An acute stressor alters steroid hormone levels and activity but not sexual behavior in male and female Ocoee salamanders (Desmognathus ocoee)

Stressors that are chronic have clear suppressive effects on reproductive behaviors in both males and females. Stressors that are acute have effects on reproductive behavior that are less clear. We measured the effects of an acute bout of handling in laboratory-housed male and female Ocoee salamanders (Desmognathus ocoee), a species with a prolonged mating season. Handling resulted in decreased locomotory activity and elevated plasma corticosterone, a hallmark of the vertebrate stress response. Handling also decreased plasma testosterone in males and elevated plasma estradiol in females. Despite the handling-induced changes in hormone levels, handling had minimal impact on courtship and mating. Other species in which reproduction is insensitive to acute stressors may live in extreme environments with limited reproductive opportunities, whereas Ocoee salamanders live in a relatively temperate environment with multiple reproductive opportunities. Together, these data indicate that an allostatic response to a stressor can alter locomotory activity and elevate corticosterone without suppressing nonessential behaviors like courtship and mating in a species in which reproductive opportunities can occur over a period of multiple months. The lack of reproductive suppression in Ocoee salamanders might be due to the low energetic cost of courtship and mating in this species combined with potentially elevated energetic stores, highlighting the importance of considering energy budgets when making predictions about behavioral effects of acute stressors.     

Effects of androgens on behavioral and vomeronasal responses to chemosensory cues in male terrestrial salamanders (Plethodon shermani)

Chemosensory stimuli and sex steroid hormones are both required for the full expression of social behaviors in many species. The terrestrial salamander, Plethodon shermani, is an emerging nonmammalian system for investigating the nature and evolution of pheromonal communication, yet little is known regarding the role of sex steroid hormones. We hypothesized that increased circulating androgen levels in male P. shermani enhance chemoreception through morphological, behavioral, and physiological mechanisms. Experimental elevation of plasma androgens increased development of cirri, morphological structures thought to enhance the transfer of chemosensory cues from the substrate to the vomeronasal organ (VNO). Elevated plasma androgens also increased expression of a chemo-investigatory behavior (nose tapping) and increased preference for some female-derived chemosensory cues. Male-produced courtship pheromones activated a large number of cells in the VNO as measured by the method of agmatine uptake. However, androgen levels did not affect the total number of vomeronasal cells activated by male-produced courtship pheromones. Future studies will determine whether androgens potentially modulate responsiveness of the VNO to female-derived (as opposed to male-derived) chemosensory cues.     

Differential effects of chronic escapable versus inescapable stress on male syrian hamster (Mesocricetus auratus) reproductive behavior

Stress decreases sexual activity, but it is uncertain which aspects of stress are detrimental to reproduction. This study used an escapable/inescapable stress paradigm to attempt to dissociate physical from psychological components of stress, and assess each component's impact on reproductive behavior in the male Syrian hamster (Mesocricetus auratus). Two experiments were completed using this protocol where two animals receive the same physical stressor (an electric footshock) but differ in the psychological aspect of control. One group (executive) could terminate the shock for themselves as well as a second group (yoked) by pressing a bar. Experiment 1 demonstrated a significant increase in plasma glucocorticoids at the end of a single 90-min stress session with no difference in glucocorticoid levels between the executive and yoked groups at any time point. Experiment 2 quantified male reproductive behavior prior to and immediately following 12 days of escapable or inescapable stress in executive, yoked, and no-stress control hamsters (n = 12/group). Repeated-measures analysis of variance revealed a number of significant changes in reproductive behavior before and after stress in the three treatment groups. The most striking difference was a decrease in hit rate observed only in the animals that could not control their stress (yoked group). Hit rate in the executive males that received the exact same physical stressor but could terminate the shock by pressing a bar was nearly identical to control animals that never received any foot shock. Therefore, we conclude that coping or control can ameliorate the negative effects of stress on male reproductive behavior.     

Relationship between androgens, environmental factors and reproductive behavior in male white rhinoceros (Ceratotherium simum simum)

We conducted a longitudinal study of the endocrine activity of free-range male white rhinos. An enzyme immunoassay to measure androgens in the feces was developed and validated to show that it can be used to study testicular activity. We identified two fecal metabolites similar to testosterone and dihydrotestosterone. Several lines of evidence suggest that these metabolites clearly reflect testicular activity. Firstly, the stimulation of testicular activity with synthetic GnRH caused a 156% increase in androgen metabolite concentrations in the feces 1 day after treatment. Secondly, androgen metabolite concentrations increased with sexual maturity in rhinos, and finally there was a correlation between testosterone concentrations in plasma and androgen metabolite concentrations in feces. Using the method that we developed, it was possible to establish whether a relationship exists between androgen metabolite concentrations, the behavior and environmental factors. Adult territorial males (n = 5) had elevated androgen metabolite concentrations during months of high rainfall (September-February) compared to months of little or no rainfall (March-August). The increase in concentrations coincided with the beginning of the rainy season, suggesting a seasonal trend in reproduction. This trend was confirmed by behavior observations showing both a higher frequency of conceptions within the first 4 months of increased androgen metabolite concentrations, and a higher number of inter-sexual conflicts, reflecting the initial aggression between the sexes during the consort period. It was also evident that males accompanying a receptive female had higher fecal androgen metabolite concentrations compared to being alone. The elevated levels were likely induced by female presence.     

