Autoradiographic investigation of uptake and storage of exogenous sperm by the ovary of the compound ascidian Diplosoma listerianum

The movement of radiolabelled non-self sperm within the female reproductive tract of cultured specimens of the hermaphroditic ascidian Diplosoma listerianum Milne Edwards was investigated by light-microscope autoradiography. Passage of male gametes up the oviduct (fertilization canal) to the ovary was demonstrated for sperm known unequivocally to be of external (non-self) origin. The lumen of the ovary was directly confirmed as a site of long-term storage of sperm, as had previously been suggested from circumstantial evidence. The ovary had a branching structure. Sperm entered blind diverticula leading from the main lumen of the ovary, and persisted there adjacent to the oocyte at the end of each of these side-branches. This arrangement included the association of stored sperm with very small, immature oocytes. An investigation of the time-course of sperm uptake showed that exogenous sperm did not enter the oviducts of recipient ramets for some time (>3 h) after they were initially available, with first presence of sperm noted in the distal half of the duct at 9 h and greatest recorded uptake at 27 h. Sperm had reached the ovary 6.6 h after the first observation of their occurrence in the distal part of the oviduct. Uptake declined steeply between 27 and 46.8 h of continual exposure to sperm released by a single genetic source, and remained low at 81 h. The significance of these observations for the mating pattern of D. listerianum is discussed.     

Sperm competition and ejaculate investment in red squirrels (<Emphasis Type="Italic">Tamiasciurus hudsonicus</Emphasis>)

Sperm competition is widespread in mammals and occurs when ejaculates from two or more males compete within the female’s reproductive tract to fertilize the ova. Enlarged testes are associated with sperm competition because they produce sperm, but the accessory glands produce fluids and proteins that are also important for fertilization success. Sperm morphology can also have consequences for fertilization success because of its influence on sperm motility. Red squirrels engage in multiple mating, and thus sperm competition is likely. Here, we assess levels of multiple paternity in a natural population of red squirrels, test the prediction that testis size is correlated with size of the accessory glands and sperm morphometry, and test the prediction that ejaculate investment is condition-dependent. Five of six litters (83%) showed evidence of multiple paternity, indicating that sperm competition is likely to have occurred. Testis size was correlated with the size of all three accessory glands (prostate, seminal vesicle, epididymides), and there was a generally positive relationship between the size of the accessory glands and sperm length. Sperm morphology showed significant variation in size and shape among individual male squirrels. There was no evidence of condition dependence of testis size or the size of the accessory glands, but sperm midpiece length was negatively related to body condition. Further work should include determining the fitness consequence of variation in sperm morphometry, testis size, and accessory gland size, and determining the effects of variation in ejaculate investment on sperm motility.     

Seminal fluid enhances sperm viability in the leafcutter ant Atta colombica

The seminal fluid that accompanies sperm in ejaculates has been shown or suggested to affect sperm competition and paternity success of insects by preventing female remating, inducing oviposition, and forming mating plugs. In Atta leafcutter ants, queens have multiple mates but never remate later in life, although they may live and produce fertilized eggs for several decades. The mating biology and life history of these ants therefore suggests that the major function of seminal fluid is to maximize sperm viability during copulation, sperm transfer, and initial sperm storage. We tested this hypothesis by comparing the viability of testis sperm and ejaculated sperm (mixed with seminal fluid) and found a significant positive effect of seminal fluid on sperm viability. We further quantified this positive effect by adding accessory gland secretion (a major component of seminal fluid) in a dilution series, to show that minute quantities of accessory gland secretion achieve significant increases in sperm viability. Sperm stored by queens for 1 year benefited in a similar way from being exposed to accessory gland compounds after dissection in control saline solution. Our results provide the first empirical evidence that seminal fluid is important for the production of viable ejaculates and that the accessory glands of Atta males—despite their small size—are functional and produce a very potent secretion.     

