Warmer temperatures reduce the costs of inducible defences in the marine toad, Rhinella marinus

Differential behavioral responses of benthic and nektonic tadpoles to predation at varying water depths

Predators influence microhabitat selection and activity level of tadpoles, but it is still unclear how such responses to predators differ among species and how water column's depth influences this predator-prey interaction. Here, we experimentally tested whether the presence of Odonata water-nymphs influenced spatial use and activity of benthic and nektonic tadpoles in different food availability contexts. Benthic tadpoles occupied and consumed more food at the bottom level, irrespective of predator’s presence. However, when predators were at bottom, benthic tadpoles remained close to the cages, suggesting a typical “stay-still” defensive behavior known for Physalaemus nattereri (Steindachner, 1863). Nektonic tadpoles occupied shallower depths on predator's presence, and they also consumed less food and avoided predator by selecting food sources far from it. When predator was at bottom level and food was available, the distance of tadpoles to the cage tended to be smaller. Scinax fuscovarius (Lutz, 1925) tadpoles were more active when food was absent regardless of predator’s presence. When food was available, these tadpoles generally occupied and consumed more food at bottom level. Tadpoles’ responses depended not only on predator’s presence, but on a complex net of factors, which include tadpoles’ habit, anti-predatory behavior, availability and location of food.

Antipredatory Responses of Mosquito Pupae to Non-Lethal Predation Threat-Behavioral Plasticity Across Life-History Stages

Antipredatory behavioral responses tend to be energetically expensive, and prey species thus need to resolve trade-offs between these behaviors and other activities such as foraging and mating. While these trade-offs have been well-studied across taxa, less is known about how costs and benefits vary in different life-history contexts, and associated consequences. To address this question, we compared responses of the yellow fever mosquito (Aedes aegypti [Diptera: Culicidae]) to predation threat from guppy (Poecilia reticulata [Cyprinodontiformes: Poeciliidae]) across two life-history stages-larvae (data from previous study) and pupae (from this study). Pupae are motile but do not feed and are comparable to larvae in terms of behavior. To understand how physiological costs affect the threat sensitivity of pupae, we used sex (with size as a covariate) as a proxy for stored energy reserves, and quantified movement and space use patterns of male (small-sized) and female (large-sized) pupae when exposed to predation threat. We found that pupae did not alter movement when exposed to predator cues but instead altered spatial use by spending more time at the bottom of the water column. We found no effect of pupa sex (or size) on the behavioral responses we measured. We conclude that pupa behavior, both antipredatory and otherwise, is primarily targeted at minimizing energy expenditure, as compared with larval behavior, which appears to balance energy expenditure between the opposing pressures of foraging and of avoiding predation. We suggest that antipredatory defenses in metamorphosing prey are modulated by varying energetic trade-offs associated with different life-history stages.