Selection For Rapid Growth Research Articles

Oxidative stress and plasma ceramides in broiler chickens.

The selection for rapid growth in chickens has rendered meat-type (broiler) chickens susceptible to develop metabolic syndrome and thus inflammation. The sphingolipid ceramide has been linked as a marker of oxidative stress in mammals, however, the relationship between sphingolipid ceramide supply and oxidative stress in broiler chickens has not been investigated. Therefore, we employed a lipidomic approach to investigate the changes in circulating sphingolipid ceramides in context of allopurinol-induced oxidative stress in birds. Day zero hatched chicks (n = 60) were equally divided into six groups; an unsupplemented control, an allopurinol group (25mg/kg body weight), a conjugated linoleic acid (CLA) group where half of the oil used in the control diet was substituted for a CLA oil mixture, a CLA and an allopurinol group utilizing the same dose of CLA and allopurinol, a berberine (BRB) group consisting of berberine supplementation (200mg/kg feed), and a BRB and allopurinol group, utilizing the same dose of BRB and allopurinol. Conjugated linoleic acid and berberine were utilized to potentially enhance antioxidant activity and suppress the oxidative stress induced by allopurinol treatment. Body weight, plasma uric acid, nonesterified fatty acids (NEFA) and sphingolipid ceramides were quantified. Allopurinol induced an inflammatory state as measured by a significant reduction in plasma uric acid - an antioxidant in birds as well as a metabolic waste product. Results showed that both total and saturated sphingolipid ceramides declined (p < 0.05) with age in unsupplemented chicks, although plasma ceramides C16:0 and 18:0 increased in concentration over the study period. Simple total and saturated sphingolipid ceremide's were further decreased (p < 0.05) with allopurinol supplementation, however, this may be an indirect consequence of inducing an inflammatory state. Neither CLA or BRB were able to significantly attenuate the decline. The administration of allopurinol specifically targets the liver which in birds, is the primary organ for fatty acids synthesis. For this reason, sphingolipid ceramide production might have been unwittingly affected by the addition of allopurinol.

A novel morphological index applied to genetic improvement of body shape in grass carp Ctenopharyngodon idella

Body shape is an economically important trait in grass carp (Ctenopharyngodon idella) that directly influences consumer acceptance and farmer profitability. It is essential to incorporate shape traits into the ongoing breeding program, as this would be expected to achieve rapid growth and maintain a slender shape for cultured populations. Thus, the aim of this study was to explore a suitable morphological index for genetic improvement of shape traits in grass carp. The viscerosomatic index (VSI) was introduced as a quantitative indicator of individual slenderness for the evaluation of various morphological ratios. Then, based on correlation and path analysis among body measurements (BMs) and weights of 290 recorded individuals, nine representative ratios that can reflect body slenderness from different angles were employed in this study, including Fulton's condition factor (K), Richter's condition factor (B), and other length ratios of different BMs (S1–S7). The results showed that each of these ratios exhibited a favorable relationship with VSI, confirming that more slender individuals always have a lower VSI. Of these ratios, S1 (body height-to-body length ratio, BH/BL), S2 (body height-to-caudal peduncle height ratio, BH/CPH), and S3, calculated as (BH-CPH)/BL, had the top three correlation coefficients with VSI (r = 0.501, 0.558, and 0.591, respectively). Furthermore, the S3 index reached the highest correlation (r = 0.732) in the sample group (n = 50) of mean body weight of 1560.8 g, suggesting that a quantitative comparison of individual slenderness would be more accurate within this fish size range. In addition, 636 pedigreed fish from 21 full-sib families were used for estimates of genetic parameters via an animal model. In comparison with the low heritability of K, the three ratios showed moderate to high heritability (h2 = 0.47 ± 0.14, 0.20 ± 0.08, and 0.31 ± 0.11, respectively), indicating significant potential for their genetic improvement. However, there were weak but undesired phenotypic and genetic correlations between body weight and the three ratios (0.13 < rp < 0.19; 0.23 < rg < 0.50), predicting that selection for rapid growth may slowly lead to the development of a rotund shape. In conclusion, the novel S3 index was suggested as the preferred candidate of shape traits for selective breeding in grass carp, especially because its expected relative genetic gain (4.07% at 10% selection intensity) was higher than those of the others (1.44%–3.99%).

