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Author: Xavier Bonnet

Short Notes Influence of size on survival in newborn asp vipers (Vipera aspis): preliminary results Xavier Bonnet Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, F-79360 Villiers en Bois, France A basic assumption related to the trade-off between offspring number versus offspring size (Charnov and Krebs, 1974; Smith and Fretwell, 1974; Brockelman, 1975; McGinley et al., 1987) is that offspring size should influence neonatal survival (Sinervo, 1990). Evidence for the existence of the above trade-off has been demonstrated in many species (Sibly and Calow, 1986; Clutton-Brock and Godfray, 1991; Stearns, 1992) including snakes (Ford and Seigel, 1989;

In: Amphibia-Reptilia

Steroid hormones are essential for vertebrate reproduction. They are involved in the regulation of major female reproductive events like ovulation, embryo implantation, or gestation. For instance, progesterone promotes foeto-maternal exchanges whereas glucocorticoids stimulate the mobilization of the required energy resources. However, glucocorticoids are key effectors of the stress response; chronic elevations of these hormones can exert negative effects on reproduction. Yet, little is known about the effects of a brief exposure to a stressor on the respective plasma concentrations of sex steroids and glucocorticoids, notably during pregnancy. We examined the impact of a brief stress (handling + 1.5 hours in a bag) on progesterone and cortisol plasma concentrations in pregnant and non-pregnant female guinea pigs. Analyses revealed that: 1) pregnant females exhibited higher baseline progesterone and cortisol concentrations compared to non-pregnant females, as expected; 2) cortisol concentrations increased rapidly following manipulation, revealing a typical hormonal stress response; and, 3) progesterone concentrations decreased on average by 50.9% following the brief stress period, both in pregnant and non-pregnant individuals. These experimental results show for the first time a drastic and rapid impact on progesterone concentration caused by a brief stress.

In: Animal Biology

Abstract

The reproductive ecology of two snakes, female Vipera aspis (terrestrial) and Elaphe longissima (semi-arboreal), was compared. Mean clutch sizes were close in the two species; 6.17 ± 2.50 (n = 69) in the asp viper, and 6.59 ± 1.38 (n = 29) in the Aesculapian snake. When controlled for body size, body condition (hence amounts of body reserves), measured at the beginning of vitellogenesis, correlated positively with litter size in the asp viper but with clutch size in the Aesculapian snake. As in most species, maternal body length positively influenced clutch or litter size. Thus, the trade-off between maternal reserves and growth may favour reserves in the asp viper, and growth in the Aesculapian snake. The asp viper is a bi- or triennial breeder (33% of reproductive-females each year), the Ausculapian snake is an annual breeder (77% of reproductive females each year). These differences may be related to their contrasting foraging ecology. The asp viper is a terrestrial ambush predator with a specialized diet (98% Microtus) based on un-predictable prey availability. This species moves slowly (9.07 ± 8.40 m/day during the active season), and has a small home range (3,024 m2); an increasing body mass (large body reserves) should not affect its activity abilities. The Aesculapian snake is a semi-arboreal predator, which feeds on a large range of prey including birds and eggs, and which is often active (118, 11 ± 134,55 m/day during the active season). This species has a large home range (11,400 m2); an increasing body mass (large body reserves) should be a handicap during arboreal displacements. Vitellogenesis depends on body reserves in the asp viper, while it depends on foraging success in the Aesculapian snake.

In: Amphibia-Reptilia

Abstract

Blood glucose levels in Vipera aspis show great variations, both between months during the annual cycle, and between males and females. The seasonal variations are clearly related to climatic conditions, and particularly air temperatures and possibilities for thermoregulation. The blood glucose levels of the snakes are very low during the hibernation period and high in summer. Nevertheless, climatic conditions alone cannot explain changes of blood glucose levels observed during the period when the vipers are active, particularly the peaks measured soon after emergence from hibernation (males in February, females in March). Testicular activation, vitellogenesis and digestion need high body temperatures for long periods, thus the blood glucose level in reptiles chould be the result of a balance between climatic and physiological conditions expressed by the thermoregulatory behaviour. Plasma glucose levels are higher when the body temperatures are high and when the vipers spend more time in the sun (e.g. males in February, females in March); however, hormonal factors probably play a role.

In: Amphibia-Reptilia

Abstract

Large snakes usually possess a higher number of scales to cover their larger bodies and their larger heads. It has been suggested that a diet based on large prey items also favours the development of scale number because the skin would be more extensible and would enable easier swallowing of voluminous prey. A recent study, however, suggested that although body size positively influences scale count in snakes, diet is probably unimportant (Shine, 2002). We took advantage of a natural experiment that separated two neighbouring and genetically indistinguishable populations of tiger snakes in the vicinity of Perth, Western Australia. In one population, situated on a small coastal Island (Carnac Island), snakes feed primarily on seagull chicks (large prey). In the second population, located on the mainland (Herdsman Lake), snakes feed mostly on frogs (small prey). Carnac Island snakes possess more scales (labial and mid-body rows) and larger relative jaw lengths compared with Herdsman Lake snakes. Although preliminary, these data suggest that tiger snakes, whose many populations show contrasted feeding habits, are suitable models to test the "dietary habits / scale count" hypothesis.

