Effect of MHC and inbreeding on disassortative reproduction: A data revisit, extension and inclusion of fertilization in sand lizards

The harmful effects of close inbreeding have been recognized for centuries and, with the rise of Mendelian genetics, was realized to be an effect of homozygosis. This historical background led to great interest in ways to quantify inbreeding, its depression effects on the phenotype and flow‐on effects on mate choice and other aspects of behavioral ecology. The mechanisms and cues used to avoid inbreeding are varied and include major histocompatibility complex (MHC) molecules and the peptides they transport as predictors of the degree of genetic relatedness. Here, we revisit and complement data from a Swedish population of sand lizards (Lacerta agilis) showing signs of inbreeding depression to assess the effects of genetic relatedness on pair formation in the wild. Parental pairs were less similar at the MHC than expected under random mating but mated at random with respect to microsatellite relatedness. MHC clustered in groups of RFLP bands but no partner preference was observed with respect to partner MHC cluster genotype. Male MHC band patterns were unrelated to their fertilization success in clutches selected for analysis on the basis of showing mixed paternity. Thus, our data suggest that MHC plays a role in pre‐copulatory, but not post‐copulatory partner association, suggesting that MHC is not the driver of fertilization bias and gamete recognition in sand lizards.

Inbreeding effects on telomeres in hatchling sand lizards (Lacerta agilis): An optimal family affair?

Telomeres are nucleotide-protein caps, predominantly at the ends of Metazoan linear chromosomes, showing complex dynamics with regard to their lengthening and shortening through life. Their complexity has entertained the idea that net telomere length and attrition could be valuable biomarkers of phenotypic and genetic quality of their bearer. Intuitively, those individuals could be more heterozygous and, hence, less inbred. However, some inbred taxa have longer, not shorter, telomeres. To understand the role of inbreeding in this complex scenario we need large samples across a range of genotypes with known maternity and paternity in telomere-screened organisms under natural conditions. We assessed the effects of parental and hatchling inbreeding on telomere length in >1300 offspring from >500 sires and dams in a population of sand lizards (Lacerta agilis). Maternal and paternal ID and their interactions predict hatchling telomere length at substantial effect sizes (R²  > .50). Deviation from mean maternal heterozygosity statistically predicts shorter offspring telomeres but this only when sibship is controlled for by paternal ID, and then is still limited (R²  = .06). Raw maternal heterozygosity scores, ignoring absolute deviation from the mean, explained 0.07% of the variance in hatchling telomere length. In conclusion, inbreeding is not a driver of telomere dynamics in the sand lizard (Lacerta agilis) study system.

High predation risk decimates survival during the reproduction season

Predators attack conspicuous prey phenotypes that are present in the environment. Male display behavior of conspicuous nuptial coloration becomes risky in the presence of a predator, and adult males face higher predation risk. High predation risk in one sex will lead to low survival and sex ratio bias in adult cohorts, unless the increased predation risk is compensated by higher escape rate.Here, we tested the hypothesis that sand lizards (Lacerta agilis) have sex-specific predation risk and escape rate. We expected the differences to manifest in changes in sex ratio with age, differences in frequency of tail autotomy, and in sex-specific survival rate.We developed a statistical model to estimate predation risk and escape rate, combining the observed sex ratio and frequency of tail autotomy with likelihood-based survival rate. Using Bayesian framework, we estimated the model parameters. We projected the date of the tail autotomy events from growth rates derived from capture-recapture data measurements.We found statistically stable sex ratio in age groups, equal frequency of tail regenerates between sexes, and similar survival rate. Predation risk is similar between sexes, and escape rate increases survival by about 5%. We found low survival rate and a low number of tail autotomy events in females during months when sand lizards mate and lay eggs, indicating high predator pressure throughout reproduction. Our data show that gravid females fail to escape predation.The risks of reproduction season in an ectotherm are a convolution of morphological changes (conspicuous coloration in males and body allometry changes in gravid females), behavior (nuptial displays), and environmental conditions which challenge lizard thermal performance. Performance of endotherm predators in cold spring months endangers gravid females more than displaying males in bright nuptial coloration.

Effects of resource availability on the web structure of female western black widows: is the web structure constrained by physiological trade-offs?

