Agalychnis callidryas and A. spurrelli egg masses

Syntopic populations of species provide a unique opportunity to examine
divergence of adaptive traits that suggest character displacement when
compared with allopatric populations of those species. Past work on
syntopic populations of tree frogs, Agalychnis callidryas and A spurrelli
documented differences in embryonic risk responses. Due to a serendipitous
opportunity, we sampled egg masses from these species oviposited during a
breeding aggregation at a forested wetland during July 2017 in the
Puntarenas Province of Costa Rica. We collected data on egg masses of the
two species including oviposition site and evidence of predation. Both
species oviposited on vegetation around the perimeter of the wetland.
Additionally, we found that A. callidryas, the species that was previously
documented as hatching quickly in response to snake predation took
advantage of canopy vegetation overhanging the wetland for oviposition,
sites more available to arboreal snakes. This canopy vegetation was not
used by A spurrelli. Conversely, A spurrelli, the species shown to respond
more strongly to submergence by hatching early, oviposited on vegetation
directly emerging from the wetland, sites not used by A callidryas. This
divergence of reproductive and ecological traits is not seen in allopatric
populations of the same species. These findings suggest that character
displacement in oviposition site may have caused differences in selection
pressure on embryonic behavior.