Turkey sperm mobility influences paternity in the context of competitive fertilization

Sperm Numbers as a Paternity Guard in a Wild Bird

Sperm competition is thought to impose strong selection on males to produce competitive ejaculates to outcompete rival males under competitive mating conditions. Our understanding of how different sperm traits influence fertilization success, however, remains limited, especially in wild populations. Recent literature highlights the importance of incorporating multiple ejaculate traits and pre-copulatory sexually selected traits in analyses aimed at understanding how selection acts on sperm traits. However, variation in a male’s ability to gain fertilization success may also depend upon a range of social and ecological factors that determine the opportunity for mating events both within and outside of the social pair-bond. Here, we test for an effect of sperm quantity and sperm size on male reproductive success in the red-back fairy-wren (Malurus melanocephalus) while simultaneously accounting for pre-copulatory sexual selection and potential socio-ecological correlates of male mating success. We found that sperm number (i.e., cloacal protuberance volume), but not sperm morphology, was associated with reproductive success in male red-backed fairy-wrens. Most notably, males with large numbers of sperm available for copulation achieved greater within-pair paternity success. Our results suggest that males use large sperm numbers as a defensive strategy to guard within-pair paternity success in a system where there is a high risk of sperm competition and female control of copulation. Finally, our work highlights the importance of accounting for socio-ecological factors that may influence male mating opportunities when examining the role of sperm traits in determining male reproductive success.

Influence of Zinc and Manganese Nanoparticles on Selected Parameters of Turkey Spermatozoa Stored in a Liquid State at 4 °C

The aim of this study was to determine the effect of semen extender supplementation with 25 or 50 μM of zinc nanoparticles (ZnNPs) or manganese nanoparticles (MnNPs) on turkey spermatozoa preserved in a liquid state. Twenty turkey ejaculates were obtained from twenty healthy males. The collected semen was preserved at 4 °C for 48 h with or without NPs. Selected qualitative and quantitative parameters of sperm (motility, plasma membrane activity, mitochondrial membrane potential (MMP) and the percentage of sperm demonstrating NO and SOD activity) were examined after 2, 24 and 48 h of storage. Sperm motility and MMP decreased in semen preserved with ZnNPs at each time point of the analysis. However, all spermatozoa remained viable throughout storage. In contrast, membrane integrity and mitochondria activity (p ≤ 0.05) increased, and the highest SOD activity (p ≤ 0.05) was observed in semen preserved with MnNPs. The addition of MnNPs to the semen extender could potentially improve the parameters of turkey semen during prolonged storage.

Improvement of sperm traits related to the high level of extra-pair fertilization in tree sparrow population under long-term environmental heavy metal pollution

Environmental stress can affect sperm traits whose changes have been reported to be associated with extra-pair fertilization (EPF) level in natural animal populations. However, little is known regarding how exposure to environmental heavy metals influences sperm traits and EPF level in free-living bird populations. In a previous study, we found that a tree sparrow (Passer montanus) population that has been exposed to heavy metal pollution over 60 years (Baiyin, BY) exhibits increased sperm quality compared with a population from a relatively unpolluted area (Liujiaxia, LJX). The high sperm quality could be related to extra-pair mating rates. Therefore, the present study investigated EPF level (the ratio of extra-pair offspring) in tree sparrow populations from BY and LJX, and analyzed the relationship between sperm traits (morphology, velocity and quantity) and EPF success. EPF success of tree sparrows was significantly correlated with their sperm velocity (p = 0.048) and total sperm length (p = 0.045), indicating that these sperm traits were important for EPF success. Tree sparrows from the BY population produced longer sperm with lower head/flagellum ratio and faster swimming sperm and showed a significantly higher EPF level than conspecifics from LJX. Thus, adaptive variation of sperm characteristics was related to the high EPF level in tree sparrows under long-term environmental heavy metal pollution. The findings are of scientific significance for exploring the evolution of mating tactics in wild bird populations under environmental stress.

