The Mongolian gerbil as an advanced model to study cone system physiology.

In this work, we introduce a diurnal rodent, the Mongolian gerbil (Meriones unguiculatus) (MG) as an alternative to study retinal cone system physiology and pathophysiology in mice. The cone system is of particular importance, as it provides high-acuity and color vision and its impairment in retinal disorders is thus especially disabling. Despite their nocturnal lifestyle, mice are currently the most popular animals to study cone-related diseases due to the high availability of genetically modified models. However, the potential for successful translation of any cone-related results is limited due to the substantial differences in retinal organization between mice and humans. Alternatively, there are diurnal rodents such as the MG with a higher retinal proportion of cones and a macula-like specialized region for improved visual resolution, the visual streak. The focus of this work was the evaluation of the MG's cone system functionality using full-field electroretinography (ERG), together with a morphological assessment of its retinal/visual streak organization via angiography, optical coherence tomography (OCT), and photoreceptor immunohistochemistry. We found that rod system responses in MGs were comparable or slightly inferior to mice, while in contrast, cone system responses were much larger, more sensitive, and also faster than those in the murine counterparts, and in addition, it was possible to record sizeable ON and OFF ERG components. Morphologically, MG cone photoreceptor opsins were evenly distributed throughout the retina, while mice show a dorsoventral M- and S-opsin gradient. Additionally, each cone expressed a single opsin, in contrast to the typical co-expression of opsins in mice. Particular attention was given to the visual streak region, featuring a higher density of cones, elongated cone and rod outer segments (OSs), and an increased thickness of the inner and outer retinal layers in comparison to peripheral regions. In summary, our data render the MG a supreme model to investigate cone system physiology, pathophysiology, and to validate potential therapeutic strategies in that context.

Mural Serum Response Factor (SRF) Deficiency Provides Insights into Retinal Vascular Functionality and Development.

Serum response factor (SRF) controls the expression of muscle contraction and motility genes in mural cells (MCs) of the vasculature. In the retina, MC-SRF is important for correct angiogenesis during development and the continuing maintenance of the vascular tone. The purpose of this study was to provide further insights into the effects of MC SRF deficiency on the vasculature and function of the mature retina in SrfiMCKO mice that carry a MC-specific deletion of Srf. Retinal morphology and vascular integrity were analyzed in vivo via scanning laser ophthalmoscopy (SLO), angiography, and optical coherence tomography (OCT). Retinal function was evaluated with full-field electroretinography (ERG). We found that retinal blood vessels of these mutants exhibited different degrees of morphological and functional alterations. With increasing severity, we found vascular bulging, the formation of arteriovenous (AV) anastomoses, and ultimately, a retinal detachment (RD). The associated irregular retinal blood pressure and flow distribution eventually induced hypoxia, indicated by a negative ERG waveform shape. Further, the high frequency of interocular differences in the phenotype of individual SrfiMCKO mice points to a secondary nature of these developments far downstream of the genetic defect and rather dependent on the local retinal context.

Time-Varying Use of Proton Pump Inhibitors and Cognitive Impairment and Dementia: A Real-World Analysis from Germany.

BACKGROUND: Cumulative evidence of dementia risk in patients taking proton pump inhibitors (PPIs) is still inconclusive, probably due to a variety of study designs. OBJECTIVE: This study aimed to compare how the association between dementia risk and use of PPIs differs by different outcome and exposure definitions. METHODS: We conceptualized a target trial using claims data with 7,696,127 individuals aged 40 years or older without previous dementia or mild cognitive impairment (MCI) from the Association of Statutory Health Insurance Physicians in Bavaria. Dementia was defined as either including or excluding MCI to compare how the results alter by different outcome definitions. We used weighted Cox models to estimate the PPI initiation effect on dementia risk and weighted pooled logistic regression to assess the effect of time-varying use versus non-use during 9 years of study period, including 1 year of wash-out period (2009-2018). The median follow-up time of PPI initiators and non-initiators was 5.4 and 5.8 years, respectively. We also evaluated the association between each PPI agent (omeprazole, pantoprazole, lansoprazole, esomeprazole, and combined use) and dementia risk. RESULTS: A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk. A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk.A total of 105,220 (3.6%) PPI initiators and 74,697 (2.6%) non-initiators were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio (HR) for dementia was 1.04 [95% confidence interval (CI) 1.03-1.05]. The HR for time-varying PPI use versus non-use was 1.85 (1.80-1.90). When MCI was included in the outcome, the number of outcomes increased to 121,922 in PPI initiators and 86,954 in non-initiators, but HRs remained similar, showing 1.04 (1.03-1.05) and 1.82 (1.77-1.86), respectively. Pantoprazole was the most frequently used PPI agent. Although the estimated HRs for the time-varying use effect of each PPI showed different ranges, all agents were associated with an increased dementia risk. CONCLUSION: Our large study supports existing evidence that PPI use is related to an increased risk of dementia.

