Intraspecific Variation in Color and Carotenoids across Environmental Extremes in an African Cichlid

AbstractHuman activities frequently alter environmental conditions and affect the use of sexually selected traits like color in animals. However, the effects of environmental stressors are unlikely to be uniform across populations that experience different environments or between sexes. We aimed to understand the underlying genetic, environmental, and gene-by-environment contributions to color expression in males and females of a sexually dimorphic fish. <i>Pseudocrenilabrus multicolor</i> is a haplochromine cichlid found in environments that vary dramatically, particularly with respect to oxygen and turbidity levels. We reared fish from one swamp (hypoxic, clear) and one river (normoxic, turbid) population in a split-brood design (hypoxic/normoxic × clear/turbid) and then quantified color and carotenoid concentrations. As expected in this sexually dimorphic species, females were far less colorful than males. In males, hypoxia and turbidity were drivers of traits associated with color, suggesting that color was modified under energetically or visually unfavorable conditions. Males in the hypoxic treatment from both populations were not as bright as males reared under normoxic conditions, which corresponds to results observed in wild fish. Males reared in turbid conditions were also marginally less bright along the ventral surface than males reared in clear water. Rearing under turbid conditions reduced carotenoid concentrations in male skin, but carotenoids were not correlated with spectral characteristics of male color. We did not find effects of population on color traits, suggesting that differences in color between wild populations are due to plastic rather than fixed genetic effects. Overall, we provide evidence that hypoxia and turbidity affect signaling traits, although the consequences for mating success remain to be determined.