Sharp decline in male fertility in F2 hybrids of the female-heterogametic silk moth Bombyx.

Sexual selection drives rapid evolution of morphological, physiological, and behavioral traits, especially in males, and it may also drive the rapid evolution of hybrid male sterility. Indeed, the faster male theory of speciation was once viewed as a major cause of Haldane's rule in male-heterogametic XY taxa, but is increasingly being replaced by the genetic conflict hypothesis partly because it cannot explain the faster evolution of hybrid female sterility in female-heterogametic ZW taxa. The theory nonetheless predicts that there should be more genes for hybrid male sterility than for hybrid female sterility even in such taxa, but this remains untested. Thus, finding evidence for the faster male theory of reproductive isolation beyond the F1 generation in ZW systems still represents a challenge to studying the impact of sexual selection. In this study, we examined F2 hybrids between the domesticated silkworm Bombyx mori and the wild silk moth Bombyx mandarina, which have ZW sex determination. We found that although only females showed reduced fertility in the F1 generation, the F2 hybrid males had a significant reduction in fertility compared with the parental and F1 males. Importantly, 27% of the F2 males and 15% of the F2 females were completely sterile, suggesting the presence of recessive incompatibilities causing male sterility in female-heterogametic taxa.

A comparative study of natural variation in hemolymph glucose levels under different dietary sugar conditions in Drosophila melanogaster and D. simulans.

Physiological responses to environmental changes play important roles in adaptive evolution. In particular, homeostatic regulatory systems that maintain constant circulating glucose levels are crucial in animals. However, variation in circulating glucose levels and the genetic effects on phenotypic variation in natural populations remain to be clarified. Here, we investigated the hemolymph glucose levels in natural populations of Drosophila melanogaster and its sibling species, D. simulans, in Japan. We quantified hemolymph glucose concentrations in third instar larvae of 27 lines for each species, which were reared on either glucose-free or glucose-rich food. In both species, genetic variation was not a major component of phenotypic variation on either glucose-free or glucose-rich food. The hemolymph glucose concentrations were much higher in D. simulans than in D. melanogaster. Genetic variance was larger in D. simulans than in D. melanogaster. The observed differences between the two species may be associated with the much more recent colonization history of D. simulans populations in Japan and/or the tolerance to environmental stresses. Our findings suggest that natural selection acting on hemolymph glucose levels in D. melanogaster is different from that in D. simulans.

A new allele of engrailed, enNK14, causes supernumerary spermathecae in Drosophila melanogaster.

A spontaneous mutation, enNK14, was a new allele of engrailed (en) in Drosophila melanogaster. Females of enNK14 have three spermathecae, instead of two in wild type, under a wide range of developmental temperatures, while the males show no abnormal phenotype. Spermathecae of the mutant female can accept inseminated sperms, albeit with a delay of at least an hour until full acceptance compared with wild type. The time course of decrease in the number of stored sperms was thoroughly similar between the mutant and wild type. enNK14 females produced fewer progeny than wild type females despite storing a larger number of sperms. The delay of sperm entry and lower fecundity suggested some functional defects in secretory products of the spermathecae. In addition, some spermathecae in the mutant were accompanied by a mass of brown pigments in the adipose tissue surrounding the capsule. Six contiguous amino acids, Ser340-Ala345, were replaced by one Thr in enNK14. In another mutant, enspt, Ser325 was also shown to be substituted by a Cys. These amino acid changes were located within a serine-rich region, in which Ser325, Ser340 and Thr341 were suggested as targets of Protein Kinase C by an in silico analysis. The splicing pattern of en mRNA did not differ between enNK14 and wild type in embryo, larva, pupa or adult. Our results suggest that en plays an important role in determining the number of spermathecae as well as in sperm storage function in the Drosophila female.

Drosophila telomere capping protein HOAP interacts with DSB sensor proteins Mre11 and Nbs.

