Dominance and competition in an herbivorous lizard

Summary A study of social organization in an herbivorous lizard Ctenosaura hemilopha investigated the role of dominance in group member behavior. Attention focused on a very populous (16 ind.) colony to examine causes and effects of crowding with respect to competitive factors. Lizards were colonial, with a top-rank male, one or more adult females, and various subadults and juveniles. Top-rank males defended harems, with colonies female-biased (1:4 in focal colony). Dominance hierarchy was observed, with females more aggressive than males, except for the top-rank male. Group awareness facilitated adaptive responses to threatening dominants and predators. Strong correlations existed among individual size, rank, and aggression. Top-rank male aggressiveness was partly explained by harem defense. Food resource competition, which causes aggression in female insectivorous lizards, did not explain female C. hemilopha behavior. Response to predators, predator fecal pellet analysis, and tail break frequencies implicate crevice escape sites for predator avoidance as a prime controller of social and population structure in these lizards.     

Social monogamy and extra-pair fertilization in an Australian lizard, Tiliqua rugosa

This study investigates social monogamy in the Australian sleepy lizard, Tiliqua rugosa. At a 70-ha site near Mount Mary, South Australia, we radio tracked 55 adult female and 39 adult male lizards during their spring activity periods. Each lizard was observed in 1–5 years. Females were observed with a single male partner on an average of 10.8 days per year, although in 17.3% of cases, females were observed on 2 or fewer days with a male. The most intense pairing period each year was 15 September–15 November when females were with male partners on an average of 36% of observation days. Partnerships lasted an average of 43.3 days each year. After mating in early November, the pairs separated. Observations of females pairing with other males were rare. Most males (82%) were also consistently monogamous, although 7 were observed pairing with 2 females within one season. To investigate paternity, we allowed 21 gravid females to give birth to 42 offspring in the laboratory. We determined genotypes at five polymorphic microsatellite DNA loci for the females, their male partners and their offspring. Four litters (19%) and 6 of the offspring from those litters (14.3%) showed evidence of extra-pair fertilization (EPF). Although the sample sizes are small, females of polygynous males were more likely to experience EPF. Received: 22 February 1998 / Accepted after revision: 23 May 1998     

Pursuit deterrence,predation risk,and escape in the lizard <Emphasis Type="Italic">Callisaurus draconoides</Emphasis>

The frequency of pursuit-deterrent signaling should vary with predation risk for factors affecting decisions to flee and hide. Distance to refuge, temperature, and microhabitat types affect risk, and their effects may differ among defenses. Because risk is greater farther from refuge and at lower temperatures that impair escape ability in ectotherms, I predicted that when farther from refuge ectothermic prey flee sooner, enter refuge more frequently, and signal more frequently. At low temperatures, prey should flee sooner, enter refuge, and signal less frequently. Because signaling sometimes deters attack, lowered risk might allow prey to permit closer approach when signaling. In the zebra-tailed lizard Callisaurus draconoides, which signals by waving its tail, signaling and the other behaviors were affected by the same risk factors. Probability of signaling before fleeing increased with distance to refuge and temperature, but variation in temperature accounted for the effect of distance to refuge. Lizards signaled not at all at low temperatures, after starting to flee at intermediate temperatures, and before, during, and after fleeing at higher temperatures. This pattern is consistent with honest signaling of escape ability. Refuge entry was more frequent nearer refuge (lower risk) and at lower temperature (higher risk). Display was less frequent on rock than ground, possibly due to conspicuousness or delay in attaining high speed. Flight initiation distance was shorter after signaling. This novel finding suggests that signaling reduces risk and prey alter escape decisions based on lower risk as a consequence of their own signaling behavior.     

