Leech Infestation Patterns between Native and Invasive Freshwater Turtles: Implications for Invasion Success.

Abstract

The increasing global introduction of alien species in recent decades underscores the need to understand the factors driving their establishment and spread in order to mitigate their ecological impacts. As alien species often thrive due to the absence of natural enemies (e.g., parasites), we investigated leech parasitism in freshwater turtles, focusing on an assemblage with over 10 years of co-occurrence between native species (Phrynops geoffroanus, Hydromedusa tectifera) and invasive sliders (Trachemys dorbigni, Trachemys scripta elegans). We used traps to capture 62 turtles to assess host characteristics (species, sex, body size, and body region) that influence leech prevalence and infestation intensity in southern Brazil. Our findings revealed that native turtles exhibited an 18-fold higher prevalence of hematophagous leech than invasive species, with T. dorbigni being the only species in which no leech infestation was observed. Infestation intensity also varied among species, with native turtles harboring more leeches. Probability of leech infestation increased with body size, and the hind limbs were significantly more infested. The diminished presence of ectoparasites on invasive Trachemys throughout this coexistence period supports the enemy release hypothesis, suggesting that the lack of natural enemies may be a potential driver facilitating their invasion success. These results provide baseline data for future studies exploring key factors in the success of the slider invasions.