Patrick T. Gregory

Regulation of Seasonal Mating Behavior in Thamnophis sirtalis parietalis

At latitudes of about 50?-55? N in Manitoba, Canada, the red-sided garter snake (Thamnophis sirtalis parietalis) hibernates in concentrated aggregations of several thousand individuals and mates shortly following emergence in late April or early May. Mating is most intense when air temperatures are above 15 C, and lasts about 4 weeks. Mating activity of about 10 days duration can be induced in the laboratory by: 1) collecting snakes at the hibernaculum site in September, subjecting them to 5 C, OL24D for at least 4 months and then transferring them to 25 C, 12L12D; and 2) collecting snakes at the hibernaculum site in late April or early May, holding them at 5 C, OL24D, and transferring them to 25 C, 12L12D at any time until August. Food intake is completely inhibited for 3 days following the transfer, and then increases progressively in an inverse relationship to declining mating activity. A transfer from 5 C, OL24D to 5 C, 12L12D does not result in mating. On the basis of these experiments we hypothesize that the increase in body temperature experienced by the red-sided garter snake during emergence from hibernation induces the intense mating activity observed shortly following emergence.

Food Habits of the Grass Snake in Southeastern England: Is Natrix natrix a Generalist Predator?

Abstract Generalist species are often both widely distributed and abundant. They also are often plastic in their ecology, both spatially and temporally, in response to variation in resources. Here, we study the food habits of the widespread European Grass Snake, Natrix natrix, in Kent in southeastern England. As elsewhere in their range, Grass Snakes at our study site mainly ate anurans (63%); however, small mammals also were fairly common in the diet (25%) and fish (10%) and birds (1%) were taken occasionally. About 65% of prey eaten by snakes were swallowed headfirst, but orientation of prey during ingestion varied among prey types. Although anurans are the major prey of Grass Snakes, the predominant species in their diet varies geographically, presumably in relation to availability; at our site, the most frequently eaten species (63%) was the introduced Marsh Frog, Rana ridibunda, which is very common and possibly influences abundance of snakes. We obtained few data on feeding habits of small snakes (< 400 mm SVL) but found anuran prey in the smallest snake in our sample; other prey types were eaten by larger snakes and therefore presumably are added to the diet as snakes grow. Maximum size of prey increased with snake size, but large snakes nonetheless continued to eat small prey as well. However, because Grass Snakes are sexually dimorphic (females larger), such size effects may be confounded with sex effects. Snakes had food in their stomachs less frequently in midsummer than they did in early and late summer. Nonetheless, even after adjusting for such seasonal variation, gravid females contained food less frequently than nongravid females. Thus, gravid females of this oviparous species apparently exhibit an anorexia similar to that seen in pregnant females of many viviparous species.

Trade‐offs between Reproductive Traits and the Influence of Food Intake during Pregnancy in the Garter Snake, Thamnophis elegans

Department of Biology, University of Victoria, Victoria, British output is thought to be largely a function of reserves acColumbia V8W 3N5, Canada cumulated the previous year or earlier (Macartney and Gregory 1988; Ford and Seigel 1989a). This is underSubmitted April 1, 1997; Accepted November 7, 1997 scored by the observation that gravid females of some species of viviparous snakes, including garter snakes, feed little or not at all during pregnancy in the field (Gregory and Stewart 1975; Farr 1988). Nonetheless, just as acqui

Geographic Variation of Multiple Paternity in the Common Garter Snake (Thamnophis sirtalis)

Abstract The common garter snake, Thamnophis sirtalis, is the most widely distributed reptile species in North America. Although multiple paternity has been documented in this species, variation in reproduction and ecology suggests that the frequency of occurrence of multiple paternity may vary. We investigated the occurrence of multiple paternity in snakes on Vancouver Island with the following aims: (1) to detect the occurrence of multiple paternity at this location; (2) to determine whether life-history variation and single versus multiple paternity were associated; and (3) to determine whether local rates of multiple paternity differ in comparison to a previous study of this species. Sixteen females and their offspring were analyzed using three highly polymorphic microsatellite loci. Only six of 16 litters showed direct evidence of multiple paternity. Results also showed evidence of a trade-off between offspring size and number of offspring per litter and that females that were multiply mated generally made a higher reproductive investment than females that were singly mated. Rates of multiple paternity in this study and in the previous study differed and were significantly different when litters of fewer than five offspring were eliminated from the analysis. Although we cannot determine the causes of variation in multiple paternity given our data, we suggest two possible mechanisms, one genetic and one ecological, that may lead to different frequencies of multiple fertilizations in this species.