In eukaryotes, specific DNA-protein structures called telomeres exist at linear chromosome ends. Telomere stability is maintained by a specific capping protein complex. This capping complex is essential for the inhibition of the DNA damage response (DDR) at telomeres and contributes to genome integrity. In Drosophila, the central factors of telomere capping complex are HOAP and HipHop. Furthermore, a DDR protein complex Mre11-Rad50-Nbs (MRN) is known to be important for the telomere association of HOAP and HipHop. However, whether MRN interacts with HOAP and HipHop, and the telomere recognition mechanisms of HOAP and HipHop are poorly understood. Here, we show that Nbs interacts with Mre11 and transports the Mre11-Rad50 complex from the cytoplasm to the nucleus. In addition, we report that HOAP interacts with both Mre11 and Nbs. The N-terminal region of HOAP is essential for its co-localization with HipHop. Finally, we reveal that Nbs interacts with the N-terminal region of HOAP.

Novel roles of Drosophila FUS and Aub responsible for piRNA biogenesis in neuronal disorders.

piRNAs, small non-coding RNAs, were considered to be restricted to germline cells. Although they have recently been detected in somatic cells including neurons, it remains unclear how piRNA biogenesis is involved in neuronal diseases. We herein examined the possible roles of Aubergine (Aub), a Piwi-family protein (PIWI) responsible for piRNA biogenesis, in the neuronal disorders, using the Cabeza (Caz) knockdown Drosophila. Caz is a Drosophila homologue of FUS, which is one of the genes causing amyotrophic lateral sclerosis (ALS). Aub overexpression enhanced the mobility defects accompanied by anatomical defects in motoneurons at neuromuscular junctions induced by the neuron-specific knockdown of Caz. In order to elucidate the underlying mechanisms, we examined pre-piRNA and mature-size piRNA levels under these conditions. qRT-PCR and RNA-seq analyses revealed that the Caz knockdown increased pre-piRNA levels, but reduced mature-size piRNA levels in the central nervous system (CNS), suggesting a role in the pre-piRNAs production. Aub overexpression did not increase mature-size piRNA levels. These results suggest that the accumulated pre-piRNAs are abnormal abortive pre-piRNAs that cannot be further processed by slicers, including Aub. We also demonstrated a relationship between Caz and pre-piRNAs in the CNS by RNA immunoprecipitation. Aub overexpression induced the abnormal cytoplasmic localization of Caz. Based on these results, we propose a model in which Caz knockdown-induced abnormal pre-piRNAs associate with Caz, then translocate and accumulate in the cytoplasm, a process that may be mediated by Aub. The novel roles for Caz and Aub demonstrated herein using the Caz-knockdown fly will contribute to a deeper understanding of the pathogenesis of ALS.

The P element invaded rapidly and caused hybrid dysgenesis in natural populations of Drosophila simulans in Japan.

Transposable elements not only can change genomic positions and disperse across the gene pool, but also can jump to another species through horizontal transmission. Of late, the P element, a DNA transposon in insects, was shown to cross the genetic boundary from Drosophila melanogaster to D. simulans in Europe around 2006. To understand the dynamics of transposable elements, especially in the early stages of invasion, we examined 63 lines of D. simulans from 11 natural populations in Japan established in 1976-2015. Based on PCR analyses, P elements were demonstrated to exist in Japan in 2008 and later. One copy of the full-length P element was identified and mapped to a site on chromosome 3 L in a genome. All of 18 copies of P elements examined shared "A" at the nucleotide position 2040, which is representative of the direct descendants of the original P element that invaded in D. simulans. We also found that some lines having P elements can induce intensive gonadal dysgenesis in D. simulans at 29°C. Our present results imply that P elements in D. simulans arrived at the east end of Asia just a few years later than or almost simultaneously to the initial invasion in Europe, Africa, and North America, suggesting a more astonishingly rapid spread than previously assumed.

Association of zygotic piRNAs derived from paternal P elements with hybrid dysgenesis in Drosophila melanogaster.

BACKGROUND: P-element transposition in the genome causes P-M hybrid dysgenesis in Drosophila melanogaster. Maternally deposited piRNAs suppress P-element transposition in the progeny, linking them to P-M phenotypes; however, the role of zygotic piRNAs derived from paternal P elements is poorly understood. RESULTS: To elucidate the molecular basis of P-element suppression by zygotic factors, we investigated the genomic constitution and P-element piRNA production derived from fathers. As a result, we characterized males of naturally derived Q, M' and P strains, which show different capacities for the P-element mobilizations introduced after hybridizations with M-strain females. The amounts of piRNAs produced in ovaries of F1 hybrids varied among the strains and were influenced by the characteristics of the piRNA clusters that harbored the P elements. Importantly, while both the Q- and M'-strain fathers restrict the P-element mobilization in ovaries of their daughters, the Q-strain fathers supported the production of the highest piRNA expression in the ovaries of their daughters, and the M' strain carries KP elements in transcriptionally active regions directing the highest expression of KP elements in their daughters. Interestingly, the zygotic P-element piRNAs, but not the KP element mRNA, contributed to the variations in P transposition immunity in the granddaughters. CONCLUSIONS: The piRNA-cluster-embedded P elements and the transcriptionally active KP elements from the paternal genome are both important suppressors of P element activities that are co-inherited by the progeny. Expression levels of the P-element piRNA and KP-element mRNA vary among F1 progeny due to the constitution of the paternal genome, and are involved in phenotypic variation in the subsequent generation.

