Hybrid origin of a parthenogenetic genus?

The origin of the obligate-parthenogenetic New Zealand stick insect genus Acanthoxyla was investigated using cytogenetics and sequencing of nuclear and mitochondrial DNA. Little mitochondrial DNA sequence variation (COI-II) was found among seven species of the genus Acanthoxyla and we found no evidence for monophyly of the morphologically distinguished lineages. In contrast, two distinct clades of nuclear sequence (ITS) were obtained, one is restricted to the genus Acanthoxyla, while the other includes sequences obtained from its sister genus Clitarchus. Although Acanthoxyla appears to be diploid (2n = 36-38), it has two ill-matched chromosome pairs. We hypothesize that two or more hybridization events involving the parental sexual species Clitarchus hookeri and an unknown taxon probably resulted in the formation of the parthenogenetic genus Acanthoxyla. However, the karyotype of Acanthoxyla bears little resemblance to the karyotype of the putative paternal species C. hookeri so the exact nature of Acanthoxyla remains in question.     

Are you my mother? Phylogenetic analysis reveals orphan hybrid stick insect genus is part of a monophyletic New Zealand clade

The hybrid stick insect genus Acanthoxyla Uvarov 1944 is unusual for an obligate parthenogen, in the extreme morphological diversity it exhibits that has led to eight species being recognised. The New Zealand sexual species Clitarchus hookeri [White, A. 1846. The zoology of the Voyage of H.M.S. Erebus and Terror. In: 1 Insects of New Zealand. E.W. Janson, London.] is the putative parental species in the hybridization that gave rise to the hybrid lineage Acanthoxyla. In an effort to identify the maternal ancestor of Acanthoxyla we sequenced nuclear 28S rDNA and/or mtDNA COI & COII of all nine endemic New Zealand stick insect genera, representing 17 of the 22 described species. We also sequenced 28S from eight non-New Zealand stick insects to supplement published 28S sequence data that provided a taxonomically and geographically broad sampling of the phasmids. We applied a novel search algorithm (SeqSSi=Sequence Similarity Sieve) to assist in selection of outgroup taxa for phylogenetic analysis prior to alignment. Phylogenetic reconstructions resolved an exclusively New Zealand clade to which the maternal lineage of Acanthoxyla belonged, but did not support existing higher level taxonomy of stick insects. We did not find a sexual maternal species for Acanthoxyla but phylogenetic relationships indicate that this species lived in New Zealand and could be classified among the New Zealand Phasmatinae. Among the available taxa, the nearest evolutionary neighbours to the New Zealand phasmid fauna as a whole were predominantly from the New Zealand region (Fiji, Australia, New Guinea, New Caledonia and South America). As it appears to be an orphan, it is interesting to speculate that a combination of parthenogenetic reproduction and/or hybrid vigour in Acanthoxyla may have contributed to the extinction of its mother.     

Origin and Genetic Diversity of Diploid Parthenogenetic Artemia in Eurasia

There is wide interest in understanding how genetic diversity is generated and maintained in parthenogenetic lineages, as it will help clarify the debate of the evolution and maintenance of sexual reproduction. There are three mechanisms that can be responsible for the generation of genetic diversity of parthenogenetic lineages: contagious parthenogenesis, repeated hybridization and microorganism infections (e.g. Wolbachia). Brine shrimps of the genus Artemia (Crustacea, Branchiopoda, Anostraca) are a good model system to investigate evolutionary transitions between reproductive systems as they include sexual species and lineages of obligate parthenogenetic populations of different ploidy level, which often co-occur. Diploid parthenogenetic lineages produce occasional fully functional rare males, interspecific hybridization is known to occur, but the mechanisms of origin of asexual lineages are not completely understood. Here we sequenced and analysed fragments of one mitochondrial and two nuclear genes from an extensive set of populations of diploid parthenogenetic Artemia and sexual species from Central and East Asia to investigate the evolutionary origin of diploid parthenogenetic Artemia, and geographic origin of the parental taxa. Our results indicate that there are at least two, possibly three independent and recent maternal origins of parthenogenetic lineages, related to A. urmiana and Artemia sp. from Kazakhstan, but that the nuclear genes are very closely related in all the sexual species and parthenogegetic lineages except for A. sinica, who presumable took no part on the origin of diploid parthenogenetic strains. Our data cannot rule out either hybridization between any of the very closely related Asiatic sexual species or rare events of contagious parthenogenesis via rare males as the contributing mechanisms to the generation of genetic diversity in diploid parthenogenetic Artemia lineages.     

