Sex Disparities After Coronary Artery Bypass Grafting and Hospital Quality.

Importance: Concern has been raised about persistent sex disparities after coronary artery bypass grafting, with female patients having higher mortality. However, whether these disparities persist across hospitals of different qualities is unknown. Objective: To evaluate sex disparities in 30-day mortality after coronary artery bypass grafting across high- and low-quality hospitals. Design, Setting, and Participants: This cross-sectional, retrospective cohort study evaluated Medicare beneficiaries undergoing coronary artery bypass grafting between October 1, 2015, and March 31, 2020. Data analysis was performed from July 1, 2023, to December 1, 2023. Exposures: The primary exposures were hospital quality and sex. For hospital quality, hospitals were placed into rank order by their overall risk-adjusted mortality rate and divided into quintiles. Main Outcome and Measures: Risk-adjusted 30-day mortality using a logistic regression model accounting for patient factors, including sex, age, comorbidities, elective vs unplanned admission, number of bypass grafts, use of arterial graft, and year of surgery. Results: A total of 444 855 beneficiaries (mean [SD] age, 71.5 [7.5] years; 120 333 [27.1%] female and 324 522 [72.9%] male) were studied. Compared with male beneficiaries, female beneficiaries were more likely to have an unplanned admission (66 425 [55.2%] vs 157 895 [48.7%], P < .001) and receive care at low-quality (vs high-quality) hospitals (odds ratio, 1.26; 95% CI, 1.23-1.29; P < .001). Overall, risk-adjusted female mortality was 4.24% (95% CI, 4.20%-4.27%), and male mortality was 2.75% (95% CI, 2.75%-2.77%), with an absolute difference of 1.48 (95% CI, 1.45-1.51) percentage points (P < .001). At the highest-quality hospitals, male mortality was 1.57% (95% CI, 1.56%-1.59%), and female mortality was 2.58% (95% CI, 2.54%-2.62%), with an absolute difference of 1.01 (95% CI, 0.97-1.04) percentage points (P < .001). At the lowest-quality hospitals, male mortality was 4.94% (95% CI, 4.88%-5.01%), and female mortality was 7.02% (95% CI, 6.90%-7.13%), with an absolute difference of 2.07 (95% CI, 1.95-2.19) percentage points (P < .001). Female beneficiaries receiving care at low-quality hospitals had a higher mortality than male beneficiaries receiving care at the high-quality hospitals (7.02% vs 1.57%, P < .001). Conclusions and Relevance: In this cohort study of Medicare beneficiaries undergoing coronary artery bypass grafting, female beneficiaries were more likely to receive care at low-quality hospitals, where the sex disparity in mortality was double that of high-quality hospitals. Quality improvement targeting low-quality hospitals as well as equitable referral of female beneficiaries to higher-quality hospitals may narrow the sex disparity after coronary artery bypass grafting.

Evaluation of sex differences in the receipt of concomitant atrial fibrillation procedures during nonmitral cardiac surgery.

OBJECTIVE: Women are less likely to receive guideline-recommended cardiovascular care, but evaluation of sex-based disparities in cardiac surgical procedures is limited. Receipt of concomitant atrial fibrillation (AF) procedures during nonmitral cardiac surgery was compared by sex for patients with preoperative AF. METHODS: Patients with preoperative AF undergoing coronary artery bypass grafting and/or aortic valve replacement at any of the 33 hospitals in Michigan from 2014 to 2022 were included. Patients with prior cardiac surgery, transcatheter AF procedure, or emergency/salvage status were excluded. Hierarchical logistic regression identified predictors of concomitant AF procedures, account for hospital and surgeon as random effects. RESULTS: Of 5460 patients with preoperative AF undergoing nonmitral cardiac surgery, 24% (n = 1291) were women with a mean age of 71 years. Women were more likely to have paroxysmal (vs persistent) AF than men (80% vs 72%; P < .001) and had a higher mean predicted risk of mortality (5% vs 3%; P < .001). The unadjusted rate of concomitant AF procedure was 59% for women and 67% for men (P < .001). After risk adjustment, women had 26% lower adjusted odds of concomitant AF procedure than men (adjusted odds ratio, 0.74; 95% CI, 0.64-0.86; P < .001). Female sex was the risk factor associated with the lowest odds of concomitant AF procedure. CONCLUSIONS: Women are less likely to receive guideline recommended concomitant AF procedure during nonmitral surgery. Identification of barriers to concomitant AF procedure in women may improve treatment of AF.

