Gurion University of the Negev; amidors@bgu.ac.il Does dietary protein limit mass gain in migrating blackcaps refueling at stopovers? Both fat and protein are used by birds as fuel during migratory flight, and need to be restored at stopovers. Mass gain is initially slow but increases after 2-3 days into the stopover. One explanation for this is the catabolism of digestive tract tissue (GIT), which causes reduced digestive function and hence slow body mass gain. We tested the prediction that

more »

... tary protein limits a bird's readiness to leave a stopover because it affects the rate at which the GIT is rebuilt, and, thereby, the rate of tissue accumulation. We measured body mass, pectoral muscle size, and body composition (by dual energy x-ray absorptiometry). Thirty migrating blackcaps (Sylvia atricapilla) were mist-netted and divided into three equal groups. The birds were deprived of food for 24 hours to assure stopover behavior. The groups were then provided semisynthetic diets, that differed only in protein content (i.e. 3%, 5.3% and 10%), and water ad libitum during the 6 day experiment. Mean daily food intake differed significantly among groups (Holm-Sidak multiple comparison F (2,172) = 4.103, p=0.018). Body mass changed differently over time among the groups (-0.13±0.08 g/d, -0.10±0.16 g/d, 0.01±0.26; RM ANOVA, time*group: F (12,168) =3.08, p<0.0006; for 3, 5.3, and 10%, respectively) as did pectoral muscle size (RM ANOVA time*group: F (12, 168) =2.11, p<0.05). There were no significant differences in the change of fat fraction from day 1 to day 7 between the groups (ANOVA F (2,6) =0.38, NS). Thus, the data suggest protein may be a limiting dietary factor, and that blackcaps require more protein than that we provided to replace fat used as fuel during migratory flight. P3.187 ABATE, M.E.*; GRACEY, A.Y.; MALAVASI, S.; TORRICELLI, P.; A comparison of brain gene expression from black goby (Gobius niger) females and males with alternate mating phenotypes The black goby (Gobius niger) is a demersal spawning fish with females that deposit their eggs in a sheltered burrow in shallow marine waters. Territorial males provide parental care. Males have accessory sperm duct glands that release sperm trail mucins to enhance sperm longevity. These glands are less developed in small males that invest energy instead into producing relatively large testes for their body size. The difference in male reproductive structure correlates with a difference in male reproductive tactics as small males utilize a sneaker strategy to enter the nest and steal spawns from the territorial male. Hence, the black goby provides a good model for investigating the neurogenetic basis for different mating phenotypes. Mature females and males were collected from the Venetian Lagoon (Northern Adriatic Sea, Italy) during the reproductive season. Brain RNA was extracted from individual fish and hybridized against a cDNA microarray prepared for the goby Gillichthys mirabilis. A machine learning algorithm was used to identify sets of genes whose expression was associated with the fish. Although gene expression profiles were generally similar between mating phenotypes the algorithm identified a number of genes whose expression was elevated in sneaker males. The top marker gene for sneaker status was Mannose-P-dolichol utilization defect 1 (MPDU1), a gene of unknown function but which may be involved in protein N-glycosylation. These data reveal that changes in mating behavior are linked to transcriptional differences in the brain and the resulting candidate genes may have utility in studies of the regulation and evolution of this trait. P3.61 Elastic mechanisms as a determinant of anuran jumping performance: do toads bounce? Anuran jumping performance varies widely among species. Biomechanical studies have proposed that some of the best jumpers use an elastic mechanism to produce power outputs that exceed available muscle capacity. Most studies of jump power have focused on good jumpers, and it is unclear whether species with less spectacular jumping performance also utilize an elastic mechanism. To better understand the underlying determinants of jumping performance, we used a force plate to quantify power output and takeoff time in Osteopilus septentrionalis (Cuban tree frogs), Rana pipiens (Leopard frogs) and Bufo marinus (Cane toads). Maximal jumps elicited from a large number of trials were analyzed. O. septentrionalis jumps were both the fastest and most powerful (takeoff time 0.0680.005 s, peak power 308.755.8 W kg -1 body mass), followed by R. pipiens (0.1120.008 s, 66.619.2 W kg -1 ), while B. marinus performed the slowest and least powerful jumps (0.1750.03 s, 14.74.3 W kg -1 ). The power output measured for B. marinus corresponds to less than 100 W kg -1 hindlimb muscle mass (16% body mass), well below the power generating capacity of typical Bufo muscle (>200 W kg -1 ). Evidence for an elastic mechanism in B. marinus is also absent in the shape of power profiles during jumping. The asymmetric power profile of O. septentrionalis is indicative of elastic energy storage early in the jump, while B. marinus symmetrical and relatively shallow power curve may indicate a jump powered directly by muscle contraction. R. pipiens power profile is intermediate and may reflect an elastic mechanism less effective than that of O. septentrionalis. These results suggest that variation in anuran jumping ability may be explained in part by variation in the effective use of elastic mechanisms. Supported by NSF grant 642428 to TJR. P3.129 ABDU, R.W.