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We examined levels of genetic variability within and among populations of three Antarctic springtail species (Arthropoda: Collembola) and tested the hypothesis that genetic divergences occur among glacially-isolated habitats. The study was conducted in southern Victoria Land, Ross Dependency, Antarctica, and samples were collected from locations in the vicinity of the Mackay Glacier. We analyzed mt DNA ( cytochrome c oxidase subunit I; COI) sequence variability for 97 individuals representing three species ( Gomphiocephalus hodgsoni, N = 67; Cryptopygus nivicolus, N = 20; and Antarcticinella monoculata, N = 8). Haplotype diversity and genetic divergences were calculated and used to indicate population variability and also to infer divergence times of isolated populations using molecular clock estimates. Two of the three species showed high levels of genetic divergence. Gomphiocephalus hodgsoni, a widespread and common species, showed 7.6% sequence divergence on opposite sides of the Mackay Glacier. The more range restricted C. nivicolus showed 4.0% divergence among populations. The third species, A. monoculata, was found in only one location. Molecular clock estimates based on sequence divergences suggest that populations separated within the last 4 Mya. We conclude that habitat fragmentation resulting from Pliocene (5 Mya) and Pleistocene (2 Mya to 10 Kya) glaciations has promoted and maintained high levels of diversity among isolated springtail populations on relatively small spatial scales. The region surrounding the Mackay Glacier is likely to have provided refugia for springtail populations during glacial maxima and remains an area of high genetic and species diversity for Collembola within the Ross Sea region. [ABSTRACT FROM AUTHOR]

Previous studies of the microarthropods of Marion Island, Southern Ocean, documented high mitochondrial COI (cytochrome c oxidase subunit I) haplotype diversity and significant genetic structure, which were ascribed to landscape subdivision. In this paper we revisit these ideas in light of new geomorphological evidence indicating a major lineament orientated along N26.5°E. Using the microarthropod Halozetes fulvus, we test the hypothesis that the eastern and western sides of the island show different population genetic patterns, corresponding to the previously unrecognized geological separation of these regions, and perhaps also with differences in climates across the island and further landscape complexity. Mitochondrial COI data were collected for 291 H. fulvus individuals from 30 localities across the island. Notwithstanding our sampling effort, haplotype diversity was under-sampled as indicated by rarefaction analyses. Overall, significant genetic structure was found across the island as indicated by ΦST analyses. Nested clade phylogeographical analyses suggested that restricted gene flow (with isolation-by-distance) played a role in shaping current genetic patterns, as confirmed by Mantel tests. At the local scale, coalescent modelling revealed two different genetic patterns. The first, characterizing populations on the south-western corner of the island, was that of low effective population size and high gene flow. The converse was found on the eastern side of Marion Island. Taken together, substantial differences in spatial genetic structure characterize H. fulvus populations across Marion Island, in keeping with the hypothesis that the complex history of the island, including the N26.5°E geological lineament, has influenced population genetic structure. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 131-145. [ABSTRACT FROM AUTHOR]

Onithochiton neglectus is a morphologically variable, brooding chiton inhabiting coastal reefs throughout New Zealand and its Sub-Antarctic Islands. Southern O. neglectus populations are typically associated with buoyant kelp (Durvillaea spp.) and are potentially connected via kelp-rafting. Northern O. neglectus populations are less likely to raft, due to lower numbers of Durvillaea in northern New Zealand. To test for the impact of kelp-rafting on the spatial distribution of variation in O. neglectus , we undertook a combined analysis of morphological and genetic variation across the range of the species. Geometric morphometrics were used to assess shell shape. We detected a northern vs. southern split in shell shape, corresponding to the frequency of the O. neglectus / Durvillaea spp. association. To assess O. neglectus genetic patterns across New Zealand, we estimated phylogenetic trees with nuclear (ITS) and mitochondrial (COI and 16S) markers, which revealed distinct northern and southern lineages, and an additional lineage in central New Zealand. Neither the morphological nor genetic groups match existing O. neglectus subspecies, but are concordant with the patterns of association of O. neglectus with Durvillaea. We suggest that shell shape may be linked to O. neglectus ' regionally variable ecological association with kelp holdfasts. [ABSTRACT FROM AUTHOR]

