The effects of relatedness and developmental temperature across the life history stages of a marine invertebrate

Supervisor: Marc Rius (University of Southampton, UK)
Genetic diversity can exert considerable influence on populations through its effects on organism fitness traits. In some scenarios populations benefit from increased diversity and in other cases, genetic diversity has a negative impact on fitness traits. Differences between the effects of diversity can be viewed in terms of two hypotheses; firstly that genetic diversity decreases competitive interactions between conspecifics by increasing division of resources (the resource partitioning hypothesis), or alternatively that reduced genetic diversity amongst closely related individuals fosters cooperative behaviour that increases lifetime fitness (the kin selection hypothesis). The effects of genetic diversity may manifest in any stage of an organisms life history and may persist between stages so that factors affecting fitness traits during one life history stage may have important effects during some, or all, subsequent stages. Diversity of phenotypes among offspring may be effected directly by genetic effects, or indirectly, through the interaction between the genome and the environment. In ectotherms temperature is arguably the most important environmental variable because of its pervasive effects on organism physiology as well as phenotypic expression. This study experimentally constructed populations of larvae of Ciona intestinalis with differing levels of relatedness (full siblings, half siblings and unrelated larvae) and ensured they experienced different, environmentally relevant temperatures (15 °C, 18 °C and 21 °C), during embryonic and larval development. The effects of both relatedness and development temperature on key fitness traits were investigated. The temperature experienced during embryonic an larval development had persistent effects across multiple life history stages, influencing the rates of settlement success in larvae and affecting the post-metamorphic final size of juveniles. Relatedness also had a significant effect on fitness, with full siblings and half siblings exhibiting significantly greater survival during the first week in the field. The increased survival of full siblings was evident of the full course of the experiment. After four weeks in the field, full siblings were significantly more likely to survive than either half siblings or unrelated individuals. The results are discussed in terms of both their ecological consequences for population structure and the evidence they provide to either support, or refute evolutionary hypotheses regarding the influence of genetic diversity.

Keywords: Phenotypic diversity, carry-over effects, sibling competition, dispersal