Sex Locus Research Articles

A new robust codominant sex-linked STS marker for asparagus

A new sex-linked codominant STS marker useful for discriminating between normal males (Mm), supermales (MM) and females (mm) is described. Primers for this marker were designed based on a reference sequence provided by an internationally funded asparagus genome sequencing consortium. According to this reference sequence, the marker is located approximately 1.3 Kb downstream from the 5’ end of the putative non-recombining sex determination region. Four female (mm) plants lack a 26 bp sequence that is present in four supermale (MM) plants aligned to the reference sequence. The primer combination RM17 surrounds this region and amplifies a 189 bp marker in plants with the m allele and a 215 bp marker in plants with the M allele. Serial dilutions of Qiagen-purified DNA from spears indicated both bands could be resolved with template concentrations ranging from 0.5 to 2000 ng of template per 10 ul reaction. We have tested this marker in numerous plants from UC Riverside asparagus germplasm, which includes material derived from ‘Mary Washington’ (selections from Hanna, Ellison and Takatori) and old Dutch and German cultivars. We found one diploid plant with an apparent crossover between the marker and the sex locus, but plan to confirm this with a new test cross. An initial survey of plants from the UC Riverside Third International Cultivar Trial indicated that at least one possible crossover event between the marker and the sex locus likely occurred in an ancestor of ‘Purple Passion’, ‘Sweet Purple’, ‘NJ1016’ and ‘Pacific Purple’. These cultivars all share ‘Violetto d'Albenga’ as a common ancestor, and this marker highlights the divergence between the tetraploid and diploid Asparagus varieties. This marker is simple to use and very robust.

Genetic Diversity in the Progeny of Commercial Australian Queen Honey Bees (Hymenoptera: Apidae) Produced in Autumn and Early Spring.

Honey bee [Apis mellifera L. (Hymenoptera: Apidae)] queens are polyandrous, mating with an average 12 males (drones). Polyandry has been shown to confer benefits to queens and the colonies they head, including avoidance of inviable brood that can arise via sex locus homozygosity, increased resilience to pests and pathogens, and increased survival and productivity, leading to improved colony-level fitness. Queens with an effective mating frequency (ke) greater than 7 are considered adequately mated, whereas queens that fall below this threshold head colonies that have increased likelihood of failure and may be less productive for beekeepers. We determined ke in queens produced in early Spring and Autumn by five Australian commercial queen producers to determine whether the queens they produced were suitably mated. Drone populations are low at these times of year, and therefore, there is an increased risk that queens would fall below the ke > 7 threshold. We found that 33.8% of Autumn-produced queens did not meet the threshold, whereas 93.8% of Spring queens were adequately mated. The number of colonies contributing drones to the mating pool was similarly high in both seasons, suggesting that although many colonies have drones, their numbers may be decreased in Autumn and management strategies may be required to boost drone numbers at this time. Finally, queens had similar levels of homozygosity to workers, and inbreeding coefficients were very low, suggesting that inbreeding is not a problem.

Sex-linked markers in pistachio

DNA markers have potential to improve the efficiency of conventional plant breeding via marker-assisted selection (MAS). Therefore, MAS can be very effective in pistachio to eliminate undesirable progenies at early stage which can save time, cost, labor, and land. This study aimed to develop sex-linked single nucleotide polymorphism (SNP) markers for MAS, to understand sex determination system and to determine the position of sex locus in pistachio. Eight male and eight female F1 progenies from 'Siirt' × 'Bagyolu' cross, along with the parents, were subjected to RAD (restriction site-associated DNA) sequencing and 38 SNP loci were detected as putative sex-associated ones in pistachio. Validation was performed by SNaPshot minisequencing analysis in mature F1 progenies and in a wide germplasm collection. Seventeen loci successfully distinguished sex in pistachio. To ascertain cost-effective application of markers in a breeding program, high-resolution melting (HRM) analysis was performed; and 10 markers were found to perfectly separate sexes in pistachio. Because of the female heterogamety in all sex-linked SNP loci, pistachio has a ZZ/ZW sex determination system. The sex locus and sex-linked SNP markers were co-segregated in the center of the chromosome at a distance of 30.8 and 31.3 cm, respectively. This study presents sex-linked markers for MAS as well as valuable information about the sex chromosome and sex locus position in pistachio.

