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Richard Shine - One of the best experts on this subject based on the ideXlab platform.
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potential targets for selection during the evolution of Viviparity in cold climate reptiles
Oecologia, 2017Co-Authors: Melanie J Elphick, Richard ShineAbstract:Viviparity (live-bearing) has evolved from oviparity (egg-laying) in more than 100 lineages of squamate reptiles (lizards and snakes). This transition generally has occurred in cool climates, where thermal differentials between eggs in the (cool) nest versus the (warm) maternal oviduct influence embryonic development, in ways that may enhance offspring fitness. To identify specific traits potentially under selection, we incubated eggs of a montane scincid lizard at conditions simulating natural nests, maternal body temperatures, and an intermediate stage (2-week uterine retention of eggs prior to laying). Incubation at maternal temperatures throughout incubation affected the hatchling lizard's activity level and boldness, as well as its developmental rate, morphology, and locomotor ability. A treatment that mimicked the initial stages of the transition toward Viviparity had a major effect on some hatchling traits (locomotor speeds), a minor effect on others (tail length, total incubation period) and no effect on yet others (offspring behaviors). More generally, different aspects of the phenotype are sensitive to incubation conditions at different stages of development; thus, the evolution of reptilian Viviparity may have been driven by a succession of advantages that accrued at different stages of embryogenesis.
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the evolution of oviparity in squamate reptiles an adaptationist perspective
Journal of Experimental Zoology, 2015Co-Authors: Richard ShineAbstract:Phylogenetically based analyses can suggest directions of evolutionary transitions, based on parsimony, but can never provide unambiguous answers. To clarify the relative frequency of phylogenetic shifts from oviparity to Viviparity versus the reverse, we need additional sources of evidence. Adaptationist thinking (i.e., consideration of selective forces) has revealed a great deal about the transition from oviparity to Viviparity, but has rarely been employed to consider the reverse transition. An evaluation of costs and benefits identifies major obstacles to the re-evolution of oviparity. For example, even a modest decrease in the degree of embryogenesis completed in utero (i.e., a shift from Viviparity back toward "normal" oviparity) requires the mother to find a suitable nest-site (often, a risky endeavor), and a minor decrease in the duration of uterine retention of eggs may not substantially reduce maternal costs (because many of those costs are minimized by maternal behavioral adaptations to pregnancy). In many climates, a small decrease in the duration of uterine retention of eggs would not allow the female to produce a second clutch within the same season; and thus, would not reduce the fecundity disadvantage of Viviparity. Life-history theory thus suggests an asymmetry in the fitness consequences of the intermediate stages between oviparity and Viviparity. That asymmetry facilitates the "forward" transition (based on thermally driven benefits to offspring viability) but opposes the "reverse" transition (based on lower fitness of heavily burdened females that need to seek nest-sites). These factors should constrain the re-evolution of oviparity to specific conditions (e.g., where abundant nest-sites are available within a female's usual home range, rather than requiring extensive migration).
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evolution of an evolutionary hypothesis a history of changing ideas about the adaptive significance of Viviparity in reptiles
Journal of Herpetology, 2014Co-Authors: Richard ShineAbstract:Abstract Most reptiles are oviparous (egg-laying), but Viviparity (live-bearing) has evolved about 100 times in lizards and snakes. Geographic biases in the distribution of viviparous species stimulated the “cold-climate hypothesis,” proposed independently by three field-based researchers in the early 1900s. Mell (in China) and Weekes (in Australia) viewed Viviparity as a mechanism for thermal buffering of embryos from nighttime frosts, whereas Sergeev (in Russia) suggested that eggs retained in utero would develop faster because they were kept warmer, enabling early hatching. Although alternative adaptationist hypotheses proliferated over the next few decades, many had logical flaws (failing to consider intermediate stages). Phylogenetically based analyses identified around 100 independent origins of Viviparity from oviparity, and revealed a strong trend for Viviparity to evolve in cold climates. After experimental studies showed that incubation temperatures affect offspring phenotypes as well as rates o...
