Genetic characterization of Artemia tibetiana (Crustacea: Anostraca)

The brine shrimp Artemia consists of a number of bisexual species and a large number of parthenogenetic forms, which collectively, inhabit a wide range of hypersaline habitats. A recently described species (A. tibetiana) from a carbonate lake (Lagkor Co) in Tibet at an altitude of 4490 m has been tested with New World (A. franciscana USA, and A. franciscana feral population Vietnam) and Old World species (A. salina, A. urmiana, A. sinica) for cross fertility. These tests show complete infertility between A. tibetiana and A. franciscana . Between A. tibetiana and A. urmiana, A. sinica partial fertility through to F₂ and F₃ generations is evident. Allozyme and RAPD comparison of A. tibetiana with A. franciscana (USA), A. franciscana (Vietnam), A. sinica (Mongolia) and A. urmiana (Iran) show that A. tibetiana is similar to other bisexual species in mean heterozygosity (0.074) but has a somewhat higher proportion of polymorphic loci (40%, similar to that of A. urmiana ). The genetic distance between A. tibetiana and A. franciscana is 0.730, between A. tibetiana and A. urmiana is 0.475 and that between A. tibetiana and A. sinica is 0.114. F_IS estimates for A. tibetiana differ significantly from zero for six loci, mainly because of lack of fit to Hardy-Weinberg expectations. This may suggest that even within the limited area of Lagkor Co there are Genétically distinct populations. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 333–344.     

Molecular phylogenetics and asexuality in the brine shrimp Artemia

Explaining cases of long-term persistence of parthenogenesis has proven an arduous task for evolutionary biologists. Interpreting sexual-asexual interactions though has recently advanced owing to methodological design, increased taxon sampling and choice of model organisms. We inferred the phylogeny of Artemia, a halophilic branchiopod genus of sexual and parthenogenetic forms with cosmopolitan distribution, marked geographic patterns and ecological partitioning. Joint analysis of newly derived ITS1 sequences and 16S RFLP markers from global isolates indicates significant interspecific divergence as well as pronounced diversity for parthenogens, matching that of sexual ancestors. Maximum parsimony, maximum likelihood, and Bayesian methods were largely congruent in reconstructing the phylogeny of the genus. Given the current sampling, at least four independent origins of parthenogenesis are deduced. Molecular clock calibrations based on biogeographic landmarks indicate that the lineage leading to A. persimilis diverged from the common ancestor of all Artemia species between 80 and 90 MYA at the time of separation of Africa from South America, whereas parthenogenesis first appeared at least 3 MYA. Common mitochondrial DNA haplotypes delineate A. urmiana and A. tibetiana as possible maternal parents of several clonal lineages. A novel topological placement of A. franciscana as a sister clade to all Asian Artemia and parthenogenetic forms is proposed and also supported by ITS1 length and other existing data.     

Review of the biogeography of the genus Artemia (Crustacea, Anostraca)

In this study, we report on the known Artemia habitats worldwide. Recent literature information is incorporated about the taxonomic status of the various populations studied. The genus is composed of di-, tri-, tetra- and pentaploid parthenogenetic populations and of the following bisexual species: A. franciscana franciscana , A. franciscana monica , A. franciscana sp., A. persimilis , A. salina , A. urmiana , A. sinica and A. sp. from Kazakhstan. The problems of characterizing new brine shrimp populations are discussed. In view of the great importance of Artemia as part of the live food chain for the culture of fish and shellfish larvae and the present cyst shortage from the market, the need for commercial exploitation and development of new Artemia sources is now, more than ever, necessary.     

用RAPD和AFLP的方法对中国卤虫(Artemia)种及亲缘关系的研究

利用ＲＡＰＤ（随机扩增多态ＤＮＡ）和ＡＦＬＰ（扩增片段长度多态性）技术对不同种及种群卤虫的关系进行分析。 １０１个随机引物对４种卤虫Ａｆｒａｎｃｉｓｃａｎａ、Ａ ｕｒｍｉａｎａ、Ａ ｓｉｎｉｃａ和Ａ．ｐａｒｔｈｅｎｏｇｅｎｅｌｉｃａ基因组ＤＮＡ进行扩增,平均每个种获得７５１条带,其中４５８条带为多态性标记,每个引物提供平均７４个标记信息,聚类结果表明Ａ．ｓｉｎｉｃａ是不同于其他旧大陆两性生殖卤虫的一个独立的种。对来自 １５个种及品系的卤虫的 ＡＦＬＰ分析显示了非常好的遗传多态性,采用 １２对引物检测到 ５９４条带,其中 ４８０个为多态性标记。聚类结果表明来自西藏的两性生殖卤虫为不同于中国内陆两性生殖卤虫的新种。而孤雌生殖卤虫在进化过程中可能是多源的,中国内陆和沿海的孤雌生殖卤虫是沿着不同的途径进化的,内陆和沿海的孤雌生殖卤虫可能为不同的种。     

