Oil Things Bright and Beautiful? How Hydrocarbon Pollution Impacts Guppy Ornamentation

Brightly coloured male ornamentation often plays an important role in sexual selection, but the extent to which the expression of these ornaments is affected by different forms of pollution is still not well understood. Guppies (Poecilia reticulata) can often be found in highly polluted and degraded habitats, including oil-polluted habitats in southwestern Trinidad. Male guppy ornamentation is polymorphic, and while colour patterns (including area cover of different ornaments) have a heritable basis, the intensity of different colour patches can be linked to phenotypic plasticity, partially modulated via guppy diet. Here, we aimed to understand how the area and colour intensity of this ornamentation varied between the Pitch Lake (a natural source of crude-oil pollution), two anthropogenically polluted and two non-polluted sites. We found that colour intensity and area of ornamentation both differed between habitat types, with males from anthropogenically polluted habitats having a greater area of iridescence ornamentation but darker orange colour intensity. However, for both area and intensity, there was considerable variation between polluted populations. Additionally, ornamentation in the Pitch Lake differed from both anthropogenically polluted and non-polluted habitats. This study demonstrates the non-uniform response to crude oil pollution even on a species level, and highlights the importance of considering both evolutionary and ecological variation when predicting and mitigating impacts of pollution.