Effects of ovariectomy and estrogen replacement on attractivity and receptivity in the red-sided garter snake (Thamnophis sirtalis parietalis)

Activation of courtship behavior in male red-sided garter snakes, Thamnophis sirtalis parietalis, is independent of the presence of sex steroids. The only consistent treatment that stimulates courtship behavior in males is prolonged exposure to low temperature followed by subsequent warming, mimicking the emergence from hibernation. We investigated whether attractivity and receptivity in female red-sided garter snakes is similarly steroid independent.Female red-sided garter snakes are attractive when they emerge from hibernation and are courted by males; most mate within an hour of emergence. In a series of experiments, groups of females were either ovariectomized (OVEX) in the late spring, fall or while in hibernation. They were tested for attractivity and receptivity upon emergence from hibernation. Females OVEX in the spring were unattractive whereas those OVEX in fall or while in hibernation were attractive. Thus, attractivity appears determined the year before emergence and is dependent on the presence of the ovaries. All OVEX females were unreceptive upon emergence. OVEX females were also given replacement estradiol (E) treatment (either in Silastic capsules or single injections) at various points of their annual cycle. The only treatment that resulted in reinstating receptivity in OVEX females was the injection of E (20 g) one hour prior to emergence. The effectiveness of E in reinstating receptivity was time dependent: the longer the period between emergence and injection, the less effective the same dosage was in stimulating receptive behavior.These experiments suggest that sexual behavior in female red-sided garter snakes is, unlike males, dependent on the presence sex steroid hormones. Although E is naturally at its lowest seasonal level upon emergence, the concentration is sufficient to stimulate receptivity. However, it appears that temperature regulates a time-limited window of sensitivity to E.     

Geographic variation in the garter snakes (Thamnophis sirtalis) of the north-central United States, a multivariate study

A study of geographic variation in three subspecies of garter snake (Thamnophis sirtalis sirtalis, T. s. parietalis, T. s. semifasciata) in the north-central United States indicates patterns of irregular non-clinal microgeographic variation for 40 characters of coloration, scalation, and internal anatomy. Multivariate analyses show that geographically close populations are not always phenetically close and that overall differentiation of the phenotype is greater in males than in females. Univariate and multivariate studies indicate that T. s. semifasciata Cope 1892, restricted to the Chicago area, is not uniform within its small range and that it has no constant distinguishing features: it is shown to be taxonomically invalid.     

Behavioural and hormonal responses to capture stress in the male red-sided garter snake, Thamnophis sirtalis parietalis

We measured the behavioural and hormonal responses to capture stress in male red-sided garter snakes. Four hours of capture stress resulted in no suppression of mating behaviour relative to control individuals. In contrast, the same stress resulted in a significant increase in plasma levels of corticosterone and a significant decrease in plasma levels of testosterone. There was a significant negative correlation between plasma levels of corticosterone and testosterone in both control and capture-stress groups, suggesting that the increase in corticosterone directly drives the decrease in testosterone. While there was no relation between body size and initial plasma levels of the two steroids, longer individuals had a significantly greater increase in corticosterone following capture stress than did shorter individuals. Snakes display indeterminate growth, suggesting that older individuals have decreased sensitivity to negative feedback in the hypothalamic-pituitary-adrenal axis and thus hypersecrete glucocorticoids. These results suggest that male red-sided garter snakes have uncoupled their behavioural stress response from their hormonal stress response to maximize reproductive opportunities. Copyright 2000 The Association for the Study of Animal Behaviour.     

Molecular phylogeography of common garter snakes (Thamnophis sirtalis) in western North America: implications for regional historical forces

Complete ND2 and partial ND4 and cytochrome b mitochondrial DNA (mtDNA) sequences were analysed to evaluate the phylogeographic patterns of common garter snakes (Thamnophis sirtalis) in western North America. This species is widely distributed throughout North America, and exhibits extensive phenotypic variation in the westernmost part of its range. The overall phylogeographic pattern based on mtDNA sequences is concordant with results from studies of other species in this region, implicating historical vicariant processes during the Pleistocene and indicating bottleneck effects of recent dispersal into postglacial habitat. Indeed, the topology is statistically consistent with the hypothesis of both southern (Great Basin and California) and northern (Haida Gwaii) refugia. Specifically, we identified genetic breaks among three major clades: Northwest Coastal populations, Intermountain populations, and all California populations. The California clade contained the only other well-supported branching patterns detected; relationships among populations within the two northern clades were indistinguishable. These molecular splits contrast sharply with all prior geographical analyses of phenotypic variation in T. sirtalis in this region. Our results suggest that the extensive phenotypic variation in western T. sirtalis has been shaped more by local evolutionary forces than by shared common ancestry. Consequently, we consider all morphologically based subspecies designations of T. sirtalis in this region invalid because they do not reflect reciprocal monophyly of the mtDNA sequences.     