Do proton pump inhibitors increase the risk of dementia? A systematic review, meta-analysis and bias analysis.

AIM: Previous studies on the association between proton pump inhibitor (PPI) intake and the increased risk of dementia has shown discrepancies in their conclusions. We aimed to provide updated evidence based on extensive bias assessments and quantitative sensitivity analyses. METHODS: We searched the databases PubMed, EMBASE, SCOPUS, CENTRAL and clinicaltrials.gov for prospective studies that examined an association between PPI use and dementia, up to February 2022. Each study was assessed using the Cochrane risk of bias assessment tools for non-randomized studies of interventions (ROBINS-I) or randomized trials (RoB2). Pooled risk ratios (RRs) and 95% prediction intervals were computed using random-effects models. Sensitivity analyses were adjusted for small-study bias. RESULTS: We included nine observational studies with 204 108 dementia cases in the primary analysis on the association between PPI use vs. non-use and dementia, and the RR was 1.16 (95% CI = 1.00; 1.35). After adjusting for small-study bias by Copas selection model and Rücker's shrinkage procedure, the RR was 1.16 (1.02; 1.32) and 1.15 (1.13; 1.17), respectively. A subgroup analysis of PPI use vs. non-use regarding Alzheimer's disease risk yielded an RR of 1.15 (0.89; 1.50). The secondary analysis on the risk of dementia by use of PPI vs. histamine-2 receptor antagonist showed an RR of 1.03 (0.66; 1.62). CONCLUSION: This meta-analysis provided no clear evidence for an association between PPI intake and the risk of dementia. Due to discrepancies in sensitivity analyses, however, some risk of dementia by PPI use cannot be ruled out. Since an unequivocal conclusion is still pending, further research is warranted.

Proton pump inhibitors and the risk of cardiovascular events and cardiovascular mortality: A systematic review and meta-analysis of observational studies.

BACKGROUND AND AIMS: Observational research has indicated that proton pump inhibitors (PPIs) might increase the long-term risk of cardiovascular events. This study evaluated the evidence from observational studies for an effect of PPI monotherapy on the risk of incident cardiovascular events and cardiovascular mortality. METHODS: The databases MEDLINE, EMBASE, and Scopus were systematically searched up to September 2021. The primary outcome was first cardiovascular event, i.e. first myocardial infarction or first ischaemic stroke. The secondary outcome was cardiovascular mortality. Studies were included following a detailed risk of bias assessment with the ROBINS-I tool. Sensitivity and bias analyses adjusted for potential publication bias, immortal time bias, and unmeasured confounding. RESULTS: We included ten studies with 75,371 first cardiovascular events, as well as seven studies on cardiovascular mortality with 50,329 cardiovascular deaths in total. The pooled hazard ratios (HRs) for PPI use and cardiovascular events were 1.05 with a 95% confidence interval of (0.96; 1.15) before and 0.99 (0.93; 1.04) after adjusting for observational study design bias. The pooled HRs for PPI use and cardiovascular mortality were 1.27 (1.11; 1.44) before and 1.06 (0.96; 1.16) after adjusting for publication bias and observational study design bias. CONCLUSION: It is questionable, whether PPI monotherapy constitutes a cardiovascular risk factor.

Inherited Retinal Degeneration: PARP-Dependent Activation of Calpain Requires CNG Channel Activity.

Inherited retinal degenerations (IRDs) are a group of blinding diseases, typically involving a progressive loss of photoreceptors. The IRD pathology is often based on an accumulation of cGMP in photoreceptors and associated with the excessive activation of calpain and poly (ADP-ribose) polymerase (PARP). Inhibitors of calpain or PARP have shown promise in preventing photoreceptor cell death, yet the relationship between these enzymes remains unclear. To explore this further, organotypic retinal explant cultures derived from wild-type and IRD-mutant mice were treated with inhibitors specific for calpain, PARP, and voltage-gated Ca2+ channels (VGCCs). The outcomes were assessed using in situ activity assays for calpain and PARP and immunostaining for activated calpain-2, poly (ADP-ribose), and cGMP, as well as the TUNEL assay for cell death detection. The IRD models included the Pde6b-mutant rd1 mouse and rd1*Cngb1-/- double-mutant mice, which lack the beta subunit of the rod cyclic nucleotide-gated (CNG) channel and are partially protected from rd1 degeneration. We confirmed that an inhibition of either calpain or PARP reduces photoreceptor cell death in rd1 retina. However, while the activity of calpain was decreased by the inhibition of PARP, calpain inhibition did not alter the PARP activity. A combination treatment with calpain and PARP inhibitors did not synergistically reduce cell death. In the slow degeneration of rd1*Cngb1-/- double mutant, VGCC inhibition delayed photoreceptor cell death, while PARP inhibition did not. Our results indicate that PARP acts upstream of calpain and that both are part of the same degenerative pathway in Pde6b-dependent photoreceptor degeneration. While PARP activation may be associated with CNG channel activity, calpain activation is linked to VGCC opening. Overall, our data highlights PARP as a target for therapeutic interventions in IRD-type diseases.

