Microsatellite analysis reveals genetic differentiation between year-classes in the icefish Chaenocephalus aceratus at South Shetlands and Elephant Island

Abstract

Chaenocephalus aceratus is one of the most abundant Antarctic icefish species in the Atlantic sector and has been a by-catch species in the fishery for mackerel icefish, Champsocephalus gunnari, between the mid-1970s and mid-1980s at South Georgia, South Orkney, and South Shetland Islands. The species became the target of the fishery in particular seasons, such as at South Georgia in 1977/78. In our paper, we report results on genetic differentiation for 11 microsatellite loci in C. aceratus samples collected at the South Shetlands and Elephant Island. This study represents the first report on microsatellite variability of an icefish species. Our results support the evidence from previous studies on differences in infestation patterns of parasites that a single panmictic population of C. aceratus exists, spanning the two sampling sites separated by about 100 km. Moreover, our study indicates the presence of a significant genetic differentiation between individual year-classes pointing out the existence of dynamic processes acting at the population genetic level, according to recent results for broadly distributed marine species. Both small effective population size and immigration from unsampled differentiated stocks may be at the base of the differentiation found in C. aceratus

Spatial and temporal boundaries to gene flow between Chaenocephalus aceratus populations at South Orkney and South Shetlands

“…Although single-loci p-value estimates varied between these 2 methods (Table A1), results revealed significant differences after sequential Bonferroni corrections in all pairwise comparisons (p < 0.0001), except between southern South Shetlands and Elephant Island collected in 2002 (p = 0.10040 from Fisher's test and p = 0.06363 from chi-squared test). This latter result confirmed, after re-codification of allele classes, the previous results of Papetti et al (2007). In addition, the present study revealed: (1) (Manni et al 2004) (Fig.…”

“…1b, Table 5). In agreement with previously published studies, effective population size (N e ) varied considerably between methods (Fraser et al 2007), with MIGRATE providing the highest estimates (Table 6); the N e values are nevertheless different from previous estimates calculated between cohorts considering drift only (N e = 96 in Papetti et al 2007). In particular, Elephant Island and South Orkney showed higher N e values than before, also when considering the 95% confidence intervals (average from 241.4 to 21 236.39 for EI06 and from 264.00 and 16 491.42 for SO06; Table 6).…”

“…The present study reveals a much more complex pattern of differentiation than shown previously in Papetti et al (2007), as genetic differences occur both at temporal (Elephant Island 2002 and2006) and at geographic scale between South Shetlands (including Elephant Island) and South Orkney. Interestingly, similar conclusions on geographic differentiation were also reached by parasitic infestation patterns and data on spawning time/maturity stages (Siegel 1980, Sosinski & Janusz 2000.…”

“…Patwary et al (1994). Eleven microsatellite loci were amplified as described in Papetti et al (2007). Seven of these were species-specific ) while 4 loci, isolated from Chionodraco rastrospinosus (Notothenioidei, Channichthyidae) (Papetti et al 2006), crossamplified in Chaenocephalus aceratus.…”

“…Moreover, in order to minimize the negative consequences of a poor allele calling, binning was automated with the software FLEXIBIN ver. 2 (Amos et al 2007) and all samples from Papetti et al (2007) were rescored. Allele calling is known to be prone to a high error rate when new alleles are found, where reference standards are not available or, as in the present case, when scoring new samples (Amos et al 2007).…”