Alternative patterns of sex chromosome differentiation in Aedes aegypti (L)

BackgroundSome populations of West African Aedes aegypti, the dengue and zika vector, are reproductively incompatible; our earlier study showed that divergence and rearrangements of genes on chromosome 1, which bears the sex locus (M), may be involved. We also previously described a proposed cryptic subspecies SenAae (PK10, Senegal) that had many more high inter-sex FST genes on chromosome 1 than did Ae.aegypti aegypti (Aaa, Pai Lom, Thailand). The current work more thoroughly explores the significance of those findings.ResultsIntersex standardized variance (FST) of single nucleotide polymorphisms (SNPs) was characterized from genomic exome capture libraries of both sexes in representative natural populations of Aaa and SenAae. Our goal was to identify SNPs that varied in frequency between males and females, and most were expected to occur on chromosome 1. Use of the assembled AaegL4 reference alleviated the previous problem of unmapped genes. Because the M locus gene nix was not captured and not present in AaegL4, the male-determining locus, per se, was not explored. Sex-associated genes were those with FST values ≥ 0.100 and/or with increased expected heterozygosity (Hexp, one-sided T-test, p < 0.05) in males. There were 85 genes common to both collections with high inter-sex FST values; all genes but one were located on chromosome 1. Aaa showed the expected cluster of high inter-sex FST genes proximal to the M locus, whereas SenAae had inter-sex FST genes along the length of chromosome 1. In addition, the Aaa M-locus proximal region showed increased Hexp levels in males, whereas SenAae did not. In SenAae, chromosomal rearrangements and subsequent suppressed recombination may have accelerated X-Y differentiation.ConclusionsThe evidence presented here is consistent with differential evolution of proto-Y chromosomes in Aaa and SenAae.

Extreme polyandry aids the establishment of invasive populations of a social insect.

Although monandry is believed to have facilitated the evolution of eusociality, many highly eusocial insects have since evolved extreme polyandry. The transition to extreme polyandry was likely driven by the benefits of within-colony genetic variance to task specialization and/or disease resistance, but the extent to which it confers secondary benefits, once evolved, is unclear. Here we investigate the consequences of extreme polyandry on the invasive potential of the Asian honey bee, Apis cerana. In honey bees and other Hymenoptera, small newly founded invasive populations must overcome the genetic constraint of their sex determination system that requires heterozygosity at a sex-determining locus to produce viable females. We find A. cerana queens in an invasive population mate with an average of 27 males (range 16-42) that would result in the founding queen/s carrying 75% of their source population's sex alleles in stored sperm. This mating frequency is similar to native-range Chinese A. cerana (mean 29 males, range 19-46). Simulations reveal that extreme polyandry reduces the risk, relative to monandry or moderate polyandry, that colonies produce a high incidence of inviable brood in populations that have experienced a founder event, that is, when sex allele diversity is low and/or allele frequencies are unequal. Thus, extreme polyandry aids the invasiveness of A. cerana in two ways: (1) by increasing the sex locus allelic richness carried to new populations with each founder, thereby increasing sex locus heterozygosity; and (2) by reducing the population variance in colony fitness following a founder event.

Variation of the meiotic recombination landscape and properties over a broad evolutionary distance in yeasts.

Meiotic recombination is a major factor of genome evolution, deeply characterized in only a few model species, notably the yeast Saccharomyces cerevisiae. Consequently, little is known about variations of its properties across species. In this respect, we explored the recombination landscape of Lachancea kluyveri, a protoploid yeast species that diverged from the Saccharomyces genus more than 100 million years ago and we found striking differences with S. cerevisiae. These variations include a lower recombination rate, a higher frequency of chromosomes segregating without any crossover and the absence of recombination on the chromosome arm containing the sex locus. In addition, although well conserved within the Saccharomyces clade, the S. cerevisiae recombination hotspots are not conserved over a broader evolutionary distance. Finally and strikingly, we found evidence of frequent reversal of commitment to meiosis, resulting in return to mitotic growth after allele shuffling. Identification of this major but underestimated evolutionary phenomenon illustrates the relevance of exploring non-model species.

