An Earthworm Riddle: Systematics and Phylogeography of the Spanish Lumbricid Postandrilus

As currently defined, the genus Postandrilus Qui and Bouché, 1998, (Lumbricidae) includes six earthworm species, five occurring in Majorca (Baleares Islands, western Mediterranean) and another in Galicia (NW Spain). This disjunct and restricted distribution raises some interesting phylogeographic questions: (1) Is Postandrilus distribution the result of the separation of the Baleares-Kabylies (BK) microplate from the proto-Iberian Peninsula in the Late Oligocene (30-28 Mya)--vicariant hypothesis? (2) Did Postandrilus diversify in Spain and then colonize the Baleares during the Messinian salinity crisis (MSC) 5.96-5.33 Mya--dispersal hypothesis? (3) Is the distribution the result of a two-step process--vicariance with subsequent dispersal?To answer these questions and assess Postandrilus evolutionary relationships and systematics, we collected all of the six Postandrilus species (46 specimens - 16 locations) and used Aporrectodea morenoe and three Prosellodrilus and two Cataladrilus species as the outgroup. Regions of the nuclear 28S rDNA and mitochondrial 16S rDNA, 12S rDNA, ND1, COII and tRNA genes (4,666 bp) were sequenced and analyzed using maximum likelihood and Bayesian methods of phylogenetic and divergence time estimation. The resulting trees revealed six new Postandrilus species in Majorca that clustered with the other five species already described. This Majorcan clade was sister to an Iberian clade including A. morenoe (outgroup) and Postandrilus bertae. Our phylogeny and divergence time estimates indicated that the split between the Iberian and Majorcan Postandrilus clades took place 30.1 Mya, in concordance with the break of the BK microplate from the proto-Iberian Peninsula, and that the present Majorcan clade diversified 5.7 Mya, during the MSC.Postandrilus is highly diverse including multiple cryptic species in Majorca. The genus is not monophyletic and invalid as currently defined. Postandrilus is of vicariant origin and its radiation began in the Late Oligocene

Statistical Parsimony Networks and Species Assemblages in Cephalotrichid Nemerteans (Nemertea)

BACKGROUND: It has been suggested that statistical parsimony network analysis could be used to get an indication of species represented in a set of nucleotide data, and the approach has been used to discuss species boundaries in some taxa. METHODOLOGY/PRINCIPAL FINDINGS: Based on 635 base pairs of the mitochondrial protein-coding gene cytochrome c oxidase I (COI), we analyzed 152 nemertean specimens using statistical parsimony network analysis with the connection probability set to 95%. The analysis revealed 15 distinct networks together with seven singletons. Statistical parsimony yielded three networks supporting the species status of Cephalothrix rufifrons, C. major and C. spiralis as they currently have been delineated by morphological characters and geographical location. Many other networks contained haplotypes from nearby geographical locations. Cladistic structure by maximum likelihood analysis overall supported the network analysis, but indicated a false positive result where subnetworks should have been connected into one network/species. This probably is caused by undersampling of the intraspecific haplotype diversity. CONCLUSIONS/SIGNIFICANCE: Statistical parsimony network analysis provides a rapid and useful tool for detecting possible undescribed/cryptic species among cephalotrichid nemerteans based on COI gene. It should be combined with phylogenetic analysis to get indications of false positive results, i.e., subnetworks that would have been connected with more extensive haplotype sampling

Genetic Networking of the Bemisia tabaci Cryptic Species Complex Reveals Pattern of Biological Invasions

BACKGROUND: A challenge within the context of cryptic species is the delimitation of individual species within the complex. Statistical parsimony network analytics offers the opportunity to explore limits in situations where there are insufficient species-specific morphological characters to separate taxa. The results also enable us to explore the spread in taxa that have invaded globally. METHODOLOGY/PRINCIPAL FINDINGS: Using a 657 bp portion of mitochondrial cytochrome oxidase 1 from 352 unique haplotypes belonging to the Bemisia tabaci cryptic species complex, the analysis revealed 28 networks plus 7 unconnected individual haplotypes. Of the networks, 24 corresponded to the putative species identified using the rule set devised by Dinsdale et al. (2010). Only two species proposed in Dinsdale et al. (2010) departed substantially from the structure suggested by the analysis. The analysis of the two invasive members of the complex, Mediterranean (MED) and Middle East - Asia Minor 1 (MEAM1), showed that in both cases only a small number of haplotypes represent the majority that have spread beyond the home range; one MEAM1 and three MED haplotypes account for >80% of the GenBank records. Israel is a possible source of the globally invasive MEAM1 whereas MED has two possible sources. The first is the eastern Mediterranean which has invaded only the USA, primarily Florida and to a lesser extent California. The second are western Mediterranean haplotypes that have spread to the USA, Asia and South America. The structure for MED supports two home range distributions, a Sub-Saharan range and a Mediterranean range. The MEAM1 network supports the Middle East - Asia Minor region. CONCLUSION/SIGNIFICANCE: The network analyses show a high level of congruence with the species identified in a previous phylogenetic analysis. The analysis of the two globally invasive members of the complex support the view that global invasion often involve very small portions of the available genetic diversity

