Native frogs (Rana pirica) do not respond adaptively to alien toads (Bufo japonicus formosus) 100 years after introduction

Abstract

AbstractBiological invasions adversely affect the survival of many native species, but long‐term consequences of the novel pressures imposed by invaders on natives are less clear. If natives can adapt to the presence of the invader, the severity of impact will decline with time. On Hokkaido, Japan, alien toads (Bufo japonicus formosus) are highly toxic to native frog tadpoles (Rana pirica) that attempt to eat their hatchlings. Therefore, the arrival of toads potentially imposes selection pressure on native frogs in the context of behavioral response (feeding aversion) and physiological resistance to toad toxins. Here, we compared the consumption tendency and toxin resistance of R. pirica from several sites with different histories of toad invasion (0 to >100 years exposure). We found no evidence of adaptive response to invasive toads. The vast majority of R. pirica tadpoles from all sites readily consumed toad hatchlings and died, regardless of time since invasion or whether hatchlings were from sympatric versus allopatric toad populations. In contrast, tadpoles of a closely related species (Rana ornativentris), which co‐occurs naturally with B. j. formosus on Honshu, readily consumed toad hatchlings without ill effect. Our results indicate that the lethal toxic effect of the alien toads on native frogs on Hokkaido is maintained over long time periods without mitigation through adaptation.