Josefina Zidar

Comparative support for the expensive tissue hypothesis: Big brains are correlated with smaller gut and greater parental investment in Lake Tanganyika cichlids

The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the energetic requirements of encephalization are suggested to impose considerable constraints on brain size evolution. Three main hypotheses concerning how energetic constraints might affect brain evolution predict covariation between brain investment and (1) investment into other costly tissues, (2) overall metabolic rate, and (3) reproductive investment. To date, these hypotheses have mainly been tested in homeothermic animals and the existing data are inconclusive. However, there are good reasons to believe that energetic limitations might play a role in large‐scale patterns of brain size evolution also in ectothermic vertebrates. Here, we test these hypotheses in a group of ectothermic vertebrates, the Lake Tanganyika cichlid fishes. After controlling for the effect of shared ancestry and confounding ecological variables, we find a negative association between brain size and gut size. Furthermore, we find that the evolution of a larger brain is accompanied by increased reproductive investment into egg size and parental care. Our results indicate that the energetic costs of encephalization may be an important general factor involved in the evolution of brain size also in ectothermic vertebrates.

Comparative support for the expensivetissue hypothesis: Big brains are correlatedwith smaller gut and greater parentalinvestment in Lake Tanganyika cichlids

The brain is one of the most energetically expensive organs in the vertebrate body. Consequently, the energetic requirements of encephalization are suggested to impose considerable constraints on brain size evolution. Three main hypotheses concerning how energetic constraints might affect brain evolution predict covariation between brain investment and (1) investment into other costly tissues, (2) overall metabolic rate, and (3) reproductive investment. To date, these hypotheses have mainly been tested in homeothermic animals and the existing data are inconclusive. However, there are good reasons to believe that energetic limitations might play a role in large‐scale patterns of brain size evolution also in ectothermic vertebrates. Here, we test these hypotheses in a group of ectothermic vertebrates, the Lake Tanganyika cichlid fishes. After controlling for the effect of shared ancestry and confounding ecological variables, we find a negative association between brain size and gut size. Furthermore, we find that the evolution of a larger brain is accompanied by increased reproductive investment into egg size and parental care. Our results indicate that the energetic costs of encephalization may be an important general factor involved in the evolution of brain size also in ectothermic vertebrates.

Scent of the enemy: behavioural responses to predator faecal odour in the fowl

Chemical communication is used by diverse organisms in a variety of contexts and can have strong fitness consequences for the individuals involved. However, despite the extensive use of birds as models for many research areas in biology, avian olfaction has been poorly investigated. Studies on bird species that lack well-developed olfactory organs and those investigating responses to predator odours are particularly scarce. We investigated behavioural responses of the domestic fowl, Gallus gallus domesticus, a ground-living species with intermediate olfactory bulb size, to several predator and nonpredator faecal odours. We found that the birds spent less time foraging and were more vigilant when exposed to predator faecal odour compared with nonpredator faecal odour. Individuals showed a similar response when exposed to increased amounts of faeces. Taken together, our results demonstrate that domestic fowl can distinguish between herbivore and predator faecal odour, and respond to predator olfactory cues alone, without prior experience. Our results have implications for the understanding of predator–prey interactions and responses to olfactory cues in general, and for chemical communication in avian species more specifically.

Early experience affects adult personality in the red junglefowl: A role for cognitive stimulation?

Despite intense research efforts, biologists are still puzzled by the existence of animal personality. While recent studies support a link between cognition and personality, the directionality of this relationship still needs to be clarified. Early-life experiences can affect adult behaviour, and among these, cognitive stimulation has been suggested theoretically to influence personality. Yet, the influence of early cognitive stimulation has rarely been explored in empirical investigations of animal behaviour and personality. We investigated the effect of early cognitive stimulation on adult personality in the red junglefowl (Gallus gallus). To this end, we assessed adult behaviour across a number of personality assays and compared behaviour of individuals previously exposed to a series of learning tasks as chicks, with that of control individuals lacking this experience. We found that individuals exposed to early stimulation were, as adults, more vigilant and performed fewer escape attempts in personality assays. Other behaviours describing personality traits in the fowl were not affected. We conclude that our results support the hypothesis that early stimulation can affect aspects of adult behaviour and personality, suggesting a hitherto underappreciated causality link between cognition and personality. Future research should aim to confirm these findings and resolve their underlying dynamics and proximate mechanisms.

Managing landscapes for multiple objectives: alternative forage can reduce the conflict between deer and forestry

Deer (Cervidae) cause considerable damage to forest plantations, crops, and protected habitats. The most common response to this damage is to implement strategies to lower population densities. However, lowering deer density may not always be desirable from hunting, recreational, or conservation perspectives. Therefore, knowledge is needed about additional factors beyond deer density that affect damage levels, and management actions that consider competing management goals. We studied the relationships between levels of bark-stripping by red deer (Cervus elaphus) on Norway spruce (Picea abies) and (1) relative deer density indices (pellet group count and deer harvest data), (2) availability of alternative natural forage (cover of forage species) and (3) proportion forest in the landscape, both at a forest stand scale and at a landscape scale. Extensive variation in damage level was evident between the six study areas. On a stand scale, the proportion of spruce damaged was positively related to pellet group density, indicating the importance of local deer usage of stands. In addition, available alternative forage in the field layer within spruce stands and proportion forest surrounding stands was negatively related to damage level. On the landscape scale, damage level was negatively related to availability of forage in the field and shrub layers and proportion forest, but was not related to any of the relative deer density indices. Increasing alternative forage may thus decrease damage and thereby reduce conflicts. Additionally, the proportion of forest in the landscape affects damage levels and should thus be considered in landscape planning and when forecasting damage risk. The relationship between local deer usage of stands and damage level suggests that future studies should try to separate the effects of local deer usage and deer density.

