Male Fecundity Research Articles

Direct fitness of group living mammals varies with breeding strategy, climate and fitness estimates

1. Understanding how variation in fitness relates to variation in group living remains critical to determine whether this major aspect of social behaviour is currently adaptive. 2. Available evidence in social mammals aimed to examine this issue remains controversial. Studies show positive (i.e. potentially adaptive), neutral or even negative fitness effects of group living. 3. Attempts to explain this variation rely on intrinsic and extrinsic factors to social groups. Thus, relatively more positive fitness effects are predicted in singularly breeding as opposed to plural breeding species. Fitness effects of sociality in turn may depend on ecological conditions (i.e. extrinsic factors) that influence associated benefits and costs. 4. We used meta-analytic tools to review how breeding strategy or ecological conditions influence the effect size associated with direct fitness-sociality relationships reported in the mammalian literature. Additionally, we determined how taxonomic affiliation of species studied, different fitness and sociality measures used, and major climatic conditions of study sites explained any variation in direct fitness effect size. 5. We found group living had modest, yet positive effects on direct fitness. This generally adaptive scenario was contingent not only upon breeding strategy and climate of study sites, but also on fitness measures examined. Thus, positive and significant effects characterized singular as opposed to plural breeding strategies. 6. We found more positive fitness effects on studies conducted in tropical as opposed to temperate or arid climates. More positive and significant effects were noted on studies that relied on group fecundity, male fecundity and offspring survival as measures of fitness. 7. To conclude, direct fitness consequences of mammalian group living are driven by interspecific differences in breeding strategy and climate conditions. Other factors not examined in this study, namely individual variation in direct and indirect fitness benefits and potential interactions between social and ecological conditions, may be important and require further studies.

Insights into sperm–fertilisation relationships in the Arthropoda with ecological significance modelled in an amphipod

Many studies have linked chemical exposure with testicular abnormalities and reductions in sperm counts; however, the ecological impact in wildlife of reduced male fertility has been difficult to predict. Very few studies have correlated sperm counts with fertilisation success in arthropods. Following a recent investigation indicating reduced sperm counts (∼20%) in field collected amphipods from an industrially polluted site when compared to reference sites, this study, first aimed to review the relationship between sperm counts and fertilisation success using available data published on arthropods, and second, to predict the long-term (10 year) impacts of reduced fertilisation through the use of an existing amphipod population model. The relationships between sperm counts and fertilisation success were compared between two crustacean (Gammarus duebeni and Armadillidium vulgare) and two insect species (Ostrinia nubialis and Agrotis segetum). All species investigated demonstrated reduced fertility with reduced sperm with the relationship varying between species. Results from this study suggest that relatively small reductions in sperm can have variable and possibly dramatic impacts on fertilisation success for the species examined. For example, based on the species reviewed, a 5% reduction in sperm is predicted to give rise to between 0.4% and 9.1% reduction in female brood size dependent on the species. Modelling the effects of reduced fertilisation using a dynamic amphipod population model revealed that whilst 5% reductions in brood size allow the population to persist after 10 years (albeit at critically low densities), brood size reductions of 10% or greater result in population collapse in less than 6–7 years. Whilst, data are limited at this stage, this study highlights the potential for small scale changes in reproductive fitness to produce effects at the population level. As a consequence, a better understanding of the relationships between male fertility and female fecundity are required to adequately assess effects of contaminants such as endocrine disruptors on reproduction in invertebrates.

Sublethal effects of Beauveria bassiana on life table parameters of two–spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

Effects of the entomopathogenic fungus Beauveria bassiana were studied on life table parameters of two-spotted spider mite, Tetranychus urticae feeding on bean and cucumber under laboratory conditions. The developmental periods for all immature stages were not affected by fungal infection on each host plant but the duration of larval stage was significantly longer on bean. The female and male longevity, oviposition period and fecundity were significantly lower on fungus-treated mites but were not different between two host plants. Significant reductions were found on the intrinsic rate of increase (r m ), the net reproductive rate (R 0), the finite rate of increase (λ), the mean generation time (T c ) and the population doubling time (D t ) as a result of mycosis. Only the mean generation time (T c ) was influenced considering the effect of host plant, which was shorter on cucumber.

