Agalychnis callidryas and A. spurrelli egg masses
Griffis-Kyle, Kerry; Perry, Gad; Vega, Andres (2022), Agalychnis callidryas and A. spurrelli egg masses, Dryad, Dataset, https://doi.org/10.5061/dryad.v41ns1s07
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.
We collected data from Agalychnis callidryas (red-eyed tree frog) and A. spurrelli (gliding tree frog) egg masses in a forested wetland on the Osa Peninsula, Corcovado National Park, Puntarenas Province, Costa Rica during July 2017. 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 Agalychnis had initiated reproduction in response to intense rainfall. Sampling lasted 6 days: hatching in A. callidryas 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 A. spurrelli 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 > 10 embryo change in count from one day to the next if this occurred early in development (< 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 A. callidryas 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.