Chromosomal evolution of Delena cancerides
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چکیده
The huntsman spider Delena cancerides (Sparassidae, Walckenaer) encompasses a number of chromosomally distinct populations (karyomorphs), including forms with entirely telocentric chromosomes, and many populations saturated for centric fusions resulting in metacentric chromosomes. Where these fusions are sex-linked, males are fi xed heterozygotes, carrying one or two sex-linked chains of chromosomes of various lengths, while females carry normal bivalents at meiosis. In the absence of X-autosome fusions however, all fusions are homozygous meaning both sexes carry metacentric bivalents. During a broad scale survey of this polytypism, a fi fth category of chromosomal confi guration was observed, where individuals were found to carry rings of various even numbers of autosomes at meiosis. Unlike the chains seen in other populations, these rings are not sex linked and so are observed as fl oating polymorphism, probably occurring in females as well as males. Rings were found at only two locations, both within the distribution of the metacentric bivalent (mII) population. One of these locations was sampled intensively, revealing six different ring types co-distributed in an area of less than 20 km2, mixed with about 50% mII individuals, and surrounded by pure mII populations. This polymorphism is interpreted as resulting from hybridization between differentiated mII forms carrying different fusion combinations. This hybrid zone appears to have tension zone dynamics, possibly resulting from malsegregation of large rings. The chromosomal diversity observed within the zone is greater than expected for a simple contact between two populations. Several models are proposed to account for this excess diversity.
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تاریخ انتشار 2009