Milk-fat globule epidermal growth factor 8 (MFGE8) is expressed at the embryo- and fetal-maternal interface in equine pregnancy.

Milk-fat globule epidermal growth factor (EGF) 8 protein (MFGE8), also known as lactadherin, promotes cell adhesion in an Arg-Gly-Asp (RGD)-dependent modus via integrins. In the present study, the expression of MFGE8 was examined in equine endometrium during oestrus and at Days 12 and 16 after ovulation in pregnant and non-pregnant mares and in mares during the 5th month of gestation. Results demonstrated that MFGE8 is expressed at the embryo- and fetal-maternal interface in equine pregnancy. In non-pregnant endometrium its expression was upregulated by oestrogen, a finding that was confirmed using endometrial explant culture. MFGE8 was expressed at similar levels by conceptuses collected 13 and 14 days after ovulation and by allantochorion sampled during the 5th month of gestation. Pericytes of endometrial blood vessels displayed strong MFGE8 expression upon in situ hybridisation. During the 5th month of gestation, the fetal side of the allantochorionic villi in particular displayed pronounced staining upon in situ hybridisation, confirming that MFGE8 expression is not restricted to early pregnancy but persists and is present at the fetal-maternal interface. Potential roles of MFGE8 in equine pregnancy include mediating cell-cell adhesion, promotion of angiogenesis and placental transfer of fatty acids.

Stressful Life Events Prior to Depression Onset and the Cortisol Response to Stress in Youth with First Onset Versus Recurrent Depression.

The strongest proximal predictors of depression onset in adolescence are stressful life events (SLEs). Changes in the hypothalamic-pituitary-adrenal (HPA) axis response to stress are theorized to mediate the etiological effect of SLEs on depression onset. The goal of the current study was to examine differences in the cortisol response to a laboratory-induced stressor between youth with versus without at least one SLE in the etiologically-central 3-month period prior to depression onset. One hundred adolescents (24 first-onset depression, 18 recurrent depression, and 58 non-depressed controls) had five salivary cortisol samples collected over the course of the Trier Social Stress Test (TSST). SLEs were assessed using a rigorous contextual interview and rating system. Among those with an SLE, youth on their first onset of depression had a flatter cortisol reactivity slope relative to non-depressed adolescents, and youth on a recurrent episode of depression had a steeper recovery slope relative to first-onsets and non-depressed adolescents. In contrast, no between-group differences were found among those with no SLE prior to onset. These results suggest that differences in the HPA axis response pattern may represent a neurobiological mechanism that distinguishes depressed and non-depressed groups but only for adolescents whose depression is precipitated by SLEs. Further, this neurobiological mechanism may play a different role in the very first episode of depression than it does in recurrent episodes.

Effects of pipothiazine palmitate on handling stress and on the characteristics of semen collected by electroejaculation in bison (Bison bison) bulls.

Handling North American bison can pose risk to the handler and evoke stress in the animal. Moreover, this induced stress might affect qualities of semen collected by electroejaculation. The objective of this study was to investigate if a long acting neuroleptic tranquilizer (LAN) would reduce the stress of bison and thereby improve the quality of electroejaculated semen. Eight experimental replicates were conducted between May and November. In each replicate, the same six bison bulls were randomly assigned into LAN-treated (n=3) and non-treated control (n=3) groups. Pipothiazine palmitate (Piportil L4) was administered intramuscularly as a single dose of 100 mg in replicates 1-4 or 200 mg in replicates 5-8. Within each replicate, semen was collected by electroejaculation at 4, 6, 11 and 13 days post treatment. Behavioral parameters, sperm morphology and motility parameters were analyzed. A blood sample was collected before each electroejaculation and serum concentrations of testosterone, cortisol and corticosterone were determined. Treatment bulls with 100 mg of Piportil L4 reduced the restraint time and the struggling of bison bulls during handling compared to the control group (P<0.05). Semen motility parameters and serum concentrations of testosterone, cortisol and corticosterone were not significantly affected when 100mg of the LAN was administered (P>0.05). However, giving 200 mg of Piportil L4 reduced the restraint time of bison bulls and the duration of semen collection (P<0.05). Also, this treatment improved total and progressive sperm motilities when compared to the respective controls (P<0.05). Interestingly, serum concentration of corticosterone, as an endocrine stress indicator, was decreased after administration of 200mg of Pipothiazine palmitate, while testosterone concentrations were increased compared to those values in untreated control bulls (corticosterone: 0.10±0.01 compared with 0.15±0.02 ng/mL; testosterone: 9.11±1.68 compared with 5.33±0.74 ng/mL; P<0.05). In conclusion, this study demonstrated that a treatment dose of 200mg of Piportil L4 can decrease the behavioral and endocrine stress responses in bison bulls, which indirectly increasing testosterone concentrations and improving semen quality.

