Sperm Complement Research Articles

The spatio-temporal partitioning of sperm by males of the prospermatogenic parasitoid Nasonia vitripennis is in line with its gregarious lifestyle

Male fitness depends on the number of lifetime progeny of their mates and could be constrained by the chance of finding a mate, lifespan and temporal patterns of sperm production and allocation. Here, we used the parasitic wasp Nasonia vitripennis with a two-week lifespan and a gregarious lifestyle, to analyze how the reproductive system is organized to allocate spermatozoa over consecutive matings. Results show that spermatogenesis is synchronized and completed one day before emergence so that males emerge with a full sperm complement. We also found a regulation of spermatozoa transfer between testis and seminal vesicles that allows males to partition small ejaculates over multiple matings. Overall, this study shows that for N. vitripennis, male fertilization potential is determined (1) at the pupal stage, when spermatogenesis takes place to generate a complete life-long stock, (2) on emergence, when transport of spermatozoa from testes to seminal vesicles is initiated and (3) in adulthood, during which spermatozoa are partitioned over successive copulations. Such life history-traits are consistent with the gregarious lifestyle of N. vitripennis.

Size-induced reproductive constraints in an egg parasitoid

The size of adult parasitoids is influenced by the quantity and quality of resources available during immature development. Gregarious development of endoparasitoids results in scramble competition where the resources are shared among individuals developing into the same host. Individuals that developed gregariously are therefore smaller and that reduced size generally translates into lower fitness due to reductions in several life history traits including longevity, mobility and traits linked to reproduction. We measured the reproductive constraints induced by size in Anaphes listronoti (Hymenoptera: Mymaridae), a facultative gregarious egg parasitoid of Curculionidae. Size decreased with number of immatures developing in a host egg for both male and female A. listronoti. This reduction in size induced a reproductive cost as both males and females produced fewer gametes when developing gregariously. Contrarily to other egg parasitoids, A. listronoti males are not prospermatogenic and produced some sperm during their adult life. Their spermatogeny index is estimated at 0.6–0.7 that places this species as moderately synspermatogenic. Female A. listronoti have an ovigeny index of 0.70 and are therefore moderately synovigenic. Large females that developed singly received a full sperm complement only when mated by a large male that also developed singly. When mating with a small triplet male, a large female received less than half her sperm complement. Large males were able to mate three females before the number of sperm transferred started to decrease.

Sperm as a limiting factor in mating success in Hymenoptera parasitoids

AbstractThe paradigm that females produce few costly eggs, whereas males produce an unlimited quantity of sperm holds true when matings are dispersed over time and males can replenish their sperm supply. In such a system, the best strategy for males is to mate with as many females as possible, as more is always better. However, in parasitoid species, mating often occurs at the emergence site and males may have to mate successively several females in a short period of time. This can lead to sperm depletion that can be temporary in synspermatogenic species whose males produce sperm throughout their adult life, or definitive in prospermatogenic species whose males emerge with their full sperm complement and do not produce more during their adult life. Both the spermatogeny index and the mating structure of a species will therefore influence the probability and intensity of sperm depletion in males. Sperm‐limited males can court and mate females even in prospermatogenic species. These males still gain some inclusive fitness by preventing competitor males to fully inseminate females, therefore increasing the representation of their daughters in the following generation. Females that mate with partially or completely sperm‐depleted males produce a constrained sex ratio that decreases their lifetime fitness. In species where sperm‐depleted males occur, female choosiness based on sperm supply is predicted, as the cost of mating sperm‐depleted males can be high. In addition, males are also expected to be choosy in prospermatogenic species as mating with sub‐optimal females can be costly when sperm is limited.

