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For various reasons, reduction or cessation of feeding (anorexia) can occur in either sex during periods of reproduction among vertebrates, from cichlids to elephant seals. Anorexia is commonly associated with gestation in snakes. Using radiotelemetry, we investigated the feeding and spatial ecology of a live-bearing viperid snake, the western diamond-backed rattlesnakes ( Crotalus atrox). Specifically, from 2001 to 2010, we determined the feeding frequency and home range size of adult females ( n = 27) during the active season ( March- October) in a population from the Sonoran Desert of Arizona. We addressed a central hypothesis: Do hunting and feeding occur throughout pregnancy? Also, we tested a corollary hypothesis: Does pregnancy influence home range size? We documented hunting and feeding from March to October and during pregnancy ( June to mid- September). Feeding frequency was significantly greater in late pregnancy, a result that is in sharp contrast to most other large-bodied vipers. Furthermore, home range sizes in gestating subjects did not differ from those in nonreproductive years. Births occurred from mid- August to mid- September and mean litter size was 3.4. Frequent feeding in C. atrox during gestation unquestionably provides energy and nutrients to the mother, which is likely important for survival, but such food consumption does not imply that nutrients are used by the fetuses. There is, however, recent evidence in other snakes, including a pitviper, that amino acids are transferred to fetuses. Feeding during pregnancy in C. atrox may be important for both income and capital mode reproduction. Hunting and feeding throughout gestation might be accomplished by having relatively small litters not burdened by a body cavity filled with fetuses. Reduction in litter size may thus be a life-history (fecundity) trade-off that permits females to survive and maintain pregnancy in regions where drought and high temperatures are often extreme and chronic. [ABSTRACT FROM AUTHOR]

In many species of snakes, particularly viperids from temperate regions, production of offspring by individuals occurs on a less-than-annual schedule. Accordingly, acquiring sufficient energy and nutrient reserves for reproduction in females often requires more than a single active season. This is termed capital mode. Yet, in some instances, annual reproduction occurs under conditions where foraging success is high and environmental factors are compliant. This is termed income mode. Here, we addressed the hypothesis of annual versus less-than-annual reproduction from a long-term radio-telemetric study involving female western diamond-backed rattlesnakes Crotalus atrox from a population of the Sonoran Desert in Arizona. From 2001 to 2008, 16 of 20 radio-telemetered females produced 36 litters, which 32 were informative in addressing the hypothesis of reproductive frequency. In 14 females, litters were produced on a biennial or at-least-biennial (≥biennial) cycle. However, seven females demonstrated annual reproduction, of which several had previously reproduced on a biennial or greater cycle. Because our study was non-experimental, we were unable to unambiguously identify specific proximate factors that contributed to the shift in annual reproduction. Nonetheless, we established that greater annual rainfall was significantly correlated with shifts to annual reproduction. Based on other studies, we hypothesize that increased rainfall was causally linked with increases in rodent densities and the foraging success of female C. atrox, which in turn is linked to reproduction. We describe, moreover, several characteristics of female C. atrox that appear to facilitate the potential for annual reproduction. In long-lived species, such as C. atrox, our research underscores the necessity to follow individuals for extended periods to gain insights on reproductive cycles not captured by point sampling methods, such as short-term field studies or reliance on museum specimens. [ABSTRACT FROM AUTHOR]

A multi-year radio-telemetric study of the copperhead Agkistrodon contortrix (Serpentes: Viperidae) was conducted at the north-eastern extreme of its range to determine the relationship of plasma sex steroids of males to the mating season. Blood samples were collected in situ approximately every 2 weeks (repeat-test group) from radio-telemetered males during the 7-month active season (April–October) from 2001 to 2003 and assayed for concentrations of testosterone (T) and progesterone (P4). Blood samples were also obtained from a large number of incidental males (single-test group) for the analysis of seasonal levels of T and P4. The profiles of T and P4 showed a peak in August–September that corresponded to the single mating season (late July to late September). Both T and P4 had similar seasonal profiles, but absolute levels of these steroids were significantly different, with concentrations of T four- to fivefold greater. The mating season of the population we investigated differs from other (e.g. southern) populations, which show two mating seasons (late summer/early fall and spring) before the period of ovulation in mid- to late spring. When a mating season is absent in spring, inseminated females are obligated to store sperm over winter until ovulation in the spring. In studies of A. contortrix that document two mating seasons, peak levels of T in males are coincident with both of these periods. In contrast, we found that peak levels of T and P4 in males coincided with the occurrence of the single mating season, and levels were basal in spring. These results further support the idea that plasma sex steroids influence the expression of sexual behaviour in A. contortrix and other snakes. Nonetheless, confirmation of this view awaits experimental studies. [ABSTRACT FROM AUTHOR]

