(One of the oldest memes on the internet. And, in my opinion, one of the best)
We all worry about stress for lots of reasons: weight gain, depression, headaches, insomnia. But have you ever worried about what stress...is doing to your 'nads?
Well, if you are the common starling, perhaps you should.
McGuire et al. "The direct response of the gonads to cues of stress in a temperate songbird species is season-dependent" PeerJ, 2013.
When we talk about gonads in science, of course, we don't just mean testes, we mean both testes AND ovaries. And it turns out that both are affected by stress...but only at the right times of year.
The authors captured a bunch of starlings, male and female, and...took out their 'nads. Half of the starlings were caught in February, when the days were relatively short and the birds are "pre-breeding", while the other half were caught in April, when the days are longer, and the birds are mating away.
When the 'nads were out, the authors cultured them up in dishes, and looked at how much hormone they released in response to corticosteone, a hormonal stressor (the human version is cortisol).
First off, there's already seasonal change in 'nad size if you're a bird. Male birds in February had teeny testes and females had unimpressive ovaries. But in April, when the breeding season is in full swing, the gonads are in full swing themselves! The boys balls get 6 TIMES bigger, and the girl's ovaries are 5 times bigger. Let us all pause for a moment, and be glad that none of us have huge variations in gonad size as a result of seasonality. Either the small season would be ludicrous, or the big season would be...uncomfortable.
But it's not just size that matters during seasonal variability. The bird's gonads are also more or less sensitive to STRESS depending on the time of year. The researchers first stimulated the gonads with leutinizing hormone and follicle stimulating hormone. When you stimulate males in this way, their testicles get to work producing testosterone, while female ovaries get to work on estradiol.
But what happens when you add stress? If it's the pre-breeding season, stress really puts a damper on the hormone party, stopping the secretion of testosterone in males and the secretion of estradiol in females. But if it's breeding season and your 'nads are NEEDED...stress doesn't mean anything at all to the boys. Adding corticosterone didn't reduce testosterone secretion. But to the ladies? Stress always matter, and corticosterone reduced estradiol secretion regardless of time of year.
So it's not only the brain that responds to stress. Stress affects all of you...all the way to your 'nads. At least, if you're a starling.