Function and composition of male accessory gland secretions in Anopheles gambiae: a comparison with other insect vectors of infectious diseases

Human malaria, a major public health burden in tropical and subtropical countries, is transmitted exclusively by the bite of a female Anopheles mosquito. Malaria control strategies aimed at inducing sexual sterility in natural vector populations are an attractive alternative to the use of insecticides. However, despite their importance as disease vectors, limited information is available on the molecular mechanisms regulating fertility in Anopheles mosquitoes. In the major malaria vector, An. gambiae, the full complement of sperm and seminal fluid required for a female’s lifelong egg production is obtained from a single mating event. This single mating has important consequences for the physiology and behavior of An. gambiae females: in particular, they become refractory to further insemination, and they start laying eggs. In other insects including Drosophila, similar post-copulatory changes are induced by seminal proteins secreted by the male accessory glands and transferred to the female during mating. In this review, we analyze the current state of knowledge on the function and characterization of male seminal proteins in An. gambiae, and provide a comparative assessment of the role of these male reproductive factors in other mosquito vectors of human disease in which female post-copulatory behavior has been studied. Knowledge of the factors and mechanisms regulating fertility in An. gambiae and other vectors can help the design of novel control strategies to fight the spread of disease.

Variation in male body size and reproductive allocation in the leafcutter ant Atta colombica: estimating variance components and possible trade-offs

Remarkably little is known about the traits that determine reproductive success of males in eusocial insects. Their window for mate choice decisions is very short, the actual mating process is very difficult to observe, and their small body sizes have likely prevented systematic studies in many species. In 2008 and 2009, we revisited a Panamanian population of Atta colombica leafcutter ants to partially repeat and complement a study of more than 15 years ago. We compared within- and between-colony variation in male body size (mass and width of head, mesosoma and gaster) and sperm characteristics (length, number and survival after exposure to saline buffer with and without added accessory gland secretion). We also measured the size of accessory glands as the main contributor of seminal fluid and the accessory testes containing all mature sperm, but we found few correlations between these variables. We also obtained little or no evidence for expected trade-offs between sperm number and sperm length and between mesosoma mass and sperm complement, although this could be due to limited sample size and unknown variation in larval resource allocation that was beyond our control. However, we found an interestingly bimodal distribution in broad-sense heritabilities (intra-class correlations) among the variables that we measured. Low heritabilities suggest that mesosoma size (mass and width), accessory testes size, sperm viability (measured as % survival in saline) and probably also accessory gland size are traits directly correlated with reproductive success. However, the much higher heritabilities for total body mass, gaster mass, head width, sperm length and sperm number suggest that these traits are less likely to make direct contributions to male fitness.

Testicular maturation in the sheep bot fly Oestrus ovis.

The process of testicular maturation in relation to intrapuparial development was studied in the sheep nasal bot fly, Oestrus ovis L. (Diptera: Oestridae). After formation of the puparium during larval-pupal apolysis and the cryptocephalic pupal stage (approximately 24-72 h), spermatogonia had undergone mitotic divisions and sperm cysts had been formed. Five days after pupariation, spermatogonia transformed into primary spermatocytes during the phanerocephalic pupal stage, and secondary spermatocytes first appeared during the pupal-adult apolysis. Secondary spermatocytes began undergoing the second meiotic division by day 8 (transparent-eye pharate adult stage). By days 9 and 10, round spermatids were present and began to elongate by day 11. By day 12, the first bundles of tailed spermatozoa had appeared. By day 15 (the yellow-orange eye pharate adult stage), round, elongated, tailed and bundled spermatids were predominant and by day 17 differentiating spermatids occupied nearly 35% of the testicular cavity, and 60% was occupied by free sperm. By day 21 (the red-brown eye pharate adult stage), spermatozoa colonized the seminal vesicle. At emergence (approximately day 22), a complement of free sperm occupied the testis and the seminal vesicle, but groups of developing cells frequently remained in certain zones. Spermatogenesis was carried out after pupariation and spermiogenesis occurred during the pharate adult stage. After emergence, males possessed fully formed spermatozoa ready for ejaculation.

Cytogenetic analysis of sperm chromosomes and sperm nuclei in a male heterozygous for a reciprocal translocation t(5;7)(q21;q32) by in situ hybridisation.

