Are lateralized and bold fish optimistic or pessimistic?

Cognitive bias is defined as the influence of emotions on cognitive processes. The concept of the cognitive judgement bias has its origins in human psychology but has been applied to animals over the past 2 decades. In this study we were interested in determining if laterality and personality traits, which are known to influence learning style, might also be correlated with a cognitive bias in the three-spined sticklebacks (Gasterosteus aculeatus). We used the judgement bias test with the go/no-go procedure where fish were first trained to discriminate between a black and white card and, after reaching a minimum learning criterion, tested their response to an ambiguous card (grey). Optimistic subjects were expected to have a high expectation of reward associated with an ambiguous stimulus, whereas pessimistic subjects a high expectation of non-reward. We used an emergence and a mirror test to quantify boldness and laterality, respectively. We hypothesised that male, bolder and more strongly lateralized fish would be more optimistic than female, shy and less strongly lateralised fish. We found that males and more strongly lateralized fish were more optimistic than females and less strongly lateralized fish. In addition, bold males were more optimistic than shy males as we predicted, but females showed the opposite pattern. Finally, fish trained on the black colour card learned the training task faster than those trained on a white card. Our results indicate that both laterality and personality traits are linked to animals' internal states (pessimistic or optimistic outlooks) which likely has broad implications for understanding animal behaviour particularly in a welfare context.

In ovo testosterone treatment reduces long-term survival of female pigeons: a preliminary analysis after nine years of monitoring.

Early exposure to steroid hormones, as in the case of an avian embryo exposed yolk testosterone, can impact the biology of an individual in different ways over the course of its life. While many early-life effects of yolk testosterone have been documented, later-life effects remain poorly studied. We followed a cohort of twenty captive pigeons hatched in 2005. Half of these birds came from eggs with experimentally increased concentrations of testosterone; half came from control eggs. Preliminary results suggest non-random mortality during the birds' first nine years of life. Hitherto, all males have survived, and control females have survived better than testosterone-treated ones. Despite inherent challenges, studies of later-life consequences of early-life exposure in longer-lived species can offer new perspectives that are precluded by studies of immediate outcomes or shorter-lived species.

Examining a pathway for hormone mediated maternal effects--yolk testosterone affects androgen receptor expression and endogenous testosterone production in young chicks (Gallus gallus domesticus).

In vertebrates maternal androgens can substantially influence developing offspring, inducing both short and long term changes in physiology and behavior, including androgen sensitive traits. However, how the effects of maternal hormones are mediated remains unknown. Two possible pathways are that maternal androgens affect parts of the hypothalamus-pituitary-gonadal axis (HPG axis) or the sensitivity to androgens by affecting androgen receptor (AR) densities within the brain. To investigate both pathways, testosterone within the physiological range or vehicle only was injected into the egg yolk of unincubated chicken eggs and AR mRNA expression in different brain nuclei as well as plasma testosterone levels were measured in two week old male and female chicks that had hatched from these eggs. Our results showed a significant sex difference in plasma testosterone levels with males showing higher levels than females. Furthermore, AR mRNA expression as well as plasma testosterone levels were significantly lower in chicks hatched from testosterone treated eggs. These results suggest a compensatory mechanism for avoiding potential detrimental effects of high testosterone levels.

Epigenesis of behavioural lateralization in humans and other animals.

Despite several decades of research, the epigenesis of behavioural and brain lateralization is still elusive, although its knowledge is important in understanding developmental plasticity, function and evolution of lateralization, and its relationship with developmental disorders. Over the last decades, it has become clear that behavioural lateralization is not restricted to humans, but a fundamental principle in the organization of behaviour in vertebrates. This has opened the possibility of extending descriptive studies on human lateralization with descriptive and experimental studies on other vertebrate species. In this review, we therefore explore the evidence for the role of genes and environment on behavioural lateralization in humans and other animals. First, we discuss the predominant genetic models for human handedness, and conclude that their explanatory power alone is not sufficient, leaving, together with ambiguous results from adoption studies and selection experiments in animals, ample opportunity for a role of environmental factors. Next, we discuss the potential influence of such factors, including perinatal asymmetrical perception induced by asymmetrical head position or parental care, and social modulation, both in humans and other vertebrates, presenting some evidence from our own work on the domestic chick. We conclude that both perinatal asymmetrical perception and later social modulation are likely candidates in influencing the degree or strength of lateralization in both humans and other vertebrates. However, in most cases unequivocal evidence for this is lacking and we will point out further avenues for research.