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Diploid males represent a cost for the viability of populations in haplodiploid species with a single-locus complementary sex determination system. In such social species as bumble bees, their presence affects colony growth and reproduction, therefore, the detection of diploid males is an important aspect to implement conservation actions and for the breeding companies of this important pollinator. In this study, we applied and compared the effectiveness of morphological analyses (sperm count and testis area) with wing morphometrics (traditional and geometric) and genetic techniques (microsatellite analysis) to discriminate between diploid and haploid males originated from laboratory-reared B. terrestris colonies. Among the five techniques, microsatellite analyses and wing geometric morphometrics showed the highest efficiency in ploidy assignment and resulted in the most valuable methods according to a cost-effectiveness analysis. [ABSTRACT FROM AUTHOR]

The buff-tailed bumblebee Bombus terrestris presents two distinct colony phenotypes in which some colonies already start producing males very early in the season, while others switch to producing sexuals much later in the season, and specialize mainly in the production of virgin queens. Despite having been extensively investigated in the past, the mechanisms underlying these two distinct phenotypes remain poorly understood. Here we use a combination of behavioral and genetic data to demonstrate that early switchers are in fact diploid male producing colonies, while late switchers produced normal, haploid males. Hence, at a proximate level, early switching to male production was caused by queens mating with males that by chance carried the same sex allele. These patterns were not the result of strong inbreeding within the study population, as the average inbreeding coefficient was very low and in fact slightly negative (−0.11). Moreover, an effect of inbreeding was further excluded because hybrids produced by crossing two distinct outbred populations also produced diploid males in early switching colonies. Finally, we found that diploid males only emerged after a first cohort of workers was produced, while we would have expected diploid males to be produced simultaneously with workers in a 50:50 ratio. We demonstrate that adult diploid males had a distinct cuticular hydrocarbon profile and propose that queens likely cull diploid males during early colony development to reduce the cost of diploid male production.

We describe and characterize eight polymorphic microsatellite loci for the orchid bee species Eulaema meriana, an abundant species and important pollinator in wet lowland forests in tropical America. We also tested the cross-species amplification of these microsatellite loci in seven other species of the genus Eulaema. For E. meriana, number of alleles per locus ranged from four to nine and expected heterozygosity ranged from 0.377 to 0.854. Seven out of the eight loci described amplified in all seven other Eulaema species. These microsatellite loci will be of practical use for population structure, mating system and inbreeding studies in euglossine bees.

In the present study on the bumblebee Bombus terrestris, we investigated the influence of inbreeding on queen fitness by comparing diapause survival and egg‐laying success of queens mated with nestmate and non‐nestmate males. We then compared the early stage of colonies with or without diploid males and analysed colony characteristics to identify a factor predictive of colony outcome. Diapause survival was no different between queens mated with nestmates and non‐nestmates, but in the latter case, egg‐laying success was significantly higher. Queens mated with nestmates gave rise to a percentage of diploid male colonies (52.6%) compatible with brother–sister coupling. We obtained 18.6% of colonies with diploid males even from queens mated with non‐nestmates, indicating that the colonies of origin were in some way related or homozygous at the sex determination loci. There was no difference in the early growth stage between colonies with or without diploid males, except in the number of workers emerging in the first brood, which was significantly higher in the latter. Among diploid male colonies, the number of workers and the male/worker ratio in the first brood was highly variable and was not a good predictor of subsequent colony growth. Out of 49 colonies with diploid males that reached full development, only 11 had a sufficient size to assume that they could survive in the field or, in a commercial breeding, to be suitable for pollination purposes. [ABSTRACT FROM AUTHOR]

Abstract: Inbreeding and inbreeding depression are processes in small populations of particular interest for a range of human activities such as animal breeding, species conservation, or pest management. In particular, biological control programs should benefit from a thorough understanding of the causes and consequences of inbreeding because natural enemies experience repetitive bottlenecks during importation, laboratory rearing, and introduction. Predicting the effect of inbreeding in hymenopteran parasitoid wasps, frequently used in biological control programs, is nonetheless a difficult endeavor. In haplodiploid parasitoids, the purge of deleterious alleles via haploid males should reduce genetic load, but if these species also have complementary sex determination (CSD), abnormal diploid males will be produced, which may jeopardize the success of biological control introductions. Mastrus ridens is such a parasitoid wasp with CSD, introduced to control the codling moth, Cydia pomonella (L.). We studied its life history traits in the laboratory under two conditions: inbred (full‐sib) and outbred (nonsib) crosses, across five generations, to examine the consequences of inbreeding in this species. We found that in inbred lines, nonreproducing females live less, the number of daughters produced was lower, and sex ratio (proportion of males) and proportion of diploid males were higher. Diploid males were able to produce fertile daughters, but fewer than haploid males. Lineage survival was similar for inbred and outbred lines across the five generations. The most significant decrease in fitness was thus a consequence of the production of diploid males, but this effect was not as extreme as in most other species with CSD, due to the fertility of diploid males. This study highlights the importance of determining the type of sex determination in parasitoid wasps used for biological control, and the importance of maintaining genetic diversity in species with CSD when importation or augmentation is the goal. [ABSTRACT FROM AUTHOR]