Risk of Pacemaker Implantation After Degenerative Mitral and Concomitant Tricuspid Valve Surgery.

BACKGROUND: A recent multicenter trial showed a reduction in tricuspid regurgitation (TR) progression when tricuspid annuloplasty was performed at the time of surgery for degenerative mitral regurgitation (MR), but with a 14% pacemaker (PPM) rate. We present real-world outcomes at a high-volume center for degenerative MR surgery with/without tricuspid annuloplasty. METHODS: Patients undergoing first-time degenerative mitral surgery between 2011-2021 were identified (n=1,738). After excluding patients undergoing aortic, aortic valve, or tricuspid replacement procedures, patients were stratified into mitral surgery alone (n=1,068) versus mitral surgery plus tricuspid annuloplasty (n=417). Outcomes including operative mortality, new PPM implantation, and postoperative length of stay as well as risk-adjusted overall mortality were compared. RESULTS: Among 1,485 patients in this study, 98% underwent mitral repair. Compared to concomitant tricuspid annuloplasty patients, those undergoing mitral surgery alone were 6 years younger and had lower median STS PROM. Among concomitant tricuspid repair patients, 85% (355/417) had moderate or less preoperative TR, while 15% (61/417) had severe TR. Operative mortality was 1.4%. The incidence of new PPM implantation was 0.7% (7/1,068) in the mitral only group and 5.5% (23/417) in the concomitant tricuspid group (p<0.001). Although unadjusted cumulative survival was lower in the concomitant tricuspid group, after risk adjustment, concomitant tricuspid surgery was not associated with worse overall mortality (HR 0.80 [95% CI, 0.53-1.19], p=0.27). CONCLUSIONS: Concomitant tricuspid annuloplasty is safe, with no difference in mortality and a less than 6% PPM rate at a high-volume mitral center. These data provide real-world context for concomitant tricuspid annuloplasty.

Sex-Based Differences in Concomitant Tricuspid Repair During Degenerative Mitral Surgery.

BACKGROUND: Women with mitral valve disease have higher rates of tricuspid regurgitation (TR) than men. Although tricuspid valve repair (TVr) decreases the progression of TR, we hypothesize that there may be sex-based differences in concomitant TVr at the time of mitral valve operations. METHODS: Adults undergoing mitral valve operation for degenerative disease with moderate or worse preoperative TR at a high-volume center from 2014 to 2023 were identified. Patients with a previous tricuspid intervention were excluded. A multivariable logistic regression identified predictors of concomitant TVr. To evaluate the clinical impact of not performing TVr, a competing risk model compared development of severe TR or valve-related reoperation by sex among patients without TVr. RESULTS: Most included patients were women (55% [n = 214 of 388]), and the median age was 73 years (quartile 1-quartile 3, 65-79 years). There was no difference in the rate of severe TR by sex (female, 28%; male, 26%; P = .63). The unadjusted rate of concomitant TVr was 57% for women and 73% for men (P < .001). Overall, women had 52% lower adjusted odds of TVr (adjusted odds ratio, 0.48; 95% CI, 0.29-0.81; P = .006), including a lower adjusted rate for moderate TR (47% [95% CI, 45%-49%] vs 66% [95% CI, 64%-69%]) and for severe TR (83% [95% CI, 81%-86] vs 92% [95% CI, 90%-93%]) Among those without TVr, 12% of women and 0% of men had severe TR or required a valve-related reoperation at 4 years (P < .001). CONCLUSIONS: Women with moderate or severe TR undergoing mitral valve operation for degenerative disease were less likely to receive concomitant TVr, severe TR was more likely to develop, or they would more likely need a valve-related reoperation. Evaluation of sex-based treatment differences is imperative to improve outcomes for women.

