Baršiene et al. 1996

Baršiene J, Tapia G, Barsyte D. 1996. Chromosomes of molluscs inhabiting some mountain springs of eastern Spain. Journal of Molluscan Studies 62: 539-543.

These authors report karyotypes for four species of molluscs (three gastropods and one bivalve) collected from small, high-altitude freshwater habitats in Spain. These habitats are quite diverse, with some very small springs occupying only 3-4 m^2 of surface area. Previous studies had associated small and isolated populations with polyploidy and its effects on tolerance of environmental stress and avoiding inbreeding depression.

Collected animals were injected with (large body) or immersed in (small body) a colchicine solution before dissection. The authors do not clearly describe what tissues from which species and populations were used, though they do describe “gonal and somatic cells”; presumably the gonadal cells were sperm, and the somatic cells are loosely described as “soft tissues” that were dissociated in 45% acetic acid by pipetting.

The high fraction of “hypodiploid” cells found in some individuals of Lymnaea peregra and some instances of apparent cell degeneration was attributed to “ecological stress”, though no supporting evidence or further discussion appears. They also state that the bivalve in their study, Pisidium casertanum, was almost certainly diploid, despite different populations having chromsome numbers ranging from 150 to 180, and other, uncited studies that found high and idiosyncratic levels of polyploidy in this family (Pisidiidae) and the closely related family Sphaeriidae (e.g. Burch and Huber 1966). As a final negative criticism of this paper, I found the frequent reference of the authors’ own unpublished data in support of presumed trends to be rather annoying.