Zoological Journal of the Linnean Society

Color polymorphism can facilitate local adaptation, maintain intraspecific diversity, or reflect early stages of speciation. Clownfishes (Amphiprion spp.) typically display a simple black, orange, and white pattern, but the saddleback clownfish (Amphiprion polymnus) shows striking variation in melanism and the number of vertical bars, which are thought to play a role in species recognition. In 2024, a revision on iNaturalist split A. polymnus into multiple species based solely on color pattern and geographic range. This raises the question of whether these morphs represent true species or intraspecific polymorphism, which we tested using genomic and image-based data. We sampled 97 individuals from seven populations across the species range and quantified color patterns from standardized photographs. Phenotypic and genomic analyses reveal a complex pattern of divergence. Image analysis identified three distinct phenotypic clusters, with A. polymnus, A. annamensis, and A. laticlavius each showing consistent differences in saddle shape and vertical bar extent. ADMIXTURE resolved three distinct genetic groups corresponding to the morphs. Pairwise FST (0.54-0.71) and dxy indicate extremely high differentiation between A. polymnus and A. annamensis, consistent with species-level divergence, whereas A. laticlavius shows much lower differentiation from A. polymnus (FST 0.09-0.18) and higher differentiation from A. annamensis (FST 0.64-0.66). Overall, phenotypic and genomic data show structured variation, but the status of A. laticlavius remains ambiguous. Our study reveals clear and structured divergence across the full range, yet the taxonomic interpretation of this variation remains inherently challenging. The key question remains: do these patterns reflect a single polymorphic species or a complex of closely related species?

This study presents a systematic revision of the suborder Astrophorina for the temperate Pacific coast of the United States and Canada. Major findings include a reduction in the number of species previously thought to range into the region from Japan; validation of most Geodia species erected by Lendenfeld (1910), which were later synonymized by de Laubenfels (1932); the formal description of 10 new species (Poecillastra alaskensis sp. nov., Vulcanella explorata sp. nov., Vulcanella rupta sp. nov., Stelletta cardenasi sp. nov., Stelletta nicolenya sp. nov., Stelletta limuwensis sp. nov., Dercitus (Stoeba) giveni sp. nov., Penares anyapax sp. nov., Penares foxi sp. nov., and Thenea diastra sp. nov.); and one new combination, Penares orientalis comb. nov. Extensive SCUBA-based collection efforts yielded new samples for 11 of the 26 species identified in the region, which enabled an integrative taxonomic approach that combined field photography, fresh material for DNA sequencing, and improved characterization of species ranges and morphological variability in previously described taxa. Illumina sequencing generated complete nuclear ribosomal haplotypes for five species, while Sanger sequencing of the 28S and cox1 loci placed 20 of the 26 species within molecular phylogenies. The use of very short "mini-barcode" amplicons also enabled sequence recovery from historic type specimens up to 137 years old. This study additionally reports the discovery of sponge grounds of abundant, large Geodia at diving depths in Southern California. Together, these results substantially advance our understanding of global astrophorid diversity and systematics, and the biogeography of sponge diversity in the Northeast Pacific. Note about species names: this pre-print is not intended to be a publication of the associated species names for the purposes of zoological nomenclature.

The moonfish Mene maculata (Bloch and Schneider, 1801), the sole extant species of the family Menidae, is widely distributed in the Indo-West Pacific. Although its spawning season has previously been inferred from seasonal variation in the gonadosomatic index (GSI), the histological basis for interpreting GSI as an indicator of spawning-capable status remains limited. Here we describe the gonadal structure of male and female M. maculata and evaluate how GSI and standard length relate to spawning-capable status based on germ cell development. The testis was lobular and exhibited an unrestricted spermatogonial distribution, a structure widely observed among neoteleosts, indicating that the phylogenetic distinctiveness of M. maculata was not associated with a distinctive testicular structure. In the spawning-capable female, oocytes at multiple developmental stages, from primary growth to oocyte maturation, co-occurred within the ovary, indicating asynchronous ovarian development. This finding suggests that M. maculata may be a batch spawner rather than a total spawner as previously inferred. The spawning-capable female had a GSI consistent with previously inferred spawning season estimates. By contrast, histologically examined males were spawning capable at GSI values lower than those previously associated with the inferred spawning season, suggesting that male spawning-capable status may persist beyond the period inferred from elevated GSI alone. This study provides the first histological description of reproductive biology in the phylogenetically distinctive M. maculata and establishes a histological basis for interpreting GSI as a reproductive indicator.

