Extreme genetic differentiation among the remnant populations of marble trout (Salmo marmoratus) in Slovenia

Populations of the marble trout (Salmo marmoratus) have declined critically due to introgression by brown trout (Salmo trutta) strains. In order to define strategies for long-term conservation, we examined the genetic structure of the 8 known pure populations using 15 microsatellite loci. The analyses reveal extraordinarily strong genetic differentiation among populations separated by < 15 km, and extremely low levels of intrapopulation genetic variability. As natural recolonization seems highly unlikely, appropriate management and conservation strategies should comprise the reintroduction of pure populations from mixed stocks (translocation) to avoid further loss of genetic diversity.     

Conspecific versus heterospecific gene exchange between populations of Darwin's finches

This study addresses the extent and consequences of gene exchange between populations of Darwin''s finches. Four species of ground finches (Geospiza) inhabit the small island of Daphne Major in the centre of the Galápagos archipelago. We undertook a study of microsatellite DNA variation at 16 loci in order to quantify gene flow within species owing to immigration and between species owing to hybridization. A combination of pedigrees of observed breeders and assignments of individuals to populations by the program Structure enabled us to determine the frequency of gene exchange and the island of origin of immigrants in some cases. The relatively large populations of Geospiza fortis and G. scandens receive conspecific immigrants at a rate of less than one per generation. They exchange genes more frequently by rare but repeated hybridization. Effects of heterospecific gene flow from hybridization are not counteracted by lower fitness of the offspring. As a result, the standing genetic variation of the two main resident populations on Daphne Major is enhanced to a greater extent by introgressive hybridization than through breeding with conspecific immigrants. Immigrant G. fuliginosa also breeds with G. fortis. Conspecific immigration was highest in the fourth species, G. magnirostris. This species is much larger than the other three and perhaps for this reason it has not bred with any of them. The source island of most immigrants is probably the neighbouring island of Santa Cruz. Evolutionary change may be inhibited in G. magnirostris by continuing gene flow, but enhanced in G. fortis and G. scandens by introgressive hybridization.     

A molecular approach to detect hybridisation between crucian carp (Carassius carassius) and non-indigenous carp species (Carassius spp. and Cyprinus carpio)

1. Releases of non‐native fish into the wild is an increasing problem posing considerable ecological and genetic threats through direct competition and hybridisation. 2. We employed six microsatellite markers to identify first generation hybrids and backcrosses between native crucian carp (Carassius carassius) and introduced goldfish (C. auratus) and common carp (Cyprinus carpio) in the U.K. We also investigated the genetic characteristics of the taxonomically controversial gibel carp (Carassius spp.) from sites across Europe. 3. Natural hybridisation between goldfish and crucian carp occurs frequently, although hybrids between all other species pairs were observed. Only 62% of British crucian carp populations (n = 21) consisted exclusively of pure crucian carp. In some populations hybrids were so frequent, that no pure crucian carp were caught, indicating a high competitive ability of hybrids. 4. Most hybrids belonged to the F1 generation but backcrossing was evident at a low frequency in goldfish × crucian carp hybrids and goldfish × common carp hybrids. Furthermore, some local populations had high frequencies of backcrosses, raising the opportunity for introgression. 5. Gibel carp from Germany and Italy belonged to two triploid clonal lineages that were genetically closely related to goldfish, whereas all individuals identified from British populations proved to be crucian carp × goldfish hybrids. 6. Our study suggests that the release of closely related exotic cyprinids not only poses a threat to the genetic integrity and associated local adaptations of native species, but may also contribute to shifts in community structure through competitive interactions.     

Hybridization and Stratification of Nuclear Genetic Variation in Macaca mulatta and M. fascicularis

We used genotypes for 13 short tandem repeats (STRs) to assess the genetic diversity within and differentiation among populations of rhesus macaques (Macaca mulatta) from mainland Asia and long-tailed macaques (M. fascicularis) from mainland and insular Southeast Asia. The subjects were either recently captured in the wild or derived from wild-caught founders maintained in captivity for biomedical research. A large number of alleles are shared between the 2 macaque species but a significant genetic division between them persists. The distinction is more clear-cut among populations that are not, or are unlikely to have recently been, geographically contiguous. Our results suggest there has been significant interspecific nuclear gene flow between rhesus macaques and long-tailed macaques on the mainland. Comparisons of mainland and island populations of long-tailed macaques reflect marked genetic subdivisions due to barriers to migration. Geographic isolation has restricted gene flow, allowing island populations to become subdivided and genetically differentiated. Indonesian long-tailed macaques show evidence of long-term separation and genetic isolation from the mainland populations, whereas long-tailed macaques from the Philippines and Mauritius both display evidence of founder effects and subsequent isolation, with the impact from genetic drift being more profound in the latter.     

