Feline communication strategies when presented with an unsolvable task: the attentional state of the person matters.

Research on social cognitive ability in domestic cats is limited. The current study investigated social referencing in cats when exposed to first, a solvable, and then, an unsolvable scenario (i.e., reachable and unreachable treats) in the presence of either an attentive or an inattentive caregiver. Cats expressed more gaze alternation (P = 0.013), but less interaction with the caregiver (P = 0.048) and approached the treat container less frequently (P = 0.017) during the unsolvable test, compared to the solvable test. When in the presence of an attentive caregiver, cats initiated first gaze at the caregiver faster (P = 0.001); gazed at the caregiver for longer (P = 0.034); and approached the treat more frequently (P = 0.040), compared to when the caregiver was inattentive. Significant interaction was observed between test and caregiver's attentional state on the expression of sequential behavior, a type of showing behavior. Cats exhibited this behavior marginally more with attentive caregivers, compared to inattentive caregivers, but only during the unsolvable test. There was a decrease in sequential behavior during the unsolvable test, compared to solvable test, but this was only seen with inattentive caregivers (P = 0.018). Our results suggest that gaze alternation is a behavior reliably indicating social referencing in cats and that cats' social communication with humans is affected by the person's availability for visual interaction.

Changes in processes downstream of the hypothalamus are associated with seasonal follicle development in a songbird, the dark-eyed junco (Junco hyemalis).

Mechanisms related to seasonal reproductive timing in vertebrates have received far more study in males than in females, despite the fact that female timing decisions dictate when rearing of offspring will occur. Production and release of gonadotropin-releasing hormone (GnRH) by the hypothalamus stimulates the pituitary to secrete gonadotropins, initiating the beginning stages of gonadal recrudescence and production of the sex steroids, testosterone and estradiol, which are necessary to prime the liver for secretion of yolk precursors in breeding female birds. While stimulation by the hypothalamus can occur during the pre-breeding period, egg development itself is likely regulated downstream of the hypothalamus. We used GnRH challenges to examine variation in breeding-stage-specific patterns of pituitary and ovarian responsiveness in free-living female dark-eyed juncos (Junco hyemalis) and also examined the ovary and liver for variation in mRNA expression of candidate genes. Baseline LH levels increased during the transition from pre-breeding to egg-development, however no significant difference was observed in post-GnRH injection levels for LH or sex steroids (testosterone and estradiol). Interestingly, a stage by time-point interaction was observed, with post-GnRH LH levels increasing over baseline during the pre-breeding stage, but not during the egg-development stage. We observed a decrease in liver mRNA expression of estradiol receptor-alpha, and glucocorticoid and mineralocorticoid receptors and a decrease in glucocorticoid receptor expression levels in the ovary. A decline in FSH receptor expression across stages was also observed in the ovary. Combined, our data suggest seasonal variation in female's sensitivity to signals of HPG activity and energetic or stress signals. These data provide additional insight into the physiological mechanisms regulating onset of clutch initiation.

Consistent individual variation in day, night, and GnRH-induced testosterone concentrations in house sparrows (Passer domesticus).

The hypothalamic-pituitary-gonadal (HPG) axis, with gonadotropin-releasing hormone (GnRH) initiating the endocrine cascade, regulates testosterone secretion. Testosterone, through its pleiotropic effects, plays a crucial role in coordinating morphology, physiology and behavior in a reproductive context. The concentration of circulating testosterone, however, varies over the course of the day and in response to other internal or external stimuli, potentially making it difficult to relate testosterone sampled at one time point with traits of interest. Many researchers now utilize the administration of exogenous GnRH to elicit a standardized stimulation of testosterone secretion. However, it has remained unclear if and how this exogenously stimulated activation of the HPG axis is related with endogenously regulated testosterone that is capable of influencing testosterone related traits. Repeated measures of a hormone can uncover consistent individual variation in hormonal differences at the HPG axis level, variation that potentially stems from underlying genetic variation in a population experiencing identical environmental cues. Thus, we asked, using the house sparrow (Passer domesticus), how daily endogenous variation in testosterone profiles relates to GnRH-induced testosterone secretion. Further, we explore the relationship between endogenous daily testosterone peaks and GnRH-induced testosterone with badge size, a morphological trait related with status within a social group. We found that GnRH-induced testosterone levels reflect a highly repeatable hormonal phenotype that is strongly correlated with nighttime testosterone levels. The results demonstrate the usefulness of GnRH-induced testosterone in studies aimed at understanding individual variation and selection on endogenously regulated testosterone levels and the potential importance of nighttime testosterone levels to physiology and behavior.

