Discovery of the bicycle gene family provides new insights into insect manipulation of plant development during gall induction.

Galls are complex structures that develop from plant tissue, providing protection and food for gall-forming organisms, such as insects or mites. However, the molecules used by insects or mites to manipulate plant development have proved elusive. A landmark study has tracked down a gene in a gall-forming aphid that controls whether galls on witch hazel are green or red. The 'green allele' is strongly expressed in aphid salivary glands and represses plant genes used for red color formation. Excitingly, the gene product is part of a large suite of proteins that aphids may use to interact with plant biology.

Stable pollination service in a generalist high Arctic community despite the warming climate.

Insects provide key pollination services in most terrestrial biomes, but this service depends on a multistep interaction between insect and plant. An insect needs to visit a flower, receive pollen from the anthers, move to another conspecific flower, and finally deposit the pollen on a receptive stigma. Each of these steps may be affected by climate change, and focusing on only one of them (e.g., flower visitation) may miss important signals of change in service provision. In this study, we combine data on visitation, pollen transport, and single-visit pollen deposition to estimate functional outcomes in the high Arctic plant-pollinator network of Zackenberg, Northeast Greenland, a model system for global warming-associated impacts in pollination services. Over two decades of rapid climate warming, we sampled the network repeatedly: in 1996, 1997, 2010, 2011, and 2016. Although the flowering plant and insect communities and their interactions varied substantially between years, as expected based on highly variable Arctic weather, there was no detectable directional change in either the structure of flower-visitor networks or estimated pollen deposition. For flower-visitor networks compiled over a single week, species phenologies caused major within-year variation in network structure despite consistency across years. Weekly networks for the middle of the flowering season emerged as especially important because most pollination service can be expected to be provided by these large, highly nested networks. Our findings suggest that pollination ecosystem service in the high Arctic is remarkably resilient. This resilience may reflect the plasticity of Arctic biota as an adaptation to extreme and unpredictable weather. However, most pollination service was contributed by relatively few fly taxa (Diptera: Spilogona sanctipauli and Drymeia segnis [Muscidae] and species of Rhamphomyia [Empididae]). If these key pollinators are negatively affected by climate change, network structure and the pollination service that depends on it would be seriously compromised.

Revision of the Amphibolips niger group with the description of a new species (Hymenoptera: Cynipini).

Amphibolips is currently divided into two species-groups, clearly differentiated by adult and gall morphology. The niger group of Amphibolips species is revised. This complex includes eight species: A. gumia Kinsey, A. jubatus Kinsey, A. elatus Kinsey, A. maturus Kinsey, A. nebris Kinsey, A. niger Kinsey, A. pistrix Kinsey and A. ufo Cuesta-Porta & Pujade-Villar sp. nov. We provide descriptions of new species and re-descriptions of known species, diagnoses, keys to complexes and species. The possibility of the niger complex belonging to a new genus is also discussed.

Re-establishment of the Nearctic oak cynipid gall wasp genus Feron Kinsey, 1937 (Hymenoptera: Cynipidae: Cynipini), including the description of six new species.

The Nearctic cynipid oak gall wasp genus Feron Kinsey, comb. rev., is re-established with 34 species: F. albicomus (Weld, 1952), comb. nov., F. amphorus (Weld, 1926), comb. nov., F. apiarium (Weld, 1944), comb. nov., F. atrimentum (Kinsey, 1922), comb. nov., F. bakkeri (Lyon, 1984), comb. nov., F. caepula (Weld, 1926), comb. nov., F. californicum (Beutenmueller, 1911), comb. nov., F. clarkei (Bassett, 1890), comb. nov., F. comatum (Weld, 1952), comb. nov., F. crystallinum (Bassett, 1900), comb. nov., F. cylindratum (Kinsey, 1937), comb. nov., F. discale (Weld, 1926), comb. nov., F. discularis (Weld, 1926), comb. nov., F. dumosae (Weld, 1957), comb. nov., F. gigas (Kinsey, 1922), comb. nov., F. izabellae Melika, Nicholls & Stone, sp. nov., F. kingi (Bassett, 1900), comb. nov., F. parmula (Bassett, 1900), comb. nov., F. pattersonae (Fullaway, 1911), comb. nov., F. roberti Melika, Nicholls & Stone, sp. nov., F. rucklei Melika, Nicholls & Stone, sp. nov., F. scutellum (Weld, 1930), comb. nov., F. serranoae Pujade-Villar & Cuesta-Porta, sp. nov., F. splendens (Weld, 1919), comb. nov., F. stellare (Weld, 1926), comb. nov., F. stellulum (Burnett, 1974), comb. nov., F. sulfureum (Weld, 1926), comb. nov., F. syndicorum Pujade-Villar & Cuesta-Porta, sp. nov., F. tecturnarum (Kinsey, 1920), comb. nov., F. tetyanae Melika, sp. nov., F. tibiale Kinsey, 1937, comb. rev., F. tubifaciens (Weld, 1926), comb. nov., F. verutum Kinsey, 1937, comb. rev., and F. vitreum Kinsey, 1937, comb. rev. Most species are known only from the asexual generation; F. clarkei, F. comatum, and F. dumosae are known only from the sexual generation, while both generations are recognised for F. atrimentum, F. crystallinum, F. gigas, F. kingi, and F. pattersonae. Matching of alternate sexual and asexual generations is established for the first time for F. kingi and F. pattersonae (= Andricus pedicellatus (Kinsey, 1922), syn. nov.) based on molecular data (both cytb and ITS2 sequences). Morphological descriptions, re-descriptions, diagnoses, and a key to species are given, as well as data on DNA sequences, biology, phenology, and distribution.

