Postdivergence gene flow can trigger a number of creative evolutionary outcomes, ranging from the transfer of beneficial alleles across species boundaries (i.e., adaptive introgression) to the formation of new species (i.e., hybrid speciation). Although neutral and adaptive introgression has been broadly documented in nature, hybrid speciation is assumed to be rare and the evolutionary and ecological context facilitating this phenomenon still remains controversial. Through combining genomic and phenotypic data, we evaluate the hypothesis that the dual feeding regime (based on both scrub legumes and gramineous herbs) of the taxonomically controversial grasshopper Chorthippus saulcyi algoaldensis resulted from hybridization between the sister taxa C. binotatus (that exclusively feeds on scrub legumes) and C. saulcyi (that only feeds on gramineous herbs). Genetic clustering analyses and inferences from coalescent-based demographic simulations confirm that C. s. algoaldensis represents an independently evolving lineage and support the ancient hybrid origin of this taxon (about 1.4 Ma), which sheds light on its uncertain phylogenetic position and might explain its broader trophic niche. We propose a Pleistocene hybrid speciation model where range shifts resulting from climatic oscillations can promote the formation of hybrid swarms and facilitate their long-term persistence through geographic isolation from parental forms in topographically complex landscapes., We are grateful to P. J. Cordero and A. Hidalgo-Galiana for their help during field and laboratory work, respectively, and two anonymous referees for their constructive and valuable comments on an earlier version of the manuscript. We wish to thank to Centro de Supercomputación de Galicia (CESGA) and Doñana’s Singular Scientific-Technical Infrastructure (ICTS-RBD) for access to computer resources. Logistical support was provided by Laboratorio de Ecología Molecular (LEMEBD) from Estación Biológica de Doñana. This work was funded by the Spanish Ministry of Science and Innovation and the European Regional Development Fund (grants CGL2011-25053, CGL2014-54671-P, CGL2016-80742-R, CGL2017-83433-P, and PID2021 123298NBI00). During this work, VN was supported by a Juan de la Cierva-Formación postdoctoral fellowship (grant FJC2018-035611-I) funded by MCIN/AEI/10.13039/501100011033., Peer reviewed

Identifying the drivers of microgeographic speciation (i.e., speciation over small, local geographic scales) is key to understand the origin of speciose groups. Here, we use genomic data to infer the demographic processes underlying diversification in Poecilimon luschani (Orthoptera: Tettigoniidae), a species complex belonging to the most diverse genus of bush crickets from the Mediterranean region (>170 taxa) that comprises three recognized subspecies with small allopatric distributions in the topographically complex Teke Peninsula, southwestern Anatolia. Phylogenomic reconstructions that include all other taxa within the species group confirmed that subspecies of P. luschani originated from a common ancestor during the Pleistocene, supporting recent (<1 Ma) diversification within a small geographical area (ca. 120 × 80 km). Genetic clustering analyses corroborated the distinctiveness of each subspecies and the cohesiveness of their respective populations, with abrupt genetic discontinuities coinciding with contemporary range boundaries. Indeed, our analyses uncovered the presence of two sympatric cryptic sister lineages that diverged <300 ka ago and do not admix despite being co-distributed. Collectively, these results support that all lineages within the complex represent independently evolving entities corresponding to full-fledged species. Statistical evaluation of alternative models of speciation strongly supports a scenario of divergence in isolation followed by a period of limited gene flow during the last glacial period, when all lineages experienced marked expansions according to demographic reconstructions. Our study exemplifies how localized allopatric divergence and fast evolution of reproductive isolation can promote microgeographic speciation and explain the high rates of endemism characterizing biodiversity hotspots., Specimens used in this study were obtained via two grants to B.Ç., one funded by Akdeniz University (grant no. 2010.02.0121.028) and the other funded by the Scientific and Technical Research Council of Turkey (TUBITAK, grant no. 210T169). This work was supported by grant PID2021-123298NB-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE and grant TED2021-129328B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR., Peer reviewed

Akdeniz University (grant no: 2010.02.0121.028); The Scientific and Technical Research Council of Turkey (TUBITAK, grant no: 210T169); PID2021-123298NB-I00; TED2021-129328B-I00, Peer reviewed