neuroendocrinological responses to alcohol intoxication in healthy males: relationship with impulsivity, drinking behavior, and subjective effects.

Ambiguous biochemical and subjective responses to alcohol may relate to preexisting individual differences in alcohol expectations, experience, or impulsivity. This study examined cortisol and alpha-amylase responses to alcohol and their association with trait impulsivity, alcohol expectancy, and subjective reports of alcohol's effects. Eighty-seven males assigned to an alcohol, sober, or placebo group provided biochemical and self-report measures. Both cortisol and alpha-amylase increased following alcohol administration. Impulsivity correlated with cortisol changes, and the greatest rise in cortisol correlated with high stimulating effects in the alcohol group. These findings emphasize the importance of individual differences in alcohol responses and support a relationship between hormonal responses and alcohol use.

Using life-histories to predict and interpret variability in yolk hormones.

Variation in yolk hormones is assumed to provide the plasticity necessary for mothers to individually optimize reproductive decisions via changes in offspring phenotype, the benefit being to maximise fitness. However, rather than routinely expecting adaptive variation within all species, the pattern and magnitude of yolk hormone deposition should theoretically relate to variation in life-histories. Here we present data on intra-clutch variation in yolk corticosterone in three species along a developmental continuum (European starling (Sturnus vulgaris): fully altricial; black guillemot (Cepphus grylle): semi-precocial; common eider (Somateria mollissima): fully precocial) to examine how and why variation in life-histories might relate to the evolution of variation in yolk steroids. Starlings and guillemots showed a significant increase in yolk corticosterone across the laying sequence; however, we found no pattern within eider clutches. Moreover, starlings showed the largest difference (94.6%) in yolk corticosterone between first- and last-laid eggs, whereas guillemots showed a moderate difference (58.9%). Despite these general species-specific patterns, individuals showed marked variation in the intra-clutch patterns of yolk corticosterone within each species indicating potential differences in intra-clutch flexibility among females. It is well documented that exposure to elevated yolk glucocorticoids reduces offspring quality at birth/hatching in many taxa and it has therefore been proposed that elevated yolk levels may modulate offspring competition and/or facilitate brood reduction under harsh conditions in birds. Our data suggests that intra-clutch variation in yolk corticosterone has the potential to act as an adaptive maternal effect in species where modulation of competition between nest-bound offspring would benefit mothers (starlings and guillemots). However, in precocial species where mothers would not benefit from a modulation of offspring quality, intra-clutch variation in yolk hormones may play little or no adaptive role. While future phylogenetically-controlled studies will be helpful in examining questions of adaptive mechanisms once more data on yolk corticosterone becomes available, our results nonetheless suggest that research on the evolutionary role of yolk hormones can benefit by a priori incorporating species-specific life-history-driven hypotheses.

In three brain regions central to maternal behaviour, neither male nor female Phodopus dwarf hamsters show changes in oestrogen receptor alpha distribution with mating or parenthood.

