New Caledonia is a biodiversity hotspot with high levels of micro-endemism, yet its gracillariid fauna remains poorly documented. Here, two new species of Caloptilia Hübner, 1825 (Gracillariidae) are described from Glochidion J.R.Forst. & G.Forst. (Phyllanthaceae) host plants in Parc des Grandes Fougères, New Caledonia: Caloptilia augeas Guiguet, Lopez-Vaamonde, van Nieukerken & Ohshima, sp. nov., and Caloptilia ceryneia Guiguet, Lopez-Vaamonde, van Nieukerken & Ohshima, sp. nov. Both species induce leaf galls on Glochidion billardierei Baill., co-occurring on the same host species, sometimes even on the same leaf. They exhibit distinct wing patterns, but very similar male and female genitalia, and DNA barcoding supports their status as separate species. These findings provide evidence for potential within-host sympatric speciation, as documented in other gall-inducing insects. The larval biology of C. augeas and C. ceryneia reveals a unique frass disposal behaviour, whereby waste is excreted through a hole and the aperture is subsequently sealed-an adaptation not previously reported in gall-inducing Lepidoptera. Our findings double the known number of gall-inducing species in Gracillariidae, highlighting that this life history strategy may be more common than currently appreciated. We also provide new information on distribution and host plants of Caloptilia xanthopharella (Meyrick, 1880), a leaf roller found on the same host plant, G. billardierei. These findings mark the first records of the subfamily Gracillariinae in New Caledonia. This study underscores the underexplored diversity of New Caledonian gracillariids and emphasises the conservation value of Parc des Grandes Fougères. Further surveys in the Indo-Pacific region may reveal additional yet undescribed Caloptilia species associated with Phyllanthaceae and help clarify the evolutionary mechanisms underpinning their diversification.

Endemism, a hallmark of island biodiversity, reaches its lowest levels among bryophytes compared with other land plants. Whether this pattern reflects low diversification rates, and why, or whether it is a result of loss of endemicity due to extinctions or subsequent continental (back-)colonization, is examined here through a review of available evidence in the Macaronesian flora. Significant genetic differentiation (GST, based on allele frequencies) was consistently found between Macaronesian and continental populations, ruling out the hypothesis that intense migrations necessarily hamper differentiation. A significant phylogeographical signal in the data (NST > GST; where NST is a GST analog incorporating phylogenetic relationships among alleles), involving higher mutation rates than dispersal rates and evidencing incipient speciation, was further found in more than 1/3 of the species investigated. The significantly higher average NST between extra-European regions and Macaronesia compared to Europe and Macaronesia suggests, however, that incipient speciation is more likely to occur between distant (Macaronesian versus extra-European) than closer (Macaronesian versus European) populations. In line with this, ancestral area estimations in Macaronesian endemic bryophyte species revealed that at least 50% of them have an extra-European origin, in contrast with the almost exclusively (>90%) European/Mediterranean origin of Macaronesian endemic spermatophytes. Allopatric speciation via long-distance dispersal and subsequent divergence of a single endemic species prevails in island bryophytes, wherein sympatric radiations virtually never occur. Such a speciation mode does not trigger high rates of endemism, in contrast to radiations in Macaronesian spermatophytes, which contribute to 56% of the total number of endemics. Several mechanisms may explain the failure of island bryophytes to diversify in situ, including the fact that oceanic islands are too small or insufficiently isolated from each other or from continents to promote sympatric speciation, the lack of key innovations, and phylogenetic niche conservatism for stable habitats not prone to trigger radiations. In comparison with spermatophytes, continental (back-)colonization further largely prevails in bryophytes and, unlike in many instances in angiosperms, is not followed by in situ speciation on the mainland. The consequent loss of the endemic status of species that did speciate on islands but subsequently enlarged their range further accounts for the low rates of endemism among island bryophyte floras and invalidates the use of endemism rates as a proxy of speciation rates in this group.

