Chromosomal diversity and evolution in the ground beetle genus Bembidion and related taxa (Coleoptera: Carabidae: Trechitae)
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- Maddison, D.R. Genetica (1985) 66: 93. doi:10.1007/BF00139715
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Chromosome numbers and sex chromosome systems of 154 previously unstudied Bembidion species are described. The genus is nearly uniform: males of 176 of 205 species are 2n=22+XY. Karyotypes are presented for 30 species. There is some variation among species in size of Y and size of autosomes. Within most species autosomes are subequal in size, and metacentric or submetacentric. Subterminal secondary constrictions and B chromosomes are reported from several species.
The supertribe Trechitae (Zolini + Trechini + Pogonini + Bembidiini) is hypothesized to be primitively male 2n=22+X or 24+X, and the ancestral Bembidion stock 2n=22+XY. Conclusions are based on the most parsimonious hypothesis of ancestral state given an inferred phylogeny of the group, rather than the widespread-is-primitive arguments used previously. Evolution within Bembidion away from the presumably-primitive 2n=22+XY is discussed. Six lineages have lost Y chromosomes; seven have undergone changes in autosome number. It is not known why such changes are so scarce, nor what particular rearrangements led to the observed diversity. Nonetheless, the cytogenetic data can be used to infer a monophyletic origin of groups possessing derived chromosome numbers or sex chromosomes, and to help resolve species limits.