A Nationwide Evaluation of Cardiothoracic Resident Research Productivity.

BACKGROUND: Evaluating the research productivity of cardiothoracic surgery residents during their training and early career is crucial for tracking their academic development. To this end, the training pathway of residents and the characteristics of their program in relation to their productivity were evaluated. METHODS: Alumni lists from integrated 6-year thoracic surgery (I-6) and traditional thoracic surgery residency programs were collected. A Python script was used to search PubMed for publications and the iCite database for citations from each trainee. Publications during a 20-year time span were stratified by the year of publication in relation to the trainee's graduation from thoracic surgery residency. Trainees were analyzed by training program type, institutional availability of a cardiothoracic surgery T32 training grant, and protected academic development time. RESULTS: A total of 741 cardiothoracic surgery graduates (I-6, 70; traditional, 671) spanning 1971 to 2021 from 57 programs published >23,000 manuscripts. I-6 trainees published significantly more manuscripts during medical school and residency compared with traditional trainees. Trainees at institutions with cardiothoracic surgery T32 training grants published significantly more manuscripts than those at non-T32 institutions (13 vs 9; P = .0048). I-6 trainees published more manuscripts at programs with dedicated academic development time compared with trainees at programs without protected time (22 vs 9; P = .004). CONCLUSIONS: I-6 trainees publish significantly more manuscripts during medical school and residency compared with their traditional colleagues. Trainees at institutions with T32 training grants and dedicated academic development time publish a higher number of manuscripts than trainees without those opportunities.

Isotopic signatures induced by upwelling reveal regional fish stocks in Lake Tanganyika.

Lake Tanganyika's pelagic fish sustain the second largest inland fishery in Africa and are under pressure from heavy fishing and global warming related increases in stratification. The strength of water column stratification varies regionally, with a more stratified north and an upwelling-driven, biologically more productive south. Only little is known about whether such regional hydrodynamic regimes induce ecological or genetic differences among populations of highly mobile, pelagic fish inhabiting these different areas. Here, we examine whether the regional contrasts leave distinct isotopic imprints in the pelagic fish of Lake Tanganyika, which may reveal differences in diet or lipid content. We conducted two lake-wide campaigns during different seasons and collected physical, nutrient, chlorophyll, phytoplankton and zooplankton data. Additionally, we analyzed the pelagic fish-the clupeids Stolothrissa tanganicae, Limnothrissa miodon and four Lates species-for their isotopic and elemental carbon (C) and nitrogen (N) compositions. The δ13C values were significantly higher in the productive south after the upwelling/mixing period across all trophic levels, implying that the fish have regional foraging grounds, and thus record these latitudinal isotope gradients. By combining our isotope data with previous genetic results showing little geographic structure, we demonstrate that the fish reside in a region for a season or longer. Between specimens from the north and south we found no strong evidence for varying trophic levels or lipid contents, based on their bulk δ15N and C:N ratios. We suggest that the development of regional trophic or physiological differences may be inhibited by the lake-wide gene flow on the long term. Overall, our findings show that the pelagic fish species, despite not showing evidence for genetic structure at the basin scale, form regional stocks at the seasonal timescales. This implies that sustainable management strategies may consider adopting regional fishing quotas.

Reference genome choice and filtering thresholds jointly influence phylogenomic analyses.

