Back off mate: which animals are aggressive with love rivals?

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

Sophie - There are some uber aggressive animals but they are very rare to be honest. Over evolutionary time we have seen the adaptation for conflicts, largely between males in order to access females. But, realistically, if you go and get yourself really badly injured in a fight, or even killed, you’re not going to pass any genes on so we see a real reluctance to use these weapons. For example, deer interlock their antlers and they have pushing contests, that’s after they’ve roared to demonstrate their size and their stamina, they don’t just stab each other with them. We see what’s called restrained fighting and “fighting” tends to be resolved via communications, especially when there’s a likelihood you’ll get really hurt.

However, if it’s really worth fighting for, if you’ve got a really good quality resource, and that in genetic terms would be a lot of females, then you do tend to see really dangerous conflict, and a good example of this are elephant seals. These fight hammer and tongue for access to a whole harem of females on a beach. If you’re a weakling male just not competitive, it’s just not worth fighting, so you're not going to have any offspring. If you try to take on the big dominant male, you’d just get really terribly injured or killed. If however, you might have a chance of taking him on if you’re possibly the same size or strength, then you can get incredibly vicious fights because you could have all of these females, and pass all of your genes on, and have lots of offspring. Losing that fight is almost the same as being that weakling male. In each case you don’t get any genes going into the next generation so it’s really really worth fighting for if you’ve got a chance. You can get really bloody encounters between these guys.

Chris - One interesting perspective that was put to me about ten years ago by a lady I interviewed who’d been studying deer in Scotland - her name was Luska Crook. She pointed out that actually the genes that make for a really big powerful male deer are not going to be the best genes, if they end up in a female offspring, to nurture a baby because these animals are sexually dimorphic. The males are quite different to the females, and this is quite a crafty way of keeping the diversity in the population because the males are not made too masculine because those genes would disadvantage a female offspring and visa versa. So it sort of keeps everyone a bit in check but there is still a difference between males and females.

Sophie - Yes. Genes, obviously, get transferred into the offspring whether they come from the male or the female, so if you have a daughter she will inherit genes for male characteristics too and could then transfer those onto her son when she eventually has that.

In deer, for example, a male may inherit the genes that determine his antler structure from his mum because they came from his grandfather. We tend to see this also in other sexually selected traits for example, famously in peafowl, in peacock, as you said earlier has this enormously elaborate train. The female however does not; she’s fairly drab. She has to incubate - he does nothing. He give her his genes but she has to do the work of looking after the eggs so she has to be cryptic and camouflaged, but she has still inherited some of those male traits. It has a bit of glossiness and that might be an evolutionary bind; she’s still a little bit spotable when she’s on the nest.

For example in the UK there’s ducks. The males are really nice and shiny and elaborate to show how good they are; they don’t do anything to help with the childrearing. Females have to incubate so they’re camouflaged because they’re a “sitting duck”; they’re really vulnerable.

Chris - You got there; beat me to it!

Sophie - Sorry, but that’s the punchline! If you look at birds, the British birds are great for this. Look at your wildfowl: if they look drastically different so the male is very colourful and the female is not, you can bet your bottom dollar she’s looking after the offspring and he’s not. If you get monogamy, Grebes for example, they look the same because they’re both having to prove to one another how good they are, and they both benefit from investing in those offspring and bringing them up together.