Biotype, genomotype, and genotype: variable effects of polyploidy and hybridity on ecological partitioning in a bisexual–unisexual community of salamanders

Abstract

It is hypothesized that coexistence of bisexual and unisexual salamanders depends upon various forms of ecological partitioning, as in analogous complexes of fishes. The mixture of clonal and nonclonal, obligately sperm-dependent reproduction occurring in unisexual mole salamanders of the genus Ambystoma suggests that some of this partitioning may be manifest in the variable reproductive attributes of different biotypes and in community structure. Within biotypes, ecological differences related to genomic composition (genomotype) and specific origin (genotype) of individuals are also expected. Using data gathered over a 4-year period from a large population of the A. laterale–jeffersonianum complex from Haliburton, Ontario, I examined four areas of reproductive ecology that may contribute to ecological partitioning: (1) fluctuating sex, hybrid, and ploidy ratios; (2) differential migratory response by triploid and tetraploid genomotypes; (3) ontogenetic differences among triploid and tetraploid genomotypes; and (4) genotypic differences within unisexual genomotypes. For each case I was able to reject a null hypothesis ascribing ecological equivalency to those biotypes involved. The most germane ecological differences among unisexuals were imbedded in the broad syndrome of delays in larval development, metamorphosis, and sexual maturity displayed by tetraploids. These findings parallel those reported in a large body of literature generated from laboratory studies of polyploid salamanders. Using these corresponding data, I conducted a broad review of potential developmental, physiological, and biotypic causes and consequences of the observed delays. The results indicated that several effects of polyploidy and hybridity directly influence community ecology and contribute to stable coexistence of bisexuals and unisexuals. Based on these findings, a strategic model summarizing interaction in these communities was constructed, from which testable hypotheses may be derived for future research. The findings of this study confirmed the ontological status of the biotypic distinctions (genomotype versus genotype) advanced here.