Aspects of sex-specific differences in the expression of an alternative life cycle in the salamander Ambystoma talpoideum

A recent evolutionary ecological model of facultative paedomorphosis predic ts that body size of mature individuals should be larger than immatures of the same cohort. We investigated sex-specific differences in body size and maturation within a single cohort of branchiate (= larval and paedomorphic) mole salamanders, Ambystoma talpoideum. In addition, we also sampled the p opulation after the breeding season, as some individuals began to undergo m etamorphosis and leave the pond. The branchiate population was female-biase d (62.7%), and mature (paedomorphic) females were significantly smaller tha n paedomorphic males or immature (larval) females. The majority of male bra nchiates were mature (86.6%), whereas significantly fewer females were matu re (64.4%). After the reproductive season, males and females underwent meta morphosis in the same proportion in which they occurred in the branchiate p opulation, although a significantly greater proportion of immature females metamorphosed (64.6%) compared to their frequency in the branchiate populat ion (35.6%). There were no significant differences in body size with regard to sex or maturation among metamorphosing individuals. Our data demonstrat e that maturation in branchiates is independent of body size in males and t hat it may negatively affect body size in females. Our findings underscore sex as a potentially important factor, and question the role of body size, in regulating this life cycle polymorphism in A. talpoideum.