True crabs (Brachyura) are among the most iconic marine arthropods, representing noteworthy examples of morphological and ecological disparity. A striking feature of brachyurans are their anterior pincer-like appendages: chelipeds. These structures showcase a large diversity of morphologies that reflect ecology and overall multifunctionality. Yet, a comprehensive assessment of appendage functional morphology within phylogenetic and ecological trait contexts has never been attempted. By combining 3D geometric morphometrics, finite element analyses, multilocus molecular phylogeny, and ecological trait data for 80 crab species, including three fossil forms, we unveil a complex evolutionary history for crab chelipeds. Despite extreme shape diversity amongst chelipeds, stress distributions are very similar across taxa and hint a many-to-one pattern. High concentrations of chelipeds within constrained morphospace regions associated with peak pinch forces illustrates that brachyuran morphologies optimised for shell crushing may have arisen in the Cretaceous. Deviations from this morphospace highlight the diversification of non-shell-crushing life modes and the influence of sexual selection on appendages. Neither cheliped shape nor pinch force show phylogenetic signal. Together these results indicate that the evolution of cheliped shape is closely associated with, and inferred to have been strongly influenced by, crab ecology, biomechanical needs and sexual selection. SIGNIFICANCE STATEMENTChelipeds, the pincer-like claws of crabs, are among the most morphologically diverse appendages within Arthropoda, yet the evolutionary forces driving this diversity remain poorly understood. By integrating 3D geometric morphometrics, biomechanical modelling, molecular phylogeny, and ecological data across 80 crab species including fossil forms, we demonstrate that cheliped morphology is driven by ecology, biomechanical demands, and sexual selection rather than phylogenetic relatedness. The multifunctionality of these structures produces strong evidence for many-to-one mapping of form to function. Morphologies optimised for durophagy appear to have originated in the Cretaceous, with subsequent diversification into manipulative and sexually selected forms from a morphologically flexible foundation. These findings demonstrate that cheliped diversity reflects a complex interplay between ecological specialisation, biomechanical optimisation, and sexual selection across Brachyura.

Mammal tails have long been recognized for their diversity of morphological form and function, however, there remains a substantial gap between the motivation to understand and emulate the various performance functions of the tail and what is known about tail anatomy. In this study, we were motivated to discover the anatomical foundations of the fast, whipping motions of the tail of the lesser Egyptian jerboa (Jaculus jaculus), which may aid in the quick changes of direction as the animal escapes from predators using ricochetal bipedal hopping. We employed microCT scans, dissections, and museum data to describe the musculoskeletal anatomy of the jerboa in comparison with the laboratory mouse (Mus musculus) and rat (Rattus norvegicus). While many aspects of tail anatomy are conserved across these species, the jerboa does possess unique characteristics such as an extremely long tail arising from caudal vertebral elongation, development of extensive dorsal musculature differentiated into lateral and medial components to increase points of skeletal attachment, and a novel anatomical feature - the bi-lobed cranial transverse process - which serves as a supernumerary dorsal tendon attachment site and possible brace to protect the ventral tendons and intrinsic muscles for a section of caudal vertebrae which likely experiences high mechanical stress.