In insect sex determination a primary signal starts the genetic sex determination cascade that, in most insect orders, is subsequently transduced down the cascade by a transformer ( tra ) ortholog. Only a female-specifically spliced tra mRNA yields a functional TRA-protein that forms a complex with TRA2, encoded by a transformer-2 ( tra2 ) ortholog, to act as a sex specific splicing regulator of the downstream transcription factors doublesex ( dsx ) and fruitless ( fru ). Here, we identify the tra2 ortholog of the haplodiploid parasitoid wasp N. vitripennis ( Nv-tra2 ) and confirm its function in N. vitripennis sex determination. Knock down of Nv-tra2 by parental RNA interference (pRNAi) results in complete sex reversal of diploid offspring from female to male, indicating the requirement of Nv-tra2 for female sex determination. As Nv-tra2 pRNAi leads to frequent lethality in early developmental stages, maternal provision of Nv-tra2 transcripts is apparently also required for another, non-sex determining function during embryogenesis. In addition, lethality following Nv-tra2 pRNAi appears more pronounced in diploid than in haploid offspring. This diploid lethal effect was also observed following Nv-tra pRNAi, which served as a positive control in our experiments. As diploid embryos from fertilized eggs have a paternal chromosome set in addition to the maternal one, this suggests that either the presence of this paternal chromosome set or the dosage effect resulting from the diploid state is incompatible with the induced male development in N. vitripennis caused by either Nv-tra2 or Nv-tra pRNAi. The role of Nv-tra2 in activating the female sex determination pathway yields more insight into the sex determination mechanism of Nasonia . [ABSTRACT FROM AUTHOR]

The current bumblebee decline leads to inbreeding in populations that fosters a loss of allelic diversity and diploid male production. As diploid males are viable and their offspring are sterile, bumblebee populations can quickly fall in a vortex of extinction. In this article, we investigate for the first time a potential premating mechanism through a major chemical reproductive trait (male cephalic labial gland secretions) that could prevent monandrous virgin queens from mating with diploid males. We focus our study on the cephalic labial gland secretions of diploid and haploid males of Bombus terrestris (L.). Contrary to initial expectations, our results do not show any significant differentiation of cephalic labial gland secretions between diploid and haploid specimens. Queens seem therefore to be unable to avoid mating with diploid males based on their compositions of cephalic labial gland secretions. This suggests that the vortex of extinction of diploid males could not be stopped through premating avoidance based on the cephalic labial gland secretions but other mechanisms could avoid mating between diploid males and queens. [ABSTRACT FROM AUTHOR]

The parasitoid wasp Mastrus ridens (Hymenoptera: Ichneumonidae) is a particularly well-suited biological model to document the history and evolution of populations used in classical biological control, repeatedly moved from laboratory to laboratory worldwide and introduced in various environments. This specialist ectoparasitoid of the codling moth was first imported from Kazakhstan to the USA in the 1990’s, and then sent to Argentina, Chile and New Zealand. More recently, it was sent to Australia and France from other laboratory colonies, and imported again from field collections in Kazakhstan to Chile. Here, we used DNA sequencing to confirm the taxonomic identity of several populations used for biological control worldwide, and developed microsatellite markers for population genetics studies. A multiplex PCR amplifying 11 polymorphic markers was designed. These markers were used to compare the genetic diversity of laboratory and field populations and evaluate genetic differentiation between them. Results showed that laboratory populations with the longest rearing history had lower genetic diversity. Moreover, the genotyping of males with the markers revealed the occurrence of diploid males, which was further confirmed by flow cytometry, suggesting complementary sex determination (CSD) in this species. The percentage of diploid males in the populations ranged from 4% to 25% and were negatively correlated with diversity indices, which is consistent with a single-locus CSD and genetic bottlenecks in laboratory rearings. Molecular tools proved to be suitable and reliable for genetic diversity analyses in M. ridens , and should be implemented more frequently in classical biological control programs. [ABSTRACT FROM AUTHOR]

Sex determination is ruled by haplodiploidy in Hymenoptera, with haploid males arising from unfertilized eggs and diploid females from fertilized eggs. However, diploid males with null fitness are produced under complementary sex determination ( CSD), when individuals are homozygous for this locus. Diploid males are expected to be more frequent in genetically eroded populations (such as islands and captive populations), as genetic diversity at the csd locus should be low. However, only a few studies have focused on the relation between population size, genetic diversity, and the proportion of diploid males in the field. Here, we developed new microsatellite markers in order to assess and compare genetic diversity and diploid male proportion ( DMP) in populations from three distinct habitat types - mainland, island, or captive -, in the parasitoid wasp Venturia canescens. Eroded genetic diversity and higher DMP were found in island and captive populations, and habitat type had large effect on genetic diversity. Therefore, DMP reflects the decreasing genetic diversity in small and isolated populations. Thus, Hymenopteran populations can be at high extinction risk due to habitat destruction or fragmentation. [ABSTRACT FROM AUTHOR]