Abstract Lenoks, species within the genus Brachymystax, are freshwater salmonids with a scattered distribution in the rivers of Siberia, Northeast China, Xinjiang, Hebei, and the Qinling Mountains. Owing to long-term population declines, all species assigned to Brachymystax are protected by law in China. However, the evolutionary history and species-level systematics of this genus remain controversial, complicating taxonomic designations and conservation efforts. In particular, the geographical separation of populations may have resulted in the formation of phenotypically similar cryptic species. We built a chromosome-level genome assembly of B. tsinlingensis and re-sequenced the genomes of 103 individuals of Chinese Brachymystax spp. from five geographically isolated locations. Population genomic and phylogenomic analyses based on nuclear single nucleotide polymorphisms (SNPs) and mitochondrial genomes revealed six different genetic lineages, of which at least one, the Hebei lineage, represents a cryptic species. Notably, the results suggest that the sympatric species B. lenok and B. tumensis are not close relatives, but the former is more closely related to the new species B. sp. Xinjiang with an estimated divergence time of c. 630 Ka, indicating that closely related sympatric species may not have evolved via sympatric speciation in areas influenced by Pleistocene climate changes. We observed mito-nuclear phylogenomic discordance in Brachymystax caused by the strong gene flow between B. lenok and B. tumensis. Phylogenetic and demographic analyses emphasize the important role of interglacial refugia in promoting speciation and underscore the impact of historical gene flow. Compared with other lenoks, the Gansu population had the lowest genetic diversity, suggesting that particular attention to protect its genetic resources may be required. Finally, we suggest that cross-regional proliferation and release of lenoks should be banned in the future to protect the genetic integrity of these divergent groups.

Abstract A major obstacle to biodiversity conservation is that thousands, if not millions, of plant and animal species have yet to be discovered and described, even in historically well‐explored regions. Carex sect. Lupulinae (Cyperaceae; “sedges”) is a small group of six showy Eastern North American species that, until recently, was thought to be well understood. However, a DNA barcoding study of North American Carex undertaken over a decade ago serendipitously revealed unsuspected molecular diversity, including one potentially undescribed cryptic species. Here, we test the hypothesis that this entity is a species on a separate evolutionary trajectory by expanding barcoding results with an integrative approach that combines a densely‐sampled molecular phylogeny (five plastid and two nuclear markers, 112 sequenced specimens), morphometric analyses (93 characters, > 300 measured specimens), ecological field surveys, and common greenhouse observations. Results all support the recognition of a new, abundant species common in the southeastern United States′ Coastal Plain that we name Carex gator . This study highlights how integrative taxonomy can help to describe cryptic plant species revealed by DNA barcoding. We provide illustrations, a distribution map, and an identification key, and discuss how C. gator may be a rare example of homoploid sympatric speciation in plants.

Phylogenetic reconstruction of African weakly electric fish (Campylomormyrus spp.) is suggestive of ancient introgression events.

Sympatric speciation has long been of key interest among biologists, investigating how selection drives speciation in the absence of geographic isolation. However, the evolutionary trajectories and genetic architectures that underlie sympatric ecological divergence remain poorly understood. For the annual fish, Neosalanx brevirostris, from lakes in the Yangtze River basin, two sympatric ecotypes exhibit differences in reproductive season, with one breeding in spring and the other in autumn. Reproductive timing is considered a 'magic trait' in sympatric speciation, as it is both ecologically relevant and facilitates assortative mating. Using population genomic approaches, we investigated the genetic architecture of the adaptive sympatric divergence in reproductive season and the evolutionary forces driving this divergence by comparing two breeding ecotype pairs from two lakes and their ancestral anadromous population. Population genetic structure results provided strong evidence that sympatric ecological divergence has evolved independently and repeatedly in both lakes. Furthermore, we identified a set of genome-wide candidate adaptive SNPs, which were present as standing genetic variations in ancestral population with high frequencies, and changes of allele frequency support that disruptive natural selection, induced by intensive resource competition, drove the reproductive season divergence. These adaptive SNPs were involved in various biological functions pertinent to reproductive timing, including photosensory, circadian entrainment, temperature sensing, and hormone signalling, highlighting the complex genetic architecture underlying reproductive seasonality. These findings provide valuable insights into the evolutionary trajectories and genetic architecture in the early stages of sympatric ecological divergence and speciation.