In pursuit of a better broiler: a comparison of the inactivity, behavior, and enrichment use of fast- and slower growing broiler chickens

Selection for rapid growth has produced heavier, more efficient broiler chickens, but has also introduced health and welfare issues, which may cause or be caused by inactivity. Rapid growth may also limit the performance of motivated behaviors, whereas the provision of enrichment may increase these behaviors and general activity. This study aimed to evaluate the inactivity, behavior patterns, and enrichment use of 2 fast- (CONV) and 12 slower growing broiler strains (categorized as fastest [FAST], moderate [MOD], and slowest slow [SLOW]), based on their growth rates; 4 strains/category]. To evaluate inactivity, one male and one female from 153 pens were outfitted with omni-directional accelerometers from d 21 until processing (14–24 birds/strain from 8 to 12 pens/strain). Additionally, to supplement inactivity data, 5-min continuous behavioral observations of four focal birds per pen (2 males, 2 females) were conducted on days 26, 42, and 56 (72–148 observations of 8–12 pens/strain) to quantify the duration and frequency of various behaviors; at the same time, 5 to 11 instantaneous scan samples were also performed for pen-based enrichment use. Inactivity peaked at 78 to 80% of the day for all strains; however, those with slower growth rates reached these levels at older ages. Compared to slower growing strains at the same age, faster growing strains were more inactive, spent more time sitting and feeding, spent less time standing and walking, and used enrichments less; these differences mostly occurred at younger ages. Generally, at the same age, strains with similar growth rates (within the same category) behaved similarly, with only a few exceptions. Results suggest that not all strains identified as “slow-growing” broilers behave differently from fast-growing broilers, nor do they all behave similarly to each other. As such, results suggest that improved broiler welfare, particularly with respect to reduced inactivity, the performance of a wider range of normal, motivated behaviors, and/or increased enrichment use, is related to the broiler strain's specific growth rate.

The Effects of Conjugated Linoleic Acid and Berberine Supplementation on Markers of Allopurinol Activated Oxidative Stress in Broiler Chickens

Selection for rapid growth in poultry can be linked to an exaggerated state of oxidative stress (reactive oxidative species). Reactive oxidative species are kept in balance by endogenous and exogenous antioxidants. Two compounds, conjugated linoleic acid (CLA) and berberine a purified compound from plant root extract have been suggested to ameliorate oxidative stress. A six-week study examined the effect of CLA and berberine supplementation on markers of oxidative-stress in poultry. Day old broiler chickens (n=60) were equally divided into six groups; a control, a CLA group where half of the regular oil used in a standard was substituted for a CLA oil mixture, a berberine group consisting of berberine supplementation, an allopurinol group, a CLA and allopurinol with the same dose as the CLA and allopurinol groups and a berberine and allopurinol group. The allopurinol was added to induce an oxidative stress state. Body weight, plasma uric acid, plasma glucose, and relative gene expression of six endogenous liver antioxidants were measured during the course of the study. The addition of allopurinol to the diet induced an oxidative stress state as measured by a significant reduction in plasma uric acid. There were no significant changes in BW and blood glucose concentrations. There was a 10-fold increase in the relative mRNA expression of superoxide dismutase 2 and 3 as well as glutathione peroxidase 1 and 3 in CLA+ALLO and BRB+ALLO treatment groups. Notably, CLA increased the expression of uncoupling protein 19-fold compared to control, while the addition of allopurinol blocked these changes. In contrast, there was a slight increase in the uncoupling protein in the BRB+ALLO treatment. Despite the increase in mRNA expression of the antioxidants genes, these results suggest that at the dosages administered, CLA and berberine were not effective in reversing the oxidative stress induced by allopurinol.

Important candidate genes for abdominal fat content identified by linkage disequilibrium and fixation index information.

