UC Riverside

Food availability during the juvenile stage can a have profound impact on adult performance and fitness. Low food availability early in life generally leads to slower growth and development and maturation at an older age and smaller size, which can then lead to reduced survival and lifetime reproductive success. There is increasing evidence that organisms can respond to these early setbacks and in ways that might be adaptive. However, our current understanding of the diversity of compensatory mechanisms utilized, the costs and benefits of these responses, and the relative importance of these responses in the wild is still in a nascent stage. For this dissertation, I investigated how juvenile food availability influences adult reproductive decisions and success in Trinidadian guppies (Poecilia reticulata).

First, I examined whether juvenile compensatory growth has negative consequences for reproduction. I found that juvenile compensatory growth did not affect adult growth rates, litter production rates, or investment in offspring size, but had negative effects on litter size. Second, I investigated whether individuals during the adult stage can mitigate the negative effects of early setbacks caused by low food availability. I found that females reared on low food matured at a later age, a smaller size and with less energy reserves than females reared on high food. In response to this setback, they changed their investment in growth, reproduction and fat storage throughout the adult stage such that they were able to catch up in body size, increase their reproductive output and restore their energy reserves to levels comparable to those of females reared on high food. Finally, I explored the relative effects of juvenile versus adult environmental conditions on adult growth strategies in the wild. I found that events occurring during early and later parts of an individual's ontogeny both had important consequences for adult growth strategies, but the direction of their influence differed. Poor conditions during the juvenile stage had a positive effect on adult growth rates, while those same conditions in the recent past and in the present had a negative effect on adult growth.