*; ABATE, M.E.; KAUFMAN, L.; Boston University, Massachusetts; abduw@bu.edu A test for the influence of offspring behavior on parental care in the convict cichlid (Archocentrus nigrofasciatus) Heterospecific predators and kidnapping by conspecific alloparents threaten the survival of the fry of the convict cichlid (Archocentrus nigrofasciatus). Parents defend their young by attacking intruders and mouthing their fry to move them to the nest site. Both adults and fledglings get advance warning of the risk of predation when they are exposed to olfactory alarm cue released from the broken skin of conspecifics, and they respond by seeking refuge and with enhanced group cohesion. It is unknown to what extent the fry can influence the level of parental care behavior. We periodically removed fry from their home aquaria and exposed them briefly to either conspecific skin extract or distilled water, and after placing them in rinse containers, returned them to their parents. We measured parental care by recording the parents aggression toward threatening juvenile convicts in a glass container placed near the nest. We tested for fry homing behavior using a mini-flume that exposed the fry to separate plumes of home aquarium water and foreign tank water and recorded how much time the fry spent in each plume for three minutes. We compare the behavior of the parents in the two treatments and examine the relationship of parental aggression and homing behavior to evaluate the influence of offspring behavior on parental care. e191 Poster Abstracts Reproductive and endocrine responses to breeding density in laboratory-housed green anole lizards Previous studies have demonstrated myriad effects of social environment on reproductive physiology, and often these effects are communicated from mother to offspring via hormone exposure. A preliminary study in 2007 suggested that female green anoles lay fewer eggs and have higher corticosterone levels when breeding densities are high. In the present work we follow up and expand upon these results. Breeding females were housed in cages with either one male (low density) or one male and three additional females (high density) to evaluate the effects of breeding density on reproductive effort and plasma and yolk testosterone (T) and corticosterone (CORT) concentrations. All animals were maintained under standard breeding conditions for ten weeks and nest boxes were checked daily for eggs which were frozen for subsequent yolk steroid analyses. Blood samples were collected from all lizards at the end of the study. We found that breeding density had no affect on body condition for either males or females, although body condition declined overall for males. We also found that, consistent with last year, although there was no treatment effect on egg mass, females in low density environments produced significantly more eggs than females in high density environments. Plasma and yolk T and CORT levels will be analyzed by radioimmunoassay to determine how males and females responded hormonally to breeding density and whether females differed in their yolk steroid content as a result of treatment. Such effects, if present, would demonstrate environmental effects on reproductive physiology as well as the opportunity for mothers to communicate information about the environment to their offspring via hormone exposure. P3.114 ADAMS, E. D. M*; LEYS, S. P.; University of Alberta; edadams@ualberta.ca Skin Deep: Examining transepithelial resistance and epithelial morphology in sponges. The phylogenetic position of sponges (Porifera) at the base of the metazoan tree makes them valuable subjects for studying the evolution of animal body plans. Unfortunately, past descriptions of features such as epithelial tissues have been vague in this diverse phylum. Sponges are said to lack true epithelia because tight junctions and basal lamina are absent. However, homoscleromorph sponges have a type IV collagen found in basal lamina and a demosponge was reported to express cell junction molecules such as MAGI and tetraspanin. Further, the recent genome project of Amphimedon queenslandica has revealed the presence of most cell junction molecules. We present evidence of functional sponge epithelia by identifying morphological and physiological similarities between true epithelia and the pinacodern of several sponge species. Ultrastructural descriptions are produced using SEM and TEM preparations of adult and juvenile sponges. Actin