Altitudinal variation in egg retention and rates of embryonic development in oviparous Zootoca vivipara fits predictions from the cold-climate model on the evolution of viviparity

The evolution of reptilian viviparity is favoured, according to the cold‐climate hypothesis, at high latitudes or altitudes, where egg retention would entail thermal benefits for embryogenesis because of maternal thermoregulation. According to this hypothesis, and considering that viviparity would have evolved through a gradual increase in the extent of intrauterine egg retention, highland oviparous populations are expected to exhibit more advanced embryo development at oviposition than lowland populations. We tested for possible differences in the level of egg retention, embryo development time and thermal biology of oviparous Zootoca vivipara near the extreme altitudinal limits of the species distribution in the north of Spain (mean altitude for lowland populations, 235 m asl.; for highland populations, 1895 m asl.). Altitude influenced neither temperature of active lizards in the field nor temperature selected by lizards in a laboratory thermal gradient, and pregnant females selected lower temperatures in the thermal gradient than did males and nonpregnant females across altitudinal levels. Eggs from highland populations contained embryos more developed at the time of oviposition (Dufaure and Hubert's stages 33–35) than eggs of highland populations (stages 30–34) and partly because of this difference incubation time was shorter for highland embryos. When analysed for clutches from both altitudinal extremes at the same embryonic stage at oviposition (stage 33), again incubation time was shorter for highland populations, indicating genuine countergradient variation in developmental rate. Our results indicate that temperature is an environmental factor affecting the geographical distribution of different levels of egg retention in Z. vivipara, as predicted by the cold‐climate hypothesis on the evolution of viviparity.     

Multiple origins of viviparity,or reversal from viviparity to oviparity? The European common lizard (Zootoca vivipara,Lacertidae) and the evolution of parity

The evolution of viviparity in squamates has been the focus of much scientific attention in previous years. In particular, the possibility of the transition from viviparity back to oviparity has been the subject of a vigorous debate. Some studies have suggested this reversal is more frequent than previously thought. However, none of them provide conclusive evidence. We investigated this problem by studying the phylogenetic relationships between oviparous and viviparous lineages of the reproductively bimodal lizard species Zootoca vivipara . Our results show that viviparous populations are not monophyletic, and that several evolutionary transitions in parity mode have occurred. The most parsimonious scenario involves a single origin of viviparity followed by a reversal back to oviparity. This is the first study with a strongly supported phylogenetic framework supporting a transition from viviparity to oviparity.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 1–11.     

The selective basis for increased egg retention: early incubation temperature determines hatchling phenotype in wall lizards (Podarcis muralis)

The thermal environment during development influences many aspects of the phenotype of hatchling reptiles. We hypothesized that temperature should differentially affect early incubation stages, in which differentiation dominates over growth, and late incubation stages, characterized by high growth rates. To test this idea, we incubated eggs of wall lizard ( Podarcis muralis ) under three regimes with the same mean temperature (29 °C), one constant and two variable with opposite sequences: first cold (25 °C) and then hot (32 °C), and vice versa. Hatchlings incubated at high temperature during the initial period had shorter hindlimbs and tails than those incubated under the other two temperature regimes and shorter heads than those incubated initially at low temperature. Thus, temperature experienced by embryos during the early external incubation period produced similar phenotypic responses compared to those reported in previous studies for the same constant temperature applied over the whole incubation period. Because female wall lizards select lower body temperatures during pregnancy, an increase of intrauterine retention would extend the time of exposure of developing embryos to suitable temperatures. Diminution of body temperature during pregnancy is contrary to the expected pattern under the hypothesis that egg retention has evolved to accelerate development, as proposed by the cold-climate model for evolution of viviparity in squamates, and the results of the present study support the alternative hypothesis of developmental optimization as a special case of the broader maternal manipulation view.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 441–447.     

Comparisons of mitochondrial DNA (mtDNA) sequences (16S rRNA gene) between oviparous and viviparous strains of Lacerta vivipara: a preliminary study

The lizard Lacerta vivipara has allopatric oviparous and viviparous populations. The mitochondrial DNA (mtDNA) gene coding for the 16S rRNA was sequenced for several viviparous lizard populations from France, Switzerland, Bulgaria, Czech Republic, The Netherlands, Sweden, and for oviparous lizard populations from the Pyrenean and Cantabric Mountains. Seven distinct groups (three oviparous and four viviparous) were identified. The net nucleotide divergence between oviparous and viviparous haplotypes was 1.3% +/- 0.5 (mean +/- standard deviation). These results on mtDNA, together with other data obtained previously, led us to formulate a biogeographical scenario that could be tested by further research.     

