Female Snakes Research Articles

Species specificity of methyl ketone profiles in the skin lipids of female garter snakes, genus Thamnophis

One of the relatively few vertebrate pheromones to be chemically identified, the female sex pheromone of the red-sided garter snake (Thamnophis sirtalis parietalis) is a series of saturated and monounsaturated methyl ketones contained within female skin lipids. During the breeding season, this pheromone is responsible for eliciting male courtship behaviors and males are able to utilize pheromonal variation to discriminate among females. While the pheromone system of the red-sided garter snake has been the subject of many studies, relatively little is known about the pheromone systems of other garter snakes. Through chemical analyses, we demonstrate that female skin lipids of the red-spotted garter snake (Thamnophis sirtalis concinnus), northwestern garter snake (Thamnophis ordinoides), and plains garter snake (Thamnophis radix) contain similar methyl ketones. The methyl ketone profiles of these snakes differ qualitatively from one another and from the methyl ketone profiles of red-sided garter snakes with differences particularly pronounced between sympatric species. Our results provide evidence that the use of methyl ketones in sexual signaling may be ubiquitous for Thamnophis species and suggest that these compounds could play a role in reproductive isolation between species in this genus.

Hematology and plasma biochemistry of wild-caught Indian cobra Naja naja (Linnaeus, 1758)

BackgroundHematology and plasma biochemistry parameters are useful in the assessment and management of snake physiological status. Although reference ranges are readily available for many snake species, they are lacking for most venomous ophidians. We determined hematology and plasma biochemistry reference ranges for the wild-caught Indian cobra, Naja naja.ResultsBlood samples, taken from the ventral tail vein, were assessed for erythrocyte count, total leukocyte count, hemoglobin concentration, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration, considering the sex of snakes.Results revealed the erythrocyte numbers (male, 390000 ± 12503.33/mm3 and female, 347500 ± 7505.55/mm3), shapes and the centrally located oval nuclei. Leukocytes were round, circular or disk-shaped, and the mean size was larger in male than female snakes. The maximum number of leukocytes was found to be 11700 ± 100/mm3 in male and 12100 ± 200/mm3 in female snakes, and mean values of differential leukocyte count differed statistically between male and female snakes. The total leukocyte levels were found to be higher in female snakes, but the levels of hemoglobin, hematocrit, and MCV values were higher in male snakes. However, the MCH and MCHC values remained higher in female snakes throughout the study period. Mean protein and cholesterol contents differed significantly between male (45.32 ± 1.76 and 3.76 ± 0.06 mg/mL) and female (12.47 ± 0.82 and 4.72 ± 0.2 mg/mL) snakes.ConclusionsIn conclusion, monitoring snake hematological and biochemical parameters can serve as a means to evaluate the physiological and health status of N. naja populations, which may be a useful indicator of their environmental status.

Intrinsic and Extrinsic Factors Influence Expression of Defensive Behavior in Plains Hog‐Nosed Snakes (Heterodon nasicus)

AbstractAnimals failing to deter predation are eaten. Among the many deterrents to predation, antipredator behaviors are perhaps the most variable, ranging from active (fight or flight) to passive (immobility). We assessed variation in the expression of a passive defensive behavior, death‐feigning, in Plains Hog‐nosed Snakes (Heterodon nasicus) and predicted that intrinsic and extrinsic factors would influence the duration of this behavior and the latency to its onset. We simulated predatory attacks on 27 snakes encountered in the field, and analyzed the behavioral responses of snakes as a function of differences among individuals (sex and size) and environmental factors (temperature and microhabitat). Larger snakes death‐feigned for longer durations than smaller ones; this relationship was stronger for female snakes than for males. Death feints were initiated sooner when snakes were encountered at higher temperatures. Extrinsic factors had a greater influence on latency to death‐feigning behavior, whereas intrinsic factors more strongly influenced its duration. Because our results involved wild snakes, they provide an improved, highly relevant understanding of individual and environmental factors that regulate the expression of immobile defensive behavior. Furthermore, additional hypotheses can now be proposed that address the evolution of defensive behaviors that leave animals prone to attack.

