And by bigger, I mean older. At least, in this case.
Do you know what makes a good burying beetle dad? One that cares for its offspring and guards the carcass (because the hotspot for beetle romance is on something dead) from invaders? It’s not the beetle who’s momma raised him right, or the beetle who took classes in women’s studies in college. Nope, in this case, he’s just a little bit older.
Benowitz et al. “Male age mediates reproductive investment and response to
paternity assurance” Proceedings of the Royal Society B, 2013.
First, the burying beetle. The burying beetle is a striking looking little guy (or girl) that feels or carrion. When mating, they find a nice old dead mouse or bird or something, and then defend it from all comers. Once the dead prize is assured, they bury it, digging a hole beneath it and rolling it into a ball, while secreting antibacterials and antifungals all overit, to keep it from decomposing and attracting competition for the delicious, delicious dead stuff.
The female then lays eggs around the buried carrion, and the male and female wait around for hatching. After hatching the mom and dad can stay around to help feed the young (though the young can feed themselves). They will also sometimes cull the young so that there is enough carcass for everyone.
Note that, throughout reproduction, and the female and the MALE help out. They both take on parenting roles. And the scientists running this study wanted to know…how much were the males really helping out, and did it have anything to do with age? Would older males care more about the offspring than younger ones? And if so, what would the females do about the lax young dads?
The scientists took a bunch of male burying beetles, all of which had never had sex or cared for offspring before, some of which were young, and some of which were old. They paired them off with females, and then looked to see how much time the males and females spent guarding the carrion they got as a honeymoon suite (prenatal care), how much time the males and females spent feeding the larvae (postnatal care), etc. They then checked to see how the baby beetles turned out, how long they took to hatch, their weight, and how many they got.
What they found was that the older males cared more for the offspring than the younger males did, exhibiting more prenatal care, and they did so even when the older males weren’t SURE the offspring where theirs (the offspring were always theirs, but the authors introduced the scents of other males into the cages to give the resident males some cause for jealousy). They spent more time around the carrion “nest”, and more time guarding the carrion before mating.
BUT, all of this tender love and care by the older males? It didn’t really improve the offspring at all. Older males and younger males had similar numbers of offspring that were in similar health. This is because, if the younger males cared less for the offspring, the females picked up the slack, prepping the nest and guarding that tasty dead mouse.
So why do the older males bother with all this attention, if the females will just pick up the slack? The authors hypothesize that this is an example of terminal investment. The males that cared more were older. This will probably be one of their only chances to mate and pass on their genes. Better make it count!
Why were the younger males so lax, though? After all, shouldn’t ever time count? Some count more than others, apparently, because the authors observed that younger beetles mated less frequently. This could be because they invest less in mating when they are younger, or it could be that a lady likes a beetle with life experience.
If older males exhibit more parental care, but the female makes up for it if the male care is lame…do females PREFER older men? I think it would be interesting to see if they do. This study didn’t address that, but it would be interesting to see if it was significant. And if they don’t prefer older men, why? Is there something the younger beetles have that’s worth making up for their lacking parenting style? Or is it just not that important to the females how much time they spend on parenting?
But if you’re a burying beetle in search of a baby daddy, save yourself some effort. Find a nice older beetle man to do some of the housekeeping, and save yourself from having to pick up the slack.