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thermal effects on reptile reproduction adaptation and phenotypic plasticity in a montane lizard
Biological Journal of The Linnean Society, 2010Co-Authors: Rajkumar S Radder, Rory S Telemeco, Troy A Baird, Richard ShineAbstract:Interspecific comparisons suggest a strong association between cool climates and Viviparity in reptiles. However, intraspecific comparisons, which provide an opportunity to identify causal pathways and to distinguish facultative (phenotypically plastic) effects from canalized (genetically fixed) responses, are lacking. We documented the reproductive traits in an alpine oviparous lizard, and manipulated thermal regimes of gravid females and their eggs to identify proximate causes of life-history variation. Embryonic development at oviposition was more advanced in eggs laid by females from high-elevation populations than in eggs produced by females from lower elevations. In the laboratory, experimentally imposed low maternal body temperatures delayed oviposition and resulted in more advanced embryonic development at oviposition. Warm conditions both in utero and in the nest increased hatching success and offspring body size. Our intraspecific comparisons support the hypothesis that Viviparity has evolved in cold-climate squamates because of the direct fitness advantages that warm temperatures provide developing offspring.
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did embryonic responses to incubation conditions drive the evolution of reproductive modes in squamate reptiles
Herpetological Monographs, 2006Co-Authors: Richard Shine, Michael B. ThompsonAbstract:Viviparity (live-bearing) has evolved from oviparity (egg-laying) more than 100 times within snakes and lizards, and thermal factors are thought to have driven this shift. However, other major features of reptilian reproduction may reflect selective pressures related to hydric rather than thermal exchanges between the egg and its incubation environment. Notably, why are intermediate stages of prolonged egg retention so rarely seen? Embryonic stages at oviposition in squamates are largely dichotomous: most oviparous species lay eggs with embryos about one-third developed, whereas viviparous taxa retain the eggs until development is complete. Why don't more species oviposit with embryos at either earlier or later stages? We suggest that the scarcity of squamates that lay eggs soon after ovulation (and thus, with very early-stage embryos) may reflect the need to delay oviposition until embryos have developed sufficient physiological control over water influx and efflux to survive in the challenging hydric environment of the nest. The scarcity of retention to later stages (intermediate between typical oviparity and Viviparity), and the apparent lack of reversals from Viviparity back to oviparity, may be due to a conflict between adaptations for water versus gas exchange; retention of larger embryos in utero requires eggshell thinning to allow gas exchange, but a thinner shell precludes effective hydric control after oviposition. Thus, although the transition from oviparity to Viviparity in squamates has been driven largely by thermal advantages, the clustering of species at two main positions along the oviparity-Viviparity continuum may be due to challenges of controlling embryonic water balance.
Daniel G Blackburn - One of the best experts on this subject based on the ideXlab platform.
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ancestral state reconstructions require biological evidence to test evolutionary hypotheses a case study examining the evolution of reproductive mode in squamate reptiles
Journal of Experimental Zoology, 2015Co-Authors: Oliver W Griffith, Daniel G Blackburn, James U. Van Dyke, Matthew C. Brandley, Camilla M Whittington, Michael B. ThompsonAbstract:To understand evolutionary transformations it is necessary to identify the character states of extinct ancestors. Ancestral character state reconstruction is inherently difficult because it requiresanaccuratephylogeny,characterstatedata,andastatisticalmodeloftransitionratesand is fundamentally constrained by missing data such as extinct taxa. We argue that model based ancestral character state reconstruction should be used to generate hypotheses but should not be considered an analytical endpoint. Using the evolution of Viviparity and reversals to oviparity in squamates as a case study, we show how anatomical, physiological, and ecological data can be used to evaluate hypotheses about evolutionary transitions. The evolution of squamate Viviparity requires changes to the timing of reproductive events and the successive loss of features responsible forbuildinganeggshell. A reversaltooviparity requiresthat those losttraitsre-evolve. Wearguethatthere-evolutionofoviparityisinherentlymoredifficultthanthereverse.Weoutline how the inviability of intermediate phenotypes might present physiological barriers to reversals from Viviparity to oviparity. Finally, we show that ecological data supports an oviparous ancestral state for squamates and multiple transitions to Viviparity. In summary, we conclude that the first squamateswereoviparous,thatfrequenttransitionstoViviparityhaveoccurred,andthatreversals tooviparityinviviparouslineageseitherhavenotoccurredorareexceedinglyrare.Asthisevidence supports conclusions that differ from previous ancestral state reconstructions, our paper highlights the importance of incorporating biological evidence to evaluate model-generated hypotheses. J. Exp. Zool. (Mol. Dev. Evol.) 00B: 1-11, 2015. © 2015 Wiley Periodicals, Inc. Howtocitethisarticle:GriffithOW,BlackburnDG,BrandleyMC,VanDykeJU,WhittingtonCM, Thompson MB. 2015. Ancestral state reconstructions require biological evidence to test evolutionary hypotheses: A case study examining the evolution of reproductive mode in squamate reptiles. J. Exp. Zool. (Mol. Dev. Evol.) 00B:1-11.