We have studied the meiotic segregation of a reciprocal translocation t(5;7)(q21;q32) in a male carrier, using the human sperm-hamster oocyte fusion technique and the whole chromosome painting. A total of 296 sperm complements were analysed by dual chromosome painting. The frequencies of alternate, adjacent-1, adjacent-2 and 3:1 segregation were 49.7%, 32.4%, 16.2% and 1.7% respectively. Aneuploidy frequencies for chromosomes not involved in the translocation were determined by FISH on decondensed sperm heads using probes from chromosomes X, Y, 6, 18 and 21. A total of 20,118 spermatozoa was analysed, 10,201 by two-colour FISH (probes for chromosomes 6 and 21) and 9917 by three-colour FISH (probes for chromosomes X, Y, and 18). There was no evidence of an interchromosomal effect, since disomy frequencies were within the range of normal controls.

Cytogenetic analysis of spermatozoa in the father of a child with a de- novo reciprocal translocation t(7;9) (q22;p23)

Analysis of sperm chromosomes was carried out in the father of a child with a de-novo reciprocal translocation t(7;9) (q22;p23) by G-banding and chromosome painting. Sperm metaphases were obtained using the zona-free hamster oocyte-human sperm fusion technique. A total of 138 complements were sequentially analysed by G-banding and fluorescence in-situ hybridization (FISH). The frequency of spermatozoa with structural chromosome abnormalities (5.1%) and the estimated conservative aneuploidy (1.4%) were within the range obtained in our control donors (6.9 and 4%). The sex ratio (45.3% X versus 54.7% Y) was not significantly different from the theoretical 1:1. A total of 309 sperm complements was analysed by FISH, 138 sequentially analysed by G-banding-FISH and another 171 analysed by FISH only. The frequencies of structural chromosome abnormalities for chromosomes 7 and 9 (0.6 and 0% respectively) were not significantly different from those obtained in our control donors (0.6 and 0.8%). No spermatozoa with the t(7;9) (q22;p23) were observed, showing no evidence for a germ-cell mosaicism. A statistically significant, positive association between sperm breakpoints and fragile sites (P = 0.0225) was observed. However, the coincidence between fragile sites and sperm breaks (80%) was not significantly different from that obtained in our control donors (79.2%). These results suggest that in this case the risk of structural chromosome abnormalities in further offspring is not increased, although an association between fragile sites and sperm chromosome breaks in the father does exist.

Influences of sex, size, and symmetry on ejaculate expenditure in a moth

Although sperm fundamentally function to fertilize eggs, forces arising from both sexes select for optimal ejaculate composition. Sperm competition is one recognized agent in the evolution of sperm and ejaculate structure. Few studies, however, have examined how female factors influence ejaculate structure, despite some behavioral evidence for male mate choice. Male Plodia interpuncteOa (Lepidoptera, Pyralidae) accrue all resources for reproduction as larvae. Adults emerge with a limited sperm complement and are therefore under intense selection to optimize gamete allocation. I detected no effect of male body weight on ejaculate size. However, female reproductive potential (ovary masses) was dictated by body weight In addition, heavier females had greater spermathecal volumes, but there was no such relationship with bursal size. Finally, heavier females showed a higher mating frequency. I found that mating males were sensitive to female size and produced larger ejaculates when mating with heavier females. Males may ejaculate more sperm into larger females either because it pays them to spend more reproductive resources on matings that provide greater reproductive potential, or because heavier (longer lived and more attractive) females mate more frequently and have larger spermathecal volumes. Alternatively, females may control spermatophore formation and accept an appropriate ejaculate to maximize fertility. Males may therefore be also selected to ejaculate more sperm into larger females to counteract greater risks of sperm competition associated with heavier females. There was no association between male or female femur asymmetry and ejaculate size. P. mterpunctella may be selected to exercise modulation of ejaculate size because males invest paternally, sperm for the single reproductive episode are limited, and female fecundity and mating pattern vary between individuals and are associated with body weight. More obvious variability in male reproductive behavior and choice may therefore be paralleled at the cryptic gametic level by plasticity in ejaculate allocation.

