Sperm Supply Research Articles

Quick Guide: γ-Tubulin

What is it?γ-Tubulin is a member of the tubulin superfamily and is required for nucleating the polymerization of microtubules in vivo. Microtubules are dynamic cytoskeletal polymers that assemble from two other members of the tubulin superfamily, α-tubulin and β-tubulin. Microtubules make up the mitotic and meiotic spindles, and are important for establishing cell polarity and vesicle trafficking. The tubulin superfamily is still growing, and now includes tubulins δ through η (delta through eta, in case you've forgotten your Greek). α-, β- and γ-tubulin are conserved in all eukaryotic groups, whereas the other superfamily members are not.How was it found?γ-Tubulin was identified by Oakley and colleagues as a suppressor of a β-tubulin mutation in Aspergillus nidulans.Where is it?γ-Tubulin does not assemble into microtubules. In most cells it is found at the microtubule organizing center, an organelle devoted to microtubule nucleation and anchoring. In animal cells the organizing center is called the centrosome, in fungi it is called the spindle pole body, and in plants it isn't called anything because plants make do without a discrete organizing center. The centrosome consists of a pair of centrioles — microtubule structures with beautiful nine-fold symmetry – surrounded by pericentriolar material. The pericentriolar material nucleates microtubules and contains γ-tubulin. In fungi too γ-tubulin is associated with the surfaces of the spindle pole body that nucleate microtubles. Although γ-tubulin is thought to act primarily at the organizing center, in most cells the majority of γ-tubulin is in the cytoplasm.What's it good for?γ-Tubulin nucleates microtubules, allowing cells to control when and where microtubules polymerize. This has been shown both in vivo, by interfering with γ-tubulin function, and in vitro, by assaying the activity of γ-tubulin. Analysis of γ-tubulin mutants in fungi suggests that γ-tubulin might also have an independent role in cell cycle control.Does it act alone? No. When purified from animal cells, γ-tubulin is a large complex with a molecular weight of several million daltons. In addition to γ-tubulin there are at least five other proteins in this complex, all of which are related to each other and are conserved in animals and plants. We call these proteins the GCPs (gamma-tubulin complex proteins), although there are several other names in the literature. Remarkably, yeast lacks all but two of the GCPs; those GCPs and γ-tubulin form a much smaller complex than that found in animal cells.Size and shape matter! Microtubules are complex polymers, with approximately 13 protofilaments arranged into a tube. The γ-tubulin complex has a size and shape that is very similar to that of a microtubule end, suggesting that it serves as a template for microtubule assembly. The γ-tubulin complex as purified from several organisms is a ring of approximately 25 nm in diameter made up of repeating subunits, with a cap structure on one end, and is often called the γ-tubulin ring complex (γTuRC). The current model for how all the proteins fit together is that the repeating subunit in the ring is γ-tubulin plus the two GCPs that are conserved in all eukaryotes, and that the cap structure is made up of the other GCPs.Getting attached to γ-tubulin Most microtubules grow from the centrosome, so there must be a way to attach the γ-tubulin complex to the centrosome. Although it is not clear how it works, this attachment is likely to be regulated in the cell cycle. The amount of γ-tubulin at the centrosome increases dramatically at the beginning of mitosis, aiding in the formation of the mitotic spindle, then decreases at the end of mitosis. Attachment of the γ-tubulin complex to the nascent centrosome is also an important part of fertilization in most animals since the sperm supplies the centrioles and the egg supplies the γ-tubulin complex; it is only after they get together that the first centrosome is formed and development proceeds.Where can I find out more?

Detecting and quantifying male sea urchin spawning with time-integrated fertilization assays