Presence of diploid males in wild bees reflects inbreeding and provides information about the health status of a colony or population. Detection of diploid males, and discrimination from haploid males and workers, has, however, been limited to molecular diagnostics. Here we present a novel method based on differences in wing shape, e.g., venation patterns in wings. The method is easy to apply and results, for Bombus terrestris, in very high discrimination success. Possible applications of the method are discussed. [ABSTRACT FROM AUTHOR]

Background: Haplodiploidy, where females develop from diploid, fertilized eggs and males from haploid, unfertilized eggs, is abundant in some insect lineages. Some species in these lineages reproduce by thelytoky that is caused by infection with endosymbionts: infected females lay haploid eggs that undergo diploidization and develop into females, while males are very rare or absent. It is generally assumed that in thelytokous wasps, endosymbionts merely diploidize the unfertilized eggs, which would then trigger female development. Results: We found that females in the parasitoid wasp Asobara japonica infected with thelytoky-inducing Wolbachia produce 0.7-1.2 % male offspring. Seven to 39 % of these males are diploid, indicating that diploidization and female development can be uncoupled in A. japonica. Wolbachia titer in adults was correlated with their ploidy and sex: diploids carried much higher Wolbachia titers than haploids, and diploid females carried more Wolbachia than diploid males. Data from introgression lines indicated that the development of diploid individuals into males instead of females is not caused by malfunction-mutations in the host genome but that diploid males are most likely produced when the endosymbiont fails to activate the female sex determination pathway. Our data therefore support a two-step mechanism by which endosymbionts induce thelytoky in A. japonica: diploidization of the unfertilized egg is followed by feminization, whereby each step correlates with a threshold of endosymbiont titer during wasp development. Conclusions: Our new model of endosymbiont-induced thelytoky overthrows the view that certain sex determination mechanisms constrain the evolution of endosymbiont-induced thelytoky in hymenopteran insects. Endosymbionts can cause parthenogenesis through feminization, even in groups in which endosymbiont-diploidized eggs would develop into males following the hosts' sex determination mechanism. In addition, our model broadens our understanding of the mechanisms by which endosymbionts induce thelytoky to enhance their transmission to the next generation. Importantly, it also provides a novel window to study the yet-poorly known haplodiploid sex determination mechanisms in haplodiploid insects. [ABSTRACT FROM AUTHOR]

Background: Single-locus complementary sex determination (sl-CSD), which occurs in some insects of the order Hymenoptera, imposes a heavy genetic load that can drive small populations to extinction. The core process in these species is the development of individuals homozygous at the sex-determining locus into unfit diploid males. The risk of extinction of populations with sl-CSD is theoretically much higher if diploid males are viable and capable of mating but sterile, because diploid males then decrease the reproductive output of both their parents and the females with which they mate. Results: In the parasitoid wasp Venturia canescens (Hymenoptera: Ichneumonidae), diploid males resembled their haploid counterparts in most respects, but their mating success was nevertheless lower than that of haploid males, especially when the two types of males were placed in competition. Furthermore, although diploid males transferred viable sperm during copulation, they sired no daughters: the females with which they mated produced only sons, like virgin females. A simulation model combining behavior, genetics and demography demonstrated that for two alternative hypotheses concerning the fertilization success of diploid sperm, the mating success of diploid males strongly affected population dynamics. Conclusion: The performance of diploid males should be estimated in competitive situations. It is a crucial determinant of the probability of extinction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Hymenoptera show a high propensity for transitions from arrhenotokous reproduction (diploid females develop from fertilized eggs, haploid males from unfertilized eggs) to thelytokous reproduction (diploid females develop from unfertilized eggs). However, the evolution of thelytoky is frequently constrained by the sex determination system. Under the ancestral system, complementary sex determination (CSD), the constraint results from the production of diploid males by thelytokous females. The magnitude of this constraint depends on the cytological mechanism of thelytoky, determining the rate at which thelytokous lines lose heterozygosity and on whether a single locus or multiple loci are involved in CSD. In this review, it is discussed how diploid male production in the case of CSD or other constraints in the case of alternative sex determination systems may impede transitions to thelytoky, but it is also shown that under particular (and presumably rare) circumstances the production of diploid males will promote rather than hamper the evolution of thelytoky. Furthermore, constraints between the evolution of thelytoky and sex determination may be mutual, because once thelytoky has evolved, it can impact on sex determination. Finally, researchers are encouraged to exploit the frequent occurrence of thelytoky as an opportunity to learn more about the mechanisms of sex determination in the Hymenoptera. © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Under the hymenopteran single-locus complementary sex-determination system, production of diploid males results from homozygosity at the sex-determiner locus. This arises when both parents transmit identical alleles at the locus to the offspring. In species reproducing asexually through thelytokous parthenogenesis, production of diploid males may also occur when the sex locus undergoes recombination and becomes homozygous in the offspring. Diploid males represent a substantial genetic load in hymenopteran populations because they often produce unviable sperm or sire sterile triploid female offspring. In the Mediterranean ant Cataglyphis cursor, the queen and workers can produce female offspring through automictic thelytokous parthenogenesis with central fusion, a mode of parthenogenesis that increases homozygosity. We report, for the first time, the presence of about 39 % of colonies producing adult diploid males (seven colonies out of 18). Overall, 8 % of adult males were diploid (12 diploid males out of the 146 males genotyped). Genotyping workers from the seven colonies producing diploid males showed that three diploid males were sons of queens and produced by thelytoky, six were probably sons of workers also produced by thelytoky and three were non-natal. Furthermore, the mating of a diploid male with two virgin queens in the laboratory led to the production of sterile triploid workers, which shows that diploid males in C. cursor are fertile, mate successfully and produce viable and functional but probably sterile female offspring. Because diploid males originate from thelytokous reproduction, they are only produced during sexual production and hence do not impair colony growth, which could explain why they are not removed at early brood stages. [ABSTRACT FROM AUTHOR]