Sperm segregation analysis of a complex chromosome rearrangement, 2;22;11, by whole chromosome painting

Using the human sperm–hamster oocyte fusion technique and whole chromosome painting, we studied sperm chromosome segregation in a male heterozygous for a complex chromosome rearrangement, 46,XY,–2,+der(2)t(2;11)(q13; q23),–11,+der(11)t(11;22)(q23;q11.2),–22,+der(22)t(2;22)(q13; q11.2). A total of 208 sperm complements were analyzed. The frequency of sperm carrying a normal or a balanced complement was 13.5% (9.62% and 3.85%, respectively). The frequency of unbalanced sperm was 86.5% (64.9% from 3:3 segregation, including 30 different types; 20.7% from 4:2 segregation, including 21 different types; and 0.96% from 5:1 segregation, including 2 different types). The sex ratio, determined in 134 sperm complements, did not differ from the expected 1:1 ratio. The results obtained in this study are compatible with the formation, during the synaptic process, of a complex hexavalent figure involving chromosomes 2, 11, and 22. The behavior and segregation of this complex figure would explain the high frequency (86.5%) of unbalanced complements observed in this carrier.

Variation in size and sperm content of sexuals in the leafcutter ant Atta colombica

We studied a population of the Panamanian leafcutter ant Atta colombica and found significant between-colony variation for several male and gyne size parameters. Male sperm complement size was highly variable between individuals and was negatively correlated with head width and thorax weight, the latter itself positively correlated with wing length. This suggests a negative covariance between two likely fitness traits of males: flight ability and insemination potential. Young queens on average stored only slightly more than one male's worth of sperm. We discuss our results in the context of reproductive strategies and mating systems.

Sperm Transfer in Gypsy Moths: Effect of Constant or Cyclic Temperature and Constant Light or Darkness during the Pupal Stage

Sperm transfer and fertility of the gypsy moth, Lymantria dispar (L.), held as pupae under constant temperature and 24-h light, 24-h darkness, or a photoperiod of 16:8 (L:D) h were compared with males held in cyclic temperature and 24-h light, 24-h darkness, or a photoperiod of 16:8 (L:D) h. Constant temperature and constant light or darkness severely reduced its ability to transfer sperm. Males held under constant light were more severely affected than males held in darkness, but sperm transfer was not correlated with light intensity (between 80 and 3960 lux). Nearly all males held under constant light and most held under constant darkness were sterile or partially sterile. In either case, sterility was caused by poor sperm transfer. Females with a full complement of sperm were fertile regardless of holding condition of male pupae. The sterilizing effect of constant light or darkness was overridden by cyclic temperature of 28°C for 16 h and 22°C for 8 h. At a photoperiod of 16:8 h, pupae held in constant 28°C transferred less sperm than those held at 25°C. Pupae held at constant 30°C were sterile, but those held at 30°C for 16 h and 25°C for 8 h transferred similar quantities of sperm as males held at constant 28°C.

Reproductive Capacity of Laboratory-Reared Gypsy Moths (Lepidoptera: Lymantriidae): Effect of Age of Female at Time of Mating

The reproductive potential of laboratory-reared gypsy moths, Lymantria dispar (L.), was studied as a function of female age at time of mating. The parameters studied were number of eggs produced, number of eggs deposited, mating, sperm transfer, egg viability, and female longevity. Delayed mating did not affect female longevity, but all other factors decreased with increased age at time of mating. With increasing age, females were less likely to mate or receive a full complement of sperm than females exposed to males within the first few days after eclosion. Females that oviposited before being placed with males were less likely to mate than those that had not. For females receiving a full complement of sperm, the number of eggs produced, the number laid, and egg viability decreased with increasing age of the female at mating. Overall, a delay in mating of 3-5 d reduced the reproductive potential of females from 40 to 90% of that of females mated within the first 36 h.

