Sex Determiners and Speciation in the Genus Chironomus

Abstract

In a group of closely related Australian Chironomus species, the position of the sex-determining region is variable, not only in different species (or forms) but , in at least one case, also within the same form. This has raised a number of questions regarding the nature of sex determination and the relevance of variable sex determiners to speciation: (I) Is the sex-determiner location altered by mutation at different steps in a genetic pathway or by translocation (e.g., as a transposable element)? (2) Do polymorphisms for sexdeterminer location exist, or do the apparent polymorphisms result from the existence of cryptic species? (3) Are changes in the location of the functional sex determiner a major component of speciation in this group? This paper considers mainly the third question. A model of speciation involving the sex determiner, compatible with either allopatry or sympatry, is proposed. Comparisons are made with other groups, both invertebrate and vertebrate, which appear to have a similar variable sex-determiner location.