Rapid phenotypic change in a polymorphic salamander over 43 years

Abstract

Color polymorphic animals offer a unique system for studying intraspecific phenotypic responses to climate change. Discrete color morphs are easy to identify, and correlated trait responses of morphs can indicate how climate warming may facilitate long-term maintenance of polymorphisms. We use a historical dataset spanning 43 years to examine temporal shifts in color morph frequency and body size in response to climate in the Eastern Red-backed Salamander, Plethodon cinereus, which contains a widespread striped/unstriped color polymorphism. We created a pipeline to extract high-throughput trait data from fluid-preserved museum specimens where we batch-photographed salamanders, de-aggregated individual specimens from photographs, and solicited help of community scientists to score color morphs. We used a linear modeling framework that includes information about spatial population structure to demonstrate that color morph frequency and body size vary in response to climate, elevation, and over time, with an overall trend of higher frequency and decreased body size of the striped morph, but increased size of the unstriped morph. These surprising results suggest that morphs may be responding to multiple climate and geographic drivers through co-adapted morphological changes. This work highlights new practices of extracting trait data from museum specimens to demonstrate species phenotypes response to climate change.

Computer vision for assessing species color pattern variation from web-based community science images

“…Our finding of a positive relationship between elevation and striped morph frequency is consistent with previous studies ( Gibbs and Karraker, 2006 ; Moore and Ouellet, 2015 ; Hantak et al., 2021 ). Following the expectation that higher elevations are typically colder than lower elevations, we predicted the observed positive correlation.…”

“…However, here and in other studies, striped morphs are not always associated with cooler temperatures. A recent study by Hantak et al. (2021) found the proportion of striped morphs increases with increasing elevation and mean annual temperature and, based on these results suggested that these predictors may be decoupled in relation to color morph frequency in P. cinereus .…”

“… Fisher-Reid et al. (2013) demonstrated that striped morphs were found in warmer, wetter habitats on Long Island, New York, while Hantak et al. (2021) found striped morphs were more associated with warmer, drier habitats in localities across Maryland, New York, and Virginia.…”

Computer vision for assessing species color pattern variation from web-based community science images

“…However, here and in other studies, striped morphs are not always associated with cooler temperatures. A recent study by Hantak et al (2021) found the proportion of striped morphs increases with increasing elevation and mean annual temperature and, based on these results suggested that these predictors may be decoupled in relation to color morph frequency in P. cinereus . While the reason for greater proportion of striped morphs in higher elevations remains unclear, it may be possible that gene flow is reduced along altitudinal gradients in this species.…”

“…In addition, some studies have found no climate-related morph trends or inconsistent patterns over time (Petruzzi et al, 2006;Muñoz et al, 2016;Evans et al, 2018). Fisher-Reid et al (2013 demonstrated that striped morphs were found in warmer, wetter habitats on Long Island, New York, while Hantak et al (2021) found striped morphs were more associated with warmer, drier habitats in localities across Maryland, New York, and Virginia. Range-wide, dense data can help examine overall trends and localize those at finer scale in a unifying framework.…”