Predation and Body Size Variation

I have examined correlations among platyfish field populations between predation risk and body size and found extensive body size variation between populations in Central America. Adult platyfish from populations with no piscivorous fish (N = 3) are smaller in size than populations in which piscivorous fish are present (N = 6, P = 0.039). This result suggests that predation has an important effect on the evolution of body size. This difference provides the basis to examine how selection and environmental variation has produced different body size optima. The existence of the well-studied, sexual maturation locus, the P-locus, and the availability of genetic stocks with known variation at this locus provides an unique opportunity to investigate how body size variation is affected by predation, sexual selection and generation time under controlled laboratory conditions. Pituitary alleles determine age and size at sexual maturation in X. maculatus, and, because male growth decreases precipitously at sexual maturation, variation at the P-locus also affects male lifetime body size. The fitness consequences of variation at the P-locus can be assessed by observing changes in allele frequencies under different conditions with known P-alleles linked to color markers, as discussed above. For a current NSF grant, I am considering how environmental factors affect variation at the pituitary locus by investigating how size affects mating success and predation risk, as well as quantifying changes in P-allele frequencies over time in experimental populations differing in predation-level. This work is underway and promises to take a major step towards understanding how predation and sexual selection affect this genetic polymorphism. Future research will incorporate additional allelic variation to further examine the maintenance of genetic variation at the P-locus. This project currently provides six undergraduate biology majors, including two minority students and three female students, with the opportunity to participate in research via NSF-REU funding, NSF Funding for Undergraduates from Underrepresented Groups, and independent research credit hours.

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