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In this study, we examined influences of maternal traits on offspring birth mass, growth rate, and weaning mass for two populations of Columbian ground squirrels (Spermophilus columbianus). We tested relationships between maternal body condition, structural size, change in mass (during gestation, during lactation, and during the entire reproductive period), timing of reproduction, and litter size on offspring traits using path analyses. To assess whether maternal investment in offspring traits extended beyond the period of direct maternal care, we examined associations between offspring traits and overwinter survival of pups. In general, females in better condition raised pups that were heavier at weaning and that had faster growth rates during lactation. Litter size had a negative effect on mass and growth rate, and only litter size had a significant effect on birth mass. For both populations, the average weaning mass of pups within a litter had a positive effect on the number of pups that survived to yearling age. In a population for which birth masses and growth rates were available, pups with faster growth rates survived better to yearling age, whereas birth mass had no effect on the number of surviving offspring in litters. We found substantial maternal influences on offspring growth and size, and evidence that these influences may extend beyond the juvenile period and constitute influences on fitness. The key to arriving at these conclusions was to take the number of offspring into account before testing for maternal effects. Key words: birth mass; body condition; Columbian ground squirrel; growth rate; litter size; mass change; maternal effects; path analysis; Spermophilus columbianus; survival; timing of reproduction; weaning mass.

Joint nesting, in which more than one pair contributes eggs to a group nest, is rare among cooperatively breeding birds. Early reports of the breeding biology of Taiwan Yuhinas (Yuhina brunneiceps) described them as joint nesters; however, these studies were preliminary and did not involve color-banded individuals. We conducted a 7-year study on the breeding biology of yuhinas. We found that the frequency of joint nesting was extremely high (90% of groups). Breeding groups were composed of two to seven adults (mode = 4). Most of the juveniles (78%) disappeared from our study site the year after they hatched. Only 6% remained in their natal groups; therefore, our study groups appeared to be composed primarily of non-kin. Within each group, there was a linear hierarchy of socially monogamous pairs. Mean reproductive skew index, as determined by microsatellite markers, was low (0.19). Alpha males had longer wings than beta males, whereas females did not show any differences in body size. Breeding group size had no significant effect on nest survival rate. Overall clutch size of the group increased while the average number of eggs laid by each pair decreased with group size. However, average number of fledged young per pair per season was similar for all group sizes. Alpha females were the major contributors during both diurnal (65% of groups) and nocturnal (77%) incubation, although beta females and males also contributed substantially toward incubation. Key words: cooperative breeding, joint nesting, mating systems, microsatellites, reproductive skew, Taiwan Yuhina, Yuhina brunneiceps.

Beef heifers (24 mo; 378 [+ or -] 32 kg of BW; 22 pregnant, PR; 17 nonpregnant, NP) were grouped in common pens and fed corn silage- and hay-based diets formulated to provide an ADG of 0.45 kg in NP heifers. Both PR and NP heifers were slaughtered on d 40, 120, 200, and 270 of the study. Intestinal and hepatic tissues were analyzed for protein, DNA, RNA (mg/g of fresh tissue), and in vitro oxygen use. Jejunal samples were analyzed for cellular proliferation via immunohistochemical analysis. For ileum, DNA, which provides an estimate of cell number per unit of tissue, revealed an interaction (P = 0.06) between pregnancy and slaughter day; both PR and NP decreased with time, but NP increased on d 270 (P = 0.09). Cell number in the ileum was reduced at d 200 and 270 in the PR heifers (P [less than or equal to] 0.09). Liver protein concentration was less (P = 0.07) in PR than in NP heifers (NP = 291.1 vs. PR = 210.5 [+ or -] 33.9 mg/g). Hepatic protein:DNA ratio was not affected (P > 0.10) by pregnancy or day. Energy use (kcal/d) of duodenum and jejunum, calculated from in vitro oxygen consumption, increased linearly (P < 0.02) with time for both PR and NP. Pregnant and NP ileal energy use increased linearly (P < 0.01), but ileal energy use by PR was less throughout gestation (P = 0.07) than ileal energy use by NP. Cellular proliferation in the crypt region of the jejunum was decreased on d 120 and 200 (P < 0.02). These data indicate that the small intestine and liver of PR heifers may conserve energy expenditure compared with NP heifers. Energy conservation can partially be explained by differences in growth and cell proliferation and by energy use of the liver and small intestine. Key Words: Cattle, Cell Growth, Growth, Oxygen Consumption, Pregnancy, Small Intestine

