Viability selection on coat spot patterns correlates with temperature anomalies in Masai giraffes

Alexia Mouchet , Derek Lee, Monica L Bond, Douglas R. Cavener, James Madeli, Arpat Ozgul

Remarkable variation in animal colour patterns is often shaped by heterogeneous selection, reflecting adaptation to variable environmental conditions. However, the adaptive functions of patterns and drivers of selection remain poorly understood. Shape and size of colour patterns may help with thermoregulation and thus be altered by temperature anomalies, which are predicted to be more frequent with current climate change. Using resighting data from 810 individuals over eight years, we studied the effects of spot patterns on survival in a population of wild giraffes and whether this relationship was affected by temperature anomalies. Shape and size of spots interactively affected survival: calves with small lobate and adult males with small lobate or large polygonal spots survived better. Viability selection on spot size was altered by temperature anomalies: calves and adult males having larger spots survived better at anomalously low temperature whereas those with smaller spots survived better at anomalously high temperature. Spot patterns only weakly affected the survival of adult females, which all suffered from anomalously high temperature. In calves, spot size may help with thermoregulation while spot shape may conceal them from predators. In adults, sex-specific selection pressures suggest other functions to thermoregulation. Spot patterns at different life-stages can affect population dynamics and their evolution may be altered by climate change. This study highlights the importance of considering spot pattern variation in conservation plans of the endangered Masai giraffe, enabling populations to adapt to climate change and extreme weather events.