New Zealand has a complex recent history of climatic and tectonic change that has left variable signatures in the geographic distribution and genetic structure of the region's flora and fauna. To identify concordant patterns, a broad range of taxa must be examined and compared. In New Zealand's North Island, a consensus is forming as to the dominant biogeographic barriers in the region although obligate freshwater taxa have not been considered in this framework. We use single-nucleotide polymorphisms to investigate phylogeography in the widespread obligate freshwater fish Gobiomorphus basalis on the North Island. Phylogeographic patterns within G. basalis reveal biogeographic disjunctions that are in some ways consistent and in other ways at odds with established patterns, providing insight into the processes that have shaped the islands' biogeography. We also use phylogeography to delineate species boundaries within the entire New Zealand radiation of Gobiomorphus and find that it contains several morphologically cryptic species. We resolve two clades within G. basalis that correspond to areas north and south of the Taupo Volcanic Zone. We confirm the distinctiveness of Gobiomorphus alpinus relative to Gobiomorphus cotidianus , as well as the presence of two lineages within Gobiomorphus breviceps that were previously identified based on mitochondrial data. [ABSTRACT FROM AUTHOR]

We examined phylogeographic structure in the direct-developing New Zealand endemic intertidal mud whelk, Cominella glandiformis. Two hundred and ninety-six whelks from 12 sites were collected from sheltered shores around New Zealand's four largest islands (North Island, South Island, Stewart Island and Chatham Island), encompassing the geographical range of this species. Despite being direct developers, gene flow among C. glandiformis populations may occur over short distances by adult floating, and over larger distances by rafting of egg masses. Primers were developed to amplify variable microsatellite regions at six loci. All loci were variable, with 8–34 alleles/loci. Observed and expected heterozygosities were high across all alleles, with minimal evidence of null alleles. The average number of alleles varied from 3.5 (Chatham Island) to 7.5 (Waitemata Harbour). Strong genetic structure was evident, with distinct 'eastern' and 'western' groups. Each group extended over a large geographic area, including regions of unsuitable habitat, but were linked by oceanic currents. We suggest that the intraspecific geographic genetic structure in C. glandiformis has arisen due a combination of ocean currents (promoting gene flow between geographically distant regions) and upwelling areas (limiting gene flow between certain regions). [ABSTRACT FROM AUTHOR]

The evolution and diversification of animal reproductive modes have been pivotal questions in behavioural ecology. Amphibians present the highest diversity of reproductive modes among vertebrates, involving various behavioural, physiological and morphological traits. One such feature is the amplexus, which is the clasp or embrace of males on females during reproduction and is found almost universally in anurans. Hypotheses about the origin of amplexus are limited and have not been tested thoroughly, nor have they taken into account evolutionary relationships in most comparative studies. However, these considerations are crucial to an understanding of the evolution of reproductive modes. Here, using an evolutionary framework, we reconstruct the ancestral state of amplexus in 685 anuran species. We investigate whether the type of amplexus has a strong phylogenetic signal and test whether sexual size dimorphism could have influenced amplexus type or male performance while clasping females. Overall, we found evidence of ≥34 evolutionary transitions in amplexus type across anurans. We found that amplexus type exhibits a high phylogenetic signal and that amplexus type does not evolve in association with sexual size dimorphism. We discuss the implications of our findings for the diversity of amplexus types across anurans. [ABSTRACT FROM AUTHOR]