Development and linkage mapping of novel sex-linked markers for marker-assisted cultivar breeding in pistachio (Pistacia vera L.)

The dioecious character of Pistacia vera L (the pistachio tree) limits its breeding capacity. Thus, early stage selection of males can save time, labor, and land. This study aimed to develop sex-linked single nucleotide polymorphism (SNP) markers, together with expressed sequence tag-derived simple sequence repeats (EST-SSRs), to determine position of the sex locus in pistachio by constructing a linkage map of its sex chromosome for the first time. Nine novel sex-linked SNP markers were successfully identified by SNaPshot minisequencing analysis of 25 SNP loci from 17 restriction site-associated DNA (RAD) reads in 309 individuals. All nine markers were heterozygous in females and homozygous in males supporting a ZW/ZZ sex determination system in pistachio. A total of 105 segregating SSRs and sex-linked markers were used to identify the sex chromosome and the position of the sex locus through analysis of a Siirt × Bagyolu F1 population with 122 progenies. Of these 105 markers, four common and four paternal SSRs were mapped onto the sex chromosome, along with the phenotypic sex locus and sex-linked markers. The resulting consensus map had a total length of 65.19 cM. The sex locus and sex-linked SNP markers were located in the center of the chromosome at a distance of 31.86 and 31.92 cM, respectively. This study presents valuable information about the sex chromosome and sex locus position as well as novel polymorphic EST-SSRs and nine sex-linked SNP markers in pistachio.

Development and Characterization of Molecular Markers Associated with Female Plants in Muscadine Grape

Muscadine (Vitis rotundifolia Michx.) vines may be male (M), female (F), or hermaphroditic (H). Male flowers have only filaments and anthers, whereas female and hermaphroditic flowers are morphologically perfect. Female flowers are distinguished from hermaphroditic flowers by their reflexed stamens (as opposed to upright) and nonfunctional pollen. Primers derived from previously identified candidate genes located at the sex locus of Vitis vinifera L. were used to generate amplicons from M, F, and H muscadine cultivars. Sequence analysis of the amplicons revealed insertion/deletion (indel) polymorphisms in a trehalose-6-phosphate phosphatase (TPP) gene (VR006) and a WRKY transcription factor 21 gene (VR009). Primers were designed to create diagnostic markers for each indel polymorphism. Associations between the marker alleles and the plant sex trait were examined in a wide range of muscadine germplasm and in segregating populations derived from F × H, F × M, and H × H crosses. VR006 produced a codominant marker that was able to differentiate the female-associated allele from the male- and hermaphroditic-associated alleles. The marker was able to detect female plants and will be suitable for screening breeding program progenies. VR009 was able to detect the presence of the female allele in most germplasm, but a crossover event appears to have separated the marker from the sex locus in some germplasm. As shown in previous muscadine genetic studies, H × H-derived populations produced male seedlings. Marker analysis of these populations indicates that male flowers only occur in seedlings which are heterozygous for F- and H-associated marker alleles and inheritance of flower type in muscadine remains unclear.

The inhibition of mating in Phycomyces blakesleeanus by light is dependent on the MadA-MadB complex that acts in a sex-specific manner

Light is an environmental signal that influences reproduction in the Mucoromycotina fungi, as it does in many other species of fungi. Mating in Phycomyces blakesleeanus is inhibited by light, but the molecular mechanisms for this inhibition are uncharacterized. In this analysis, the role of the light-sensing MadA-MadB complex in mating was tested. The MadA-MadB complex is homologous to the Neurospora crassa White Collar complex. Three genes required for cell type determination in the sex locus or pheromone biosynthesis are transcriptionally-regulated by light and are controlled by MadA and MadB. This regulation acts through the plus partner, indicating that the inhibitory effect of light on mating is executed through only one of the two sexes. These results are an example whereby the mating types of fungi have acquired sex-specific properties beyond their role in conferring cell-type identity, and provide insight into how sex-determining chromosomal regions can expand the traits they control.

VviAPRT3 and VviFSEX: Two Genes Involved in Sex Specification Able to Distinguish Different Flower Types in Vitis.

