Dirk Bauwens

Altitudinal variation of the thermal biology and running performance in the lizard Podarcis tiliguerta

SummaryWe studied, in the field and laboratory, aspects of the thermal biology in two populations of the lizard Podarcis tiliguerta along a 1450 m altitudinal gradient. Body temperatures (Tb) at high altitudes average lower, are more variable, but are more elevated above environmental temperatures than at sea level. Lizards partially reduced the impact of altitudinal changes in thermal loads through presumable subtle behavioural adjustments. A comparison of the thermal preferences in the laboratory, the maximal operative temperatures predicted from a biophysical model, and the activity Tbs at both sites, indicates that the main response to changing environmental conditions is an active shift in thermoregulatory set points. Integration of field Tbs and laboratory data on temperature specific sprint speeds, predicts that the mountainous lizards experience reduced running abilities that are especially acute in the early morning. Despite this impairment of running performance, the thermal sensitivity of running speed has not evolved to match the Tbs experienced by both populations. This result supports the view that the thermal physiology of this lizard is evolutionarily conservative, but the lack of information on the relation between running performance and fitness components impedes rejection of alternative hypotheses.

Selected body temperatures in the lizard Lacerta vivipara: variation within and between populations

Abstract 1. 1.|Selected body temperatures (SBT) of adult male, female and subadult Lacerta vivipara from a Belgian population, were measured monthly in a laboratory thermogradient. 2. 2.|Monthly mean SBTs varied between 29.9 and 34.0°C and differed significantly among months in all three lizard groups, and among lizard groups in 4 out of 6 months. 3. 3.|Evidence for a positive relationship between monthly SBT and air temperature was found in the subadults, but not in the adult lizards. 4. 4.|Monthly mean SBTs measured in this study were consistently higher (mean difference = 2.0°C) than those obtained by Patterson and Davies (1978) in a similar study on Lacerta vivipara from southern England.

Evolutionary rigidity of thermal physiology: the case of the cool temperate lizard Lacerta vivipara

We compared the thermal dependence of sprint speed in two populations of the common lizard, Lacerta vivipara, from different altitudes. Although field body temperatures in the montane population were consistently 3-5°C below those of the lowland population, we found no parallel shift in the optimal temperatures for sprint speed. Lizards from both populations also selected similar temperatures in the laboratory. In the field, lizards from the montane population were frequently active at body temperatures that seriously impair locomotion. These observations give support to the static view of thermal physiology, which claims that thermal physiology is evolutionary stationary and resistant to directional selection.

Diet composition of the lizard Lacerta lepida in central Spain

-We studied diet composition of Lacerta lepida in a sample of 325 specimens from central Spain. This large lacertid lizard feeds predominantly on Coleoptera, but also consumes other arthropods, snails, small vertebrates, and some plant material. Composition of the animal fraction of the diet and trophic diversity were virtually identical in adult males and females. Juveniles fed upon a restricted number of prey types which were small in size, whereas adults consumed a large number of prey taxa, covering a wider range of prey sizes. Trophic segregation among individual lizards was highest in the smaller size classes. The incidence of plant material increased with lizard size and was highest in males, but it never represented a substantial fraction of the total diet. The contribution of small vertebrates to total prey numbers also increased with lizard body size. Our results indicate that vertebrates are of marginal numerical importance to the diet of L. lepida. Most lizards feed primarily on arthropods, although some species have adopted a diet consisting mainly of molluscs, plant material or small vertebrates (see Greene, 1982). Insectivorous lizards are often opportunistic feeders, eating any suitable sized arthropods. Hence, diet composition has been shown to exhibit seasonal or (micro)geographic variation, in response to a shift in prey availability which is either presumed (e.g., Avery, 1966; Mou and Barbault, 1986; Arnold, 1987) or documented (e.g., Ballinger and Ballinger, 1979; Stamps et al., 1981; 4 Present Address: University of Antwerp (U.I.A.), Department of Biology, Universiteitsplein 1, B-2610 Wilrijk, Belgium. Mou, 1987). Body size is another factor that influences prey choice and diet composition (Pough, 1973). Although most evidence for a relation between body size and dietary composition derives from interspecific comparisons, ontogenetic changes in prey choice within single lizard species have been described (see Pough, 1973; Greene, 1982). European lizards of the family Lacertidae are basically insectivorous, although some forms occasionally eat other invertebrates, small vertebrates or plants (see Arnold, 1987). Lacerta lepida, the largest European lacertid (adult snoutvent-length 140-220 mm), is a diurnal, heliothermic, ground-dwelling lizard that is found in a variety of mediterranean habitats throughout most of Spain and Portugal, in southern 30 This content downloaded from 207.46.13.133 on Fri, 22 Jul 2016 06:04:36 UTC All use subject to http://about.jstor.org/terms DIET COMPOSITION IN LACERTA LEPIDA France and extreme northwest Italy. Diet composition, one of the best studied features of the biology of this lizard, has been treated by a large number of authors (Peters, 1962; Valverde, 1967; Mellado et al., 1975; Escarre and Vericad, 1981; Perez-Mellado, 1981; Bas, 1982; Seva, 1982; Bischoff et al., 1984; Brafia, 1984; Mateo, 1988; and Busack and Visnaw, 1989). However, most studies were based on small samples, and made no distinction between lizard sex or size classes. Lacerta lepida experiences a >100-fold increase in body mass during its ontogeny (from 2 to 280 g), and the sexes differ notably in maximum body size and head dimensions (Castilla, 1989). We hypothesized that such morphological differences might induce diverging prey choices. One of the most controversial aspects of this lizards feeding ecology is the common belief that it preys extensively on small vertebrates, particularly eggs and chicks of the Redlegged Partridge (Alectoris rufa), an important game bird in Spain. Although published studies do not support this opinion, one could argue that the dietary contribution of vertebrate prey might have been underestimated due to the examination of small numbers of lizards from re-

