Speciation towards tetraploidization after intermediate processes of non-sexual reproduction

Polyploidy, hybridization and variation in mating systems are central issues for a deeper understanding of animal evolution. The Iberian species Squalius alburnoides represents an example combining all three phenomena. Previous studies showed that S. alburnoides populations are mainly composed of triploid and diploid hybrid forms (mainly females), and that the tetraploid forms are rare or absent. Both populations from the Douro drainage reveal a distinct scenario: tetraploid individuals represent 85.6-97.5% of the population, with no sex ratio bias observed. Based on the flow cytometry measurements of blood and spermatozoa cells, microsatellite loci and experimental crosses, we describe here, for the first time, two symmetric allotetraploid populations (CCAA) that resumed normal meiosis after undergoing intermediate processes of non-sexual reproduction to give rise to a new sexually reproducing polyploid species. Prezygotic (habitat selection and assortative mating) and postzygotic mechanisms (nonviable embryos) are responsible for the reproductive isolation from other forms of the S. alburnoides complex (e.g. CA, CAA). This example illustrates how hybrid polyploid complexes may lead to speciation.     

Genetic distinction of four haplochromine cichlid fish species in a satellite lake of Lake Victoria,East Africa

Lake Victoria is famous for its in evolutionary terms young but species‐rich assemblage of cichlid fishes. This ‘superflock’ also includes additional species from adjacent water systems. Lake Victoria is surrounded by several smaller lakes that are connected to the main water body of Lake Victoria only through swampy areas. Lake Kanyaboli is one such lake, harbouring a much poorer species diversity, mostly comprised of Lake Victoria endemics, some of which are now considered extirpated from the main lake. The focus of this study was on the modern haplochromine component of the cichlid fauna, represented by Lipochromis maxillaris, Astatotilapia nubila, Xystichromis phytophagus and Astatotilapia sp. ‘Bigeye’, as well as a number of morphologically distinct haplochromine specimens that could not be assigned to any of the recognized species. We used five microsatellite markers to distinguish these five taxa. Genetically, L. maxillaris was clearly differentiated from all other taxa, and A. sp. ‘Bigeye’ was moderately differentiated from the remaining three. Astatotilapia nubila, X. phytophagus and the unidentified specimens constituted a partially overlapping cluster. As each of the clusters had several (5–14) private alleles, extremely recent divergence is suggested. As all taxa except for A. sp. ‘Bigeye’ and the unidentified specimens also occur or at least occurred in Lake Victoria, it is likely that they evolved as part of the Lake Victoria superflock, while A. sp. ‘Bigeye’ and the unidentified specimens may have currently evolved in situ. The observation of slightly distinct albeit overlapping body shapes and the extremely close genetic relationship between three of the five taxa are fully compatible and in support of the hybrid swarm theory of adaptive radiation.     

Genetic characterization of Bhutanese native chickens based on an analysis of Red Junglefowl (Gallus gallus gallus and Gallus gallus spadecieus), domestic Southeast Asian and commercial chicken lines (Gallus gallus domesticus)

The genetic diversity of Bhutanese chickens needs to be understood in order to develop a suitable conservation strategy for these birds in Bhutan. In this, work, we used microsatellite markers to examine the genetic diversity of Bhutanese chickens. Four Bhutanese chicken varieties (Black plumage, Frizzle, Naked neck and Red Junglefowl-like, corresponding to Yuebjha Narp, Phulom, Khuilay and Seim, respectively), two subspecies of Red Junglefowl (Gallus gallus gallus and Gallus gallus spadecieus), two varieties of Thai native chickens (Pradhu Hang Dam and Chee; Gallus gallus domesticus) representing the Southeast Asian domestic chicken, and two commercial lines (Broiler and Single Comb White Leghorn) were genotyped with 18 microsatellites that included 16 loci recommended by the FAO/ISAG for investigations of genetic variability in chickens. All loci were polymorphic, with the number of alleles ranging from six (MCW0111) to 23 (MCW0183). Substantial genetic variation was observed in all populations, with the Bhutanese native chicken Yuebjha Narp (Black plumage chicken) showing the lowest genetic variability. Despite extensive intrapopulation variation, the genetic differentiation among 10 populations was moderate. A neighbor-joining tree revealed the genetic relationships involved while principal component analysis showed that Bhutanese native chickens should be given priority in conservation efforts because of their genetic distinctiveness. Chee chickens are especially valuable as a reservoir of predomestic diversity, as indicated by their greater genetic variation and their position in the phylogenetic tree.     