A major challenge of biological research is to understand what generates and maintains consistent behavioral variation among animals. Time and energy trade-offs, where expressing one behavior is achieved at the expense of another, are often suggested to favor the maintenance of behavioral differences between individuals. However, few studies have investigated how individuals adjust their allocation to different functions over time and depending on resource abundance. Black widow spiders of the genus Latrodectus build persistent webs that include structural threads which protect against predators and sticky trap threads to capture prey. Web structure consistently differs among individuals in the number of trap and structural threads. To quantify the intensity of a trade-off, we assessed the relationship between the number of structural and trap threads and tested whether varying food abundance affected individual differences in web structure. We further quantified how these individual differences change over time and with food abundance. We subjected spiders to three different levels of prey abundance and monitored the structure of their webs every twelve hours. We found no evidence for a trade-off between trap and structural threads. Instead, spiders that produced more structural threads also produced more trap threads, showing that spiders invested equally in both types of threads. Interestingly, the magnitude of individual differences in web structure was greatest when spiders were fed ad libitum and at the beginning of web construction. We suggest that variation in web structure between spiders could be the result of stable developmental differences in morphology or genetic differences.

Reproductive Biology, Sperm storage, and Sexual Maturity of Thamnodynastes strigatus (Serpentes: Dipsadidae)

Life history strategies determine and influence many aspects of species fitness. In this study, we describe the reproductive biology - reproductive cycle, sperm storage, and sexual maturity - of Thamnodynastes strigatus in South Brazil. We analyzed 49 individuals (25 males and 24 females) from herpetological collections. The reproductive cycle of males and females was described considering the morpho-anatomical and histological changes in the testes, ductus deferens, and kidney, as well in the ovary and oviduct. The age at the onset of sexual maturity was determined by skeletochronology of the caudal vertebra. The reproductive cycle is seasonal semi-synchronous and most individuals have a reproductive peak in spring and summer. The seasonal biennial reproductive cycle and viviparity are two phylogenetically conserved characters in Tachymenini snakes. Thamnodynastes Strigatus females store sperm in the utero-vaginal junction furrows during autumn. There were no differences between the ages of sexual maturity of males (4-11y) and females (4-12y). Females reach sexual maturity at larger body sizes, and this may confer an adaptive advantage due to a higher fecundity potential. Herein, we confirmed the previously described seasonal biennial reproductive cycle of T. strigatus through histological analysis.

Beneficial Effects of Warming Temperatures on Embryonic and Hatchling Development in a Low-Latitude Margin Population of the High-Latitude Lizard Lacerta agilis

The effects of warming temperatures on embryonic and hatchling development are critical for determining the vulnerability of species to climate warming. However, these effects have rarely been investigated in high-latitude oviparous species, particularly in their low-latitude margin populations. This study investigated the embryonic and hatchling development and fitness-related traits of a low-latitude margin population of a high-latitude lizard (Lacerta agilis). These traits were examined under present (24°C), moderate warming (27 and 30°C), and severe warming scenarios (33°C). Based on embryonic and hatchling responses to thermal variation, this study aimed to predict the vulnerability of the early life stages of low-latitude margin population of Lacerta agilis to climate warming. The incubation period of the low-latitude margin population of Lacerta agilis decreased as the temperature increased from 24 to 33°C. Hatching success was similar at 24, 27, and 30°C but decreased significantly at 33°C. No differences with temperature were observed for hatchling snout-vent length and hatchling body mass. The sprint speed was higher for hatchlings from temperatures of 24 and 33°C. The growth rate of hatchlings was highest at 30°C; however, the survival rate of hatchlings was not affected by the thermal environment. This study demonstrated that even for a low-latitude margin population of the high-latitude lizard, Lacerta agilis, moderate warming (i.e., 27 and 30°C) would benefit embryonic and hatchling development. This was indicated by the results showing higher hatching success, growth rate, and survival rate. However, if temperatures increase above 33°C, development and survival would be depressed significantly. Thus, low-latitude margin population of high-latitude species Lacerta agilis would benefit from climate warming in the near future but would be under stress if the nest temperature exceeded 30°C.

Trade-off between flight capability and reproduction in Acridoidea (Insecta: Orthoptera)

In many insect taxa, there is a well-established trade-off between flight capability and reproduction. The wing types of Acridoidea exhibit extremely variability from full length to complete loss in many groups, thus, provide a good model for studying the trade-off between flight and reproduction. In this study, we completed the sampling of 63 Acridoidea species, measured the body length, wing length, body weight, flight muscle weight, testis and ovary weight, and the relative wing length (RWL), relative flight muscle weight (RFW), and gonadosomatic index (GSI) of different species were statistically analyzed. The results showed that there were significant differences in RWL, RFW, and GSI among Acridoidea species with different wing types. RFW of long-winged species was significantly higher than that of short-winged and wingless species (p < .01), while GSI of wingless species was higher than that of long-winged and short-winged species. The RWL and RFW had a strong positive correlation in species with different wing types (correlation coefficient r = .8344 for male and .7269 for female, and p < .05), while RFW was strong negatively correlated with GSI (r = -.2649 for male and -.5024 for female, and p < .05). For Acridoidea species with wing dimorphism, males with relatively long wings had higher RFW than that of females with relatively short wings, while females had higher GSI. Phylogenetic comparative analysis showed that RWL, RFW, and GSI all had phylogenetic signals and phylogenetic dependence. These results revealed that long-winged individuals are flight capable at the expense of reproduction, while short-winged and wingless individuals cannot fly, but has greater reproductive output. The results support the trade-off between flight and reproduction in Acridoidea.