The combined effects of temperature and insecticide on the fecundity of adult males and adult females of the brown planthopper Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Extreme temperatures are thought to be one of the main factors suppressing natural population growth of the brown planthopper Nilaparvata lugens (Stål) (Hemiptera: Delphacidae). In contrast, sublethal doses of some pesticides (such as triazophos) stimulate reproduction of adult males and adult females of N. lugens. However, the combined effects of high or low temperature and sublethal doses of pesticides on the reproduction of adult males or adult females have not been investigated. This study examined the effects of high (34 °C), typical (26 °C) and low (20 °C) temperature and the insecticide triazophos on the protein content of male accessory glands (MAGs) and adult female ovaries and on the fecundity of adult females. The study demonstrated that temperature and triazophos concentration significantly influence the protein content of MAGs and of adult female ovaries before and after mating. The protein content in MAGs before mating attained a maximum value at 26 °C (45.1 μg per adult male, grand mean of all concentrations), followed by an intermediate value of 38.0 μg at 20 °C and a minimum value of 10.4 μg at 34 °C. These results indicate that the reproduction of males is more sensitive to high temperature compared to adult females. Protein content in MAGs after mating at 26 °C remained at a maximum value (25.6 μg per adult male, grand mean of all concentrations), followed by 21.9 μg at 20 °C and a minimum value of 8.3 μg at 34 °C. The protein content of MAGs after mating decreased with increasing triazophos concentration at the three temperatures. This result indicates that treated males transferred more MAG protein to adult females through mating. For example, MAG protein after mating at 26 °C for 0, 10, 20, 40 and 80 ppm triazophos treatments decreased by 16.5, 39.2, 42.8, 53.5 and 58.2%, respectively, compared with the corresponding values before mating. The protein content of adult female ovaries both before and after mating at three temperatures for all concentrations was significantly higher than in the control. However, the increase of ovary protein (percent) both before and after mating for all concentrations attained its maximum value at 34 °C, an intermediate value at 26 °C, and its minimum value at 20 °C, compared with the control. Similarly, percent increases in the number of eggs laid for 10, 20, 40 and 80 ppm triazophos treatments at 34 °C and 20 °C (except for 80 ppm) were greater than those at 26 °C.

Strategic mating effort in a simultaneous hermaphrodite

Sexual selection theory for simultaneously hermaphroditic animals predicts an overall preference for inseminating partners that have a relatively higher female fecundity. Previous work on the link between male mating decisions and female fecundity has primarily focused on the effect of the partners’ body size using existing variation in this trait within a study population. On the assumption that the body size is positively correlated with female fecundity, sperm donors should preferentially inseminate relatively larger individuals to obtain a higher fitness gain through their male sex function. However, empirical evidence for such size-dependent mate choice in simultaneous hermaphrodites is equivocal, possibly because of confounding variables. We studied the mating behavior of the simultaneously hermaphroditic flatworm Macrostomum lignano and tested for a strategic mating effort in response to the feeding status of the partner. We experimentally manipulated the feeding status of potential mating partners in order to generate variation in female fecundity among them and tested whether this affected the copulation number and the number of sperm that the focal worm managed to store in the partner’s sperm storage organ. We found that the manipulation of the feeding status had a strong effect on the body size of the potential mating partners and that focal worms copulated more frequently with, and stored more sperm in well-fed partners compared to unfed partners. Our results suggest that M. lignano adjusts its mating effort in response to the feeding status of the mating partner.