labeling is used to highlight organized epithelial architecture and identify points of cell-cell contact. Transepithelial resistance (TER) measurements and the transport of labeled dyes are used to test whether sponge epithelia are leaky or have the ability to seal off a defined internal milieu. This research informs theories on the origin of cell-cell junctions and functional tissue layers within Metazoa. Breeding variation of testosterone in the high latitude Rufous-collared sparrow, Zonotrichia capensis australis In vertebrates, testosterone regulates many aspects of reproductive function. In birds, testosterone is important for sperm production and the development of some secondary sex characteristics, including activation of sexual behavior and territorial aggression. The challenge hypothesis addresses trade-offs between circulating levels of testosterone and male breeding behavior in birds. Two important postulates of the challenge hypothesis are (1) testosterone levels are high during periods of social instability and territory establishment when male-male interactions are common and (2) testosterone levels decrease during the parental phase of breeding if males exhibit substantial parental care. Most tests of the challenge hypothesis have been conducted in northern temperate and arctic birds. Investigations of the Rufous-collared sparrow (Zonotrichia capensis) in Ecuador and Costa Rica show no correlation between testosterone and aggressive behavior, suggesting a decoupling of testosterone and aggression. To further explore this seeming discrepancy, we tested the challenge hypothesis in a subspecies of the Rufous-collared sparrow, Z.c.australis, breeding at high latitude in the southern hemisphere. These results were additionally compared with our previous exploration of testosterone and aggression in the Rufous-collared sparrow at mid-latitudes of the southern hemisphere. P1.155 ALAM, J. L.*; Are the immune systems of tropical birds glucocorticoid resistant? Corticosterone alters immune function, but its effects vary depending on magnitude and duration, immune response characterized, species studied, and environmental context. In a previous study, we found that a cutaneous inflammatory response was not affected by chronically elevated corticosterone in house sparrows (Passer domesticus) from Panama but similar corticosterone elevation in birds from New Jersey (USA) reduced the same immune response. This differential sensitivity to corticosterone, coupled with a more persistent threat of infection in the Panamanian population, led to the hypothesis that tropical birds generally may decouple stress hormones from immune responses to maximize immune defense at all times. To test this hypothesis, we conducted an experiment on different tropical (Kenya) and temperate (Arizona) populations of house sparrows. This time, however, we compared the effects of 30 minutes in a cloth bag on the capacity of plasma to kill gram-negative bacteria (E. coli) to determine whether i) other tropical house sparrows are immunologically resistant to corticosterone; ii) acute (versus chronic) stress differentially affects immune function depending on latitude; and iii) stress affects other components of house sparrow immunity. Corticosterone release in response to the stressor was lower in Kenyan than Arizonan birds, but much less so than in the prior study. Further, bactericidal capacity of blood was not affected by acute stress in either population, and Arizonan sparrows killed almost all bacteria while Kenyan sparrows killed almost none. Collectively these results indicate population differences in immune and endocrine physiology, but not in the manner predicted. Ongoing studies of these and other sparrow populations are testing whether patterns are better explained by invasion history than latitude. Assessing the Fight-or-Flight Response in the Brazilian Free-tailed Bat (Tadarida brasiliensis) Using Heart Rate Telemetry As human populations expand, increased encroachment on natural landscapes and wildlife habitats is likely. We can expect that organisms able to adapt or acclimate to human-altered habitats will have a selective advantage over those unable to do so. One example of a human-altered landscape condition is the increasing availability and use of highway bridges by bats. Evidence from previous research, based on measured levels of the hormone cortisol, suggests that bridge-roosting Brazilian free-tailed bats (Tadarida brasliensis) experience lower levels of stress and are in better overall health than their cave-roosting counterparts. This unexpected result suggests the ability of this species to rapidly acclimate to the potential stressors we observed at highway bridges. Heart rate telemetry allows direct and continuous monitoring of an acute response to a stressor and, thus is ideal for assessing acclimation to repeated stimuli. Heart rate telemetry has been used on several avian and mammalian species; however, its use on small, free-ranging bats has not been