Ins. Soc. 43:309-317 (1996) 1015-1621/96/030309-09 $1.50 + 0.20/0 9 1996 Birkh~iuser Verlag, Basel Researeh a~ide Temporal and spatial variation in reproduction in the facultatively polygynous ant Myrmica tahoensis (Hymenoptera: Formicidae) J.D. Evans* Department of Biology, Universityof Utah, Salt Lake City, UT84112, USA and Rocky Mountain Biological Laboratory, P.O. Box 519, CrestedButte, CO 81224, USA Key words: Myrmica tahoensis, sex ratio, relatedness, microsatellite DNA, sex allocation. Summary Sex allocation was measured across six seasons in colonies of the facultatively polygynous ant Myrmica tahoensis. The overall proportion of colonies that produced sexuals was constant throughout the study, but population-level sex ratios varied considerably. In 1991, 1993, and 1995, a significantly greater proportion of colonies produced females than in 1990, 1992, and 1994. Sex ratios were similar across six sites within individual years, suggesting a population-wide cause of sex-ratio variation. Individual colonies tended, on average, to produce similar sex ratios in con- secutive years. Within-colony genetic relatedness, while strongly correlated with sex ratios within years, did not explain the year-to-year variation. It is suggested that extrinsic factors can limit the production of female sexuals, even when genetic relatedness is high enough to favor female production. Introduction In the eusocial Hymenoptera, intercolony variation in sex allocation might reflect conflicts among individuals within nests (Trivers and Hare, 1976; Boomsma and Grafen, 1990, 1991), variation in resource availability (Nonacs, 1986), or competi- tion among sexual offspring (Frank, 1987). In the facultatively polygynous ant Myrmica tahoensis, sex-ratio variation across colonies is strongly correlated with differences in genetic relatedness (Evans, 1995). Colonies that produce female sexuals (gynes) have higher levels of genetic relatedness (and a greater relatedness asymmetry between workers and the female and male sexuals they rear; Trivets and * Current address: Department of Entomology, University of Georgia, Athens, GA 30602, USA e-maih evans@bscr.uga.edu