Genomic tools have advanced our understanding of species and population structure, but distinguishing neutral from adaptive evolution remains challenging due to limited methods for measuring a broad spectrum of phenotypic traits. We used spectroscopic data from preserved leaves to test for adaptive divergence among populations of live oaks (Quercus section Virentes), a monophyletic group of seven species that diversified under sympatric, parapatric, and allopatric speciation. We used 427 individuals to test for isolation-by-distance (IBD) and isolation-by-environment (IBE), as well as the influences of selection and phylogenetic inertia on traits. Finally, we examined how phylogenetic signals are distributed across their foliar reflectance spectra. Partial redundancy analyses revealed that IBE explains more phenotypic variation than IBD among sympatric species, particularly in certain spectral regions and traits derived from spectra. Phylogenetic generalized least squares models show that environmental variables - including minimum temperature of the coldest month and annual precipitation - predict traits related to stress tolerance across climatic gradients, such as lignin concentration and anthocyanin levels. These results demonstrate that foliar reflectance spectra can be used to capture adaptive differentiation and evolutionary history across scales, offering a powerful, nondestructive tool for linking phenotype, environment, and evolutionary processes in long-lived plant lineages.

Abstract While conducting a population genetic study aiming at refining previous conclusions about cladogenesis in the Oxera genus (Lamiaceae) in New Caledonia, we uncovered an unexpected result for the well‐known Oxera palmatinervia Dubard species. To better understand the preliminary molecular results that revealed two distinct sister species, we performed extensive field studies in order to sample, measure, hand‐pollinate, and observe the flower and fruit visitors on different populations of O. palmatinervia and other species of the “robusta” clade. We found flower morphology differences to be congruent with the molecular results, so that we propose to describe a new species as O. sympatrica Gâteblé & Karnadi sp. nov. The differences in flower morphology between the two species, which can grow in true sympatry and flower at the same time of the year, are striking so that flower visitors and pollination syndromes were investigated as far as possible. We find that two species of honeyeaters Glycifohia undulata and Philemon diemenensis are likely the preferred pollinators, respectively, of O. palmatinervia and O. sympatrica sp. nov. because of their respective sizes, bill and tongue lengths, and behavior. Even though, to date, it cannot be proven that initial speciation of both Oxera occurred in sympatry, today's sympatry is observed along with a remarkable supposed coevolution pollination syndrome. The new species is fully described, mapped, evaluated against Red List criteria, and illustrated. Pollination syndromes are discussed and illustrated.

Sensory adaptation is widely hypothesized to drive ecological speciation, yet empirical evidence from natural populations undergoing early stage divergence remains limited. In Lake Masoko, a young crater lake in East Africa, the haplochromine cichlid Astatotilapia calliptera is undergoing early stage sympatric speciation into shallow-water littoral and deep-water benthic ecotypes that experience contrasting light environments. Here, we integrate retinal transcriptomics, phenotypic analyses, and visual modeling to uncover rapid sensory divergence associated with this ecological transition. We find striking shifts in cone opsin expression, with the benthic ecotype exhibiting a switch from short-wavelength sensitive SWS2B to SWS2A and an overall narrowing of cone sensitivity toward the center of the light spectrum, consistent with changes in deep-water light environment. In contrast, coding sequence variation in opsin genes was limited and no significant differences in allele frequencies were detected across nine polymorphic sites, pointing to expression regulation as the primary axis of early divergence in visual systems. In parallel, we observed divergence in male signaling traits, with benthic males displaying deeper red egg-spots, aligning with predictions from visual modeling of signal efficiency in different light environments. These results demonstrate rapid transcriptomic and phenotypic divergence in associated signaling traits—within ∼1,000 years—supporting a potential role for regulatory evolution in sensory adaptation during early ecological speciation.