Calving difficulty was analyzed under threshold and linear models considering either a fixed or random herd-year effect. The aim of the study was to compare models for predicting breeding values according to the size of herd-year groups. When simulating data sets with small herds, in order to obtain an unbiased evaluation under a nonrandom and negative association of sire and herd effects, the best model for a practical evaluation was the fixed linear model. Field data included 246,576 records of the largest Charolais herds in France. Models were compared using the correlations of estimated breeding values between the different models. Although the best model from a theoretical point of view was a threshold model with a fixed herd-year effect, a linear model with a fixed herd-year effect was the best choice from a practical point of view for predicting direct effects for calving difficulty in beef cattle and was a sufficient choice for predicting the associated maternal effects for data set with large herds. Correlations between direct estimated breeding values under the reference model and the fixed linear model and the random threshold model were 0.94 and 0.91, respectively. Correlations between the corresponding maternal estimated breeding values were 0.94 and 0.98. Heritabilities of direct effects were 0.27 and 0.14 under fixed threshold and fixed linear models, respectively. The corresponding heritabilities of maternal effects were 0.18 and 0.13, and the genetic correlation between direct and maternal effects were -0.36 and -0.34, respectively. Key Words: Contemporary Comparisons, Dystocia, Linear Models, Threshold Models

Economic weights are obtained for feed intake using a growth model and an economic model. The underlying concept of the growth model is the linear plateau model. Parameters of this model are the marginal ratio (MR) of extra fat and extra protein deposition with increasing feed intake (FI) and the maximum protein deposition ([Pd.sub.max]). The optimum feed intake (F[I.sub.0]) is defined as the minimum feed intake that meets energy requirements for [Pd.sub.max]. The effect of varying FI and MR on performance traits was determined. An increase in FI results in a larger increase in growth rate with lower MR. For a given MR, feed conversion ratio is lowest when FI equals F[I.sub.0]. Lean meat percentage (LMP) is largest for a low MR in combination with a low FI. The decrease in LMP with higher FI is largest when FI exceeds F[I.sub.0]. Economic weights for FI, MR and [Pd.sub.max] depend on FI in relation to F[I.sub.0]. Economic weights for FI are positive when FI is less than F[I.sub.0] and negative when FI is larger than F[I.sub.0]. The MR has only then a negative economic weight, when FI is below F[I.sub.0]. Economic weights of FI and MR have a larger magnitude with lower MR and lower FI. In contrast, economic weights for growth rate and FI derived from the economic model only change in magnitude and not in sign with different levels of these traits. The economic model always puts a negative economic weight on FI since it expresses profit due to a decrease in FI with constant growth rate and LMP. This holds the risk of continuous decrease in FI in pig breeding programs. In contrast, the use of growth models for genetic improvement allows direct selection for an optimum feed intake which maximizes feed efficiency in combination with maximum lean meat growth. It is concluded that recording procedures have to be adapted to collect the data necessary to implement growth models in practical pig breeding applications. Key Words: Breeding, Economic Evaluation, Feed Intake, Growth Models, Pigs

