Larval and metamorph traits of cane toads

As an invasive organism spreads into a novel environment, it may encounter
strong selective pressures to adapt to abiotic challenges. We examined the
effect of water temperature during larval life on rates of survival and
growth of the early life-history stages of cane toads (Rhinella marina)
from two geographic regions (tropical vs. temperate) in the species’
invaded range in eastern Australia. If local adaptation at the southern
(cool-climate) invasion front has extended the cold-tolerance of early
life-stages, we would expect to see higher viability of
southern-population toads under cooler conditions. Our comparisons
revealed no such divergence: the effects of water temperature on rates of
larval survival and growth, time to metamorphosis, size at metamorphosis
and locomotor performance of metamorphs were similar in both sets of
populations. In two cases where tropical and temperate-zone populations
diverged in responses to temperature, the tropical animals performed
better at low to medium temperatures than did conspecifics from cooler
regions. Adaptation to low temperatures in the south might be constrained
by behavioural shifts (e.g., in reproductive seasonality, spawning-site
selection) that allow toads to breed in warmer water even in cool
climates, by gene flow from warmer-climate populations, or by phylogenetic
conservatism in these traits.