I’m so happy that our work on the fitness effects of sex ratio in flour beetles is finally out in the American Naturalist! I say “finally” because this work represents multiple years of hard work by a large-ish team, including people from Radhika Venkatesan’s lab at NCBS. In fact, apart from me, all other lab members who are authors on this paper have long left the lab for other pursuits. Altogether, this project has been a fine example of the typical scientific process: you observe something strange; you formulate some hypotheses to explain the observation given prior work in the area; you test these hypotheses and find that none of them explain the pattern; you mope around frustrated for a while; eventually you come up with new hypotheses, perhaps after expanding your “related prior work” universe; and finally you get somewhere and learn something new!
In this case, we found that flour beetle females have higher fitness in male-biased groups, contradicting prior results in various animals that female fitness is lower in male-biased groups. Typically, most explanations of female fitness given biased sex ratio have revolved around sexual conflict. After testing many hypotheses that might explain this pattern, we found that female fitness is inversely proportional to the number of females in the group, with almost no role for males. We could also reject potential mechanisms that relied on direct interactions between individuals – including sexual competition, a crowd favourite – because we saw that flour that had been used by many females elicited the same response as the females themselves. Radhika’s lab helped us pinpoint female-secreted benzoquinones as the primary chemicals responsible for this indirect, flour-mediated effect. Quinones are toxic compounds secreted by flour beetles; females produce more quinones than males, and increase production in the presence of other females or high quinone concentration. Apart from governing female fitness effects in the context of sex ratio, the positive feedback in quinone production may thus allow it to broadly regulate population density. We are very excited about this possibility, and in the coming years we hope to figure out the physiological effects, and broader evolutionary impacts, of quinones .