Low food availability during gestation enhances offspring post-natal growth, but reduces survival, in a viviparous lizard

The environment experienced by a mother can have profound effects on the fitness of her offspring (i.e., maternal effects). Maternal effects can be adaptive when the developmental environments experienced by offspring promote phenotypes that provide fitness benefits either via matching offspring phenotype to the post-developmental environment (also known as anticipatory maternal effects) or through direct effects on offspring growth and survival. We tested these hypotheses in a viviparous lizard using a factorial experimental design in which mothers received either high or low amounts of food during gestation, and resultant offspring were raised on either high or low amounts of food post-birth. We found no effect of food availability during gestation on reproductive traits of mothers or offspring traits at birth. However, offspring from mothers who received low food during gestation exhibited a greater increase in condition in the post-birth period, suggesting some form of priming of offspring by mothers to cope with an anticipated poor environment after birth. Offspring that received low food during gestation were also more likely to die, suggesting a trade-off for this accelerated growth. There were also significant effects of post-birth food availability on offspring snout-vent length and body condition growth, with offspring with high food availability post birth doing better. However, the effects of the pre- and post-natal resource evnironment on offspring growth were independent on one another, therefore, providing no support for the presence of anticipatory maternal effects in the traditional sense.

Family aggression in a social lizard

The evolution of family living is underpinned by conflict and cooperation between family members. While family groups can be maintained by reducing conflict between parents and offspring, interactions between siblings may play an equally important role. Here, we compared the level of aggressive interactions between siblings to that between parents and their offspring in the family living skink Liopholis whitii. Aggressive interactions occurred much more frequently between siblings and between fathers and offspring than between mothers and their offspring. These results suggest that ecological and social conditions that reduce conflict between siblings and between males and offspring will be fundamental in the evolutionary maintenance and diversification of family living in these lizards.

Early social environment influences the behaviour of a family-living lizard

Early social environment can play a significant role in shaping behavioural development. For instance, in many social mammals and birds, isolation rearing results in individuals that are less exploratory, shyer, less social and more aggressive than individuals raised in groups. Moreover, dynamic aspects of social environments, such as the nature of relationships between individuals, can also impact the trajectory of development. We tested if being raised alone or socially affects behavioural development in the family-living tree skink, Egernia striolata. Juveniles were raised in two treatments: alone or in a pair. We assayed exploration, boldness, sociability and aggression repeatedly throughout each juvenile's first year of life, and also assessed social interactions between pairs to determine if juveniles formed dominant-subordinate relationships. We found that male and/or the larger skinks within social pairs were dominant. Developing within this social environment reduced skink growth, and subordinate skinks were more prone to tail loss. Thus, living with a conspecific was costly for E. striolata. The predicted negative effects of isolation failed to materialize. Nevertheless, there were significant differences in behavioural traits depending on the social environment (isolated, dominant or subordinate member of a pair). Isolated skinks were more social than subordinate skinks. Subordinate skinks also became more aggressive over time, whereas isolated and dominant skinks showed invariable aggression. Dominant skinks became bolder over time, whereas isolated and subordinate skinks were relatively stable in their boldness. In summary, our study is evidence that isolation rearing does not consistently affect behaviour across all social taxa. Our study also demonstrates that the social environment plays an important role in behavioural development of a family-living lizard.

Repeatable intra-individual variation in plasma testosterone concentration and its sex-specific link to aggression in a social lizard

Individual hormone profiles can be important generators of phenotypic variation. Despite this, work on the consequences of hormone profiles has traditionally ignored the large inter-individual variation within natural populations. However, recent research has advocated the need to explicitly consider this variation and address its consequences for selection. One of the key steps in this process is examining repeatability in hormone profiles and their links to behavioral traits under selection. In this study we show that individuals within a free-ranging population of the Australian lizard Egernia whitii exhibit temporal repeatability in their circulating baseline testosterone concentrations as well as their aggressive response towards conspecific intruders. Furthermore, we show significant, sex-specific links between testosterone and aggression. Specifically, testosterone and aggression is negatively linked in males, while there is no relationship in females. As conspecific aggression has significant consequences for fitness-related traits (parental care, mating strategies) in this species, inter-individual variation in testosterone concentrations, through their effects on aggression, could have important implications for individual fitness. We discuss the potential causes and consequences of hormonal repeatability as well as provide explanations for its sex-specific links with aggression. Specifically, we suggest that these patterns are the result of alternative hormonal pathways governing aggression within Egernia and may indicate a decoupling of aggression and testosterone across the sexes.