河北地区沿海盐场卤虫品系的组成

对河北地区海丰盐场和王凤玉盐场的卤虫品系组成情况进行了分析,结果显示,由于人为引种及在虾蟹育苗中不同品系卤虫卵的不当使用,使得该地区卤虫由原来单一的孤雌生殖品系组成变为目前的本地孤雌生殖卤虫、两性生殖的旧金山卤虫(Artemia franciscana)以及中华卤虫(A.sinica)混杂组成,其中外来种旧金山卤虫为优势种群,中华卤虫只是偶尔见到。由于竞争排斥效应,孤雌生殖和两性生殖卤虫产生了生态位的分化,孤雌生殖卤虫主要分布在低盐度的盐池,两性生殖卤虫主要分布在高盐度的盐池。     

Morphology and morphometry of the scutellum of six species in the genus Meccus (Hemiptera: Triatominae)

We studied the morphology and morphometry of scutella from six species of the hemipteran genus Meccus to identify new tools to help solve taxonomic problems in closely related insect species of epidemiological relevance. Scutellum samples were observed by scanning electron microscopy and were subjected to morphometric analysis. The results mainly show differences in central depression shape, posterior process, and vestiture. We found significant dimensional differences in scutellum morphometry and a clear sexual dimorphism among species. A combination of morphology and morphometry can be used to differentiate among species of the genus Meccus.     

On shortcomings of using mtDNA sequence divergence for the systematics of hares (genus Lepus): An example from cape hares

Despite the well-known fact that evolutionary patterns of single genes or sequences are not necessarily paralleled by organismic evolution, using mitochondrial sequence divergence for inferring phylogenetic relationships among hare species is not uncommon. Earlier studies reported interspecific introgression in the genus Lepus that may slur systematic conclusions drawn exclusively from mtDNA data. We examined pairwise divergence in partial mtHV-1 sequences and nuclear gene pools based on microsatellite and allozyme loci separately in a South and North African population of cape hares, Lepus capensis, and did not find significant correspondence on the individual level within either population. Also, the former population had a significantly higher level of mtHV-1 sequence divergence compared to the latter, but levels of individual nuclear gene pool divergence did not differ significantly between the two populations. Hence, the absence of correspondence between mtHV-1 sequence divergence and nuclear gene pool divergence among individuals within a population might be independent of the population-specific level of differentiation among individuals. Our results complement earlier findings in hares, and strongly recommend to include nuclear gene pool evidence for systematic inferences within this genus, even under the absence of mitochondrial introgression.     

MORPHOMETRICS AND CLADISTICS: MEASURING PHYLOGENY IN THE SEA URCHIN ECHINOCARDIUM

A phylogenetic approach to the study of evolutionary patterns is based on taxic homologies (synapomorphies). In contrast, the recognition of evolutionary processes (namely heterochronies) involves analysis of the entire morphology. Recent developments in geometric morphometry permit analysis of morphological similarities grounded in operational homologies. Such morphometric techniques are explored (1) at the level of evolutionary processes, and (2) as a complement in exploration of phylogenetic relationships. To examplify this, we perform a two-part study of the ontogeny and phylogeny of the spatangoid sea urchin Echinocardium. First, a phylogenetic analysis of ten Recent species in the genus is performed on 18 informative characters of the test. Second, morphological divergences among the species are analyzed using procrustean (superimposition) methods based on 49 homologous points. An additive distance tree is built from a matrix of morphometric distances among adult specimens. This tree is fully congruent with the phyletic results. Ontogenetic processes are explored by inserting ontogenetic series into the analysis. A distance tree including the juvenile stages shows that the general evolutionary trend of the genus is peramorphic, but species-to-species comparisons attest that no general clinal trend exists. Our analysis emphasizes the importance of morphometric approaches in evolutionary studies (1) for the understanding of heterochronies; (2) to trace the morphological implications of phylogenetic patterns; and (3) to estimate the impact of homoplasies.     