Eastern Hognose Snakes (Heterodon platirhinos) Avoid Crossing Paved Roads, but Not Unpaved Roads

Roads can directly impact animal populations by increasing the risk of mortality; however, a more subtle ecological effect may lie in the way roads impede gene flow by creating barriers to animal movement. We investigated the effect a road network, containing both paved and unpaved surfaces, has on the movement patterns of the Eastern Hognose Snake (Heterodon platirhinos) in the Long Point region of Ontario, Canada by radio-tracking 17 adult snakes over two years. We used telemetry data collected in the field to infer the minimum number of road crossings made by snakes, and random walk simulations to estimate the number of road crossings snakes would have made if they moved randomly in relation to roads. Comparing the inferred and expected number of crossings allowed us to test the hypothesis that roads constrain movements because snakes avoid crossing them. Overall, the road network did not impede snake movements. When examined separately, however, we showed that road substrate affected movement: snakes avoided crossing paved roads while they crossed sand roads readily. Male and female snakes crossed roads at the same frequency. While the risk of road mortality is reduced by road avoidance, such avoidance of paved roads may contribute to the genetic isolation and further decline of this species-at-risk.

Responses to capture stress and exogenous corticosterone vary with body condition in female red-sided garter snakes (Thamnophis sirtalis parietalis)

This study examined whether hormonal and behavioral responses to capture stress and exogenous corticosterone (CORT) vary with body condition in female red-sided garter snakes (Thamnophis sirtalis parietalis). Female snakes were collected during the spring mating season and treated with 4h of capture stress. We measured plasma CORT and estradiol before, during and after capture stress treatment followed by latency to copulate, a measure of female receptivity. Body condition was determined as the residual from a regression of body mass on snout-vent-length. Baseline CORT did not differ between females in positive and negative body condition, but females in negative body condition showed a significantly larger increase in plasma CORT in response to capture stress. Estradiol, which is generally low during the mating season in this population, did not change in response to capture stress. Body condition, but not capture stress, influenced latency to copulate, suggesting that females are resistant to the behavioral effects of capture stress during the spring mating season. In a second experiment, only females in negative body condition increased latency to copulate in response to injection of a physiological (15μg) dose of exogenous CORT, while all females responded to a pharmacological (60μg) dose. These results indicate that behavioral responses to exogenous CORT vary with female body condition during the short mating season. Taken together, our data suggest that variation in body condition may be associated with differences in HPA axis sensitivity and/or glucocorticoid receptor density in the brain.

The Vernal Spatial Ecology and Mating Behaviors of the Rhombic Skaapsteker, Psammophylax rhombeatus rhombeatus (Serpentes: Psammophiidae), from the Western Cape, South Africa

We used radiotelemetry to investigate the movement patterns of nine Psammophylax rhombeatus rhombeatus during spring 2006 on the west coast of South Africa. Snakes were on average tracked for 28 days and relocated twice per day. For each snake we calculated vernal home range size using minimum convex polygons, and 50 and 95% isopleths. These data show that male snakes moved significantly greater distances, had larger home ranges (average MCP = 2.219 ha for males and 0.619 ha for females), and were thus more active than female snakes. Telemetered female snakes displayed non-overlapping activity zones. Skaapstekers exhibited most activity from 0900–1700 h and in ambient temperatures greater than 19°C. Overall these movement patterns are consistent with reports of other active-foraging snakes in mating season; however, it is possible these characteristics vary across seasons and populations for this wide-ranging species. Conspecific interactions observed during the study also provide insight into the matin...