The Triatoma rubrovaria subcomplex, comprising several triatomine species, plays a significant role in the transmission of Chagas disease in southern Brazil. Despite morphological distinctions among these species, their genetic differentiation remains poorly understood, particularly in sympatric regions. This study investigates the genetic diversity and phylogenetic relationships through DNA sequencing analysis of five sympatric species within the T. rubrovaria subcomplex (T. rubrovaria, T. carcavalloi, T. klugi, T. circummaculata, and T. pintodiasi), using a 542-bp fragment of the mitochondrial cytochrome b (mtCytb) gene. A total of 84 specimens were collected from six municipalities in Rio Grande do Sul, Brazil, and analyzed alongside laboratory-reared specimens and sequences from the GenBank. Bayesian phylogenetic reconstructions, haplotype networks, and population structure analyses revealed a lack of clear genetic differentiation among the five species, with overlapping intra- and interspecific divergences and shared haplotypes. These findings suggest either a single species exhibiting phenotypic plasticity or a group of incipient species with ongoing gene flow. This study highlights the need for a taxonomic revision and suggests that this group could serve as a valuable model for further genomic research to elucidate potential aspects of phenotypic plasticity and/or sympatric speciation in triatomines.

Juvenile bull trout (Salvelinus confluentus Suckley, 1859) of migratory populations most often remain in natal creeks 2–3 years before moving downstream. Because migratory adult bull trout then begin to return to spawn as age-5 fish, abundant age-4 fish in the natal creek would indicate the nonmigratory life-history form. Population-specific, age-length keys, age-specific length frequencies, and Monte Carlo simulation were used to assign ages 0–5 to bull trout (n = 14 553) electrofished annually (1998–2023) from eight proximate populations in the St. Mary River catchment, north-central Montana, USA. Resident (that is, nonmigratory) bull trout, characterized as fish < 330 mm total length that had coloration and external morphology indicative of mature fish, were obvious in four populations and regularly captured from distinctive, high-gradient reaches that included large boulders and deep plunge pools. These resident bull trout were not of the common isolated life-history form, which occur upstream from a physical barrier to upstream movement, but were consistent with the unconfined resident form. Age structures showed age-4 residents were abundant in three of the populations; the fourth had inadequate age-length data. Size-based, assortative mating may preclude resident interbreeding with the larger migratory bull trout and thus foster sympatric speciation.

The sympatric speciation is an important phenomenon in the Evolution where a population able to express two different phenotypes gives rise to a new species without a physical separation from the initial population. Our goal is to show as simple assumptions on the initial population phenotypes and the selection process induced by a fluctuating environment allow to define a simple stochastic model that can explain the sympatric speciation via a stochastic bifurcation mechanism. We analyze the dynamical properties of the model and its possible relevance to describe the evolution of the speciation process as the result of enviromental fluctuations, highlighting the control parameters.

ABSTRACTSympatric speciation is defined as the formation of new species in the absence of geographic barriers, but the genomic and life history strategy mechanisms underpinning sympatric speciation are still far from clear. It has recently been discovered that the cichlid fish Astatotilapia calliptera from crater Lake Masoko in Tanzania have diverged sympatrically into littoral (shallow water) and benthic (deep water) ecotypes, which differ in head and pharyngeal jaw morphology. Carbon stable isotope analysis has also broadly indicated trophic differentiation between ecotypes. Here, we explore trophic niche divergence on a finer scale, using metabarcoding of stomach contents. A combination of the mitochondrial COI region and 18S V4 region from the eukaryotic nuclear small subunit ribosomal DNA was used to target macroinvertebrate and broader eukaryotic taxonomic diversity, respectively, revealing dietary divergence between the ecotypes. Large proportions of Arthropoda (dipterans and copepod) were found in both ecotypes, indicating some food sources common to both microhabitats. However, gut contents of benthic A. calliptera individuals were characterized by an abundance of annelids and diatoms, while Lepidoptera, mayflies, fungi, freshwater mussels, and bivalves were common in littoral ecotypes. The variation observed in the dietary contents of the ecotypes indicates the presence of resource partitioning, facilitating adaptation to unique feeding strategies.