Changes in the content and fatty acid composition of lipid in an isolated population of the capelin Mallotus villosus during sexual maturation and spawning

Changes in the wet weights and lipid contents of muscle, liver and gonad were determined in male and female Mallotus villosus in Balsfjorden, northern Norway, in 1981, from January, when gonadal development becomes noticeable, until May when the fish are spawning. Fatty acid compositions of tissue lipids were also determined. Over 4 mo prior to spawning, the weight of muscle in female capelin decreased by 32% while the weight of the ovary increased exponentially by 830%. In males the weight of the muscle remained constant and that of the testis decreased slightly. The lipid contents of the muscle of both males and females decreased by 76% over the period and an inverse relationship existed between the water and lipid contents of muscle in both sexes. Male liver weight remained constant over the period of study whereas female liver weight increased transiently by 300% between January and March. 38% of the lipid lost from female muscle was accounted for by lipid deposited in ovary whereas negligible amounts of the lipid lost from male muscle was accounted for by lipid in the testis. Gonadal lipid was always richer in polyunsaturated fatty acids than muscle lipid and, immediately prior to spawning, 42% of the fatty acids in ovarian lipid were polyunsaturated. Muscle lipid of males and females showed a progressive increase in the percentage of the long-chain monoenes 20:1 and 22:1 between January and May. It is concluded that male capelin catabolise more of their muscle lipid reserves than females in the 4 mo prior to spawning and that most of the lipid catabolism in males is associated with physical activity. Conversely, females deposit much more of their muscle lipid in gonads than males, although considerable selectivity occurs in the mobilisation of fatty acids from muscle lipid into ovarian lipid. Additionally, biosynthesis of gonadal constituents accounts for a considerable proportion of the lipid catabolised in females.     

Observations on the reproductive cycles of Monodonta lineata,Gibbula umbilicalis and G. cineraria

Monthly samples of gonads of 3 common species of intertidal trochids, Monodonta lineata (da Costa), Gibbula umbilicalis (da Costa) and G. cineraria (L.) were fixed for examination by light microscopy. Numbers and proportions of immature and mature oocytes in sections of ovaries were determined. In M. lineata and G. umbilicalis, the annual reproductive cycles were very similar, the testis and ovary of both species being empty brown structures from September to January/February, when gametogenesis began and the gonads began to swell and turn green in both sexes. As ripening continued, the ovary remained green in G. umbilicalis, but in M. lineata turned greygreen by the end of May. The testis of both species changed, to yellowish in G. umbilicalis and creamy-pink in M. lineata. Spawning occurred throughout summer and early autumn, and the gonads reverted to their former empty state. These changes were matched by the increase and subsequent decrease in proportion of ripe oocytes in the gonad. Some ripe oocytes are not shed during the spawning season, but no evidence of cytolysis of such oocytes was found. In G. cineraria, in contrast, the ovary remained green and swollen and the testis remained creamy-white and packed with sperm throughout the year. The proportion of ripe to unripe oocytes in the ovary fluctuated for the entire sampling period, and did not indicate the time of spawning. In the testis of all three species, spermatogonia were rarely seen, and spermatid stages were uncommon.     

Effect of malathion on reproductive system of male rats

The pesticides are one of the most potentially harmful chemicals liberated in the environment in an unplanned manner Malathion is widely used as a potent pesticide in many countries and has been shown to produce some adverse health effects. A study was conducted to asses the effects of malathion on the male reproductive system of wistar rats. The pesticide was administered to rats orally at dose levels of 50, 150 and 250 mg/kg/body wt/day for 60 days. In comparison to the control rats, there was a significant reduction in the weight of testes, epididymis, seminal vesicle and ventral prostate. Testicular and epididymal sperm density were decreased in the animals treated with malathion. Pre and post fertility test showed 80% negative results after treatment Biochemical profile of the testis revealed a significant decline in the contents of sialic acid and glycogen. Whereas a significant increase in the protein content of testis and testicular cholesterol was observed. The activity of testicular enzyme acid phosphatase increased significantly while decreased alkaline phosphatase activity was found. Malathion also suppressed the level of testosterone significantly Results of the present study clearly suggest that malathion induce toxic effects on the male reproductive system of rats.     