Estimating paternity with spatial behaviour and DNA fingerprinting in the striped plateau lizard, Sceloporus virgatus (Phrynosomatidae)

The association between spatial proximity and paternity was studied in a population of the striped plateau lizard, Sceloporus virgatus. The relationship between estimated mating success and male phenotypic traits was examined for a sample of 55 males. DNA samples were obtained from 13 female-offspring families. The males with the closest spatial proximity to each female were tested as possible sires within each family. Fingerprinting with two multilocus hypervariable minisatellite probes revealed a strong correspondence between male-female spatial proximity and actual paternity. Paternity could be assigned for 72 of the 100 hatchlings. Most hatchlings with identifiable sires were attributed to a male with the highest category of spatial proximity to the mother. However, there was a low to moderate level of multiple paternity within clutches, and for some clutches probable sires could not be identified even though the most likely behavioural candidates were tested. Thus, nonterritorial males or other males lacking strong social and spatial relationships with females may achieve some degree of reproductive success. Analysis of mating success revealed that male success increased with body size, up to a point beyond which larger size conferred no advantage. Received: 7 January 1997 / Accepted after revision: 16 June 1997     

The influence of refuge sharing on social behaviour in the lizard Tiliqua rugosa

Refuge sharing by otherwise solitary individuals during periods of inactivity is an integral part of social behaviour and has been suggested to be the precursor to more complex social behaviour. We compared social association patterns of active versus inactive sheltering individuals in the social Australian sleepy lizard, Tiliqua rugosa, to empirically test the hypothesis that refuge sharing facilitates social associations while individuals are active. We fitted 18 neighbouring lizards with Global Positioning System (GPS) recorders to continuously monitor social associations among all individuals, based on location records taken every 10 min for 3 months. Based on these spatial data, we constructed three weighted, undirected social networks. Two networks were based on empirical association data (one for active and one for inactive lizards in their refuges), and a third null model network was based on hypothetical random refuge sharing. We found patterns opposite to the predictions of our hypothesis. Most importantly, association strength was higher in active than in inactive sheltering lizards. That is, individual lizards were more likely to associate with other lizards while active than while inactive and in shelters. Thus, refuge sharing did not lead to increased frequencies of social associations while lizards were active, and we did not find any evidence that refuge sharing was a precursor to sleepy lizard social behaviour. Our study of an unusually social reptile provides both quantitative data on the relationship between refuge sharing and social associations during periods of activity and further insights into the evolution of social behaviour in vertebrates.     

Mate fidelity in an Australian lizard Trachydosaurus rugosus

Summary The Australian sleepy lizard Trachydosaurus rugosus is a large mainly herbivorous skink, which occupies overlapping home ranges. In the Mt. Mary study area, South Australia, 6567 captures were made of 2412 different individuals between February 1982 and December 1986. The mating season when male and female lizards formed pairs was in the spring months of October and November. Some lizards were captured in pairs more than once in the same mating season. Amongst this group over 90% of females and over 70% of males were found with the same partner. These monogamous pair-bonds lasting up to eight weeks, had been predicted by Stamps (1983) for large lizards with overlapping home ranges. In addition 79% of females and 68% of males recaptured in pairs in subsequent years were found with the same partner. This mate fidelity is too high to be accounted for by chance encounters. The selective advantages of actively choosing the same partner each year are discussed.     

Locomotor kinematics and behaviour in the escape response of European sea bass, Dicentrarchus labrax L., exposed to hypoxia

To assess the effect of oxygen reduction on the escape response of sea bass, Dicentrarchus labrax, an integrative experimental approach was employed. The effect of hypoxia was tested on locomotor variables, i.e. cumulative distance (D), maximum swimming speed (V _max) and maximum acceleration (A _max). Behavioural variables, such as responsiveness (i.e. the proportion of individuals responding out of the total number of fish tested), response latency (i.e. the time interval between stimulus onset and the first detectable movement leading to the escape of the animal) and directionality (i.e. the proportion of escape responses in which the first detectable movement of the head was oriented away or towards the stimulus at its onset) were also considered. Four levels of oxygen were used: >85% (i.e. normoxia, the control treatment), 50, 20 and 10% of air saturation. Sea bass responsiveness decreased significantly at 10% of air saturation, while hypoxia did not have any effect on the response latency. At the onset of the escape response, the proportion of away/towards responses was random when oxygen was ≤50% of air saturation, suggesting an impairment of the left–right discrimination. Whatever the level of hypoxia, none of the locomotor variables (i.e. D, V _max and A _max) was significantly different from normoxia. Our study suggests that hypoxia may reduce sea bass elusiveness facing a predator by directly affecting its escape behaviour, possibly related to an impairment of the mechano-sensory performance and/or in the Mauthner cells involved in triggering the escape response.     