Rapid diversification of the cotton genus (Gossypium: Malvaceae) revealed by analysis of sixteen nuclear and chloroplast genes

Previous molecular phylogenetic studies have failed to resolve the branching order among the major cotton (Gossypium) lineages, and it has been unclear whether this reflects actual history (rapid radiation) or sampling properties of the genes evaluated. In this paper, we reconsider the phylogenetic relationships of diploid cotton genome groups using DNA sequences from 11 single-copy nuclear loci (10?293 base pairs [bp]), nuclear ribosomal DNA (695 bp), and four chloroplast loci (7370 bp). Results from individual loci and combined nuclear and chloroplast DNA partitions reveal that the cotton genome groups radiated in rapid succession following the formation of the genus. Maximum likelihood analysis of nuclear synonymous sites shows that this radiation occurred within a time span equivalent to 17% of the time since the separation of Gossypium from its nearest extant relatives in the genera Kokia and Gossypioides. Chloroplast and nuclear phylogenies differ significantly with respect to resolution of the basal divergence in the genus and to interrelationships among African cottons. This incongruence is due to limited character evolution in cpDNA and either previously unsuspected hybridization or unreliable phylogenetic performance of the cpDNA characters. This study highlights the necessity of using multiple, independent data sets for resolving phylogenetic relationships of rapidly diverged lineages.     

Recent hybridization between Taenia asiatica and Taenia saginata

Five Taenia tapeworms collected from humans in Tibetan Plateau, Sichuan, China, where three species of human Taenia are sympatrically endemic, were examined for the mitochondrial cox1 gene and two nuclear genes, ef1 and elp. Phylogenetic analyses of these genes revealed that two adult worms showed nuclear-mitochondrial discordance, suggesting that they originated from hybridization between Taenia saginata and Taenia asiatica. One of two worms had T. asiatica-type mtDNA, whereas another worm had T. saginata-type mtDNA, indicating that reciprocal hybridization between T. saginata and T. asiatica could occur. The worm having T. asiatica-type mtDNA was heterozygous at both nuclear loci with T. saginata-type alleles and T. asiatica-type alleles. In another worm, the ef1 locus was heterozygous with a T. saginata-type alleles and T. asiatica-type alleles, while the elp locus was homozygous with T. saginata-type alleles. Self-fertilization is the main reproductive method of the genus Taenia. Since self-fertilization represents a type of inbreeding, each locus in the offspring would become homozygous over generations with genetic drift. The fact that some nuclear loci are still heterozygous means that hybridization might have occurred recently. Hybridization between T. asiatica and T. saginata is probably an ongoing event in many areas in which they are sympatrically endemic.     

Speciation via introgressive hybridization in East African cichlids?

Speciation caused by introgressive hybridization occurs frequently in plants but its importance remains controversial in animal evolution. Here we report a case of introgressive hybridization between two ancient and genetically distinct species of Lake Tanganyika cichlids that led to the formation of a new species. Neolamprologus marunguensis contains mtDNA haplotypes from both parental species varying on average by 12.4% in the first section of the control region and by 5.2% in a segment of the cytochrome b gene. All individuals have almost identical DNA sequences in the flanking regions of the single-copy nuclear DNA locus TmoM27, and show a mosaic of alleles derived from both parental lineages in six microsatellite loci. Hence, our finding displays another mode of speciation in cichlid fishes. The increase of genetic and phenotypic diversity due to hybridization may contribute to the uniquely rapid pace of speciation in cichlids.     

