Relatedness and avoidance of inbreeding in the lizard, Tiliqua rugosa

Two potential mechanisms for reducing the level of inbreeding, sex-biased dispersal and kin avoidance, were examined in the Australian sleepy lizard, Tiliqua rugosa. The home range centres, and the genotypes at four polymorphic microsatellite DNA loci were determined for adult lizards in a 70-ha study area near Mount Mary, South Australia. From estimates of genetic relatedness, females were as closely related to other females as they were to males, both within the whole study area, and within home ranges. Similarly, males were as closely related to other males as they were to females. This suggests that dispersal in the population is not sex-biased. Sleepy lizards form monogamous pairs during the spring. Partners were less closely related to each other than to other potential partners in the home range area. This suggests active choice of unrelated partners. The mechanism for recognising related from unrelated individuals is unknown, but the behaviour could reduce inbreeding. Received: 7 November 1998 / Accepted: 30 May 1999     

Chemical ornaments of male lizards <Emphasis Type="Italic">Psammodromus algirus</Emphasis> may reveal their parasite load and health state to females

Evidence for parasite-mediated sexual selection has been found in many species that use visual ornaments to attract females. However, in many animals, variation in female responses to scents of parasitized males suggests that parasitic infections might also affect information conveyed by pheromones (i.e., chemical ornaments). Thus, pheromones might also function in parasite-mediated sexual selection. We show here that female lizards Psammodromus algirus responded differently to femoral gland secretions of males according to the parasite load and health of these males. Scents of healthier males elicited more tongue flicks (a chemosensory behavior) by females, suggesting that these scents were more attractive. Chemical analyses showed that parasite load and the T-cell-mediated immune response were related to the variability in the proportions of some lipids in secretions of males. Further trials testing the chemosensory responses of females to chemical standards indicated that females actually discriminated the chemicals related to males’ health from other chemicals found in secretions. We suggest that these chemical ornaments may provide reliable information on the health and degree of parasitic infection of a male.     

Individual dispersal status influences space use of conspecific residents in the common lizard, Lacerta vivipara

The effects of immigration on the behaviour of residents may have important implications for the local population characteristics. A manipulative laboratory experiment with yearlings of the common lizard (Lacerta vivipara) was performed to test whether the introduction of dispersing or philopatric individuals influences the short-term spacing behaviour of resident individuals. Staged encounters were carried out to induce interactions within dyads. The home cage of each responding individual was connected by a corridor to an unfamiliar “arrival cage” to measure the latency to leave their own home cage after each encounter. Our results showed that the time that pairs spent in close proximity was longer when a dispersing individual was introduced in the home cage. The latency to leave the home cage was longer after the introduction of a dispersing individual. These response variables were not influenced by the relative body sizes of contestants nor by the level of aggression towards each other. In contrast, the aggressive response was significantly influenced by the residency asymmetry established experimentally (“owner” of the home cage vs introduced individual). Our results suggest that the space use by resident individuals is influenced by the dispersal status of conspecifics. The potential ultimate causes driving this effect are discussed.     

Network structure and parasite transmission in a group living lizard,the gidgee skink, <Emphasis Type="Italic">Egernia stokesii</Emphasis>

Gidgee skinks (Egernia stokesii) form large social aggregations in rocky outcrops across the Flinders Ranges in South Australia. Group members share refuges (rock crevices), which may promote parasite transmission. We measured connectivity of individuals in networks constructed from patterns of common crevice use and observed patterns of parasitism by three blood parasites (Hemolivia, Schellackia and Plasmodium) and an ectoparasitic tick (Amblyomma vikirri). Data came from a 1-year mark-recapture study of four populations. Transmission networks were constructed to represent possible transmission pathways among lizards. Two lizards that used the same refuge within an estimated transmission period were considered connected in the transmission network. An edge was placed between them, directed towards the individual that occupied the crevice last. Social networks, a sub-set of same-day only associations, were small and highly fragmented compared with transmission networks, suggesting that non-synchronous crevice use leads to more transmission opportunities than direct social association. In transmission networks, lizards infested by ticks were connected to more other tick-infested lizards than uninfected lizards. Lizards infected by ticks and carrying multiple blood parasite infections were in more connected positions in the network than lizards without ticks or with one or no blood parasites. Our findings suggest higher levels of network connectivity may increase the risk of becoming infected or that parasites influence lizard behaviour and consequently their position in the network. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. This contribution is part of the special issue “Social Networks: new perspectives” (Guest Editors: J. Krause, D. Lusseau and R. James).     

Fighting rules and rival recognition reduce costs of aggression in male lizards, Podarcis hispanica

The establishment of fighting rules and the ability to recognise individual conspecifics and to assess their fighting ability and/or roles may help to reduce costs of fighting. We staged encounters between males of the lizard Podarcis hispanica to examine whether lizards used fighting strategies and whether a previous agonistic experience affects the outcome and characteristics of a subsequent encounter. The results showed that simple rules such as body size differences and residence condition were used to determine the outcome of agonistic interactions as quickly as possible. Thus, larger males were dominant in most encounters. However, when size differences between opponents are smaller, they may be more difficult to estimate and, then, residence condition was more important. In addition, the intensity of interactions between males could be explained according to the ”sequential assessment game”, supporting the idea that P. hispanica males acquire information about fighting ability gradually during the progress of a fight. Our results also showed that the second fight of the same pair of males was less aggressive, even when its outcome was the opposite of the first. This result suggests that male P. hispanica can recognise individual opponents and that they use this information to reach a contest outcome more quickly, thus reducing unnecessary aggression levels in subsequent interactions. These fighting strategies and assessment mechanisms may help to stabilise the social system of this lizard. Received: 2 November 1999 / Revised: 26 August 2000 / Accepted: 4 September 2000     

