Meeting Abstract
Sex chromosomes have evolved independently and repeatedly in a wide range of taxa. In some groups, the sex chromosomes are relatively stable, having been conserved for millions of years, while in others, the sex chromosomes undergo frequent turnovers. One possible explanation for the high frequency of turnovers in some organisms is the presence of reproductive endosymbionts such as Wolbachia. In terrestrial isopods, for instance, Wolbachia can induce host feminization and is thought to drive rapid sex chromosome turnover in this group. The terrestrial isopod Trachelipus rathkei, which is widespread throughout North America and Europe, is described as having a ZZ/ZW sex chromosome system in a cytogenetics study. We tested this hypothesis using crosses with experimentally sex-reversed individuals, and surprisingly found that sex is determined by an XX/XY system in our population. Moreover, genomic sequencing and PCR found evidence of past Wolbachia infections, plus a male-specific, Y-linked duplication of the androgenic gland hormone gene, which triggers male development in isopods. These results support the idea of frequent transitions in isopod sex chromosomes, and suggest that hosts may evolve mechanisms to counteract the effects of reproductive endosymbionts.