The macroevolutionary drivers for disparities in plant species richness across Australia are understudied, hindered by lack of densely sampled comparative phylogenetic data. Here, we address this gap by analysing plant diversification dynamics and quantifying macroevolutionary trajectories of 22 plant clades (4289 species in 14 families) across two Australian regions. We show the southwest Australian (SWA) floristic region differs from southeastern Australia (SEA) in having relatively low speciation and extinction rates, fewer recent rapid radiations, declining speciation rates, relatively high rates of sympatric speciation indicative of greater niche space saturation, and an absence of mass extinction events since the Eocene. We show that low diversification rates in SWA can be attributed to the early diversification and old age of its flora. By contrast, the SEA extant flora largely diversified after the Eocene-Oligocene boundary extinction event. The paucity of diversification rate shifts across the two floras is likely linked to the lack of extreme environmental pulse events on the geologically stable Australian continent. Our results uncover the dynamics, which have shaped the SWA region as a current centre of hyperdiversity in a continental and global context and suggests an alternate pathway to diversity, not found in other biodiversity hotspots.

ABSTRACT We present light and scanning electron microscopical observations of two species from North America that resemble the original concept of Epithemia reicheltii Fricke. We review the history of that taxon, its similarity with Epithemia cistula, and present data to suggest the two North American species considered herein, which are sympatric in their distribution in Douglas Lake, Michigan, are different from one another. One of those species is described as new, Epithemia lacusdouglasi sp. nov. and we discuss the possibility of sympatric speciation in this locality. Epithemia reicheltii has also been reported from South Africa, and we review that report with original material. Based on our observations of the size diminution series of the taxon, we propose E. schoemanii sp. nov. and discuss its systematic position based on its valve morphology.

Late Cretaceous Earth was dominated by theropods such as tyrannosauroids and megaraptorans; however, it is unclear how these clades diversified and grew to massive proportions. This study aimed to conduct a biogeographical analysis and test climate as a potential mechanism for the increase in size. We used published phylogenetic matrices with the R package BioGeoBears to test different biogeographical hypotheses for both clades. We mapped body mass (BM) and body length against known climate data to test this potential hypothesis. Continental-scale variance did not drive tyrannosauroid biogeography and instead widespread ancestral populations, sympatric speciation and localized extinctions throughout these clades constricted geographic range. Both patterns were supported by statistical analyses. This biogeographical model also indicates the ancestor of the clade Tarbosaurus and Tyrannosaurus was present in both Asia and Laramidia, and therefore the ancestor of Tyrannosaurus came from Asia. Statistical data illustrated no correlation between Mean Annual Temperature (MAT) and BM but potential climatic shifts may be associated with gigantism in derived megaraptorids and eutyrannosaurians. This biogeographical model implies megaraptorans may have had a cosmopolitan distribution prior to the splitting of Laurasia and Gondwana. Also, gigantism in these clades may be associated with climatic shifts in the Late Cretaceous.

Abstract The process of speciation, where an ancestral species divides in two or more new species, involves several geographic, environmental and genetic components that interact in a complex way. Understanding all these elements at once is challenging and simple models can help unveiling the role of each factor separately. The Derrida-Higgs model describes the evolution of a sexually reproducing population subjected to mutations in a well mixed population. Individuals are characterized by a string with entries ±1 representing a haploid genome with biallelic genes. If mating is restricted by genetic similarity, so that only individuals that are sufficiently similar can mate, sympatric speciation, i.e. the emergence of species without geographic isolation, can occur. Only four parameters rule the dynamics: population size N, mutation rate µ, minimum similarity for mating qmin and genome size B. In the limit B → ∞, speciation occurs if the simple condition qmin > (1 + 4µN)-1 is satisfied. However, this condition fails for finite genomes, and speciation does not occur if the genome size is too small. This indicates the existence of a critical genome size for speciation. In this work, we develop an analytical theory of the distribution of similarities between individuals, a quantity that defines how tight or spread out is the genetic content of the population. This theory is carried out in the absence of mating restrictions, where evolution equations for the mean and variance of the similarity distribution can be derived. We then propose a heuristic description of the speciation transition which allows us to numerically calculate the critical genome size for speciation as a function of the other model parameters. The result is in good agreement with the simulations of the model and may guide further investigations on theoretical conditions for species formation.