Re-establishment of the Nearctic oak cynipid gall wasp genus Druon Kinsey, 1937 (Hymenoptera: Cynipidae: Cynipini), with description of five new species.

The Nearctic cynipid oak gall wasp genus Druon Kinsey comb. rev. is re-established, with 5 new species and 10 species previously placed in the genus Andricus Hartig 1840: D. alexandri Melika, Nicholls Stone, sp. nov., D. flocculentum (Lyon), comb. nov., D. fullawayi (Beutenmller), comb. nov., D. garciamartinonae Pujade-Villar, sp. nov., D. gregori Melika, Nicholls Stone, sp. nov., D. hansoni Cuesta-Porta, Melika Pujade-Villar, sp. nov., D. ignotum (Bassett), comb. nov., D. linaria Kinsey, comb. rev., D. pattoni (Bassett), comb. nov., D. protagion Kinsey, comb. rev. (D. malinum Kinsey, syn. nov., D. polymorphae Kinsey, syn. nov.), D. quercusflocci (Walsh), comb. nov., D. quercuslanigerum (Ashmead), comb. nov., D. receptum Kinsey, comb. rev., D. rusticum Kinsey, comb. rev. and D. serretae Pujade-Villar, Cuesta-Porta Melika, sp. nov.. All species are known only from their asexual generation except for D. ignotum and D. quercuslanigerum, for which alternating asexual and sexual generations are known. The sexual generation of D. ignotum and a new morphological variety of D. quercuslanigerum from Mexico are both described for the first time. We provide descriptions, redescriptions, diagnoses, keys to species, DNA sequence data and analyses, and information on biology, phenology, and distribution. Additionally, four Andricus species with woolly galls and striato-reticulated metasomas are transferred to Striatoandricus Pujade-Villar: S. furnessulus, comb. nov., S. furnessae, comb. nov., S. guatemalensis, comb. nov., and S. tenuicornis, comb. nov.

A catalogue, revision, and regional perspective of Eastern Palaearctic and Oriental oak gall wasps and their inquilines (Hymenoptera: Cynipidae: Cynipini, Synergini, Ceroptresini).

Recent years have seen rapid advances in the study of Fagaceae-associated gall wasps (Hymenoptera: Cynipidae) of the Eastern Palaearctic and the Oriental (EPO) regions, for both the gall inducing Cynipini (commonly termed oak gall wasps though many species gall non-oak Fagaceae) and the predominantly inquiline tribes Synergini and Ceroptresini. This process has propagated some taxonomic errors and involves many taxa whose taxonomic status is uncertain. To provide a stable foundation for further advance, here we review the taxonomic status of the 212 species (133 oak gall wasps and 79 oak cynipid inquilines) that have been described or recorded in these regions. Of this total, we treat 171 as valid species names (103 oak gall wasps and 68 oak cynipid inquilines) in 20 genera; 22 as synonym names, 13 as incertae sedis, three as nomen dubium, and three as species inquirenda. Callirhytis kunugicola Shinji, 1944 is proposed as syn. nov. of C. kunugicola Shinji, 1943, as Shinji described the same species twice. For all valid species names, we provide taxonomic references, synonyms, and geographical distributions. We summarize what is known of host plant associations and gall locations for gall inducers, and host associations for inquilines. We discuss geographic patterns in the known richness of currently valid species for both groups of organisms, and place this in the context of the biogeography of available Fagaceae host plants. We provide a brief historical review of the study of oak gall wasps and their inquilines in the EPO regions.

