| dc.description.abstract | Phenotypic plasticity is defined as the environmentally sensitive expression of alternative phenotypes produced within a single genotype. The majority of research on plasticity has been demonstrating its evolutionary implications, specifically highlighting how plasticity can drive, direct and constrain genetic evolution and how plasticity will evolve. However, our current understanding of plasticity and evolution is limited by a lack of empirical studies investigating individuals and how multiple environmental variables interact influencing the direction or the degree of the plastic response. Yet, this is important to consider in future research as population level responses are determined by how individuals respond, furthermore by studying individuals rather than populations we can quantify the extent of variation amongst individuals in which selection acts upon. Studying the response on a multivariate environment also has significant benefits if we want to improve our knowledge of phenotypic plasticity. This is because generally studies focus on manipulating only one environmental variable, yet interactions between environments alter the benefits and costs of plasticity/the optimal response to environmental change, thus potentially changing the direction or the magnitude of selection acting on plasticity.
In this thesis, I address this gap by investigating how individuals in a multivariate environment respond to environmental change using burying beetles (Nicrophorus vespilloides) as our model system. Burying beetles are considered highly plastic, largely because they reproduce exclusively on carrion, a resource that is unpredictable in space and time, meaning the environment is never consistent between breeding attempts. The aim of this thesis was therefore to explore further and in more detail, how burying beetles respond to environmental change and to investigate the importance and potential benefits of plasticity in burying beetles. Additionally, this thesis also aimed to answer two overlooked questions in research. Firstly, looking at how females respond to changes in the competitive environment and variation in resource quality, predicting that plasticity in maternal behaviour would aim to maximise offspring traits (i.e. offspring size) in a competitive environment. And secondly, assessing how individual age affects the plastic response to reproductive resource quality, in which I expected our data to follow theoretical predictions that it would be adaptive for old individuals to be unresponsive.
The results in chapter 2 revealed that parental behaviour, whether it being direct care (feeding offspring) or indirect care (carcass maintenance), significantly declined in a competitive environment, following more closely with a costly competitive hypothesis. This suggests that competitive stress limited the level of energetic resources available for maternal investment, and that evolution between the traits is potentially negatively correlated. However, contrary to the above result, the chapter also found that female burying beetles adjusted brood size adaptively, by reducing offspring number and increasing larval mass in a competitive environment, thus matching offspring phenotypes with the environment, a form of adaptive transgenerational plasticity.
In chapter 3 I demonstrate that to a certain extent plasticity is age-dependant. It was found that, on average, old individuals do not adjust their reproductive traits in relation to the size of the breeding resource (carrion), while young individuals do. However, this pattern in response is only illustrated within certain environmental conditions, as the chapter found that the results above are dependent on a population’s current and previous breeding environment. The chapter also reveals that there is substantial variation in the plastic response amongst individuals. Specifically illustrating that old individuals are responsive, demonstrating that studying at a population level doesn’t provide sufficient information to fully understand how individuals are responding to the environment. This result would therefore indicate that while age may have some effect on influencing the plastic response to environmental change, shown at a population level, it is only likely to play a minor role influencing plasticity, as individuals of the same age substantially differed in their plastic response.
In this thesis, I conclude by discussing how the results have improved our understanding of plasticity in female burying beetles and how selection may be expected to act on plasticity in such a species given our results. I also talk about how the theses has improved our broader understanding of phenotypic plasticity and how it may develop research for the future. | en_GB |