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evolution of vertebrate Viviparity and specializations for fetal nutrition a quantitative and qualitative analysis
Journal of Morphology, 2015Co-Authors: Daniel G BlackburnAbstract:Phylogenetic analyses indicate that Viviparity (live-bearing reproduction) has originated independently in more than 150 vertebrate lineages, including a minimum of 115 clades of extant squamate reptiles. Other evolutionary origins of Viviparity include 13 origins among bony fishes, nine among chondrichthyans, eight in amphibians, one in Paleozoic placoderms, six among extinct reptiles, and one in mammals. The origins of Viviparity range geologically from the mid-Paleozoic through the Mesozoic to the Pleistocene. Substantial matrotrophy (maternal provision of nutrients to embryos during pregnancy) has arisen at least 33 times in these viviparous clades, with most (26) of these origins having occurred among fishes and amphibians. Convergent evolution in patterns of matrotrophy is widespread, as reflected by multiple independent origins of placentotrophy, histotrophy, oophagy, and embryophagy. Specializations for nutrient transfer to embryos are discontinuously distributed, reflecting the roles of phylogenetic inertia, exaptation (preadaptation), and constraint. Ancestral features that function in gas exchange and nutrition repeatedly and convergently have been co-opted for nutrient transfer, often through minor modification of their components and changes in the timing of their expression (heterochrony). Studies on functional and evolutionary morphology continue to play a central role in our attempts to understand Viviparity and mechanisms of fetal nutrition.
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Evolution of Viviparity in squamate reptiles: Reversibility reconsidered.
Journal of experimental zoology. Part B Molecular and developmental evolution, 2015Co-Authors: Daniel G BlackburnAbstract:Viviparity in squamate reptiles is widely recognized as having evolved convergently from oviparity more than 100 times. However, questions persist as to whether reversals from Viviparity back to oviparity have ever occurred. Based on a theoretical model, a recent paper (Pyron and Burbrink, 2014) has proposed that Viviparity is ancestral for squamates and that Viviparity—oviparity reversals have far outnumbered origins of Viviparity in reproductive history. Close examination of this analysis reveals features that cast doubt on its plausibility, notably the requirement of repeated, sequential transformations back and forth between these reproductive modes, as well as numerous, uncounted evolutionary transformations that have produced inaccurate estimates of parsimony. Evidence derived from studies of anatomy, physiology, and developmental biology strongly supports the inference that oviparity is ancestral for squamates and has given rise to Viviparity on numerous occasions. Biological data provide important insights into the likelihood of evolutionary transformations, and deserve to be incorporated fully into future analyses of the evolution of reproductive modes. J. Exp. Zool. (Mol. Dev. Evol.) 324B: 473–486, 2015. © 2015 Wiley Periodicals, Inc.
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SQUAMATE REPTILES AS MODEL ORGANISMS FOR THE EVOLUTION OF Viviparity
Herpetological Monographs, 2006Co-Authors: Daniel G BlackburnAbstract:For over a century, research has been conducted on squamates in order to reveal how Viviparity has evolved in mammals and other vertebrates. The recent proliferation of studies has yielded much information on anatomical, physiological, ecological, and evolutionary aspects, allowing a reassessment of squamates as model organisms for the study of Viviparity. Strong support for the ''squamate model'' comes from phylogenetic analyses that have shown that squamates have evolved Viviparity with great frequency (. 108 origins), at low taxonomic levels, and in geologically recent times. However, available data also indicate that Viviparity has evolved by different chronologies and mechanisms in squamates, fishes, and mammals. Further, generalizations about squamates are difficult to make, given the diverse mechanisms by which they achieve Viviparity. Thus, similarities between squamates must be demonstrated empirically, and generalizations should be based on quantitative, phylogenetic analyses of multiple lineages. Explanations for similarities between squamate clades can invoke such concepts as evolutionary constraints, exaptations, and selection pressures, and should distinguish between adaptations, correlated attributes, and features that predate Viviparity. However, homocentric assumptions of an orthogenetic transformation towards the eutherian condition should be abandoned, along with untested assumptions that Viviparity squamates and mammals is similar. The value of the squamate model ultimately may lie in insights it provides into physiological problems rather than in universality of specific mechanisms that have evolved to meet those problems.
