A general framework for modelling trade-offs in adaptive behaviour

An animal's behaviour can influence many variables, such as its energy reserves, its risk of injury or mortality, and its rate of reproduction. To identify the optimal action in a given situation, these various effects can be compared in the common currency of reproductive value. While this idea has been widely used to study trade-offs between pairs of variables, e.g. between energy gain versus survival, here we present a unified framework that makes explicit how these various trade-offs fit together. This unification covers a wide range of biological phenomena, highlighting similarities in their logical structure and helping to identify knowledge gaps. To fill one such gap, we present a new model of foraging under the risk of predation and damage accumulation. We conclude by discussing the use and limitations of state-dependent optimisation theory in predicting biological observations.

Environmental temperature during early life affects the personality of mosquitofish in adulthood

Personality has been observed in a variety of animal taxa with important implications in ecology and evolution. Exploring the influence of environmental temperature during early life on personality could help to understand the ontogeny of this phenotypic trait in animals. In this study, we reared newborn mosquitofish Gambusia affinis at high (30°C) and low (25°C) water temperatures and measured their shyness and exploration upon sexual maturity. We tested the repeatability of each behavioral trait; the correlation between them; and the effects of rearing temperature, sex, and body length on the behaviors. When growing up at low temperatures, female fish exhibited repeatability in shyness and exploration, and males exhibited marginal repeatability in shyness. However, neither of the 2 behaviors were repeatable when the fish were reared at high temperatures. There was a negative correlation between shyness and exploration, indicating that the 2 behaviors comprise a behavioral syndrome in this species. Mosquitofish reared at high temperatures were more explorative than those reared at low temperatures, while there was no difference in shyness between the 2 treatments. Body length and sex had no significant effects on the average values of the 2 behaviors. The results indicate that environmental temperature during early life could shape the personality of mosquitofish and modify the average of the behavioral traits. These findings might provide insights to understand the ontogeny of animal personality and how changes in environmental temperature influence animal dispersal by shaping their personality.

Parasite infestation influences life history but not boldness behavior in placental live-bearing fish

Parasites can negatively affect the reproductive success of hosts. Placental species may be particularly susceptible, because parasite-induced stress during pregnancy could potentially influence embryo development. Here, we examine the consequences of a trematode infestation (black spot disease, BSD) for fetal development and adult behavior in 19 natural populations of the placental live-bearing fish species Poeciliopsis retropinna (Poeciliidae) in Costa Rica. First, we observed substantial variation in parasite infestation among populations which correlated with a number of local environmental conditions (elevation, river width, depth, and flow velocity). Furthermore, we observed substantial variation in parasite infestation among females within populations associated with maternal age and size. We found that the infestation rate significantly influenced embryonic development, with more heavily parasitized females producing smaller and worse-conditioned offspring at birth, possibly, because a costly immune response during pregnancy limits, either directly or indirectly, nourishment to developing embryos. Finally, a behavioral experiment in the field showed that the infestation rate did not affect an individual's boldness. Our study indicates that in placental live-bearing fish parasite infestation leads to reduced embryo provisioning during pregnancy, resulting in a smaller offspring size and quality at birth potentially with negative implications for offspring fitness.

Morphological Correlates of Personality in Female Asian Particolored Bats (Vespertilio sinensis)

Simple Summary

Personality emerges because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. Our study showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among exploration, activity, and aggression. This finding suggested that female Asian particolored bats may not have a behavioral syndrome. Additionally, the body mass of female Asian particolored bats was correlated with aggression and activity, suggesting that body mass may have an impact on the behavioral characteristics of bats. Our findings not only added to the literature concerning personality in bats but are also helpful for understanding the maintenance of an animal’s personality.

