Non-reproductive Females Research Articles

Water availability and successful lactation by bats as related to climate change in arid regions of western North America

1. Climate change in North America is happening at an accelerated rate, reducing availability of water resources for bats and other wildlife that require it for successful reproduction. 2. We test the water-needy lactation hypotheses directly by tracking the drinking habitats of individual lactating and non-reproductive female fringed myotis at an artificial water source located near a maternity roost. 3. We used a submerged passive integrative transponder (PIT) tag reader system designed to track fish to instead record numbers of water source visitations by tagged bats. 4. Of 24 PIT-tagged adult females, 16 (67%) were detected repeatedly by the plate antenna as they passed to drink between 18 July and 28 August 2006. 5. The total number of drinking passes by lactating females (n = 255) were significantly higher than those of non-reproductive adult females (n = 22). Overall, lactating females visited 13 times more often to drink water than did non-reproductive females. On average, lactating females visited six times more often per night. Drinking bouts occurred most frequently just after evening emergence and at dawn. 6. Drinking patterns of non-reproductive females correlated significantly with fluctuating ambient temperature and relative humidity recorded at the water source, whereas lactating females drank extensively regardless of ambient conditions. 7. We provide a mathematical model to predict the rate of decline in bat populations in the arid West in relation to climate change models for the region.

Intersexual variation in the seasonal behaviour and depth distribution of a freshwater temperate fish, the largemouth bass

Because fish are poikilothermic, water temperature is regarded as a primary factor influencing their activity and behaviour. Rarely have field studies been conducted with the spatiotemporal resolution to enable rigorous quantitative assessments of that relationship. Furthermore, there have been few studies that have considered the influence of sex on the seasonal behaviour of fish. Twenty largemouth bass ( Micropterus salmoides (Lacepède, 1802)) were implanted with coded acoustic telemetry transmitters and remotely tracked in near real time in a small lake in Ontario, Canada, via a whole-lake hydrophone array between 1 November 2004 and 30 September 2005. Fish inhabited the deepest waters and were least active during the winter months under ice. During the warmest months, fish were most active and inhabited the littoral zone. Sex-specific differences were noted year-round. Reproductive males were less active and inhabited shallower depths during the spawning and post-reproductive periods. Reproductive males inhabited the deepest depths during winter and fall, with nonreproductive males at the shallowest depths. Throughout the year, the behaviour of nonreproductive males and females was similar. While differences in behaviour of bass are primarily driven by water temperature, sex and reproductive status play important roles year-round, especially during and after the reproductive period.

Could a big gut be too costly for muskoxen ( Ovibos moschatus) in their first winter?

Young mammalian herbivores are more vulnerable to harsh winter conditions than adults, especially among large circumpolar species like the muskox ( Ovibos moschatus). We compared feeding responses of muskox calves (body mass 95 kg) with those of mature, non-reproductive females (body mass 227 kg) in mid-winter when air temperatures fell to −40 °C. Food intakes (1.8–2.2 kg digestible dry matter (DM) d −1), digesta fill (27–32 kg wet mass) and digestibility of hay (52–58% of DM; 49–55% of gross energy) were similar between age groups even though calves were much smaller than adults. Calves fed more frequently (12 vs. 8 feeding bouts per day) and thus spent more time feeding each day than adults (387 vs. 343 min per day). High mass-specific food intakes of calves indicate higher requirements for maintenance of body tissue than adults, which could be related to a larger intestinal tract in young muskoxen. Notably, cows and calves maintained a constant body mass throughout, indicating that they were feeding at maintenance levels and that the relatively higher intakes of calves were not related to growth. Together, these data suggest that limited food availability due to snow cover or high animal density may reduce the survival of muskoxen in their first winter.