New herb gall wasps from Iran (Hymenoptera: Cynipidae).

Five new gall wasp species, Aulacidea koeiana Melika, Tavakoli Stone, sp. nov., A. lorestanica Melika, Tavakoli Stone, sp. nov., A. piroziae Melika, Stone Pujade-Villar, sp. nov., Phanacis strigosa Melika, Stone Tavakoli, sp. nov., P. tavakolii Melika, Stone Pujade-Villar, sp. nov. are described from Lorestan, Iran. Descriptions, diagnoses, plus information on biology and host associations are given for all new species, and we provide the first description of the male of Isocolus beheni Melika Karimpour, 2008.

Pairing of sexual and asexual generations of Nearctic oak gallwasps, with new synonyms and new species names (Hymenoptera: Cynipidae, Cynipini).

Most oak gallwasps (Hymenoptera; Cynipidae, Cynipini) have lifecycles involving obligate alternation between a sexual and an asexual generation. Many species are currently known from only one of these generations, with the alternate generation either unknown or separately described with a different name. Here we describe previously unknown generations for 12 Nearctic oak cynipids. We describe the sexual generation for ten species previously known only from an asexual generation: Acraspis quercushirta (Bassett, 1864), Acraspis villosa Gillette, 1888, Amphibolips spinosa Ashmead, 1887, Andricus balanaspis (Weld, 1922), comb. nov., Antron quercusnubila (Bassett, 1881), Bassettia pallida Ashmead, 1896, Neuroterus floccosus (Bassett, 1881), comb. rev., Philonix fulvicollis Fitch, 1859, Phylloteras poculum (Osten Sacken, 1862) and Sphaeroteras carolina (Ashmead, 1887), comb. rev.. We describe the asexual generation of Bassettia flavipes (Gillette, 1889), comb. nov. and Melikaiella tumifica (Osten Sacken, 1865), both previously known only from a sexual generation. Three described taxa (Neuroterus vernus Gillette, 1889, syn. nov., Neuroterus papillosus Beutenmueller, 1910, syn. nov. and Neuroterus perminimus Bassett, 1900, syn. nov.) are all identified as the sexual generation of Neuroterus niger Gillette, 1888. We also comment on the presence of previously unknown non-functional males reared from galls of the asexual generation of Neuroterus niger. We identify two further synonyms: Acraspis macrocarpae Bassett, 1890 is syn. nov. of A. quercushirta (Bassett, 1864), and Bassettia archboldi Melika Abrahamson, 2007 is syn. nov. of Bassettia pallida Ashmead, 1896. In addition, we formally synonymise multiple varieties described by Kinsey within his Acraspis quercushirta, A. villosa, Antron quercusnubila, Neuroterus niger and Philonix fulvicollis species complexes. We provide descriptions and diagnoses for these taxa, and summarise what is known of their biology, including host associations. All taxa and relationships between alternate generations are supported by morphological and molecular data.

Delimiting the cryptic diversity and host preferences of Sycophila parasitoid wasps associated with oak galls using phylogenomic data.

Cryptic species diversity is a major challenge regarding the species-rich community of parasitoids attacking oak gall wasps due to a high degree of sexual dimorphism, morphological plasticity, small size and poorly known biology. As such, we know very little about the number of species present, nor the evolutionary forces responsible for generating this diversity. One hypothesis is that trait diversity in the gall wasps, including the morphology of the galls they induce, has evolved in response to selection imposed by the parasitoid community, with reciprocal selection driving diversification of the parasitoids. Using a rare, continental-scale data set of Sycophila parasitoid wasps reared from 44 species of cynipid galls from 18 species of oak across the USA, we combined mitochondrial DNA barcodes, ultraconserved elements (UCEs), morphological and natural history data to delimit putative species. Using these results, we generate the first large-scale assessment of ecological specialization and host association in this species-rich group, with implications for evolutionary ecology and biocontrol. We find most Sycophila target specific subsets of available cynipid host galls with similar morphologies, and generally attack larger galls. Our results suggest that parasitoid wasps such as Sycophila have adaptations allowing them to exploit particular host trait combinations, while hosts with contrasting traits are resistant to attack. These findings support the tritrophic niche concept for the structuring of plant-herbivore-parasitoid communities.

