Morphological correlates of invasion in Florida cane toad (Rhinella marina) populations: Shortening of legs and reduction in leg asymmetry as populations become established

Abstract

Exotic organisms have traits that allow them to effectively disperse and propagate into novel environments. The ability to adapt to new environments has enabled the cane toad (Rhinella marina) to successfully invade novel ecosystems. Their leg length correlates with dispersal success and is selected for in invading populations. Given their successful invasion of multiple continents, R. marina represent a unique opportunity to understand the generality of invasion strategies within a species. Here we test for spatial and temporal shifts in leg length (length of tibio-fibula relative to snout-vent length) of invasive R. marina in Florida populations to assess their adaptation to novel environments. Individuals experiencing new conditions are susceptible to physiological stress, which may negatively affect their development and inhibit their dispersal potential. To this end, we tested for spatial and temporal trends in fluctuating asymmetry, an indicator of physiological stress during development. We compared patterns between two regions of Florida (central vs southern Florida) with different invasion histories. We found that relative leg length of R. marina decreased over time in both regions, and experienced shifts in fluctuating asymmetry over time from initial colonization to population establishment. Our results suggest that successful invasive species rapidly adjust to novel environments. In addition, our results support predictions that morphological change plays a role in aiding dispersal for rapidly dispersing species.