In this study, we employ a geometric morphometric approach to quantify morphological differences among taxa of the genus Oropodisma Uvarov,1942, a complex of alpine grasshoppers comprising several narrow endemic species distributed across different mountain ranges of the Balkan Peninsula. The genus was described by Uvarov in 1942 and currently includes 10 recognized species, primarily distinguished by subtle differences in the shape of the male phallus apex and furculae. Some populations from central Greece exhibit an uncertain taxonomic status, suggesting the possible existence of undescribed species. Quantitative morphological comparisons with specimens collected from the type localities of all currently recognized taxa revealed the presence of two new species in the Pindus Range, Greece: O.tzoumerkae sp. nov. from Mount Tzoumerka and O.agrafae sp. nov. from Mount Agrafa. Geometric morphometric analyses indicate that O.tymphrestosi and O.willemsei, which occur in adjacent mountain ranges from central Greece, do not exhibit statistically significant differences in the shapes of either the phallus apex or the furculae. This finding raises doubts about their current taxonomic status but may also reflect the limitations of geometric morphometric approaches in capturing subtle differences in the complex structures that characterize male genitalia. Overall, our analyses highlight the value of quantitative approaches in formally reassessing the taxonomic status of species complexes. The description of two new and geographically restricted species within Oropodisma further emphasizes the role of Mediterranean mountains as key centers of microgeographic speciation for alpine biotas., Grant TED2021-129328B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR and grant PID2021-123298NB-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE., Peer reviewed

In this study we employ a geometric morphometric approach to quantify morphological differences among taxa of the genus Oropodisma Uvarov, a complex of alpine grasshoppers that includes several narrow endemic species distributed across different mountain ranges of the Balkan Peninsula. The genus was described by Uvarov in 1942 and currently comprises ten recognized species, primarily distinguished by subtle differences in the shape of the phallus apex and furculae of males. Some populations from central Greece exhibit an uncertain taxonomic status, suggesting the possible existence of undescribed species. Quantitative morphological comparisons with specimens collected from the type localities of all currently recognized taxa revealed the presence of two new species in the Pindus Range, Greece: O. tzoumerkae sp. nov. from Mt. Tzoumerka and O. agrafae sp. nov. from Mt. Agrafa. Geometric morphometric analyses indicate that the taxa O. tymphrestosi and O. willemsei, distributed in adjacent mountain ranges from central Greece, do not show statistically significant differences in either of the two studied traits. This finding raises doubts about their taxonomic status but may also reflect the limitations of geometric morphometric approaches in capturing subtle differences in the complex structures that characterize internal male genitalia. Overall, our analyses highlight the importance of quantitative approaches in formally reassessing the taxonomic status of species complexes. The description of two new and geographically restricted species of Oropodisma further emphasizes the role of Mediterranean mountains as key centers of microgeographic speciation for alpine biotas., TED2021-129328B-I00; PID2021-123298NB-I00, Peer reviewed

Mountains contribute disproportionately to global biodiversity, yet the ecological and evolutionary processes that make them important centres of speciation remain poorly understood. Here, we use a complex of Gomphocerinae grasshoppers distributed across the Pyrenees as a model system to investigate the process of speciation in mountain regions. Clustering analyses revealed a marked genetic fragmentation of populations and divergence time estimates indicated that all lineages split during the Pleistocene (<0.9 Mya). Although all taxa currently exhibit allopatric distributions, fine-scale temporal distribution modelling suggests that their ranges probably overlapped across extensive areas during glacial periods. Despite ample opportunities for historical hybridization, introgression tests indicate that gene flow was restricted to peripheral populations and only one population exhibited a high degree of admixed ancestry. Accordingly, our analyses reveal abrupt genetic discontinuities corresponding to the distributional boundaries of each taxon. Although taxa have probably not achieved complete reproductive isolation, semi-permeable species boundaries do not appear to have compromised their evolutionary independence. These results emphasize the interplay between high rates of lineage formation and the rapid evolution of reproductive barriers in promoting microgeographic speciation in topographically complex landscapes, shedding light on the proximate processes underlying the high levels of neo-endemism observed across mountain ranges worldwide., This work was supported by grant TED2021-129328B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR and grant PID2021-123298NB-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE. Víctor Noguerales was supported by a Viera y Clavijo postdoctoral fellowship funded by the Agencia Canaria de Investigación, Innovación y Sociedad and the Universidad de La Laguna., Peer reviewed