Fistulobalanus albicostatus Pilsbry, 1916 (Thoracica: Balanidae) is a tropical to temperate species distributed in the NW Pacific. The previously known northernmost record of this species in Japan was from Aomori Prefecture, at the northern end of Honshu Island, Japan. However, field surveys conducted in 2023 and 2026 confirmed the occurrence of F. albicostatus in Hakodate Bay, the southern end of Hokkaido, Japan, across the Tsugaru Strait, thereby extending the northern limit of its known distribution. A line transect survey conducted in May 2026 recorded seven living individuals within an area of 128 m. F. albicostatus was rare on the mid-high shores, accounting for only 2% of all barnacle individuals in a quadrat survey. The basal diameter of the living individuals ranged from 0.76 to 1.23 cm, and all individuals possessed ovaries. Based on characteristics of both morphological and COI gene, the specimens were identified as F. albicostatus, and belonged to the same haplotype of populations that are present in Honshu Island. The establishment of F. albicostatus in Hokkaido suggests an ongoing northward range shift of this warm-water species, with the potential for further expansion under continued ocean warming.

Reliable species delimitation underpins biodiversity assessment but remains difficult for organisms with plastic morphology and few diagnostic characters. Multispecies coalescent (MSC) methods can delimit species from genomic data, yet they are rarely tested in taxonomically complex, marine invertebrate groups where they are arguably most needed. We used the three Mediterranean species of the genus Tethya, a rare, well-characterised system within the otherwise taxonomically difficult phylum Porifera-distinguished by multiple independent morphological and ecological characters-to evaluate how robust MSC-based delimitation is in such groups. Analysing 64 single-copy nuclear loci in BEAST2 and BPP, we compared constrained, hypothesis-testing approaches (BFD*, BFdriver, A10) with freer, heuristic ones (SPEEDEMON, A11), and examined their sensitivity to data type, clock model, priors, and the species-collapse threshold. All methods recovered the three recognised Mediterranean species, but the resolution of within-lineage structure was method-dependent. The hypothesis-testing approaches consistently supported six lineages, robustly across data types and model assumptions, whereas the heuristic approaches proved less stable. Configurations without a priori species hypotheses often failed to converge or were computationally intractable, a problem compounded by the relaxed clock. In SPEEDEMON the outcome changed with the collapse threshold. Because our system lacks an independent reference point to calibrate this threshold, any delimitation based on it is poorly constrained. We conclude that constrained, hypothesis-testing delimitation is the most robust and reproducible MSC approach, yielding a quantitative, model-based hypothesis that can be weighed against other lines of evidence to inform taxonomic decisions. By clarifying how these methods behave and how their outcomes should be interpreted, our study offers a practical guide for researchers working on comparably complex systems.

In most vertebrates, social play among peers is considered essential for behavioral development. Yet in solitary species bearing single offspring, opportunities for social play are inherently scarce. Whether mothers of such species actively facilitate play opportunities for their offspring, and at what cost, remains unknown. We used 15 years of behavioral and movement data ([~]30,000 observation hours) from 31 wild Bornean orangutan (Pongo pygmaeus wurmbii) mother-offspring pairs to test whether mothers adjust ranging behavior to increase their offsprings access to play with neighboring peers. Neighboring mothers with similarly aged offspring showed disproportionately high annual overlap in space use, independent of their relatedness or fruit availability. They intensified use of shared areas within existing range boundaries rather than shifting or expanding their ranges, indicating a fine-scaled ranging strategy. Mothers also incurred energetic costs; on days their offspring played with peers, mothers traveled farther and spent less time feeding. Travel distances were also elevated on the days before and after play, with mothers orienting movement toward play partners core areas before play and back toward their own core areas after play. This suggests these encounters are planned and actively pursued over multiple days rather than arising by chance. These findings reveal that orangutan mothers incorporate their infants social needs into daily ranging decisions, at a cost to their own energy budgets. This points toward an underappreciated form of maternal investment and illustrates how the social requirements of development can be met even near the solitary extreme of animal social organization.