Thermoregulatory behaviour of gravid and non‐gravid female grass snakes (Natrix natrix) in a thermally limiting high‐latitude environment

All else being equal, ectotherms should maintain body temperatures ( T b s) favourable for temperature-sensitive biological functions, such as digestion and locomotion. Physical environments in the temperate zone are often thermally variable, however, thus making it difficult to maintain optimum T b s. Radiotelemetry and a semi-natural enclosure were used to monitor T b s of grass snakes Natrix natrix at Canterbury, Kent, U.K. Operative temperatures ( T e s) were measured using snake models (copper-pipe models) placed in a variety of microhabitats to determine availability of thermoregulatory opportunities. A modification of Huey & Slatkins (1976) regression model, piecewise regression, was used to evaluate thermoregulatory behaviour. Grass snakes could achieve high mean T b s (>30°C) most often during midday (08:00–20:00), but only for 55–61% of the study period. Overall, non-gravid snakes maintained higher and less variable mean daytime T b s than gravid snakes. From piecewise regression, it was determined that grass snakes initiated thermoregulation at a T e of 38.44°C, corresponding to a T b of 27.7°C. Three main conclusions can be drawn from this study: (1) thermoregulatory opportunities for grass snakes were limited; (2) nonetheless, when conditions were sufficiently warm, there was clear evidence that grass snakes could thermoregulate; (3) contrary to expectation, gravid females actually maintained lower and more variable T b s than non-gravid females. The consequences of these thermoregulatory patterns for the fitness of snakes have yet to be determined.

Sources of variation in estimating litter characteristics of the Garter Snake, Thamnophis elegans

--Studies of snake demography usually involve the estimation of litter size and neonate size, but potential sources of variation resulting from the methods used to obtain this information are rarely considered. Using data from four populations of Thamnophis elegans, we found that estimates of litter size obtained by holding gravid snakes in captivity were less variable when dead young or undeveloped eggs were included rather than excluded; we recommend that all components of litters be reported in future studies. Litter sizes obtained by palpation of gravid snakes in the field were similar to estimates from captive births in two of three populations we examined, but not the third. There was some evidence that litters from longer-term captives were more likely to contain dead young, and, in one population, smaller young. Access to substrate heat by gravid snakes was correlated with smaller progeny in another population. In general, captive-born snakes were smaller than neonates born in the field, but some growth may have occurred in the latter. Factors that might influence the size of snakes born in captivity are temperature, feeding level of mother, and stress; in order to minimize their potential effects, we recommend that gravid snakes be held for as short a time as possible. The study of life history variation in snakes has lagged behind that of other kinds of organisms (Parker and Plummer, 1987), mainly because of the difficulties of sampling snake populations (Turner, 1977). Although field measurements of important parameters such as survivorship have rarely been measured adequately (Parker and Plummer, 1987), reports of clutch or litter size are abundant (Seigel and Ford, 1987). These data can be obtained by dissection of preserved specimens, gentle hand palpation of gravid snakes in the field, or holding gravid snakes in captivity until they have laid eggs or produced young. The accuracy of clutch or litter size estimates obtained by palpation is unclear, but with practice, embryos can usually be distinguished from one another and from lumps of fecal material within the large intestine (Fitch, 1987; Farr and Gregory, pers. obs.). Sometimes, especially in the later stages of gestation, embryos may be more difficult to distinguish from one another; an embryo and its yolk sac may also be felt as two separate lumps (Fitch, 1987). Difficulties such as these will influence estimates of litter

Activity patterns of garter snakes, Thamnophis sirtalis, in relation to weather conditions at a fish hatchery on Vancouver island, British Columbia.