Frequencies of chromosomal inversions in Drosophila melanogaster in Fukushima after the nuclear power plant accident.

In order to investigate genetic impact of a large amount of radionuclides released by the Fukushima Dai-ichi Nuclear Power Plant accident in 2011, we surveyed 2,304 haploid genomes of Drosophila melanogaster collected in three localities in Fukushima in 2012 and 2013 for chromosomal inversions. No unique inversion was found in 298 genomes in 2012 and only two in 2,006 genomes in 2013. The observed frequencies were even lower than the long-term average frequency of unique inversions in Japan. The common cosmopolitan inversions were also examined in Fukushima, Kyoto, and Iriomote (Okinawa) in 2012. Among three samples in Fukushima, the flies in Iizaka, where environmental radiation level was the highest, showed the lowest frequency of In(2L)t, but the highest frequency of In(3R)P, contrary to the expectation of decreasing of their frequencies in higher polluted areas. These results suggest that, at this level of genetic analysis, Fukushima populations of D. melanogaster would not have been negatively impacted following the release of radionuclides. Transposable P-element mobility was not likely to induce DNA damage solely or synergistically with radioactivity, because their transposition activity was totally repressed in the Fukushima strains. However, it should be noted that, because of limitations in access to the exclusion zone, we could only sample the populations in areas of relatively low radioactive contamination (0.39-0.63 µSv/h). Therefore, the present study is likely to be underpowered to detect any effects that might be expected in heavily contaminated areas.

Diversity of P-element piRNA production among M' and Q strains and its association with P-M hybrid dysgenesis in Drosophila melanogaster.

BACKGROUND: Transposition of P elements in the genome causes P-M hybrid dysgenesis in Drosophila melanogaster. For the P strain, the P-M phenotypes are associated with the ability to express a class of small RNAs, called piwi-interacting small RNAs (piRNAs), that suppress the P elements in female gonads. However, little is known about the extent to which piRNAs are involved in the P-M hybrid dysgenesis in M' and Q strains, which show different abilities to regulate the P elements from P strains. RESULTS: To elucidate the molecular basis of the suppression of paternally inherited P elements, we analyzed the mRNA and piRNA levels of P elements in the F1 progeny between males of a P strain and nine-line females of M' or Q strains (M' or Q progenies). M' progenies showed the hybrid dysgenesis phenotype, while Q progenies did not. Consistently, the levels of P-element mRNA in both the ovaries and F1 embryos were higher in M' progenies than in Q progenies, indicating that the M' progenies have a weaker ability to suppress P-element expression. The level of P-element mRNA was inversely correlated to the level of piRNAs in F1 embryos. Importantly, the M' progenies were characterized by a lower abundance of P-element piRNAs in both young ovaries and F1 embryonic bodies. The Q progenies showed various levels of piRNAs in both young ovaries and F1 embryonic bodies despite all of the Q progenies suppressing P-element transposition in their gonad. CONCLUSIONS: Our results are consistent with an idea that the level of P-element piRNAs is a determinant for dividing strain types between M' and Q and that the suppression mechanisms of transposable elements, including piRNAs, are varied between natural populations.

Robust increase of microglia proliferation in the fornix of hippocampal axonal pathway after a single LPS stimulation.

