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Biomedical subjects

G M Burghardt

Publications and source records attributed to G M Burghardt.

At least 19 recordsLinked to original sources
PubMed2000

Does prey matter? Geographic variation in antipredator responses of hatchlings of a Japanese natricine snake (Rhabdophis tigrinus).

Rhabdophis tigrinus, which typically forages on toads, has unusual nuchal glands on its dorsal neck region containing secretions chemically comparable to cardiac steroids found in toads. R. tigrinus also has several peculiar antipredator displays involving the neck region. If the nuchal gland secretions of R. tigrinus are derived from toads obtained as prey, populations of R. tigrinus that have not eaten toads over an evolutionary time scale would be expected to lose antipredator displays related to the nuchal glands. We found that laboratory-hatched R. tigrinus from a small toad-free island exhibited displays related to nuchal glands less frequently and flight responses more frequently than hatchling snakes from areas sympatric with toads. These results are consistent with the hypothesis of the dietary origin of the nuchal gland secretions and also support the genetic origin of the behavioral differences between the populations.

Animals↗
PubMed2000

The genetics of dietary experience in a restricted natural population.

The sources of individual differences in human and non-human animals remain controversial. We demonstrate that diet and genetics interact in determining the ontogenetic trajectory of chemosensory and prey preferences in the common garter snake, Thamnophis sirtalis, a dietary generalist. In litters of neonate snakes from a single small field in an earthworm-ingesting population, initial responses to chemical cues from fish and worm were similar, with zero heritabilities. After 12 meals on fish, however, the heritability of both fish and worm chemosensory responses increased markedly, the change in response to fish but not worm chemicals was heritable, the relative preference for fish versus worm was heritable, and the change in relative preference was heritable. In addition, growth rates on each diet were related to changes in chemoreceptive responses. Such genetic-environment variation that emerges only after equivalent ontogenetic experience may be a factor in responses to environmental change in many species.

Animals↗
PubMed1993

Feeding behavior and an oropharyngeal component of satiety in a two-headed snake.

We studied the feeding behavior of a dicephalous Black Rat Snake (Elaphe o. obsoleta) whose heads attack and ingest prey independently. Both heads were given satiation feedings with mouse prey at either 5-day intervals (1989, n = 16 feedings) or 9-11 day intervals (1990, n = 4 feedings). In 1989, a meal pattern was manifested as a negative correlation between total (left + right) meal size (g) and total size of the last meal. Meal sizes of the heads were consistently different (L > R) despite their apparently identical genotypes. We confirmed tongue-flicking rate and swallowing time as indices of satiety/hunger in each head. In order to test whether oropharyngeal stimulation is involved in satiation, we analyzed three measures: willingness to feed, and intrameal changes in swallowing, and tongue-flicking rates. Data for these tests were taken from experimental feedings in which one head was fed to satiation (first head) before the other head (second head) was fed. The second head generally did eat (8 of 10 experimental feedings) after the first head had become satiated. In addition, while the time to swallow a mouse generally increased as the snake neared satiety, swallowing time decreased significantly (p = 0.04) from the first head's last mouse to the second head's first mouse. Finally, in two of three feedings, the first head's tongue-flicking rate decreased before the second head's. These results, which take advantage of this unique animal, indicate that oropharyngeal stimulation is involved in meal termination.

Animals↗
PubMed1993

Responses to escalating predatory threat in garter and ribbon snakes (Thamnophis).

Several models suggest that animals perform a stable sequence of responses during increasing threat from a potential predator. To test the comparative utility of such models, 45 garter and ribbon snakes from four species (genus Thamnophis) were given an antipredator behavior test in which the snakes were exposed to a series of five levels of escalating threat: (a) threat is out of view, (b) threat looms over arena, (c) threat is nonmoving human hand near snake's head, (d) threat is moving human hand, and (e) threat is experimenter's tapping the snake's body. Five different antipredator behaviors were measured. It was found that both qualitative and quantitative changes in behavior occurred between threat levels. However, species differences were also found in the occurrence and amount of every behavior recorded, which indicates that even closely related species may differ in behaviors exhibited in different phases of a predatory encounter.

Animals↗
PubMed1993

The comparative imperative: genetics and ontogeny of chemoreceptive prey responses in natricine snakes.