tested. In July 2008 we assessed the suitability of heart rate telemetry in the Brazilian free-tailed bat and evaluated the ability of these bats to rapidly acclimate to environmental stressors in a large highway bridge roost. To measure heart rate, a small (0.06 g) custom-made heart rate transmitter was affixed to each bat (~12g) and the signal was recorded on an MP3 recorder, while the bat was in the roost and at the onset of nightly emergence. We subjected lactating females (N=4) to several novel disturbance events (simulated predator) over the course of the experiment (12-36 hours), as well as noted other potentially disturbing stimuli (noise and vibration from passing freight trains) that the roosting bats may experience while roosting in bridge crevices. P2.70 ALUCK, R. J.*; WARD, A. B.; Adelphi University; robertaluck@adelphi.edu Use of contact points during aquatic and terrestrial locomotion in polypteriform fishes Fishes are found in a variety of habitats: from open water to extremely vegetated areas. Highly elongated fishes are often found in structured habitats and appear to use these structures to propel themselves while swimming. Previous studies have shown that limbless lizards and snakes will use contact points in their environment during locomotion. Research on terrestrial locomotion in American eels Anguilla rostrata indicated that eels will move through a field of pegs by pushing against them. In this study, we tested the effects of structure in the environment during aquatic and terrestrial locomotion using two species of polypteriform fishes, the highly elongated Erpetoichthys calabaricus and its close relative, Polypterus senegalus. This research will determine whether there is a relationship between body elongation and the use of contact points in the environment during locomotion. We examined the use of contact points during locomotion using high-speed video of individuals moving through a field of pegs. We found that P. senegalus avoids contact points during swimming, but will use them for forward propulsion during terrestrial locomotion. E. calabaricus, however, uses contact points for forward propulsion during both aquatic and terrestrial locomotion. This work is part of a larger study to understand the evolution of body elongation in fishes in which we assess the effects of habitat on locomotion. Through this work, we will provide a basis for understanding the interplay between habitat and body shape in fishes. P1.117 ALVINE, Chorioallantoic Membrane Vascular Function of the Embryonic Domestic Chicken (Gallus gallus) Vascular function and regulation is poorly understood in most fetal/embryonic vertebrates. Given the complexity of the vascular tree in developing animals, specifically the presence of the chorioallantoic membrane (CAM) vascular bed, a thorough investigation of vascular function must be completed. The CAM vasculature is critical as a gas exchange surface, and thus changes in vascular resistance will have direct effects on convective gas transport. To characterize CAM vasculature function, an isolated embryonic chicken CAM perfusion preparation was used. This model is particularly useful because it eliminates potential fetal-maternal physiological interactions. Eggs of the domestic chicken (Gallus gallus) incubated at 38C were selected for study at days 15 and 19 of the developmental period, days corresponding to maximal CAM development and the period just prior to lung ventilation, respectively. On the day of study, the CAM vascular tree was isolated from euthanized embryos, and the major CAM artery was occlusively catherized. The preparation was perfused with saline (0.9% NaCl) at rates that mimicked previously published blood flow rates on these days of development. Responses of CAM vascular function were studied via pharmacological manipulation with selective receptor agonists, phenylephrine (alpha-adrenergic), isoprenaline (beta-adrenergic), and Angiotensin II. Preliminary data indicate that the embryonic chicken CAM responds to both beta and alpha-adrenergic receptor stimulation at day 15 and 19. These data, in combination with molecular in situ hybridization used to localize receptor mRNA, imply regulation of CAM vascular resistance may be an important mechanism of altering cardiovascular function in embryonic birds. P1.110 AMITAI, Oren*; BAUCHINGER, Ulf; MCCUE, Marshall D; PINSHOW, Berry; Ben-Gurion University of the Negev; orenamit@bgu.ac.il The effects of dietary (n-3) and (n-6) oils on basal metabolic rate in zebra finches. Dietary fatty acid (FA) profiles play an important role in the composition of cell membranes. The unsaturation level of cell membranes of birds and mammals have been shown to be positively correlated with basal metabolic rate (BMR), but it is unclear whether the unsaturation levels of dietary FAs are the underlying cause of alterations in metabolic rate. Docosahexaenoic acid (DHA; 22:5 n-3), produced from dietary linolenic acid (18:3 n-3) , is a highly unsaturated FA found in cell membranes of all