Growth and sexual maturation in diploid and polyploid salamanders (genus Ambystoma)

Abstract

On Pelee Island, Ontario, mole salamanders, Ambystoma laterale and Ambystoma texanum, coexist with their diploid, triploid, and tetraploid hybrids. In an initial study, A. laterale and hybrid larvae were raised in groups, but from metamorphosis to 5 months postmetamorphosis, individuals were raised in isolation. In a second study, A. texanum and hybrids were raised as isolated individuals under uniform feeding and laboratory conditions from the egg stage to 22 months postmetamorphosis. The total length of larvae at 14 days posthatching was correlated with size of eggs. Tetraploids originated from larger eggs, were larger at 2 weeks posthatching, and maintained their larger size throughout larval development. Tetraploids metamorphosed later and were heavier than all other genotypes. The heavier mass at metamorphosis was maintained and relatively increased so that by 22 months postmetamorphosis, when compared with other groups, tetraploids were heavier in mass, but not larger in snout–vent length. Bodies of tetraploids were more robust and tails, although not longer, were thicker. In contrast to A. texanum and diploid and triploid hybrids, among which 50% of individuals developed fully pigmented, yolk-filled ova by 22 months, no tetraploids showed such signs of sexual maturity. The growth and reproductive patterns of diploids and polyploids are discussed.