Morphology of the reproductive system and spermatozoa of Mesodasys adenotubulatus (Gastrotricha: Macrodasyida)

Mesodasys adenotubulatus Hummon, Todaro and Tongiorgi 1993 is a simultaneous hermaphrodite. Two club-shaped testes extend along the sides of the anterior intestine and show spermatogenetic stages maturing in a caudo-cephalic and centripetal direction. Sperm ducts join together dorsally to the intestine before opening into a pear-like caudal organ. An unpaired, dorsal ovary lies anteriorly to the confluence of sperm ducts. Oocytes mature in a caudo-cephalic direction; no oviduct nor female pore is present. The spermatozoa are fusiform, with a very short tail. The anterior end of the sperm is a small, conic hood which corresponds to the acrosome. The following, spindle-shaped corkscrew region contains a nuclear helix surrounding a central axis made of a single, giant mitochondrion. The 9+2 axoneme is enclosed by a bilayered, obliquely striated cylinder only in the proximal tract. The morphology of the reproductive system and spermatozoa of Mesodasys species is discussed, and the hypothesis of hypodermic impregnation in this genus is supported. Received: 20 November 1998 / Accepted: 6 July 1999     

Östrogenartige wirkungen von bisphenol a auf vorderkiemenschnecken (Mollusca: Gastropoda: Prosobranchia)

Within a Federal Environmental Agency research project to develop a biological test for hormone-mimetic compounds using the freshwater snail Marisa cornuarietis, the effects of the suspected xenoestrogenic substance bisphenol A (BPA), not only on freshwater but also on marine prosobranch snails, were investigated. For the laboratory experiments the ramshorn snail Marisa cornuarietis and the ovoviviparous snail Potamopyrgus antipodarum were considered as freshwater species and two marine prosobranchs, the netted whelk Nassarius reticulatus and the dog whelk Nucella lapillus, were additionally employed. N. reticulatus, as a typical sediment-living species, was exposed via artificial sediments, while the three other prosobranchs were exposed via water. The test series with Marisa cornuarietis covered a nominal concentration range between 1 and 100 μg BPA/l in a 5 month experiment with adult snails and a complete life cycle test for 12 months. Additionally, a third test in the nominal range between 0.05 and 1 μg BPA/l (measured: 0.0079–0.404 μg/l) was performed with adults snails for 6 months. In these experiments, BPA induced a complex syndrome of physiological and morphological alterations in female Marisa referred to as the induction of ‘superfemales’. Affected specimens were characterised by the formation of additional female organs, an enlargement of the accessory pallial sex glands, gross malformations of the pallial oviduct section resulting in an increased female mortality, and a massive stimulation of oocyte and spawning mass production. For these tests, an LOEC of 48.3 ng/l, an NOEC of 7.9 ng/l and an EC₁₀ of 13.9 ng/l were calculated. Superfemales occurred also in the BPA exposure experiment with the other snail species, but comparable oviduct malformations as in Marisa were not found, probably due to species differences in the gross anatomical structure of the pallial oviduct. During the 9 week test with Potamopyrgus antipodarum in the nominal concentration range between 1 and 100 μg/l, BPA induced an enhancement of embryo production even in the sexual repose phase of the reproductive cycle. A characteristic inverted U-type concentration response relationship was found. Nassarius reticulatus was exposed via BPA-spiked artificial sediments (nominal concentration range: 10–1000 μg/kg dry wt.) for 3 months. BPA exhibited a significant and concentration dependent uterotrophic effect which could be detected not only by an enlargement but also by a weight increase of the accessory pallial gland complex in the pallial oviduct section. Adult Nucella lapillus were tested for three months in the laboratory in a nominal concentration range between 1 and 100 μg BPA/l. Superfemales in the dog whelk were also characterised by enlarged accessory pallial sex glands and an enhancement of egg production, but the test compound also affected the males in this species. A lower percentage of exposed specimens had ripe sperm stored in their vesicula seminalis and male Nucella exhibited a reduced length of penis and prostate gland when compared to the control. Because statistically significant effects were observed already at the lowest nominal test concentration (1 μg/l), it can be assumed that even lower concentrations may have a negative impact on the snails. The results show that prosobranch snails are affected by BPA at lower concentrations compared to other systematic taxa in the animal kingdom. Consequently, it has to be claimed that the results of these experiment have to be considered for the current EU risk assessment for BPA in order to achieve a sufficient protection of wildlife in aquatic ecosystems.     

