New information about the costs of autotomy (tail loss) in scorpions

 

I have previously reported about the facinating discovery of autotomy of the cauda (tail) as an anti-predatory behavior in the scorpion Ananteris mauryi Lourenco, 1982 (Buthidae). The cauda contains important parts of the scorpion's nervous, circulatory and digestive systems, and of course the very important sting and the venom glands. The tail doesn't regenerate and an automized scorpion will eventually die from constipation (but can survive for several months befor it die).

I was recently made aware of three papers authored by Solimary García-Hern
andez and Glauco Machado presenting research into the cost of autotomy (tail loss) in scorpions. One article stufy the effect of autotomy on predation success, the second article adresses short- and long-term consequences on locomotor performance of male and female sorpions with tail loss, and finally the third article studies the effects of autotomy on reproductive sucess.

To sum up, tail loss in scorpions has negative effects prey capture, exposure to predators, and reproductive success, but the size of the effects differ between the sexes. The reduction of reproductive succcess was much more dramatic for females than for males. For details on the results and conclusion I refer to the abstracts below.

Abstracts:

Paper1:
Predation success depends on factors such as hunger, prey size, prey availability and intensity of competition. A neglected factor that may also influence predation success is the proper function of morphological traits related to prey search, capture and manipulation. Injuries that compromise the functionality of these morphological traits may reduce predation success. In many invertebrates, autotomy can compromise predation success because the detached body part may be crucial for hunting. However, empirical evidence linking autotomy and predation success is relatively scarce. We filled this gap using the scorpion Ananteris balzani, which autotomizes the last abdominal segments, known as the ‘tail’. This is a unique form of autotomy as ‘tail’ autotomy implies the loss of the stinger, an organ used for venom inoculation, which is the main form of large prey subjugation. Using a paired experimental design, we found that for both small and large prey, subduing success was higher when individuals were intact than when they were autotomized. After autotomy, subduing success of male scorpions decreased
from 90% to 17% for small prey and from 47% to 1% for large prey. Subduing success of female scorpions after autotomy decreased from 98% to 93% for small prey and from 97% to 70% for large prey. Autotomized individuals took longer than intact individuals to subdue both small and large prey, but the effect size was higher for large prey. Considering that the tail does not regenerate, autotomized individuals (especially males) will experience a lifelong reduction in trophic niche breadth because their diet will be mostly composed of small prey. Moreover, autotomized individuals probably move more to enhance the likelihood of finding small prey, which may increase their exposure to predators and consequently the costs related to tail loss.

Paper 2:
In many taxa, individuals voluntarily detach a body part as a form to increase their chances of escaping predation. This defense mechanism, known as autotomy, has several consequences, such as changes in locomotor performance that may affect fitness. Scorpions of the genus Ananteris autotomize the “tail”, which in fact corresponds to the last abdominal segments. After autotomy, individuals lose nearly 25% of their body mass and the last portion of the digestive tract, including the anus, which prevents defecation and leads to constipation, because regeneration does not occur. Here, we experimentally investigated the short- and long-term effects of tail loss on the locomotor performance of Ananteris balzani. In a short-term experiment, the maximum running speed (MRS) of males and females did not change after autotomy. Moreover, the relative mass of the lost tail did not affect the change in MRS after autotomy. In a long-term experiment, autotomy had a negative effect on theMRS of males, but not of females. Autotomized over-fed individuals suffered from severe constipation but were not slower than autotomized normally fed individuals. In conclusion, tail loss has no immediate effect on the locomotor performance of scorpions. The long-term decrease in the locomotor performance of autotomized males may impair mate searching. However, because death by constipation takes several months, males have a long time to find mates and reproduce. Thus, the prolonged period between autotomy and death by constipation is crucial for understanding the evolution of one of the most extreme cases of autotomy in nature.

Paper 3:
The ability to detach a body part in response to a predation attempt is known as autotomy, and it is perhaps the most
intensively studied form of nonlethal injury in animals. Although autotomy enhances survival, it may impose reproductive costs on both males and females. We experimentally investigated how autotomy affects the reproductive success of males and females of a scorpion species. Individuals of Ananteris balzani autotomize the last abdominal segments (the tail), losing the anus and leading to lifelong constipation, since regeneration does not occur. Although the male tail is used during courtship and sperm transfer, autotomy has no effect on male mating success. The combined effect of increased mortality and reduced fecundity resulted in autotomized females producing nearly 35% fewer offspring than intact females. In conclusion, the negative effects of tail autotomy are clearly sex dependent, probably because the factors that influence reproductive success in males and females are markedly different.

References:

Paper1:
García-Hernández S, Machado G. ‘Tail’ autotomy and consequent stinger loss decrease predation success in scorpions. Anim Behav. 2020;169:157-67. [Subscription required for full text]

Paper 2:
Garcia-Hernandez S, Machado G. Short- and long-term effects of an extreme case of autotomy: does 'tail' loss and subsequent constipation decrease the locomotor performance of male and female scorpions? Integr Zool. 2021;Accepted Manuscript:1-17. [Subscription required for full text]

Paper 3:
García-Hernández S, Machado G. Fitness implications of nonlethal injuries in scorpions: Females, but not males, pay reproductive costs. Am Nat. 2021;197(3):379-89. [Open Access]

Thanks to Solimary García-Hern
andez for sending me their articles on this interesting topic!