Introduction: Allelic incompatibility between individuals of the same species should select for mate choice based on the genetic make-up of both partners at loci that influence offspring fitness. As a consequence, mate choice may be an important driver of allelic diversity. A complementary sex determination (CSD) system is responsible for intraspecific allelic incompatibility in many species of ants, bees, and wasps. CSD may thus favour disassortative mating and in this, resembles the MHC of the vertebrate immune system, or the self-incompatibility (SI) system of higher plants. Results: Here we show that in the monogamous parasitic wasp Bracon brevicornis (Wesmael), females are able to reject partners with incompatible alleles. Forcing females to accept initially rejected partners resulted in sex ratio distortion and partial infertility of offspring. Conclusions: CSD-disassortative mating occurred independent of kin recognition and inbreeding avoidance in our experiment. The fitness consequences of mate choice are directly observable, not influenced by environmental effects, and more severe than in comparable systems (SI or MHC), on individuals as well as at the population level. Our results thus demonstrate the strong potential of female mate choice for maintaining high offspring fitness in this species. [ABSTRACT FROM AUTHOR]

Inbreeding can lead to the expression of deleterious recessive alleles and to a subsequent fitness reduction. In Hymenoptera, deleterious alleles are purged in haploid males moderating inbreeding costs. However, in these haplodiploid species, inbreeding can result in the production of sterile diploid males. We investigated the effects of inbreeding on the individual and colony level in field colonies of the highly inbred ant Hypoponera opacior. In this species, outbreeding winged sexuals and nest-mating wingless sexuals mate during two separate reproductive periods. We show that regular sib-matings lead to high levels of homozygosity and the occasional production of diploid males, which sporadically sire triploid offspring. On the individual level, inbreeding was associated with an increased body size in workers. On the colony level, we found no evidence for inbreeding depression as productivity was unaffected by the level of homozygosity. Instead, inbred colonies altered their allocation strategies by investing more resources into sexuals than into workers. This shift towards sexual production was due to an increased investment in both males and queens, which was particularly pronounced in the dispersive generation. The absence of inbreeding depression combined with increased reproductive investment, especially in outbreeding sexuals, suggests that these ants have evolved active strategies to regulate the extent and effects of frequent inbreeding. [ABSTRACT FROM AUTHOR]

Complementary sex determination in Hymenoptera implies that heterozygosity at the sex locus leads to the development of diploid females, whereas hemizygosity results in haploid males. Diploid males can arise through inbreeding. In social species, these pose a double burden on colony fitness, from significant reduction in its worker force and through being less viable and fertile than haploid males. Apart from being 'misfits', diploid males are of interest to assess molecular correlates for possibly ploidy-related bionomic differences. Herein, we generated suppression subtractive cDNA libraries from newly emerged haploid and diploid males of the stingless bee Melipona quadrifasciata to enrich for differentially expressed genes. Gene Ontology classification revealed that in haploid males more DEGs were related to stress responsiveness, biosynthetic processes, reproductive processes and spermatogenesis, whereas in diploid ones differentially expressed genes were associated with cellular organization, nervous system development and amino acid transport were prevalent. Furthermore, both libraries contained over 40 % ESTs representing possibly novel transcripts. Quantitative RT-PCR analyses confirmed the differential expression of a representative DEG set in newly emerged males. Several muscle formation and energy metabolism-related genes were under-expressed in diploid males. On including 5-day-old males in the analysis, changes in transcript abundance during sexual maturation were revealed. [ABSTRACT FROM AUTHOR]

Natural enemies may go through genetic bottlenecks during the process of biological control introductions. Such bottlenecks are expected to be particularly detrimental in parasitoid Hymenoptera that exhibit complementary sex determination (CSD). CSD is associated with a severe form of inbreeding depression because homozygosity at one or multiple sex loci leads to the production of diploid males that are typically unviable or sterile. We observed that diploid males occur at a relatively high rate (8-13% of diploid adults) in a field population of Cotesia rubecula in Minnesota, USA, where this parasitoid was introduced for biological control of the cabbage white Pieris rapae. However, our laboratory crosses suggest two-locus CSD in a native Dutch population of C. rubecula and moderately high diploid males survival (approximately 70%), a scenario expected to produce low proportions of diploid males. We also show that courtship behavior of diploid males is similar to that of haploid males, but females mated to diploid males produce only very few daughters that are triploid. We use our laboratory data to estimate sex allele diversity in the field population of C. rubecula and discuss the possibility of a sex determination meltdown from two-locus CSD to effective single-locus CSD during or after introduction. [ABSTRACT FROM AUTHOR]

