Evolution and Conservation in a Changing World: Empirical and Conceptual Lessons from Bats, Salamanders, and Beyond

Abstract

Environmental change, particularly exceptionally rapid shifts triggered by humans, can be leveraged to understand factors underlying species survival outcomes and associated evolutionary processes. Such environmental shifts can trigger micro-evolutionary forces. For instance, increased mutation rates due to carcinogenic chemicals, increased inbreeding and genetic drift due to isolation of previously connected populations, and altered adaptation due to shifts in selective pressures. In Chapters II and III, I explore the impacts of human-altered environments on one species of bat and salamander, respectively. In Chapter II, I ask whether little brown bats (Myotis lucifugus) suddenly faced with the disease white-nose syndrome (caused by an introduced fungal pathogen) are experiencing corresponding natural selection. I consider one population in Michigan, USA, which experienced losses of roughly 75% in the first few years following introduction of the disease. Survivors are apparently evolving in response to it, with evidence of some alleles undergoing natural selection (they are more common than would be expected among the surviving bats, as compared to bats that died from the disease). However, the survivors also apparently have reduced genetic diversity compared to the pre-disease population. In Chapter III, I consider whether coastal giant salamanders (Dicamptodon tenebrosus) have experienced negative genetic consequences due to habitat disturbance. Sampled throughout Oregon, USA included disturbed versus less-disturbed sites. Some populations exhibit genetic signatures of potential conservation concern, including genetic bottlenecks and moderate levels of inbreeding. Many sites had experienced logging or fires, and sites were often separated by inhospitable landscapes, such as agricultural land. However, genetic signatures of concern were not clearly connected to any of the anthropogenic disturbances considered. This is likely, at least in part, because of the species’ own mixed response to disturbance—populations have been documented to increase in abundance, at least temporarily, following logging events. Thus, our ability to detect genetic signatures is limited by both evolutionary timescales, but also by ecological ones. Species’ responses to anthropogenic change are likely to be at least partially conditioned on previous environmental changes they have experienced. These background changes, which are often cyclical, include regimes of glacial retreat and expansion as well as annual seasonal changes. Cold temperatures, in particular, can present a challenge to which species must adapt or succumb. The salamanders in Chapter III, for example, are relatively cold-susceptible, and bore the genetic legacy of the last glacial maximum—having been extirpated from much of their northern range by Pleistocene Glaciation, contemporary populations that had recolonized northern areas exhibit relatively reduced genetic diversity. The bats in Chapter II had winter hibernation cycles carefully calibrated to seasonal regimes, which became a problem when their hibernations were disrupted by the introduced pathogen. Given the potential importance of categorizing and quantifying species’ cold-survival strategies in a comparable manner, in Chapter IV, I present a conceptual framework for doing so. I propose a framework with three clearly delimited axes of cold-survival and four tenants underlying relationships between axes. Species can use either 1) seasonal migration (cold avoidance), 2) torpor (cold tolerance), or 3) cold resistance, and cold-survival strategies i) are comprehensively encompassed within the framework, ii) can be used in conjunction, iii) are used to variable degrees, and iv) should vary (collectively) inversely and proportionally to one another to meet minimum survival thresholds (when comparing populations that are sympatric in the summer range).