Habitat effects on intra-species variation in functional morphology: Evidence from freshwater fish

Biotic-environment interactions have long been considered an important factor in functional phenotype differentiation in organisms. The differentiation processes determining functional phenotypes can reveal important mechanisms yielding differences in specific functions of animal traits in the ecosystem. In the present study, we examined functional morphological variations in relation to increasing geographic altitude. Six fish species were examined for how environment factors affect intra-specific functional morphology in the subtropical Pearl River in southern China. Functional morphology traits revealed variable effects due to geographic elevation, although spatial autocorrelation existed among the species tested. The results showed that high-elevation individuals had a more narrow-bodied morphology, with more flexible maneuvrability when swimming, and more evenly distributed musculature than low-elevation individuals. Low-elevation individuals preyed upon larger food sources than high-elevation individuals in some species. Fish functional morphology was strongly affected by regional environmental factors (such as elevation and water temperature) and physical characteristics of local rivers (such as flow velocity, river fractals, and coefficients of fluvial facies). In addition, the effects of the regional factors were stronger than those of the local factors in the Pearl River. Furthermore, it was found that morphological traits associated with locomotion were primarily effected by the river's physical characteristics. While morphological traits associated with food acquisition were primarily affected by water chemical factors (such as DO, water clarity, NH ₄-N concentration, and TDS). These results demonstrated that habitat has an influence on the biological morphology of fish species, which further affects the functioning of the organism within the ecosystem.