An introduced generalist parasite, the sticktight flea (Echidnophaga gallinacea), and its pathology in the threatened Florida scrub-jay (Aphelocoma coerulescens).

The sticktight flea, (Echidnophaga gallinacea), a major pest of the domestic chicken (Gallus gallus) that can cause severe pathology or death if untreated, is rarely recorded in free-living avian species. Sticktight fleas, however, were observed on the federally threatened Florida scrub-jay (Aphelocoma coerulescens) in February 2004, in south central Florida. Of the 81 Florida scrub-jays (FSJs) sampled before the 2004 breeding season, 12 were infested, with from 1 to as many as 57 fleas. Subsequent survivorship and variation in health indices led us to conclude that the sticktight flea caused the death of several jays. Within 4 mo, 46% of sticktight flea-infested (INF) jays died, whereas in the nonflea-infested (NINF) jays, only 5.9% died. Adult INF birds lost body mass in the time since a previous capture compared with NINF jays, and mass gain was slowed in 1-yr-old INF jays. Hematocrit of INF jays was dramatically impacted, as low as 17%, and was negatively correlated with the extent of infestation. Leukocyte counts were highest in INF jays; however, plasma immunoglobulin levels were lowest. Physiological stress levels, measured using plasma corticosterone, increased more rapidly in INF jays than NINF jays and were positively correlated with heterophil/lymphocyte ratios. The impact of the sticktight flea on the federally threatened FSJ negates previous findings that sticktight fleas are benign in wild avian hosts.

Effects of vasoactive intestinal peptide on plasma prolactin in passerines.

Vasoactive intestinal peptide (VIP) is a potent releaser of prolactin (PRL) in domestic fowl, turkey, and ring doves. However, few comparative studies have investigated this in wild species. We tested the effects of intravenously administered chicken VIP on plasma PRL concentrations in four passerine species: the white-crowned sparrow (Zonotrichia leucophrys gambelii), the dark-eyed junco (Junco hyemalis), the Florida scrub-jay (Aphelocoma coerulescens), and the western scrub-jay (A. californica). In the white-crowned sparrow, junco, and Florida scrub-jay, which were tested during the breeding season, VIP induced a rapid increase in plasma PRL. Serial plasma samples taken after VIP injection in the white-crowned sparrow show a 10-fold increase in PRL within 2 min of treatment, followed by a gradual decline. Effects of VIP, as compared to saline, remained significant for at least 20 min after treatment. Western scrub-jays did not respond to intravenous VIP with a significant rise in PRL secretion, possibly because they were tested after termination of the breeding season. This study indicates that VIP control of PRL release may be widespread among avian species, and that seasonal changes in plasma PRL may be mediated in part at the level of the pituitary. In addition, analysis of the control data revealed no increase in plasma PRL as a result of injection or restraint, suggesting that unlike in mammals, PRL is not released during acute stress in passerines.

Effects of ambient temperature on photo-induced prolactin secretion in three subspecies of white-crowned sparrow, Zonotrichia leucophrys.

We tested the effects of naturally relevant ambient temperatures (5, 20, and 30 degrees C) on photoinduced prolactin (PRL) secretion in three subspecies of white-crowned sparrow, Zonotrichia leucophrys. In all three subspecies, transfer from short to long days triggered an increase in plasma PRL typical of an avian seasonal breeder. In Z. l. gambelii, which breeds at high latitudes, temperature does not affect the rate of photoinduced gonadal maturation or luteinizing hormone (LH) secretion. In this subspecies, we found that changes in plasma PRL concentrations were similar in all temperature treatments. In Z. l. pugetensis, which breeds in the Pacific Northwest, high temperatures accelerate gonadal development in females but not males and does not affect LH secretion. In this subspecies, we found that like gonadal growth, photoinduced changes in PRL secretion in Z. l. pugetensis vary with ambient temperature in females but not males. In Z. l. oriantha, which breeds in alpine regions of the West, both males and females respond to temperature cues by modulating gonadal growth but not LH secretion. We found in Z. l. oriantha that ambient temperature affects PRL secretion in both sexes. These results suggest that PRL may be involved in the transduction of ambient temperature cues used to time reproductive development and the termination of seasonal breeding. Alternatively, temperature-mediated differences in plasma PRL may be a result rather than a cause of differences in gonadal development, since sex steroids affect PRL secretion in some species.

