California Gulls nesting at Mono Lake (ML) have a modal clutch size of two eggs, while at Great Salt Lake (GSL) the mode is three. We used starch gel electrophoresis to determine whether the populations are genically different. Average individual heterozygosity at ML averages 2.67% and at GSL 2.95%, both slightly below the average for other birds. The average number of alleles per locus is 1.2 for both sites. Variation between sites is insignificant, with a genetic distance of 0.001 and an FST of 0.0044. Therefore, the clutch size differences are without genic correlates. In fact, at the loci studied, the two samples are indistinguishable from two random samples drawn from a panmictic unit. Five morphological characteristics also exhibited little between-site difference, in agreement with the electrophoretic analysis. A marked historical reduction (bottleneck) in the Mono Lake population seems not to have affected levels of genetic variation. We conclude that the clutch size differences are either recently evolved, and determined by loci not surveyed by us, or they are environmentally induced. At the population level, these gulls are similar to passerines in terms of heterozygosity and among population differentiation.
Bibliographical noteFunding Information:
Acknowledgements - Funds for electrophoresis were provided by an Alexander Grant-in-Aid, Museum of Vertebrate Zoology. Field work was supported by a Frank M. Chapman Memorial Fund Grant (DVVVV) and contracts from the California Department of Fish and Game, and the United States Fish and Wildlife Service. Field assistance was provided by Michael Green, Jasper Hand, Marsha Heidt, Ronald Mumme and Virginia Norris. Logistic support at ML was provided by the California Department of Fish and Game. ML field work was conducted under permit from the Bureau of Land Management. Field work at GSL was conducted on the properW of the Morton Salt Company, with the kind permission and assistance of Mr. Norman Helgren and his staff. GSL base camp was provided by Amber and Tietjen Openshaw. Don Paul of the Utah Division of Wildlife Resources allowed us access to unpublished information on Great Salt Lake gull populations. George F. Barrowclough performed the test of the IC model against our data. George F. Barrowclough and Allan Larson offered useful advice on the project. Michael Braun, David A. Good, Ned K. Johnson, Ronald Mumme, and Kay P. Yanev provided helpful comments on the manuscript.
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- California Gulls
- Larus californicus
- clutch size
- gene flow
- genetic distance