Squamate Eggs Research Articles

Natural history of Xenodon matogrossensis (Scrocchi and Cruz, 1993) (Serpentes, Dipsadidae) in the Brazilian Pantanal

Xenodon mattogrossensis is a neotropical snake restricted to the central part of South America, in the Pantanal wetlands and a few neighbouring areas. The available information about this specie in the literature is restricted to geographical distribution, morphological variation and anecdotal information on habitat use. Here we present data on diet, sexual dimorphism and reproduction of X. matogrossensis . We gathered information on diet and reproduction from 72 specimens of X. matogrossensis deposited in scientific collections. This species feeds mainly on amphibians, but also consumes squamate eggs and other small vertebrates. Mature females are generally bigger than mature males considering body size and head width, but males have longer tail than females. The number of follicles and eggs is not related with body size in females of X. matogrossensis . Females showed larger follicle sizes from October to April, suggesting that reproduction is seasonal, even though individuals may be active through the year. The information provided here, associated with others available in the literature can contribute to the assessment of the conservation status of this species and even to design conservation actions in case they are needed in the future.

Viviparity does not affect the numbers and sizes of reptile offspring.

Viviparity (live-bearing) has independently evolved from oviparity (egg-laying) in more than 100 lineages of squamates (lizards and snakes). We might expect consequent shifts in selective forces to affect per-brood reproductive investment (RI=total mass of offspring relative to maternal mass) and in the way in which that output is partitioned (number vs. size of offspring per brood). Based on the assumption that newly born offspring are heavier than eggs, we predicted that live-bearing must entail either increased RI or a reduction in offspring size and/or fecundity. However, our phylogenetically controlled analysis of data on 1,259 squamate species revealed no significant differences in mean offspring size, clutch size or RI between oviparous and viviparous squamates. We attribute this paradoxical result to (1) strong selection on offspring sizes, unaffected by parity mode, (2) the lack of a larval stage in amniotes, favouring large eggs even in the ancestral oviparous mode and (3) the ability of viviparous females to decrease the mass of uterine embryos by reducing extra-embryonic water stores. Our analysis shows that squamate eggs (when laid) weigh about the same as the hatchlings that emerge from them (despite a many-fold increase in embryo mass during incubation). Most of the egg mass is due to components (such as water stores and the eggshell) not required for oviductal incubation. That repackaging enables live-born offspring to be accommodated within the mother's body without increasing total litter mass. The consequent stasis in reproductive burden during the evolutionary transition from oviparity to viviparity may have facilitated frequent shifts in parity modes.

A developmental synapomorphy of squamate reptiles

The reptilian clade Squamata is defined primarily by osteological synapomorphies, few of which are entirely unambiguous. Studies of developing squamate eggs have revealed a uniquely specialized feature not known to occur in any other amniotes. This feature-the yolk cleft/isolated yolk mass complex-lines the ventral hemisphere of the egg. During its formation, extraembryonic mesoderm penetrates the yolk and an exocoelom (the yolk cleft [YC]) forms in association with it, cutting off a thin segment of yolk (the "isolated yolk mass" [IYM]) from the main body of the yolk. The YC-IYM complex has been observed and described in more than 65 squamate species in 12 families. In viviparous species, it contributes to the "omphaloplacenta," a type of yolk sac placenta unique to squamates. The only squamates known to lack the IYM are a few highly placentotrophic skinks with minuscule eggs, viviparous species in which it clearly has been lost. Given its absence in mammals, chelonians, crocodylians, and birds, the YC-IYM complex warrants recognition as a developmental synapomorphy of the squamate clade. As in extant viviparous lizards and snakes, the YC-IYM complex presumably contributed to the placenta of extinct viviparous squamates.