Temperature is one of many factors that may have an important influence on activity of ectotherms. We investigated the influence of weather conditions on activity of common garter snakes, Tham- nophis sirtalis, at a fish hatchery on Vancouver Island where the water in which they forage is cold (<14?C). We used reduced major axis regression to partition the relationship between air temperature and number of snakes seen into subsets, and the uppermost subset of data was used to describe the upper boundary of the overall relationship At the hatchery site, the maximum number of snakes observed increased in relation to maximum daily air temperatures, with the highest numbers of snakes being observed on days when maximum daily air temperatures exceeded 25?C. By contrast, at a nearby reference site where snakes do not consume fish, the maximum number of snakes observed decreased in relation to maximum daily air tem- peratures, with very few snakes being observed on days with high maximum daily air temperatures. Ra- diotagged snakes were observed swimming in hatchery channels only on days when maximum daily air temperatures were high. Body temperatures of these snakes decreased extremely rapidly when the snakes entered the water, and remained low while they were in the hatchery channels. The body temperature of one snake that captured a fish while swimming in the channels was just over 14?C. We hypothesize that hot weather conditions permit snakes at hatchery sites to achieve high body temperatures rapidly subse- quent to foraging activity.

Northern Lights and Seasonal Sex: The Reproductive Ecology of Cool-Climate Snakes

Abstract Each year, as the warmth of summer turns into the cool of autumn and the cold of winter, snakes disappear from the Canadian landscape. For several months of the year, winter weather at high latitudes is much too cold for snakes to be active in the open and they must seek subterranean shelter to hibernate. This long period underground is one during which these animals are subject not only to the possibility of mortality, but also to lost opportunity for activities such as foraging and the acquisition of resources for reproduction. Winter is thus a major constraint on the life histories of temperate-zone snakes. Short, cool summers further restrict their foraging and reproductive opportunities. In apparent response to this challenge, most high-latitude snake species are viviparous, counter to what is seen in warmer climes. Viviparity allows gravid females to “manipulate” the developmental temperature of their progeny, via behavioral thermoregulation, until those offspring are independent, an option not open to oviparous species. However, viviparity also has costs, not least of which is a pronounced reduction in feeding during pregnancy, which means that the post-partum female has only a short time before winter to make up the reserves (“capital”) that she spent on reproduction and will need for future reproduction; therefore, reproduction in consecutive years is not always possible. Evidently, the demographic costs of viviparity are outweighed by its advantages, but what remains unexplained is how some oviparous species manage to persist at high latitudes. Demographic advantages of oviparous over viviparous species, due to shorter “pregnancy” of the former, are not apparent from limited temperate-zone studies. More likely, cool-climate oviparous species also reproduce successfully by taking advantage of the thermal heterogeneity of the environment, especially by thermoregulating precisely while gravid and/or by careful selection of nest sites.

Feeding Rate and Weight Gain in Postpartum Rattlesnakes: Do Animals That Eat More Always Grow More?

Effets de 2 regimes alimentaires sur la prise de poids de 30 femelles post-partum de C. viridis sous des conditions semi-naturelles a 22˚C et sous une photoperiode naturelle

The effects of body size, age, and food intake during pregnancy on reproductive traits of a viviparous snake, Thamnophis ordinoides

ABSTRACT Litter characteristics of viviparous snakes presumably can be influenced by the mothers state (e.g., mass) at the onset of pregnancy, by food acquired during vitellogenesis, or by food eaten by the mother during pregnancy and delivered to the developing embryos via the placenta. Alternatively, food consumed while pregnant could be allocated to the female herself, potentially influencing her future survivorship and/or reproduction. We tested the effects of food consumption during pregnancy on litter traits of the garter snake, Thamnophis ordinoides, along with the effects of body size and age of mother. We also measured trade-offs between traits. Age was significantly correlated with body size of female snakes, but it had no direct influence on reproductive traits. Initial body size, by contrast, especially snout-vent length, significantly and positively influenced litter size and mass. Food intake by gravid females declined during pregnancy, and snakes became relatively anorexic prior to giving birth; their appetite resumed following parturition. Snakes offered smaller amounts of food while pregnant ate less than those fed ad lib, but had similar postpartum appetites. Higher food intake during pregnancy resulted in higher postpartum mass of females, but not higher litter mass or size of offspring. There was strong evidence of a trade-off between litter size and offspring size and between postpartum mass and litter mass. Overall, our data are consistent with the hypothesis that reproductive traits of viviparous snakes are determined proximately by previously accumulated stores (capital) and/or food consumed during vitellogenesis (income), but not by resources acquired during pregnancy.