Effects of p,p'-DDE on male reproductive organs in peripubertal Wistar rats following a single intraperitoneal injection

The effects of p,p'-DDE on male reproductive organs were investigated in detail in peripubertal Wistar rats following a single intraperitoneal injection. 220 mg/kg of p,p'-DDE (1/4 of LD50) were injected once into prepubertal and postpubertal Wistar rats and its effects were observed until 20 weeks of age. Weights of the body and reproductive organs in p,p'-DDE-injected rats were similar to those in control rats, who were injected with corn oil only. Sperm profile parameters such as spermatid number within the testis, sperm number within the epididymis, sperm motility and its morphology were not different between the prepubertal or postpubertal p,p'-DDE-exposed group and the control group. Like-wise, the histopathological examination at stage VII of the seminiferous epithelium cycle, when the germ cells are sensitive to testosterone, was similar in all three groups during the observation period. Serum levels of testosterone also showed no significant changes by exposure to p,p'-DDE under the conditions of this study. From these results, the antiandrogenic or estrogenic activity attributed to p,p'-DDE was not confirmed in male reproductive organs and no impairment of sperm profile was observed. This study confirmed that the reproductive functions of matured animals are scarcely affected by p,p'-DDE exposure during the peripubertal period and revealed that they might be relatively resistant to exogenous endocrine-disrupting chemicals. p,p'-DDE may threaten the hormonal equilibrium required for normal gonadal development during the organogenesis period, at an earlier stage of life. Further studies are necessary to fully reveal all the effects of p,p'-DDE on male reproductive organs and sperm profile.     

High divergence of reproductive tract proteins and their association with postzygotic reproductive isolation in Drosophila melanogaster and Drosophila virilis group species

The possible association between gonadal protein divergence and postzygotic reproductive isolation was investigated among species of the Drosophila melanogaster and D. virilis groups. Protein divergence was scored by high-resolution two-dimensional electrophoresis (2DE). Close to 500 protein spots from gonadal tissues (testis and ovary) and nongonadal tissues (malpighian tubules and brain) were analyzed and protein divergence was calculated based on presence vs absence. Both testis and ovary proteins showed higher divergence than nongonadal proteins, and also a highly significant positive correlation with postzygotic reproductive isolation but a weaker correlation with postzygotic reproductive isolation. Particularly, a positive and significant correlation was found between proteins expressed in the testis and postzygotic reproductive isolation among closely related species such as the within-phylad species in the D. virilis group. The high levels of male-reproductive-tract protein divergence between species might be associated with F1 hybrid male sterility among closely related species. If so, a lower level of ovary protein divergence should be expected on the basis that F1 female hybrids are fully fertile. However, this is not necessarily true if relatively few genes are responsible for the reproductive isolation observed between closely related species, as recent studies seem to suggest. We suggest that the faster rate of evolution of gonadal proteins in comparison to nongonadal proteins and the association of that rate with postzygotic reproductive isolation may be the result of episodic and/or sexual selection on male and female molecular traits.     

Information asymmetries among males: implications for fertilization success in the thirteen-lined ground squirrel

The classical view of mammalian mating competition focuses on combat and threat. By contrast, field studies have revealed that male mating success in some species is more strongly determined by mate location ability than by physical dominance. In thirteen-lined ground squirrels, competition in locating oestrous females is exacerbated by sperm competition that favours the first male to mate with a female. We used a female-removal experiment to identify the distinguishing characteristics of males that were the first at finding and mating with females. Each focal female was observed the day before she entered oestrus; the identities of males that made contact with her and the locations of their interactions were recorded. The following morning the females were temporarily removed, and we monitored male search behaviour in their absence. Males that arrived first were those that had spent more time with the female the previous day relative to their rivals. Time invested the day before, in turn, was highly correlated with male search persistence and familiarity with the female's likely whereabouts. These results demonstrate that differential fertilization success can arise from information asymmetries among males: the advantaged individuals are those that have greater a priori knowledge of the reproductive state and spatial locations of prospective mates than rivals.     

Absence makes the adaptations grow fonder: Proportion of time apart from partner, male sexual psychology, and sperm competition in humans (Homo sapiens).