One or two eggs: what underlies clutch size variation within a gecko species?

Although the majority of reptiles show variable clutch sizes, geckos have a fixed clutch size (one or two eggs) and modify reproductive output by changing the offspring size or clutch frequency. However, the clutch size of several geckos is not strictly fixed at the species level; they actually lay both single- and double-egg clutches. We still do not fully understand if clutch size variation within a gecko species is due to adaptive control or reproductive failure like accidental absorption of one of two eggs. This study investigated differences between single- and double-egg clutches of a gecko species in terms of reproductive frequency, egg size, and offspring trait. I housed mourning geckos Lepidodactylus lugubris in a controlled environment and observed their reproduction for seven years. No large differences between single- and double-egg clutches were detected in reproductive frequency and egg size, indicating that life-history trade-offs do not explain much about clutch size variation. Single-egg was comparable in egg size to double-egg, but hatchlings from single-egg showed significantly lower body condition than did those from double-egg. These results suggest that the single-egg is not only a reduction of reproductive output per clutch, but it may provide negative effect on ontogeny.

Drought-induced Suppression of Female Fecundity in a Capital Breeder

Human-induced global climate change is exerting increasingly strong selective pressures on a myriad of fitness traits that affect organisms. These traits, in turn, are influenced by a variety of environmental parameters such as temperature and precipitation, particularly in ectothermic taxa such as amphibians and reptiles. Over the past several decades, severe and prolonged episodes of drought are becoming commonplace throughout North America. Documentation of responses to this environmental crisis, however, is often incomplete, particularly in cryptic species. Here, we investigated reproduction in a population of pitviper snakes (copperhead, Agkistrodon contortrix), a live-bearing capital breeder. This population experienced a severe drought from 2012 through 2016. We tested whether declines in number of progeny were linked to this drought. Decline in total number offspring was significant, but offspring length and mass were unaffected. Reproductive output was positively impacted by precipitation and negatively impacted by high temperatures. We hypothesized that severe declines of prey species (e.g., cicada, amphibians, and small mammals) reduced energy acquisition during drought, negatively impacting reproductive output of the snakes. Support for this view was found using the periodical cicada (Magicicada spp.) as a proxy for prey availability. Various climate simulations, including our own qualitative analysis, predict that drought events will continue unabated throughout the geographic distribution of copperheads which suggests that long-term monitoring of populations are needed to better understand geographic variation in drought resilience and cascading impacts of drought phenomena on ecosystem function.

Differential reproductive investment in co-occurring oviparous and viviparous common lizards (Zootoca vivipara) and implications for life-history trade-offs with viviparity

Live-bearing reproduction (viviparity) has evolved from egg-laying (oviparity) independently many times and most abundantly in squamate reptiles. Studying life-history trade-offs between the two reproductive modes is an inherently difficult task, as most transitions to viviparity are evolutionarily old and/or are confounded by environmental effects. The common lizard (Zootoca vivipara) is one of very few known reproductively bimodal species, in which some populations are oviparous and others viviparous. Oviparous and viviparous populations can occur in sympatry in the same environment, making this a unique system for investigating alternative life-history trade-offs between oviparous and viviparous reproduction. We find that viviparous females exhibit larger body size, smaller clutch sizes, a larger reproductive investment, and a higher hatching success rate than oviparous females. We find that offspring size and weight from viviparous females was lower compared to offspring from oviparous females, which may reflect space constraints during pregnancy. We suggest that viviparity in common lizards is associated with increased reproductive burden for viviparous females and speculate that this promoted the evolution of larger body size to create more physical space for developing embryos. In the context of life-history trade-offs in the evolution of viviparity, we suggest that the extent of correlation between reproductive traits, or differences between reproductive modes, may also depend on the time since the transition occurred.

