Tuesday, October 18, 2016

New paper published: Genetic diversity and demography of the red starfish

A beautiful specimen of the red starfish Echinaster sepositus.
by Alex Garcia-Cisneros

One of the most wonderful starfish of the Mediterranean suffered a large demographic expansion since the last maximum glacial period. However, its demographic expansion does not prevent it to have a weakness point: a low genetic diversity that might indicate the vulnerability of the species. These and more results were recently published by the ChallenGen team in a manuscript entitled “Low genetic diversity and demographic expansion in the red starfish Echinaster sepositus (Retzius 1816)” at the Scientific Reports.

The authors used both mitochondrial and nuclear markers to resolve the phylogeography and population genetics of the commonly named “red starfish” (Echinaster sepositus). The authors analysed samples from most of the distribution range of the species, with 15 localities distributed between both Mediterranean basins and the Atlantic Ocean.

Besides to demonstrate the low genetic diversity of the species compared with other echinoderms, the species showed a weak genetic structure within marine basins despite the a priori low dispersal potential of its lecithotrophic larva. The lecithotrophic larva in this species does not live more than few days before the settlement and therefore, it makes it difficult to connect distant or isolated populations. Furthermore, we found sharp differences in two Mediterranean localities, Cartagena and Livorno, that are located close to large marine harbours and coastal areas affected by industry, although our experimental design does not allow us to assess the effects of pollutants on the genetic structure.

Bar plots of the Bayesian clustering analysis obtained using STRUCTURE for different K values and based on the combination of both mitochondrial sequences (COI) and microsatellite loci.

Monday, October 10, 2016

Crossing Borders: Temporal genetic differentiation over oceanographic fronts

by Ferran Palero

A new paper from the CHALLENGEN team entitled “Temporal and spatial genetic differentiation in the crab Liocarcinus depurator across the Atlantic-Mediterranean transition” has been recently published in the JCR journal Scientific Reports.

Median joining haplotype network. Each circle represents a haplotype and its size is proportional to its frequency. Location acronyms are DELT (Delta de l’Ebre), VALE (València), ALAC (Alacant), WALB (Málaga) CADI (Cádiz).

Proportion of individuals assigned to the MED haplogroup in each location and sampled year from 1000 pseudoreplicates.
Spatial genetic studies often require sampling broadly separated areas, difficult to access simultaneously. Although comparing localities surveyed at different time periods might result in spurious genetic differentiation, there is a general believe on the stability of genetic structure through time, particularly if sampled localities are isolated or very distant. However, should we really expect stable genetic patterns in marine species? To test this important question, Marta Pascual and collaborators have assessed the time-variation of phylogeography patterns of the portunid crab Liocarcinus depurator across the Atlantic-Mediterranean transition. A partial fragment of the cytochrome oxidase I gene was sequenced in 366 individuals collected during three time periods from localities at both sides of each of the three main oceanographic discontinuities in the area: Gibraltar Strait, Almeria-Oran Front and Ibiza Channel. Although localities showed genetic fluctuations through time, a significant gradient was detected along the coast for all sampling periods. Significant inter-annual differences identified within the Alicante area, north of the Almeria-Oran Front, were associated with shifts in the relative contribution of Atlantic and Mediterranean water masses. The authors conclude that the persistence of a clinal pattern in the Atlantic-Mediterranean transition area despite local fluctuations suggests a complex balance of dispersal and selection.

Despite the Alicante population from 2007 had a larger proportion of Atlantic haplotypes, an overall genetic cline remains stable across the 3-year sampling period.