Personality traits and the effects of DHA supplementation in the budgerigar (Melopsittacus undulatus)

Evolutionary trade-off between innate and acquired immune defences in birds

BACKGROUND

The development, maintenance, and use of immune defences are costly. Therefore, animals face trade-offs in terms of resource allocation within their immune system and between their immune system and other physiological processes. To maximize fitness, evolution may favour investment in one immunological defence or subsystem over another in a way that matches a species broader life history strategy. Here, we used phylogenetically-informed comparative analyses to test for relationships between two immunological components. Natural antibodies and complement were used as proxies for the innate branch; structural complexity of the major histocompatibility complex (MHC) region was used for the acquired branch.

RESULTS

We found a negative association between the levels of natural antibodies (i.e., haemagglutination titre) and the total MHC gene copy number across the avian phylogeny, both at the species and family level. The family-level analysis indicated that this association was apparent for both MHC-I and MHC-II, when copy numbers within these two MHC regions were analysed separately. The association remained significant after controlling for basic life history components and for ecological traits commonly linked to pathogen exposure.

CONCLUSION

Our results provide the first phylogenetically robust evidence for an evolutionary trade-off within the avian immune system, with a more developed acquired immune system (i.e., more complex MHC architecture) in more derived bird lineages (e.g., passerines) being accompanied by an apparent downregulation of the innate immune system.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Cognition, personality, and stress in budgerigars, Melopsittacus undulatus

To study the fitness effects of individual variation in cognitive traits, it is paramount to understand whether traits such as personality and physiological stress influence cognitive performance. We first tested whether budgerigars showed both consistent personalities and cognitive performance across time and tasks. We tested object and food neophobia, and exploratory behavior. We measured cognitive performance in habituation, ability to solve foraging problems, spatial memory, and seed discrimination tasks. Budgerigars showed consistency in their neophobic tendencies and these tendencies were associated with their exploratory behavior. Birds were also consistent in how they performed in most of the cognitive tasks (temporal consistency), but were not consistent in their performance across tasks (context consistency). Neither corticosterone levels (baseline and stress-induced) showed a significant relationship with either cognitive or personality measures. Neophobic and exploratory tendencies determined the willingness of birds to engage only in the seed discrimination task. Such tendencies also had a significant effect on problem-solving ability. Our results suggest that consistent individual differences in cognitive performance along with consistent differences in personality could determine response to environmental change and therefore have important fitness consequences.

Personality types in Budgerigars, Melopsittacus undulatus

The current study further characterized personality types in Budgerigars, an avian model that only recently demonstrated individual consistencies in behavior (Callicrate et al., 2011). Several methodological techniques, commonly used in previous examinations of other animal models, were employed. Specifically, Phase I assessed the relationship between Budgerigar personality types and Hypothalamic-Pituitary-Adrenal (HPA) activity, while Phase II sought to examine the persistence of individual behavioral tendencies across varying testing contexts. In comparison to other species, our findings failed to illustrate a clear relationship between Budgerigar personality types and concentrations of corticosterone. However, results provided significant evidence for the consistency of personalities across multiple contexts. In sum, our investigation further defined the expression of personality in the Budgerigar and substantiated the claim for individual tendencies in this species.

Testosterone stimulates the expression of male-typical socio-sexual and song behaviors in female budgerigars (Melopsittacus undulatus): An experimental study

The hormonal control of sex differences in behavior has been extensively studied, particularly in mammals and birds. Studies have shown that the activational potential of the androgenic sex steroid testosterone (T) on male-typical behaviors in females seems to be species- as well as behavior-specific in birds. It is therefore important to study the activational effects of T in a great variety of bird species and on a wide range of behaviors, preferably in social conditions that favor their expression. Here, we investigated the activational effects of T on vocal, socio-sexual (i.e. affiliative and non-vocal courtship behaviors), aggressive and approach behavior in females of the budgerigar, Melopsittacus undulatus, a highly social monogamous parrot species. We experimentally supplemented T-females with male-like plasma T levels compared to controls. First, we observed females when they were individually housed. We found that T-females performed male-like levels of warbling song, sang significantly longer, but not more song bouts and produced more socio-sexual behaviors than controls. Then, we consecutively confronted females with a female, a dummy, and a male conspecific. T-females showed a significantly shorter latency to interact in all three social contexts. In both intrasexual and intersexual contexts, T-females performed significantly higher levels of approach and socio-sexual behavior, including "mounting (attempts)", a strictly male behavior, which was not observed in control females. Aggression in a non-reproductive context did not appear to be sensitive to T supplementation. Our data indicate that in the budgerigar even marked sex differences in socio-sexual behavior may depend on the activational effects of T, while this is generally not the case in other species.