The effects of maternal corticosterone levels on offspring behavior in fast- and slow-growth garter snakes (Thamnophis elegans)

During embryonic development, viviparous offspring are exposed to maternally circulating hormones. Maternal stress increases offspring exposure to corticosterone and this hormonal exposure has the potential to influence developmental, morphological and behavioral traits of the resulting offspring. We treated pregnant female garter snakes (Thamnophis elegans) with low levels of corticosterone after determining both natural corticosterone levels in the field and pre-treatment levels upon arrival in the lab. Additional measurements of plasma corticosterone were taken at days 1, 5, and 10 during the 10-day exposure, which occurred during the last third of gestation (of 4-month gestation). These pregnant snakes were from replicate populations of fast- and slow-growth ecotypes occurring in Northern California, with concomitant short and long lifespans. Field corticosterone levels of pregnant females of the slow-growth ecotype were an order of magnitude higher than fast-growth dams. In the laboratory, corticosterone levels increased over the 10 days of corticosterone manipulation for animals of both ecotypes, and reached similar plateaus for both control and treated dams. Despite similar plasma corticosterone levels in treated and control mothers, corticosterone-treated dams produced more stillborn offspring and exhibited higher total reproductive failure than control dams. At one month of age, offspring from fast-growth females had higher plasma corticosterone levels than offspring from slow-growth females, which is opposite the maternal pattern. Offspring from corticosterone-treated mothers, although unaffected in their slither speed, exhibited changes in escape behaviors and morphology that were dependent upon maternal ecotype. Offspring from corticosterone-treated fast-growth females exhibited less anti-predator reversal behavior; offspring from corticosterone-treated slow-growth females exhibited less anti-predator tail lashing behavior.     

Behavioral and physiological control of yolk synthesis and deposition in the female red-sided garter snake (Thamnophis sirtalis parietalis)

Ovarian recrudescence in female garter snakes, Thamnophis sirtalis parietalis, follows spring emergence from hibernation and mating. In the laboratory, courtship and mating stimuli significantly increased the proportion of female garter snakes becoming pregnant, although some noncourted nonmated controls also became pregnant. Females given artificial mating stimuli under anesthetic, without courtship stimuli, were no more likely than either noncourted, nonmated or anesthetized controls to become pregnant. Hormonal changes and yolk synthesis rapidly followed mating in both laboratory and field females; serum estradiol increased more than 10-fold in 2 days and serum calcium, a measure of yolk precursor lipoprotein (vitellogenin) concentration, increased more than two times in 10 days. Administration of exogenous estradiol stimulated yolk synthesis, but did not result in yolk deposition into ovarian follicles. However, administration of ovine follicle-stimulating hormone induced both hepatic yolk synthesis and yolk deposition. Our results are consistent with the hypotheses that courtship and copulation are facilitatory to ovarian recrudescence but neither alone nor in combination is necessary nor sufficient, and in this species yolk synthesis and yolk deposition are separately regulated.     

Effects of sex, body size, temperature, and location on the antipredator tactics of free-ranging gartersnakes (Thamnophis sirtalis, Colubridae)

Gartersnakes (Thamnophis sirtalis parietalis) in southern Manitoba are subject to intense predation (primarily by crows) duringtheir spring breeding season. The huge numbers of snakes providea unique opportunity to quantify behavioral traits. We simulatedpredator attacks by "pecking" more than 500 free-ranging snakes,to explore the determinants of snake response. Snakes respondedto a human finger in the same way as they did to a more realisticstimulus (a model crow). A snake's response to attack dependedon several factors, which interacted in complex ways. The primaryinfluences on response were body temperature (warmer snakes tended to flee, whereas colder snakes remained cryptic or flattenedand/or gaped and struck) and sex (males were more likely toflee). Responses also depended on microhabitat (i.e., insidethe winter den versus in adjacent grassland) and on the snake'sprior activity (e.g., courting snakes often ignored our closeapproach). These factors interacted in significant ways; for example, snakes outside the den were smaller and warmer thanthose inside, male snakes were smaller and warmer than females,and mean body temperatures were higher in larger snakes withineach sex. Thus, a snake's body size and its location affectedits defensive response indirectly (via their influence on bodytemperature). Our results differ from those of previous studiesand suggest that antipredator responses in these animals dependin a flexible and complex way upon biotic and abiotic variables.Interactions among these variables also must be consideredbefore we can identify underlying causal processes.     

