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The Ambystoma laterale-jeffersonianum Complex in Central Ontario: Ploidy Structure, Sex Ratio, and Breeding Dynamics in a Bisexual-Unisexual Community

Leslie A. Lowcock, Hugh Griffith and Robert W. Murphy
Copeia
Vol. 1991, No. 1 (Feb. 7, 1991), pp. 87-105
DOI: 10.2307/1446251
Stable URL: http://www.jstor.org/stable/1446251
Page Count: 19
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The Ambystoma laterale-jeffersonianum Complex in Central Ontario: Ploidy Structure, Sex Ratio, and Breeding Dynamics in a Bisexual-Unisexual Community
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Abstract

Ploidy ratio was investigated in six Ontario populations of the Ambystoma laterale-jeffersonianum complex by collecting blood from individual salamanders during spring migrations, and analyzing the nuclear DNA content of erythrocytes by flow cytometry. All populations contained diploid male and female A. laterale as well as a potential mixture of diploid, triploid, and tetraploid female hybrids, which occurred at variable frequencies. Triploid males, pentaploid females and possible polyploid A. laterale (3n and 4n) were found in one extensively sampled population. Initial separation of A. laterale from hybrids based on morphological criteria was tested for accuracy by comparison with the cytometric results and found to be exceptionally high (99.6%). Sex ratios in all populations were biased overwhelmingly towards females, primarily because female hybrids accounted for up to 84% of a breeding aggregate; however, diploid female A. laterale outnumbered males in several populations and in two instances, near the northern limit of hybrid biotypes, these account for much of the biased sex ratio. Timing of breeding, always triggered by precipitation (rain or snow), varied between sites and was correlated with altitude/latitude. Initial immigrations at all sites contained biotypes indicative of local primary composition with respect to both ploidy and hybridity. The breeding dynamics of one population were investigated by daily sampling throughout the breeding period. Migration occurred in distinct waves. In A. laterale, frequency of immigrating males declined over the breeding period while frequency of females increased, a pattern conforming to the typical Ambystoma breeding dynamic. Within hybrids, the percentage of tetraploids increased over the breeding period. Within waves, there was a general increase in hybrids over time.

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