Variation in eggshell characteristics and in intrauterine egg retention between two oviparous clades of the lizard Lacerta vivipara: insight into the oviparity-viviparity continuum in squamates

The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.     

Evolutionary and biogeographical implications of the karyological variations in the oviparous and viviparous forms of the lizard Lacerta (Zootoca) vivipara

The lizard Lacerta ( Zootoca ) vivipara has two modes of reproduction and is variable karyologically. We describe its karyological variation from literature data and from new data on two viviparous populations from France, on two oviparous populations from the Pyrenees in south-western France and on three oviparous populations recently discovered in Slovenia. Males have 36 chromosomes, whereas females have only 35 chromosomes in all viviparous populations and in the Pyrenean oviparous populations. This karyotype has been interpreted to result from a fusion of an ancestral sexual W chromosome with an autosome from the Zl or from the Z2 pair. The karyotype formula is 32 autosomes + ZIZ2W for the female and 32 autosomes + Z1Z1Z2Z2 for the male. The karyotype of the Slovenian oviparous populations, 34 autosomes + ZW in the male and 34 autosomes +ZW in the female, represents an evolutionary stage that preceded the chromosomal fusion. There is minor karyological variation, mainly concerning the W and Z2 chromosomes, within the Pyrenean oviparous populations. This parallels the geographic variation of the W-linked alleles of the MPI enzyme and suggests that allopatric differentiation of these oviparous populations might have occurred in the vicinity of the Pyrenees during the Pleistocene.
The viviparous populations from western Europe carry a metacentric W chromosome, whereas oviparous populations from south-western Europe and eastern viviparous populations both show an acrocentrie, or a subtelocentrie. W chromosome. This suggests that the acrocentric-subtelocentric W is a primitive character and that viviparity probably arose in an eastern lineage of the species.     

Cytogenetical approaches to the problem of form-formation and subspeciation in the complex Lacerta (Zootoca) vivipara (Lacertidae, Sauria)

Results of the author's long-term study of the karyotype of Lacerta (Zootoca) vivipara (family Lacertidae, Sauria) have been generalized and supplemented with relevant literature data. Within the species an interpopular karyotype variability was established, and several chromosomal forms were described. Karyotypes of L. (Z.) vivipara from four new, previously not examined populations have been first presented in this paper, and cytogenetical features of their chromosomes are given. Finally, cytogenetical analysis of particular specimens from different localities enabled the author to reveal a new chromosomal form and to define the limits of distribution of other forms of the species. The complex L. (Z.) vivipara has appeared to be more complicated than earlier believed. This complex includes several chromosomal forms of unclear taxonomic status, and some subspecies characterized by various modes of reproduction and distinct distribution ranges. It has been confirmed that in the complex L. (Z.) vivipara intensive chromosomal changes accompany the processes of form-formation and subspeciation. Some cytogenetical regularities of these processes have been demonstrated and compared with hybridogeneous form-formation and speciation. Based on the critical analysis of the available karyological data, some mechanisms of chromosomal changes were described, and their tendencies were determined. In addition, intraspecific relationships were analysed. The proposed scheme was compared with the pattern of intraspecific phylogeny of L. (Z.) vivipara based on molecular data. It has been shown that a high cytogenetical differentiation of the found chromosomal forms and subspecies is correlated with their low morphological differentiation and with a rather low genetical differentiation. The results of the combined analysis suggest the leading role of cytogenetical data for understanding the processes of form-formation and subspeciation. The importance of chromosomal rearrangements in these processes is emphasized, with special reference to their role in the evolution and phylogeny of the complex L. (Z.) vivipara. Some modes of form-formation and subspeciation in this complex are discussed.     

Copulation and egg retention in an oviparous Caecilian (Amphibia: Gymnophiona)

Viviparity (i.e., the bearing of live young) has evolved from oviparity (egg laying) independently in various major vertebrate lineages, and several transitional stages have been described. The transition from oviparity to viviparity requires the retention of fertilised eggs in the female reproductive tract. Caecilian amphibians (Gymnophiona) display a considerable diversity of reproductive modes, including oviparity and viviparity. Among amphibians, caecilians have also modified the process of internal fertilisation through a special intromittent organ, or phallus, in males. Here we report the oviposition of “embryonated” eggs ranging from various gastrula-to-neurula stages by female Ichthyophis cf. kohtaoensis (Ichthyophiidae) from North-eastern Thailand. In addition, we describe a copulation resulting in an oviposition of embryonated eggs. Our findings will have implications for the further understanding of the evolutionary reproductive biology of amphibians.     

