand station. More specifically, insectivores and mollusc-shellers had higher numbers of species over sand than over mud, whereas for mollusc-crushers no difference was found. Laboratory experiments revealed that mollusc shelling was more affected by decreased light intensities than mollusc crushing. During the pre-collapse period, spawning occurred year-round in shallow areas with hard substrates and relatively clear water. In deeper areas with mud bottoms, spawning mainly occurred during months in which water clarity was high. No effects of hypoxia on spawning periods were found. It follows that clearer water seems to support differentiation in feeding techniques as well as year-round spawning, and both may facilitate species coexistence. Water clarity is also known to be important for mate choice. These observations may explain why, since the decline of Nile perch, haplochromine densities have recovered, the numbers of hybrids increased and species diversity in the current eutrophic sub-littoral waters has remained 70 % lower than before the environmental changes.

Background The Nile tilapia (Oreochromis niloticus) is the second most farmed fish species worldwide. It is also an important model for studies of fish physiology, particularly because of its broad tolerance to an array of environments. It is a good model to study evolutionary mechanisms in vertebrates, because of its close relationship to haplochromine cichlids, which have undergone rapid speciation in East Africa. The existing genomic resources for Nile tilapia include a genetic map, BAC end sequences and ESTs, but comparative genome analysis and maps of quantitative trait loci (QTL) are still limited. Results We have constructed a high-resolution radiation hybrid (RH) panel for the Nile tilapia and genotyped 1358 markers consisting of 850 genes, 82 markers corresponding to BAC end sequences, 154 microsatellites and 272 single nucleotide polymorphisms (SNPs). From these, 1296 markers could be associated in 81 RH groups, while 62 were not linked. The total size of the RH map is 34,084 cR3500 and 937,310 kb. It covers 88% of the entire genome with an estimated inter-marker distance of 742 Kb. Mapping of microsatellites enabled integration to the genetic map. We have merged LG8 and LG24 into a single linkage group, and confirmed that LG16-LG21 are also merged. The orientation and association of RH groups to each chromosome and LG was confirmed by chromosomal in situ hybridizations (FISH) of 55 BACs. Fifty RH groups were localized on the 22 chromosomes while 31 remained small orphan groups. Synteny relationships were determined between Nile tilapia, stickleback, medaka and pufferfish. Conclusion The RH map and associated FISH map provide a valuable gene-ordered resource for gene mapping and QTL studies. All genetic linkage groups with their corresponding RH groups now have a corresponding chromosome which can be identified in the karyotype. Placement of conserved segments indicated that multiple inter-chromosomal rearrangements have occurred between Nile tilapia and the other model fishes. These maps represent a valuable resource for organizing the forthcoming genome sequence of Nile tilapia, and provide a foundation for evolutionary studies of East African cichlid fishes.

The ecology of sympatric African pike, Hepsetus odoe (Hepsetidae), and tiger fish, Hydrocynus forskahlii (Characidae), were compared during high (May-August) and falling water (September-December) conditions in the Upper Zambezi R. drainage of Zambia. Both species were common in the central and southern regions of the river and associated floodplain, and Hydrocynus was common in the northern region in swift flowing tributaries where Hepsetus was rare. Hepsetus inhabited vegetated environments of river backwaters, lagoons, and sluggish tributaries, whereas Hydrocynus occupied the open water of the main river channel almost exclusively. During the period of annual flooding, juveniles of both species coexist in flooded savanna regions. Size distributions of adult Hydrocynus and Hepsetus changed relatively little between high and low water conditions. Stomach contents analysis indicated that adult size classes of both species are almost entirely piscivorous, and both show diet shifts with changes in size. Only very small seasonal diet shifts were noted. Approximately 50% of the diet of Hepsetus consisted of haplochromine cichlid fishes, but also included large numbers of tilapine cichlids and mormyrids, Hydrocynus consumed primarily cichlid fishes, but also consumed large percentages of Hepsetus and small characid fishes. Small size classes of Hepsetus fed heavily on small machokid catfishes (Synadontis spp.) and later shifted to a diet of cichlids and mormyrids, and small Hydrocynus preyed heavily on Barbus spp. (Cyprinidae), small characids, and mormyrids. Ratios of prey length-predator length averaged approximately 0·26 for Hydrocynus and nearly 0·40 for Hepsetus. The large potential for food resource competition appears not to be realized due to a very high degree of habitat partitioning between larger size classes of the two species. At the interface between river backwaters and channel habitats, Hydrocynus is a significant predator of Hepsetus, a factor that should further restrict the occurrence of the latter in open areas of the main channel.

