High Selection Lines Research Articles

Divergent selection for natural antibodies in poultry in the presence of a major gene

BackgroundNatural antibodies (NAb) are antibodies that are present in a healthy individual without requiring previous exposure to an exogenous antigen. Selection for high NAb levels might contribute to improved general disease resistance. Our aim was to analyse the genetic background of NAb based on a divergent selection experiment in poultry, and in particular the effect of a polymorphism in the TLR1A gene.MethodsThe study population consisted of a base population from a commercial pure-bred elite white leghorn layer line and seven generations of birds from a High and Low selection line. Birds were selected for total KLH-binding NAb titer (IgTotal). An enzyme-linked immunosorbent assay was performed to determine NAb titers in blood plasma for IgTotal and the antibody isotypes IgM and IgG. NAb titers were available for 10,878 birds. Genotypes for a polymorphism in TLR1A were determined for chickens in generations 5, 6 and 7. The data were analysed using mixed linear animal models.ResultsThe heritability estimate for IgM was 0.30 and higher than that for IgG and IgTotal (0.12). Maternal environmental effects explained 2 to 3% of the phenotypic variation in NAb. Selection for IgTotal resulted in a genetic difference between the High and Low line of 2.4 titer points (5.1 genetic standard deviation) in generation 7. For IgM, the selection response was asymmetrical and higher in the Low than the High line. The frequency of the TLR1A C allele was 0.45 in the base population and 0.66 and 0.04 in generation 7 of the High and Low line, respectively. The TLR1A polymorphism had large and significant effects on IgTotal and IgM. Estimated genotypic effects suggest full dominance of the TLR1A C allele. Significant TLR1A by generation interactions were detected for IgM and IgTotal.ConclusionsThe effect of a polymorphism in the TLR1A gene on IgTotal and IgM NAb was confirmed. Furthermore, we provide experimental verification of changes in allele frequencies at a major gene with dominant gene action on a quantitative trait that is subjected to mass selection. TLR1A by generation interactions indicate sensitivity to environmental factors.

High and low feather pecking selection lines of laying hens differ in response to a judgment bias test

Feather pecking represents a serious problem in the poultry industry that can negatively affect production as well as the welfare of laying hens. Although feather pecking has been studied from many different angles, there are only a few studies of the relationship between feather pecking and cognition. This study aims to compare the cognitive performance of hens from the high feather pecking (HFP) and the low feather pecking (LFP) lines in a visual discrimination (Go/No-Go) task and to study their decision making under ambiguity using the judgment bias test.Twenty HFP and 20 LFP hens were trained in a visual discrimination task to approach a coloured feeder (white for half of the hens and black for the other half) containing a reward (one mealworm) and to refrain from approaching a feeder with a different colour (colour opposite to positive, i.e. black or white) to avoid punishment (water spraying). During the subsequent judgment bias tests hens were tested in the presence of the positive, negative or ambiguous stimulus (grey coloured feeder), always one type of stimulus at a time. The latencies to reach each of the stimuli were recorded. At the end of the visual discrimination training phase, 36 out of 40 hens successfully discriminated the positive and the negative coloured feeder. There was a slower association of the coloured feeder with the reward in the HFP line and HFP hens did not suppress the response to the negative stimulus as effective as HFP hens, which could be a sign of their high motor impulsiveness. However, in the judgment bias test HFP hens approached the ambiguous feeder significantly faster than LFP hens (HFP 13.59 ± 1.11 s, LFP 16.68 ± 1.10 s, P < 0.05), that can be interpreted as evidence that hens from the HFP line are more optimistic, i.e. that they are in a more positive affective state. The high motor impulsiveness of HFP hens provides another possible explanation for their response to the ambiguous stimulus. However, higher motor activity of the HFP line did not affect the results of the judgment bias test. Furthermore, there were no significant differences in plasma corticosterone levels between the lines, suggesting that differences in stress levels might not explain the results of the judgment bias test.