Vitis vinifera vinifera is a hermaphrodite subspecies, while its ancestor, Vitis vinifera sylvestris, is dioecious. We have identified two genes that together allow the discrimination between male, female and hermaphrodite Vitis plants. The sex locus region on chromosome 2 was screened resulting in the discovery of a new gene, VviFSEX. The same screening revealed another gene, VviAPRT3, located in the sex region, that be used as a sex marker. Both genes are good candidates to be involved in flower sex differentiation in grapevine. To assess their role in sex specification, spatial and temporal expression analysis was performed. The expression of VviFSEX is detected in petals, stamens and carpel primordia of all flower types, making its putative function unclear; however, female plants display a single allele for this gene, while male and hermaphrodites display two alleles. On the other hand, the specific expression of VviAPRT3 in the carpel primordial of male plants suggests a possible role in the abortion of pistil structures. We propose a model to explain the carpel abortion in male flowers and the absence of stamen viability in female flowers. In addition, this work reinforces the presence of a sex locus on Vitis chromosome 2.

Psychosocial Correlates of Dietary Supplement Use: Results from the National Survey of Midlife Development in the United States

ABSTRACTDrawing on data gathered in the National Survey of Midlife Development in the United States, this study examined internal and external locus of control, self-esteem, neuroticism, perceived health status, uniqueness, and somatic amplification as correlates of dietary supplement use. With sex, race, and age measures also included in the study, bivariate analyses showed greater supplement use among women and older respondents as well as those scoring higher on internal locus of control, self-esteem, perceived health status, and somatic amplification. Regression analyses identified sex and internal locus of control as the strongest predictors. Interactions between age and external locus of control also emerged.

An invasive social insect overcomes genetic load at the sex locus.

Some invasive hymenopteran social insects found new populations with very few reproductive individuals. This is despite the high cost of founder effects for such insects, which generally require heterozygosity at a single locus-the complementary sex determiner, csd-to develop as females. Individuals that are homozygous at csd develop as either infertile or subfertile diploid males or not at all. Furthermore, diploid males replace the female workers that are essential for colony function. Here we document how the Asian honey bee (Apis cerana) overcame the diploid male problem during its invasion of Australia. Natural selection prevented the loss of rare csd alleles due to genetic drift and corrected the skew in allele frequencies caused by founder effects to restore high average heterozygosity. Thus, balancing selection can alleviate the genetic load at csd imposed by severe bottlenecks, and so facilitate invasiveness.

The sex locus is tightly linked to factors conferring sex-specific lethal effects in the mosquito Aedes aegypti.

In many taxa, sex chromosomes are heteromorphic and largely non-recombining. Evolutionary models predict that spread of recombination suppression on the Y chromosome is fueled by the accumulation of sexually antagonistic alleles in close linkage to the sex determination region. However, empirical evidence for the existence of sexually antagonistic alleles is scarce. In the mosquito Aedes aegypti, the sex-determining chromosomes are homomorphic. The region of suppressed recombination, which surrounds the male-specific sex-determining gene, remains very small, despite ancient origin of the sex chromosomes in the Aedes lineage. We conducted a genetic analysis of the A. aegypti chromosome region tightly linked to the sex locus. We used a strain with an enhanced green fluorescent protein (EGFP)-tagged transgene inserted near the male-determining gene to monitor crossing-over events close to the boundary of the sex-determining region (SDR), and to trace the inheritance pattern of the transgene in relation to sex. In a series of crossing experiments involving individuals with a recombinant sex chromosome we found developmental abnormalities leading to 1:2 sex biases, caused by lethality of half of the male or female progeny. Our results suggest that various factors causing sex-specific lethal effects are clustered within the neighborhood of the SDR, which in the affected sex are likely lost or gained through recombination, leading to death. These may include genes that are recessive lethal, vital for development and/or sexually antagonistic. The sex chromosome fragment in question represents a fascinating test case for the analysis of processes that shape stable boundaries of a non-recombining region.