The effect of exogenous testosterone on parental behavior, plasma prolactin, and prolactin binding sites in dark-eyed juncos.

Numerous studies have shown that parental behaviors are mediated by prolactin (PRL), while testosterone (T) interferes with their full expression. The limited data available suggest that reduced parental behavior induced by T is not mediated by reduced concentrations of plasma PRL. We hypothesized that T reduces parental behaviors by reducing PRL receptor binding activity at central neural sites that promote the expression of parental behaviors. To test this hypothesis we implanted male dark-eyed juncos (Junco hyemalis) with testosterone-filled or empty implants and measured T and PRL levels, paternal behavior, and specific binding of radio-labeled PRL at selected brain regions that have been implicated in the mediation of parental behaviors. Our findings concurred with previous studies in that T-treated males reduced their parental contributions, had higher levels of T, and had equivalent levels of PRL compared with controls. We found no differences in the capacity to bind 125I-oPRL in three brain regions previously implicated in the mediation of parental care in birds, i.e., the preoptic area, ventromedial nucleus of the hypothalamus, and paraventricular nucleus of the hypothalamus. Thus our findings do not support the hypothesis that T interferes with the expression of parental behavior by reducing PRL receptor binding activity at central sites.

Effects of day length and temperature on gonadal development, body mass, and fat depots in white-crowned sparrows, Zonotrichia leucophrys pugetensis.

We tested the effects of ambient temperature (5 degrees, 20 degrees, and 30 degrees) on photoperiodically induced reproductive functions in male and female white-crowned sparrows, Zonotrichia leucophrys pugetensis. Transfer from short days (9L 15D) to long days (16L 8D) resulted in rapid testicular growth and partial ovarian development in all three temperature treatments. There were no differences in sizes of testes and cloacal protuberance following 30 or 70 days of exposure to long days at the different temperatures. However, brood patch and follicular development were enhanced in females at 30 degrees compared with the 5 degrees and 20 degrees groups. Many of these females exposed to 30 degrees had large yolky follicles by Day 70. This enhancement was evident only when females were housed in the same room with males, however. Despite the effects of high temperature on ovarian development, there were no differences among groups in plasma levels of follicle-stimulating hormone or luteinizing hormone, suggesting that differential ovarian development may have been mediated by gonadal sensitivity to gonadotropins rather than by differential secretion of these hormones. We examined circulating levels of corticosterone (B) and both tri-iodothyronine (T3) and thyroxine (T4) as possible regulators of this differential ovarian sensitivity to gonadotropins. Plasma B levels showed transitory increases in males at 5 degrees and 20 degrees, but were suppressed in males at 30 degrees. Titers of B were not influenced by temperature treatments in females. Circulating T4 increased following photostimulation in both sexes, but this increase was reduced at 5 degrees. T3 concentrations in plasma were highly variable and not influenced by either photo-period or temperature in males, but were significantly lower in females exposed to 30 degrees by Day 70. Thus, B and T4 levels do not appear to help explain differential ovarian development, but circulating T3 levels cannot yet be excluded as a regulator of ovarian sensitivity to gonadotropins. Long days resulted in no change, or a gradual decrease, in body mass and fat deposit in males and females, and temperature regimes had no further effects on fattening or body mass. Thus, reproductive development under long days appears to be resistant to naturally relevant temperature extremes in male Z.l. pugetensis, whereas follicular development (i.e., yolk deposition in follicles leading to ovulation and onset of nesting) can be enhanced by high temperature. Reasons for the dimorphism in this response are unknown, but may be explained by the role of females in determining onset of final ovarian maturation and nesting in relation to favorable environmental conditions. In a second experiment, in which the sexes were isolated from one another, we determined the effects of the same treatments on.Z.I. pugetensis. Again there was no effect of temperature on photoperiodically induced testicular growth, and the enhancement of follicular development in females at 30 degrees was greatly reduced in the absence of males. We also continued this experiment up to 116 days of treatment to investigate effects on onset of photorefractoriness (spontaneous gonadal regression) and onset of prebasic moult. In both sexes it was clear that low temperature (5 degrees) retarded gonadal regression and high temperature (30 degrees) advanced it. Similarly, the prebasic moult score was greater at 30 degrees and less at 5 degrees in both sexes. There were no effects of temperature on plasma levels of LH at Day 116 of treatment, but plasma levels of T4 were higher in the 5 degrees group of both males and females sampled at Day 116. Clearly, the effects of temperature can have different effects on gonadal recrudescence, onset of breeding (yolk deposition), and termination of breeding. Whether these influences of temperature on reproductive function at different stages in the breeding cycle have different mechanisms remains to be determ