Emulating a target trial of proton pump inhibitors and dementia risk using claims data.

BACKGROUND AND PURPOSE: Understanding the adverse effects of proton pump inhibitors (PPIs) is important due to their widespread use, but the available evidence for an increased dementia risk amongst patients taking PPIs is inconclusive. The present study aimed to estimate the causal effect of PPIs on the risk of dementia by target trial emulation and time-varying exposure modeling. METHODS: Using claims data of 2,698,176 insured people of a large German statutory health insurer, a target trial was conceptualized in which individuals aged 40 years and older were classified as PPI initiators or non-initiators between 2008 and 2018, and were followed until diagnosis of dementia, death, loss to follow-up or end of study. Incidence of dementia (International Classification of Diseases 10 codes F00, F01, F03, F05.1, G30, G31.0, G31.1, G31.9 and F02.8+G31.82) was defined applying a 1-year lag window. Weighted Cox models were used to estimate the effect of PPI initiation versus non-initiation on dementia risk and weighted pooled logistic regression was used to estimate the effect of time-varying use versus non-use. RESULTS: In all, 29,746 PPI initiators (4.4%) and 26,830 non-initiators (1.3%) were diagnosed with dementia. Comparing PPI initiation with no initiation, the hazard ratio for dementia was 1.54 (95% confidence interval 1.51-1.58). The hazard ratio for time-dependent PPI use versus non-use was 1.56 (95% confidence interval 1.50-1.63). Differentiated subtypes, including unspecified dementia, Alzheimer's disease and vascular dementia, showed increased risk by PPI initiation and time-varying PPI use. CONCLUSIONS: This study suggests that PPI initiation and time-varying PPI use may increase overall dementia risk.

Who gets prescriptions for proton pump inhibitors and why? A drug-utilization study with claims data in Bavaria, Germany, 2010-2018.

PURPOSE: The German annual drug prescription-report has indicated overuse of proton pump inhibitors (PPIs) for many years; however, little was known about the characteristics of people using PPIs. This study aimed to provide comprehensive utilization data and describe frequencies of potential on- and off-label PPI-indications in Bavaria, Germany. METHODS: Claims data of statutorily insured people from 2010 to 2018 were used. Defined daily doses (DDDs) of PPIs by type of drug, prevalence of PPI-use and DDDs prescribed per 1000 insured people/day were analyzed. For 2018, proportions of users and DDDs per 1000 insured people were calculated by age and sex. To elucidate changes in prescribing practices due to a suspected drug-drug interaction, we examined co-prescribing of clopidogrel and PPIs between 2010 and 2018. For PPI new users, sums of DDDs and frequencies of potential indications were examined. RESULTS: PPI prescribing increased linearly from 2010 to 2016 and gradually decreased from 2016 to 2018. In 2018, 14.7% of women and 12.2% of men received at least one prescription, and 64.8 DDDs (WHO-def.) per 1000 insured people/day were prescribed. Overall, omeprazole use decreased over the observation period and was steadily replaced by pantoprazole, especially when co-prescibed with clopidogrel. An on-label PPI-indication was not reported at first intake in 52.0% of new users. CONCLUSIONS: The utilization of prescribed PPIs has decreased since 2016. However, a large proportion of new PPI-users had no documentation of a potential indication, and the sums of DDDs prescribed often seemed not to comply with guidelines.

The long-term risk for myocardial infarction or stroke after proton pump inhibitor therapy (2008-2018).

