Accurate species delimitation is essential for taxonomy, ecology, and pest management, yet remains challenging in groups with subtle morphological variation. The Holotrichia gebleri complex, a group of widely distributed subterranean pests in China, causes serious agricultural damage and remains difficult to control. The complex primarily includes H. diomphalia, H. oblita, H. gebleri, and H. szechuanensis. Although these taxa are highly similar morphologically and differ only slightly in biological traits, their taxonomic statuses have long been debated. Here, based on samples from 48 localities, we present an integrative taxonomic assessment of the H. gebleri complex. Evidence from adult and larval morphology, molecular phylogeny, geographic distribution, and hybridization experiments consistently supports the hypothesis that the four nominal taxa belong to a single biological species. The only observed distinction lies in the structure of the male genital parameres, but this variation does not correspond to clear reproductive isolation. Hybridization experiments confirmed the absence of reproductive isolation between H. diomphalia and H. oblita, the two nominal taxa showing the greatest divergence in paramere morphology.These lines of evidence are most consistent with the hypothesis that the four nominal species do not represent clearly distinct species-level entities.
Abstract Ongoing biodiversity loss poses an increasing threat to insect pollinators, with serious consequences for ecosystem functioning and human wellbeing. Accurate and comprehensive knowledge of species is essential for the effective conservation of pollinators. Hoverflies (Diptera: Syrphidae) represent a key pollinator group, contributing not only to plant reproduction but also to ecosystem functioning as bioindicators, decomposers, and natural enemies of crop pests. However, their diversity remains insufficiently resolved. As genetic approaches increasingly underpin biodiversity assessment, DNA barcoding has become a widely used tool for species delimitation, but its reliability remains debated. The Merodon ruficornis group (Vujić et al., 2007) of hoverfly species remains obscured due to persistent inconsistencies among data types. Therefore, we applied an integrative, multilocus framework combining mitochondrial and nuclear markers, environmental analyses, and Wolbachia Hertig, 1936 screening to resolve group diversity and investigate the processes shaping it. Mitochondrial data revealed extensive haplotype sharing and deep intraspecific divergence, obscuring species boundaries. In contrast, nuclear markers, particularly ITS2, consistently delimited morphologically defined species, indicating pronounced mitonuclear discordance. Environmental analyses identified key temperature and precipitation-related bioclimatic predictors of mitochondrial haplotype distribution, indicating that environmental factors structure mtDNA variation and may mask species boundaries. Patterns of mitochondrial diversity are best explained by a combination of historical processes, including Pleistocene range dynamics, incomplete lineage sorting, and past introgression, rather than ongoing gene flow. Wolbachia infection was widespread but showed no clear association with mitochondrial patterns. These findings reveal how interacting historical and environmental processes shape diversity in M. ruficornis group and highlight the limitations of relying solely on mitochondrial markers; underscoring the necessity of integrative approaches in hoverfly systematics.
Abstract Shell morphology in terrestrial gastropods is widely assumed to reflect climatic adaptation, yet empirical support for body size-climate relationships remains inconsistent across scales. We investigated how shell morphology is associated with large-scale climatic gradients in nine rock-dwelling Pyramidula species across 228 sites in the Western Palearctic. We hypothesised that climatic conditions linked to high solar radiation and low precipitation are associated primarily with shell traits potentially mediating conductive heat exchange with sun-exposed limestone substrates rather than with overall body size. For 519 adult shells, we analysed shell width, height, width/height ratio and a novel composite shell geometry index ( SGI ) using linear mixed-effects models with species and locality as random factors. Shell width showed the strongest and most consistent climatic associations, decreasing with increasing solar radiation and decreasing precipitation. In contrast, shell height and body volume exhibited weak or no independent climatic relationships. The SGI displayed intermediate but consistent responses, particularly to precipitation of the driest month. An additive model combining solar radiation and low precipitation explained nearly 19% of shell width variation. Responses were directionally consistent across species, suggesting shared morphological responses to similar climatic conditions. Observed patterns indicate that shell geometry, particularly shell width, is more closely associated with climatic gradients related to heat and drought stress than is overall body size.
Understanding how closely related sympatric species achieve coexistence through niche partitioning is a central question in ecology. Lepidopteran larvae provide powerful models for studying niche differentiation owing to their host-plant specificity, diverse feeding strategies, and pronounced morphological adaptations. We investigated the coexistence of two congeneric butterfly larvae, Papilio xuthus Linnaeus, 1767 and P. machaon Linnaeus, 1758, on their shared host plant Dictamnus dasycarpus by integrating field surveys, ultrastructural morphological analyses, and quantitative color measurements. The two species exhibited clear niche differentiation across temporal, spatial, trophic, and defensive dimensions. P. xuthus emerged earlier, fed cryptically on leaves, and possessed mouthparts and crochets suited for horizontal movement. By contrast, P. machaon emerged later, fed openly on flowers and fruits, displayed stronger grasping adaptations, and showed conspicuous coloration consistent with aposematism. These multidimensional differences are consistent with niche partitioning and may facilitate coexistence between the two sympatric congeners, providing an empirical case that advances understanding of niche differentiation and species coexistence.
Zoraptera represents a species-poor evolutionary lineage of polyneopteran insects with a relict circumtropical distribution. This study presents a comprehensive phylogeny, evolutionary timeline, and historical biogeography of all recognized Zoraptera subfamilies, based on analyses of 18 species representing eight genera using multi-gene datasets from both mitochondrial and nuclear loci. It utilizes 12 polyneopteran fossils as calibration points, including two amber fossils of Zoraptera. The Bayesian time-calibrated molecular phylogenetic tree inferred in BEAST suggests that the major Zoraptera lineages, Zorotypidae and Spiralizoridae, probably originated on the supercontinent Pangaea (similar to 309 Mya). Zorotypinae and Latinozorinae maintained a circumtropical distribution until the Mesozoic/Cenozoic boundary. Subsequently, both subfamilies became extinct in Africa, and Latinozorinae also disappeared in Asia. We estimate that the Spiralizorinae diversified during the Late Triassic period in south-western Gondwana, while the ancestor of Spermozorinae emerged in the eastern Laurasia and remained restricted to present-day Southeast Asia. The current circumtropical distribution reflects a complex evolutionary history marked by significant distributional changes and extinctions, and contributes to our understanding of tropical insect biogeography.