A Partial Albino Hatchling Northern Ring-necked Snake, <em>Diadophis punctatus edwardsii</em>, from Big Tancook Island, Mahone Bay, Lunenburg County, Nova Scotia, Canada

On 10 June 2012 a sample of seven gravid female Northern Ring-necked Snakes (Diadophis punctatus edwardsii), from Big Tancook Island, Lunenburg County, Nova Scotia, was selected for a seasonal live display at the Nova Scotia Museum of Natural History in Halifax. A total of 13 eggs was removed from the display in late June 2012 and incubated for public viewing. The eggs began hatching on 22 August 2012. One of the hatchlings was partial albino (with zanthophores or amelanistic). This is the first record of an albinistic Northern Ring-necked Snake in Nova Scotia.

Oxygen consumption during gravidity compared to digestion and exhaustive activity in the viviparous Checkered Garter Snake

The goal of this research was to measure oxygen consumption (i.e. VO2) associated with exhaustive activity, digestion, and gravidity in the viviparous Checkered Garter Snake. To determine gravidity, female snakes were imaged with a portable ultrasound. Gas analysis was performed using flow through respirometry with carbon dioxide and oxygen sensors. Current results indicate that gravid female Checkered Garter Snakes increase resting VO2 up to 1.6 fold the values the non‐gravid state. Furthermore, gravid females demonstrate a higher VO2 during digestion (scope = 1.5), but demonstrate a lower peak VO2 during fasting exhaustive activity (scope= .83). Both gravid and non‐gravid females exhibit a higher VO2 during post‐prandial exhaustive activity compared peak VO2 during either exhaustive activity or digestion. Therefore, this species demonstrates an additional capacity for oxygen consumption that is revealed only when simultaneously digesting a large meal and maximally active. Funding was provided by NSF grant IOS 0922756 to JWH.

Cholecystectomy for the Treatment of Mycobacterial Cholecystitis in a Pacific Gopher Snake (Pituophis catenifer)

A captive 19-yr-old female Pacific gopher snake (Pituophis catenifer) presented for evaluation after keeper staff noticed a midbody swelling. Physical examination revealed a 6.6 × 3 × 3-cm slightly mobile mass approximately midway between the head and tail. Distension of the gallbladder was diagnosed using radiographs, ultrasonography, and fine needle aspiration. Pre-operative coelomic ultrasound revealed close association between the gallbladder, aorta, and vena cava. Repeated cholecystocentesis failed to resolve the distension and a cholecystectomy was performed. Mycobacterium chelonae was isolated from the removed gallbladder and the snake was treated with azithromycin 10 mg/kg PO every 7 days for 6 months. Acid fast organisms were identified on a fecal smear during the peri-operative period. None of the usual clinical signs of mycobacteriosis in reptiles, such as respiratory disease, weight loss, or lethargy, were observed in the present case and the patient continues to thrive. Cholecystectomy is rarely reported in snakes, and this case describes an appropriate pre-operative evaluation, surgical approach, and postoperative management plan. This is the first report of antemortem diagnosis of cholecystitis in a snake caused by M. chelonae infection, which is a potentially zoonotic pathogen.

Effects of season, sex and body size on the feeding ecology of turtle-headed sea snakes (Emydocephalus annulatus) on IndoPacific inshore coral reefs

In terrestrial snakes, many cases of intraspecific shifts in dietary habits as a function of predator sex and body size are driven by gape limitation and hence are most common in species that feed on relatively large prey and exhibit a wide body-size range. Our data on sea snakes reveal an alternative mechanism for intraspecific niche partitioning, based on sex-specific seasonal anorexia induced by reproductive activities. Turtle-headed sea snakes (Emydocephalus annulatus) on coral reefs in the New Caledonian Lagoon feed entirely on the eggs of demersal-spawning fishes. DNA sequence data (cytochrome b gene) on eggs that we palpated from stomachs of 37 snakes showed that despite this ontogenetic stage specialization, the prey comes from a taxonomically diverse array of species including damselfish (41 % of samples, at least 5 species), blennies (41 %, 4 species) and gobies (19 %, 5 species). The composition of snake diets shifted seasonally (with damselfish dominating in winter but not summer), presumably reflecting seasonality of fish reproduction. That seasonal shift affects male and female snakes differently, because reproduction is incompatible with foraging. Adult female sea snakes ceased feeding when they became heavily distended with developing embryos in late summer, and males ceased feeding while they were mate searching in winter. The sex divergence in foraging habits may be amplified by sexual size dimorphism; females grow larger than males, and larger snakes (of both sexes) feed more on damselfish (which often lay their eggs in exposed sites) than on blennies and gobies (whose eggs are hidden within narrow crevices). Specific features of reproductive biology of coral reef fish (seasonality and nest type) have generated intraspecific niche partitioning in these sea snakes, by mechanisms different from those that apply to terrestrial snakes.