Corticosterone, reproductive status, and body mass in a cooperative breeder, the Florida scrub-jay (Aphelocoma coerulescens).

In the cooperatively breeding Florida scrub-jay, nonbreeders are subordinate to the breeders with which they share a territory. Corticosterone is secreted in response to a wide range of stressors, including social stress, and suppresses reproductive and territorial behaviors in several taxa; thus, elevated baseline levels of corticosterone might be a causal mechanism of reproductive suppression. To test the hypothesis that nonbreeder Florida scrub-jays are reproductively suppressed through the actions of corticosterone, we compared corticosterone levels of nonbreeders and breeders and found no differences. However, baseline corticosterone levels only provide information about a bird's current hormonal status. Virtually all species exhibit a rapid rise in glucocorticoids in response to an acute stressor. If the adrenocortical response of nonbreeders is greater than that of breeders, this might be a mechanism whereby nonbreeders remain reproductively quiescent. We compared the responses of breeders and nonbreeders to the acute stress of being captured and held for 1 h. Both exhibited significant but equivalent increases in corticosterone titers. Because in some species heavier or fatter individuals have reduced glucocorticoid responses to stressors, we examined whether body mass was correlated with corticosterone titers. Both baseline and maximum corticosterone levels covaried with body mass, and the effect of body mass on corticosterone levels explained the increase due to capture and handling. Our data do not support the hypothesis that Florida scrub-jay nonbreeders are reproductively suppressed through the actions of corticosterone.

Interrelationship of day length and temperature on the control of gonadal development, body mass, and fat score in white-crowned sparrows, Zonotrichia leucophrys gambelii.

We tested the effects of naturally relevant environmental temperatures on long day-induced reproductive development in male and female white-crowned sparrows, Zonotrichia leucophrys gambelii. Transfer from short days (8L 16D) to long days (20L 4D) resulted in rapid testicular development and partial ovarian development as has been reported many times previously. Exposure of experimental groups to low (5 degrees), moderate (20 degrees), and high (30 degrees) temperature during photostimulation had only subtle effects on plasma levels of follicle-stimulating hormone and luteinizing hormone over time and no effects on the size of testes, cloacal protuberance, ovaries, or brood patch at Day 30 of treatment. Long days resulted in the well known increase in body mass and fat score, indicative of preparations for migration. In females, treatment with low temperature resulted in a reduction in the premigratory increase in fat and body mass when transferred to long days. This was accompanied by an increase in plasma levels of corticosterone during the early stages of photostimulation at low temperature. Temperature regimes had no effects on fattening or body mass in males, despite an early increase in plasma corticosterone at low temperature. Circulating levels of thyroxine (T4) and triiodothyronine (T3) increased to varying degrees following photostimulation. Temperature treatment had no effect on plasma levels of thyroid hormones in males, but low temperature did inhibit thyroid hormone secretion (particularly T4) in females. Although reproductive development appears to be resistant to naturally relevant temperature extremes in both sexes, low environmental temperature impaired preparations for migration in females but not males. This effect may be mediated through glucocorticosteroids and not thyroid hormones. Reasons for the sexual dimorphism in this response are unknown, but may be related to sexual selection for males to arrive on the breeding grounds ahead of females regardless of local weather conditions.