Postweaning growth, feed efficiency, and carcass traits were analyzed on 1,422 animals obtained by mating [F.sub.1] cows to [F.sub.1] (Belgian Blue x British breeds) or Charolais sires. Cows were obtained from mating Hereford, Angus, and MARC III (1/4 Hereford, 1/4 Angus, 1/4 Pinzgauer, and 1/4 Red Poll) dams to Hereford or Angus (British breeds), Tuli, Boran, Brahman, or Belgian Blue sires. Breed groups were fed in replicated pens and slaughtered serially in each of 2 yr. Postweaning average daily gain; live weight; hot carcass weight; fat depth; longissimus area; estimated kidney, pelvic, and heart fat (percentage); percentage Choice; marbling score; USDA yield grade; retail product yield (percentage); retail product weight; fat yield (percentage); fat weight; bone yield (percentage); and bone weight were analyzed in this population. Quadratic regressions of pen mean weight on days fed and of cumulative ME consumption on days fed were used to estimate gain, ME consumption and efficiency (Mcal of ME/kg of gain) over time (0 to 200 d on feed), and weight (300 to 550 kg) intervals. Maternal grandsire breed was significant (P < 0.01) for all traits. Maternal granddam breed (Hereford, Angus, or MARC III) was significant (P < 0.05) only for fat depth, USDA yield grade, retail product yield, fat yield, fat weight, and bone yield. Sire breed was significant (P < 0.05) for live weight, hot carcass weight, longissimus area, and bone weight. Sex class was a significant (P < 0.001) source of variation for all traits except for percentage Choice, marbling score, retail product yield, and fat yield. Interactions between maternal grandsire and sire breed were nonexistent. Sire and grandsire breed effects can be optimized by selection and use of appropriate crossbreeding systems. Key Words: Beef Cattle, Breeds, Carcass Composition, Growth

Seventy-three crossbred steers (initial BW = 170.5 [+ or -] 5.5 kg) from The Ohio State University (Exp. 1) and 216 crossbred steers (initial BW 135.4 [+ or -] 4.4 kg) from the University of Illinois (Exp. 2) were used to determine the effect of source of energy and rate of growth on performance, carcass characteristics, and glucose and insulin profiles on early-weaned steers. Effects of the diets used in Exp. 1 and 2 on ruminal pH and VFA concentrations were quantified using ruminally fistulated steers (Exp. 3). Cattle were weaned at an average age of 119 d in all experiments and were allotted by age, BW, and breed to one of four diets: high-concentrate, fed ad libitum (ALCONC), high-concentrate fed to achieve a gain of either 1.2 kg/d (1.2CONC) or 0.8 kg/d (0.8CONC), or high-fiber, fed ad libitum (ALFIBER). At 218 d of age, all steers were placed on the ALCONC diet until slaughter. Steers were implanted with Compudose at the initiation of all experiments and with Revalor-S when they were estimated to be 100 d from slaughter. When steers in Exp. 1 averaged 181 and 279 d of age, serum samples were collected to determine glucose and insulin concentrations. Steers were slaughtered when a fat thickness of 1.27 cm was reached (Exp. 1) or after 273 d on feed (Exp. 2). In Exp. 1, days in the feedlot (P < 0.01) and age at slaughter (P < 0.01) were lowest for ALCONC and ALFIBER steers, and greatest for 0.8CONC steers. Overall, ADG was greatest for ALCONC and lowest for 0.8CONC steers; feed efficiency was lowest (P < 0.01) for ALFIBER steers. Final BW did not differ (P > 0.57) among treatments. At 181 and 218 d of age, serum insulin was increased (P < 0.10) and intramuscular fat percentage was greatest (P < 0.07), respectively, for ALCONC steers. In Exp. 2, overall ADG (P < 0.06) and final BW (P < 0.04) were greatest for ALCONC and lowest for 1.2CONC and 0.8CONC steers. Overall feed efficiency was greatest for 0.8CONC and lowest for ALFIBER (P < 0.01). Growing phase diet did not affect marbling score at 218 d of age or at slaughter (P > 0.81). In Exp. 3, differences in ruminal pH after feeding may have been a consequence of increasing acetate (ALFIBER), propionate (ALCONC), or a combination of VFA (0.8CONC and 1.2CONC), respectively (diet x time after feeding, P < 0.10). Controlling growth by limit-feeding a high-concentrate diet for only 100 d does not extend the growth curve of early-weaned steers or enhance intramuscular fat deposition at slaughter compared to ad libitum intake of a high-concentrate or high-fiber diet. Key Words: Beef Cattle, Carcass Composition, Early Weaning, Feedlots, Insulin

