In the eastern Adriatic, Podarcis siculus, an invasive species, competitively excludes the native Podarcis melisellensis. Monoamine neurotransmitters-serotonin (5HT), dopamine (DA), and noradrenaline (NA)-are implicated in social behavior, and could lie at the basis of the direct behavioral interference of P. siculus with P. melisellensis. To understand the relationship between social behavior and monoamines, as well as the differences in behavior between P. siculus and P. melisellensis, we developed a high-performance liquid chromatography (UV/VIS detection) method with which we were able to reliably measure concentrations of 5HT, DA, and NA in 32 brains of the two lizard species. We observed no statistically significant influence of species, sex, or their interaction on brain NA and 5HT concentrations. Statistically significant influence of species on dopamine levels were recorded, with P. siculus having twice as much dopamine in their brains. Taking into account that a significant aggressive relationship, with P. siculus dominating over P. melisellensis, has been previously observed, and that dopamine directly influences this behavior, the observed differences in dopamine levels could represent a trait in these species and may contribute to the competitive exclusion of P. melisellensis by P. siculus in the eastern Adriatic.
Keywords: Aggressive behavior; Competitive exclusion; Eastern Adriatic; HPLC; Monoamines.