Jane Lecomte

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.

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.

High diversity of oilseed rape pollen clouds over an agro-ecosystem indicates long-distance dispersal

Estimating the frequency of long‐distance pollination is important in cultivated species, particularly to assess the risk of gene transfer following the release of genetically modified crops. For this purpose, we estimated the diversity and origin of fertilizing pollen in a 10 × 10 km French oilseed rape production area. First, the cultivar grown in each field was identified through surveys to farmers and using microsatellite markers. Examination of the seed set in fields indicated high rates of seed contamination (8.7%) and pollination from other sources (5%). Then, male‐sterile plants were scattered over the study area and their seed genotyped using the same markers. Most pollination was local: 65% of the seeds had a compatible sire in the closest field, i.e. at 50 or 300 m depending on site, but the nearest compatible field was found more than 1000 m away for 13% of the seeds. To assess the diversity of fertilizing pollen, each seed was assigned to the nearest putative siring cultivar. The observed diversity of pollen was then compared to that predicted by simulations using three empirical dispersal models with increasing proportion of long‐distance pollination. The diversity was sensitive to the dispersal kernel used in the simulations, fatter‐tailed functions predicting higher diversities. The dispersal kernel that was more consistent with our data predicted more long‐distance dispersal than the exponential function.

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

Age-specific mating strategies and reproductive senescence.

While males gain obvious direct advantages from multiple mating, the reproductive capacity of females is more constrained. The reason why polyandry evolved in females is therefore open to many conjectures. One hypothesis postulates that females gain indirect benefits by increasing the probability of siring young from high quality males. To explore this hypothesis, we used the natural variation of the reproductive value that males and females undergo through age. The age‐related variation of phenotypic performance might then induce variations in mating strategies in males and females. Using the common lizard (Lacerta vivipara) as our model system, we showed that reproductive immaturity and senescence created variability in both male and female reproductive success (including survival of offspring). Consistent with theory, males at their best‐performing phenotype adopted a polygynous strategy. These males were of an intermediate age and they produced offspring of higher viability than younger and older males. In contrast, females at their best performing phenotype, also of an intermediate age, were less polyandrous than other less‐ performing females. Middle‐aged females tended to mate with males of an intermediate age and produced litters with higher viability independently from their reproductive strategy. Males of an intermediate age enhanced their fitness by additional matings with young or old females. Young and old females increased their fitness by being more polyandrous. Polyandry therefore appears as means to seek for good males. A positive correlation between males and their partners’ fitness disagree with the idea that polyandry is the result of a sexual conflict in this species.

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.

Long-lasting fitness consequences of prenatal sex ratio in a viviparous lizard.

Abstract Maternal effects and early environmental conditions are important in shaping offspring developmental trajectories. For example, in laboratory mammals, the sex ratio during gestation has been shown to influence fitnessrelated traits via hormonal interaction between fetuses. Such effects have the potential to shape, or constrain, many important aspects of the organisms life, but their generality and importance in natural populations remain unknown. Using long‐term data in a viviparous lizard, Lacerta vivipara, we investigated the relationship between prenatal sex ratio and offspring growth, survival, and reproductive traits as adults. Our results show that females from male‐biased clutches grow faster, mature earlier, but have lower fecundity than females from female‐biased clutches. Furthermore, male reproduction was also affected by the sex ratio during embryonic development, with males from male‐biased clutches being more likely to successfully reproduce at age one than males from female‐biased clutches. Thus, the sex ratio experienced during gestation can have profound and long‐lasting effects on fitness in natural populations of viviparous animals, with important implications for life‐history evolution and sex allocation.

Optimal level of inbreeding in the common lizard.

Mate choice with regard to genetic similarity has been rarely considered as a dynamic process. We examined this possibility in breeding populations of the common lizard (Lacerta vivipara) kept for several years in semi-natural conditions. We investigated whether they displayed a pattern of mate choice according to the genetic similarity and whether it was context-dependent. Mate choice depended on genetic similarity with the partner and also on age and condition. There was no systematic avoidance of inbreeding. Females of intermediate ages, more monogamous, did not mate with genetically similar partners, whereas younger and older females, more polyandrous, did but highest clutch proportions were associated with intermediate values of pair-relatedness. These results indicate dynamic mate choice, suggesting that individuals of different phenotypes select their partners in different ways according to their genetic similarity. We consider our results in the light of diverse and apparently contradictory theories concerning genetic compatibility, and particularly, optimal inbreeding and inclusive fitness.

Evolution in the Anthropocene

Taking account of the evolutionary effects of human actions is crucial for humans and nonhumans Most current conservation strategies focus on the immediate social, cultural, and economic values of ecological diversity, functions, and services (1). For example, the Intergovernmental Platform on Biodiversity and Ecosystem Services (2) mostly addresses the utilitarian management of biodiversity from local to global scales. However, besides urgent diagnosis and actions (3, 4), processes that occur over evolutionary time scales are equally important for biodiversity conservation. Strategizing for conservation of nature at such long time scales will help to preserve the function—and associated services—of the natural world, as well as providing opportunities for it to evolve. This approach will foster a long-term, sustainable interaction that promotes both the persistence of nature and the wellbeing of humans.

Seed Spillage from Grain Trailers on Road Verges during Oilseed Rape Harvest: An Experimental Survey

Context Anthropogenic vectors enhance the natural dispersal capacity of plant seeds significantly in terms of quantity and distance. Human-mediated seed dispersal (i.e. anthropochory) greatly increases the dispersal of crop species across agroecosystems. In the case of oilseed rape (OSR), spillage of seeds from grain trailers during harvest has never been quantified. Methods Our experimental approach involved establishing 85 seed trap-sites on the road verges of an agricultural area around the grain silo of Selommes (Loir-et-Cher, France). We recorded OSR spillage during harvest and applied a linear model to the data. Results The amount of seed spilled was related positively to the area of the OSR fields served by the road, whereas the amount of seed spilled decreased with other variables, such as distance from the trap-site to the verge of the road and to the nearest field. The distance to the grain silo, through local and regional effects, affected seed loss. Local effects from fields adjacent to the road resulted in a cumulative spillage on one-lane roads. On two-lane roads, spillage was nearly constant whatever the distance to the silo due to a mixture of these local effects and of grain trailers that joined the road from more distant fields. From the data, we predicted the number of seeds lost from grain trailers on one road verge in the study area. We predicted a total spillage of 2.05×106 seeds (±4.76×105) along the road length, which represented a mean of 404±94 seeds per m2. Conclusion Containment of OSR seeds will always be challenging. However, seed spillage could be reduced if grain trailers were covered and filled with less seed. Reducing distances travelled between fields and silos could also limit seed loss.