We used four DNA microsatellite markers and detected diploid males in two out of three species of North American bumble bees from Alberta, Canada. The estimated average proportion of diploid males, φ, in Bombus occidentalis Greene and Bombus perplexus Cresson was ≈3% (n = 112) and 6% (n = 104), respectively. However, there was no significant difference between these estimates. Because no diploid males were detected in the sample (n = 81) of Bombus terricola Kirby, no estimate of φ could be made directly, but the upper limit to φ that would be found in a sample of this size, was ≈4%. The average over the three species was ≈4%. This is the first report of diploid males in natural populations of North American bumble bees. [ABSTRACT FROM AUTHOR]

Thelytokous parthenogenesis, the production of diploid female offspring from unfertilized eggs, can be caused by several cytological mechanisms, which have a different impact on the genetic variation on the offspring. The ponerine ant Platythyrea punctata is widely distributed throughout the Caribbean Islands and Central America and exhibits facultative parthenogenesis. Workers in many field colonies from the Caribbean Islands have identical multilocus genotypes and are thus probably clonal, but the occurrence of males makes an ameiotic mechanism of thelytoky unlikely. To clarify the details of thelytoky in this species we compared the multilocus genotypes of mothers and their offspring in experimental colonies and analyzed the genotypes of haploid and diploid males. Additionally, we screened a large number of field colonies from thelytokous populations for the occurrence of recombination events. According to these data, automixis with central fusion and a reduced recombination rate is the most likely mechanism of thelytoky, as in the Cape honeybee and the ant Cataglyphis cursor. [ABSTRACT FROM AUTHOR]

Discrimination against kin as mates, via genetic or environmentally derived cues of relatedness, can prevent inbreeding and thus enhance individual fitness and promote population survival. Sex in the parasitoid wasp Cotesia glomerata L. (Hymenoptera: Braconidae) is determined by one locus with multiple alleles, a mechanism termed single-locus complementary sex determination (sl-CSD). Under sl-CSD, haploid individuals are males, whereas diploid individuals are females when heterozygous at the sex determination locus but males when homozygous. In species with sl-CSD, inbreeding leads to increased incidence of matings between individuals sharing an allele at the sex locus and thus to increased diploid male production. Diploid males cause an undesirable sex ratio distortion and can be of inferior fitness. To evade these deleterious effects, species with sl-CSD are expected to avoid inbreeding. We investigated whether C. glomerata females discriminate against close kin as mating partners. We performed a mate choice experiment, which allowed us to distinguish between kin discrimination based on the perception of phenotype-related cues and kin discrimination based on the perception of cues associated with the developmental environment. As kin discrimination is often mediated through cuticular hydrocarbons (CHCs), we additionally examined composition of the CHC profiles of males. We found no evidence for discrimination against related or familiar males nor for differences in the CHC profiles of males. These results indicate that kin discrimination is not a relevant inbreeding avoidance strategy in C. glomerata. [ABSTRACT FROM PUBLISHER]

Many social insect species have mating systems or recognition abilities that minimize the chance of inbreeding. In haplodiploid systems, inbreeding is especially costly due to the production of sterile offspring such as diploid males. Diploid males (and their triploid offspring) have been identified in invasive populations of the paper wasp, Polistes dominulus, but to date have not been reported in its native populations. Due to the degree of genetic diversity in the invasive populations, it is unlikely that the production of these genetic 'misfits' is the result of a genetic bottleneck alone, but rather that errors in nestmate recognition may play a role. Here, we investigated sexual interactions and nestmate recognition in male and female P. dominulus. We observed nine types of behavioral interactions (55 h of behavioral observation consisting of 1,514 interactions) from triads of paper wasps composed of one gyne (female) and two males-one nestmate male and one non-nestmate male. The frequency of male- or female-initiated aggressive behavior did not differ between nestmates or non-nestmates. Non-nestmates were more likely to attempt to copulate with the gyne, but successful copulations were very rare and occurred between non-nestmates and nestmates. We discuss these results within the context of invasion biology. [ABSTRACT FROM AUTHOR]

Inbreeding occurs in numerous animal and plant species. In haplodiploid hymenopterans with the widespread single locus complementary sex determination, the frequency of diploid males, which are produced at the expense of females, is increased under inbreeding. Diploid males in species of bees, ants and wasps are typically either unviable or effectively sterile and thus impose a severe genetic load on populations. However, a recent study indicated that diploid males can be reproductive in the gregarious parasitoid wasp Cotesia glomerata, effectively reducing the diploid male load. To understand the role of inbreeding as a potential selective pressure towards the evolution of diploid male fertility, we genotyped specimens collected in the field at four locations using microsatellite markers to estimate the ratio of sibling matings under natural conditions. Results show that more than half of all matings involved siblings. We argue that the frequent occurrence of inbreeding has driven the evolution of diploid male fertility. [ABSTRACT FROM AUTHOR]