Phenotypic variation in an oviparous montane lizard (Bassiana duperreyi): the effects of thermal and hydric incubation environments

Recent studies have shown that incubation temperatures can profoundly affect the phenotypes of hatchling lizards, but the effects of hydric incubation environments remain controversial. We examined incubation-induced phenotypic variation in Bassiana duperreyi (Gray, 1938; Sauria: Scincidae), an oviparous montane lizard from south-eastern Australia. We incubated eggs from this species in four laboratory treatments, mimicking cool and moist, cool and dry, warm and moist, and warm and dry natural nest-sites, and assessed several morphological and behavioural traits of lizards after hatching. Incubation temperature influenced a lizard's hatching success, incubation period, tail length and antipredator behaviour, whereas variation in hydric conditions did not engender significant phenotypic variation for most traits. However, moisture affected incubation period slightly differently in males and females, and for a given snout-vent length moisture interacted weakly with temperature to affect lizard body mass. Although incubation conditions can substantially affect phenotypic variation among hatchling lizards, the absence of strong hydric effects suggests that hatchling lizards react less plastically to variation in moisture levels than they do to thermal conditions. Thus, our data do not support the generalization that water availability during embryogenesis is more important than temperature in determining the phenotypes of hatchling reptiles.     

Ultraviolet and carotenoid‐based coloration in the viviparous lizard Zootoca vivipara (Squamata: Lacertidae) in relation to age,sex, and morphology

Lizards display structural and pigment‐based colorations, and their visual system is sensitive to wavelengths of 300–700 nm. However, few studies in squamate reptiles have quantified interindividual colour variation that includes the structural ultraviolet (UV) component (300–400 nm). In the present study, we investigated variability of a ventral UV/yellow–red ornamentation in the common lizard Zootoca vivipara, including an analysis of spatial distribution, as well as sex and age differences. We also investigated whether the expression of coloration is related to body size and condition. Our analyses revealed two distinct patches: a gular patch with a strong UV reflectance and a belly patch with a dominant yellow–red reflectance. Males displayed a less saturated throat coloration with higher UV chroma and UV hue, and had a redder but duller belly coloration than females. Yearlings had less elaborate ornaments than adults, although they already displayed a yellow–red sexual dichromatism on the belly. UV sexual dichromatism was only apparent in adults as a result of a weaker UV reflectance in females, suggesting potential fitness costs of a bright UV coloration in that sex. Different colour traits were related to body size in both sexes, as well as to body condition in males. We discuss the potential evolutionary scenarios leading to the maintenance of this ornament in common lizards. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 128–141.     

湿度对黄喉拟水龟胚胎发育与新生幼体特征的影响

黄喉拟水龟(Mauremys mutica Cantor)为东亚常见的淡水水生龟类之一,主要分布于中国、日本和越南.在中国,黄喉拟水龟已成为潜在的水产养殖品种,研究了湿度对黄喉拟水龟胚胎发育和新生幼体的影响.恒温29℃时,用未受精卵做对比,在-12、-150kPa和-300kPa 3种孵化湿度下,观察并记录了黄喉拟水龟胚胎发育过程中卵重的变化、孵化周期、孵化成功率、卵壳龟裂率、卵壳受精斑变化规律及新生幼体的特征.在-12kPa和-150kPa处理组,受精卵在孵化中期开始持续增重;而在-300kPa处理组,受精卵在孵化中期开始持续减轻;孵化湿度显著影响卵壳受精斑的变化,-12kPa处理组的受精斑绕卵短径合拢的时间显著长于-150kPa和-300kPa处理组;受精卵的卵壳龟裂率随着孵化湿度的增加而增加;湿度显著影响新生幼体体重和背甲宽,但对体高、背甲长、腹甲长、腹甲宽以及尾长无明显影响;孵化湿度对孵化周期及新生幼体的运动能力影响不明显.     