Optimization of a Protocol for the Cryopreservation of Sperm in Pellets for the Common Pheasant (Phasianus colchicus mongolicus)

The sperm of each avian species and breed have unique characteristics that render them more or less susceptible to the freezing-thawing process; therefore, a suitable cryopreservation protocol that is specific for the sperm of each type of bird is needed. In this context, little information about the common pheasant's sperm is available. Therefore, the aim of this study was to test different parameters at each step of the process of freezing into pellets and thawing to detect the least deleterious parameter settings. Sixteen different protocols were tested by studying two levels in each of the four steps (dilution, equilibration at 5 °C, final dimethylacetamide concentration, and dimethylacetamide equilibration time) comprising the freezing process. The pheasant sperm exhibited a high susceptibility to the damage caused by freezing into pellets; however, the survival of the sperm reached 29%, and the greatest recovered mobility was 22%. The mobility of the sperm was affected by the dilution and the dimethylacetamide concentration, and the viability of the sperm was affected by the equilibration at 5 °C and the dimethylacetamide equilibration. The protocols that caused the least damage to the pheasant sperm were found to be those with higher dilution rates, 10 min of equilibration at 5 °C, and 6% dimethylacetamide equilibrated for 1 or 5 min. In the present study, we individualise some applicable parameters for certain critical steps of the freezing-thawing process; however, further investigations are needed in order to improve upon and complete a suitable protocol for the cryopreservation and thawing of pheasant sperm.

Longer and faster sperm exhibit better fertilization success in Japanese quail

In birds, sperm storage tubules (SST) located in the utero-vaginal junction are thought to be a site of sperm selection; however, the exact mechanism of sperm selection is poorly understood. Here, we investigated sperm entry into the SST and subsequent fertilization success under a competitive situation created by artificial insemination of a sperm mixture obtained from 2 males. We employed 2 quail strains, a wild-type and a dominant black (DB) type, as this allows easy assessment of paternity by feather coloration. We found paternity of embryos was biased toward DB males when a sperm mix with similar sperm numbers from the 2 males strains was artificially inseminated into females. Our novel sperm staining method with 2 different fluorescent dyes showed that the DB-biased fertilization was because of the better ability of DB sperm to enter the SST. Moreover, we found that DB sperm had a longer flagellum and midpiece. These characteristics probably allow sperm to swim faster in a high viscosity medium, which may be a similar environment to the lumen of the female reproductive tract. Our results indicated that sperm competition occurs to win a place in the SST and that filling the SST with their own spermatozoa is a critical step to achieve better fertilization success for the male Japanese quail.

Ejaculate testosterone levels affect maternal investment in red junglefowl (Gallus gallus gallus)

Substantial concentrations of testosterone are not only present in a male’s circulation, but also in its ejaculate. Surprisingly, the regulation of ejaculate T and its effects on females and their offspring, potentially a cryptic paternal trait, are not known. We found lower circulating and higher ejaculate T concentrations in subordinate red junglefowl (Gallus gallus gallus) males compared to dominant males, suggestive of an adaptive trade-off in T allocation to circulation and their ejaculate. Subsequently, we artificially inseminated females with either testosterone enriched (TE) or control ejaculates (CE) in a cross-over design. TE females produced heavier eggs than CE females. Offspring growth and tonic immobility were affected in a sex-specific way by TE. TE sons were heavier with shorter TI duration than CE sons, and TE daughters were lighter than CE daughters but daughters did not differ in TI score. However, the chicks competitiveness was not influenced by the TE nor CE. This indicates a previously unknown function of ejaculate testosterone as well as a new form of interaction between a cryptic paternal trait and a maternal effect that may be widespread in the animal kingdom.

Dog sperm swimming parameters analysed by computer-assisted semen analysis of motility reveal major breed differences

Dogs have undergone an intensive artificial selection process ever since the beginning of their relationship with humans. As a consequence, a wide variety of well-defined breeds exist today. Due to the enormous variation in dog phenotypes and the unlikely chance of gene exchange between them, the question arises as to whether they should still be regarded as a single species or, perhaps, they be considered as different taxa that possess different reproductive traits. The aim of this study was therefore to characterize some male reproductive traits, focusing on kinematic characteristics of dog spermatozoa from several breeds. Thirty-seven dogs from the following breeds were used: Staffordshire Bull Terrier, Labrador Retriever, Spanish Mastiff, Valencian Rat Hunting Dog, British Bulldog and Chihuahua. Semen samples were obtained via manual stimulation and diluted to a final sperm concentration of 50 million/ml, and they were subsequently analysed by the computer assisted semen analysis (CASA-Mot) ISAS^® v1 system. Eight kinematic parameters were evaluated automatically. All parameters showed significant different values among breeds and among individuals within each breed. The fastest sperm cells were those of Staffordshire Bull Terriers and the slowest were recorded in Chihuahuas. The intra-male coefficient of variation (CV) was higher than the inter-male CV for all breeds with the Staffordshire Bull Terrier showing the lowest values. When taking into consideration the cells by animal and breed, discriminant analyses showed a high capability to predict the breed. Cluster analyses showed a hierarchical classification very close to that obtained after phylogenetic studies with genome markers. In conclusion, future workers on dog spermatozoa should bear in mind major differences between breeds and realize that results cannot be extrapolated from one to another. Because sperm characteristics are associated with breed diversity, dogs may represent a good model to examine changes in reproductive parameters associated with selection processes.

