Losing stability: tail loss and jumping in the arboreal lizard Anolis carolinensis
Gary B Gillis 1, Lauren A Bonvini, Duncan J Irschick
Abstract
Voluntary loss of an appendage, or autotomy, is a remarkable behavior that is widespread among many arthropods and lower vertebrates. Its immediate benefit, generally escape from a predator, is balanced by various costs, including impaired locomotor performance, reproductive success and long-term survival. Among vertebrates, autotomy is most widespread in lizards, in which tail loss has been documented in close to 100 species. Despite numerous studies of the potential costs of tail autotomy in lizards, none have focused on the importance of the tail in jumping. Using high-speed video we recorded jumps from six lizards (Anolis carolinensis) both before and after removing 80% of the tail to test the hypothesis that tail loss has a significant effect on jumping kinematics. Several key performance metrics, including jump distance and takeoff velocity, were not affected by experimental tail removal, averaging 21 cm and 124 cm s(-1), respectively, in both tailed and tailless lizards. However, in-air stability during jumping was greatly compromised after tail removal. Lizards without tails rotated posteriorly more than 30 deg., on average, between takeoff and landing (and sometimes more than 90 deg.) compared with an average of 5 deg. of rotation in lizards with intact tails. Such exaggerated posterior rotation prevents coordinated landing, which is critical for animals that spend much of their time jumping to and from small branches. This work augments recent experiments demonstrating the importance of the tail as a mid-air stabilizer during falling in geckos, and emphasizes new and severe functional costs associated with tail autotomy in arboreal lizards.
Geographic variation, frequency-dependent selection, and the maintenance of a female-limited polymorphism
Ryan Calsbeek, Lauren Bonvini, Robert M Cox
Abstract
A central problem in evolutionary biology is to understand how spatial and temporal variation in selection maintain genetic variation within and among populations. Brown anole lizards (Anolis sagrei) exhibit a dorsal pattern polymorphism that is expressed only in females, which occur in “diamond,”“bar,” and intermediate “diamond-bar” morphs. To understand the inheritance of this polymorphism, we conducted a captive breeding study that refuted several single-locus models and supported a two-locus mode of inheritance. To describe geographic variation in morph frequencies, we surveyed 13 populations from two major islands in The Bahamas. Morph frequencies differed substantially between major islands but were highly congruent within each island. Finally, we measured viability selection on each island to test two hypotheses regarding the maintenance of the polymorphism: (1) that spatial variation in selection maintains variation in morph frequencies between islands, and (2) that temporal variation in selection across years maintains variation within islands. Although bar females had relatively lower survival where they were rare, our data do not otherwise suggest that selection varies spatially between islands. However, diamond-bar females were subject to positive frequency-dependent selection across years, and the relative fitness of bar and diamond females alternated across years. We propose that this polymorphism is maintained by temporal variation in selection coupled with the sheltering of alleles via a two-locus inheritance pattern and sex-limited expression.
Jumping behavior and the effects of caudal autotomy on performance in Anolis carolinensis
Abstract
Maximal locomotor performance in Anolis lizards has been studied extensively within and across species. Hindlimb length is correlated with jump distances in a number of species of anoles, and differences in the structural habitat can have effects on individual performance. Anolis carolinensis lizards were videotaped undisturbed in two habitat matrices of different perch densities. Neither maximal performance nor morphological features appear to affect locomotor behavior. Caudal autotomy, or tail-loss, is an anti-predator strategy in a variety of lizard species, including anoles, and presents immediate benefits to the animal, allowing for survival in an otherwise potentially fatal situation. However it is also accompanied by numerous costs including changes in locomotor ability. For example, sprint speed, climbing speed, and endurance are affected in different species of lizards. A. carolinensis use jumping frequently as a form of locomotion, often have long tails, and have the ability to autotomize their tails as an anti-predator strategy. Before autotomy, the angle of a lizard s body during jumping remains slightly above the horizontal throughout the jump. Following autotomy, body angles are extremely variable, and jump distances may be reduced.
Tree lizards quick release escape system makes jumpers turn somersaults
If you’ve ever tried capturing a lizard, you’ll know how difficult it is. But if you do manage to corner one, many have the ultimate emergency quick release system for escape.
They simply drop their tails, leaving the twitching body part to distract the predator as they scamper to safety. According to Gary Gillis from Mount Holyoke College, USA, up to 50% of some lizard populations seem to have traded some part of their tails in exchange for escape. This made Gillis wonder how this loss may impact on a lizard’s mobility and ability to survive. Specifically how do branch hopping, tree dwelling lizards cope with their loss. Teaming up with undergraduate student Lauren Bonvini, the pair began encouraging lizard leaps to see how well the reptiles coped without their tails and publish their results on 13th February 2009 in The Journal of Experimental Biology at http://jeb.biologists.org/.
The tail lizard to become an acrobatic actor
If you’ve ever tried to catch a lizard, you’ll find it a difficult task because the animal has an emergency self-defense system to hide. They simply break their tail to distract predators while they flee. According to Gary Gillis of Mount Hokyoke School, USA, about 50% of lizard individuals are able to trade a part of their tail to escape.
This caused Gillis to wonder if this loss had any effect on the lizard’s ability to function and survival. Especially the lizards that live on trees how to deal with this loss. Collaborating with university student Lauren Bonvini, Gillis studied the lizard dance activities to observe their adaptability without tails.