A tale of two tissues: Probing gene expression in a complex insect-induced gall.

Plant galls are novel and sometimes dramatic plant organs whose development is initiated and controlled by parasitic microbes, nematodes, insects and mites. For arthropods, galls provide relative safety from enemies and abiotic stresses while providing nutrition. Galls are formed entirely by the plant, whose transcriptional pathways are modified and coopted to produce a structure specific to the galler species; they comprise a classic example of Dawkins' "extended phenotype". Arthropod-elicited galls are unique in that they are often anatomically complex (Figure 1a), with multiple differentiated tissue types (Figure 1b). A growing number of investigators have studied changes in hostplant gene expression to understand arthropod gall development. In this issue of Molecular Ecology, Martinson et al. (2021) report using RNA sequencing to explore tissue-specific gene expression associated with anatomical and functional gall complexity, demonstrating for the first time that gall tissues are as different transcriptionally as they are anatomically.

Discordant Pleistocene population size histories in a guild of hymenopteran parasitoids.

Signatures of past changes in population size have been detected in genome-wide variation in many species. However, the causes of such demographic changes and the extent to which they are shared across co-distributed species remain poorly understood. During Pleistocene glacial maxima, many temperate European species were confined to southern refugia. While vicariance and range expansion processes associated with glacial cycles have been widely documented, it is unclear whether refugial populations of co-distributed species have experienced shared histories of population size change. We analyse whole-genome sequence data to reconstruct and compare demographic histories during the Quaternary for Iberian refuge populations in a single ecological guild (seven species of chalcid parasitoid wasps associated with oak cynipid galls). For four of these species, we find support for large changes in effective population size (Ne ) through the Pleistocene that coincide with major climate events. However, there is little evidence that the timing, direction and magnitude of demographic change are shared across species, suggesting that demographic histories in this guild are largely idiosyncratic, even at the scale of a single glacial refugium.

Three new Nearctic genera of oak cynipid gall wasps (Hymenoptera: Cynipidae: Cynipini): Burnettweldia Pujade-Villar, Melika amp; Nicholls, Nichollsiella Melika, Pujade-Villar amp; Stone, Disholandricus Melika, Pujade-Villar amp; Nicholls; and re-establishment of the genus Paracraspis Weld.

We describe three new genera of cynipid oak gall wasps from the Nearctic: Burnettweldia Pujade-Villar, Melika Nicholls, gen. nov., Nichollsiella Melika, Pujade-Villar Stone, gen. nov., and Disholandricus Melika, Pujade-Villar Nicholls, gen. nov. (Hymenoptera: Cynipidae: Cynipini). Burnettweldia includes five species, B. californicordazi Cuesta-Porta, Melika Pujade-Villar, sp. nov., B. conalis (Weld), comb. nov., B. corallina (Bassett), comb. nov., B. plumbella (Kinsey), comb. nov., B. washingtonensis (Gillette), comb. nov.. Nichollsiella includes three species, N. arizonica (Cockerell), comb. nov., N. sulcata (Ashmead), comb. nov., and N. puigi Melika, Cuesta-Porta Pujade-Villar, sp. nov.. Disholandricus includes four species, D. chrysolepidis (Ashmead), comb. nov., D. lasius (Ashmead), comb. nov., D. reniformis (McCracken Egbert), comb. nov., D. truckeensis (Ashmead), comb. nov. The genus Paracraspis Weld, comb. rev. is re-established with three species, P. guadaloupensis (Fullaway), P. insolens (Weld), and P. patelloides (Trotter). Descriptions, re-descriptions, diagnoses, keys to genera and species are given, including data on DNA sequences, biology, phenology and distribution.

Re-description and systematic re-appraisal of the genus Kokkocynips Pujade-Villar amp; Melika, (Hymenoptera: Cynipidae: Cynipini), including new combinations of Nearctic species and the description of a new species from Panama.