BACKGROUND: Proton pump inhibitors (PPIs) are well tolerated in the short term but have recently been associated with increased long-term cardiovascular risk in observational studies. AIMS: To evaluate long-term risks of myocardial infarction (MI) and ischaemic stroke (IS) associated with PPI vs H2 -receptor antagonist (H2 RA) therapy in adults without pre-existing cardiovascular or cerebrovascular disease METHODS: Using administrative claims data (2008-2018), we emulated a target trial comparing MI and IS risks in new users of PPIs vs H2 RAs. Treatment was identified using dispensed prescriptions. MI and IS were defined using hospital discharge codes. Inverse probability weighting was used to adjust for confounding, and Cox models to estimate hazard ratios (HRs). Survival curves were estimated using weighted Kaplan-Meier estimators. RESULTS: We identified 1 143 948 new users of PPIs and 36 229 new users of H2 RAs who were free of prevalent cardiovascular or cerebrovascular disease. The mean follow-up time was 6.2 years for PPI initiators and 5.3 years for H2 RA initiators. After 10 years, the HRs for MI and IS were 0.96 (95% confidence interval (CI): 0.80-1.16) and 0.98 (95% CI: 0.89-1.08), respectively. CONCLUSIONS: This analysis of claims data of a large German health insurer did not provide evidence that PPI therapy increased the risk of MI or IS in the first decade after treatment initiation.

[Measuring, assessing, acting: A practice test of quality indicators for coronary heart disease]. / Messen, Bewerten, Handeln: Qualitätsindikatoren zur Koronaren Herzkrankheit im Praxistest.

BACKGROUND: There are only limited possibilities for doctors in outpatient services to establish quality management that is based on data-driven feedback regarding the quality of health care. However, transparency about one's own activities is a prerequisite for refining this quality. The aim of this project was to make the quality of care for patients with coronary heart disease (CHD) more transparent, use this as a basis to initiate improvement processes, and explore the framework conditions and factors promoting or inhibiting the intended improvement of health care quality. METHOD: 48 general practitioners (GPs) in 32 GP practices from a Bavarian doctors' network (Qualität und Effizienz, QuE) participated in the project. On the basis of claims data from the AOK-Bayern (a statutory health insurance in Bavaria), data from disease management programs (DMP) and medically documented data, 11 quality indicators for patients with CHD were calculated. The indicator scores were individually presented in feedback reports for each doctor's practice. These were the basis for two quality circles. The indicators were measured again after 12 months, and changes against the baseline measurement were registered. GPs from Bavaria formed the control group. Focus groups with the quality circle moderators and two participant surveys were used to identify promoting and inhibiting factors. RESULTS: The baseline values showed a good level of care. Potential for improvement became apparent for pharmacotherapy with beta blockers and statins. After conducting the quality circles four of the eleven indicators showed an increase as intended ("beta blockers for CHD and cardiac insufficiency", "beta blockers after myocardial infarction", "statins", "successful blood pressure control"). For three of these indicators the increase rates were higher than those in the Bavarian control group. One indicator ("statins") was striking because of the wide variation of practice values suggesting differences in care within the network. The majority of participating doctors regarded the database as valid. Quality circles were highly appreciated as an opportunity for professional exchange among colleagues. The data-based feedback reports helped to make deficits in health care transparent and to identify actions that need to be taken. Barriers to implementing quality improvement measures in clinical practice became apparent. DISCUSSION: Reflecting quality indicators in quality circles can effectively trigger quality improvement processes. Barriers would appear to exist, in particular, to the implementation of measures into daily practice routine. Additional organizational support offered by higher-level quality management structures, IT solutions for patient-related data processing as well as a system of financial compensation, which rewards professional concern for quality, may help to overcome the existing barriers.

Neuro-glial cannabinoid receptors modulate signaling in the embryonic avian retina.

Endocannabinoids are endogenous lipids that activate selective G protein coupled receptors (CB1 and CB2), mostly found at neuronal presynaptic sites in the nervous system. One of the main consequences of the activation of CB receptors is a decrease in GABA or glutamate release, controlling cell excitability. Here we studied the expression of CB1 and CB2 receptors in E8C8 cultured retina cells (embryonic day 8 and 8 days in vitro) using immunocytochemistry and western blot analysis. We also evaluated their functions in terms of cyclic AMP (cAMP) production, single cell calcium imaging (SCCI) and GABA release induced in basal conditions or activated by l-Aspartate (L-ASP) in cell cultures or under ischemia in young chick retina. We show that both cannabinoid receptors are expressed in retinal neurons and glial cells. WIN 55,212-2 (WIN, a CB1/CB2 agonist) decreased cAMP production in cultured avian embryonic retinal cells in basal conditions. WIN also led to a decrease in the number of glial cells that increased Ca2+ levels evoked by ATP, but had no effect in Ca2+ shifts in neuronal cells activated by KCl. Finally, WIN inhibited [3H]-GABA release induced by KCl or L-ASP, accumulated in amacrine cells, but had no effect in the amount of GABA released in an oxygen glucose deprivation (OGD) condition. Altogether, our data indicate that cannabinoid receptors function as regulators of avian retina signaling at critical embryonic stages during synapse formation.