Male reproductive biology of the red frog crab,Ranina ranina,off Hachijojima,Izu Islands,Japan

Male red frog crabs, Ranina ranina, were collected year round in 1990 and 1991 off Hachijojima for histological study of the reproductive system and cycle. The testis containing the lobules and seminiferous ducts is surrounded by connective tissue. The seminiferous duct connects to the anterior end of the vas deferens, which can be histologically divided into three portions similar to one another in appearance. It was surrounded by fibrous connective tissue, muscle fibrils and columnar epithelium. Muscle fibrils were absent in the anterior portion. Multiple sperm masses were not formed in the vas deferens and ejaculatory duct, but the sperm mass was covered with a capsule composed of two layers. The outer layer of the capsule was periodic acid Schiff (PAS)-positive, but the inner layer was negative. Both layers were Alcian Blue negative, except the vacuoles in the outer layer that were stained blue. The small round androgenic gland was attached to the posterior end of the vas deferens of the coxa of the eighth thoracic appendage. The ejaculatory duct was distinguishable from the vas deferens by the absence of columnar epithelium and the presence of thick longitudinal muscle fibers. Spermatogenesis was histochemically examined. The acrosomal vesicle appeared to be derived from PAS-positive vesicles in the cytoplasm of the spermatid at the early stage of spermiogenesis. The arms were positive to the Feulgen reaction and the subacrosomal region was negative to PAS. Seasonal changes in reproductive cycle were inconspicuous histologically and microscopically. Sperm were always present in the testis and vas deferens throughout the year and occupied 5.1 to 19.6% of testis observed in cross sections. The minimum size of maturity is less than 39 mm carapace length, but the minimum size capable of successful mating was estimated to be ca. 55 mm.     

Spermiogenesis and sperm structure in the shrimp Parapenaeus longirostris (Crustacea: Dendrobranchiata): comparative aspects among decapods

Early spermatids of the dendrobranchiate shrimp Parapenaeus longirostris (Lucas, 1846) have a spherical nucleus with large patches of heterochromatin, surrounded by a cytoplasmic mass that contains the conspicuous proacrosomal vesicle. The highly polarized mid spermatid mainly consists of the nuclear region, displaying a discontinuous nuclear envelope, and a large proacrosomal vesicle located at the opposite side of the cell. The most recent spermiogenic transformations primarily concern elongation of the proacrosomal vesicle to form a tapering spike. This results in the typically tack-shaped sperm of natantian decapods. The initial steps of spermiogenesis in the two studied dendrobranchiates prove to be parallel to reptant spermiogenesis in some respects, namely rupture of the nuclear envelope, chromatin decondensation and differentiation of electron-dense regions within the proacrosomal vesicle content. Specifically, whereas the anteriormost condensation gives rise to the operculum in brachyurans, in dendrobranchiates it becomes the apical portion of the spike. Despite an unquestionable morphological similarity between the sperm of carideans and dendrobranchiates, spermiogenesis in both groups displays meaningful differences. Spermatids of caridean shrimps lack a distinct proacrosomal vesicle. In the course of spermiogenesis, the spike arises from aggregated cytosolic materials; hence it is not membrane-bound. Unlike in other decapods, caridean sperm do not undergo a conventional acrosome reaction, since exocytotic events are not involved in this process. The above arguments suggest that, in the Decapoda, separation into three sperm classes is more suitable than the two traditionally accepted classes. The dendrobranchiate and reptant sperm types share a number of spermiogenic and functional features, while the caridean sperm type appears to represent an independent evolutive line with regard to sperm development and function.     