Re-evaluation on the diversity of the polyphyletic genus Metaurostylopsis (Ciliophora, Hypotricha): ontogenetic, morphologic, and molecular data suggest the establishment of a new genus Apourostylopsis n. g

The urostylid genus Metaurostylopsis Song et al., 2001 was considered to be a well-outlined taxon. Nevertheless, recent evidence, including morphological, ontogenetic, and molecular information, have consistently revealed conflicts among congeners, regarding their systematic relationships, ciliature patterns, and origins of ciliary organelles. In the present work, the morphogenetic and morphogenetic features were re-checked and compared, and the phylogeny of nominal species was analysed based on information inferred from the small subunit ribosomal RNA (SS rRNA) gene sequence. In addition, the binary divisional process in a new isolate of Metaurostylopsis struederkypkeae Shao et al., 2008 is described. All results obtained reveal that the genus is a polyphyletic assemblage whose nominal congeners fall into three clades within the core Urostylida, based on SS rRNA gene sequences. These three clades not match the groups inferred from morphological/morphogenetical evidences. Some conflicting data from molecular and ontogenetic studies also indicate that single-gene information might not be consistently reliable in detecting the phylogenetic relationships among closely related groups and comprehensive multi-gene analyses are necessary to give a more exact evaluation for this divergent assemblage. According to our new understandings, five forms are confirmed to be true Metaurostylopsis. The morphotype Metaurostylopsis sinica Shao et al., 2008 should be excluded from the genus and represents a distinct type, and, thus, a new genus Apourostylopsis n. g. with it as the type specie, i.e. Apourostylopsis sinica (Shao et al., 2008) n. comb.     

Genetic isolation and cryptic variation within the Lycaena xanthoides species group (Lepidoptera: Lycaenidae)

Species exist as biological entities with patterns of discontinuous phenotypic variation. However, the distinctness of taxa is called into question when morphological intermediates exist in areas of sympatry, reflecting either gene flow among variants of a species or hybridization between different species. Studying the partitioning of genetic variation provides a means to discern between the two possibilities. We used genetic and morphometric approaches to investigate the degree of isolation among the three members of the Lycaena xanthoides species group. Lycaena xanthoides, L. editha, and L. dione are predominantly allopatric and have been treated both as three separate species and as a single polytypic species. Using 618 bp of the mitochondrial gene COII, we found little phylogenetic resolution, but significant among-taxa genetic variance partitioning. Divergence among these taxa has been relatively recent, as evidenced by relatively low pairwise sequence divergence. Also, the existence of two well-supported clades within L. xanthoides sensu stricto, concordant with the Transverse Ranges of southern California, indicates divergence within this taxon, and a possible cryptic species. Significant morphological differentiation between L. editha and L. xanthoides supports the hypothesis that these taxa represent separate gene pools. Populations occurring in a narrow zone where the two species' ranges approach are characterized by intermediate morphology, suggesting incomplete morphological divergence or recent hybridization. These findings highlight the utility of genetic data in inferring species boundaries and the identification of cryptic lineages.     

Gene flow in Dubautia arborea and D. ciliolata: the roles of ecology and isolation by distance in maintaining species boundaries despite ongoing hybridization

The relative roles of gene flow and natural selection in maintaining species differentiation have been a subject of debate for some time. The traditional view is that gene flow constrains adaptive divergence and maintains species cohesiveness. Alternatively, ecological speciation posits that the reverse is true: that adaptive ecological differentiation constrains gene flow. In this study, we examine gene flow and population differentiation among populations of two species of the Hawaiian silversword alliance, Dubautia arborea and D. ciliolata. We compare divergence in putatively neutral microsatellite markers with divergence in leaf morphometric traits, which may be selectively important or physiologically linked to selectively important traits. Gene flow between populations was found to be significant in only one of the two species, D. arborea. Leaf morphometric differentiation between species was significant, though not among populations within species. No evidence of effective genetic introgression was observed between apparently 'pure' populations of these species. Gene flow as measured by microsatellites was not correlated with geographic distance between populations, but was correlated with the linear placement of the widest part of the leaf. Because these two species are interfertile, as demonstrated by the presence of active hybrid zone, the lack of genetic introgression and the maintenance of species boundaries may be associated with natural selection on differential habitat.     

Evolutionary and demographic history of the Californian scrub white oak species complex: an integrative approach

Understanding the factors promoting species formation is a major task in evolutionary research. Here, we employ an integrative approach to study the evolutionary history of the Californian scrub white oak species complex (genus Quercus). To infer the relative importance of geographical isolation and ecological divergence in driving the speciation process, we (i) analysed inter‐ and intraspecific patterns of genetic differentiation and employed an approximate Bayesian computation (ABC) framework to evaluate different plausible scenarios of species divergence. In a second step, we (ii) linked the inferred divergence pathways with current and past species distribution models (SDMs) and (iii) tested for niche differentiation and phylogenetic niche conservatism across taxa. ABC analyses showed that the most plausible scenario is the one considering the divergence of two main lineages followed by a more recent pulse of speciation. Genotypic data in conjunction with SDMs and niche differentiation analyses support that different factors (geography vs. environment) and modes of speciation (parapatry, allopatry and maybe sympatry) have played a role in the divergence process within this complex. We found no significant relationship between genetic differentiation and niche overlap, which probably reflects niche lability and/or that multiple factors, have contributed to speciation. Our study shows that different mechanisms can drive divergence even among closely related taxa representing early stages of species formation and exemplifies the importance of adopting integrative approaches to get a better understanding of the speciation process.     