Visual sensitivity to a conspicuous male cue varies by reproductive state inPhysalaemus pustulosusfemales

The vocal sac is a visually conspicuous attribute of most male frogs, but its role in visual communication has only been demonstrated recently in diurnally displaying frogs. Here we characterized the spectral properties of the inflated vocal sac of male túngara frogs (Physalaemus pustulosus), a nocturnal species, and túngara visual sensitivity to this cue across reproductive state and sex. We measured the spectral and total reflectance of different male body regions, including inflated and non-inflated vocal sacs, along with samples of the visual background against which males are perceived. Inflated vocal sacs were the most reflective of all body parts, being one log unit more reflective than background materials. We utilized an optomotor drum with black stripes and stripes that mimicked the spectral reflectance of the inflated vocal sacs with various nocturnal light intensities to measure the visual sensitivity thresholds of males, non-reproductive females and reproductive females. All three groups exhibited visual sensitivities corresponding to intensities below moonless conditions in open habitats or at the edge of secondary tropical forests. Reproductive females exhibited the greatest visual sensitivity of all groups, and were significantly more sensitive than non-reproductive females. Though the mechanism for this physiological difference between reproductive and non-reproductive females is unknown, it is consistent with previously observed patterns of light-dependent phonotaxic behavior in túngaras. We suggest that the visual ecology of the vocal sac, especially in nocturnal frogs, offers a rich source for investigations of visual ecology and physiological regulation of vision.

Behavioral and Olfactory Responses of Female Salaria pavo (Pisces: Blenniidae) to a Putative Multi-component Male Pheromone

The peacock blenny, Salaria pavo (Risso 1810), typically breeds in rocky shores of the Mediterranean and adjacent Atlantic coast. Males defend a territory around a hole or cavity wherein females deposit eggs that the male guards until hatching. A pair of exocrine glands on the anal fin (anal glands) of males produces a putative pheromone involved in attraction of reproductively competent females to the nest. We used behavioral assays to assess species-specific attraction of reproductively competent females to putative male pheromones, including the anal gland pheromone. Additionally, chromatographic fractions of anal glands and male-conditioned water were tested for olfactory potency in females by electro-olfactogram analysis (EOG). In a flow-through tank or fluviarium, reproductive females were attracted to male-conditioned water and to the anal gland macerate from conspecifics but not to those of a closely related heterospecific. In addition, attraction of reproductive females to conspecific anal gland macerate occurred only during their initial upstream movement in the fluviarium; this was an ephemeral response when compared with the response to male-conditioned water that attracted females throughout the entire period of observation (5 min). Reproductive females also were attracted during the entire period of observation to water-conditioned by conspecific males whose anal glands had been removed. However, the attraction was more variable than that to water conditioned by intact males. Moreover, females were not attracted to male (without anal glands) odor during their initial upstream movement in the fluviarium. Finally, non-reproductive females were not attracted to the conspecific anal gland macerate. The EOG responses of females to molecular weight fractions and solid-phase extraction and high-performance liquid chromatography fractions of anal gland macerates and male-conditioned water (with and without anal glands) suggest that the anal glands release hydrophilic odorants that consist mainly of molecules smaller than 500 Da. Furthermore, males released potent odorants that do not originate from the anal glands. We hypothesize that females respond to a multi-component male pheromone to find mates. The putative anal gland pheromone is possibly comprised of hydrophilic odorants, whereas the other component(s), presumably of gonadal origin, may be less water-soluble.

Spotted Bats (Euderma maculatum) from Mt. Taylor, New Mexico

The spotted bat (Euderma maculatum) is an elusive and rarely captured species in western North America. In the United States, it is known from 12 western states. In New Mexico, few individuals have been reported in recent years, and multiple individuals are known from 9 of 12 capture sites. This study reports on additional captures of E. maculatum from Mt. Taylor (Cibola County) for 2 consecutive summers and includes evidence of a reproducing population in the area. On 30 June/1 July 2006, I captured 4 individuals of E. maculatum, including a lactating female, and on 5 June 2007, I captured a nonreproductive female. The flight of this species was directional and deliberate; I captured 5 of 6 spotted bats that came low over the earthen pond. This study demonstrates how human-made sources of water in an arid region provide opportunities for many species of bats to drink.

