Intra‐population variation in male nuptial coloration and diet across anthropogenically altered visual microhabitats in an African cichlid

Abstract

Human activities are altering natural ecosystems, leading to widespread environmental change that can vary across spatiotemporal scales, thus creating dynamic, novel conditions at both large and small scales. In highly disturbed aquatic systems, elevated turbidity is one common stressor that alters the sensory environment of fishes and can disrupt communication, including mate choice, driving population-level shifts in visual communication traits such as nuptial coloration. At a smaller, within-population scale, we can expect similar adaptive divergence to a heterogeneous visual landscape. Using the cichlid fish, Pseudocrenilabrus multicolor, we investigated within-population variation in diet and nuptial coloration by sampling fish from microhabitats within a relatively small site (~0.14 km2). These visual microhabitats are affected by different types of human disturbance at a very small scale leading to significant differences in water clarity (i.e. turbidity). We used three, non-mutually exclusive working hypotheses to test if (1) males in low turbidity invest more in carotenoid-based coloration (economy of pigments hypothesis), (2) fish from low-turbidity sites eat more carotenoid-rich foods (diet hypothesis), and (3) fish are habitat matching. Stomach content analyses revealed relatively high overlap in diet across microhabitats; however, fish from stations with the lowest turbidity consumed relatively more plant material (high in carotenoid content) than fish captured at high-turbidity stations. Males from clearer waters displayed significantly more carotenoid-based, red and yellow coloration than fish found in microhabitats with higher turbidity, similar to between-population color variation in this species. Furthermore, larger fish displayed more carotenoid coloration overall, but there was no difference in mean male size among microhabitats suggesting that fish were not sorting into microhabitats. Our results suggest that within-population variation in nuptial coloration could be associated with microhabitat heterogeneity in the visual landscape driven by turbidity, a diet with more carotenoid-rich prey items, or a combination of both.