Sperm competition occurs when the sperm of multiple males concurrently occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 237 men in committed, sexual relationships. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) greater sexual interest in his partner, (b) greater distress in response to his partner's sexual rejection, and (c) greater sexual persistence in response to his partner's sexual rejection. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses limitations of the current research and situates the current results within the broader comparative literature on adaptation to sperm competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cytotoxic and cell transforming effects of the insecticide, lindane (gamma-hexachlorocyclohexane) on BALB/c 3T3 cells

The present study was designed to elucidate the correlation between findings from reproductive performance testing and those from histopathological examination of the testis and sperm analysis in rats given a benzodiazepine derivative, nitrazepam, for 2 and 4 weeks. The mechanisms of toxicological action of nitrazepam on the male reproductive organs were also investigated. Nitrazepam was given orally to Sprague-Dawley male rats (6-week-old) at a daily dose of 80 mg/kg for 2 weeks or at daily doses of 20, 40 or 80 mg/kg for 4 weeks. Treated males were mated to examine reproductive performance with untreated females after each dosing period, and after 4 and 9 week of recovery periods. Necropsy was performed for histopathological examination of the testis and epididymis and for sperm analysis after each dosing period and the final mating trial (total of 11 weeks recovery). In the findings from reproductive performance testing, significant decrease in the fertility index was observed in the 80 mg/kg group even after 2 weeks dosing and thereafter until 4 weeks recovery, though the mating index did not significantly differ from that of controls through the experiment. In the histopathological examination and sperm analysis, testicular signs of toxicity, decrease in number of sperm heads in the testis and increase in number of sperm with abnormal heads in the seminiferous tubules were noted in the 80 mg/kg group after 2 weeks dosing and in the 40 and 80 mg/kg groups after 4 weeks dosing. Concentrations of plasma testosterone and content of testis testosterone in nitrazepam-treated groups were not significantly different from those of controls. Plasma FSH concentration was significantly elevated in the 80 mg/kg group through the experiment, although significant elevation of plasma LH was observed only after 2 weeks dosing. These results indicate that histopathological examination is the most reliable approach to detect male reproductive adverse effects induced by nitrazepam rather than using parameters from mating trials. The four-week-dosing period is appropriate for their detection. Hypospermatogenesis induced by nitrazepam is suggested to be caused by direct action of nitrazepam on germ cells and/or Sertoli cells rather than by indirect action through inhibition of testosterone secretion.     

The function of Barbary macaque copulation calls

In a wide variety of animal species, females produce vocalizations specific to mating contexts. It has been proposed that these copulation calls function to incite males to compete for access to the calling female. Two separate advantages of inciting male-male competition in this way have been put forward. The first suggests that as a result of calling, females are only mated by the highest ranking male in the vicinity (indirect mate choice hypothesis). The second proposes that copulation calling results in a female being mated by many males, thus promoting competition at the level of sperm (sperm competition hypothesis). In this paper, I give results from the first experimental study to test these hypotheses. Playback was used to examine the function of copulation calls of female Barbary macaques (Macaca sylvanus) in Gibraltar. Although rank did not affect lone males' likelihood of approaching copulation calls, when playbacks were given to pairs of males only the higher ranking individual approached. Moreover, females were mated significantly sooner after playback of their copulation call than after playback of a control stimulus. These results suggest that the copulation calls of female Barbary macaques play a key role in affecting patterns of male reproductive behaviour, not only providing an indirect mechanism of female choice, but also promoting sperm competition by reducing the interval between copulations. Potential fitness benefits of inciting male-male competition at these two levels are discussed.     

Sperm competition I: basic model, ESS and dynamics

We examine models of sperm competition to determine which strategies are evolutionarily stable according to game theory. Games are considered in which the males of a species must divide a fixed amount of sperm between a fixed number of rounds in competition over fertilization of a given set of eggs. Sperm success with a single female is allocated using the raffle principle". A two round model is formulated and we show that the evolutionarily stable strategy (ESS) is a pure strategy in which a male should use at least half his sperm in the first round if given the opportunity to mate. The ESS is unique and globally stable, in contrast to most classical ESSs which are only locally stable. The model is extended to include the effects of sperm replenishment and egg oviposition between rounds. Both serve to increase the ESS amount of sperm inseminated in round one.     

