Long-Term Changes in the Diet of Gymnogobius isaza from Lake Biwa,Japan: Effects of Body Size and Environmental Prey Availability

Body size and environmental prey availability are both key factors determining feeding habits of gape-limited fish predators. However, our understanding of their interactive or relative effects is still limited. In this study, we performed quantitative dietary analysis of different body sizes of goby (Gymnogobius isaza) specimens collected from Lake Biwa between 1962 and 2004. First, we report that the diet was composed mainly of zooplankton (cladocerans and copepods) before the 1980s, and thereafter, shifted to zoobenthos (gammarids). This foraging shift coincided with, and thus can be linked to, known historical events in the lake at that time: decrease in zooplankton abundance with the alleviation of eutrophication, increase in fish body size resulting from fish population collapse, and increase in gammarid abundance due to reduced fish predation pressure. Supporting this view, our data analyses revealed how the long-term changes in the diet composition would be co-mediated by changes in fish body size and environmental prey availability. Specifically, while zoobenthos abundance strongly affected the fish diet composition, larger (smaller) fish preferred zoobenthos (zooplankton). Furthermore, the body size effects were stronger than those of prey availability. These results provide the best long-term evidence that fish feeding habits vary over decades with its body size and prey community due to anthropogenic disturbances.     

Annual variations in length–weight relationship of Gymnogobius isaza (Tanaka, 1916) from Lake Biwa,Japan

The study describes length–weight relationships (LWRs) of Gymnogobius isaza (Tanaka, 1916) collected from Lake Biwa, Japan, between 1975 and 2002. Annual values of the allometric exponent of LWRs ranged from 2.47 to 3.42. This study is one of the few to report annual variations in LWR.     

Somatic immunoglobulin sequence divergence and its implications for studies of evolutionary divergence

The divergence of immunoglobulin genes due to somatic mutation provides a natural example of DNA sequence divergence. This divergence was examined to gain insight into the processes of evolution and the determinants of the variance-to-mean ratio of sequence divergence. Normally, this ratio is found to be larger than expected (1.0 under Poisson assumptions) for the evolutionary divergence or most genes. Although not significantly less than one, all seven groups of immunoglobulin amino acid sequences have ratios smaller than expected, contrary to the evolutionary pattern generally observed. The substitutions in the immunoglobulin genes appear to be highly nonrandom and an excess of parallel changes (the major nonrandom feature of these mutations) is shown to cause smaller ratios. Because convergent or parallel mutations are often observed in the evolutionary divergence of genes, this suggests that forces causing the large observed ratios may actually have to be more powerful than previously expected. Further, since selection is one of the likely causes of parallel mutations, it should be noted that selection could significantly decrease the variance-to-mean ratio. The high frequency of parallel mutations and their resulting effects, as observed in the immunoglobulin genes, suggest that only poor inferences of sequence divergence can be made without actual knowledge of the ancestral sequence.     

Genetic variation and its evolutionary implications in a Mediterranean island endemic lizard

The peculiar bioclimatic and geographic features of Corso–Sardinian islands may provide an ideal scenario for investigating microevolutionary processes, given their large heterogeneity of environments, which could affect dispersal and gene flow among populations, as well as processes of local adaptation. The genetic variation and differentiation among populations of the endemic lizard Archaeolacerta bedriagae were studied by allozyme electrophoresis at 20 presumptive loci. The genetic structure of this species is characterized by relatively high levels of polymorphism and low differentiation among populations. The pattern of genetic differentiation cannot be explained by genetic drift as a function of geographic distance. Genetic distance data show that genetic variation is distributed into three geographically coherent population groups and suggest a recent (Late Pleistocene) origin for the observed geographic fragmentation. The analysis of environmental correlates of allozymic variation indicates a strong correlation of the Idh-1 locus with climatic variables. The frequency of the Idh-1¹⁰⁶ allele is negatively correlated with annual temperature, and positively correlated with annual precipitation. In addition, the observed heterozygosity at this locus decreases towards more arid climatic regimes. The results obtained support the assumption of differential selection acting on Idh-1 allozymes under diverse climates. An association between Idh-1 allozymes and local bioclimatic regimes was also observed for the sympatric lizard Podarcis tiliguerta , suggesting a key role for such selective agents on Idh-1 polymorphism in these two Corso–Sardinian lacertids.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 661–676.     

