Data from: Tradeoffs affect the adaptive value of plasticity: Stronger cannibal-induced defenses incur greater costs in toad larvae

Adaptive developmental plasticity allows individuals to match their
phenotype with their environment, which can increase fitness where threats
are inconsistently present. Because adaptive traits are not ubiquitously
nor infinitely plastic, tradeoffs between benefits and costs or limits are
theoretically necessary to constrain plastic responses. Systems in which
extreme risk can be reliably detected are ideal for investigating
mechanisms that constrain plasticity, as even costly responses may be
adaptive where risk is severe. Cane toads (Rhinella marina) are abundant
in Australia and produce large clutches (frequently >10,000 eggs),
but asynchronous breeding and rapid development result in variable larval
densities within breeding pools. In the field, we found that cannibalism
by older cohorts often reduces the survival of conspecific eggs and newly
hatched pre-feeding larvae (“hatchlings”) by >99%, as feeding
larvae (“tadpoles”) use chemical cues from the relatively immobile
hatchlings to locate and consume them. After hatchlings become
free-swimming, however, they are safe from cannibalism. Hatchlings can
reduce this period of vulnerability by accelerating development when they
detect conspecific tadpole cues. However, this developmental acceleration
decreases initial tadpole mass, reduces subsequent survival, growth, and
development, affects behavior, and compromises feeding structures.
Reaction norms differ among clutches, and greater developmental
acceleration is followed by greater impairment of larval function in
plastic clutches, whereas nonresponsive clutches are unaffected by
exposure to cannibal cues. More plastic clutches ultimately exhibit both
poorer performance and greater variation among siblings in exposed and (to
a lesser degree) control treatments. Variation among clutches in tadpole
viability is driven by differences in plasticity rather than phenotype;
fitness reductions are linked to developmental acceleration, not rapid
development per se. Clutches with intrinsically slow pre-feeding
developmental rates exhibit stronger acceleration (i.e., steeper reaction
norms), but clutches with intrinsically rapid development reach
invulnerable stages more quickly than those that accelerate development.
As a result, high cannibalism risk may favor canalized rapid development
rather than facultative developmental acceleration. Cannibalism plays an
important role in the recruitment of this invasive species, and hatchling
defenses against this threat demonstrate how the limits and tradeoffs
associated with an inducible defense can favor canalized defenses over
phenotypic plasticity.