vertebrates and is central to the Hulbert and Else membrane "pacemaker" theory. We therefore tested the prediction that birds fed a diet enriched with (n-3) FAs have higher BMR than birds fed a diet enriched with (n-6) FAs. We used 18 Zebra finches (Taeniopygia guttata, 9 males and 9 females) that were separated by sex and divided into three groups and fed millet diets supplemented with 8% safflower (n-6), 8% flaxseed oil (n-3), or no oil for 7-12 days. BMR was measured by indirect calorimetry on 6 birds at a time (2 from each group) on days 7, 9 and 12. Mean BMR's for control, (n-3) and (n-6) were 0.29±0.02, 0.26±0.05 and 0.32±0.06 W, respectively, and were not significantly different (ANOVA, F (2,14) =2.79, P = 0.095). The data in hand do not support the prediction; in fact they indicate that BMR is lower in (n-3) fed birds. We conclude that, as has been suggested (D.J. McKenzie, 2000) for sturgeon and other fish, the BMR response to dietary fat may not be confined to the cell membrane, but may operate at the whole cell, or organ level as well. e193 Downloaded from https://academic.oup.com/icb/article-abstract/49/suppl_1/e191/771067 by guest on 20 November 2018 P3.157 AN, Y*; KRIENGWATANA, B.P.; NEWMAN, A.E.M.; MACDOUGALL-SHACKLETON, E.A.; MACDOUGALL-SHACKLETON, S.A.; Univ. Western Ontario, Univ. British Columbia; yan4@uwo.ca The relationship between social rank, neophobia and observational learning in black-capped chickadees (Poecile atricapillus) Analogous to human personality differences, behavioural syndromes are consistent patterns in behavioural tendencies across varying situations in individual animals. Although studies of behavioural syndromes are becoming more common, few studies connect individual differences in behaviour with social dominance. Black-capped chickadees flock in the winter, and dominance hierarchies are critical to their survival and reproduction. We tested the relation between social rank, neophobia and observational learning in black-capped chickadees and investigated whether social dominance is part of a wider behavioural syndrome. We captured twenty-one chickadees from five different sites in London, Ontario, and measured individual reactions to novelty and individual differences in ability to learn a novel foraging task from a conspecific tutor. The latency to approach novel objects and foods was correlated within individuals which indicates consistent individual variation in neophobia. Social rank was related to latency to approach novel objects and food. Lower ranking individuals were less neophobic, consistent with the characteristic of their dominance hierarchy in which the dominants control preferential access to resources and limit the subordinates to forage in riskier environment. Future work will address whether reduced neophobia and riskier foraging predisposes birds to becoming subordinate, or vice versa. Scanning EM of the Placental Membranes in the Viviparous Lizard Sceloporus jarrovi In viviparous lizards, placentas sustain the developing embryos inside the pregnant female through gas exchange and provision of nutrients. We used scanning EM to reveal the fetal -maternal interface in the spiny lizard Sceloporus jarrovi (Phrynosomatidae) during the last trimester of gestation. Two distinct placentas are formed and persist until parturition. The allantoplacenta consists of the chorioallantois in direct apposition to the uterine epithelium. SEM reveals that fetal and maternal epithelia at the placental interface are highly attenuated, but not eroded, and lack surface specializations. The yolk sac placenta consists of an avascular omphalopleure (with its isolated yolk mass) in conjunction with the uterus. The omphalopleure forms elaborate folds, consisting of epithelium and yolk droplets. These folds protrude into a thick mass of material in the uterine lumen, formed from degenerating shell membrane, cellular debris, and yolk. Scanning EM indicates that this material is sequestered into a restricted, elongated region at the ventral pole, possibly to free up adjacent regions for placental exchange. The presence of elaborate placental specializations in a generalized viviparous lizard is unexpected, and underscores the need for continued explorations of placental diversity in the numerous clades of viviparous squamates. P3.179 ANSON, J.Y.