Speciation reversal and biodiversity dynamics with hybridization in changing environments

A considerable fraction of the world's biodiversity is of recent evolutionary origin and has evolved as a by-product of, and is maintained by, divergent adaptation in heterogeneous environments. Conservationists have paid attention to genetic homogenization caused by human-induced translocations (e.g. biological invasions and stocking), and to the importance of environmental heterogeneity for the ecological coexistence of species. However, far less attention has been paid to the consequences of loss of environmental heterogeneity to the genetic coexistence of sympatric species. Our review of empirical observations and our theoretical considerations on the causes and consequences of interspecific hybridization suggest that a loss of environmental heterogeneity causes a loss of biodiversity through increased genetic admixture, effectively reversing speciation. Loss of heterogeneity relaxes divergent selection and removes ecological barriers to gene flow between divergently adapted species, promoting interspecific introgressive hybridization. Since heterogeneity of natural environments is rapidly deteriorating in most biomes, the evolutionary ecology of speciation reversal ought to be fully integrated into conservation biology.     

极濒危植物中华水韭休宁居群的遗传结构

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对极濒危蕨类植物中华水韭(Isoetes sinensis)现存于安徽休宁的5个亚居群的等位酶多样性和遗传结构进行了研究。结果表明：中华水韭居群每位点平均等位基因数A=1．7,平均多态位点比率P=55．56％,平均预期杂合度He=0．201。居群中半数的多念位点表现为等位基因的“固定杂合”,5个亚居群的遗传多样性无显著差异,但都表现出严重偏离Hardy—Weinberg平衡的杂合子过昔;其遗传变异主要发生于亚居群内(94．27％),亚居群之间的遗传分化较小(Gsl=0．0573),亚居群间遗传一致度较高(I=0．960—0．999)。我们推断这可能是由于居群构建之初的奠基者效应或者原种群曾经历了较为严重的遗传瓶颈所导致;此外亚居群间便利的基因交流也可能起到了很大作用(Nm=4．5062)。取自休宁居群的75株样品由13个专一多位点基因型(18个位点等位酶基因型)组成,亚居群及个体间高度遗传均质。本文还就中华水韭休宁野生居群濒危的遗传因素进行了探讨,并提出了相应的保育策略。     

Morphotypes or distinct species? A multilocus assessment of two East Asian scimitar babblers (Aves,Timaliidae)

In birds, widespread species complexes often exhibit dramatic plumage differences across their distribution, which can give rise to discordance between morphotypes and phylogroups. Accurate identification of species diversity may require an integrated approach in which multilocus genetic data are used for inference and further corroborated by ecological, morphometric or behavioural data. Pomatorhinus gravivox and P. swinhoei, which were formerly considered component races of P. erythrogenys, were recently split using a delimitation system that mainly relied on the quantification of differences in phenotypic traits. We therefore carried out a reassessment of this taxonomic recommendation by conducting phylogenetic and population genetic analyses with multilocus genetic data. A deep mitochondrial split with a Kimura 2-parameter distance of 0.061 was observed, mainly corresponding to the two morphologically defined species. However, one individual from P. swinhoei harboured a haplotype of P. gravivox. Individual-based analyses of nuclear loci identified two distinct clusters that were exactly congruent with the two species. BPP delimitation also provided support for the separation. These congruencies support the notion that these two taxa are best regarded as two separate species. The presence of the P. gravivox mitochondrial haplotype in P. swinhoei was most likely a result of hybridization, due to the clear separation of nuclear loci. The speciation might be attributed to paleoclimatic changes but requires further evaluation due to the likelihood of ecological speciation. This study was in accordance with the results inferred from the quantitative system but highlighted the importance of sampling various data, especially in contact zones, in the study of taxonomy and speciation history.