Host Adaptation and Speciation through Hybridization and Polyploidy in Phytophthora

It is becoming increasingly evident that interspecific hybridization is a common event in phytophthora evolution. Yet, the fundamental processes underlying interspecific hybridization and the consequences for its ecological fitness and distribution are not well understood. We studied hybridization events in phytophthora clade 8b. This is a cold-tolerant group of plant pathogenic oomycetes in which six host-specific species have been described that mostly attack winter-grown vegetables. Hybrid characterization was done by sequencing and cloning of two nuclear (ITS and Ypt1) and two mitochondrial loci (Cox1 and Nadh1) combined with DNA content estimation using flow cytometry. Three different mtDNA haplotypes were recovered among the presumed hybrid isolates, dividing the hybrids into three types, with different parental species involved. In the nuclear genes, additivity, i.e. the presence of two alleles coming from different parents, was detected. Hybrid isolates showed large variations in DNA content, which was positively correlated with the additivity in nuclear loci, indicating allopolyploid hybridization followed by a process of diploidization. Moreover, indications of homeologous recombination were found in the hybrids by cloning ITS products. The hybrid isolates have been isolated from a range of hosts that have not been reported previously for clade 8b species, indicating that they have novel pathogenic potential. Next to this, DNA content measurements of the non-hybrid clade 8b species suggest that polyploidy is a common feature of this clade. We hypothesize that interspecific hybridization and polyploidy are two linked phenomena in phytophthora, and that these processes might play an important and ongoing role in the evolution of this genus.     

Phylogenetic evidence for hybrid origins of asexual lineages in an aphid species

Understanding the mode of origin of asexuality is central to ongoing debates concerning the evolution and maintenance of sexual reproduction in eukaryotes. This is because it has profound consequences for patterns of genetic diversity and ecological adaptability of asexual lineages, hence on the outcome of competition with sexual relatives both in short and longer terms. Among the possible routes to asexuality, hybridization is a very common mechanism in animals and plants. Aphids present frequent transitions from their ancestral reproductive mode (cyclical parthenogenesis) to permanent asexuality, but the mode of origin of asexual lineages is generally not known because it has never been thoroughly investigated with appropriate molecular tools. Rhopalosiphum padi is an aphid species with coexisting sexual (cyclically parthenogenetic) and asexual (obligately parthenogenetic) lineages that are genetically distinct. Previous studies have shown that asexual lineages of R. padi are heterozygous at most nuclear loci, suggesting either that they have undergone long-term asexuality (under which heterozygosity tends to increase) or that they have hybrid origins. To discriminate between these alternatives, we conducted an extensive molecular survey combining the sequence analysis of alleles of two nuclear DNA markers and mitochondrial DNA haplotypes in sexual and asexual lineages of R. padi. Both nuclear and cytoplasmic markers clearly showed that many asexual lineages have hybrid origins, the first such demonstration in aphids. Our results also indicated that asexuals result from multiple events of hybridization between R. padi and an unknown sibling species, and are of recent origin (contradicting previous estimates that asexual R. padi lineages were of moderate longevity). This study constitutes another example that putatively ancient asexual lineages are actually of much more recent origin than previously thought. It also presents a robust approach for testing whether hybrid origin of asexuality is also a common phenomenon in aphids.     

