ALBERT

Description: The fitness and survival of organisms ultimately depend on their feeding. Therefore, foraging behaviors should be selected to maximize cost-benefit ratio. Wind may restrict and modify animal movements increasing the cost of foraging, especially when the animal carries resources that intercept wind. We quantified the effect of wind on the foraging of leaf-cutting ants and evaluated whether this effect varies with 1) leaf fragment traits, such as area, mass, and shape, and 2) the characteristics of the foraging trail system. We also tested whether these ants show a short-term response to wind by selecting loads with characteristics that reduce wind interception, and a long-term response, by arranging the spatial design of the trail system in a way that reduces that effect. We found that in windy conditions, the speed of loaded ants was reduced by 55%, and ants were blown off the trail 28 times more than in windless conditions. However, wind only affected ants walking along trails that were perpendicular to wind direction or parallel upwind. Wind effect increased with area, mass, and shape of loads. At the short term, ants reduced the negative effect of wind by selecting smaller, lighter, or more elongated loads. However, trails showed no particular spatial distribution in relation to wind direction. This is the first study that quantifies the negative consequences of wind on leaf-cutting ants’ foraging and reports behaviors that can reduce this effect. Our work illustrates how short-term behavioral responses can mitigate the negative effect of an understudied environmental factor on ant foraging.

Description: The temporal partitioning hypothesis suggests that the evolution of different diel activity rhythms in animals might facilitate the coexistence between prey and predators. However, the temporal shift of habitat use induced by predation has rarely been observed. The study of such a mechanism is particularly relevant for introduced species because it might explain how native species can persist or decline in response to the presence of alien species. The introduction of fish into ponds inhabited by amphibians has severe consequences for their occurrence and abundance. Fish particularly affect an alternative newt phenotype, the paedomorph, which does not undergo metamorphosis and maintains larval traits such as gills at the adult stage. In a laboratory design, we assessed the diel patterns of habitat use in the 2 distinct morphological phenotypes of palmate newt ( Lissotriton helveticus ) in the presence or absence of goldfish ( Carassius auratus ). Both newt phenotypes avoided a risky habitat more in the presence than in the absence of fish. This habitat shift was more pronounced during the daytime (i.e., when the risk could be considered higher for the newts) than during nighttime. However, in contrast to metamorphs, paedomorphs showed less adaptive changes according to temporal risk and remained in their shelter for most of the time. Temporal and habitat partitioning at the diel scale between native and alien species might promote their coexistence, but diel change can also imply a cost in the overall reduction of the time allocated to essential activities, showing that species interactions remain complex.

Description: Translocation is an important conservation management tool. However, not all individuals are equally suited to translocation, and temperament traits (e.g., boldness, reactivity, exploration, sociability, and aggression) are likely to influence survival in a new environment. A few empirical studies have examined the consequences of personality differences on captive-bred translocated animals, but this has not been done for wild-caught animals. We compared behavioral responses to trapping, processing, holding, and release for 56 wild common brushtail possums ( Trichosurus vulpecula ). Twenty individuals were captured twice, once to attach radio-tracking collars, the second time (2 weeks later) for the translocation. Consistency of behavioral responses was compared between capture events and radio-tracking allowed estimates of pretranslocation home range, rest site selection, and foraging behavior. Survivors ( n = 10 survivors, 5 months later) were individuals showing the most fear or emotional reactivity during holding (less likely to have slept, eaten, defecated, or nested) and those that had the smallest home ranges and selected the safest den sites in their original habitat. Conversely, the greatest increase in body mass was recorded for individuals that had demonstrated "unsafe" behavior in their original habitat. To our knowledge, this is the first time this type of behavioral screening during handling and holding prior to release as part of a translocation has been undertaken. These methods have broad applicability for screening potential translocation candidates and are easily translated to a range of threatened and vulnerable animal species.

