A new article has brought forth the memory of a particular passage, more aside than discussion, from back when research was written in the plainest language. Kenneth Mellanby once confined individual virgin female bed bugs with several males in glass tubes. It was an experiment designed to study the influence of the amount of sperm on the production of eggs. He first tried a dozen males:
The females were repeatedly fertilized, and dissections showed immense quantities of sperm inside their bodies. It appeared, however, that 12 males were too many, as some of the females died.
6 males to 1 female did finally allow the female subjects to survive the experimental conditions and the experiment to proceed. There was still “a great deal more of sperm.”1
We hear a lot about the costs of mating—and indeed the culture is awash in references to “nasty” bed bug sex—and about the risk that female mating avoidance may cause the spread of infestations. But as we should now expect, things are more interesting and complex. An article published last month in the Proceedings of the National Academy of Science shows that, controlling for mating frequency, bed bug semen, which contains potentially beneficial antioxidant and antibacterial substances, elicits female reproductive benefits.
Reinhardt, K., Naylor, R.A. & Siva-Jothy, M.T., 2009. Ejaculate components delay reproductive senescence while elevating female reproductive rate in an insect. Proceedings of the National Academy of Sciences, 106(51), 21743-21747. doi:10.1073/pnas.0905347106
Females in this study either received 1 ejaculate unit (low exposure rate, n = 79) or 3 units (high exposure rate, n = 80) every week of their adult life. Even our low treatment rate exceeds the ejaculate provision rate required to maintain female fecundity, because 1 ejaculate unit sustains female fecundity and fertility for 4–8 weeks (20, 36). Females in both treatments received 3 copulatory intromissions per week, thus experimentally controlling for the 2 processes that have been implicated in reducing female fitness: the wounding of the female (38), which occurs at every mating in bedbugs (traumatic insemination; ref. 20), and infection from male genital contamination with microbes (39, 40). Although all females were fully fed and did not experience macronutrient limitation, females receiving the high ejaculate dose showed a significant increase in reproductive rate compared with females receiving the low ejaculate dose (Fig. 1A and B).
Emphasis added.
The age at which female reproductive rate declined was delayed by 11.4% (0.9 to 3.6 weeks) in the high ejaculate exposure females.
I’m not sure I understand what this may mean for the mortality of females, yet to be explored if I understand correctly. High ejaculate exposure increased mortality in only one of the populations tested.
- This strong image that I guess I’ve now burdened you with is from Mellanby, K. 1939. Fertilization and egg production in the bed-bug, Cimex lectularius L. Parasitology 31, 193-199 doi:10.1017/S0031182000012750 [↩]
These pages may be of related interest:
The whole time I was reading that, the James Brown song Doin’ it to Death was going through my mind.
Listen to you, John. But alas there is no evidence of a good time! Previously these very same researchers have shown just how females flatten themselves against a surface to prevent copulation, and I guess that’s only one among several strategies.
By the way, the way that they ensured only one unit of sperm deposition for one group while exposing them all to three copulations a week was by interrupting two of the three.
I just hope that if I’m lucky to reach old age, I won’t remember all these bed bug word pictures quite so vividly.