Rank dependent seasonal levels of IGF-1, cortisol and reproductive hormones in male pudu (Pudu puda)

Insulin-like growth factor 1 and the hormonal mediation of sibling rivalry

In altricial animals, young are completely dependent on parents for provisioning. The ability to outcompete siblings to receive parental provisioning has clear fitness benefits, and may be mediated by hormones that influence growth. We analyzed the effects of insulin-like growth factor 1 (IGF-1) on body size, growth, and sibling rivalry in eastern bluebirds (Sialia sialis). To determine whether IGF-1 is upregulated in response to the competitive environment, we manipulated brood sizes and examined the effect on IGF-1 levels, nestling body size, growth rate, and behavior. In a separate experiment, we injected nestlings with exogenous IGF-1 to study its impacts on body size, growth rate, and sibling competition. Brood size manipulation did not influence endogenous IGF-1 levels, but male nestlings with higher IGF-1 levels early in the nestling period tended to have greater mass gain than males with lower IGF-1 levels. Nestlings with higher IGF-1 levels also tended to be fed more frequently by parents. In the injection experiment, IGF-1 injected individuals tended to be heavier than vehicle injected young by the end of the nestling period, which suggests that IGF-1 can influence mass gain in bluebirds. IGF-1 has been proposed to be a mediator of life-history strategies and post-hatching behavior. Our results suggest that although bluebird nestlings do not adaptively elevate IGF-1 in response to the presence or number of siblings, IGF-1 may influence growth during the nestling period. These findings shed light on sibling competition, life history strategies, and the hormones that underlie them.

Physiological Regulation of Growth during Social Ascension in a Group-Living Fish

In social groups, dominant animals typically are larger and have better access to resources than subordinates. When subordinates are given the opportunity to ascend to a dominant position, they will elevate their rates of growth to help secure dominance. This study investigated the physiological mechanisms facilitating this increased growth. Using the group-living cichlid, Neolamprologus pulcher, we investigated whether the insulin-like growth factor (IGF) system-a key regulator of growth-is involved in the regulation of growth during social ascension. We also assessed differences in energy storage and expenditure among dominant, subordinate, and ascending males to determine the energetic costs associated with ascension. Daily growth rates tripled during ascension, and ascending males expended more energy after ascension, owing to higher rates of energetically costly social behaviors, increased locomotor activity, and larger home ranges. Ascenders did not increase food intake to offset increasing energetic costs but had half the liver glycogen energy stores of subordinates. Together, these results indicate a reliance on stockpiled energy reserves to fuel the high energetic demands associated with ascension. Transcript abundance of IGF binding proteins 1 (igfbp1) and 2a (igfbp2a) were low in ascenders relative to subordinates, suggesting a higher capacity for growth during ascension through increased bioavailability of circulating IGF-1. Our findings provide clear evidence of the energetic costs of social ascension and offer novel insight into the physiological mechanisms modulating the social regulation of growth.

Motile Sperm Output by Male Cheetahs (Acinonyx jubatus) Managed Ex Situ Is Influenced by Public Exposure and Number of Care-Givers

The collective cheetah (Acinonyx jubatus) population in zoological institutions has never been self-sustaining because of challenges in natural reproduction. A retrospective analysis of North American zoo-breeding records has revealed that >90% of litters produced since 2003 occurred in facilities ‘off-display’ from the public. We examined seminal, endocrine, and behavioral traits of 29 adult male cheetahs that were: 1) managed in public exhibit or off-display facilities; 2) maintained by different numbers of cheetah-specific care-givers; and 3) living adjacent to varying numbers of adult conspecifics. Cheetahs housed off-display produced more total motile sperm/ejaculate (P = 0.04) than on-exhibit males. This finding was mirrored in our laboratory’s historical records where two-fold more total motile sperm (P < 0.01) were measured in ejaculates from individuals with no public exposure (n = 43) compared to on-exhibit (n = 116) counterparts. Males at institutions with ≤3 care-givers also produced more total motile sperm/ejaculate (P < 0.03) and spent more time behaviorally active (P < 0.01) than at facilities using >3 care-givers. Exposure to high numbers of conspecifics within the same institution did not impact (P > 0.05) seminal traits, and presence of the public, care-giver number, or animals/facility had no influence (P > 0.05) on androgen or glucocorticoid excretion or other behavioral metrics. Findings indicate that male cheetahs are sensitive to general public exposure and too many care-givers, resulting in compromised motile sperm output/ejaculate with mechanism of action unrelated to altered androgen or glucocorticoid excretion.