Cardinium is a bacterial symbiont infecting many species of arthropods, and is associated with manipulation of host reproduction. Cardinium is the causal agent of asexual reproduction, or thelytoky, in the chalcidoid parasitoid wasp Encarsia hispida. Feeding antibiotics to the infected adult females results in uninfected male offspring. Here, we show that these males are diploid. Diploid males are extremely unusual in the large hymenopteran superfamily Chalcidoidea, and, to our knowledge, have never before been associated with symbiont infection in this group. These findings indicate that at least in E. hispida, diploidy restoration is a necessary condition but not sufficient to elicit female development. Cardinium is required to feminize diploid male embryos and thus must interact with elements of the host sex determination system. In addition, our data suggest that Cardinium is necessary for the fertility of E. hispida; antibiotic curing of Cardinium reduces offspring production of adult females.Heredity (2009) 102, 365–371; doi:10.1038/hdy.2008.135; published online 4 February 2009 [ABSTRACT FROM AUTHOR]

In the Hymenoptera, single locus complementary sex determination ( sl-CSD) describes a system where males develop either from unfertilized haploid eggs or from fertilized diploid eggs that are homozygous at a single polymorphic sex locus. Diploid males are often inviable or sterile, and are produced more frequently under inbreeding. Within families where sl-CSD has been demonstrated, we predict that sl-CSD should be more likely in species with solitary development than in species where siblings develop gregariously (and likely inbreed). We examine this prediction in the parasitoid wasp genus Cotesia, which contains both solitary and gregarious species. Previous studies have shown that sl-CSD is absent in two gregarious species of Cotesia, but present in one gregarious species. Here, we demonstrate CSD in the solitary Cotesia vestalis, using microsatellite markers. Diploid sons are produced by inbred, but not outbred, females. However, frequencies of diploid males were lower than expected under sl-CSD, suggesting that CSD in C. vestalis involves more than one locus. [ABSTRACT FROM AUTHOR]

Owing to habitat loss populations of many organisms have declined and become fragmented. Vertebrate conservation strategies routinely consider genetic factors, but their importance in invertebrate populations is poorly understood. Bumblebees are important pollinators, and many species have undergone dramatic declines. As monoandrous social hymenopterans they may be particularly susceptible to inbreeding due to low effective population sizes. We study fragmented populations of a bumblebee species, on a model island system, and on mainland Great Britain where it is rare and declining. We use microsatellites to study: population genetic structuring and gene flow; the relationships between genetic diversity, population size and isolation; and frequencies of (sterile) diploid males — an indicator of inbreeding. We find significant genetic structuring (θ = 0.12) and isolation by distance. Populations > 10 km apart are all significantly differentiated, both on oceanic islands and on the mainland. Genetic diversity is reduced relative to closely related common species, and isolated populations exhibit further reductions. Of 16 populations, 10 show recent bottlenecking, and 3 show diploid male production. These results suggest that surviving populations of this rare insect suffer from inbreeding as a result of geographical isolation. Implications for the conservation of social hymenopterans are discussed. [ABSTRACT FROM AUTHOR]

Summary 1. Inbreeding can negatively affect various fitness components. Here we examine how immune response and body size of a social insect are affected by inbreeding, sex and ploidy. 2. In the bumble-bee, Bombus terrestris (L.), the offspring of colonies resulting from brother–sister matings were compared with that of outbred colonies. Immune response was measured as the degree of encapsulation of a novel antigen, body size as the length of the radial cell in the forewings. 3. Inbreeding affected neither immune response nor body size in either workers or haploid males under laboratory conditions. However, fitness characteristics varied significantly among maternal families and colonies. The lack of detectable inbreeding depression for two fitness components might help explain why B. terrestris is a good colonizer in nature. 4. In addition, sex and ploidy strongly affected the fitness components studied: diploid males had a significantly lower immune response than haploid males, who in turn had a significantly lower immune response than workers of the same colony. The body size of diploid males was intermediate between the body size of workers and haploid males. [ABSTRACT FROM AUTHOR]

Beyond helping the queen's reproductive function, the worker caste of Polistes wasps is expected to have an alternative reproductive strategy; to become a replacement queen, following copulation with early males that emerge along with the first brood workers. We analyzed genotypes and chromosome numbers of the early males in a natural population of P. chinensis antennalis. The frequency of early-male-producing colonies within a population was 5.2% (4/77) in 1993 through 1995. The numerical sex ratios in the 4 colonies for the 3 years and another early male-producing colony in 1999 were 1:1. For one early-male producing colony in 1995, we genotyped 31 females and all 128 males. All 31 genotyped females out of 67 emerged females showed heterozygosity and 69 out of 128 genotyped males were heterozygous; the remaining 59 males were homozygous or hemizygous. The ratio between the number of females and diploid males in this colony was 67:69, which is almost identical with one-to-one ratio. The cytological analysis of male chromosome for one early-male producing colony in 1999 revealed that the early males laid by a queen had 46 chromosomes, while worker laid males had 23. Our results revealed that the early males in this species are diploid males and eventually sterile. Secondly, the single locus complementary sex determination model is most plausible to explain the diploid male production in this species. [ABSTRACT FROM AUTHOR]