The Small Heat Shock Protein ODF1/HSPB10 Is Essential for Tight Linkage of Sperm Head to Tail and Male Fertility in Mice

Sperm motility and hence male fertility strictly depends on proper development of the sperm tail and its tight anchorage to the head. The main protein of sperm tail outer dense fibers, ODF1/HSPB10, belongs to the family of small heat shock proteins that function as molecular chaperones. However, the impact of ODF1 on sperm tail formation and motility and on male fecundity is unknown. We therefore generated mutant mice in which the Odf1 gene was disrupted. Heterozygous mutant male mice are fertile while sperm motility is reduced, but Odf1-deficient male mice are infertile due to the detachment of the sperm head. Although headless tails are somehow motile, transmission electron microscopy revealed disturbed organization of the mitochondrial sheath, as well as of the outer dense fibers. Our results thus suggest that ODF1, besides being involved in the correct arrangement of mitochondrial sheath and outer dense fibers, is essential for rigid junction of sperm head and tail. Loss of function of ODF1, therefore, might account for some of the cases of human infertility with decapitated sperm heads. In addition, since sperm motility is already affected in heterozygous mice, impairment of ODF1 might even account for some cases of reduced fertility in male patients.

Semen Analysis From A Point Of View Of Gynecologist And Recent Developments

SUMMARY Infertility is defined as the time of one year of unprotected intercourse without conception and affects approximately 15% of the couples. Data available over the years reveal that pathology is found among 55% of cases in women, 35% of cases in men and the remaining 10% of cases are defined as unexplained infertility. Male infertility is commonly due to deficiencies in the semen and semen quality is used as a surrogate measure of male fecundity. A semen analysis evaluates certain characteristics of a male's semen and the sperm contained in the semen. It should be the first laboratory investigation for men while evaluating a couple's infertility. Here, we tried to review the semen analysis as a very important laboratory investigation in evaluating the infertile couples with all points in the light of last published World Health Organization (WHO) criteria.

Male fecundity and pollen dispersal in hill dipterocarps: significance of mass synchronized flowering and implications for conservation

Summary1. To understand pollinator–plant symbioses and to conserve forest resources effectively, we need an understanding of pollen dispersal patterns and the heterogeneity (spatial and temporal) of male fecundity.2. We investigated pollen dispersal patterns of the hill dipterocarp species Shorea curtisii using a modified Neighbourhood model. Seeds were collected following a sporadic general flowering (GF) event in 2002 and two mass GF events in 1998 and 2005. Seed paternity was then determined to investigate pollen dispersal patterns and the heterogeneity of male fecundity.3. Pollen dispersal distances were longer, and the effective number of males lower, in the sporadic GF of 2002, than in the mass GF events of 1998 and 2005.4. There was high between‐individual variation in male fecundity, and small trees contributed less than large trees to the analysed seed pool. The results indicate that selective logging may adversely affect the reproduction of such species due to the removal of large trees from the reproductive population.5. Synthesis. The large number of effective male individuals during the mass GF events provides evidence of Allee effects, suggesting that the mass GF events are of evolutionary significance and may contribute to the maintenance of genetic diversity. Future forestry practice needs to take into account variation in male fecundity, pollen dispersal and the mating system to ensure sustainable regeneration.

Rapid Functional Divergence of a Newly Evolved Polyubiquitin Gene in Drosophila and Its Role in the Trade-off between Male Fecundity and Lifespan

The cost of reproduction is a pivotal trade-off with various biological processes during the evolution of organisms. However, the genes and molecular mechanisms underlying the evolution of balancing reproductive capacity and its cost are still largely unknown. Here, we present a comprehensive study on the evolution, expression, and biological functions of a newly evolved pair of X-linked polyubiquitin tandemly duplicated genes, CG32744 and CG11700, of which the duplication event occurred in Drosophila melanogaster lineage after the split from D. simulans clade. We found that CG32744 retains conserved polyubiquitin-coding sequences across Drosophila species and is ubiquitously expressed, whereas CG11700 has accumulated numerous amino acid changes and shows a male-specific expression pattern. Null mutants of CG11700 have a higher male fecundity but shorter lifespan, whereas its overexpression decreases male fecundity. In contrast, the null mutants of the peptide-conserved CG32744 do not exhibit such phenotypes. These results suggest that CG11700 might have experienced neofunctionalization and evolved important functions in the trade-off between male fecundity and lifespan and that CG32744 likely has retained the ancestral function.

