The warmer, the yellower? Colour patterns of fire salamanders across different scales in the face of rising temperatures

Carolin Dittrich , Kristin Rose Szydlik, Anni-Kaisa Karoliina Jokinen, Doris Preininger, Bibiana Rojas

The unprecedented increase in global temperatures might lead to phenotypical changes in many species to account for increased thermoregulatory processes. This could be due to increased selection pressures on traits such as colouration or body size. Using specimens from the Natural History Museum in Vienna for a long-term series and recent data from an ongoing fire salamander monitoring programme as a short-term series, we test the hypotheses that increasing temperatures over time are associated with reduced amount of black colouration of fire salamanders (yellower individuals), smaller body size and relatively longer limbs. We found no relationship between environmental temperature and proportion of yellow and black colouration at either time scale. In the long-term dataset, differences in colouration were only explained by location, whereas in the short-term dataset it was best predicted by body size, body condition and sex, with females being larger, heavier and less yellow than males. Likewise, we did not detect any decrease in body size or differences in limb length over time. The size and sex related patterns we observed are consistent with ontogenetic colour change and with potentially greater predation pressure on the smaller, more mobile males. Therefore, we conclude that yellow colouration is more pronounced during early life stages, strengthening the aposematic signal when individuals are most vulnerable towards predation. Yellow colouration is further influenced by resource availability during early life, individual age, predator community composition and natural selection, factors which cannot be resolved with our museum based and recent dataset.