Polyploidization is an important evolutionary force. It drives sympatric speciation through reproductive isolation of different cytotypes, and often leads to loss of sexual reproduction in polyploid lineages. Polyploidization and asexuality can change how other species engage in ecological interactions with the polyploid lineage and may change coevolutionary dynamics. Here, we quantified the phenotypic divergence in the freshwater oligochaete worm Lumbriculus variegatus, the California blackworm, among its co-occurring sexual diploid (Lineage II) and asexual polyploid (Lineage I) lineages. We further investigated variation in parasite communities and infection prevalence among sympatric and allopatric diploid/polyploid populations. 10 out of 18 populations showed co-existence of both lineages, with 7 populations harbouring only the polyploid lineage. Both worm lineages hosted endoparasitic nematodes, an ectoparasitic rotifer, and one potentially symbiotic gut ciliate. The parasite community similarity and overlapping size range of diploid and polyploid worms points to the ecological similarity of the worm lineages, despite the substantial ploidy and reproductive strategy differentiation. Although parasite prevalence varied independently of worm lineage, the prevalence was associated with the frequency of local cytotypes. Specifically, the rotifer prevalence was highest on the rare local cytotype, and nematode prevalence was highest on the common local cytotype. These results suggest the presence of both positive and negative frequency-dependent parasitism, which may contribute to the co-existence in the L. variegatus species complex.

The Aedes (Stegomyia) albopictus (Skuse, 1985) (Diptera: Culicidae) is one of the major vectors for Dengue and Chikungunya. However, our study uncovered another mosquito species morphologically similar to Ae. albopictus but is genetically different. The male genitalia of this species possess minute differences in the IX tergum with Ae. albopictus. Nucleotide diversity and mean genetic distance analysis confirmed the genetic difference from Ae. albopictus and other Aedes species. However, this species has a significant degree of genetic similarity with the cryptic species of Ae. albopictus earlier reported from Vietnam and China. The time tree revealed the median divergence time of this species and Ae. albopictus species to be approximately 36.13 million years ago. This study marks the discovery of an Aedes nr. Albopictus species resembling Ae. albopictus in India and third in the world, also reports the distinct morphological feature of the male genitalia for the first time. Our study indicates the sympatric behavior of this species as it shares the breeding habitat of Ae. albopictus. The absence of endosymbiont Wolbachia in this species raises the possibility of reproductive isolation with Ae. albopictus leading to sympatric speciation and increasing virus-carrying capability for this species, having significant implications for vector-borne disease control.

Dermacentor marginatus is a medically important tick species due to its preference humans and domestic animals as hosts and its vectorial competence, yet it remains understudied in many regions. This study aimed to examine the population structure and demographic history of D. marginatus using the cox1 and ITS2 genes, focusing on populations from Central and Northeast Anatolia—two regions on either side of the Anatolian Diagonal, a natural biogeographical barrier. A total of 361 host-seeking adult D. marginatus ticks from 31 sampling sites were analyzed, revealing 131 haplotypes for cox1 and 104 genotypes for ITS2. Neutrality tests and mismatch distribution patterns rejected the null hypothesis of the neutral theory, indicating that the population of D. marginatus in Anatolia has undergone a recent demographic expansion. Significant genetic differentiation and population structuring were observed between the Central and Northeastern Anatolian populations of D. marginatus, correlating with geographic distance and suggesting that the Anatolian Diagonal acts as a potential barrier to gene flow. Intrapopulation gene flow was higher in Central Anatolian populations compared to Northeastern Anatolian populations. Bayesian phylogeny revealed a highly divergent D. marginatus haplotype within the Northeastern Anatolian population, clustering into a Central Asian clade. Additionally, phylogenetic trees of the subgenus Serdjukovia revealed taxonomic ambiguities, including the absence of a distinct clade for D. niveus and potential misidentifications of D. marginatus and D. raskemensis specimens. Furthermore, the monophyletic relationship between D. marginatus and D. raskemensis supports the likelihood of sympatric speciation. These findings enhance our understanding of the genetic structure, phylogeography, and evolutionary dynamics of D. marginatus while providing a framework for future research on tick populations.