Thermoregulation during gravidity in the children's python (Antaresia childreni): a test of the preadaptation hypothesis for maternal thermophily in snakes

Pregnant squamate reptiles (i.e. lizards and snakes) often maintain higher and more stable body temperatures than their nonpregnant conspecifics, and this maternal thermophily enhances developmental rate and can lead to increased offspring quality. However, it is unclear when this behaviour evolved relative to the evolution of viviparity. A preadaptation hypothesis suggests that maternal thermophily was a preadaptation to viviparity. Oviparous squamates are unique among oviparous reptiles for generally retaining their eggs until the embryos achieve one fourth of their development. As a result, maternal thermophily by gravid squamates may provide the same thermoregulatory benefits, at least during early development, that have been associated with viviparity. Thus, the evolution of viviparity in squamates may reflect an expanded duration of a pre-existing maternal thermoregulatory behaviour. Despite its evolutionary relevance, thermoregulation during gravidity in oviparous squamates has not yet been explored in depth. In the present study, we examined whether gravidity was associated with thermoregulatory changes in the oviparous children's python, Antaresia childreni. First, we discovered that, compared to most snakes, A. childreni is at an advanced stage of embryonic development at oviposition. Second, using surgically implanted temperature loggers, we detected a significant influence of reproductive status on thermoregulation. Reproductive females maintained higher and less variable body temperatures than nonreproductive females and this difference was most pronounced during the last 3 weeks of gravidity. Overall, these results highlight the continuum between oviparity and viviparity in squamate reptiles and emphasize the importance of thermal control of early embryonic development independent of reproductive mode.

Comparison of spermatheca morphology between reproductive and non-reproductive females in social wasps

Social wasps show an obvious evolution of the differentiation in behavior and external size between reproductive and non-reproductive females, with no clear differences in the Stenogastrinae, via overlap in the Polistinae, to clear differences in the Vespinae. In this study, we examined the morphological appearance of the spermatheca in representative species of these three subfamilies. The general anatomical organization of the spermatheca comprises a reservoir, a duct and two spermathecal glands, and is in line with its common structure in other social Hymenoptera. All examined wasp species have a spermathecal reservoir with uniform wall thickness, which is similar to the situation in the bees, but differentiates them from the ants. Within the wasps, the shape of the reservoir, the shape of the spermathecal glands and their attachment site to the spermatheca differs among the Stenogastrinae, Polistinae and Vespinae. The reservoir wall is thick in the Polistinae and Vespinae, while in the Stenogastrinae, it varies from thin in Parischnogaster to thick in Eustenogaster, with an intermediate situation in Liostenogaster. In all examined species, we found no differences in the spermathecal development between reproductive and non-reproductive wasps.

Expression and localization of Ca 2+-ATPase in the uterus during the reproductive cycle of king quail ( Coturnix chinensis) and zebra finch ( Poephila guttata)

Calcium ATPase (Ca 2+-ATPase) is a key enzyme that participates in the translocation of calcium in the uterus of oviparous amniotes during eggshell formation. We used Western blot and indirect immunofluorescence microscopy to determine expression and localisation of uterine Ca 2+-ATPase during the reproductive cycle of king quail and zebra finch. The pattern of Ca 2+-ATPase expression and localisation during the reproductive cycle was similar for both species. Immunoblots of uterine extracts from quail and finch indicated that Ca 2+-ATPase expression is reduced in non-reproductive compared to reproductive females. Similarly, in non-reproductive females, weak apical immunofluorescent staining of Ca 2+-ATPase is localised to epithelial cells in a small number of uterine tubular glands. A large increase in apical immunofluorescent staining of tubular gland epithelia occurs in both vitellogenic and reproductive females. The presence of Ca 2+-ATPase on the apical surface of tubular gland epithelial cells suggests that the enzyme is involved in the translocation of calcium out of the tubular gland epithelia and into the concentrated fluid of the uterine lumen. Presence of Ca 2+-ATPase in vitellogenic females indicates that the enzyme is expressed prior to the time of ovulation and eggshell calcification.