Geographical isolation is a key element in allopatric speciation. If gene flow is interrupted for long enough by geographical barriers, populations can evolve independently and eventually form distinct species. Aegla singularis provides an ideal model to study this process due to the characteristics of the geographical area that it occupies and its limited dispersal ability. Aegla singularis inhabits streams of the Uruguay and Paraná River basins in the Neotropical region of South America. The basins are separated by the Sierra Central Mountains. Here we studied the speciation of A. singularis resulting from geographical isolation by using molecular and morphometric data. Individuals of A. singularis were analysed using geometric morphometrics and genetic data (COII and EFα1). We found significant differences in shape and genetics between A. singularis populations from the two basins. These differences suggest ongoing divergence due to restricted gene flow caused by the geographical barrier of the Sierra Central Mountains, indicating that the populations of the Parana and Uruguay River slopes are undergoing divergence. [ABSTRACT FROM AUTHOR]

Plant–herbivore interactions play an important role in the evolution of small terrestrial and marine herbivores. Some authors consider marine herbivorous amphipods to be ecologically equivalent to terrestrial insects, in that both are small relative to larger host plants, and host choices are often chemically mediated. Different host species provide distinct selective pressures for their associated animal populations, which may act as divergent selection pressure towards adaptive traits related to each host. This phenomenon, termed host-associated differentiation (HAD), has been documented in insects, and can lead to local adaptation, or even ecological speciation. However, whether HAD occurs within marine amphipod species remains unexplored. Here, Cymadusa filosa (Amphipoda, Ampithoidae) and its host macroalgae were used as models to test whether amphipods from different host macroalgae are genetically or morphologically differentiated. Furthermore, we tested for differentiation among geographically separated populations resulting from dispersal limitation. Ten microsatellite loci were used to assess genetic diversity, along with geometric morphometric analyses for morphology. The results indicate that there was no HAD with regard to genetic and morphological features. Individuals seem to be highly mobile on local scales or to disperse as juveniles, and they seem capable of dispering among sites. Two distinct morphological groups were formed, probably related to the environmental conditions at those sites. HAD in marine environments is probably context-dependent, and should be explored for different species and scales to better appraise marine plant–herbivore interactions. [ABSTRACT FROM AUTHOR]

Cominella maculosa and C. virgata are common whelk species that inhabit rocky shores around much of the North Island of New Zealand, the northern South Island and, for C. maculosa, the Chatham Islands. This study used DNA sequences from the mitochondrial gene CO1 to examine the phylogeographical structure of populations of both species in areas that have not previously been sampled. Collections of both species were made from sites in the Cook Strait region, C. maculosa from the Chatham Islands and C. virgata from the northern North Island. Both species were found to have a considerable degree of genetic differentiation, but genetic diversity and phylogeographical patterns differed greatly between regions. South Island populations of C. virgata may have originated, or been supplemented, by human-mediated translocations. Phylogenetic analyses were conducted using the mitochondrial genes CO1 and 16S rRNA, and the nuclear gene 18S rRNA. The northern subspecies C. virgata brookesi did not form a monophyletic lineage and is synonymized with C. virgata. A lectotype is designated for Buccinum lineolatum Quoy & Gaimard, 1833, of which C. virgata is a replacement name. [ABSTRACT FROM AUTHOR]

The spotted whelk, Cominella maculosa, is a common intertidal species endemic to New Zealand with crawl-away juveniles that hatch from benthic egg capsules. The aim of this study was to determine the fine-scale pattern of genetic differentiation and over what distances this direct-developing species can form isolated populations, across a region that includes a known genetic disjunction. Whelks were collected from seven locations, 10–26 km apart, along 125 km of a linear coastline, and DNA sequences from the mitochondrial cytochrome c oxidase subunit I (COI) gene were compared. Four northern sites were genetically differentiated from each other and from the group of three southern sites. The three southern sites showed no genetic differentiation, consistently clustered together in a single group, shared a dominant haplotype and were characterized by a low number of private haplotypes and low haplotype and nucleotide diversity. The two sites located ~10 km north of the southern group lacked private haplotypes and contained high frequencies of both dominant northern and southern haplotypes. The lack of an isolation-by-distance pattern of structure, and a leapfrog-like dispersal grouping of non-neighbouring sites, suggests sporadic long-distance dispersal events occur in this species, even if rarely. [ABSTRACT FROM AUTHOR]