The biodiversity crisis is exacerbated by persistent gaps in taxonomic, geographic, and conservation knowledge. This study provides a comprehensive assessment of Linnean, Wallacean, and conservation shortfalls in Rivulidae (Cyprinodontiformes), one of the most diverse families of Neotropical freshwater fishes. To this end, an extensive dataset was compiled, comprising 494 valid species, 51 synonyms, 3,419 occurrence records, and information on life cycle, distribution, and conservation status. The Linnean shortfall remains open: after 1975, the rate of species description increased sharply, and estimates indicate that 103 species remain undescribed (95% CI: 53-212). The year of species description was influenced by detectability and accessibility factors, with larger species, more widely distributed species, and species occurring in more densely populated areas being described earlier. The Wallacean shortfall was broad and spatially uneven: only 5.34% of the region was considered adequately sampled. The conservation shortfall was also substantial: 179 species are threatened with extinction, 69 species remain Not Evaluated, and 62 are Data Deficient. The mean time between taxonomic description and first IUCN extinction-risk assessment was 25.7 years. Moreover, 59.9% of species have no records within protected areas, including 69.3% of threatened species. These findings synthesize an urgent challenge: biodiversity knowledge and conservation shortfalls must be overcome simultaneously to protect species that are still being discovered, remain poorly documented spatially, and are restricted to habitats under intense anthropogenic pressure. The conservation of Rivulidae cannot wait for complete knowledge; action amid uncertainty is necessary to prevent both known and unknown species from disappearing.

Biological invasions on islands provide a natural framework to study how dispersal and connectivity influence evolutionary and ecological processes. The avian nest parasitic fly, Philornis downsi - first recorded in Darwin's finch nests in 1997 - causes high mortality in endemic land birds, yet its inter-island and sex-specific patterns of dispersal and genetic structure remain poorly understood. We use low-coverage whole genome sequencing to investigate genome-wide patterns of genetic diversity, directional migration and effective population size in P. downsi across five major Galapagos Islands and its native range in mainland Ecuador. We find evidence for a genetic bottleneck in the Galapagos, isolation by distance, and evidence that the island closest to the Ecuadorian mainland, San Cristobal, is genetically divergent from the other four islands sampled, despite retaining the highest genetic diversity. No evidence was found for sex-biased dispersal; however, sex-biased genetic structure was detected using only markers from inferred autosomal scaffolds. We found asymmetric gene flow with higher migration rates from San Cristobal westward to the other islands, matching the direction of both southeast trade winds and major cargo shipping routes. Our results suggest both natural and human-mediated colonisation of P. downsi from the mainland through San Cristobal to the other islands, followed by high inter-island dispersal among closely situated sink islands. Our findings are critical for prioritising islands for control strategies that will reduce P. downsi impacts on vulnerable endemic birds and underscore the value of understanding directional migration patterns for managing invasive species in metapopulations.