Selection for rapid growth in chickens has always been accompanied by increased fat deposition and excessive fat deposition, especially abdominal fat, cannot only decrease feed efficiency but also cause many diseases. Finding the candidate genes associated with abdominal fat deposition is essential for breeding. To identify these candidate genes, we applied linkage disequilibrium and selection signature analysis using chicken 60 k single nucleotide polymorphism (SNP) chips in two broiler lines divergently selected for abdominal fat content for 11 generations. After quality control, 46,033 SNPs were left for analysis. Using these SNPs, we found that r2 was 0.06 to 0.14 in the lean line and 0.07 to 0.13 in the fat line for all 28 chromosomes (except GGA16). Pairwise SNP distances <25 kb showed a mean r2 = 0.33 in the lean line and r2 = 0.32 in the fat line. The fixation index (FST) analysis was carried out and 46 SNPs with the top 0.1% of the FST value was detected as the loci with selection signatures. Besides FST, hapFLK was also used to detect selection signatures for abdominal fat content. A total of 11 genes, including transient receptor potential cation channel subfamily C member 4, estrogen related receptor gamma, fibroblast growth factor 13, G-protein-signaling modulator 2, RAR related orphan receptor A, phospholipase A2 group X, mitochondrial ribosomal protein L28, metadherin, calcitonin receptor like receptor, serine/threonine kinase 39, and nuclear factor I A, were detected as the important candidate genes for abdominal fat deposition based on their basic functions. The results of the present study may benefit the understanding of genetic mechanism of abdominal fat deposition in chicken.

A Polymorphism of Insulin-Like Growth Factor Binding Protein 2 Gene Associated with Growth and Body Composition Traits in Kampong Chickens

Insuline-like growth factor binding protein 2 (IGFBP2) is one of the principal binding proteins that has biological functions involved in growth, development, and differentiation. Selection for rapid growth based on molecular Marker Assisted Selection is required to increase production performance. The present study was designed to analyze the associations of IGFBP2 gene polymorphisms with chicken growth and body composition traits. Kampong chicken, a native chicken in Indonesia, is slow-growing chicken. A total of 59 males were used in the current study. Growth and body composition were measured in 24 wk of age. Primers for intron 2 region were designed from genomic chicken sequence. A c.1032C&gt;T SNP of the IGFBP2 gene intron 2 region was detected and PCR-RFLP method was then used to genotype Kampong chicken population. The result showed that IGFBP2 polymorphism was significantly associated with body, carcass, breast, breast muscle, pectoralis minor, leg, and wings weight in Kampong chicken population (P &lt; 0.05). The research suggests that the IGFBP2 gene could be a candidate gene that affects growth and body composition traits in chicken.

Functionally Structured Genomes in Lactobacillus kunkeei Colonizing the Honey Crop and Food Products of Honeybees and Stingless Bees.

Lactobacillus kunkeei is the most abundant bacterial species in the honey crop and food products of honeybees. The 16 S rRNA genes of strains isolated from different bee species are nearly identical in sequence and therefore inadequate as markers for studies of coevolutionary patterns. Here, we have compared the 1.5 Mb genomes of ten L. kunkeei strains isolated from all recognized Apis species and another two strains from Meliponini species. A gene flux analysis, including previously sequenced Lactobacillus species as outgroups, indicated the influence of reductive evolution. The genome architecture is unique in that vertically inherited core genes are located near the terminus of replication, whereas genes for secreted proteins and putative host-adaptive traits are located near the origin of replication. We suggest that these features have resulted from a genome-wide loss of genes, with integrations of novel genes mostly occurring in regions flanking the origin of replication. The phylogenetic analyses showed that the bacterial topology was incongruent with the host topology, and that strains of the same microcluster have recombined frequently across the host species barriers, arguing against codiversification. Multiple genotypes were recovered in the individual hosts and transfers of mobile elements could be demonstrated for strains isolated from the same host species. Unlike other bacteria with small genomes, short generation times and multiple rRNA operons suggest that L. kunkeei evolves under selection for rapid growth in its natural growth habitat. The results provide an extended framework for reductive genome evolution and functional genome organization in bacteria.

Feed restriction ameliorates metabolic dysregulation and improves reproductive performance of meat-type country chickens

Restricted feed intake improves egg production in Cornish×Plymouth Rock (broiler) hens. Red-feather (RF) and Black-feather (BF) chickens are 2 local strains of non-broiler meat-type chickens whose egg production has declined with continued selection for meat yield, and which are unstudied regarding restricted feeding and egg-laying improvement. Sixteen week old RF and BF pullets were either fed ad libitum (AL) or restricted to 85% AL intake (R). At 35wk and 50wk R-hens showed improved egg production and less abnormal ovarian morphology than AL-hens. Obesity, hepatic steatosis, lipotoxic change to plasma lipids, and systemic inflammation induced by AL feeding in RF and BF hens were similar to those observed previously in AL-broiler hens. Egg production was negatively correlated to body weight, fractional abdominal fat weight and plasma NEFA concentrations in AL hens (P<0.05). AL-hen hierarchical follicles accumulated ceramide and increased interleukin-1β production (P<0.05) in conjunction with increased granulosa cell apoptosis, follicle atresia, ovarian regression, and reduced plasma 17β-estradiol concentrations (P<0.05). The present outcomes from non-broiler but nevertheless meat-type country chicken strains indicate that selection for rapid growth and increased meat yield fundamentally changes energy metabolism in a way that renders hens highly susceptible to reproductive impairment from lipid dysregulation and pro-inflammatory signaling rather than impaired resource allocation per se.