A new species of pelagic haplochromine cichlid of the genus Diplotaxodon is described from Lake Malawi, Africa. The species, which attains a size of 14cm s. L., feeds mainly on zooplankton, shows no sexual dimorphism in size or body proportions, breeds throughout the year and lives at depths of 20 to at least 120 m. Approximately 600 tonnes of the species were caught by trawlers in 1990–1991, in the south–eastern arm of the lake alone. It appears that this species is a major component of the pelagic community, and occupies an ecological role similar to that of the clupeid Limnothrissa miodon in Lake Tanganyika.

Isolated, small ecosystems associated with springs and sinkholes in semi-arid regions of the western Transvaal, South Africa, are under threat as there is a growing need to tap the dolomitic waters which maintain these systems. Part of a programme to demonstrate that these systems are unique and worthy of conservation is to characterize fish populations genetically and morphologically. The data presented here indicate that the populations of Tilapia sparrmanii from the Malemani and Molopo Oog springs and the Wondergat sinkhole differ from each other genetically when examined using polyacrylamide gel electrophoresis (PAGE) of total soluble protein. The outgroups in the analysis were Tilapia guinasana , a closely related substratum-spawning cichlid endemic in Guinas sinkhole, Namibia, and Pseudocrenilabrus philander , a distantly related mouthbrooder of the haplochromine lineage. The findings of this study were (a) that PAGE can distinguish between species and between conspecific populations and (b) that the isolated populations of the dolomitic ecosystems of the western Transvaal are unique and should be conserved.

The haplochromine cichlid fishes inhabiting Lake Victoria in East Africa are of great inter-est to evolutionary biologists. We have isolated and optimized six tetranucleotide and a sin-gle dinucleotide locus from a hybrid of the haplochromine cichlid fishes, Pundamiliapundamilia and P. nyererei . Characterization in 18 individuals of P. nyererei from a singlewild population revealed between six and 18 alleles per locus, with expected heterozygos-ity ranging from 0.68 to 0.94. These loci will prove useful for investigations of populationstructure, and elucidating relationships between closely related species. An additional 26unoptimized loci have been deposited with GenBank and the MEN database. Keywords : cichlid, haplochromine, microsatellites, Pundamilia Received 1 April 2002; revision received 9 May 2002; accepted 30 May 2002 The cichlid fishes inhabiting Lake Victoria represent one ofthe most spectacular vertebrate radiations on the planet.As many as 500 species are thought to have evolved withinthe last 200 000 years (Meyer 1993) or possibly as littleas 14 600 years (Owen

Does hybridization play a broad innovative role in evolution? Many studies have shown hybrid origins of individual species, particularly in major adaptive radiations, but this may be a consequence, rather than a cause, of the existence of many closely related species. Cases of hybridization in the early stages of major adaptive radiations are comparatively rare. Here, we report phylogenetic evidence for ancient introgression between distinct lineages of the species-rich Lake Malawi haplochromine cichlid fishes. Mitochondrial DNA (mtDNA) sequences indicated surprisingly close relationships between the shallow-water rocky habitat "Mbuna" species and a group of dark-adapted "Deep-Benthic" species specialized for feeding in low-light conditions (dawn/dusk, under overhangs, and deep water). By contrast, analyses of nuclear amplified fragment length polymorphism data demonstrated that these Deep-Benthic cichlids were more closely related to shallow water "Shallow-Benthic" soft-sediment feeders, a group that shares similar head and body morphology. A coalescent-based computer simulation indicated that the mtDNA similarity of rocky habitat Mbuna species and dark-adapted Deep-Benthic species was due to hybridization rather than incomplete lineage sorting. Comparisons of morphology indicated that some Deep-Benthic species possessed novel morphology not present in other Lake Malawi species groups. Thus, these analyses support the hypothesis that ancient hybridization occurred within the Lake Malawi cichlid radiation, that the event occurred before the radiation of a species group adapted to low-light benthic habitats, and that this group went on to dominate the deep-water regions of Lake Malawi. The results of this study contribute to a growing literature consistent with a creative role of hybridization in the evolution of species diversity and adaptive radiations.

