Induction of phenotypic plasticity in rattlesnake trophic morphology by diet manipulation

Gape‐limited predators are restricted in the shape and size of prey items they can ingest by their trophic morphology. Evolutionary theory predicts that gape‐limited predators, such as rattlesnakes, should possess plasticity in their trophic morphology to allow them to respond to environmental cues about their prey base. This study examined the effects of two possible influences over trophic morphology in the pit‐viper Crotalus viridis viridis. Snakes from six litters were exposed to diet manipulations performed over 480 days. By day 480, snakes from two prey‐size treatments exhibited significantly different head shapes. Snakes reared on whole rodents had broader heads, whereas snakes force‐fed homogenized prey had narrower heads. Shape differences varied among litters, suggesting that not all litters responded the same to diet manipulations. Results suggest that trophic morphology of rattlesnakes is plastic, at least in some litters, and can be induced by prey items. J. Morphol. 275:1339–1348, 2014. © 2014 Wiley Periodicals, Inc.     

Serum and urine biochemical diversity among adult wild-caught Aotus nancymae and Saimiri peruviensis

Serum and urine analytes were compared between adult wild-caught owl monkeys (Aotus nancymae) and adult wild-caught squirrel monkeys (Saimiri peruviensis) to determine if normative clinical pathology data were similar. An objective of the study was to confirm that species of neotropical primates are distinct with regard to physiologic parameters, and should not be considered interchangeable in biomedical research. Significant differences (P < 0.05) were noted in many serum and urine analytes between the two groups. The results suggest that reference data for wild-caught owl monkeys are not applicable to squirrel monkeys, and the differences are sufficiently large to be of clinical significance. These findings illuminate the diversity among species of neotropical primates.     

Serum and urine biochemical diversity among wild-caught and colony-born Aotus nancymae

Serum and urine analytes were compared between adult wild-caught and adult colony-born owl monkeys (Aotus nancymae), to determine if normative clinical pathology data were similar. Significant differences (P ≤ 0.05) were noted in serum protein, glucose, sodium, urine calcium, calcium clearance, and fractional clearance of calcium between the two groups. The results suggest that reference data for feral owl monkeys is not completely applicable to colony-born animals, however, the differences are too small to be of clinical significance.     

Factors influencing paternity success in Antechinus agilis: last‐male sperm precedence,timing of mating and genetic compatibility

We describe the patterns of paternity success from laboratory mating experiments conducted in Antechinus agilis, a small size dimorphic carnivorous marsupial (males are larger than females). A previous study found last‐male sperm precedence in this species, but they were unable to sample complete litters, and did not take male size and relatedness into account. We tested whether last‐male sperm precedence regardless of male size still holds for complete litters. We explored the relationship between male mating order, male size, timing of mating and relatedness on paternity success. Females were mated with two males of different size with either the large or the small male first, with 1 day rest between the matings. Matings continued for 6 h. In these controlled conditions male size did not have a strong effect on paternity success, but mating order did. Males mating second sired 69.5% of the offspring. Within first mated males, males that mated closer to ovulation sired more offspring. To a lesser degree, variation appeared also to be caused by differences in genetic compatibility of the female and the male, where high levels of allele‐sharing resulted in lower paternity success.     

The Effect of Weaning Weight on Offspring Fitness in Wild House Mice (Mus musculus domesticus): A Preliminary Study

Sex allocation theory is frequently applied to mammalian reproductive traits although the basic assumptions are rarely assessed. In particular, it has been proposed that the finding of negative correlations between sex ratio (percentage males) and litter size in a variety of mammals could ultimately be seen as an adaptation according to the Trivers-Willard hypothesis. Thereby it is supposed 1) that individual young of small litters are weaned at heavier weight than young of larger litters, 2) that this litter-size effect on individual weights persists into adulthood, and 3) that such small weight advantages increase male fitness more strongly than female fitness. In this study, during each of 4 trials, I introduced 4 male and 4 female mice from 8 different litters of wild-caught breeding pairs to a semi-natural enclosure and followed up the social and reproductive events for about 10 weeks. It appeared that small weight differences attributable to litter size variation had a significant positive effect on male fitness, but not on female fitness. As the sample size was small and the social development did vary considerably between trials, this result deserves further clarification.     

