Do animals in the wild ever suffer from infertility? Do female mammals ‘know’ whether they are pregnant or not, or do they act as if they’re pregnant after the breeding season regardless? If infertility does occur, do animals that form pair bonds split up and seek new mates? And what about species where females typically mate only with the alpha male? If he’s not doing the job, will they sneakily mate with another male? Or leave and find a new ‘harem’ to join?
A late biologist professor friend who did his dissertation on penguin divorce said that of the breeds of penguins who are monogamous (versus serially monogamous), the female will find a new mate if she doesn’t get pregnant within a few seasons.
Penguin divorce! I wonder if penguins lay eggs even if they are not fertilised, like chickens do, and so waste time trying to incubate them? That would make having an infertile partner a lot more costly.
Oops, that should be “if she doesn’t produce offspring”.
Yeah, I knew what you meant. 
Not in the wild exactly, but it’s certainly known in zoos for a pair of mammals to be infertile and stay pair bonded. Where I used to work had a pair of marmosets in which- as we discovered at autopsy- the female had no uterus, but they had stayed paired for life as normal. Of course, in that situation, there were no opportunities to find an alternative mate (they weren’t part of a breeding scheme- if they had been the zoo would normally have split them up and swapped with another non-breeding pair if possible).
We also had a pair of finches of a species where males and females are virtually identical, at least to human eyes. After a while, we noticed that, although they were building a nest every season, no eggs were being laid, and realised that they were both male. We acquired two females and in subsequent seasons we had one nest with no eggs in and one nest absolutely jam-packed with eggs, none of which ever hatched…
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Yes, infertility can occur in pretty much any species, for a variety of reasons. These can be genetic or environmental. Obviously such genetic factors are strongly selected against.
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Female mammals will generally behave differently depending on whether they are pregnant or not.
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In general, if a pair fails to successfully produce offspring in a breeding season, they are likely to try to find a new partner the following season. However, this varies between species.
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It has been found that, regardless of breeding systems, females will often seek out matings with males that are not the primary partner. In many songbirds that were once thought to be monogamous, genetic analysis has shown many offspring are due to “extra-pair copulations.” In many polygynous (harem) species, females will accept matings with non-dominant males if they can get away with it. In red deer, subordinate males may steal matings when the dominant male is engaged in a fight, which has been referred to as the “sneaky fucker” strategy.
Lol. I guess that must have been environmental, it would be a pretty big coincidence if all 4 birds just happened to be gay.
I guess what I was picturing would never occur then: a whole herd of deer failing to produce offspring one year because the dominant male happened to be infertile.
In animals, as in humans, sexuality is not a simple binary matter. It might be that, if all four birds had met each other at the same time, they’d pair off in two heterosexual pairs. But the first two had nobody to choose from but each other, and so paired up, because they preferred a “gay marriage” to remaining single. And then the next two came in, and the pair-bond between the two males was too strong for that pairing to “divorce”, and so the females found themselves in the same situation that the males had, with nobody to pair with but each other.
Or, yeah, it’s possible that they just got four homosexual birds, and they would have paired up that way even given alternatives. Homosexuality isn’t that rare.
It would depend on how successful a male was in defending his females. But as a practical matter, the more females he has the harder they are to defend. I doubt a male could prevent more than a handful of females from mating with other males at all.
I remember a discussion with a co-worker many years ago (he would have retired in the late 80’s). He grew up on a farm and mentioned that it was not unusual for animals exhibited non-binary behaviour, or even cross-species. “As nature intended” was rarely as binary as some would like to believe, and horniness knows no bounds. Besides which, humans will raise pets and pen animals in arrangements rarely found in the wild.
Hinds (adult female deer) that are in season are pretty determined to get pregnant. Their preference will generally be to the stag (adult male deer) that’s leading the harem they belong to. It’s not apparent that a dominant stag’s sterility will lead the hinds to seek mates outside the harem. However, the hinds’ preference for the dominant stag is limited and they’re quite likely to stray from the harem. It then becomes a question of how good the stag is in corralling his harem. Stags aren’t really that good at that concept. Posturing, fighting, and sex, they’re accomplished at. Rounding up a herd of hinds like a sheepdog, not so much. So a sterile male having a childless, uncuckolded harem is fairly unlikely.
Especially if the hinds’ pattern isn’t “mate with the alpha stag as much as possible”, but rather “mate with whatever male I can, as often as possible”. If most of the matings are with the alpha stag, and if all animals involved are fertile, then you’ll end up with the fawns being mostly from the alpha… but if the alpha is infertile, there will still be plenty of opportunities for those “sneaky fuckers” to sire fawns.
Makes sense. And presumably also true of animals like elephant seals. What about things like gorillas and lions which might only have one male in a group? Or does that not really happen?
It’s pretty damn obvious when you are pregnant – in ways that I expect any mammal is able to notice. I would be truly shocked if any significant fraction of female mammals didn’t behave differently when they were pregnant.
Most animals have much less invasive pregnancies than humans. I’m sure I remember a documentary where they said the females automatically go through the hormonal changes of pregnancy after the breeding season, because in evolutionary terms it was really unlikely they wouldn’t be fertilised, so it wasn’t worth evolving a signalling mechanism. But I have zero idea what kind of animal it was.
In gorillas and lions, there may be several males in a group, including a dominant and subdominant ones. Although it is possible for there to be single male groups, in which the male is unfertile, that will be rare.