Cytological studies in Atlantic salmon from Canada, in hybrids between Atlantic salmon from Canada and Sweden and in hybrids between Atlantic salmon and sea trout

Abstract

Atlantic salmon, Salmo salar, from the Chaleur‐Bay district in eastern Canada has the same chromosome number, 2n = 58, as Atlantic salmon from Sweden. Hybrids between salmon from Chaleur and the river Lule in Sweden also have the chromosome number 2n = 58 and form multivalents and bivalents of the same type and proportion as in Scandinavian salmon. Hence, salmon from Canada and Scandinavia are presumed to have the same origin and, therefore, may be utilized in intraspecific crosses in order to improve the different strains used for breeding on both sides of the Atlantic. Hybrids between Atlantic salmon and sea trout have chromosome numbers around 2n = 69. In the meiosis rodshaped units only, and no rings, are formed together with a high number of univalents. Thus, apparently, reciprocal translocations have caused the occurrence of multivalents in the meiosis of salmon and not autopolyploidy as was earlier assumed.

Chromosome polymorphisms track trans‐Atlantic divergence and secondary contact in Atlantic salmon

“…Individual heterozygosity for the Ssa26/28 fusion was also found in the previous study (Brenna‐Hansen et al, ), but we did not detect outlier blocks associated with this rearrangement, potentially indicating the Ssa26/28 fusion has not reached significant LD thresholds or that this variation is not present in our current samples. Nonetheless, variation in all three rearrangements suggests that chromosome number (2 N ) could range between 54 and 58 in North America, consistent with karyotyping studies reporting this range of population‐specific mode 2 N with evidence of inter‐ and intrapopulation variability (Boothroyd, ; Brenna‐Hansen et al, ; Nygren, Nilsson, & Jahnke, ; Roberts, ,). Within individuals, it may be possible for rearranged chromosomes to pair and recombine, with crossing over highly restricted at the fusion and fission points, thus leading to high LD blocks detected here that are further strengthened by patterns of recombination in male salmonids that are highly localized towards telomeric regions (Lien et al, ).…”

“…Chromosome number itself has also been suggested to influence adaptive potential in salmonids, where a higher chromosome number has been hypothesized to increase the likelihood of adaptation to different environments (Makhrov, 2017;Phillips & Rab, 2001). In our study, we identify extensive karyotype vari- (Boothroyd, 1959;Brenna-Hansen et al, 2012;Nygren, Nilsson, & Jahnke, 1972;Roberts, 1968Roberts, ,1970.…”

Chromosomal differences between European and North American Atlantic salmon discovered by linkage mapping and supported by fluorescence in situ hybridization analysis

“…Indeed, several other karyotypes have been reported for Atlantic salmon from Maine and Canada. For example, Roberts [34] reported a 2n of 56 or 57 in landlocked salmon from Maine, while Nygren [35] reported that salmon from Baie de Chaleur (Quebec) have a 2n of 58, similar to salmon from Sweden. Boothroyd [36] surveyed chromosomes from three river populations (Gaspe, Quebec; Miramichi, New Brunswick; and River Phillip, Nova Scotia) and reported a 2n of 56 for all.…”

Meiotic chromosome configurations in triploid progeny from reciprocal crosses between wild-type diploid and natural tetraploid loach Misgurnus anguillicaudatus in China

“…Such polyploid cells were considered to have resulted from spontaneous endomitosis (endoreduplication) (Li et al 2011). Similar polyploid cells were also noticed in spermatocytes of salmonids (Nygren et al 1972). Such unusual polyploids presumably due to endomitosis have been observed in the unreduced egg production process of triploid (Zhang et al 1998) and clonal diploid (Itono et al 2006), and in the unreduced sperm formation of sex-reversed clonal diploid (Yoshikawa et al 2009) in the loach.…”

“…These previous results suggest that the formation of bivalents should take precedence of all other configurations like quadrivalents and trivalents even in polyploid germ cells. Relatively low frequencies of quadrivalents and predominance of bivalents were reported in meiosis of salmonid species which were considered as evolutionary tetraploidy (Nygren et al 1972;Davisson et al 1973;Lee and Wright 1981).…”