Reptiles offer a rich diversity for the study of chemoreception, and snakes are a particularly appropriate group for comparative, evolutionary, genetic, developmental, and mechanistic studies. A long-term program of research is described that attempts to integrate these approaches, focusing on the widespread North American genus Thamnophis (Natricinae). Prior to their first meal, neonatal snakes respond to aqueous surface substances from species-typical prey with increased tongue-flicking and open-mouth attacks; these responses are mediated by the vomeronasal organ. Such responses predict what prey snakes will eat and can also predict relative prey preference. Species, population, litter, and individual differences exists and are important at different levels of analysis. Chemoreceptive responses are heritable, although they may show different developmental trends. Some species respond to prey types they do not eat in nature. In the earthworm specialist, T. butleri, response to fish chemicals can be interpreted as a chemoreceptive response inertially inherited from ancestral species, decoupled from prey capture techniques, and in the process of being lost. Ontogeny and experience can modify behavior of the neonate in various ways. Feeding experience can alter response to some prey more than others, and ambient prey odor may shift prey preference. Psychophysical studies show that prey preference and threshold sensitivity to prey chemicals can be independent and differ between closely related species, indicating that neural tissue is devoted to recognition of specific types of prey. In site choice tests, garter snakes can also discriminate between feces derived from conspecific snakes fed similar or different diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1992

Development of antipredator responses in snakes: V. Species differences in ontogenetic trajectories.

The ontogeny of antipredator responses in five species of Natricine snakes was examined. In a split-litter experiment, neonates were given a standardized defensive behavior test at 1 and/or 20 days of age. Thamnophis sirtalis and Thamnophis melanogaster showed a significant increase in both striking and fleeing from a threatening stimulus. Thamnophis butleri was not reactive in terms of striking at either age but did flee frequently at both ages. Thamnophis radix showed low rates of striking and high rates of fleeing; only fleeing increased significantly between the two tests. Nerodia rhombifer exhibited moderate rates of both striking and fleeing at both ages with no developmental effects. Subsets of most of these species tested at 40 or 60 days of age found no further developmental changes.

Age Factors↗
PubMed1991

Effect of food competition on aggregation: evidence for social recognition in the plains garter snake (Thamnophis radix).

Competition for food and aggregating behavior were examined in plains garter snakes (Thamnophis radix), in 11 groups of 1 noncompetitor and 2 competitors. Aggregation data were obtained in 48 daily scans. During food competition, success at obtaining food was asymmetrical across pairs. For aggregation, competitors were mostly associated with noncompetitors. After removal of noncompetitors, competitors were more likely to be solitary, but associations between competitors increased. After a 5-month separation, 5 of the original groups were reconstituted; aggregation patterns similar to the 1st experiment were observed. In a 3rd experiment, unfamiliar animals with and without competitive experience did not aggregate preferentially. Garter snakes discriminate on the basis of sex and species; in this study individual relationships (prior competition) affected aggregation, and the data suggest individual recognition both occurs and persists over time.

Agonistic Behavior↗
PubMed1989

Development of antipredator responses in snakes: IV. Interspecific and intraspecific differences in habituation of defensive behavior.

Habituation of defensive attacks directed toward a threatening stimulus was investigated in neonatal garter snakes. The focus of the experiments was on differential effects of a simple experimental process in relation to species, litter, sex, and individual. In Experiment 1 newborn Thamnophis melanogaster from four liters and newborn Thamnophis butleri from three liters were given daily tests in which snakes were confronted with a nonmoving and moving human hand. Over five successive test days the T melanogaster neonates showed a decline in number of strikes directed toward the stimuli. When retested 10-13 days later the animals showed significant response recovery. Although some of the T? butleri newborns demonstrated significant habituation, there was no overall habituation of strike scores in this species. The T? melanogaster had high strike scores, more rapid habituation to moving than nonmoving stimuli, and significant liter differences in habituation rates. The T? melanogaster, but not the T? butleri neonates, showed significant habituation of flight responses over the five tests. In T? butleri, but not T? melanogaster, males were more prone to attack than were females. In both species there were large differences in both overall strike scores and habituation rates of individual newborn animals. In Experiment 2, T? melanogaster 2-months old, were tested for short-term habituation to either a moving or nonmoving stimulus for 10 successive tests on one day. Habituation of strikes was similar to both stimuli, but more animals confronted with the moving stimulus showed an initial increase in strikes, lending support to the dual-process theory of habituation. As in Experiment 1, there were large individual differences in habituation rates. The results are discussed in terms of the ecological and methodological implications for developmental studies.