A Late Cretaceous madtsoiid snake from Romania associated with a megaloolithid egg nest – Paleoecological inferences

Here we report on the taphonomy and paleoecological implications of the first record of a small madtsoiid snake (Nidophis insularis) closely associated with a megaloolithid dinosaur egg nest. Taphonomic and sedimentologic evidence suggest that the snake was buried autochthonously within or nearby the egg nest, with at least partially articulated skeleton. Count of growth rings on the vertebral zygapophyses indicates that the holotype of Nidophis belonged to an adult individual approaching the limit of its maximum body size of about 1 m length. The presence of layers of arrested growth on the zygapophyses, together with other independent data (e.g., paleomagnetic data, sedimentology, paleosol development stage, stable isotope geochemistry) indicates that Nidophis lived under a semi-arid, seasonally variable subtropical climate, having alternative periods of active feeding. The trunk vertebrae with relatively low neural spines and without prezygapophyseal accessory processes indicate a relatively heavy-bodied, slowly-moving animal, one that probably had a semifossorial habit and was an active forager, but definitively not a dinosaur nest raider as suggested for certain large madtsoiid snakes (the Indian Sanajeh). Potential prey items, available around the dinosaur nesting area, probably ranged from small squamate eggs to various small vertebrates. Finally, one anterior trunk vertebra of the holotype displays distinct bite marks left by a small-sized and pointed-toothed predator, most probably a crocodyliform or a theropod, thus documenting that madtsoiids were also preyed upon.

Salinity and Egg Shape Variation: A Geometric Morphometric Analysis

The harvest and incubation of American Alligator (Alligator mississippiensis) eggs is an important component to the commercial alligator harvest industry in the southeastern United States. As a result, various methodologies have been used to monitor alligator populations including abundance counts, stress quantification, and nesting surveys. Past studies have dismissed the importance of egg shape in crocodilians, Squamates, and turtles and deemed egg shape in birds and other amniotes as similar, in relation to functionality. The complexity of crocodilian eggs has been examined, and both turtle and Squamate eggs have been regarded recently as physiologically more intricate than bird eggs. This study introduces a physiological approach to monitor alligator populations in freshwater and low salinity environments by quantifying egg shape in correlation with varying salinity. We introduce a fractional semilandmark-shape template method to quantify egg shape within a geometric morphometric framework. This approach is beneficial because it allows for the quantification of shape for curved structures, such as eggs, which lack homologous landmarks. The results from this study suggest that alligator egg shape is correlated with varying salinity levels, such that variation in alligator egg shape at low salinities changes in gradient-like fashion, whereas salinities high enough to be deemed stressful result in reversion back to a low salinity egg shape or desiccation. This study elucidates a correlation that can be implemented in management and breeding techniques and opens the door to in-depth physiological examination of the system.

Water Vapor Permeability of the Rigid‐Shelled Gecko Egg

The vast majority of squamate reptiles (lizards and snakes) produce parchment-shelled eggs that absorb water during incubation, and thus increase in mass, volume, and surface area. In contrast, females from a single monophyletic lineage of gekkotan lizards produce rigid-shelled eggs. These eggs are functionally comparable to those of birds, that is, at oviposition, eggs contain all the water needed for development, and their mass decreases during incubation via the diffusion of water vapor through the shell. I determined patterns of water loss and shell permeability to water vapor from oviposition to hatching for the rigid-shelled eggs of the gekkonid Chrondrodactylus turneri and compared permeability of C. turneri eggs to those of birds and other squamates. Chrondrodactylus turneri eggs incubated at 28.5°C and 40% relative humidity (RH) decreased in mass by 14% over the course of a 68-day incubation period. The rate of water loss varied during incubation; egg mass decreased rapidly during the first 8 days of incubation, declined at a low constant rate during the next 35 days, and then decreased rapidly during the final 25 days of incubation. Overall permeability was 0.17 mg/day/kPa/cm(2) . Percent water loss of rigid-shelled gecko eggs during incubation is similar to that exhibited by birds, but water vapor permeability is about one-third that of bird eggs and several orders of magnitude lower than that of parchment-shelled squamate eggs. In general, the water economy of their eggs may be associated with the adaptive radiation of the rigid-shelled sphaerodactylid, phyllodactylid, and gekkonid geckos.