There has been much modeling and experimentation on factors affecting fertilization success in free-spawning marine invertebrates, but for many species spawning has rarely been observed in nature, if at all, and then mostly qualitatively. Understanding the dynamics of spawning and fertilization is especially important for species, such as the green sea urchin, Strongylocentrotusdroebachiensis (O.F. Muller), that have been widely depleted by harvesting. Time-integrated fertilization assays provide measures of sperm-availability adjacent to spawning populations for extended periods and with unprecedented temporal resolution. In such assays unfertilized eggs are held in baskets permeable to sperm and suspended in the water column as long as the eggs remain viable. In a consecutive series of 24- to 72-h assays the time course and spatial extent of sperm availability were measured near an aggregation of 250 sea urchins suspended in a cage at a field site in West Boothbay Harbor, Maine, USA. The assays were conducted in March and April, 2000, the spawning season of the green sea urchin. The distribution of embryonic stages within the assays revealed fine-scale temporal information on the timing of fertilization. The time series of multiple assays indicated that over a substantial portion of the spawning season there was an almost continuous low level of male spawning, a pattern consistent with a slow decline in gonad index observed in both male and female urchins. Fertilization rates averaged only 17% for the eggs in the basket nearest the spawning urchins (20 cm away), and the rates declined sharply over a distance of <1 m. Thus, despite the potential benefits of long egg life in integrating sperm supply over several days, the spatial effects on fertilization success were marked. Owing to the urchins' captivity and the lack of site replication, the generality of the observed spawning pattern must be confirmed. Nonetheless, the method lends itself to wider application among natural populations.

Sambia Sexual Culture: Essays from the Field

Gilbert Herdt, Sexual Culture: Essays from the Field, Chicago and London: University of Chicago Press, 1999, xi + 327 pages.Reviewer: Andrew P. LyonsWilfrid Laurier UniversityTwenty years have now passed since the publication of Guardians of the Flutes which was arguably the best ethnographic examination of sexuality since Malinowski's Sexual Life of Savages. Gilbert Herdt returned to New Guinea several times until 1993 when a nearly fatal bout of malaria led him to curtail his visits. This volume draws on those later field trips. Herdt re-examines and develops themes which he first discussed in Guardians. He also discusses the significance of his work not only for social anthropology but also for the Gay Liberation Movement. All of the nine essays in the volume originally appeared elsewhere and most readers will have read a few of them already. However, they fit very well together, and the author has contributed an excellent theoretical introduction. Readers unacquainted with Herdt's ethnography should note that it describes a population which prescribed homoerotic fellatio as a necessary part of male social development. There was no sexual play in the period prior to initiation. Prepubertal youths in the first stages of initiation were fellators; adolescents in the third stage of initiation were fellated by the younger boys. Marriage to females occured at the end of the initiation cycle. These customs reflected a system of thought in which mature male sexuality was tenuously achieved and always threatened by feminine, specifically menstrual pollution. An adequate supply of sperm was stored in the growing boy as a result of fellation. The receipt of sperm in heterosexual intercourse enabled women to produce breast milk.The notes on the book cover describe Herdt as a renowned anthropologist, a description which may provoke some jealousy but which does attest to his achievement. Until 1980 the anthropology of sexuality occupied a marginal place in our discipline. This was partly because sexuality was excluded by existing paradigms such as structural-functionalism and cultural ecology, and, more surprisingly, by later developments in psychological anthropology. In large measure this was because there was little middle ground between sociological approaches which regarded sexuality as too natural, too universal (see p. 4) and too threatening to sociological method to be worthy of consideration, and behaviouristic or ethological approaches which are neglectful of social meanings Within anthropology the study of sexuality could only be subsumed under such headings as kinship and gender.Another cause of neglect was the degree of professional, political and humanitarian risk involved in such investigations. Esther Newton has complained that her work on drag-queens was not regarded as legitimate research (Newton, 2000: 223). Of course the homosexual student of sexuality faces additional barriers. Sometimes they reflect pure prejudice; on other occasions biases may be more subtle. Kath Weston (1998: 189-211) has complained that her own work on lesbian sexuality within the USA has led to a degree of professional marginalization (such research, argue critics is not real fieldwork).Very often, the disclosure of information may be perceived as harmful to populations and individuals who are subject to the surveillance of outsiders as well as exploitation by sexual tourists. Such reports may also embarrass cultural insiders who wish to distance themselves from tribal traditions. It is for this reason that Herdt disguised the identity of the Sambia of the Eastern Highlands of Papua New Guinea. Last but not least the obtaining of information on matters sexual involves the establishing and affirming of a degree of trust which is most difficult to create as well as linguistic skills of a high order. There is no society without sexual taboos; there are few without rules of privacy or secrecy with respect to some matters. …

