Diversity Among Mixed-ploidy Salamander Communities Reflects the Influence of Keystone Host Species

Understanding processes governing and sustaining biological diversity is a central goal of community ecology. Unisexual community complexes, where successful reproduction relies on sperm transfer from males of one or more bisexual host species, are relatively rare and poorly understood in terms of the drivers of community diversity and structure. Unisexual salamanders of the genus Ambystoma produce mostly clonal offspring but can also produce distinct biotypes (‘genomotypes’), each with their own ecological niche. Within unisexual communities, individual hosts are often relatively rare, however, the number, identity, and relative abundances of distinct host species may govern community structure. We studied Ambystoma communities on Pelee Island, Ontario, Canada, to determine if the bisexual hosts (A. texanum, A. laterale) determine community structure of unisexual Ambystoma. From 2015-2018, we genomotyped 2027 Ambystoma tissue samples (1184 adults, 843 larvae) from 11 different sites. The relative abundance of bisexual hosts ranged from 0-18% across sites. Composition and diversity of ecological communities was highly variable and could be largely ascribed to variation in the presence and/or relative abundance of keystone host species. Additionally, the site where both hosts were present had the greatest unisexual diversity, with genomotypes reflecting contributions from both hosts, suggesting that multi-host communities generate enhanced diversity. Our results indicate that keystone hosts are pivotal in determining structure and composition of unisexual community complexes. Unisexual complexes clearly offer unique opportunities to examine the factors impacting community structure and provide a useful model for studying the role of keystone species in ecological communities.