Copy number lability and evolutionary dynamics of the Adh gene family in diploid and tetraploid cotton (Gossypium)

Nuclear-encoded genes exist in families of various sizes. To further our understanding of the evolutionary dynamics of nuclear gene families we present a characterization of the structure and evolution of the alcohol dehydrogenase (Adh) gene family in diploid and tetraploid members of the cotton genus (Gossypium, Malvaceae). A PCR-based approach was employed to isolate and sequence multiple Adh gene family members, and Southern hybridization analyses were used to document variation in gene copy number. Adh gene copy number varies among Gossypium species, with diploids containing at least seven Adh loci in two primary gene lineages. Allotetraploid Gossypium species are inferred to contain at least 14 loci. Intron lengths vary markedly between loci, and one locus has lost two introns usually found in other plant Adh genes. Multiple examples of apparent gene duplication events were observed and at least one case of pseudogenization and one case of gene elimination were also found. Thus, Adh gene family structure is dynamic within this single plant genus. Evolutionary rate estimates differ between loci and in some cases between organismal lineages at the same locus. We suggest that dynamic fluctuation in copy number will prove common for nuclear genes, and we discuss the implications of this perspective for inferences of orthology and functional evolution.     

Phylogeny and molecular evolution of the DMC1 gene in the polyploid genus Leymus (Triticeae: Poaceae) and its diploid relatives

The level and pattern of nucleotide variation in duplicate genes provide important information on the evolutionary history of polyploids and divergent processes between homoeologous loci within lineages. Leymus, a group of allopolyploid species with the NsXm genomes, is a perennial genus with a diverse array of morphology, ecology, and distribution in Triticeae. To estimate the phylogeny and molecular evolution of a single-copy DMC1 gene in Leymus and its diploid relatives,DMC1 homoeologous sequences were isolated from the sampled Leymus species and were analyzed with those from 30 diploid taxa representing 18 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that: (i) different Leymus species might derive their Ns genome from different Psathyrostachys species; (ii) Pseudoroegneria has contributed to the nuclear genome of some Leymus species, which might result from recurrent hybridization or incomplete lineage sorting; (iii) the Xm genome origin of Leymus could differ among species; (iv) rapid radiation and multiple origin might account for the rich diversity, numbers of species, and wide ecological adaptation of Leymus species; and (v) the DMC1 sequence diversity of the Ns genome in Leymus species was lower than that in the Psathyrostachys diploids, while the level of DMC1 sequence diversity in Leymus was higher than that in diploid Pseudoroegneria. Our results provide new insight on the evolutionary dynamics of duplicate DMC1 genes, polyploid speciation, and the phylogeny of Leymus species.     

High-throughput identification of informative nuclear Loci for shallow-scale phylogenetics and phylogeography

One of the major challenges for researchers studying phylogeography and shallow-scale phylogenetics is the identification of highly variable and informative nuclear loci for the question of interest. Previous approaches to locus identification have generally required extensive testing of anonymous nuclear loci developed from genomic libraries of the target taxon, testing of loci of unknown utility from other systems, or identification of loci from the nearest model organism with genomic resources. Here, we present a fast and economical approach to generating thousands of variable, single-copy nuclear loci for any system using next-generation sequencing. We performed Illumina paired-end sequencing of three reduced-representation libraries (RRLs) in chorus frogs (Pseudacris) to identify orthologous, single-copy loci across libraries and to estimate sequence divergence at multiple taxonomic levels. We also conducted PCR testing of these loci across the genus Pseudacris and outgroups to determine whether loci developed for phylogeography can be extended to deeper phylogenetic levels. Prior to sequencing, we conducted in silico digestion of the most closely related reference genome (Xenopus tropicalis) to generate expectations for the number of loci and degree of coverage for a particular experimental design. Using the RRL approach, we: (i) identified more than 100,000 single-copy nuclear loci, 6339 of which were obtained for divergent conspecifics and 904 of which were obtained for heterospecifics; (ii) estimated average nuclear sequence divergence at 0.1% between alleles within an individual, 1.1% between conspecific individuals that represent two different clades, and 1.8% between species; and (iii) determined from PCR testing that 53% of the loci successfully amplify within-species and also many amplify to the genus-level and deeper in the phylogeny (16%). Our study effectively identified nuclear loci present in the genome that have levels of sequence divergence on par with mitochondrial loci commonly used in phylogeography. Specifically, we estimated that ～7% of loci in the chorus frog genome are >3% divergent within species; this translates to a prediction of approximately 50,000 single-copy loci in the genome with >3% divergence. Moreover, successful amplification of many loci at deeper phylogenetic levels indicates that the RRL approach represents an efficient method for rapid identification of informative loci for both phylogenetics and phylogeography. We conclude by making recommendations for minimizing the cost and maximizing the efficiency of locus identification for future studies in this field.     