Selective breeding for high natural antibody level increases resistance to avian pathogenic Escherichia coli (APEC) in chickens

Keyhole limpet hemocyanin (KLH)-binding natural antibody (NAb) titers in chickens are heritable, and higher levels have previously been associated with a higher survival. This suggests that selective breeding for higher NAb levels might increase survival by means of improved general disease resistance. Chickens were divergently selected and bred for total NAb levels binding KLH at 16 weeks of age for six generations, resulting in a High NAb selection line and a Low NAb selection line. To for test differences in disease resistance, chickens were challenged with avian pathogenic Escherichia coli (APEC) in two separate experiments. Chickens at 8 days of age received one of four intratracheal inoculations of 0.2 mL phosphate buffered saline (PBS): 1) mock inoculate, 2) with 0.2 mL PBS containing 108.20 colony-forming units (CFU)/mL APEC, 3) with 0.2 mL PBS containing 106.64 CFU/mL APEC, and 4) with 0.2 mL PBS containing 107.55 CFU/mL APEC. Mortality was recorded during 7 days post inoculation. Overall, 50–60% reduced mortality was observed in the High line compared to the Low line for all APEC doses. In addition, morbidity was determined of the surviving chickens at 15 days of age. The High line had lower morbidity scores compared to the Low line. We conclude that selective breeding for high KLH-binding NAb levels at 16 weeks of age increase APEC resistance in early life. This study and previous studies support the hypothesis that KLH-binding NAb might be used as an indicator trait for to selective breed for general disease resistance in an antigen non-specific fashion.

Artificial selection on ant female caste ratio uncovers a link between female-biased sex ratios and infection by Wolbachia endosymbionts.

Social insect sex and caste ratios are well-studied targets of evolutionary conflicts, but the heritable factors affecting these traits remain unknown. To elucidate these factors, we carried out a short-term artificial selection study on female caste ratio in the ant Monomorium pharaonis. Across three generations of bidirectional selection, we observed no response for caste ratio, but sex ratios rapidly became more female-biased in the two replicate high selection lines and less female-biased in the two replicate low selection lines. We hypothesized that this rapid divergence for sex ratio was caused by changes in the frequency of infection by the heritable bacterial endosymbiont Wolbachia, because the initial breeding stock varied for Wolbachia infection, and Wolbachia is known to cause female-biased sex ratios in other insects. Consistent with this hypothesis, the proportions of Wolbachia-infected colonies in the selection lines changed rapidly, mirroring the sex ratio changes. Moreover, the estimated effect of Wolbachia on sex ratio (~13% female bias) was similar in colonies before and during artificial selection, indicating that this Wolbachia effect is likely independent of the effects of artificial selection on other heritable factors. Our study provides evidence for the first case of endosymbiont sex ratio manipulation in a social insect.

Genetic and Genomic Response to Selection for Food Consumption in Drosophila melanogaster.

Food consumption is an essential component of animal fitness; however, excessive food intake in humans increases risk for many diseases. The roles of neuroendocrine feedback loops, food sensing modalities, and physiological state in regulating food intake are well understood, but not the genetic basis underlying variation in food consumption. Here, we applied ten generations of artificial selection for high and low food consumption in replicate populations of Drosophila melanogaster. The phenotypic response to selection was highly asymmetric, with significant responses only for increased food consumption and minimal correlated responses in body mass and composition. We assessed the molecular correlates of selection responses by DNA and RNA sequencing of the selection lines. The high and low selection lines had variants with significantly divergent allele frequencies within or near 2081 genes and 3526 differentially expressed genes in one or both sexes. A total of 519 genes were both genetically divergent and differentially expressed between the divergent selection lines. We performed functional analyses of the effects of RNAi suppression of gene expression and induced mutations for 27 of these candidate genes that have human orthologs and the strongest statistical support, and confirmed that 25 (93%) affected the mean and/or variance of food consumption.

Response of the goat mammary gland to infection with Staphylococcus aureus revealed by gene expression profiling in milk somatic and white blood cells