Eggs under Pressure: Components of Water Potential of Chameleon Eggs during Incubation

Water exchange of squamate eggs is driven by the difference between the water potentials of eggs and of their nest environment. While osmotic potential is generally assumed to dominate the net water potential of eggs, resistance of the eggshell to stretching also affects egg water potential. We therefore determined osmotic potentials and pressure potentials (mechanical pressure) of eggs of the veiled chameleon Chamaeleo calyptratus over the course of incubation. Because embryos are diapausing gastrulae when eggs are laid and diapause persists several months, the water potential of eggs can be evaluated before it is influenced by the developing embryo. Water uptake during the first 2 wk of incubation was rapid as a result of the large difference between the total water potential of the egg (-848 kPa) and that of its incubation substrate. After about 2 wk, water potential of the egg stabilized at -460 kPa. By day 80 of incubation, the developing embryo and allantois affected water exchange of the egg. The allantoic fluid was initially very dilute, but its osmotic potential decreased to about -200 kPa by the end of incubation. Pressure potential of the egg averaged 25 kPa, with no systematic trend during incubation. The pressure potential exerted by the eggshell reduced the difference between the water potential of the egg and the water potential of the environment, that is, the ability of eggs to take up water. At the time of oviposition, this effect was relatively small, producing a 4%-6% reduction in water potential difference. Once the yolk osmotic potential stabilized, however, the reduction was 12% or more. This observation means that the dynamics of water uptake by squamate eggs cannot be fully understood without consideration of the pressure that is exerted on the contents of eggs by their shells.

Feeding ecology of the Great Basin Rattlesnake (Crotalus lutosus, Viperidae)

Documenting variation in organismal traits is essential to understanding the ecology of natural populations. We relied on stomach contents of preserved specimens and literature records to assess ontogenetic, intersexual, temporal, and geographic variations in the feeding ecology of the North American Great Basin Rattlesnake ( Crotalus lutosus Klauber, 1930). Snakes preyed mainly on rodents, occasionally on lizards, and less frequently on birds; squamate eggs and frogs were rarely eaten. There was a positive relationship between predator and prey size. The best predictors of this relationship were prey diameter as a function of snake body length and head size, underscoring the importance of prey diameter for gape-limited predators such as snakes. Crotalus lutosus displayed ontogenetic, sexual, and seasonal variations in diet. Smaller rattlesnakes fed predominantly on lizards, whereas larger individuals mostly fed on mammals. Females fed on lizards more often than males. The proportion of mammals in the diet was highest during the summer, a temporal variation that may be related to behavioral shifts in the diel activity and prey selectivity of C. lutosus, and (or) to differential abundance of rodents between seasons. Great Basin Rattlesnakes also displayed geographic variation in feeding habits, with snakes from the Great Basin Desert eating a higher proportion of lizards than serpents from the more northern Columbia Plateau.

Sympatric Ecology of Five Species of Fossorial Snakes (Elapidae) in Western Australia

Snakes have very different ecologies and habits from other non-ophidian squamates (''lizards''); yet ecological data from sympatric populations of lizards are often used as models to explain resource partitioning in sympatric groups of all squamates. Most snake assemblages show greatest ecological divergence in use of dietary resources. We use dietary, spatial, and reproductive data in a clade of five sympatric snake species with similar ecologies to test previous assumptions of how snakes partition resources in a species-rich community. Species show dietary specializations, with species of Simoselaps and Brachyurophis fasciolatus feeding exclusively on lizards and Brachyurophis semifasciatus eating only squamate eggs. Some species show trends regarding differential habitat use; Simoselaps bertholdi and B. semifasciatus are habitat generalists, whereas the other species are not captured in flat areas between sand ridges. Time of peak activity is not partitioned seasonally because all species, except B. fasciolatus, are most active in December. Partitioning of dietary resources is a stronger structuring agent than is partitioning of habitat resources in this community as indicated by the amount of resource overlap. Diet is the most important dimension in explaining ecological divergence among these elapid species, in agreement with prior studies of resource partitioning in snake assemblages.