Characterization of polymorphic microsatellite markers in the brine shrimp Artemia (Branchiopoda, Anostraca)

The brine shrimp Artemia is a complex genus containing sexual species and parthenogenetic lineages. Artemia franciscana is native to America and its cysts (diapausing eggs) are used worldwide as a food source in aquaculture. As a consequence, this anostracan has become an invasive species in many hypersaline aquatic ecosystems of other continents. Parthenogenetic Artemia lineages occur only in the Old World. Ten and five microsatellite markers were developed to characterize two populations for A. franciscana and two populations for diploid parthenogenetic Artemia, respectively. For A. franciscana the number of alleles ranged from 11 to 58 per locus, while for parthenogens the number of alleles ranged from three to 10. The levels of heterozygosity in A. franciscana and in parthenogens ranged from 0.115 to 0.976 and from 0.000 to 0.971, respectively. These microsatellite loci showed a high population assignment power, which will be useful for future studies of population genetics and invasive processes in Artemia.     

Molecular Characterization of Natural Hybrids Formed between Five Related Indigenous Clade 6 Phytophthora Species

Most Phytophthora hybrids characterized to date have emerged from nurseries and managed landscapes, most likely generated as a consequence of biological invasions associated with the movement of living plants and germplasm for ornamental, horticultural and agricultural purposes. Presented here is evidence for natural hybridization among a group of five closely related indigenous clade 6 Phytophthora species isolated from waterways and riparian ecosystems in Western Australia. Molecular characterization of hybrids consisted of cloning and sequencing two nuclear genes (ITS and ASF), sequencing of two further nuclear loci (BT and HSP) and of two mitochondrial loci (COI and NADH). Additionally, phenotypic traits including morphology of sporangia and optima and maxima temperatures for growth were also determined. In most cases the nuclear genes were biparentally and in all cases the mtDNA were uniparentally inherited, indicating hybrid formation through sexual crosses. Some isolates bear the molecular signature of three parents suggesting additional hybrid events, although it cannot be determined from the data if these were sequential or simultaneous. These species and their hybrids co-exist in riparian ecosystems and waterways where their ability for rapid asexual proliferation would enable them to rapidly colonize green plant litter. The apparent ease of hybridization could eventually lead to the merging of species through introgression. However, at this point in time, species integrity has been maintained and a more likely scenario is that the hybrids are not stable evolutionary lineages, but rather transient hybrid clones.     

The plant pathogen Phytophthora andina emerged via hybridization of an unknown Phytophthora species and the Irish potato famine pathogen, P. infestans

Emerging plant pathogens have largely been a consequence of the movement of pathogens to new geographic regions. Another documented mechanism for the emergence of plant pathogens is hybridization between individuals of different species or subspecies, which may allow rapid evolution and adaptation to new hosts or environments. Hybrid plant pathogens have traditionally been difficult to detect or confirm, but the increasing ease of cloning and sequencing PCR products now makes the identification of species that consistently have genes or alleles with phylogenetically divergent origins relatively straightforward. We investigated the genetic origin of Phytophthora andina, an increasingly common pathogen of Andean crops Solanum betaceum, S. muricatum, S. quitoense, and several wild Solanum spp. It has been hypothesized that P. andina is a hybrid between the potato late blight pathogen P. infestans and another Phytophthora species. We tested this hypothesis by cloning four nuclear loci to obtain haplotypes and using these loci to infer the phylogenetic relationships of P. andina to P. infestans and other related species. Sequencing of cloned PCR products in every case revealed two distinct haplotypes for each locus in P. andina, such that each isolate had one allele derived from a P. infestans parent and a second divergent allele derived from an unknown species that is closely related but distinct from P. infestans, P. mirabilis, and P. ipomoeae. To the best of our knowledge, the unknown parent has not yet been collected. We also observed sequence polymorphism among P. andina isolates at three of the four loci, many of which segregate between previously described P. andina clonal lineages. These results provide strong support that P. andina emerged via hybridization between P. infestans and another unknown Phytophthora species also belonging to Phytophthora clade 1c.     

