SFB-TRR 212

Fitness consequences of niche choice and conformance in a colonially breeding marine mammal: roles of the social environment, genetic quality and offspring behaviour

Population density is an important niche dimension that varies dynamically over both space and time. Consequently, selection should favour plastic responses such as niche choice (individuals selecting niches to which their own phenotypes are a good fit) and niche conformance (individuals altering their behaviour or physiology to fit their niche). These responses could have major implications for individual fitness, ecological and evolutionary dynamics, adaptation to environmental change and evolutionary potential, yet they remain poorly understood in natural populations. Furthermore, recent studies have identified an important component of individual fitness in the form of inbreeding, a measure of genetic quality, but it remains unclear how this may influence niche choice and niche conformance.

An unprecedented opportunity to study niche choice and conformance in the wild is provided by a long term study of Antarctic fur seals (Arctocephalus gazella) breeding at South Georgia in the south west Atlantic. Here, naturally occurring variation in the density of breeding colonies presents opportunities and challenges to fur seal mothers and their pups, as high density colonies offer breeding females greater freedom to exercise mate choice but are also associated with increased social stress and offspring mortality. Female niche choice thus determines the social environment of their offspring, leading to the prediction that pups should maximise their fitness by altering their behaviour and physiology accordingly. In turn, individual responses could conceivably depend on the level of inbreeding, as this correlates with virtually every fitness component so far measured in this species.

This project will exploit a natural experiment provided by two neighboring fur seal colonies of high and low density to evaluate the fitness consequences of maternal niche choice, offspring niche conformance and genetic quality. This will be achieved by collecting highly detailed observational and biometric data from mother-offspring pairs and using next generation sequencing to accurately quantify each individual's genomic inbreeding coefficient. Furthermore, behavioural, endocrine, immune, transcriptomic and epigenetic data will be combined to investigate the mechanistic basis of niche conformance. The unusually large and diverse dataset generated by this project will place me in a unique position to determine how maternal niche choice affects offspring growth and survivorship, as well as to evaluate how genetic quality interacts with behaviour, immunology, endocrinology and gene expression to facilitate niche conformance. The following hypotheses (among others) will be tested:

1. Maternal choice of high versus low density niches affects offspring fitness (growth and survival).
2. Offspring conform behaviourally to their respective niches, with traits such as mobility and aggressiveness being preferentially associated with fitness under high density conditions.
3. If plasticity is constrained by genetic quality, outbred individuals should exhibit greater niche conformance and thus have higher fitness.
4. Niche conformance is facilitated by hormonally mediated maternal effects.
5. Niche conformance is associated with changes in gene expression.
6. Niche conformance is mediated by heritable epigenetic changes, thus providing a potential mechanism for trans-generational adaptation.

In summary, this project will provide a novel evolutionary genetic perspective on the individualised niche while also generating detailed insights into how genetic, epigenetic, physiological and behavioural factors contribute towards fitness variation and potentially also long-term adaptation.