Male Reproductive Traits Research Articles

Inbreeding, fluctuating asymmetry, and ejaculate quality in an endangered ungulate.

An ever-increasing number of species are suffering marked reductions in population size as a consequence of human activities. To understand the impact of these changes it is essential to assess how small population size affects individual fitness and the viability of populations. This issue acquires special relevance among endangered species in which numbers have decreased to such an extent that captive breeding must be established with a few founders. A major risk associated with small population size is inbreeding depression. The effects of inbreeding upon male reproductive traits are the subject of an ongoing controversy, since the evidence linking lack of genetic variability and poor ejaculate quality at the population level has been criticized recently by several authors. We report that among Gazella cuvieri males, inbreeding coefficient shows a strong inverse relationship with ejaculate quality. Furthermore, the degree of fluctuating asymmetry is positively related to the coefficient of inbreeding and negatively related to the proportion of normal sperm, suggesting that it is a reliable indicator of genetic stress and of ejaculate quality.

Nutrient Levels and Salinity Affect Gender and Floral Traits in the Autogamous Spergularia marina

The effects of nutrient levels and salinity on prezygotic components of gender (number of ovules and of anthers per flower), on secondary accessory structures (number and size of petals), and on possible indicators of normal development (number of abnormal anthers and staminodes) were investigated for six maternal families of the highly autogamous Spergularia marina, cultivated under controlled conditions in hydroponic tubs. Mean ovule number and mean staminode number per flower were not affected by changes in nutrient levels and salinity, while mean anther number per flower decreased and mean petal size increased under the harsher growing conditions (low-nutrient level or salinity). Mean petal and abnormal anther numbers per flower were affected by nutrient levels but not by the salinity treatment. We observed few significant phenotypic correlations among the seven studied traits but observed strong phenotypic correlations between petal number and abnormal anther number under all growing conditions. The overall lack of treatment-specific correlations indicates that evolutionary trajectories in this species may not be strongly affected by the environmental conditions under which natural selection occurs. In contrast to other studies, we report that, for traits expressed prior to pollination, male reproductive traits (number of normal and abnormal anthers per flower) were more sensitive to growing conditions than were traits related to female reproduction (ovule number per flower). Finally, in partial opposition to our initial prediction, we found that the anther/ovule ratio was highly sensitive to salinity but not to nutrient level.

Floral Phenology of Sex-Changing Dwarf Ginseng (Panax trifolium L., Araliaceae)

-This report documents phenological differences between the gender phases of a diphasic plant, Panax trifolium. Pollen presentation by males peaks later than pollen presentation by hermaphrodites and closely coincides with presentation of receptive stigmas by hermaphrodites. Males also have longer periods of pollen presentation than do hermaphrodites. Our results suggest that male-male competition has affected the differentiation of gender phases with respect to male reproductive traits.

Estimates of covariances between reproduction and growth in Australian beef cattle1

Estimates of covariance components between scrotal circumference, serving capacity, days to calving, and yearling and final weight were obtained for Hereford, Angus, and Zebu cross cattle in temperate and tropical Australia. Analyses were carried out by REML employing a derivative-free algorithm and fitting bivariate animal models. Aspects of modeling and computational requirements related to the use of this method are discussed. Estimates of heritabilities agreed closely with those from univariate analyses, being low for female reproductive performance and moderate to high for male reproduction and growth. Estimates of genetic correlation between male and female fertility traits were low but favorable, being -.25, -.28, and -.41 between scrotal circumference and days to calving for Herefords, Angus, and Zebu crosses, respectively. Genetic correlations between male reproductive traits and weights ranged from .24 to .52 for the temperate breeds and were higher (.65 to .69) for Zebu crosses. Phenotypic correlations between scrotal circumference and weights were similar for all breeds, ranging from .32 to .47, whereas serving capacity and weights were phenotypically unrelated. Estimates of correlations between days to calving and weights were less consistent. Phenotypically, there was little association between the two traits. Genetic correlations for Zebu crosses were negative and low to moderate (-.36 to -.66) and estimates for Angus were close to zero.

