Mitochondrial DNA panmixia in the little brown seastar Echinaster spinulosus suggests a recent population expansion

Shallow Genetic Structure among the European Populations of the Six-Toothed Bark Beetle Ips sexdentatus (Coleoptera, Curculionidae, Scolytinae)

The six-toothed bark beetle, Ips sexdentatus, is one of the most abundant scolytid species of the central and southern European countries. It mostly feeds on Pinus sp., whereas during population outbreaks it can also attack Picea sp. In spite of its broad distribution, its phylogeography has never been studied before. To do that, we employed an mtDNA marker on 489 individuals that covered most of its native range in Europe. Geographic distribution of the 86 haplotypes showed that at least three glacial refugia have played a significant role in shaping the currently observed pattern of genetic divergence in Europe, without excluding the contribution of minor refugial areas that acted in a similar manner. The revealed shallow structure can be considered an artifact of factors that reduced intraspecific diversity, at the same time favoring gene flow. As such, biological traits of the species itself (flying ability and host preference) and even human-mediated transport of wood seem to be the most prevailing and probable reasons that gave rise to the observed pattern.

Evidence for panmixia despite barriers to gene flow in the hooked mussel, Ischadium recurvum (Mytilidae; Brachidontinae) along the North American coastline

The discovery of phylogeographic patterns within broadly distributed marine species can be particularly challenging because absolute physical barriers to dispersal can be inconspicuous. Genetic boundaries often lie where ocean currents meet, forming sharp physical and ecological gradients, which may act as barriers to successful migrants. In eastern North America, coastal species often show phylogeographic differentiation associated with two recognized genetic barriers: the Gulf/Atlantic and the Virginia/Carolina discontinuities. We examined 185 specimens of the intertidal hooked mussel Ischadium recurvum collected from 15 locations along the eastern coastline of North America to examine phylogeographic, migration and historical demographic patterns associated climate change associated with Pleistocene glacial patterns. Hypothesis testing using Bayes factors in Migrate-n rejected the presence of phylogeographic breaks consistent with either maritime discontinuity and favoured a panmictic population model. The migration rate from the Gulf to the Atlantic was approximately three times higher than the migration from the Atlantic to the Gulf whereas the Carolina-Virginia migration rates were nearly equal. The summary statistics (Tajima's D, Fu's Fs) were significant and the demographic analyses (mismatch distributions, Bayesian skyline plot) were consistent with patterns of population expansion following glacial retreat during the Pleistocene epoch.

Low genetic diversity and recent demographic expansion in the red starfish Echinaster sepositus (Retzius 1816)

Understanding the phylogeography and genetic structure of populations and the processes responsible of patterns therein is crucial for evaluating the vulnerability of marine species and developing management strategies. In this study, we explore how past climatic events and ongoing oceanographic and demographic processes have shaped the genetic structure and diversity of the Atlanto-Mediterranean red starfish Echinaster sepositus. The species is relatively abundant in some areas of the Mediterranean Sea, but some populations have dramatically decreased over recent years due to direct extraction for ornamental aquariums and souvenir industries. Analyses across most of the distribution range of the species based on the mitochondrial cytochrome c oxidase subunit I gene and eight microsatellite loci revealed very low intraspecific genetic diversity. The species showed a weak genetic structure within marine basins despite the a priori low dispersal potential of its lecithotrophic larva. Our results also revealed a very recent demographic expansion across the distribution range of the species. The genetic data presented here indicate that the species might be highly vulnerable, due to its low intraspecific genetic diversity.