The loneliness of the long-distance toad: invasion history and social attraction in cane toads (Rhinella marina)

Abstract

Individuals at the leading edge of a biological invasion constantly encounter novel environments. These pioneers may benefit from increased social attraction, because low population densities reduce competition and risks of pathogen transfer, and increase benefits of information transfer. In standardized trials, cane toads (Rhinella marina) from invasion-front populations approached conspecifics more often, and spent more time close to them, than did conspecifics from high-density, long-colonized populations.

Keywords: Bufo marinus; aggregation; evolution; sociality.

Figure 1.

Arena testing social attraction in cane toads (Rhinella marina). The arena contained a transparent pod housing a stimulus toad and an empty transparent pod opposite the focal toad's start point.

Figure 2.

In standardized trials, cane toads (Rhinella marina) from three areas with different invasion histories (WA = invasion front, Western Australia; QLD = long-colonized, Queensland, Australia; HW = long-colonized, Hawai'i) and of different sexes (males = dark grey bars, females = light grey bars) exhibited different levels of social attraction (as quantified by the proportion of individuals that approached the stimulus toad (a) and the amount of time spent within 100 mm of a stimulus toad (b)). Letters above error bars represent significant (α = less than 0.05) differences between populations calculated from a Tukey's post hoc test.