Sex, Sport, IGF-1 and the Community Effect in Height Hypothesis

We test the hypothesis that differences in social status between groups of people within a population may induce variation in insulin-like growth factor-1(IGF-1) levels and, by extension, growth in height. This is called the community effect in height hypothesis. The relationship between IGF-1, assessed via finger-prick dried blood spot, and elite level sport competition outcomes were analysed for a sample of 116 undergraduate men and women. There was a statistically significant difference between winners and losers of a competition. Winners, as a group, had higher average pre-game and post-game IGF-1 levels than losers. We proposed this type of difference as a proxy for social dominance. We found no evidence that winners increased in IGF-1 levels over losers or that members of the same team were more similar in IGF-1 levels than they were to players from other teams. These findings provide limited support toward the community effect in height hypothesis. The findings are discussed in relation to the action of the growth hormone/IGF-1 axis as a transducer of multiple bio-social influences into a coherent signal which allows the growing human to adjust and adapt to local ecological conditions.

Evidence of higher levels of testosterone during the velvet period in muntjac than in other cervids

Previous studies have shown that despite having a clear seasonal fluctuation in fecal testosterone concentration, the significantly lower testosterone levels found in velvet stags of the nonseasonal breeder muntjac (Muntiacus sp.) apparently did not stop their spermatogenesis as in other deer species. In the present study, in vitro cultivated Leydig cells isolated from adult stags of three native deer species of Taiwan were treated with androstenedione, with or without adding human chorionic gonadotropin. Results showed that, unlike the two seasonal breeders, sika deer (Cervus nippon) and sambar deer (Rusa unicolor), Leydig cells of velvet muntjac had no dramatic reduction in or even maintained the full capability of their testosterone productivity compared with the hard-antlered stage. The decrease in fecal testosterone level observed earlier in muntjac during the velvet period was probably due to a reduction of number of Leydig cells. These results support the hypothesis that testosterone production in muntjac during its velvet period might never be low enough to trigger the quiescent phase of the reproduction cycle.

Photo-induced toxicity of four polycyclic aromatic hydrocarbons (PAHs) to embryos and larvae of the carpet shell clam Ruditapes decussatus

In this work, we assessed the photo-toxicity of four polycyclic aromatic hydrocarbons (PAHs) to embryos and larvae of the European clam Ruditapes decussatus. The exposure of R. decussatus embryos (24 h) and larvae (96 h) to anthracene, fluoranthene, pyrene and benzo[a]pyrene resulted in reduction of normal D-veliger percentages and high larval mortality, both in darkness and under sunlight conditions. Based on the calculated EC(50) and LC(50) values, the toxicity of the forementioned PAHs was respectively enhanced 72, 35, 60 and 23 times in the embryotoxicity test and 32, 31, 12 and 61 times in the larval mortality test when exposures were performed under sunlight conditions. Simultaneous exposure to sunlight and these PAHs enhanced their toxicity in comparison to dark conditions. The clam embryos and larvae appear to be environmentally relevant life-stages in assessing the toxic and photo-toxic risk of PAHs that enter the marine environment.

Anatomical study of the gastrointestinal tract of a pudu (Pudu puda) using contrast-enhanced abdominal computed tomography

The pudu (Pudu puda), which is the smallest deer in the world and inhabits central and southern Chile and Argentina, is a ruminant and a browsing herbivore. The aim of this study was to provide a reference for interpretation of the normal anatomy of the pudu's gastrointestinal tract as imaged by abdominal computed tomography (CT). For the study, one adult female pudu was used. After a 24-h fast, the pudu was anaesthetized and positioned in sternal recumbency at the CT table. Image acquisition began immediately after intravenous injection of contrast media (MD-76(®); 370 mgI/ml) into the cephalic vein. Injection of contrast material was administered as a biphasic protocol. First, a manual bolus of contrast material was injected at a rate of 4 ml/s. Then, an additional continuous infusion injection (0.1 ml/min) was performed for adequate opacification of vascular structures. Transverse images of 5 mm thickness and 5 mm interval were obtained with a fourth-generation CT scanner, from the ninth thoracic vertebra (T9) until the first sacral (S1) vertebrae. CT images were labelled and compared with anatomical reference images for ruminants. Structures that were identified in the abdominal cavity included the stomach with its four compartments (rumen, reticulum, omasum and abomasum), the small and large intestines, liver, spleen, kidneys and some major blood vessels (aorta, caudal vena cava). The distal loop of the ascending colon, the transverse colon, the pancreas and lymph nodes could not be identified. The resulting CT images provide a reference for normal cross-sectional abdominal anatomy of the adult pudu.