Effects of multiple mating and male eye span on female reproductive output in the stalk-eyed fly, Cyrtodiopsis dalmanni

Females of the stalk-eyed fly, Cyrtodiopsis dalmanni, mate repeatedly during their lifetime and exhibit mating preference for males with large eye span. How these mating decisions affect female fitness is not fully understood. In this study, we examined the effects of multiple mating and male eye span on short-term reproductive output in this species. Experiments that manipulated the number of copulations and partners a female received suggested that obtaining a sufficient sperm supply is an important benefit associated with multiple mating. The average percentage of fertile eggs laid by females increased as a function of mating frequency and ranged from 40% for females mated once, to 80% for females mated continuously. In addition, a high proportion of copulations in this species appeared to be unsuccessful. One-third of all females mated once laid less than 10% fertile eggs. There was no significant difference in reproductive performance between females mated to multiple partners and females mated to a single partner. There was also no indication that females received any short-term reproductive benefits from mating with males with large eye span. In fact, females mated to males with short eye span laid a higher percentage of fertile eggs than females mated to large eye span males.

Pick on someone your own size: ontogenetic shifts in mate choice by male garter snakes result in size-assortative mating

Data on over 950 natural matings of red-sided garter snakes,Thamnophissirtalisparietalis , in Manitoba revealed size-assortative pairing: large males tended to mate with large females, and small males with small females. Unlike previously reported cases of size-assortative mating, the causal mechanism in these snakes involved a size-related shift in active mate selection by males. In the field, courtship as well as mating was size assortative (albeit, with considerable scatter around the trend line). Staged trials in outdoor arenas showed that males of all sizes preferred to court large rather than small females, but this preference was stronger in large males. Males adjusted their courtship intensity in response to the numbers and sizes of females and competing males, but did not change their preferences with respect to female body size. Thus, size-assortative mating was not a direct consequence of large males excluding their smaller rivals from large females. Males may be selective courters in this species because they have a limited supply of sperm and mating plugs, and hence can copulate effectively only a few times within the mating season. Given intense competition from large males (which primarily court large females), small males may benefit from focusing on small females. Alternatively, small males may be less capable of inducing sexual receptivity from large females. Mark–recapture data confirmed that males grow rapidly from one year to the next. Thus, the size-related shift in male mate choice was due to an ontogenetic change rather than the existence of multiple male morphs differing in both body size and courtship preference.

Material Benefits from Multiple Mating in Female Mealworm Beetles (Tenebrio molitor L.)

In yellow mealworm beetles (Tenebrio molitor), females are sexually receptive throughout their adult lives. We examined how access to mates affected female fecundity by varying the number of matings per female and quantifying cumulative egg production. Also, we dissected females at successive intervals after a single mating to assess the relationship among time since mating, sperm supplies, egg load, and oviposition rate. Females that mated at intervals greater than 2 days did not produce as many eggs as females that mated every 2 days or were allowed to mate ad libitum. Dissections showed that the amount of sperm remaining in a female spermatheca was correlated with the number of eggs she had laid recently, which suggests sperm replenishment as the material benefit gained through multiple mating. However, females mate more frequently than necessary for sperm replenishment, and therefore material benefits alone may not fully explain the continuous receptivity of T. molitor females.

Sperm economy and limitation in spiny lobsters

Sperm limitation, when female fertilisation success is constrained by the supply of sperm, is generally perceived to be an uncommon feature of reproduction in species which directly transfer gametes during copulation. Male size, previous copulations, and the balance of expected reproductive return and future mating opportunity may, however, limit the amount of sperm males transfer to females. We used laboratory experiments where mate size could be manipulated and its consequences on spermatophore size and clutch size determined, to show that in two genera of spiny lobsters (Crustacea: Palinuridae) male reproductive output limits the size of clutches brooded by females. In Panulirus argus from the Florida Keys, we show that while male size affects spermatophore area, males also vary the amount of ejaculate positively with female size. Furthermore, the area of the spermatophore has a greater influence than female size on subsequent clutch weight. In Jasus edwardsii from New Zealand, female size, male size and mate order all affect clutch weight. In both species, clutches fertilised by small males in the laboratory are significantly smaller than clutches fertilised by large males. These results suggest that to ensure they receive sufficient sperm, females should either mate several times prior to oviposition, mate as early as possible in the reproductive season, or choose large, preferably unmated males as partners and thus compete with other females for preferred males. Sperm-limited female fecundity has the potential to limit the egg production of fished populations where large males are typically rare.

