膜翅目昆虫的性别决定机制

昆虫性别决定机制存在多样性和复杂性,其中膜翅目昆虫的性别决定由单双倍体决定,单倍体为雄性,二倍体为雌性。本文就膜翅目昆虫的性别决定模式和分子机制进行综述。膜翅目昆虫性别决定有6种模式,即互补性性别决定(complementary sex determination, CSD)、多位点互补性性别决定(multiple-locus CSD, ml-CSD)、基因组印记、母体效应、内共生体诱导产雌单性生殖、父本遗传基因组消除(paternal genome elimination, PGE)。其中,CSD机制是目前在膜翅目昆虫中普遍接受的性别决定模式。而蜜蜂的CSD性别决定机制是膜翅目昆虫性别决定模式中的典型代表,受csd→fem→dsx这一调控级联的控制。     

Single-locus complementary sex determination in the inbreeding wasp Euodynerus foraminatus Saussure (Hymenoptera: Vespidae)

The Hymenoptera have arrhenotokous haplodiploidy in which males normally develop from unfertilized eggs and are haploid, while females develop from fertilized eggs and are diploid. Multiple sex determination systems are known to underlie haplodiploidy, and the best understood is single-locus complementary sex determination (sl-CSD) in which sex is determined at a single polymorphic locus. Individuals heterozygous at the sex locus develop as females; individuals that are hemizygous (haploid) or homozygous (diploid) at the sex locus develop as males. sl-CSD can be detected with inbreeding experiments that produce diploid males in predictable proportions as well as sex ratio shifts due to diploid male production. This sex determination system is considered incompatible with inbreeding because the ensuing increase in homozygosity increases the production of diploid males that are inviable or infertile, imposing a high cost on matings between close relatives. However, in the solitary hunting wasp Euodynerus foraminatus, a species suspected of having sl-CSD, inbreeding may be common due to a high incidence of sibling matings at natal nests. In laboratory crosses with E. foraminatus, we find that sex ratios and diploid male production (detected as microsatellite heterozygosity) are consistent with sl-CSD, but not with other sex determination systems. This is the first documented example of sl-CSD in a hymenopteran with an apparent natural history of inbreeding, and thus presents a paradox for our understanding of hymenopteran genetics.     

Do Psyttalia concolor (Hymenoptera: Braconidae) males gain in mating competitiveness from being courted by other males while still young?

The role of male–male courtship in parasitic wasps is not well understood and nothing has been reported on the implication of learning in regard to homosexual behavior in hymenopteran parasitoids. In Psyttalia concolor (Hymenoptera: Braconidae), a synovigenic koinobiont larval–pupal endoparasitoid of many Diptera Tephritidae of economic importance, courtship and mating attempts are frequently displayed among males. Here we determine whether P. concolor males that are courted while still young by sexually mature males can compete better with other males when they court females. The results showed that P. concolor immature males do not appear to gain from receiving male courtship, but they develop a higher intensity (more wing fanning and shorter latency time) in the successive courtship of the females. The hypothesis that, under some conditions, such higher courtship intensities may increase the probability of gaining a mating advantage is discussed.     

Insemination potential of male Trichogramma evanescens

Reproduction strategies of male parasitoids have received less attention than those of the females. In hymenopteran parasitoids that reproduce by arrhenotokous parthenogenesis, virgin females are able to reproduce, but they are constrained to produce only males. In such species, the number of sperm transferred to females is of prime importance for female reproductive success. In this study, we measured the insemination potential of male Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae). Independent of their age and their sperm‐depletion status, males continued to mate with females until the end of their life. They quickly depleted their sperm supply by fertilizing 18 females during their lifetime, among which 80% were inseminated during the first 24 h. They fathered around 400 daughters over their lifetime. Our results suggest an absence of imaginal spermatogenesis in T. evanescens males that can be designated as prospermatogenic. Sperm is thus a limited resource in this species and females might encounter males with varying amounts of sperm.     