Genetic variability and phylogeography of the cyprinid Telestes muticellus within the Italian peninsula as revealed by mitochondrial DNA

A phylogeographic analysis of 12 populations of Telestes muticellus was performed on the basis of mitochondrial DNA sequences of the cytochrome b gene. The main aims were to determine phylogenetic relationships from congener species and to highlight the patterns of genetic differentiation within the Italian peninsula. The results obtained showed a significant divergence with the congener species, indicating a possible Miocene origin for the genus. Divergence was found to be low for T. muticellus , yet distinct lineages resulted as being allopatric within the two main Italian biogeographic districts, the Padano-Venetian and the Tuscano-Latium, suggesting the existence of recent vicariance coupled with past demographic regression. The high level of genetic differentiation found between populations highlighted the low dispersal ability of this rheophilic Cyprinid, whose migration was mainly related to connections between the upper parts of river basins. The distribution of sequence characteristics found suggests that particular attention should be paid to the conservation management of this species.     

Stable persistence of relict populations involved evolutionary shifts of reproductive characters in the genus Tanakaea (Saxifragaceae)

Tertiary relicts often show evolutionary stasis in morphology and ecology and have been hypothesized to retain stable population sizes in refugia. However, recent studies have reported that some relicts evolutionarily shifted their physiology, ecology, and morphology and experienced various patterns of demography. To understand the historical survival of relict plants, a multidimensional study investigating the evolution of ecological and morphological traits as well as population demographic history is needed. The genus Tanakaea (Saxifragaceae) comprises two species in China and Japan. These species share most vegetative characteristics and are sometimes treated as a single species. The distribution pattern is relictual, as the populations are confined to small areas in mesic warm temperate forests less influenced by Quaternary glacial climates. Focusing on the relictual plant group, this study tested the hypotheses of evolutionary stasis and population stability in long-term refugia. Genetic analyses using plastome sequences and genome-wide single-nucleotide polymorphisms revealed divergence of the two species approximately 6.8 million years ago and strong genetic differentiation of the regional populations. Demographic analysis revealed that almost all populations retained stable population sizes during glacial–interglacial climate changes, supporting the traditional view. However, morphological assessments revealed a simultaneous shift in breeding systems (from hermaphrodite to dioecy/non-clonal to clonal reproduction) in Japanese species and intraspecific differentiation of leaf traits. Therefore, the relict species do not show evolutionary stasis in every aspect. Changes in reproductive characteristics may have contributed to their long-term in situ survival.     

Genetic and morphological divergence between Littorina fabalis ecotypes in Northern Europe

Low dispersal marine intertidal species facing strong divergent selective pressures associated with steep environmental gradients have a great potential to inform us about local adaptation and reproductive isolation. Among these, gastropods of the genus Littorina offer a unique system to study parallel phenotypic divergence resulting from adaptation to different habitats related with wave exposure. In this study, we focused on two Littorina fabalis ecotypes from Northern European shores and compared patterns of habitat‐related phenotypic and genetic divergence across three different geographic levels (local, regional and global). Geometric morphometric analyses revealed that individuals from habitats moderately exposed to waves usually present a larger shell size with a wider aperture than those from sheltered habitats. The phenotypic clustering of L. fabalis by habitat across most locations (mainly in terms of shell size) support an important role of ecology in morphological divergence. A genome scan based on amplified fragment length polymorphisms (AFLPs) revealed a heterogeneous pattern of differentiation across the genome between populations from the two different habitats, suggesting ecotype divergence in the presence of gene flow. The contrasting patterns of genetic structure between nonoutlier and outlier loci, and the decreased sharing of outlier loci with geographic distance among locations are compatible with parallel evolution of phenotypic divergence, with an important contribution of gene flow and/or ancestral variation. In the future, model‐based inference studies based on sequence data across the entire genome will help unravelling these evolutionary hypotheses, improving our knowledge about adaptation and its influence on diversification within the marine realm.     