Butterflies tailor their ejaculate in response to sperm competition risk and intensity

Males of many insects eclose with their entire lifetime sperm supply and have to allocate their ejaculates at mating prudently. In polyandrous species, ejaculates of rival males overlap, creating sperm competition. Recent models suggest that males should increase their ejaculate expenditure when experiencing a high risk of sperm competition. Ejaculate expenditure is also predicted to vary in relation to sperm competition intensity. During high intensity, where several ejaculates compete for fertilization of the female9s eggs, ejaculate expenditure is expected to be reduced. This is because there are diminishing returns of providing more sperm. Additionally, sperm numbers will depend on male9s ability to assess female mating status. We investigate ejaculate allocation in the polyandrous small white butterfly Pieris rapae (Lepidoptera). Males have previously been found to ejaculate more sperm on their second mating when experiencing increased risk of sperm competition. Here we show that males also adjust the number of sperm ejaculated in relation to direct sperm competition. Mated males provide more sperm to females previously mated with mated males (i.e. when competing with many sperm) than to females previously mated to virgin males (competing with few sperm). Virgin males, on the other hand, do not adjust their ejaculate in relation to female mating history, but provide heavier females with more sperm. Although virgin males induce longer non–receptive periods in females than mated males, heavier females remate sooner. Virgin males may be responding to the higher risk of sperm competition by providing more sperm to heavier females. It is clear from this study that males are sensitive to factors affecting sperm competition risk, tailoring their ejaculates as predicted by recent theoretical models.

The posterior determinant gene nanos is required for the maintenance of the adult germline stem cells during Drosophila oogenesis.

In a variety of tissues in eukaryotes, multipotential stem cells are responsible for maintaining a germinal population and generating a differentiated progeny. The Drosophila germline is one such tissue where a continuous supply of eggs or sperm relies on the normal functioning of stem cells. Recent studies have implicated a possible role for the posterior determinant gene nanos (nos) in stem cells. Here, I report that nanos is required in the Drosophila female germline as well as in the male germline. In the female, nos is required for the functioning of stem cells. In nos mutants, while the stem cells are specified, these cells divide only a few times at the most and then degenerate. The loss of germline stem cells in nos mutant mothers appears to be due to a progressive degeneration of the plasma membrane. Furthermore, following germ cell loss, the germaria in the nos mutant mothers appear to carry on massive mitochondrial biogenesis activity. Thus, the syncytia of such germaria are filled with mitochondria. In the male germline, the male fertility assay indicates that nos appears to be also required for the maintenance of stem cells. In these mutant males, spermatogenesis is progressively affected and these males eventually become sterile. These results indicate novel requirements for nos in the Drosophila germline.

Receptivity of female remating and sperm number in the sperm storage organ in the bean bug, Riptortus clavatus (Heteroptera: Alydidae)

AbstractThis study examines the relationship between the number of sperm in the seminal receptacle (spermatheca) and the receptivity of female remating in the bean bug Riptortus clavatus Thunberg. On the 21 st day after the first mating when receptivity to remating was &gt; 70%, females receptive to remating had significantly fewer sperm (&lt; 40 on average) in the spermathecae than females reluctant to do (about 150 on average). However, averages of the number of eggs laid by receptive and reluctant females within 21 days were almost same. The proportion of fertilized eggs for receptive females at 15–21 days after copulation was significantly lower than that for reluctant females. Spermatozoa transferred from a male to a female's spermatheca were detected 5 min after copulation and then increased continuously to about 500 with the first hour. When copulation durations were manipulated artificially, the shorter the copulation period (=females had less sperm in their spermathecae), the higher the remating rate became. Females may perceive the number of sperm in their seminal receptacles and then determine whether they copulate or not. These results support the hypothesis that females mate multiply in order to replenish inadequate sperm supplies to fertilize all eggs produced.

