Fit Fathers, Unfit Daughters
The BBC's Autumnwatch programme last year featured the antics of a group of Scottish Red Deer. Loeske Kruuk, from the University of Edinburgh has been studying them, and re-writing some scientific textbooks.
Chris - Loeske, what have you found by looking at these Deer?
Loeske - What we've found is that the genes that make a successful male do not always make a successful female.
Chris - What does that actually mean?
Loeske - Successful fathers, those who sire many offspring, will have daughters who actually have relatively low breeding success.
Chris - Because Darwin would have us believe that as you breed populations you get survival of the fittest, and so everyone should get better as time goes on.
Loeske - Exactly, but what our results are suggesting is that maybe the idea that some genes are better than others, that we can have a single measure of fitness, may just be too simplistic. It may depend on the sex of the individual animal carrying the genes.
Chris - So when you look at a male deer, for instance, what makes a good male would be big muscles, big antlers for fighting... Those genes wouldn't help a female very much, is that what you're saying?
Loeske - Exactly, there are very different traits that contribute to breeding success in males. As you say, fighting ability, antler size and also their skills at roaring, as anyone who watched Autumnwatch will have seen they spend a lot of time [roaring] during the mating season.
Chris - Does this apply to football hooligans as well?
Loeske - [Laughs] It may well do! But those are very different traits from those that determine breeding success in females. With females, those who produce the most number of calves over a lifetime will have the highest fitness, the highest breeding success.
Chris - How did you actually do the study and find these results?
Loeske - Well, we have data from more than 30 years of very intensive study of this population of red deer. And, as anyone who saw Autumnwatch will have seen, we can recognise all the individual deer in the population. It is an entirely wild population.
Chris - Have you named them?
Loeske - We do have names for every animal in the population, yes.
Chris - And your favourite?
Loeske - Well there was Caesar on Autumnwatch as people will have seen.
Chris - That's a kind of dog food, isn't it?
Loeske - [Laughs] Yes and many other attributes as well. There have been some every successful females along the way as well; Aphrodite was one with a very nice name.
Chris - She was very popular with the males, presumably?
Loeske - She did very well...
Chris - So why is it that the males have unfit daughters? Does the same work in the reverse direction? Do you end up with females who are very successful, they have lots of offspring, in the same way as the males' daughters are compromised, are the females' sons compromised?
Loeske - It's slightly more complicated when you look at it that way round, because with females they contribute not only their genes to their offspring's later performance, but they also provide maternal care. So in the Red Deer, all the males contribute to their offspring are their genes, the females provide both genes and maternal care. So a good quality female, although she may be passing on genes which are detrimental in a son, she will also provide very high quality maternal care to both her daughters and her sons. Those two effects seem to balance one another out when you look at the performance of the offspring of the females. It doesn't quite pick up the same relationship in relation to mothers offspring performance.
Chris - So what would you say the bottom line with this study is? That because of the effects you've found, this mechanism contributes to a huge amount of genetic diversity and variation in a population?
Loeske - It's intuitively a very appealing explanation for a lot of the biological diversity that we see in nature. This is important because genetic differences that we see between individuals within a single species have always been quite a puzzling fact for evolutionary biologists, because as you mentioned, the process of natural selection is expected to favour only the best adapted individuals; Darwin's survival of the fittest. What we're suggesting is that maybe the idea of a single 'fittest' genotype is a bit too simplistic.