Oestrogen receptor (ER)alpha immunoreactivity in three brain regions relevant to maternal behaviour (medial preoptic area, bed nucleus of the stria terminalis and medial amygdala) was measured in two species of dwarf hamster that both mate during a postpartum oestrous but differ in expression of paternal behaviour. Male and female Phodopus campbelli and Phodopus sungorus were sampled as sexually naive adults, following mating to satiety, and as new parents. In all brain regions, females expressed higher levels of ER alpha than males. Species did not have an effect on ER alpha distribution except in the medial amygdala, where P. sungorus females had higher expression levels than all other groups. Behavioural status was not associated with altered ER alpha expression. These results were not expected for females and suggest that a primary activational role for oestrogen, acting through ER alpha in these regions, does not generalize to maternal behaviour in Phodopus. In males, these results are consistent with previous manipulations of the ER alpha ligand, oestrogen, and suggest that paternal behaviour in P. campbelli is likely to be regulated by developmental effects of oestrogen on the brain during early life (similar to Microtus ochrogaster), rather than through activation by oestrogen at the time of fatherhood (similar to Peromyscus californicus).

Analysis of steroids in songbird plasma and brain by coupling solid phase extraction to radioimmunoassay.

It is a common practice to extract steroids from plasma, serum, or tissue samples prior to steroid measurement by radioimmunoassay (RIA) or enzyme immunoassay (EIA). Steroid extraction is critical because it can remove substances that interfere with the RIA or EIA. Steroid extraction is commonly achieved using organic solvents, such as diethyl ether or dichloromethane. However, organic solvent extractions can suffer from low recovery, imprecise recovery, or incomplete removal of assay interference. Here, we describe validations of a simple protocol to extract steroids (e.g., dehydroepiandrosterone, corticosterone, and estradiol) from avian plasma, serum, and brain tissue using solid phase extraction (SPE) with commercially available C18 columns. We compare various methods for (1) eluting steroids from columns, (2) drying eluates, and (3) resuspending dried eluates prior to RIA. The SPE method yields high and consistent recoveries. The SPE method also effectively separates steroids from interfering substances, even when extracting steroids from lipid-rich plasma and brain tissue. These data indicate that SPE is superior to organic solvent extraction on several measures. SPE should be broadly useful for extracting steroids from plasma or tissue samples.

Determinants of within- and among-clutch variation in yolk corticosterone in the European starling.

Maternal glucocorticoids are known to affect offspring phenotype in numerous vertebrate taxa. In birds, the maternal transfer of corticosterone to eggs was recently proposed as a hormonal mechanism by which offspring phenotype is matched to the relative quality of the maternal environment. However, current hypotheses lack supporting information on both intra- and inter-clutch variation in yolk corticosterone for wild birds. As such, we examined variation in yolk corticosterone levels in a wild population of European starlings (Sturnus vulgaris). Maternal condition, clutch size and nesting density were all negatively related to yolk corticosterone deposition; females with high condition indices, those laying larger clutches and those nesting in high-density associations deposited lower amounts of the hormone into eggs than those with low condition indices, laying small clutches and nesting in isolation. Alternatively, we found no effects of maternal age or human disturbance on yolk corticosterone deposition. Intra-clutch variation of yolk corticosterone was significant, with levels increasing across the laying sequence in all clutch sizes examined, with the difference between first and last-laid eggs being greater in large versus small clutches. Given the reported effects of yolk corticosterone on offspring size and growth, intra-clutch variation in yolk corticosterone has the potential to alter the competitive environment within a brood. Furthermore, our results indicate that variation in yolk corticosterone can originate from variation in both the mother's quality as well as the quality of her breeding environment. The presence of inter-female variation in particular is an important pre-requisite in testing whether the exposure of offspring to maternally-derived corticosterone is a mechanistic link between offspring phenotypic plasticity and maternal quality.

Male and female prolactin receptor mRNA expression in the brain of a biparental and a uniparental hamster, phodopus, before and after the birth of a litter.

