Geographic contrasts between pre- and postzygotic barriers are consistent with reinforcement in Heliconius butterflies.

Identifying the traits causing reproductive isolation and the order in which they evolve isfundamental to understanding speciation. Here, we quantify prezygotic and intrinsicpostzygotic isolation between allopatric, parapatric and sympatric populations of thebutterflies Heliconius elevatus and Heliconius pardalinus. Sympatric populations from theAmazon (H. elevatus and H. p. butleri) exhibit strong prezygotic isolation and rarely mate incaptivity; however, hybrids are fertile. Allopatric populations from the Amazon(H. p. butleri) and Andes (H. p. sergestus) mate freely when brought together in captivity, butthe female F1 hybrids are sterile. Parapatric populations (H. elevatus and H. p. sergestus)exhibit both assortative mating and sterility of female F1s. Assortative mating in sympatricpopulations is consistent with reinforcement in the face of gene flow, where the driving force,selection against hybrids, is due to disruption of mimicry and other ecological traits ratherthan hybrid sterility. In contrast, the lack of assortative mating and hybrid sterility observedin allopatric populations suggests that geographic isolation enables the evolution of intrinsicpostzygotic reproductive isolation. Our results show how the types of reproductive barriersthat evolve between species may depend on geography

Hybrid sterility and genetic incompatibilities in Ficedula flycatchers

Although the theory behind the mechanisms generating intrinsic post-zygotic isolation is well established, very few concrete examples of genetic incompatibilities have been described, especially in vertebrates. Consequently, our understanding of the evolutionary forces shaping the appearance of genetic incompatibilities between natural populations and the overall role of genetic incompatibilities in the speciation process is limited. In this doctoral thesis I will contribute to filling this gap in knowledge by using different approaches to investigate the causes and genetic basis of male hybrid sterility in a natural Ficedula flycatcher hybrid zone. I started by analyzing hybrid inviability patterns using 17 years of long-term monitoring data and found evidence for hybrid inviability at different life stages (Paper I). Early developmental failure of hybrids as revealed by the lower hatching success of mixed-species pairs suggesting emerging severe but non-fixed incompatibilities between the two species. Subtler differences in terms of lower growth potential and shorter lifespan indicate mito-nuclear incompatibilities as elevated metabolic rate can cause accumulation of toxic by-products in the form of Reactive Oxygen Species (ROS). Because previous evidence indicated problems during spermatogenesis in male hybrids, I characterized collared and pied flycatcher spermatogenesis at a single-cell level (Paper II). Since this was the first single-cell study investigating avian spermatogenesis, I identified the three main stages of spermatogenesis and described expression patterns of autosomes and Z-linked genes. By analyzing differential gene expression and estimates of protein evolution, I found that meiosis appears to be less evolutionary constraint in birds than in mammals. I propose that this fundamental difference is caused by the lack of MSCI in the spermatogenesis of ZW systems. Using the spermatogenesis characterization as a baseline, I then explored hybrid spermatogenesis to detect the stage of failure and associated genes (Paper III). By using a combination of histology sections, single-cell RNA sequencing and whole genome re-sequencing data, I found strong evidence of meiosis failure in hybrid spermatogenesis. I identified genes with non-synonymous fixed differences between the two species that were also DE during spermatogenesis. This enabled me to identify candidate genes causing genetic incompatibilities leading to meiosis failure in hybrid flycatchers. Finally, I explored the role of the enigmatic Germline restricted chromosome (GRC) in flycatcher spermatogenesis (Paper IV). I sequenced the GRC and revealed the gene contents for both species of flycatchers. Then we verified the transcription of the contents of the GRC and identified testis cell clusters containing GRC transcripts to reveal at what developmental stages of spermatogenesis the GRC linked genes are transcribed. I found big differences in the patterns of expression of GRC-linked genes between the two species, adding support for the notion that GRC evolution is very fast. Among the transcribed GRC genes, I found three relevant genes for spermatogenesis, sex-determination and germline maintenance shared by both species, suggesting a possible role of the GRC in those processes. The main conclusion from my work is that, in contrast to expectations, incompatibilities causing hybrid sterility can be found in genes with conserved functions. This is because a few changes in these genes may disrupt important networks of genes and quickly cause post-zygotic isolation at secondary contact.