Why did the sperm cross the cumulus? To get to the oocyte. Functions of the sperm surface proteins PH-20 and fertilin in arriving at, and fusing with, the egg

The sperm surface has an active role in the events of fertilization. The definition of the sperm surface in both its composition and domain organization begins during spermatogenesis and continues until the moment of sperm-egg fusion. Alterations of the surface proceed as a result of internal programming and environmental cues from both the male and female reproductive tracts, including interactions with the egg itself. We have investigated the sperm surface to understand its domain organization and the ongoing changes in this organization as well as the role of specific surface proteins in fertilization. Much of our research has concentrated on two surface proteins: PH-20 and fertilin. PH-20 is a single-chain protein, anchored in the membrane via a glycosyl phosphatidylinositol (GPI) anchor. The N-terminal domain of the molecule has a hyaluronidase activity. The hyaluronidase activity of PH-20 on the sperm plasma membrane enables sperm to penetrate the layer of cumulus cells surrounding the oocyte. PH-20 has a second function, unrelated to its hyaluronidase activity, in the binding of acrosome-reacted sperm to the zona pellucida (secondary sperm-zona binding). The fertilin molecule is an alpha,beta heterodimer whose two subunits are closely related transmembrane proteins. Fertilin beta has a disintegrin domain that has high sequence homology with the snake disintegrins, a known class of soluble integrin ligands. The binding site of the beta disintegrin domain functions to bind sperm to the egg plasma membrane via a mechanism that leads to sperm-egg fusion. The precursor of fertilin alpha, made in the testis, has an active metalloprotease site that could function in spermatogenesis. This metalloprotease domain is removed by proteolytic processing in the testis. Mature fertilin alpha on sperm also has a hydrophobic, putative "fusion peptide" that may promote the process of lipid bilayer fusion between sperm and egg plasma membranes. Fertilin alpha and beta are the first identified members of a new gene family of transmembrane proteins, the ADAM family, so called because they contain A Disintegrin And Metalloprotease domain. Many distinct ADAMs have now been found in diverse tissues and species (Drosophila to human) and are proposed to have a variety of functions in development and the adult. In addition to fertilin, other ADAMs are also present on the sperm plasma membrane and may participate with fertilin in sperm-egg fusion.     

Interferon-gamma differentially regulates antigen-processing functions in distinct endocytic compartments of macrophages with constitutive expression of class II major histocompatibility complex molecules

Treatment of pregnant female Sprague-Dawley rats on Gestational Day 15 with a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0.5, 1.0, or 2.0 micrograms/kg) or indole-3-carbinol (I3C, 1.0 or 100 mg/kg), an aryl hydrocarbon (Ah) receptor agonist which is found in cruciferous vegetables, resulted in reproductive abnormalities in the male offspring (three to five litters in each treatment group). Anogenital distance and crown to rump length were altered by both compounds; however, the timing of the effects (Day 1 or 5) was variable and the responses were not necessarily dose-dependent. In 62-day-old offspring, seminal vesicle (24 to 26%), prostate (32 to 44%), testicular parenchymal (14%), and epididymal weight (19%) were decreased by one or more doses of TCDD. In contrast, I3C at one or more doses decreased daily sperm production/g testicular parenchyma (13 to 20%) and daily sperm production/testis (22%). Total number of sperum in the epididymis was significantly decreased (30 to 33%) in rats perinatally exposed to TCDD and this was due to a decreased (49 to 51%) number of sperm in the tail of the epididymis. Perinatal exposure to I3C did not affect any of these parameters. TCDD did not affect epididymal transit time of sperm through the complete epididymis at any of the doses (0.5 to 2.0 micrograms/kg). However, at the two highest doses (1.0 and 2.0 micrograms/kg), TCDD increased epididymal transit rate of sperm through the tail of the epididymis by 33 and 37%, respectively. In contrast, primarily due to decreased transit rate (39%) of sperm through the head plus body of the epididymis. I3C (1 mg/kg) significantly increased total epididymal transit time by 31%. In conclusion, perinatal exposure of pregnant rats to I3C, an Ah receptor agonist similar to TCDD, causes reproductive abnormalities in male rat offspring; however, I3C and TCDD elicited both common and different responses.     