Sperm morphology, adenosine triphosphate (ATP) concentration and swimming velocity: unexpected relationships in a passerine bird

The relationship between sperm energetics and sperm function is poorly known, but is central to our understanding of the evolution of sperm traits. The aim of this study was to examine how sperm morphology and ATP content affect sperm swimming velocity in the zebra finch Taeniopygia guttata. We exploited the high inter-male variation in this species and created extra experimental power by increasing the number of individuals with very long or short sperm through artificial selection. We found a pronounced quadratic relationship between total sperm length and swimming velocity, with velocity increasing with length up to a point, but declining in the very longest sperm. We also found an unexpected negative association between midpiece length and ATP content: sperm with a short midpiece generally contained the highest concentration of ATP. Low intracellular ATP is therefore unlikely to explain reduced swimming velocity among the very longest sperm (which tend to have a shorter midpiece).

The dynamics of sperm cooperation in a competitive environment

Sperm cooperation has evolved in a variety of taxa and is often considered a response to sperm competition, yet the benefit of this form of collective movement remains unclear. Here, we use fine-scale imaging and a minimal mathematical model to study sperm aggregation in the rodent genus Peromyscus. We demonstrate that as the number of sperm cells in an aggregate increase, the group moves with more persistent linearity but without increasing speed. This benefit, however, is offset in larger aggregates as the geometry of the group forces sperm to swim against one another. The result is a non-monotonic relationship between aggregate size and average velocity with both a theoretically predicted and empirically observed optimum of six to seven sperm per aggregate. To understand the role of sexual selection in driving these sperm group dynamics, we compared two sister-species with divergent mating systems. We find that sperm of Peromyscus maniculatus (highly promiscuous), which have evolved under intense competition, form optimal-sized aggregates more often than sperm of Peromyscus polionotus (strictly monogamous), which lack competition. Our combined mathematical and experimental study of coordinated sperm movement reveals the importance of geometry, motion and group size on sperm velocity and suggests how these physical variables interact with evolutionary selective pressures to regulate cooperation in competitive environments.

Competition drives cooperation among closely related sperm of deer mice

Among the extraordinary adaptations driven by sperm competition is the cooperative behaviour of spermatozoa. By forming cooperative groups, sperm can increase their swimming velocity and thereby gain an advantage in intermale sperm competition. Accordingly, selection should favour cooperation of the most closely related sperm to maximize fitness. Here we show that sperm of deer mice (genus Peromyscus) form motile aggregations, then we use this system to test predictions of sperm cooperation. We find that sperm aggregate more often with conspecific than heterospecific sperm, suggesting that individual sperm can discriminate on the basis of genetic relatedness. Next, we provide evidence that the cooperative behaviour of closely related sperm is driven by sperm competition. In a monogamous species lacking sperm competition, Peromyscus polionotus, sperm indiscriminately group with unrelated conspecific sperm. In contrast, in the highly promiscuous deer mouse, Peromyscus maniculatus, sperm are significantly more likely to aggregate with those obtained from the same male than with sperm from an unrelated conspecific donor. Even when we test sperm from sibling males, we continue to see preferential aggregations of related sperm in P. maniculatus. These results suggest that sperm from promiscuous deer mice discriminate among relatives and thereby cooperate with the most closely related sperm, an adaptation likely to have been driven by sperm competition.

Comparative evidence for the evolution of sperm swimming speed by sperm competition and female sperm storage duration in passerine birds

Sperm swimming speed is an important determinant of male fertility and sperm competitiveness. Despite its fundamental biological importance, the underlying evolutionary processes affecting this male reproductive trait are poorly understood. Using a comparative approach in a phylogenetic framework, we tested the predictions that sperm swim faster with (1) increased risk of sperm competition, (2) shorter duration of female sperm storage, and (3) increased sperm length. We recorded sperm swimming speed in 42 North American and European free-living passerine bird species, representing 35 genera and 16 families. We found that sperm swimming speed was positively related to the frequency of extrapair paternity (a proxy for the risk of sperm competition) and negatively associated with clutch size (a proxy for the duration of female sperm storage). Sperm swimming speed was unrelated to sperm length, although sperm length also increased with the frequency of extrapair paternity. These results suggest that sperm swimming speed and sperm length are not closely associated traits and evolve independently in response to sperm competition in passerine birds. Our findings emphasize the significance of both sperm competition and female sperm storage duration as evolutionary forces driving sperm swimming speed.

