Effects of an herbicide on physiology, morphology, and fitness of the dung beetle Euoniticellus intermedius (Coleoptera: Scarabaeidae).

Some agrochemical compounds threaten nontarget organisms and their functions in the ecosystem. The authors experimentally evaluated the effects of one of the most common herbicide mixtures used worldwide, containing 2,4-dichlorophenoxyacetic acid and picloram, on dung beetles, which play fundamental roles in the function of natural and managed ecosystems. The present study employed techniques of physiology and geometric morphometrics, besides including fitness measurements, to assess the effects of the herbicide in the introduced beetle Euoniticellus intermedius. Because herbicide components promote oxidative stress and affect survival in certain insects, the authors predicted negative effects on the beetles. Unexpectedly, no effect of herbicide concentration was found on clutch size, sex ratio, and fluctuating asymmetry, and it even increased physiological condition and body size in exposed beetles. Because the studied species presents 2 male morphs, the authors, for the first time, evaluated the effect of a pollutant on the ratio of these morphs. Contrary to the prediction, the herbicide mixture increased the proportion of major males. Thus, the herbicide does not threaten populations of the studied beetles. The present study discusses how both negative and positive effects of pollutants on wild animals modify natural and sexual selection processes occurring in nature, which ultimately impact population dynamics. The authors recommend the use of physiological and geometric morphometrics techniques to assess the impact of pollutants on nontarget animals. Environ Toxicol Chem 2017;36:96-102. © 2016 SETAC.