Meeting Abstract
Offspring size and number are essential components of individual fitness. However, the ideal phenotype (producing many, large eggs) generally cannot be achieved because individuals have limited energy to invest in reproduction or because the two traits are negatively genetically correlated. Such trade-offs are often studied at the phenotypic level, but mangrove rivulus fish (Kryptolebias marmoratus) have a unique, mixed-mating reproductive system that allows for isolated analysis of the genetic contribution to phenotypic variation with replication within a genotype. We can thus determine whether genetic trade-offs exist between fitness-related traits and how this might impact life history evolution. We hypothesized that there would be significant genetic variation underlying life history traits and their relationships. Eggs were collected once weekly for 6 weeks from 14 genotypes with 5 replicate fish/genotype, and the number of eggs laid by each fish was recorded. Eggs were photographed and size (diameter) quantified with ImageJ software. We predicted a strong trade-off between egg size and egg number and that there would be a significant negative genetic correlation between these life history traits, allowing us to project evolutionary responses to natural selection. Egg size and egg number both showed significant among-genotype variance (i.e., were heritable). At the phenotypic level, egg size and egg number were positively correlated but preliminary evidence suggests that the relationship is reversed at the genetic level. These results raise the question of how the environment alters relationships between fitness-related life history characteristics.
