Smaller size of harlequin toads from populations long exposed to the fungal disease chytridiomycosis

Abstract

AbstractPathogens can exert great selective pressures on the life history traits of their hosts. Species experiencing high mortality throughout their adulthood can benefit from breeding earlier. Chytridiomycosis, a fungal disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has been a major driver of extinction for harlequin toads (Atelopus) and continues to be frequent cause of adult mortality for species persisting with endemic infections. We compared the body size of Atelopus cruciger between a remnant population long exposed to Bd (post‐epidemic) and populations sampled before the presumed Bd outbreak in the late 80s (pre‐epidemic). Reproductive female and male toads from pre‐epidemic populations were significantly bigger than those from post‐epidemic populations at similar altitudes, suggesting that toads from post‐epidemic populations are breeding earlier. A significant positive relationship between body size and the number of eggs in oviducts suggests a trade‐off between the benefit of breeding earlier and the cost of smaller clutch sizes. This cost–benefit relationship is likely to change along elevation gradients because the number of eggs relative to body size tends to be lower at higher elevations. By breeding earlier harlequin toad populations long exposed to Bd can increase their demographic competence, particularly in lowland habitats, where the cost–benefit relationship of breeding earlier tends to be more favorable.Abstract in Spanish is available with online material.