Microglia are resident immunocompetent cells having important roles in innate immunity in the brains. In the present study, we found that a single lipopolysaccharide (LPS) administration significantly increased microglial proliferation in the fornix and dentate gyrus (DG) but not the cerebral cortex and corpus callosum of adult mice. LPS-induced microglial proliferation was especially robust at the white matter of the fornix. The density of microglia increased in the fornix and DG for roughly one week and returned to basal levels at least 20days after a single LPS administration. Consecutive LPS administration did not induce such dramatic increase of microglial proliferation in the fornix. The inhibition of vascular endothelial growth factor signaling by AZD2171 largely suppressed LPS-induced increase of microglial proliferation in the fornix. In conclusion, the present study indicates that the hippocampal neuronal system has a higher proliferative microglial capability against LPS-induced inflammatory administration compared with other brain regions.

VEGF-dependent and PDGF-dependent dynamic neurovascular reconstruction in the neurohypophysis of adult mice.

Hypothalamo-neurohypophysial system (HNS) releases arginine vasopressin (AVP) and oxytocin (OXT) from axonal terminals of the neurohypophysis (NH) into blood circulation for controlling body fluid homeostasis and lactation. Chronic osmotic and suckling stimulations have been shown to cause neurovascular and neuroglial reconstruction in the NH of adult mammals and no study has been reported for vascular dynamics. The aim of this study was to elucidate the occurrence of continuous angiogenesis and growth factor-dependent neurovascular reconstruction in the NH of adult mice. Active proliferation of endothelial cells and oligodendrocyte progenitor cells (OPCs) was observed using the immunohistochemistry of bromodeoxyuridine and Ki-67. Vascular endothelial growth factor A (VEGFA) and VEGF receptor 2 (VEGFR2 (KDR)) were highly expressed at pituicytes and endothelial cells respectively. Moreover, prominent expression of platelet-derived growth factor B (PDGFB) and PDGF receptor beta was observed at OXT-containing axonal terminals and pericytes respectively. Administration of the selective tyrosine kinase inhibitor AZD2171 for VEGFRs and STI571 for PDGFRs significantly decreased proliferation of endothelial cells and OPCs. Moreover, AZD2171 treatment decreased vascular density by facilitating apoptosis of endothelial cells and the withdrawal of its treatment led to remarkable rebound proliferation of endothelial cells, so that vascular density rapidly returned to normal levels. AZD2171 decreased the density of both AVP- and OXT-containing axonal terminals, whereas STI571 selectively decreased the density of AVP-containing ones. Thus, this study demonstrates that the signaling pathways of VEGF and PDGF are crucial mediators for determining proliferation of endothelial cells and OPCs and the density of AVP- and OXT-containing axonal terminals in the HNS.

Starvation-induced elevation of taste responsiveness and expression of a sugar taste receptor gene in Drosophila melanogaster.

Animals increase their feeding motivation under starved conditions. Here the authors test if the starvation-induced increase of feeding motivation is different among wild-derived strains of Drosophila melanogaster. In behavioral experiments comparing the feeding behaviors of the strains Mel6 and TW1, only TW1 exhibited a decreased feeding threshold to sucrose following a 24-h starvation period. Starved TW1 preferably ingested a low concentration of sucrose. Starved TW1 also exhibited significant elevation of taste responsiveness to low concentrations of sucrose and enhanced expression of the Gr64a sucrose sugar receptor gene. TW1 survived longer than Mel6 when provided a less nutritious food (10 mM sucrose). Thus, the starvation-induced decrease in the behavioral and the sensory thresholds could be an advantage in searching for and utilizing less nutritious foods. These results show that the starvation-induced functional change in the taste sensory system is a possible strategy for survival during starvation or suboptimal nutrient periods.

Cuticular Hydrocarbon Content that Affects Male Mate Preference of Drosophila melanogaster from West Africa.

Intraspecific variation in mating signals and preferences can be a potential source of incipient speciation. Variable crossability between Drosophila melanogaster and D. simulans among different strains suggested the abundance of such variations. A particular focus on one combination of D. melanogaster strains, TW1(G23) and Mel6(G59), that showed different crossabilities to D. simulans, revealed that the mating between females from the former and males from the latter occurs at low frequency. The cuticular hydrocarbon transfer experiment indicated that cuticular hydrocarbons of TW1 females have an inhibitory effect on courtship by Mel6 males. A candidate component, a C25 diene, was inferred from the gas chromatography analyses. The intensity of male refusal of TW1 females was variable among different strains of D. melanogaster, which suggested the presence of variation in sensitivity to different chemicals on the cuticle. Such variation could be a potential factor for the establishment of premating isolation under some conditions.