Hypothalamic-pituitary-adrenal axis activity is not elevated in a songbird (Junco hyemalis) preparing for migration.

During spring, increasing daylengths stimulate gonadal development in migratory birds. However, late-stage reproductive development is typically postponed until migration has been completed. The hypothalamic-pituitary-adrenal (HPA) axis regulates the secretion of glucocorticoids, which have been associated with pre-migratory hyperphagia and fattening. The HPA-axis is also known to suppress the hypothalamic-pituitary-gonadal (HPG) axis, suggesting the possibility that final transition into the breeding life history stage may be slowed by glucocorticoids. We hypothesized that greater HPA-axis activity in individuals preparing for migration may foster preparation for migration while simultaneously acting as a "brake" on the development of the HPG-axis. To test this hypothesis, we sampled baseline corticosterone (CORT), stress-induced CORT, and negative feedback efficacy of Dark-eyed Juncos (Junco hyemalis) in an overwintering population that included both migratory (J.h. hyemalis) and resident (J.h. carolinensis) individuals. We predicted that compared to residents, migrants would have higher baseline CORT, higher stress-induced CORT, and weaker negative feedback. Juncos were sampled in western Virginia in early March, which was about 2-4wk before migratory departure for migrants and 4-5wk before first clutch initiation for residents. Contrary to our predictions, we found that migrants had lower baseline and stress-induced CORT and similar negative feedback efficacy compared with residents, which suggests that delayed breeding in migrants is influenced by other physiological mechanisms. Our findings also suggest that baseline CORT is not elevated during pre-migratory fattening, as migrants had lower baseline CORT and were fatter than residents.

Onset of Daily Activity in a Female Songbird Is Related to Peak-Induced Estradiol Levels.

Research in captive birds and mammals has demonstrated that circadian (i.e., daily) behavioral rhythms are altered in response to increases in sex-steroid hormones. Recently, we and others have demonstrated a high degree of individual repeatability in peak (gonadotropin-releasing hormone [GnRH]-induced sex) steroid levels, and we have found that these GnRH-induced levels are highly correlated with their daily (night-time) endogenous peak. Whether or not individual variation in organization and activity of the reproductive endocrine axis is related to daily timing in wild animals is not well known. To begin to explore these possible links, we tested the hypothesis that maximal levels of the sex steroid hormone estradiol (E2) and onset of daily activity are related in a female songbird, the dark-eyed junco (Junco hyemalis). We found that females with higher levels of GnRH-induced E2 departed from their nest in the morning significantly earlier than females with lower stimulated levels. We did not observe a relationship between testosterone and this measure of onset of activity. Our findings suggest an interaction between an individual's reproductive endocrine axis and the circadian system and variation observed in an individuals' daily activity onset. We suggest future studies examine the relationship between maximal sex-steroid hormones and timing of daily activity onset.

Repeated immune challenges affect testosterone but not sperm quality.

Mounting an immunological response is energetically demanding and necessarily redirects allocation of resources toward immune system activation and away from other energetically expensive processes, such as reproduction. Lipopolysaccharide (LPS), a major component of the outer membrane of the cell wall of Gram-negative bacteria Escherichia coli, mimics a bacterial infection without producing the cost of replicating the pathogen and is one of the most commonly used agents to induce an acute phase immune response. Here, we ask if a trade-off can be induced between activation of the acute phase immune response and sperm function, a key indicator of sperm competitive ability. Further, we ask whether repeated exposure to this endotoxin in a social species such as the house sparrow (Passer domesticus), where repeated pathogen exposure may be common, may have a more pronounced effect. To address our questions, we exposed individuals to two rounds of LPS treatment or control, to mimic a repeated pathogen exposure in the wild. We predicted that repeated pathogen exposure would have detrimental effects on sperm quality, and therefore, reproductive success. We compared a measure of sperm quality (straight-line velocity) in captive male house sparrows between LPS-treated and control individuals. We found that although LPS treatment impaired circulating testosterone and induced a hypothermic state when compared with controls, it did not affect sperm quality within days or weeks following a single or repeated LPS exposure.