Jettisoning Ballast or Fuel? Caudal Autotomy and Locomotory Energetics of the Cape Dwarf GeckoLygodactylus capensis(Gekkonidae)

Abstract

Many lizard species will shed their tail as a defensive response (e.g., to escape a putative predator or aggressive conspecific). This caudal autotomy incurs a number of costs as a result of loss of the tail itself, loss of resources (i.e., stored in the tail or due to the cost of regeneration), and altered behavior. Few studies have examined the metabolic costs of caudal autotomy. A previous study demonstrated that geckos can move faster after tail loss as a result of reduced weight or friction with the substrate; however, there are no data for the effects of caudal autotomy on locomotory energetics. We examined the effect of tail loss on locomotory costs in the Cape dwarf gecko Lygodactylus capensis (∼0.9 g) using a novel method for collecting data on small lizards, a method previously used for arthropods. We measured CO 2 production during 5-10 min of exhaustive exercise (in response to stimulus) and during a 45-min recovery period. During exercise, we measured speed (for each meter moved) as well as total distance traveled. Contrary to our expectations, tailless geckos overall expended less effort in escape running, moving both slower and for a shorter distance, compared with when they were intact. Tailless geckos also exhibited lower excess CO 2 production (CO 2 production in excess of normal resting metabolic rate) during exercising. This may be due to reduced metabolically active tissue (tails represent 8.7% of their initial body mass). An alternative suggestion is that a change in energy substrate use may take place after tail loss. This is an intriguing finding that warrants future biochemical investigation before we can predict the relative costs of tail loss that lizards might experience under natural conditions.

Tail loss and narrow surfaces decrease locomotor stability in the arboreal green anole lizard (Anolis carolinensis)

“…(2) I recorded all postautotomy trials within 1-2 days of initiating autotomy, whereas McElroy and Bergmann recorded their trials 14 days post-autotomy. Following autotomy, it is known that body condition declines as resources are diverted towards regeneration (Dial and Fitzpatrick, 1981;Maginnis, 2006;Naya et al, 2007;Wrinn and Uetz, 2007;Fleming et al, 2009;Jagnandan et al, 2014) and could decrease maximum sprint speeds Fleming et al, 2009). In this study, the autotomized tail represented 6-10% of the intact body weight, which could have enabled greater running speeds immediately after tail loss because lizards had less weight to carry.…”

Autotomy, Tail Regeneration and Jumping ability in Cape Dwarf Geckos (Lygodactylus capensis) (Gekkonidae)

“…Decreased stamina may be due to the loss of adipose tissue (fuelling metabolism) in the tail; although we do not know the tissue composition of tails in this species, the tails of these animals are between 9 and 13% of body mass (Medger et al 2008;Fleming et al 2009) and therefore are likely to represent a substantial portion of their body reserves.…”

“…has a scansorial pad, similar to those on the feet, which acts as a fifth point of attachment, while the tail itself appears to act as a brace to prevent the animal falling backwards (Bauer & Russell 1994;Medger et al 2008). Fleming et al (2009) reported that autotomized L. capensis incur energetic costs on horizontal surfaces, expending less effort in running, moving both slower and for a shorter distance than intact geckos and having lower excess CO2 production (CO2 production in excess of normal resting metabolic rate) when running.…”

“…Although their tails are therefore important for locomotion, a high proportion (over 50%) of natural populations of L. capensis have regenerated tails (Medger et al 2008;Fleming et al 2009), suggesting that caudal autotomy is an important defence tactic in these animals. The tail regenerates quickly in Lygodactylus spp.…”

Consequences of lost endings: caudal autotomy as a lens for focusing attention on tail function during locomotion

“…In some lizards, the tail is also an important site for storing lipids, so that in addition to losing mass and having their CoM position shift, animals may also be losing critical energy stores when parts of a tail are lost (e.g. Dial and Fitzpatrick, 1981;Fleming et al, 2009).…”