The key role of lamb presence in affecting flight response in Sardinian mouflon (Ovis orientalis musimon)

Observations of the flight response in mammals are commonly used to test the behavioural response to predation risk. Such a response is likely to be stronger in more sensitive individuals such as females, and females with offspring in particular, as well as during such periods as the birth season. From August 2005 to July 2006 we recorded the flight distances of different mouflon group types in a natural population in Sardinia. The comparison of the flight distances of the groups (n groups=375, n mouflons=1303) provided evidence for the key role of lamb presence. Female groups with lambs fled at greater distances than male groups and female groups without lambs. This difference was linked to the females' priority to secure the survival of their offspring. Indeed, the uniformity of the flight distances of males and non-reproductive females was in contrast to the general expectations regarding ungulate species. In fact, smaller females were expected to be more sensitive to predation risk than larger males. The absence of major differences is probably due to the low sexual dimorphism of mouflon. Flight distances were shorter during the rut than during the lambing season, arguably because during the mating less time and energies were available for anti-predator behaviour. However, during the rut females with lambs still fled at greater distances than females without lambs, arguably because mothers took it as a priority to protect their parental investment rather then to find a potential mate.

Energetic efficiency of reproduction may constrain litter size in northern grasshopper mice

A growing body of evidence shows that lactation is energetically costly for mammals. Although lactation costs are positively correlated with litter size, the shape of this relationship remains largely unexplored. Understanding physiological efficiencies of metabolic investment in reproduction should provide valuable insight concerning trade-offs between number and size of offspring and limits to litter size. I used data from northern grasshopper mice (Onychomys leucogaster) to explore these constraints. The relationship between litter size and cost of lactation was best described by a non-linear regression such that intermediate litter sizes were the most cost-effective. Lactation costs at the upper range of natural litters for this species required mothers to ingest more than twice as much food as non-reproductive females. Young at 15 d of age from the largest litters were smaller than same-age young from smaller litters. In contrast, young from litters at the lower end of the species range were larger than average. These data suggest that the distribution of litter sizes within this species is selected against at the lower end by inefficient conversion of energy into viable offspring and at the upper end by simple limits on digestive efficiency or capacity.

LIZARDS TRADE-OFF ENERGY SUPPLIES

Life is about compromises, and energy-hungry processes such as reproduction and immunity compete for an organism's sometimes limited energy supplies. A female tree lizard's energy demands go up when she is reproductive and producing lots of eggs, but if there isn't enough energy to go around, then another process suffers. The availability of energy is probably partially regulated by corticosterone (CORT), which mobilises energy stores and regulates the stress response. Susannah French from Arizona State University and her colleagues tested the idea that CORT regulates the distribution of limited energy between the reproductive and immune systems by manipulating CORT levels in reproductive and non-reproductive female tree lizards under different stresses (p. 2859).However, as French explains, `one major problem with trying to manipulate hormone levels is measuring the response'. Handling animals is stressful for them, and so is giving them regular injections. `The best thing to do is leave them alone', she says. So when French's colleague Dale DeNardo saw a talk by bioengineer Brent Vernon on an injectable gel implant which releases substances into the body at a controlled rate, French knew that they had arrived at a solution. Collaborating with Vernon, the team developed a lizard implant consisting of a mixture of polymers, plus CORT, which they mixed up and injected into the animals under sedation such that the implant set in the lizards' bodies just after the injection.For their experiments, the team captured non-reproductive and reproductive female lizards in their Sonoran desert home before transporting them back to the lab in cloth bags. They placed half of both groups on a restricted diet of two crickets a week, while the others could gorge themselves on as many crickets as they could eat. Within each dietary group, half the animals received CORT implants.Two days after receiving their slow-releasing CORT implants and starting their new diets, the team gave each of the lizards a small circular wound in the top layer of their skin. They were surprised by what they found when they measured the area of the wounds five days later to see how CORT affected wound healing in the different groups. `We expected that all the CORT animals would have a suppressed [immune] response', French says. Instead, the team found that CORT had an effect only when the lizards were energy limited.They found that the non-reproductive females on a restricted diet had slower wound healing when they received a CORT implant than untreated animals. This suggests that CORT is effective in compromising non-reproductive females'immune response only when they are in energy debt.Turning their attention to the reproductive females, the team found that all those on restricted and unrestricted diets who had also received a CORT implant had restricted wound healing. So the added stress of reproduction,which uses up a lot of energy, makes a bad energetic situation worse. Having unlimited access to crickets isn't enough to redress the energy deficit. `CORT is involved in mobilising resources, but not directly involved in the immune response', says French, who is working next on tracking down what other factors affect the wound healing response.

