Abandoning ship – sex and dormancy strategies in Daphnia

ended

The ability to switch between sexual and asexual reproduction may be critical for many taxa when securing survival in varying environmental conditions. For these organisms, sex is often associated with harsh conditions, typically found at the end of the growing season. Sexual recombination in facultative sexuals commonly results in the formation of a dormant form that is considered a strategy to overcome adverse environmental conditions. When engaging in sex, organisms have been shown to specialize by producing males or sexual females, but not necessarily both, potentially reducing the chance of inbreeding. Sexual reproduction among those ‘gender specialists’ may vary with contrasting environments. The association between different environments and the production of a distinct phenotype (i.e., males or sexual females) suggests that sex specialisation may be adaptive. However, little is known about whether sex specialization is associated more with inbreeding avoidance or local adaptation. In the work proposed here, we will use the ecological and genomic model organism Daphnia to experimentally test if genetic variation in the production of males and ephippia is strongly environment dependent or not. Specifically, we will use a high-throughput phenotyping approach to assess genotype x environment interaction among 100 Daphnia pulex genotypes originating from a UK meta-population. We will also assess the molecular mechanisms that drive the production of males and ephippia. Using a gene expression approach, we aim to resolve the network of gene expressions that underpins the shift from diploid egg production to male and ephippia production. Obtained data will help to resolve whether inbreeding avoidance or local adaptation/dormancy underpins sexual specialisation. Findings from this work will advance our understanding of why and how facultative sexual reproduction is maintained in populations. Our conclusions will be relevant to evolutionary ecology and beyond.