Biological Invasions Lead to Increased Aggressiveness in Endemic Lizards

Male of A. oculatus (background), displaying to the conspecific robot (foreground). Credit: Claire M.S. Dufour

Invasive species can have large negative effects on the environment and the economy, and this is a major driver of research interest. We want to understand what makes invasive species succeed or fail, so that we can tip the balance in favor of native counterparts. Increasingly, biological invasions are also recognized for their research value. These “accidental experiments” can help us answer questions about community assembly, species interactions and evolution (Losos et al. 1993; Stuart et al. 2014; Stroud 2019).

Much of the research on introduced species has focused on obtaining information that can help us predict the next invasion event. This includes efforts to understand pathways of invasion (which can be done using population genetic data) or to identify the traits that make invasive species so successful (which can be done by comparing invasive and non-invasive taxa). Less research has focused on what happens shortly after an invasive species gains a foothold. In particular, we know little about early behavioral interactions between invasive and native species. Might these exchanges determine invasion outcomes and patterns of spread?

Enter the anoles of Dominica

In a recent paper, Dufour and collaborators address this gap using native and invasive anoles in Dominica. The authors built lizard robots that mimic the morphology and display behavior of the invasive species (A. cristatellus) and the endemic species (A. oculatus). With these robots, they tested the responses of A. oculatus males when presented with conspecific and heterospecific displays. The authors used sites where both species are found, and sites where only the endemic is found. Therefore, they could contrast the responses of A. oculatus with and without prior experience with the invader.

Interspecific fight between A. oculatus (left) and A. cristatellus (right). Credit: Claire M.S. Dufour

Robots elicited the expected response. In addition, A. oculatus could discriminate a conspecific robot from a heterospecific robot. Intriguingly, a response to heterospecific displays was recorded even in A. oculatus populations with no prior experience with A. cristatellus. This finding is surprising given the lack of shared evolutionary history of the two species, and remains to be explained. Lastly, A. oculatus males that co-occur with A. cristatellus had a more aggressive display response.

A. oculatus are typically larger and are expected to be the dominant species during aggressive encounters (Dufour et al. 2018a,b). Therefore, it is possible that observed behavioral shifts will impact species coexistence and ultimately decide the long-term outcome of this invasion. Read all about Claire’s exciting new study!