Apyrene Sperm Research Articles

Movement ofTurritella spermatozoa: Direction of propagation and chirality of flagellar bends

The marine snail, Turritella communis, produces two types of spermatozoa, named apyrene and eupyrene. Eupyrene spermatozoa are usually paired, but unpaired ones are involved in fertilization. Movements of these spermatozoa were analyzed using a video camera with a high-speed shutter. The eupyrene spermatozoa usually swim with the head foremost but are able to swim flagellum foremost. A reversal of the direction of their swimming was found to be the result of a change in the direction of flagellar bend propagation, which changed with calcium concentration. Reversal of the direction of bend propagation was accompanied by a reversal of direction of the rotational movement of the spermatozoa around their long axis, suggesting that the bending waves keep the sense of their three-dimensional form. The swimming speed of apyrene spermatozoa in natural seawater was about one-eighth of that of the eupyrene ones and remained almost constant in highly viscous medium. The swimming speed of conjugated eupyrene spermatozoa was the same as that of unpaired spermatozoa over a wide viscosity range (<3,000 cP). No advantage of swimming by two spermatozoa could be detected in Turritella spermatozoa.

Movement of turritella spermatozoa: direction of propagation and chirality of flagellar bends.

The marine snail, Turritella communis, produces two types of spermatozoa, named apyrene and eupyrene. Eupyrene spermatozoa are usually paired, but unpaired ones are involved in fertilization. Movements of these spermatozoa were analyzed using a video camera with a high-speed shutter. The eupyrene spermatozoa usually swim with the head foremost but are able to swim flagellum foremost. A reversal of the direction of their swimming was found to be the result of a change in the direction of flagellar bend propagation, which changed with calcium concentration. Reversal of the direction of bend propagation was accompanied by a reversal of direction of the rotational movement of the spermatozoa around their long axis, suggesting that the bending waves keep the sense of their three-dimensional form. The swimming speed of apyrene spermatozoa in natural seawater was about one-eighth of that of the eupyrene ones and remained almost constant in highly viscous medium. The swimming speed of conjugated eupyrene spermatozoa was the same as that of unpaired spermatozoa over a wide viscosity range (<3,000 cP). No advantage of swimming by two spermatozoa could be detected in Turritella spermatozoa.

Morphological changes in eupyrene and apyrene spermatozoa in the reproductive tract of the male butterfly Atrophaneura alcinous Klug

Summary Eupyrene and apyrene spermatozoa are contained in separate cysts in the testis of the butterfly Atrophaneura alcinous. Spermatozoa of both types from various parts of the male reproductive tract were examined with particular reference to their morphological characteristics. All spermatozoa collected from the vas deferens and the vesicula seminalis were found to be immotile under a dissecting microscope. No spermatozoa of either type were recognized in any part of the ejaculatory duct. Within the testis, eupyrene spermatozoa are present in bundles and each spermatozoon has a slender nucleus with an acrosome and a long flagellum containing mitochondrial derivatives. Two kinds of appendages, lacinate and reticular, are present on the surface of the sperm membrane. They are replaced with an extracellular sheath during passage through the vas deferens. In contrast, apyrene spermatozoa have neither nucleus nor acrosome, whereas a cup-shaped structure was found at the sperm tip instead of the acrosome. Unlike eupyrene spermatozoa, they are surrounded by a concentric sheath outside the sperm membrane in the vas deferens. Individual apyrene spermatozoa and coiled bundles of eupyrene spermatozoa were both found to accumulate in the vesicula seminalis before mating. These morphological changes during passage through the male reproductive tract suggests the occurrence of a kind of maturation and capacitation process reminiscent of mammalian spermatozoa.