Genetic divergence in Greek populations of the genus Leuciscus and its evolutionary and biogeographical implications

In 23 populations of Greek Leuciscus ( Squalius ), the percentage of polymorphic allozyme loci ranged between 0·034 and 0·379 (P=0·19) and expected heterozygosity was 0·011–0·166 (H_e=0·067). Current taxonomy is confusing and does not correspond to genetic data that support the presence in Greece of at least seven different species: L. cephalus , L. peloponnensis , L. prespensis , L. moreoticus , L. borysthenicus , L. keadicus and Leuciscus sp. from Euboea Island. The maximum Nei modified genetic distance was found among L. keadicus and the rest of subgenus Squalius populations D * Nei=0·446–0·705). Accepting the molecular clock hypothesis, speciation for the genus Leuciscus in Greece must have occurred during the Cenozoic period (between the Middle Miocene and the Later Pliocene). The two main biogeographical events causing speciation on mainland Greece were the Uplift of the Pindic cordillera and the isolation of the southern part of Peloponnesus. The faunistic composition of the lakes studied, in which new taxa are reconsidered, suggests the same faunistic origin in the Early Pliocene for Lakes Prespa and Stymphalia and a younger one in the Late Pliocene for Lake Trichonis. Euboea Island was not a zoogeographical unit during the Cenozoic. The isolation of all the freshwater fish fauna of Euboea has occurred since the Pliocene. The biogeographical model proposed here differs from classical hypotheses in considering of lesser importance the dispersion of L. cephalus on the Greek mainland during the Neogene and Quaternary.     

Analysis of mitochondrial DNA diversity in the aleuts of the commander islands and its implications for the genetic history of beringia

The Aleuts are aboriginal inhabitants of the Aleutian archipelago, including Bering and Copper (Medny) Islands of the Commanders, and seem to be the survivors of the inhabitants of the southern belt of the Bering Land Bridge that connected Chukotka/Kamchatka and Alaska during the end of the Ice Age. Thirty mtDNA samples collected in the Commanders, as well as seven mtDNA samples from Sireniki Eskimos in Chukotka who belong to the Beringian-specific subhaplogroup D2, were studied through complete sequencing. This analysis has provided evidence that all 37 of these mtDNAs are closely related, since they share the founding haplotype for subhaplogroup D2. We also demonstrated that, unlike the Eskimos and Na-Dene, the Aleuts of the Commanders were founded by a single lineage of haplogroup D2, which had acquired the novel transversion mutation 8910A. The phylogeny of haplogroup D complete sequences showed that (1) the D2 root sequence type originated among the latest inhabitants of Beringia and (2) the Aleut 8910A sublineage of D2 is a part of larger radiation of rooted D2, which gave rise to D2a (Na-Dene), D2b (Aleut), and D2c (Eskimo) sublineages. The geographic specificity and remarkable intrinsic diversity of D2 lineages support the refugial hypothesis, which assumes that the founding population of Eskimo-Aleut originated in Beringan/southwestern Alaskan refugia during the early postglacial period, rather than having reached the shores of Alaska as the result of recent wave of migration from interior Siberia.     

Ecological studies on the population of isaza,Chaenogobius Isaza Tanaka,in Lake Biwa,with special reference to the effects of population density upon its growth

1. In order to get the knowledge on the age composition of “isaza” population in Lake Biwa and the effect of population density on growth, monthly distribution of mean body length and mean body weight has been analyzed on the basis of monthly haul by “isazabiki” trawl during 1949 to 1953 and also 1960 to 1965.
2. There is no apparent sex difference in the growth in the first and second years of life.
3. “Isaza” population is composed of two age groups, age 0 and 1 groups (1+fish), the latter occupying by far the greater part in commercial catch.
4. During the growth season fishes of both ages feed mainly on zooplankton, though in winter frequently take chironomid larvae, gammaridae and others in volume.
5. The growth season falls in the period from April to October in both age groups.
6. A considerable yearly variation occurring in growth is in close connection with the fluctuation of population density of all ages.
7. The influence affected by the density of age 1 group is larger than that by age 0 group.