Loss of mating opportunities influences refuge use in the Iberian rock lizard,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.Communicated by A. Mathis     

Roles of male residence and relative size in the social behavior of Iberian rock lizards, Lacerta monticola

Many studies on contest competition used residency asymmetry as a discrete variable. However, the probability of winning an interaction may change as a continuous function of the value of the location where the encounter occurs. We performed a field study to examine the importance of location within a home range and relative body size to the outcomes of agonistic interactions between male lizards, Lacerta monticola. The distances to activity centers (the most used locations based on a density function of sightings) and relative size play important roles in agonistic interactions and had interacting effects in natural conditions. On the other hand, previous studies with lizards suggested that inferior competitors are able to avoid agonistic interactions in the field. Thus, we staged encounters in the laboratory to examine the behavioral responses of smaller individuals. The responses of each focal smaller male were measured in its own home cage (resident), in the cage of a larger male (intruder) and in a cage in which no male was previously present (control). The predominant behavioral tactics of smaller males were avoidance when they are the intruders and displaying when they are the residents. Submissive displays by smaller males may help reduce the costs of agonistic encounters.     

Correlated evolution of prey chemical discrimination with foraging, lingual morphology and vomeronasal chemoreceptor abundance in lizards

Comparative data from ten families of lizards suggest that correlated evolution has occurred between the ability to identify prey chemicals and several aspects of lingual function and morphology, abundance of vomeronasal chemoreceptor cells, and foraging behavior. Ability to discriminate prey chemicals from control substances was measured experimentally and correlated with other variables by Felsenstein's method. This ability increased with evolutionary increases in degree of lingual protrusion during tongue-flicking, which may reflect the tongue's ability to reach substrates to be sampled. It increased with deepened lingual forking and greater lingual elongation, which may be important for scent-trailing and sampling ability, respectively. Discriminatory ability also increased with abundance of vomerolfactory chemoreceptors, which presumably reflects some aspects of analytical capacities of the vomeronasal system. Prey chemical discrimination increased with degree of active foraging. Natural selection for improved vomerolfactory sampling and analysis of prey chemicals by active, but not ambush, foragers appears to account for the observed relationships. In active foragers that use vomerolfaction to locate prey, natural selection favors increased abilities to lingually sample chemicals from environmental substrates, analyze the samples for prey chemicals, and respond appropriately if prey chemicals or possible prey chemicals are detected. Such selection can account for the observed relationships among the sampling device and its movements, the sense, the discriminations, and variations in foraging ecology. Received: 13 February 1997 / Accepted after revision: 12 June 1997     

Acute toxicity of acaricide in lizards (Agama agama) Inhabiting dog kennel in Ibadan, Nigeria: An environmental hazard in urban vector control

Acute toxicity of an acaricide (Nuvan^® 1000 EC) in lizards (Agama agama) was observed within 2 minutes spraying of the acaricide in an enclosed dog kennel; heavily infested by ticks in urban area of Ibadan city, South western Nigeria. The acaricide was used at the 0.5% concentration recommended by the manufacturer (Novartis). A lizard which emerged from the kennel during the acaricide spraying exhibited acute signs of toxicity which consisted of shivering, gasping and death. The clinical signs of the acute toxicity manifested in the affected lizard resembled central nervous system (CNS) breakdown or neurotoxicity. Also, two lizards (one female and one male) were found dead in the kennel in the second and third days after the single acaricide spraying operation. The acute acaricide toxicity in lizards observed in this study portrayed the danger of environmental hazard to non-target commensal organisms and it is the first reported case in the area.     

Circannual variations of lizard circadian activity rhythms in constant darkness

The daily pattern of locomotor activity of Podarcis sicula in the field changes from unimodal in spring to bimodal in summer, becoming unimodal again in autumn. Short-term experiments in which P. sicula collected in different months were tested under constant conditions immediately after capture showed that the activity pattern typical of each season is retained in the lizard circadian locomotor rhythm. In constant conditions, the bimodal pattern is associated with a short free-running period (τ) of the circadian locomotor rhythm and a long circadian activity (α), while the unimodal pattern is associated with a long τ and short α. To test whether seasonal changes in circadian locomotor rhythms are driven by a circannual clock, we recorded locomotor activity of lizards over 12–15 months in constant temperature and darkness. The present results demonstrate, for the first time in a vertebrate, the existence of circannual changes in constant darkness of both τ and α. In most lizards, the longest τ along its circannual cycle is associated with a short α, and the shortest τ in the same cycle with a long α, so that the pattern of mutual association between τ and α is the same as in short-term experiments. Most lizards, however, stayed unimodal all the time. This shows that changes in activity pattern from unimodal to bimodal (and vice versa) are induced by seasonal changes in environmental factors, instead of being incorporated into a circannual rhythm. Circannual changes in τ and α of locomotor rhythms may adaptively predispose the circadian system of P. sicula to a change in activity pattern as soon as seasonal changes in the environment demand it. Received: 22 January 1999 / Received in revised form: 14 April 1999 / Accepted: 19 April 1999