The effects of litter-size variation on the development of play behaviour in the domestic cat: litters of one and two

In many litter-bearing species, litter-mates interact with each other in a variety of ways during early life. In the domestic cat, Felis catus, social play is a prominent form of interaction between litter-mates. The present study investigated how the lack of a litter-mate affected the development of kitten play and of the mother-kitten relationship. The subjects were 14 litters of domestic kittens living with their mothers in large indoor cages. Seven litters contained two male kittens, and the other seven contained single male kittens. Social interactions within the families were observed from day 22 to day 83 after birth. Single kittens played a more active part in maintaining close proximity to their mothers and directed more playful behaviour at them than did kittens with a sibling. Although single-kitten mothers avoided their offspring more than did mothers of litters of two, they also directed much higher levels of play behaviour at them. Despite the marked difference in the mother-kitten play relationship in the two litter types, single kittens experienced quantitatively less social play than did kittens with siblings. As the kittens grew older, single-kitten mothers showed higher levels of aggression towards their young than did mothers of litters of two.     

Field Evaluations of Augmentative Releases of Delphastus catalinae (Horn) (Coleoptera: Coccinellidae) for Suppression of Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae) Infesting Cotton

In 1992 and 1993, field evaluations were conducted to determine the efficacy of Delphastus catalinae (Horn) releases for the suppression of Bemisia argentifolii Bellows & Perring infesting cotton in the Imperial Valley of California. Augmentative releases of adult beetles, totaling 3.5 and 5.5 beetles per plant for 1992 and 1993, respectively, were made into four 0.2-hectare cotton plots and four exclusion cages covering 40 cotton plants. Equal numbers of field plots and cages served as controls for the D. catalinae releases. Open field evaluations revealed no significant difference in the whitefly densities between the release and the nonrelease fields. In addition, no differences in plant growth measures were detected in the year that these data were collected. Releases of D. catalinae into whitefly exclusion cages resulted in a 55% and a 67% decrease in whitefly densities in 1992 and 1993, respectively. Observational data suggested that intraguild predation on D. catalinae by the existing predator fauna may have limited the potential for D. catalinae to provide biological whitefly control in open field plots relative to the levels observed within the cages. Releases of D. catalinae did not adversely affect population densities of indigenous parasitoids, suggesting an absence of statistically significant, antagonistic predator–parasitoid interactions.     

GENETIC BASIS OF ACTIVITY METABOLISM. I. INHERITANCE OF SPEED,STAMINA, AND ANTIPREDATOR DISPLAYS IN THE GARTER SNAKE THAMNOPHIS SIRTALIS

Recent conceptual advances in physiological ecology emphasize the potential selective importance of whole-animal performance. Empirical studies of locomotor performance in reptiles have revealed surprising amounts of individual variation in speed and stamina. The present study is the first in a series examining the genetic basis of variation in locomotor performance, activity metabolism, and associated behaviors in garter snakes. Maximal sprint crawling speed, treadmill endurance, and antipredator displays (Arnold and Bennett, 1984; exhibited as snakes reached exhaustion on the treadmill) were measured for approximately six offspring (presumed to be full siblings) from each of 46 wild-caught gravid garter snakes (Thamnophis sirtalis). Each character was measured on two days; all were individually repeatable. Correlations of these characters with body mass, snout–vent length, age at testing, litter size, dam mass, and dam snout–vent length were removed by computing residuals from multiple-regression equations. These residuals were used in subsequent genetic analyses. Approximate coefficients of variation of residuals were 17% for speed, 48% for endurance, and 31% for antipredator displays. Broad-sense heritabilities were significant for all characters: speed h² = 0.58; stamina h² = 0.70; antipredator display h² = 0.42. All three residual characters showed positive and statistically significant phenotypic correlations (r = 0.19–0.36). Genetic correlations (estimated and tested by restricted maximum likelihood) among residuals were positive and highly significant between speed and endurance (0.58), but nonsignificant between speed and antipredator display (0.43), and between endurance and antipredator display (0.26). All environmental correlations were nonsignificant. These data suggest that, contrary to expectations based on previous physiological studies, there may be no necessary evolutionary trade-off between speed and stamina in these animals. This tentative conclusion will have important implications for future theoretical studies of the evolution of locomotor performance and associated antipredator behaviors.     

Development of Antipredator Responses in Snakes

Individual and litter differences in the number of attacks directed by Mexican garter snakes (Thamnophis melanogaster) at a threatening stimulus were studied over the first year of life. Newborn snakes born to wildcaught females from the same population were tested the day after they were born and at 7, 16, 31, and 54 weeks of age on reactivity to a potent nonmoving and moving stimulus (a human finger). There were significant individual and interlitter differences in number of strikes directed at both stimuli but no significant effect of sex. Intercorrelations among the strike scores of individuals across test days averaged .54 for the nonmoving stimulus presentations and .63 for trials with the moving stimulus. Strike scores to the moving and nonmoving stimuli were significantly correlated at each age, however, attack responses to the moving stimulus declined over the year while those to the nonmoving stimulus remained constant. Measures of concordance showed that both individual strike scores and litter means were highly consistent, whereas consistency within litters was reduced. The results indicate that litter and individual differences among newborn snakes in the tendency to engage in antipredator behavior (“defensive temperament”) remain relatively stable from the first day after birth throughout the first year of life.     