Genetic structure of island and mainland populations of a Neotropical bumble bee species

As a consequence of founder effects, small population size and demographic constraints, island populations are often characterized by low genetic diversity and high inbreeding. The effects of inbreeding are more pronounced in haplo-diploid insects like bees than in similar diploid species, because their method of sex determination requires heterozygosity at a sex locus. Inbreeding leads to homozygosity at the sex locus and the production of non-viable diploid males. This means that island populations of bees are particularly prone to extinction. Here we determine the levels of diversity and isolation between islands and mainland populations of the bumble bee Bombus morio in southeast Brazil. We analyzed 659 individuals from 24 populations, sequencing two mitochondrial genes (COI and Cytb) and genotyping all individuals at 14 microsatellite loci. Surprisingly, genetic diversity was high and genetic isolation was low in all populations except Teodoro Sampaio (mainland) and Ilha da Vitoria (island). Genetic diversity is not significantly correlated with island area, but is lower in populations that are more distant from the mainland. Except perhaps for Ilha da Vitoria, we suggest that the island populations are unlikely to go extinct due to genetic factors. Finally, based on its genetic distance from all other populations, we identify a putative new subspecies in the Teodoro Sampaio region.

Long Term Clinical Outcome of Hematopoietic Cell Transplantation for Intermediate to High-Risk Adult AML in Complete Remission; Can We Enhance the Survival Outcome Using Alternative Donor Types?

Background: Standard therapy for intermediate to high-risk acute myeloid leukemia (AML) consists of several hematopoietic cell transplantation (HCT) strategies including autologous-HCT (AUTO), allogeneic-HCT from matched-sibling donor (MSD) or well-matched unrelated donor (WM-URD). When a conventional donor is not available, HCT from partially-matched unrelated donor (PM-URD) or familial mismatched/haploidentical transplantation (FMMT) or umbilical cord blood transplantation is also considered for an alternative choice. Although HCT outcomes of those alternative strategies are advancing with optimization of pre-conditioning regimens with immunosuppressive agents, there are still subjects to debate. We tried to analyze the long-term HCT outcomes according to the donor types including FMMT and PM-URD as an alternative choice.Methods: We enrolled 561 AML patients (median 41 years old, range: 16-68) in complete remission (CR) who were transplanted in Catholic BMT Center in Korea from 2002 to 2013. Patients in at least second CR were excluded. All patients presented intermediate to high-risk karyotype according to the NCCN guidelines, and all of the patients received standard 3+7 chemotherapy followed by consolidation chemotherapy. In the absence of MSD and WM-URD, we allocated PM-URD or AUTO as an alternative choice first, and then FMMT was considered. We divided patients according to the 5 donor types (i.e. MSD (n=252), WM-URD (n=112), PM-URD (n=41), AUTO (n=104), and FMMT (n=52)), and survival outcomes with the cumulative incidence of relapse (CIR), non-relapse mortality (NRM), acute/chronic GVHD and CMV reactivation were analyzed.Results: Engraftment was successful and showed similar recovery pattern in all donor types. Our data showed mismatch in ABO, sex, and certain HLA locus was not influential, and stem cell source and conditioning-intensity were not also influential for survival outcome and incidence of GVHD. After median follow-up of 54.3 month (range: 6.6-145.6), MSD, WM-URD and FMMT showed similar 5-year OS around 62% except for AUTO at 47.4% and PM-URD at 36.7%. DFS at 5-years was 59% for MSD, 56% for WM-URD, 62% for FMMT, 44.3% for AUTO, and 33.5% for PM-URD. Five-year CIR rate was highest in AUTO (50.3%) followed by PM-URD (33.1%) and WM-URD (29.8%). Lower CIR-rate was identified in MSD (22.4%) and FMMT (21.4%), and the lowest NRM rate was identified in AUTO subgroup (5.1%) followed by WM-URD (11.4%), FMMT (15.6%) and MSD (18.0%). PM-URD showed the highest NRM rate (33.3%) with higher incidence (26.7%) of Gr°Ã3 acute GVHD compared to 9.3% of MSD. Incidence of chronic GVHD was not significantly different. In adverse-risk subgroup, 5-year OS of MSD, WM-URD, and FMMT was 46%, 47%, and 58% respectively, while AUTO and PM-URD was 11% and 0%, which was caused by significantly higher CIR rate of 79.7% and 83.5%, respectively, compared to 31.1% of MSD. In intermediate-risk subgroup, 5-year OS of AUTO (55.2%) was not inferior to that of MSD (67.2%, p =0.330) or FMMT (64.9%, p =0.451), which showed the highest CIR rate (42.8%) and the lowest NRM (5.4%). PM-URD also showed highest NRM (39.4%) with high incidence (27.3%) of Gr°Ã3 acute GVHD.Conclusions: FMMT should be considered prior to PM-URD in intermediate to adverse-risk AML and GVHD prophylaxis should be intensified when we have to use PM-URD. AUTO might be considered in intermediate-risk AML in selected patients and prospective study should validate the utility of FMMT or AUTO in addition to the conventional donor types. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Genomic Instability of the Sex-Determining Locus in Atlantic Salmon (Salmo salar).

