Search

The two toothed jaws of cichlid fishes provide textbook examples of convergent evolution. Tooth phenotypes such as enlarged molar-like teeth used to process hard-shelled mollusks have evolved numerous times independently during cichlid diversification. Although the ecological benefit of molar-like teeth to crush prey is known, it is unclear whether the same molecular mechanisms underlie these convergent traits. To identify genes involved in the evolution and development of enlarged cichlid teeth, we performed RNA-seq on the serially homologous-toothed oral and pharyngeal jaws as well as the fourth toothless gill arch of Astatoreochromis alluaudi. We identified 27 genes that are highly upregulated on both tooth-bearing jaws compared with the toothless gill arch. Most of these genes have never been reported to play a role in tooth formation. Two of these genes (unk, rpfA) are not found in other vertebrate genomes but are present in all cichlid genomes. They also cluster genomically with two other highly expressed tooth genes (odam, scpp5) that exhibit conserved expression during vertebrate odontogenesis. Unk and rpfA were confirmed via in situ hybridization to be expressed in developing teeth of Astatotilapia burtoni. We then examined expression of the cluster’s four genes in six evolutionarily independent and phylogenetically disparate cichlid species pairs each with a large- and a small-toothed species. Odam and unk commonly and scpp5 and rpfA always showed higher expression in larger toothed cichlid jaws. Convergent trophic adaptations across cichlid diversity are associated with the repeated developmental deployment of this genomic cluster containing conserved and novel cichlid-specific genes.

Summary Phenotypic plasticity in the form of alterations to teleost skeletons can result from a range of environmental factors, such as the hardness of the prey, particularly when exposure occurs early during development. Determining the molecular underpinnings of teleost skeletal plasticity is hampered by a limited understanding of the molecular basis of bone remodeling in derived teleost fish, whose bones are acellular, lacking the cell type known to orchestrate bone remodeling in mammals. We are using a fitting molecular model for phenotypic plasticity research: the East African cichlid Astatoreochromis alluaudi, with the aim to shed light on the molecular basis of phenotypic plasticity and on the remodeling of acellular bones. For this fish, sustained ingestion of a hard diet induces a ‘molariform’ lower pharyngeal jaw (LPJ), with molar-like teeth set in an enlarged, relatively dense jaw, while a softer diet results in a smaller, finer ‘papilliform’ LPJ morphology, representing the ‘ground state’ for this species. Through comparing genome-wide transcription in molariform and papilliform LPJs, our previous research has shed light on the molecular basis of phenotypic plasticity in the teleost skeleton and by extension, on acellular bone remodeling. In this manuscript we construct a model for the molecular basis of mechanically induced skeletal plasticity in teleosts, which involves iterative cycles of strain and compensatory cellular proliferation. Furthermore, we propose a framework for testing the potential influence of phenotypic plasticity and genetic assimilation on adaptive radiations.

A taxonomic revision of the cichlid genus Astatoreochromis is presented. Eighteen meristic and 23 morphometric measurements were taken on 185 individuals, including type specimens. While fin counts separate populations from the Lake Victoria region (Astatoreochromis alluaudi) from those of the Rusizi and Malagarazi rivers in the Lake Tanganyika basin (A. vanderhorsti and A. straeleni respectively), clear differentiation was not detected between the latter two. Mann-Whitney U-tests on specimens of comparable size from the two Tanganyika populations revealed significant differences in specimens < 75 mm SL, mainly in pharyngeal jaw proportions, but also in some other measurements on the head and body. However, these differences were not detected in specimens > 75 mm SL and Astatoreochromis vanderhorsti is herein considered a junior synonym of A. straeleni. A redescription of the two valid species of Astatoreochromis, A. alluaudi and A.straeleni, is provided.