BackgroundS. aureus is one of the main pathogens responsible for the intra-mammary infection in dairy ruminants. Although much work has been carried out to understand the complex physiological and cellular events that occur in the mammary gland in response to S. aureus, the protective mechanisms are still poorly understood. The objectives of the present study were to investigate gene expression during the early response of the goat mammary gland to an experimental challenge with S. aureus, in order to better understand the local and systemic response and to compare them in two divergent lines of goat selected for high and low milk somatic cell scores.ResultsNo differences in gene expression were found between high and low SCS (Somatic Cells Score) selection lines. Analysing the two groups together, an expression of 300 genes were found to change from T0 before infection, and T4 at 24 hours and T5 at 30 hours following challenge. In blood derived white blood cells 8 genes showed increased expression between T0 and T5 and 1 gene has reduced expression. The genes showing the greatest increase in expression following challenge (5.65 to 3.16 fold change) play an important role in (i) immune and inflammatory response (NFKB1, TNFAIP6, BASP1, IRF1, PLEK, BATF3); (ii) the regulation of innate resistance to pathogens (PTX3); and (iii) the regulation of cell metabolism (CYTH4, SLC2A6, ARG2). The genes with reduced expression (−1.5 to −2.5 fold) included genes involved in (i) lipid metabolism (ABCG2, FASN), (ii) chemokine, cytokine and intracellular signalling (SPPI), and (iii) cell cytoskeleton and extracellular matrix (KRT19).ConclusionsAnalysis of genes with differential expression following infection showed an inverse relationship between immune response and lipid metabolism in the early response of the mammary gland to the S. aureus challenge. PTX3 showed a large change in expression in both milk and blood, and is therefore a candidate for further studies on immune response associated with mastitis.

Onset of puberty and early-life reproduction in Angus females divergently selected for post-weaning residual feed intake

Angus cattle that had been divergently selected for Low and High post-weaning residual feed intake (RFI) were used in two projects to evaluate early-life reproductive performance and onset of puberty in females. In the first project, data on the 1999-born females (n = 64) were evaluated for weight, subcutaneous fat (P8 fat depth) and reproductive performance over two breeding cycles. These females that were the result of 1.0–2.5 (mean of 1.8) generations of selection, had mean (±s.e.) post-weaning RFI of –0.82 ± 0.19 kg/day and 0.57 ± 0.18 kg/day for the Low and High RFI selection lines, respectively. In the second project, ultrasonography was used to scan the ovaries of the 2008-born heifers (n = 121) on four occasions following weaning. In these heifers the presence of corpus luteum provided evidence of ovulation, and hence the commencement of onset of puberty. The average of the estimated breeding value (EBV) for RFI of the parents of the Low RFI and the High RFI selection line heifers were –0.72 ± 0.05 and 0.37 ± 0.03 kg/day, respectively. In the first project, no significant selection line differences were evident for weight, age at first mating, pregnancy and calving rates (percentage of females that were pregnant, or the percentage that calved out of the total number used for mating), calf birthweight and weight of calf born per female exposed to bull. Females from the Low RFI line had significantly (P &lt; 0.05) lower P8 fat depth relative to their High RFI contemporaries at most of the measurement dates (e.g. 9.2 ± 0.5 versus 12.0 ± 0.5 mm at the start of first mating). Low RFI females also calved significantly (P &lt; 0.05) later in the calving season than High RFI females (35.7 ± 3.0 versus 27.6 ± 2.4 days). The results indicate that there is a delayed pregnancy date during the first mating season leading to a later calving date for the Low RFI heifers. The later first calving date was then maintained at subsequent calving. The later calving, however, did not impact on pregnancy and calving rates. In the second project, it was observed that irrespective of selection line, heifers that had attained onset of puberty had significantly (P &lt; 0.05) greater P8 fat depth than those that had not. Hence the expectation was that, relative to High RFI heifers, the Low RFI heifers with their lower P8 fat, will attain onset of puberty at a slightly older age. This expected trend was observed but the difference was not significant, and further investigations are recommended.

Analysis of severe feather pecking behavior in a high feather pecking selection line

Even though feather pecking (FP) in laying hens has been extensively studied, a good solution to prevent chickens from this behavior under commercial circumstances has not been found. Selection against FP behavior is possible, but for a more effective selection across different populations, it is necessary to characterize the genetic mechanism associated with this behavior. In this study, we use a high FP selection line, which has been selected for 8 generations. We present evidence of the presence of a major dominant allele affecting the FP behavior by using an argument based on the presence of mixture in the distribution of the observed FP and by studying the evolution of the proportion of very high FP along the sequence of 8 generations. This hypothesis is further supported by the fact that the gene transcription profile of the birds performing high FP differs from the profile of the other birds performing FP (456 genes differentially expressed from a total of 14,077 investigated genes).