MICROEVOLUTION OF S-ALLELE FREQUENCIES IN WILD CHERRY POPULATIONS: RESPECTIVE IMPACTS OF NEGATIVE FREQUENCY DEPENDENT SELECTION AND GENETIC DRIFT

Negative frequency dependent selection (NFDS) is supposed to be the main force controlling allele evolution at the gametophytic self-incompatibility locus (S-locus) in strictly outcrossing species. Genetic drift also influences S-allele evolution. In perennial sessile organisms, evolution of allelic frequencies over two generations is mainly shaped by individual fecundities and spatial processes. Using wild cherry populations between two successive generations, we tested whether S-alleles evolved following NFDS qualitative and quantitative predictions. We showed that allelic variation was negatively correlated with parental allelic frequency as expected under NFDS. However, NFDS predictions in finite population failed to predict more than half S-allele quantitative evolution. We developed a spatially explicit mating model that included the S-locus. We studied the effects of self-incompatibility and local drift within populations due to pollen dispersal in spatially distributed individuals, and variation in male fecundity on male mating success and allelic frequency evolution. Male mating success was negatively related to male allelic frequency as expected under NFDS. Spatial genetic structure combined with self-incompatibility resulted in higher effective pollen dispersal. Limited pollen dispersal in structured distributions of individuals and genotypes and unequal pollen production significantly contributed to S-allele frequency evolution by creating local drift effects strong enough to counteract the NFDS effect on some alleles.

Effects of male fecundity, interindividual distance and anisotropic pollen dispersal on mating success in a Scots pine (Pinus sylvestris) seed orchard

Quantifying the effect of pollen dispersal and flowering traits on mating success is essential for understanding evolutionary responses to changing environments and establishing strategies for forest tree breeding. This study examined, quantitatively, the effects of male fecundity, interindividual distance and anisotropic pollen dispersal on the mating success of Scots pine (Pinus sylvestris), utilizing a well-mapped Scots pine seed orchard. Paternity analysis of 1021 seeds sampled from 87 trees representing 28 clones showed that 53% of the seeds had at least one potential pollen parent within the orchard. Pronounced variation in paternal contribution was observed among clones. Variations in pollen production explained up to 78% of the variation in mating success, which was 11.2 times greater for clones producing the largest amount of pollen than for clones producing the least pollen. Mating success also varied with intertree distance and direction, which explained up to 28% of the variance. Fertilization between neighboring trees 2.3 m apart was 2.4 times more frequent than between trees 4.6 m apart, and up to 12.4 times higher for trees downwind of the presumed prevailing wind direction than for upwind trees. The effective number of pollen donors recorded in the seed orchard (12.2) was smaller than the theoretical expectation (19.7). Based on the empirical observations, a mating model that best describes the gene dispersal pattern in clonal seed orchards was constructed.

Testicular Failure and Male Infertility in the Monogenic Mulibrey Nanism Disorder