The effect of breed and diet on insulin response to glucose challenge and its relation to intra-muscular fat deposition was determined in 36 steers with 12 each of greater than 87% Wagyu (referred to as Wagyu), Wagyu x Limousin, and Limousin breeds. Weaned steers were blocked by weight into heavy, medium, and light calves and placed in six pens with two pens per weight type and with two steers of each breed per pen. Three pens with steers from each weight class were fed backgrounding and finishing diets for 259 d, while the other three pens were fed the same diets where 6% of the barley grain was replaced with sunflower oil. Prior to initiation of the finishing phase of the study the intravenous glucose tolerance test (IVGTT) was conducted in all steers. Once steers were judged as carrying adequate 12th-rib fat, based on weight and days on feed, they were harvested and graded and samples of the longissimus muscle were procured for determination of fat content and fatty acid composition. Dietary oil improved (P = 0.011; 0.06) ADG and feed conversion efficiency of steers during the latter part of backgrounding and only ADG during early part of the finishing period. Generally percent kidney, pelvic, and heart fat was the only adiposity assessment increased (P = 0.003) by dietary oil. The IYGTT results indicated that insulin response to intravenous glucose was lower in Limousin steers than in Wagyu steers. Dietary oil decreased (P = 0.052) fasting plasma insulin concentration in Wagyu steers compared with Limousin steers. The correlation coefficients among the IVGTT measures and intramuscular fat content or marbling score were less than 0.4, and only a negative trend existed between fasting insulin and USDA marbling scores. However, the carcasses of the Wagyu steers graded US Choice, and 66% of the Wagyu carcasses graded US Prime, which were substantially better than the quality grades obtained for the carcasses from the other breed types. Dietary oil did not affect muscle fat content but increased (P = 0.01) conjugated linoleic acid (CLA) concentrations by 339%. Results indicated that IVGTT measures were not appropriate indices of marbling potential in cattle and that dietary oil can enhance CLA content of beef. Key Words: Carcass Quality, Conjugated Linoleic Acid, Dietary Fat, Glucose, Insulin

An experimental [F.sub.2] cross between Iberian and Landrace pig strains was performed to map quantitative trait loci (QTL) for diverse productive traits. Here we report results for meat quality traits from 369 [F.sub.2] animals with records for pH 24 h postmortem (pH 24 h), muscle color Minolta measurements [L.sup.*] (lightness), [a.sup.*] (redness), and [b.sup.*] (yellowness), [H.sup.*] (hue angle), [C.sup.*] (chroma), intramuscular fat (IMF) and haematin pigment content measured in the longissimus thoracis. Pigs were genotyped for 92 markers covering the 18 porcine autosomes (SSC). Results of the genome scan show evidence for QTL for IMF (SSC6; F = 27.16), pH 24 h (SSC3; F = 7.73), haematin pigments (SSC4 and SSC7; F = 8.68 and 9.47 respectively) and Minolta color measurements [L.sup.*] (SSC4 and SSC7; F =16.42 and 7.17 respectively), and [a.sup.*] (SSC4 and SSC8; F = 8.05 and 7.36 respectively). No QTL were observed for the color measurements [b.sup.*], [H.sup.*], and [C.sup.*]. Alternative models fitting epistasis between QTL were also tested, but detected epistatic interactions were not significant at a genome-wise level. In this work we identify genomic regions related with meat quality traits. Improvement by traditional selection methods is complicated, and finer mapping would be required for their application in introgression programs. Key Words: Meat Quality, Pigs, Quantitative Trait Loci

Rearing animals in small litters induces a permanent increase in body weight and body fat. To determine whether changes in sympathoadrenal activity contribute to this effect, litter size was adjusted the day after birth and maintained until weaning at 21 days. Sympathetic nervous system (SNS) activity was measured in adult animals using [[sup.3]H]norepinephrine ([[sup.3]H]NE) turnover in peripheral tissues. Although litter size was without effect on [[sup.3]H]NE turnover in chow-fed animals, acceleration of [[sup.3]H]NE turnover by dietary Sucrose was completely abolished in heart and attenuated in interscapular brown adipose tissue and kidney of rats reared in small litters. Body and epididymal fat-pad weights were heavier in rats reared in small litters; however, weight gain in response to dietary enrichment with sucrose did not differ as a function of litter size. Thus litter size alters dietary activation of the SNS, and this effect presumably reflects changes in central nervous system regulation. interscapular brown adipose tissue; body fat; [[sup.3]H]norepinephrine; nervous system activity; sympathoadrenal function