Edwardsiella tarda Associated Subcutaneous Abscesses in A Captive Grass Snake (Natrix natrix, Squamata: Colubridae)

Summary Edwardsiella tarda is an opportunistic pathogen associated with aquatic environments. It has been identified as part of the normal flora of the digestive tract of healthy crocodiles, alligators, turtles, lizards and snakes. However, data on its association with different clinical diseases in reptiles, especially in snakes, is scarce. A female grass snake (Natrix natrix) was presented with low body condition and with multiple subcutaneous nodules. After surgical cleaning of a nodule, E. tarda was cultivated in pure culture from the abscesses. To the author’s best knowledge, this is the first reported clinical case linked to E. tarda in snakes and one of the first case reports in grass snake.

Preliminary evaluation of total protein concentration and electrophoretic protein fractions in fresh and frozen serum from wild Horned Vipers (Vipera ammodytes ammodytes)

Determination of the health status of reptiles is based on physical examination and evaluation of hematologic and biochemical values. Evaluation of serum total protein (TP) concentration and protein fractions plays an important role in health assessment; however, little is known about references value for these analytes in wild viperoid snakes. In addition, studies evaluating the stability of proteins in frozen viperoid serum are lacking. The aims of this study were to establish preliminary reference values for concentrations of TP and protein fractions in serum from wild vipers and to evaluate the stability of serum proteins in frozen serum samples from viperoid snakes. Blood samples were collected from wild Horned Vipers (Vipera ammodytes ammodytes). Using fresh serum, TP concentrations were determined using the biuret method and protein fractions were analyzed using agarose gel electrophoresis (AGE); albumin/globulin ratios were calculated. Analyses were also performed on serum frozen at -20°C for 70 days and then thawed. Pre- and post-storage results were compared using the Mann-Whitney U-test. Five adult wild Horned Vipers were sampled and comprised 4 males and 1 female. The female snake had higher TP concentrations than the male snakes. The electrophoretic patterns demonstrated 6 protein fractions that were similar for all 5 snakes. There were no significant changes in the concentrations of the 6 protein fractions post-storage; the percentage of the alpha-1 fraction was increased in frozen/thawed serum. Total protein concentrations in serum from Vipera ammodytes ammodytes were in agreement with published reference intervals for healthy reptiles and viperoid snakes. Serum protein fractions were easy to identify using AGE electrophoresis.

Female Eastern Hog-nosed Snakes (Heterodon platirhinos) choose nest sites that produce offspring with phenotypes likely to improve fitness

Nest-site selection is an important behaviour in oviparous reptiles because incubation conditions affect offspring phenotype, with favourable conditions leading to higher offspring fitness. We aimed to identify the habitat characteristics involved in nest-site selection in Eastern Hog-nosed Snakes ( Heterodon platirhinos Latreille, 1801) and to determine whether females select nest sites that result in offspring with phenotypes likely to improve fitness. We compared the habitat characteristics and temperature profiles of 21 nests with 21 randomly selected sites. Eastern Hog-nosed Snakes selected open, grassy sites with less herbs and shrubs than random sites, and nests were significantly warmer than random sites during the 2 years of the study. In the second year of the study, we incubated 215 eggs from eight nests in a split-clutch design at mean nest (24 °C) and random site (22 °C) temperatures approximating those of the first year of the study. Eggs incubated at 24 °C resulted in neonates that hatched earlier, had fewer scale anomalies, were larger, and swam faster than neonates from eggs incubated at 22 °C. Our results indicate that Eastern Hog-nosed Snakes select nest sites that lead to offspring with phenotypes likely to improve fitness.