Current Husbandry of Red Pandas (Ailurus fulgens) in Zoos

The endangered red panda (Ailurus fulgens) is held in zoos worldwide. The aim of this study was to examine how red pandas are kept and managed in captivity and to compare it with the management guidelines. Sixty-nine zoos, mainly from Europe but also from North America and Australia/New Zealand, responded to our survey. The results revealed that in general zoos follow the management guidelines for most of the investigated issues. The average enclosure is almost four times larger than the minimum size recommended by the management guidelines, although seven zoos have smaller enclosures. About half the zoos do not follow the guidelines concerning visitor access and number of nest boxes. Other issues that may compromise animal welfare include proximity of neighboring carnivore species and placement of nest boxes.

A comparison of animal personality and coping styles in the red junglefowl

There is an increased focus in biology on consistent behavioural variation. Several terms are used to describe this variation, including animal personality and coping style. Both terms describe bet ...

Heritabilities and co-variation among cognitive traits in red junglefowl

Natural selection can act on between-individual variation in cognitive abilities, yet evolutionary responses depend on the presence of underlying genetic variation. It is, therefore, crucial to determine the relative extent of genetic versus environmental control of these among-individual differences in cognitive traits to understand their causes and evolutionary potential. We investigated heritability of associative learning performance and of a cognitive judgement bias (optimism), as well as their covariation, in a captive pedigree-bred population of red junglefowl (Gallus gallus, n > 300 chicks over 5 years). We analysed performance in discriminative and reversal learning (two facets of associative learning), and cognitive judgement bias, by conducting animal models to disentangle genetic from environmental contributions. We demonstrate moderate heritability for reversal learning, and weak to no heritability for optimism and discriminative learning, respectively. The two facets of associative learning were weakly negatively correlated, consistent with hypothesized trade-offs underpinning individual cognitive styles. Reversal, but not discriminative learning performance, was associated with judgement bias; less optimistic individuals reversed a previously learnt association faster. Together these results indicate that genetic and environmental contributions differ among traits. While modular models of cognitive abilities predict a lack of common genetic control for different cognitive traits, further investigation is required to fully ascertain the degree of covariation between a broader range of cognitive traits and the extent of any shared genetic control. This article is part of the theme issue ‘Causes and consequences of individual differences in cognitive abilities’.

Evolution of brain–body allometry in Lake Tanganyika cichlids

Brain size is strongly associated with body size in all vertebrates. This relationship has been hypothesized to be an important constraint on adaptive brain size evolution. The essential assumption behind this idea is that static (i.e., within species) brain–body allometry has low ability to evolve. However, recent studies have reported mixed support for this view. Here, we examine brain–body static allometry in Lake Tanganyika cichlids using a phylogenetic comparative framework. We found considerable variation in the static allometric intercept, which explained the majority of variation in absolute and relative brain size. In contrast, the slope of the brain–body static allometry had relatively low variation, which explained less variation in absolute and relative brain size compared to the intercept and body size. Further examination of the tempo and mode of evolution of static allometric parameters confirmed these observations. Moreover, the estimated evolutionary parameters indicate that the limited observed variation in the static allometric slope could be a result of strong stabilizing selection. Overall, our findings suggest that the brain–body static allometric slope may represent an evolutionary constraint in Lake Tanganyika cichlids.

Environmental complexity buffers against stress-induced negative judgement bias in female chickens

Cognitive processes are often biased by emotions. In humans, affective disorders are accompanied by pessimistic judgement, while optimistic judgement is linked to emotional stability. Similar to humans, animals tend to interpret ambiguous stimuli negatively after experiencing stressful events, although the long-lasting impact on judgement bias has rarely been investigated. We measure judgement bias in female chicks (Gallus gallus domesticus) after exposure to cold stress, and before and after exposure to additional unpredictable stressors. Additionally, we explore if brain monoamines can explain differences in judgement bias. Chicks exposed to cold stress did not differ in judgement bias compared to controls, but showed sensitivity to additional stressors by having higher motivation for social reinstatement. Environmental complexity reduced stress-induced negative judgement bias, by maintaining an optimistic bias in individuals housed in complex conditions even after stress exposure. Moreover, judgement bias was related to dopamine turnover rate in mesencephalon, with higher activity in individuals that had a more optimistic response. These results demonstrate that environmental complexity can buffer against negative effects of additive stress and that dopamine relates to judgement bias in chicks. These results reveal that both internal and external factors can mediate emotionally biased judgement in animals, thus showing similarities to findings in humans.