Molecular phylogenies are a cornerstone of modern comparative biology and are commonly employed to investigate a range of biological phenomena, such as diversification rates, patterns in trait evolution, biogeography, and community assembly. Recent work has demonstrated that significant biases may be introduced into downstream phylogenetic analyses from processing genomic data; however, it remains unclear whether there are interactions among bioinformatic parameters or biases introduced through the choice of reference genome for sequence alignment and variant-calling. We address these knowledge gaps by employing a combination of simulated and empirical data sets to investigate to what extent the choice of reference genome in upstream bioinformatic processing of genomic data influences phylogenetic inference, as well as the way that reference genome choice interacts with bioinformatic filtering choices and phylogenetic inference method. We demonstrate that more stringent minor allele filters bias inferred trees away from the true species tree topology, and that these biased trees tend to be more imbalanced and have a higher center of gravity than the true trees. We find greatest topological accuracy when filtering sites for minor allele count >3-4 in our 51-taxa data sets, while tree center of gravity was closest to the true value when filtering for sites with minor allele count >1-2. In contrast, filtering for missing data increased accuracy in the inferred topologies; however, this effect was small in comparison to the effect of minor allele filters and may be undesirable due to a subsequent mutation spectrum distortion. The bias introduced by these filters differs based on the reference genome used in short read alignment, providing further support that choosing a reference genome for alignment is an important bioinformatic decision with implications for downstream analyses. These results demonstrate that attributes of the study system and dataset (and their interaction) add important nuance for how best to assemble and filter short read genomic data for phylogenetic inference.

Postoperative atrial fibrillation in mitral valve surgery is not benign.

OBJECTIVE: Postoperative atrial fibrillation (POAF) is common after cardiac surgery and is often considered to be benign despite recent data suggesting worse outcomes. There are no guidelines for the amount of POAF that triggers anticoagulation or for postoperative surveillance. We examined the rate of POAF, incidence of neurologic events, development of permanent atrial fibrillation, and mortality in patients undergoing isolated mitral valve surgery at a Mitral Foundation reference center. METHODS: This is a retrospective cohort study of 922 adult patients from 2011 to 2022 with no preoperative history of arrhythmias. Multivariable logistic regression was used to identify independent risk factors for the primary outcomes. Kaplan-Meier analysis and Cox proportional-hazards model were used to characterize long-term survival. RESULTS: The incidence of POAF was 39%. Median follow-up was 4.9 months (interquartile range, 1.1-42.6 months). Diabetes (odds ratio [OR], 2.2; 95% CI, 1.2-4.1; P = .01) and increasing age (OR, 1.1; 95% CI, 1.0-1.1; P < .001) were risk factors for POAF, whereas New York Heart Association functional class was not. POAF was a risk factor for the development of permanent atrial fibrillation (OR, 3.2; 95% CI 1.9-5.4; P < .001), which was associated with increased risk of neurologic events (OR, 3.8; 95% CI, 1.5-9.7; P = .004). Ultimately, patients with POAF had worse unadjusted (P < .001) and adjusted long-term mortality (hazard ratio, 1.8; 95% CI, 1.1-3.1; P = .03). CONCLUSIONS: POAF is associated with an increased rate of neurologic events, portends development of permanent atrial fibrillation, and is associated with worse long-term survival. POAF is not benign and carries a long-term mortality implication.

Cycles of fusion and fission enabled rapid parallel adaptive radiations in African cichlids.

Although some lineages of animals and plants have made impressive adaptive radiations when provided with ecological opportunity, the propensities to radiate vary profoundly among lineages for unknown reasons. In Africa's Lake Victoria region, one cichlid lineage radiated in every lake, with the largest radiation taking place in a lake less than 16,000 years old. We show that all of its ecological guilds evolved in situ. Cycles of lineage fusion through admixture and lineage fission through speciation characterize the history of the radiation. It was jump-started when several swamp-dwelling refugial populations, each of which were of older hybrid descent, met in the newly forming lake, where they fused into a single population, resuspending old admixture variation. Each population contributed a different set of ancient alleles from which a new adaptive radiation assembled in record time, involving additional fusion-fission cycles. We argue that repeated fusion-fission cycles in the history of a lineage make adaptive radiation fast and predictable.

Conceptual and empirical bridges between micro- and macroevolution.

