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Autotomy, or self-amputation, is an active form of defense from predators in which an animal sheds a body part when attacked. Despite sounding strange, it is performed by many species of reptiles, insects, arachnids and mollusks. In insects and arachnids, the amputated body part is usually a leg, so that even when the part cannot be regrown, it has some sort of backup (insects and arachnids have lots of legs, in case you didn’t recall).

Recently, however, a very unusual and unexpected kind of autotomy has been discovered in arachnids: some scorpions of the family Butidae may self-amputate their tails. This it surprising because the tail does not have a backup and cannot grow back, which means that the scorpions discard their main weapon. But there is more: the “tail” of the scorpion is actually the end of its abdomen, and by losing it the scorpion loses its anus! And yes, this does generate the sort of problem you are thinking about right now. Nevertheless, tailess scorpions can endure for months and can even reproduce.

1. Build a general mathematical model to describe the situation in which an individual that meets a predator increases its survival chances if it sheds some body part. Remember that once the body part is “autotomized”, the individual will stay more exposed to predators and may suffer other effects from the amputation.
2. Advance into making your model more inspired in the specific case of the scorpion in the example. Remove from the model the option of re-growing lost body parts, and add the dynamics of losing additional tail sections described in the texts (after all, it is only via this process that the “autotomized” scorpions can poop). Can you use this model to make evolutionary predictions? For instance, assuming that the scorpions’ tendency to autotomize its tail is heritable, what should influence its frequency in the population?
3. Bonus quest – females, apparently, are less likely to amputate their tails than males, which may be related to their longer life-span. However, male scorpions may use their tails to court females, so that a male scorpion without a tail will have more difficulty in mating. Keeping in mind that males may attain higher reproductive success than any female by mating with several females, can you predict in which scenarios males should be less willing to shed their tails than females? <wrap tip>

P.S.:</wrap> remember that if some males attain a very high mating success, others may remain unmated - each new scorpion has a single father and a single mother, so that the mean reproductive success of males and females must be the same. This is known as the Fisher condition.

• Mattoni, C.I., García-Hernández, S., Botero-Trujillo, R., Ochoa, J.A., Ojanguren-Affilastro, A.A., Pinto-da-Rocha, R. and Prendini, L., 2015. Scorpion sheds ‘tail’to escape: consequences and implications of autotomy in scorpions (Buthidae: Ananteris). PloS one, 10(1), p.e0116639
• How the Scorpion Lost Its Tail (And Its Anus), from the blog “Not exactly Rock Science”