Symptomatologie des morsures d'ophidiens d'après le papyrus Brooklyn nos47.218.48 et 85 : aspects épistémologiques d'un texte égyptien ancien recopié au IVesiècle avant notre ère

Symptomatology of Ophidian bites according to Brooklyn Papyrus no. 47.218.48–85: epistemological aspects of an ancient Egyptian text copied out at IVth century B. C.EThis paper reconsiders the content of the ophiological Papyrus Brooklyn Museum no 47.218.48 and 85, edited by Serge Sauneron (1989), a remarkable document containing two treatises. The first one —*(Treatise entitled) symptomatology of snakes bites — consists of a catalogue of thirty-eight reptiles (including the Chameleon) whose bites are considered either as lethal, dangerous or having no consequences. The items include both a description and an analysis of bites. The second one is entitled Collection for making men extract venom of any male or female snake, of any scorpion, of any animal j(n)tš and any reptile, which is at the exorcist-of-Selkis' disposal, and which is used to expel any reptile as well as to seal their mouth. It consists of a group of prescriptions for treating non lethal bites. Moreover the author wonders about when this document has been copied (IVth Century B.C.), the personality of its writer and the priestly background within which it was created. He specially puts the emphasis on the first treatise (complete translation), yet with regard to the second treatise by means of several tables so as to give an objective general survey concerning ancient Egyptian ophiological knowledge and how treatments were applied to snakes bites. The paper opens iatromagical and mythological perspectives showing that a specific link between Egypt and the Ophidian world was supposed to exist in Antiquity.

CARDIAC HEMANGIOMA IN A CORN SNAKE (PANTHEROPHIS GUTTATUS)

A 3-yr-old female corn snake, Pantherophis guttatus guttatus, was presented for clinical examination of anorexia and a coelomic mass. Radiographs and ultrasound demonstrated a fluid-filled mass in the cardiac region. Surgical exploration revealed an approximately 1.2-cm, round, multilobulated, fluid-filled, nodular lesion firmly attached to the left atrial wall. Resection was attempted but proved unsuccessful and the animal was euthanized. Histopathological examination of the lesion revealed a large cystic structure associated with a cluster of variably sized, vascular channels lined by a one-cell-thick layer of endothelium, consistent with a cardiac hemangioma of the left atrium. This, to the best of the authors' knowledge, is the first report of such an occurrence in a snake.

The energetics of oviparous reproduction in the African Brown House Snake

The energetic cost of reproduction in the oviparous snake, Lamprophis fuliginosus (African Brown House Snake) was compared to other elevated metabolic states, specifically exhaustive activity and digestion. To determine gravidity, female snakes were imaged with a portable ultrasound (CTS‐3300, SIUI America, Inc.). Oxygen consumption was determined using flow through respirometry with carbon dioxide and oxygen sensors (Sable Systems International & AEI Technologies, Inc.). Results indicate that female L. fuliginosus exhibit a significant 29.6% (P=.0310) increase in standard metabolic rate while gravid. An additive effect of gravidity in female snakes during digestion and/or activity could not be measured. Compared to the metabolic cost of exhaustive activity (scope = 4.3; P<.00100) or digestion (scope = 6.70; P=.00100), gravidity (scope = 1.30; P=.0310) is significantly less energetically expensive. Furthermore, our data demonstrate that gravidity does not have a significant influence on time to exhaustion during exhaustive activity (mean = 28.6 minutes P=.400), or the time to peak digestive peak oxygen consumption (mean = 41.7 hours; P=.260). Digestion and activity are inevitable stresses a gravid female must endure. The potentially vulnerable time periods between ingestion and peak oxygen consumption during a meal, and the time it takes for a female to become exhausted during activity are not altered during gravidity. Besides a modest gravid metabolic scope of 1.30, our research has not identified any additional energetic physiological constraints. These results may have significant fitness implications for this species, which we plan to examine further in subsequent studies. Funding for this research was provided by NSF grant IOS 0922756 to JWH.

