Predator-induced transgenerational plasticity in animals: a meta-analysis.

There is growing evidence that the environment experienced by one generation can influence phenotypes in the next generation via transgenerational plasticity (TGP). One of the best-studied examples of TGP in animals is predator-induced transgenerational plasticity, whereby exposing parents to predation risk triggers changes in offspring phenotypes. Yet, there is a lack of general consensus synthesizing the predator-prey literature with existing theory pertaining to ecology and evolution of TGP. Here, we apply a meta-analysis to the sizable literature on predator-induced TGP (441 effect sizes from 29 species and 49 studies) to explore five hypotheses about the magnitude, form and direction of predator-induced TGP. Hypothesis #1: the strength of predator-induced TGP should vary with the number of predator cues. Hypothesis #2: the strength of predator-induced TGP should vary with reproductive mode. Hypothesis #3: the strength and direction of predator-induced TGP should vary among offspring phenotypic traits because some traits are more plastic than others. Hypothesis #4: the strength of predator-induced TGP should wane over ontogeny. Hypothesis #5: predator-induced TGP should generate adaptive phenotypes that should be more evident when offspring are themselves exposed to risk. We found strong evidence for predator-induced TGP overall, but no evidence that parental predator exposure causes offspring traits to change in a particular direction. Additionally, we found little evidence in support of any of the specific hypotheses. We infer that the failure to find consistent evidence reflects the heterogeneous nature of the phenomena, and the highly diverse experimental designs used to study it. Together, these findings set an agenda for future work in this area.

Covariation between glucocorticoids, behaviour and immunity supports the pace-of-life syndrome hypothesis: an experimental approach.

The biomedical literature has consistently highlighted that long-term elevation of glucocorticoids might impair immune functions. However, patterns are less clear in wild animals. Here, we re-explored the stress-immunity relationship considering the potential effects of behavioural profiles. Thirteen captive roe deer (Capreolus capreolus) were monitored over an eight-week period encompassing two capture events. We assessed how changes in baseline faecal cortisol metabolite (FCM) concentrations following a standardized capture protocol and an immune challenge using anti-rabies vaccination affected changes in 13 immune parameters of innate and adaptive immunity, and whether these changes in baseline FCM levels and immune parameters related to behavioural profiles. We found that individuals with increased baseline FCM levels also exhibited increased immunity and were characterized by more reactive behavioural profiles (low activity levels, docility to manipulation and neophilia). Our results suggest that the immunity of large mammals may be influenced by glucocorticoids, but also behavioural profiles, as it is predicted by the pace-of-life syndrome hypothesis. Our results highlight the need to consider covariations between behaviour, immunity and glucocorticoids in order to improve our understanding of the among-individual variability in the stress-immunity relationships observed in wildlife, as they may be underpinned by different life-history strategies.

Classification of pig calls produced from birth to slaughter according to their emotional valence and context of production.

Vocal expression of emotions has been observed across species and could provide a non-invasive and reliable means to assess animal emotions. We investigated if pig vocal indicators of emotions revealed in previous studies are valid across call types and contexts, and could potentially be used to develop an automated emotion monitoring tool. We performed an analysis of an extensive and unique dataset of low (LF) and high frequency (HF) calls emitted by pigs across numerous commercial contexts from birth to slaughter (7414 calls from 411 pigs). Our results revealed that the valence attributed to the contexts of production (positive versus negative) affected all investigated parameters in both LF and HF. Similarly, the context category affected all parameters. We then tested two different automated methods for call classification; a neural network revealed much higher classification accuracy compared to a permuted discriminant function analysis (pDFA), both for the valence (neural network: 91.5%; pDFA analysis weighted average across LF and HF (cross-classified): 61.7% with a chance level at 50.5%) and context (neural network: 81.5%; pDFA analysis weighted average across LF and HF (cross-classified): 19.4% with a chance level at 14.3%). These results suggest that an automated recognition system can be developed to monitor pig welfare on-farm.

Personality traits change after an opportunity to mate.

There is growing evidence that personality traits can change throughout the life course in humans and nonhuman animals. However, the proximate and ultimate causes of personality trait change are largely unknown, especially in adults. In a controlled, longitudinal experiment, we tested whether a key life event for adults--mating--can cause personality traits to change in female threespine sticklebacks. We confirmed that there are consistent individual differences in activity, sociability and risk-taking, and then compared these personality traits among three groups of females: (i) control females; (ii) females that had physically mated, and (iii) females that had socially experienced courtship but did not mate. Both the physical experience of mating and the social experience of courtship caused females to become less willing to take risks and less social. To understand the proximate mechanisms underlying these changes, we measured levels of excreted steroids. Both the physical experience of mating and the social experience of courtship caused levels of dihydroxyprogesterone (17α,20ß-P) to increase, and females with higher 17α,20ß-P were less willing to take risks and less social. These results provide experimental evidence that personality traits and their underlying neuroendocrine correlates are influenced by formative social and life-history experiences well into adulthood.

Individual variation in an acute stress response reflects divergent coping strategies in a large herbivore.

Individuals differ in the manner that they cope with risk. When these behavioral differences are manifested in risky or challenging environments (i.e. stressful situations), they are generally interpreted within the "coping style" framework. As studying inter-individual variability in behavior is particularly challenging in the wild, we used a captive facility to explore consistency in the individual behavioral response to an acute stress in roe deer (Capreolus capreolus). Using behavioral and physiological parameters measured six times across a calendar year, we first quantified individual repeatability and, second, explored the correlations among these parameters that might indicate a coherent stress response. Finally, we analyzed the link between the stress response and individual body mass, a reliable indicator of phenotypic quality in roe deer. We found that the measured parameters were highly repeatable across seasons, indicating that the individual stress response is consistent over time. Furthermore, there was considerable covariation among the stress response parameters, describing a proactivity-reactivity gradient at the individual level. Finally, proactive individuals had higher body mass than reactive individuals. We suggest that consistent individual differences in energy metabolism and physiology may promote consistent individual differences in behavioral traits, providing a mechanistic link between food acquisition tactics and demographic performance.