The monophyly and taxonomic validity of some currently accepted genera of gall wasps in the Cynipini (Hymenoptera: Cynipidae) are being challenged by recent systematic studies. Here we used morphological and molecular data to re-describe and revise the taxonomic limits of the monotypic genus Kokkocynips Pujade-Villar Melika, previously recorded only from Mexico.                We describe a new species from Panama, Kokkocynips panamensis Medianero Nieves-Aldrey, reared from galls on Quercus salicifolia Neé, and add new records from Mexico for the type species of the genus K. doctorrosae Pujade-Villar. Six Nearctic species, Dryocosmus rileyi (Ashmead, 1896), D. imbricariae (Ashmead, 1896), D. coxii (Basset, 1881), D. deciduus (Beutenmueller, 1913), Callirhytis difficilis (Ashmead, 1887) and C. attractans (Kinsey, 1922) are transferred to Kokkocynips. Species of Kokkocynips are associated only with red oaks (Quercus section Lobatae (Fagaceae)) and are distributed in the Nearctic and Neotropical regions, from Canada through Mexico and Panama. Taxonomic limits of Kokkocynips are discussed in light of the molecular phylogenetic relationships of the studied species. Diagnostic characters, gall description, distribution, and biological data of Kokkocynips species are given, including a key for the identification of the asexual generations of seven species.

The gall wasp fauna of Iran (Hymenoptera: Cynipidae: Cynipinae): species checklist and biogeographical assessment.

We provide a checklist of the gall wasps (Hymenoptera: Cynipidae: Cynipinae) of Iran, and place these records in a biogeographical perspective on three spatial scales, comprising (i) the Western Palaearctic, (ii) Western Asia (Turkey, the southern Caucasus and the Middle East) and (iii) regions within Iran. We present distribution and biological data for 121 species in 24 genera, representing nine of the 12 known cynipid gall wasp tribes. The most species-rich tribe in Iran is the oak gall wasp tribe Cynipini, with 74 species and 11 genera. Cynipid species richness is highest in the central and northern Zagros, with a distinctively different fauna in the forests along the southern shores of the Caspian Sea. Of the species found in Iran, 63 have distributions that extend westwards far into Europe, and can be considered Western Palaearctic species. Twenty four species comprise a distinct eastern component within the Western Palaearctic, with distributions that include Iran and some or all of Turkey, the Middle East and the Caucasus. Twenty one species are apparently endemic to Iran, with distinct Zagros and Caspian components. We highlight biological and phylogeographic processes that may underlie these patterns.

New species of Nearctic oak gall wasps (Hymenoptera: Cynipidae, Cynipini).

Twenty nine new species of cynipid oak gall wasps from the Nearctic region (America north of Mexico) are described: Andricus archboldi Melika Abrahamson, sp. nov., A. catalinensis Melika, Nicholls Stone, sp. nov., A. chapmanii Melika Abrahamson, sp. nov., A. chiricahuensis Melika, Nicholls Stone, sp. nov., A. coconinoensis Melika, Nicholls Stone, sp. nov., A. columbiensis Melika, Nicholls Stone, sp. nov., A. cooki Melika, Nicholls Stone, sp. nov., A. fitzpatricki Melika Abrahamson, sp. nov., A. highlandensis Melika, Nicholls Stone, sp. nov., A. mellificus Nicholls, Stone Melika, sp. nov., A. menkei Melika Abrahamson, sp. nov., A. mogollonensis Melika, Nicholls Stone, sp. nov., A. nichollsi Melika Stone, sp. nov., A. schickae Nicholls, Melika Stone, sp. nov., A. torreyaensis Melika Abrahamson, sp. nov., A. williami Melika, Nicholls Stone, sp. nov., Antron lovellae Melika, Nicholls Stone, sp. nov., A.tomkursari Melika, Nicholls Stone, sp. nov., Dryocosmus archboldi Melika Abrahamson, sp. nov., Loxaulus virginianae Melika Buss, sp. nov., Neuroterus alexandrae Nicholls Melika, sp. nov., N. aliceae Melika, Nicholls Stone, sp. nov., N. bussae Melika Nicholls, sp. nov., N. oblongifoliae Nicholls, Stone Melika, sp. nov., N. quaili Melika, Nicholls Stone, sp. nov., N. rosieae Melika, Nicholls Stone, sp. nov., N. stonei Melika Nicholls, sp. nov., Zapatella abrahamsoni Melika, sp. nov., Z. brooksvillei Melika Abrahamson, sp. nov.. Alternate asexual and sexual generations are described for four species, Andricus archboldi Melika Abrahamson, sp. nov., A. fitzpatricki Melika Abrahamson, sp. nov., A. schickae Nicholls, Melika Stone, sp. nov., Neuroterus aliceae Melika, Nicholls Stone, sp. nov.. Descriptions, diagnoses, plus information on biology and host associations are given for all new species. All taxa are supported by morphological data; matching of generations is established using DNA sequence data. We also demonstrate that Neuroterus niger var. alimas Kinsey should be considered as a nomen dubium.