Snail sperm production characteristics vary with sperm competition risk

Sperm competition is widespread and influences both male investment in spermatogenic tissue and ejaculate characteristics. Sperm competition models assume trade-offs between sperm size and number, although such trade-offs may be difficult to detect. This study examines the effects of sperm competition risk on the sperm production characteristics of the freshwater snail Viviparus ater. In this prosobranch, females mate frequently and store sperm, generating sperm competition. Males produce two sperm morphs, fertile eupyrene sperm and non-fertilizing oligopyrene sperm. Non-fertilizing sperm may play a role in sperm competition and therefore, like fertilizing sperm, the number produced could vary relative to sperm competition risk. In addition, trade-offs between sperm number and sperm size may be expected. We manipulated the sex ratio of sexually mature snails and found the presence of rivals affected the ratio of oligopyrene/eupyrene sperm males produced. In experimental and natural populations, the number of oligopyrene sperm produced, but not the number of eupyrene sperm, was significantly higher when the sex ratio was male biased. Testis mass did not vary between experimental treatments. We also found a negative relationship between the number and size of oligopyrene sperm produced, which is consistent with evolutionary models of sperm competition, and is, to our knowledge, the first intraspecific demonstration of a trade-off between these traits.

Effects of a fertility‐reducing baculovirus on sperm numbers and sizes in the Indian Meal Moth, Plodia interpunctella

1. A dose‐dependent decrease in male fertility occurs in the Indian Meal Moth, Plodia interpunctella, when sub‐lethally infected with granulovirus during the larval stage. 2. Here, the causes for this decline are investigated by examining eupyrene and apyrene sperm numbers and sizes produced by males across four levels of viral challenge. 3. The results could not explain how reduced male fertility is caused in this host–pathogen interaction. While a reduction in both eupyrene and apyrene sperm numbers from all virus‐treated males was found, this was not significant and neither was there a difference in sperm lengths across the four treatments. There were also no differences in the variances of sperm numbers or lengths between the doses, and no associations between sperm numbers or lengths and body size were found. 4. A significant correlation between eupyrene and apyrene numbers was found, but this was independent of dose. Significant between‐male variance in apyrene sperm lengths was found, indicating that individual males differ in the range of apyrene sperm sizes they produce. 5. It is suggested that further intracellular and behavioural study is needed to identify the causes of the granulovirus‐induced reduction in fertility of P. interpunctella.

The Effect of Repeated Matings on Sperm Numbers in Successive Ejaculates of the Cabbage White Butterfly Pieris rapae (Lepidoptera: Pieridae)

The effect of repeated matings on sperm numbers in successive ejaculates of the cabbage white butterfly, Pieris rapae, was examined. First ejaculates were larger than successive ones, which did not differ among themselves. Moreover, the cumulative mass of previous spermatophores was not correlated with that of the last mating. The number of eupyrene sperm bundles in the ejaculate did not differ between first and successive matings. Multiplying by 256, a male transfers about 11,000 eupyrene sperm at every mating. First ejaculates contained about 46,000 apyrene sperm, whereas successive ejaculates contained higher numbers. The sperm density increased after the first mating, though the spermatophore mass decreased. The significance of change in sperm quantity with mating number is discussed from the viewpoint of male investment.

Variations in sperm number in relation to larval crowding and spermatophore size in the armyworm, Pseudaletia separata

1. Number of sperm and its relationship with larval rearing density were investigated in the armyworm Pseudaletia separata. Males that emerged from crowded larvae produced significantly more apyrene sperm than those from solitary larvae (375 700 ± 116 600 and 290 300 ± 99 600 at a mating with a 3‐day old virgin, respectively), with no significant difference in number of eupyrene sperm between the two types being observed.2. For both solitary‐ and crowded‐type, the amount of fertile sperm the males produced at a mating exceeded the number needed to fertilize all of a female’s eggs, suggesting that sperm competition may be a major selective force for keeping sperm numerous. The production of more apyrene sperm by crowded‐type males may be an adaptation to cope with the increased sperm competition from rival males at high density.3. The relationship between number of sperm and spermatophore size was also studied using solitary‐type moths. Large spermatophores were found to have more eupyrene and apyrene sperm than small ones.

