Abstract
Life history theory predicts how organisms will partition limited resources to optimize reproductive success. The theory argues that there is a trade-off between egg size and fecundity; organisms can allocate limited resources towards producing fewer, larger eggs, or towards producing more, smaller eggs. Fish are indeterminate growers, and fecundity commonly increases with body size of the female parent; therefore, investigating the trade-off between egg size and fecundity requires consideration of female parent size. The objective of my study is to understand the trade-off involved with producing either few large eggs or many small eggs, by determining the direct cost to fecundity associated with producing larger eggs, while considering female parent body size. To achieve this objective, I developed four hypotheses; I hypothesized that [1] larger females would produce more eggs, [2] egg size would remain constant within each individual species regardless of female parent body size, [3] a species that produces a smaller egg would lay more eggs than a species that produces larger eggs, while controlling for body size, and [4] fecundity of an individual cichlid from any species could be predicted from egg size and female parent body size. I tested my hypotheses in three chapters. For Chapter 2, I traveled to Costa Rica in January of 2022 and 2023 to test my hypothesis on Tomocichla tuba, a species that produces large eggs, by collecting egg size, female parent body size, and fecundity data from 55 nests in six rivers near La Selva Research Station in Heredia Province, Costa Rica. Data analysis consisted of two linear regressions to elucidate the relationship between fecundity and egg size, as well as between egg size and female parent body size. The data support my hypotheses that larger females produce more eggs than smaller females within a species, and that egg size remains constant within the species, regardless of female parent body size. For Chapter 3 of my study, I collected and analyzed data on a species that lays a smaller egg, namely the Convict cichlid, Amatitlania nigrofasciata, in the Evolutionary Ecology of Fishes Laboratory at California State University, Sacramento. I compared the regression between fecundity and body size of the Convict cichlid to that of Tomocichla tuba and found that the Convict cichlid produced significantly more eggs than Tomocichla tuba, when controlling for body size. For the Chapter 4 of my study, I tested my hypothesis that fecundity could be predicted by egg size and female parent body size by breeding 35 cichlid species, one individual per species, in the laboratory and obtaining a dataset of egg size, fecundity, and female parent body size. I then analyzed the relationship between egg size, fecundity, and female parent body size using a multiple regression and ultimately developed an equation for the plane of fecundity, which can be used to predict fecundity of any individual cichlid given egg size and female body size. To my knowledge, this study is the first to quantify the trade-off between fecundity and egg size in fishes by determining the direct cost to fecundity associated with producing larger eggs. This study will provide critical data for understanding cichlids.