Numerous experimental studies providing extra food have concluded that food availability at the beginning of the breeding season constrains the start of egg-laying for female birds (Food Supply Hypothesis) because supplemented females usually lay earlier than nonsupplemented ones. This conclusion has recently been questioned because food addition studies may be confounded by ordered habitat selection. Ordered habitat selection occurs when territories or nests provided with extra food are chosen by individuals of higher quality that may be able to initiate breeding early, regardless of food supply (Habitat Selection Hypothesis). To test these two hypotheses, we performed an experiment using the Lesser Kestrel (Falco naumanni). To reveal effects of ordered habitat selection, extra food was provided to half of the nests in two colonies in which the other nests remained unsupplemented (mixed colonies). We provided extra food to all nests in two colonies (all-fed colonies) and to no nests in three colonies (all-unfed colonies). In these colonies, ordered habitat selection could not occur because all nests received equal treatment. In mixed colonies, fed pairs laid earlier than unfed ones. In contrast to the prediction of the Habitat Selection Hypothesis, there was no significant difference in mean laying date between unfed pairs of mixed colonies and pairs in all-unfed colonies, or between fed pairs of mixed colonies and pairs in all-fed colonies. Moreover, laying date was significantly earlier in all-fed than in all-unfed colonies. Therefore, the results support the Food Supply Hypothesis and refute the Habitat Selection Hypothesis. Key words: egg laying; Falco naumanni; food limitation; food supply; habitat selection; laying date; Lesser Kestrel; Spain; supplementary food; timing of breeding.

Hormonal manipulations with implants allow examination of the costs and benefits of behaviors and physiologic states mediated by a given hormone. As a part of ongoing research into the effects of the steroid hormone testosterone (T) in Dark-eyed Juncos (Junco hyemalis), we measured the corticosterone (B, a steroid hormone secreted by the adrenal in response to stress) response to the stress of capture and handling in males treated with T (T-males) and in control males (C-males). Although B may be essential for energy mobilization, chronic or repeated exposure to elevated levels of B can have many negative effects. Because T mediates many behaviors that may increase the likelihood that an individual will encounter stressors, we predicted that plasma B would rise more rapidly in T-males than in controls. In the first few minutes post-capture, the increase in B levels was significantly higher in T-males than in controls. B levels in samples collected 10, 30, and 60 min post-capture were consistently higher in T-males than in C-males; however, the difference was not statistically significant. Because previous work has shown that T-males reduce their parental contribution, we compared females that were mated to T-males and C-males (hereafter T- and C-females). B levels of T-females increased sharply in the first few minutes post-capture, whereas in C-females they did not; however, the responses were not statistically different. Males had higher initial levels and a greater B-response to stress than females when data were compared irrespective of treatment. Our results suggest that the behaviors or physiological changes induced by T are potentially costly and that such costs may in part be incurred through elevated B.

Direct and maternal breed effects on birth and 200-d weights were estimated for nine parental breeds (Hereford [H], Angus [A], Braunvieh [B], Limousin [L], Charolais [C], Simmental [S], Gelbvieh [G], Red Poll [R], and Pinzgauer [P]) that contributed to three composite populations (MARC I = 1/4B, 1/4C, 1/4L, 1/8H, 1/8A; MARC II = 1/4G, 1/4S, 1/4H, 1/4A; and MARC III = 1/4R, 1/4P, 1/4H, 1/4A). Records from each population, the composite plus pure breeds and crosses used to create each composite, were analyzed separately. The animal model included fixed effects of contemporary group (birth year-sex-dam age), proportions of individual and maternal heterosis and breed inheritance as covariates, and random effects of additive direct genetic (a) and additive maternal genetic (m) with covariance (a,m), permanent environment, and residual. Sampling correlations among estimates of genetic fixed effects were large, especially between direct and maternal heterosis and between direct and maternal breed genetic effects for the same breed, which were close to -1. This resulted in some large estimates with opposite sign and large standard errors for direct and maternal breed genetic effects. Data from a diallel experiment with H, A, B, and R breeds, from grading up and from a top cross experiment were required to separate breed effects satisfactorily into direct and maternal genetic effects. Results indicate that estimation of direct and maternal breed effects needed to predict hybrid EPD for multibreed populations from field data may not be possible. Information from designed crossbreeding experiments will need to be incorporated in some way. Key Words: Breeds, Crossbreeding, Beef Cattle