RNA editing in P transposable element read-through transcripts in Drosophila melanogaster.

RNA editing is proposed as a modulator of transcriptomes, but its biological impact has not been fully elucidated. In particular, its importance for transposable elements is controversial. We found RNA editing on antisense read-through transcripts of KP elements, one of the deletion derivatives of P transposable elements in Drosophila melanogaster. Three kinds of RNA editing were detected at 20 sites around the terminal inverted repeats (TIR); 15 A-to-G, four U-to-C, and one C-to-U conversions. A-to-G conversions are suggested to be attributed to A-to-I RNA editing on KP element RNAs, because inosine (I) in RNA is recognized as G by reverse transcriptase. TIRs were deduced to form dsRNAs as a putative target of ADAR. This is the first report of RNA editing on mobile elements of Drosophila.

Seasonal changes in the long-distance linkage disequilibrium in Drosophila melanogaster.

Seasonal environmental changes have the potential to influence the genetic structure of species with a short generation time, such as Drosophila. We previously found the seasonal change in linkage disequilibrium (LD) between the chemoreceptor (Cr) genes in a local Japanese population (Kyoto [KY]). This could be caused by fluctuation in the population size or selection in temporally heterogeneous environments or both. Here, we analyzed the scale of LD between 51 X-linked polymorphisms (10 Cr and 41 non-Cr gene markers) in the 2 seasonal samples from the KY population and an autumn sample from 106 localities in and around Japan (Ja03au). Many of the non-Cr genes have receptor function but fewer functional connections to each other. The magnitude of LD in Ja03au did not significantly differ from that in the KY autumn sample. The lack of local differentiation was confirmed in an autumn sample from another local Japanese population. On the other hand, the magnitude of LD was significantly larger in spring than in autumn in the 2 independent KY samples. This suggests that reduction in the population size during winter increased the magnitude of LD in spring in the mainland population in Japan. Long-distance LD could be a useful measure for assessing seasonal fluctuation in effective population size.

Characteristics of genes up-regulated and down-regulated after 24 h starvation in the head of Drosophila.

Starvation is a common experience under fluctuating food conditions in nature, and response to it is vital for many organisms. Many studies have investigated the response at physiological and behavioral level, whereas the studies on starvation-induced transcriptional changes in the brain and the surrounding tissues are still limited. We here investigated global changes in transcript abundance in the head after 24 h starvation by microarray expression profiling of 2 wild-derived inbred strains of Drosophila melanogaster, and identified a core set of 65 up-regulated and 48 down-regulated genes upon starvation. Among these up-regulated genes, 22 genes were circadian oscillating genes previously identified in the head of Drosophila. Interestingly, most (86%) of these circadian genes show their expression peak in a narrow time range of ZT7.0-12.0, when flies are relatively restless and less feeding in the normal condition. Among the down-regulated genes, 2 genes with highest fold-differences, fit and CG8147, are known to have female-biased expression in the head, and 1 gene, Obp99b, is known to be male-biased. Together with the realtime qPCR experiments on female and male transcripts, our data suggest that these sex-specific genes are candidate genes mediating a possible trade-off between starvation resistance and reproduction. Eleven down-regulated genes are known to be involved in the immune response. These changes in head transcriptome upon starvation reflect modulation of expression in some normally oscillating rhythmic genes and reduction in the resource allocation toward sexual activity and immunity.

A novel Drosophila Girdin-like protein is involved in Akt pathway control of cell size.

The Akt signaling pathway is well known to regulate cell proliferation and growth. Girdin, a novel substrate of Akt, plays a crucial role in organization of the actin cytoskeleton and cell motility under the control of Akt. We here identified a novel Girdin-like protein in Drosophila (dGirdin), which has two isoforms, dGirdin PA and dGirdin PB. dGirdin shows high homology with human Girdin in the N-terminal and coiled-coil domains, while diverging at the C-terminal domain. On establishment of transgenic fly lines, featuring knockdown or overexpression of dGirdin in vivo, overexpression in the wing disc cells induced ectopic apoptosis, implying a role in directing apoptosis. Knockdown of dGirdin in the Drosophila wing imaginal disc cells resulted in reduction of cell size. Furthermore, this was enhanced by half reduction of the Akt gene dose, suggesting that Akt positively regulates dGirdin. In the wing disc, cells in which dGirdin was knocked down exhibited disruption of actin filaments. From these in vivo analyses, we conclude that dGirdin is required for actin organization and regulation of appropriate cell size under control of the Akt signaling pathway.