Experimental evidence that high levels of inbreeding depress sperm competitiveness

The effects of inbreeding on sperm quantity and quality are among the most dramatic examples of inbreeding depression. The extent to which inbreeding depression results in decreased fertilization success of a male's sperm, however, remains largely unknown. This task is made more difficult by the fact that other factors, such as cryptic female choice, male sperm allocation and mating order, can also drive patterns of paternity. Here, we use artificial insemination to eliminate these extraneous sources of variation and to measure the effects of inbreeding on the competitiveness of a male's sperm. We simultaneously inseminated female guppies (Poecilia reticulata) with equal amounts of sperm from an outbred (f = 0) male and either a highly (f = 0.59) or a moderately inbred (f = 0.25) male. Highly inbred males sired significantly fewer offspring than outbred males, but share of paternity did not differ between moderately inbred and outbred males. These findings therefore confirm that severe inbreeding can impair the competitiveness of sperm, but suggest that in the focal population inbreeding at order of a brother-sister mating does not reduce a male's sperm competitiveness.

Sperm morphology and sperm velocity in passerine birds

Sperm velocity is one of the main determinants of the outcome of sperm competition. Since sperm vary considerably in their morphology between and within species, it seems likely that sperm morphology is associated with sperm velocity. Theory predicts that sperm velocity may be increased by enlarged midpiece (energetic component) or flagellum length (kinetic component), or by particular ratios between sperm components, such as between flagellum length and head size. However, such associations have rarely been found in empirical studies. In a comparative framework in passerine birds, we tested these theoretical predictions both across a wide range of species and within a single family, the New World blackbirds (Icteridae). In both study groups, sperm velocity was influenced by sperm morphology in the predicted direction. Consistent with theoretical models, these results show that selection on sperm morphology and velocity are likely to be concomitant evolutionary forces.

High variation in sperm precedence and last male advantage in the scorpionfly Panorpa germanica L. (Mecoptera, Panorpidae): possible causes and consequences

In the last decades, many insect species have been studied in terms of sperm competition. Patterns of sperm use are often inferred from the mean species value of P(2), defined as the mean proportion of offspring sired by the second male in double-mating trials. In Panorpa germanica (Mecoptera, Panorpidae), P(2) largely depends on relative copulation durations of both males, but with the second male on average having some advantage over the first male. Estimating the presence of fertile sperm inside the female's reproductive tract in relation to time after copulation we conclude this partial last male sperm precedence not to be caused by natural death, loss, or depletion of first male sperm. Estimating sperm transfer rates of both mates of a female we, furthermore, found that the high intraspecific variance in P(2) that can be observed cannot solely be explained by variances in sperm transfer rates among P. germanica males. Other factors possibly causing the observed patterns of paternity success are discussed.

Reproductive isolation in birds: postcopulatory prezygotic barriers

Reproductive isolation is an important part of the speciation process. Recent studies of birds have highlighted not only the significance of postcopulatory postzygotic barriers, but also the almost complete absence of information about postcopulatory prezygotic barriers. Here, we draw attention to studies that provide an opportunity to test whether prezygotic barriers to heterospecific sperm exist in birds. We show that, compared with other taxa, such barriers in birds are relatively inefficient, possibly because, similar to postcopulatory postzygotic barriers, they take a long time to evolve. These data also raise questions about the mechanisms of sperm-female and sperm-egg recognition in birds. Future research will serve the dual purpose of providing more detail of the mechanisms of both heterospecific and conspecific prezygotic processes.

Effects of liquid storage on amidase activity, DNA fragmentation and motility of turkey spermatozoa

Short-term liquid storage of turkey semen is of great interest in the management of turkey reproduction due to the extensive use of artificial insemination. This study examined changes in DNA fragmentation (using a comet assay), sperm motility characteristics (using computer-aided sperm analysis), and amidase activity (using a colorimetric assay) of turkey sperm stored for 24 and 48 h. In addition we found that turkey spermatozoa contain besides acrosin, additional two serine proteinases of molecular weight of 34 and 42 kDa. We found that, after 48 h of liquid storage, decreases in sperm motility characteristics and increases in amidase activity and DNA fragmentation occurred. An increase of amidase activity was found after 24h. Decreases in sperm motility and increase in DNA fragmentation were found after 48 h of storage. These data suggest that a decrease in turkey sperm quality during short-term storage is related to disturbances to the acrosome, presumably related to premature activation of acrosomal serine proteinases, and to a lesser extent a decrease in sperm motility characteristics and damage of sperm DNA.