Most organisms reproduce episodically rather than continuously. Forms of discontinuity may include seasonal breeding in annual cycles, and delayed breeding and/or senescence over the lifespan of individuals. In addition, age can have profound effects on the annual reproductive success (RS) of a wide variety of animals. Explanations of the effects of age on RS can be confounded, however, by the acquired breeding experience of individuals, and the duration of pair-bonds, both of which have effects on RS similar to those of age itself. However, most studies of the effects of age on RS prior to senescence have not accounted for the effects of pair-bond duration, and many have treated age and experience as synonyms. In this paper I summarize the effects of all three factors, discuss the simultaneous and interrelated nature of their effects, and suggest ways to separate the relative contributions of each.

We measured nipple sizes of 29 captive wolves (Canis lupus), of known breeding histories, throughout the year and tested distinctions among various known breeding statuses of 20 wild wolves examined in northeastern Minnesota from May through September. For ca. 8 mo of the year only breeders and nonbreeders can be classified. Distinctions between current and former breeders were not reliable.

Age at puberty is a major determinant of lifetime reproductive efficiency of beef cows. Research conducted during the past 20 yr has documented the major endocrine events leading to first ovulation in heifers. The critical event seems to be a prepubertal increase in pulsatile LH secretion. Environment influences timing of puberty onset in beef heifers. Nutrition and season are two of the better-defined variables that have been studied. Age at puberty is related inversely to plane of nutrition. The effect of nutrition on sexual maturation involves effects on timing of the prepubertal increase in LH secretion and seems to involve the LH pulse generating system located in the hypothalamus. The precise mechanism by which nutrition influences pulsatile LH secretion has not been elucidated, but signals reflecting metabolic status seem to be involved. Seasonal conditions of the early (birth to 6 mo of age) and late (6 to 12 mo of age) postnatal periods also influence timing of puberty onset in the heifer. Autumn-born heifers attain puberty at younger ages than do spring-born heifers, and exposure to spring-summer temperatures and photoperiods during the second 6 mo of life reduces age at puberty regardless of season of birth. Photoperiod may be the major seasonal cue that influences puberty onset in cattle. Limited evidence suggests that melatonin, a pineal hormone, is involved with transducing photic stimuli into neuroendocrine signals that influence LH secretion. If the physiological mechanisms mediating the effects of nutrition and season on timing of puberty onset are determined, then management strategies for reducing age at puberty can be enhanced.

Our hypothesis was that cows with greater body condition at parturition would respond to the presence of bulls (biostimulation) by having shorter periods of postpartum anestrus than cows with a lesser body condition. Multiparous cows in good body condition at the initiation of the study were either maintained on a high dietary regimen or switched to a low dietary regimen during the 90 d preceding parturition. After parturition, half of the cows from each group were placed in pastures with sterile bulls, and the remaining half were placed in pastures without bulls. This study was replicated during a 2nd yr. Blood samples were collected twice weekly and assayed for concentrations of progesterone to estimate time of onset of luteal function after parturition. There was a significant interaction (P < .05) between body condition at parturition and presence of bulls postpartum on the duration of postpartum anestrus. Cows of lesser body condition that were in the presence of bulls after calving initiated estrous cycles 14 d earlier than cows with lesser body condition that were isolated from bulls. In cows with a greater body condition, presence of bulls after calving only shortened postpartum anestrus by 6 d. Thus, we reject our initial hypothesis.

