Heterospecific juvenile sociability between invasive guppies and native goodeids

Invasive species, often driven by environmental changes produced by anthropogenic activities, pose significant threats to biodiversity, ecosystem functioning, and human well-being. Among invasive species, guppies ( Poecilia reticulata ) have demonstrated remarkable adaptability and sociability, contributing to their successful establishment in new habitats. Heterospecific associations are particularly important during the early stages of invasion, as invaders derive benefits from group living, including reduced predation risk, increased conspecific availability. This study investigates the association tendencies of juvenile guppies and the endangered twoline skiffia ( Skiffia bilineata ), a native Mexican species, to understand heterospecific shoaling behaviour’s role in overcoming the Allee effects during the early stages of invasion. Using a controlled experimental setup, we evaluated the time juvenile guppies and juvenile twoline skiffias spent associating with conspecific and heterospecific shoals. Our findings revealed that juvenile twoline skiffias exhibit a longer latency association time with conspecific shoals compared to heterospecific shoals, while guppies show no discrimination between both, demonstrating a sociability trait that likely enhances their invasive potential. These findings highlight that the sociability of juvenile guppies could provide them with some protection, helping them overcome Allee effects. Our study proves juveniles form heterospecific shoals, which can play a crucial role in invasive success of guppies, particularly during the early stages of the invasion process when population numbers are low. These insights can inform conservation strategies aimed at mitigating the impacts of invasive species on native biodiversity, particularly in vulnerable aquatic ecosystems.