Corticosterone modulation of reproductive and immune systems trade-offs in female tree lizards: long-term corticosterone manipulationsviainjectable gelling material

Physiological trade-offs arise because multiple processes compete for the same limiting resources. While competition for resources has been demonstrated between reproduction and immune function, the regulation of this competition remains unclear. Corticosterone (CORT) is a likely mediator due to its dual role in mobilizing energy stores throughout the body and regulating physiological responses to stressors. We manipulated CORT concentrations and resources in pre-reproductive and reproductive female tree lizards (Urosaurus ornatus) to test the hypothesis that CORT regulates the distribution of limiting resources between the reproductive and immune systems. To manipulate circulating concentrations of CORT we utilized a novel method of hormone implantation, in which a polymeric compound is mixed with hormone and injected in liquid form into the animal. After injection, the liquid quickly gels in situ forming a slow release hormone implant. This method of hormone delivery eliminated the need for substantial wounds to the animal or repeated handling required by other methods. In this study, the hormone-treated animals had plasma CORT concentrations comparable to high physiological concentrations. We found that CORT treatment suppressed immune function, but only when animals were energetically compromised. We assessed immune function by measuring the healing rate of a cutaneous biopsy. Healing was suppressed in all CORT-treated reproductive animals and in all CORT-treated animals (pre-reproductive and reproductive) undergoing food restriction, but CORT had no effect in ad libitum non-reproductive females. The context-dependent action of CORT renders its response adjustable to changing environmental conditions and may allow for the suppression of specific functions depending on resource availability.

Is Basking Opportunity in the Viviparous Lizard, Eulamprus Tympanum, Compromised by the Presence of a Predator Scent?

Chemoreception is a common mechanism used by many species to detect the presence of a potential predator and subsequently respond to it. The perceived risk of predation may force retreat to suboptimal conditions, forcing a trade-off between the risk of predation and the ability to acquire resources. Responses to chemical cues of predators vary as a result of past experience, ontogeny, or reproductive state. The basking regime maintained by gravid females of the viviparous skink, Eulamprus tympanum, may directly alter sex ratios of offspring produced through temperature-dependent sex determination. The avoidance of predator scents may restrict basking ability and, in turn, alter the sex of offspring produced. We measured responsiveness to chemical cues using tongue flicks as an indicator of chemical discrimination in adult females and neonates and in females of different reproductive condition. We then measured activity rates and basking behavior of females in experimental enclosures in the presence of various chemical stimuli to determine whether basking opportunity is compromised by the presence of a predator scent. Neonates respond significantly more than nonreproductive adult females to all chemical stimuli suggesting an age-specific shift in response, whereas adult females respond differently depending upon reproductive state. Under laboratory conditions, gravid females modify their behavior and forego the opportunity to bask when there is a perceived predation risk. However, further experimentation conducted under field conditions would be necessary to test fully the hypothesis that basking opportunity is compromised by the presence of a predator stimulus and, in turn, could alter offspring sex ratios.