Anatomical and biomechanical traits of broiler chickens across ontogeny. Part I. Anatomy of the musculoskeletal respiratory apparatus and changes in organ size.

Genetic selection for improved meat yields, digestive efficiency and growth rates have transformed the biology of broiler chickens. Modern birds undergo a 50-fold multiplication in body mass in just six weeks, from hatching to slaughter weight. However, this selection for rapid growth and improvements in broiler productivity is also widely thought to be associated with increased welfare problems as many birds suffer from leg, circulatory and respiratory diseases. To understand growth-related changes in musculoskeletal and organ morphology and respiratory skeletal development over the standard six-week rearing period, we present data from post-hatch cadaveric commercial broiler chickens aged 0, 2, 4 and 6 weeks. The heart, lungs and intestines decreased in size for hatch to slaughter weight when considered as a proportion of body mass. Proportional liver size increased in the two weeks after hatch but decreased between 2 and 6 weeks. Breast muscle mass on the other hand displayed strong positive allometry, increasing in mass faster than the increase in body mass. Contrastingly, less rapid isometric growth was found in the external oblique muscle, a major respiratory muscle that moves the sternum dorsally during expiration. Considered together with the relatively slow ossification of elements of the respiratory skeleton, it seems that rapid growth of the breast muscles might compromise the efficacy of the respiratory apparatus. Furthermore, the relative reduction in size of the major organs indicates that selective breeding in meat-producing birds has unintended consequences that may bias these birds toward compromised welfare and could limit further improvements in meat-production and feed efficiency.

Bone characteristics and femoral strength in commercial toms: The effect of protein and energy restriction

Selection for rapid growth in turkeys has resulted in skeletal problems such as femoral fractures. Slowing growth rate has improved bone structure, but the effect on mechanical properties of the bone is unclear. The current study's hypothesis was that slowing the growth of turkeys by reducing energy and CP in the diet would result in increased femur integrity. Commercial turkeys were fed 1 of 3 diets: control with 100% of NRC energy and CP levels, as well as a diet feeding 80 or 60% of NRC energy and CP levels. All other nutrients met or exceeded NRC requirements. Control birds were grown to 20 wk of age, whereas the 80 and 60% NRC birds were sampled when BW matched that of control birds at wk 4, 8, 12, 16, and 20. Both femurs were extracted, with one being measured and ashed and the other twisted to failure to evaluate mechanical properties. Total bone length, diameter, cortical thickness, and cortical density were measured. The total femur length was longer in the 60% NRC birds at 5 and 10 kg of BW compared with control (P < 0.05); this significance was lost by the time birds reached 16 kg of BW. At 5 and 10 kg of BW, ash content was higher in the control birds than in the 60% NRC birds (P < 0.05). At 16 kg of BW, the 60% NRC birds had the highest femur ash (P < 0.05). The mechanical testing parameters were failure torque, shear strength, and shear modulus of the bones. The 60% diet produced the highest failure torque (P < 0.05), at 16 kg of BW and onward. The shear strength was greater (P = 0.01) once the birds reached 5 kg of BW for the 60% diet than other diets. In conclusion, reducing the energy and protein in the diet to 60% of NRC recommendations, thus slowing growth, improved bone strength, as measured by failure torque, and bone quality, as measured by shear strength, without altering bone length or ash content by the time birds reached market weight.