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reptilian Viviparity past research future directions and appropriate models
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2000Co-Authors: Daniel G BlackburnAbstract:Squamate reptiles represent an ideal group for studies of Viviparity, because they have evolved this reproductive pattern frequently, relatively recently, and at low taxonomic levels. A phylogenetic approach shows particular promise in helping us interpret anatomical, physiological, and ecological diversity. This review summarizes four major categories of active investigation: (1) reproductive anatomy and physiology; (2) placental structure and function; (3) reproductive endocrinology; and (4) reproductive and physiological ecology. Evolutionary reconstructions suggest that on many occasions Viviparity has evolved concomitantly with functional placentation, through reduction of the shell membrane and hormonal modifications that prolong gestation. Studies of placentotrophic clades as well as reproductively bimodal species offer great potential for explaining the evolution of Viviparity and placentation. However, live-bearing squamates are reproductively diverse, and appear to have solved physiological problems associated with Viviparity by a variety of mechanisms. Consequently, studies on one or a few squamate species appear increasingly unlikely to yield all-inclusive explanations. Future studies and analyses should abandon assumptions of universal physiological mechanisms and a single historical sequence, in favor of the documentation of diversity in phylogenetic and quantitative terms.
Robin M. Andrews - One of the best experts on this subject based on the ideXlab platform.
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natural history of reptilian development constraints on the evolution of Viviparity
BioScience, 2000Co-Authors: Robin M. Andrews, Tom MathiesAbstract:OViParity, or egg-laying, is the dominant mode 01 reproduction among vertebrates. Nevertheless, Viviparity, the retention of the egg within the reproductive tract until embryonic development is complete, characterizes almost all mammals; it has also had at least 150 independent origins within the fishes, amphibians, and reptiles (Shine 1985, Blackburn 1992, Wourms and Lombardi 1992). These multiple origins suggest pervasive benefits to Viviparity across a wide range of taxa, life histories, and habitats. In the squamate reptiles (lizards and snakes), for example, Viviparity is the most common reproductive mode in cold climates, and recent origins of Viviparity in this group are also associated with cold climates (Shine 1985). Gravid females in cold climates can thermoregulate to keep embryos warmer than they would be in a nest, thus enhancing development. Thermo regulation by the female may thus ensure that birth occurs at the appropriate season or even that reproduction is successful at all. Viviparity is also advantageous in very wet or dry habitats, for example, because it obviates the need for females to find suitable sites in which to lay their eggs. In reptiles, Viviparity is associated with a plethora of integrated morphological and physiological features that are not present in oviparous reptiles; these features are presumed necessary for successful embryonic develop ment in the oviduct (Packard et al. 1977, Guillette 1993). Early insights into the evolution of these reproductive fea tures were based on comparisons between typical oviparous and viviparous species. Some of the distin guishing features of the viviparous species examined were the major reduction or absence of an eggshell and the presence of some form of placentation (Weekes 1935 and included references). However, because the species used in these comparisons represented the extremes of a putative evolutionary sequence, their use as a model for elucidating the actual sequence or timing of the morphological and physiological changes attending the evolution of vivipari ty is limited. In fact, these observations are consistent with both a saltation model that posits that the characteristic features of Viviparity arise suddenly and simultaneously, and a gradualist model that posits incremental evolution from one reproductive mode to the other (Blackburn 1992,1995).