Aggression↗
PubMed1987

Diet and growth in juveniles of the garter snakes Thamnophis sirtalis infernalis and Thamnophis radix radix.

The effects of diets consisting of different food types on the growth of juvenile garter snakes was tested using a litter each of Thamnophis sirtalis infernalis and T. radix radix. The snakes were fed diets consisting of earthworms, Lumbricus terrestris, and mosquitofish, Gambusia affinis. The results reveal differences in growth per unit of mass, calories, and protein consumed on the different diets with differences in length being more pronounced than differences in mass. The results indicate that the total mass, calories, or protein consumed are insufficient to reliably predict the amount of growth to be expected in these species. All results are given plus and minus one standard error with an analysis of variance for the production-ingestion ratios.

Animals↗
PubMed1985

The role of feeding regimens in the growth of neonate broad-banded water snakes, Nerodia fasciata confluens, and possible effects on reproduction.

The effect of different feeding regimens on the growth pattern of Nerodia fasciata confluens was tested using a litter of 18 captive-born neonates. The snakes were divided among three feeding groups: one group fed once per week, another fed twice per week, and the third fed on alternate days. The once per week and the twice per week groups were offered the same weight of food each week, while the alternate-day group was offered food in excess of ingestion levels during each feeding session. The results indicate that there is a shift in the allocation of energy for growth in weight, snout-vent length, and tail length with a change in the feeding regimen. Females were affected more than the males. The results are discussed in relation to their possible effect on reproduction.

Animals↗
PubMed1978

Behavior and phylogeny: constriction in ancient and modern snakes.

Comparative analyses of behavior have an underappreciated potential for revealing the role of ethoecological factors in the origins of higher taxa. Twenty-seven species (13 genera) in the advanced family Colubridae exhibited 19 patterns of coil application; one or two patterns were usually consistent within a genus. Forty-eight species (26 genera) in the primitive families Acrochordidae, Aniliidae, Boidae, and Xenopeltidae usually used a single pattern, despite differences in age, size, shape, habitat, and diet. This implies the shared retention of an action pattern used by their common ancestor no later than the early Paleocene. Constriction must have been used as a prey-killing tactic very early in the history of snakes and might have been a behavioral "key innovation" in the evolution of their unusual jaw mechanism.

Animals↗
PubMed1977

Vocalization in juvenile crocodilians.

Evidence is presented that the grunts and distress calls of juvenile alligators (Alligator mississipiensis) are examples of graded calls, which are given in different form depending largely on contest. Representative sonagrams of the distress calls of three other species of crocodilians (Caiman crocodilus, Crocodylus niloticus, and Crocodylus siamensis) are presented and compared with sonagrams of alligator distress calls. These findings are discussed in light of current knowledge of the bioacoustics of other vertebrates.

Age Factors↗
PubMed1975

Role of the tongue and senses in feeding of naive and experienced garter snakes.

Prey attack behavior was studied in two species of garter snakes (Thamnophis sirtalis and T. radix). Newborn, ingestively naive, and experienced snakes had their tongues severed surgically, while control groups retained their tongues. Attack latency, tongue flick frequency and an orientation-interest measure were recorded for each subject on responses to extracts prepared from species-characteristic prey. Feeding, as well as responses to prey extracts, were found to be suppressed almost totally in the tongueless naive snakes. A detongued adult, however, readily ate although its behavior was abnormal. Temporary blind and anosmic conditions did not have a significant effect on response rates of the tongueless or control groups. While importance of the tongue-Jacobson's organ system is demonstrated, the length of tongue removed and presurgery experience are important factors.

Animals↗
PubMed1971

Chemical-cue preferences of newborn snakes: influence of prenatal maternal experience.

Newborn garter snakes (Thamnophis sirtalis) responded similarly to worm and fish surface extracts regardless of whether the mothers were fed exclusively on fish or worms during the gestation period. Worm extract was the more effective. This result is in contrast with the easy modifiability of chemical-cue preferences in young snakes after birth. The initial stimulus control of the attack response in newborn snakes thus seems relatively unmodifiable.

Animals↗