RELATIONSHIPS AMONG FORAGING VARIABLES, PHYLOGENY, AND FORAGING MODES, WITH NEW DATA FOR NINE NORTH AMERICAN LIZARD SPECIES

Thirteen polymorphic microsatellite DNA loci from whiptails of the genus Aspidoscelis (Teiidae: Squamata) and related cnemidophorine lizards

We describe polymerase chain reaction primers and amplification conditions for 13 microsatellite DNA loci isolated from two bisexual species of whiptail lizards Aspidoscelis costata huico and Aspidoscelis inornata. Primers were tested on either 16 or 48 individuals of A. c. huico and/or 26 individuals of A. inornata. Ten of the 13 primers were also tested against a panel of 31 additional whiptail taxa. We detected three to nine alleles per locus in A. c. huico and four to 19 alleles per locus in A. inornata, with observed heterozygosity ranging from 0.60 to 0.87 and from 0.15 to 1.00, respectively. These primers will be an important resource for surveys of genetic variation in these lizards.

Running for your life or running for your dinner: what drives fiber-type evolution in lizard locomotor muscles?

Despite its role in whole-animal performance, the adaptation of muscle physiology related to terrestrial locomotion remains underexplored. We tested evolutionary models based on predator escape and foraging strategies of lizards to assess whether fiber-type composition of a leg muscle is adaptive for behavior. The best-fitting model for fast-twitch fiber-type evolution was one based on predator-escape strategy, while the foraging-mode model fared poorly (Akaike Information Criterion with small sample size correction; DeltaAICc=29.7). According to the predator-escape model, lizards relying on sprints to avoid predators are predicted to have relatively higher proportions of fast glycolytic (FG) fibers (70%), while cryptic lizards are predicted to have relatively higher fast oxidative glycolytic (FOG) fiber proportions (77%). This pattern suggests an evolutionary trend toward greater FG (FOG) fiber composition among lizards that specialize in sprinting (crypsis). The best-fitting model for slow-twitch fibers had a single optimum, suggesting a common selective pressure across these lizards. The second-best model explaining slow-twitch fiber-type evolution was Brownian motion (DeltaAICc=0.80), indicating some support for neutral evolution. We find evidence suggesting that different fiber types occurring in the same muscle can evolve under different evolutionary pressures.

The correlated evolution of biomechanics, gait and foraging mode in lizards

Foraging mode has molded the evolution of many aspects of lizard biology. From a basic sit-and-wait sprinting feeding strategy, several lizard groups have evolved a wide foraging strategy, slowly moving through the environment using their highly developed chemosensory systems to locate prey. We studied locomotor performance, whole-body mechanics and gaits in a phylogenetic array of lizards that use sit-and-wait and wide-foraging strategies to contrast the functional differences associated with the need for speed vs slow continuous movement during foraging. Using multivariate and phylogenetic comparative analyses we tested for patterns of covariation in gaits and locomotor mechanics in relation to foraging mode. Sit-and-wait species used only fast speeds and trotting gaits coupled with running (bouncing) mechanics. Different wide-foraging species independently evolved slower locomotion with walking(vaulting) mechanics coupled with several different walking gaits, some of which have evolved several times. Most wide foragers retain the running mechanics with trotting gaits observed in sit-and-wait lizards, but some wide foragers have evolved very slow (high duty factor) running mechanics. In addition, three evolutionary reversals back to sit-and-wait foraging are coupled with the loss of walking mechanics. These findings provide strong evidence that foraging mode drives the evolution of biomechanics and gaits in lizards and that there are several ways to evolve slower locomotion. In addition, the different gaits used to walk slowly appear to match the ecological and behavioral challenges of the species that use them. Trotting appears to be a functionally stable strategy in lizards not necessarily related to whole-body mechanics or speed.

Wide home ranges for widely foraging lizards

Space usage by animals may be influenced by a range of factors. In this study we investigate whether foraging behaviour affects the home range size of lizards. Two distinct tactics of foraging have been recognized in predators: sit-and-wait foraging (SW) and active foraging (AF). Foraging activity level of a data set of lizard species, mainly compiled from literature, is compared with their home range sizes. Two opposite predictions can be made about foraging in connection with home range area: on the one hand, SW species may exhibit larger home ranges due to their mating system; on the other hand, AF species have higher metabolic energy and thus food requirements and can be expected to have larger home ranges that have to yield this food. This study shows that percentage of the time moving (as an index of foraging mode) correlates positively with home range, even after correcting for body mass, and these patterns remain when phylogenetic relationships are taken into account. We thus conclude that home range areas parallel activity levels in lizards.

Compensatory changes in escape and refuge use following autotomy in the lizard Sceloporus virgatus

Following autotomy of a body part to escape from a predator, prey may alter antipredatory strategies to compensate for the inability to use autotomy and impaired escape ability. Because prey that have been captured may increase their assessment of risk posed by a predator, effects of capture may have been attributed to autotomy. I conducted an experiment using three groups of striped plateau lizards ( Sceloporus virgatus Smith, 1938): control, captured, and autotomized. Captured and autotomized lizards were less active on the day after autotomy than controls. Flight initiation distance and distance fled were greater in both experimental groups than in the control group, but did not differ between experimental groups. Flight initiation distance was greater in autotomized than in captured lizards only in males. No sex difference occurred for distance fled. Autotomized lizards entered refuges more than other groups. Escape strategy changed after autotomy to increased reliance on refuge and, in males, to increased flight initiation distance; behaviours that are appropriate to compensate for impaired escape ability. Decreased activity and increased distance fled might erroneously have been considered effects of autotomy, had effects of capture not been assessed. Predictions of escape theory that flight initiation distance and distance fled increase with predation risk were supported.