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cold climates and the evolution of Viviparity in reptiles cold incubation temperatures produce poor quality offspring in the lizard sceloporus virgatus
Biological Journal of The Linnean Society, 1999Co-Authors: Carl P Qualls, Robin M. AndrewsAbstract:Abstract Evolutionary origins of Viviparity among the squamate reptiles are strongly associated with cold climates, and cold environmental temperatures are thought to be an important selective force behind the transition from egg-laying to live-bearing. In particular, the low nest temperatures associated with cold climate habitats are thought to be detrimental to the developing embryos or hatchlings of oviparous squamates, providing a selective advantage for the retention of developing eggs in utero , where the mother can provide warmer incubation temperatures for her eggs (by actively thermoregulating) than they would experience in a nest. However, it is not entirely clear what detrimental effects cold incubation temperatures may have on eggs and hatchlings, and what role these effects may play in favouring the evolution of Viviparity. Previous workers have suggested that Viviparity may be favoured in cold climates because cold incubation temperatures slow embryogenesis and delay hatching of the eggs, or because cold nest temperatures are lethal to developing eggs and reduce hatching success. However, incubation temperature has also been shown to have other, potentially long-term, effects on hatchling phenotypes, suggesting that cold climates may favour Viviparity because cold incubation temperatures produce offspring of poor quality or low fitness. We experimentally incubated eggs of the oviparous phrynosomatid lizard, Sceloporus virgatus , at temperatures simulating nests in a warm (low elevation) habitat, as is typical for this species, and nests in a colder (high elevation) habitat, to determine the effects of cold incubation temperatures on embryonic development and hatchling phenotypes. Incubation at cold nest temperatures slowed embryonic development and reduced hatching success, but also affected many aspects of the hatchlings» phenotypes. Overall, the directions of these plastic responses indicated that cold-incubated hatchlings did indeed exhibit poorer quality phenotypes; they were smaller at hatching (in body length) and at 20 days of age (in length and mass), grew more slowly (in length and mass), had lower survival rates, and showed greater fluctuating asymmetry than their conspecifics that were incubated at warmer temperatures. Our findings suggest that cold nest temperatures are detrimental to S. virgatus , by delaying hatching of their eggs, reducing their hatching success, and by producing poorer quality offspring. These negative effects would likely provide a selective advantage for any mechanism through which these lizards could maintain warmer incubation temperatures in cold climates, including the evolution of prolonged egg retention and Viviparity.
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Constraints on the Evolution of Viviparity in the Lizard Genus Sceloporus
1998Co-Authors: Robin M. Andrews, Jack Cranford, Michael D. Denbow, Alan G. Heath, Paul Siegel, Tom MathiesAbstract:I evaluated possible constraints on the evolution of Viviparity in the lizard genus Sceloporus by experimentally extending the length of egg retention past the normal time of oviposition for a number of oviparous species. Observations also included a representative of the genus Urosaurus, the sister genus to Sceloporus. I determined the effects of retention on embryonic development, hatchlings, and gravid females. Results indicated that the proximate constraints on longer retention times and Viviparity are 1) embryonic development becomes arrested or severely retarded in ut ro, and 2) the ability to maintain gravidity past the normal time of oviposition is limited in some species. Observations on Urosaurus further showed that extended egg retention results in hatchlings with traits that are associated with lower fitness. I also tested the hypothesis that reproductive Sceloporus lower their body temperatures during activity because their normal body temperatures are detrimental to embryos. Observations on a viviparous species of Sc loporus indicated that the normal body temperature of the female was detrimental to embryonic development. This result is indicates that Viviparity would be constrained in some squamate lineages if maternal bod
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evolution of Viviparity in the lizard genus sceloporus
Herpetologica, 1998Co-Authors: F Mendezde R La Cruz, Villagransanta M Cruz, Robin M. AndrewsAbstract:According to the cold-climate model, Viviparity in squamate reptiles evolves at high elevations and latitudes. The lizard genus Sceloporus has been used to support this model; viviparous species are found at higher elevations than oviparous species. For example, in the scalaris species group, a viviparous species replaces its oviparous sister species at elevations above 3000 m. We used recent literature to evaluate four aspects of the evolution of Viviparity within the genus and concluded that (1) Viviparity has evolved a minimum of four times within the genus. (2) Viviparity has not evolved at high latitudes, because the oviparous species found at high latitudes lack the morphological and physiological features that facilitate prolonged egg retention, the intermediate stage between oviparity and Viviparity. (3) Viviparous species have not invaded high latitudes because Viviparity in Sceloporus is associated with gestation during winter months. This is a viable reproductive mode at high elevations at tropical latitudes, because ambient temperatures during the winter are similar to those in the summer. At high latitudes, in contrast, winters may be too cold to support embryogenesis, or perhaps even survival of embryos. (4) Viviparity evolved from oviparity through three major transitions. The first was the evolution of Viviparity from oviparity; this transition was associated with the invasion of high elevations. The second transition was a shift from summer to winter gestation such that birth was shifted from autumn to spring. With birth in the spring, neonates are able to mature by autumn, and consequently they can produce a litter within a year of their own birth. The third transition was a shift from asynchronous reproductive cycles of males and females (mating in spring and fertilization in autumn) to synchronous reproductive cycles (mating and fertilization in the autumn).