外源氮素调控C/N比对杉木林凋落叶细菌群落结构的影响

为探究不同C/N比对杉木凋落叶分解特性的影响,通过添加外源氮,采用分解袋法,分析林下植被保留和林下植被去除2种林分中不同C/N比值的杉木凋落叶分解300 d时细菌群落结构差异。研究显示：一定范围内,初始C/N比降低有利于杉木凋落叶分解和细菌群落多样性提升,过低的C/N比则具有抑制作用;相比于林下植被去除,林下植被保留管理措施更有利于杉木凋落叶的分解,且细菌群落多样性更高,但当初始C/N比值为20.3时,杉木凋落叶分解所受的抑制作用更为明显;在门水平上,变形菌门、放线菌门和浮霉菌门为杉木凋落叶中主要优势种群;在属水平上,慢生根瘤菌属、嗜酸栖热菌属和Singulisphaera属在杉木凋落叶中相对丰度较高;不同处理间的杉木凋落叶细菌群落结构具有显著差异,变形菌门、放线菌门和酸杆菌门等细菌门中的多类细菌相对丰度差异显著;在门分类水平上,杉木凋落叶C/N比值与主要细菌种群相对丰度的相关性最高,C/P比值与杉木凋落叶细菌群落结构变异的相关性最高;在属水平上,杉木凋落叶全碳含量、C/N比值和全钾含量与主要细菌种群相对丰度的相关性最高,全钾含量与杉木凋落叶细菌群落结构变异的相关性最高。结果表明初始C/N比的降低改变了杉木凋落叶细菌群落结构,进而作用于杉木凋落叶的分解。     

TETRODOTOXIN RESISTANCE IN GARTER SNAKES: AN EVOLUTIONARY RESPONSE OF PREDATORS TO DANGEROUS PREY

The use of the “arms race” analogy as a conceptualization of evolutionary predator-prey interactions has been criticized because of the lack of evidence that predators can and do adapt to increased antipredator ability of prey. We present evidence that the garter snake Thamnophis sirtalis has evolved resistance to tetrodotoxin (TTX) in response to the toxicity of the newt Taricha granulosa on which the snake feeds. A bioassay (locomotor performance before and after injection of TTX) was used to obtain repeated measures of resistance for individual snakes. We studied interpopulation and interspecific variation by comparing resistance in Thamnophis sirtalis from populations occurring sympatrically and allopatrically with Taricha granulosa, and in Thamnophis ordinoides (which does not feed on the newt) occurring sympatrically with Taricha granulosa. We also examined intrapopulation variation in TTX resistance using snakes from a population known to feed on Taricha granulosa. Resistance differed significantly among individuals and litters; repeatability and heritability estimates of the assay were significantly different from zero, demonstrating the potential for response to selection. The population of Thamnophis sirtalis that occurs with Taricha granulosa exhibited levels of resistance much greater than either of the other groups. These results suggest that the predator-prey arms race analogy may be applicable to this system.     

Maternal aggression in hamsters: effects of stage of lactation, presence of pups, and repeated testing

This study investigated maternal aggression in hamsters and examined the effects of early versus late lactation, presence or absence of the litters during the tests, and prior aggressive encounters. There was a total of six experimental groups. Two groups were tested in the presence of their litters on both Days 5 and 15 of lactation; two groups were presented with intruders after a 6-hr interval of mother-litter separation on Days 5 and 15 of lactation. The last two experimental groups were tested on Day 15 only in the presence of their litters or after a 6-hr separation from their litters. Estrous-cycling animals were also tested twice (10 days apart) or once to control for periods of social isolation. Animals were tested in their home cages for 10 min with weight-matched estrous-cycling intruders. Sexually receptive females were not used as controls or intruders. Measures of aggression included fights, attacks, chases, and intruder retreats. Lactating animals initiated significantly higher levels of all measures of aggression than cycling controls. There were no differences in aggression between Days 5 and 15 of lactation or between the groups tested in the presence or absence of their litters. Prior testing on Day 5 had little effect on aggressive responses on Day 15. The results are discussed in terms of comparisons to other species and the factors responsible for high levels of aggression during lactation.     