Paraspermatogenesis in gastropod molluscs

Summary Dimorphic, and sometimes polymorphic, spermatozoa are a feature of many caenogastropod and some archaeogastropod (s.l.) taxa. The two types of sperm, named euspermatozoa (fertilizing) and paraspermatozoa (non-fertilizing) by Healy and Jamieson (1981), are produced simultaneously in the same testicular acini. Paraspermatozoa develop from spermatogonia which are similar in structure to those producing euspermatozoa. Formation of parasperm from paraspermatocytes proceeds by atypical meiotic divisions. Despite the variability in the structure of parasperm of prosobranchs, the morphological changes which occur during paraspermatogenesis are remarkably similar between taxa. Multiple flagella develop from numerous basal bodies which in turn originate from two parent and their satellite centrioles (procentrioles). In parasperm which loose all the chromatin (apyrene sperm), the nucleus initially fragments into a number of vesicles. The chromatin in the vesicles gradually degenerates, the remaining material being discharged from the cell by exocytosis. In those parasperm in which a proportion of the chromatin is retained, the nucleus gradually decreases in size as the chromatin condenses. Electron-dense bodies (vesicles) which are produced either by granular endoplasmic reticulum or Golgi bodies begin to form in paraspermatocytes. These vesicles gradually increase in size and coalesce to form larger dense glycoprotein blocks which form the bulk of the head region of the parasperm. It is suggested that the material which forms these electron-dense blocks is derived from nuclear degeneration.

Centrosome structure is very similar in eupyrene and apyrene spermatocytes of Ephestia kuehniella (Pyralidae, Lepidoptera, Insecta)

Summary The higher Lepidoptera produce two types of sperm, eupyrene and apyrene. Eupyrene spermatozoa are fertile, while apyrene spermatozoa are anucleate and, therefore, sterile. Meiosis differs between the two developmental lines. One of the most obvious differences is the aberrant organization of the apyrene spindles. They possess fewer microtubules than eupyrene spindles and chromosome segregation is irregular. To determine whether micotubule nucleation is impaired in the aprene spindles, the present fine structure study concentrated on the centrosomes in both spermatocyte types. In addition, the presence of gamma-tubulin, a newly discovered tubulin isoform which is prevalent in centrosomes, was determined by anti-tubulin immunofluorescence. The observations showed that centrosome fine structure and appearance of gamma-tubulin containing polar masses were very similar in eupyrene and apyrene spermatocytes in late prophase I and in more advanced cells with spindle formation completed. In particular, pericentriolar material was present in about equal quantities in both cell types. Thus, the aberrant structure and behaviour of apyrene spindles are probably not caused by deficiencies in the amount of pericentriolar material and gamma-tubulin, a molecule which is crucial for microtubule nucleation.

Ejaculate dynamics in butterflies: a strategy for maximizing fertilization success?

The butterfly spermatophore is a complex structure containing both sperm and accessory substances. Most of the sperm are anucleated ‘apyrene’ sperm, which do not fertilize the eggs. The fertilizing ‘eupyrene’ sperm comprise only 10-15 % of the total sperm number transferred to the female at mating. In addition to sperm, some butterfly species also provide the female with nutrients that are used for egg production and/or somatic maintenance. Many butterflies eclose with most resources available for reproduction already present. Consequently, resources have to be allocated to the different spermatophore components over consecutive matings. This study is the first to quantify eupyrene and apyrene sperm numbers in relation to spermatophore mass, mating history and larval diet. Spermatophore mass was significantly reduced on the male’s second mating. However, both eupyrene and apyrene sperm numbers were dramatically increased, as was the proportion of eupyrene sperm. Theory predicts that sperm numbers should increase under sperm competition. On males’ second matings, the probability of encountering virgin females is reduced. Males may therefore maximise fertilization success by providing these females with large numbers of sperm. Simultaneously, it may be advantageous for males to reduce their nutrient donation because of their lower paternity assurance. Larval diet affected mass of the first spermatophore but had no effect on sperm number. This suggests that males maintain sperm numbers when resources are limited, prioritising fertilization success over investment in offspring.

