Research conducted for a Behavioral Ecology course in Spring 2019
Male Bean Beetles (Callosobruchus maculatus) Show a Preference for Virgin Females
McKeon, E. J., Dyer, Z., Umana, J., and Levin, I. I.
Agnes Scott College
Abstract
The male bias for choosing virgin mates has been shown in many different invertebrate species, and has many consequences for male fitness. The current study sought to explore male mate choice in Callosobruchus macalatus and to provide more evidence for the virgin mate bias. We hypothesized that male bean beetles prefer virgin mates, and we predicted that if we presented virgin male simultaneously with the choice between a virgin and a non-virgin female to mate with, the male would chose the virgin female. Our results supported a significant bias for virgin females in open field mate trials, X2(1, N = 20) = 19.80, p < 0.0001, and showed an 8:1 bias for virgin:mated females. These findings also provide many options for future research in the field.
Discussion
Our hypothesis that male bean beetles prefer virgin mates was highly supported (p < .0001), and we found that there was no influence of female size on male choice latency (p = .607). Another group of researchers in our lab investigating the effects of female and male size on mate choice and copulation success found no significant effects of female size on male choice. Therefore, we can reasonably assume that mate choice in bean beetles is at least strongly influenced by female mating status, and is in line with previous studies investigating this bias in other animal species (Baruffaldi & Costa, 2014; Burris & Dam, 2015; McNamara, Jones, & Elgar, 2004).
Our study did have a few weaknesses, including our small sample size (N=20) and the lack of knowledge about the actual mechanism(s) males use to identify female mating status, although McNamara, Jones, and Elgar (2004) suggest olfaction plays a key role in this process in a similar species, the Hide Beetle (Dermestes maculatus). However, the latter weakness is in itself a strength in that it identifies a possible avenue of research in the area of male mate choice.
Our findings also support the idea that male mate choice is a crucial aspect in increasing paternity and lowering sperm competition in polygamous species, as seen in other past studies (Archer & Elgar, 1999; Gromko & Pyle, 1978). This bias for virgin females makes sense in this context, as males who mate with virgin females are not faced with automatic sperm competition as males who mate with virgin females do. Virgin females are also often younger, which possibly could be related to an increase in fecundity. Conversely, if a male encounters an older virgin, she likely either has valuable characteristics that have allowed her to maintain this virginity into her old age, or she might live in an area with a low concentration of competing males, which could also decrease the chances of sperm competition. Either way, having a bias for virgin females is a effective, and evidently common, method males can use to assure paternity and direct fitness. Further research could be done to see if this bias exists in other species, such as avians or mammals.
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