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     

Homing behaviour in the sleepy lizard (Tiliqua rugosa): the role of visual cues and the parietal eye

To investigate how visual cues are integrated into a navigational strategy for homing in the Australian sleepy lizard (Tiliqua rugosa), lizards were displaced beyond their home range, either with full access to visual cues or with no access to visual cues during the displacement. Homeward orientation was significantly worse when lizards were denied visual cues during the displacement than when they were not. However when lizards were displaced with their field of view restricted to the sky, their homeward orientation was equally as good as that of lizards displaced with no visual restriction. These experiments suggest that sleepy lizards use celestial cues to determine the compass bearing of the outward journey, and reverse this bearing to orient in the homeward direction (course reversal). In a subsequent experiment, lizards oriented randomly with respect to home when the parietal eye was entirely covered with a patch during the displacement and return, while control lizards fitted with a sham parietal eye patch were well oriented towards home. In both groups, the lateral eyes were unobstructed and had complete access to visual cues including celestial cues and landmarks. These results suggest that the parietal eye plays a highly significant role in sleepy lizard homing, perhaps mediating a sky polarization compass sense.     

Dominance and reproduction in a parthenogenetic lizard

Summary In most vertebrates, males and females are believed to differ in terms of their investment in offspring. Dominance theory suggests that one way individuals of the sex with lower parental investment can increase reproductive success would be to dominate others of the same sex. The dominant competitors are thought to achieve preferred access to mates, and thus, have greater reproductive success than subordinates.Reproduction in parthenogenetic Cnemidophorus uniparens normally proceeds without males, but individuals exhibit mounting behaviors in captivity that are typical of closely related Cnemidophorus species that reproduce sexually. Thus, these animals provide an unusual opportunity to study the effects of behavior on reproduction apart from copulation and fertilization. In this study relationships between dominance and reproduction were investigated in the unisexual lizard species, C. uniparens. Dominance hierarchies were rapidly established and maintained in the laboratory by agonistic encounters among individuals. The number of times an individual charged its cagemates was positively correlated with the number of clutches and eggs laid. Also, dominant animals who charged their cagemates were likely to win agonistic encounters; recipients of charges usually fled. Hierarchies based on different behaviors were not all related to reproduction. Charges as a predictor of dominance was unrelated to body length, percent increase in body length and time spent in the basking site. However, individuals with a high percent increase in body length spent more time basking. This is likely a result of the increased energy demands of growth in addition to reproduction. Physiological stress as measured by plasma corticosterone titers was unrelated to dominance. We suggest that dominance is an important factor affecting reproduction in C. uniparens.     

Shifted balance of risk and cost after autotomy affects use of cover,escape, activity,and foraging in the keeled earless lizard (<Emphasis Type="Italic">Holbrookia propinqua</Emphasis>)

Autotomy of expendable body parts is often a successful last-chance antipredatory defense for a variety of invertebrates and vertebrates, especially lizards. However, loss of a body part imposes costs and risks, some of which may be reduced by modifying subsequent behavior. I studied effects of experimentally induced autotomy of the tail in the keeled earless lizard (Holbrookia propinqua) on use of cover, escape behavior, activity, and feeding. Autotomized lizards stayed closer to plant cover than sham-autotomized lizards (having intact tails) when approached by an investigator simulating a predator. Autotomized males, but not females, fled further than sham-autotomized lizards. Autotomy did not affect the distance from an approaching predator when the lizards began to flee. After autotomy, the number of days on which lizards were active differed between sexes and lizards made fewer attempts to catch prey per unit time than lizards with intact tails. Tail loss did not affect the percentage of time spent moving. Staying closer to refuge, fleeing further after autotomy, and decreasing surface activity may compensate for decreased maximum escape speed or agility, and may reflect use of a greater margin of safety when the tail is unavailable for autotomy. Decrease in surface activity may be comparable to use of safer microhabitats reported for other lizards and damselflies subsequent to autotomy. Several possible reasons for the lower rate of feeding attempts by autotomized lizards are discussed.     