Explaining broad molecular, phenotypic and species biodiversity patterns necessitates a unifying framework spanning multiple evolutionary scales. Here we argue that although substantial effort has been made to reconcile microevolution and macroevolution, much work remains to identify the links between biological processes at play. We highlight four major questions of evolutionary biology whose solutions require conceptual bridges between micro and macroevolution. We review potential avenues for future research to establish how mechanisms at one scale (drift, mutation, migration, selection) translate to processes at the other scale (speciation, extinction, biogeographic dispersal) and vice versa. We propose ways in which current comparative methods to infer molecular evolution, phenotypic evolution and species diversification could be improved to specifically address these questions. We conclude that researchers are in a better position than ever before to build a synthesis to understand how microevolutionary dynamics unfold over millions of years.

Parallel shifts in trout feeding morphology suggest rapid adaptation to alpine lake environments.

Eco-evolutionary interactions following ecosystem change provide critical insight into the ability of organisms to adapt to shifting resource landscapes. Here we explore evidence for the rapid parallel evolution of trout feeding morphology following eco-evolutionary interactions with zooplankton in alpine lakes stocked at different points in time in the Wind River Range (Wyoming, USA). In this system, trout predation has altered the zooplankton species community and driven a decrease in average zooplankton size. In some lakes that were stocked decades ago, we find shifts in gill raker traits consistent with the hypothesis that trout have rapidly adapted to exploit available smaller-bodied zooplankton more effectively. We explore this morphological response in multiple lake populations across two species of trout (cutthroat trout, Oncorhynchus clarkii, and golden trout Oncorhynchus aguabonita) and examine the impact of resource availability on morphological variation in gill raker number among lakes. Furthermore, we present genetic data to provide evidence that historically stocked cutthroat trout populations likely derive from multiple population sources, and incorporate variation from genomic relatedness in our exploration of environmental predictors of feeding morphology. These findings describe rapid adaptation and eco-evolutionary interactions in trout and document an evolutionary response to novel, contemporary ecosystem change.

Repeat crossclamp after failed initial degenerative mitral valve repair is safe and successful.

Objective: Surgical risk and long-term outcomes when re-crossclamp is required during degenerative mitral valve repair are unknown. We examined the outcomes of patients who required re-crossclamp for mitral valve reintervention. Methods: Adults undergoing mitral valve repair for degenerative mitral valve disease at a single center from 2007 to 2021 who required more than 1 crossclamp for mitral valve reintervention were included. Outcomes including major morbidity and 30-day mortality were collected. Kaplan-Meier analysis characterized survival and freedom from recurrent mitral regurgitation. Results: A total of 69 patients required re-crossclamp for mitral valve reintervention. Of those, 72% (n = 50) underwent successful re-repair and the remaining underwent mitral valve replacement (28%, n = 19). Major morbidity occurred in 23% (n = 16). There was no 30-day mortality, and median long-term survival was 10.9 years for those undergoing re-repair and 7.2 years for those undergoing replacement (P = .79). Midterm echocardiography follow-up was available for 67% (33/50) of patients who were successfully re-repaired with a median follow-up of 20 (interquartile range, 7-37) months. At late follow-up, 90% of patients had mild or less mitral regurgitation. Of those re-repaired, 2 patients later required mitral valve reintervention. Conclusions: Patients requiring re-crossclamp for residual mitral regurgitation had low perioperative morbidity and no mortality. Most patients underwent successful re-repair (vs mitral valve replacement) with excellent valve function and long-term survival. In the event of unsatisfactory repair at the time of mitral valve repair, attempt at re-repair is safe and successful with the appropriate valvar anatomy.

Alfieri versus conventional repair for bileaflet mitral valve prolapse.

