Reproduction: Unisexual mole salamanders are not true hybrids but instead members of a strange hybrid complex where a distinct lineage of all female salamanders are able to reproduce by stealing the DNA of pure form salamanders via spermatophores. This DNA is often discarded and only used to stimulate the organs needed to produce young using different combinations of the female’s own DNA. Other times the DNA is used to give the offspring an extra set of chromosomes. Individuals can have up to five different sets of chromosomes from a number of different species of mole salamander. Pelee Island is unusual in that the unisexual mole salamanders here only have DNA from blue-spotted salamanders (𝘈. 𝘭𝘢𝘵𝘦𝘳𝘢𝘭𝘦) and small-mouthed salamanders (𝘈. 𝘵𝘦𝘹𝘢𝘯𝘶𝘮). Elsewhere they can also have DNA from Jefferson salamanders (𝘈. 𝘫𝘦𝘧𝘧𝘦𝘳𝘴𝘰𝘯𝘪𝘢𝘯𝘶𝘮) and eastern tiger salamanders (𝘈. 𝘵𝘪𝘨𝘳𝘪𝘯𝘶𝘮).
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Genetics: Unisexual mole salamanders are spawned with different frequencies of chromosomes from different species. Often times, if an individual has more chromosomes originating from one species, they tend to display more features from that species. In this case, this individual has a mix of features from the blue-spotted salamander and the small-mouthed salamander suggesting a relatively even array of chromosomes. This individual also has a fifth leg and a rather “Jabba-like” appearance which may be due to a large amount of chromosomes. While having three sets of chromosomes is more common for unisexual mole salamanders, individuals can have up five sets. Those with four to five sets of chromosomes tend to display more physical mutations such as the individual depicted. One can not conclusively determine the exact ploidy of an individual without DNA testing however.
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Natural History: This hybrid complex originated between two and five million years ago, making it the oldest hybrid complex known. According to Mitochondrial DNA (mtDNA), the complex is derived from a hybridization between a female Streamside Salamander and another species within the genus Ambystoma. This hybrid was the first of the Unisexual Mole Salamanders and as it reproduced, it creating more Unisexual Mole Salamanders and expanded to new areas. By interbreeding with native species they encountered, the Unisexual Mole Salamanders were able to inherit the features that made those species successful in that environment. During this time, Unisexual Mole Salamanders would make up only a small percentage of the population and with enough migration from other populations, there was a steady increase of pure form species, keeping the Unisexual Mole Salamanders balanced. With the construction of buildings, cities, roads and towns, many of these populations became isolated, restricting gene flow. Without a steady flow of pure forms, they became outbred by the Unisexual Mole Salamanders. Now in some areas such as mainland southern Ontario, the Unisexual Mole Salamanders make up 90% of the population with only 10% being pure forms.
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Sources:
Hossie, Thomas J. "Declines in Blue-Spotted Salamanders on Pelee Island, ON Merit Formal Risk Assessment and Protection." Canadian Herpetological Society Conference, 6 Dec. 2020 Hossie, Thomas J. "Establishing Baseline Ecological Data." Trent University, 3 Mar. 2017, Peterborough, Canada "Small-Mouthed Salamander." Ontario Nature, 2021, ontarionature.org/programs/community-science/reptile-amphibian-atlas/small-mouthed-salamander/. Accessed 2 Nov. 2021. Ward, Meghan. "Herpetology From Home #1." Trent Herpetology Society, 2 Dec. 2019, Peterborough, Canada |