PERMANENT GENETIC RESOURCES: Isolation, characterization and cross-species amplifications of microsatellite loci from Conradina (Lamiaceae)

We report the isolation of microsatellite loci from three species in the genus Conradina (Lamiaceae). To ensure their utility for multiple species, loci were screened for amplification and variability in all six Conradina species; 11 loci demonstrated high levels of amplification and polymorphism in most species. These 11 loci were characterized in 20 individuals from one population of Conradina brevifolia; alleles per locus ranged from five to 15, and observed heterozygosity ranged from 0.30 to 0.90. These microsatellites will be used to clarify species limits, detect interspecific hybridization, and understand the partitioning of genetic variation in each species of Conradina.     

Multiple cryptic species of sympatric generalists within the avian blood parasite Haemoproteus majoris

The avian haemosporidian parasite Haemoproteus majoris has been reported to infect a wide range of passerine birds throughout the Holarctic ecozone. Five cytochrome b (cyt b) lineages have been described as belonging to the morphological species H. majoris, and these form a tight phylogenetic cluster together with 13 undescribed lineages that differ from each other by < 1.2% in sequence divergence. Records in a database (MalAvi) that contains global findings of haemosporidian lineages generated by universal primers suggest that these lineages vary substantially in host distribution. We confirm this pattern in a data set collected at Lake Kvismaren, Sweden, where three of the generalist lineages have local transmission. However, whether these lineages represent intraspecific mitochondrial diversity or clusters of cryptic species has previously not been examined. In this study, we developed novel molecular markers to amplify the partial segments of four nuclear genes to determine the level of genetic diversity and gene phylogenies among the five morphologically described cyt b lineages of H. majoris. All five cyt b lineages were strongly associated with unique nuclear alleles at all four nuclear loci, indicating that each mitochondrial lineage represents a distinct biological species. Within lineages, there was no apparent association between nuclear alleles and host species, indicating that they form genetically unstructured populations across multiple host species.     

Genetic variation and de novo mutations in the parthenogenetic Caucasian rock lizard Darevskia unisexualis

Unisexual all-female lizards of the genus Darevskia that are well adapted to various habitats are known to reproduce normally by true parthenogenesis. Although they consist of unisexual lineages and lack effective genetic recombination, they are characterized by some level of genetic polymorphism. To reveal the mutational contribution to overall genetic variability, the most straightforward and conclusive way is the direct detection of mutation events in pedigree genotyping. Earlier we selected from genomic library of D. unisexualis two polymorphic microsatellite containing loci Du281 and Du215. In this study, these two loci were analyzed to detect possible de novo mutations in 168 parthenogenetic offspring of 49 D. unisexualis mothers and in 147 offspring of 50 D. armeniaca mothers. No mutant alleles were detected in D. armeniaca offspring at both loci, and in D. unisexualis offspring at the Du215 locus. There were a total of seven mutational events in the germ lines of four of the 49 D. unisexualis mothers at the Du281 locus, yielding the mutation rate of 0.1428 events per germ line tissue. Sequencing of the mutant alleles has shown that most mutations occur via deletion or insertion of single microsatellite repeat being identical in all offspring of the family. This indicates that such mutations emerge at the early stages of embryogenesis. In this study we characterized single highly unstable (GATA)(n) containing locus in parthenogenetic lizard species D. unisexualis. Besides, we characterized various types of mutant alleles of this locus found in the D. unisexualis offspring of the first generation. Our data has shown that microsatellite mutations at highly unstable loci can make a significant contribution to population variability of parthenogenetic lizards.     