Association of Intron Loss with High Mutation Rate in Arabidopsis: Implications for Genome Size Evolution

Despite the prevalence of intron losses during eukaryotic evolution, the selective forces acting on them have not been extensively explored. Arabidopsis thaliana lost half of its genome and experienced an elevated rate of intron loss after diverging from A. lyrata. The selective force for genome reduction was suggested to have driven the intron loss. However, the evolutionary mechanism of genome reduction is still a matter of debate. In this study, we found that intron-lost genes have high synonymous substitution rates. Assuming that differences in mutability among different introns are conserved among closely related species, we used the nucleotide substitution rate between orthologous introns in other species as the proxy of the mutation rate of Arabidopsis introns, either lost or extant. The lost introns were found to have higher mutation rates than extant introns. At the genome-wide level, A. thaliana has a higher mutation rate than A. lyrata, which correlates with the higher rate of intron loss and rapid genome reduction of A. thaliana. Our results indicate that selection to minimize mutational hazards might be the selective force for intron loss, and possibly also for genome reduction, in the evolution of A. thaliana. Small genome size and lower genome-wide intron density were widely reported to be correlated with phenotypic features, such as high metabolic rates and rapid growth. We argue that the mutational-hazard hypothesis is compatible with these correlations, by suggesting that selection for rapid growth might indirectly increase mutational hazards.

Carcass Variables and Chemical Composition of Commercial Broiler Chickens and the Red Jungle Fowl

The carcass characteristics and composition of both male and female commercial broiler chickens (CB) and the red jungle fowl (RJF) were compared at a common body weight of 800±25.6 g. The RJF and CB were 133 and 17 d of age, respectively, when they reached 800 g. The yields of breast and thigh portions and their muscle to bone ratios were higher for RJF as compared to CB. On the other hand, the latter had significantly greater hearts, livers and gizzards. The weights of the whole thigh and drumstick, and their muscles were lower in females than males. The CB had more abdominal fat than RJF. While sex had no significant effect on the absolute weights of abdominal fats in CB, the female RJF were fatter than their male counterparts. The fat and cholesterol contents of the breast and leg muscles of CB were significantly higher than those of RJF. The opposite was noted for protein content of both muscles. The effect of sex on fat and cholesterol contents varied according to muscle type. Comparison of CB and RJF at a common body weight suggested that the rate of development of body components have changed concomitantly with selection for rapid growth in the former.

Wild Atlantic salmon Salmo salar L. strains have greater growth potential than a domesticated strain selected for fast growth

A study was undertaken to examine the responses of three Atlantic salmon Salmo salar strains to growth hormone (GH) treatment. A positive growth response to sustained‐release GH implants was found in two wild strains (Namsen and Imsa) as well as one domesticated strain (AquaGen). The data revealed that the growth‐selected AquaGen strain has further growth potential, however, a stronger growth response was observed in the wild strains which outgrew the domesticated strain after GH treatment. These observations suggest that some growth potential may have been lost during the selection for rapid growth in the AquaGen strain. In September, the parr were GH implanted and in December sampled for plasma GH and insulin‐like growth factor I (IGF‐I) levels, liver, muscle and gill GH receptor, IGF‐I mRNA levels, gill Na+,K+‐ATPase activity, muscle and liver lipid content and body silvering. Low temperature and seasonal growth cessation probably explains the relatively limited GH effects found. Body silvering in all strains was positively correlated to size. GH increased IGF‐I plasma levels in the Namsen strain inspite of liver IGF‐I mRNA levels being lower in GH‐treated fish.

Growth Rate, Protein Accumulation, and Catabolic Enzyme Activity of Skeletal Muscles of Galliform Birds

We measured the mass and several potential indices of functional capacity of the leg and pectoral muscles through 21 d of age in chicks of three species of galliform birds and the domesticated turkey. The study was conducted to test the hypothesis that the growth rate of a tissue is inversely related to its capacity for mature function across species. We measured the proportion of protein and the activities of the catabolic enzymes citrate synthase (CS), pyruvate kinase (PK), and beta -hydroxy-acyl-CoA-dehydrogenase (HOAD) and estimated exponential growth rate (EGR) from growth increments. EGR was negatively related to proportion of protein, PK, and HOAD and positively related to CS activity. In a multiple regression, EGR was uniquely related only to proportion of protein; it was higher in pectoral muscles and increased in this order: wild turkey<pheasant<domestic turkey<chukar. Thus, among wild species, the muscles of smaller species grew more rapidly for a given proportion of protein, but domestication and selection for rapid growth and large muscle size in turkeys resulted in substantially elevated growth rate. When the proportion of protein was normalized by its maximum value for each species and muscle type, the relationship between EGR and normalized protein did not differ significantly among species or muscle type. Thus, if we accept the proportion of protein relative to the mature level as an index of functional capacity--presumably representing the assembly of the contractile apparatus--then growth rate is consistently inversely related to a muscle's capacity for mature function, that is, force generation.