In: Amphibia-Reptilia

Swimming and pregnancy in Tiger snakes, Notechis scutatus Fabien Aubret 1,2,3 , Xavier Bonnet 1 , Richard Shine 4 , Stéphanie Maumelat 2 Reduced locomotor ability may increase sus- ceptibility to predation and hence may repre- sent a proximate mechanism by which “costs” of reproduction are expressed (Shine, 1980). In squamate reptiles, many examples of such ef- fects have been documented, where non-gravid females and/or males showed higher survival rates than gravid females (Shine, 1980; Andren, 1982, 1985; Madsen, 1987). For instance, preg- nancy may entail a reduction in locomotor per- formances in lizards and snakes (Shine, 1980; Shine, 2003;

In: Amphibia-Reptilia

Abstract

Foraging behaviour is influenced by an animal's level of hunger, and may reflect a trade-off between optimizing food acquisition and avoiding predation. Young tiger snakes were raised either on a high or low food diet and exposed to a predation threat while foraging. Under these circumstances, lower condition snakes (low food diet) were prone to take additional feeding/foraging risks: food was accepted at a much higher rate compared with the higher condition animals (high food diet) that were less inclined to risk feeding under a predation threat. This study provides the first direct example of predation risk-associated foraging decisions in snakes.

In: Amphibia-Reptilia

Long term population monitoring is essential to ecological studies; however, field procedures may disturb individuals. Assessing this topic is important in worldwide declining taxa such as reptiles. Previous studies focussed on animal welfare issues and examined short-term effects (e.g. increase of stress hormones due to handling). Long-term effects with possible consequences at the population level remain poorly investigated. In the present study, we evaluated the effects of widely used field procedures (e.g. handling, marking, forced regurgitation) both on short-term (hormonal stress response) and on long-term (changes in body condition, survival) scales in two intensively monitored populations of sea kraits (Laticauda spp.) in New Caledonia. Focusing on the most intensively monitored sites, from 2002 to 2012, we gathered approximately 11 200 captures/recaptures on 4500 individuals. Each snake was individually marked (scale clipping + branding) and subjected to various measurements (e.g. body size, head morphology, palpation). In addition, a subsample of more than 500 snakes was forced to regurgitate their prey for dietary analyses. Handling caused a significant stress hormonal response, however we found no detrimental long-term effect on body condition. Forced regurgitation did not cause any significant effect on both body condition one year later and survival. These results suggest that the strong short-term stress provoked by field procedures did not translate into negative effects on the population. Although similar analyses are required to test the validity of our conclusions in other species, our results suggest distinguishing welfare and population issues to evaluate the potential impact of population surveys.

In: Amphibia-Reptilia

In many organisms, including snakes, trophic niche partitioning is an important mechanism promoting species coexistence. In ectotherms, feeding strategies are also influenced by lifestyle and thermoregulatory requirements: active foragers tend to maintain high body temperatures, expend more energy, and thus necessitate higher energy income. We studied diet composition and trophic niche overlap in two south European snakes (Hierophis viridiflavus and Zamenis longissimus) in the northern part of their range. The two species exhibit contrasted thermal adaptations, one being highly mobile and thermophilic (H. viridiflavus) and the other being elusive with low thermal needs (Z. longissimus). We analyzed feeding rate (proportion of snakes with indication of a recent meal) and examined more than 300 food items (fecal pellets and stomach contents) in 147 Z. longissimus and 167 H. viridiflavus. There was noticeable overlap in diet (overlap of Z. longissimus on H. viridiflavus = 0.62; overlap of H. viridiflavus on Z. longissimus = 0.80), but the similarity analyses showed some divergence in diet composition. Dietary spectrum was wider in H. viridiflavus, which fed on various mammals, birds, reptiles, and arthropods whereas Z. longissimus was more specialized on mammals and birds. The more generalist nature of H. viridiflavus was consistent with its higher energy requirements. In contrast to our expectation, feeding rate was apparently higher in Z. longissimus than in H. viridiflavus, but this could be an artifact of a longer transit time in Z. longissimus, given its lower mean body temperature. These results allow a better understanding of the ability to coexist in snakes belonging to temperate climate colubrid communities.

In: Amphibia-Reptilia

Abstract

Ontogenic melanism (progressive darkening of the skin) has been documented in snakes. Black coloration of the skin often compromises the cryptic effects associated with other patterns (e.g. zigzags) and exposes individuals to predation; however, the mortality risk can be balanced, for example by a thermoregulatory advantage during sun basking. Such adaptive context has been proposed to explain the appearance and the maintenance of melanism within snake populations. Based on a very large captures and re-captures sample (>8000 observations) gathered on two species of sea-kraits (Laticauda saintgironsi and L. laticaudata in New Caledonia), we observed that melanism occurred in only one species (L. laticaudata), was infrequent and concerned adult snakes solely. None of three adaptive hypotheses respectively linked to thermoregulation, predation, or protection against sun radiations, provided a satisfactory account for the occurrence of melanism in our study populations. Therefore, we suggest that melanism was a fortuitous phenomenon.

In: Amphibia-Reptilia