This morning I have been reading about evolutionary stable strategies and one of the examples given in this week’s lecture was reciprocal food sharing in Vampire Bats so I have done some reading on it. I think it is really interesting how these bats behave so I’m going to tell you a bit about it from what I have learnt! First we need a definition of what an evolutionary stable strategy actually is. If most members of a population adopt the same strategy and this cannot be bettered by any other strategy then it can be defined as an evolutionary stable strategy (or an ESS). These are frequency dependent and this is because the successfulness of the strategy depends on what the organisms around you are doing. It can also depend on whether there are “cheats” around as these can take advantage of the ESS and lead to its downfall.
The research I read this morning was done by Gerald S. Wilkinson in 1984 and it is an example of an evolutionary stable strategy in the Vampire Bat (Desmodus rotundus). Vampire bats who do not manage to get a blood meal during the night often beg blood from successful individuals in the roost during the day. The successful individual may regurgitate some blood for the other bat to take in and therefore increase its chance of survival. Wilkinson investigated how this behaviour was an evolutionary stable strategy and came up with three conditions that need to be fulfilled in order for it to be considered an ESS. These were:
- There must be enough repeated regurgitations between pairs of bats so that they each get a chance to regurgitate and receive blood
- The benefit of receiving the blood must be greater than the cost of donating
- Donors need to be able to recognise and not feed previous bats that have not reciprocated
When doing a census of the roost, it was found that the main social unit is the female group. This is because males tend to leave their natal group when they become one year old. Female bats tend to stay in their maternal groups and this means that female groups are usually made up of close relatives with only a few exceptions. Most of the regurgitation of blood occurs between a mother and her offspring and any others tend to be between animals that are frequent roost mates. Blood is donated preferentially to individuals that are likely to die in the next 24 hours if they are not fed. This shows that the giving of blood is to increase the chances of a survival of a related bat. If the bat survives to adulthood it is more likely to reproduce and pass on the family genes. This is called Kin Selection and is quite common in the animal kingdom.
References
Wilkinson, G.S., 1984, Reciprocal food sharing in the vampire bat, Nature, Vol 308, pp 181-185
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