A cytogenetic survey of 25 species of lower termites from Australia

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Abstract
A survey of 25 species of lower termites (familes Mastotermitidae, Termopsidae, and Kalotermitidae) in Australia revealed that centric fusions are a common theme in karyotype evolution in these insects. All but one of the species studied have a basis XX/XY mechanism of sex determination, secondarily complicated in about a third of a species by centric fusions between autosomes and sex chromosomes. There is no obvious relationship between systematic position and presence or absence of these fusions. Fusions between Y chromosomes and autosomes were more common than fusions between X chromosomes and autosomes, in accord with the prediction of the hypothesis that differential selection between the two sexes is the basis for the spread of sex-linked fusions. The absence of these fusions in many species does not favor the idea that a high degree of sex linkage is a necessary condition for the establishment or maintenance of eusocial behavior in termites. The difference in the mechanism of sex determination from that of cockroaches (XX/XO) argues against the evolutionary derivation of termites from ancestral cockroaches; derivation of both groups from some common ancestor with XX/XY sex determination is more likely.