Biogeography of Lacerta (Zootoca) vivipara: reproductive mode and enzyme phenotypes in Bulgaria

Lacerta (Zootoca) vivipara , has allopatric oviparous and viviparous populations viviparity is observed from central France and the British Isles to Scandinavia and Russia, while oviparity is restricted to northern Spain and southwestern France, i e the extreme southwestern part of the range Recent observations in the Rila, Balkan, Vitocha, Pirin and Rhodopes mountains indicate that Bulgarian populations of Lacerta (Zootoca) vivipara are indeed viviparous The electrophoretic study of allozymes and the estimation of genetic distances indicate that viviparous lizards from northwest and central France are more closely related to those of Bulgaria, than to the oviparous lizards of southwest France and northwest Spain Variations in reproductive mode and allozymes are not directly related to geographic distances between populations, nor to their latitude populations located at the southwest limit of distribution are oviparous and exhibit alleles ATA^-150 or ATA^-200, whereas, at a comparable latitude, the Bulgarian populations are viviparous and exhibit allele ATA^-100 characteristic of other distant viviparous populations These findings underline the orginality of the oviparous southwestern populations They do not contradict our previous biogeographic scenario     

孵化温度对灰鼠蛇卵孵化期、孵化成功率和孵出幼体特征的影响

用4个恒定温（24－32℃）孵化灰鼠蛇卵,检测温度对孵化期,孵化成功率和孵出幼体特征的影响。在24－32℃范围内,孵化温度显影响孵化期及孵出幼体的体长和剩余卵黄大小,但不影响孵化成功率和孵出幼体的性别,体重,躯干重和脂肪体重。24,26,30和32℃孵化期分别为99．0,72．2,54．7和48．7d。24℃和26℃孵出幼体的体筮大于30℃和32℃孵出幼体;24℃和32℃孵同幼体内的卵黄较多。不同温度下发育的胚胎对卵内物质和能量的利用一定的差异,但差异不显。雌性幼体的体长,尾长和总长均大于雄性幼体,这些两性差异与孵化温度无关。孵出幼体和新生卵内容的灰分含量无显差异,孵化前后卵壳灰分含量也无显差异,表明灰鼠蛇的卵黄可提供胚胎发育所需的所有无机物。     

Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia,Scincidae, Saiphos)

The eggshell of lizards is a complex structure composed of organic and inorganic molecules secreted by the oviduct, which protects the embryo by providing a barrier to the external environment and also allows the exchange of respiratory gases and water for life support. Calcium deposited on the surface of the eggshell provides an important nutrient source for the embryo. Variation in physical conditions encountered by eggs results in a tradeoff among these functions and influences eggshell structure. Evolution of prolonged uterine egg retention results in a significant change in the incubation environment, notably reduction in efficiency of gas exchange, and selection should favor a concomitant reduction in eggshell thickness. This model is supported by studies that demonstrate an inverse correlation between eggshell thickness and length of uterine egg retention. One mechanism leading to thinning of the eggshell is reduction in size of uterine shell glands. Saiphos equalis is an Australian scincid lizard with an unusual pattern of geographic variation in reproductive mode. All populations retain eggs in the uterus beyond the embryonic stage at oviposition typical for lizards, and some are viviparous. We compared structure and histochemistry of the uterus and eggshell of two populations of S. equalis, prolonged egg retention, and viviparous to test the hypotheses: 1) eggshell thickness is inversely correlated with length of egg retention and 2) eggshell thickness is positively correlated with size of shell glands. We found support for the first hypothesis but also found that eggshells of both populations are surprisingly thick compared with other lizards. Our histochemical data support prior conclusions that uterine shell glands are the source of protein fiber matrix of the eggshell, but we did not find a correlation between size of shell glands and eggshell thickness. Eggshell thickness is likely determined by density of uterine shell glands in this species. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Evolution and ecology of developmental processes and of the resulting morphology: directional asymmetry in hindlimbs of Agamidae and Lacertidae (Reptilia: Lacertilia)

In this paper, the evolution and ecology of directional asymmetry (DA) during the developmental trajectory (DT) is compared with that of its product, morphological DA (MDA). DT and MDA are calculated for two bilateral morphological scale characters of lizards, the number of subdigital lamellae beneath the fourth toe in 10 agamid and 28 lacertid taxa, and the number of rows of ventral scales in 12 lacertid taxa. MDA, the subtraction between left and right sides (classical measure of DA), is functional in adult animals. Results confirm the hypodiesis that, in DT, the regression parameters a (constant) and b (regression slope) of counts on the right side with those on the left describe a developmental process. No phylogenetic or environmental effects were observed on a and b , but analyses considering both a and b together show non-random phyletic patterns. Independent analyses deduced the same ancestral DT in Agamidae and Lacertidae. In Lacertidae, distance between pairs of taxa in a + b (standardized values) correlates positively with die phylogenetic distance between taxa. Phyletic trends in MDA are indirect, and due to the link of MDA with a + b . The MDA of species is more dissimilar in sympatry than in allopatry. The phyletic trends suggest evolution of DT, while die association of MDA witii sympatry suggests that ecological pressures shape MDA in adult animals. Evolution of DT is independent from tiiat of its product, MDA–adaptive determinism defines the result of, but not the mechanistic process of, development. Deterministic environmental processes define MDA, and deterministic evolutionary processes define the interactive result of a and b , but not each separately. According to circumstances, different DTs produce similar or different MDA, and a particular DT can produce different MDAs.     