Mountains contribute disproportionately to global biodiversity, yet the ecological and evolutionary processes that make them important centers of speciation remain poorly understood. Here, we use a complex of Gomphocerinae grasshoppers distributed across the Pyrenees as a model system to investigate the process of speciation in mountain regions. Clustering analyses revealed a marked genetic fragmentation of populations and divergence time estimates indicated that all lineages split during the Pleistocene (<0.9 Ma). Although all taxa currently exhibit allopatric distributions, fine-scale temporal distribution modeling suggested that their ranges likely overlapped across extensive areas during glacial periods. Despite ample opportunities for historical hybridization, introgression tests indicated that gene flow was restricted to peripheral populations and only one population exhibited a high degree of admixed ancestry. Accordingly, our analyses revealed abrupt genetic discontinuities corresponding to the distributional boundaries of each taxon. Although taxa have probably not achieved complete reproductive isolation, semi-permeable species boundaries do not appear to have compromised their evolutionary independence. These results emphasize the interplay between high rates of lineage formation and the rapid evolution of reproductive barriers in promoting microgeographic speciation in topographically complex landscapes, shedding light on the proximate processes underlying the high levels of neo-endemism observed across mountain ranges worldwide., TED2021-129328B-I00; PID2021-123298NB-I00; Viera y Clavijo postdoctoral fellowship, Peer reviewed

[Data Availability Statement] Raw Illumina reads have been deposited at the NCBI Sequence Read Archive (SRA) (https://www.ncbi.nlm.nih.gov/) under BioProject PRJNA702631., Recent Pleistocene radiations often generate cryptic diversity and semi-permeable species boundaries, challenging species delimitation and the reconstruction of evolutionary histories. Here, we investigate these processes in a species complex of Chorthippus grasshoppers from Greece using genome-wide ddRAD-seq data combined with geometric morphometrics. Phylogenomic analyses indicate that diversification occurred during the Middle Pleistocene and identify two major geographic clades separated by the Corinthian Gulf, followed by finer-scale divergence within the Peloponnese Peninsula. Most taxa form well-supported, reciprocally monophyletic lineages despite recent divergence, although several populations at range margins show signatures of historical hybridization, revealing semi-permeable species boundaries shaped by secondary contact. Introgression is geographically restricted and strongly asymmetric, occurring primarily from long-winged into short-winged taxa, consistent with differences in dispersal capacity. Species delimitation analyses largely support current taxonomy but also identify three previously unrecognized evolutionary lineages corresponding to geographically restricted populations, uncovering additional cryptic diversity. Morphological analyses reveal pronounced stasis in shape-related traits across lineages, with wing length emerging as the main axis of differentiation. Phylogenetic reconstructions indicate multiple independent reductions in wing size, highlighting repeated evolutionary transitions toward reduced dispersal. In at least one lineage, a pronounced geographic cline in wing length is mirrored by shallow phylogenetic structure, supporting an incipient evolutionary shift in dispersal capacity rather than phenotypic plasticity. Admixed populations consistently retain short-winged phenotypes, suggesting strong selection on dispersal-related traits despite genomic introgression. Overall, our results demonstrate how topographic complexity, Pleistocene climatic oscillations and dispersal-related morphology interact to shape diversification and maintain lineage integrity in a Mediterranean biodiversity hotspot., Grant TED2021-129328B-I00 funded by Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033) and European Union NextGenerationEU/PRTR; Grant PID2021-123298NB-I00 funded by Ministerio de Ciencia e Innovación and European Regional Development Fund (MCIN/AEI/10.13039/501100011033/FEDER, UE)., Peer reviewed

Understanding the geological, ecological, and microevolutionary processes that shape range size in alpine organisms is key to explaining the high rates of local endemism that characterise mountain ecosystems. Here, we investigate the geography of speciation in Oropodisma, a radiation of alpine grasshoppers from the Balkan Peninsula that includes several narrow-endemic species distributed along a latitudinal gradient of > 600 km. Phylogenomic-based species delimitation clarified taxonomic uncertainties and revealed striking variation in range size, with the northernmost species occupying an area nearly as large as all other congeneric taxa combined. Phylogenetic network analyses and divergence dating indicate a Pleistocene origin for the group, with recent speciation events (< 0.2 Ma) and limited post-divergence gene flow, suggesting rapid evolution of reproductive isolation and short speciation times. Distributional shifts inferred from environmental niche modelling show that all taxa underwent severe range contractions during interglacial periods, leading to population fragmentation and demographic declines. Despite the ubiquity of these processes across taxa, both demographic stability and genetic connectivity among conspecific populations decreased at lower latitudes relative to the genus' distribution. This suggests that greater genetic connectivity at higher relative latitudes, likely driven by regional range shifts and a more continuous availability of suitable habitats through time, has limited opportunities for microgeographic speciation and maintained genetic cohesiveness among populations across broader distributional ranges. Collectively, our findings support a model of interglacial speciation and illustrate how latitudinal variation in the balance between lineage formation and fusion—shaped by Pleistocene climatic oscillations—determines the rates at which alpine microendemic species emerge and accumulate in temperate mountain regions., Sampling permits were granted by the Ministry of the Environment and Energy from Greece (permit no. YPEN/DDD/34736/1134 and YPEN/DDD/32363/1054) and the Ministry of Environment and Physical Planning from North Macedonia (permit no. 03-403/2). Logistic support was provided by Unidad de Análisis de Imagen y Microscopía (IMIC-EBD) and Laboratorio de Ecología Molecular (LEM-EBD) from Estación Biológica de Doñana (CSIC). We also thank Centro de Supercomputación de Galicia (CESGA) and Doñana's Singular Scientific-Technical Infrastructure (ICTS-RBD) for access to computer resources. This work was supported by grant TED2021-129328B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR and grants PID2021-123298NB-I00 and PID2025-168840NB-I00 funded by MICIU/AEI/10.13039/501100011033/FEDER, UE., Peer reviewed