EVOLUTION OF GENERALISTS AND SPECIALISTS IN SPATIALLY HETEROGENEOUS ENVIRONMENTS.

Quantitative genetic models are used to investigate the evolution of generalists and specialists in a coarse-grained environment with two habitat types when there are costs attached to being a generalist. The outcomes for soft and hard selection models are qualitatively different. Under soft selection (e.g., for juvenile or male-reproductive traits) the population evolves towards the single peak in the adaptive landscape. At equilibrium, the population mean phenotype is a compromise between the reaction that would be optimal in both habitats and the reaction with the lowest cost. Furthermore, the equilibrium is closer to the optimal phenotype in the most frequent habitat, or the habitat in which selection on the focal trait is stronger. A specialist genotype always has a lower fitness than a generalist, even when the costs are high. In contrast, under hard selection (e.g., for adult or female-reproductive traits) the adaptive landscape can have one, two, or three peaks; a peak represents a population specialized to one habitat, equally adapted to both habitats, or an intermediate. One peak is always found when the reaction with the lowest cost is not much different from the optimal reaction, and this situation is similar to the soft selection case. However, multiple peaks are present when the costs become higher, and the course of evolution is then determined by initial conditions, and the region of attraction of each peak. This implies that the evolution of specialization and phenotypic plasticity may not only depend on selection regimes within habitats, but also on contingent, historical events (migration, mutation). Furthermore, the evolutionary dynamics in changing environments can be widely different for populations under hard and soft selection. Approaches to measure costs in natural and experimental populations are discussed.

Heritability Estimates of Male Reproductive and Morphological Traits and Their Genetic Correlations with Female Egg Production and Other Related Traits in Chickens

Three unselected control strains and four strains selected for high egg production were studied. Semen weight (SW), packed sperm volume (PSV), and total sperm weight (TSW) were evaluated on two consecutive days. The female traits were age at first egg (AFE), hen-housed egg number (HHEN), hen-day rate of egg production (HDREP), egg weight (EW), and four egg-quality traits. Wattle and testes size were also measured in the males.Sire-plus-dam component heritabilities ± SE of SW, PSV, and TSW in the selected strains, were .36 ± .08, .42 ± .08 and .32 ± .06. The full sibling component heritabilities for the control strains were: .42 ± .15 for SW, .50 ± .15 for PSV, and .41 ± .15 for TSW. The heritabilities of wattle and testes weights computed by regression of son on father were: .54 ± .10 and .58 ± .11, respectively. The genetic correlations between semen and egg-production traits, estimated by intraclass and regression procedures were generally consistent in sign. The mean genetic correlations of SW, PSV, and TSW with EW were .23, .06 and .17, respectively. Semen traits were unfavorably correlated with HHEN (mean −.23, range −.60 to .04), HDREP (mean −.10, range −.36 to .14), and AFE (mean .27, range .03 to .40). Wattle size measured on 14-mo-old males was favorably correlated with HHEN (mean .36, range .26 to .55), HDREP (mean .23, range .05 to .44), and AFE (mean −.31, range −.17 to −.43). Semen traits as well as size of the testes and wattle appeared to be unrelated to egg-quality traits. Hence, wattle size, measured at an early age, could be useful in selecting for high egg production; and selection for semen production could increase egg size.

Relationships among bovine male and female reproductive traits

No significant relationship (p greater than 0.05) was found between age at puberty in heifers and the age and scrotal circumference at puberty in related bulls. There was a significant effect (p less than 0.01) of genotype and sire on age at puberty of heifers and a significant effect (p less than 0.05) of genotype on weight at puberty in heifers. There was a significant effect of genotype on age (p less than 0.01) and weight (p less than 0.05) at puberty of bulls. A significant difference (p less than 0.05) in age at puberty of bulls was found between the 2 methods of assessing puberty. It is possible that the assessment of puberty of heifers at 2-month intervals may not have been precise enough to detect such a relationship and/or that the variation in genotypes and ages in this study were too great to establish such a relationship.