Asymmetric reproductive isolation between terminal forms of the salamander ring species Ensatina eschscholtzii revealed by fine-scale genetic analysis of a hybrid zone

<p>Abstract</p> <p>Background</p> <p>Ring species, exemplified by salamanders of the <it>Ensatina eschscholtzii </it>complex, represent a special window into the speciation process because they allow the history of species formation to be traced back in time through the geographically differentiated forms connecting the two terminal forms of the ring. Of particular interest is the nature and extent of reproductive isolation between the geographically terminal forms, in this case <it>E. e. eschscholtzii </it>and <it>E. e. klauberi</it>. Previous studies have documented infrequent hybridization at the end of the ring. Here, we report the first fine-scale genetic analysis of a hybrid zone between the terminal forms in southern California using individual-based Bayesian analyses of multilocus genetic data to estimate levels and direction of hybridization and maximum-likelihood analysis of linkage disequilibrium and cline shape to make inferences about migration and selection in the hybrid zone.</p> <p>Results</p> <p>The center of the hybrid zone has a high proportion of hybrids, about half of which were classified as F1s. Clines are narrow with respect to dispersal, and there are significant deviations from Hardy-Weinberg equilibrium as well as nonrandom associations (linkage disequilibria) between alleles characteristic of each parental type. There is cytonuclear discordance, both in terms of introgression and the geographic position of mitochondrial versus nuclear clines. Genetic disequilibrium is concentrated on the <it>eschscholtzii </it>side of the zone. Nearly all hybrids possess <it>klauberi </it>mtDNA, indicating that most hybrids are formed from female <it>klauberi </it>mating with male <it>eschscholtzii </it>or male hybrids (but not vice versa).</p> <p>Conclusions</p> <p>Our results are consistent with a tension zone trapped at an ecotone, with gene combinations characteristic of <it>klauberi </it>showing up on the <it>eschscholtzii </it>side of the zone due to asymmetric hybridization. We suggest that the observed asymmetry is best explained by increased discriminatory power of <it>eschscholtzii </it>females, or asymmetric postzygotic isolation. The relatively high frequency of hybrids, particularly F1s, contrasts with other contacts between the terminal forms, and with other contacts between other divergent <it>Ensatina </it>lineages, highlighting the diverse outcomes of secondary contact within a single species complex.</p

Mitochondrial phylogeography of baboons (Papio spp.) – Indication for introgressive hybridization?

<p>Abstract</p> <p>Background</p> <p>Baboons of the genus <it>Papio </it>are distributed over wide ranges of Africa and even colonized parts of the Arabian Peninsula. Traditionally, five phenotypically distinct species are recognized, but recent molecular studies were not able to resolve their phylogenetic relationships. Moreover, these studies revealed para- and polyphyletic (hereafter paraphyletic) mitochondrial clades for baboons from eastern Africa, and it was hypothesized that introgressive hybridization might have contributed substantially to their evolutionary history. To further elucidate the phylogenetic relationships among baboons, we extended earlier studies by analysing the complete mitochondrial cytochrome <it>b </it>gene and the 'Brown region' from 67 specimens collected at 53 sites, which represent all species and which cover most of the baboons' range.</p> <p>Results</p> <p>Based on phylogenetic tree reconstructions seven well supported major haplogroups were detected, which reflect geographic populations and discordance between mitochondrial phylogeny and baboon morphology. Our divergence age estimates indicate an initial separation into southern and northern baboon clades 2.09 (1.54–2.71) million years ago (mya). We found deep divergences between haplogroups within several species (~2 mya, northern and southern yellow baboons, western and eastern olive baboons and northern and southern chacma baboons), but also recent divergence ages among species (< 0.7 mya, yellow, olive and hamadryas baboons in eastern Africa).</p> <p>Conclusion</p> <p>Our study confirms earlier findings for eastern Africa, but shows that baboon species from other parts of the continent are also mitochondrially paraphyletic. The phylogenetic patterns suggest a complex evolutionary history with multiple phases of isolation and reconnection of populations. Most likely all these biogeographic events were triggered by multiple cycles of expansion and retreat of savannah biomes during Pleistocene glacial and inter-glacial periods. During contact phases of populations reticulate events (i.e. introgressive hybridization) were highly likely, similar to ongoing hybridization, which is observed between East African baboon populations. Defining the extent of the introgressive hybridization will require further molecular studies that incorporate additional sampling sites and nuclear loci.</p

The evolution of a highly variable sex chromosome in Gehyra purpurascens (Gekkonidae)

A karyotypic survey of the gekkonid lizard Gehyra purpurascens revealed a distinctive sex chromosome system. G-banding showed that the Z Chromosome of males is derived from a tandem fusion of two acrocentric chromosomes of a presumed ancestral Gehyra with 2n=44. Through the application of G-; N- and C-banding, a total of six morphs of the W chromosome were identified. These differ by paracentric and pericentric inversions and, in one case, by a centric shift. The possible reasons for such extensive variation in the W chromosome are considered, and it is suggested that increased mutability of the W chromosome may be a causal factor. In contrast to earlier speculations, this example demonstrates that sex chromosomes can evolve without significant changes in the amount of C-band heterochromatin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47361/1/412_2004_Article_BF00292447.pd