A new genus of Neotropical oak gall wasp, Prokius Nieves-Aldrey, Medianero amp; Nicholls, gen. nov. (Hymenoptera: Cynipidae: Cynipini), with description of two new species from Panama.

A new genus, Prokius Nieves Aldrey, Medianero Nicholls, gen. nov., and two new species of oak gall wasps (Hymenoptera: Cynipidae: Cynipini), Prokius cambrai Medianero Nieves-Aldrey sp. nov. and Prokius lisethiae Medianero Nieves-Aldrey sp. nov., are described from adults reared from galls on Quercus bumelioides Liebm (Fagaceae, sect. Quercus, white oaks) collected in Panama. The new genus is phylogenetically and morphologically close to Dros Kinsey and forms part of a large clade that includes species from several other genera that appear to require revision, including Andricus Hartig and Phylloteras Ashmead. Molecular and morphological data, diagnostic characters, gall descriptions, distribution and biological data of the new genus and the new species are given. This new genus represents the fourth recently described genus of Cynipidae endemic to the Neotropical region.

From Inquilines to Gall Inducers: Genomic Signature of a Life-Style Transition in Synergus Gall Wasps.

Gall wasps (Hymenoptera: Cynipidae) induce complex galls on oaks, roses, and other plants, but the mechanism of gall induction is still unknown. Here, we take a comparative genomic approach to revealing the genetic basis of gall induction. We focus on Synergus itoensis, a species that induces galls inside oak acorns. Previous studies suggested that this species evolved the ability to initiate gall formation recently, as it is deeply nested within the genus Synergus, whose members are mostly inquilines that develop inside the galls of other species. We compared the genome of S. itoensis with that of three related Synergus inquilines to identify genomic changes associated with the origin of gall induction. We used a novel Bayesian selection analysis, which accounts for branch-specific and gene-specific selection effects, to search for signatures of selection in 7,600 single-copy orthologous genes shared by the four Synergus species. We found that the terminal branch leading to S. itoensis had more genes with a significantly elevated dN/dS ratio (positive signature genes) than the other terminal branches in the tree; the S. itoensis branch also had more genes with a significantly decreased dN/dS ratio. Gene set enrichment analysis showed that the positive signature gene set of S. itoensis, unlike those of the inquiline species, is enriched in several biological process Gene Ontology terms, the most prominent of which is "Ovarian Follicle Cell Development." Our results indicate that the origin of gall induction is associated with distinct genomic changes, and provide a good starting point for further characterization of the genes involved.

Low-coverage genomic data resolve the population divergence and gene flow history of an Australian rain forest fig wasp.

Population divergence and gene flow are key processes in evolution and ecology. Model-based analysis of genome-wide data sets allows discrimination between alternative scenarios for these processes even in nonmodel taxa. We used two complementary approaches (one based on the blockwise site frequency spectrum [bSFS], the second on the pairwise sequentially Markovian coalescent [PSMC]) to infer the divergence history of a fig wasp, Pleistodontes nigriventris. Pleistodontes nigriventris and its fig tree mutualist Ficus watkinsiana are restricted to rain forest patches along the eastern coast of Australia and are separated into The Northern population is to the north of the Southern populations by two dry forest corridors (the Burdekin and St. Lawrence Gaps). We generated whole genome sequence data for two haploid males per population and used the bSFS approach to infer the timing of divergence between northern and southern populations of P. nigriventris, and to discriminate between alternative isolation with migration (IM) and instantaneous admixture (ADM) models of postdivergence gene flow. Pleistodontes nigriventris has low genetic diversity (π = 0.0008), to our knowledge one of the lowest estimates reported for a sexually reproducing arthropod. We find strongest support for an ADM model in which the two populations diverged ca. 196 kya in the late Pleistocene, with almost 25% of northern lineages introduced from the south during an admixture event ca. 57 kya. This divergence history is highly concordant with individual population demographies inferred from each pair of haploid males using PSMC. Our analysis illustrates the inferences possible with genome-level data for small population samples of tiny, nonmodel organisms and adds to a growing body of knowledge on the population structure of Australian rain forest taxa.