| Popis: |
In this thesis, I explore how an individual’s environment, or the environment of its mother, affects its reproductive life-history characteristics (age at maturity, size at maturity, offspring size, offspring number). I attempt to explain observed responses using adaptive reasoning and/or mathematical modelling. I find that mean egg size decreases with increasing clutch size in Daphnia, and explore possible causes of this using a mathematical model. This pattern could be an adaptive response, if larger offspring have greater fitness advantages in food-limited environments. However, such a pattern can also result from a minimum viable egg size that is similar to the optimal egg size. I also empirically test the fitness effects of hatching from a small or large egg in Daphnia. I find that offspring from food-limited mothers are larger, but that they mature later, produce less offspring per clutch, do not produce larger offspring and produce fewer offspring per unit time. I find that the nematode parasites Strongyloides ratti and Nippostrongylus brasiliensis mature at different rates depending on the efficacy of the host immune response, but that differences are species-dependent. In addition, female N. brasiliensis suffer decreased fecundity at higher densities, but only in hosts with fully-functioning immune systems; in hosts with no thymus-based immune system, there is no density-dependent fecundity effect. This suggests that the density-dependent effects often observed in parasitic nematodes are mediated by the host immune system. This thesis reminds us that small differences in an individual’s surroundings, or even its mother’s surroundings, can profoundly affect when, how, and how successfully an animal reproduces. Often, these effects can be explained using adaptive reasoning, and/or mathematical modelling. When and how an animal reproduces is certain to have consequences for its fitness. Implications and future research directions are also discussed. |