SNP detection in Na/K ATP-ase gene α1 subunit of bisexual and parthenogenetic Artemia strains by RFLP screening

In order to find a marker for differentiating between a bisexual and a parthenogenetic Artemia strain, Exon-7 of the Na/K ATPase α(1) subunit gene was screened by RFLP technique. The results revealed a constant synonymous SNP (single nucleotide polymorphism) in digestion by the Tru1I enzyme that was consistent with these two types of Artemia. This SNP was identified as an accurate molecular marker for discrimination between bisexual and parthenogenetic Artemia. According to the Nei's genetic distance (1973), the lowest genetic distance was found between individuals from Artemia urmiana Günther 1890 and parthenogenetic populations, making the described marker the first marker to easily distinguish between these two cooccurring species.     

High mortality and female‐biased operational sex ratio result in low encounter rates and moderate polyandry in a spider

The taxonomy of the Old World bat genus Otomops (Chiroptera: Molossidae) has been the subject of considerable debate. The failure of classical morphological studies to provide consistent patterns regarding interspecific relationships within Otomops has limited any understanding of the evolutionary history of the genus. We used traditional and geometric morphometric approaches to establish the species limits of taxa from sub‐Saharan Africa, the Arabian Peninsula, and Madagascar. Morphometric data supported the recent recognition of three distinct Afrotropical taxa: Otomops madagascariensis from Madagascar; Otomops martiensseni s.s. from southern, eastern, central, and western Africa; and an undescribed taxon from north‐east Africa and the Arabian Peninsula. Analyses of craniodental measurements and landmark‐based data showed significant cranial size and shape divergence between the three taxa. Cranial size and shape variation within Afro‐Arabian Otomops were strongly influenced by altitude, seasonality of precipitation, and precipitation in the driest month. Based on morphometric patterns and molecular divergence estimates, we suggest that morphological evolution within Afro‐Arabian Otomops occurred in response to the fluctuating climate during the Pleistocene on the one hand, and the increasing aridity and seasonality over north‐eastern Africa on the other. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, •• , ••–••.     

Importance of genetic drift during Pleistocene divergence as revealed by analyses of genomic variation

Determining what factors affect the structuring of genetic variation is key to deciphering the relative roles of different evolutionary processes in species differentiation. Such information is especially critical to understanding how the frequent shifts and fragmentation of species distributions during the Pleistocene translates into species differences, and why the effect of such rapid climate change on patterns of species diversity varies among taxa. Studies of mitochondrial DNA (mtDNA) have detected significant population structure in many species, including those directly impacted by the glacial cycles. Yet, understanding the ultimate consequence of such structure, as it relates to how species divergence occurs, requires demonstration that such patterns are also shared with genomic patterns of differentiation. Here we present analyses of amplified fragment length polymorphisms (AFLPs) in the montane grasshopper Melanoplus oregonensis to assess the evolutionary significance of past demographic events and associated drift-induced divergence as inferred from mtDNA. As an inhabitant of the sky islands of the northern Rocky Mountains, this species was subject to repeated and frequent shifts in species distribution in response to the many glacial cycles. Nevertheless, significant genetic structuring of M. oregonensis is evident at two different geographic and temporal scales: recent divergence associated with the recolonization of the montane meadows in individual sky islands, as well as older divergence associated with displacements into regional glacial refugia. The genomic analyses indicate that drift-induced divergence, despite the lack of long-standing geographic barriers, has significantly contributed to species divergence during the Pleistocene. Moreover, the finding that divergence associated with past demographic events involves the repartitioning of ancestral variation without significant reductions of genomic diversity has intriguing implications - namely, the further amplification of drift-induced divergence by selection.     

Morphological differentiation in Carduelis finches: Adaptive vs. constraint models

In this study we show that morphological diversification in the avian genus Carduelis (Carduelinae) has to a large extent been conservative. Using multivariate methods, we found only minor deviations from the common (ancestral) body-plan. In particular, variation in bill morphology was found to be more conservative than variation in other parts of the body. We argue that constraint models of population differentiation can successfully account for the variation in bill morphology in this genus, but are less successful in accounting for variation in other traits. This can be interpreted as a result of long-term overall stabilizing selection for a certain bill morphology which is related to the way the birds open seeds. A trait combination that is adaptive on the evolutionary time scale may thus act as a constraint on changes in bill morphology on the microevolutionary scale. We conclude that the most parsimonious explanation for low divergence in bill morphology in this genus is that all species have retained the ancestral bill morphology. This may mean that each species chooses its environment rather than being moulded by it. This argument seems to apply to bill morphology, but other traits studied in this genus appear to have evolved in a less constrained fashion. A new index of morphometric integration is introduced to describe covariance structures.