Many organisms can produce alternative phenotypes in direct response to different environmental conditions, a phenomenon known as phenotypic plasticity. The environmentally sensitive gene regulatory networks (GRNs) that mediate such developmental flexibility are largely unknown. Yet, characterizing these GRNs is important not only for elucidating plasticity’s molecular basis, but also for shedding light onto whether and how plasticity might impact evolution. In this issue of Molecular Ecology, Schneider et al.) describe one of the first efforts to determine the GRN underlying a plastic trait. They focus on diet-induced plasticity in the cichlid fish, Astatoreochromis alluaudi. Depending on whether soft food (e.g. insects) or hard food (e.g. molluscs) is consumed, this species forms a lower pharyngeal jaw (LPJ) with many fine teeth or with fewer molar-like teeth, respectively (Fig. 1). The authors previously identified genes that are differentially expressed between LPJ morphs during early development. In the present study, they examine the expression of 19 of these genes across development and diet. By analysing these transcriptional data in combination with information on putative transcription factor binding sites, they construct a GRN that explains observed gene expression patterns and is likely to control LPJ morphology. This work advances our understanding of how plasticity can arise as a consequence of environmentally sensitive GRNs and promises to help illuminate how changes in such GRNs could facilitate evolution. Fig. 1 The cichlid fish, Astatoreochromis alluaudi, exhibits diet-induced plasticity in the morphology of its lower pharyngeal jaw. Keywords: adaptation, fish, gene regulatory networks, macroevolution, molecular evolution, phenotypic plasticity The flexible organism Among evolutionary biology’s central challenges is to explain why there are so many different species and where their distinctive traits come from. Phenotypic plasticity is increasingly viewed as playing a crucial role in both diversification and innovation (West-Eberhard 2003). When selection acts on quantitative genetic variation regulating the expression of an environmentally induced trait, it can promote the evolution of either increased or decreased plasticity through an evolutionary process known as ‘genetic accommodation’ (sensu West-Eberhard 2003). If the affected trait evolves decreased plasticity to the point of becoming constitutively expressed, ‘genetic assimilation’ occurs (sensu Waddington 1953). Through this process – in which a novel, complex trait evolves from a trait that was originally induced by the environment – new traits and possibly even new species can emerge (Pfennig et al. 2010). Yet, little is known about whether and how genetic accommodation/assimilation shape ecologically and evolutionarily relevant traits in natural populations (Pfennig et al. 2010). East African cichlids are ideal for studying genetic accommodation/assimilation. This group is renowned both for its spectacular species richness (there are over 500 species in Lake Victoria alone) and for its stunning array of highly specialized feeding morphologies (Seehausen 2006). Indeed, this impressive diversity is thought to stem (in part) from the cichlid’s ability to rapidly evolve specializations for utilizing diverse feeding niches: these fish possess a versatile pharyngeal jaw, which has been modified repeatedly to exploit different resource (Liem 1974). One recent hypothesis holds that the cichlid adaptive radiation arose when ecological circumstances favoured diversification in ancestral lineages that possessed a phenotypically plastic pharyngeal jaw; later, this flexible jaw repeatedly underwent genetic assimilation to produce the present-day diversity among species in feeding morphologies (West-Eberhard 2003). Astatoreochromis alluaudi is well suited for testing this hypothesis. This species is a dietary generalist, ancestral to modern East African cichlids. Moreover, it exhibits diet-induced phenotypic plasticity in its lower pharyngeal jaw (LPJ). If its preferred diet of soft food (e.g. insects) is present, A. alluaudi develops a slender ‘papilliform’ LPJ, bearing numerous fine teeth. However, if soft food is scarce, individuals feed on hard-shelled molluscs, which induces formation of a robust ‘molariform’ LPJ, bearing fewer, molar-like teeth (Fig. 1). Thus, LPJ plasticity in A. alluaudi represents a valuable model for examining how phenotypic plasticity might have contributed to the diversity of jaw morphologies among East African cichlids.

Interspecific studies have demonstrated that trophic morphology and ecology are not always tightly matched: a phenomenon rarely reported at the intraspecific level. In the present study, we explored relationships among diet, morphology and the environment in a widespread cichlid fish, Astatoreochromis alluaudi (Pellegrin 1904), from 6 sites in southern Uganda to test for evidence of eco-morphological matching at the interdemic level. Previous studies of Astatoreochromis alluaudi have demonstrated developmental plasticity in trophic morphology in response to diet: a mollusk diet produces specimens with large pharyngeal jaws and muscles, whereas a soft-food diet produces smaller pharyngeal jaws and corresponding changes in musculature. Sites were chosen to maximize variability in environmental variables that might directly or indirectly affect trophic morphology. We found significant differences in pharyngeal jaw and muscle morphology among populations. Similarly, we found differences in diets among sites: mollusks were found in the stomachs of fish from only 2 populations sampled, despite the presence of mollusks in 5 of the 6 sites. Although trophic morphology did match the observed diet in 2 sites, diet did not correlate with either morphology or environmental variables across sites, nor were environmental variables correlated with morphological variation among sites. These results suggest that mismatch can occur among different populations of a single species for reasons such as seasonality in resources, developmental plasticity and/or complex indirect interactions. Intraspecific mechanisms should be further studied in order to better understand the complex relationships between morphological specialization and ecological generalization.

Environmental factors can directly influence phenotype such that a tight correlation between morphological and environmental variation is expected. However, morphological response to environmental variation may also reflect constraints imposed by interactions between adjacent structures such as the gills and the trophic apparatus in fishes. Such complex interactions help to explain why an organism’s phenotype may appear mismatched with its environment. This study quantified relationships between morphological traits related to feeding and respiration and the physico-chemical environment in a widespread cichlid fish Astatoreochromis alluaudi, from six sites in Uganda. This species is known to be plastic in jaw morphology with enlarged jaw morphs specialized for mollusk eating, and reduced jaw morphs for insect eating. However, recent studies suggest a mismatch between the trophic morphology and feeding ecology in field populations of this species that could reflect interactions with the branchial apparatus; the development of large gills in low-oxygen habitats may constrain or affect pharyngeal jaw size. MANCOVA results for morphometric data showed a strong population effect for both gill and jaw traits. We found a significant negative correlation between composite morphological variables (principle components) relating to the size and shape of gill apparatus and pharyngeal jaw size across all populations. Furthermore, gill traits generated from principle component analysis were positively correlated with water conductivity, which was highly correlated with dissolved oxygen (DO) across the six sites. These results suggest that a particular morphological trait (pharyngeal jaw size) can be indirectly altered by the physico-chemical environment (conductivity and DO) due to correlated effects on a functionally unrelated morphology (gill size). These results have important implications for understanding species distribution patterns because trade-offs between suites of traits may constrain an individual’s ability to exploit an otherwise suitable habitat or resource.