Frequent but asymmetric niche shifts in Bulbophyllum orchids support environmental and climatic instability in Madagascar over Quaternary time scales.

BACKGROUND: Species or clades may retain or shift their environmental niche space over evolutionary time. Understanding these processes offers insights into the environmental processes fuelling lineage diversification and might also provide information on past range dynamics of ecosystems. However, little is known about the relative contributions of niche conservatism versus niche divergence to species diversification in the tropics. Here, we examined broad-scale patterns of niche evolution within a Pliocene-Pleistocene clade of epiphytic Bulbophyllum orchids (30 spp.) whose collective distribution covers the northwest and eastern forest ecosystems of Madagascar. RESULTS: Using species occurrence data, ecological niche models, and multivariate analyses of contributing variables, we identified a three-state niche distribution character for the entire clade, coinciding with three major forest biomes viz. phytogeographical provinces in Madagascar: A, Northwest 'Sambirano'; B, 'Eastern Lowlands'; and C, 'Central Highlands'. A time-calibrated phylogeny and Bayesian models of niche evolution were then used to detect general trends in the direction of niche change over the clade's history (≤5.3 Ma). We found highest transitions rates between lowlands (A and B) and (mostly from B) into the highland (C), with extremely low rates out of the latter. Lowland-to-highland transitions occurred frequently during the Quaternary, suggesting that climate-induced vegetational shifts promoted niche transitions and ecological speciation at this time. CONCLUSIONS: Our results reveal that niche transitions occurred frequently and asymmetrically within this Madagascan orchid clade, and in particular over Quaternary time scales. Intrinsic features germane to Bulbophyllum (e.g., high dispersal ability, drought tolerance, multiple photosynthetic pathways) as well as extrinsic factors (ecological, historical) likely interacted to generate the niche transition patterns observed. In sum, our results support the emerging idea of dramatic environmental and climatic fluctuations in Madagascar during the recent geological past, which overturns the long-held paradigm of long-term stability in tropical forest settings. The generality of the patterns and timings reported here awaits the availability of additional comparative studies in other Madagascan endemics.

Multiple independent origins of auto-pollination in tropical orchids (Bulbophyllum) in light of the hypothesis of selfing as an evolutionary dead end.

BACKGROUND: The transition from outcrossing to selfing has long been portrayed as an 'evolutionary dead end' because, first, reversals are unlikely and, second, selfing lineages suffer from higher rates of extinction owing to a reduced potential for adaptation and the accumulation of deleterious mutations. We tested these two predictions in a clade of Madagascan Bulbophyllum orchids (30 spp.), including eight species where auto-pollinating morphs (i.e., selfers, without a 'rostellum') co-exist with their pollinator-dependent conspecifics (i.e., outcrossers, possessing a rostellum). Specifically, we addressed this issue on the basis of a time-calibrated phylogeny by means of ancestral character reconstructions and within the state-dependent evolution framework of BiSSE (Binary State Speciation and Extinction), which allowed jointly estimating rates of transition, speciation, and extinction between outcrossing and selfing. RESULTS: The eight species capable of selfing occurred in scattered positions across the phylogeny, with two likely originating in the Pliocene (ca. 4.4-3.1 Ma), one in the Early Pleistocene (ca. 2.4 Ma), and five since the mid-Pleistocene (ca. ≤ 1.3 Ma). We infer that this scattered phylogenetic distribution of selfing is best described by models including up to eight independent outcrossing-to-selfing transitions and very low rates of speciation (and either moderate or zero rates of extinction) associated with selfing. CONCLUSIONS: The frequent and irreversible outcrossing-to-selfing transitions in Madagascan Bulbophyllum are clearly congruent with the first prediction of the dead end hypothesis. The inability of our study to conclusively reject or support the likewise predicted higher extinction rate in selfing lineages might be explained by a combination of methodological limitations (low statistical power of our BiSSE approach to reliably estimate extinction in small-sized trees) and evolutionary processes (insufficient time elapsed for selfers to go extinct). We suggest that, in these tropical orchids, a simple genetic basis of selfing (via loss of the 'rostellum') is needed to explain the strikingly recurrent transitions to selfing, perhaps reflecting rapid response to parallel and novel selective environments over Late Quaternary (≤ 1.3 Ma) time scales.