An experimental demonstration of direct behavioural interference in two Mediterranean lacertid lizard species

Podarcis sicula of Italian origin has expanded its range along the Adriatic coast of Croatia, apparently replacing the autochthonous species P. melisellensis by competitive exclusion. We used an experimental approach on newborn lizards to test the hypothesis that direct behavioural interference occurs between P. sicula and P. melisellensis, whereby the former obtains an advantage over the latter. Brief encounters between P. sicula and P. melisellensis were more aggressive and more likely to result in clear dominant– subordinate relationships than were brief encounters between pairs of conspecific P. melisellensis. When they cohabited for 3 weeks, individuals in heterospecific pairs were less likely to occupy a thermal microhabitat simultaneously than individuals from homospecific pairs. Contrasts of individuals in heterospecific pairs showed that behavioural interference was asymmetric in favour of P. sicula. During brief encounters P. sicula were more aggressive and dominant than P. melisellensis opponents. When the two species cohabited for longer periods P. sicula used better, and P. melisellensis poorer, thermal microhabitats than when reared in isolation. In addition, P. sicula grew faster, and P. melisellensis slower, than in isolation. These within-species shifts in microhabitat use and growth were not evident for homospecific pairs living together. Thus, our observations indicate that asymmetric aggressive interactions between hatchlings of our study species reduce an important fitness component (i.e. growth rate) of P. melisellensis. These findings are consistent with the hypothesis that direct behavioural interference by P. sicula is the mechanistic basis of the competitive exclusion of P. melisellensis.

Constraints on Temperature Regulation in Two Sympatric Podarcis Lizards during Autumn

Abstract We studied the impact of restrictions by the thermal environments on body temperatures (Tbs) and microhabitat use of the lacertid lizards Podarcis melisellensis and Podarcis muralis in a Mediterranean area (Croatia) during autumn. The thermal conditions at available microhabitats were assessed with copper models that measured the operative temperatures (Te) at different sites. We estimated the thermal suitability of microhabitats by quantifying the extent of similarity between the Tes and the range of selected temperatures (i.e., the Tbs that lizards maintain in zero-cost conditions in a laboratory thermogradient; Tsel). Both species maintained, throughout most of day, Tbs that were on average 2–4 C below both Tsel and the Tbs recorded in the field during summer. Nevertheless, the Tbs measured during autumn were in the upper range of available Tes and were much closer to the Tsel than were the Tes. In addition, lizards were most often observed in the warmest microhabitats and were often seen basking. These results indicate that lizards were actively thermoregulating. The Te measurements show that lizards encounter suitable thermal conditions (i.e., where Tes is within Tsel) in only a restricted subset of the available microhabitats and during only a relatively short period of the day. Thus, lizards are constrained to maintain relatively low Tbs during autumn by the generally low available Tes. Although lizards were clearly thermoregulating, they appeared to accept lower Tbs during activity in autumn than in summer. A possible reason for this seasonal shift in activity Tbs is that achievement of higher Tbs during autumn is only feasible by confining activities to some specific microhabitats, which may severely constrain other behaviors, such as foraging.