Effective population size in Hymenoptera with complementary sex determination

Complementary sex determination in the haplodiploid Hymenoptera leads to the production of inviable or effectively sterile diploid males when diploid progeny are homozygous at the sex-determining locus. The production of diploid males reduces the number of females in a population and biases the effective breeding sex ratio in favor of haploid males. This in turn will reduce the effective population size (Ne) of hymenopteran populations with complementary sex determination relative to the expected reductions due to haplodiploidy alone. The effects of diploid male production on Ne in hymenopterans with complementary sex determination when diploid males are either inviable or effectively sterile are assessed theoretically. In both models, low allelic diversity at the sex locus reduces the Ne of hymenopteran populations, and this effect is largest when diploid males are effectively sterile.     

Is love in the air or at first sight? Mate finding cues used by sympatric male velvet ants (Hymenoptera: Mutillidae)

Mate finding has been examined in a wide range of hymenopteran families, with the greatest knowledge from social species and parasitoids used in pest management. Velvet ants (Hymenoptera: Mutillidae) provide a unique system to study mate finding because short‐lived flying males must find solitary, wingless females that have spatially and temporally dispersed emergence. Based on limited field observations, it is thought that male velvet ants may use visual, chemical, and vibratory cues for mate finding, though there have been no controlled experiments to test these hypotheses. Using choice experiments, this study aims to determine the role of visual and airborne chemical cues used in female detection by three sympatric species of Dasymutilla males. We find that visual cues are not used for initial female detection and that airborne chemicals are sufficient for female detection. We also discover that males readily approach females of different species, indicating airborne chemicals are not used for species recognition. Despite the lack of discrimination by males, we determined that the sympatric, morphologically similar species show no genetic introgression, and therefore some other isolating mechanism must be at play after males make initial contact with the females.     

Relationship of DNA methylation level to the presence of heterochromatin in mealybugs.

Purified nuclear DNA from two mealybug species was analyzed for its 5-methylcytosine (m5C) content by reversed-phase high-pressure liquid chromatography. We observed that the percent m5C (percentage of cytosines which are methylated) varied between the two species, between males and females of the same species, and between lines with and without supernumerary B chromosomes. This is the first case of a sex-specific difference in overall DNA methylation level. In contrast to a recent report (Deobagkar et al., J. Biosci. [India] 4:513-526, 1982), we found no other modified bases in the DNA. Overall, the percent m5C in Pseudococcus obscurus was two to three times higher than in Pseudococcus calceolariae. In both species, the percent m5C in males was higher than in females, although only in P. calceolariae was the difference statistically significant (0.68 +/- 0.02 versus 0.44 +/- 0.04). The high m5C content in males was correlated with the presence of a paternally derived, genetically inactive set of chromosomes which is facultatively heterochromatic. The presence of constitutive heterochromatin, however, was associated with a lower m5C content. Thus, for example, the percent m5C in females of a P. obscurus line with heterochromatic B chromosomes (1.09 +/- 0.04) was significantly lower than that of a related line lacking such chromosomes (1.26 +/- 0.06). Our findings are discussed with respect to the possible relationship between DNA methylation and heterochromatization.     

Viability of diploid males in the parasitic wasp,Diadromus pulchellus (Hym.: Ichneumonidae)

In the HymenopteraDiadromus pulchellus diploid males have been observed in samples collected in the wild and bred in the laboratory. Using a yellow body color mutant strain, a protocol of crosses, involving inbred individuals, allows the routine production of such diploid males. These males result from the development of fertilized ova and emerge normally. Their preimaginal viability is similar to those of other individuals, and their imaginal viability does not differ from that of haploid males. Diploid males present normal external morphology and neither mosaicism nor intersexuality was observed. However, they are bigger than haploid males and have head size and wing length similar to those of females. The significance of diploid male viability in hymenopteran populations is discussed.     