Testicular Ecdysteroid Level in the Silkmoth, Bombyx mori, with Special Reference to Heat Treatment during the Wandering Stage

Abstract To elucidate the induction mechanism of abnormal apyrene sperm by high temperature (32°C, 72 hr) treatment during the wandering stage of the silkmoth, Bombyx mori, ecdysteroid titres in the haemolymph and in the testes were determined. The fluctuation of ecdysteroids in the haemolymph was not disturbed by the high temperature treatment. The amount of ecdysteroids in the testes of control animals was low during the two-thirds of the last larval stage and an abrupt increase was observed on day 8. On the other hand, the elevation of ecdysteroid titre was suppressed in the testes of the treated animals during the period of treatment. After pupation, the fluctuation pattern of the ecdysteroid titre was almost the same both in control and treated animals. These results indicate that the deficiency of ecdysteroids in the testes could be the cause of the abnormal differentiation of the apyrene spermatozoa brought about by the high temperature treatment during the wandering stage of the silkmoth, Bombyx mori.

Eupyrene and apyrene sperm and their numerical fluctuations inside the female reproductive tract of the armyworm, Pseudaletia separata

At 1 h after copulation both eupyrene (average length = 1.4 ± 0.1 mm) and apyrene (average length = 0.5 ± 0.1 mm) sperm were found in the sperm storage organ, spermatheca, and at 6 h after copulation, almost all of the sperm (293,900 ± 122,100, with 92.5 ± 2.9% being apyrene sperm) finished their travel from the spermatophore to spermatheca. The number of sperm inside the female reproductive tract did not decrease until 19 h after copulation. The spermatheca between 9 and 15 h after copulation was the best time and place for counting the sperm a male transferred to a female. Unlike the moderate decrease in the number of eupyrene sperm after copulation, the number of apyrene sperm decreased sharply within 3 days after copulation, especially within the first 24 h. This decrease in apyrene sperm correlates with the female's remating pattern, suggesting that the number of apyrene sperm may have some influence on female remating.

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

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

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.

Associations between body size, mating pattern, testis size and sperm lengths across butterflies

This paper investigates mechanisms of sperm competition by comparing reproductive characteristics across 74 butterfly species. Testis size scales with body size and, after controlling for this allometry, relative testis size increases with risk of sperm competition, as defined by female mating frequency. Both eupyrene (fertilizing) and apyrene (non-fertile) sperm lengths correlate positively with body size. After controlling for body size, relative eupyrene sperm lengths are greater in species where males experience higher risks of sperm competition. These results suggest that sperm competition in butterflies selects for increased investment in spermatogenesis, and specifically longer fertilizing sperm. Because longer sperm may be faster and more powerful, eupyrene sperm may therefore compete energetically, and are not selected to be minimally sized to maximize numbers for a purely raffle-based sperm competition mode. Apyrene sperm lengths are not affected directly by risk of encountering rival sperm. Instead, apyrene sperm show closer associations with body size which, if female tract morphometry correlates with body size, is consistent with the hypothesis that apyrene sperm retard female sexual receptivity by moving while in storage.

Sperm Size or Numbers? Effects of Nutritional Stress Upon Eupyrene and Apyrene Sperm Production Strategies in the Moth Plodia interpunctella (Lepidoptera: Pyralidea)

Sperm Size or Numbers? Effects of Nutritional Stress Upon Eupyrene and Apyrene Sperm Production Strategies in the Moth Plodia interpunctella (Lepidoptera: Pyralidea)

Multiple Mating in Laboratory-Reared Gypsy Moths (Lepidoptera: Lymantriidae)

Multiple mating was studied in a laboratory colony of gypsy moths, Lymantria dispar (L.). Males transferred reduced quantities of eupyrene sperm with each mating, and few were able to fully inseminate one female daily for 4 d. Nonetheless, some males could remate and fully inseminate a second female within a few hours, suggesting that not all of the sperm stored in the duplex was transferred during the first mating. Females that had mated with males incapable of full insemination would remate up to 2 d later, and sperm from the second mating was used in fertilization. Fecundity, as measured by egg mass weight, was dependent upon sperm transfer. Females with no sperm or only apyrene sperm laid fewer eggs than females with eupyrene sperm. However, the quantity of eupyrene sperm had little effect on the weight of the egg mass.

