Egg clutch dehydration induces early hatching in red-eyed treefrogs, Agalychnis callidryas

Terrestrial eggs have evolved repeatedly in tropical anurans exposing embryos to the new threat of dehydration. Red-eyed treefrogs, Agalychnis callidryas, lay eggs on plants over water. Maternally provided water allows shaded eggs in humid sites to develop to hatching without rainfall, but unshaded eggs and those in less humid sites can die from dehydration. Hatching responses of amphibian eggs to dry conditions are known from two lineages with independent origins of terrestrial eggs. Here, we experimentally tested for dehydration-induced early hatching in another lineage (Agalychnis callidryas, Phyllomedusidae), representing a third independent origin of terrestrial eggs. We also investigated how dehydration affected egg and clutch structure, and egg mortality. We collected clutches from a pond in Gamboa, Panama, and randomly allocated them to wet or dry treatments at age 1 day. Embryos hatched earlier from dry clutches than from wet clutches, accelerating hatching by ∼11%. Clutch thickness and egg diameter were affected by dehydration, diverging between treatments over time. Meanwhile, mortality in dry clutches was six-fold higher than in control clutches. With this study, early hatching responses to escape mortality from egg dehydration are now known from three anuran lineages with independent origins of terrestrial eggs, suggesting they may be widespread. Further studies are needed to understand how terrestrial amphibian eggs can respond to, or will be affected by, rapid changes in climate over the next decades.Fil: Salica, María José. Universidad Nacional de Jujuy. Facultad de Ciencias Agrarias. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico CONICET - Salta. San Salvador de Jujuy; ArgentinaFil: Vonesh, James R.. Virginia Commonwealth University; Estados UnidosFil: Warkentin, Karen M.. Smithsonian Tropical Research Institute; Panamá. Boston University; Estados Unido

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

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

Non-lethal effects of dragonfly predators on the interactions between the tadpoles of two Neotropical hylid frogs [poster]

Background/Question/Methods Prey frequently alter their phenotype in response to perceived predation risk in order to reduce vulnerability. Differences in the costs and benefits of such plastic responses to predators can lead to differences in non-consumptive predator effects. Such differences can occur between taxa or through ontogeny for a given species, and may alter interactions between prey and other species in the food web. Less vulnerable prey may respond less to predator cues compared to vulnerable prey and thus may have higher performance in risky environments. Here we build upon previous research on the tadpoles of two hylid treefrogs, Agalychnis callidryas and Dendropsophus ebraccatus, and predaceous dragonfly nymphs, Anax amazili. Agalychnis callidryas appears to be the more effective competitor, A. amazili consumes both species, but A. callidryas is more vulnerable. Here we examine whether there are differences between the two species in their responses to A. amazili cues, whether these responses change through ontogeny, and how their responses to predator cues alter interactions with each other and their resources. We conducted a 2 x 4 factorial experiment in 400 L mesocosms in which the presence or absence of a caged predator was crossed with no tadpoles, 25 tadpoles of each species alone, or 25 tadpoles of each species combined. Mesocosms were given standardized aliquots of filtered inoculate collected from a nearby pond and left for 3 weeks to allow the establishment of primary producers and microorganisms before tadpole additions. Tadpole growth, periphyton and phytoplankton were sampled at intervals though the experiment. Our study was conducted in October 2010 at the Smithsonian Tropical Research Institute in Gamboa, Panama. Results/Conclusions Tadpoles differed in their response to predator cues as A. callidryas reduced their growth, but D. ebraccatus did not. Furthermore, A. callidryas’ response changed through ontogeny, reducing early growth relative to no predator treatments, but increasing growth later in development such that their were no size difference between treatments at the end of the experiment. Consistent with previous studies, A. callidryas reduced D. ebraccatus final size, but only in the absence of predators. Both predators and tadpoles altered algal standing biomass, but these effects were independent of each other. Tadpoles decreased periphyton and increased phytoplankton, while predators increased both. Our results suggest that differences in early responses to predators may have altered competitive interactions between these species, but non-consumptive effects did not have strong cascading effects to resources

Terrestrial predators and abiotic conditions affect hatching survival of arboreal frog eggs: Implications for aquatic food web dynamics [poster]