Early Male Emergence and Reproductive Phenology of the Adult Overwintering Butterfly Gonepteryx rhamni in Sweden

In insects males usually emerge before females. This is known as protandry and can be understood in terms of sexual selection acting on males to maximise the number of matings, or on females to minimise the prereproductive period. A corollary of protandry theory is that males should not emerge before females when the advantage of protandry is nullified, as is the case when diapause intervenes between adult eclosion and the mating season. The brimstone butterfly, Gonepteryx rhamni, has such a life cycle, and in Sweden it develops from egg to adult during April/May to July, and overwinters in the adult stage before the onset of the mating season in April the following year. The first objective of this paper was to test the predictions that (1) there should be no difference between the sexes in egg to adult development time, and that (2) males should emerge from hibernation earlier than females, i.e. protandry should be expected during the mating season. A second objective was to test what proximate mechanisms were responsible for the eventual sex difference in time of emergence from hibernation. Protandry theory shows that late emerging males are heavily penalized in terms of mating opportunities, and so male G. rhamni may benefit from being able to mate directly after emerging from hibernation, whereas females may not be in such a hurry to start laying eggs because the bud break of the host plant Frangula alnus occurs in late May. Hence male G. rhanmi may have to allocate their fat reserves both to winter survival and sperm production, whereas females can most likely allocate all their fat reserves to winter survival, and so the third objective was to document the reproductive phenology of males and females and to test if male G. rhamni suffered higher winter mortality than females. As expected from theory there was no sex difference in egg to adult development time, whereas three years of census data from the field showed that the first males emerged from hibernation on average 21 d earlier than the first females (with the peak of male abundance occurring on average 8 d before that of female peak abundance). The earlier male emergence from hibernation seemed to be the result of the combined effects of males having a slightly lower temperature threshold for flight, and males being ready to fly as soon as environmental conditions were suitable after 4 months of hibernation, whereas females seemed to require a higher temperature summation before being ready to fly. Dissections of males and females throughout the year showed that male sperm production started soon after eclosion with males entering hibernation with a substantial sperm complement, and experiments showed that both males and females mated within minutes after having spent at least 6 months in hibernation at 4°C. By contrast, female eggs were small and unyolked throughout winter, and egg development started only after females had emerged from hibernation. Females brought from hibernation, and mated, towards the end of March started to lay eggs only after spending between 7 and 14 d at room temperature. Although males divide their fat reserves between survival and reproduction during winter, there was no difference in winter survival between the sexes under laboratory conditions, and the sex ratio assessed in the field did not differ before versus after hibernation giving no support for the idea that males suffer higher winter mortality than females.

An analysis of human sperm chromosome aneuploidy.

A sperm chromosome analysis of 24 men with normal or balanced karyotypes was carried out to study the frequency of sperm chromosome aneuploidy. A total of 3,446 human sperm complements (36-315 per donor) was analyzed after in vitro penetration of hamster eggs. Two sets of donors were studied at two different centers in the United States (center 1) and Spain (center 2). The frequencies of hyperhaploidy and hypohaploidy in control donors were similar between center 1 (1.9% vs. 7.7%) and center 2 (1.8% vs. 10.3%). In carrier donors there were no significant differences between the two centers in the frequency of hyperhaploidy (0.8% vs. 1.9%), but that of hypohaploidy was significantly higher in center 2 (11.0%) than in center 1 (4.6%). A significant excess of hypohaploid complements, as compared to hyperhaploid complements, was found in both centers in both control and carrier donors. The sex ratio was similar in both centers and did not differ significantly from a 1:1 sex ratio. The larger chromosomes in the complement (1, 2, 3, 4, 5, 7, and 10) presented a significantly lower frequency of hypohaploidy, while some of the smaller chromosomes (13, 19, and 21) showed a higher frequency of hypohaploidy than expected. Chromosome 21 and the sex chromosomes showed an increase in the percentage of hyperhaploidy, as compared to other chromosomes, that was close to statistical significance (P = 0.08). Our results reflect a preferential loss of small chromosomes during slide preparation and suggest that chromosome 21 and the sex chromosomes could be more frequently involved in aneuploidy.

Remating by Gypsy Moths (Lepidoptera: Lymantriidae) Mated with F1-Sterile Males as a Function of Sperm Within the Spermatheca

The relationship between sperm content of the spermatheca and the propensity to remate was studied in females of the gypsy moth, Lymantria dispar (L.). Females were mated with nonirradiated or F1-sterile males. The quantity of sperm in the spermatheca of females that remated was compared with that of females that did not remate. Nearly all females that received less than a full complement of sperm remated regardless of type of male involved in the first mating. The propensity of females with a full complement of sperm to remate depended on male type. Seventy percent of the females with a full complement of sperm from F1-sterile males remated, or >4-fold the percentage of females remating after receiving similar quantities of sperm from nonirradiated males. Such remating disparity in nature may impede the chance of eradicating gypsy moth populations by releasing F1-sterile males.