Can snakes hide in plain view? Chromatic and achromatic crypsis of two colour forms of the Western Terrestrial Garter Snake (Thamnophis elegans)

Colours influence numerous aspects of an animal's ecology. One possibility is that colour helps make an animal cryptic against the background on which it is resting. We test this hypothesis for two different, geographically separated colour forms (dark forms and light forms) of the Western Terrestrial Garter Snake, Thamnophis elegans. We quantified crypsis of snakes, in terms of colour (chromatic crypsis) and brightness (achromatic crypsis), by using objective measures of spectral reflectance of snakes and the surrounding habitat. These data were visually modelled from the perspective of potential snake predators and human researchers. Overall, snakes of both colour forms selected basking sites that increased chromatic crypsis over that which would have been achievable on random backgrounds. Both colour forms of T. elegans appear to exhibit similar achromatic and chromatic crypsis when viewed by potential predators, such as mammals and birds. From the perspective of the human visual model, dark T. elegans were generally more chromatically cryptic than light T. elegans, contrary to our a priori subjective impression. The main contribution of the present study is that we provide one of the first objective comparisons of snakes and their backgrounds as a measure of crypsis. Although we found some evidence for crypsis as a factor in choice of basking sites for snakes, other factors (e.g. thermoregulatory opportunities) undoubtedly play important roles as well. We also have not addressed whether snakes involved in other activities are cryptic or whether there are differences between the sexes or between reproductive and nonreproductive females. The adaptive significance of colour variation has been studied in diverse taxonomic groups. Although the mechanisms are not straightforward, the opportunities to carry out further work in this area are enhanced by the availability of objective approaches. © 2013 The Linnean Society of London,     

The Effect of Cage Space on Behavior and Reproduction in Crl:CD1(Icr) and C57BL/6NCrl Laboratory Mice

Recommendations for the amount of cage space required for female mice with litters were first made in the 2011 Guide for the Care and Use of Laboratory Animals. We hypothesized that if a difference in mouse behavior and reproduction exists within the limits of commercially available caging, this difference would be detected between the smallest and largest cages. C57BL/6NCrl and Crl:CD1(Icr) breeding mice were randomly assigned to a cage treatment: LP 18790 (226cm²); A RC1 (305cm²); A N10 (432cm²); T 1291 (800cm²) and a breeding configuration: single (male removed after birth); pair (1 male + 1 female); or trio (1 male + 2 females) in a factorial design for 12 weeks. All cages received 8-10g of nesting material and nests were scored weekly. Pups were weaned between post-natal day 18 and 26 and were weighed at weaning. Adult behavior and location in the cage were recorded by scan samples every 30 min over 48 hr of video recorded on PND 0-8 and PND 14-21 when pups were in the cage. Press posture and play behavior were recorded by 1/0 sampling method. Cage space did not significantly alter typical reproductive measures. Pups in the smallest cage played less than in the other cages. Adults in the smallest cage displayed more press posture than in the two largest cages. Mice in the largest cage spent more time under the feeder than in other areas of the cage. Nest score was also the highest in the largest cage. Housing breeding groups of mice in a range of commercially available cage sizes does not affect reproduction but behavioral measures suggest that the smallest cage tested, LP 18790, may be stressful for outbred mice when pups are present.     

Do laboratory studies predict parasitoid interaction outcomes in the field?

Studying competitive interactions among natural enemies is important to elucidate the success and non-target impact of candidate biological control agents. Increased regulation of new introductions requires that studies on non-target species be carried out in confined conditions. Hypotheses about potential impacts of biological control agents in the field are based on data from Petri dish or small cage experiments conducted in the laboratory. This study compared the performance of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), parasitoids Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and Microplitis plutellae (Muesebeck) (Hymenoptera: Braconidae) in experiments conducted in small cages in the laboratory and in large cages in the field. Results showed no significant differences between laboratory and field outcomes for D. insulare alone and when D. insulare and M. plutellae were combined. For M. plutellae alone, parasitism in the laboratory cages was significantly less than in the field cages. These results demonstrate that laboratory studies may be useful to develop hypotheses on competitive interactions of candidate parasitoid biological control agents.     

High infection intensities,but negligible fitness costs,suggest tolerance of gastrointestinal nematodes in a tropical snake

We investigated patterns of prevalence and intensity of gastrointestinal nematode infections in a tropical natricine snake, the keelback (Tropidonophis mairii). Ninety‐eight per cent of keelbacks were infected with Tanqua anomala (Gnathostomidae), with infection intensities of up to 243 worms per snake. Infection with T. anomala caused severe inflammation of stomach mucosa and submucosa at the sites of parasite attachment and encystment. Nonetheless, we did not detect detrimental effects of nematode infection on measures of fitness among wild or captive snakes. Snakes with heavier nematode infections had higher body condition scores than less‐infected individuals. Deworming captive snakes had no measurable effect on their growth rate, body condition or locomotor performance. In combination with an earlier study on blood‐dwelling hepatozoons, our work suggests that keelbacks have a high tolerance to parasites. The ‘fast‐pace’ life history and short lifespan of these snakes may make it beneficial for them to tolerate infection, rather than expend energy on resisting parasite attack.     