Background/Question/MethodsRecent work in food web studies has highlighted the importance of terrestrial and aquatic linkages and the trait and density-mediated effects of predators and abiotic conditions. Many studies have focused on species with complex life histories (amphibians and aquatic insects) because they encompass a variety of trophic levels and form important linkages between terrestrial and aquatic food webs. For example, red-eyed treefrog, Agalychnis callidryas eggs are deposited on vegetation overhanging ponds and risk mortality from a variety of terrestrial predators and abiotic stressors. Red-eyed treefrog embryos, however, exhibit phenotypic plasticity in hatching time in response to these terrestrial stressors. As a result, both predators and abiotic conditions can alter the density and phenotype (size) of tadpoles entering the pond. Because tadpoles are important herbivores affecting both total algal biomass and species composition, these terrestrial sources of mortality can spill over to influence ecosystem processes in the aquatic environment. Moreover, the spill-over effects of changes in density could have markedly different effects on ecosystem processes than changes in phenotype. Here we quantify the effects of terrestrial stressors on hatchling phenotypes and survival and the relative magnitudes of the phenotypic and density spillover effects on the aquatic ecosystem. Specifically we use a combination of field monitoring, laboratory and mesocosm experiments to investigate how changes in both density and phenotype of tadpoles entering the pond affect ecosystem function (e.g., primary productivity) via consumption and competition. Results/ConclusionsBoth egg predators and dehydration had strong effects on both hatching success and timing. The largest effects occurred early in the season (July), when dehydration reduced tadpole inputs by an estimated 28% and later (October) little desiccation occurred but snakes reduced inputs by 79%. Over the course of the season the mean age of hatching of embryos from dehydrated clutches was 19% earlier than those from undisturbed clutches followed by embryos from clutches attacked by snakes (12% earlier). In feeding trials per capita ingestion rates increased with tadpole size and decreased with increasing density. However, hatching early had no effect on primary productivity, or zooplankton abundance or diversity. In contrast, increasing initial tadpole densities (e.g., due to arboreal egg predators) reduced primary productivity and also zooplankton abundance. Thus, there is the potential for terrestrial predators to indirectly impact aquatic primary productivity and consumer abundance (i.e., zooplankton), primarily through their consumptive effects, on an organism with a complex life cycle

The Ecology of Fear: Colonization and Oviposition in Aquatic Systems [poster]

Introduction Amphibians and aquatic invertebrates have complex life histories that link aquatic and terrestrial food webs. It has been suggested that amphibian reproduction is an important source of carbon to some aquatic systems. Movement of organisms across the aquatic-terrestrial habitat boundary can represent important subsidies to the receiving habitat. Subsidies are organisms, nutrients, or detritus that cross habitat boundaries and are consumed, and these allochthonous inputs can affect food web structure. Predators can alter subsidies by consuming organisms that would otherwise move across habitat boundaries. Predator induced shifts in habitat selection are a well known non-lethal effect in aquatic systems. In certain aquatic beetles, mosquitoes and frogs, the chemical cues of a predator can trigger avoidance behavior and fewer eggs are oviposited in pools. Inputs called active subsidies involve these behavioral choices of habitat selection. We hypothesized that presence of a predator will decrease active subsidies from the terrestrial system. However, passive allochthonous inputs like leaf litter fall involuntarily and should be unaffected by predation risk. Thus predation risk should shift the relative importance of these active and passive aquatic subsidies. Conclusions Although it has been speculated that active inputs contribute a significant source of carbon and energy, our study shows that in open pool aquatic systems, passive allochthonous inputs contribute larger amounts of carbon and energy. In this study, there is an effect of predators on habitat selection in organisms with complex life cycles, but predators are not significantly affecting overall carbon and energy inputs to mesocosm

Interactions between competition and predation shape early growth and survival of two Neotropical hylid tadpoles [poster]