Sperm viability matters in insect sperm competition

Experimental studies in insects have shown how sperm competition can be a potent selective force acting on an array of male reproductive traits . However, the role of sperm quality in determining paternity in insects has been neglected, despite the fact that sperm quality has been shown to influence the outcome of sperm competition in vertebrates . A recent comparative analysis found that males of polyandrous insect species show a higher proportion of live sperm in their stores . Here, we test the hypothesis that sperm viability influences paternity at the within-species level. We use the cricket Teleogryllus oceanicus to conduct sperm competition trials involving prescreened males that differ in the viability of their sperm. We find that paternity success is determined by the proportion of live sperm in a male's ejaculate. Furthermore, we were able to predict the paternity patterns observed on the basis of the males' relative representation of viable sperm in the female's sperm-storage organ. Our findings provide the first experimental evidence for the theory that sperm competition selects for higher sperm quality in insects. Between-male variation in sperm quality needs to be considered in theoretical and experimental studies of insect sperm competition.

Kin selection and cooperative courtship in wild turkeys

In the few species of birds in which males form display partnerships to attract females, one male secures most or all of the copulations. This leads to the question of why subordinate males help in the absence of observable reproductive benefits. Hamilton's concept of kin selection, whereby individuals can benefit indirectly by helping a relative, was a crucial breakthrough for understanding apparently altruistic systems. However in the only direct test of kin selection in coordinated display partnerships, partners were unrelated, discounting kin selection as an explanation for the evolution of cooperation. Here I show, using genetic measures of relatedness and reproductive success, that kin selection can explain the evolution of cooperative courtship in wild turkeys. Subordinate (helper) males do not themselves reproduce, but their indirect fitness as calculated by Hamilton's rule more than offsets the cost of helping. This result confirms a textbook example of kin selection that until now has been controversial and also extends recent findings of male relatedness on avian leks by quantifying the kin-selected benefits gained by non-reproducing males.

Sperm mobility: phenotype in roosters (Gallus domesticus) determined by mitochondrial function

Previously, inheritance of sperm mobility entailed a maternal additive genetic effect, and sperm ATP content was correlated (r = 0.80) with phenotype. The present study was conducted to determine if mitochondrial function was critical to phenotypic expression. Whereas phenotype was independent of mitochondrial helix length, phenotype was correlated with sperm oxygen consumption (r = 0.83) using random-bred roosters. Aberrant mitochondria characterized immobile sperm, as evidenced by transmission-electron microscopy. Such mitochondria were swollen and contained disorganized cristae. Additional experiments were performed with roosters from lines selected for low or high sperm mobility. A threefold difference in sperm oxygen consumption was observed between lines. Single nucleotide polymorphisms were observed in mitochondrial DNA by sequencing replicate mitochondrial genomes from each line. An A-to-G substitution in the gene encoding tRNA(Arg) was inherited consistently, as evidenced by restriction fragment length polymorphism analysis using two male and two female progeny per family group and 14 family groups per line. Motile concentration in semen from low-line males was half that observed in semen from high-line males, as evidenced by computer-assisted sperm motion analysis. Likewise, 47% of sperm from low-line males contained aberrant mitochondria, compared to 4% for high-line males. In summary, sperm mobility phenotype was dependent on mitochondrial function, which in turn was altered by genetic selection. Fowl deferent duct fluid contains a high concentration of glutamate. We propose that variation in sperm mobility phenotype stems from the extent to which glutamate induces excessive mitochondrial Ca2+ uptake before ejaculation.

Microsatellite Loci for Genetic Mapping in the Turkey (Meleagris gallopavo)

New microsatellite loci for the turkey (Meleagris gallopavo) were developed from two small insert DNA libraries. Polymorphism at these new loci was examined in domestic birds and two resource populations designed for genetic linkage mapping. The majority of loci (152 of 168) was polymorphic in domestic turkeys and informative in two mapping resource populations and thus will be useful for genetic linkage mapping.

Attributes of broiler breeder males characterized by low and high sperm mobility

The attributes of broiler breeder males characterized by sperm mobility phenotype were studied in replicate experiments. Low and high phenotypes were observed in the first experiment over a 10-wk interval. Average straight line velocity differed between phenotypes (P < or = 0.05) as evidenced by computer-assisted sperm motion analysis. The second experiment compared low and high phenotypes from the same broiler breeder strain over a 29-wk interval. Body weight and fertility were measured in this experiment. Body weight data approximated parallel lines. The low phenotype averaged 227 g more than the high phenotype over the course of the experiment. Individual males were used as semen donors at 50, 54, 58, 62, and 65 wk of age. Eggs were collected for 2 wk after a single insemination at each age. Mean overall fertility (+/- SEM) was 44 +/- 4 and 69 +/- 2% for low and high sperm mobility phenotypes, respectively (P < or = 0.0001). As determined by transmission electron microscopy, the percentage of sperm with aberrant mitochondria was greater for the low sperm mobility phenotype (P < or = 0.0001). Neither blood plasma testosterone concentration nor testis weight differed between phenotypes. Sperm mobility is a biologically significant predictor of broiler breeder semen quality. The relationship between sperm mobility phenotype and body weight warrants further investigation.