Male competition in Cardiocondyla ants

The two types of males in the ant genus Cardiocondyla differ remarkably in morphology and behavior. Ergatoid males are wingless fighters whose spermatogenesis continues throughout their entire adult lives and which therefore have an “unlimited” sperm supply. They attempt to kill all eclosing ergatoid rivals and thus to increase their share in copulations with the virgin queens reared in their nests. Winged males, on the other hand, are docile and emigrate from the nests a few days after eclosion, probably to mate with queens from other colonies. By this time, their testes have fully degenerated and all sperm is stored in the seminal vesicles. Before emigration, winged males may mate with virgin queens in their maternal nests, but they are nevertheless rarely attacked by ergatoid males. In the laboratory, the life expectancy of ergatoid males is only slightly higher than that of winged males, but because of the emigration of the latter the difference is likely to be more pronounced in the field. Both male morphs are capable of inseminating more than 35 virgin queens. However, winged males older than 14 days mate less often than ergatoid males of similar age, probably due to sperm depletion in later life. The spermathecae of queens inseminated by ergatoid males contained significantly more sperm than those of queens which mated with winged males. We discuss the evolution of intranidal mating and male polymorphism in ants.

Fertilization in the sea: are the hazards of broadcast spawning avoided when free–spawned sperm fertilize retained eggs?

In broadcast-spawning marine animals, rapid dilution and short lifespan of sperm following release may impose severely localized patterns of mating. Partial or total failure of external fertilization due to sperm limitation appears commonplace. However, it is not clear to what extent the restrictive kinetics of fertilization in water also constrain mating in animals that release sperm but retain their eggs for fertilization. The compound ascidian Diplosoma listerianum liberates sperm that are dispersed to other colonies and taken in prior to internal cross-fertilization. The fertile lifespan of sperm was found to be long (half-life ca. 8 hours), and a substantial number of fertilizations occurred with 24-hour-old sperm. Fertilizations were obtained from sperm concentrations that would typically produce little or no external fertilization. In a separate experiment, a very small piece of D. listerianum (dry weight less than 2 mg) sired abundant progeny throughout a 3840 l tank. Paternity of progeny in these experiments was confirmed by molecular markers. The same markers were used to extend, to over seven weeks, the known maximum period of storage of exogenous sperm prior to fertilization in this species. The production of only a few thousand sperm at a time by each zooid, poor synchronization of release between zooids, and the existence of many well-spaced exhalant openings in large colonies suggest that D. listerianum is incapable of generating a dense plume of sperm, even close to the source. It is suggested that, unlike external fertilization, successful internal cross-fertilization in D. listerianum is not dependent upon the interception of a dense cloud of gametes just released by a near neighbour. It seems instead that dilute, long-lived sperm can be extracted efficiently from seawater by this suspension feeder, potentially over a period of time. This capability, and other features of the life history, make it unlikely that sperm limitation is an acute problem in this species and comparable taxa, a conclusion with potential significance for expected patterns of mating, sex allocation and gamete attributes in sessile aquatic invertebrates. Variance in reproductive success between individuals due to differences in fertilization rate may be much lower than in broadcast spawners exhibiting external fertilization.

Sperm Allocation in Coral Reef Fishes

In the past, sperm production was often viewed as the least of a male's problems. After all, males of most species produce millions of sperm, so it seemed highly unlikely that sperm supply could ever be a major factor in limiting reproductive success. Production of sperm is cheap compared with that of an egg, the argument went, and so males will always have sufficient sperm and thus need concentrate only on acquiring mates. Over the years, however, there has been a striking change in the thinking of scientists concerned with male reproductive strategies (e.g., Birkhead and Hunter 1990, Dewsbury 1982, Moller and Briskie 1995). In some species males are, in fact, limited in their reproductive success by sperm production, and sperm output may be the object of careful

