Colour Pattern Variation and the Ecological Significance of Melanism in an Insular Mediterranean Population of Testudo hermanni

Colour pattern polymorphisms are widespread in reptiles and may have important ecological and evolutionary implications. This study confirms the presence of colour pattern polymorphisms in Testudo hermanni populations from Mallorca (Balearic Islands, Spain), with a particular concentration of melanistic individuals in the municipality of Llucmajor. Using a combination of field surveys and citizen science data collected between 2016 and 2019, the degree of dark colouration in over 1200 individuals was quantified. Melanism was categorised into four groups based on the percentage of dark colouration, and its distribution was analysed according to sex and season. The results show that while intermediate patterns were predominant across the island, individuals exhibiting high degrees of melanism (> 90% dark colouration) were spatially restricted. Statistical analyses revealed significant differences in the distribution of melanism categories across seasons, with a higher proportion of melanistic individuals captured during winter. This pattern supports the thermal melanism hypothesis, suggesting a potential thermoregulatory advantage for darker individuals under colder conditions. Additionally, a high incidence of shell malformations and injuries was observed in the studied melanistic population. These findings provide new insights into the distribution, ecological significance and conservation concerns associated with colour polymorphisms in T. hermanni populations. Further research is needed to clarify the genetic and environmental drivers of melanism and to assess its implications for the long‐term viability of insular reptile populations.