Biogeographic history of the world's marmots and the genetic basis of melanism in an Alaskan population of hoary marmots

Abstract

This dissertation addresses questions related to the phylogenetics, molting phenology, and genetic basis of melanism in marmots. Marmots (genus Marmota) are large, diurnal ground squirrels that hibernate for 7-8 months each year and have a broad Holarctic distribution. In Chapter 1, I use ultraconserved elements from all 15 extant species to better resolve the phylogeny of Marmota and shed light on the biogeographic history of marmots. The results indicate marmots originated in North America ~16.3 Ma and crossed the Bering Land Bridge into Eurasia ~3-4 Ma. In addition, the Woodchuck (M. monax) and the Alaska Marmot (M. broweri) are more closely related to Eurasian species than to other North American species, and the Hoary Marmot (M. caligata) may be paraphyletic with respect to the Vancouver Island Marmot (M. vancouverensis) and the Olympic Marmot (M. olympus). Chapter 2 is a review of molt phenology in mammals, with a primary emphasis on marmots. Molting is a metabolically expensive process that is generally timed around other costly events such as lactation, parturition, and dispersal. In this chapter I summarize what is known of molting phenology in marmots, which may be particularly informative as to how precise control over molt timing evolved because of the short active period over which molting and all other costly life history events must occur. In addition, I present evidence that the Olympic Marmot only molts once annually, in contrast to other reports that it is the only biannually molting marmot. Chapter 3 is an investigation of melanism in the Hoary Marmot, which is observed in this species only in SE Alaska. I show that melanism is at least partially caused by a gain-of-function mutation in melanocortin-1-receptor (MC1R), a gene that affects melanin deposition in the skin and hair. The mutation affects hair agouti banding such that the middle light band is reduced in length relative to the brown base and black tip, resulting in the melanistic phenotype.