It’s well-known that within seahorse circles, it’s the males who bear the responsibility of pregnancy, not the females. The same goes for their relatives, the pipefish, whose males are equipped with a specialised external brood pouch into which the females will deposit eggs during copulation. But a recent examination of pipefish male pregnancy and mate selection by Kimberley Paczolt and Adam Jones from Texas A&M University has found that this process is nothing to coo over, Henry Gee, Senior Editor at Nature, describing it as “sinister.”
Observing the reproductive behaviour of 22 captive male Gulf pipefish (Syngnathus scovelli), a small-mouthed, pencil-shaped species with a relatively poor swimming technique, Paczolt and Jones discovered just how much control the males have over their prospective progeny. By pairing the males with either large or small females, they found that that the males wasted no time in mating with larger, more attractive females, but were significantly less eager when paired with smaller females. What they also found is that the eggs deposited by larger females had a much higher rate of survival to the point of birth, the males selectively aborting those from a less attractive partner by either retaining vital nutrients, or absorbing (ie cannibalising) the embryos.
By also looking at successive pregnancies in male pipefish, the team were able to make sense of their rather callous tendencies. Not only did broods from smaller females have a low survival rate to begin with, but if a male first mates with an attractive female and bears a large brood, he’s unlikely to want to invest more resources into a following pregnancy, particularly from a less attractive partner. Instead of nurturing these offspring, his specially evolved brood pouch allows him to retain or absorb the nutrients to ready himself for the possibility of meeting a more attractive mate. “When a male mates with a female that’s not necessarily all that ‘attractive,’ instead of investing a lot in those offspring, he’s recharging for the next pregnancy – at least this is what our results suggest,” Dr Jones reports.
That the male pipefish are actively trying to control the quality of their offspring during pregnancy is evidence of post-copulatory sexual selection, which follows the initial competition for mates by way of combat and elaborate courtship displays. Dr Jones explains, ”When Darwin proposed the theory of sexual selection, he dealt entirely with pre-mating sexual selection… But after mating there are things that happen within the female’s reproductive tract or competition among sperm from different males that also results in sexual selection. So it turns out that post-mating sexual selection has hardly been studied at all in these sex role-reversed species.”
Well Gulf Pipefish Boys, you might think this is all pretty great, being able to pick and choose (and cannibalise) your own progeny with nary a qualm in the world. But the thing is, those ugly pipefish girls you mated with in the past, they’re not just going to disappear. The ocean might be big, but it’s not that big, and you know what they say – “Mate with one ugly pipefish that time you had nine vodkas, three gins and no dinner, and you’ll end up with six months of whiny text messages and a lifetime of really awkward encounters whenever you try and go back to that particular bar because they happen to serve $5 spirits till 1am.”
So you’ll decide to brave said bar one night, all, “Five tequila sunrises please. Yes, I’m serious. Oh. Hi…”
And that unattractive pipefish girl you once mated with, let’s call her… Martin, will be like, “OMG, I haven’t seen you in ages. How are the offspring?”
“You know, the offspring. Our offspring?”
“Oh. Umm. Hmm.”
“You ate them, didn’t you?”
“Well technically I absorbed… Shit. Five more tequila sunrises please.”
But it won’t end there, Gulf Pipefish Boys, with you simultaneously drinking and wearing a good deal of very cheap alcohol and orange juice, because everyone will know about that time you mated with Martin, especially her really short and ugly friends, and they’ll look at her and then at you and then back at her and figure they’ve got a shot.
So you’ll be at a completely different bar, trying to chat up some cute pipefish girl who really likes the Internet and stuff, like, “I aborted a brood twenty hoping to meet someone so… long. How many millimetres are you anyway? A hundred and twenty? Hundred and thirty? Wait right there, I’m going to get you a vat of gin.”
“And a Redbull.”
“And a Rebull. Right.”
But you’ll only get halfway to the bar before a bunch of Martin’s short and ugly friends swarm and engulf you, all, “Hey can I buy you a drink?”
“You want my number? I might be only ninety-five millimetres, but I sure know how to use them…”
“Ew. No thanks.”
“Hey can I buy you a drink?”
And meanwhile the cute pipefish girl who really likes the Internet and stuff will fully think you’re into ugly chicks or something and clear off without her vat of gin, or Redbull, and you’ll either have to go home alone, or pick one of the short and ugly pipefish girls to take with you, like, “Alright, fine. You. What’s your name? Brian? Yeah okay, whatever, come on.”
And you thought having a brood pouch would be a riot, Gulf Pipefish Boys.
Edit: I’m entering this post for the The National Evolutionary Synthesis Center’s Travel Award competition, which awards a $750 grant to two bloggers to attend ScienceOnline2011, a science communication conference held on January 13-15, 2011, in North Carolina. The best posts that highlight current or emerging evolutionary research appearing in peer-reviewed literature within the last five years win, so fingers crossed tightly for me please!!