Comparing the incidence of spontaneous autopolyploidy in wild and hatchery Lake Sturgeon

Abstract

Objective: Living species of Acipenseriformes, sturgeons and paddlefishes, are characteristically polyploid, having more than two complete sets of chromosomes (>2n). They undergo spontaneous autopolyploidy, an unintentional one and a half times increase in genome size, more frequently than any other order of fish. For Lake Sturgeon Acipenser fulvescens, which are evolutionary octoploids (8n), spontaneous autopolyploidy results in fertile dodecaploid (12n) progeny. When 12n individuals reproduce with octoploids, it is possible that resulting decaploid (10n) offspring will have poor physiological performance and survivorship. Spontaneous autopolyploidy in the wild is very low; however, incidence in fish hatcheries is greater, as seen in other 8n sturgeon species. We investigated this disparity in Lake Sturgeon, predicting to find more dodecaploid individuals in hatchery populations than in the wild. Methods: Ploidy was determined using red blood cells from individuals in three hatchery and two wild populations of Lake Sturgeon in Manitoba, Canada (n = 1004). Red blood cell volume was evaluated with a Z2 Coulter counter and used to determine ploidy, based on the average of triplicate measures of the erythrocyte modal nuclei volume (fL). A subsample from each environment type was further examined using blood smear analysis (n = 130) and flow cytometry (n = 27). Result: One 12n hatchery individual was found, along with significant differences in erythrocyte morphometry between the five populations. Fluctuations in modal nuclei volume were also observed over 169 days of repeated measurement within a single hatchery population. Conclusion: The well-developed relationship between erythrocyte size and fishes external and physiological environment may explain the variance both between and within populations. These results demonstrate the need for ploidy monitoring in artificial hatcheries, as releasing even a single 12n fish could produce thousands of 10n offspring that, if recruited, would have a detrimental effect on the population fitness.