Few monogenic mutations causing human male infertility have been identified to date. We studied pubertal development and fecundity in males with Mulibrey nanism (MUL) caused by mutations in the TRIM37 gene. Twenty-eight male MUL patients of the Finnish national cohort aged 8.7 to 50.0 yr (median age, 28.8) at the end of observation were followed for 10 yr beginning from 2000-2001. Clinical characteristics, reproductive hormone levels, semen quality, and testicular histology were assessed. The external genital phenotype was normal. In childhood and prepuberty, serum levels of FSH, LH, testosterone (T), and inhibin B were normal. Puberty started spontaneously at a median age of 12.6 yr (range, 11.1-15.0), and FSH, LH, T, and inhibin B levels increased adequately until midpuberty. Thereafter, testicular growth and virilization proceeded slowly. Concomitantly, FSH, and to a lesser extent LH, showed a progressive increase to hypergonadotropic levels in all patients, whereas inhibin B decreased and T leveled off. Testicular size was small (median volume, 8.7 ml; range, 3.5-18.3 ml in adults). All semen samples showed severe oligoasthenozoospermia or azoospermia. None of the patients had a history of spontaneous fertility, but four men had undergone infertility treatment, which in one case was successful. All histological MUL samples showed varying degrees of degeneration. All adult MUL males have a unique disorder of testicular function with small testes, elevated FSH and LH, and low inhibin B. In MUL, mutations in TRIM37 lead to disturbance of sexual maturation, and fertility is severely compromised. Thus, TRIM37 is a novel gene causing male infertility.

Cutting-Edge Issues in Autoimmune Orchitis

Autoimmune orchitis is a relevant cause of decreased fecundity in males, and it is defined as a direct aggression to the testis with the concomitant presence of anti-sperm antibodies (ASA). The presence of these specific antibodies has been observed in approximately 5-12% of infertile male partners. Primary autoimmune orchitis is defined by isolated infertility with ASA but without evidence of a systemic disease. Secondary causes of orchitis and/or testicular vasculitis are uniformly associated with autoimmune diseases, mainly in primary vasculitis such as polyarteritis nodosa, Behçet's disease, and Henoch-Schönlein purpura. The overall frequencies of acute orchitis and ASA in rheumatic diseases are 2-31% and 0-50%, respectively. The pathogenesis of primary/secondary autoimmune orchitis is not completely understood but probably involves the access of immune cells to the testicular microenvironment due to inflammation, infection or trauma, leading to apoptosis of spermatocytes and spermatids. Glucocorticoids and immunosuppressive drugs are indicated in autoimmune orchitis-associated active systemic autoimmune diseases. However, there are no standardized treatment options, and the real significance of ASA in infertile men is still controversial. Assisted reproductive technologies such as intrauterine insemination, in vitro fertilization, and intracytoplasmic sperm injection (ICSI) are therapeutic options for male infertility associated with these autoantibodies. ICSI is considered to be the best choice for patients with severe sperm autoimmunity, particularly in males with low semen counts or motility.

Distribution and reproductive biology of the little cuttlefish Sepiola atlantica (Cephalopoda: Sepiolidae) around Anglesey, North Wales

Sepiola atlantica were captured in seine nets at twelve locations around the coast of Anglesey, UK. Animals were most abundant on the very sheltered shore of Y Foryd Bay and the wave-exposed shore of Traeth Penrhos, and these two locations were further sampled seasonally to examine the seasonal occurrence, population structure and reproductive biology of S. atlantica. Sepiola atlantica (5–28 mm dorsal mantle length (DML)) migrated inshore seasonally and first appeared in July where they attained peak abundances between July and August at seawater temperatures of 17°C. Numbers declined between September and October as temperatures fell below 15–16°C, and in late October, they migrated offshore. Male S. atlantica was significantly smaller and matured at a smaller DML than females. The number of spermatangia on the bursa copulatrix of female S. atlantica varied seasonally attaining maximum numbers in October with a mean of 22 spermatangia on the bursa copulatrix of Y Foryd Bay females. At Y Foryd Bay and Traeth Penrhos, the number of spermatophores in male and potential fecundity in female S. atlantica ranged between 1 and 147 and 25 and 141, respectively. The spermatophoric complex and gonadosomatic index showed a high degree of variability in individuals of similar wet body weight with the female gonad constituting a far greater percentage of the total wet body weight than the male gonad. It is concluded that S. atlantica of all sizes and maturity stages congregate in the shallow waters around Anglesey between July and October when environmental conditions are favourable for enhanced growth and maturation and where the high numbers of animals enhance opportunities for mating.

