Integrity in the midst of sympatry: does sexual incompatibility facilitate the coexistence of metamorphic and paedomorphic mole salamanders (Ambystoma talpoideum)?

Abstract

The integrity of genetically determined morphs of the same species in sympatry may be facilitated by sexual incompatibility (and thus reduced gene flow) between morphs. A test for such incompatibility was carried out between fully metamorphosed and paedomorphic forms of the North American mole salamander Ambystoma talpoideum, which differ greatly in life-history characteristics. A few significant differences were found in the content and timing of courtship between homomorphic (within-morph) and heteromorphic (between-morph) encounters during 2-h observation sessions. However, no significant differences were apparent in the incidence of spermatophore deposition (which is an index of the potential for sperm transfer), both as recorded at the end of observation sessions and as determined for pairs left to interact for 16 h overnight. Fertilized and viable eggs were laid by females of both morphs that were exposed to spermatophores from either homomorphic or heteromorphic males, but not to both. We conclude that sexual incompatibility probably plays little or no role in preventing gene flow between sympatric morphs of A. talpoideum. Gametic incompatibility may also be of little or no importance. We suggest that differences in the phenology of breeding are of greater significance in the maintenance of discrete morphs of the mole salamander in sympatry.