     

Reconstruction of caribou evolutionary history in Western North America and its implications for conservation

The role of Beringia as a refugium and route for trans-continental exchange of fauna during glacial cycles of the past 2million years are well documented; less apparent is its contribution as a significant reservoir of genetic diversity. Using mitochondrial DNA sequences and 14 microsatellite loci, we investigate the phylogeographic history of caribou (Rangifer tarandus) in western North America. Patterns of genetic diversity reveal two distinct groups of caribou. Caribou classified as a Northern group, of Beringian origin, exhibited greater number and variability in mtDNA haplotypes compared to a Southern group originating from refugia south of glacial ice. Results indicate that subspecies R. t. granti of Alaska and R. t. groenlandicus of northern Canada do not constitute distinguishable units at mtDNA or microsatellites, belying their current status as separate subspecies. Additionally, the Northern Mountain ecotype of woodland caribou (presently R. t. caribou) has closer kinship to caribou classified as granti or groenlandicus. Comparisons of mtDNA and microsatellite data suggest that behavioural and ecological specialization is a more recently derived life history characteristic. Notably, microsatellite differentiation among Southern herds is significantly greater, most likely as a result of human-induced landscape fragmentation and genetic drift due to smaller population sizes. These results not only provide important insight into the evolutionary history of northern species such as caribou, but also are important indicators for managers evaluating conservation measures for this threatened species.     

Population genetic structure of the round goby in Lake Michigan: implications for dispersal of invasive species

Understanding subsequent dispersal of non-native species following introduction is important for predicting the extent and speed of range expansion and is critical for effective management and risk assessment. Post-introduction dispersal may occur naturally or via human transport, but assessing the relative contribution of each is difficult for many organisms. Here, we use data from seven microsatellite markers to study patterns of dispersal and gene flow among 12 pierhead populations of the round goby (Neogobius melanostomus) in Lake Michigan. We find significant population structure among sampling sites within this single Great Lake: (1) numerous populations exhibited significant pairwise F _ST and (2) a Bayesian assignment analysis revealed three distinct genetic clusters, corresponding to different pierhead locations, and genetic admixture between these clusters in the remaining populations. Genetic differentiation (F _ST) is generally related to geographic distance (i.e., isolation by distance), but is periodically interrupted at the scale of Lake Michigan due to gene flow among geographically distant sites. Moreover, average genetic differentiation among populations exhibit a significant, negative correlation with the amount of shipping cargo at ports. Our results, therefore, provide evidence that genetic structure of the round goby in Lake Michigan results from limited natural dispersal with frequent long-distance dispersal through anthropogenic activities such as commercial shipping. Our study suggests that while round gobies can undoubtedly disperse and found new populations through natural dispersal mechanisms, their spread within and among the Great Lakes is likely aided by transport via ships. We, therefore, recommend that ballast-water treatment and management may limit the spread of non-native species within the Great Lakes after the initial introduction in addition to preventing the introduction of non-native species to the Great Lakes.     

The first diplodocid from Asia and its implications for the evolutionary history of sauropod dinosaurs

Abstract: An isolated anterior caudal vertebra from the Qingshan (= Ch'ing shan) Formation (Early Cretaceous) of Shandong Province, China, is redescribed and shown to be an advanced diplodocid sauropod. This specimen possesses several derived character states that are typically observed in advanced diplodocoids or diplodocids, including the following: a mildly procoelous centrum; a deep pit‐like pneumatic fossa immediately below the caudal rib; wing‐ or fan‐shaped caudal ribs; and complex lamination of the neural spine. The neural spine is apomorphically short and the centrum is short relative to its height compared to those of other diplodocids, which, when coupled with the specimen’s unique geographical location and stratigraphical age, suggests that it probably represents a new taxon. This caudal vertebra provides the first convincing evidence that diplodocids were present in Asia, perhaps as a result of the dispersal of neosauropod lineages from Europe and/or North America during the Early Cretaceous. The discovery of a member of the Diplodocidae in the Early Cretaceous also indicates that this clade did not become extinct at the Jurassic/Cretaceous boundary as previously supposed.     

