Autotomy and Regeneration
Hulali Alford & Rose Driscoll
Reed College Biology 342 Fall 2015
How does an individual animal’s expression of the behavior change over the animal’s lifetime? Is it learned? Does it develop as the animal matures?
The development of and changes to autotomy during an animal’s lifetime differ across species and clades. While some animals become increasingly successful at the use of autotomy as they mature, other animals lose the ability to autotomize as they get older, or decrease their use of autotomy in favor of different strategies. In these species, the benefits of autotomy decrease sharply, and the costs increase (see Adaptive Value), as an individual grows (Lizards: Arnold 1984).
The mechanisms of autotomy, such as fracture planes, develop with the animal.
1. Fracture planes develop in lizards during a period of resegmentation in the vertebra, when fusion occurs between parts of different somites (structures which ultimately develop into vertebrae.) Incomplete fusion produces fracture planes (Evans 1981).
2. P. marmoratus geckos’ success at escaping from a predator through autotomy increases as the animals mature. Adult tails are relatively longer, wider, and heavier than juvenile tails, and have much higher lipid content; it is proposed that these attributes might make the waving motions of an autotomized tail more salient to a predator, so that it is more likely to be distracted from the gecko (Daniels et al 1986).
Table 1. Use of two escape strategies, autotomy and running, by P. mamoratus geckos of different ages. (Use is represented as both numbers and percentages.) Captured adults escaped from a predator with much higher frequency (62%) than captured juveniles (7%). This data also shows that tailless adults and juveniles are captured at much higher rates and escape at much lower rates than tailed geckos, demonstrating that autotomy is an adaptive strategy (see Adaptive Value.) (From Daniels, 1986.)
3. The Balkan Green Lizard (Lacerta trilineata) is a good sprinter, but the loss of the tail seems to be costly enough to running that autotomy is only worthwhile when individuals are small and escape via running is not an effective tactic. Additionally, adults’ tails contain protein, lipid, and carbohydrate resources which may be important nutrients for females during egg production, and for all animals during periods of low resources. The result is that in this species, each animal “grows out of” autotomy as it matures (Pafilis & Valakos 2008).
4. In blackworms (L. variegatus), the frequency of autotomy in response to a given stimulus (in this case, 95% compression of body segments) increases as individuals mature from newly hatched to mid-sized to subadult size; subadults display adult frequencies of autotomy. However, the time taken to autotomize does not differ across age groups (Lesiuk & Drewes 1999).