Prolactin receptor (PRL-R) mRNA transcript level was quantified in the choroid plexus (ChP) of a naturally biparental hamster, Phodopus campbelli, and its otherwise similar, yet nonpaternal, sibling species, Phodopus sungorus. Pair-housed males and females on the day before the birth of their first litter (G17), the day after birth (L1), lactation day 5 (L5), and unpaired animals that were sexually naïve, were tested. PRL-R mRNA transcript level relative to total RNA, was evaluated by reverse transcriptase-polymerase chain reaction using primers common to the long- and short-form of the PRL-R in Phodopus. In the ChP, a region implicated in prolactin transport into the central nervous system, females had the expected increase in PRL-R mRNA transcript from dioestrus to L5, consistent with known actions of prolactin. As predicted, males and females of the biparental species were similar, although PRL-R mRNA in naive males was higher than in dioestrus females. Males of the two species also differed as predicted. PRL-R mRNA transcript levels were higher in the biparental males. In addition, P. campbelli males had low PRL-R mRNA at G17 compared to L5. By contrast, non-paternal P. sungorus males had elevated PRL-R mRNA transcript levels on G17 relative to unpaired males. We conclude that PRL-R mRNA in the ChP is differentially regulated before and after birth in a paternal and a nonpaternal male.

Photoperiodic control of oestrous cycles in Syrian hamsters: mediation by the mediobasal hypothalamus.

To assess whether the mediobasal hypothalamus (MBH) is necessary for photoperiodic control of oestrous cycles and prolactin secretion, we tested intact female Syrian hamsters (controls) and those that had sustained unilateral or bilateral lesions of the MBH. All hamsters displayed 4-day oestrous cycles postoperatively in the long-day photoperiod (14 h light/day); control females and those with unilateral MBH damage ceased to undergo oestrous cycles approximately 8 weeks after transfer to a short-day photocycle (10 h light/day), whereas 12 of 15 females with bilateral MBH lesions continued to generate 4-day oestrous cycles throughout 22 weeks in short days. Serum prolactin concentrations were either undetectable or low in all hamsters 8 or 14 weeks after the transfer to short-day lengths, but increased above long-day baseline values by week 22. We conclude that melatonin-binding sites in the MBH mediate suppression of oestrous cycles but not prolactin secretion by short-day lengths; recovery of prolactin secretion in females during prolonged exposure to short-day lengths reflects development of refractoriness to melatonin in a substrate distinct from the MBH. These findings suggest that separate neural pathways mediate photoperiodic control of gonadotropin and prolactin secretion in female hamsters.

Photorefractoriness of immune function in male Siberian hamsters (Phodopus sungorus).

Short days induce multiple changes in reproductive and immune function in Siberian hamsters. Short-day reproductive inhibition in this species is regulated by an endogenous timing mechanism; after approximately 20 weeks in short days, neuroendocrine refractoriness to short-day patterns of melatonin develops, triggering spontaneous recrudescence of the reproductive system. It is unknown whether analogous mechanisms control immune function, or if photoperiodic changes in immune function are masked by prevailing photoperiod. In Experiment 1, 3 weeks of exposure to long days was not sufficient to induce long-day-like enhancement of in vitro lymphocyte proliferation in short-day adapted male Siberian hamsters. Experiment 2 tested the hypothesis that immunological photorefractoriness is induced by prolonged exposure to short days. Adult male hamsters were gonadectomized or sham-gonadectomized and housed in long (14 h light/day) or short (10 h light/day) photoperiods for 12, 32 or 40 weeks. Somatic and reproductive regression occurred after 12 weeks in short days, and spontaneous recrudescence was complete after 32-40 weeks in short days, indicative of somatic and reproductive photorefractoriness. In gonad-intact hamsters, 12 weeks of exposure to short days decreased the number of circulating granulocytes and increased the number of B-like lymphocytes. After 32 weeks in short days, these measures were restored to long-day values, indicative of photorefractoriness; castration eliminated these effects of photoperiod. In both intact and castrated hamsters, in vitro proliferation of splenic lymphocytes was inhibited by 12 weeks of exposure to short days. After 40 weeks in short days lymphocyte proliferation was restored to long-day values in intact hamsters, but remained suppressed in castrated hamsters. These results suggest that short-day-induced inhibition of lymphocyte function does not depend on gonadal regression, but that spontaneous recrudescence of this measure is dependent on gonadal recrudescence. In Experiment 3, in vitro treatment with melatonin enhanced basal proliferation of lymphocytes from male hamsters exposed to short days for 12 weeks, but had no effect on lymphocytes of photorefractory hamsters or long-day control hamsters. Lymphocytes of castrated hamsters were unresponsive to in vitro melatonin, suggesting that photoperiodic changes in gonadal hormone secretion may be required to activate mechanisms which permit differential responsiveness to melatonin depending on phase in the annual reproductive cycle. Together, these data indicate that, similar to the reproductive system, the immune system of male Siberian hamsters exhibits refractoriness to short days.