QTL Underlying Voluntary Exercise in Mice: Interactions with the "Mini Muscle" Locus and Sex

Exercise improves many aspects of human health, yet many people remain inactive even when exercise is prescribed. We previously created a backcross (BC) between mice selectively bred for high levels of voluntary wheel running (VWR) and fixed for "mini muscle" (MM), a recessive mutation causing approximately 50% reduction in triceps surae mass. We previously showed that BC mice having the MM trait ran faster and further than mice without MM and that MM maps to chromosome 11. Here, we genotyped the BC with genome-wide single nucleotide polymorphisms to identify quantitative trait loci (QTL) controlling voluntary exercise and tissue and body mass traits and to determine whether these QTL interact with the MM locus or with sex. We detected 3 VWR QTL, representing the first voluntary exercise QTL mapped using this high running selection line, and 5 tissue mass QTL. Several interactions between trait QTL and the MM locus as well as sex were also identified. These results begin to explain the genetic architecture of VWR and further support MM as a locus having major effects, including its main effects on the muscle phenotype, its pleiotropic effects on wheel running and tissue mass traits, and through its interactions with other QTL and with sex.

Quantitative analysis of performance, carcass and meat quality traits in cattle from two Australian beef herds in which a null myostatin allele is segregating

Two Australian beef cattle herds, in which selection for muscularity was a primary objective, were used in this study to identify bovine myostatin (MSTN) mutations associated with increased muscling, and to assess associations between genotype and performance, carcass and meat quality traits. One was a research herd (herd A) established from Angus × Hereford cows, and comprised a high and low muscle selection line. The other (herd B) was a commercial beef enterprise with cattle of Angus and Charolais origin. Sequencing of the MSTN coding region and flanking splice junctions in an initial sample of 34 animals from both herds identified the 821 del11 mutation as well as six other polymorphic sites. The nucleotide 374–50C &gt; T polymorphism in intron 1 was found to be in linkage disequilibrium with the 821 del11 mutation, with both variants confined to the high muscle selection line in herd A. No other variants were exclusive to either of the two herd A selection lines. The effect of the 821 del11 mutation was further investigated in a total of 803 cattle from both herds. A relatively high prevalence of 821 del11 heterozygotes (herd A 16%; herd B 23%) was found and heterozygotes had significant advantages in eye muscle area and muscle score over their wildtype counterparts, and did not differ in meat quality. Retail beef yield from steers was higher for the 821 del11 heterozygotes from herd A (67.0 v. 63.5%) and herd B (71.8 v. 68.6%), relative to homozygous wildtype contemporaries, demonstrating the benefits of incorporating single null MSTN alleles into breeding programs.

Crawl-out behaviour in response to predation cues in an aquatic gastropod: insights from artificial selection

Local adaptation to predation often occurs in populations experiencing stable predator regimes. Under such conditions, prey species may respond by fine-tuning their behavioural defences towards a local optimum, although it is often difficult to ascertain whether such local adaptation is due to selection on fixed traits, developmental plasticity that is dependent on relatively long term exposure to environmental cues or phenotypic plasticity that can respond rapidly to a changing environment. Here we investigate whether anti-predator behaviour in two populations of the freshwater gastropod Lymnaea stagnalis responded to artificial selection. Previous work had shown that populations of this species showed a higher level of innate avoidance behaviour (crawling above the water line) in the presence of predatory fish compared with sites lacking this predation threat. By selectively breeding from high and low response selection lines, we demonstrated that this crawl-out behaviour responds rapidly to artificial selection: high response selection lines showed a significant increase and low response selection lines a significant decrease in avoidance compared with non-selected control lines. This suggests that the crawl out response in this species is heritable, and that there is potential for a response to selection in natural populations, which may produce the divergence in the plasticity of crawl out behaviour found between gastropod populations experiencing high and low predation intensity.

Effects of divergent selection for serum insulin-like growth factor-I concentration on performance, feed efficiency, and ultrasound measures of carcass composition traits in Angus bulls and heifers