All versions are available at DOI 10.6084/m9.figshare.29046218, Mountains contribute disproportionately to global biodiversity, yet the ecological and evolutionary processes that make them important centers of speciation remain poorly understood. Here, we use a complex of Gomphocerinae grasshoppers distributed across the Pyrenees as a model system to investigate the process of speciation in mountain regions. Clustering analyses revealed a marked genetic fragmentation of populations and divergence time estimates indicated that all lineages split during the Pleistocene (<0.9 Ma). Although all taxa currently exhibit allopatric distributions, fine-scale temporal distribution modeling suggested that their ranges likely overlapped across extensive areas during glacial periods. Despite ample opportunities for historical hybridization, introgression tests indicated that gene flow was restricted to peripheral populations and only one population exhibited a high degree of admixed ancestry. Accordingly, our analyses revealed abrupt genetic discontinuities corresponding to the distributional boundaries of each taxon. Although taxa have probably not achieved complete reproductive isolation, semi-permeable species boundaries do not appear to have compromised their evolutionary independence. These results emphasize the interplay between high rates of lineage formation and the rapid evolution of reproductive barriers in promoting microgeographic speciation in topographically complex landscapes, shedding light on the proximate processes underlying the high levels of neo-endemism observed across mountain ranges worldwide., TED2021-129328B-I00; PID2021-123298NB-I00; Viera y Clavijo postdoctoral fellowship, Peer reviewed

[Data Availability Statement] Raw Illumina reads have been deposited at the NCBI Sequence Read Archive (SRA) under BioProjects PRJNA1450054 and PRJNA702631., [Aim] Pleistocene climatic oscillations profoundly shaped Mediterranean mountain biotas through recurrent cycles of isolation and connectivity. Yet, despite the Central Apennines being a major centre of local endemism, this region has received limited attention in genomic studies addressing biogeographic processes. Here, we examine how climatically driven distributional shifts have promoted microgeographic diversification and endemism in sky-island systems of this mountain region., [Location] Central Apennines, Italy., [Taxon] Italohippus (Orthoptera: Acrididae)., [Methods] We used genome-wide ddRAD-seq data to infer phylogenetic relationships, divergence times, species limits, population structure, demographic history and introgression. Morphological differentiation was quantified using geometric and linear morphometrics of forewings. Past range dynamics and spatial patterns of climatic suitability were reconstructed by projecting species-specific environmental niche models from the Last Glacial Maximum to the present., [Results] Phylogenomic analyses reveal a Middle–Late Pleistocene diversification of Italohippus structured along a continuum of evolutionary divergence across the Central Apennines. Northern populations, corresponding to the taxon I. modestus, form a distinct allopatric lineage likely originating under geographic isolation and the evolution of partial reproductive barriers. In contrast, populations at the southern rear edge of the genus range, corresponding to I. albicornis, show weak genomic and morphological differentiation from I. monticola, consistent with incipient but incomplete speciation. Paleodistribution models and demographic reconstructions indicate marked latitudinal contrasts in glacial impacts, with higher availability and continuity of climatically suitable habitats and introgression in northern and central sectors and more persistent isolation in the south., [Main Conclusions] Our results support a biogeographic model of intermittently connected sky-island refugia in the Central Apennines, generating spatially heterogeneous opportunities for divergence and persistence across latitudes. By integrating different sources of data, we show how climatically driven distributional shifts have shaped the emergence and maintenance of geographically structured evolutionary lineages in Mediterranean mountain systems, highlighting key processes underlying the origin and persistence of endemic alpine biodiversity in the face of rapid climate warming., This work was supported by the following grants: TED2021-129328B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR; PID2021-123298NB-I00 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE; NBFC—National Biodiversity Future Center, funded by the Italian Ministry of University and Research, PNRR, Missione 4 Componente 2, ‘Dalla ricerca all'impresa’, Investimento 1.4, Project CN00000033; and the Departments of Excellence—L. 232/2016—art.1, commi 314–337 awarded to Dept. of Science—University Roma Tre—Rome—Italy for 2023–2027., Peer reviewed