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thermal and reproductive biology of high and low elevation populations of the lizard sceloporus scalaris implications for the evolution of Viviparity
Oecologia, 1995Co-Authors: Tom Mathies, Robin M. AndrewsAbstract:Viviparity in squamate reptiles is presumed to evolve in cold climates by selection for increasingly longer periods of egg retention. Longer periods of egg retention may require modifications to other reproductive features associated with the evolution of Viviparity, including a reduction in eggshell thickness and clutch size. Field studies on the thermal and reproductive biology of high (HE) and low (LE) elevation populations of the oviparous lizard, Sceloporus scalaris, support these expectations. Both day and night-time temperatures at the HE site were considerably cooler than at the LE site, and the activity period was 2 h shorter at the HE than at the LE site. The median body temperature of active HE females was 2°C lower than that of LE females. HE females initiated reproduction earlier in the spring than LE females, apparently in order to compensate for relatively low temperatures during gestation. HE females retained eggs for about 20 days longer than LE females, which was reflected by differences in the degree of embryonic development at the time of oviposition (stages 35.5–37.0 versus stages 31.0–33.5, respectively). These results support the hypotheses that evolution of Viviparity is a gradual process, and is favored in cold climates. Females in the HE population exhibited other traits consistent with presumed intermediate stages in the evolution of Viviparity; mean eggshell thickness of HE eggs (19.3 μm) was significantly thinner than that of LE eggs (26.6 μm) and the size-adjusted clutch sizes of HE females (9.4) were smaller than those of LE females (11.2).
Kathryn R Elmer - One of the best experts on this subject based on the ideXlab platform.
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evolutionary origins of Viviparity consistent with palaeoclimate and lineage diversification
Journal of Evolutionary Biology, 2021Co-Authors: Hans Recknagel, Nicholas A Kamenos, Kathryn R ElmerAbstract:It is of fundamental importance for the field of evolutionary biology to understand when and why major evolutionary transitions occur. Live-bearing young (Viviparity) is a major evolutionary change and has evolved from egg-laying (oviparity) independently in many vertebrate lineages and most abundantly in lizards and snakes. Although contemporary viviparous squamate species generally occupy cold climatic regions across the globe, it is not known whether Viviparity evolved as a response to cold climate in the first place. Here, we used available published time-calibrated squamate phylogenies and parity data on 3,498 taxa. We compared the accumulation of transitions from oviparity to Viviparity relative to background diversification and a simulated binary trait. Extracting the date of each transition in the phylogenies and informed by 65 my of global palaeoclimatic data, we tested the nonexclusive hypotheses that Viviparity evolved under the following: (a) cold, (b) long-term stable climatic conditions and (c) with background diversification rate. We show that stable and long-lasting cold climatic conditions are correlated with transitions to Viviparity across squamates. This correlation of parity mode and palaeoclimate is mirrored by background diversification in squamates, and simulations of a binary trait also showed a similar association with palaeoclimate, meaning that trait evolution cannot be separated from squamate lineage diversification. We suggest that parity mode transitions depend on environmental and intrinsic effects and that background diversification rate may be a factor in trait diversification more generally.
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Differential reproductive investment in co-occurring oviparous and viviparous common lizards (Zootoca vivipara) and implications for life-history trade-offs with Viviparity
Oecologia, 2019Co-Authors: Hans Recknagel, Kathryn R ElmerAbstract: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.
Tom Mathies - One of the best experts on this subject based on the ideXlab platform.