Age-related reproduction of female Mongolian racerunners (Eremias argus; Lacertidae): Evidence of reproductive senescence

The reproductive maturation hypothesis, the terminal investment hypothesis, and the senescence hypothesis are the most extensively evaluated hypotheses proposed to explain age-related patterns of reproduction in iteroparous organisms. Here, we evaluated these hypotheses for the Mongolian racerunner (Eremias argus), a short-lived lacertid lizard, by comparing reproductive traits between females that completed reproductive cycles under the same laboratory conditions in two consecutive years (2008 and 2009). Reproductive females gained linear size (snout-vent length) not only as they got 1 year older but also during the breeding season. Larger females generally laid eggs earlier and invested more in reproduction than did smaller ones. Females switched from laying smaller eggs in the first clutch to larger eggs in the subsequent clutches but kept clutch size and postpartum body mass constant between successive clutches in a breeding season and between years. Females that laid more clutches or eggs in 2008 did not lay fewer clutches or eggs in 2009. Of the traits examined, only clutch frequency, annual fecundity, and annual reproductive output were susceptible to ageing. Specifically, the clutch frequency was reduced by 1.1 clutches, annual fecundity by 3.1 eggs and annual reproductive output by 1.0 g in 2009 compared with 2008. Our results suggest that the reproductive maturation hypothesis better explains patterns of reproduction in young or prime-aged females of E. argus, whereas the senescence hypothesis better explains reproductive patterns in old females. The terminal investment hypothesis does not apply to any trait examined because no trait value was maximized in old females.

How accurately do behavioural observations predict reproductive success in free-ranging lizards?

Behavioural ecologists often use data on patterns of male-female association to infer reproductive success of free-ranging animals. For example, a male seen with several females during the mating season is predicted to father more offspring than a male not seen with any females. We explored the putative correlation between this behaviour and actual paternity (as revealed by microsatellite data) from a long-term study on sand lizards ( Lacerta agilis), including behavioural observations of 574 adult males and 289 adult females, and paternity assignment of more than 2500 offspring during 1998-2007. The number of males that contributed paternity to a female's clutch was correlated with the number of males seen accompanying her in the field, but not with the number of copulation scars on her body. The number of females that a male accompanied in the field predicted the number of females with whom he fathered offspring, and his annual reproductive success (number of progeny). Although behavioural data explained less than one-third of total variance in reproductive success, our analysis supports the utility of behavioural-ecology studies for predicting paternity in free-ranging reptiles.

Extreme plasticity in reproductive biology of an oviparous lizard

Most oviparous squamate reptiles lay their eggs when embryos have completed less than one-third of development, with the remaining two-thirds spent in an external nest. Even when females facultatively retain eggs in dry or cold conditions, such retention generally causes only a minor (<10%) decrease in subsequent incubation periods. In contrast, we found that female sand lizards (Lacerta agilis) from an experimentally founded field population (established ca. 20 years ago on the southwest coast of Sweden) exhibited wide variation in incubation periods even when the eggs were kept at standard (25°C) conditions. Females that retained eggs in utero for longer based on the delay between capture and oviposition produced eggs that hatched sooner. In the extreme case, eggs hatched after only 55% of the "normal" incubation period. Although the proximate mechanisms underlying this flexibility remain unclear, our results from this first full field season at the new study site show that females within a single cold-climate population of lizards can span a substantial proportion of the continuum from "normal" oviparity to viviparity.

Muscles provide an internal water reserve for reproduction

The use of fat to support the energy needs of reproduction (i.e. capital breeding) has been studied in a diversity of taxa. However, despite reproductive output (i.e. young or eggs) being approximately 70% water, little is known about the availability of internal resources to accommodate the hydric demands of reproduction. Recent research suggests that dehydration increases the catabolism of muscle as a means of maintaining water balance. Accordingly, we investigated the interactive effects of reproductive investment and water deprivation on catabolism and reproductive output in female Children's pythons (Antaresia childreni). Both reproductive and non-reproductive females were either provided water ad libitum or were water-deprived for three weeks at the time when reproductive females were gravid. We found that water-deprived reproductive females had, in general, greater body mass loss, epaxial muscle loss, plasma osmolality and plasma uric acid concentrations relative to the other groups. Furthermore, water-deprived females had similar clutch sizes compared with females with access to water, but produced lighter eggs and lower total clutch masses. Our results provide the first evidence that selective protein catabolism can be used to support water demands during reproduction, and, as a result, these findings extend the capital breeding concept to non-energetic resources.

