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Sexual Selection and Resource-Accruing Abilities in Anolis garmani

Robert L. Trivers
Evolution
Vol. 30, No. 2 (Jun., 1976), pp. 253-269
DOI: 10.2307/2407700
Stable URL: http://www.jstor.org/stable/2407700
Page Count: 17
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Sexual Selection and Resource-Accruing Abilities in Anolis garmani
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Abstract

1. The social behavior of A. garmani was studied for a total of eight months during seven separate visits to a study area of nine acres in Jamaica. 2. Adult males are 2.25 times larger by weight than adult females. At all times of the year and at all sizes for which there are data males grow faster than females. Growth rates for the same individuals in different four month periods are positively correlated. 3. By measuring reproductive success as frequency of copulation, it was discovered that in adults of both sexes increasing size increases reproductive success, but that this tendency is significantly stronger in males than in females. There is no evidence that age makes an independent contribution to a male's frequency of copulation. 4. The steep slope of the function relating reproductive success to adult male size results apparently from sexual selection: males compete aggressively to occupy exclusive territories containing females. There is a strong tendency for large males to occupy correspondingly large territories which in turn contain large numbers of females. About 90% of copulations were performed by a territorial male within his territory. 5. As young males mature they tend to be found less frequently within the territories of large males. Males 105 mm and larger are almost never seen within the territories of other males in this category. Males 100-104 mm must disperse if they are still within a large male's territory and males within this size range show a significantly lower frequency of copulation than would be expected from the function relating size to reproductive success for other adult males. 6. Two homosexual copulations were observed and are described. 7. The adult sex ratio is biased in favor of females. 8. Recapture data appear to show that females survive better with increasing size up to 90 mm. Males appear to survive better up to 110 mm but probably not at larger sizes.

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