The adaptive radiations of cichlid fishes in East Africa have been associated with the acquisition of evolutionary novelties as well as the ecological opportunities existing in the East African Great lakes. Two remarkable evolutionary innovations are the pharyngeal jaw apparatus, found in all cichlid species, and the anal fin egg-spots of mouthbrooding cichlids. Based on their conserved functions during the development of both the jaw apparatus and pigmentation, the endothelin ligands and receptors form a putative link between these naturally and sexually selected traits. Here we study the evolutionary history of four members of two endothelin pathways (Edn1/EdnrAa and Edn3b/EdnrB1a) to elucidate their possible roles during the evolution and development of key innovations in East African cichlids species. The analyses performed on partial sequences (ca. 6,000 bp per taxon) show that all four endothelin family members evolved under purifying selection, although both ligands are characterized by an accelerated rate of protein evolution in comparison to the receptors. In accordance with earlier findings, we show that the mature protein sequence of Edn1 and Edn3 are highly conserved, also in cichlids, whereas the preproendothelin parts are variable indicating relaxed selective constraints. In the receptors, nonsynonymous substitutions were mainly found in the ligand-binding domains suggesting functional divergence. Gene expression assays with Real-Time PCR indeed reveal that the two studied endothelin pathways are expressed in the cichlid pharyngeal jaw and in the haplochromine egg-spot (among other pigment-cell containing tissues), suggesting their involvement during morphogenesis of naturally and sexually selected traits in cichlids.

It has been suggested that intrasexual competition can be a source of negative frequency-dependent selection, causing agonistic character displacement and facilitating speciation and coexistence of (sibling) species. In this paper we synthesise the evidence that male-male and female-female competition contributes to cichlid diversification, showing that competition is stronger among same-coloured individuals than those with different colours. We argue that intrasexual selection is more complex because there are several examples where males do not bias aggression towards their own type. In addition, sibling species or colour morphs often show asymmetric dominance relationships. We briefly discuss potential mechanisms that might promote the maintenance of covariance between colour and aggression-related traits even in the face of gene-flow. We close by proposing several avenues for future studies that might shed more light on the role of intrasexual competition in cichlid diversification.

The symposium ‘‘Genomics and Vertebrate Adaptive Radiation: A Celebration of the First Cichlid Genome’’ was held at the annual meeting for the Society of Integrative and Comparative Biology in Boston in January, 2009. While the central topic was the genomics of adaptive radiation in cichlid fishes, the symposium integrated speakers studying genotype-to-phenotype maps in other model organisms. Genomic studies investigating cichlid phenotypes were paralleled with studies using similar techniques to answer questions in other adaptive radiations. The topics were not restricted to any one research area in order to foster interdisciplinary discussions from developmental, physiological, and behavioral research with the common goal to apply and enhance genome-level analyses. Research programs such as the genetics and development of craniofacial diversity, behavior, and color patterns in zebrafish, mouse, and stickleback were described and then augmented with speakers focusing on the genetic and developmental architecture of cichlids’ jaws, behavior, and color. This integration across both established model systems and the new cichlid model sought to capitalize upon a comparative organismal framework that focused on how linking genomic information to studies of phenotype could hasten scientific discovery. The comparative and integrative approach inherent in most cichlid research extends to the current genome sequencing effort. Multiple cichlids have been chosen for genome sequencing because of their important applied as well as scientific value. The genomes of the cichlid fish Tilapia nilotica and as many as three other species representing the faunas of the largest East African Rift lakes will be sequenced. Astatotilapia burtoni could represent the 400 species present within Lake Tanganyika and its surrounding rivers because it is a genomic model for social regulation of behavior (Renn et al. 2008). Paralabidochromis chilotes could provide a representative for the !350 species from Lake Victoria, a radiation being strongly affected by ecological change (Seehausen et al. 2008). Metriaclima zebra could also be sequenced because it has been used to build a haplochromine linkage map (Albertson et al. 2005) and is a member of the !500–1000 species in the very recent radiation from Lake Malawi. These three other cichlid species, representing independent radiations within the East African Rift Lakes, span the incredible craniofacial, color, and behavioral diversity of the nearly 2000 species that inhabit this region (Salzburger 2008). Tilapia nilotica will be the first cichlid genome completed, and it is not only a major source of protein for much of the world but also is a focal organism for comparative renal physiology, ion balance, and endocrinology (Rengmark et al. 2007; Inokuchi et al. 2009). The sequencing of these cichlid genomes will provide an unprecedented view simultaneously into the genetics of one of the world’s major protein sources and into the unequalled phenotypic diversity of these fishes. In the symposium, researchers studying cichlids and other model vertebrate organisms focused on exploring the ways in which genomic studies can inform our mechanistic understanding of adaptive phenotypic diversity. The repeated phenotypic convergence in cichlid fishes makes this diverse vertebrate group exceptional for comparative analyses of genetics and development. Dr Darrin Hulsey described how cichlids are an ideal group to examine the similarities and differences in genomic and developmental changes that have lead to repeated convergence in neuralcrest-derived attributes as diverse as jaws, color