Differential effects of mate competition and mate choice on eastern tiger salamanders

Male tiger salamanders, Ambystoma tigrinum tigrinumare slightly larger in body size and have considerably higher and longer tails than females. To determine how these dimorphic traits affected reproductive performance and success, we conducted breeding trials using 12 males and six females per trial and monitored male-female and male-male interactions. Larger males had an advantage in most aspects of mate competition investigated. Males with higher tails had no advantage in either mate competition or mate choice. Males with longer tails also had no advantage in mate competition but were preferred as mates by females. Larger males interrupted courting males more often than smaller males did. The form of male-male interference was conditional on body size and not on either tail dimension. If the intruder was larger than the courting male, it would shove the female away from the courting male and initiate courtship; if the intruder was smaller, it adopted a female mimicry tactic in which it positioned itself between the courting male and female and performed female behaviours to the courting male while simultaneously courting the female. Our trials indicated that the two components of sexual selection may influence the evolution of different male morphological traits in tiger salamanders. Mate competition may favour increased male body length; mate choice may select for greater male tail length.     

Mate choice and mate competition influence male body size in Japanese medaka

A sexual size dimorphism usually occurs when size-dependent reproductive advantages exist in only one sex. Studies on Japanese medaka, Oryzias latipes, have demonstrated reproductive size advantages in females but not in males, even though males and females are similar in body size. We conducted mate-choice and mate-copying tests in which a female could first associate with, then mate with, either a large (>/=1 sd+X standard length) or a small male (相似文献   

Biological monitoring of exposure to chlorpyrifos by high performance liquid chromatography

Sixteen patients with hypogonadotropic hypogonadism received gonadotropin replacement therapy. Two patients treated with HCG alone showed induction of spermatogenesis 2 and 12 months after the start of treatment. Three subjects receiving combination therapy showed sperm appearance 6-28 months after treatment. The patients showing sperm appearance, whose testicular volume was > or = 4 ml, showed a higher sperm count and impregnated their partners, although no relationship was found between pretreatment testicular volume and sperm appearance. The response to HCG test correlated with sperm appearance after gonadotropin therapy. Sperm appearance was not observed in any subject except for one who showed no response to luteinizing hormone-releasing hormone (LH-RH) test and none of the patients without response of FSH to LH-RH demonstrated any induction of spermatogenesis. In conclusion, the responses to LH-RH test and possibly to HCG test could predict the induction of spermatogenesis after gonadotropin replacement therapy, and a large testicular volume is associated with post-treatment fertility.     

Effect of Ambilhar (niridazole) on spermatogenesis in guinea-pigs

Niridazole (Ambilhar), a new antibilharzial drug was fed for 5 days to 20 male guinea pigs at 50 mg/kg while testicular and epididymal biopsies were examined histologically for 10 weeks. Only 10 animals survived the treatment. On the 5th day sperm numbers were reduced in testis tubules. On Day 8 variations in tubule size and in degrees of inhibition of spermatogenesis were at their maximum. Some tubules had recovered spermatogenesis at 15 days, and all had at 3 weeks. Guinea pigs are more sensitive to niridazole than are rats.     

Germ cells and germ cell transplantation

The germ cell lineage in mice is established about a week after fertilization, in a group of cells that have left the epiblast and moved to an extraembryonic site. They migrate back into the embryo, along the hind gut and into the gonads. Germ cells in male and female embryos then pursue different pathways: in the testis the germ cells cease proliferating and enter mitotic arrest, while germ cells in the ovary, like those in male embryos that remain outside the gonads, enter meiotic prophase. Studies on explanted germ cells suggest that all germ cells may enter meiosis at a certain stage of their development, unless prevented from doing so by some inhibitory influence of the testis. Germ cells during the migratory stage can be cultured, but do not enter meiosis unless embedded in somatic tissue. Addition of certain growth factors and cytokines to the culture medium allows germ cells to proliferate indefinitely in vitro: Like embryonic stem cells, these immortalized EG (embryonic germ) cells will colonize all cell lineages if introduced into a blastocyst. After birth, germ cells undergo gametogenesis; oogenesis in the female, spermatogenesis in the male. Brinster and his colleagues have shown that spermatogonial stem cells injected into a germ-cell depleted testis will repopulate the seminiferous tubules and undergo spermatogenesis, giving rise to functional spermatozoa. Stem cells from frozen testicular tissue are still capable of giving rise to spermatogenesis in a host testis. Rat testicular tissue can undergo spermatogenesis in a mouse testis, to form morphologically normal rat spermatozoa, even though the Sertoli cells that support them are of endogenous mouse origin. These findings are of fundamental importance for our understanding of spermatogenesis and the interactions between germ cells and Sertoli cells; but they also have significant practical implications, in relation to both agricultural practice and clinical treatment of infertility.     