Reproduction in <Emphasis Type="Italic">Heteroteuthis dispar</Emphasis> (Rüppell, 1844) (Mollusca: Cephalopoda): a sepiolid reproductive adaptation to an oceanic lifestyle

Small cephalopods of the genus Heteroteuthis are the most pelagic members in the family Sepiolidae. This study examines the reproductive biology of Heteroteuthis dispar (Rüppell, 1844), the first such study on any member of the genus, based on 46 specimens (27 females and 19 males) collected during the Mar-Eco cruise in the North Atlantic in the region of the Mid-Atlantic Ridge in 2004, and compares it with reproductive features in the less pelagic members of the family. The unusually large spermatophores of the males have a very small ejaculatory apparatus and cement body, relative to the size of the sperm mass. Females first mate when they are still maturing: a large sperm mass (up to 3.4% of the female body mass), consisting of one to several spermatangia, was found in an internal seminal receptacle of the majority of the females examined regardless of their maturity state. The seminal receptacle has a unique form and position in this species. The receptacle is a thin-walled sac at the posterior end of the visceral mass that is an outpocketing of, and opens into, the visceropericardial coelom. Spermatangia and sperm from the spermatangia apparently enter into the visceropericardial coelom (which is mostly occupied by the ovary) from the seminal receptacle indicating that ova are fertilised internally, a strategy unknown for decapodiform cephalopods (squid and cuttlefish), but present in most octopods. Fecundity of Heteroteuthis dispar (1,100–1,300 oocytes) is much higher than in other sepiolids whereas the egg size (mean max. length ∼1.6 mm) is the smallest within the family. Spawning is continuous (sensu Rocha et al. in Biol Rev 76:291–304, 2001). These and other reproductive traits are discussed as being adaptations to an oceanic lifestyle.     

An updated scheme of imposex for<Emphasis Type="Italic"> Cantharus cecillei</Emphasis> (Gastropoda: Buccinidae) and a new mechanism leading to the sterilization of imposex-affected females

The morphological expressions of imposex in gastropods have been classified into seven stages (S₀–S₆) with three types (a, b and c). This typical imposex scheme, however, fails to cover some new findings such as specimens with the proximal vas deferens section passing by the vaginal opening (VDSP) and aborted egg capsules. In the present study, Cantharus cecillei was sampled from the coastal waters of China from May to November in 2003. This species showed all the morphological expressions in the typical imposex scheme with the exception of S_1b and S_2b. In addition, specimens with VDSP occurred in all stages other than stage 4, and were documented for the first time with scanning electron micrographs or in histological sections. Besides VDSP, which was observed exteriorly, excrescent tissue, e.g. the vas deferens, also originated in the ventral channel or the inner wall of the pallial oviduct was extruded. Based on these new findings, the typical imposex scheme was modified to obtain one valid for C. cecillei. Types a*, b* and c* were added as new types corresponding to types a, b and c, respectively. S_4* was also rearranged to correspond to S₄; S_4*, thus, no longer represented the end of imposex development. The updated scheme was not only valid for describing diverse expressions of imposex development in C. cecillei and Nassarius reticulatus, but could also be generalized to define various forms of VDSP in other species. Histological observation indicated that egg capsules would be blocked by the tissues of the vas deferens section or the extrusion of the pallial oviduct wall. This new mechanism, leading to the sterilization of imposex-affected females, was first conclusively revealed and described in the present scheme.Communicated by T. Ikeda, Hakodate     

Studies on the family hemiuridae (Trematoda: Digenea), with a description of a new genus from marine fish of Indian waters

A new digenetic trematode, collected 1969–1970 at Ratnagiri (India) from the marine eel Leptocephalus conger, is described as Indostomachicola kinnei n. g., n. sp. The new genus differs from Stomachicola Yamaguti, 1934 and Allostomachicola Yamaguti, 1958 in many characteristics. The new species is characterized by an unlobed ovary, absence of receptaculum seminis, and presence of post-acetabular seminal vesicle and a ventral pit.     

