Using invasive toads to test evolutionary hypotheses

What principles limits the geographic ranges of species, and can invasive species help us understand these?

GBIF-mediated data resources used : 3,384 species occurrences
Cane Toad (Rhinella marina)

Cane Toad (Rhinella marina) by Lek Khauv via iNaturalist. Photo licensed under CC BY-NC 4.0.

In evolutionary ecology, the central marginal hypothesis (CMH) predicts that a species cannot adapt to conditions outside their current range as genetic diversity decreases from core the edge, because of smaller, more isolated populations in the latter. In this study, researchers tested the predictions of CMH on invasive ranges of the cane toad (Rhinella marina) in Australia, originally introduced as a biocontrol against sugar canes beetles. Using a combination of ecological niche modelling based on GBIF-mediated occurrences and high-throughput genetic sequencing, the researchers found the highest overall habitat suitability in Arnhem Land on the northern coast of the Northern Territory, but in this region, genetic differentiation patterns showed limited support for CMH. In the south-eastern part of the range, diversity and differentiation were, however, consistent with CMH. The study is an example of how species invasions, unfortunate as they might be, can be utilized in evolutionary hypothesis testing.

Trumbo DR, Epstein B, Hohenlohe PA, Alford RA, Schwarzkopf L and Storfer A (2016) Mixed population genomics support for the central marginal hypothesis across the invasive range of the cane toad (Rhinella marina) in Australia. Molecular Ecology. Wiley-Blackwell 25(17): 4161–4176. Available at doi:10.1111/mec.13754.