The global study of freshwater clams in the genus Corbicula is frequently confounded by invasive androgenetic lineages that experience mitochondrial DNA capture and clonal propagation. In contrast, the endemic Corbicula of Sulawesi's ancient lakes reproduce sexually, offering a uniquely reliable system for mitochondrial population genetics. This study provides the first population-genetic framework for two endemic species, Corbicula possoensis (Lake Poso) and C. linduensis (Lake Lindu), using the cytochrome c oxidase subunit I (COI) marker. We analysed 90 newly generated COI sequences from C. possoensis (six stations) and C. linduensis (three stations), integrated with reference sequences from GenBank, to assess genetic diversity, population structure, and phylogeographic patterns. Hierarchical AMOVA revealed deep divergence between the two lakes ({Phi}_CT = 0.607), consistent with prolonged independent isolation rather than a single shared vicariance event, as the two species do not form a sister pair in the phylogeny. Within Lake Poso, C. possoensis exhibited exceptionally high genetic diversity (24 haplotypes; h = 0.876; {pi} = 0.016) and pronounced micro-geographic structuring into three phylogeographic zones (North: Tentena and Siuri; East: Tando Nceppo and Busogo Beach; Southwest: Bancea and Pendolo), each characterised by distinct haplogroups. Remarkably, the maximum divergence between zones (K2P = 2.33%) approached the interspecific distance between C. possoensis and C. linduensis (K2P = 2.42%), indicating that within-lake mitochondrial divergence has reached near-interspecific levels. Conversely, C. linduensis displayed near-panmixia and extreme genetic depauperation (3 haplotypes; h = 0.246; {pi} = 0.0004), indicating long-term demographic stasis within a restricted habitat. The deep phylogeographic zonation in C. possoensis suggests that its discrete populations should be treated as separate Management Units (MUs) in conservation planning to preserve locally adapted gene complexes, whereas the severely depauperate gene pool of C. linduensis renders it critically vulnerable to environmental disturbance and invasive species, warranting urgent IUCN Red List assessment. To validate these mitochondrial boundaries and inform future conservation strategies, multi-marker and genome-wide reassessments are strongly recommended.

The preparation of multi panel figures remains a labor intensive step in scientific publication. Albeit there are specific tools available to solve this problem, they are often highly specialized, difficult to install, or time consuming to learn. Griphus is a standalone graphical application designed for rapid composition and experimentation with multi panel figures, developed by and for zoological taxonomists. Functions specifically designed for multi panel composition include automatic figure numbering and placement, aspect ratio operations, spacers, layout rotation, layout suggestions, and automatic generation of figure legends, including scale bar descriptions. The software can perform both spatial interpretation of images on the canvas and work with a simple, editable layout formula. It also enables instant multi panel composition, with numbered images and automatic contrast selection for the numbers, obtained simply by loading images. User defined parameters such as target printable dimensions, resolution, spacing, and color mode are preserved throughout the work. The program produces coordinated outputs consisting of the final composite figure, a readable file describing the layout structure, and a .gri file storing images, transformations, and parameters for exact regeneration. Griphus is intended as a complementary tool to professional image software, providing a simple and efficient environment for constructing high quality multi panel figures.

The hallmark of sessile adult ascidians is a vase-like shape with a single oral and atrial siphon. Ciona, however, develops two atrial siphons after metamorphosis, which subsequently fuse into one. The mechanisms underlying this fusion are unknown. This study suggests that Hox2 controls this process. Hox2-knockout animals using Transcription-Activator-Like Effector Nuclease (TALEN) retain two atrial siphons throughout their lives. During normal fusion, epidermal cells between the siphons flatten along the anterior-posterior axis. This cellular flattening does not occur in Hox2-knockout animals, suggesting that the shape change in the epidermal cells produces tension, allowing the atrial siphon openings to converge at the midline for fusion. Hox2-knockout animals lack cupular organs, which are suspected hydrodynamic sensors in the internal epithelium of the fused atrial siphon and on the sperm duct. Among several knockout attempts, atrial siphon fusion was reproduced by only one TALEN pair, suggesting that this phenotype is driven by a mutation having a broader effect than those abolishing protein function. Many ascidians, unlike Ciona, develop a single atrial siphon shortly after metamorphosis. Our findings suggest that a phylogenetically conserved gene, Hox2, establishes this group-specific atrial siphon formation mechanism in Ciona.