Molecular genetics has proven to be an essential tool for studying the ecology, evolution and epidemiology of parasitic nematodes. However, research effort across nematode taxa has not been equal and biased towards nematodes parasitic in vertebrates. We characterize the evolutionary genetics of the mermithid nematode Thaumamermis zealandica Poinar, 2002 and its host, the sandhopper Bellorchestia quoyana (Milne-Edwards, 1840) (Talitridae: Amphipoda), across sandy beaches of New Zealand's South Island. We test the hypothesis that parasite population genetic structure mirrors that of its host. Sandhoppers and their parasites were sampled at 13 locations along the island's southeastern coast. Sequencing of the mitochondrial gene cytochrome c oxidase subunit 1 (CO1) from B. quoyana reveals a regional pattern of population structure that suggests a northward pattern of dispersal. Surprisingly, no population structure was observed for T. zealandica. In fact, sequencing of three commonly used markers revealed no intraspecific parasite variation. This result suggests that mermithid mtDNA may evolve at an extraordinarily slow pace, perhaps as a result of extensive and frequent changes in gene order and mitochondrial genome length. Furthermore, a mermithid phylogeny based on sequences of the 18S and 28S ribosomal RNA genes suggests that a systematic revision of the family is necessary. [ABSTRACT FROM AUTHOR]

Three sympatric springtail species, from the South Shetland Islands archipelago in the maritime Antarctic, are analysed here in a common biogeographic and evolutionary framework. This study was designed to compare their population genetic structure using the same molecular marker. Haplotype data for the mitochondrial cox1 gene have been obtained for seven populations of Folsomotoma octooculata and are compared with the data obtained, in previous studies and the current one, for the sympatric species Cryptopygus antarcticus antarcticus, and Friesea grisea. Molecular data obtained are consistent with the hypothesis that all species have been present in the archipelago since well before the last glacial maximum (around 20 000 ybp) and that their early diversifications appear to be linked with known interglacial periods in the region. These springtails may have survived the last glacial cycle in local refugia, from which they dispersed subsequently to ice-free ground re-exposed during the current interglacial period. The populations of the different species diversified at different times, although all of them are within the Pleistocene epoch. We propose that the earliest diversification of haplotypes in all three springtails in this archipelago occurred from local refugia in Livingston I., with subsequent spread of some haplotypes throughout the South Shetland Islands. [ABSTRACT FROM AUTHOR]

The postglacial European colonization history has come into the focus of biogeographical interest and the study of phylogenetic relatedness within and between regional faunas and floras has proven to be an effective tool for the reconstruction of postglacial colonization trajectories. In the present study, we used a faunal compilation of 2078 European springtail species and data on taxonomic relatedness to investigate whether phylogenetic diversity increases along the gradients from southern glacial refugia towards northern Europe and also whether glacial refugia are phylogenetically segregated, as predicted by models of glacial evolutionary processes and postglacial colonization. In addition, we investigated whether species of restricted range sizes differ in phylogenetic diversity from widespread species as expected by niche models. Proportions of species with restricted range size were highest in glacial refugia, particularly in Spain, as well as on Northern European islands. We found contrasting latitudinal gradients of phylogenetic diversity decreasing in widespread species and increasing in restricted species. Endemic relatedness was negatively correlated with island size. Peaks of phylogenetic diversity in the Pannonian regions and on islands far north indicate a faunal contribution from several glacial refugia and additional refugia north of the Alps, respectively. High phylogenetic clustering in the Iberian Peninsula corroborates models of glacial speciation pulses within major refugia. [ABSTRACT FROM AUTHOR]