Variability of breeding resource partitioning in a lacertid lizard at field scale

Human activities cause increasingly deep alterations to natural environments. Yet, the effects on vertebrates with low dispersal capacity are still poorly investigated, especially at field scale. Life history variation represents one means by which species can adapt to a changing environment. Among vertebrates, lizards exhibit a high degree of variation in life-history traits, often associated with environmental variability. We examined the female breeding output ofPodarcissiculus(Lacertidae) inside agricultural habitats, to test whether different cultivation and management influence the life-history traits of this species. Interestingly, we recorded variability of female breeding output at a very fine scale, namely among adjacent vineyards and olive orchards under different management levels. Lizards displayed the lowest breeding effort in the almost unmanaged sites, while clutch mass, relative fecundity and mean egg mass slightly increased in more intensively managed sites. However, in the most intensive cultivations we detected a life-history trade-off, where eggs from larger clutches tended to be relatively smaller than eggs from smaller clutches. This pattern suggests that agriculture can influence lizard reproductive output, partly favouring it in the presence of medium intensity cultivation but causing, in the most intensively managed sites, some environmental constraints that require a peculiar partitioning of the breeding resources. Even though further studies are needed to clarify the mechanisms driving the observed pattern, our results can be considered a starting point for evaluating the analysis of lizard breeding features as a tool to assess the impact of human activities, at least in agricultural environments.

Selection and constraints on offspring size-number trade-offs in sand lizards (Lacerta agilis)

The trade-off between offspring size and number is a central component of life-history theory, postulating that larger investment into offspring size inevitably decreases offspring number. This trade-off is generally discussed in terms of genetic, physiological or morphological constraints; however, as among-individual differences can mask individual trade-offs, the underlying mechanisms may be difficult to reveal. In this study, we use multivariate analyses to investigate whether there is a trade-off between offspring size and number in a population of sand lizards by separating among- and within-individual patterns using a 15-year data set collected in the wild. We also explore the ecological and evolutionary causes and consequences of this trade-off by investigating how a female's resource (condition)- vs. age-related size (snout-vent length) influences her investment into offspring size vs. number (OSN), whether these traits are heritable and under selection and whether the OSN trade-off has a genetic component. We found a negative correlation between offspring size and number within individual females and physical constraints (size of body cavity) appear to limit the number of eggs that a female can produce. This suggests that the OSN trade-off occurs due to resource constraints as a female continues to grow throughout life and, thus, produces larger clutches. In contrast to the assumptions of classic OSN theory, we did not detect selection on offspring size; however, there was directional selection for larger clutch sizes. The repeatabilities of both offspring size and number were low and we did not detect any additive genetic variance in either trait. This could be due to strong selection (past or current) on these life-history traits, or to insufficient statistical power to detect significant additive genetic effects. Overall, the findings of this study are an important illustration of how analyses of within-individual patterns can reveal trade-offs and their underlying causes, with potential evolutionary and ecological consequences that are otherwise hidden by among-individual variation.

Sand lizard (Lacerta agilis) phenology in a warming world

BACKGROUND

Present-day climate change has altered the phenology (the timing of periodic life cycle events) of many plant and animal populations worldwide. Some of these changes have been adaptive, leading to an increase in population fitness, whereas others have been associated with fitness decline. Representing short-term responses to an altered weather regime, hitherto observed changes are largely explained by phenotypic plasticity. However, to track climatically induced shifts in optimal phenotype as climate change proceeds, evolutionary capacity in key limiting climate- and fitness-related traits is likely to be crucial. In order to produce realistic predictions about the effects of climate change on species and populations, a main target for conservation biologists is thus to assess the potential of natural populations to respond by these two mechanisms. In this study we use a large 15-year dataset on an ectotherm model, the Swedish sand lizard (Lacerta agilis), to investigate how higher spring temperature is likely to affect oviposition timing in a high latitude population, a trait strongly linked to offspring fitness and survival.

RESULTS

With an interest in both the short- and potential long-term effect of rising temperatures, we applied a random regression model, which yields estimates of population-level plasticity and among-individual variation in the average, as well as the plastic, response to temperature. Population plasticity represents capacity for short-term adjustments whereas variation among individuals in a fitness-related trait indicates an opportunity for natural selection and hence for evolutionary adaptation. The analysis revealed both population-level plasticity and individual-level variation in average laying date. In contrast, we found no evidence for variation among females in their plastic responses to spring temperature, which could demonstrate a similarity in responses amongst females, but may also be due to a lack of statistical power to detect such an effect.

CONCLUSION

Our findings indicate that climate warming may have positive fitness effects in this lizard population through an advancement of oviposition date. This prediction is consistent over shorter and potentially also longer time scales as the analysis revealed both population-level plasticity and individual-level variation in average laying date. However, the genetic basis for this variation would have to be examined in order to predict an evolutionary response.

