Stuck in a bad relationship are you? Join the club. Many members of the animal kingdom are 'doing it' with mediocre mates on a daily basis for a variety of reasons including the lack of ability to find someone better, forced copulations, social protocols and much more. But have you ever considered that hooking up with a 'bad' partner could be hazardous to your health? Inadequate partners provide inadequate genetic material, territories, parental care or protection -- leading to an increased level of stress for those mating with them. Increased stress levels are associated with a plethora of medical maladies, so it's certainly possible that a bad boyfriend really can be physiologically damaging.
Researchers recently set out to examine the physiological impacts of mate choice for the Gouldian finch (Erythrura gouldiae) by paring females with crappy boyfriends... and the results are rather astonishing. Gouldian finches have two distinct color-morphs: those with black heads and those with red. Mating pairs are generally formed between individuals of the same color morph (i.e., black with black, red with red) because there are genetic incompatibilities between the two types. In other words, for any given female there are two sets of potential mates: good (same color morph) and bad. Despite the fact that the offspring of mixed pairs have a much lower rate of survival, mixed morph couplings do occur in the natural world because mates are not always easy to find. By creating experimental conditions in which virgin females were mated with either a good mate (same color) or a bad one, researchers could measure various phyisological parameters associated with stress levels.
It turns out that females mated to bad boyfriends had a 3.5 increase in plasma levels of corticosterone -- the major hormone linked to stress in birds. In addition to the negative physiological effects associated with corticosterone (i.e., bad partner = negative effects on health), a very interesting side-effect of the changes in hormone levels was observed. Females with high levels of corticosterone produced clutches of eggs that were extremely male-biased. It is well known that female birds have a substantial amount of control over the sex ratio of their offspring; however, the physiological mechanisms for such control remain elusive. This work shows a direct connection between elevated levels of corticosterone and the sex ratio of resultant offspring, leading researchers to conclude that corticosterone may directly influence sex chromosome segregation during meiosis, or may lead to differential maturation rates of differentially sexed ova.
This research is very interesting on a few levels. First, it shows that having a crappy mate can have clear adverse effects on one's health. Second, it shows that high levels of stress hormones in females can directly affect the sex-ratio of egg clutches, providing some much needed input into the mechanistic framework for sex allocation in birds. Fascinating stuff!
Pryke, S., Rollins, L., Buttemer, W., & Griffith, S. (2011). Maternal stress to partner quality is linked to adaptive offspring sex ratio adjustment Behavioral Ecology, 22 (4), 717-722 DOI: 10.1093/beheco/arr040