Lake Kanyaboli, an isolated satellite lake of Lake Victoria, has been suggested as a potential refugium for haplochromine cichlids that have gone extinct in the main basin of Lake Victoria. Mitochondrial DNA (mtDNA) molecular markers, as well as feeding ecology studies, were employed in this study to re-evaluate the evolutionary and ecological significance of six common Lake Kanyaboli haplochromines. The mtDNA marker revealed high genetic variability within four of the six haplochromine cichlids. Five haplotypes were discerned in Astatoreochromis alluaudi (n = 27), seven in Lipochromis maxillaris (n = 29), five in Astatotilapia nubila (n = 12) and 11 in the endangered Xystichromis phytophagus (n = 205). A haplotype genealogy suggests that Lake Kanyaboli harbours mtDNA haplotypes that could have been lost or not sampled in Lake Victoria, or could have arisen in situ. Lipochromis maxillaris appears to have undergone a recent demographic expansion. The pairwise FSTs indicated that only the comparison between X. phytophagus and A. nubila led to a non-significant FST value. All other comparisons were significant at the 0.01 level, indicating the genetic distinctiveness of the haplochromines in the satellite lake. This could suggest that the lake harbours 'pure' relict populations of the haplochromines and therefore that Lake Kanyaboli can be considered a 'genetic reservoir'. Gut content analysis of the six haplochromine species revealed that eight different food items were consumed. No single species fed exclusively on a single food item, but certain food items contributed higher proportions of the fish diet for each fish species. Resource partitioning therefore could be discerned within this haplochromine community. Thus, Lake Kanyaboli and similar satellite lakes provide an opportunity for conservation of both genetic and trophic diversity threatened by introduction of exotics in the Lake Victoria basin. Lake Kanyaboli should be recognized and conserved as important evolutionary significant units for Lake Victoria region haplochromine species.

(2008). Feeding ecology and diet overlap in riverine cichlids from western Uganda. SIL Proceedings, 1922-2010: Vol. 30, No. 2, pp. 283-286.

The East African cichlid fishes provide text book examples of adaptive radiation. Diversification and speciation of cichlids associate with variation in diet and trophic morphologies among other ecological, behavioural and morphological phenotypes (Kocher 2004). Numerous case studies in cichlids reveal a role of developmental plasticity in generating jaw ecomorphs in response to variation in feeding ecology that can facilitate niche exploitation and subsequent diversification (e.g. Meyer 1987). Specifically, genetic divergence among such environmentally induced morphs can occur via reproductive isolation due to divergence in habitat and resource use in combination with genetic assimilation of environmentally induced phenotypes (West-Eberhard 2003; Pfennig et al. 2010). Expansion of this conceptual model has been hampered in part by the limited knowledge of the molecular mechanisms of plasticity in nonstandard model systems and the associated lack of evidence linking the molecular mechanisms of plasticity to those that generate phenotypic divergence among populations and taxa. In this issue of Molecular Ecology, Gunter et al. (2013) identify the transcriptional mechanisms of diet-induced lower pharyngeal jaw (LPJ) plasticity in the cichlid fish Astatoreochromis alluaudi. Natural populations of A. alluaudi exhibit variation in jaw morphology in relation to diet hardness. Among the plastic responses to diet are adjustments to the LPJ ranging from a robust molariform morph in response to a hard diet to a more gracile papilliform morph in response to a soft diet (Fig. 1). Gunter and colleagues induced developmental plasticity of the A. alluaudi jaw using diet manipulations and compared LPJ transcriptomic profiles of the resulting morphs. In this foundational work, the authors identify 187 differentially expressed genes that underlie the development and maintenance of diet-induced LPJ morphologies. This list includes a wide range of genes spanning from broad-acting transcription factors to signalling molecules and structural genes. Here, I examine the ontogeny of the molecular response to mechanical strain imposed by diet hardness and discuss the role of the stages of this response in the evolution of plasticity and plasticity-driven diversification.

Phenotypic plasticity is the ability of organisms with a given genotype to develop different phenotypes according to environmental stimuli, resulting in individuals that are better adapted to local conditions. In spite of their ecological importance, the developmental regulatory networks underlying plastic phenotypes often remain uncharacterized. We examined the regulatory basis of diet-induced plasticity in the lower pharyngeal jaw (LPJ) of the cichlid fish Astatoreochromis alluaudi, a model species in the study of adaptive plasticity. Through raising juvenile A. alluaudi on either a hard or soft diet (hard shelled or pulverized snails) for between one and eight months, we gained insight into the temporal regulation of 19 previously identified candidate genes during the early stages of plasticity development. Plasticity in LPJ morphology was first detected between three and five months of diet treatment. The candidate genes, belonging to various functional categories, displayed dynamic expression patterns that consistently preceded the onset of morphological divergence and putatively contribute to the initiation of the plastic phenotypes. Within functional categories we observed striking co-expression, and transcription factor binding site analysis was used to examine the prospective basis of their co-regulation. We propose a regulatory network of LPJ plasticity in cichlids, presenting evidence for regulatory cross-talk between bone and muscle tissues, which putatively facilitates the development of this highly integrated trait. Through incorporating a developmental time-course into a phenotypic plasticity study, we have identified an interconnected, environmentally responsive regulatory network that shapes the development of plasticity in a key innovation of East African cichlids.

