The E and Z pheromone strains of the European corn borer (ECB) provide an exceptional model system for examining the genetic basis of sexual isolation. Differences at two major genes account for variation in female pheromone production and male behavioral response, components of the pheromone communi- cation system known to be important for mate recognition and mate choice. Strains of ECB are morphologi- cally indistinguishable, and surveys of allozyme and DNA sequence variation have revealed significant allele frequency differences at only a single sex-linked locus, Tpi. Here we present a detailed genetic linkage map of ECB using AFLP and microsatellite markers and map the factors responsible for pheromone production (Pher) and male response (Resp). Our map covers 1697 cM and identifies all 31 linkage groups in ECB. Both Resp and Tpi map to the Z (sex) chromosome, but the distance between these markers (⬎20 cM) argues against the hypothesis that patterns of variation at Tpi are explained by tight linkage to this “speciation gene.” However, we show, through analysis of marker density, that Tpi is located in a region of low recombination and suggest that a second Z-linked reproductive barrier could be responsible for the origin and/or persistence of differentiation at Tpi.
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Sexual isolating mechanisms that act before fertilization are often considered the most important genetic barriers leading to speciation in animals. While recent progress has been made toward understanding the genetic basis of the postzygotic isolating mechanisms of hybrid sterility and inviability, little is known about the genetic basis of prezygotic sexual isolation. Here, we map quantitative trait loci (QTL) contributing to prezygotic reproductive isolation between the sibling species Drosophila simulans and D. mauritiana. We mapped at least seven QTL affecting discrimination of D. mauritiana females against D. simulans males, three QTL affecting D. simulans male traits against which D. mauritiana females discriminate, and six QTL affecting D. mauritiana male traits against which D. simulans females discriminate. QTL affecting sexual isolation act additively, are largely different in males and females, and are not disproportionately concen- trated on the X chromosome: The QTL of greatest effect are located on chromosome 3. Unlike the genetic components of postzygotic isolation, the loci for prezygotic isolation do not interact epistatically. The observation of a few QTL with moderate to large effects will facilitate positional cloning of genes underlying sexual isolation.
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S TUDIES of the genetics of speciation have, until very recently, been hindered by a paucity of candi- date genes for detailed analysis (S wanson and V acquier 2002; N oor 2003). Reproductive isolation, responsible for speciation, is likely to involve complex, coevolved, polygenic traits (leading to a ‘‘type I’’ genetic architecture in the terminology of T empleton 1981, i.e., numerous genes of small effect). Most empirical studies of repro- ductive isolation, especially of sexual isolation, have con- firmed polygenic effects (H ollocher et al. 1997; R itchie and P hillips 1998; T ing et al. 2001); however, a few large effect genes have been identified for both postmating (T ing et al. 1998; B arbash et al. 2003; P resgraves et al. 2003) and premating isolation (W heeler et al. 1991; G reenberg et al. 2003). In Drosophila, most of these large effect genes have been identified by mutagene- sis of D. melanogaster or by association analysis with geo- graphic variation. Quantitative trait loci (QTL) studies, in contrast, can identify the minimum number and location of genes influencing complex traits (M ackay 2001) and therefore identify the traits that are likely to be influenced by genes of large effect underlying naturally occurring variation. QTL studies may also in-
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Wolbachia are a group of intracellular bacteria, ma- ternally transmitted from infected females to their offspring, which affect a wide range of arthropods. Their presence is associated with Cytoplasmic In- compatibility (CI) in crosses between infected males and uninfected females and between populations carrying different strains of Wolbachia. The negative influence of Wolbachia infection on progeny fitness in incompatible crosses can be considered a first step in the appearance of reproductive isolation between infected and uninfected individuals. In this work, we examined the possibility of assortative mating in re- sponse to Wolbachia infection, a response that evolved as an incipient mechanism of sexual isolation in the species D. melanogaster and D. simulans. We found that the females of each species could detect the presence of the bacterium in the other sex and chose to mate with males who had the same state of infec- tion, whereas the males randomly attempted to mate with both infected and uninfected females. Thus, Wolbachia may act as an additive factor influencing sexual isolation in Drosophila populations and may play a role in speciation events.
Behavioural isolation has been found to be asymmetric in a number of taxa, and several mutually non-exclusive theories have been proposed to explain these asymmetries (reviewed in Arnold et al., 1996; Coyne & Orr, 2004; Svensson et al., 2016). Asymmetries in prezygotic barriers appear to occur at a lower rate than in postzygotic barriers (Lowry et al. 2008; Veen et al. 2013). Prezygotic barriers may be expected to exhibit less consistent patterns due to the complexity of traits involved, whose development, expression and fitness is often dependent on the environment (Grant & Grant, 1993; Pfennig, 2007), in contrast to intrinsic genetic incompatibilities which may be more functionally constrained (Turelli & Moyle, 2007). In Australian Teleogryllus, we found behavioural isolation to be symmetrical. This may reflect the allopatric origin of the populations we studied. Further comparative work is needed to determine whether asymmetries in prezygotic barriers are more common or predictable in certain groups than others (e.g. in sympatry vs. allopatry, Yukilevich, 2012).