Hormonal changes in mammalian fathers.

Known and hypothesized relationships between steroid (estradiol, testosterone, and cortisol) and peptide (oxytocin, vasopressin, and prolactin) hormones and the expression of mammalian paternal behavior are reviewed. Emphasis is placed on newly emerging animal models, including nonhuman primates and men, with elaborate paternal behavior repertoires. Currently available data are broadly consistent with a working hypothesis that the expression of parental behavior will involve homologous neuroendocrine circuits in male and females. Understanding the neuroendocrinology of paternal behavior is an emerging research opportunity in behavioral neuroscience.

Evolutionary biology of plant defenses against herbivory and their predictive implications for endocrine disruptor susceptibility in vertebrates.

Hormone disruption is a major, underappreciated component of the plant chemical arsenal, and the historical coevolution between hormone-disrupting plants and herbivores will have both increased the susceptibility of carnivores and diversified the sensitivities of herbivores to man-made endocrine disruptors. Here I review diverse evidence of the influence of plant secondary compounds on vertebrate reproduction, including human reproduction. Three of the testable hypotheses about the evolutionary responses of vertebrate herbivores to hormone-disrupting challenges from their diet are developed. Specifically, the hypotheses are that a) vertebrate herbivores will express steroid hormone receptors in the buccal cavity and/or the vomeronasal organ; b) absolute sex steroid concentrations will be lower in carnivores than in herbivores; and c) herbivore steroid receptors should be more diverse in their binding affinities than carnivore lineages. The argument developed in this review, if empirically validated by support for the specific hypotheses, suggests that a) carnivores will be more susceptible than herbivores to endocrine-disrupting compounds of anthropogenic origin entering their bodies, and b) diverse herbivore lineages will be variably susceptible to any given natural or synthetic contaminant. As screening methods for hormone-disrupting potential are compared and adopted, comparative endocrine physiology research is urgently needed to develop models that predict the broad applicability of those screening results in diverse vertebrate species.

Changes in testosterone, cortisol, and estradiol levels in men becoming fathers.

OBJECTIVE: To quantify longitudinally steroid hormone (testosterone, cortisol, and estradiol) concentrations in men becoming fathers for the first time ("dads"). SUBJECTS AND METHODS: Volunteer study subjects were recruited from first-trimester prenatal classes in Kingston, Ontario, in February 1999. Twenty-three dads provided saliva samples from recruitment through 3 months after the birth of their children. Fourteen men who were not fathers were recruited from the general population to serve as age-matched controls for season and time of day. Estradiol, testosterone, and cortisol levels were quantified. RESULTS: After controlling for effects of time of day and season, dads had lower mean +/- SE testosterone (6.5+/-0.7 vs 10.0+/-0.9 ng/dL; P<.005) and cortisol (morning values, 0.30+/-0.05 vs 0.53+/-0.05 microg/dL; P<.005) concentrations, a higher proportion of samples with detectable estradiol concentrations (68% [308/454] vs 57% [87/154]; P=.01), and higher estradiol concentrations in those detectable samples (3.81+/-0.09 pg/mL [13 dads] vs 3.26+/-0.11 pg/mL [9 controls]; P<.002) than did control men. Within 10 individual dads with frequent samples before and after the birth, the percentage of samples with detectable estradiol was lower during the month before the birth than during the month after (51% vs 71%; P=.02), and cortisol concentration was increased in the week before the birth (to a mean of 0.16 microg/dL). In each of 13 dads providing frequent samples, testosterone concentration and variance were low immediately after the birth (no change from previous levels in 5, decrease after prebirth increase in 3, and decrease relative to all other times in 5). CONCLUSIONS: In this population of Canadian volunteers attending prenatal classes, expectant fathers had lower testosterone and cortisol levels and a higher proportion of samples with detectable estradiol concentrations than control subjects. Individual patterns of testosterone variance relative to the birth and estradiol and cortisol concentrations immediately before the birth may be worthy of further investigation. The physiologic importance of these hormonal changes, if any, is not known. However, they are hormones known to influence maternal behavior.

