Manuel Massot

Erosion of lizard diversity by climate change and altered thermal niches

Demise of the Lizards Despite pessimistic forecasts from recent studies examining the effects of global climate change on species, and observed extinctions in local geographic areas, there is little evidence so far of global-scale extinctions. Sinervo et al. (p. 894; see the Perspective by Huey et al.) find that extinctions resulting from climate change are currently reducing global lizard diversity. Climate records during the past century were synthesized with detailed surveys of Mexican species at 200 sites over the past 30 years. Temperature change has been so rapid in this region that rates of adaptation have not kept pace with climate change. The models were then extended to all families of lizards at >1000 sites across the globe, and suggest that climate change-induced extinctions are currently affecting worldwide lizard assemblages. A historical record of lizard populations in Mexico is used to parameterize models that predict global effects of climate change. It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change.

CONSPECIFIC REPRODUCTIVE SUCCESS AND BREEDING HABITAT SELECTION: IMPLICATIONS FOR THE STUDY OF COLONIALITY

Habitat selection is a crucial process in the life cycle of animals because it can affect most components of fitness. It has been proposed that some animals cue on the reproductive success of conspecifics to select breeding habitats. We tested this hypothesis with demographic and behavioral data from a 17-yr study of the Black-legged Kittiwake (Rissa tridactyla), a cliff-nesting seabird. As the hypothesis assumes, the Black-legged Kittiwake nesting environment was patchy, and the relative quality of the different patches (i.e., breeding cliffs) varied in time. The average reproductive success of the breeders of a given cliff was predictable from one year to the next, but this predictability faded after several years. The dynamic nature of cliff quality in the long term is partly explained by the autocorrelation of the prevalence of an ectoparasite that influences reproductive success. As predicted by the performance-based conspecific attraction hypothesis, the reproductive success of current breeders on a given cliff was predictive of the reproductive success of new recruits on the cliff in the following year. Breeders tended to recruit to the previous year’s most productive cliffs and to emigrate from the least productive ones. Consequently, the dynamics of breeder numbers on the cliffs were explained by local reproductive success on a year-to-year basis. Because, on average, young Black-legged Kittiwakes first breed when 4 yr old, such a relationship probably results from individual choices based on the assessment of previous-year local quality. When breeders changed breeding cliffs between years, they selected cliffs of per capita higher reproductive success. Furthermore, after accounting for the potential effects of age and sex as well as between-year variations, the effect of individual breeding performance on breeding dispersal was strongly influenced by the average reproductive success of other breeders on the same cliff. Individual breeding performance did not appear to influence the probability of dispersing for birds breeding on cliffs with high local reproductive success, whereas individual breeding performance did have a strong effect on dispersal for birds that bred on cliffs with lower local reproductive success. This suggests that the reproductive success of locally breeding conspecifics may be sufficient to override an individual’s own breeding experience when deciding whether to emigrate. These results, which are supported by behavioral observations of the role of prospecting in recruitment, suggest that both first breeders and adults rely on the reproductive success of conspecifics as “public information” to assess their own chances of breeding successfully in a given patch and to make settling decisions. A corollary prediction is that individuals should attempt to breed near successful conspecifics (a form of social attraction) in order to benefit from the same favorable local environmental conditions. Such a performance-based conspecific attraction mechanism can thus lead to an aggregative distribution of nests and may have played a role in the evolution of coloniality.

DENSITY DEPENDENCE IN THE COMMON LIZARD: DEMOGRAPHIC CONSEQUENCES OF A DENSITY MANIPULATION'

Density dependence plays an important role in the regulation of most pop- ulations. Descriptive studies provide only limited evidence, while density manipulations are thought to be a more powerful tool. Here, we describe such a manipulation. We experimentally analyzed demographic responses to changes in density in common lizard (Lacerta vivipara) populations. Two neighboring sites were studied from 1986 to 1988. At the end of the first year, density was artificially decreased at one site and increased at the other. The evolution of demographic parameters over time (before and after ma- nipulation) was compared between the two sites. We found that: (1) density in each age and sex class quickly converged to pre-experimental values at both sites; (2) survival rates (introduced individuals excluded) were unchanged, except that juvenile mortality was pos- itively related to density; (3) emigration rates remained low and did not seem to be influ- enced by density, while immigration rates were negatively influenced by density; (4) the proportion of young reproductive females was negatively influenced by density; (5) body length and growth rate were negatively influenced by density only in yearlings, and at least in females, no catchup on growth is apparently possible; no difference in reserve storage was found; and (6) female reproduction was modified by the manipulation through clutch size and hatching success, which were negatively influenced by density; however, no dif- ference was detected for hatching date, number of abortive (clear) eggs, prenatal mortality, reproductive investment, and body mass of live neonates. Rapid density readjustments were mostly explained by immigration into the site where density was decreased, and by high mortality of introduced individuals and of native juveniles where density was increased. Other parameters that were influenced by the ma- nipulation could only have induced delayed effects on population density. Different age and sex classes showed different responses to density. These responses indicate that density dependence plays a key role in shaping the demography of this lizard species.

