Camouflage mismatch in seasonal coat color due to decreased snow duration

Abstract

Most examples of seasonal mismatches in phenology span multiple trophic levels, with timing of animal reproduction, hibernation, or migration becoming detached from peak food supply. The consequences of such mismatches are difficult to link to specific future climate change scenarios because the responses across trophic levels have complex underlying climate drivers often confounded by other stressors. In contrast, seasonal coat color polyphenism creating camouflage against snow is a direct and potentially severe type of seasonal mismatch if crypsis becomes compromised by the animal being white when snow is absent. It is unknown whether plasticity in the initiation or rate of coat color change will be able to reduce mismatch between the seasonal coat color and an increasingly snow-free background. We find that natural populations of snowshoe hares exposed to 3 y of widely varying snowpack have plasticity in the rate of the spring white-to-brown molt, but not in either the initiation dates of color change or the rate of the fall brown-to-white molt. Using an ensemble of locally downscaled climate projections, we also show that annual average duration of snowpack is forecast to decrease by 29–35 d by midcentury and 40–69 d by the end of the century. Without evolution in coat color phenology, the reduced snow duration will increase the number of days that white hares will be mismatched on a snowless background by four- to eightfold by the end of the century. This novel and visually compelling climate change-induced stressor likely applies to >9 widely distributed mammals with seasonal coat color.

Evolutionary tipping points in the capacity to adapt to environmental change

“…For example, reversibly plastic adaptations like torpor (23) and hibernation (24) have been shown to occur in response to frequent (i.e., daily or yearly) and predictable changes in environmental conditions. In some examples of reversible phenotypic changes, such as the seasonal change in coat coloration in temperate mammals, there is even evidence that the increasing unpredictability of relevant environmental parameters is currently exerting strong selection on natural populations (e.g., snow cover for snowshoe hares) (25). Another potential example of reversible plasticity is cognitive ability, particularly given its role in enabling behavioral flexibility (26).…”

Color change and camouflage in juvenile shore crabs Carcinus maenas

“…In contrast, the ability to change color more slowly, over periods of hours, days, and even weeks and months is likely to be more common in nature, yet has received relatively little study. Comparatively slow color change for camouflage has been shown to occur in, for example, prawns (Keeble and Gamble, 1900), caterpillars (Grayson and Edmunds, 1989), crabs (Stevens et al, 2013), and fish (Clarke and Schluter, 2011), in addition to seasonal changes in mammals and birds in line with the presence and absence of snow cover in winter and summer, respectively (Mills et al, 2013).…”

Predicting the Fitness Effects of Climate Change on Snowshoe Hares

“…Recent evidence suggests that hares have limited plasticity in their rate of colour change in the spring, but not in the fall rate, and not in the date the change initiates in either season (Mills et al, 2013;Zimova et al, 2014). The populations examined in these studies are expected to become severely mismatched over time (Mills et al, 2013).…”

“…The populations examined in these studies are expected to become severely mismatched over time (Mills et al, 2013). For at least one population, Zimova et al (2014) observed large differences in completion dates for the colour change that matched differences in snow cover.…”

“…Hares undergo seasonal moults to a white or brown coat colour to match the presence or absence of snow. Later onset of snow in the fall and earlier spring melts would cause hares to be increasingly mismatched to their background under climate change, reducing their concealment from predators (see Fig 2; Mills et al, 2013). This mismatch limits cryptic abilities, increases detection by predators, and consequently affects survival (Zimova et al, 2016).…”