DOI: 10.5061/dryad.v41ns1s07
title: Agalychnis callidryas and A. spurrelli egg masses

description: 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.
description: We collected data
 from <em>Agalychnis callidryas</em> (red-eyed tree frog) and
 <em>A. spurrelli</em> (gliding tree frog) egg masses in a
 forested wetland on the Osa Peninsula, Corcovado National Park, Puntarenas
 Province, Costa Rica during July 2017.<em> </em>The main body
 of the wetland (08° 28.530’ N,
 083°
 35.566’ W) was approximately 45 x 20 m with a narrow and shallow area of
 wetland extending an additional 20 m to the west. The two species of
 <em>Agalychnis</em> had initiated reproduction in response to
 intense rainfall. Sampling lasted 6 days: hatching in <em>A.
 callidryas</em> can occur in as early as 4 days and generally lasts
 5-8 days in both species.  Information on
 timing, oviposition sites, and predation (egg mass general development,
 size, oviposition site including substrate, orientation, location in
 respect to canopy and water surface, and evidence of predation) was
 collected in the field. We searched the wetland for egg masses on plants
 in and directly around the wetland, from the water surface up to
 approximately 3 m above. We would not have been able to reliably see egg
 masses higher in the canopy and literature suggests that most eggs of
 <em>A. spurrelli</em> occur lower than 3 m in height (Scott
 and Starrett 1974). All egg masses we found were within 1.6 m of the
 water’s surface. We temporarily marked each mass location and visited
 daily to count embryos and document evidence of predation, disease, or
 developmental abnormalities. We documented predation when there was direct
 evidence (sections of embryos and envelopes missing, popped eggs) or
 &gt; 10 embryo change in count from one day to the next if this
 occurred early in development (&lt; 4 days based on Cohen et al.
 2016). We categorized type of predation as none, missing volume (likely
 snake predation), envelope remaining but embryo missing (if early in
 development) or popped (likely invertebrate predation). Masses that were
 missing embryos but had the envelope after day four of development were
 assumed to have started hatching.  We calculated
 additional variables including the volume, embryo density, and oviposition
 date for each egg mass based on development at time of detection. We
 calculated the volume of egg masses based on a spheroid ((4/3*pi*a*b*c)/2
 = volume where a, b, and c are the radii for length, width and depth):
 half the spheroid on leaves or relatively flat surfaces, and the full
 spheroid for masses surrounding twigs or vines. We calculated density of
 embryos in an egg mass (maximum number of embryos counted/mass volume)
 only for egg masses that showed no sign of predation via missing sections
 of jelly when we initially started counting embryos. An estimated day of
 oviposition was calculated for those masses we did not find immediately
 based on subtracting 7, the median time to hatching in both species
 (Savage 2002), from the hatching date. There was a large rain event on the
 evening before the last day of sampling and <em>A. callidryas
 </em>responded with a new flush of laying. To not overinflate
 confidence in our statistical tests, we did not include egg masses
 oviposited on the last day in the analyses of oviposition date.
 This work was
 approved by the Texas Tech University Animal Care and Use Committee
 (17063-07) and covered under research permit INV-ACOSA-053-17 to A. Vega
 and was conducted in accordance with relevant institutional and national
 guidelines.