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.

Adaptive phenotypic plasticity, the ability of an organism to change its phenotype to match local environments, is increasingly recognized for its contribution to evolution. However, few empirical studies have explored the molecular basis of plastic traits. The East African cichlid fish Astatoreochromis alluaudi displays adaptive phenotypic plasticity in its pharyngeal jaw apparatus, a structure that is widely seen as an evolutionary key innovation that has contributed to the remarkable diversity of cichlid fishes. It has previously been shown that in response to different diets, the pharyngeal jaws change their size, shape and dentition: hard diets induce an adaptive robust molariform tooth phenotype with short jaws and strong internal bone structures, while soft diets induce a gracile papilliform tooth phenotype with elongated jaws and slender internal bone structures. To gain insight into the molecular underpinnings of these adaptations and enable future investigations of the role that phenotypic plasticity plays during the formation of adaptive radiations, the transcriptomes of the two divergent jaw phenotypes were examined. Our study identified a total of 187 genes whose expression differs in response to hard and soft diets, including immediate early genes, extracellular matrix genes and inflammatory factors. Transcriptome results are interpreted in light of expression of candidate genes-markers for tooth size and shape, bone cells and mechanically sensitive pathways. This study opens up new avenues of research at new levels of biological organization into the roles of phenotypic plasticity during speciation and radiation of cichlid fishes.

