Cane toads (Rhinella marina) rely on water access, not drought tolerance, to invade xeric Australian environments
The invasion of habitats with novel environmental challenges may require physiological tolerances not seen in conspecifics from the native range. We used a combination of field and laboratory-based experiments to assess physiological tolerance to limited water access at four sites distributed across the historical invasion path of cane toads (Rhinella marina) in Australia that, from east to west, alternated between mesic and seasonally xeric habitats. Toads from all locations were well hydrated at the time of capture. However, experimental dehydration caused greater mass loss, higher plasma osmolality, and inhibition of lytic ability in toads from xeric compared to mesic locations. These results suggest somewhat surprisingly that toads from xeric environments are physiologically more vulnerable to water loss. In contrast, bactericidal ability was not sensitive to hydric state and was greater in toads from eastern (long-colonized) areas. Similar patterns in lytic ability in hydrated toads and agglutination ability in wild toads suggest that toads along the invasion front face a tradeoff between enhanced dispersal ability and physiological responses to dehydration. The ability of this invasive species to spread into drier environments may be underpinned by a combination of phenotypic plasticity and evolved (heritable) traits.
KeywordsBufo marinus Hydroregulation Innate immunity Invasive species Osmolality
We wish to thank all members of the Shine lab at Middle Point, the staff at the Australian Academy of Sciences (especially S. Owen), and faculty and staff at Charles Darwin University for their assistance. GABIV wishes to particularly thank the Christian-Gibb family for their generosity. Finally, we wish to thank Drs. M. Greenlees, K. Gibb, and M. Angilletta for their contributions. This work was supported by the National Science Foundation Graduate Research Fellowship, Directorate for Biological Sciences (Grant #1311230), National Science Foundation East Asia and Pacific Summer Institute Fellowship, Directorate for Biological Sciences (Grant #1606367), and Arizona State University’s College of Liberal Arts & Sciences Graduate Excellence Fellowship for First-Generation Students for GABIV.
Author contribution statement
GABIV, KC, GPB, RS and DD designed the study. GABIV and KC conducted the field work. GABIV conducted all assays, performed the statistical analyses, and led the writing of the manuscript. DD, KC, GPB, and RS contributed to revisions and gave final approval for publication.
Compliance with ethical standards
The datasets supporting this article can be accessed at https://doi.org/10.6084/m9.figshare.6431108.
Conflict of interest
The authors declare no conflicts of interest.
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