Host-parasite co-evolution can lead to genetic differentiation among isolated host-parasite populations and local adaptation between parasites and their hosts. However, tests of local adaptation rarely consider multiple fitness-related traits although focus on a single component of fitness can be misleading. Here, we concomitantly examined genetic structure and co-divergence patterns of the trematode Coitocaecum parvum and its crustacean host Paracalliope fluviatilis among isolated populations using the mitochondrial cytochrome oxidase I gene ( COI). We then performed experimental cross-infections between two genetically divergent host-parasite populations. Both hosts and parasites displayed genetic differentiation among populations, although genetic structure was less pronounced in the parasite. Data also supported a co-divergence scenario between C. parvum and P. fluviatilis potentially related to local co-adaptation. Results from cross-infections indicated that some parasite lineages seemed to be locally adapted to their sympatric (home) hosts in which they achieved higher infection and survival rates than in allopatric (away) amphipods. However, local, intrinsic host and parasite characteristics (host behavioural or immunological resistance to infections, parasite infectivity or growth rate) also influenced patterns of host-parasite interactions. For example, overall host vulnerability to C. parvum varied between populations, regardless of parasite origin (local vs. foreign), potentially swamping apparent local co-adaptation effects. Furthermore, local adaptation effects seemed trait specific; different components of parasite fitness (infection and survival rates, growth) responded differently to cross-infections. Overall, data show that genetic differentiation is not inevitably coupled with local adaptation, and that the latter must be interpreted with caution in a multi-trait context. [ABSTRACT FROM AUTHOR]

Population genetic research has transformed from the study of genetic structures into a much wider and highly multidisciplinary research field. In this contribution, we outline the limitations of classic population genetic data and highlight the potential of combining molecular data with additional environmental, ecological and biological data sets in multidisciplinary approaches. The combination of data sets from various fields allows a more comprehensive understanding of extrinsic and intrinsic evolutionary processes affecting populations such as the distinction between genetic drift and natural selection. The integration of population size estimates and demographic dynamics as well as individual behaviour (embracing aspects like dispersal behaviour) allows for testing of adaptations to local environments and understanding time-lags frequently observed in molecular data. Modelling approaches are integrated at increasing rates into population genetic research to identify potential barriers and corridors. In our review, we therefore highlight multiple synergistic effects when combining population genetic data with morphological, ecological, behavioural data and modelling. We outline strengths and limitations and indicate future possibilities and challenges. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 1-12. [ABSTRACT FROM AUTHOR]

The deep ocean supports a highly diverse and mostly endemic fauna, yet little is known about how or where new species form in this remote ecosystem. How speciation occurs is especially intriguing in the deep sea because few obvious barriers exist that would disrupt gene flow. Geographic and bathymetric patterns of genetic variation can provide key insights into how and where new species form. We quantified the population genetic structure of a protobranch bivalve, Neilonella salicensis, along a depth gradient (2200-3800 m) in the western North Atlantic using both nuclear (28 S and calmodulin intron) and mitochondrial (cytochrome c oxidase subunit I) loci. A sharp genetic break occurred for each locus between populations above 2800 m and below 3200 m, defining two distinct clades with no nuclear or mitochondrial haplotypes shared between depth regimes. Bayesian phylogenetic analyses provided strong support for two clades, separated by depth, within N. salicensis. Although no morphological divergence was apparent, we suggest that the depth-related population genetic and phylogenetic divergence is indicative of a cryptic species. The frequent occurrence of various stages of divergence associated with species formation along bathymetric gradients suggests that depth, and the environmental gradients that attend changes in depth, probably play a fundamental role in the diversification of marine organisms, especially in deep water. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 897-913. [ABSTRACT FROM AUTHOR]

Honest-advertisement models of sexual selection suggest that condition-dependent male secondary sexual characters could function as reliable signals of male quality, enabling females to discriminate among potential partners, both in the pre- and post-copulatory phases. In this context, many studies have revealed the importance of promiscuous mating systems and female sperm storage in determining the occurrence of such a model of sexual selection. By contrast, few studies have investigated the presence and extent of post-copulatory female choice in chelonian species. The present study aimed to investigate the effect of male size, male-male competition, and courtship intensity on paternity distribution in Testudo hermanni hermanni, combining behavioural and genetic data. We created experimental groups composed of two males of different sizes and three or four randomly selected females. Observations conducted during social interactions between males revealed that a hierarchy, unrelated to male size, was soon established: Alpha males were more aggressive towards competitors and courted females more intensively. Alpha males also achieved a higher mounting success than Beta males. Paternity analysis performed on hatchlings produced from experimental females revealed that male reproductive success was not correlated with male-female size ratio. Finally, despite the higher mounting success of Alpha males, paternity analysis revealed that male reproductive success did not differ between Alpha and Beta males. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 656-667. [ABSTRACT FROM AUTHOR]

