Electrophoretic evidence for multiple origins of triploid forms in the Ambystoma laterale–jeffersonianum complex

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Abstract
Variable allele frequencies and a wide range of genotypes in samples of triploid Ambystoma laterale–jeffersonianum (LLJ) hybrids indicate that these forms have arisen on many occasions. Though suggested previously, we show here the first clear evidence that this has taken place, with examples from two loci (Pgm-B, M-Aat-A) that have different biogeographic allele distributions. (i) A polymorphism at Pgm-B in Ambystoma laterale, otherwise restricted to northwestern Ontario, was found in both diploid A. laterale and co-occurring LLJ triploids in southern Ontario, where it is confined to the tip of the Bruce Peninsula. Diploids and triploids not possessing the allele also occur here and throughout the range of the A. laterale–jeffersonianum complex in eastern North America. (ii) An east coast A. laterale polymorphism at the M-Aat-A locus is also represented in both the homozygous and heterozygous condition within syntopic diploids and triploids in single populations. These data demonstrate multiple origins of triploidy, suggest continual gene exchange between diploids and triploids, and are analogous to data presented for other hybrid complexes of Ambystoma. The origins and distribution of the alleles in question are briefly considered, as they are of some biogeographic interest.