In social insect colonies, male production may involve conflicts over the sex ratio, worker vs. queen reproduction, and each queen's contribution to the males when there are multiple queens. We examined male production in the swarm-founding, multiple-queened wasp, Polybioides tabidus , for which previous work suggested worker control of the sex ratios. We found that queens produced the males in accord with the collective worker preference. We also found that diploid males were produced, but only in association with haploid males. Simulations show they should have been produced in other colonies as well and their absence indicates that they were killed in some of these other colonies. The pattern of their removal indicates that P. tabidus cannot distinguish diploid from haploid males, and that haploid males would have been removed from these colonies too. This provides evidence that the workers are able to manipulate male production when collective preferences dictate. [ABSTRACT FROM AUTHOR]

We constructed a linkage map of Bombus terrestris (Hymenoptera, Apidae) phase unknown. The map contains 79 markers (six microsatellite and 73 RAPD markers) in 21 linkage groups and spans over 953.1 cM. The minimal recombinational size of the B. terrestris genome was estimated to be 1073 cM. Using flow cytometry, the physical size of the haploid genome of B. terrestris was calculated to be 274 Mb. This is the second linkage map for a social insect species. Bombus terrestris has on average five times less recombinational events per kb than the honey bee Apis mellifera. Male haploidy, chromosome size, and eusociality can now be excluded as reasons for the high recombination frequency of Apis mellifera. Finally, the sex determination locus of B. terrestris was placed on the map using bulked segregant analysis. [ABSTRACT FROM AUTHOR]

The Vespinae wasps ( Vespa, Provespa, Dolichovespula, and Vespula) are an excellent group for testing kin selection predictions. There is considerable variation in kin structure and conflict resolution in a group of known phylogeny where all species have a similar basic biology: morphologically distinct queens and workers, and annual nests headed by a single queen. Vespine kin structure can be described by a single variable "effective paternity", which is defined by queen mating frequency and sperm use. Low effective paternity, which causes high worker relatedness, is basal in the group ( Vespa, Dolichovespula), with high paternity (ca >2) restricted to Vespula whose queens mate more and use sperm more equally. Paternity variation correlates well with observed patterns of reproduction and conflict. As predicted by theory, male production by workers is common in Dolichovespula but not in Vespula where worker policing occurs ( Vespula vulgaris). The theory is also supported by intercolony variation in Dolichovespula, with facultative worker policing ( Dolichovespula saxonica) and sex allocation biasing by workers ( D. arenaria) occurring in response to paternity. In addition, queen loss in reproductive colonies of nine species is negatively correlated with paternity, in line with the prediction that matricide is only expected at low paternity. However, paternity does not explain the reproductive characteristics of Vespa crabro. Although paternity in V. crabro is only 1.1, the same as the mean in six Dolichovespula species, its reproductive behaviour is different from Dolichovespula. More like Vespula, V. crabro has worker policing, workers that rarely have active ovaries, and little queen loss in reproductive-phase colonies. [ABSTRACT FROM AUTHOR]

Some Hymenoptera have single locus Complementary Sex Determination (sl-CSD); heterozygous individuals are female (diploid fertilised eggs) and hemizygous individuals are male (haploid unfertilised eggs). Through inbreeding homozygous diploids can arise which develop into males that are often sterile and sometimes inviable. The phylogenetic distribution of sl-CSD is unclear. In this study, we used inbred crosses to demonstrate that the parasitoid wasp Venturia canescens (Gravenhorst) has sl-CSD. Diploid males were detected through heterozygosity at a marker locus (Virus Like Particle protein). They were fully viable at 20°, 25° and 30°C as the sex ratios of inbred crosses did not deviate from controls after adjustment for diploid male frequency. These results further confirm the existence of sl-CSD in the family Ichneumonidae. [ABSTRACT FROM AUTHOR]

The diploid chromosome number in the female formicine ant, Lasius sakagamii, is 30, while the haploid number in normal males is 15. Six of the 30 studied colonies (20%), however, contained many diploid males. Although the body size of the diploid males was, on average, larger than that of the haploid males, both types of males showed normal external and internal morphologies. Furthermore, there was no reduction in chromosome numbers in either diploid or haploid males during spermatogenesis. The spermatid nuclei of diploid males, however, were significantly larger than those of haploid males, and the amount of DNA in the diploid males, as measured by flow cytometry, was twice as much as that in the haploid males, clearly indicating that diploid males produce diploid sperm. [ABSTRACT FROM AUTHOR]