Effect of Genotype on Whole-body and Intestinal Metabolic Response to Monensin in Mice

Two lines of mice, M16 selected for rapid growth and a randomly selected control ICR as well as their reciprocal crosses were used to study the effects of genotype on whole-body energetics and intestinal responses to monensin. Six mice, eight weeks of age, from each line or reciprocal cross were assigned to one of two treatments, 1) drinking water containing 20 mmol/L monensin dissolved in 0.5% V/V ethanol, and 2) drinking water containing 0.5% V/V ethanol (control) for two weeks. After 11 days (age of 9 weeks and 4 days), whole-body O2 consumption was measured. At the end of two weeks, jejunal O2 consumption, intestinal tissue composition and histomorphometrics as well as the rate and efficiency of glucose absorption were estimated. In comparison with the control, monensin administration in drinking water resulted in less daily water intake (13.4 vs. 15.5 ml/mouse, p 0.05) effect on variables measured in either line of mice or their reciprocal cross. In contrast, the M16 line, selected for rapid growth, as compared to the ICR controls or the reciprocal crosses, had less initial (pre-monensin treatment) whole-body O2 consumption per gram of body weight (1.68 vs. 2.11-2.34 µmol/min⋅g BW, p 0.05) effect on whole-body O2 consumption and jejunal function, whilst selection for rapid growth resulted in an apparent down-regulation of intestinal function. These data suggest that genetic selection for increased growth does not result in concomitant changes in intestinal function. This asynchrony in the selection for production traits and intestinal function may hinder full phenotypic expression of genotypic growth potential. (Asian-Aust. J. Anim. Sci. 2006. Vol 19, No. 4 : 554-562)

The Relationship Between Sperm Hydrolysis of the Perivitelline Layer and Embryonic Livability

The hypothesis was proposed that altered sperm hydrolysis of the germinal disc area of the ovum affects embryonic survival. Genetics and damaged spermatozoa were the 2 factors tested. Both factors affect embryonic livability. The mechanism of sperm selection was proposed to be in the oviduct or at the ovum during fertilization. To test the hypothesis, sperm hydrolysis from the creation of holes in the perivitelline layer and embryonic mortality were compared in 3 lines of turkeys representing the past 50 yr of turkey genetics. In the newer lines compared with older, sperm hydrolysis decreased and embryo livability at the first week of embryonic development declined, but embryo livability during the fourth week improved. The same lines were inseminated with 0- or 24-h-stored semen. Although penetration of the perivitelline layer by fresh sperm cells declined in modern lines, penetration of 24-h-stored sperm cells did not. When inseminated with 24-h-stored semen, all 3 lines showed depressed embryo livability compared with fresh semen at wk 1 of embryo development but improved embryo livability at wk 4 of development. In experiment 2, specific comparisons of single-trait selected lines with unselected control lines indicated that selection for rapid growth has increased sperm hydrolysis of the perivitelline layer by 24-h-stored sperm, but selection for increased egg production has not. In vitro sperm hydrolysis of the perivitelline layer was examined only for the growth-selected line in experiment 3. The in vitro technique was used to examine perivitelline layer hydrolysis without oviduct effects. The data indicated no differences in holes in the perivitelline layer for lines or sperm storage. Thus, the data suggest that a reduction in the penetration of sperm through the perivitelline layer results in improved embryo livability at wk 4 of development, but we saw no association with wk 1 embryo livability.

Tissue Damage Precludes the Use of the Everted Sleeve Technique to Measure Nutrient Uptake in a Small Migratory Shorebird, the Western Sandpiper (Calidris mauri)

In vitro measurement of nutrient (e.g., glucose and proline) uptake rates across the brush border of the small intestine has played an integral role in the current understanding of the adaptive responses of the digestive system to artificial selection for rapid growth in domestic poultry (Gallus gallus; Obst and Diamond 1992; Jackson and Diamond 1996) and the energetic demands of provisioning young (Dykstra and Karasov 1992; Konarzewski and Diamond 1994; Hammond et al. 1996). In 1983, Karasov and Diamond introduced a simplified methodology for making in vitro measurements of nutrient uptake across the brush border of the small intestine, called the everted sleeve technique. Accurate assessment of modulation of mediated uptake with the everted sleeve technique requires measurement of (1) passive uptake and (2) the sum of passive and mediated (combined) uptake across intact mucosal epithelium with cytologically intact enterocytes (Starck et al. 2000). Recently, Starck et al. (2000) demonstrated that extensive tissue damage may occur due to eversion and, subsequently, to stirring during incubation with the everted sleeve technique. They recommended that histological evaluations of tissue damage be conducted to assess the reliability of uptake measurements when this technique is applied to a new species or life stage. The majority of the studies that have examined changes in digestive performance, that is, modulation of mediated nutrient uptake rates, of small endotherms (mainly rodents and birds)