ECOLOGICAL TRAITS OF THE COLUBRID SNAKE CONOPHIS LINEATUS CONCOLOR (GUARDA CAMINO) IN THE YUCATÁN PENINSULA

Abstract Aspects of ecology are described for the Yucatan colubrid snake Conophis lineatus concolor, as inferred from examinations of museum specimens and a review of published literature records. Adult males of this distinctive subspecies are larger than females (> 890 mm versus < 760 mm SVL) and at the same body size males also have longer tails, although sexual dimorphism in other proportional features of morphology is negligible. Food habits are diverse; of 29 prey items identified to main taxonomic group, the most important in terms of relative composition (lx) were lizards (0.394) and arthropods (0.391), followed by squamate eggs (0.061) and thereafter in equal measure by frogs, snakes, and mammals (0.044). More than 90% of the arthropods were engorged cattle ticks, Boophilus microplus, and several snakes had fed exclusively on this prey type. An ontogenetic increase was evident in the proportion of larger prey consumed, although samples were inadequate to allow an assessment of the relationship bet...

Historical Contingency and Animal Diets: The Origins of Egg Eating in Snakes

Evolutionary changes in animal diets must often begin through the inclusion of a novel food type as a minor component of the diet. An aspect of this initial change that has rarely been studied is the relationship between the existing diet and the use of specific novel foods. We used comparative analyses to test the hypothesis that, in snakes, feeding on squamate (lizard and snake) eggs or bird eggs--items that represent evolutionarily derived and, in most cases, minor components of the diet--is associated with feeding on squamates or birds, respectively. Phylogenetic concentrated-changes tests indicate a significant tendency for predation on eggs to arise in snake lineages characterized by feeding on the corresponding animals. These results also generally hold for analyses including only snake species that are likely to encounter eggs and are large enough to ingest them. The inferred histories of specialized egg eaters also support the hypothesis. Because snakes often use chemical cues to recognize prey, the observed phylogenetic patterns might be explained by chemical similarities between eggs and adult animals. Our results suggest broad effects of predispositions on snake diets and thus illustrate how historical contingencies can shape the ecology of organisms.

DIET OF THE LEAF-NOSED SNAKES, PHYLLORHYNCHUS (SQUAMATA: COLUBRIDAE): SQUAMATE-EGG SPECIALISTS

Phyllorhynchus have been proposed to eat a wide variety of food items. The leading hypothesis is that the tails of the gecko Coleonyx variegatus are an important food source. We dissected museum specimens of P. decurtatus and P. browni. The diet of P. decurtatus consisted primarily of squamate eggs; few individuals of that species contained the tails of C. variegatus. The diet of P. browni consisted entirely of squamate eggs. We compared the monthly diet patterns between the sexes, as well as between the species.

Feeding Ecology of the California Mountain Kingsnake, Lampropeltis zonata (Colubridae)

Abstract Based on stomach contents of museum specimens and published records (n = 51 prey items), Lampropeltis zonata eats lizards (37, 72.5%), squamate eggs (6, 11.8%), mammals (6), and birds (2, 3.9%). Juveniles feed on lizards, especially Sceloporus (spiny lizards) and Eumeces (skinks), whereas adults supplement their diet with squamate eggs and endothermic prey. Prey items are located by active foraging, usually swallowed head-first, and average 33% of snake mass. The diet of L. zonata overlaps substantially with that of several other species of sympatric, medium- to large-sized snakes in mesic western North American woodlands; it is narrower than that of the more widely distributed L. getula, and similar to that of allopatric, more closely related L. alterna and L. pyromelana.

The origin of lactation as a water source for parchment-shelled eggs.

Available evidence indicates that mammary gland secretions first evolved in synapsids that laid parchment-shelled eggs. Unlike the rigid-shelled eggs of birds and some other sauropsids, parchment-shelled eggs lose water very rapidly when exposed to ambient air of lower vapor pressure, whether due to differences in relative humidity or to differences in temperature. This precludes endothermic incubation of parchment-shelled eggs in an open nest. Synapsids may have avoided egg desiccation by incubating eggs in a pouch, but this would limit maternal activity. Parchment-shelled eggs are able to take up liquid water across the eggshell. I propose that mammary secretion originally evolved as a means of supplying water to eggs, and as such was essential to the evolution of endothermy among the egg-laying cynodonts that were ancestral to mammals. It is possible that synapsid eggs, like parchment-shelled squamate eggs, were also capable of uptake of some nutrients, such as sodium and ionic calcium. Living monotremes still produce parchment-shelled eggs. The porous eggshell and bilaminar yolk sac membrane of these eggs permit substantial uptake of uterine secretions during the intrauterine period, and might also facilitate uptake of mammary secretions during egg incubation. In its simplest form, mammary secretion may be an ancient trait of egg-laying synapsids, having had an important role long before milk became obligatory for suckling young.

