Abstract
The energy allocation decisions that organisms make can differ between sexes and populations and can be influenced by factors such as age and parasite infection. We conducted experimental parasite infections on common-garden reared cane toads originating from sites across the species' invasive range in Australia to assess how sex, parasite infection, and invasion history affected the toad's food intake, growth rate, and organ weights. Female toads had larger fat stores, larger livers, and larger gonads than did males, reflecting increased investment into gametes. Growth rate did not differ between the sexes. Lungworm infection increased feeding by male but not female toads and increased fat storage in all toads. Fat body, liver, gonad sizes, and feeding rates all differed among toads from different locations within the toad's invasion transect across Australia, even though our measurements were made under standardized conditions on captive animals. Toads from populations close to the invasion front ate more, had heavier fat bodies, and had larger livers than did toads from long-colonized areas, but they had smaller gonads. This pattern reflects the evolution of a more dispersive phenotype among invasive populations, whereby the rate of dispersal is enhanced by increased energy intake and storage, and delayed reproduction.