Background/Question/Methods Recent literature reviews reveal that competition typically has stronger effects on growth than the presence of predators, while predation has larger effects on survival. Further, past studies show that predators typically lessen the negative effect of competition on growth and also make interspecific competition beneficial for the survival of focal species. We examine the independent and combined effects of competition and predation for survival and growth of the tadpoles of two co-occurring Neotropical hylid frogs (Agalychnis callidryas and Dendropsophus ebraccatus). Our experiment crossed tadpole species composition (single and mixed at single total density) with the presence or absence of a free-roaming predator (Anax sp. dragonfly larva) using a 3x2 factorial design. Six replicates were conducted in 300 L mesocosms at the Smithsonian Tropical Research Center, Gamboa, Panama. Results/Conclusions Dragonfly larvae were effective predators of both species, but had larger effects on A. callidryas survival. A. callidryas grew faster in the presence of D. ebraccatus, suggesting it is a more effective competitor. A. callidryas reduced D. ebraccatus growth in the absence of dragonflies; however, this effect disappeared when predators were present. Though our results are largely consistent with similar previous studies, one interesting difference did emerge. Not only did predation have larger effects on survival than competition, but predator presence resulted in a much larger reduction in tadpole growth than competition – even though predation increased per capita resource levels. This can be attributed to either changes in feeding behavior or metabolic costs of alteration of phenotypically plastic traits. Thus, in our study, predator effects dominated survival and growth and highlight the importance of top-down effects, as well as costs associated with phenotypic plasticity, in shaping interactions between these species

Emergent non-consumptive predator effects alter habitat colonization by mosquitoes

Top-down consumptive control (suppression) is an important driver of populations and communities of prey organisms. Diverse predator assemblages often yield non-linear suppression with respect to constituent species’ effects (emergence); most often diversity enhances suppression. Predators also affect prey organisms non-consumptively through changes in prey physiological, physical, spatial, temporal, and behavioral responses to predators. Role of predator diversity in non-consumptive response by prey is relatively un-studied. Role of predator diversity in shaping prey populations and communities through habitat colonization is a novel question

Persistence of carry-over effects in the spotted salamander.

Most organisms have complex life cycles. Early conditions can constrain phenotype and influence growth and survival later in life. Linkages between life stages are important for conservation and management

Habitat Use and Population Densities of Rain Forest Chameleons in the East Usambara Mountains of Tanzania [poster]

Conclusions: Chamaeleo dilepis and Ri. brevicaudatus are absent from forest at this elevation (852-1103m), while K. matschiei, K. vosseleri, K. tenuis, and R. spinosus are relatively scarce in the forest. Trioceros deremensis and R. temporalis are common, but density varies greatly. The endemic and scarce K. matschiei and K. vosseleri may be of concern given their scarcity in forest habitat. Density estimates in other habitat types are needed to determine status. For accurate density estimates, it is important to consider seasonal variation in density and animals too high to be observed in surveys

Effects of hatching timing on red-eyed treefrog tadpoles: relative vulnerability varies among predators but not with hatchling age-structure, growth varies with the presence of more vulnerable tadpoles [poster]

In Gamboa, Panama, undisturbed red-eyed treefrog embryos typically hatch at age 6 days, but they can hatch as early as 4 days if attacked by egg predators. Early hatchlings are less developed and more vulnerable to predatory shrimp and fish. Here we assess the effect of hatching timing on risk of predation by three common insects, with different foraging styles, that prey on red-eyed treefrog larvae. Further, we examine whether the consequences of hatching early vary with the presence of later-hatched tadpoles. We induced hatching at 4 and 6 days and exposed tadpoles to giant water bugs or aeshnid or libellulid dragonfly larvae over 24 hrs, quantifying tadpole behavior and mortality. We used substitutive designs with three treatments: early hatched, late hatched and mixed hatching ages. In no case did presence of the other age class alter mortality. Hatching age did not affect libelullid predation, which was low in both cases. Early-hatched tadpoles had higher mortality than late hatchlings with water bugs, which move throughout the water column. In contrast, early hatchlings had lower mortality than late hatchlings with aeshnids, which cue strongly on movement. Late-hatched tadpoles were more active than early hatchlings, and movement was reduced in the presence of aeshnids. Combining across this and previously published studies, early hatchlings are more vulnerable than late hatchlings to most (3/5) predators. Variation in relative, age-specific hatchling vulnerability to predators with different foraging styles is consistent with developmental changes in tadpole behavior