Geographic variation of life-history traits in the sand lizard, Lacerta agilis: testing Darwin's fecundity-advantage hypothesis

The fecundity-advantage hypothesis (FAH) explains larger female size relative to male size as a correlated response to fecundity selection. We explored FAH by investigating geographic variation in female reproductive output and its relation to sexual size dimorphism (SSD) in Lacerta agilis, an oviparous lizard occupying a major part of temperate Eurasia. We analysed how sex-specific body size and SSD are associated with two putative indicators of fecundity selection intensity (clutch size and the slope of the clutch size-female size relationship) and with two climatic variables throughout the species range and across two widespread evolutionary lineages. Variation within the lineages provides no support for FAH. In contrast, the divergence between the lineages is in line with FAH: the lineage with consistently female-biased SSD (L. a. agilis) exhibits higher clutch size and steeper fecundity slope than the lineage with an inconsistent and variable SSD (L. a. exigua). L. a. agilis shows lower offspring size (egg mass, hatchling mass) and higher clutch mass relative to female mass than L. a. exigua, that is both possible ways to enhance offspring number are exerted. As the SSD difference is due to male size (smaller males in L. a. agilis), fecundity selection favouring larger females, together with viability selection for smaller size in both sexes, would explain the female-biased SSD and reproductive characteristics of L. a. agilis. The pattern of intraspecific life-history divergence in L. agilis is strikingly similar to that between oviparous and viviparous populations of a related species Zootoca vivipara. Evolutionary implications of this parallelism are discussed.

Variation of Reproductive Traits and Female Body Size in the Most Widely-Ranging Terrestrial Reptile: Testing the Effects of Reproductive Mode, Lineage, and Climate

The European common lizard, Zootoca vivipara, is the most widespread terrestrial reptile in the world. It occupies almost the entire Northern Eurasia and includes four viviparous and two oviparous lineages. We analysed how female snout-vent length (SVL), clutch size (CS), hatchling mass (HM), and relative clutch mass (RCM) is associated with the reproductive mode and climate throughout the species range and across the evolutionary lineages within Z. vivipara. The studied variables were scored for 1,280 females and over 3,000 hatchlings from 44 geographically distinct study samples. Across the species range, SVL of reproductive females tends to decrease in less continental climates, whereas CS corrected for female SVL and RCM tend to decrease in climates with cool summer. Both relationships are likely to indicate direct phenotypic responses to climate. For viviparous lineages, the pattern of co-variation between female SVL, CS and HM among populations is similar to that between individual females within populations. Consistent with the hypothesis that female reproductive output is constrained by her body volume, the oviparous clade with shortest retention of eggs in utero showed highest HM, the oviparous clade with longer egg retention showed lower HM, and clades with the longest egg retention (viviparous forms) had lowest HM. Viviparous populations exhibited distinctly lower HM than the other European lacertids of similar female SVL, many of them also displaying unusually high RCM. This pattern is consistent with Winkler and Wallin’s model predicting a negative evolutionary link between the total reproductive investment and allocation to individual offspring.

Reproduction and morphology of the common lizard (Zootoca vivipara) from montane populations in Slovakia

The common lizard, Zootoca vivipara (Lichtenstein, 1823), shows high variation in life histories and morphology across its range, which comprises almost the entire Palearctic region. However, this variation is not congruent with the species phylogeny. This suggests an important role of the environment in shaping the variation in morphology and life histories of this species. As most data on life histories originate from only a small number of populations and do not cover the species' geographic range and phylogenetic diversity, to fill a gap and provide more information for future comparative studies we investigated reproduction and morphology in two montane populations from Slovakia, central Europe. This region is characterized by taxonomic and phylogenetic diversity and both montane and lowland ecological forms of the common lizard occur here. The common lizards from the Slovak populations are sexually dimorphic, with females having larger body and abdomen lengths and males having larger heads and longer legs. Female common lizards start to reproduce at a relatively large size compared to most other populations. This is consistent with a relatively short activity season, which has been shown to be the main factor driving variation in body size in the common lizard. Clutch size was also relatively high and positively correlated with body size, abdomen size and head size. One third of all females attaining the size of the smallest gravid female showed no signs of reproductive activity despite mating opportunities, suggesting that not all females reproduce annually in this population.