The present study investigated the fine-scale population genetic structure of sympatric asterinid sea stars with contrasting modes of larval development (benthic versus pelagic). Parvulastra exigua lacks a dispersive life phase yet is one of the worlds most widely distributed and abundant sea stars, whereas Meridiastra calcar, a sea star with a dispersive larva, has a more limited regional scale distribution. Populations of P. exigua sampled from tide pools on three adjacent headlands showed significant genetic substructure (mitochodrial DNA control region) at fine spatial scales (tide pools < 300 m apart: FST = 0.249, P < 0.01; headlands 5-15 km apart: FST = 0.125, P = 0.04). As expected, M. calcar populations sampled from the same headlands did not exhibit significant genetic structuring ( FST = 0.029, P = 0.14). The life-history traits of P. exigua, a mixed mating system (selfing + outcrossing), pseudocopulation among closely-related conspecifics, and an entirely benthic life cycle with a philopatric larva, undoubtedly influence its strong genetic structure across fine spatial scales. Localized genetic structure, especially at the very fine-scale of tide pools, would not be detected in the more typical regional scale approaches adopted by most studies of marine invertebrate populations. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, ●●, ●●-●●. [ABSTRACT FROM AUTHOR]

Vicariant geographic isolation and resource partitioning have long been independently identified as processes contributing to the morphological divergence of closely-related species. However, little is known about the extent to which vicariant history influences the adaptive ecological divergence associated with resource partitioning and trophic specialization within species. The present study thus quantified the contribution of vicariant historical genetic divergence to the adaptive contemporary morphological divergence of intraspecific feeding specialists in the Rainbow smelt (Pisces: Osmerus mordax). This species is characterized by the polyphyletic origin of two lacustrine feeding specialists originating in two intraspecific lineages associated with independent glacial refuges. The historical genetic segregation was initiated approximately 350 000 years ago, whereas the lacustrine trophic segregation arose within the past 10 000 years. Wild caught lacustrine smelt populations were grouped a priori based on known historical genetic identities (Acadian and Atlantic mitochondrial DNA clades) and contemporary feeding specializations (microphageous and macrophageous morphotypes). The present study demonstrated that independent suites of correlated morphological traits are associated with either vicariant history or contemporary feeding specializations. Second, functionally-similar feeding specialists exhibit distinct morphologies resulting largely from vicariant historical processes. Although, the evolutionary processes producing historical phenotypes remains unknown, the results obtained demonstrate how adaptive radiation associated with ecological resource partitioning and feeding specializations can be strongly influenced by intraspecific phenotypic diversification resulting from relatively recent vicariant histories. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 140–151. [ABSTRACT FROM AUTHOR]

In the present study, we employed three mitochondrial DNA genetic markers in a phylogenetic analysis aiming at the delineation of the relationships amongst nominal Trachelipus kytherensis populations, as well as between populations of this species and of Trachelipus aegaeus and a new form, occurring syntopically with the latter. Both the phylogenetic analysis and the genetic distances separating populations, show the presence of several distinct and well differentiated clades that undermine the monophyly of T. kytherensis. On the other hand, despite the insular distribution of T. aegaeus populations, their divergence is low and the monophyly of this taxon can be rescued by the inclusion of two more insular populations previously assigned to T. kytherensis. The patterns of genetic divergence among clades are only partially congruent with the geographic distribution of populations. The validity of taxonomic characters used so far in the genus appears to be questionable; therefore, a more comprehensive phylogenetic study at a population level is deemed necessary for understanding the divergence of Trachelipus lineages. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 361–370. [ABSTRACT FROM AUTHOR]

