Rapid and repeated divergence of animal chemical signals in an island introduction experiment

Studies of animal communication have documented myriad rapid, context-dependent changes in visual and acoustic signal design. In contrast, relatively little is known about the capacity of vertebrate chemical signals to rapidly respond, either plastically or deterministically, to changes in context.
Four years following an experimental introduction of lizards to replicate experimental islets, we aimed to determine if chemical signal design of the experimental populations differed from that of the source population.
In 2014, we translocated Podarcis erhardii lizards from a large, predator-rich island to each of five replicate predator-free islets. Mean population densities increased five-fold over the following four years and bite scars suggest significantly more intraspecific fighting among these experimental populations. In 2018 we analyzed the chemical signal design of males in each of the experimental populations and compared it to the chemical signals of the source population.
We found that males consistently presented a significantly more complex chemical signal compared to the source population. Moreover, their chemical signals were marked by high proportions of octadecanoic acid, oleic acid, and α-tocopherol, three compounds that are known to be associated with lizard territoriality and mate choice.
Our island introduction experiment thus suggests that the chemical signal design of animals can shift rapidly and predictably in novel ecological contexts. 

Methods
Chemical composition of the femoral gland secretions of male Podarcis erhardii lizards from the source population (Alyko; population 1) and the five experiment islands: Agios Artemios (population 2), Galiatsos (population 3), Kambana (population 4), Mavronissi (population 5), and Petalida (population 6). The relative amount of each component was determined as the percent of the total ion current (TIC) and reported for each individual. The specific names of the lipophilic compounds can be found in table S1 (supplementary materials).