Does the reproductive status of male round gobies (Neogobius melanostomus) influence their response to conspecific odours?

While pheromone communication has been well documented in the female round goby, male responses have not been examined. We determined if male round gobies responded to odours of their conspecifics, and whether that response varied with their reproductive status (reproductive and non-reproductive). No significant differences were observed for any treatment (dechlorinated water, or water conditioned by reproductive males (RM) and non-reproductive males (NRM) and females), although RM spent more time inside shelter than NRM (p < 0.05). Morphologically, length and weight did not vary, but gonadosomatic index, seminal vesicle somatic index and relative head width did differ between the two male groups (p = 0.000). Round goby males guard nests in cavities, and so a preference for shelter with increasing reproductive status is expected. Also, a lack of male responses to conspecific odours may be adaptive in this species, since males nest together in high densities, where increased aggression might prove detrimental for nesting males.

Uterine epithelial changes during placentation in the viviparous skink Eulamprus tympanum

We used scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to describe the complete ontogeny of simple placentation and the development of both the yolk sac placentae and chorioallantoic placentae from nonreproductive through postparturition phases in the maternal uterine epithelium of the Australian skink, Eulamprus tympanum. We chose E. tympanum, a species with a simple, noninvasive placenta, and which we know, has little net nutrient uptake during gestation to develop hypotheses about placental function and to identify any difference between the oviparous and viviparous conditions. Placental differentiation into the chorioallantoic placenta and yolk sac placenta occurs from embryonic Stage 29; both placentae are simple structures without specialized features for materno/fetal connection. The uterine epithelial cells are not squamous as previously described by Claire Weekes, but are columnar, becoming increasingly attenuated because of the pressure of the impinging underlying capillaries as gestation progresses. When the females are nonreproductive, the luminal uterine surface is flat and the microvillous cells that contain electron-dense vesicles partly obscure the ciliated cells. As vitellogenesis progresses, the microvillous cells are less hypertrophied than in nonreproductive females. After ovulation and fertilization, there is no regional differentiation of the uterine epithelium around the circumference of the egg. The first differentiation, associated with the chorioallantoic placentae and yolk sac placentae, occurs at embryonic Stage 29 and continues through to Stage 39. As gestation proceeds, the uterine chorioallantoic placenta forms ridges, the microvillous cells become less hypertrophied, ciliated cells are less abundant, the underlying blood vessels increase in size, and the gland openings at the uterine surface are more apparent. In contrast, the yolk sac placenta has no particular folding with cells having a random orientation and where the microvillous cells remain hypertrophied throughout gestation. However, the ciliated cells become less abundant as gestation proceeds, as also seen in the chorioallantoic placenta. Secretory vesicles are visible in the uterine lumen. All placental differentiation and cell detail is lost at Stage 40, and the uterine structure has returned to the nonreproductive condition within 2 weeks. Circulating progesterone concentrations begin to rise during late vitellogenesis, peak at embryonic Stages 28-30, and decline after Stage 35 in the later stages of gestation. The coincidence between the time of oviposition and placental differentiation demonstrates a similarity during gestation in the uterus between oviparous and simple placental viviparous squamates.

Thermogenesis, food intake and serum leptin in cold-exposed lactating Brandt's volesLasiopodomys brandtii

Lactation is the most energetically expensive period for mammals and is associated with increased metabolism and energy intake, but decreased thermogenic capacity. It is well known that small mammals increase both food intake and thermogenesis in the cold. The present study aimed to examine whether Brandt's voles Lasiopodomys brandtii could adjust energy intake and thermogenesis to accommodate simultaneous lactation and cold exposure. The voles were placed into two temperature treatments: warm (23+/-1 degrees C) and cold (5+/-1 degrees C). Animals at each temperature treatment were further divided into two groups: non-reproductive (NR) and lactating females. We found that lactating voles at peak lactation in the cold enhanced food intake by 2.6 g day(-1) compared with those in the warm, and increased uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT), to the same level as the cold-exposed NR females. Serum leptin levels decreased significantly during lactation and were positively correlated with body mass and fat mass. After correcting for the effects of body mass, residual serum leptin was negatively correlated with residual gross energy intake and residual RMR. In addition, residual serum leptin levels were positively correlated with UCP1 contents in the warm, but not in the cold. Together, these data suggest that lactating voles can increase thermogenic capacity and energy intake to meet the high energetic costs of simultaneous lactation and cold exposure. Further, serum leptin appears to be involved in the energy intake regulation and thermoregulation, but the thermoregulation in the cold may be mainly mediated by other factors.

