Eastern Black Kingsnake Lampropeltis nigra dorsal scale colouration primarily adapted for thermoregulation

Abstract

The Eastern Black Kingsnake Lampropeltis nigra exhibits variation in colouration and pattern throughout its range. Drivers behind this colour variation remain largely unknown. To elucidate patterns in the percentage of light pigmentation in L. nigra dorsal scales (% light) we compared two primary hypotheses. Our first hypothesis posited that L. nigra colouration has been adapted for thermoregulation (thermoregulation). Alternatively, we hypothesised that L. nigra colouration has been adapted to avoid detection by predators and prey (crypsis). To test our hypotheses, we modeled L. nigra % light from 46 counties within Mississippi as a function of average temperature, average maximum temperature (thermoregulation) and soil value (darkness of soil colour; crypsis). We included percentage forest cover as a modifying variable in the thermoregulation hypothesis and an interacting variable in the crypsis hypothesis. The best competing model included average temperature and percent forest cover as explanatory variables (LOOIC = -291.3, weight = 0.84, Bayesian R2 = 0.37 [fixed] and 0.55 [total]). There was a positive relationship between % light and average temperature (β = 0.23, 95% CIs = 0.13, 0.34) and average maximum temperature (β = 0.11, 95% CIs = -0.00, 0.21), and a negative relationship with percent forest cover (β = -0.14, 95% CIs = -0.23, -0.04). These results support the thermoregulation hypothesis. The climate in Mississippi, as in most of the world, is expected to experience shifts over the next century. If ambient temperatures experienced through these changes are outside of L. nigra’s thermal optima, as based on colour patterns and relationships observed in our study, then behavioural adaptations may result in some individuals experiencing thermal advantages that influence this species’ distribution. The patterns observed in our study, and expected changes in L. nigra behaviour and distribution, are likely to occur among other ectothermic species with relatively static colouration. Keywords: Colour adaptation, homeostasis, Mississippi