Response of grazing impacts of an algivorous fish (Pseudogastromyzon myersi: Balitoridae) to seasonal disturbance in Hong Kong streams

1. Manipulative experiments were carried out in four Hong Kong streams (two shaded, two unshaded) to investigate the impact of grazing by an algivorous fish, Pseudogastromyzon myersi, on benthic algal biomass and assemblage composition. Experiments were conducted and repeated during both the dry and wet seasons to determine whether spate‐induced disturbance modified any grazing effect. Treatments comprised fish exclusion and inclusion via closed and open cages, with a no‐cage treatment used as a control for the cage effect. Treatments were maintained for 4 weeks in each experimental run. 2. Grazing by P. myersi reduced benthic algal biomass and the organic matter content of periphyton in open cages and the no‐cage treatment relative to closed cages. The similarity between open‐cage and no‐cage treatments was evidence that the overall difference among treatments was caused by limiting fish access to closed cages and not merely an artifact of caging. Grazing effects were broadly similar in all streams, but there was a significant statistical interaction between treatments and seasons. 3. Analysis of dry‐season data matched the overall trend in inter‐treatment differences, confirming the effects of grazing by P. myersi on algal biomass and periphyton organic matter. Significant differences in algal assemblage composition between closed‐cage and no‐cage treatments during the dry season reflected reductions in the abundance of erect, stalked diatoms (Gomphonema) and filamentous cyanobacteria (Homeothrix). Removal of these vulnerable overstorey algae by P. myersi resulted in greater abundance of understorey diatoms (Achnanthes and Cocconeis) in the no‐cage treatment in all streams during the dry season. The composition of algal assemblages in open cages was intermediate between the other two treatments. 4. Although fish densities were greater in all streams during the wet season, spate‐induced disturbance obscured grazing effects and there were no significant differences among treatments attributable to fish grazing. Seasonal variation in impacts of P. myersi grazing provides support for the harsh‐benign hypothesis, and confirms that biotic factors are less important controls of stream algal biomass and assemblage structure during periods (i.e. the wet season in Hong Kong) when abiotic disturbances are frequent or intense.     

Offspring growth, survival and reproductive success in the bank vole: a litter size manipulation experiment

To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs. Received: 14 December 1997 / Accepted: 1 March 1998     

Temporal changes in food preferences of wood mice (Apodemus sylvaticus L.)

Diet choice was determined for wild-caught wood mice (Apodemus sylvaticus L.), temporarily confined to cages in the field and offered a choice of 24–26 types of seeds and fruits in 2-h sessions throughout the night. The mice showed an overall preference for some foods over others. The set-up minimized influences on food preferences of predation risk, hunger, food availability and competition. Variation in food preferences was not attributable to differences between individuals, but followed a temporal pattern. The variety of foods eaten showed a bimodal pattern with peaks corresponding to the two most active periods at the beginning and end of the night. Both the amount of food eaten and variation in the amount diminished from the first to the second active period. An expected selection for carbohydrates early in the night and proteins at the end of the night was not found, but sugars were selected for early in the night. These results are discussed in relation to the conflict between an animal's continuous energy requirements and the essentially periodic activity of foraging.     

Are gobiid fish more susceptible to predation if parasitized by Eustrongylides excisus? An answer from robbed snakes

Aspects of the predator–prey relationship between dice snake, Natrix tessellata and gobiid fish infected with Eustrongylides excisus were studied in Lake Sinoe, Romania. A population of snakes residing here shows a high prevalence of subcutaneous larvae of this nematode. The hypothesis of the altered motility in infected fish leading to increased depredation by snakes was tested by comparing gobiids collected from dice snakes with gobiids caught via electrofishing. Out of a total of seven identified gobiid species, three were used for analysis: syrman goby Neogobius syrman, mushroom goby Neogobius eurycephalus, and round goby Neogobius melanostomus. No significant differences in prevalence and intensity of E. excisus infection were found between fish caught by snakes and those obtained by electrofishing. However, significantly higher abundance of E. excisus larvae in fish caught by snakes was reported. These findings suggest limited influence of the presence of E. excisus larvae in studied gobiids regarding their susceptibility to predation by dice snakes.