Queen-specific selective pressures and caste dimorphism in the social wasp V. maculifrons

The mating decisions made by social insect males and females profoundly affect the structure of colonies and populations. However, few studies have used experimental approaches to understand mating behavior and mate choice in social insect taxa. This study investigated mating success in the polyandrous social wasp Vespula maculifrons. Mating trials were designed to test predictions that characteristics of body size and colony-of-origin would affect mating success. We first investigated if size differences existed among individuals and found that males from different colonies differed significantly in the size of nine morphological traits. However, male trait size was not significantly associated with male mating success. In contrast, females from different colonies differed significantly in only six of the nine measured traits, and four of these traits were associated with successful mating behaviors. Specifically, the correlated traits of gaster length, third tergum length, antennal length, and total length were positively associated with female mating success. Thus long females experience mating advantages over females that are short. We also found that males and females from one particular colony displayed significantly greater mating activity than individuals from other colonies. Thus the colony from which individuals originate plays an important role in determining mating success. Finally, our experiments failed to detect any evidence of 1 This chapter is published in Ethology (2008) 114: 340-350. J.L. Kovacs is first author, performed lab work and data analyses, and wrote the manuscript. E.A. Hoffman is second author, performed lab work, and commented on the manuscript. M.A.D. Goodisman is senior author; supervised lab work; oversaw experimental layout, data analysis, and manuscript preparation; and is corresponding author. 12 nestmate avoidance during the mating trials. Overall, our data suggest that social insect reproductives may experience differential mating success based on their phenotype or developmental environment. Introduction The females of many species mate with multiple males (polyandry; BIRKHEAD & MØLLER 1998; ARNQVIST & NILSSON 2000; EBERHARD 2000; JENNIONS & PETRIE 2000). However, polyandry is relatively rare among social hymenopteran insects (ants, some bees and wasps; STRASSMANN 2001; BROWN & SCHMID-HEMPEL 2003; KRONAUER et al. 2004). Nevertheless, polyandry has profound and far-reaching consequences on social insect ecology and evolution because of the effects that multiple mating ultimately have on colony structure and diversity (CROZIER & FJERDINGSTAD 2001; STRASSMANN 2001). Both polyandrous and monandrous females may choose particular males as mates based on the direct or indirect benefits that the males provide. For example, females may mate with males providing substantial direct benefits, such as large nuptial gifts. However, social insect males apparently do not provide these types of direct benefits (FJERDINGSTAD & KELLER 2004). Thus, it is posited that females in polyandrous social insect taxa mate multiply to obtain indirect benefits such as greater genetic variability among offspring, which may be associated with increased colony fitness (PALMER & OLDROYD 2000; BROWN & SCHMID-HEMPEL 2003). If females mate multiply to obtain indirect genetic benefits, female mate choice may be based on male traits that reflect some aspect of high fitness. These male fitness characteristics may be male specific ornaments or large size, which demonstrate a male’s genetic quality or health status (ANDERSSON 1994; ANDERSSON & SIMMONS 2006).