Data from: Flexible oviposition behavior enabled the evolution of terrestrial reproduction

In vertebrates, nearly all oviparous animals are considered to have either
obligate aquatic or terrestrial oviposition, with eggs that are
specialized for developing in those environments. The terrestrial
environment has considerably more oxygen but is dry and thus presents both
opportunities and challenges for developing embryos, particularly those
adapted for aquatic development. Here, we present evidence from field
experiments examining egg-laying behavior, egg size and egg jelly function
of 13 species of Central and South American treefrogs in the genus
Dendropsophus, which demonstrates that flexible oviposition (individuals
laying eggs both in and out of water) and eggs capable of both aquatic and
terrestrial development are the likely factors which enable the transition
from aquatic to terrestrial reproduction. Nearly half of the species we
studied had previously undescribed degrees of flexible oviposition.
Species with obligate terrestrial reproduction have larger eggs than
species with aquatic reproduction, and species with flexible reproduction
have eggs of intermediate sizes. Obligate terrestrial breeding frogs also
have egg masses that absorb water more quickly than those with flexible
oviposition. We also examined eight populations of a single species,
Dendropsophus ebraccatus, and document substantial intraspecific variation
in terrestrial oviposition; populations in rainy, stable climates lay
fewer eggs in water than those in drier areas. However, no differences in
egg size were found, supporting the idea that the behavioral component of
oviposition evolves before other adaptations associated with obligate
terrestrial reproduction. Collectively, these data demonstrate the key
role that behavior can have in facilitating major evolutionary
transitions.