Melanin-based color variation in response to changing climates in snakes

Area of Science:

• Ecology and Evolutionary Biology
• Herpetology
• Climate Change Adaptation

Background:

• Melanism, or increased melanin, influences organismal color evolution and climate adaptation.
• Intraspecific variation in melanism is understudied, hindering understanding of climate adaptation.
• Dark coloration presents conflicting adaptive potentials (heat absorption vs. UV protection).

Purpose of the Study:

• To investigate the effect of climate on melanism variation in barred grass snakes (Natrix helvetica) and green whip snakes (Hierophis viridiflavus).
• To test hypotheses regarding the adaptive significance of different melanistic morphs in relation to temperature, UV radiation, and humidity.

Main Methods:

• Examined 150 Natrix helvetica and 383 Hierophis viridiflavus across Italy from 2002-2021.
• Utilized melanistic morphs (charcoal, picturata, abundistic) and correlated their presence with climate variables.
• Employed statistical analyses to identify associations between morphs and environmental factors.

Main Results:

• The charcoal morph of Natrix helvetica was associated with high UV environments, suggesting a role in UV protection.
• The charcoal morph of Hierophis viridiflavus did not optimize heat absorption in cold environments as predicted.
• Both picturata and abundistic morphs in N. helvetica and H. viridiflavus, respectively, did not align with humidity-based concealment expectations.
• Hierophis viridiflavus showed an association with high precipitation, potentially indicating antimicrobial benefits.

Conclusions:

• Melanistic color morphs in snakes exhibit climate-specific associations, suggesting adaptive roles.
• Natrix helvetica's charcoal morph appears to provide UV protection, while Hierophis viridiflavus's association with precipitation may relate to antimicrobial defense.
• Further research is needed to elucidate the precise mechanisms driving these climate-melanism correlations and adaptive responses.