To assess whether urbanization influences the spatial ecology of a rare and protected venomous reptilian predator, the Gila monster Heloderma suspectum, we compared home range (HR) size and movement parameters at three sites varying in degree of urbanization in the Sonoran Desert. We predicted that the urban population of H. suspectum would exhibit smaller HRs, avoid human structures and show less movement. Multivariate analysis indicated that males generally exhibited larger HRs and had higher movement rates and activity levels than females at all three sites. Contrary to our predictions, however, HR size and movement parameters did not vary across the sites in relation to the level of urbanization. At the urban site, individuals often crossed narrow roads and regularly used artificial structures as refuges for extended periods. Furthermore, the population sex ratio at the urban site was female-biased, consistent with the expectation that occupation of larger HRs and higher movement rates results in higher mortality for males in urbanized areas. Gila monsters did not appear to alter certain aspects of their spatial ecology in response to low levels of human activity but additional work will be required to assess population viability and possible effects in the long term and with higher levels of urbanization. [ABSTRACT FROM AUTHOR]

Information on behavioural and physiological processes of newborn reptiles is often difficult to obtain under natural conditions, especially in lizards and snakes. Consequently, we lack information on a wide range of biological phenomena (e.g. thermoregulation, digestion, circadian activity rhythms) in neonates of these taxa. Here, we report novel behaviour in newborn sibling sidewinder rattlesnakes Crotalus cerastes, a desert-inhabiting species of south-western North America. At the entrances of their natal burrows, neonates formed aggregations (‘balls’) during daylight hours, which involved frequent movements of individuals within these balls. Through the study of two radio-telemetered females and their litters ( n=20 offspring), we obtained temperature data from the mothers, centre of the snake balls, and from multiple sites in the immediate environment for 10 days post-birth, the period that is coincident with maternal attendance and the first cycle of ecdysis. The core temperatures of the snake balls showed significant stability over the extreme thermal ranges of the environment. Although other functions are possible, such as those related to water conservation and antipredator defence, we suggest that frequent movements of individuals within the balls involved selection of a thermal optimum to enhance ecdysis. Based on other studies of aggregation in animals, dynamic aggregative behaviour in newborn sibling C. cerastes implicates self-assembly and suggests that individuals benefit from behavioural interactions with their siblings. One plausible scenario for the evolution of this type of dynamic aggregation involves thermal selection among sibling neonates for optimal basking sites within natal refugia in extreme environments such as desert landscapes. Moreover, it is possibly limited to species of vipers (and other snakes) that are viviparous and where maternal care is present up to the time of shedding in neonates. [ABSTRACT FROM AUTHOR]

Sexual dimorphisms – phenotypic dissimilarities between the sexes – are common and widespread among plants and animals, and classical examples include differences in body size, colour, shape, ornamentation and behaviour. In general, sexual dimorphisms are hypothesized to evolve by way of sexual selection acting on one sex through priority-of-access for sexual partners via mate choice and/or intra-sexual competition. In snakes, males are the mate-searching sex and one form of sexual selection involves male–male competition in locating females by following pheromone trails using their forked tongues, the structure used to sample environmental chemicals for transduction in the vomeronasal chemosensory system (VNS). Based on several lines of empirical evidence, increased tongue forking (bifurcation) in snakes (and some lizard taxa) appears to enhance chemical trail-following abilities through tropotaxis (the simultaneous comparison of stimulus intensities on two sides of the body) and thus aids in prey location and mate searching in males. We predicted that male copperheads, Agkistrodon contortrix, a North American pitviper, should have more deeply forked tongues than females owing to male–male competition for priority-of-access to widely dispersed females during the mating seasons. We examined formalin-fixed, ethanol-preserved museum specimens of adult A. contortrix for sexual size dimorphism (SSD) of the tongue. Tongue dimensions showed differences indicative of SSD, and the degree of bifurcation (i.e. mean tine length) was significantly greater in males. Various structures of the VNS and associated regions (e.g. muscles) in some vertebrate taxa show sexual dimorphism, but our study is the first to document dimorphism in the tongue of a tetrapod vertebrate. [ABSTRACT FROM AUTHOR]

Facultative parthenogenesis (FP) is asexual reproduction in plant and animal species that would otherwise reproduce sexually. This process in vertebrates typically results from automictic development (likely terminal fusion) and is phylogenetically widespread. In squamate reptiles and chondrichthyan fishes, FP has been reported to occur in nature and can result in the production of reproductively viable offspring; suggesting that it is of ecological and evolutionary significance. However, terminal fusion automixis is believed to result in near genome-wide reductions in heterozygosity; thus, FP seems likely to affect key phenotypic characters, yet this remains almost completely unstudied. Snake venom is a complex phenotypic character primarily used to subjugate prey and is thus tightly linked to individual fitness. Surprisingly, the composition and function of venom produced by a parthenogenetic pitviper exhibits a high degree of similarity to that of its mother and conspecifics from the same population. Therefore, the apparent loss of allelic diversity caused by FP appears unlikely to have a significant impact on the prey-capturing ability of this snake. Accordingly, the pitviper offspring produced by FP retained complex phenotypic characteristics associated with fitness. This result reinforces the potential ecological and evolutionary importance of FP and questions our understanding of the inheritance of venom-associated genes. [ABSTRACT FROM AUTHOR]