Patterns of courtship behavior and ejaculate characteristics in male red-winged blackbirds

Sperm competition in birds is likely to have important effects on the behavior and physiology of reproduction in both sexes. For males, such competition should select for large sperm reserves and behavioral adjustment of copulation when reserves are low. We investigated both these possibilities in free-living red-winged blackbirds (Agelaius phoeniceus), a highly polygynous species with apparently strong sperm competition. We found that the recent copulatory behavior of males did not affect the propensity to copulate with a model female. Ejaculates collected from individual males at 1-h intervals showed no evidence of sperm depletion, yet repeated ejaculates collected less than 10 min apart did. Male ejaculate size was significantly larger if it was the first one of the day (i.e., after an overnight rest). The average ejaculate size was 12.5 (±12.5 SD) million sperm. Males captured during the breeding season had an average of 111.7 (±52.8) million sperm stored in their seminal glomera. Because males average a peak copulation rate of six per female per day, in one day a male might utilize all the sperm in his seminal glomera if more than two females on his territory are fertilizable. We hypothesize that polygyny and sperm competition in this species have combined to select for rapid replenishment of the seminal glomera throughout the day, in contrast to other species that have been studied. Testis size and sperm reserves of male red-winged blackbirds are intermediate between monogamous species and species with intense sperm competition. Several possible explanations for this are discussed. Received: 21 October 1997 / Accepted after revision: 15 February 1998     

Induction of oxidative stress by benzo(a)pyrene in the epididymis of Wistar rats

The present study was undertaken to evaluate the effect of sub-chronic exposure to benzo(a)pyrene on the antioxidant system and histology of rat epididymal sperm. Intraperitoneal administration of benzo(a)pyrene to male Wistar rats at doses between 1 and 100 µg/kg body weight for 60 days entailed a decrease in the weight of the epididymis (caput and cauda), seminal vesicle, and prostate, while the body weight was not affected. Epididymal sperm reserves were reduced in a dose-dependent manner. Indicators of lipid peroxidation were increased while activities of superoxide dismutase and catalase in all three epididymal regions decreased. Histological malformations were observed in the epididymis. Exposure to benzo(a)pyrene deranges the antioxidant defense system and induces histological changes in the epididymis.     

原尾蜥虎(Hemidactylus bowringii)雄性生殖周期的研究

对福州产的原尾蜥虎（Ｈｅｍｉｄａｃｔｙｌｕｓｂｏｗｒｉｎｇｉｉ） 雄性生殖周期的研究结果表明：１０ 月份精子发生开始新的周期性复生，精原细胞发育进入增殖期，中旬曲细精管除精原细胞外尚有较多的初级精母细胞；１１ 月初已有较多的精细胞，曲细精管管腔中开始出现少量的精子；１２ 月份，生精活动非常活跃，输精管始见有成熟的精子，１２ 月下旬进入冬眠期，成熟的精子释放到输精管中过冬，冬眠期间生精活动趋于停滞，表现为曲细精管管径和生精上皮厚度都有所下降；次年３ 月底４ 月初陆续出蛰，生精活动又恢复并逐渐增强，４、５ 月份精子发生相当活跃，６ 月份是精子发生的高峰期，也是交配繁殖的高峰期；原尾蜥虎一年只繁殖一次，繁殖期过后，７ ～９ 月份，生精活动逐渐减弱，曲细精管的管腔逐渐消失，初级、次级精母细胞、精细胞逐渐减少、退化，精子逐渐退化、消失，到９ 月下旬曲细精管和输精管都见不到精子，此时的曲细精管主要由精原细胞组成，一个周期到此结束．     