Objective: Mitral valve repair for bileaflet prolapse can be complex, involving multiple chords or resection. The Alfieri technique for bileaflet disease is simple but may be associated with mitral stenosis or recurrent mitral regurgitation. Outcomes of patients with bileaflet prolapse undergoing mitral valve repair using the Alfieri versus conventional chord/resection techniques were compared. Methods: Adults undergoing mitral valve repair for bileaflet prolapse for degenerative disease from 2017 to 2023 were stratified by repair technique. Outcomes including operative mortality and echocardiogram data were compared. Time to event analysis was used to characterize freedom from recurrent mitral regurgitation (moderate or greater mitral regurgitation). Results: Among 188 patients with bileaflet prolapse, 37% (70) were repaired with the Alfieri and the remaining patients were repaired with chords/resection. Compared with chords/resection, patients undergoing the Alfieri had shorter cardiopulmonary bypass and crossclamp times. Operative mortality (0% [0/70] vs 2% [2/118], P = .27) was similar between both techniques. The mean mitral gradient was low and similar for the Alfieri versus chords/resection (3 vs 3, P = .34). Development of recurrent mitral regurgitation at 2 years, incorporating the competing risk of death and mitral reintervention, was 4.3% (95% CI, 1.5%-9.3%) for the Alfieri technique and 5.8% (95% CI, 2.2%-11.8%) for chord/resection (P = .83). Conclusions: Both the Alfieri and chord/resection techniques had low rates of recurrent mitral regurgitation at 2 years. The mitral valve gradient was low and similar regardless of technique; thus, those who received the Alfieri technique did not have an increased rate of mitral stenosis. The Alfieri may be an underused technique for bileaflet prolapse.

Surgical outcomes of patients at prohibitive risk who are reconsidered for surgery.

Objectives: Transcatheter treatment of advanced mitral and tricuspid valve disease is largely limited to patients at prohibitive surgical risk, although many are not candidates for transcatheter treatment. Here, we describe surgical outcomes of patients at prohibitive risk who were ineligible for transcatheter therapies to guide surgeons in management of this unique population. Methods: Patients at prohibitive risk, defined per surgeon or cardiologist discretion, who were initially referred for a transcatheter mitral or tricuspid intervention in a multidisciplinary atrioventricular valve clinic, were identified from 2019 to 2022. Preoperative risk, operative outcomes, and long-term mortality were evaluated. Results: A total of 337 patients at prohibitive risk were referred for evaluation in a multidisciplinary atrioventricular valve clinic. Of those, 161 underwent transcatheter therapy, 130 patients underwent continued medical management, and 45 were reevaluated and had high-risk surgery. Among surgical patients, 51% were women with a median age of 76 years (quartile 1-quartile 3, 65-81 years). Most patients presented in heart failure (83%; n = 37 out of 45), and 73% were in New York Heart Association functional class III or IV. Most patients (94%; n = 43) had a mitral valve intervention, of whom 56% (24 out of 43) had a mitral valve replacement. The 30-day mortality rate was 4% (2 out of 45) and major morbidity occurred in 33% (15 out of 45). By Kaplan-Meier analysis, 1-year survival was 86% ± 9%. Conclusions: Select patients at prohibitive risk who were ineligible for transcatheter mitral or tricuspid valve intervention underwent surgery with overall low operative mortality and excellent 1-year survival. Patients a prohibitive risk whose anatomy is not amenable to transcatheter devices should be reconsidered for surgery.

Complete mitochondrial genomes and updated divergence time of the two freshwater clupeids endemic to Lake Tanganyika (Africa) suggest intralacustrine speciation.