Assessment of dominance hierarchy through urine scent marking and its chemical constituents in male blackbuck Antelope cervicapra, a critically endangered species

In ungulates the process of chemical communication by urinary scent marking has been directly related to reproductive dominance, territorial defense and proximity to resources. The differences in the frequency of urine marking and chemical composition of urine of males Antelope cervicapra before, during and after the dominance hierarchy period were assessed. The variations in the urine marking and its chemical profiles of dominant males (n=9), bachelors (n=5) and sub-adult males (n=5) were compared to find out how the dominance hierarchy influences the confined blackbuck herd under semi-natural captive conditions. The frequency of urine marking is significantly higher (p<0.001) in dominant males. Twenty-eight major constituents were identified in the urine of dominant males (before, during and after the dominance hierarchy period), bachelor and sub-adult males. Among these, three specific compounds namely, 3-hexanone (I), 6-methyl-5-hepten-2-one (II) and 4-methyl-3-heptanone (III) were seen only in dominant males urine during the dominance hierarchy period. Based on the behavioural observation and the unique chemical constituents in the urine, it is concluded that the dominant male scent odor suppresses aggression, scent marking, scent production and territorial patrolling activities of subordinate males, through which the dominant male establish their hierarchy and attains success in reproduction.

Testosterone, but not IGF-1, LH, prolactin or cortisol, may serve as antler-stimulating hormone in red deer stags (Cervus elaphus)

The role of androgens and insulin-like growth factor 1 (IGF-1) in antler growth has been disputed. We predicted that the secretory of IGF-1 may be associated with an acceleration of body growth rather than with antler growth. Furthermore we anticipated a relationship between the increase of testosterone and the progress of antler growth. If IGF-1 is involved in the stimulation of antler growth, this should be more obvious in young than in mature stags. Eight two-year-old red deer stags (Cervus elaphus), and twelve adult red deer stags were blood sampled and the length of their velvet antlers was measured in one-week intervals during the period of antler growth. Concentrations of testosterone, cortisol, IGF-1, luteinizing hormone (LH), and prolactin were determined in plasma by enzyme immunoassay or radioimmunoassay. Antler growth per day was primarily dependent on changes in testosterone concentration per day in both groups of stags. As expected, only in two-year-old stags we detected a possible role of IGF-1 in the antler growth regulation, but that was not in agreement with previously published studies. Nevertheless, this effect was still utilized in interaction with testosterone. In addition to total antler length, only concentrations of testosterone and LH were significantly higher in adult males in comparison to two-year-old males. Our present results lead us to conclude that it is not IGF-1 but testosterone which is responsible for the intensity of antler growth in subadult and adult red deer stags.

Seasonal glucocorticoid responses to capture in wild free-living mammals

We determined baseline and capture-induced glucocorticoid concentrations during two different seasons in three species of wild free-living rodents: brown lemmings ( Lemmus trimucronatus), golden-mantled ground squirrels ( Spermophilus saturatus), and yellow-pine chipmunks ( Tamias amoenus). Initial blood samples were obtained within 3 min of capture, so that initial glucocorticoid levels reflect baseline titers of undisturbed animals. Animals were held for an additional 30 min, when a second blood sample was taken to measure stress-induced glucocorticoid titers. The primary glucocorticoid differed in each species. Lemmings secreted extremely large amounts of corticosterone (as high as 8,000 ng/ml). These high concentrations were accompanied by high corticosterone-binding globulin capacity and resistance to negative feedback. Squirrels and chipmunks secreted a mixture of cortisol and corticosterone (10–400 ng/ml). In males of all three species and female squirrels and chipmunks, glucocorticoid levels were significantly elevated 30 min after capture. Baseline and 30-min glucocorticoid levels differed seasonally in each species. Levels were higher during summer (with no snow cover) than in spring (with ∼60% snow cover) in female lemmings, higher during breeding than before hibernation in squirrels, and higher postreproductively than during breeding in chipmunks. Together, these data indicate that glucocorticoid responses to stress in these free-living species are similar to those in laboratory species, but the magnitude of the response appears to depend on life-history features specific to each species.

Photoinduced toxicity of selected PAHs to the marine microalga Phaeodactylum tricornutum

In this study, the effects of different concentrations of pyrene, phenanthrene, fluoranthene, and chrysene within the solubility limits of the chemicals on marine microalgal species of Phaeodactylum tricornutum were examined under UV-A and UV-B lights by application of batch toxicity tests. The algal species were also exposed to the individual PAHs under cool-white fluorescent bulbs in the same laboratory conditions in order to compare the results with the responses of UV-exposed organisms. EC50 values calculated with the trimmed Spearman Karber method demonstrate that the UV light dramatically enhances the toxicity of the selected model PAHs. In most cases, the magnitude of increase in PAH toxicity was directly related to the concentration of individual PAHs and the duration of UV-lighting.