Comparative fertilization biology of gymnolaemate bryozoans

Locations and oogenic stages of eggs at the time of sperm-egg fusion were determined for nine gymnolaemate species exhibiting different reproductive strategies with respect to site of embryonic development (e.g., water column, introvert, embryo sac, or ovicell) larval type, and zooid sexuality. Ovarian, coelomic, and recently spawned oocytes obtained from freshly collected colonies between 1988 and 1995 were stained with aceto-orcein and examined for the presence of a sperm nucleus. All nine species are shown to have a similar fertilization biology in which sperm fuse with eggs in or near ovaries and egg activation is delayed until eggs are spawned. In species such as the etenostomeAlcyonidium sp. and the cheilostomeElectra pilosa (Linnaeus, 1767), which produce marierons oocytes that are spawned into the water column and have cyphonautes larvae, sperm fuse with late growth stage ovarian oocytes after germinal vesicle breakdown (GVBD) at or near ovulation. In species that produce few oocytes, brood embryos, and release coronate larvae, sperm fuse with late growth stage ovarian primary oocytes before GVBD, as in the ctenostomeBowerbankia gracilis Leidy, 1855, or with very early growth stage ovarian primary oocytes, as in the cheilostomesCribrilina corbicula (O'Donoghue, 1923),Dendrobeania lichenoides (Robertson, 1900),Hippodiplosia insculpta (Hincks, 1882),Schizoporella serialis (Heller, 1867),T ricellaria gracilis (Smitt, 1867), andWatersipora arcuata Banta, 1969. Fertilization success was high in all nine species, with 83 to 100% of oocytes at an appropriate oogenic stage containing a sperm nucleus or early male pronucleus. Gymnolaemate bryozoans may maintain high levels of fertilization success by: (1) concentrating spawned sperm from the water column using colony feeding currents; (2) localizing sperm-egg encounters in or near the ovary, (3) using sperm when available by permitting sperm to fuse with early growth stage oocytes; and (4) selfing.     

Intraspecific variation of testis size and sperm length in the yellow-pine chipmunk (<Emphasis Type="Italic">Tamias amoenus</Emphasis>): implications for sperm competition and reproductive success

Comparative analyses have found that relative testis size is a strong predictor of the prevalence of sperm competition for many taxa, including mammals, yet underlying this pattern is the assumption that intraspecific variation in testis size is related to individual fitness. Because intraspecific variation in ejaculate investment underlies interspecific patterns, it is critical to understand the causes and consequences of intraspecific variation in ejaculate investment. We examined relationships between ejaculate investment (testis size and sperm length) and reproductive success, body size and condition in the yellow-pine chipmunk (Tamias amoenus), a small ground squirrel in which sperm competition occurs. We examined genetic estimates of male reproductive success from a wild population of yellow-pine chipmunks and determined that males with large testes had higher annual reproductive success than males with small testes. This result provides empirical support for the numerous comparative studies that indicate testis size is associated with the intensity of sperm competition. In addition, males in good condition had relatively larger testes than males in poor condition, but there was no evidence of sperm length being dependent on condition. Finally, contrary to many predictions, males that invested more in sperm production (relatively heavy testes) produced shorter sperm, not longer sperm, than males that invested less.Communicated by P.M. Kappeler     

Testis size variation in frogs: testing the alternatives

While sperm competition may be a major factor affecting relative testis size in vertebrates as a whole, additional hypotheses have not been given much attention in frogs. This is important because sperm competition is relatively uncommon in frogs and relative testis size varies in frogs that do not have multiple-male breeding systems. This paper tests two additional hypotheses for differences in relative testis size among frogs: relative clutch size (number of eggs/snout vent length) and androgen level. Testis size was measured in 90 species of frogs belonging to five families. Relative testis size was found to be positively correlated with relative clutch size in species that lack sperm competition. Mean androgen levels of species also positively covaried with relative testis size. However, there was no correlation between relative testis size and level of male agonistic behavior among species, despite other work indicating that testosterone levels are positively correlated with agonistic behavior in at least some species. These findings suggest that a number of factors in addition to sperm competition are important in the evolution of testis size in male frogs. Received: 17 January 1997 / Accepted after revision: 23 June 1997