Astatoreochromis alluaudi Pellegrin, 1904 Fig. 5 Alluaud’s haplo, local names: ‘Ifuro muhunde, Ifuro y’itanza, Ifuro y’ikomagi’ where ‘Ifuro’ is the local name given to all haplochromine species (Upper Akagera system, Burundi), ‘Icyasamyi’, ‘Ikaje’ or ‘Nyiramuhundi’ (Middle Akagera system, Rwanda). Astatoreochromis alluaudi Pellegrin, 1904: 385. Astatoreochromis alluaudi alluaudi Greenwood, 1959: 174, figs 1-3. Astatoreochromis alluaudi occidentalis Greenwood, 1959: 174-175, figs 2-3. Diagnosis Astatoreochromis alluaudi can be distinguished from A. straeleni by the possession of 4-7 anal spines (usually 5-6) vs. 3-4 (usually 3), 17-19 dorsal spines [rarely 16 (f2) or 20 (f2)] vs. 16-18 [exceptionally 19 (f1)]. Etymology Named after Charles A. Alluaud, who collected the type specimens. Type material Lectotype MNHN 1904.137, Kavirondo Gulf, Lake Victoria, Kenya, designated by Greenwood (1959: 167). Paralectotypes MNHN 1904.138–139, BMNH 1904.6.281, same data as lectotype. Specimens examined KENYA: MNHN 1904.137, lectotype, 121.7 mm SL, Kavirondo Gulf Lake Victoria, coll. Alluaudi; BMNH 1904.6.28.1, paralectotype, 116.0 mm SL, same data as lectotype; MNHN 1904.138–139, paralectotypes, 92.8-113.8 mm SL, same data as lectotype. UGANDA: AMNH 216258 (3 specimens), 53.5-70.7 mm SL, Lake Nabugabo, coll. L.J. Chapman & C.A. Chapman, 19 May 1994; BMNH 1964.7.1.109, 85.5 mm SL, Lake Nabugabo, coll. Cambridge University; BMNH 1933.2.23.146 (11 specimens), 55.2-137.5 mm SL, Lake Nakavali, coll. E. Worthington; BMNH 1958.12.5.74-75, 63.8- 121.4 mm SL, Lake Nakavali, coll. C. Pitman; BMNH 1972.6.5.23-25, 44.8-101.6 mm SL, Lake George, coll. I. Dunn; BMNH 1933.2.23.137-141, 61.4-79.8 mm SL, Lake Edward, coll. E.Worthington; BMNH 1929.1.24.4, 87.8 mm SL, Lake Kyoga, coll. E. Worthington; BMNH 1929.1.24.278, 70.9 mm SL, Lake Kyoga, coll. E. Worthington; MRAC A5.42.P.2-5, 66.3-128.4 mm SL, Lake Kayanza, Kasese factory, coll. M. Marquet, 22 Oct. 2005; MRAC 14862-3, 95.9-111.1 mm SL, Nyanza, Lake Victoria, coll. D.E. Bayon; MRAC 90.035.P. 12, 124.2 mm SL, Gaba near Kampala, Lake Victoria, 0°15’ S – 32°28’ E, coll. D. Nyeko, 18 Mar. 1990. DEMOCRATIC REPUBLIC OF CONGO: MRAC 66003, 51.3 mm SL, Semliki River, Ishango, coll. H. Damas. TANZANIA: MRAC 81.30.P.4-5, 94.5-96.5 mm SL, Mwanza gulf, Lake Victoria, collector. HEST-Collection, 1977-1980; MRAC 90.16.P.1-3, 73.7-79.7 mm SL, Kiboko, Lake Victoria. BURUNDI: MRAC 81.P.47.512-535, 63.7-112.7 mm SL, Nyagisozi, Lake Rweru, 02°28’ S – 30°18’ E, coll. G. Ntakimazi, 6 May 1981; MRAC 93.149.P.27, 71.7 mm SL, Yaranda, maison Turquien, Lake Cohoha, 02°32’ S – 30°06’ E, coll. J. Snoeks et al., 28-29 Jul. 1993; MRAC 93.149.P.41, 83.8 mm SL, Yaranda, maison Turquien, Lake Cohoha, 02°32’ S – 30°06’ E, coll. J. Snoeks et al., 28-29 Jul. 1993; MRAC 93.149.P.28-40, 57.2-121.6 mm SL, Lake Rwihinda, ‘lac aux oiseaux’, 02°35’ S – 30°06’ E, coll. J. Snoeks et al., 9-10 Aug. 1993. RWANDA: MRAC 87.11.P. 2827- 2828, 73.6-83.4 mm SL, Lake Hago, Akagera park, coll. L. De Vos, 12 Oct. 1986; MRAC 87.P. 11.2852, MRAC 87.11.P. 2852-55, 61.5-71.9 mm SL, Lake Mpanga, ‘à l’entrée du parc Akagera’ coll. L. De Vos, 5 Nov. 1986; MRAC 86.01.P.1955, 99.2 mm SL, Lake Birengero, Akagera park, coll. L. De Vos, 14 Sep. 1985. Redescription Based on 87 specimens including lectotype and three paralectotypes. Morphometrics and meristics are given in Table 5. Small to medium-sized species [maximum size, 163 mm SL (Greenwood 1959)] with moderately compressed body; dorsal head profile fairy steeply sloping, straight or decurved, becoming concave in large individuals. Mouth horizontal or slightly oblique. Jaws equal anteriorly or lower somewhat projecting; posterior tip of maxilla reaching, or almost reaching, vertical to anterior orbital margin. Gill rakers short and stout; generally 8 or 9 [7(f1), 8 (f30), 9 (f49), 10 (f7)] on the lower limb of the first gill-arch. Flank scales around lateral line ctenoid, elsewhere cycloid; generally 29-32 longitudinal line scales, excluding the small scales on caudal fin base [26 (f1), 27(f2), 28 (f5), 29 (f8), 30 (20), 31 (f29), 32 (f14)]; cheek with 3 (f24), 4 (f57) or 5 (f5) series of scales; scales between pectoral and pelvic fins 4 (f35), 5 (f40) or 6 (f8) [rarely 3 (f1)]. Dorsal fin spines 17-19 [rarely 16 (f2) or 20 (f2)], soft rays 7 (f29) or 8 (f51) [occasionally 6 (f2) or 9 (f5)]. Anal fin spines 4-7 [(4 (f7), 5 (f63), 6 (f17) and 7 (f2)], rays 6 (f9), 7 (f56) or 8 (f20) [rarely 9 (f2)]. Pectoral fin rays 13 (f32) or 14 (f54) [rarely 15 (f1)]. Caudal fin rounded. Posteriormost teeth in outer row of upper jaw unicuspid. In small specimens, outer row teeth unequally bicuspid and relatively stout (occasionally only stout unicuspid teeth in small specimens) becoming a mixture of weakly bicuspid and unicuspid in large specimens. 28-48 outer row teeth in upper jaw and 20-42 outer row teeth in lower jaw with numbers increasing with size, 1 or 2 (occasionally 3) inner rows of small tricuspid or occasionally unicuspid teeth in both lower and upper jaws. LPJ triangular, longer than, or almost as long as, wide (LPJ width 78.1-108.5% of LPJ length); lateral teeth in the posterior rows slender and cuspidate, the central two to four (occasionally six) rows with a mixture of molariform (anterior part of the dentigerous area) and enlarged but cuspidate teeth. The specimens from Lake Victoria have a more massive LPJ and a greater proportion of molariform teeth compared to the similarly sized specimens from other lakes and rivers in the Victoria basin. Colour pattern of live specimens See Fig. 5 for general appearance. Anteriorly and dorsally grey yellowish, posterior-ventrally grey greenish to bluish. A dark band, continuous with lachrymal stripe, runs obliquely backwards through, or a little behind, the eye to near the gill opening. Lower jaw faint grey bluish. Fins grey yellowish, dorsal fin somewhat darker and with blackish spots on soft part; caudal fin with similar spots, pelvic blackish distally; anal fin of specimens (males and females) larger than 80 mm SL with 2-3 horizontal rows of bright orange-yellow ocelli. In specimens less than 80 mm SL, anal ocelli may be absent or hardly visible. According to Greenwood (1959), sexual dimorphism is less marked in this species than in other haplochromine cichlids and the colour pattern of breeding males resembles that of females except that the soft dorsal fin is more densely spotted, the spinous dorsal and entire caudal fin are suffused with maroon, and the cephalic marking are more intense than in females. Colour pattern of preserved specimens General appearance greyish-brown to brown, lighter ventrally; five or six dark transverse bars often interrupted ventrally on the flanks (lacking in some specimens). No mid-lateral band present. A vertical, or posteriorly directed, blackish bar below the eye, runs to posterior corner of mouth, occasionally extending onto lower jaw. Blackish dots arranged in interrupted horizontal rows on soft dorsal fin and in interrupted vertical rows on caudal fin; these are strongly marked in large males. Edge of fins dark to blackish, anal ocelli in males, when present dark grey. Distribution Known from lakes Edward, Victoria, Kyoga, George, Nakavali and Kachira, and the rivers and streams associated with these lakes, including the Semliki (Greenwood 1959). The species has been introduced into many areas of East Africa for biological mollusc control (Greenwood 1965b; Welcomme 1988) and now has a widespread distribution within the Victoria basin (Kenya, Uganda & Tanzania including the Upper Akagera basin in the Bugesera depression (Burundi & Rwanda)). Slootweg (1989) discussed the possibility of the introduction of A. alluaudi into northern Cameroon (Benue River basin), which indeed took place (Vreven et al. 2007). There are no reports that the introduction of this species in the Congo Republic, the Democratic Republic of Congo, the Republic of Central Africa and Zambia (Welcomme 1988) has succeeded. Ecology According to Greenwood (1959), A. alluaudi is not confined to a particular type of substrate and is ubiquitous in all areas where the water is less than 20 m deep. It also occurs in papyrus swamps and feeds mainly on molluscs. Ntakimazi (1985) confirmed the occurrence of the species in papyrus swamps in Lake Rweru, Bugesera depression (Burundi & Rwanda). However, he did not find any shell fragments of snails in the gut contents of 80 specimens, but instead found a large amount of organic debris, algae, fish remains and benthic invertebrates. He concluded that A. alluaudi might be an omnivorous species that switches to the most abundant food source in its environment. He noticed, however, that the molariform teeth of the lower pharyngeal jaw are well developed, and suspected they are instrumental in crushing the exoskeletons of aquatic invertebrates and vegetal debris. Reproduction The species is a mouth-brooder. Most of the females caught in December 2012 in Lake Rweru in Burundi had fry in their mouth. Though its breeding period is not well documented, the species may reproduce at the end of the short rain season from November to December. Whether this is the only reproductive season cannot be determined from our data., Published as part of Banyankimbona, Gaspard, Vreven, Emmanuel & Snoeks, Jos, 2013, A revision of the genus Astatoreochromis (Teleostei, Cichlidae), East-Africa, pp. 1-21 in European Journal of Taxonomy 39 on pages 10-13, DOI: 10.5852/ejt.2013.39, http://zenodo.org/record/3814023, {"references":["Pellegrin J. 1904. Contribution a l'etude anatomique, biologique et taxonomique des poissons de la famille des Cichlides. Memoire de la Societe Zoologique 16: 41 - 399.","Greenwood P. H. 1959. The monotypic genera of cichlid fishes in Lake Victoria, part II. Bulletin of the British Museum (Natural History), Zoology 5: 165 - 177.","Greenwood P. H. 1965 b. The Cichlid fishes of Lake Nabugabo, Uganda. Bulletin of the British Museum (Natural History), Zoology 9: 349 - 357.","Welcomme R. L. 1988. International Introductions of Inland Aquatic Species. FAO Fisheries, Rome, Italy.","Slootweg R. 1989. Proposed introduction of Astatoreochromis alluaudi, an East African mollusk crushing cichlid, as a means of snail control. Annales en Sciences zoologiques 257: 61 - 64.","Vreven E. J., Musschoot T., Boden G. & Stiassny M. 2007. Introduced or alien species of Lower Guinea. In: Stiassny M. L. J., Teugels G. G. & Hopkins C. D. (eds) The Fresh and Brackish Water Fishes of Lower Guinea, West-Central Africa, Vol. 1: 57 - 101. IRD, MNHN, Paris; MRAC, Tervuren.","Ntakimazi G. 1985. Hydrobiologie du Bugesera (Akagera - Haut-Nil), en particulier des lacs Cohoha Sud et Rweru en vue d'une gestion qualitative de la faune piscicole. Volume I-II. Dissertation, Fondation Universitaire Luxembourgeoise, Luxembourg."]}