Male gametocyte fecundity and sex ratio of a malaria parasite, Plasmodium mexicanum

Evolutionary theory predicts that the sex ratio of Plasmodium gametocytes will be determined by the number of gametes produced per male gametocyte (male fecundity), parasite clonal diversity and any factor that reduces male gametes' ability to find and combine with female gametes. Despite the importance of male gametocyte fecundity for sex ratio theory as applied to malaria parasites, few data are available on gamete production by male gametocytes. In this study, exflagellating gametes, a measure of male fecundity, were counted for 866 gametocytes from 26 natural infections of the lizard malaria parasite, Plasmodium mexicanum. The maximum male fecundity observed was 8, but most gametocytes produced 2-3 gametes, a value consistent with the typical sex ratio observed for P. mexicanum. Male gametocytes in infections with higher gametocytaemia had lower fecundity. Male fecundity was not correlated with gametocyte size, but differed among infections, suggesting genetic variation for fecundity. Fecundity and sex ratio were correlated (more female gametocytes with higher fecundity) as predicted by theory. Results agree with evolutionary theory, but also suggest a possible tradeoff between production time and fecundity, which could explain the low fecundity of this species, the variation among infections, and the correlation with gametocytaemia.

Multiple Mating, Fecundity, and Longevity in Female Northern Corn Rootworm (Coleoptera: Chrysomelidae) in Relation to Body Size

AbstractDiabroticite corn rootworms are significant maize, Zea mays L., pests that have evolved resistance to cultural and chemical management methods. Transgenic maize synthesizing a rootwormtoxic protein originating from the bacterium Bacillus thuringiensis Berliner is an important new management technology. Its use requires a refuge of nontransgenic maize to delay evolution of resistance by generating susceptible beetles capable of copulating with any resistant individuals surviving on the transgenic crop. The evolution of such resistance may concurrently influence a variety of fitness-related characters. Here, we examined multiple mating by female Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae) in relation to the following fitness-related traits: female longevity, fecundity, and body size of males and females at the first copulation. For the first copulation, large and small males were reciprocally paired to large and small females for comparison with average-sized beetles. Once-mated females were then maintained under conditions conducive to oviposition and paired with averaged-sized males at weekly intervals until death. Although female age at second copulation varied significantly with size category, female age at first copulation, longevity and fecundity did not. Females that mated multiple times lived longer and laid more eggs than did those that mated once. The results suggest that resistance management models may need to consider those females deriving fitness benefits from a second mating.

Male mating history and body size influence female fecundity and longevity of the dengue vector Aedes aegypti.

Male reproductive success is dependent on insemination success and reproductive output. During mating, male mosquitoes transfer not just sperm, but also seminal fluid proteins that may have profound effects on mated female biology and behavior. In this study, we investigated the role of male body size and mating history on semen depletion, female longevity, and reproductive success in Aedes aegypti L. Small and large males were mated in rapid succession with up to five females. Our results indicate that large males had greater mating capacity than small males. A reduction in fecundity by >50% was observed in females that were fourth to mate with small males in comparison with females that mated earlier in sequence. For females mated to large males, this reduction became evident for females that mated fifth in sequence. No loss of fertility (measured as hatch rate) was observed in females that were third-fifth in mating sequence compared with females mated to virgin males. When females were maintained on a low-quality (5% sucrose) diet, those mated to virgin males had a greater longevity compared with females mated third in sequence. We conclude that small males experience more rapid seminal depletion than large males, and discuss the role of semen depletion in the mated female. Our results contribute toward a better understanding of the complexity of Ae. aegypti mating biology and provide refined estimates of mating capacity for genetic control efforts.