Description: The distribution and abundance of food resources are among the most important factors that influence animal behavioral strategies. Yet, spatial variation in feeding habitat quality is often difficult to assess with traditional methods that rely on extrapolation from plot survey data or remote sensing. Here, we show that maximum entropy species distribution modeling can be used to successfully predict small-scale variation in the distribution of 24 important plant food species for chimpanzees at Gombe National Park, Tanzania. We combined model predictions with behavioral observations to quantify feeding habitat quality as the cumulative dietary proportion of the species predicted to occur in a given location. This measure exhibited considerable spatial heterogeneity with elevation and latitude, both within and across main habitat types. We used model results to assess individual variation in habitat selection among adult chimpanzees during a 10-year period, testing predictions about trade-offs between foraging and reproductive effort. We found that nonswollen females selected the highest-quality habitats compared with swollen females or males, in line with predictions based on their energetic needs. Swollen females appeared to compromise feeding in favor of mating opportunities, suggesting that females rather than males change their ranging patterns in search of mates. Males generally occupied feeding habitats of lower quality, which may exacerbate energetic challenges of aggression and territory defense. Finally, we documented an increase in feeding habitat quality with community residence time in both sexes during the dry season, suggesting an influence of familiarity on foraging decisions in a highly heterogeneous landscape.

Description: Despite parents are equally related to all of their progeny, they may differentially invest in offspring that provide the highest fitness return. Sons and daughters can differ in reproductive value, especially in species where fitness is predicted by the expression of sexually selected traits. In many birds, offspring plumage coloration functions as a honest signal of individual quality, thus allowing parents to differentially invest in offspring of either sex accordingly. Here, we tested whether parents allocate different amounts of food depending on plumage color of their male and female offspring. As a model, we used the barn swallow ( Hirundo rustica ), a species where large among- and within-brood variation in ventral plumage color exists and male reproductive success varies according to ventral plumage coloration. We recorded the proportion of feedings obtained and body mass variation by dyads of same-sex and similar-sized nestlings subjected to either experimental darkening of their ventral plumage color or to a sham treatment. Plumage darkening enhanced food provisioning and body mass gain of males but not of females. Because darker ventral coloration is associated with larger reproductive success in male barn swallows, these results suggest that parents tune their effort toward more valuable male offspring that are likely to provide the greatest fitness returns. Our study thus suggests that parents are selected to differentially invest in offspring of either sex according to a trait expressed in early life, which is relevant to intrasexual competition for access to mates at sexual maturity.

Description: The iconic red hourglass of the black widow spiders (genus Latrodectus ) is traditionally considered an aposematic signal, yet experimental evidence is lacking. Here, we present data that suggest that black widow coloration may have evolved to be an aposematic signal that is more conspicuous to their vertebrate predators than to their insect prey. In choice experiments with wild birds, we found that the red-and-black coloration deters potential predators: Wild birds were ~3 times less likely to attack a black widow model with an hourglass than one without. Using visual-system appropriate models, we also found that a black widow’s red-and-black color combo is more apparent to a typical bird than a typical insect. Additionally, an ancestral reconstruction reveals that red dorsal coloration is ancestral in black widows and that at some point some North American widows lost their red dorsal coloration. Behaviorally, differences in red dorsal coloration between 2 North American species are accompanied by differences in microhabitat that affects how often a bird will view a black widow’s dorsal region. All observations are consistent with a cost–benefit trade-off of being more conspicuous to predators than to prey. We suggest that limiting detection by prey may help explain why red and black aposematic signals occur frequently in nature.

Description: While conducting a toxicity assessment of the antidepressant paroxetine (Paxil®), in wild-derived mice ( Mus musculus ), we observed that exposed dams (P 0 ) produced female biased litters (32:68 M:F). Though numerous experimental manipulations have induced sex ratio bias in mice, none have assessed the fitness of the offspring from these litters relative to controls. Here, we retrospectively analyze experimentally derived fitness data gathered for the purpose of toxicological assessment in light of 2 leading hypothesis (Trivers–Willard hypothesis [TWH] and cost of reproduction hypothesis [CRH]), seeking to test if this facultative sex ratio adjustment fits into an adaptive framework. Control F 1 males were heavier than F 1 females, but no differences in mass were detected between exposed F 1 males and females, suggesting that exposed dams did not save energy by producing fewer males, despite producing 29.2% lighter litters relative to controls. F 1 offspring of both treatments were released into seminatural enclosures where fitness was quantified. In enclosures, the relative reproductive success of F 1 -exposed males (compared with controls) was reduced by ~20% compared with the relative reproductive success of F 1 -exposed females. Thus, exposed dams increased their fitness by adjusting litters toward females who were less negatively affected by the exposure than males. Collectively, these data provide less support that the observed sex ratio bias results in energetic savings (CRH), and more support for the TWH because fitness was increased by biasing litters toward female offspring. These mammalian data are unique in their ability to support the TWH through the use of relevant fitness data.