Correlation of body weight with hatchling blood glucose concentration and its relationship to embryonic survival

The negative correlation between selection for rapid growth and embryonic survival was investigated. Embryonic growth was assessed with hatchling weights of a closed population of commercial turkey breeders. Hatchling weights were highly significantly (P < 0.0001) and positively correlated with blood glucose concentrations at hatching. This relationship existed for both tom and hen poults. Significant differences among dams for hatchling blood glucose were observed. Further experiments examined dams selected for producing poults hatching with high (High) or low (Low) blood glucose concentrations. The High embryos were in larger-sized eggs with the same eggshell conductance but with significantly lower conductance constants than the Low embryos, suggesting that Low had longer incubation periods. High embryos grew faster than Low embryos with elevated organ glycogen concentrations. Organic acid analysis indicated elevated plasma alpha-ketoglutarate, urate, and beta-hydroxy butyrate concentrations, suggesting a greater reliance on gluconeogenesis for the High group. Posthatch growth was significantly positively correlated with hatchling blood glucose concentrations in toms but not in hens. Tom poults hatching with elevated glucose were heavier than low glucose hatch mates until 22 wk of age, but hen poults displayed no differences until 16 wk when High hens weighed less than Low hens. These data suggest that the negative correlation between rapid growth and embryonic survival is related to egg-shell conductance constants and embryonic energy metabolism.

Countergradient Selection for Rapid Growth in Pumpkinseed Sunfish: Disentangling Ecological and Evolutionary Effects

Countergradient Selection for Rapid Growth in Pumpkinseed Sunfish: Disentangling Ecological and Evolutionary Effects

FORAGING TRADE-OFFS ALONG A PREDATOR–PERMANENCE GRADIENT IN SUBALPINE WETLANDS

We conducted a series of field and laboratory experiments to determine the direct and indirect effects of a top predator, the tiger salamander (Ambystoma tigrinum nebulosum), on larvae of two species of limnephilid caddisflies (Limnephilus externus and Asynarchus nigriculus) in subalpine wetlands in central Colorado. Asynarchus larvae pre- dominate in temporary wetlands and are aggressive intraguild predators on Limnephilus larvae, which only predominate in permanent basins with salamanders. We first conducted a field experiment in mesocosms (cattle tanks) to quantify the predatory effects of different life stages of salamanders on the two caddisfly species. Two life stages of the salamanders (larvae and paedomorphs) preferentially preyed on Asynarchus relative to Limnephilus. Subsequent laboratory experiments revealed that high Asynarchus activity rates and rela- tively ineffective antipredatory behaviors led to higher salamander detection and attack rates compared to Limnephilus. In a second field experiment (full factorial for presence and absence of each of the three species), we found that salamander predation on Asynarchus had an indirect positive effect on Limnephilus: survival was higher in the presence of salamanders + Asynarchus than with just Asynarchus. In the laboratory we compared the predatory effects of salamanders with and without their mouths sewn shut and found the observed indirect positive effect on Limnephilus survival to be mainly the result of reduced numbers of Asynarchus rather than salamander-induced changes in Asynarchus behavior. We argue that indirect effects of predator-predator interactions on shared prey will be mainly density-mediated and not trait-mediated when one of the predators (in this case, Asynarchus) is under strong selection for rapid growth and therefore does not modify foraging behaviors in response to the other predator. The reciprocal dominance of Lim- nephilus and Asynarchus in habitats with and without salamanders probably reflects a trade- off between competitive superiority and vulnerability to predation. The high activity levels and aggressiveness that enable Asynarchus to complete development in temporary habitats result in strong asymmetric competition (via intraguild predation) with Limnephilus. In permanent habitats these same behaviors increase Asynarchus vulnerability to salamander predation, which indirectly benefits Limnephilus. This and previous work implicate sala- manders as keystone predators that exert a major influence on the composition of benthic and planktonic assemblages in subalpine wetlands.