Estimating the variance of male fecundity from genotypes of progeny arrays: evaluation of the Bayesian forward approach

Summary 1. Characterizing fine scale mating patterns in plant populations makes it possible to investigate genetic drift, gene flow and selection gradients at a contemporary time scale. Molecular markers are valuable tools for this type of analysis, and numerous statistical methods have been developed to make the best of the information they can provide. In particular, we recently proposed a Bayesian approach based on a paternity analysis wherein we estimate jointly the variance in male fecundity and the pollen dispersal kernel. 2. Here, we use simulated data sets to investigate the accuracy of the Bayesian approach compared to (i) classical maximum likelihood approaches (e.g. Neighbourhood model) that ignore variance in male fecundity or explain it through a few covariates and (ii) indirect methods (KinDist and TwoGener) that integrate the variance in fecundity in an ‘effective population density’. 3. The Bayesian estimates correctly considered the over‐dispersion resulting from the variance in fecundity, resulting in wider but more accurate confidence intervals, in particular in high‐density populations. The maximum likelihood methods resulted in confidence intervals with low coverage probabilities and in widespread false‐positive tests when testing the effect of covariates on male fecundity. 4. Estimated individual fecundities and estimated empirical variance in fecundity were robust to the distribution assumed for the individual random fecundities (log‐normal or Gamma). In contrast, the theoretical variance estimate critically depended on the assumed distribution. 5. The indirect methods provided much more variable estimators, as expected because they use less information about pollen sources and consider the molecular information only through genetic structure indices. 6. Disentangling the fecundity from the spatial effects in paternity analyses is necessary when studying selection in natura and or when addressing the effects of spatial distribution on effective gene flow. The Bayesian approach studied here successfully accounts for the variance in fecundity when a large fraction of it is not explained by the studied covariates. The Mixed Effect Mating Model computer program introduced here is devoted to its implementation.

Semen analysis and sperm function tests: How much to test?

Semen analysis as an integral part of infertility investigations is taken as a surrogate measure for male fecundity in clinical andrology, male fertility, and pregnancy risk assessments. Clearly, laboratory seminology is still very much in its infancy. In as much as the creation of a conventional semen profile will always represent the foundations of male fertility evaluation, the 5th edition of the World Health Organization (WHO) manual is a definitive statement on how such assessments should be carried out and how the quality should be controlled. A major advance in this new edition of the WHO manual, resolving the most salient critique of previous editions, is the development of the first well-defined reference ranges for semen analysis based on the analysis of over 1900 recent fathers. The methodology used in the assessment of the usual variables in semen analysis is described, as are many of the less common, but very valuable, sperm function tests. Sperm function testing is used to determine if the sperm have the biologic capacity to perform the tasks necessary to reach and fertilize ova and ultimately result in live births. A variety of tests are available to evaluate different aspects of these functions. To accurately use these functional assays, the clinician must understand what the tests measure, what the indications are for the assays, and how to interpret the results to direct further testing or patient management.

CRYPTIC POSTZYGOTIC ISOLATION IN AN ERUPTIVE SPECIES OF BARK BEETLE (DENDROCTONUS PONDEROSAE)

Studies of postzygotic isolation often involve well-differentiated taxa that show a consistent level of incompatibility, thereby limiting our understanding of the initial stages and development of reproductive barriers. Dendroctonus ponderosae provides an informative system because recent evidence suggests that distant populations produce hybrids with reproductive incompatibilities. Dendroctonus ponderosae shows an isolation-by-distance gene flow pattern allowing us to characterize the evolution of postzygotic isolation (e.g., hybrid inviability, hybrid sterility) by crossing populations along a continuum of geographic/genetic divergence. We found little evidence of hybrid inviability among these crosses. However, crosses between geographically distant populations produced sterile males (consistent with Haldane's rule). This effect was not consistent with the fixation of mutations in an isolation-by-distance pattern, but instead is spatially localized. These reproductive barriers are uncorrelated with a reduction in gene flow suggesting their recent development. Crosses between geographically proximal populations bounding the transition from compatibility to hybrid male sterility showed evidence of unidirectional reduction in hybrid male fecundity. Our study describes significant postzygotic isolation occurring across a narrow and molecularly cryptic geographic zone between the states of Oregon and Idaho. This study provides a view of the early stages of postzygotic isolation in a geographically widespread species.