Maternal influences on early development: preferred temperature prior to oviposition hastens embryogenesis and enhances offspring traits in the Children’s python, Antaresia childreni

Embryonic life is particularly sensitive to its surroundings, and the developmental environment can have long-lasting effects on offspring. In oviparous species, the impacts of the developmental environment on offspring traits are mostly examined during development within the egg. However, as more than 25% of the development of squamate reptiles can occur prior to oviposition, we explored the effect of thermal conditions on development prior to oviposition in an oviparous snake species, the Children’s python (Antaresia childreni). We housed gravid female pythons under three thermal cycles: an optimal regime that reflected maternal preference in a non-constrained environment (constant preferred body temperature of gravid females, Tset=31.5°C) and two mildly suboptimal regimes that shared the same mean temperature of 27.7°C, but differed in the duration at Tset. In one of the constraining regimes, females had access to Tset for 4 h daily whereas in the other regime, females never reached Tset (maximal temperature of 29.0°C). Thermal treatments were maintained throughout gravidity in all three groups, but, after oviposition, all eggs were incubated at Tset until hatching. Compared with the optimal regime, the two suboptimal regimes had a longer duration of gravidity, which resulted in delayed hatching. Between the two suboptimal regimes, gravidity was significantly shorter in the treatment that included time at Tset. Furthermore, suboptimal regimes influenced offspring traits at hatching, including body morphology, antipredator behavior, strength and metabolism. However, partial access to maternal Tset significantly enhanced several offspring traits, including performance. Our results demonstrate the importance of time at Tset on early development and suggest an adaptive significance of maternal thermoregulation prior to oviposition.

The effect of operational sex ratio on sex allocation and neonate phenotype in a viviparous lizard Eremias multiocellata

Maternal investment in the production of male versus female neonates was approximately equal in most animal species. However, sex allocation theory predicts that under certain conditions, selection may favor the females’ ability to adjust the sex ratio of their offspring, which females tend to use more for an investment of the rare sex. The mechanism of operational sex ratio (OSR) influence on sex allocation is still unclear, and recent studies conducted on lizards have reached conflicting conclusions. Here, we selected a viviparous lizard Eremias multiocellata to test whether pregnant females could adjust the sex ratio of their offspring in response to OSRs. Our results showed that mothers did not adjust the sex ratios or phenotypes of neonates in the laboratory and field-based experiments, except tail length. However, the OSRs subsequently affected growth in both mass and SVL of the offspring in laboratory experiments; whereas only the mass was affected in the semi-nature field experiments. Our results, thus, contradict the predictions of sex allocation theory and challenge the idea that female investment in the scarcity sex might serve as a mechanism which is used for adjusting the population sex ratio.

Potentially adaptive effects of maternal nutrition during gestation on offspring phenotype of a viviparous reptile

Viviparous reptiles have been used as model species for many studies that seek to explain the evolution of viviparity. The vast majority of such studies have focused on the advantage viviparity provides with regards to maternal control of embryonic developmental temperature. However, viviparity may also allow increased control of nutrient transfer, such that mothers adaptively manipulate offspring phenotype through varying maternal nutritional support. Because maternal nutritional transfer is temperature dependent, maternal nutritional strategies may vary between climatically distinct populations. In this study we used an orthogonal experimental design in which mothers and offspring from climatically distinct populations of a viviparous skink (Niveoscincus ocellatus) were allocated randomly to either a protein-rich or a protein-poor diet. Our results suggest that N. ocellatus mothers are able to compensate for sub-optimal nutritional conditions and can adaptively manipulate offspring phenotype to best fit the postnatal nutritional environment. Furthermore, maternal nutritional strategies appear to vary between climatically distinct populations. These results suggest that in viviparous reptiles, matrotrophy provides a means of producing an adaptive offspring phenotype, in addition to maternal control of developmental temperature.

Life-history variation with respect to experienced thermal environments in the lizard, Eremias multiocellata (Lacertidae)

We compared adult size, female reproductive traits, and offspring phenotypes between multiocellated racerunners (Eremias multiocellata) from two thermally different sites (populations) in Inner Mongolia (North China): the colder one in Wulatehouqi (WQ) and the warmer one in Dalateqi (DQ). Both adults and neonates were smaller in the colder site. Females from the two sites both produced a single litter of 2-5 young per season, and did not differ in allocation of energy to reproduction after accounting for differences in body size. Female neonates had more ventral scales than did males, and the WQ neonates had fewer ventral scales than did the DQ neonates. The WQ neonates were slower than the DQ neonates. When body length was normalized across populations, we found that (1) hindlimb length correlated positively with sprint speed in both WQ and DQ neonates, (2) forelimb length correlated positively with sprint speed only in the DQ neonates, and (3) tail length correlated positively with sprint speed only in the WQ neonates. Hindlimb length played a more important role in locomotion than did tail length or forelimb length. Though differing in size and morphology, neonates from the two sites did not differ in early growth and survival under identical laboratory conditions. Our data are consistent with many studies that have shown countergradient variation in physiological traits (growth rate and reproductive output) and cogradient variation in morphological traits.