The evolutionary history of the order Antipatharia (Cnidaria: Anthozoa: Hexacorallia) as inferred from mitochondrial and nuclear DNA: implications for black coral taxonomy and systematics

Although black corals inhabit all the world's oceans, they have been relatively understudied as ～185 of 247 species occur at depths > 50 m. Antipatharians have been included in several phylogenetic studies; however, sample sizes are small and taxonomic coverage minimal. Low levels of mitochondrial (mt) sequence divergence within Scleractinia and Octocorallia are assumed to apply to all anthozoans, although no formal study has been conducted on the order Antipatharia. To quantify genetic variation in the black coral mitogenome, we analysed DNA sequences of the two longest intergenic regions (IGRs) and cox3‐cox1 for 26 of 41 genera, representing all families and subfamilies. We also quantified divergence at the intraspecific level using six mtIGRs and their flanking protein‐coding genes and rRNA for 100+ colonies of Antipathes griggi. Utilizing sequence data from the two mtIGRs, cox3‐cox1, as well as nuclear 18S and 28S, we constructed the first multi‐locus phylogenies of the Antipatharia. Reconstructions revealed that species in the genus Stichopathes are split across two families, Sibopathes macrospina groups among North Atlantic Parantipathes (suggesting the actinopharynx and mesenteries were secondarily lost), and three families are polyphyletic. These and other results provide novel, independent insights into the evolutionary history of antipatharians and support placement of species into higher‐level groupings based on microscopic skeletal features rather than gross colony morphology. An illustrated key to the seven currently recognized families is also provided. © 2013 The Linnean Society of London     

A new cytochrome b phylogroup of the common vole (Microtus arvalis) endemic to the Balkans and its implications for the evolutionary history of the species

The phylogeographic architecture of the common vole, Microtus arvalis, has been well‐studied using mitochondrial DNA and used to test hypotheses relating to glacial refugia. The distribution of the five described cytochrome b (cyt b) lineages in Europe west of Russia has been interpreted as a consequence of postglacial expansion from both southern and central European refugia. A recently proposed competing model suggests that the ‘cradle’ of the M. arvalis lineages is in western central Europe from where they dispersed in different directions after the Last Glacial Maximum. In the present study, we report a new cyt b lineage of the common vole from the Balkans that is not closely related to any other lineage and whose presence might help resolve these issues of glacial refugia. The Balkan phylogroup occurs along the southern distributional border of M. arvalis in central and eastern Bosnia and Herzegovina, Montenegro, and eastern Serbia. Further north and west in Slovenia, Bosnia and Herzegovina, and Serbia, common voles belong to the previously‐described Eastern lineage, whereas both lineages are sympatric in one site in Bosnia and Herzegovina. The Balkan phylogroup most reasonably occupied a glacial refugium already known for various Balkan endemic species, in contrast to the recently proposed model. South‐east Europe is an absolutely crucial area for understanding the postglacial colonization history of small mammals in Europe and the present study adds to the very few previous detailed phylogeographic studies of this region. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 788–796.     

Relationships and origin of endemic Lake Baikal gastropods (Caenogastropoda: Rissooidea) based on mitochondrial DNA sequences

The phylogenetic relationships and the origin of two groups of rissooid freshwater snails endemic to Lake Baikal were investigated using partial mitochondrial COI, 12S rDNA, and 16S rDNA sequences. The Baikalian Benedictiinae proved to be closely related to the Lithoglyphinae. According to a molecular clock estimate the two groups diverged in the Paleogene. The Benedictiinae might have evolved autochthonously in precursors of Lake Baikal. The Baikalian Baicaliidae are probably most closely related to the Amnicolidae and the Bithyniidae. These groups diverged at the latest during the Cretaceous. Thus the origin of the Baicaliidae predates the origin of the Baikal rift zone. The Baicaliidae evolved probably in other Central Asian freshwater reservoirs. However, the radiation of the extant Baicaliidae only started in the Neogene and might have occurred autochthonously in Lake Baikal. The conchological similarity of the Baicaliidae and the Pyrgulidae is due to convergence. The Pyrgulidae diverged from the common stem lineage of the other hydrobiid families at the latest in the Jurassic. The Bithyniidae is derived from hydrobiids and is related to the Amnicolidae.     