All versions are available at DOI 10.6084/m9.figshare.31136593, Recent Pleistocene radiations often generate cryptic diversity and semi-permeable species boundaries, challenging species delimitation and the reconstruction of evolutionary histories. Here, we investigate these processes in a species complex of Chorthippus grasshoppers from Greece using genome-wide ddRAD-seq data combined with geometric morphometrics. Phylogenomic analyses indicate that diversification occurred during the Middle Pleistocene and identify two major geographic clades separated by the Corinthian Gulf, followed by finer-scale divergence within the Peloponnese Peninsula. Most taxa form well-supported, reciprocally monophyletic lineages despite recent divergence, although several populations at range margins show signatures of historical hybridization, revealing semi-permeable species boundaries shaped by secondary contact. Introgression is geographically restricted and strongly asymmetric, occurring primarily from long-winged into short-winged taxa, consistent with differences in dispersal capacity. Species delimitation analyses largely support current taxonomy but also identify three previously unrecognized evolutionary lineages corresponding to geographically restricted populations, uncovering additional cryptic diversity. Morphological analyses reveal pronounced stasis in shape-related traits across lineages, with wing length emerging as the main axis of differentiation. Phylogenetic reconstructions indicate multiple independent reductions in wing size, highlighting repeated evolutionary transitions toward reduced dispersal. In at least one lineage, a pronounced geographic cline in wing length is mirrored by shallow phylogenetic structure, supporting an incipient evolutionary shift in dispersal capacity rather than phenotypic plasticity. Admixed populations consistently retain short-winged phenotypes, suggesting strong selection on dispersal-related traits despite genomic introgression. Overall, our results demonstrate how topographic complexity, Pleistocene climatic oscillations, and dispersal-related morphology interact to shape diversification and maintain lineage integrity in a Mediterranean biodiversity hotspot., CLOSING THE GAP BETWEEN DEMOGRAPHY AND DIVERSIFICATION: PERSPECTIVES FROM AN EVOLUTIONARY RADIATION OF GRASSHOPPERS, State Research Agency (AEI), PID2021-123298NB-I00, EVOLUTIONARY, DEMOGRAPHIC AND EXTINCTION RISK ASSESSMENT OF ALPINE BIOTAS IN MEDITERRANEAN MOUNTAIN ISLAND ARCHIPELAGOES WITH EXTREME VULNERABILITY TO CLIMATE CHANGE, State Research Agency (AEI), TED2021-129328B-I00, Peer reviewed

All versions are available at DOI 10.6084/m9.figshare.31136593, Recent Pleistocene radiations often generate cryptic diversity and semi-permeable species boundaries, challenging species delimitation and the reconstruction of evolutionary histories. Here, we investigate these processes in a species complex of Chorthippus grasshoppers from Greece using genome-wide ddRAD-seq data combined with geometric morphometrics. Phylogenomic analyses indicate that diversification occurred during the Middle Pleistocene and identify two major geographic clades separated by the Corinthian Gulf, followed by finer-scale divergence within the Peloponnese Peninsula. Most taxa form well-supported, reciprocally monophyletic lineages despite recent divergence, although several populations at range margins show signatures of historical hybridization, revealing semi-permeable species boundaries shaped by secondary contact. Introgression is geographically restricted and strongly asymmetric, occurring primarily from long-winged into short-winged taxa, consistent with differences in dispersal capacity. Species delimitation analyses largely support current taxonomy but also identify three previously unrecognized evolutionary lineages corresponding to geographically restricted populations, uncovering additional cryptic diversity. Morphological analyses reveal pronounced stasis in shape-related traits across lineages, with wing length emerging as the main axis of differentiation. Phylogenetic reconstructions indicate multiple independent reductions in wing size, highlighting repeated evolutionary transitions toward reduced dispersal. In at least one lineage, a pronounced geographic cline in wing length is mirrored by shallow phylogenetic structure, supporting an incipient evolutionary shift in dispersal capacity rather than phenotypic plasticity. Admixed populations consistently retain short-winged phenotypes, suggesting strong selection on dispersal-related traits despite genomic introgression. Overall, our results demonstrate how topographic complexity, Pleistocene climatic oscillations, and dispersal-related morphology interact to shape diversification and maintain lineage integrity in a Mediterranean biodiversity hotspot., CLOSING THE GAP BETWEEN DEMOGRAPHY AND DIVERSIFICATION: PERSPECTIVES FROM AN EVOLUTIONARY RADIATION OF GRASSHOPPERS, State Research Agency (AEI), PID2021-123298NB-I00, EVOLUTIONARY, DEMOGRAPHIC AND EXTINCTION RISK ASSESSMENT OF ALPINE BIOTAS IN MEDITERRANEAN MOUNTAIN ISLAND ARCHIPELAGOES WITH EXTREME VULNERABILITY TO CLIMATE CHANGE, State Research Agency (AEI), TED2021-129328B-I00, Peer reviewed