Conflicts between courtship and thermoregulation: the thermal ecology of amorous male garter snakes (Thamnophis sirtalis parietalis, colubridae)

Thermoregulatory behavior is an important component of daily activities for many reptiles, especially for small heliothermic (sun-basking) species that inhabit cold climates. However, the relative costs and benefits of thermoregulation depend on numerous factors, such that reptiles may sometimes accord a low priority to precise control of body temperatures. We observed and radio tracked garter snakes (Thamnophis sirtalis parietalis) in central Manitoba during the mating season (spring). Previous studies on this species have documented precise behavioral regulation of body temperatures during summer. In contrast, the courting snakes that we studied in springtime spent little time in overt thermoregulatory behavior. Body temperatures were extremely variable (both in outdoor enclosures and in the field) despite abundant opportunities for more precise thermal control. These small elongate reptiles cool so quickly (relative to the time periods needed for effective courtship) that any benefit to higher body temperatures would be transitory at best. Experiments show that hotter males are no better at obtaining matings or at detecting predators. Thus, male garter snakes concentrate on courtship rather than on basking. In the face of conflicting priorities, reptiles may often forgo precise thermoregulation because its benefits are too low, and its costs too high, compared with alternative behaviors.     

Temperature and light effects on the circadian rhythm and locomotory activity of the plains garter snake (Thamnophis radix hayendi)

Abstract

The Locomotory activity of the Plains Garter snake was determined under L/D: 12/12 conditions at five constant temperatures and three light intensities during the light period. The snakes were diurnal at low temperatures with nocturnal activity increasing in various amounts at higher temperatures. The different light intensities had relatively small effects on the activity rhythm.

Activity was recorded under four constant light conditions at five constant temperatures and the characteristics of the free‐running rhythm measured. A comparison of the characteristics of the free‐running rhythm to Aschoff's circadian rule indicates that this snake is an exception to this rule.

Increase light intensity decreased total activity under all conditions. Under a L/D: 12/12 cycle the decrease in activity was more pronounced during the dark period than the light period.

It is suggested that crepuscular or nocturnal activity shown by snakes at high temperatures may be an effect the temperature level has on the biological clock and activity controlling mechanisms rather than temperature selection by the snake.     

The photoreceptors and visual pigments of the garter snake (Thamnophis sirtalis): a microspectrophotometric, scanning electron microscopic and immunocytochemical study

Scanning electron microscopy, immunocytochemistry, and single cell microspectrophotometry were employed to characterize the photoreceptors and visual pigments in the retina of the garter snake, Thamnophis sirtalis. The photoreceptor population was found to be comprised entirely of cones, of which four distinct types were identified. About 45.5% of the photoreceptors are double cones consisting of a large principal member joined near the outer segment with a much smaller accessory member. About 40% of the photoreceptors are large single cones, and about 14.5% are small single cones forming two subtypes. The outer segments of the large single cones and both the principal and accessory members of the doubles contain the same visual pigment, one with peak absorbance near 554 nm. The small single cones contain either a visual pigment with peak absorbance near 482 nm or one with peak absorbance near 360 nm. Two classes of small single cones could be distinguished also by immunocytochemistry and scanning electron microscopy. The small single cones with the 360-nm pigment provide the garter snake with selective sensitivity to light in the near ultraviolet region of the spectrum. This ultraviolet sensitivity might be important in localization of pheromone trails. Accepted: 10 March 1997     

Effects of arginine vasotocin (AVT) on the behavioral, cardiovascular, and corticosterone responses of starlings (Sturnus vulgaris) to crowding

Previous studies in European starlings have concluded that conspecific crowding can be a significant stressor that is capable of simultaneously altering behavior, heart rate, and corticosterone (CORT) concentrations. It was hypothesized that the peptide hormone arginine vasotocin (AVT) has a role in the regulation of these three types of responses to crowding. Four male and four female resident starlings were submitted to nine combinations of 3 crowding treatments (0, 1, or 5 intruder starlings) and 3 subcutaneous injections (1, 4 microg AVT, and saline control). Resident starlings were given a treatment injection, their heart rate and behavior were monitored for 30 min, 0, 1, or 5 intruder Starlings were allowed to enter the residents cage, and HR and behavior were monitored for another 30 min. Blood samples were taken before and after all treatments to assess CORT concentrations. Exogenous AVT decreased the frequency of maintenance behaviors (feeding, drinking, preening, and beak wiping), as well as activity in resident starlings. Although aggressive behaviors upright posture, head feather expansion, and pecking) increased during crowding, these increases were significantly attenuated by AVT. Heart rate was significantly lower during these behavioral effects, and the CORT data indicate that the cardiovascular and behavioral effects are not dependent on significant increases in CORT. These data support the hypothesis that AVT's attenuation of general behavior and crowding induced aggression are modulated by a cardiovascular mechanism.     