We field-tested the hypothesis that substandard water intake contributes to reproductive failure of northern bobwhites (Colinus virginianus) during drought because laboratory studies have implicate cause. Specifically, we examined 2 predictions: that availability of preformed water in forbs would demonstrably insufficient during drought, and that water supplementation would reverse reproductive during drought. Our laboratory results indicated that bobwhites could lay successfully with preforme in greens as the sole source of exogenous water, although rate of laying was lower (P < 0.05) for he receiving preformed water than for those receiving ad libitum free water (0.5 vs.0.3 eggs/day). Unde conditions in the Rio Grande Plains of Texas, daily water demand of the quail population during repr periods represented 0.1% (SE = 0.0009%) of preformed water available in forbs during drought. Year-r water supplementation had no apparent effect on density trends or percent summer gain in density in (1986-1987) or drought years (1988-89). Field results failed to support the 2 predictions and theref

Survival from 1984 to 1985 was compared among known-aged California Gulls 4-23 yr old. Data supported a hypothesis of increasing reproductive effort with age. A flood during 1984 terminated breeding during the incubation phase of part of the colony, thus permitting an estimate of reproductive costs. Yearly survival of gulls whose nest flooded was 92% compared to 72% among gulls that carried out the reproductive cycle. Adult survival was inversely related to level of fledging success in 1984. Survival declined and fledging success increased with increasing age. However, gulls of differing ages within the same fledging success category had the same probability of survival. No evidence supported the hypothesis that fledging success increased with age because disproportionately larger numbers of individuals with 'good phenotypes' survived to old age. Cross-sectional data showed that fledging success peaked at ages 16-19 and declined among gulls 20-23, suggesting senescence in extremely old gulls. However, longitudinal data indicated that fledging success did not decline among old gulls. The few gulls surviving to extreme old age did so by consistently exerting low reproductive effort and fledging few offspring.

Endangered Florida panthers have maintained their distinctive faces despite crossbreeding. Human activity in the twentieth century drove this subspecies of Puma concolor (pictured) towards extinction and confined it to the [...]

Impact of high testosterone presence in red grouse on their breeding success is examined.

Research has been conducted on hybridization between populations. The hypothesis that this hybridization may cause increased fitness or decreased fitness has been tested, and the results are reported.

Reliabilities for a multiple-trait maternal model were obtained by combining reliabilities obtained from single-trait models. Single-trait reliabilities were obtained using an approximation that supported models with additive and permanent environmental effects. For the direct effect, the maternal and permanent environmental variances were assigned to the residual. For the maternal effect, variance of the direct effect was assigned to the residual. Data included 10,550 birth weight, 11,819 weaning weight, and 3,617 postweaning gain records of Senepol cattle. Reliabilities were obtained by generalized inversion and by using single-trait and multiple-trait approximation methods. Some reliabilities obtained by inversion were negative because inbreeding was ignored in calculating the inverse of the relationship matrix. The multiple-trait approximation method reduced the bias of approximation when compared with the single-trait method. The correlations between reliabilities obtained by inversion and by multiple-trait procedures for the direct effect were 0.85 for birth weight, 0.94 for weaning weight, and 0.96 for postweaning gain. Correlations for maternal effects for birth weight and weaning weight were 0.96 to 0.98 for both approximations. Further improvements can be achieved by refining the single-trait procedures. Key Words: Beef Cattle, Breeding Value, Maternal Effects, Reliability

Many recent papers have investigated the relationship between plasma levels of testosterone (T) and male behavior during the breeding season. One question of interest is whether male reproductive behavior is associated or dissociated with maximal levels of circulating T. Data concerning patterns of association are scarce for amphibians, particularly for salamanders studied in the field. We measured sex steroid levels (T, DHT, E) for 6 adult male tiger salamanders (Ambystoma tigrinum nebulosum) collected during their spring breeding season from ponds in the Wasatch Mountains near Ogden, UT (elev. 8000 n 8500 ft.) Blood samples were taken within 5 minutes of capture. Mean hormone values (range) were: T = 2.25 (0.3 - 6.22) ng/ml, DHT = 481 (114 - 1785) pg/ml, and E = 17 (7 - 28) pg/ml. These values are comparable to plasma levels measured for spring-breeding Colorado A. tigrinum that are neotenic (aquatic adults breed despite retaining larval morphology.) The dissociated pattern described for these two A. triginum populations is in contrast with maximal T and DHT levels recorded for a fall breeding congener, A. opacum. These data suggest that elevated levels of plasma androgens are not required for concurrent breeding behavior in spring-breeding ambystomatid salamanders.