Colour variation and alternative reproductive strategies in females of the common lizard Lacerta vivipara

Within‐sex colour variation is a widespread phenomenon in animals that often plays a role in social selection. In males, colour variation is typically associated with the existence of alternative reproductive strategies. Despite ecological conditions theoretically favourable to the emergence of such alternative strategies in females, the social significance of colour variation in females has less commonly been addressed, relative to the attention given to male strategies. In a population of the common lizard, females display three classes of ventral colouration: pale yellow, orange and mixed. These ventral colours are stable through individuals life and maternally heritable. Females of different ventral colourations displayed different responses of clutch size, clutch hatching success and clutch sex‐ratio to several individual and environmental parameters. Such reaction patterns might reflect alternative reproductive strategies in females. Spatial heterogeneity and presence of density‐ and frequency‐dependent feedbacks in the environment could allow for the emergence of such alternative strategies in this population and the maintenance of colour variation in females.

THE CONTRIBUTION OF PHENOTYPIC PLASTICITY TO ADAPTATION IN LACERTA VIVIPARA

Correlation between intraspecific phenotypic variability and variation of environmental conditions could reflect adaptation. Different phenotypes may result from differential expression of a genotype in different environments (phenotypic plasticity) or from expression of different genotypes (genetic diversity). Populations of Lacerta vivipara exhibit larger adult body length, lower age at maturity, higher fecundity, and smaller neonatal size in humid habitats compared to dry habitats. We conducted reciprocal transplants of juvenile L. vivipara to test for the genetic or plastic origin of this variation. We captured gravid females from four populations that differed in the relative humidity of their habitats, and during the last 2 to 4 weeks of gestation, we manipulated heat and water availability under laboratory conditions. Juveniles were released into the different populations and families were divided to compare growth rate and survival of half‐sibs in two environments. Growth rate and survival were assessed using capture‐recapture techniques. Growth rate was plastic in response to postnatal conditions and did not differ between populations of origin. Survival differed between populations of origin, partially because of differences in neonatal body length. The response of juvenile body length and body condition to selection in the different habitats was affected by the population of origin. This result cannot be simply interpreted in terms of adaptation; however, phenotypic plasticity of fecundity or juvenile size most probably resulted in adaptive reproductive strategies. Adaptation to the habitat by means of genetic specialization was not detected. Further investigation is needed to discriminate between genetic and long‐term maternal effects.

Influence of maternal food availability on offspring dispersal

Prenatal effects caused by the maternal environment during gestation are known to contribute to the phenotype of the offspring. Whether they have some adaptive value is currently under debate. We experimentally tested the existence of such a maternal effect (food availability during gestation) on dispersal of offspring in the common lizard (Lacerta vivipara). Pregnant females were captured and kept in the laboratory until parturition. During this period, females were offered two rates of food delivery. After parturition, we released mothers and offspring at the mothers capture point. Dispersal of young was significantly affected by the mothers nutrition. To our knowledge, this is the first evidence of a prenatal effect on dispersal. Offspring of well fed mothers dispersed at a higher rate than those of less well fed mothers. As current hypotheses clearly predict the opposite result, our evidence calls for their reassessment. Dispersers are not always the least fit individuals or those coming from the poorest environments.

Multiple paternity in clutches of common lizard Lacerta vivipara: data from microsatellite markers

The common lizard (Lacerta vivipara) is a small live‐bearing lacertid that reproduces once a year. In order to document the poorly known mating system of this species, we present here an assessment of multiple paternity using microsatellite markers. Paternities were established within 122 clutches belonging to two wild populations from contrasted areas and to four seminatural enclosed populations. The proportion of multiply sired clutches was found to be very high (between 50.0% and 68.2%) and similar among populations, which suggests that the mating system of this species may be insensitive to environmental and population conditions.

Incumbent Advantage in Common Lizards and their Colonizing Ability

Settlement in a new environment is a key phase in effective dispersal. We investigated this phase in the common lizard (Lacerta vivipara Jacquin) by an experimental introduction of known individuals. Introducing lizards in an already occupied environment revealed a prior-residence advantage and some differences in the ability of individuals to face a new environment under conditions of high intraspecific competition. Transplanted individuals (TI) died in larger numbers than resident ones (RI) immediately after the introduction, except for juveniles. This prior-residence advantage could arise from the difference of familiarity with the local environment or from a dominant behaviour of RI on TI

Sex identification in juveniles of Lacerta vivipara

Sex of juveniles was identified by counting ventral scales in the lizard Lacerta vivipara. Sex can be determined accurately in more than 95 % of cases in the studied populations. Some aspects of the sexual size dimorphism are discussed.

Vertebrate Natal Dispersal: The Problem of Non-Independence of Siblings

The studies on natal dispersal in vertebrates often ignore the family structure and treat the behaviour or siblings as if they were statistically independent. This might lead to erroneous conclusions since the non-independence or siblings is supported empirically. We show the possible misinterpretations that may arise from such approaches and propose a method allowing to avoid this problem. We illustrate this method by using data on natal dispersal or the common lizard Lacerta vivipara