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.

Organisms are tightly packed with structures so architectonic interdependency of structures is an obvious aspect of integration. This aspect of functional morphology, however, has received remarkably little attention. The present paper presents an example of the spatial relations among several apparatuses in the head of the cichlid fish, Astatoreochromis alluaudi . It investigates the transformations of these apparatuses and their functions due to a change in the pharyngeal jaw apparatus resulting from a functional shift (insect eating to snail crushing or vice versa ). The volume of the pharyngeal jaw apparatus differs 55% between the insect eating- and the snail eating morph. The increase in volume of the pharyngeal jaw apparatus has an impressive number of spatial effects, both direct and indirect, on other structures. Reallocation of space within the pharyngeal jaw apparatus occurs. Total head volume increases 31% but a reallocation of space is still necessary as the increase of the opercular compartment where the pharyngeal jaw apparatus is situated compensates for only 59% of the volume increase of that. Not all spatial effects do impose constraints. Spatial constraints are avoided when one of the apparatuses can use a topographically different volume of space. The respiratory apparatus shows internal reallocations of space without loss of total volume. The same solution occurs for elements of the expansion apparatus and the buccal cavity. The eyes are not influenced. Finally spatial effects can have positive repercussions. The muscles of the oral jaw apparatus increase in size. This may be an example of an epiphenomenon.

