Male nuptial ornamentation of invasive guppies (Poecilia reticulata) responds to water pollution via phenotypic plasticity and microevolutionary change

Invasive alien species are increasingly replacing native species, with human habitat alterations often favoring invasive taxa. The Brazilian Rio Uberabinha, for instance, was found to harbor more invasive guppies (Poecilia reticulata) at polluted than non-polluted sites. Studies in other regions reported numeric frequencies of certain nuptial color ornaments of guppy males to either in- or decrease along pollution gradients, which has been interpreted to largely reflect population differences of (heritable) male ornamentation patterns. But could plasticity play an additional, or possibly even greater role in creating phenotypic variation of nuptial ornaments? Here, we examined male guppies along a gradient of diffuse water pollution of domestic and industrial origins in the Rio Uberabinha and quantified not only the number of ornaments (and percentage body cover), but also population differences in color intensity (total coloration, ΔE). The latter metric likely reflects plasticity during ornament development, e.g., through general challenges to physiological homeostasis or suppression of male ornamentation following xenestrogen exposure. We found numbers and % body cover of violet ornaments to increase as water pollution intensified. Black, orange, blue and violet ornaments responded to additional components of environmental variation that were not the focus of our present study (e.g., stream velocity, dissolved oxygen). Moreover, we found systematic variation of ΔE along the examined pollution gradient in the case of white/iridescent ornaments, with fish becoming more brightly colored at more polluted sites, possibly related to an alteration of uric acid and guanine biosynthesis and/or accumulation. White/iridescent and green ornaments also responded to additional components of environmental variation. Hence, it appears that both, plasticity and evolutionary changes, jointly create phenotypic diversification of different ornament types. Our study provides novel insights into the manifold ways by which man-made habitat alterations can alter evolutionary trajectories (here: components of sexual selection) of the populations exposed to them.