Cortisol and prolactin concentrations during repeated blood sample collection from freely moving, mouse-sized mammals (Phodopus spp.).

BACKGROUND AND PURPOSE: Validation of a method for obtaining blood samples that does not change cortisol or prolactin concentrations yet allows serial blood samples to be collected from animals under anesthesia, without prior handling, from freely interacting social groups of small mammals. METHODS: Results from five experiments are reported. Male dwarf hamsters (Phodopus spp.) were housed in modified home cages under continuous flow of compressed air that could be switched to isoflurane in O2 vehicle without approaching the cages. RESULTS: Dwarf hamsters respond to manual restraint with behavioral distress and increase in the concentration of the dominant glucocorticoid, cortisol, and decrease in prolactin concentration. Both effects are evident within one minute. In contrast, when this new method was used, neither cortisol nor prolactin changed in response to repeated sample collection (up to 8 successive samples at 2 hour intervals), prolonged isoflurane exposure, or substantial blood volume reduction (30%). Prolactin concentration was suppressed and cortisol concentration was increased in response to stimuli from other hamsters tested without anesthesia. Suppression of prolactin concentration was graded in response to the degree of stress and equaled the pharmacologic reduction caused by bromocryptine mesylate (50 microg of CB154 x 3 days). CONCLUSIONS: The technique is superior to alternatives for studies of behavioral endocrinology of freely interacting small mammals.

Fathers, fat, and maternal energetics in a biparental hamster: paternal presence determines the outcome of a current reproductive effort and adipose tissue limits subsequent reproductive effort.

Djungarian hamster females, Phodopus campbelli, are severely constrained in their ability to reproduce successfully and lose 20% of their body weight by the time pups are weaned. In the wild and in the laboratory, biparental care improves maternal reproductive success. Two experiments quantified the effects of paternal presence and partial lipectomy [surgical depletion of parametrial white adipose tissue (PWAT) on day 8 of the 18-day gestation] on maternal energy balance, reproductive success, and investment in a subsequent reproductive attempt. Paired females reproduced successfully, maintained body weight, and invested in a second litter. Removal of the male decreased pup survival, growth, and readiness for dispersal by 18 days of age. Solitary females lost 10% of their body weight by the birth and a further 10% by day 18 after the birth. Thus, paternal presence balanced maternal energy budgets during reproduction and prevented a 20% loss in body weight. Equivalent weight loss occurs in response to other maternal stressors, therefore 20% may be the maximum tolerable weight loss in this species. Fresh weight of interscapular brown adipose tissue was predicted by the extent of maternal hyperthermia but not by maternal energy balance or lipectomy. Partial lipectomy did not adversely affect the female or the first litter but decreased the probability of investment in a second reproductive attempt and halved the size of the second litter. This effect may have been due to the 0.1% of body weight amount of lipid removed or may reflect a specialized role for PWAT in adjusting maternal investment.

Paternal hamsters mechanically assist the delivery, consume amniotic fluid and placenta, remove fetal membranes, and provide parental care during the birth process.

We report the first description of a male mammal behaviorally participating in the birth of his young. Djungarian hamsters, Phodopus campbelli, are naturally biparental and males contribute to pup survival and growth through direct paternal care and indirect effects on maternal physiology. Males of the closely related Siberian hamster, P. sungorus, have only seasonal opportunities to interact with pups and neither contribute to pup survival and growth nor provide extensive paternal care under laboratory conditions. Male P. campbelli undergo a series of hormonal changes prior to the birth of their first litter which are not shared with P. sungorus males and may "prime" males to express paternal behavior. We hypothesized that P. campbelli males would behave paternally on first contact with pups during the birth process, whereas P. sungorus males would not. In addition to showing paternal behavior toward neonates, male P. campbelli licked amniotic fluid before the birth, mechanically assisted the delivery, opened an airway by clearing the nostrils (so that pups flushed red with oxygenation), licked and sniffed pups in the moments and minutes after birth to clean the pups of membranes, and ate the placenta. None of these behaviors were observed in P. sungorus. We anticipate that P. campbelli will not be the only species with highly developed paternal behavioral repertoires during the birth.