The AMY2B gene encodes pancreatic amylase, a critical enzyme for starch digestion. While previous studies have examined AMY2B copy number variation (CNV) in domestic and some wild animals, less is known about wild carnivores inhabiting regions with limited anthropogenic starch exposure. We analyzed blood samples for serum amylase activity and copy number variation in AMY2B gene from 8 wolves (Canis lupus), 11 brown bears (Ursus arctos), and 3 red foxes (Vulpes vulpes) from Bosnia and Herzegovina. AMY2B gene copy number was assessed using droplet digital PCR (ddPCR), and serum amylase activity and glucose levels were quantified. Although the number of fox samples was limited, foxes and wolves consistently harbored two copies of AMY2B, while brown bears exhibited higher CNV (3.67-8.40, mean 5.88). Serum amylase activity was highest in foxes, moderate in wolves, and variable but lower in bears. Despite differences in AMY2B copy number and serum amylase activity, circulating glucose concentrations did not differ significantly among species. Our findings suggest that variation in AMY2B copy number among wild carnivores may be associated with species-specific evolutionary histories and dietary adaptations, providing insight into genomic mechanisms underlying carbohydrate utilization in natural populations.

The European flat oyster (Ostrea edulis), like numerous other oyster species, has been exploited for millennia and cultivated and translocated for centuries. Following a severe population decline, and in the context of ongoing conservation and restoration programs, genetic considerations must now be addressed to avoid mistakes. The objective of our study was to complement population genetic studies conducted at various scales along European coasts. Our sampling primarily targeted the French Atlantic, English Channel, and Mediterranean coasts, aiming to provide a fine-scale genetic characterization of populations in these regions. By integrating SNP array and low-coverage sequencing datasets, we obtained a comprehensive overview of the population genetic structure of Ostrea edulis across western Europe. Most previously identified clusters in Western Europe were confirmed. In France, populations assigned to these clusters exhibited notable within-patch homogeneity. However, two key findings emerged: (1) an extensive overlap zone between the Atlantic and western Mediterranean clusters, spanning at least from southern Portugal to southern France, and (2) the detection of a novel, clearly distinct cryptic cluster east of the English Channel, whose geographic range remains to be better delineated. These insights are critical for informing management decisions, particularly as restoration and conservation plans are currently being implemented across the species range.

Knowledge regarding variation in habitat use among individuals is crucial for understanding population dynamics and for management and conservation measures. This is especially important for diadromous fishes that shift between habitats, being affected by external pressures and environmental change in different habitats over ontogeny. Herer, we assessed individual variation in habitat use of European eel along a salinity gradient, ranging from fully marine to freshwater in northern Europe, using otolith microchemistry data from >3600 eel together with established time-series segmentation and clustering methods. We show that eel display high degree of individual variation in habitat use. Assigned life-histories included coastal resident, freshwater resident, and coastal and freshwater habitat shifting individuals. Coastal resident eels were observed in a large range of salinities. Given the widespread occurrence of migration barriers in freshwater, it is unknown whether the coastal resident eel preferred that habitat, or if it was the only available habitat for them. Our findings nonetheless highlight the need to include coastal habitats when assessing population development and silver eel production of the critically endangered European eel.

The origin of novel phenotypes can influence access to new ecological resources, which may have positive, neutral, or negative effects on subsequent phenotypic diversification. In this study, we tested the macroevolutionary consequences of a pair of putative functional innovations occurring in deep-sea fishes of the order Stomiiformes. Integrating phylogenetic comparative methods, micro-CT scans, and external body measurements, we recover a mosaic of diversification trends associated with these innovations. We found some evidence for elevated evolutionary rates in tooth morphology associated with the predatory dragonfishes, which possess a gap between their vertebral column and skull that exposes the notochord and enables neck-like flexibility. However, a second novelty building upon the first, a functional neck joint enabling extreme cranial kinesis, was linked to faster rates of skull evolution. Our results suggest that innovations that help shift ecological roles and overcome functional constraints related to those roles, like gape-limitation in prey depauperate habitats, may play an important role in promoting phenotypic diversification. This work builds on a growing body of evidence highlighting how the deep sea promotes phenotypic diversity, generating the extreme forms that are celebrated by scientists and the public alike.