Phenotypic differences of the pharyngeal jaw apparatus between morphs of Astatoreochromis alluaudi are well known. But only a limited number of elements have been described in detail. In this study an anatomical description of elements markedly differing between the two extremes of the phenotypic range - the snail-eating and the non-snail-eating morph - is provided, and compared with the anatomy of a generalized Haplochromis species, H. elegans. Many skeletal elements and muscles of the pharyngeal jaw apparatus show hypertrophy in the snail-eating (hypertrophied) morph. However, the elements of the pharyngeal jaw apparatus of the non-snail-eating (non-hypertrophied) morph, which mainly feeds on insects, are generally more hypertrophied than the elements in the obligate insectivorous species H. elegans. Many of the differences between the two morphs can be interpreted functionally as adaptations to the increased crushing force of the hypertrophied morph. Differences between the morphs were compared with literature data of differences between non-durophagous and durophagous trophic types in other labroid taxa and in the Centrarchidae. Comparable differences are found for the pharyngeal jaw bones and the two largest pharyngeal muscles. The functional demands of crushing hard prey types appear to be very similar for the different groups. The small muscles show only slight similarity. Demands of other functions may co-determine their shape.

The potentially molluscivorous cichlid fish Astatoreochromis alluaudi is known to exhibit a pronounced phenotypic plasticity in its pharyngeal jaw apparatus. Two phenotypes (wild-caught snail-eating specimens and specimens raised on soft food) were examined for differences in the number, size, shape, spacing and wear of functional teeth on the lower pharyngeal jaw. During growth, snail-eating specimens maintain tooth numbers but invest in teeth of a larger size (width and depth). In contrast, specimens fed a soft diet invest in more teeth, their size remaining unchanged except for the central, most posterior teeth. All changes in the dentition must be achieved through successive tooth generations. Serial microradiographs in the caudal area of the lower pharyngeal jaw, a region that is most significant in food processing, indicated that functional teeth in hard-food specimens more often show a successor below. This may be due to more time needed for larger replacement teeth to form and possibly to a shorter replacement cycle linked to the greater wear of the functional teeth. It is hypothesized that maintenance of tooth numbers and increase of tooth size in hard-food specimens is achieved by a one-for-one replacement and expansion of the tooth-bearing region and possibly by closer spacing of the teeth. Increase of tooth numbers in the soft-food specimens is probably achieved through the establishment of new tooth loci at the margins of the dentigerous area in addition to a one-for-one replacement.

The use of molluscivorous fish for biological control of snail intermediate hosts of schistosomiasis is a regularly reappearing theme in the literature on schistosomiasis control. The effectiveness of this control method has not yet been demonstrated, and conclusive field evidence is lacking. In this article the literature on snail control by fish is critically reviewed. Special attention is paid to the cichlid fish Astatoreochromis alluaudi that has been used in well-documented field trials in Kenya and Cameroon. After some small initial success, after a longer period the fish appeared to be ineffective in snail control. Moreover, the fish reproduces at a pace too slow to be of use in large-scale biocontrol trials. Laboratory observations on foraging behaviour and anatomy of the fish give essential cues to explain the failure of the fish in snail control. An observed reduction in the fishes' pharyngeal jaw apparatus, used to crush snails shells, results in a lower profitability of snails. As predicted by a simple foraging model, the prey preference of the fish shifts towards other more profitable prey items, such as benthic and pelagic macrofauna. Although eradication of snails by fish will not be feasible in most cases, the role of natural predators of snails cannot be neglected, and may still be of importance in integrated control efforts.

The haplochromine cichlids of the African Great Lakes have evolved into a spectacularly ecologically diverse 1 800 species. However, even within the same lake, not all cichlid lineages have radiated equally and many lineages have remained relatively species depauperate. Multiple biological factors particular to superflock species have been proposed, one of which is extreme environmental sensitivity (stenotopy) resulting in restricted dispersal, which ultimately fosters microallopatric speciation. We use DNA microsatellite loci to estimate neutral genetic diversity and the level of gene flow among populations of two cichlid species from southern Lake Victoria, Africa: the endemic and stenotopic superflock species Pundamilia nyererei and the non-endemic, widespread species Astatoreochromis alluaudi. The two species have similar levels of overall gene diversity (A. alluaudi H = 0.689; P. nyererei H = 0.737). Both species show limited spatial-genetic structure among individuals. Our findings suggest that contemporary gene flow at small spatial scales may not be very different between these two cichlid species with different ecologies. We suggest that the level of contemporary gene flow at fine spatial scales may not be related to the historical rate of speciation. Key words: cichlid fishes; gene flow; spatial-genetic autocorrelation; population genetics; microsatellites; Lake Victoria