Divergent reproductive endocrinology of the estrous cycle and pregnancy in dwarf hamsters (phodopus).

Progesterone (P4) and prolactin (PRL) in peripheral circulation of Siberian hamsters (Phodopus sungorus) throughout an estrous cycle and pregnancy were determined by repeated, small volume sampling from individuals housed in modified home cages. As predicted, the endocrinology of P. sungorus reproduction is similar to the rat, mouse and golden hamster and shows none of the eight distinctive features known for Djungarian hamsters (Phodopus campbelli). Specifically, in P. sungorus there is no evidence for resumption of pituitary PRL surges in late pregnancy, P4 concentrations during the differentiation of the corpus luteum on day 2 of pregnancy are higher (as opposed to lower) than concentrations on the comparable day of an unmated estrous cycle (diestrus 1), P4 concentrations increase throughout pregnancy, PRL surges are common during the estrous cycle, including a reliable surge on proestrus, and P4 plays an important role in facilitating the expression of behavioral receptivity. We conclude that 'novel' P. campbelli reproductive endocrinology has evolved since a common ancestor was shared with P. sungorus. With a time frame (the available time since the divergence of the two species) and an ecological context (known niches and behavior in the wild) these species offer the opportunity to study endocrinological evolution in progress.

Hormonal changes in males of a naturally biparental and a uniparental mammal.

Blood samples from male hamsters (Phodopus) during their mate's gestation and early lactation show that key hormones important in maternal behavior are also changing in males and differ for two closely related species with different levels of paternal care. Results of study 1 were consistent with a relationship between higher prolactin, lower testosterone and paternal behavior during early lactation in P. campbelli and provided no evidence for similar hormonal changes in P. sungorus. Study 2 sampled males before or after the birth. Prolactin did not increase until at least one day after the birth in P. campbelli but was high at the end of the pregnancy in P. sungorus. Increasing testosterone concentrations in P. campbelli as the birth approached were consistent with mate guarding, high testosterone concentrations on L5 were consistent with paternal aggression in defense of the litter, and the drop in testosterone after the birth was consistent with reduced aggression toward the new pups. Results confirmed that cortisol concentrations were reduced following the establishment of a pair-bond and found that P. campbelli males had elevated cortisol before the birth. Results support the hypothesis that mammalian paternal behavior has a hormonal basis which is analogous to maternal behavior.

Maternal and pup contributions to different patterns of pup growth in Phodopus species.

A cross-fostering approach was used to compare and quantify patterns of pup growth in Phodopus sungorus and P. campbelli. Standard litters of five pups were reared by a foster mother of the same or the opposite species. Individual pups were weighed daily, and maternal and pup body condition were quantified. Studies were conducted at an ambient temperature of 23 degrees C, which constrains maternal contact with pups in P. campbelli but not P. sungorus, to maximize the difference in pup growth curves between the species. Results confirmed that the similar Day 18 weights in the two species of Phodopus were a complex result of laboratory conditions that masked different patterns of pup growth. The primary determinants of that pup growth were 1) constraints on maternal investment by P. campbelli mothers, which arose from the thermoregulatory stresses of a 23 degrees C ambient temperature and may have involved different milk energetic value or water content; 2) an intrinsic pup difference in the threshold weight for independent thermoregulation, which increased energetic expenditures for P. sungorus pups several days earlier than for P. campbelli pups; and 3) a longer lactation in P. campbelli, which improved access to dry food. Results also confirmed that within-litter variation in pup weights was considerably larger in P. campbelli, but forced rejection of the hypothesis that the difference arose from different maternal investment strategies during lactation. Species-typical patterns of variation were already established on Day 1 after birth.