Direct and socially-mediated effects of food availability late in life on life-history variation in a short-lived lizard

Food availability is a major environmental factor that can influence life history within and across generations through direct effects on individual quality and indirect effects on the intensity of intra- and intercohort competition. Here, we investigated in yearling and adult common lizards (Zootoca vivipara) the immediate and delayed life-history effects of a prolonged food deprivation in the laboratory. We generated groups of fully fed or food-deprived yearlings and adults at the end of one breeding season. These lizards were released in 16 outdoor enclosures together with yearlings and adults from the same food treatment and with food-deprived or fully fed juveniles, creating four types of experimental populations. Experimental populations were then monitored during 2 years, which revealed complex effects of food on life-history trajectories. Food availability had immediate direct effects on morphology and delayed direct effects on immunocompetence and female body condition at winter emergence. Also, male annual survival rate and female growth rate and body size were affected by an interaction between direct effects of food availability and indirect effects on asymmetric competition with juveniles. Reproductive outputs were insensitive to past food availability, suggesting that female common lizards do not solely rely on stored energy to fuel reproduction. Finally, food conditions had socially-mediated intergenerational effects on early growth and survival of offspring through their effects on the intensity of competition. This study highlights the importance of social interactions among cohorts for life-history trajectories and population dynamics in stage-structured populations.

Income breeding and temperature-induced plasticity in reproductive traits in lizards

We used the northern grass lizard Takydromus septentrionalis as a model animal to examine the energy allocation strategy and whether body temperature can affect maternal reproductive traits in lizards. We maintained adult females collected from the field soon after winter dormancy under three thermal conditions (24.0+/-1.0 degrees C, 28.0+/-1.0 degrees C and 32.0+/-1.0 degrees C) throughout the subsequent reproductive season, and then recorded their energy intake, digestive efficiency, body size and mass changes, and reproductive parameters. Manipulation of body temperature in reproducing females affected energy intake and several maternal reproductive characteristics. Females allocated energy to reproduction following the fulfillment of energetic requirements for metabolism and growth. The reduced energy availability for reproduction constrained females at low or high body temperatures to produce fewer and smaller eggs per season but had no role in influencing the number of eggs produced in single reproductive bouts. Females used currently acquired energy to fuel reproduction, and this strategy did not shift seasonally from the first to subsequent clutches. Our study supports the idea that the use of currently acquired energy for reproduction may be more widespread in ectotherms than thought before, and shows for the first time that egg size is thermally plastic in T. septentrionalis, where eggs produced in single reproductive bouts are believed to be well optimized for size.

An experimental test of body volume constraint on female reproductive output

The body volume constraint hypothesis is a widely accepted notion that explains proximate limitation of female reproductive output, but lacks empirical support. To examine how body volume determines reproductive output, we experimentally manipulated the body volume of female lacertid lizard (Takydromus septentrionalis), to examine whether a reduction in body volume caused a reduction in reproductive output. Clutch size and mass decreased with a reduction in body volume. Reproductive output (residual clutch mass, R(CM)) was negatively related to body volume reduction (BVR) (R(CM)=-0.008BVR+0.225). In contrast, neither egg size nor offspring size was affected by the manipulation. Relative clutch mass was lower in manipulated females than in control females, but the actual physical burden (egg plus pearls) carried by manipulated females was much bigger than that of the control females. A normal clutch of eggs only filled 55% of maternal body volume, whereas manipulated females used 75% of body volume to contain eggs and pearls. Therefore, females are capable of carrying more eggs than a normal clutch. Our observations provide unequivocal empirical support for the maternal body volume constraint hypothesis. In addition, these results suggest that female T. septentrionalis may produce a clutch of eggs that fill the available abdomen space to an optimal level rather than the physical limit.

Factors influencing offspring traits in the oviparous multi-clutched lizard, Calotes versicolor (Agamidae)

The determinants of offspring size and number in the tropical oviparous multi-clutched lizard, Calotes versicolor, were examined using both univariate and multivariate (path) analyses. In C. versicolor maternal snout-vent length (SVL) and body condition influence clutch mass and clutch size but have no significant influence on offspring size. The positive effect of maternal SVL and body condition on offspring number is counterbalanced by a negative effect of breeding time on egg mass. In fact, breeding time directly influences the offspring body mass and condition through variation in the egg mass. There is a trade-off between offspring mass and condition with offspring number, and breeding time influences both. Offspring hatched from the eggs of early (May-June) or mid (July-August) breeding periods invariably show lower mass and condition than those hatched from the eggs of late breeding season (September-October). Yet, there is no variation in offspring SVL among early, mid and late clutches. Thus, in C. versicolor offspring SVL is optimized while body mass and condition are not optimized.