Geographic variation of sex-linked translocation heterozygosity in the termite Kalotermes approximatus snyder (Insecta: Isoptera)

Abstract

The primitive termite Kalotermes approximatus carries a number of reciprocal translocations (segmental interchanges) that are linked to the sex-determining mechanism in such a way that males are permanent structural heterozygotes, forming long chains or rings of chromosomes in meiosis, while females are structural homozygotes, forming only bivalents. A survey of male meiosis from collections covering nearly the whole species range in the southeastern United States reveals considerable variation in the number of translocations: males with a diploid number of 32 or 33 have meiotic chains of 11, 13, 14, 15, 16, and 17 or 19 chromosomes. The different types can be arranged in an evolutionary series of rearrangements involving translocations or Robertsonian fusions between chromosomal elements in the ring and those outside. In addition, the existence of a closed chain (ring) of 16, and of four different types of chain of 13, indicate that similar rearrangements have occurred among chain elements. The geographic pattern of these rearrangements suggests that their selection accompanied the expansion of the species northward from southern Florida sometime since the last glaciation or, alternatively, that as they arose the new translocation types successively supplanted the ancestral types, preferentially in the east-central portion of the range.