Demographic history and population structure of the Antarctic silverfish Pleuragramma antarcticum

Abstract

The Antarctic silverfish Pleuragramma antarcticum (Nototheniidae) is the most abundant pelagic fish inhabiting Antarctic waters. In this study we investigated, through partial sequencing of the D-loop mitochondrial region, samples collected at four different locations in the Southern Ocean, three in the Atlantic and one in the Pacific sector. Sampling was replicated in two different years at two locations. Sequence analysis showed a remarkably high polymorphism, with 110 haplotypes over the 256 investigated specimens, and about 80% of haplotypes occurring only once. Neutrality tests indicated that all samples were not at mutation-drift equilibrium, and suggested a past population expansion. This result was supported by the presence of a star-like topology in the D-loop gene tree, and by results of mismatch distribution. The start of the expansion was dated, using a specifically calibrated clock, between 111 and 126 thousand years ago. This value corresponds to the start of the cooling period that led to the last glaciation peak, and is in close agreement with a recently suggested range expansion for pelagic Antarctic ecosystems. Analysis of molecular variation indicated a small, though highly significant, value of differentiation between samples. This result, together with the lack of association between clades and geographical locations, indicates a weak population structure for the species.

Genetic homogeneity and circum-Antarctic distribution of two benthic shrimp species of the Southern Ocean, Chorismus antarcticus and Nematocarcinus lanceopes

“…Allozymes provided evidence for negligible polymorphisms in the iceWsh Champsocephalus gunnari (Duhamel et al 1995), while RFLP analysis of whole mtDNA molecules showed moderate nucleotide diversity but little evidence of population subdivision (Williams et al 1994). Another study using the partial mitochondrial control region (D-loop) revealed a weak population structure for the abundant Antarctic silverWsh Pleuragramma antarcticum (Zane et al 2006). For invertebrates, evidence for a homogeneous genetic structure of populations sampled south of the Antarctic Polar Front was also shown for the abundant nemertean ribbon worm Parborlasia corrugatus using two mitochondrial gene fragments (Thornhill et al 2008) and the pycnogonid Colossendeis megalonyx from the Atlantic sector of the Southern Ocean (Krabbe et al 2010).…”

Stable isotopes reveal Holocene changes in the diet of Adélie penguins in Northern Victoria Land (Ross Sea, Antarctica)

“…Conversely, the Wsh-rich Adélie penguin diet, occurring between 7,000 and 2,000 years BP, could be related to the presence of permanent sea ice as the great spread of Adélie penguin colonies (penguin optimum) would document (Baroni and Orombelli 1994a, b). This environmental condition would also represent a suitable setting for a demographic expansion of Pleuragramma antarcticum (Zane et al 2006).…”

Comparative phylogeography of three trematomid fishes reveals contrasting genetic structure patterns in benthic and pelagic species

“…In a multiocus analyses of the Trematominae, Janko et al (2011) found no evidence for change of speciation or extinction rates in relation to Pleistocene glaciations. Altogether it seems that although the Quaternary climatic fluctuations had a dramatic effect on population size and structure especially in benthic fish (Zane et al, 2006;Janko et al, 2007;Rogers, 2007), they did not provoke mass extinctions or vicariant speciation and postglacial dispersal among temporarily fragmented populations was strong enough to prevent the achievement of reciprocal monophyly.…”

“…There is increasing evidence that Southern Ocean fish display not only geographical variability, but also considerable temporal variability in the genetic composition of recruits (Zane et al, 2006;Papetti et al, 2007Papetti et al, , 2009Patarnello et al, 2003). This may result from sweepstakes effects.…”