Biochemical composition of the Atlantic bonito Sarda sarda from the Aegean Sea (eastern Mediterranean Sea) in different stages of sexual maturity

The content (% wet mass) in water, ash, lipid, crude protein, DNA and RNA of different tissues was determined during sexual maturation of bonitos Sarda sarda from the Aegean Sea. A total of 220 specimens were collected in the following stages of sexual maturity: immature, resting, developing, mature, spawning and spent. Highest lipid levels in the white muscle, red muscle and liver were measured in immature specimens, while lowest levels were found in spawning bonitos. The gradual percentage of lipid reduction from immature to spawning bonitos was relatively higher in the liver (females 71·2% and males 64·4%) than in the white (females 59·2% and males 53·5%) and red (females 62·1% and males 51·7%) muscle. Lipid levels in the gonads increased gradually from the immature to spawning stage. The decrease of lipid in the somatic tissues was more intense in females than in males, and gonadal lipid content was higher in females than in males. There was a strong reverse correlation between water and lipid percentage in all tissues. Protein content decreased significantly only in spawning bonitos. The percentage of protein reduction from immature to spawning stage was relatively higher in males than in females in both white (females 3·4% and males 4·6%) and red (females 4·6% and males 5·1%) muscles. Protein content in the liver was significantly lower than in the other tissues, being highest in mature females. Gonadal protein content in females increased with maturation and decreased after spawning. The content in ash exhibited considerable stability. The RNA:DNA ratio exhibited a similar pattern of variation in both muscles. The RNA:DNA ratio increased during gonadal development gradually from the developing to spent stage. It was concluded that in S. sarda during gonadal development, there was an increase in gonadal lipid accompanied by a decrease in somatic tissue lipid reserves. Thus, reproductive inactive bonitos have more lipid in their edible part and a higher nutritional value than active ones.     

Philopatry and reproductive success in Bornean orang-utans (Pongo pygmaeus)

Behavioural observations suggest that orang-utans are semi-solitary animals with females being philopatric and males roaming more widely in search of receptive partners, leading to the prediction that females are more closely related than males at any given site. In contrast, our study presents evidence for male and female philopatry in the orang-utan. We examined patterns of relatedness and parentage in a wild orang-utan population in Borneo using noninvasively collected DNA samples from animals observed to defecate, and microsatellite markers to assess dispersal and mating strategies. Surprisingly, resident females were equally as related to other resident females (mean r(xy) = 0.303) as resident males were to other resident males (mean r(xy) = 0.305). Moreover, resident females were more related to each other and to the resident males than they were to nonresident females, and resident males were more related to each other (and resident females) than they were to nonresident males. We assigned genetic mothers to 12 individuals in the population, while sires could be identified for eight. Both flanged males and unflanged males achieved paternity, similar to findings reported for Sumatran orang-utans.     

Consequences of genetic incompatibility on fitness and mate choice: the male point of view

Hymenopterans under single‐locus complementary sex determination (sl‐CSD) face inbreeding costs due to this sex determination mode. Under sl‐CSD, homozygote eggs at the sl‐CSD locus usually develop into unviable or sterile diploid males. Production of such costly males increases when sib‐mating happens because related individuals share half of their genome. In the hymenopteran Venturia canescens (a solitary parasitoid wasp), diploid males are sterile, leading to fitness costs through genetic incompatibility between parents. Whereas the costs of producing diploid males and behavioural strategies that would reduce such costs have been studied in females, the potential fitness costs faced by males have not. Here, we aimed to investigate fitness costs that males endure after a single sib‐mating and tested whether they have the ability to avoid sib‐mating through kin recognition. Our results show that males have a reduced fitness (i.e. they produce fewer daughters) when mating with their sibs. We also show that males have the ability to distinguish between non‐sib and sib females (i.e. kin). They use chemical marks emitted by the females to discriminate kin from non‐kin. We discuss the evolution of kin recognition in males in the context of mate choice for genetic compatibility. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 279–286.     

Diploid males and their triploid offspring in the paper wasp Polistes dominulus

Although the hymenopteran sex-determining mechanism generally results in haploid males and diploid females, diploid males can be produced via homozygosity at the sex-determining locus. Diploid males have low fitness because they are effectively sterile or produce presumably sterile triploid offspring. Previously, triploid females were observed in three species of North American Polistes paper wasps, and this was interpreted as indirect evidence of diploid males. Here we report what is, to our knowledge, the first direct evidence: four of five early male-producing Polistes dominulus nests from three populations contained diploid males. Because haploid males were also found, however, the adaptive value of early males cannot be ignored. Using genetic and morphological data from triploid females, we also present evidence that both diploid males and triploid females remain undetected throughout the colony cycle. Consequently, diploid male production may result in a delayed fitness cost for two generations. This phenomenon is particularly relevant for introduced populations with few alleles at the sex-determining locus, but cannot be ignored in native populations without supporting genetic data. Future research using paper wasp populations to test theories of social evolution should explicitly consider the potential impacts of diploid males.     