Hybrid sterility and genetic incompatibilities in Ficedula flycatchers

Although the theory behind the mechanisms generating intrinsic post-zygotic isolation is well established, very few concrete examples of genetic incompatibilities have been described, especially in vertebrates. Consequently, our understanding of the evolutionary forces shaping the appearance of genetic incompatibilities between natural populations and the overall role of genetic incompatibilities in the speciation process is limited. In this doctoral thesis I will contribute to filling this gap in knowledge by using different approaches to investigate the causes and genetic basis of male hybrid sterility in a natural Ficedula flycatcher hybrid zone. I started by analyzing hybrid inviability patterns using 17 years of long-term monitoring data and found evidence for hybrid inviability at different life stages (Paper I). Early developmental failure of hybrids as revealed by the lower hatching success of mixed-species pairs suggesting emerging severe but non-fixed incompatibilities between the two species. Subtler differences in terms of lower growth potential and shorter lifespan indicate mito-nuclear incompatibilities as elevated metabolic rate can cause accumulation of toxic by-products in the form of Reactive Oxygen Species (ROS). Because previous evidence indicated problems during spermatogenesis in male hybrids, I characterized collared and pied flycatcher spermatogenesis at a single-cell level (Paper II). Since this was the first single-cell study investigating avian spermatogenesis, I identified the three main stages of spermatogenesis and described expression patterns of autosomes and Z-linked genes. By analyzing differential gene expression and estimates of protein evolution, I found that meiosis appears to be less evolutionary constraint in birds than in mammals. I propose that this fundamental difference is caused by the lack of MSCI in the spermatogenesis of ZW systems. Using the spermatogenesis characterization as a baseline, I then explored hybrid spermatogenesis to detect the stage of failure and associated genes (Paper III). By using a combination of histology sections, single-cell RNA sequencing and whole genome re-sequencing data, I found strong evidence of meiosis failure in hybrid spermatogenesis. I identified genes with non-synonymous fixed differences between the two species that were also DE during spermatogenesis. This enabled me to identify candidate genes causing genetic incompatibilities leading to meiosis failure in hybrid flycatchers. Finally, I explored the role of the enigmatic Germline restricted chromosome (GRC) in flycatcher spermatogenesis (Paper IV). I sequenced the GRC and revealed the gene contents for both species of flycatchers. Then we verified the transcription of the contents of the GRC and identified testis cell clusters containing GRC transcripts to reveal at what developmental stages of spermatogenesis the GRC linked genes are transcribed. I found big differences in the patterns of expression of GRC-linked genes between the two species, adding support for the notion that GRC evolution is very fast. Among the transcribed GRC genes, I found three relevant genes for spermatogenesis, sex-determination and germline maintenance shared by both species, suggesting a possible role of the GRC in those processes. The main conclusion from my work is that, in contrast to expectations, incompatibilities causing hybrid sterility can be found in genes with conserved functions. This is because a few changes in these genes may disrupt important networks of genes and quickly cause post-zygotic isolation at secondary contact.

Should females prefer old males?

Whether females should prefer to mate with old males is controversial. Old males may sire offspring of low quality because of an aging germline, but their proven ability to reach an old age can also be an excellent indicator of superior genetic quality, especially in natural populations. These genetic effects are, however, hard to study in nature, because they are often confounded with direct benefits offered by old males to the female, such as experience and high territory quality. We, therefore, used naturally occurring extra-pair young to disentangle different aspects of male age on female fitness in a natural population of collared flycatchers because any difference between within- and extra-pair young within a nest should be caused by paternal genetic effects only. Based on 18 years of long-term data, we found that females paired with older males as social partners experienced an overall reproductive advantage. However, offspring sired by old males were of lower quality as compared to their extra-pair half-siblings, whereas the opposite was found in nests attended by young males. These results imply a negative genetic effect of old paternal age, given that extra-pair males are competitive middle-age males. Thus, offspring may benefit from being sired by young males but raised by old males, to maximize both genetic and direct effects. Our results show that direct and genetic benefits from pairing with old males may act in opposing directions and that the quality of the germline may deteriorate before other signs of senescence become obvious.De två första författarna delar förstaförfattarskapet</p