Angus bulls and heifers from lines divergently selected for serum IGF-I concentration were used to evaluate the effects of IGF-I selection line on growth performance and feed efficiency in 2 studies. In study 1, bulls (low line, n = 9; high line, n = 8; initial BW = 367.1 +/- 22.9 kg) and heifers (low line, n = 9; high line, n = 13; initial BW = 286.4 +/- 28.6 kg) were adapted to a roughage-based diet (ME = 1.95 Mcal/kg of DM) for 24 d and fed individually for 77 d by using Calan gate feeders. In study 2, bulls (low line, n = 15; high line, n = 12; initial BW = 297.5 +/- 34.4 kg) and heifers (low line, n = 9; high line, n = 20; initial BW = 256.0 +/- 25.1 kg) were adapted to a grain-based diet (ME = 2.85 Mcal/kg of DM) for 32 d and fed individually for 70 d by using Calan gate feeders. Blood samples were collected at weaning and at the start and end of each study, and serum IGF-I concentration was determined. Residual feed intake (RFI) was calculated, within study, as the residual from the linear regression of DMI on midtest BW(0.75), ADG, sex, sex by midtest BW(0.75) and sex by ADG. In study 1, calves from the low IGF-I selection line had similar initial and final BW and ADG, compared with calves from the high IGF-I selection line. In addition, DMI and feed conversion ratio were similar between IGF-I selection lines; however, calves from the low IGF-I selection line tended (P < 0.10) to have lesser RFI than calves from the high IGF-I selection line (-0.26 vs. 0.24 +/- 0.31 kg/d). In study 2, IGF-I selection line had no influence on performance or feed efficiency traits. However, there was a tendency (P = 0.15) for an IGF-I selection line x sex interaction for RFI. Bulls from the low IGF-I selection line had numerically lesser RFI than those from the high IGF-I selection line, whereas in heifers, the IGF-I selection line had no effect on RFI. In studies 1 and 2, weaning and initial IGF-I concentrations were not correlated with either feed conversion ratio or RFI. However, regression analysis revealed a sex x IGF-I concentration interaction for initial IGF-I concentration in study 1 and weaning IGF-I concentration in study 2 such that the regression coefficient was positive for bulls and negative for heifers. These data suggest that genetic selection for postweaning serum IGF-I concentration had a minimal effect on RFI in beef cattle.

Selection for salt tolerance and its genetic basis in perennial ryegrass (Lolium perenne L.)

Salt tolerance of two selected lines of Lolium perenne L. (high selection and low selection) was assessed in comparison with control unselected line after three weeks growth in solution culture at 0, 50, 100, 150, 200, 250, and 300 mol m-3 NaCl. The high selection line had significiantly higher root growth compared with the low selection and unselected lines at all salt concentrations. In order to assess the usefulness of a second cycle of selection, 8000 seeds of each of the high selection and unselected (control) lines were screened after three weeks growth in 325 mol m-3 NaCl. A large number of individuals in the high selection line produced remarkably longer roots than the control lines. Pair crosses were made between the high selection and the low selection in order to investigate additive genetic component at two NaCl treatments, 150 and 250 mol m-3, Additive genetic component was quite high at both the salt treatments.

Different effects of temperature on recombination in lines of Neurospora crassa selected for high and for low recombination frequency

Wild-type isolates of Neurospora crassa, picked out from lines selected for high and for low frequency of second division segregation (SDS) at 25oC for asco in linkage group (LG) VI, were scored for temperature effects on SDS-frequency for asco and on recombination frequencies in two adjacent intervals in LG II. Results obtained at 25oC and 17oC were compared. In the high selection line, the SDS-frequency for asco in both mating types (mt:s) decreased at 17oC compared to results obtained at 25oC. In the low selection line the SDS-frequency for asco in mt A increased at 17oC compared to results obtained at 25oC, while no significant effect of temperature on SDS-frequency for asco could be established in mt a. In LG II, temperature effects on recombination frequencies could only be established in the interval spanning the centromere, in one of the crosses involving an isolate from the high selection line. The recombination frequency increased at 17oC compared to results obtained at 25oC. The results are interpreted in terms of varying access in different genotypes, to gene products promoting and obstructing meiotic recombination, respectively.

Recombination in other chromosomal regions than the interval subjected to selection, in lines of Neurospora crassa selected for high and for low recombination frequency

Recombination studies involving regions of the linkage groups (LG:s) I, II, III, IV, V and VI were performed in wild-type isolates of Neurospora crassa picked out from lines selected for high and for low frequency of second division segregation (SDS) for asco in the left arm of LG VI. Significant differences in recombination frequencies between high and low selection lines were obtained when proximal regions in the LG:s I, IV, V and the left arm of LG VI were scored, while no difference between lines could be established in the regions located in the LG:s II, III and in the right arm of LG VI. The correlation between SDS-frequencies for asco obtained with different asco tester strains was much stronger than the correlation between SDS-frequencies for asco and the recombination frequency in any of the other regions tested. This suggests that some of the genetic factors separating the recombination frequencies of the two selection lines operate mainly within the asco-centromere interval.