Sexual dimorphism in nuclear DNA content and floral morphology in populations of Silene latifolia (Caryophyllaceae)

The evolution of flower size has become a major focus of plant population biology. In order to gain insight into the causal basis for flower-size variation, we have explored the relationship between nuclear DNA content, flower size, and cell size within and among populations of the dioecious plant Silene latifolia. We found significant variation among populations for both DNA content and flower size, with a consistent sexual dimorphism within all populations (males have a bigger genome, but smaller flowers). The overall correlation between DNA content and flower size was negative, especially within males. The cell dimensions of calyx and petal cells were not significantly different between the sexes, indicating that females have bigger flowers because they contain more cells. These findings are discussed in the context of nucleotype theory, which predicts a slower growth rate (division rate) for cells with greater DNA content. This leads to the suggestion that males have smaller flowers because of the relatively slow rate of cell division due to their larger genome. It would be of great interest to know whether associated effects on flower size of changes in genome size of the type investigated in the present study can be generalized to other species.     

A QUANTITATIVE GENETIC ANALYSIS OF THERMAL SENSITIVITY IN THE LOCOMOTOR PERFORMANCE CURVE OF APHIDIUS ERVI

The thermal sensitivity of locomotor performance in Aphidius ervi, a parasitic hymenopteran, conforms to the “jack-of-all-trades is master of none” model of specialist-generalist trade-offs. Performance breadth and maximal performance at the phenotypic level are negatively correlated in both sexes. A strong, negative genetic correlation was found for males, but not for females. In males, the broad-sense heritability of performance breadth was about 0.16, and that of maximum walking velocity was about 0.29. Neither heritability was significantly different from zero in females. The broad-sense heritability of body mass was about 0.3 in females and 0.6 in males, with a strong negative genetic correlation between size and maximum velocity in males only. These data provide the first quantitative genetic analysis of performance curves in eukaryotic animals, and one of the few demonstrations of the specialist-generalist trade-off that underlies much theory in evolutionary ecology.     

Single-locus complementary sex determination absent in Heterospilus prosopidis (Hymenoptera: Braconidae)

In the haplodiploid Hymenoptera, haploid males arise from unfertilized eggs, receiving a single set of maternal chromosomes while diploid females arise from fertilized eggs and receive both maternal and paternal chromosomes. Under single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. Sex locus heterozygotes develop as females, while hemizygous and homozygous eggs develop as haploid and diploid males, respectively. Diploid males, which are inviable or sterile in almost all cases studied, are therefore produced in high frequency under inbreeding or in populations with low sex allele diversity. CSD is considered to be the ancestral form of sex determination within the Hymenoptera because members of the most basal taxa have CSD while some of the more derived groups have other mechanisms of sex determination that produce the haplo-diploid pattern without penalizing inbreeding. In this study, we investigated sex determination in Heterospilus prosopidis Viereck, a parasitoid from a relatively primitive subfamily of the Braconidae, a hymenopteran family having species with and without CSD. By comparing sex ratio and mortality patterns produced by inbred and outbred females, we were able to rule out sl-CSD as a sex determination mechanism in this species. The absence of sl-CSD in H. prosopidis was unexpected given its basal phylogenetic position in the Braconidae. This and other recent studies suggest that sex determination systems in the Hymenoptera may be evolutionary labile.     