The all-cone retina of the garter snake: spectral mechanisms and photopigment

Summary The retina of the garter snake contains 3 morphologically distinct classes of cone photoreceptor. The spectral mechanisms in the retinas of garter snakes (Thamnophis sirtalis and T. marcianus) were studied by recording a retinal gross potential, the electroretinogram, using a flicker photometric procedure. Spectral sensitivity functions recorded with stimuli presented at high temporal frequency (62.5 Hz) are broadly peaked in the region of 550–570 nm. These functions remain spectrally invariant (a) in the face of significant changes in stimulus pulse rate (8–62.5 Hz), (b) whether the eye is light or dark adapted, and (c) under conditions of intense chromatic adaptation. It is concluded that the garter snake has only a single class of cone pigment. The results from a curve fitting analysis suggests that this pigment has peak absorbance at about 556 nm.     

Effects of water salinity on melatonin levels in plasma and peripheral tissues and on melatonin binding sites in European sea bass (Dicentrarchus labrax)

Sea bass is an euryhaline fish that lives in a wide range of salinities and migrates seasonally from lagoons to the open sea. However, to date, the influence of water salinity on sea bass melatonin levels has not been reported. Here, we evaluated the differences in plasma and tissue melatonin contents and melatonin binding sites in sea bass under four different salinity levels: seawater (36‰), isotonic water (15‰), brackish water (4‰) and freshwater (0‰). The melatonin content was evaluated in plasma, whole brain, gills, intestine and kidney, while melatonin binding sites were analyzed in different brain regions and in the neural retina. Plasma melatonin levels at mid-dark varied, the lowest value occurring in seawater (102 pg/mL), and the highest in freshwater (151 pg/mL). In gills and intestine, however, the highest melatonin values were found in the seawater group (209 and 627 pg/g tissue, respectively). Melatonin binding sites in the brain also varied with salinity, with the highest density observed at the lower salinities in the optic tectum, cerebellum and hypothalamus (30.3, 13.0, and 8.0 fmol/mg protein, respectively). Melatonin binding sites in the retina showed a similar pattern, with the highest values being observed in freshwater. Taken together, these results reveal that salinity influences melatonin production and modifies the density of binding sites, which suggests that this hormone could play a role in timing seasonal events in sea bass, including those linked to fish migration between waters of different salinities for reproduction and spawning.     

Effects of castration and androgen replacement on male courtship behavior in the red-sided garter snake (Thamnophis sirtalis parietalis)

Following artificial hibernation, sexually mature male garter snakes (Thamnophis sirtalis parietalis) exhibited a decline in courtship behavior irrespective of castration, sham operation, or castration with testosterone replacement therapy. Behavior declined more rapidly in castrated animals with testosterone replacement than in castrated or sham-operated animals. In sham-operated animals, the decline in courtship was accompanied by changes in testicular weight and spermatogenic state from small spermatogenically inactive testes to large spermatogenically active testes. Serum androgen levels were more than fourfold greater in sham-operated animals than in castrated animals; cell height of the androgensensitive renal sex segment was greatest in castrated animals with testosterone replacement and least in castrated animals. These findings indicate that following artificial hibernation, male courtship behavior of T.s. parietalis is independent of the presence of the testes.     

Influence of exogenous gonadotropin-releasing hormone on seasonal reproductive behavior of the coyote (Canis latrans)

Wild Canis species such as the coyote (C. latrans) express a suite of reproductive traits unusual among mammals, including perennial pair-bonds and paternal care of the young. Coyotes also are monestrous, and both sexes are fertile only in winter; thus, they depend upon social and physiologic synchrony for successful reproduction. To investigate the mutability of seasonal reproduction in coyotes, we attempted to evoke an out-of-season estrus in October using one of two short-acting gonadotropin-releasing hormone (GnRH) agents: (1) a GnRH analogue, deslorelin (6-d-tryptophan-9-(N-ethyl-l-prolinamide)-10-deglycinamide), 2.1 mg pellet sc; or (2) gonadorelin, a GnRH (5-oxoPro-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GlyNH₂) porcine hypothalamic extract, 2.0 μg/kg im once daily for 3 consecutive days. A transient increase in serum concentrations of estradiol and progesterone (1 and 2 wk, respectively) was detected after treatment with deslorelin but not gonadorelin. Also, socio-sexual behaviors reminiscent of winter mating (including courtship, mate-guarding, precoital mounts, and copulatory ties) were observed among the deslorelin group. During the subsequent breeding season (January and February), however, preovulatory courtship behavior and olfactory sampling appeared suppressed; emergence of mounts and copulations were delayed in both deslorelin and gonadorelin treatment groups. Furthermore, whereas 8 of 12 females treated in October ovulated and produced healthy litters in the spring, 4 naïve coyotes failed to copulate or become pregnant. Thus, perturbation of hormones prior to ovulation in species with complex mating behaviors may disrupt critical intrapair relationships, even if fertility is not impaired physiologically.     