Prostaglandin levels in seminal plasma and sperm extracts of the domestic turkey, and the effects of cyclooxygenase inhibitors on sperm mobility

BACKGROUND

Turkey reproduction is by artificial insemination using pooled semen so there is interest in storing semen. Fertilizing capacity declines after six hours storage, possibly due to poor sperm mobility. Prostaglandins (PG) affect mammalian sperm motility, but avian sperm has not been widely studied. For this study, levels of PG E1, E2, and F2 alpha in turkey seminal plasma and sperm extract, and effects of cyclooxygenase (COX) inhibitors on sperm mobility were determined.

METHODS

Seminal Plasma and sperm extract PG E1, E2, and F2 alpha, from 1.0 mL pooled semen, were measured by ELISA. In Trial 1, PG were determined from 122 wk old toms (n = 4). Trial 2 used 36 wk old toms (n = 7). For Trial 3, PGE2 only was measured from 48 wk (n = 6) and 154 wk old toms (n = 3). The effects of non-specific COX inhibitors indomethacin, diclofenac, tolmetin, or aspirin (n = 10), or specific COX-1 or COX-2 inhibitors (n = 3) on sperm mobility were measured (Accudenz swim-down test).

RESULTS

Seminal plasma PG (pg/mL) in Trials 1 and 2, respectively, were 185.2 +/- 88.4 and 187.2 +/- 33.7 for PGE1; 141.4 +/- 43.1 and 100.4 +/- 14.6 for PGF2 alpha; and 431.0 +/- 155.1 for PGE2 (Trial 1 only). Sperm extract PG (pg/10 billion cells) in Trials 1 and 2, respectively, were 215.1 +/- 38.1 and 208.9 +/- 41.5 for PGE1; 133.7 +/- 51.7 and 49.8 +/- 8.3 for PGF2 alpha; and 52.3 +/- 8.6 for PGE2 (Trial 1 only). In Trial 3, seminal plasma PGE2 (pg/mL) in older versus younger males was 1097.9 +/- 99.3 versus 853.2 +/- 144.6 and sperm extract PGE2 (pg/10 billion cells) was 208.0 +/- 56.1 versus 102.4 +/- 14.8. Cyclooxygenase inhibitors (0.001 to 10 mM) decreased sperm mobility: indomethacin 15 to 100%; diclofenac 4 to 100%; tolmetin 27 to 74%; aspirin (tested at 0.01 to 15 mM) 22 to 42%; resveratrol (COX-1) and NS-398 (COX-2), both tested at 0.1 to 10 mM, 38 to 98% and 44 to 85%, respectively.

CONCLUSION

These results indicate that PG are present in turkey seminal plasma and sperm, and COX inhibitors decrease turkey sperm mobility.

Deduction of a model for sperm storage in the oviduct of the domestic fowl (Gallus domesticus)

The mechanism of sperm storage in the fowl oviduct has remained a mystery since the 1960s, when sperm storage tubules (SST) were discovered between the shell gland and vagina. Previously, it was known that only motile sperm could ascend the vagina and enter these tubules. However, the means by which sperm resided therein was not clear. Research with computer-assisted sperm motion analysis has demonstrated that 1) seminal plasma glutamate acts as a motility agonist via N-methyl-d-aspartate receptors; 2) motility depends on extracellular Ca2+ and Na+; 3) straight-line velocity is a variable with a skewed distribution; 4) sperm cell trajectory is a function of straight-line velocity; and 5) specific inhibition of phospholipase A2 renders sperm immotile. An additional experiment demonstrated that Ca2+ acts as a second messenger and thereby modulates the content of long-chain acylcarnitine within sperm. Therefore, it is proposed that 1) the release of endogenous fatty acids fuels sperm as they ascend the vagina; (2) on entering the SST, motile sperm maintain position against a fluid current generated by SST epithelial cells; 3) resident sperm metabolize exogenous fatty acids released from lipid-laden epithelial cells; (4) motile sperm emerge from the SST when their velocity declines to a threshold at which retrograde movement begins; and 5) the skewed distribution of straight-line velocity accounts for the exponential pattern of sperm emergence from the SST. In summary, sperm residence within and emergence from the SST are phenomena most likely explicable in terms of sperm cell motility.