HEMATOLOGY AND PLASMA BIOCHEMISTRY VALUES FOR THE GIANT GARTER SNAKE (THAMNOPHIS GIGAS) AND VALLEY GARTER SNAKE (THAMNOPHIS SIRTALIS FITCHI) IN THE CENTRAL VALLEY OF CALIFORNIA

Hematology and plasma biochemistry parameters are useful in the assessment and management of threatened and endangered species. Although reference ranges are readily available for many mammalian species, reference ranges for snakes are lacking for most species. We determined hematology and plasma biochemistry reference ranges for giant garter snakes (Thamnophis gigas) and valley garter snakes (Thamnophis sirtalis fitchi) living in four management areas in the Central Valley of California. White blood cell, heterophil, lymphocyte, and azurophil counts in giant garter snakes were approximately twice the values of valley garter snakes. Statistically significant differences in aspartate aminotransferase, globulin, and potassium between the two species did not appear clinically significant. No significant differences were found in the measured parameters between male and female giant garter snakes. Some differences were found among collection sites. These reference ranges provide baseline data for comparisons over time and between collection sites.

Reproduction in Female Copperhead Snakes (Agkistrodon contortrix): Plasma Steroid Profiles during Gestation and Post-Birth Periods

We investigated levels of plasma progesterone (P4), 17β-estradiol (E2), testosterone (T), and corticosterone (CORT) during gestation and post-birth periods in wild-collected female copperhead snakes (Viperidae; Agkistrodon contortrix). We also sought to determine whether CORT levels at (or near) birth dramatically increase and were correlated with duration of labor and litter size. Specifically, pregnant subjects (N = 14) were collected during early- to mid-gestation, held in the laboratory, and repeatedly bled to obtain plasma for steroid analyses. Progesterone showed significant changes during gestation, with the highest levels at the onset of sampling (circa 50 days prior to birth); P4 progressively declined up to parturition, and basal levels were observed thereafter. At the onset of sampling, E2 was at peak levels and fell sharply at circa 30 days prior to birth, a trend observed throughout the post-birth sampling period. Throughout the entire sampling period, T was undetectable. Although CORT showed no significant changes during gestation and several days following parturition, there was a highly significant peak at the time of birth. Our findings mirror the results of previous studies on pregnancy and steroid hormones of other live-bearing snakes, lizards, and mammals. As expected, there was a significant relationship between duration of labor and litter size; however, although levels of CORT did not achieve significance, there was a positive trend with litter size. We suggest that elevation of CORT at birth is involved in the mobilization and regulation of energy stores necessary for the physiological process of parturition and as a possible mechanism to trigger birth.

Dwarfs on the Move: Spatial Ecology of the World's Smallest Viper, Bitis schneideri

