Do animals cheat on each other?

20 February 2018

Question

Most of us have probably encountered a two timer on the dating scene, but what about animals? Do they ever cheat the rules?

Answer

Chris Smith put this question to behavioural ecologist Sophie Mowles...

Sophie - Well actually, yes. For the most part in the animal kingdom polygamy is the name of the game so animals mate multiply. From a male’s perspective that makes sense because, as I said earlier, sperm is cheap to make; they're very small cells and males can fertilise multiple females. So, from an evolutionary standpoint, in getting genes into the next generation for many animals it makes sense for males to mate multiply.

But that doesn’t mean that the females are losing out because females can mate multiply too. They can mate once and get some genes for their offspring, but they could maybe mate twice and get some better genes for their offspring. In some animals, females can store sperm so they can actually let sperm competition sort it out.

Chris - Bees do that don’t they? I was gobsmacked when a bee expert when I interviewed him at the University of Western Australia said that the queen bee, in some cases, mates once and can store sperm for years and continue to fertilise offspring from that one-off mating with many many males.

Sophie - Indeed. In the hive, that’s her family; they’re all very genetically related to her. She won’t want to mate with any males that enter that hive because they’ll be her sons. But yeah, many insects can store sperm for a long time. It’s not a bad thing if you then mate with another male because you might get some new sperm, or better ones so you get better quality offspring. They may be compatible genes as well which makes for better offspring too, or you might be able to provision them with different immunities so if a disease breaks out you don’t lose all of your offspring because you’ve mated with multiple males who offer different immunities through their genes.

But you do get genuine cheats as well. Some animals can offer nuptial gifts as a kind of mating gift to a female.

Chris - Like what?

Sophie - Food is a good nuptial gift.

Chris - It always works - food. It’s a sure fire winner.

Sophie - Food, flowers, that sort of thing. Food is great because females have to produce offspring so they need a lot of energy to make a baby or an egg so males can give females nuptial gifts involving food. There are some famous examples in spiders where they wrap the gift in silk, and the female has to unwrap it and while she’s unwrapping the gift he gets to mate with her.

Chris - Unwrap a present?

Sophie - Unwrap a present. So the more well wrapped the present is the longer the mating. He transfers more sperm but some of these cheating male spiders wil wrap something that isn’t actually food.

Chris - Aww, that’s awful!

Sophie - So a bit of a leaf or a twig that he’s found and that’s a real cheat really.

Chris - Does the female pay him back by eating him which seems to be what most spider females do the male?

Sophie - If he’s not quick enough, then yes that can happen.

Chris - How quickly does she discover and become disappointed?

Sophie - Well, it will be on unopening of the gift but sometimes males want to be eaten; some spiders once they’ve mated twice they lose the ability to mate again so they may as well sacrifice themselves and then the protein that makes their bodies will make more eggs containing their genes so that ultimate sacrifice can be really good for him.

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