Molecular systematics of New World lampropeltinine snakes (Colubridae): implications for biogeography and evolution of food habits

We used mitochondrial gene sequences to infer phylogenetic relationships among North American snakes of the colubrid tribe Lampropeltini (Arizona, Bogertophis, Cemophora, New World Elaphe,Lampropeltis , Pituophis, Rhinocheilus, Senticolis, Stilosoma), and assessed the implications of our findings for the biogeography and evolution of food habits among these serpents. The maximum likelihood phylogeny identified Rhinocheilus as the sister taxon to all other lampropeltinines, and supported the monophyly ofLampropeltis (including Stilosoma), New World Elaphe, and Pituophis, but not that ofBogertophis . This phylogeny also suggested a sister group relationship between Cemophora andLampropeltis , and between New World Elaphe and Pituophis, and strongly supported thatSenticolis belongs within Lampropeltini, thus contradicting previous suggestions that Senticolis is not a lampropeltinine. Using a method for approximating ancestral areas of clades, we determined that western North America was most likely the ancestral area of lampropeltinines. Our survey of published studies, combined with unpublished data, indicated that lampropeltinines as a group feed mainly on mammals, less frequently on lizards, birds, and bird eggs, and only rarely on squamate eggs, snakes, anurans, and insects. Some individual species indeed emphasize mammals in their diets, but others most frequently eat lizards, squamate eggs, bird eggs, or snakes, whereas others take two prey types with similar frequency. Our reconstruction of the evolution of food habits among lampropeltinines suggests that a diet emphasizing lizards is ancestral, and therefore diets that mostly consist of mammals, squamate and bird eggs, and snakes are derived within the clade. In at least some species, smaller individuals prey mostly on lizards and larger ones add mammals to their diets.

Molecular systematics of New World lampropeltinine snakes (Colubridae): implications for biogeography and evolution of food habits

We used mitochondrial gene sequences to infer phylogenetic relationships among North American snakes of the colubrid tribe Lampropeltini (Arizona, Bogertophis, Cemophora, New World Elaphe, Lampropellis, Pituophis, Rhinocheilus, Senticolis, Stilosoma), and assessed the implications of our findings for the biogeography and evolution of food habits among these serpents. The maximum likelihood phylogeny identified Rhinocheilus as the sister taxon to all other lampropeltinines, and supported the monophyly of Lampropeltis (including Stilosoma), New World Elaphe, and Pituophis, but not that of Bogertophis. This phylogeny also suggested a sister group relationship between Cemophora and Lampropeltis, and between New World Elaphe and Pituophis, and strongly supported that Sentkolis belongs within Lampropeltini, thus contradicting previous suggestions that Senticolis is not a lampropeltinine. Using a method for approximating ancestral areas of clades, we determined that western North America was most likely the ancestral area of lampropeltinines. Our survey of published studies, combined with unpublished data, indicated that lampropeltinines as a group feed mainly on mammals, less frequently on lizards, birds, and bird eggs, and only rarely on squamate eggs, snakes, anurans, and insects. Some individual species indeed emphasize mammals in their diets, but others most frequently eat lizards, squamate eggs, bird eggs, or snakes, whereas others take two prey types with similar frequency. Our reconstruction of the evolution of food habits among lampropeltinines suggests that a diet emphasizing lizards is ancestral, and therefore diets that mosdy consist of mammals, squamate and bird eggs, and snakes are derived within the clade. In at least some species, smaller individuals prey mostly on lizards and larger ones add mammals to their diets.

Food habits of the long‐nosed snake (Rhinocheilus lecontei), a ‘specialist’ predator?