Namaqua Dwarf Adders (Bitis schneideri) are small viperids that inhabit sandy coastal habitats within the Succulent Karoo Biome in southern Africa. Their ecology, and the faunal ecology within the region in general, is poorly documented, hampering effective conservation planning for this biodiversity hotspot. We used radio telemetry to investigate the spatial ecology of a population of B. schneideri. We measured mean daily displacement (MDD) of 19 male and 18 female snakes during the austral spring, summer, and winter. We also compared mean squared displacement from center of activity range (MSD), a measure of home range area, for males and females between the three seasons. Finally, we compared MDD of another 60 individuals collected using mark–recapture techniques. In general, snakes did not move great distances. Males moved further during spring (47.3 ± 3.9 m.day−1) than during summer (3.3 ± 4.5 m.day−1) or winter (3.0 ± 5.0 m.day−1). Female MDD did not vary significantly across spring (6.4 ± 4.6 m.day−1), summer (2.7 ± 3.7 m.day−1), or winter (0.8 ± 6.5 m.day−1), nor was it different from the MDD of males during summer and winter. MDD in the mark–recapture group did not differ among adult males, adult females, or juveniles. Home range area estimates varied between sexes and within seasons, generally corresponding to patterns shown for MDD. Overall mean home range size was larger in males (0.85 ± 0.09 ha) than females (0.10 ± 0.09 ha). Our data suggest that gene flow in Bitis schneideri is likely to be facilitated through the movement of male snakes during spring. However, the relatively short distances over which males range (even the most mobile males are sedentary compared to other species), and the apparent lack of any significant dispersal in juveniles, implies that the species may be vulnerable to fragmentation at relatively fine spatial scales. Thus, conservation management of the Succulent Karoo, the biome to which the species is restricted, should be aimed at minimizing habitat fragmentation.

OESTROGEN KEY TO FEMALE SNAKE’S SEXINESS

Every spring, the Interlake region of Manitoba, Canada, is the scene of a mating frenzy. Lured by female sex pheromones, ‘Tens of thousands of red-sided garter snakes bubble out of the ground’, says chemical ecologist Rocky Parker. ‘Male mate choice comes down to a matter of tongueflicks. But we don’t know what triggers pheromone production.’ Parker teamed up with Robert Mason of Oregon State University to decode the secrets of chemical signalling in red-sided garter snakes. Knowing that the hormone oestrogen activates sexual signal expression in birds, and given that snakes and birds are closely related, Parker and Mason wondered whether oestrogen triggers the production of a snake sexual signal: the garter snake sex pheromone (p. 723).The pair reasoned that, if oestrogen was the key to their puzzle, exposing male snakes to oestrogen should make them smell like females and therefore irresistible to other males. To find out, they collected male red-sided garter snakes in Manitoba and brought them back to Oregon, where they surgically inserted oestrogen implants into the males’ body cavities. The next spring, they took the snakes back to Manitoba to test whether oestrogen had made them alluring. Placing the altered males in an outdoor arena, the pair was delighted to see that wild males courted the implanted males. But, seeing that the altered males tried to avoid their love-struck suitors, Parker and Mason devised an additional test. Starting a mating ball composed of a female surrounded by courting males, they placed an altered male near the mating ball and counted how many males lost interest in the female and began wooing the altered male instead. Again, wild males were keen to court implanted males; they believed that they were pursuing females. Parker and Mason also found that the effects were entirely reversible, as wild males were no longer fooled by altered males once their implants were removed. The hormone functions as an ‘on/off switch’ for female pheromone production.So far, Parker and Mason’s suspicions had been confirmed. But when they laid scent trails in a Y-maze – by rubbing male and female snakes’ bellies along the maze’s arms – they were astonished to find that implanted males were more attractive than small females. ‘Longer females have more babies, so it’s best to court large females’, says Parker. ‘For some reason, oestrogen made males as alluring as large females.’To find out why, the pair collected altered males’ skin lipids and examined their pheromone composition using mass spectrometry. Garter snake sex pheromones are made up of light and heavy methyl ketones, with large females producing mostly heavier ketones. When Parker and Mason plotted the pheromone profiles, they saw that altered males had a heavy pheromone composition, just like large females. ‘It turns out that oestrogen triggers the production of the heaviest, and therefore sexiest, methyl ketones’, Parker concludes.So, in red-sided garter snakes, oestrogen triggers female pheromone production. This may offer an explanation for the puzzling existence of ‘she-males’ – wild males who naturally produce female sex pheromone but have negligible circulating oestrogen levels. ‘Exposure to oestrogen-mimicking pollutants could explain the presence of she-males’, says Parker; bad news for a species whose reproduction depends solely on chemical cues. ‘But the good news is that the changes are at least reversible’, he adds.