Single-Cell Transcriptomics reveals relaxed evolutionary constraint of spermatogenesis in two passerine birds as compared to mammals

Spermatogenesis is a complex process where spermatogonia develop into haploid, mobile sperm cells. The genes guiding this process are subject to an evolutionary trade-off between preserving basic functions of sperm while acquiring new traits ensuring advantages in competition over fertilization of female gametes. In species with XY sex chromosomes, the outcome of this trade-off is found to vary across the stages of spermatogenesis but remains unexplored for species with ZW sex chromosomes. Here we characterize avian spermatogenesis at single cell resolution from testis of collared and pied flycatchers. We find evidence for relaxed evolutionary constraint of genes expressed in spermatocyte cells going through meiosis. An overrepresentation of Z-linked differentially expressed genes between the two species at this stage suggests that this relaxed constraint is associated with the lack of sex-chromosome silencing during meiosis. We conclude that the high throughput of bird spermatogenesis, at least partly, is explained by relaxed developmental constraint

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Abstract Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play.</jats:p

Toward the integration of speciation research

International audienceSpeciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges and argue that integration is a team effort in which we all have a role to play

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play

Clinical features, damage accrual, and survival in patients with familial systemic lupus erythematosus: data from a multi-ethnic, multinational Latin American lupus cohort

Objectives This study aimed to compare the clinical features, damage accrual, and survival of patients with familial and sporadic systemic lupus erythematosus (SLE). Methods A multi-ethnic, multinational Latin American SLE cohort was studied. Familial lupus was defined as patients with a first-degree SLE relative; these relatives were interviewed in person or by telephone. Clinical variables, disease activity, damage, and mortality were compared. Odds ratios (OR) and 95% confidence intervals (CI) were estimated. Hazard ratios (HR) were calculated using Cox proportional hazard adjusted for potential confounders for time to damage and mortality. Results A total of 66 (5.6%) patients had familial lupus, and 1110 (94.4%) had sporadic lupus. Both groups were predominantly female, of comparable age, and of similar ethnic distribution. Discoid lupus (OR = 1.97; 95% CI 1.08-3.60) and neurologic disorder (OR = 1.65; 95% CI 1.00-2.73) were significantly associated with familial SLE; pericarditis was negatively associated (OR = 0.35; 95% CI 0.14-0.87). The SLE Disease Activity Index and Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) were similar in both groups, although the neuropsychiatric (45.4% vs. 33.5%;p = 0.04) and musculoskeletal (6.1% vs. 1.9%;p = 0.02) domains of the SDI were more frequent in familial lupus. They were not retained in the Cox models (by domains). Familial lupus was not significantly associated with damage accrual (HR = 0.69; 95% CI 0.30-1.55) or mortality (HR = 1.23; 95% CI 0.26-4.81). Conclusion Familial SLE is not characterized by a more severe form of disease than sporadic lupus. We also observed that familial SLE has a higher frequency of discoid lupus and neurologic manifestations and a lower frequency of pericarditis

Toward the integration of speciation research

Acknowledgements: We thank the staff of the Tvärminne Zoological Station (University of Helsinki) for their hospitality during the workshop. We are also grateful to everyone who applied to attend the workshop.Funder: European Society for Evolutionary Biology; DOI: https://doi.org/10.13039/501100013632Speciation research—the scientific field focused on understanding the origin and diversity of species—has a long and complex history. While relevant to one another, the specific goals and activities of speciation researchers are highly diverse, and scattered across a collection of different perspectives. Thus, our understanding of speciation will benefit from efforts to bridge scientific findings and the diverse people who do the work. In this paper, we outline two ways of integrating speciation research: (i) scientific integration, through the bringing together of ideas, data, and approaches; and (ii) social integration, by creating ways for a diversity of researchers to participate in the scientific process. We then discuss five challenges to integration: (i) the multidisciplinary nature of speciation research, (ii) the complex language of speciation; (iii) a bias toward certain study systems; (iv) the challenges of working across scales; and (v) inconsistent measures and reporting standards. We provide practical steps that individuals and groups can take to help overcome these challenges, and argue that integration is a team effort in which we all have a role to play