Understanding the geological, ecological, and microevolutionary processes that shape range size in alpine organisms is key to explaining the high rates of local endemism that characterize mountain ecosystems. Here, we investigate the geography of speciation in Oropodisma, a radiation of alpine grasshoppers from the Balkan Peninsula that includes several narrow-endemic species distributed along a latitudinal gradient of > 600 km. Phylogenomic-based species delimitation clarified taxonomic uncertainties and revealed striking variation in range size, with the northernmost species occupying an area nearly as large as all other congeneric taxa combined. Phylogenetic network analyses and divergence dating indicate a Pleistocene origin for the group, with recent speciation events (<0.2 Ma) and limited post-divergence gene flow, suggesting rapid evolution of reproductive isolation and short speciation times. Distributional shifts inferred from environmental niche modelling show that all taxa underwent severe range contractions during interglacial periods, leading to population fragmentation and demographic declines. Despite the ubiquity of these processes across taxa, both demographic stability and genetic connectivity among conspecific populations decreased at lower latitudes relative to the genus’ distribution. This suggests that greater genetic connectivity at higher relative latitudes, likely driven by regional range shifts and a more continuous availability of suitable habitats through time, has limited opportunities for microgeographic speciation and maintained genetic cohesiveness among populations across broader distributional ranges. Collectively, our findings support a model of interglacial speciation and illustrate how latitudinal variation in the balance between lineage formation and fusion —shaped by Pleistocene climatic oscillations— determines the rates at which alpine microendemic species emerge and accumulate in temperate mountain regions., CLOSING THE GAP BETWEEN DEMOGRAPHY AND DIVERSIFICATION: PERSPECTIVES FROM AN EVOLUTIONARY RADIATION OF GRASSHOPPERS, State Research Agency (AEI), PID2021-123298NB-I00, EVOLUTIONARY, DEMOGRAPHIC AND EXTINCTION RISK ASSESSMENT OF ALPINE BIOTAS IN MEDITERRANEAN MOUNTAIN ISLAND ARCHIPELAGOES WITH EXTREME VULNERABILITY TO CLIMATE CHANGE, State Research Agency (AEI), TED2021-129328B-I00, Peer reviewed