The effect of the F gene on male reproductive traits in Booroola × South Australian Merino rams

The effect of the Booroola (Bo) F gene on the reproductive development of Bo × South Australian Merino ( 1 2 Bo ) rams was examined. Half Bo rams were offspring of FF (homozygous carrier), F+ (heterozygous carrier) or ++ (homozygous non-carrier) Bo sires, so that the expected frequency of 1 2 Bo rams carrying the gene should be approximately 1.0, 0.5 or 0.0, respectively. The genotype of each Bo sire was defined on the basis of the proportion of daughters with ⩾ 3 ovulations. The reproductive development of the 1 2 Bo rams corresponding with each sire genotype was studied between 5 and 15 months of age. Traits recorded were: live weight, testicular volume, preputial adhesion score, semen volume, semen density, proportion of rams with ejaculates containing spermatozoa, proportion of rams that mounted and proportion of rams that served oestrous ewes. There were no significant differences among sire genotypes in the traits studied, except for preputial adhesion score (FF < F+ = ++, P < 0.05) and proportion of rams that mounted (FF = F+ < ++, P < 0.05) at 5 months of age. The relevance of these differences is not known but could result from sampling problems. It is concluded that (1) the F gene had no discernible role in male reproductive development between 5 and 15 months of age and (2) the traits examined did not allow a distinction between carrier and non-carrier rams of the F gene.

The development of male reproductive traits in progeny of Merino strains of different reproductive performance

Rams of the control South Australian Merino (Bungaree) (Bu) and of the highly fecund Booroola (Bo) and Trangie Fertility (TF) Merino strains were mated to Bu ewes to produce Bu, 1 2 Bo and 1 2 TF experimental progeny. Testicular volume, preputial adhesion score, the percentage of rams with spermatozoa, semen volume and density and components of mating performance were examined periodically between 5 and 15 months of age in the ram progeny. The 1 2 TF and 1 2 Bo outperformed the Bu in all traits; differences were most obvious in testicular volume, penis adhesion score, the percentage of rams with spermatozoa and semen density. Differences also existed between the 1 2 Bo and 1 2 TF ; significant differences occurred at least once during the study period in all traits except testicular volume and the components of mating performance. Most of the differences between the three experimental groups were evident at 5 months and some were still evident at 15 months of age. The ranking of strains on male development ( Bu 1 2 Bo s 1 2 TF ) was dissimilar to that already reported for female performance ( Bu s 1 2 TF 1 2 Bo ) and it is suggested that this inconsistency resulted from a gene of large effect influencing female performance but not male performance of the 1 2 Bo . A preliminary assessment, across strains, of the association between male traits and the reproductive performance of female relatives is provided.

Estimates of genetic correlations between testicular measurements and female reproductive traits in cattle.

Data from 528 male and 645 female progeny of 63 sires were used to estimate genetic correlations between female and male reproductive traits. Data were from two Hereford herds involved in a long-term selection program of the North Carolina Agricultural Experiment Service. Testicular measurements of circumference, diameter, length and volume were obtained on bulls at 205 and 365 d. Testicular growth measures were defined as differences between 205-and 365-d measurements. Heifers were placed in the breeding herd as yearlings and given two breeding seasons to produce a calf. Traits utilized from females were three age-at-first-breeding traits, two age-at-first-calving traits, two pregnancy rate traits, rebreeding interval and calving interval. Genetic correlations were estimated from half-sib and from sire-daughter analyses. Seventy-five percent or more of the correlations of testicular measurements with pregnancy rats, age at first breeding and age at first calving were in the favorable direction. Average correlations were .62, -.55 and -.66, respectively. For each of the remaining female traits, approximately 50% of the correlations were favorable and the average correlations were small. Correlations were summarized by testicular measurement with favorable correlations given a negative sign. Testicular diameter had more favorable correlations (80%) than length, volume or circumference (70%). However, average correlations were similar (-.31, -.30, -.34 and -.26, respectively). Testicular measurements taken at either 205 or 365 d had the same percentage of favorable correlations (72%), while testicular growth measurements had a slightly higher percentage of favorable correlations (78%). Average correlations of 365-d measures were higher (-.38) than either 205-d or growth measures (-.25 and -.28, respectively). Heritabilities for testicular measurements tended to be moderate to high, while those for female reproduction tended to be low to moderate. These results suggest that selection for increased testicular size would lead to improvement in female reproduction, particularly an increase in calving rate and a decrease in age at first breeding.