Induction of micronuclei in human sperm‐hamster egg hybrids at the two‐cell stage after in vitro gamma‐irradiation of human spermatozoa

The efficiency of the micronucleus test to assess radiation-induced chromosomal damage in human spermatozoa has been investigated. Micronuclei were scored in human sperm-hamster egg hybrids at the two-cell stage, after exposure of human spermatozoa to in vitro gamma-rays at doses of 0.00, 0.10, 0.25, 0.50, 1.00, 2.00, and 4.00 Gy. The relationship between the yield of micronuclei per two-cell stage as well as the percentage of two-cell stages with micronuclei and the different doses of irradiation were fitted to linear equations. To evaluate whether scoring micronuclei is useful for the quantification of chromosomal damage occurring in human spermatozoa, induced micronuclei at the different doses of sperm irradiation were compared to the induction of breaks and fragments in sperm-derived chromosomes. After interspecific fertilization of zona-free hamster oocytes by irradiated spermatozoa, a total of 699 fertilized eggs at the two-cell stage and a total of 387 sperm-derived complements were analyzed. The incidence of fertilized eggs with micronuclei at the two-cell stage coincided well with the incidence of sperm-derived chromosome breaks and fragments (e.g., 8.9% vs. 6.7% in the 0.25 Gy group and 52.8% vs. 58.6% in the 4.00 Gy group). A similar correlation was found between the number of micronuclei per two-cell stage and the number of breaks and fragments per sperm complement (0.09 vs. 0.07 in the 0.25 Gy group and 0.71 vs. 0.81 in the 4.00 Gy group). The results show that this test system can be used for the quantification of spontaneous or induced chromosomal damage in human spermatozoa.

EVOLUTION OF SPERM SHORTAGE IN A SELFING HERMAPHRODITE

EVOLUTION OF SPERM SHORTAGE IN A SELFING HERMAPHRODITE

The frequency of aneuploidy among individual chromosomes in 6,821 human sperm chromosome complements

The human sperm/hamster egg fusion technique has been used to analyse 6,821 human sperm chromosome complements from 98 men to determine if all chromosomes are equally likely to be involved in aneuploid events or if some chromosomes are particularly susceptible to nondisjunction. The frequency of hypohaploidy and hyperhaploidy was compared among different chromosome groups and individual chromosomes. In general, hypohaploid sperm complements were more frequent than hyperhaploid complements. The distribution of chromosome loss in the hypohaploid complements indicated that significantly fewer of the large chromosomes and significantly more of the small chromosomes were lost, suggesting that technical loss predominantly affects small chromosomes. Among the autosomes, the observed frequency of hyperhaploid sperm equalled the expected frequency (assuming an equal frequency of nondisjunction for all chromosomes) for all chromosome groups. Among individual autosomes, only chromosome 9 showed an increased frequency of hyperhaploidy. The sex chromosomes also showed a significant increase in the frequency of hyperhaploidy. These results are consistent with studies of spontaneous abortions and liveborns demonstrating that aneuploidy for the sex chromosomes is caused by paternal meiotic error more commonly than aneuploidy for the autosomes.

Human sperm chromosome studies in a reciprocal translocation t(2;5)

Sperm chromosome complements have been studied in a man heterozygous for a reciprocal translocation t(2;5)(p11;q15). Human sperm chromosomes were obtained after fertilization of zona-free hamster eggs. A total of 75 human sperm metaphases were analysed. On the complements studied, 59 (78.6%) resulted from a 2:2 segregation and 16 (21.3%) from a 3:1 segregation, 4:0 segregation was not observed. Our results indicate that at least 36% of sperm complements were unbalanced with respect to the translocation. The frequency of other chromosome anomalies unrelated to the translocation was 16%.