Lead pollution impacts the dynamics and resolution of contests between the native Mexican mojarra and invasive convict cichlid

Abstract

Both pollution and invasive species are threats for freshwater environments and their native ichthyofauna. The Mexican mojarra is the only cichlid fish species native to the Amacuzac River of central Mexico. Its habitat has been modified by the presence of invasive cichlid fishes, such as the convict cichlid, and by the presence of heavy metals such as lead. Since pollutants may affect invasive and native species differently, the combined effects of these two threats on native fish are not easily predictable and may be synergistic. We evaluated the effects of Pb exposure on interspecific contest dynamics and resolution between juvenile Mexican mojarras and convict cichlids. We performed ten interspecific contests between native and invasive cichlid at an environmentally relevant water concentration of Pb (38.2 µg L⁻¹) in three phases: Pb absence, Pb exposure, and Pb depuration, as well as ten interspecific control contests without Pb. The Mexican mojarra consistently won the contests, regardless of Pb exposure, showing no differences in contest resolution between the Pb group and control group. The presence of Pb increased the number of aggressions in convict cichlids but reduced them in the Mexican mojarra, and contest duration decreased in the Pb exposure relative to the control group. However, these differences were not maintained during the Pb depuration period. Thus, we found effects of Pb on the agonistic interactions between the native Mexican mojarra and the invasive convict cichlid. Other invasive cichlid fishes and pollutants deserve attention in the context of the conservation of the Amacuzac River and its native ichthyofauna.

Significance statement

Native cichlid Mexican mojarra have been negatively affected by the introduction of the invasive convict cichlid and by the presence of heavy metals such as lead (Pb). Here, we evaluated the effects of Pb exposure on contest dynamics and outcome between Mexican mojarras and convict cichlids. Pb did modify the contest dynamics, augmenting the aggression in the Mexican mojarra and reducing fight duration. Our results show that invasive species may be favored in contaminated environments and that native species are more sensitive to pollution, further increasing their vulnerability to biological invasions.