AbstractColonies of the European hornet, Vespa crabro, are typically founded by a single queen mated to a single male. From the resulting colony relatedness pattern we predicted strong worker–queen conflict over male production where both the workers and the queen attempt to produce the colony’s males. To test for this conflict, male production was studied in 15 hornet nests using a combination of DNA microsatellite analysis (282 males), worker ovary dissections (500 workers from eight nests) and 50 h of observation (four nests). In contrast to our prediction, the data show that hornet males are queens’ sons, that workers never attempt to lay eggs, rarely have activated ovaries, and that there is no direct aggression between the queen and the workers. This contrasts with other data for vespine wasps, which support relatedness predictions. Dolichovespula arenaria has the same kin structure as V. crabro and workers produce males in many colonies. The similarity between these two species makes it difficult to explain why workers do not reproduce in V. crabro. Self-restraint is expected if worker reproduction significantly reduces colony productivity but there is no obvious reason why this should be important to V. crabro but not to D. arenaria. Alternatively, queen control may be important. The absence of expressed queen–worker conflict rules out physical control. Indirect pheromonal control is a possibility and is supported by the occurrence of royal courts and queen pheromone in Vespa but not Dolichovespula. Pheromonal queen control is considered evolutionarily unstable, but could result from a queen–worker arms race over reproductive control in which the queen is ahead. The genetic data also revealed diploid males in one colony, the first example in the vespine wasps, and two colonies with double matrilines, suggesting that occasional usurpation by spring queens occurs. [ABSTRACT FROM AUTHOR]

In many hymenopterans, sex is determined at a single polymorphic ‘sex locus’. Individuals that are heterozygous at this locus develop as females whereas homozygotes and hemizygotes develop as diploid and haploid males, respectively. Diploid males are developmentally inviable or sterile, and the likelihood of diploid male production depends in large part on allelic diversity at the sex locus. We assessed sex allele diversity within and among five U.S. populations of the parasitoid wasp Bracon hebetor using a series of crosses between isofemale lines. The study included two laboratory populations originating in Wisconsin, two field populations originating in Kansas and California, and a population purchased from a commercial insectary. Given the number of isofemale lines that we established, the maximum number of alleles that we could detect per population was 10. The number of sex alleles identified within populations ranged between three or four (for the two Wisconsin populations) and nine (for the California population). Subsampling three or four alleles from each population for between-population crosses led to identification of 12 alleles. Of these, four were unique to the California population, three were unique to one other population each, and one was found in only two populations. Extrapolation of the relationships between the subsampled lines led to a total estimate of 20 alleles within our lines. The relatively high allele diversity in the field and commercial insectary populations suggests that the sex determination load is relatively low in B. hebetor, and the differences in allele profiles between populations suggest that interpopulation dispersal can increase sex allele diversity within populations. [ABSTRACT FROM AUTHOR]

It is suggested that the evolution of polyandry by social hymenopteran queens is caused by colony-level selection, either because polyandry affects the distribution of non-functional diploid males in colonies (the load hypothesis) or because it increases the genetic diversity of the worker force (the diversity hypothesis). Diploid males that arise from fertilized eggs thai are homozygous at the sex-determining locus (or loci) are inviable or infertile. Models of the load hypothesis analysed in this study suggest that slow growth and high mortality of colonies with diploid males favour single mating by queens. The longer the period ol colony growth (the period with selective differences) and the heavier the mortality, the stronger is the selection for monandry. The load hypothesis also predicts an association between monogyny and monandry. In contrast, the diversity hypothesis predicts an association between monogyny and polyandry, as multiple mating offers a way by which a monogynous colony could increase its genetic heterogeneity. Up to 10% of all males are diploid in species and populations of Formica ants with highly polygynous colonies (F. aqnilonia, F. polyctena, F. truncorum). No diploid males were found in two mainly monogynous species (F. exsecta, F. pratensis) which also have a high level of monandry. This agrees with the prediction of the load hypothesis. A surprisingly high frequency of nests in three other species (F. rufa, F. lugubris, F. truncorum) with monogynous/weakly polygynous colonies produce diploid males, although the frequency varies among their populations. In extreme cases half of the diploid sexuals within a colony develop into males. Diploid males have been observed only at the time of normal sexual production. It seems that at other times they are eliminated at early developmental stages, so as to minimize the load on the colony. [ABSTRACT FROM PUBLISHER]

In B. terrestris diploid males develop normally into adults (Duchateau et al., 1994). The diploid males are similar in appearance to the haploid males, except that they are smaller. The size of the testis of diploid males, relative to the length of the radial cell, is smaller than that of haploid males. There is overlap in the frequency distribution with respect to body size and testis size. The spermatozoa of diploid males are larger than those of the haploids and the vasa deferentia contain fair less spermatozoa than those of haploid males of the same age. Countings and measurements of the spermatozoa, therefore, can give the best indication about the ploidy of the males. Diploid males are successful in mating. They mate at a younger age than haploid males and they die sooner. The number of vial offspring of diploid males, however, is very low. No queen that mated with a diploid male produced a colony, but a few queens did produce some progeny. These might have been triploid males and workers. In B. terrestris higher ploidy results in smaller individuals, whereas in several other species of the Hymenoptera it has been found to result in larger individuals. [ABSTRACT FROM AUTHOR]