Estimation of relative reproductive expenditure in the courtship-role-reversed bean weevil, Bruchidius dorsalis (Fahraeus)

It is often difficult to measure the parental expenditure on reproduction by both sexes, because even in species where both sexes invest only nutrient to produce eggs, the nutrition invested by the male is inevitably mixed with that from the female in the body of the female. In this paper, I propose a regression-analysis-based method to estimate the relative amount of investment by both sexes separately, which I have applied to the bean weevil Bruchidius dorsalis (Fahraeus: Bruchidae; Coleoptera), which shows role-reversal in its courtship behavior. The results indicated that lifetime maternal expenditure (the estimated intercept) was fivefold higher than paternal expenditure in a single copulation (the estimated coefficient). Although the number of copulations by wild males was not measured in this study, it is unlikely that they copulate fewer than six times during their lifetime, judging from their longevity and the frequency of copulation in the laboratory. In the experiment, males were divided into two different feeding regimes to test whether their nutritional condition affected their paternal expenditure, but no significant effect was detected.     

The pineal complex and melatonin affect the expression of the daily rhythm of behavioral thermoregulation in the green iguana

Daily variation in the body temperature of the green iguana (Iguana iguana) was studied by telemetry in laboratory photo-thermal enclosures under a 12Light12Dark (LD) photoperiod. The lizards showed robust daily rhythms of thermoregulation maintaining their body temperatures (T_b) at higher levels during the day than during the night. Some animals maintained rhythmicity when kept in constant darkness. On lightdark cycles parietalectomy produced only a transient increase of median T_b in the first or second night following the operation. Pinealectomized lizards on the other hand maintained their body temperatures at significantly lower levels during the day and at significantly higher levels during the night than did sham-operated or intact lizards. This effect was apparently permanent, since one month after pinealectomy lizards still displayed the altered pattern. Plasma melatonin levels in intact animals were high during the night and low during the day and were unaffected by parietalectomy. Pinealectomized lizards showed low levels of plasma melatonin during both the day and the night. A daily intraperitoneal injection of melatonin in pinealectomized animals given a few minutes after the light to dark transition decreased the body temperatures selected by the lizards during the night and increased the body temperatures selected during the following day. Control injections of saline solution had no effect. The significance of these results is discussed in relation to the role of the pineal complex and melatonin in the mediation of thermoregulatory behavior.Abbreviations LD LightDark - T _b body temperature - PAR-X parietalectomy - PIN-X pinealectomy     

Effects of elevated egg corticosterone levels on behavior, growth, and immunity of yellow-legged gull (Larus michahellis) chicks

Eggs of vertebrates contain steroid hormones of maternal origin that may influence offspring performance. Recently, it has been shown that glucocorticoids, which are the main hormones mediating the stress response in vertebrates, are transmitted from the mother to the egg in birds. In addition, mothers with experimentally elevated corticosterone levels lay eggs with larger concentrations of the hormone, which produce slow growing offspring with high activity of the hypothalamo-adrenal axis under acute stress. However, the effects and function of transfer of maternal corticosterone to the eggs are largely unknown. In the present study, we injected corticosterone in freshly laid eggs of yellow-legged gulls (Larus michahellis), thus increasing the concentration of the hormone within its natural range of variation, and analyzed the effect of manipulation on behavioral, morphological, and immune traits of the offspring in the wild. Eggs injected with corticosterone had similar hatching success to controls, but hatched later. Mass loss during incubation was greater for corticosterone-treated eggs, except for the last laid ones. Corticosterone injection reduced rate and loudness of late embryonic vocalizations and the intensity of chick begging display. Tonic immobility response, reflecting innate fearfulness, was unaffected by hormone treatment. Elevated egg corticosterone concentrations depressed T-cell-mediated immunity but had no detectable effects on humoral immune response to a novel antigen, viability at day 10, or growth. Present results suggest that egg corticosterone can affect the behavior and immunity of offspring in birds and disclose a mechanism mediating early maternal effects whereby stress experienced by females may negatively translate to offspring phenotypic quality.