Monday, June 7, 2010

Violent mating habits of certain invertebrates

Two days ago I was watching a show on Animal Planet called "Monsters Inside Me" and one of the cases on the show was of a woman who was being infected with bed bugs. That's when I first heard of "traumatic insemination."

Traumatic insemination is a mating practice that takes place among some species of invertebrates (including bed bugs and even some spiders). The process apparently differs slightly depending on the species, but generally involves the male piercing the female's back and injecting sperm into the abdomen.

Of course I had to do more research on this topic and came across this piece (including pictures that may be NSFW) about male seed beetles whose penises are covered with spikes that injure the females. It also discussed the violent sexual practices of some other species which made me cringe while reading.

Despite explaining how the female seed beetle has developed some defenses "so that the damage inflicted by the males doesn't affect her too badly," my new knowledge of the violent mating practices of some species was rather disturbing because it seems that females of many species are no strangers to sexual violence.


quixote said...

The media loves this stuff, but it's a case of generalizing from apples to seaweed. As an evolutionary biologist, this stuff makes me want to send them to the back of the class and order remedial tests.

1) Evolution is about survival. Anything that survives passes on its genes, whether that's by chance (eg the asteroid strike was far away), random drift, negative selection, balancing selection, or positive selection. Survival says nothing about whether anything is an efficient or happy way to do things.

2) In a creature with a brain big enough to understand the feelings of others, violence has a completely different meaning than it does in, say, a beetle. The beetle-equivalent in humans is walking down the sidewalk and happening to step on an ant. From the ant's standpoint, it's not good, but the violence involved is not planned or even perceived as violence by either party. To the ant it's a natural disaster; to the human, they just went from Point A to Point B.

3) If the media really wanted to talk about evolution and human behavior, they would take into account that we can guess each other's feelings and that we remember.

Taking sex, as everyone's favorite example:

Women (unlike beetles) don't show external signs of ovulation. The main symptom is that the woman is more interested in sex. She'll find the men of her choice. Sex during ovulation has about a one third chance of resulting in pregnancy. A male she associates with pain is unlikely to be her choice (except after cultural conditioning perhaps). Sex at random with respect to ovulation, such as the male choosing the time without input from the female, has about a 0.02 chance of resulting in pregnancy.

So, let's see. A 33% chance versus a 2% chance. That's a huge selective pressure, from a purely biological standpoint, to make sure the females choose when to have sex. Violence in that situation puts you into the closed-for-cleaning-with-bleach end of the gene pool. Regardless of what works for beetles.

quixote said...

(Math mistake. There's a 2% chance of getting the timing right, and then a one third chance of pregnancy, so under random timing, the chance of pregnancy is 0.9%. The right comparison is 33% versus less than 1%.)

Amelia said...

All your points are very well taken, quixote. Thank you.

You are absolutely correct about the idea of "generalizing from apples to seaweed" and your points about evolution are well-stated.

If I could re-write the last sentence of this post, I would, because really, I was just shocked to hear about these mating practices, mostly because of the term "traumatic insemination". They did make me think of sexual violence in humans, but I was and am aware (but did not make clear) that there are differences that mean that the two types of violence cannot be rightly compared.

Anonymous said...

Women (unlike beetles) don't show external signs of ovulation.

Not at all true. It's all in knowing what to look for. Humans are more subtle, sure, but the signs are still there.

Amelia said...

Can you elaborate on your claim, Anon?

ZoBabe said...

Giving "Anon" the benefit of the doubt, I've seen far too many pseudo-scientific articles lately claiming that there are "differences."
"Knowing what to look for" however, does seem to scream "Her lips are saying no, but her [eyes/waste-line/preference in clothing/gait/skin tone/voice pitch/etc/etc/etc] are saying yes."
There may be subtle "cues," but no one "knows what to look for."
Human beings have been blessed with this amazing way of communicating with each other.

Iany said...

You should see what dolphins do.
(They arrange in packs of males that look for females in estrous.)
Whales are almost as bad.

Pretty much all species have something "violent" going on, unless the female is too huge to harass (leopard seals, spiders, so on).

As quixotic said, it's a bit apples and oranges. A beetle doesn't really have violence as a concept, though it does have the ability to try to sustain itself in a way that is beneficial to it.

Traumatic insemination isn't necessarily an adaptive trait, strictly speaking. The lab I work in has a guy who specialises in it and has said, "I get to study bug sex for a living. I'm pretty ok with it."

Iany said...

Oh! And it's only traumatic insemination if the female's body is pierced outside of the reproductive tract.

You heard me, it's only traumatic if the female is actually /stabbed/. Just using a spiked aedeagus isn't enough to be considered traumatic!