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Gene transfer in bacteria is notoriously promiscuous. Genetic material is known to be transferred between groups as distantly related as the Gram positives and Gram negatives. However, the frequency of homologous recombination decreases sharply with the level of relatedness between the donor and recipient. Several studies show that this sexual isolation is an exponential function of DNA sequence divergence between recombining substrates. The two major factors implicated in producing the recombina- tional barrier are the mismatch repair system and the requirement for a short region of sequence identity to initiate strand exchange. Here we demonstrate that sexual isolation in Bacillus transformation results almost exclusively from the need for regions of identity at both the 59 and 39 ends of the donor DNA strand. We show that, by providing the essential identity, we can effectively eliminate sexual isolation between highly divergent sequences. We also present evidence that the potential of a donor sequence to act as a recombinogenic, invasive end is determined by the stability (melting point) of the donor-recipient complex. These results explain the exponential relationship between sexual isolation and sequence diver- gence observed in bacteria. They also suggest a model for rapid spread of novel adaptations, such as antibiotic resistance genes, among related species.
The different experimental designs employed in this study did not always yield similar results; premating iso- lation was significant in experimental designs where females were able to choose between their own and for- eign males, but not in no-choice situations. Choice experiments have been shown to yield higher and more realistic estimates of sexual isolation, based on evidence from the field, than no-choice experiments in other Dro- sophila species as well (e.g., [40,41]). Our data are also concordant with previous work with D. montana which demonstrated that female discrimination is stronger when the females are provided with a choice of mates . In nature, flies of this species may occasionally encounter problems finding mates when population densities are low, so females may exercise choice when they have a possibility to do so and accept less-favoured males when there are no “ better ” ones available .
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The natural variation of sex-specific characters between populations can favor their behavioral isolation, eventually leading to the formation of new species. Marked variations for male courtship, mating and the production of sex pheromones – three complex characters potentially inducing sexual isolation – were found between Drosophila melanogaster populations of various origins acclimated for many generations in research laboratories. However, the natural variation of these three characters between natural populations and their evolution after long-term acclimation in the laboratory remains unknown. We measured many traits involved in these characters in six stocks initiated with distinct populations sampled in a restricted geographic area. Several sex- specific traits varied between stocks freshly brought back to the laboratory. After 100 generations spent in the laboratory without any experimental selection, traits varied in a strain-dependent manner. This variation was not related to a reduction of their variance except for copulation duration. This indicates that reproduction-related characters can diverge between neighboring D. melanogaster populations, and differently adapt to stable laboratory conditions.
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Sexual isolating mechanisms that act before fertilization are often considered the most important genetic barriers leading to speciation in animals. While progress has been made toward understanding the genetic basis of the postzygotic isolating mechanisms of hybrid sterility and inviability, little is known about the genetic basis of prezygotic sexual isolation. Here, we map quantitative trait loci (QTL) con- tributing to prezygotic reproductive isolation between the sibling species Drosophila santomea and D. yakuba. We mapped at least three QTL affecting discrimination of D. santomea females against D. yakuba males: one X-linked and one autosomal QTL affected the likelihood of copulation, and a second X chromosome QTL affected copulation latency. Three autosomal QTL also affected mating success of D. yakuba males with D. santomea. No epistasis was detected between QTL affecting sexual isolation. The QTL do not overlap between males and females and are not disproportionately concentrated on the X chro- mosome. There was some overlap in map locations of QTL affecting sexual isolation between D. santomea and D. yakuba with QTL affecting sexual isolation between D. simulans and D. mauritiana and with QTL affecting differences in pigmentation between D. santomea and D. yakuba. Future high-resolution mapping and, ultimately, positional cloning, will reveal whether these traits do indeed have a common genetic basis.
Sandflies (Diptera: Psychodidae: Phlebotominae) - Lutzomyia longipalpis, the main vector of visceral leishmaniasis in the Americas, constitutes a complex of cryptic species (Ward et al. 1988, Lanzaro et al. 1993). For some time it was not clear whether the Brazilian populations of this vector represented one species or several sibling species [reviewed by Bauzer et al. (2007) and Maingon et al. (2008)]. Among the best pieces of evidence that there are more than one species in Bra- zil are the distinctive “songs” produced by males from different populations (de Souza et al. 2002, Souza et al. 2004, Araki et al. 2009). These songs are produced by wing vibrations, as in Drosophila, but are unusual in that they are produced during copulation rather than during pre-copulatory courtship. The copulatory court- ship songs of Lu. longipalpis s.l. are likely to be involved in reproductive isolation since mating experiments show a high level of insemination failure in copulations be- tween sibling species that produce different songs (Ward et al. 1988, Souza et al. 2008). Why female choice should be based on copulatory courtship is not well understood, but it may suggest that cryptic female choice (Eberhard 1996) possibly related to sperm competition (Hoikkala & Crossley 2000), is important during mating in this in- sect vector.