BACKGROUND: The hydrogeological history of Lake Tanganyika paints a complex image of several colonization and adaptive radiation events. The initial basin was formed around 9-12 million years ago (MYA) from the predecessor of the Malagarasi-Congo River and only 5-6 MYA, its sub-basins fused to produce the clear, deep waters of today. Next to the well-known radiations of cichlid fishes, the lake also harbours a modest clade of only two clupeid species, Stolothrissa tanganicae and Limnothrissa miodon. They are members of Pellonulini, a tribe of clupeid fishes that mostly occur in freshwater and that colonized West and Central-Africa during a period of high sea levels during the Cenozoic. There is no consensus on the phylogenetic relationships between members of Pellonulini and the timing of the colonization of Lake Tanganyika by clupeids. RESULTS: We use short-read next generation sequencing of 10X Chromium libraries to sequence and assemble the full mitochondrial genomes of S. tanganicae and L. miodon. We then use Maximum likelihood and Bayesian inference to place them into the phylogeny of Pellonulini and other clupeiforms, taking advantage of all available full mitochondrial clupeiform genomes. We identify Potamothrissa obtusirostris as the closest living relative of the Tanganyika sardines and confirm paraphyly for Microthrissa. We estimate the divergence of the Tanganyika sardines around 3.64 MYA [95% CI: 0.99, 6.29], and from P. obtusirostris around 10.92 MYA [95% CI: 6.37-15.48]. CONCLUSIONS: These estimates imply that the ancestor of the Tanganyika sardines diverged from a riverine ancestor and entered the proto-lake Tanganyika around the time of its formation from the Malagarasi-Congo River, and diverged into the two extant species at the onset of deep clearwater conditions. Our results prompt a more thorough examination of the relationships within Pellonulini, and the new mitochondrial genomes provide an important resource for the future study of this tribe, e.g. as a reference for species identification, genetic diversity, and macroevolutionary studies.

Variable hybridization between two Lake Tanganyikan cichlid species in recent secondary contact.

Closely related taxa frequently exist in sympatry before the evolution of robust reproductive barriers, which can lead to substantial gene flow. Post-divergence gene flow can promote several disparate trajectories of divergence ranging from the erosion of distinctiveness and eventual collapse of the taxa to the strengthening of reproductive isolation. Among many relevant factors, understanding the demographic history of divergence (e.g. divergence time and extent of historical gene flow) can be particularly informative when examining contemporary gene flow between closely related taxa because this history can influence gene flow's prevalence and consequences. Here, we used genotyping-by-sequencing data to investigate speciation and contemporary hybridization in two closely related and sympatrically distributed Lake Tanganyikan cichlid species in the genus Petrochromis. Demographic modelling supported a speciation scenario involving divergence in isolation followed by secondary contact with bidirectional gene flow. Further investigation of this recent gene flow found evidence of ongoing hybridization between the species that varied in extent between different co-occurring populations. Relationships between abundance and the degree of admixture across populations suggest that the availability of conspecific mates may influence patterns of hybridization. These results, together with the observation that sets of recently diverged cichlid taxa are generally geographically separated in the lake, suggest that ongoing speciation in Lake Tanganyikan cichlids relies on initial spatial isolation. Additionally, the spatial heterogeneity of admixture between the Petrochromis species illustrates the complexities of hybridization when species are in recent secondary contact.

Hybridization decreases native cutthroat trout reproductive fitness.

Examining natural selection in wild populations is challenging, but crucial to understanding many ecological and evolutionary processes. Additionally, in hybridizing populations, natural selection may be an important determinant of the eventual outcome of hybridization. We characterized several components of relative fitness in hybridizing populations of Yellowstone cutthroat trout and rainbow trout in an effort to better understand the prolonged persistence of both parental species despite predictions of extirpation. Thousands of genomic loci enabled precise quantification of hybrid status in adult and subsequent juvenile generations; a subset of those data also identified parent-offspring relationships. We used linear models and simulations to assess the effects of ancestry on reproductive output and mate choice decisions. We found a relatively low number of late-stage (F3+) hybrids and an excess of F2 juveniles relative to the adult generation in one location, which suggests the presence of hybrid breakdown decreasing the fitness of F2+ hybrids later in life. Assessments of reproductive output showed that Yellowstone cutthroat trout are more likely to successfully reproduce and produce slightly more offspring than their rainbow trout and hybrid counterparts. Mate choice appeared to be largely random, though we did find statistical support for slight female preference for males of similar ancestry. Together, these results show that native Yellowstone cutthroat trout are able to outperform rainbow trout in terms of reproduction and suggest that management action to exclude rainbow trout from spawning locations may bolster the now-rare Yellowstone cutthroat trout.