The effect of life cycle stage and genotype on desiccation tolerance in the colonizing parthenogenetic cockroach Pycnoscelus surinamensis and its sexual ancestor P-indicus

We compared the desiccation tolerance of nymphs of diploid and triploid clones of the colonizing parthenogenetic cockroach, Pycnoscelus surinamensis, and strains of its sexual ancestor, P. indicus, as a test of the general-purpose genotype hypothesis and the polyploidy hypothesis for geographic parthenogenesis in this species complex. Desiccation tolerance is strongly associated with nymphal size. Clones of P. surinamensis are highly variable in nymphal desiccation tolerance, adjusted for body weight by analysis of covariance. This heterogeneity is mirrored by significant differences among recently isolated sublines of a lab population of P. indicus. As a group, the clones are not more tolerant than the sexual strains. Likewise, the four triploid clones were not more resistant to desiccation than the four diploid clones tested. A second experiment revealed a negative association between adult and last instar desiccation tolerance, due to developmental factors not associated with size. These patterns of variation in the sexual and parthenogenetic forms are consistent with the conclusion that extensive genetic variation in desiccation tolerance in the sexual ancestor has been preserved in the clonal lineages, but that desiccation tolerance has not been selected on strongly during the dispersal of clones of P. surinamensis.