Two-step acquisition of motility by insect spermatozoa

High motility of eupyrene sperm of a grasshopper (Omocestus ventralis) was induced by cAMP. Both trypsin and cAMP were necessary for high motility of eupyrene sperm of three other species of grasshoppers. The same was found for apyrene sperm of the silkmoth,Bombyx mori, when they had been wahsed free from seminal plasma. On the other hand, in locusts (Locusta migratoria), in which the yellow gland has high Arg-C endopeptidase activity, sperm motility was induced by trypsin, like that of apyrene sperm of Lepidoptera. Thus in these two orders of Insecta, sperm motility appears to be induced by the same two-step process: the first step by Arg-C endopeptidase, and the second by cAMP.

Induction of inherited sterility in the tobacco hornworm Manduca sexta (Lepidoptera: Sphingidae) by substerilizing doses of ionizing radiation

AbstractMale pupae of the tobacco hornworm, Manduca sexta (Linnaeus), were exposed to γ–radiation from a 60Co source. This treatment induced mortality and malformations in the emerging adult insects. The incidence of these adverse effects of radiation declined with increasing pupal age at the time of treatment. Within any one age class, the effects of radiation treatment increased with increasing dose. When 16 d old pupae were irradiated, the resulting adult male insects exhibited adverse effects on mating behaviour and fertility when tested against unirradiated females. These effects were dose dependent in the range 0–30 krad. The major cause of reduced fertility was the failure of eggs to hatch. These eggs mostly showed no sign of embryonic development. F1 progency of moths given substerilizing doses of radiation showed significantly elevated larval mortality, pupal and adult malformations, and a slightly prolonged developmental period, but nevertheless a high proportion of the F1 insects survived to adults. The sex ratio of the F1 generation was markedly skewed in favour of males. When F1 insects, male or female, were mated with normal insects of the opposite sex, they were significantly less fertile than the irradiated parental (P1) generation. The F1 male moths transferred spermatophores to normal females only slightly less well than normal males, but the F1 females were much less successful than controls in mating with normal males. Examination of spermathecae of normal females mated with F1 males showed that both eupyrene and apyrene spermatozoa were successfully transferred from the spermatophore in all cases where the P1 insects had received 10 krad, but there was a slight reduction in the cases of higher doses. There was a dose-related decline in the number of eggs laid per mated female, and a dose-related reduction in hatching rate for the matings of both male and female F1 insects, but the effect on males was more severe than on females. The longevity of both F1 males and F1 females was reduced. The reduction in fertility of the F1 insects was in part due to a reduction in the number of eggs laid, but also to an increase in the number of eggs which failed to hatch. In contrast to the P1 generation, the reduction in hatching success of eggs laid by F1 insects was due mostly to the death of partly developed embryos.

Intratesticular ecdysteroid titres and the arrest of sperm production during pupal diapause in the tobacco hornworm, Manduca sexta

Lepidopteran spermatogenesis, which is a dichotomous process producing concomitantly both eupyrene (nucleate) and apyrene (anucleate) spermatozoa, discontinues during diapause. In diapause-averting pupae of Manduca sexta, the intratesticular titre of 20-hydroxyecdysone increases sharply to a post-pupation peak in day-10 pupae, and then drops sharply. In contrast, the titre is persistently low throughout diapause. In diapause-averting pupae, the post-pupation ecdysteroid peak and its abrupt decline, occur shortly before cessation of eupyrene meiosis. Accordingly, eupyrene meiosis continues uninterruptedly in diapausing larvae having experienced neither the peak, nor the fall of the ecdysteroid titre. The advance of apyrene spermatocytes towards meiotic metaphases coincides in diapause-averting pupae with the post-pupation rise in ecdysteroid titre. Accordingly, in diapausing pupae lacking this rise, apyrene spermatocytes stop developing, and lyse, before entering metaphase. The lack of the post-pupation peak of ecdysteroid may be related also to the lysis of eupyrene spermatids in the diapausing larvae. Fluctuations of the intratesticular ecdysteroid content follow the corresponding patterns of fluctuations in haemolymph ecdysteroid content in both diapausing and diapause-averting pupae. These findings do not support the idea that testicular ecdysteroids may play a separate, major role on controlling discontinuity of sperm production during diapause in Manduca.