Atlantic salmon and rainbow trout, like other members of the subfamily Salmoninae, are gonochoristic with male heterogamety. The finding that sex-linked genetic markers varied between species suggested that the sex-determining gene differs among salmonid species, or that there is one sex-determining gene that has the capacity to move around the genome. The discovery of sdY, the sex-determining gene in rainbow trout, and its presence in many male salmonids gave support to the latter. Additional evidence for a salmonid-specific, sex-determining jumping gene came from the mapping of the sex-determining locus to three different chromosomes in Tasmanian male Atlantic salmon lineages. To characterize the sex-determining region, we isolated three sdY containing BACs from an Atlantic salmon male library. Sequencing of these BACs yielded two contigs, one of which contained the sdY gene. Sequence analysis of the borders of male-specific and female/male common regions revealed highly repetitive sequences associated with mobile elements, which may allow an sdY cassette to jump around the genome. FISH analysis using a BAC or a plasmid containing the sdY gene showed that the sdY gene did indeed localize to the chromosomes where SEX had been mapped in different Tasmanian Atlantic salmon families. Moreover, the plasmid sdY gene probe hybridized primarily to one of the sex chromosomes as would be expected of a male-specific gene. Our results suggest that a common salmonid sex-determining gene (sdY) can move between three specific loci on chromosomes 2, 3, and 6, giving the impression that there are multiple SEX loci both within and between salmonid species.

Diploid males of Scaptotrigona depilis are able to join reproductive aggregations (Apidae, Meliponini)

The sex determination system in the eusocial stingless bees (Apidae, Meliponini) is based on the combination of alleles at the complementary sex determination (CSD) locus. In this system, males are haploid and females are diploid. However, diploid males can develop from fertilized eggs when they are homozygous at single or multiple sex loci. The production of such males can negatively affect population viability, since they are usually infertile or inviable. Moreover, when they are viable but infertile, or siring sterile triploid offspring, this could cause another load on the population, leading the fertilized offspring of other females to be only haploid males or triploid sterile daughters. In this context, our aim was to verify whether diploid males of the stingless beeScaptotrigonadepilisdo in fact join reproductive aggregations. We showed that of 360 marked males from two different colonies, five were participating in a reproductive aggregationca.20 meters from their natal colonies. Using microsatellites markers, it was confirmed that three of these five males were diploid. They were captured in the mating aggregations when they were 15 to 20 days old. Further research is necessary to determine the mating success of stingless bee diploid males under natural conditions and to determine their impact on stingless bee population extinction risks.

Heterozygous Mapping Strategy (HetMappS) for High Resolution Genotyping-By-Sequencing Markers: A Case Study in Grapevine.