One of the possible negative side-effects of aquaculture in tropical areas is the spread of water-related diseases, in particular schistosomiasis. Fish ponds can provide breeding sites for freshwater snails transmitting schistosomiasis (Berrie 1966). Scientific attention has long been concentrated on the use of molluscicides as the most effective means of snail and schistosomiasis control. However, molluscicides have limited use in aquaculture as they are expensive, hazardous to many other forms of aquatic life including fish, and have to be applied regularly because of the rapid recolonization by snails. This paper describes a study made on snail populations in an aquaculture station in northern Cameroon and their possible relation with water quality, pond management and cultured fish species. Together with production experiments, the development of snail populations in the fish ponds has been monitored during 2 years, and the biological control potentiality of two fish species has been tested. The experiments are part of a larger programme on the integrated control of schistosomiasis in the upper Benue Valley of northern Cameroon (Slootweg 1991). Three species of fish were used in the pond experiments. The tilapia, Oreochromis niloticus (L.), was used for production experiments under different nutritional regimes. To control the excessive reproduction by O. niloticus, the African catfish, Clarias gariepinus Burchell, was introduced in several experiments. C. gariepinus is also known to eat snails; based on stomach contents analyses of fish caught in an irrigation scheme in Sudan, Coates (1984) suggested using C. gariepinus in the control of schistosomiasis vector snails. As a third species, the East African cichlid fish Astatoreochromis alluaudi Pellegrin was introduced solely to test its capability to control molluscs (Slootweg 1989). In the literature A. alluaudi has often been recommended as a means of biological snail control, but the number of actual field trials is very limited. One experiment in Xenya showed a significant reduction in snail populations over a long period (McMahon 1960; McMahon, Highton & Marshall 1977), although contradictory evidence is given by recent research (Kat SL Kibberenge 1990). One successful experiment has been described from an aquaculture station near Yaounde in Cameroon (Bard & Mvogo 1963; Mvogo & Bard 1964), but has never been repeated afterwards.

The stable isotope ratio and seasonal changes in diet of Alluaud’s haplo Astatoreochromis alluaudi ,a cichlid fish with massive pharyngeal jaws well known for its ability to process hard-bodied prey, are described. The diet of A. alluaudi was quantified in Lake Saka, Uganda, over a period of 30 months. Variation in physico-chemical variables (mean monthly rainfall, water temperature, turbidity and dissolved oxygen), as well as potential competitor density and food abundance, was measured throughout the second half of the study (14 months). Stomach contents and isotope analysis revealed a diet comprised mainly of fishes and insects, with a low contribution of molluscs (0–33%) in any given month. No correlation was detected between diet and either macroinvertebrate abundance or competitor abundance. The running average rainfall was positively related to the percentage of fish consumed per month. Although A. alluaudi exhibits an apparent molluscivorous trophic morphology in Lake Saka, molluscs did not appear to compose a major portion of its diet. Gradients of rainfall seemed to be the most important environmental predictor of diet choice in Lake Saka. These results are discussed with reference to Liem’s Paradox that apparently morphologically specialized fishes often function as generalist feeders in the wild.

The recent explosive adaptive radiation of cichlids in the great lakes of Africa has attracted the attention of both morphologists and molecular biologists. To decipher the phylogenetic relationships among the various taxa within the family Cichlidae is a prerequisite for answering some fundamental questions about the nature of the speciation process. In the present study, we used the random amplification of polymorphic DNA (RAPD) technique to obtain sequence differences between selected cichlid species. We then designed specific primers based on these sequences and used them to amplify template DNA from a large number of species by the polymerase chain reaction (PCR). We sequenced the amplified products and searched the sequences for indels and shared substitutions. We identified a number of such characters at three loci--DXTU1, DXTU2, and DXTU3--and used them for phylogenetic and cladistic analysis of the relationships among the various cichlid groups. Our studies assign an outgroup position to Neotropical cichlids in relation to African cichlids, provide evidence for a sister-group relationship of tilapiines to the haplochromines, group Cyphotilapia frontosa with the lamprologines of Lake Tanganyika, place Astatoreochromis alluaudi to an outgroup position with respect to other haplochromines of Lakes Victoria and Malawi, and provide additional support for the monophyly of the remaining Lake Victoria haplochromines and the Lake Malawi haplochromines. The described approach holds great promise for further resolution of cichlid phylogeny.

Among the many food resources exploited by cichlids, molluscs are exceptional because they are enclosed in a shell of hard, dense and indigestible material. This study investigates some of the implications of this for prey processing in Astatoreochromis alluaudi, one of many cichlid species which crush the shell of their prey between their pharyngeal jaws. These so-called pharyngeal mollusc crushers were believed to ingest together with the molluscs flesh the entire, crushed shell. However, my study revealed that they eject shell fragments before ingesting their prey. The amount of mollusc shell ejected by A. alluaudi depends on the type and size of the mollusc and the size of the fish. The percentage of shell ejected increases with prey size and decreases with predator size for all prey species. More shell of gastropods than of bivalves is ejected. Shell fragments are ejected because shell ingestion affects (1) the buoyancy of the fish and (2) the space available for food storage in the guts. One model illustrates to what extent (1) the swimbladder volume has to increase to compensate for loss of buoyancy and (2) the storage space for mollusc flesh in the intestines is decreased when shell is ingested. A second model, which is based on the change of swimbladder volume in vertical movements, illustrates how prey ingestion may affect vertical movements and vice versa. Ingestion of more shell will decrease the upward vertical movement of the fish on the one hand and increased allowance for upward vertical movements will decrease the intestinal storage space on the other. The relevance of the results to foraging models and to theories on the evolution of shell form is indicated.