Prenatal phencyclidine exposure alters hippocampal cell proliferation in offspring rats.

Multiple case reports have described pregnancy in phencyclidine hydrochloride (PCP) abusers. Characteristic clinical symptoms of PCP-exposed infants have revealed neurobehavioral or physical abnormalities. We designed this study to evaluate whether chronic prenatal exposure to PCP during the last 2 weeks of gestation in rats produces alterations of hippocampal neurogenesis in offspring. Rats received repeated subcutaneous injection of PCP (5 mg/kg) once daily during the last 2 weeks of gestation. Control animals received subcutaneous injection of physiological saline during gestation. Dams receiving repeated PCP administrations showed markedly increased locomotor activities on days 1, 5, and 10 during the last 2 weeks of gestation. At 21 days after birth, 5-bromo-2'-deoxyuridine (BrdU)-positive cells of offspring were counted in the granule cell layer (GCL) and subgranular zone of the dentate gyrus. The numbers of BrdU-positive cells in the GCL in male and female offspring of the PCP-treated group were significantly increased by approximately 77% compared with those from the control group. At 56 days, the number of surviving BrdU-positive cells also remained to be increased by 74% in the GCL in PCP-treated group. At 21 days, locomotor activities of offspring in the PCP-treated group were significantly decreased by approximately 30% compared with those in the control group. However, neuronal differentiation of newly formed cells and cell survival were not influenced at 5 weeks after BrdU injections. Some altered biochemical or physiological conditions of offspring from dams receiving repeated PCP injections during pregnancy could influence changes in cell proliferation in the GCL of offspring during early development. Changes to cell proliferation in the hippocampus may affect behavioral abnormalities during infancy in offspring.

Genetic screening for modifiers of the DREF pathway in Drosophila melanogaster: identification and characterization of HP6 as a novel target of DREF.

The DNA replication-related element-binding factor (DREF) regulates cell proliferation-related gene expression in Drosophila. By genetic screening, taking advantage of the rough eye phenotype of transgenic flies that express DREF in the eye discs, we identified 24 genes that suppressed and 12 genes that enhanced the rough eye phenotype when heterozygous for mutations. Five genes, HP6, pigeon, lace, X box binding protein 1 and guftagu were found to carry replication-related element (DRE) sequences in their 5'-flanking regions. Of these, the HP6 gene carries two sequences that match seven out of eight nucleotides of DRE and two additional sequences that match six out of eight nucleotides of DRE in the 5'-flanking region. Band mobility shift assays using Drosophila Kc cell nuclear extracts demonstrated DREF binding to two of these sites and chromatin immunoprecipitation using anti-DREF antibodies confirmed that this occurs in vivo. Knockdown of DREF in Drosophila S2 cells decreased the HP6 mRNA level. The results, taken together, indicate that DREF directly regulates expression of the HP6 gene. HP6 mRNA was detected throughout development by RT-PCR with highest levels in adult males. In addition, immunostaining analyses revealed colocalization of HP6 and DREF in nuclei at the apical tips in the testes.

Molecular spectrum of spontaneous de novo mutations in male and female germline cells of Drosophila melanogaster.

We carried out mutation screen experiments to understand the rate and molecular nature of spontaneous de novo mutations in Drosophila melanogaster, which are crucial for many evolutionary issues, but still poorly understood. We screened for eye-color and body-color mutations that occurred in the germline cells of the first generation offspring of wild-caught females. The offspring were from matings that had occurred in the field and therefore had a genetic composition close to that of flies in natural populations. We employed 1554 F(1) individuals from 374 wild-caught females for the experiments to avoid biased contributions of any particular genotype. From approximately 8.6 million alleles screened, we obtained 10 independent mutants: two point mutations (one for each sex), a single deletion of approximately 6 kb in a male, a single transposable element insertion in a female, five large deletions ranging in size from 40 to 500 kb in females, and a single mutation of unknown nature in a male. The five large deletions were presumably generated by nonallelic homologous recombination (NAHR) between transposable elements at different locations, illustrating the mutagenic nature of recombination. The high occurrence of NAHR that we observed has important consequences for genome evolution through the production of segmental duplications.