The Influence of Daylength, Body Weight, and Age on the Reproductive Ability of Broiler Breeder Cockerels

June-hatched broiler breeder cockerels of two strains were evaluated for reproductive performance in mating pens from 22 to 48 weeks of age. Two light programs with maximum daily daylengths of 15.5 or 16.5 hr were studied.An increase in the light day to 16.5 hr did not significantly affect the male reproductive traits except in number of completed matings and percent packed sperm volume (PSV). The males on 16.5 hr of light had significantly fewer completed matings than did the males on 15.5 hr. Strain 1 males on 16.5 hr produced significantly more spermatozoa at 35 and 40 weeks of age than males on 15.5 hr of light. Male body weights of both strains were significantly lower at 30 weeks of age on the longer daylength. Body weights of cockerels in all treatment groups increased with aging. The range in male body weight markedly influenced the percentage of producing cockerels with aging. During the late egg cycle, the number of producing males increased as body weight increased.The overall mean age of peak in the percentage of males in semen production was 44 weeks of age, which was 7 weeks later than peak egg production. Hatchability was significantly lower for male Strain 2, which had a higher percent PSV and a higher number of attempted matings than did Strain 1.Body weight was significantly correlated with male vent feather-wear at all ages and with the percentage of producing males at 48 weeks of age. The percentage of producing males was correlated with vent feather-wear, evert score, semen volume, and PSV.These results emphasize the importance of body weight selection for optimum breeding flock performance.

Correlated responses in male reproductive traits in mice selected for litter size and body weight.

Correlated responses in male reproductive traits were determined at 4, 6 and 8 weeks of age in lines of mice selected for large litter size (L+), large 6-week body weight (W+), large litter size and small body weight (L+W-) and small litter size and large body weight (L-W+), and in an unselected control (K). Concentration of serum testosterone and weights of testes, seminal vesicles, epididymides and adrenal glands increased with age. Line differences in testosterone concentration were not detected. L+ and W+ males exhibited positive correlated responses in testes, epididymides and seminal vesicle weights. Testis weight adjusted for body weight was significantly larger for L+ than controls and approached significance for W+. Realized genetic correlation be-testis weight and litter size was 0.60 +/- 0.04, and the realized partial genetic correlation holding body weight constant was 0.42. Therefore, pleiotropic loci, acting via the hypothalamic-pituitary axis, affect testis weight and litter size independently of body weight. Additionally, genes influencing overall growth have a pleiotropic effect on testis weight and litter size in mice; the realized genetic correlations of body weight with testis weight and with litter size were 0.60 +/- 0.03 and 0.52 +/- 0.10. Testis weight increased in both L+W- and L-W+ males. The positive correlated response in L+W- may have resulted from changes in frequency of genes controlling reproductive processes; whereas, in L-W+ it could have been the result of changes in the frequency of genes associated with body weight.

Influence of Dietary Protein during the Pre-Breeder Period on Subsequent Reproductive Performance of Large White Turkeys: 2. Growth, Feed Consumption, and Male Sex-Limited Reproductive Traits

The effect of low dietary protein during the rearing and breeding periods on the reproductive performance of Large White turkey males was examined. At 12 weeks of age 251 males were randomly divided into two groups and fed either 12 or 17% protein through 56 weeks of age. Body weight gains from 12 to 20 weeks and 20 to 28 weeks of age were significantly reduced for the males receiving the 12% dietary protein. However, after 28 weeks of age, weight differences decreased and by 56 weeks of age body weights of both groups were approximately the same. In addition, a significant reduction in feed consumption was noted for the males fed 12% protein. Males on the high protein diet experienced a higher mortality than those on the low protein diet.Low dietary protein reduced semen volume and spermatozoa concentration at 33 weeks of age, but there were no significant differences thereafter. The percentages of normal, abnormal, or dead spermatozoa were unaffected by dietary protein levels. Feeding 12% protein from 12 to 56 weeks of age to Large White turkey breeder males was adequate for high quality semen production.