*; RICHMOND, R.H.; MARTINEZ, J.A.; Kewalo Marine Laboratory, Honolulu, HI; jorg@hawaii.edu Effects of Anthropogenic Stressors on Larval Recruitment in the Reef Coral Porites hawaiiensis Anthropogenic stressors affecting nearshore ecosystems are an important problem throughout the Pacific Islands. Due to the rapid rate of coastal development in island nations, activities conducted within watersheds have immediate impacts on adjacent coastal zones. In Hawaii, the coral Porites hawaiiensis is primarily distributed in shallow water (0-3m) coastal ecosystems. P. hawaiiensis broods its larvae which are released daily, year-round. The availability of P. hawaiiensis larvae makes this a good model organism for analyzing the effects of anthropogenic stressors on coral recruitment and survival. Recruitment bioassays were performed using larvae exposed to environmentally relevant concentrations of freshwater, terrigenous sediments and the anti-microbial soap additive Triclosan, in the presence of a suitable settlement cue. Our data revealed that these putative stressors can either prevent or enhance recruitment. This study revealed that both freshwater and sediment inhibited larval recruitment and Triclosan caused a slight increase in settlement and metamorphosis. These findings demonstrated larval sensitivity to water and substratum quality, and the importance of these parameters to the early life-history stages of corals and the persistence of coral reefs. P3.113 ARMFIELD, Brooke A. *; THEWISSEN, J. G. M.; VINYARD, Christopher J.; NEOUCOM; Rootstown, OH.; bgarner@neoucom.edu Diversity in gene expression patterns during mammalian early tooth development Tooth morphology is one of the distinguishing features of mammalian species, however, little is known about how differences in form along a tooth row are genetically determined in mammals other than mice. To further explore the genetic patterning underlying the diversity of tooth morphologies seen in mammals we looked at early dental development of pigs and dolphins. These mammals are good models to address this question because they represent two variations in dental patterns. The domestic pig (Sus scrofa) dentition maintains several features representative of many mammals. They have two generations of bunodont teeth and a primitive-heterodont dental formula (3-1-4-3). In contrast the pan-tropical spotted dolphin (Stenella attenuata) has a highly derived homodont dentition, only one generation of teeth and an increased tooth number. It is known that in mice tooth type is determined early in development by signaling pathways establishing distinct boundaries for incisors and molars. We looked for expression patterns of these genes and proteins to establish associations between molecular events and dental classes across the three different dentitions. We used immunohistochemistry on dolphin embryos and in situ hybridization on pig embryos to determine the timing and location of proteins and genes (BMP4, FGF8, SHH) that influence early tooth type determination in mice. We found a range of expression patterns among these three mammal species. For example in dolphins, BMP4 expression was found to extend much more distally, perhaps contributing to the teeths incisor-like form. The variability in expression patterns suggest future developmental studies hold great promise in helping to explain the diversity in dental patterns across mammals. multiple camera traps were placed at the site of Mainaro, within the Kibale National Park of Uganda. A single digital infrared camera trap recorded three images of a golden cat. The cat, presumably the same individual, used the same trail over different nights, suggesting the camera was within the cat's core range. The Mainaro site consists of a mosaic forest habitat, including mature, disturbed, and colonizing patches. The images were recorded in the mature forest. Duikers and primates are common at Mainaro, which are preferred prey items for the golden cat. The occurrence of the golden cat within this disturbed habitat is a hopeful sign that this species can persist even in small fragmented forests. Continued management and monitoring, combined with new research on golden cat biology and behavior, will maintain and support both the cat population and the park. P1.118 AXTMAN, L.M.*; CHAO, E.; HJELMFELT, S.H.; STRATTON, M.S.; IMAN, J.D.; COVI, J.A.; MYKLES, D.L.; Colorado State Univ., Fort Collins; lisa.axtman@gmail.com Cloning of a cDNA encoding a myostatin-like factor from lobster skeletal muscle Claw muscles of decapod crustaceans undergo a premolt atrophy, controlled by molting hormones (ecdysteroids), to enable withdrawal of the claws at ecdysis. Myostatin-like factors (Mstn), a negative regulator of muscle growth in mammals, is expressed in scallop, insect, and crustacean muscles, which suggests it also plays a role in controlling muscle size in invertebrates. The American lobster, Homarus americanus, is being used to study the effects of claw size and fiber composition on Mstn-mediated signaling. The larger crusher claw contains only slow-twitch (S1) fibers, while the smaller cutter claw contains fast, S1, and slow-tonic (S2) fibers. We have sequenced a cDNA that encodes Mstn using RT-PCR and RACE-PCR. The conserved RXXR cleavage site was present, indicating the presence of a mature peptide and its N-terminal inhibitory propeptide domain. The nucleotide percent identity for lobster Mstn versus land crab Mstn was approximately 79%, while the amino acid percent identity was approximately 90%. We are quantifying the tissue-and fiber-type-specific expression of Mstn using end-point and quantitative RT-PCR. The results will be related to the control of muscle size by steroid hormones.