Direct and correlated responses to selection for high or low faecal nematode egg count in Perendale sheep

A selection experiment with Perendale sheep was established in 1986, with lines selected solely on the basis of high or low faecal nematode egg count (FEC) in lambs after weaning. Ranking for FEC involved a natural mixed‐species challenge in all years, although in early years this was augmented by an artificial challenge with Haemonchus contortus larvae. Faecal samples were taken from each animal for FEC on two occasions, separated by an anthelmintic drench. A total of 1840 lambs were recorded for FEC in the high and low selection lines from 1986 up to the 2002‐born lamb crop. Direct responses to divergent selection for or against FEC were estimated, along with indirect responses in live weights (lambs, yearlings, and adult mixed‐age ewes), in fleece weights (yearlings and ewes) and in breech soiling ("dag") scores. Analyses of both lines across all years were carried out using animal‐model restricted maximum likelihood techniques and also fixed‐effects models. The realised heritabilities of loge(FEC + 100) at the two sampling times were 0.22 ± 0.03 and 0.16 ± 0.03; the genetic correlation estimates between loge(FEC1 + 100) and yearling live weight and fleece weight were 0.36 ± 0.17 and 0.54 ± 0.16, respectively. Averaging the breeding value results for the 1998–2002 crops, the back‐transformed FEC means averaged 556 and 114 eggs/g for the high and low lines, respectively, representing a 4.9‐fold line difference. When exposed to equal parasite challenge, lambs from the high FEC line were heavier than low‐line lambs by 6–12% (breeding ewes 8%), with all differences being significant (P < 0.001); corresponding figures for fleece weight were 24–26% (breeding ewes 15%), again with all differences significant (P< 0.001), and dag scores averaged 0.55 units higher in low‐line animals (P < 0.001). It is concluded that, under natural mixed‐species parasite challenge on pasture, small rates of genetic change for FEC were achieved in small, closed populations of Perendales. There were unfavourable correlated responses to selection to reduce FEC, comprising lower weights, reduced fleece weights, and more dags. The prospect of index selection to break the unfavourable genetic correlations with FEC is discussed.

Effect of the O chromosome of Drosophila subobscura on abdominal bristle number.

The role of the O chromosome of D. subobscura on the control of abdominal bristle number was analyzed. The study was performed using four strains derived from four lines selected for high (H1 and H2) and low (L1 and L2) bristle number. In all the lines, the factors for abdominal bristle number carried on the O chromosome showed additive effects and diminished the number of abdominal bristles. The negative effect of the O chromosomes from low selection lines was found to be stronger than the negative effect of the O chromosomes from high selection lines.

Plant chemical defense against herbivores and pathogens: generalized defense or trade-offs?

Plants are often attacked by multiple enemies, including pathogens and herbivores. While many plant secondary metabolites show specific effects toward either pathogens or herbivores, some can affect the performance of both these groups of natural enemies and are considered to be "generalized defense compounds". We tested whether aucubin and catalpol, two iridoid glycosides present in ribwort plantain (Plantago lanceolata), confer in vivo resistance to both the generalist insect herbivore Spodoptera exigua and the biotrophic fungal pathogen Diaporthe adunca using plants from P. lanceolata lines that had been selected for high- and low-leaf iridoid glycoside concentrations for four generations. The lines differed approximately three-fold in the levels of these compounds. Plants from the high-selection line showed enhanced resistance to both S. exigua and D. adunca, as evidenced by a smaller lesion size and a lower fungal growth rate and spore production, and a lower larval growth rate and herbivory under both choice and no-choice conditions. Gravimetric analysis revealed that the iridoid glycosides acted as feeding deterrents to S. exigua, thereby reducing its food intake rate, rather than having post-ingestive toxic effects as predicted from in vitro effects of hydrolysis products. We suggest that the bitter taste of iridoid glycosides deters feeding by S. exigua, whereas the hydrolysis products formed after tissue damage following fungal infection mediate pathogen resistance. We conclude that iridoid glycosides in P. lanceolata can serve as broad-spectrum defenses and that selection for pathogen resistance could potentially result in increased resistance to generalist insect herbivores and vice versa, resulting in diffuse rather than pairwise coevolution.