Brain size and structure are hypothesized to be adaptively designed to satisfy the behavioral requirements of securing food and living socially. The importance of these socioecological and sociobiological selective forces in brain evolution is constantly debated. Socioecological divergence is striking in the Neotropical ant genus Neoponera: N. apicalis is a generalist solitary predator forming small colonies of ~100 whereas N. commutata colonies are approximately 10 times as large and workers pheromonally organize cooperatively raids only on Syntermes termite colonies. We interspecifically compared the size and structure of the compound eyes, size and number of antennal glomeruli, mosaic brain scaling and synaptic processing (microglomeruli-MG). Our results indicate that N. apicalis workers have a larger number of ommatidia, antennal lobe glomeruli, and allometrically larger antennal and optic lobes than N. commutata. These sensory traits were associated with differences in higher-order processing architectures in the mushroom body (MB) microglomeruli (MG). N. commutata workers had an allometrically larger MB, perhaps due to their socially complex chemical foraging communication, although MG density in N. apicalis was higher in both the MB lip and collar, regions associated with processing olfactory and visual information, respectively. The increase in MG density in N. apicalis may be associated with higher demands for navigation, learning, and memory, as well as a higher density of antennal lobe glomeruli to support prey odor discrimination. In contrast, N. commutata workers had larger ommatidia and antennal lobe glomeruli. Larger ommatidia correlate with their diurnal/nocturnal habits and a larger MB Our findings indicate that differences in behavioral performance demands associated with socioecological differentiation are reflected in variation in visual and olfactory system structure, brain size, mosaicism, and synaptic organization. Our results support both social and ecological brain hypothesis as drivers of mosaic brain evolution.

In search of recurrent patterns of postzygotic hybrid incompatibility, we investigated the Holarctic 'Old World Swallowtail' (Papilio machaon Linnaeus) butterfly complex, whose members can easily be crossed in the laboratory. How many species this model system comprises remains unclear, as taxa with highly distinctive larvae but uncertain status come into contact with authentic P. machaon subspecies in Southern parts of the Palearctic region. By determining mitochondrial and ITS2 haplotypes within and away from contact zones, we found that these neighboring populations do exchange genes, as expected from F1 hybrids being generally fertile in our laboratory crosses. Nevertheless, recurrent instances of dysregulation of diapause were uncovered in hybrid progenies. In keeping with Haldane's Rule, pupae of the heterogametic (female) sex were either unable to enter diapause or, in reciprocal crosses, unable to resume development after having initiated diapause, whereas F1 males experienced normal, photoperiod-regulated diapause, but passed on abnormal diapause regulation to part of their female offspring when backcrossed. Comparing male and female pupal weights in hybrid progenies provides estimates of parental incompatibility that allow to rank taxa and predict quantitatively the outcome of additional crosses, as expected if the same regulatory system were involved. A survey of the entomological literature confirms that diapausing pupae that cannot resume development ('perpetual nymphs') are a recurrent feature of interspecific lepidopteran crosses. Moreover, of the two parent species of a perpetual nymph, the paternal one generally has fewer broods per year. These observations are discussed in the light of models of the speciation process.

Limb loss in vertebrate animals is surprisingly common despite imposing strong functional constraints. These pressures funnel species towards regions of limited ecological and phenotypic space. To date, snakes have been considered unique in having escaped this pattern. Using a new species-level phylogeny and comparative morphological and dietary datasets, we show that pygopods, a group of limbless Australo-Papuan geckos, have undergone a similar evolutionary trajectory to snakes. Our analyses provide evidence of exceptional morphological and diet evolution. This is exemplified by strong niche partitioning among genera through dietary specialization and greater than expected dietary disparity. Diversification in pygopods has also been driven by extreme phenotypic evolution, with pygopods encompassing much of the morphological space covered by all other limb-reduced lizards. Interestingly, the diversification of pygopods has resulted in only a modest number of species, emphasizing the decoupling of diversity and richness possible in adaptive radiations.