Is sperm really so cheap? Costs of reproduction in male adders,Vipera berus

Reproduction is energetically expensive for males as well as for females, but evolutionary biologists have typically regarded the energy costs of sperm production as trivial compared to the energy costs of overt reproductive behaviours, such as mate-searching, courtship, copulation and male–male combat. Adders ( Vipera berus ) offer an ideal model system in which to quantify the relative costs of spermatogenesis (and associated physiological preparations for reproductive activity) versus the costs of overt reproductive behaviours, because (i) these two activities occur sequentially rather than simultaneously, and are separated by a clear indicator (sloughing of the skin); and (ii) males do not feed during either of these phases. Hence, the rate of mass loss by males can be used as an index of energy costs. Surprisingly, the rate of mass loss is at least as high during the phase when males are immobile, building up sperm supplies, as when they move about and engage in reproductive behaviour. Rates of mass loss are not significantly correlated with male size or measures of the male9s participation in reproductive activities. Our data suggest that sperm production may be a major energy cost to reproducing male adders, and that this species offers a useful system in which to further investigate this possibility.

Nutritional Status of Males and Sperm Transfer in the Scorpionfly Panorpa vulgaris (Mecoptera: Panorpidae)

The results demonstrate that in the scorpionfly Panorpa vulgaris (Imhoff & Labram 1836), (a) the number of sperm transferred into the female's spermatheca during mating depends on the copulation duration; (b) differences in the nutritional status which have a significant effect on the mass of the salivary gland in males [MM] do not affect the number of sperm transferred during discrete copulation durations; (c) the number of sperm transferred by the MM during repeated copulations does not depend on the nutritional status; (d) a correlation between the number of sperm transferred during a first and second mating could not be demonstrated; (e) the nutritional status of females [FF] has no effect on the number of sperm transferred by the MM; (f) the loss of body mass of MM during a copulation of 200 min increases significantly with increasing condition index of their mates. These results indicate that within the scope of food availability tested in the present study it is not possible to decide clearly whether sperm supply is nutritionally limited. However, the great inter-male variation in the number of sperm transferred to the FF' spermatheca is consistent with the hypothesis that the sperm supply of some MM is limited. This study points up that the energetic cost of copulation of MM is not trivial.

Lack of Sperm Storage by Female Migrants and the Significance of Copulations En Route

In all species studied thus far, female birds store sperm in specialized sperm storage tubules (SSTs) located at the junction of the uterus and vagina (Fujii 1963, Shugart 1988, Birkhead et al. 1990, Briskie and Montgomerle 1993). SSTs appear necessary for the long-term survival of spermatozoa within the female reproductive tract, because sperm not stored within SSTs soon die or are displaced by the passage of subsequent eggs (Lorenz 1966). The length of time that sperm can remain viable in storage varies from species to species, ranging from about six days in the Ring Dove (Streptopelia roseogrisea; Zenone et al. 1979) to over 72 days in the domestic Turkey (Meleagris gallopavo; Lorenz 1950). Why sperm storage duration varies among species is not clear, but it may be related to the proximity of males and females during pre-laying (Birkhead and Moiler 1992a). For example, sperm storage durations are particularly long in seabirds, in which females are separated from their mates for prolonged periods prior to laying. In contrast, males of many passerine species typically remain close to females throughout pre-laying and these species have correspondingly shorter durations of sperm storage (Birkhead and Moiler 1992a). In most birds, copulations are generally restricted to a brief prelaying period, with the greatest frequency occurring just prior to the laying of the first egg. For migratory species, pairing and mating are thought to take place largely on the breeding grounds after the end of spring migration. However, by using lavages to census sperm within the cloacae of male and female migrant passerines, Quay (1985a, 1989) found that many Tennessee Warbler (Vermivora peregrina) females and possibly some Blackpoll Warbler (Dendroica striata) females had been inseminated during migration and south of their nearest breeding grounds. In the Tennessee Warbler, about 25% of females contained sperm in their cloacae, indicating that copulatory behavior during migration may be widespread (Quay 1989). Recently, Moore and McDonald (1993) suggested that en route copulations may have an adaptive function, such as minimizing the time and costs of mate choice or ensuring females have an adequate supply of sperm should they not find a mate on the breeding grounds. Unfortunately, the role that en route inseminations play in the eventual fertilization of eggs remains unknown.

