Skinks phylogeography in southern Africa

Last monday, Catherine presented an interesting paper presenting phylogeographic data on rock skinks distributed from south Angola to the west part of South Africa. They used an impressive data set representing <1Kb of mitochondrial region and >2.5Kb of nuclear region. Using samples from different regions they could propose a scenario for the colonization history (from north to south) and found some geographical breaks. Moreover, they found signs of hybridization between the lineages. The paper is a good example of phylogeographic studies in the region. Thanks Catherine and sorry for being late!

From PORTIK DM, BAUER AM & JACKMAN TR. Molecular Ecology, 2011, 20: 1744–1748

Title: Bridging the gap: western rock skinks (Trachylepis sulcata) have a short history in South Africa

Abstract

Phylogeographic patterns in wide-ranging species in southern Africa remain largely unexplored, especially in areas north of South Africa. Here, we investigate population structuring, demographic history, and the colonization pattern of the western rock skink (Trachylepis sulcata), a rock-dwelling species with a range extending from southwestern South Africa into Angola. Using 1056 bp from the mitochondrial marker ND2 and > 2.5 kb from three nuclear genes (EXPH5, KIF24, RAG-1), we constructed allele networks, generated extended Bayesian skyline plots and performed population clustering analyses. Analyses of historical demographic patterns show an overall southward range expansion from Northern Namibia into Southern Namibia and South Africa, although we find contrasting genetic breaks across these geographic regions using nuclear and mitochondrial data. We suggest that mtDNA has introgressed across a nuclear break corresponding to the Knersvlakte region of South Africa, a previously proposed biogeographic barrier for rupicolous species. This pattern of mitochondrial variation contrasts sharply to that of other South African taxa previously investigated, which all show significant mtDNA differentiation across the Knersvlakte region. Additionally, while other taxa show divergences dating to the Pliocene, T. sulcata appears to be a recent arrival in southern Africa, having crossed this barrier and colonized South Africa in the mid-Pleistocene. The complex phylogeographic history of T. sulcata corroborates the intricate patterns of genetic variation found in South African taxa and provides novel insight into historical processes affecting species distributed across Namibia.

Panmixia of european eels

Next monday, Emilie will present a very interesting paper assessing the level of panmixia in the European eel. From samples of both larvae in the spawning area of the Sargasso Sea and glass eels recruiting in European rivers, they used an impressive body of population genetics methods to assess the demographic status of the European eels. The paper is well written and probably represents one of the best recent examples of population genetic studies. Thanks Emilie

From ALS TD, HANSEN M, MAES GE, CASTONGUAY M, RIEMANN L, AARESTRUP K, MUNK P, SPARHOLT H, HANEL R & BERNATCHEZ L, Molecular Ecology, 2011, 20: 1333–1346

Title: All roads lead to home: panmixia of European eel in the Sargasso Sea

Abstract

European eels (Anguilla anguilla) spawn in the remote Sargasso Sea in partial sympatry with American eels (Anguilla rostrata), and juveniles are transported more than 5000 km back to the European and North African coasts. The two species have been regarded as classic textbook examples of panmixia, each comprising a single, randomly mating population. However, several recent studies based on continental samples have found subtle, but significant, genetic differentiation, interpreted as geographical or temporal heterogeneity between samples. Moreover, European and American eels can hybridize, but hybrids have been observed almost exclusively in Iceland, suggesting hybridization in a specific region of the Sargasso Sea and subsequent nonrandom dispersal of larvae. Here, we report the first molecular population genetics study based on analysis of 21 microsatellite loci in larvae of both Atlantic eel species sampled directly in the spawning area, supplemented by analysis of European glass eel samples. Despite a clear East–West gradient in the overlapping distribution of the two species in the Sargasso Sea, we only observed a single putative hybrid, providing evidence against the hypothesis of a wide marine hybrid zone. Analyses of genetic differentiation, isolation by distance, isolation by time and assignment tests provided strong evidence for panmixia in both the Sargasso Sea and across all continental samples of European eel after accounting for the presence of sibs among newly hatched larvae. European eel has declined catastrophically, and our findings call for management of the species as a single unit, necessitating coordinated international conservation efforts.