The influence of maternal care duration on offspring phenotypes in African cichlids

The first environment that an individual experiences is created by its parents and, for many species, the female parent has a particularly central role in caring for offspring throughout early development. Through maternal care, mothers can shape how their offspring interact with the environment and increase offspring growth and survival. Maternal care quality, as a measure of number of positive interactions, and duration, as a measure of length of time until individuals are independent, varies among individual females, possibly resulting in variation in offspring phenotypes. Investigating the effects of variation in maternal care quality or duration can provide insights into how and why offspring phenotypic variation develops. Examining maternal care effects can then increase our understanding of phenotypic variation that may affect how individuals interact with and succeed in their environment. An individual’s morphological development is at least partially influenced by its environment, and morphology can in turn shape the interaction between an individual and its environment. To begin to understand how the maternal environment influences morphological development, I investigated how natural and artificial variation in maternal mouthbrooding duration alters craniofacial shape in four African cichlid species (Chapter Two). Craniofacial shape is an important morphological trait for food acquisition, which can be highly species specific. Using geometric morphometric techniques, I found that craniofacial shape became less convex as maternal care duration decreased, but that this relationship was most pronounced in species with a generalist diet. These findings indicate that duration of maternal care may be related to food acquisition and preferences, which could lead to differential success in unpredictable environments. Behavioural traits such as boldness and aggression can be important for growth, reproduction and survival. Behavioural development can be influenced by maternal care, which also influences brain development. Brain morphology has been linked to specific behaviours, though it is not understood what role maternal care has in the development of this link. I examined the relationship between reduced maternal mouthbrooding duration and brain anatomy and the relationships among morphological variation in brain volume and behaviours (Chapters Three and Four). I also examined how a reproductively essential trait, aggression between males in a competitive environment, is related to maternal care duration (Chapter Four). Overall, I found that maternal care duration was not directly related to behaviour or brain volume in adult offspring. However, individuals reared under different maternal care durations exhibited different sets of correlated behaviours. Aggression and inactivity in reduced care individuals was positively associated with the volume of the hypothalamus, while aggression, shyness and lack of exploration in full care individuals was negatively associated with the hypothalamus (Chapter Three). Further investigation of the relationship between aggressive behaviours and the hypothalamus indicated that a greater number of bites per second was negatively associated with the volume of the hypothalamus (Chapter Four). Taken together these results suggest that maternal care duration influences the relationship between the hypothalamus and aggression. Additionally, I examined the associations among bi-parental presence during early development and aggression in sub-adult offspring (Chapter Five). Parental absence did not have a direct relationship with offspring timidity or fight escalation but did relate to offspring size and offspring size, in turn, was associated with escalation. The results of Chapters Three, Four and Five suggest that maternal care duration may be related to boldness and aggression, though it may be through different mechanisms (i.e. brain anatomy or offspring size). Furthermore, Chapters Four and Five indicated that individuals with reduced duration of parental care had greater variation in the expression of behaviours than individuals receiving full care. These differences in ranges of phenotypic variation between treatment groups, suggest that increased maternal care duration may restrict phenotypic variation and reduce plasticity within stable environments. Overall, these results suggest that variation in maternal care is related to variation in offspring development and can alter how individuals interact with their environment. Individual phenotypic variation, in terms of morphology and behaviour, is shaped by some of the earliest experiences individuals have with their environment. The morphological and behavioural variation observed could alter how individuals acquire food, protect resources such as shelter and mates, and could potentially extend to reproductive success. These findings suggest that maternal care, as the first environment offspring experience is exceedingly important to how individuals develop and interact with their environment. Furthermore, variation in maternal care duration among females may serve as pathway through which evolution may occur, due to resulting in phenotypic variation and plasticity in offspring.