Comparative morphology of cephalic exocrine glands among castes of the black ant Lasius niger

The glandular system is crucially involved in main aspects of ant social life. The function of glands has been primarily studied in the workers (the non-reproductive individuals in a colony). In contrast, little information is available on queens (the reproductive females in a colony) or males in spite of the obvious functional differences between these castes. Here we report a comparison of the general morphology of the mandibular, propharyngeal and postpharyngeal glands between the three castes of the black ant Lasius niger. The analysis clearly shows that all these cephalic glands differ in relative size between castes and suggests a link between gland structure and its behavioral role in queens, workers and males. In particular, males present a hypertrophied mandibular gland. This is consistent with the fact that these glands might be the source of the sex pheromone in this caste. By contrast, queens exhibited the most developed postpharyngeal glands. This is consistent with the production of particular cues by queens for workers to help them to distinguish between reproductive and non-reproductive females. Finally, the propharyngeal glands were most developed in the worker caste and of similar relative size in males and queens. Their function is still enigmatic.

Sex steroid hormones and sexual dimorphism of chemosensory structures in a terrestrial salamander ( Plethodon shermani)

The volume of the vomeronasal organ (VNO) in the terrestrial salamander Plethodon shermani was approximately 1.7 times larger in adult males compared to adult females, even though male body size was, on average, slightly smaller than female body size. VNO cell density, however, was the same in adult males and females. The sex difference in VNO volume was found in sexually immature animals as well, indicating that the increase of plasma androgens that occurs at sexual maturity does not produce the sex difference in VNO volume. There was no difference in VNO volume between reproductive and nonreproductive adult females, despite differences in plasma estradiol (E2) levels. The volumes of the main olfactory epithelium and muscles regulating diameter of the external nares were similar between males and females, indicating that the VNO per se, and not other aspects of the nasal cavity, was sexually dimorphic. To conclude, the sex difference in VNO volume appears to be a permanent sex difference that develops before sexual maturity. Future studies will examine the functional consequences of this structural sexual dimorphism in a peripheral sensory organ, the VNO.

Resources, not male mating strategies, are a determinant of social structure in Gunnison's prairie dogs (Cynomys gunnisoni)

AbstractPrevious studies of Gunnison's prairie dogs, Cynomys gunnisoni, have reached different conclusions about the factors influencing sociality in this species. In this study I tested whether Gunnison's prairie dog social structure was resource-based or whether male mating strategies drive the organizational patterns observed. Group size, where the term group refers to individuals occupying the same territory, was predicted by territory size and density of food available. The spatial overlap of adults within territories was positively correlated with spatial patchiness of food resources. All group members participated in territory defense, although adult males engaged in significantly more intergroup aggressive interactions. There was no significant difference in adult male and female home range size. The number of female home ranges that any given male home range overlapped was not correlated with male body mass, male home range size, or territory size. Contrary to predictions of typical mammalian male mating strategies, adult females ranged significantly further than males during the mating period. Body mass of males and nonreproductive females was similar, whereas that of reproductive females was smaller. In addition, males and females did not differ in size, based on skull length and skull width. Results from this study strongly suggest that patterns of space use and social structure in Gunnison's prairie dogs are the result of individual responses to resource abundance and distribution and are not due to male mating strategies, such as resource defense or female defense polygyny.