Evidence Of Recent Introgression Research Articles

Reproductive isolation between oviparous and viviparous lineages of the Eurasian common lizardZootoca viviparain a contact zone

Contact zones between two evolutionary lineages are often useful for understanding the process of speciation because the observed genetic pattern reflects the history of differentiation. The Eurasian lacertid lizard Zootoca vivipara is a potentially interesting model for studying the role of reproductive mode in the speciation of squamate reptiles because it has both oviparous (Zootoca vivipara carniolica) and viviparous (Zootoca vivipara vivipara) populations that have recently been shown to be genetically distinct. We studied a newly-discovered syntopic area of these two Zootoca subspecies in the central Italian Alps using genetic markers to investigate the level of introgression between them. Patterns of genetic differentiation in a fragment of the mitochondrial DNA cytb gene and a set of nuclear microsatellites show that the speciation process is complete in this area, with no evidence of recent introgression. Phylogenetic and genotypic divergence suggests that the two subspecies have experienced long independent evolutionary histories, during which genetic and phenotypic differences evolved. The possible roles of biogeography, reproductive mode, and cytogenetic differentiation in this speciation process are dis- cussed. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 566-573.

Polymorphic sex-specific sequences in birds of prey

A red kite (Milvus milvus) clone, which cross-hybridizes to a human minisatellite, reveals complex polymorphic patterns in members of the Accipitridae, a family of 217 species of birds of prey, which includes the kites, hawks and eagles. The total absence of hybridization to males implies that the sequence is located on the W chromosome, and stable inheritance from mother to daughter suggests that the patterns evolve as haploid matrilines. This has allowed not only the development of a simple and rapid sexing technique but may also provide a means of monitoring matriarchal success and dispersion. As an example, a survey of 36 continental European red kite nests revealed 24 different haplotypes, whereas only 2 were found among 53 Welsh nests. The results show the effect of a dramatic bottleneck in Wales and may provide evidence of recent introgression from the continent.

Allozyme variation and evolutionary relationships of grain amaranths (Amaranthus spp.)

Allozyme studies in amaranth provided useful assays of genetic variation in order to verify the patterns inferred from morphological traits, for elucidating the genetic structure of landraces, and for the studies of evolutionary relationships among wild, weedy and crop species. Thirty-four populations of cultivated New World amaranths were surveyed along with 21 weedy New World populations for allozyme variation at nine electrophoretic enzyme loci. Eleven populations of cultivated amaranths from the Indian State of Uttar Pradesh and six from Nepal were also surveyed for a comparison. In the New World populations, heterozygosity was low, and different populations ranged from 0 to 44% polymorphic loci. Adjacent populations were often fixed for different alleles or had very different allele frequencies at certain loci, with no apparent geographical patterns. Diversity index H' was partitioned into the intra- and interpopulation as well as the interspecific components of variability. The crop versus weed genetic distances were the largest, whereas the intra- and interpopulation components of H' were about equal. Genetic structure of all three species of the New World amaranths together can be described as a collection of distinct populations, each more or less a heterogeneous collection of highly homozygous individuals. The North Indian populations showed relatively less allozyme variability with the most common alleles same as those of Mexican landraces. Alleles at several loci proved to be diagnostic of the crop and weed groups, and of the three individual crop species. Genetic distances based on pooled gene frequencies showed the three crop species to be generally more closely related inter se than they were to their putative weedy progenitor species, respectively (with the exception of the weed-crop pair A. quitensis and A. caudatus). This implies a single domestication event involving A. hybridus as the common ancestor rather than three separate domestication events. Close similarity between A. caudatus and A. quitensis might have resulted from transdomestication based on a weedy or semi-domesticated species having migrated from Meso-America to South America. This preliminary report must now be expanded by further ecogeographical, cytogenetic and population studies on new extensive collections from the areas of early domestication. Some evidence of recent introgression and/or segregation of crop-weed hybrids between A. caudatus and A. retroflexus is available in the form of rare individuals in crop populations with crop allozyme genotypes except for a single homozygous weedy allele.