Insulin and insulin-like growth factor-I receptor mediated differentiation of 3T3-F442A cells into adipocytes: effect of PI 3-kinase inhibition

Sperm-zona pellucida binding, a crucial step in the process of fertilization, takes place in vivo in the upper portion of the fallopian tube. The presence of GnRH-like peptides in the female and the male genital tract has been described. In this work, the effect of GnRH and related peptides upon sperm-zona pellucida binding ability was studied. Sperm aliquots, capacitated for 4.5 h, were incubated for 5 min with saline (control) or 20 nM of GnRH, C-terminal (1-5) or N-terminal (5-10) fragments of GnRH, Substance P, dynorphin, bombesin, or mixed GnRH (a synthetic peptide with the same amino acids as GnRH but in different order). Sperm were also incubated with the GnRH antagonist Ac-3,4-dehydro-Pro1, -p-fluoro-D-Phe2, D-Trp3,6-LHRH, alone or before adding GnRH. The sperm were then tested using the hemizona assay. After 10 min, the number of zona-bound sperm was determined. In addition, the effect of GnRH upon the acrosome reactions, sperm movement characteristics, and sperm-zona collisions was evaluated. Sperm treated with GnRH bound in higher numbers to the zona than did control sperm (p < 0.005). The GnRH fragments, the GnRH antagonist, and related peptides did not have any effect on sperm-zona interaction; however, the GnRH antagonist totally blocked the stimulatory effect of GnRH. GnRH did not affect the percentage of acrosome-reacted sperm, pattern of sperm movement, or frequency of sperm-zona collisions. I suggest that the increased ability of the sperm to bind to the zona may be due to exposure and/or change of affinity of zona receptors on the sperm plasma membrane.     

Relationship among hormonal treatments, suppression of spermatogenesis, and testicular protection from chemotherapy-induced damage

To further elucidate the mechanism by which hormonal pretreatment protects the rat testis from damage by procarbazine, we investigated the relationship between the suppression of hormone levels and spermatogenesis and the recovery of spermatogenesis from stem spermatogonia. LBNF1 rats were implanted with capsules containing testosterone or testosterone plus estradiol. After hormone treatment, rats were injected with procarbazine, and recovery of spermatogenesis was assessed. Testosterone (2 cm) plus estradiol (0.5-cm) reduced serum LH levels causing intratesticular testosterone (ITT) to fall to 3% of control levels within 2 weeks, but testis weights and sperm head counts were not appreciably suppressed until 4 weeks. Two weeks' hormone pretreatment, only slightly enhanced spermatogenesis recovery, but 4 weeks markedly increased it. Testosterone (2 cm) alone produced slower suppression of spermatogenesis and less protection from procarbazine than did testosterone plus estradiol implants, despite equivalent suppression of LH and ITT. Long testosterone implants (24-cm) partially maintained ITT at 14% of control despite undetectable LH levels, prevented any decline in sperm counts, and nearly completely abrogated the protective effect of the hormone treatment. Protection appeared to be best correlated with the testis weight reduction by hormone treatment. Thus, recovery of spermatogenesis after chemotherapy is dependent on the degree of suppression of spermatogenesis caused by the reduction of ITT levels at the time of chemotherapy and likely involves cells, such as the Sertoli cells, that are both androgen-responsive and affected by the numbers of germ cells present.     

Endogenous formaldehyde as a potential factor of vulnerability of atherosclerosis: involvement of semicarbazide-sensitive amine oxidase-mediated methylamine turnover

Several adaptive explanations regarding the function of lengthy copulations in insects have been proposed. They may represent a form of mate guarding, where the male physically prevents the female from copulating with rival males. Alternatively, they may function to ensure full insemination of the male's sperm when copulation duration covaries with the amount of sperm transferred and male fertilization success. Finally, lengthy copulations may serve to allow males to assess female quality in terms of mating status and body weight. In this study I examine these hypotheses for the function of lengthy copulations in the Australian bushcricket Coptaspis sp. 2 (Orthoptera: Tettigoniidae). Unlike most other bushcrickets, males of this species do not produce a large spermatophylax that the female feeds on during insemination, but remain attached to the female's genitals up to 6 h after spermatophore attachment. Experimental manipulation of the duration of spermatophore attachment showed it to be related to the amount of sperm transferred. This suggests that the main function of copulation duration is to ensure complete transfer of the male's ejaculate. Males also discriminated between females, and provided mated females with more sperm which resulted in longer copulations than with virgin females. It is possible that possession of a large spermatophylax has been lost evolutionarily in this species, with males themselves acting as a sperm protection device during insemination.Copyright 1998 The Association for the Study of Animal Behaviour     