Ram mating behavior after long-term selection for reproductive rate in Rambouillet ewes1

Mating behavior is known to be heritable in several species, but it is not known if selection schemes for ewe reproductive traits affect mating behavior of rams. Therefore, our objectives were to determine if divergent (high vs low index) selection of a female reproductive trait (lambs born divided by age of ewe minus one) affects mating behavior patterns of male offspring during training to service an artificial vagina (AV) in a less than natural setting (Exp. 1) or during serving capacity tests (SCT) in simulated natural mating conditions (Exp. 2). The method for evaluating male mating behavior was a series of serving capacity tests to estimate sexual performance. For Exp. 1, five, 30-min observations were conducted to assess the mating behavior of 29 rams (22 mo old) being trained to service an AV. In Exp. 1, percentages of rams mounting (73 vs 36%) and ejaculating (67 vs 29%) differed (P < 0.05) between rams from high and low Rambouillet ewe selection lines, respectively. In Exp. 2, ram classification consisted of exposing each 22- to 24-mo-old ram (n = 48) to three unrestrained ewes in estrus for 18, 30-min tests. Any ram that had not mounted or ejaculated during SCT was evaluated for sexual orientation in a 30-min preference test in which each ram had access to both restrained estrual ewes and restrained rams. In Exp. 2, there was no difference (P > 0.2) in percentages of rams mounting (92 vs 78%) and ejaculating (88 vs 74%) between rams from high and low Rambouillet ewe selection lines, respectively. There was no difference (P > 0.33) between high and low ewe selection line rams for mounts or ejaculations for 18 SCT. Only one male-oriented ram was identified, which was from the high line. In Exp. 2, six SCT were necessary to obtain 95% reliability in sexual performance scores. Results of these studies indicate that long-term selection of ewes for litter size did not alter ram sexual performance after SCT under simulated natural mating conditions or affect incidence of male-oriented rams. Mating behavior observed during training to service an AV was lower for rams from ewes of the low selection line than for rams from ewes of the high selection line. We concluded that long-term selection for reproductive rate in ewes did not alter mating behavior patterns of male offspring; however, test conditions, such as restrained and unrestrained ewes and number of serving capacity tests, may affect conclusions in studies that evaluate sexual performance of rams.

Ram mating behavior after long-term selection for reproductive rate in Rambouillet ewes

Mating behavior is known to be heritable in several species, but it is not known if selection schemes for ewe reproductive traits affect mating behavior of rams. Therefore, our objectives were to determine if divergent (high vs low index) selection of a female reproductive trait (lambs born divided by age of ewe minus one) affects mating behavior patterns of male offspring during training to service an artificial vagina (AV) in a less than natural setting (Exp. 1) or during serving capacity tests (SCT) in simulated natural mating conditions (Exp. 2). The method for evaluating male mating behavior was a series of serving capacity tests to estimate sexual performance. For Exp. 1, five, 30-min observations were conducted to assess the mating behavior of 29 rams (22 mo old) being trained to service an AV. In Exp. 1, percentages of rams mounting (73 vs 36%) and ejaculating (67 vs 29%) differed (P < 0.05) between rams from high and low Rambouillet ewe selection lines, respectively. In Exp. 2, ram classification consisted of exposing each 22- to 24-mo-old ram (n = 48) to three unrestrained ewes in estrus for 18, 30-min tests. Any ram that had not mounted or ejaculated during SCT was evaluated for sexual orientation in a 30-min preference test in which each ram had access to both restrained estrual ewes and restrained rams. In Exp. 2, there was no difference (P > 0.2) in percentages of rams mounting (92 vs 78%) and ejaculating (88 vs 74%) between rams from high and low Rambouillet ewe selection lines, respectively. There was no difference (P > 0.33) between high and low ewe selection line rams for mounts or ejaculations for 18 SCT. Only one male-oriented ram was identified, which was from the high line. In Exp. 2, six SCT were necessary to obtain 95% reliability in sexual performance scores. Results of these studies indicate that long-term selection of ewes for litter size did not alter ram sexual performance after SCT under simulated natural mating conditions or affect incidence of male-oriented rams. Mating behavior observed during training to service an AV was lower for rams from ewes of the low selection line than for rams from ewes of the high selection line. We concluded that long-term selection for reproductive rate in ewes did not alter mating behavior patterns of male offspring; however, test conditions, such as restrained and unrestrained ewes and number of serving capacity tests, may affect conclusions in studies that evaluate sexual performance of rams.