Table S10 Results of the AICc-based model selection for models explaining host mortality from the parasitoid in terms of the effects of habitat isolation at different spatial scales, host mortality from the virus AbgrNPV, site elevation and plant height.
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migrants; undocumented migrants; legal status; irregular; illegal; LGBTI; conflict related sexual violence; war; EU; Europe; high-income countries; Western countries; help-seeking; help-seeking behaviour; disclosure; selective disclosure; health care; access; barriers;
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Bacigalupe LD, Crudgington HS, Hunter F, Moore AJ, Snook RR. 2007. Sexual conflict does not drive reproductive isolation in experimental populations of Drosophila pseudoobscura. Journal of Evolutionary Biology 20: 1763-1771. Bailey NW, Zuk M. 2009. Same-sex sexual behaviour and evolution. Trends in Ecology
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Lekking fruit flies offer an excellent opportunity to explore the ontogenetic effect of light regimes on sexual selection because lekking takes place under specific environmental conditions that favour male signalling. In tephritid flies, lekking takes place on trees that offer both visual and olfactory stimuli (Hendrichs et al., 1991; Kaspi and Yuval, 1999a). Plant spectral quality (particularly hue and intensity) appears to be the principal stimulus that elicits landing on living plants (Prokopy and Owens, 1983). Tephritid males select lekking sites based on tree size and architecture (Shelly and Whittier, 1994; Field et al., 2002), and inside the lekking tree, leaves, which represent male territories, are chosen based on light and microclimatic conditions (Kaspi and Yuval, 1999a; Kaspi and Yuval, 1999b). From these territories, males display complex visual and acoustic signals combined with the release of pheromones (Prokopy and Hendrichs, 1979; Field et al., 2002). Furthermore, the transparent areas of tephritids’ wings exhibit striking and stable structural colour patterns, called wing interference patterns, that could play an important role in the sexual selection process because there is sexual dimorphism (Shevtsova et al., 2011). Additionally, sexual
Given the continued prevalence and serious consequences of homophobic behavior and harassment in schools (Birkett, Russell, & Corliss, 2014; Collier, Bos, & Sandfort, 2013), more studies are aiming to identify factors that perpetuate this behavior. Though studies have focused on individual attributes and characteristics (for a review, see Rivers, 2011), emerging studies have begun to adopt a broader ecological framework, in greater alignment with the general bullying literature (Birkett & Espelage, 2015; Hong & Garbarino, 2012; Poteat, 2007). With this attention to larger social systems, an immediate focus has been on the roles of peers and peer group norms and dynamics related to this behavior. Attention to the peer context is highly relevant, as adolescence is a period during which peers exert a strong influence on individuals’ behaviors through group norms and ongoing interactions (Berndt, 2002; Veenstra, Dijkstra, Steglich, & Van Zalk, 2013). There has been an expansive range of documented peer effects on various behaviors (e.g., academic achievement, substance use; Brechwald & Prinstein, 2011), though few studies have focused on discrimination or homophobic behavior, specifically. To provide a more comprehensive understanding of homophobic behavior (e.g., homophobic epithet use, derogatory jokes against sexual minorities, disparaging behaviors toward others based on their assumed sexual minority identity), research must consider how individual attributes and contextual factors combine and interact in ways to perpetuate this behavior.
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Regarding process, these outcomes naturally intersect with the interactional process between the individuals involved insofar as pleasure and/or no regret might derive from participation in a process of sexual practice that is chosen, satisfying, and involved emotional connection and negotiation over non-penetrative safer practices or the effective use of condoms. Overall, it would meet the desired outcomes and honour the rights of all involved. In more negative terms, a ‘positive’ outcome would exclude post-sex worries over contracting STI and/or conception, having no regrets over the person or circumstances in which sex took place, and having not been coerced or acted against one’s will. There is also the outcome - more likely at the start of sexual careers and/or beginnings of a relationship – where a sexual encounter might be emotionally desired and enjoyed but not yet physically pleasurable (because of naiveté in technique, for instance) but nevertheless judged as positive overall. These relative variations are important to highlight in order to resist a sense of competence in research enquiry that is absolute, i.e. either ‘achieved’ or ‘not achieved’.
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their social inclusion, discrimination, sexual identity, social isolation and the associated impact on their mental health and the development of mental illness. While there are specific policies focusing on the wider needs of LGBT people, there is a need to ensure that the needs of transgender people are fully integrated and represented and clearly linked to impact and outcomes that improve the lives of transgender people. Given the extent of the mental health needs of transgender people, access to culturally appropriate psychological treatment options is an area that requires development. This needs to be supported by access to social networks and groups as part of the wider supports available that build resilience and sustain positive self-identity. Ensuring that care services are sensitive to and responsive to the needs of transgender people is central to ensuring that their health needs are met and health inequalities reduced, thereby providing care that is both person-centered and responsive. Linked to this is the need for sustained developments within education and practice development programs that include transgender people, their families and the practitioners who deliver services. Building new collaborative international research networks is necessary to enable large-scale studies to be undertaken.
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