Constrained sex allocation in a parasitoid due to variation in male quality

The theory of constrained sex allocation posits that when a fraction of females in a haplodiploid population go unmated and thus produce only male offspring, mated females will evolve to lay a female-biased sex ratio. I examined evidence for constrained sex ratio evolution in the parasitic hymenopteran Uscana semifumipennis. Mated females in the laboratory produced more female-biased sex ratios than the sex ratio of adults hatching from field-collected eggs, consistent with constrained sex allocation theory. However, the male with whom a female mated affected her offspring sex ratio, even when sperm was successfully transferred, suggesting that constrained sex ratios can occur even in populations where all females succeed in mating. A positive relationship between sex ratio and fecundity indicates that females may become sperm-limited. Variation among males occurred even at low fecundity, however, suggesting that other factors may also be involved. Further, a quantitative genetic experiment found significant additive genetic variance in the population for the sex ratio of offspring produced by females. This has only rarely been demonstrated in a natural population of parasitoids, but is a necessary condition for sex ratio evolution. Finally, matings with larger males produced more female-biased offspring sex-ratios, suggesting positive selection on male size. Because the great majority of parasitic hymenoptera are monandrous, the finding of natural variation among males in their capacity to fertilize offspring, even after mating successfully, suggests that females may often be constrained in the sex allocation by inadequate number or quality of sperm transferred.     

Evolutionarily stable oviposition and sex ratio in parasitoid wasps with single‐sex broods

Abstract 1. The flexibility of hymenopteran sex ratios is well documented, particularly in structured populations featuring sib mating. 2. Using game theoretic models, the present study examines species producing single‐sex broods in which sib mating is unlikely, and focuses on the role of population density in determining evolutionarily stable oviposition strategies. 3. Since only mated females can produce offspring of both sexes while unmated females produce only male offspring, mated females are under selection to produce more females overall to balance the primary sex ratio. 4. As the proportion of all females that are mated should increase with density, offspring sex ratio of mated females is strongly linked to density at low to moderate densities. The present study shows that when density becomes low enough for fewer than half of all females to have mated, then female offspring generate higher fitness. 5. In this low density situation, females may gain a fitness benefit from waiting at their emergence site or from using other costly means to find and mate with males before ovipositing. 6. The predicted correspondence between females waiting at the emergence site and fewer than half of females in the population containing sperm, can be tested empirically, as can the somewhat counter‐intuitive prediction that greater access to males should yield a more male‐biased sex ratio in the offspring of mated females. 7. The present study also indicates how measuring the variance in giving up times by females waiting for males at low density, can provide insight into mechanisms determining waiting times.     

Causes of a non-random pairing by size in the brine shrimp,Artemia salina: (Crustacea: Anostraca)

Summary Brine shrimp (Artemia salina) males and females entered precopula assortatively by size in the laboratory; large males also had a pairing advantage over smaller males. We investigated the causes of such nonrandom pairing to test hypotheses on size-assortative mating.We found precopulatory biases with respect to male size in the absence of direct competition among males (which produces pairing biases in other species). Large males encountered females significantly more often than did small males. Similarly, large females encountered males more often than did small females, but showed less willingness than small females to enter precopula when housed with small males. Consequently, large females took longer than small females to enter precopula with small males. Although large males entered precopula readily with small females, such size-mismatched pairs appeared short-lived.We conclude that non-random pairing by size in A. salina is determined by several factors including: encounter rates between males and females of different sizes, female behavior, and time following initial pair formation. Our results are likely applicable to other species and can help explain variation for selection on size or other traits.     

Oxidative DNA damage (8-hydroxydeoxyguanosine) and body iron status: a study on 2507 healthy people

To clarify the relationship of oxidative stress and body iron status, we detected urinary 8-hydroxydeoxyguanosine (8-OHdG) as a biomarker of oxidative DNA damage, and measured serum ferritin and total iron-binding capacity (TIBC), both reflecting body iron store, on 2507 healthy people aged between 22 and 89 years (males, 1253; females, 1254). The urinary 8-OHdG excretion of males showed almost no change with age, but the excretion of premenopausal females was lower than that of males, whereas postmenopausal females excreted significantly more than males. The values of serum ferritin showed no remarkable change with age in males, but increased gradually in postmenopausal females without iron loss due to bleeding, although the males' values remained higher than those of females at all ages (p<.05). On the other hand, the values of TIBC remained within the narrow limits in males, regardless of age, whereas those of females always stayed at a higher level than the males (p<.05). Conclusively, urinary 8-OHdG correlated with serum ferritin positively and with TIBC inversely, which suggested that body iron status would control the generation of 8-OHdG in vivo. After all, the increase of urinary 8-OHdG excretion in postmenopausal females may be caused by the decrease of body iron loss.