Male fertility in rats treated with etretinate for 4 weeks

The toxicity of Etretinate, a retinoid compound, on the male reproductive system was studied in male rats. The drug was administered for four weeks at the dose levels of 0 (control: Vehicle, Peanut oil), 5 and 25 mg/kg/day. The animals were then allowed to mate, and their male reproductive functions and organs were examined in detail. No significant changes due to toxicity were observed in male reproductive functions and organs in the 5 mg/kg/day group after the 4-week treatment. In contrast, males in the 25 mg/kg/day group showed drug-related changes in their reproductive performance (decrease of mating ability and fertility rate), testosterone blood level, sperm head counts, sperm viability and number in the caudal epididymis, organ weight and in the histopathology of their reproductive organs (atrophy of seminiferous tubules, necrosis of spermatocytes and spermatids, vacuolation of nuclei of spermatocytes and spermatids). Even though Etretinate belong to the retinoid group of compounds, the changes seen in the 25 mg/kg/day group were almost the same as those observed in Vitamin A-deficient animals. In conclusion, there is a correlation between changes due to toxicity observed for parameters of male fertility and for histopathological evaluation of the testis of rats that receiving high dose, treatment with Etretinate for 4 weeks.     

Determinants of female dispersal in Thomas langurs

Female dispersal occurs in a number of primate species. It may be related to: avoidance of inbreeding, reduction in food competition, reduction of predation risk, or avoidance of infanticide in combination with mate choice. Female dispersal was studied for a 5-year period in a wild population of Thomas langurs (Presbytis thomasi) that lived in one-male multi-female groups. Juvenile and adult individuals of both sexes were seen to disperse. Females appeared to transfer unhindered between groups, mostly from a larger group to a recently formed smaller one. They transferred without their infants and when not pregnant, and seemed to transfer preferentially during periods when extra-group males were harassing their group. During these inter-group encounters extra-group males seemed to try to commit infanticide. Thus, the timing of female transfer was probably closely linked to infanticide avoidance. Moreover, females seemed to transfer when the resident male of their group was no longer a good protector. The observations in the present study suggest that females transferred to reduce the risk of infanticide. Female dispersal may have another ultimate advantage as well, namely inbreeding avoidance. Due to the dispersal of both females and males the social organization of Thomas langurs was rather fluid. New groups were formed when females joined a male; male takeovers were not observed. Bisexual groups had only a limited life span, because all adult females of a bisexual group could emigrate. This pattern of unhindered female dispersal affects male reproductive strategies, and in particular it might lead to infanticidal behavior during inter-group encounters.     

Timing of mating, sperm dynamics, and ovulation in a wild population of agile Antechinus (Marsupialia: dasyuridae)

Timing of mating, sperm transport and storage, and ovulation were examined in a wild population of agile Antechinus (Marsupialia: Dasyuridae) in order to ascertain the validity of direct comparisons between captive and field-based mating studies in this species. Mating commenced in early August, and all females had ovulated by the 27th of the month. Fifty-five percent of the mated females caught that had not yet ovulated were captured on 19-20 August. This corresponded with a peak (67%) in the ovulation date determined for pregnant females. Approximately 25.9 x 10(3) spermatozoa per side were recovered from the reproductive tract of each mated female captured (range: 1.7 x 10(3)-75.5 x 10(3) spermatozoa per side). Spermatozoa were consistently found in greater numbers in the lower isthmus (19.7 x 10(3) +/- 19.9 x 10(3) spermatozoa per side) of the oviduct ( approximately 67% of all sperm found in the female tract; range 17-94%) than elsewhere in the reproductive tract. Few spermatozoa were found in the upper isthmus, and none were detected in the ampulla. Sperm number in the female reproductive tract supports the hypothesis that females will mate several times within the one estrus. At the conclusion of the rut, approximately 80.0 x 10(3) spermatozoa remained in each testis and approximately 630 x 10(3) spermatozoa in each epididymis. Most epididymal spermatozoa were restricted to the distal corpus/proximal cauda regions of the duct. This study shows that both field and laboratory reproductive data correlate well in the agile Antechinus and that successful breeding is indeed an exercise in reproductive brinkmanship.