Consequences of life history switch point plasticity for juvenile morphology and locomotion in theTúngara frog

Abstract

Many animals with complex life cycles can cope with environmental uncertainty by altering the timing of life history switch points through plasticity. Pond hydroperiod has important consequences for the fitness of aquatic organisms and many taxa alter the timing of life history switch points in response to habitat desiccation. For example, larval amphibians can metamorphose early to escape drying ponds. Such plasticity may induce variation in size and morphology of juveniles which can result in carry-over effects on jumping performance. To investigate the carry-over effects of metamorphic plasticity to pond drying, we studied the Túngara frog, Physalaemus pustulosus, a tropical anuran that breeds in highly ephemeral habitats. We conducted an outdoor field mesocosm experiment in which we manipulated water depth and desiccation and measured time and size at metamorphosis, tibiofibula length and jumping performance. We also conducted a complimentary laboratory experiment in which we manipulated resources, water depth and desiccation. In the field experiment, metamorphs from dry-down treatments emerged earlier, but at a similar size to metamorphs from constant depth treatments. In the laboratory experiment, metamorphs from the low depth and dry-down treatments emerged earlier and smaller. In both experiments, frogs from dry-down treatments had relatively shorter legs, which negatively impacted their absolute jumping performance. In contrast, reductions in resources delayed and reduced size at metamorphosis, but had no negative effect on jumping performance. To place these results in a broader context, we review past studies on carry-over effects of the larval environment on jumping performance. Reductions in mass and limb length generally resulted in lower jumping performance across juvenile anurans tested to date. Understanding the consequences of plasticity on size, morphology and performance can elucidate the linkages between life stages.

How to recover from a bad start: size at metamorphosis affects growth and survival in a tropical amphibian

“…For example, if smaller individuals have compensating mechanisms, such as more intense growth rates, metamorphic size may not have a significant effect on adult traits like mortality, age and size at first reproduction, or fecundity [20,21]. The detrimental consequences of a small size at metamorphosis can also be compensated by changes in the morphology of juveniles [22,23]. For example, the small froglets can have, proportionally to their body size, larger heads or longer legs than the bigger individuals.…”

Starting on the Right Foot: Carryover Effects of Larval Hydroperiod and Terrain Moisture on Post-metamorphic Frog Movement Behavior

“…Evidence from other amphibian species have also found reduced growth rates in dry conditions creating potential multiplicative effects of environmental conditions, as size was the central determinant of movement (Gomez-Mestre and Tejedo, 2005;Charbonnier et al, 2018). Other research on carry-over effect in amphibians has supported the need for longitudinal studies (Johansson et al, 2010;Charbonnier and Vonesh, 2015;Yagi and Green, 2018). With this broader understanding, we would be better able to combine aquatic structure with terrestrial habitat management to provide for essential habitat components of threatened species (Fellers and Kleeman, 2007;Bartelt and Klaver, 2017).…”

“…Early life stages can be more susceptible to shifting environmental conditions than adults, an effect that has been observed in diverse taxa from reptiles to butterflies (Radchuk et al, 2013;Levy et al, 2015). Several carryover effects to larval stress in anurans have been observed: for example, drying conditions experienced by developing Túngara frog tadpoles reduced leg length and jumping performance (Charbonnier and Vonesh, 2015), and high larval densities of Red-eyed treefrogs resulted in smaller juveniles with reduced livers and fat bodies (Bouchard et al, 2016).…”

“…We chose movement behavior as our response variable because of its importance in a range of ecological aspects, such as foraging, predator avoidance, refuge discovery, and population connectivity Schwalm et al, 2016;Székely et al, 2017). We selected pond permanence as a larval stressor because of the extensive documentation of amphibian plasticity in response to drying conditions (Johansson et al, 2010;Charbonnier and Vonesh, 2015;Thurman and Garcia, 2017). Rana aurora utilizes both ephemeral and permanent lentic waters for breeding habitat, with ephemeral ponds being important for larval success (Adams, 2000;Hayes et al, 2008).…”

Thermal sensitivity of a Neotropical amphibian (Engystomops pustulosus) and its vulnerability to climate change

“…Puddles may have last for a shorter period of time and exhibit more variable concentrations of ions, oxygen, and food. Desiccation will likely affect the development and phenotype of t ungara frog larvae (Charbonnier & Vonesh 2015).…”