The establishment of reproductive barriers between populations can fuel the evolution of new species. A genetic framework for this process posits that “incompatible” interactions between genes can evolve that result in reduced survival or reproduction in hybrids. However, progress has been slow in identifying individual genes that underlie hybrid incompatibilities. We used a combination of approaches to map the genes that drive the development of an incompatibility that causes melanoma in swordtail fish hybrids. One of the genes involved in this incompatibility also causes melanoma in hybrids between distantly related species. Moreover, this melanoma reduces survival in the wild, likely because of progressive degradation of the fin. This work identifies genes underlying a vertebrate hybrid incompatibility and provides a glimpse into the action of these genes in natural hybrid populations.

The establishment of reproductive barriers between populations is the key process that fuels the evolution of new species. A genetic framework for this process was proposed over 80 years ago, which posits “incompatible” interactions between genes that result in reduced survival or reproduction in hybrids. Despite this foundational work, progress has been slow in identifying individual genes that underlie hybrid incompatibilities, with only a handful known to date. Here, we use a combination of approaches to precisely map the genes that drive the development of a melanoma incompatibility in swordtail fish hybrids. We find that one of the genes involved in this incompatibility also causes melanoma in hybrids between distantly related species. Moreover, we show that this melanoma reduces survival in the wild, likely due to progressive degradation of the fin. Together, this work represents only the second case where the genes underlying a vertebrate hybrid incompatibility have been identified and provides the first glimpse into the action of these genes in natural hybrid populations.One sentence summaryUsing a combination of mapping approaches, we identify interacting genes that lead to melanoma in hybrids and characterize their effects in natural hybrid populations.

Biologists since Darwin have been fascinated by the evolution of sexually selected ornaments, particularly those that reduce viability. Uncovering the genetic architecture of these traits is key to understanding how they evolve and are maintained. Here, we investigate the genetic architecture of a sexually selected ornament, the "sword" fin extension that characterizes many species of swordtail fish (Xiphophorus). Using sworded and swordless sister species of Xiphophorus, we generated a mapping population and show that the sword ornament is polygenic -with ancestry across the genome explaining substantial variation in the trait. After accounting for the impacts of genome-wide ancestry, we identify one major effect QTL that explains ~5% of the overall variation in the trait. Using a series of approaches, we narrow this large QTL interval to a handful of likely candidate genes, including the gene sp8. Notably, sp8 plays a regulatory role in fin regeneration and harbors several derived substitutions that are predicted to impact protein function in the species that has lost the sword ornament. Furthermore, we find evidence of selection on ancestry at sp8 in four natural hybrid populations, consistent with selection against the sword in these populations..

Background Smartphone studies provide an opportunity to collect frequent data at a low burden on participants. Therefore, smartphones may enable data collection from people with progressive neurodegenerative diseases such as amyotrophic lateral sclerosis at high frequencies for a long duration. However, the progressive decline in patients’ cognitive and functional abilities could also hamper the feasibility of collecting patient-reported outcomes, audio recordings, and location data in the long term. Objective The aim of this study is to investigate the completeness of survey data, audio recordings, and passively collected location data from 3 smartphone-based studies of people with amyotrophic lateral sclerosis. Methods We analyzed data completeness in three studies: 2 observational cohort studies (study 1: N=22; duration=12 weeks and study 2: N=49; duration=52 weeks) and 1 clinical trial (study 3: N=49; duration=20 weeks). In these studies, participants were asked to complete weekly surveys; weekly audio recordings; and in the background, the app collected sensor data, including location data. For each of the three studies and each of the three data streams, we estimated time-to-discontinuation using the Kaplan–Meier method. We identified predictors of app discontinuation using Cox proportional hazards regression analysis. We quantified data completeness for both early dropouts and participants who remained engaged for longer. Results Time-to-discontinuation was shortest in the year-long observational study and longest in the clinical trial. After 3 months in the study, most participants still completed surveys and audio recordings: 77% (17/22) in study 1, 59% (29/49) in study 2, and 96% (22/23) in study 3. After 3 months, passively collected location data were collected for 95% (21/22), 86% (42/49), and 100% (23/23) of the participants. The Cox regression did not provide evidence that demographic characteristics or disease severity at baseline were associated with attrition, although it was somewhat underpowered. The mean data completeness was the highest for passively collected location data. For most participants, data completeness declined over time; mean data completeness was typically lower in the month before participants dropped out. Moreover, data completeness was lower for people who dropped out in the first study month (very few data points) compared with participants who adhered long term (data completeness fluctuating around 75%). Conclusions These three studies successfully collected smartphone data longitudinally from a neurodegenerative population. Despite patients’ progressive physical and cognitive decline, time-to-discontinuation was higher than in typical smartphone studies. Our study provides an important benchmark for participant engagement in a neurodegenerative population. To increase data completeness, collecting passive data (such as location data) and identifying participants who are likely to adhere during the initial phase of a study can be useful. Trial Registration ClinicalTrials.gov NCT03168711; https://clinicaltrials.gov/ct2/show/NCT03168711

Biologists since Darwin have been fascinated by the evolution of sexually selected ornaments, particularly those that reduce viability. Uncovering the genetic architecture of these traits is key to understanding how they evolve and are maintained. Here, we investigate the genetic architecture of a sexually selected ornament, the “sword” fin extension that characterizes many species of swordtail fish (Xiphophorus). Using sworded and swordless sister species of Xiphophorus, we generated a mapping population and show that the sword ornament is polygenic – with ancestry across the genome explaining substantial variation in the trait. After accounting for the impacts of genome-wide ancestry, we identify one major effect QTL that explains ∼5% of the overall variation in the trait. Using a series of approaches, we narrow this large QTL interval to a handful of likely candidate genes, including the gene sp8. Notably, sp8 plays a regulatory role in fin regeneration and harbors several derived substitutions that are predicted to impact protein function in the species that has lost the sword ornament. Furthermore, we find evidence of selection on ancestry at sp8 in four natural hybrid populations, consistent with selection against the sword in these populations.