The present study investigated the morphological and genetic differentiation pattern between two sympatric dung beetle sister species, Onthophagus taurus and Onthophagus illyricus. The geometric morphometric approach coupled with the use of molecular markers allowed examination of the nature of interspecific relationships and an outline of the evolutionary and geographical processes that might have led to interspecific differentiation and the present-day partial sympatric and syntopic pattern of distribution. Geometric morphometrics failed to discrimininate the two species on the ground of external morphological traits, but revealed interspecific differences when the shape of the primary sexual traits was taken into account. The use of two different molecular markers (cytochrome oxidase subunit I gene and amplified fragment-length polymorphism) demonstrates that the two species are genetically well differentiated, forming two distinguishable lineages probably diverged during the Pliocene by allopatric speciation. No evidence of past or recent introgression and no support for hybridization were found, suggesting that sympatry was established subsequently, when speciation was accomplished. Both molecular markers and genital shape indicate that phenotypically intermediate individuals, despite their ambiguous appearance, are members of O. illyricus species rather than hybrids. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89, 197–211. [ABSTRACT FROM AUTHOR]

In North America, several species in the freshwater amphipod genusHyalellaoccur as one of two alternative phenotypic types, or‘ecomorphs’, each possessing life history traits that allow success in alternative habitats that differ in predation regime. This study documents life history diversification, reproductive isolation and allozyme differentiation ofHyalellaecomorphs in Oklahoma, and compares these results to previously reported patterns of phenotypic and systematic diversification in Michigan. As in Michigan, two ecomorphs are common in Oklahoma, with an early maturing, small sized ecomorph found in habitats containingLepomissunfish, which prey onHyalella, and a late reproducing, large sized ecomorph found in fishless habitats and in very shallow margins of large reservoirs. Allozyme analysis and laboratory interbreeding trials demonstrated that ecomorphs in Oklahoma are reproductively isolated species. Phenotypically, these species are very similar to species of the same ecomorph in Michigan. Large ecomorph species in the two regions differ substantially in allozyme allele composition in a pattern consistent with reproductive isolation, yet these species did not differ in a comparison of phenotype. The small ecomorph in Oklahoma is similar in phenotype to two of three small ecomorph species in Michigan. Overall, this study supports the hypothesis thatHyalelladiversification in North America is characterized by the evolution of similar phenotypic solutions to comparable ecological challenges. © 2005 The Linnean Society of London,Biological Journal of the Linnean Society, 2005,84, 161–175. [ABSTRACT FROM AUTHOR]

Allozyme electrophoresis was used to examine population genetic structure at inter- and intraspecific levels for the New Zealand endemic corophiid amphipods, Paracorophium lucasi and P. excavatum. Individuals were collected from estuarine and freshwater habitats from North, South and Chatham Islands. Analyses of genetic structure among interspecific populations indicated clear allelic differentiation between the two Paracorophium species (Nei's genetic distance, D = 1.62), as well as considerable intraspecific substructuring ( D = 0.15–0.65). These levels of divergence are similar to interspecific levels for other amphipods and it is proposed that at least two groups from the P. lucasi complex and three from the P. excavatum complex correspond to sibling species. In most cases allopatry can account for the differentiation among the putative sibling species. For populations that share a common coastline we found low levels of differentiation and little or no correlation with geographical distance, suggesting that gene flow is adequate to maintain homogeneous population genetic structure. By contrast, populations on separate coastlines (i.e. isolated by land) showed moderate levels of geographical differentiation indicating restricted gene flow. The juxtaposition of population genetic and biogeographical data for Paracorophium in conjunction with the geological record infers past histories of glacial extirpation, and possible isolating effects of sea-level and landmass changes that have occurred throughout the Plio-Pleistocene. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 119–133. [ABSTRACT FROM AUTHOR]