[Aim] Pleistocene climatic oscillations profoundly shaped Mediterranean mountain biotas through recurrent cycles of isolation and connectivity. Yet, despite the Central Apennines being a major centre of local endemism, this region has received limited attention in genomic studies addressing biogeographic processes. Here, we examine how climatically driven distributional shifts have promoted microgeographic diversification and endemism in sky-island systems of this mountain region., [Location] Central Apennines, Italy., [Taxon] Italohippus (Orthoptera: Acrididae)., [Methods] We used genome-wide ddRAD-seq data to infer phylogenetic relationships, divergence times, species limits, population structure, demographic history and introgression. Morphological differentiation was quantified using geometric and linear morphometrics of forewings. Past range dynamics and spatial patterns of climatic suitability were reconstructed by projecting species-specific environmental niche models from the Last Glacial Maximum to the present., [Results] Phylogenomic analyses reveal a Middle–Late Pleistocene diversification of Italohippus structured along a continuum of evolutionary divergence across the Central Apennines. Northern populations, corresponding to the taxon I. modestus, form a distinct allopatric lineage likely originating under geographic isolation and the evolution of partial reproductive barriers. In contrast, populations at the southern rear edge of the genus range, corresponding to I. albicornis, show weak genomic and morphological differentiation from I. monticola, consistent with incipient but incomplete speciation. Paleodistribution models and demographic reconstructions indicate marked latitudinal contrasts in glacial impacts, with higher availability and continuity of climatically suitable habitats and introgression in northern and central sectors and more persistent isolation in the south., [Main Conclusions] Our results support a biogeographic model of intermittently connected sky-island refugia in the Central Apennines, generating spatially heterogeneous opportunities for divergence and persistence across latitudes. By integrating different sources of data, we show how climatically driven distributional shifts have shaped the emergence and maintenance of geographically structured evolutionary lineages in Mediterranean mountain systems, highlighting key processes underlying the origin and persistence of endemic alpine biodiversity in the face of rapid climate warming., EVOLUTIONARY, DEMOGRAPHIC AND EXTINCTION RISK ASSESSMENT OF ALPINE BIOTAS IN MEDITERRANEAN MOUNTAIN ISLAND ARCHIPELAGOES WITH EXTREME VULNERABILITY TO CLIMATE CHANGE, State Research Agency (AEI) TED2021-129328B-I00, CLOSING THE GAP BETWEEN DEMOGRAPHY AND DIVERSIFICATION: PERSPECTIVES FROM AN EVOLUTIONARY RADIATION OF GRASSHOPPERS, State Research Agency (AEI) PID2021-123298NB-I00, NBFC – National Biodiversity Future Center, funded by the Italian Ministry of University and Research, PNRR, Missione 4 Componente 2, “Dalla ricerca all’impresa”, Investimento 1.4, Project CN00000033, Departments of Excellence—L. 232/2016—art.1, commi 314–337 awarded to Dept. of Science—University Roma Tre—Rome—Italy for 2023-2027, Peer reviewed

[Data Availability Statement] The newly obtained mitochondrial Cox1 sequences are available on GenBank (see Table S1). Raw Illumina reads have been deposited at the NCBI Sequence Read Archive (SRA) under BioProject PRJNA1479345., [Aim] Biological invasions are a global challenge, largely driven by human-mediated introductions beyond species' native ranges. Island ecosystems are particularly vulnerable, as invasions have caused some of the most profound and detrimental impacts on native and endemic biota. Here, we test whether populations of a bush-cricket species in Madeira Island originated through natural colonization or recent human-mediated introduction., [Location] Madeira archipelago and Iberian Peninsula., [Methods] We combined genomic ddRAD-seq data and mitochondrial Cox1 sequences to reconstruct the evolutionary history of the bush-cricket Antaxius spinibrachius. We inferred the timing and mode of divergence between the insular population of Madeira and the Iberian Peninsula. Furthermore, we assessed niche dynamics during the colonization process, specifically testing for niche conservatism versus expansion into novel environmental spaces., [Results] Genomic data reveal a pattern consistent with ring diversification around the Northern Iberian Plateau, with lineages expanding around a geographic barrier and accumulating genetic divergence along the expansion front. Phylogenetic analyses show that Madeiran populations are monophyletic with populations from northwestern Portugal, identifying this region as the most likely source population. Demographic modelling supports a strict isolation scenario and reveals a strong founder effect, consistent with recent colonization by a small number of individuals. Despite a marked reduction in genetic diversity relative to Iberian source populations, Madeiran populations retain relatively high levels of diversity across the island. Finally, our results provide evidence for climatic niche conservatism during the colonization of Madeira: while Iberian populations occupy a broad and heterogeneous climatic space, Madeiran populations are restricted to a narrower, more specialized subset of this space., [Main Conclusions] Overall, our findings highlight the need to critically evaluate the origin of taxa currently regarded as native island taxa in order to distinguish truly native species from those resulting from historical or recent introductions., This work was supported by MCIN/AEI/10.13039/501100011033/FEDER, UE, PID2021-123298NB-I00; MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR, TED2021-129328B-I00; Doctores Junta de Andalucía (European Regional Development Fund/Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía, DOC_00668); Estancias Posdoctorales por México Convocatoria 2025, CVU: 895877., Peer reviewed