The Organization of Genetic Diversity in the Parthenogenetic Lizard CNEMIDOPHORUS TESSELATUS

The parthenogenetic lizard species Cnemidophorus tesselatus is composed of diploid populations formed by hybridization of the bisexual species C. tigris and C. septemvittatus, and of triploid populations derived from a cross between diploid tesselatus and a third bisexual species, C. sexlineatus. An analysis of allozymic variation in proteins encoded by 21 loci revealed that, primarily because of hybrid origin, individual heterozygosity in tesselatus is much higher (0.560 in diploids and 0.714 in triploids) than in the parental bisexual species (mean, 0.059). All triploid individuals apparently represent a single clone, but 12 diploid clones were identified on the basis of genotypic diversity occurring at six loci. From one to four clones were recorded in each population sampled. Three possible sources of clonal diversity in the diploid parthenogens were identified: mutation at three loci has produced three clones, each confined to a single locality; genotypic diversity at two loci apparently caused by multiple hybridization of the bisexual species accounts for four clones; and the remaining five clones apparently have arisen through recombination at three loci. The relatively limited clonal diversity of tesselatus suggests a recent origin. The evolutionary potential of tesselatus and of parthenogenetic forms in general may be less severely limited than has generally been supposed.     

Phylogeny and species delimitation of the C-genome diploid species in Oryza

The diploid Oryza species with C-genome type possesses abundant genes useful for rice improvement and provides parental donors of many tetraploid species with the C-genome (BBCC,CCDD).Despite extensive studies,the phylogenetic relationship among the C-genome species and the taxonomic status of some taxa remain controversial.In this study,we reconstructed the phylogeny of three diploid species with C-genome (Oryza officinalis,O.rhizomatis,and O.eichingeri) based on sequences of 68 nuclear single-copy genes.We obtained a fully resolved phylogenetic tree,clearly indicating the sister relationship of O.officinalis and O.rhizomatis,with O.eichingeri being the more divergent lineage.Incongruent phylogenies of the C-genome species found in previous studies might result from lineage sorting,introgression/hybridization and limited number of genetic markers used.We further applied a recently developed Bayesian species delimitation method to investigate the species status of the Sri Lankan and African O.eichingeri.Analyses of two datasets (68 genes with a single sample,and 10 genes with multiple samples) support the distinct species status of the Sri Lankan and African O.eichingeri.In addition,we evaluated the impact of the number of sampled individuals and loci on species delimitation.Our simulation suggests that sampling multiple individuals is critically important for species delimitation,particularly for closely related species.     

DNA EVIDENCE FOR NONHYBRID ORIGINS OF PARTHENOGENESIS IN NATURAL POPULATIONS OF VERTEBRATES

Naturally occurring unisexual reproduction has been documented in less than 0.1% of all vertebrate species. Among vertebrates, true parthenogenesis is known only in squamate reptiles. In all vertebrate cases that have been carefully studied, the clonal or hemiclonal taxa have originated through hybridization between closely related sexual species. In contrast, parthenogenetic reproduction has arisen in invertebrates by a variety of mechanisms, including likely cases of “spontaneous” (nonhybrid) origin, a situation not currently documented in natural populations of vertebrates. Here, we present molecular data from the Neotropical night lizard genus Lepidophyma that provides evidence of independent nonhybrid origins for diploid unisexual populations of two species from Costa Rica and Panama. Our mitochondrial and nuclear phylogenies are congruent with respect to the unisexual taxa. Based on 14 microsatellite loci, heterozygosity (expected from a hybrid origin) is low in Lepidophyma reticulatum and completely absent in unisexual L. flavimaculatum. The unique value of this system will allow direct comparative studies between parthenogenetic and sexual lineages in vertebrates, with an enormous potential for this species to be a model system for understanding the mechanisms of nonhybrid parthenogenesis.