Tradeoffs between courtship, fighting, and antipredatory behavior by a lizard, Eumeces laticeps

Male fitness in many species depends strongly on social behaviors needed to obtain fertilizations and prevent loss of fertilizations to other males, but courtship, copulation, and fighting may incur increased risk of predation. When demands for reproductive and antipredatory behaviors conflict, fitness may be maximized by accepting some degree of risk to enhance reproductive success. To examine such tradeoffs, I introduced tethered conspecific males or females to adult male broad-headed skinks, Eumeces laticeps, in the field and observed how close they allowed a simulated predator (me) to approach before fleeing, or their latency to approach an introduced female located at different distances from the predator. When conspecific males were introduced, isolated and mate-guarding males initiated agonistic behaviors and permitted closer approach than control males, and mate-guarding males permitted closer approach than isolated males. When females were introduced, both isolated and mate-guarding males courted the introduced females and isolated males permitted closer approach than did mate-guarding males. These results for introduced males and females suggest that increasing risk was accepted when reproductive benefits were greater. Latency for isolated males to approach a conspecific female was greater when the predator was closer to the female, further suggesting sensitivity to predation risk during a reproductive opportunity. Relationships between reproductive and antipredatory behaviors have been studied much less than those between feeding and antipredatory behaviors, but this study indicates that animals balance increased risk of predation with the opportunity to perform several reproductively important behaviors. Received: 5 March 1999 / Received in revised form: 15 July 1999 / Accepted: 25 July 1999     

Symmetry, male dominance and female mate preferences in the Iberian rock lizard, Lacerta monticola

Female preference for dominant males is widespread and it is generally assumed that success in male-male competition reflects high quality. However, male dominance is not always attractive to females. Alternatively, relatively symmetric individuals may experience fitness advantages, but it remains to be determined whether males with more symmetrical secondary sexual traits experience advantages in both intra- and intersexual selection. We analysed the factors that determine dominance status in males of the lizard Lacerta monticola, and their relationship to female mate preference, estimated by the attractiveness of males' scents to females. Sexually dimorphic traits of this lizard (head size and femoral pores) appear to be advanced by different selection pressures. Males with relatively higher heads, which give them advantage in intrasexual contests, were more dominant. However, head size was unimportant to females, which preferred to be in areas marked by relatively heavier males, but also by males more symmetric in their counts of left and right femoral pores. Chemicals arising from the femoral pores and other glands might honestly indicate quality (i.e. related to the symmetry levels) of a male to females and may result from intersexual selection. Females may use this information because the only benefit of mate choice to female lizards may be genetic quality. Chemical signals may be more reliable and have a greater importance in sexual selection processes of lizards than has previously been considered.     

Mate choice games, context-dependent good genes, and genetic cycles in the side-blotched lizard, Uta stansburiana

According to mate choice models, a female should prefer males with traits that are reliable indicators of genetic quality which the sire can pass on to their progeny. However, good genes may depend on the social environment, and female choice for good genes should be context dependent. The side-blotched lizard, Uta stansburiana, exhibits genetically based throat colors (orange, blue, or yellow) that could be used as a sexually selected signal since they reliably predict the genetic quality of mates. The frequencies of male and female morphs cycle between years, and both male and female morphs have an advantage when rare; thus genetic quality will depend on morph frequency. A female should choose a sire that maximizes the reproductive success of both male and female progeny. We examine a game theoretical model that predicts female mate choice as a function of morph frequency and population density. The model predicts the following flexible mate choice rule: both female morphs should prefer rare males in ’boom years’ of the female cycle (e.g., ’rarest-of-N rule’), but prefer orange males in ’crash years’ of the female cycle (’orange-male rule’). Cues from the current social environment should be used by females to choose a mate that maximizes the future reproductive success of progeny, given the social environment of the next generation. We predict that the cue is the density of aggressive orange females. In the side-blotched lizard, cycling mate choice games and context-dependent mate choice are predicted to maintain genetic variation in the presence of choice for good genes. Received: 8 March 2000 / Revised: 26 August 2000 / Accepted: 4 September 2000     