AbstractWe explored predator specialization by examining dietary variation in the widespread North American long‐nosed snake, Rhinocheilus lecontei. We examined the stomach contents of more than 800 museum specimens, and supplemented our findings with published dietary records. Sixty‐six percent of 135 prey eaten by R. lecontei were lizards, 26% were mammals, and 7% were squamate eggs; teiid lizards of the genus Cnemidophorus comprised 72% (64 of 89) of all lizard prey. Ninety‐four percent of specimens with food contained a single item, and all 79 prey for which we determined direction of ingestion were swallowed head‐first. Among those specimens containing food, long‐nosed snakes from Mexico were significantly larger, and ate a higher percentage of mammals, than specimens from the United States. Larger R. lecontei sometimes fed on larger prey, and perhaps excluded smaller prey from their diet. To assess relative trophic niche breadth for R. lecontei, we compared the percentage of lizards and of Cnemidophorus in the diet of long‐nosed snakes with the percentage with which other terrestrial snakes consumed lizards as their modal prey, and with which these same snakes ate members of their preferred lizard prey genus. Although we uncovered no statistical basis for labelling R. lecontei a specialist, its diet may often be restricted to lizards and even to Cnemidophorus, and therefore recognizing long‐nosed snakes as specialist predators remains a subjective decision. Our study also demonstrates that quantitative natural history can place related species in a resource use continuum, and thereby can help to elucidate the evolutionary basis for specialization.

Gape size and evolution of diet in snakes: feeding ecology of erycine boas

AbstractThe Macrostomata accounts for more than 85% of extant snakes and is characterized by increased mobility of the jaws and increased gape size. We used stomach contents of museum specimens and specific literature records to describe the food habits of a basal clade of macrostomatan snakes – the erycine boas (Erycinae) – with an emphasis on the North American Charina bottae. Mammals, lizards, birds, and squamate eggs composed 66%, 17%, 7%, and 5%, respectively, of the prey of C. bottae. Smaller C. bottae fed on squamate eggs and lizards, whereas larger snakes added mammals and birds to their diet, and ceased to take squamate eggs. Ten of 12 snakes with multiple prey had eaten nestling birds or mammals, and snakes that ate multiple prey were not significantly larger than those that had single prey. Charina trivirgata and C. reinhardtii also prey on mammals, whereas species of Eryx feed mainly on mammalian prey, but also eat lizards and occasionally birds. Evolutionarily more basal groups of snakes primarily feed on elongate prey, which suggests that innovations of the feeding apparatus of macrostomatans allowed these snakes to eat heavier and bulkier prey, particularly mammals. Erycines appeared and diversified at approximately the same geological time as rodents, suggesting that rodents perhaps constituted an abundant prey resource that favoured the diversification of early macrostomatans.

Feeding Ecology of the Desert Nightsnake, Hypsiglena torquata (Colubridae)

We studied the diet of the North American desert nightsnake, Hypsiglena torquata, based on the stomach contents of 397 museum specimens, field observations, and published dietary records. Based on 92 prey from throughout much of its distribution, H. torquata, feeds mainly on sceloporine lizards and squamate eggs and occasionally eats frogs, snakes, insects, and amphisbaenians. Lizards are typically swallowed head- first, whereas frogs are swallowed from the rump. Prey mass increases with snake mass and prey/predator mass ratios range from 0.03 to at least 0.50. Three genera of abundant lizards (Cnemidophorus, Coleonyx, Xantusia) are infrequently eaten, which suggests that these lizards chemosensorily avoid desert nightsnakes. Hypsiglena arose within a Neotropical clade of predominantly nocturnal, frog-eating snakes, and its occupancy of arid western North America correlates with two derived feeding traits: at least occasional ambush predation on diurnal lizards, and inclusion of squamate eggs in its diet.

The Micro-Environment of a Natural Lizard Nest

perature cycle of the nest of any squamate. Knowledge of nest micro-environments is urgently needed in order to evaluate work on physiological tolerances of squamate eggs. Two species of gekkonid lizards which lay calcareous-shelled eggs have been the subject of a population study in a commercially exploited forest in northern New South Wales, Australia for six years (Bustard, 1968, 1969a, b). One (Gehyra variegata) is strictly arboreal, the other (Heteronotia binoei) is terrestrial. Both species almost always lay their eggs under cover on the ground. Because the eggs were not camouflaged, as they are in many gecko species (Bustard, 1957, 1965), nests were easily found and over 120 have been examined. Nine nests were found near