Multiple Mating and Its Effect on Female Reproductive Output in the Bean Bug Reptortus clavatus (Heteroptera: Alydidae)

Multiple mating and its effects on fecundity and fertility in the female bean bug Reptortus clavatus (Thunberg) were investigated under laboratory conditions. Multiply mated females showed higher fecundity and fertility than singly mated females, suggesting that natural selection may favor multiple mating in R. clavatus females. However, females were unwilling to remate for 15-20 d after 1st mating, indicating that remating may be costly to females. Nearly 50% (24/50) of singly mated females exhausted most sperm from their seminal receptacles (spermathecae) by 28 d after beginning to oviposit and began laying infertile eggs, but their fertility recovered after remating. These results support the hypothesis that females remate to replenish an inadequate sperm supply if absence of stored sperm outweighs the cost of remating in terms of higher productivity.

Courtship feeding and repeated mating in Zorotypus barberi (Insecta: Zoraptera)

The mating behaviour of Zorotypus barberi Gurney (Insecta: Zoraptera) involves courtship feeding and repeated mating. The male performs an elaborate sequence of pre-copulatory courtship, during which he secretes a liquid substance from the cephalic gland and uses it as a courtship gift to entice females to mate. The female allows the male to copulate with her, only after she has successfully obtained the gift. Females continue to assess the mate quality even after genitalic intromission has begun and mate rejection by females is common during copulation as well as during pre-copulatory courtship. The majority of prematurely terminated copulations occur before sperm are transferred. Mating pairs usually copulate three or more times in succession and the entire sequence of courtship is repeated prior to each copulation. Females that mated three or more times lay considerably more eggs than those mated only once or twice, suggesting that sufficient sperm supplies are required for females to achieve full fecundity. By copulating repeatedly with the same male, females could obtain courtship gifts at a greater rate than mating multiply with different males because the courtship duration with the same male decreases significantly after the first copulation. Observations on females that mated with multiple males suggest that such females may copulate repeatedly with a preferred male in order to dilute the sperm from inferior males and thus affect the paternity of offspring.

Effects of risks of sperm competition on the numbers of eupyrene and apyrene sperm ejaculated by the moth Plodia interpunctella (Lepidoptera: Pyralidae)

This study examines the effects of different risks of sperm competition upon ejaculate characteristics in the moth Plodia interpunctella. In this short-lived species, females will remate and thus generate sperm competition, while males have a limited sperm supply. We therefore predict males to have evolved prudence in ejaculate allocation and investigate the effects of (1) rival male presence, (2) female mating history and (3) female age, upon the ejaculation of eupyrene (fertilizing) and apyrene (non-fertile) sperm numbers. We found no effect of the presence of rival males upon ejaculate characteristics, and conclude, due to the mating system of P. interpunctella, that rival males do not represent a proximate risk of sperm competition. We controlled female mating history by allowing females to receive different and predictable numbers of sperm which they then store for at least 7 days. In subsequent matings (7 days later) we found that new males ejaculated significantly more eupyrene sperm to females that had previously received larger numbers of sperm. We conclude that males increase numbers of eupyrene sperm to maintain success in sperm competition with rival sperm already in storage in the female. We found no effect of female mating history upon the ejaculation of apyrene sperm. Female age, however, had a significant negative effect upon both sperm types. We discuss these results in relation to sperm competition theory and apyrene sperm function.

Ultrastructure of the spermatheca and its associated gland in the ant Crematogaster opuntiae (Hymenoptera, Formicidae)

Sperm storage by females has reached an extreme degree of development in ants. Ant queens, which are unusually long-lived insects, typically store and maintain an unreplenished supply of viable sperm for ten or more years. The spermatheca of Crematogaster opuntiae includes a receptacle and a discrete pair of accessory, or spermathecal, glands, structures commonly found in sperm storage organs of insects. The bean-shaped receptacle consists of a layer of simple epithelium externally and a cuticular layer internally. In the hilar region, the epithelium is highly columnar and exhibits ultrastructural features characteristic of transport epithelia, such as infolded basal membranes, abundant polymorphic mitochondria, and apical microvilli. The spermathecal glands contain cells that have long, dense microvilli that project into a central lumen, abundant mitochondria, and large fields of glycogen. The valve and pump region of the spermatheca provide a mechanism to conserve sperm by controlling the rate of sperm release. The columnar epithelium may function as excretory tissue that serves to maintain an environment in which sperm can remain viable for many years.