Inferring the phylogeography and evolutionary history of the splendid fairy-wren Malurus splendens from mitochondrial DNA and spectrophotometry

The phylogeographic structure of the widely distributed arid and semi-arid Australian splendid fairy-wren Malurus splendens was investigated by using variation in plumage characters and mitochondrial DNA (mtDNA). We examined sequences of the mtDNA ND2 gene and used spectrophotometry to quantify chromatic variation in plumage in order to test the current morphology-based intraspecific taxonomy of M. splendens and to discriminate between hypotheses invoking allopatric and parapatric processes in the origin of diversity in the complex. Genetic diversity of M. splendens fell into three divergent geographically structured clades. One represents populations ascribed to the western subspecies M. s. splendens , the other populations of central M. s. musgravi and the third all eastern populations currently ascribed to M. s. emmottorum and M. s. melanotus . Plumage patterns clearly differentiate M. s. splendens and M. s. musgravi, and spectrophotometry identified a step-wise transition in spectra between M. s. melanotus and M. s. emmottorum . Congruence of patterns of phenotypic and genetic variation among western, central and eastern populations of M. splendens strongly suggests that these populations have diverged in allopatry on either side of historical biogeographic barriers in this region. Decoupled patterns of phenotypic and genetic diversity suggest that the divergence of M. s. melanotus and M. s. emmottorum may have occurred without periods of isolation perhaps in response to differences in local environmental conditions, or alternatively, mtDNA and plumage may have different rates of evolution. Critically, we encountered issues with the placement of the root of the M. splendens complex. The root was placed within the subspecies M. s. splendens separating its northern and southern populations and rendering the subspecies paraphyletic.     

Introgressive hybridization and the evolutionary history of the herring gull complex revealed by mitochondrial and nuclear DNA

Background  

Based on extensive mitochondrial DNA (mtDNA) sequence data, we previously showed that the model of speciation among species of herring gull (Larus argentatus) complex was not that of a ring species, but most likely due more complex speciation scenario's. We also found that two species, herring gull and glaucous gull (L. hyperboreus) displayed an unexpected biphyletic distribution of their mtDNA haplotypes. It was evident that mtDNA sequence data alone were far from sufficient to obtain a more accurate and detailed insight into the demographic processes that underlie speciation of this complex, and that extensive autosomal genetic analysis was warranted.     

Phylogeography of shy and white-capped albatrosses inferred from mitochondrial DNA sequences: implications for population history and taxonomy

The evolutionary relationship between shy (Thalassarche cauta) and white-capped (T. steadi) albatrosses was examined using mitochondrial control region sequences. Results were interpreted in the context of a recent and contentious taxonomic revision that recommended full species status for shy and white-capped albatrosses. Low sequence divergence between shy and white-capped albatrosses (1.8%) and between their close relatives, Salvin's and Chatham albatrosses (2.9%), was observed. Much higher sequence divergence was found between the shy/white-capped pair and the Salvin's/Chatham pair (7.0%). Phylogenetic analyses confirmed the separation of the shy/white-capped pair from the Salvin's/Chatham pair but did not provide species-level resolution. Phylogeographic analyses, including a nested clade analysis, FST estimates and an analysis of molecular variance, indicated unambiguous genetic structuring between shy and white-capped albatrosses, thus confirming the demographic isolation of the species, but showed little to no structuring within each species. The geographical distribution of mtDNA haplotypes and other evidence suggest that shy albatrosses arose through range expansion by white-capped albatrosses.     

Genetic differentiation among populations of the blackfin goodea Goodea atripinnis (Cyprinodontiformes: Goodeidae): implications for its evolutionary history

Central Mexico is characterized by a complex topography that is the result of historic and contemporary tectonic and climatic factors. These events have influenced the evolutionary history of numerous freshwater fishes in the region. Nonetheless, recent studies have shown that life-history traits and ecological characteristics of species may influence dispersal capabilities and the degree of genetic connectivity. Goodea (Cyprinodontiformes: Goodeidae) is one of the most widely distributed and environmentally tolerant genera of goodeids. In this study, the authors analysed variation in the mitochondrial cytochrome b gene to evaluate the phylogeographic relationships, genetic structure, genetic diversity and demographic history of Goodea from across its distribution range. They found low genetic differentiation and identified shared haplotypes among several regions. Geographic segregation was found in samples southwest and northeast of the Lower Lerma region, with some internal isolated groups showing phylogeographic differentiation and unique haplotypes. The AMOVA best explained genetic structure when grouped by haplogroups rather than when grouped by recognized biogeographic regions. Several regions showed null genetic diversity, raising the possibility of dispersal mediated by humans. Finally, Bayesian Skyline Plot analysis showed a population expansion for the Southwest haplogroup, except for the Armería population and sub-group II of the Northeast haplogroup. All this suggests a recent colonization of Goodea atripinnis throughout some of the biogeographic regions currently inhabited by this species.