Meeting Abstract

77.1  Friday, Jan. 7  Density-dependent digestive plasticity in red-eyed treefrogs before and after metamorphosis. BOUCHARD, S. S.*; JENNEY, C. R.; CHARBONNIER, J. F.; WARKENTIN, K. M.; Otterbein Univ., Westerville, OH; Otterbein Univ., Westerville, OH; Virginia Commonwealth Univ., Richmond; Boston Univ., MA sbouchard@otterbein.edu

Red-eyed treefrogs display size-dependent post-metamorphic growth. Small froglets emerging from high density larval environments initially gain mass, while large ones from low density environments lose mass. We assessed effects of larval density on digestive processing before and after metamorphosis as a potential mechanism underlying this pattern. We hypothesized that higher larval densities would increase relative gut length and diet retention times and that these phenotypes would have carry-over effects post-metamorphosis. We reared larvae at three densities (5, 25 and 50 individuals per 400 L tank) and assessed diet transit times by quantifying the appearance of a carbon marker in feces. Size-matched tadpoles from the highest density took longer to pass the marker than those from the lowest density (16 vs. 8 h). We reared metamorphs emerging from these treatments to assess the onset of feeding and diet retention times. We fed froglets insects and quantified intake by counting insect heads in feces. Many metamorphs fed before completing tail resorption; this was much more likely and intake was greater in animals from high density tanks. Time from emergence onto land to production of the first fecal pellet varied substantially (2–12 d) and increased with body size, reflecting either an effect of size itself or larval density. Post-metamorphic diet retention time did not vary with density, despite a threefold difference in mass across treatments. Small froglets from high density tanks therefore had longer gut retention times relative to body size. This, coupled with an earlier onset of feeding after emergence onto land, could explain the size-dependent growth pattern.