Big-Hearted Invaders: The Impacts of Range Expansion and Parasite Infection on Heart Mass in Cane Toads.

The invasion of cane toads (Rhinella marina) across tropical Australia has resulted in the rapid evolution of traits that enable higher rates of dispersal, and that adapt toads to hot dry climates. In anurans, a larger heart facilitates both locomotor activity and desiccation tolerance. Heart size is also often affected, either directly or indirectly, by parasite infections. To test the effects of invasion history and parasite exposure on heart size, we studied common garden-reared toads whose parents were sourced from diverse locations, and experimentally exposed them to larvae of a nematode lungworm (Rhabdias pseudosphaerocephala). Offspring of invasion-front parents had larger hearts than did conspecifics from long-established populations. Exposure to infective lungworm larvae decreased heart mass in toads from all populations. Our study suggests that cardiovascular function, like other traits, has evolved rapidly during the toad invasion; and that lungworm parasites can modify the cardiovascular function and hence aerobic capacity of their host.