Description: Understanding how seabirds and other central place foragers locate food resources represents a key step in predicting responses to changes in resource abundance and distribution. Where prey distributions are unpredictable and ephemeral, seabirds may gain up-to-date information by monitoring the direction of birds returning to the colony or by monitoring the foraging behavior of other birds through local enhancement. However, search strategies based on social information may require high population densities, raising concerns about the potential loss of information in declining populations. Our objectives were to explore the mechanisms that underpin effective search strategies based on social information under a range of population densities and different foraging conditions. Testing relevant hypotheses through field observation is challenging because of limitations in the ability to manipulate population densities and foraging conditions. We therefore developed a spatially explicit individual-based foraging model, informed by data on the movement and foraging patterns of seabirds foraging on pelagic prey, and used model simulations to investigate the mechanisms underpinning search strategies. Orientation of outbound headings in line with returning birds enables departing birds to avoid areas without prey even at relatively low population densities. The mechanisms underpinning local enhancement are more effective as population densities increase and may be facilitated by other mechanisms that concentrate individuals in profitable areas. For seabirds and other central place foragers foraging on unpredictable and ephemeral food resources, information is especially valuable when resources are spatially concentrated and may play an important role in mitigating poor foraging conditions.

Description: Experiments designed to quantify the effects of increasing numbers of carers on levels of offspring care are rare in cooperative breeding systems, where offspring are reared by individuals additional to the breeding pair. This paucity might stem from disagreement over the most appropriate manipulations necessary to elucidate these effects. Here, we perform both carer removal and brood enhancement experiments to test the effects of numbers of carers and carer:offspring ratios on provisioning rates in the cooperatively breeding chestnut-crowned babbler ( Pomatostomus ruficeps ). Removing carers caused linear reductions in overall brood provisioning rates. Further analyses failed to provide evidence that this effect was influenced by territory quality or disruption of group dynamics stemming from the removals. Likewise, adding nestlings to broods caused linear increases in brood provisioning rates, suggesting carers are responsive to increasing offspring demand. However, the 2 experiments did not generate quantitatively equivalent results: Each nestling received more food following brood size manipulation than carer removal, despite comparable carer:offspring ratios in each. Following an at-hatching split-design cross-fostering manipulation to break any links between prehatching maternal effects and posthatching begging patterns, we found that begging intensity increased in larger broods after controlling for metrics of hunger. These findings suggest that manipulation of brood size can, in itself, influence nestling provisioning rates when begging intensity is affected by scramble competition. We highlight that carer number and brood size manipulations are complimentary but not equivalent; adopting both can yield greater overall insight into carer effects in cooperative breeding systems.

Description: Dispersal affects the social contexts individuals experience by redistributing individuals in space, and the nature of social interactions can have important fitness consequences. During the vagrancy stage of natal dispersal, after an individual has left its natal site and before it has settled to breed, social affiliations might be predicted by opportunities to associate (e.g., distance in space and time between natal points of origin) or kin preferences. We investigated the social structure of a population of juvenile great tits ( Parus major ) and asked whether social affiliations during vagrancy were predicted by 1) the distance between natal nest-boxes, 2) synchrony in fledge dates, and 3) accounting for spatial and temporal predictors, whether siblings tended to stay together. We show that association strength was affected predominantly by spatial proximity at fledging and, to a lesser extent, temporal proximity in birth dates. Independently of spatial and temporal effects, sibling pairs associated more often than expected by chance. Our results suggest that the structure of the winter population is shaped primarily by limits to dispersal through incomplete population mixing. In addition, our results reveal kin structure, and hence the scope for fitness-related interactions between particular classes of kin. Both spatial-mediated and socially mediated population structuring can have implications for our understanding of the evolution of sociality.