A four-year study of the association between male dominance rank, residency status, and reproductive activity in rhesus macaques (Macaca mulatta)

Considerable controversy exists on the nature of the relationship between male dominance rank and reproductive activity. The nature of this relationship has important implications for understanding the manner in which males compete for access to limited resources. Behavioral data on mating patterns were collected over a four-year period from one social group of rhesus macaques on Cayo Santiago. Correlations between dominance rank and reproductive activity were not stable over a four-year period, but changed yearly. Positive, significant correlations were present in the first two years of the study while non-significant correlations were found in the second two years. The variation found in the correlations between rank and mating activity could be accounted for by changes in the mating frequencies of different classes of males. The long-term resident males had declines in ejaculation frequencies over the duration of the study. Males who immigrated into the group had yearly increases in reproductive behavior over three consecutive years. Maturing natal males also increased their levels of reproductive activity from year-to-year. Combining these mating patterns over time resulted in shifting the proportions of matings away from the long-term residents and in favor of the new males. High-ranking males had an advantage in reproductive activity over the first two years of the study, as measured by both the total number of ejaculations and the mean number of ejaculation per male. New males, comprised of recent immigrants and maturing natal males, had a greater level of reproductive activity over the last two years. These results suggest that the effect of rank on reproductive activity is variable and that males utilize alternative tactics to attain access to limited resources. Simple one-factor models explaining the relationship between rank and reproductive activity must be replaced with models explaining how alternate strategies affect male competition and reproductive success in primates.     

Mating behavior induces changes of expression of Fos protein,plasma testosterone and androgen receptors in the accessory olfactory bulb (AOB) of the male mandarin vole Microtus mandarinus

In order to investigate the neuroendocrine mechanism of the mating behavior in the adult male mandarin voles Microtus mandarinus,the radioimmunoassay(RIA)and immunohistochemistry methods were used to investigate the differences in plasma testosterone(T)concentrations and distribution of T immunoreactive neurons(T-IRs),androgen receptor immunoreactive neurons(AR-IRs)and Fos protein immunoreactive neurons(Fos-IRs)in the accessory olfactory bulb(AOB)and the main olfactory bulb(MOB)following exposure to clean h...     

The reproductive behavior of the longspine snipefish,Macrorhamphosus scolopax (Syngnathiformes,Macrorhamphosidae)

Synopsis About two hundred Macrorhamphosus scolopax were observed in a large tank and their behavior was videotaped for subsequent analysis. When not disturbed, the fish moved slowly in a head-down position. Spawning in the tank took place in the last two hours before dark. Courting males change color and actively interact aggressively with other males. They push against each other while swimming in parallel or they charge their opponents with their erected dorsal spine directed at them. Courtship begins near the bottom. After following and swimming parallel to the female the two fish unite tightly by their caudal peduncle, with their ventral regions in close proximity and rise slowly in the water column. During the ascent, the genital papilla of the female extends repeatedly and contacts the genital region of the male.     

The acquisition process of a novel behavior pattern in a group of ring-tailed lemurs (Lemur catta)

The process of acquisition and propagation of a novel behavior pattern in a group of 18Lemur catta was examined. Six of eight animals that acquired the new habit were infants or juveniles. Adult males did not take up the new behavior pattern. Effects of rank and kinship on the aquisition process were not obvious.     

The influence of horn and body size on the reproductive behavior of the horned rainbow scarab beetlePhanaeus difformis (Coleoptera: scarabaeidae)

The reproductive behavior of horned rainbow scarab beetles,Phanaeus difformis, was studied to determine the influence of morphological traits on intersexual and intrasexual interactions.Phanaeus difformis is a sexually dimorphic dung beetle in which males possess much larger horns than females, and males can be grouped into major and minor male morph categories based on horn size. Male-female pairs cooperated in nest construction and provisioning. In the laboratory, males of both morphs assisted females and were equally successful at copulating. However, in the field larger individuals had a pairing advantage due to greater success in intrasexual competition. Some males used an alternative mating tactic which involved sneaking copulations with paired females. In most cases the sneak male was smaller than the paired male.