Effects of environmental conditions, human activity, reproduction, antler cycle and grouping on fecal glucocorticoids of free-ranging Pampas deer stags (Ozotoceros bezoarticus bezoarticus)

In this study, a commercial enzyme immunoassay (EIA) was validated in detecting glucocorticoids in Pampas deer feces, in order to investigate the influence of several factors on the adrenocortical function. Fecal samples, behavioral data and information concerning male grouping and antlers status were collected at a monthly basis during a 1 year period from free-ranging stags living at Emas National Park, Brazil (18 degrees S/52 degrees W). The results revealed that concentrations of fecal glucocorticoids in winter were significantly higher than those corresponding to spring and summer. In addition, dry season data presented higher levels than during the wet season. Significant difference was found between fecal levels of breeding stags in summer and nonbreeding stags, whereas no difference was observed between breeding stags in winter and nonbreeding stags. On the other hand, males from areas with frequent human disturbance exhibited higher glucocorticoid concentrations and flight distances than individuals from areas of lower human activity. Males with antlers in velvet had elevated levels compared with animals in hard antler or antler casting. Also, we found that glucocorticoid levels were higher in groups with three or more males than in groups with only one male. The flight distances showed positive correlation with fecal glucocorticoid. These data indicate that fecal glucocorticoid provides a useful approach in the evaluation of physiological effects of environment, inter-individuals relationship and human-induced stressors on free-ranging Pampas deer stags.

Seasonal changes in plasma glucocorticoid concentrations in free-living vertebrates

The vertebrate stress response helps animals respond to environmental dangers such as predators or storms. An important component of the stress response is glucocorticoid (GC) release, resulting from activation of the hypothalamic-pituitary-adrenal axis. After release, GCs induce a variety of behavioral and physiological changes that presumably help the animal respond appropriately to the situation. Consequently, GC secretion is often considered an obligatory response to stressful situations. Evidence now indicates, however, that free-living species from many taxa can seasonally modulate GC release. In other words, the magnitudes of both unstressed and stressed GC concentrations change depending upon the time of year. This review examines the growing evidence that GC concentrations in free-living reptiles, amphibians, and birds, but not mammals, are commonly elevated during the breeding season. This evidence is then used to test three hypotheses with different focuses on GC's energetic or behavioral effects, as well as on GC's role in preparing the animal for subsequent stressors. These hypotheses attempt to place annual GC rhythms into a physiological or behavioral context. Integrating seasonal differences in GC concentrations with either different physiological states or different life history stages provides clues to a new understanding of how GCs actually help in survival during stress. Consequently, understanding seasonal modulation of GC release has far-reaching importance for both the physiology of the stress response and the short-term survival of individual animals.

Concentrations of insulin-like growth factor-I in adult male white-tailed deer (Odocoileus virginianus): associations with serum testosterone, morphometrics and age during and after the breeding season

Our understanding of insulin-like growth factor-I (IGF-I) in cervids has been limited mostly to its effects on antler development in red deer (Cervus elaphus), roe deer (Capreolus capreolus), fallow deer (Dama dama), and pudu (Pudu puda). Although IGF-I has been found to play a critical role in reproductive function of other mammals, its role in reproduction of deer is unknown. The objectives of the present study were to determine if serum levels of IGF-I change during the breeding season, assess whether age influences serum IGF-I, compare levels of IGF-I measured during and following the breeding season, and determine if IGF-I is associated with body and antler characteristics in free-ranging adult, male white-tailed deer (Odocoileus virginianus). We collected serum and morphometric data from hunter-harvested and captured white-tailed deer to investigate these objectives. Mean level of serum IGF-I during the breeding season was 63.6 ng/ml and was greatest in deer between 2.5 and 5.5 years old (57.4-79.9 ng/ml). Levels of serum IGF-I decreased by approximately 40% as the breeding season progressed, but levels were less in deer following the breeding season (34.6 ng/ml). Both body and antler size were associated positively with IGF-I when controlling for age. Serum testosterone was also associated positively with IGF-I. Levels of serum testosterone during the breeding season generally increased with age from 4.82 (1.5 years old) to 18.79 ng/dl (5.5 years old), but decreased thereafter. These data suggest that IGF-I may be an important hormone in breeding, male white-tailed deer.