Locomotory behaviour and swimming performance of the Norway lobster,Nephrops norvegicus,in the presence of an acoustic tag

Observations have been made on the locomotory behaviour and swimming performances of the Norway lobster, Nephrops norvegicus (L.), fitted with an acoustic transmitter ventrally under the cephalothorax. The walking behaviour of adult males (44 mm carapace length) appeared to be unaffected, but the tag caused significant reductions in certain measures of tail-flip swimming performance such as swimming speed and endurance. Flume-tank experiments in low water currents suggested that the transmitter would increase hydrodynamic drag during swimming by 9 to 32%, depending on lobster size. Given the weight and dimensions of the acoustic transmitters currently available, it is considered advisable to confine acoustic tracking studies to relatively large N. norvegicus.Correspondence to: C. J. Chapman     

Home range overlap of mothers and their offspring in the sleepy lizard, Tiliqua rugosa

This paper reports a field investigation of interactions between juveniles and their mothers in the Australian sleepy lizard, Tiliqua rugosa. In their first spring season, juvenile lizards maintain home ranges largely within the home range of their mother. Juvenile home ranges are significantly smaller than those of adult males and females, and juveniles move significantly less often and significantly shorter distances than adults. While siblings were never found together in the spring, they showed a significant tendency to be closer to each other than if they were randomly located in their home ranges. Juveniles and mothers were never found together, nor was there any evidence for any positive (or negative) spatial association. Nevertheless, the extended tolerance of home range overlap represents a greater degree of mother-offspring association than has been previously reported for other lizards. Despite this, the level of parental care can only be described as minimal. Received: 20 June 1997 / Accepted after revision: 29 December 1997     

Inter-colony movements,at-sea behaviour and foraging in an immature seabird: results from GPS-PPT tracking,radio-tracking and stable isotope analysis

Seabird populations contain large numbers of immatures––in some instances comprising >50% of the fully grown adults in the population. These birds are significant components of marine food webs and may contribute to compensatory recruitment and dispersal, but remain severely understudied. Here, we use GPS-PTTs, radio-tracking and analysis of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes to investigate the movements and foraging ecology of immature seabirds. Our study focussed on immature northern gannets Morus bassanus aged 2–4 attending non-breeding aggregations alongside a large breeding colony. GPS-PTT tracking of five birds revealed that immatures have the ability to disperse widely during the breeding season, with some individuals potentially prospecting at other colonies. Overall, however, immatures were faithful to the colony of capture. During returns to the focal colony, immatures acted as central place foragers, conducted looping and commuting flights, and analysis of the variance in first-passage time revealed evidence of area-restricted search (ARS) behaviour. In addition, stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope analyses indicate that immatures were isotopically segregated from breeders. Our findings provide insights into the foraging, prospecting and dispersal behaviour of immature seabirds, which may have important implications for understanding seabird ecology and conservation.     

Odour-guided social behaviour in newborn and young cats: an analytical survey

Summary. This article surveys early chemosensory mechanisms regulating behaviour in neonatal and juvenile domestic cats (Felis sylvestris catus). It aims to retrieve material from the available literature which may promote a better understanding of the semiochemical system that supports female-to-kitten exchanges. Studies dealing with the development of olfaction from birth through weaning are presented in three sections. The first aims at locating developmental periods suitable for applying analytical procedures combining behaviour and chemistry. The second section offers a survey of observational and experimental work related to the role of olfaction in the social and feeding behaviour of kittens before weaning. The final section traces the current knowledge on the odour sources and substrates that may be involved in early mother-kitten transactions.