Genotyping by sequencing (GBS) provides opportunities to generate high-resolution genetic maps at a low genotyping cost, but for highly heterozygous species, missing data and heterozygote undercalling complicate the creation of GBS genetic maps. To overcome these issues, we developed a publicly available, modular approach called HetMappS, which functions independently of parental genotypes and corrects for genotyping errors associated with heterozygosity. For linkage group formation, HetMappS includes both a reference-guided synteny pipeline and a reference-independent de novo pipeline. The de novo pipeline can be utilized for under-characterized or high diversity families that lack an appropriate reference. We applied both HetMappS pipelines in five half-sib F1 families involving genetically diverse Vitis spp. Starting with at least 116,466 putative SNPs per family, the HetMappS pipelines identified 10,440 to 17,267 phased pseudo-testcross (Pt) markers and generated high-confidence maps. Pt marker density exceeded crossover resolution in all cases; up to 5,560 non-redundant markers were used to generate parental maps ranging from 1,047 cM to 1,696 cM. The number of markers used was strongly correlated with family size in both de novo and synteny maps (r = 0.92 and 0.91, respectively). Comparisons between allele and tag frequencies suggested that many markers were in tandem repeats and mapped as single loci, while markers in regions of more than two repeats were removed during map curation. Both pipelines generated similar genetic maps, and genetic order was strongly correlated with the reference genome physical order in all cases. Independently created genetic maps from shared parents exhibited nearly identical results. Flower sex was mapped in three families and correctly localized to the known sex locus in all cases. The HetMappS pipeline could have wide application for genetic mapping in highly heterozygous species, and its modularity provides opportunities to adapt portions of the pipeline to other family types, genotyping technologies or applications.

Diploid males of Scaptotrigona depilis are able to join reproductive aggregations (Apidae, Meliponini)

The sex determination system in the eusocial stingless bees (Apidae, Meliponini) is based on the combination of alleles at the complementary sex determination (CSD) locus. In this system, males are haploid and females are diploid. However, diploid males can develop from fertilized eggs when they are homozygous at single or multiple sex loci. The production of such males can negatively affect population viability, since they are usually infertile or inviable. Moreover, when they are viable but infertile, or siring sterile triploid offspring, this could cause another load on the population, leading the fertilized offspring of other females to be only haploid males or triploid sterile daughters. In this context, our aim was to verify whether diploid males of the stingless bee Scaptotrigona depilis do in fact join reproductive aggregations. We showed that of 360 marked males from two different colonies, five were participating in a reproductive aggregation ca. 20 meters from their natal colonies. Using microsatellites markers, it was confirmed that three of these five males were diploid. They were captured in the mating aggregations when they were 15 to 20 days old. Further research is necessary to determine the mating success of stingless bee diploid males under natural conditions and to determine their impact on stingless bee population extinction risks. JHR 45: 125–130 (2015) doi: 10.3897/JHR.45.4769 http://jhr.pensoft.net Copyright Ayrton Vollet-Neto et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. SHORT COMMUNICATION Ayrton Vollet-Neto et al. / Journal of Hymenoptera Research 45: 125–130 (2015) 126

Population-level consequences of complementary sex determination in a solitary parasitoid.

BackgroundSex determination mechanisms are known to be evolutionarily labile but the factors driving transitions in sex determination mechanisms are poorly understood. All insects of the Hymenoptera are haplodiploid, with males normally developing from unfertilized haploid eggs. Under complementary sex determination (CSD), diploid males can be produced from fertilized eggs that are homozygous at the sex locus. Diploid males have near-zero fitness and thus represent a genetic load, which is especially severe under inbreeding. Here, we study mating structure and sex determination in the parasitoid Cotesia vestalis to investigate what may have driven the evolution of two complementary sex determination loci in this species.ResultsWe genotyped Cotesia vestalis females collected from eight fields in four townships in Western Taiwan. 98 SNP markers were developed by aligning Illumina sequence reads of pooled DNA of eight different females against a de novo assembled genome of C. vestalis. This proved to be an efficient method for this non-model species and provides a resource for future use in related species. We found significant genetic differentiation within the sampled population but variation could not be attributed to sampling locations by AMOVA. Non-random mating was detected, with 8.1% of matings between siblings. Diploid males, detected by flow cytometry, were produced at a rate of 1.4% among diploids.ConclusionsWe think that the low rate of diploid male production is best explained by a CSD system with two independent sex loci, supporting laboratory findings on the same species. Fitness costs of diploid males in C. vestalis are high because diploid males can mate with females and produce infertile triploid offspring. This severe fitness cost of diploid males combined with non-random mating may have resulted in evolution from single locus CSD to CSD with two independent loci.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0340-2) contains supplementary material, which is available to authorized users.