荒漠麻蜥的染色体核型观察

采用常规骨髓细胞制片法,对采自甘肃省民勤县的荒漠麻蜥Eremias przewalskii染色体核型进行分析。荒漠麻蜥染色体核型为2n=38=36I+2m,具18对大型端部着丝粒型和1对微小染色体,属丽斑麻蜥型,与蜥蜴科和麻蜥属的染色体核型一致。系统整理已报道的麻蜥属核型资料,在此基础上探讨麻蜥属的染色体核型特征与演化。     

Unlocking the Black Box between Genotype and Phenotype: Cell Condensations as Morphogenetic (modular) Units

Embryonic development and ontogeny occupy whatis often depicted as the black box betweengenes – the genotype – and the features(structures, functions, behaviors) of organisms– the phenotype; the phenotype is not merelya one-to-one readout of the genotype. Thegenes home, context, and locus of operation isthe cell. Initially, in ontogeny, that cell isthe single-celled zygote. As developmentensues, multicellular assemblages of like cells(modules) progressively organized as germlayers, embryonic fields, anlage,condensations, or blastemata, enable genes toplay their roles in development and evolution.As modules, condensations are fundamentaldevelopmental and selectable units ofmorphology (morphogenetic units) that mediateinteractions between genotype and phenotype viaevolutionary developmental mechanisms. In ahierarchy of emergent processes, gene networksand gene cascades (genetic modules) link thegenotype with morphogenetic units such ascondensations, while epigenetic processes suchas embryonic inductions, tissue interactionsand functional integration, link morphogeneticunits to the phenotype. To support theseconclusions I distinguish units of heredityfrom units of transmission and discussepigenetic inheritance by tracing the historyof relationship between embryology andevolution, especially the role(s) assigned tocells or to cellular components in generatingtheories of morphological change in evolution.The concept of cells as modular morphogeneticunits is modeled and illustrated using themammalian dentary bone.     

Responses of embryonic stages of the estuarine mud crab,Macrophthalmus hirtipes (Jacquinot), to salinity

Females of the estuarine mud crab, Macrophthalmus hirtipes (Jacquinot, 1853) (Ocypodidae) carrying newly-deposited eggs were maintained in salinities of 11‰, 18‰, and 36‰ at 10°C. In 11‰ salinity eggs swelled more than in the other salinities; embryonic development was retarded; and eggs did not hatch. In 18‰ and 36‰, rates of development were generally similar and successful hatching occurred after approximately 75 days. However, late-stage eggs in 18‰ were significantly (P<0.001) larger than those in 36‰, even though initial egg volumes were the same. Zoeae were morphologically similar, except that the dorsal spine was significantly (P<0.001) longer in 36‰ compared with 18‰.     

Refuge areas and suture zones in the Pyrenean and Cantabrian regions: geographic variation of the female MPI sex-linked alleles among oviparous populations of the lizard Lacerta (Zootoca) vivipara

The viviparous lizard Lacerta (Zootoca) vivipara exhibits several alleles of the mannose-6-phosphate isomerase (MPI) enzyme that are carried exclusively on the female W sex-chromosome. Previous studies showed that both the oviparous and viviparous forms of L. (Zootoca) vivipara have these female sex-linked alleles. We document the existence of geographic variation of these alleles among the oviparous populations of southwestern France and northwestern Spain. Two oviparous subgroups were identified: all females from the eastern and central Pyrenees and most females from Aquitaine and from the northern slope of the western Pyrenees exhibited the fast migrating alleles MPI¹¹⁰ or MPI¹²⁰, whereas all females from the Cantabric mountains, Spanish Basque country, and from the south slope of the western Pyrenees exhibited the slow migrating allele MPI⁹⁰. Populations with both fast and slow migrating alleles occurred at some stations in the upper Ossau valley (western Pyrenees) and also at a lowland station of south Aquitaine. The hypothesis that several oviparous forms could have retreated to different places of the Pyreneo-Iberian refugia during the Quaternary glaciations could explain the conservation or the evolution of the polymorphism of the MPI alleles, and that is consistent with the phylogeographic scenario previously proposed to account for the reproductive and cytogenetical variation observed in this species.