Plio-Pleistocene history of West African Sudanian savanna and the phylogeography of the Praomys daltoni complex (Rodentia): the environment/geography/genetic interplay

Rodents of the Praomys daltoni complex are typical inhabitants of the Sudanian savanna ecosystem in western Africa and represent a suitable model for testing the effects of Quaternary climatic oscillations on extant genetic variation patterns. Phylogeographical analyses of mitochondrial DNA sequences (cytochrome b) across the distribution range of the complex revealed several well‐defined clades that do not support the division of the clade into the two species currently recognized on the basis of morphology, i.e. P. daltoni (Thomas, 1892) and Praomys derooi ( Van der Straeten & Verheyen 1978 ). The observed genetic structure fits the refuge hypothesis, suggesting that only a small number of populations repeatedly survived in distinct forest‐savanna mosaic blocks during the arid phases of the Pleistocene, and then expanded again during moister periods. West African rivers may also have contributed to genetic differentiation, especially by forming barriers after secondary contact of expanding populations. The combination of three types of genetic markers (mtDNA sequences, microsatellite loci, cytogenetic data) provides evidence for the presence of up to three lineages, which most probably represent distinct biological species. Furthermore, incongruence between nuclear and mtDNA markers in some individuals unambiguously points towards a past introgression event. Our results highlight the importance of combining different molecular markers for an accurate interpretation of genetic data.     

Hybridization between subspecies of waterbuck (Kobus ellipsiprymnus) in zones of overlap with limited introgression

Two subspecies of waterbuck (Kobus ellipsiprymnus), common (Kobus ellipsiprymnus ellipsiprymnus) and defassa (Kobus ellipsiprymnus defassa), are recognized based on differences in rump pattern, coat colour and geographical distribution. These forms are parapatrically distributed with an area of range overlap in East Africa, where phenotypically intermediate populations occur. Variation in 478 bp of the mitochondrial DNA control region and 14 polymorphic microsatellite loci were used to describe the genetic structure and phylogeographical pattern of the species, and to assess if the intermediate populations are the results of hybridization. In total, 186 individuals from 11 localities were analysed. A high degree of genetic differentiation was found between subspecies, although this was most evident from the microsatellite data. Hybridization was suggested in the phenotypically and geographically intermediate Nairobi NP population in Kenya. A neighbour-joining (NJ) tree based on microsatellite population genetic distances grouped Nairobi between the common and defassa populations, and a Bayesian analysis clearly showed introgression. Individuals sampled in Samburu NP, Kenya, had a common waterbuck phenotype, but introgression was suggested by both markers. Although a high degree of maternal defassa input was indicated from the sequence data, the Samburu population grouped with the common waterbuck in the microsatellite population genetic distance tree, with high support. Analyses of linkage disequilibrium and maximum-likelihood estimates of genetic drift suggested that admixture between subspecies is a recent event. The fact that introgression is limited between subspecies could be caused by chromosomal differences, hindering gene flow between common and defassa waterbuck.     

基于微卫星标记探讨同域分布竹蝗间的基因渐渗

竹蝗是我国竹林的重要害虫。同域分布物种间基因渐渗方面的研究较少,针对竹蝗属的尚未见报道。本文应用5对微卫星标记检测了安徽金寨县青脊竹蝗和黄脊竹蝗同域分布种群的遗传多样性、遗传结构及种群间的渐渗。结果表明,5对微卫星引物检测到的等位基因共60个,每个位点拥有等位基因10~13个,平均为12个;各位点的期望杂合度(He)范围为0.711~0.885,观测杂合度(Ho)均为1。每个位点都具有较高的多态性,平均多态信息含量(PIC)为0.799,说明这些位点都存在着丰富的遗传信息。在整体水平上,所有微卫星位点对之间为显著的连锁不平衡。同域分布的黄脊竹蝗和青脊竹蝗种群个体间发生了基因渐渗,且基因流从黄脊竹蝗转移到青脊竹蝗。最后,讨论并提出了对竹蝗属基因渐渗深入研究的建议。