[Aim] Island archipelagos serve as natural laboratories for understanding how geological history, climate change and dispersal limitation interact to shape diversification. Here, we examine how these forces influence patterns of genomic divergence, demographic dynamics and phenotypic variation in island-endemic taxa, with a particular focus on evaluating whether contrasting connectivity regimes among archipelagos are associated with distinct microevolutionary outcomes., [Location] Ionian and Aegean archipelagos, Greece., [Taxon] Brachypterous grasshoppers including the Ionian-endemic Chorthippus sangiorgii and the Aegean-endemic Chorthippus biroi (Orthoptera: Acrididae)., [Method] We generated genome-wide ddRAD-seq data to estimate divergence times, infer genetic structure, assess relative levels of genetic connectivity and reconstruct the demographic trajectories of populations. In addition, geometric morphometric analyses of forewing and pronotum-head shape were conducted to evaluate morphological differentiation among island populations. Genomic and phenotypic patterns were interpreted in the context of palaeogeographic reconstructions of island connectivity associated with Quaternary sea-level oscillations., [Results] Both species show strong genetic structuring within and among islands, consistent with extremely limited dispersal. Whereas C. sangiorgii exhibits relatively shallow divergence compatible with recent and recurrent connectivity among the Ionian Islands, C. biroi displays deeper genetic structure consistent with the long-term isolation of Crete and the Cyclades. Demographic reconstructions for both species indicate population expansions during the Last Glacial Maximum followed by contractions throughout the Holocene, suggesting broadly similar responses to Late Quaternary climatic oscillations. Geometric morphometric analyses detected modest but statistically significant phenotypic differentiation among some island pairs in both species., [Main Conclusions] Our findings indicate that the microevolutionary and demographic dynamics in Mediterranean island grasshoppers are shaped by the interplay between limited dispersal, historical isolation and palaeogeographic connectivity driven by Quaternary sea-level oscillations. Phenotypic differentiation appears more limited and heterogeneous than genomic divergence, suggesting a partial decoupling between patterns of genetic and phenotypic variation. This study highlights the value of integrating genomic and phenotypic data to better characterize the microevolutionary trajectories in low-dispersal taxa inhabiting complex island systems., This work was supported by grant TED2021-129328B-I00 funded by MCIN/AEI/http://doi.org/10.13039/501100011033 and the European Union NextGenerationEU/PRTR, and grant PID2021-123298NB-I00 funded by MCIN/AEI/http://doi.org/10.13039/501100011033/FEDER, EU., Peer reviewed

[Aim] Island archipelagos serve as natural laboratories for understanding how geological history, climate change and dispersal limitation interact to shape diversification. Here, we examine how these forces influence patterns of genomic divergence, demographic dynamics and phenotypic variation in island-endemic taxa, with a particular focus on evaluating whether contrasting connectivity regimes among archipelagos are associated with distinct microevolutionary outcomes., [Location] Ionian and Aegean archipelagos, Greece., [Taxon] Brachypterous grasshoppers including the Ionian-endemic Chorthippus sangiorgii and the Aegean-endemic Chorthippus biroi (Orthoptera: Acrididae)., [Method] We generated genome-wide ddRAD-seq data to estimate divergence times, infer genetic structure, assess relative levels of genetic connectivity and reconstruct the demographic trajectories of populations. In addition, geometric morphometric analyses of forewing and pronotum-head shape were conducted to evaluate morphological differentiation among island populations. Genomic and phenotypic patterns were interpreted in the context of palaeogeographic reconstructions of island connectivity associated with Quaternary sea-level oscillations., [Results] Both species show strong genetic structuring within and among islands, consistent with extremely limited dispersal. Whereas C. sangiorgii exhibits relatively shallow divergence compatible with recent and recurrent connectivity among the Ionian Islands, C. biroi displays deeper genetic structure consistent with the long-term isolation of Crete and the Cyclades. Demographic reconstructions for both species indicate population expansions during the Last Glacial Maximum followed by contractions throughout the Holocene, suggesting broadly similar responses to Late Quaternary climatic oscillations. Geometric morphometric analyses detected modest but statistically significant phenotypic differentiation among some island pairs in both species., [Main Conclusions] Our findings indicate that the microevolutionary and demographic dynamics in Mediterranean island grasshoppers are shaped by the interplay between limited dispersal, historical isolation and palaeogeographic connectivity driven by Quaternary sea-level oscillations. Phenotypic differentiation appears more limited and heterogeneous than genomic divergence, suggesting a partial decoupling between patterns of genetic and phenotypic variation. This study highlights the value of integrating genomic and phenotypic data to better characterize the microevolutionary trajectories in low-dispersal taxa inhabiting complex island systems., This work was supported by grant TED2021-129328B-I00 funded by MCIN/AEI/http://doi.org/10.13039/501100011033 and the European Union NextGenerationEU/PRTR, and grant PID2021-123298NB-I00 funded by MCIN/AEI/http://doi.org/10.13039/501100011033/FEDER, EU., Peer reviewed