Field body temperatures and thermoregulatory behavior of the high altitude lizard, Lacerta bedriagae

Many species of lizards are known to maintain relatively high and constant body temperatures (Avery, 1982; Huey, 1982). Their abilities to do so depend largely on regulatory behaviors that alter heat exchange with the environment and on the thermal conditions within their habitats. Ectotherms living at high altitudes (and latitudes) offer unique opportunities to study thermoregulatory responses to the rather unfavorable and strongly variable thermal characteristics of these regions. High altitude lizards often exhibit lower and more variable activity body temperatures, and/or thermoregulate less precisely than conspecific or congeneric populations living at lower elevations (Brattstrom, 1965; Hertz and Nevo, 1981; Vial, 1984; Crowley, 1985). We report here results of a short-term study on field body temperatures and aspects of thermoregulatory behavior of the lizard Lacerta bedriagae. This mediumsized lizard (adult male body size = 66-84 mm, mass = 7-14 g; adult female body size = 66-80 mm, mass = 7-11 g) is endemic to the Mediterranean islands Corsica and Sardinia, where its distribution is usually retricted to altitudes >1000 m (Schneider, 1984 reviews information on the habits of this poorly known species). We hypothesized that this lizard, living in an environment characterized by low and variable ambient temperatures, would be active over a relatively wide range of body temperatures. Our main aim therefore was to examine changes in body temperature and thermoregulatory behavior in relation to diel variations in the thermal environment.

Reproductive and Fat Body Cycles of the Lizard, Lacerta lepida, in Central Spain

We studied the annual reproductive and fat body cycles of the oviparous lizard Lacerta lepida in central Spain. Testicular recrudescence started in late summer and testes attained their maximal sizes during the following spring. Females exhibited ovarian growth during spring and most oviposited in July. Fat bodies of males were smallest during the mating period. Female fat body volumes declined during vitellogenesis. No significant decline of lipid stores was detected during the hibernation period (October-March).

Proximate Causes of Intraspecific Variation in Locomotor Performance in the Lizard Gallotia galloti

To understand the evolution of biological traits, information on the degree and origins of intraspecific variation is essential. Because adaptation can take place only if the trait shows heritable variation, it is important to know whether (at least) part of the trait variation is genetically based. We describe intra‐ and interindividual variation in three performance measures (sprint speed, climbing, and clambering speed) in juvenile Gallotia galloti lizards from three populations and examine how genetic, environmental (incubation temperature), and ontogenetic (age, size) effects interact to cause performance variation. Moreover, we test whether the three performance traits are intercorrelated phenotypically and genetically. Sprint speed is highest in juveniles incubated at the lowest temperature (26°C) irrespective of population. Climbing speed differs among populations, and the differences persist at least until the lizards are 30 wk old. This suggests that the three populations experience different selective pressures. Moreover, mass, snout‐vent length, and hindlimb length seem to affect climbing performance differently in the three populations. The variation in sprinting and climbing ability appears to be genetically based. Moreover, the two performance traits are intercorrelated and thus will not evolve independently from each other. Clambering speed (i.e., capacity to climb up an inclined mesh) varies among individuals, but the origin of this variation remains obscure.

Synchronization of spring molting with the onset of mating behavior in male lizards, Lacerta vivipara

BURGER, W. L. 1950. Novel aspects of the life history of two ambystomas. J. Tenn. Acad. Sci. 25:252-257. COLLINS, J. P., AND J. R. HOLOMUZKI. 1984. Intraspecific variation in diet within and between trophic morphs in larval tiger salamanders (Ambystoma tigrinum nebulosum). Can. J. Zool. 62:168-174. DODSON, S. I., AND V. E. DODSON. 1971. The diet of Ambystoma tigrinum larvae from western Colorado. Copeia 1971:614-624. GEHLBACH, F. R. 1965. Herpetology of the Zuni Mountains region, northwestern New Mexico. Proc. U.S. Nat. Mus. 116:243-332.