Sperm mobility phenotype not determined by sperm quality index

We tested the capacity of the AviMate sperm quality analyzer to predict sperm mobility phenotype. A preliminary experiment was performed to determine a sperm concentration that afforded maximal sperm quality index (SQI) values with sperm from males with high sperm mobility. In order to facilitate comparison of sperm motility indexes, semen was diluted to aconstant concentration of 1.25 million sperm/mL rather than a constant ratio of 1:75 as recommended for the sperm quality analyzer. Thereafter, sperm mobility, motile concentration, and SQI were measured from a single ejaculate collected from each of 70 broiler breeders. Coefficients of variation were 60, 37, and 30%, respectively. Neither sperm mobility (r = 0.01) nor motile concentration (r = 0.14) was highly correlated with SQI. Neither motile concentration nor straight line velocity (VSL) differed (P > or = 0.05) among roosters whose SQI values were below or above one standard deviation from the population mean (n = 10 per group). In contrast, both motile concentration (P < or = 0.01) and VSL (P < or = 0.05) differed between roosters whose sperm mobility values were below or above a standard deviation from the population mean (n = 10 per group). Sperm mobility was a function of the size of a highly motile subpopulation of sperm. A replicate experiment was performed with a flock of New Hampshire roosters (n = 126). Neither the properties of motile sperm nor fertility differed among males characterized by extreme SQI scores. We concluded that variation in SQI scores was enigmatic because sperm concentration was controlled in our experiments, sperm viability was invariant, and motile concentration did not differ among roosters characterized by extreme SQI scores. In summary, the AviMate sperm quality analyzer did not predict sperm mobility phenotype.

Fertility estimation: a review of past experience and future prospects

Fertility has many components and stages which require that males and females be functionally capable of carrying out all critical stages if each generational reproductive cycle is to be completed. To accomplish this, the male must produce and ejaculate normal fertile sperm. The female must produce, store and ovulate normal fertilizable oocytes. Furthermore, the female must provide a reproductive system compatible with sperm transport, capacitation, and fertilization of the oocytes, embryo and fetal development, and finally birth of healthy young. Reproductive success or failure at several of these points can be estimated quantitatively on a population basis, and in a few situations on an individual basis. It is important that fertility estimates be determined accurately and with precision to be most useful to researchers and managers of animal enterprises. Many studies have underestimated the biological relationship of fertility to other traits because the estimates lacked precision. Many in vitro manipulations of sperm in artificial insemination, of gametes in various assisted reproductive technologies, and of embryos in embryo transfer are utilized in animal breeding programs. Accurate estimation of reproductive efficiency of these in vitro procedures also is important. Conditions surrounding different sets of fertility estimates almost certainly will be different. These conditions should be described as precisely as possible, and appropriate controls included in all experiments. When possible, experiments should be replicated over time and place to determine the repeatability of the various criteria used to estimate fertility and reproductive efficiency. Advances in genomic information and molecular biology should facilitate characterizing more fully inherent potential fertility of animals at birth. In vitro tests will improve, and automated techniques will facilitate making multiple determinations possible on a large scale. Reliability of fertility estimates will increase, with the potential for enhanced animal reproductive performance through more accurate selection, genetic engineering, and enlightened animal care. Simultaneously, it is important to recognize that prediction of future fertility is more hazardous than estimating fertility, as a completely new set of circumstances may occur which are not predictable. Because fertility estimation may be applied under a myriad of conditions, principles and factors affecting fertility will be emphasized in this review as being more useful than a compilation of numerical examples.

Sperm viability and sperm competition in insects

Sperm quality plays an important role in vertebrates in determining which male has the advantage when two or more males compete to fertilize a female's ova. In insects, however, the importance of sperm quality has never been considered, despite sperm competition being widespread and well studied in this group. We tested the hypothesis that sperm viability, measured as the proportion of live sperm, covaried with the intensity of sperm competition in insects. In a pairwise comparison of seven closely related species pairs, each comprising a monandrous and a polyandrous species (i.e., with and without sperm competition, respectively), we found that in all cases the polyandrous species had a higher proportion of live sperm in their sperm stores. The distribution of the percentage of live sperm showed considerable inter- and intraspecific variation, suggesting that, all else being equal, males will vary in their ability to fertilize ova on the basis of sperm viability alone. Our results suggest that sperm viability is one of a suite of male adaptations to sperm competition in insects.

