Population genetic structure of the ascidian Styela rustica at Kongsfjorden, Svalbard, Arctic

Abstract

The actual Arctic biota shows a strong affinity with that of the Boreal Atlantic and Pacific ones, as a result of an active recolonization process after the Quaternary glaciations. The geographic distribution of sessile species is usually linked to larvae dispersive capabilities which can be directly related with time spent in the plankton. Ascidians larvae are lecitothorphic and short-lived, which suggest that ascidians could be not efficient dispersers. However, the solitary ascidian Styela rustica (Linnaeus, 1767) (Tunicata, Ascidiacea) shows a wide distribution pattern from the North Atlantic to the Arctic that, together with the relatively recent colonization of the Arctic system could indicate that this species efficiently disperses and colonizes new habitats. In this study we used ISSR-PCR markers to study the genetic structure of five populations of the ascidian Styela rustica at Kongsfjorden, west Spitsbergen (Svalbard archipelago). We analyzed whether this species presents a low genetic structure, as can be expected due to the historical process of recent post glaciations colonization, or if there is genetic differentiation at a local scale, caused by short-lived larvae and limited dispersal potential. The genetic diversity in each population assessed using the marker diversity index (M) ranged from 0.288 to 0.324. Population HN, situated close to a fast retreating glacier, showed the lowest diversity. Processes associated with deglatiation (icebergs calving from the glacier that scour the benthos and the increment of inorganic particulate matter on the water column) would drive to reduced population sizes and explain the reduced genetic variability observed in the HN population with respect to the others in the fjord. This suggests a possible linkage with the global warming process. Although the weak genetic structure found among the studied populations could indicate a founder effect, the genetic landscape shape analysis together with a positive relationship between genetic and geographic distances also suggest possible current gene flow among populations in the fjord.

The genetic structure of the exotic ascidian Styela plicata (Tunicata) from Italian ports, with a re‐appraisal of its worldwide genetic pattern

“…This result is consistent with that obtained in an inter‐simple sequence repeat study carried out by Demarchi et al . () on Styela rustica , in which no genetic divergence was found among five close local samples (approximately 3–23 km apart). It is therefore reasonable to suggest that many ports have only a single S. plicata population.…”

Climate change, glacier retreat and a new ice‐free island offer new insights on Antarctic benthic responses

“…This favours a longer pelagic larval duration of solitary forms, allowing increased dispersal potential compared to colonial species (Svane and Young , Ayre et al , Lambert ). In the polar Arctic and Antarctic species that have been studied, solitary ascidians showed a lower genetic structure than colonial or brooding species (Demarchi et al , ).…”

Reproductive biology of the ascidians Styela rustica and Halocynthia pyriformis from Kongsfjorden, Svalbard, Arctic

“…To test whether there were significant variations in mean oocyte size, a nonparametric Kruskal-Wallis (K-W) variance test was performed due to the lack of variance homogeneity (Levene test) even after transformation. When medians were different, the multiple range test described by Conover (1999) was used to identify which months statistically differed.…”