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natural history of reptilian development constraints on the evolution of Viviparity
BioScience, 2000Co-Authors: Robin M. Andrews, Tom MathiesAbstract:OViParity, or egg-laying, is the dominant mode 01 reproduction among vertebrates. Nevertheless, Viviparity, the retention of the egg within the reproductive tract until embryonic development is complete, characterizes almost all mammals; it has also had at least 150 independent origins within the fishes, amphibians, and reptiles (Shine 1985, Blackburn 1992, Wourms and Lombardi 1992). These multiple origins suggest pervasive benefits to Viviparity across a wide range of taxa, life histories, and habitats. In the squamate reptiles (lizards and snakes), for example, Viviparity is the most common reproductive mode in cold climates, and recent origins of Viviparity in this group are also associated with cold climates (Shine 1985). Gravid females in cold climates can thermoregulate to keep embryos warmer than they would be in a nest, thus enhancing development. Thermo regulation by the female may thus ensure that birth occurs at the appropriate season or even that reproduction is successful at all. Viviparity is also advantageous in very wet or dry habitats, for example, because it obviates the need for females to find suitable sites in which to lay their eggs. In reptiles, Viviparity is associated with a plethora of integrated morphological and physiological features that are not present in oviparous reptiles; these features are presumed necessary for successful embryonic develop ment in the oviduct (Packard et al. 1977, Guillette 1993). Early insights into the evolution of these reproductive fea tures were based on comparisons between typical oviparous and viviparous species. Some of the distin guishing features of the viviparous species examined were the major reduction or absence of an eggshell and the presence of some form of placentation (Weekes 1935 and included references). However, because the species used in these comparisons represented the extremes of a putative evolutionary sequence, their use as a model for elucidating the actual sequence or timing of the morphological and physiological changes attending the evolution of vivipari ty is limited. In fact, these observations are consistent with both a saltation model that posits that the characteristic features of Viviparity arise suddenly and simultaneously, and a gradualist model that posits incremental evolution from one reproductive mode to the other (Blackburn 1992,1995).
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Constraints on the Evolution of Viviparity in the Lizard Genus Sceloporus
1998Co-Authors: Robin M. Andrews, Jack Cranford, Michael D. Denbow, Alan G. Heath, Paul Siegel, Tom MathiesAbstract:I evaluated possible constraints on the evolution of Viviparity in the lizard genus Sceloporus by experimentally extending the length of egg retention past the normal time of oviposition for a number of oviparous species. Observations also included a representative of the genus Urosaurus, the sister genus to Sceloporus. I determined the effects of retention on embryonic development, hatchlings, and gravid females. Results indicated that the proximate constraints on longer retention times and Viviparity are 1) embryonic development becomes arrested or severely retarded in ut ro, and 2) the ability to maintain gravidity past the normal time of oviposition is limited in some species. Observations on Urosaurus further showed that extended egg retention results in hatchlings with traits that are associated with lower fitness. I also tested the hypothesis that reproductive Sceloporus lower their body temperatures during activity because their normal body temperatures are detrimental to embryos. Observations on a viviparous species of Sc loporus indicated that the normal body temperature of the female was detrimental to embryonic development. This result is indicates that Viviparity would be constrained in some squamate lineages if maternal bod
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thermal and reproductive biology of high and low elevation populations of the lizard sceloporus scalaris implications for the evolution of Viviparity
Oecologia, 1995Co-Authors: Tom Mathies, Robin M. AndrewsAbstract:Viviparity in squamate reptiles is presumed to evolve in cold climates by selection for increasingly longer periods of egg retention. Longer periods of egg retention may require modifications to other reproductive features associated with the evolution of Viviparity, including a reduction in eggshell thickness and clutch size. Field studies on the thermal and reproductive biology of high (HE) and low (LE) elevation populations of the oviparous lizard, Sceloporus scalaris, support these expectations. Both day and night-time temperatures at the HE site were considerably cooler than at the LE site, and the activity period was 2 h shorter at the HE than at the LE site. The median body temperature of active HE females was 2°C lower than that of LE females. HE females initiated reproduction earlier in the spring than LE females, apparently in order to compensate for relatively low temperatures during gestation. HE females retained eggs for about 20 days longer than LE females, which was reflected by differences in the degree of embryonic development at the time of oviposition (stages 35.5–37.0 versus stages 31.0–33.5, respectively). These results support the hypotheses that evolution of Viviparity is a gradual process, and is favored in cold climates. Females in the HE population exhibited other traits consistent with presumed intermediate stages in the evolution of Viviparity; mean eggshell thickness of HE eggs (19.3 μm) was significantly thinner than that of LE eggs (26.6 μm) and the size-adjusted clutch sizes of HE females (9.4) were smaller than those of LE females (11.2).