Efficacy of sperm mobility assessment in commercial flocks and the relationships of sperm mobility and insemination dose with fertility in turkeys

Our objectives were to evaluate: 1) the efficacy of the Sperm Mobility Test on commercial turkey farms, and 2) the influence of sperm mobility phenotype on fertility when insemination parameters are varied. In research flocks, differences in sperm mobility among toms are predictive of fertility. We wanted to test the efficacy of this sire selection test in practical, real-world situations, evaluating its usefulness in terms of assessing large numbers of toms, different strains of turkeys, and variable management practices. Utilizing field study results, controlled studies were then conducted to improve test parameters. For the field trials, semen from each of 405 breeder toms (11 strains or lines) was evaluated either in duplicate (n = 285) or in triplicate (n = 120). Sperm mobility was normally distributed among all toms tested, except for one strain. Because the sperm mobility indices for toms evaluated in these field trials were higher than those observed in research flocks, the Sperm Mobility Test was modified to increase the separation between high and low sperm mobility phenotypes by increasing the concentration of Accudenz. To determine the effects of sperm mobility and insemination dose on sustained fertility through time, hens from a research flock were inseminated twice before the onset of lay with sperm from toms classified as high-, average-, or low-mobility in concentrations of 25 to 400 million sperm per artificial insemination dose, and egg fertility was evaluated over a 5-wk period. Toms with the high-mobility sperm phenotype maintained higher fertility (P < 0.05) over the 5-wk period at all insemination doses compared with toms with low-mobility sperm. Toms with high-mobility sperm sired equal numbers of poults in a sperm competition study in which numbers favored low-mobility toms by 3:1. These results demonstrate that the Sperm Mobility Test can be used for on-farm evaluation of semen quality of toms in commercial flocks and that sperm mobility influences fertility and sire fitness.

The effects of methylxanthines on the mobility of stored turkey sperm

The mobility of pooled turkey sperm following various storage regimens was assessed by objectively measuring the ability of sperm to penetrate a 2% Accudenz [5-(N-2,3-dihydroxypropylacetamido)-2,4,6-tri-iodo-N,N'-bis(2,3-dihydroxypropyl)isophthalamide] solution at 41 C. When semen was diluted with Beltsville poultry semen extender and stored at 5 C with agitation at 150 rpm, sperm mobility declined as the storage interval increased (P < or = 0.05), with mobility scores (mean +/- SEM) of 0.440+/-0.029, 0.374+/-0.031, 0.282+/-0.011, 0.202+/-0.019, and 0.130+/-0.019 for 0-, 3-, 6-, 24-, and 48-h storage, respectively. For a 10-wk fertility trial using the same storage method, sperm mobility and fertilizing capacity of semen were significantly reduced following 24-h storage compared with values for unstored semen. The sperm mobility scores were 0.404+/-0.051 and 0.101+/-0.046 for unstored and 24-h stored semen, respectively, whereas the percentage of fertilized eggs was 95.9+/-5.1 for unstored semen and 48.0+/-5.1 for 24-h stored semen. When caffeine or pentoxifylline was added to semen at 2.5, 5, or 10 mM, no significant effect on sperm mobility was seen, regardless of whether these compounds were added to unstored semen, were present during 6-h storage, or were added following the 6-h storage interval. These studies demonstrate that sperm mobility and fertilizing capacity of pooled turkey semen declines with storage, and that addition of caffeine or pentoxifylline either during or after storage does not affect sperm mobility.

No evidence for killer sperm or other selective interactions between human spermatozoa in ejaculates of different males in vitro

This study examines one of the possible mechanisms of sperm competition, i.e. the kamikaze sperm hypothesis. This hypothesis states that sperm from different males interact to incapacitate each other in a variety of ways. We used ejaculates from human donors to compare mixes of semen in vitro from the same or different males. We measured the following parameters: (i) the degree of sperm aggregation, velocity and proportion of morphologically normal sperm after 1 and 3 h incubation in undiluted semen samples, (ii) the proportion of viable sperm plus the same parameters as in (i) in 'swim-up' sperm suspensions after 1 and 3 h incubation, (iii) the degree of self and non-self sperm aggregation using fluorescent dyes to distinguish the sperm of different males, and (iv) the extent of sperm capacitation and acrosome-reacted sperm in mixtures of sperm from the same and different males. We observed very few significant changes in sperm aggregation or performance in mixtures of sperm from different males compared with mixtures from the same male and none that were consistent with previously reported findings. The incapacitation of rival sperm therefore seems an unlikely mechanism of sperm competition in humans.