Date of Award

Spring 5-13-2017

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Advisor

Michael T. Kinnison

Second Committee Member

Cynthia S. Loftin

Third Committee Member

Rebecca L. Holberton

Abstract

Island populations of terrestrial species have an increased potential, compared to mainland populations, to adapt and diverge, as these populations often are isolated with respect to gene flow from other populations and may be subjected to novel pressures. Indeed, extended isolation of individuals can elicit dramatic changes within populations and is recognized as a common driver of speciation. It is for these reasons that island populations are often a priority for conservation. Plethodontid salamanders are among the most terrestrial of Maine’s amphibians and are not tolerant of prolonged exposure to seawater, and yet, they are found on a number of Maine’s coastal islands. Here I present findings of the first study of the population genetic structure of Maine’s island red-backed salamanders to elucidate their probable origins. I collected samples from 12 coastal island and 10 mainland sites. Using nine microsatellite loci, I found that 199 of 210 pairwise comparisons showed significant multilocus differentiation. Island populations had fewer alleles and lower heterozygosity than most mainland populations. Islands farthest from shore displayed particularly strong divergence from all other sites, a finding consistent with ancient colonization. Phylogenetic and Bayesian structure analyses supported weak regional affiliation, which may be the result of extended isolation and divergence of distant island populations. Salamanders from island sites displayed no overall pattern of isolation by distance, whereas, those from mainland sites showed a weakly positive trend, implying a greater dispersal limitation among island populations.

Isotopic analyses revealed that Maine’s coastal islands vary from one another and from mainland systems in productivity baselines and trophic structure, indicating potential differences in sources of primary productivity and food web structure. Alternative ecological dynamics such as these have the potential to instigate adaptive divergence of island salamanders from their mainland counterparts. Consistent with this idea, red-backed salamanders on Maine’s coastal islands appear to feed at a higher mean trophic level than mainland salamanders, with smaller, seabird nesting islands featuring the highest estimated trophic position. Salamander populations varied widely in body size and morphological trait allometry suggesting potentially widespread trait divergence that may be linked to local adaptations. Within this general population variation, island populations featured larger head proportions (snout-gular length) for their body size, a pattern that may be adaptive given the higher mean trophic position of these populations. These findings suggest some island populations of P. cinereus likely represent isolated and potentially unique components of post-glacially derived variation within this widespread species and support the operation of mechanisms generating at least limited phenotype-environment associations in Maine’s red-back salamanders. Indeed, Maine’s island red-backed salamanders encourage a closer look at other widespread species on these coastal islands for the possibility that they similarly represent cryptic components of Maine’s biodiversity.

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