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Predation and competition induce variable organ size tradeoffs in larval anurans


Neptune, Troy; Bouchard, Sarah (2021), Predation and competition induce variable organ size tradeoffs in larval anurans, Dryad, Dataset,


Inducible-defenses allow organisms that live in variable environments to invest energy into defense when necessary.  These responses are common in aquatic organisms and are particularly notable in larval anurans, which tend to develop deeper tails under sit-and-wait macroinvertebrate predation threat.  Although tradeoffs between defense and growth have been well-studied, tradeoffs with internal organ sizes have rarely been considered.  The purpose of our study was to investigate the effects of predation and competition on tradeoffs associated with total length (body + tail), tail size, and internal organ size (gut, pancreas, liver, and fat body) in two larval anurans, red-eyed treefrogs (Agalychnis callidryas) and gray treefrogs (Hyla versicolor).  In two separate experiments, we reared larvae in outdoor mesocosms with and without competition in the presence and absence of a caged predator.  We subsampled larvae from each mesocosm and measured tail and internal organ sizes.  Both competition and predation exerted strong effects on total length and morphology, although each experiment produced unique results.  Competition increased gut size in both species, supporting a previously reported tradeoff between gut and tail size.  Competition also reduced total length in both experiments: gray treefrogs balanced total length with lipid deposition, and red-eyed treefrogs favored total length at the expense of lipid reserves.  Predation threat elicited an increase in tail depth but a reduction in tail muscle size in gray treefrogs, which may have allowed larvae to maintain pancreas size and total length.  Conversely, red-eyed treefrogs developed larger tails with more muscle area, allocating resources in a way that sacrificed both liver and pancreas size, as well as total length.  Although the specific tail response was different, both species prioritized larger guts over tail modifications when faced with both competition and predation, as large gut sizes were maintained in competitive environments even when predators were present.