Vol. 62: 211-217, 1990 MARINE ECOLOGY PROGRESS SERIES Mar. Ecol. Prog. Ser. Published April 19 Multilocus heterozygosity and sexual selection in the brine shrimp Artemia franciscana C. Zapata', G. Gajardo", J. A. Beardmore School of Biological Sciences, University College of Swansea, Singleton Park, Swansea SA2 8PP. United Kingdom ABSTRACT: A study to test for an association between multilocus heterozygosity and male sexual selection was conducted in an experimental population of the brine shrimp Artemia franclscana. A significant positive correlation between male mating success and heterozygosity was detected This is the first report of an association between male sexual selection and multilocus heterozygosity. The results add to the evidence suggesting that a correlation of this type applies to all components of total Darwinian fitness. The observed correlation is interpreted in the light of the major hypotheses proposed to explain such correlations. INTRODUCTION In the last decade much work has been devoted to searching for correlations between multilocus hetero- zygosity and traits related to fitness in a variety of species including many from marine environments (see reviews by Mitton & Grant 1984, Zouros & Foltz 1987). Multilocus heterozygosity has been studied mainly in relation to growth rate (Zouros et al. 1980, Ledig et al. 1983, Koehn & Caffney 1984, Koehn et al. 1988, Alvarez et al. 19891, but also with respect to developmental stability (Leary et al. 1983, 1984), via- bility (Beardmore & Ward 1977, Zouros et al. 1983. Diehl & Koehn 1985, Alvarez et al. 1989), fecundity (Schaal & Levin 1976, Rodhouse et al. 1986), response to physiological stress (Koehn & Shumway 1982) and, at an interpopulation level, a range of fitness compo- nents including fecundity (Quattro & Vrijenhoek 1989). Positive associations between multilocus allozyme heterozygosity and fitness have, thus, fre- quently been detected although contrary evidence has also been reported (Mukai et al. 1974, McAndrew et al. 1982). Present address: Departamento de Biologia Fundamental, Facultad de Biologia, Universidad de Santiago de Com- postela, Santiago de Compostela, Spain ' ' Present address: Departamento de Acuicultura y Alimen- tos, Instituto Profesional de Osorno, Casilla 933, Osorno, Chile O Inter-Research/Printed in F. R. Germany To our knowledge, the relationship between mul- tilocus allozyme heterozygosity and male sexual selec- tion has not yet been tested in a way comparable to other fitness components. Many studies have been addressed to examining the effect of protein variation on sexual selection but not specifically to test for an association between multilocus protein heterozygosity and sexual selection (Marinkovic & Ayala 1975a, b, Christiansen 1977, Eanes et al. 1977, Aslund & Rasmu- son 1976, Carter & Watt 1988). In addition, evidence based largely on data from Drosophila shows that fertil- ity (which includes sexual selection and fecundity) is at least as important as viability in determining total Dar- winian fitness (Polivanov & Anderson 1969, Sved & Ayala 1970, Marinkovic & Ayala 1975a, b, Anderson et al. 1979, Brittnacher 1981). More detailed evidence from some studies indicates that sexual selection may be the most important single fitness component of net fitness (Prout 1971a, b, Bungaard & Christiansen 1972). The influence of heterozygosity on female reproduc- tive success in Artemia has, however, been examined recently (Gajardo & Beardmore 1989). The results obtained show clearly that greater heterozygosity con- fers both greater overall reproductive success and greater capacity to switch resources into the ovivivi- parous mode of reproduction. This paper considers the relationship between multilocus allozyme heterozygosity and male sexual selection in an experimental population of Arternia franciscana.