Abstract

Personality traits represent a leading edge in the evolutionary process, as natural selection acts directly on variations in individual phenotypes within populations. Recent theoretical models have focused on the concept of adaptive state-dependent behavior, proposing that repeatable differences in behavior emerge because of individual differences in repeatable state variables, such as metabolic rate, age, sex, or body size. Personality and its correlation with body size, however, have been relatively unexplored in bats. We used female Asian particolored bats (Vespertilio sinensis) to investigate three personality characteristics (exploration, activity, and aggression) using the classic hole-board test and examined their relationships with body size using an information-theoretical approach. Our results showed that the exploration of female Asian particolored bats was significantly repeatable, but we did not find significant correlations among the three personality traits. This finding suggested that the female Asian particolored bat may not have a behavioral syndrome. In addition, the body mass of female Asian particolored bats was positively correlated with aggression but was negatively correlated with activity, suggesting that body mass was an important physiological basis affecting the behavioral characteristics of female Asian particolored bats.

Ideal free distribution of Daphnia under predation risk-model predictions and experimental verification

The vertical distribution of planktonic animals, such as Daphnia, in overlapping gradients of food concentration and risk of visual predation should depend on Daphnia population density and should be the result of the group effect of optimizing decisions taken by each individual (juvenile or adult), trading-off a high growth rate to low mortality risk. We tested this hypothesis by comparing the theoretical distributions from simulations based on an experimentally parameterized, optimizing individual-based model (consistent with the assumptions of the concept of the interference ideal free distribution with costs) with distributions observed in laboratory experiments. The simulations were generated for two scenarios, where the shape of the functional response of fish is consistent with either type II or III. The results confirmed the hypothesis. The greatest similarity of the distributions obtained in the experiments and simulations was found for the simulations based on the scenario assuming the type III rather than type II for both age classes of Daphnia. This was consistent with the results of the experiments for the model parameterization, which revealed the type III functional response of fish. Therefore, the results suggest that aggregating may be maladaptive as an anti-vertebrate-predation defense in the case of zooplankton.

Predation environment affects boldness temperament of neotropical livebearers

Behavioral traits of individuals are important phenotypes that potentially interact with many other traits, an understanding of which may illuminate the evolutionary forces affecting populations and species. Among the five axes of temperament is the propensity to behave boldly in the presence of a perceived risk. To determine the effect of different predatorial regimes on boldness and fearfulness, we assessed the behavior of individuals in a novel portable swim chamber (i.e., forced open‐field test) by Brachyrhaphis rhabdophora (n = 633). We used an information theoretic framework to compare generalized (logistic) linear fixed‐effects models of predatorial regime (predator‐free [n = 6] and predator [n = 4] sites), sex, and standard length (SL). Fish from predator sites were much more fearful in the novel arena than fish from nonpredator sites. This varied by length, but not by sex. At 48 mm SL, fish from nonpredator sites were 4.9 times more likely to express bold behavior (ambulation) in the novel swim chamber as fish from predator sites. Probabilities of “ambulating” within the swim chamber increased with size for nonpredator sites and decreased with size for predator sites.

Population dynamics of thrips prey and their mite predators in a refuge

Prey refuges are expected to affect population dynamics, but direct experimental tests of this hypothesis are scarce. Larvae of western flower thrips Frankliniella occidentalis use the web produced by spider mites as a refuge from predation by the predatory mite Neoseiulus cucumeris. Thrips incur a cost of using the refuge through reduced food quality within the web due to spider mite herbivory, resulting in a reduction of thrips developmental rate. These individual costs and benefits of refuge use were incorporated in a stage-structured predator-prey model developed for this system. The model predicted higher thrips numbers in presence than in absence of the refuge during the initial phase. A greenhouse experiment was carried out to test this prediction: the dynamics of thrips and their predators was followed on plants damaged by spider mites, either with or without web. Thrips densities in presence of predators were higher on plants with web than on unwebbed plants after 3 weeks. Experimental data fitted model predictions, indicating that individual-level measurements of refuge costs and benefits can be extrapolated to the level of interacting populations. Model-derived calculations of thrips population growth rate enable the estimation of the minimum predator density at which thrips benefit from using the web as a refuge. The model also predicted a minor effect of the refuge on the prey density at equilibrium, indicating that the effect of refuges on population dynamics hinges on the temporal scale considered.