A comprehensive molecular phylogeny of the terrestrial Parasitengona (Acariformes, Prostigmata) provides insights into the evolution of their metamorphosis, invasion into aquatic habitats and classification.

Parasitengona (velvet mites, chiggers and water mites) is a highly diverse and globally distributed mite lineage encompassing over 11,000 described species, inhabiting terrestrial, freshwater and marine habitats. Certain species, such as chiggers (Trombiculidae), have a great medical and veterinary importance as they feed on their vertebrate hosts and vector pathogens. Despite extensive previous research, the classification of Parasitengona is still contentious, particularly regarding the boundaries between superfamilies and families, exacerbated by the absence of a comprehensive phylogeny. The ontogeny of most Parasitengona is distinct by the presence of striking metamorphosis, with parasitic larvae being heteromorphic compared to the predatory free-living deutonymphs and adults. The enigmatic superfamily Allotanaupodoidea is an exception, with larvae and active post-larval stages being morphologically similar, suggesting that the absence of metamorphosis may be either an ancestral state or a secondary reversal. Furthermore, there is disagreement in the literature on whether Parasitengona had freshwater or terrestrial origin. Here, we inferred phylogenetic relationships of Parasitengona (89 species, 36 families) and 307 outgroups using five genes (7,838 nt aligned). This phylogeny suggests a terrestrial origin of Parasitengona and a secondary loss of metamorphosis in Allotanaoupodoidea. We recovered the superfamily Trombidioidea (Trombidioidea sensu lato) as a large, well-supported, higher-level clade including 10 sampled families. We propose a new classification for the terrestrial Parasitengona with three new major divisions (epifamilies) of the superfamily Trombidioidea: Trombelloidae (families Audyanidae, Trombellidae, Neotrombidiidae, Johnstonianidae, Chyzeriidae); Trombidioidae (Microtrombidiidae, Neothrombiidae, Achaemenothrombiidae, Trombidiidae, Podothrombiidae); and Trombiculoidae (=Trombiculidae sensu lato). Adding them to previously recognized superfamilies Allotanaupodoidea, Amphotrombioidea, Calyptostomatoidea, Erythraeoidea, Tanaupodoidae and Yurebilloidae.

One-way ticket to the blue: A large-scale, dated phylogeny revealed asymmetric land-to-water transitions in acariform mites (Acari: Acariformes).

Acariform mites are an ancient and megadiverse lineage that may have experienced a complex pattern of invasions into terrestrial and aquatic habitats. These among-realm transitions may relate to periods of turmoil in Earth's history or be simply results of uneven biodiversity patterns across habitats. Here, we inferred a dated, representative acariform phylogeny (five genes, 9,200 bp aligned, 367 terminals belonging to 150 ingroup plus 15 outgroup families, 23 fossil calibration points) which was used to infer transitions between marine/freshwater/terrestrial habitats. We detected four unambiguous transitions from terrestrial to freshwater habitats (Hydrozetes, Naiadacarus, Fusohericia, Afronothrus, Homocaligus); one from freshwater to marine (Pontarachnidae), and four from marine to brackish or freshwater transitions (all among Halacaridae: Acarothrix; Halacarellus petiti; Copidognathus sp.; clade Limnohalacarus + Soldanellonyx + Porohalacarus + Porolohmannella). One transition to the sea was inferred ambiguously with respect to the ancestor being either terrestrial or freshwater (Hyadesiidae), and another must be most carefully examined by adding potential related taxa (Selenoribatidae + Fortuyniidae). Finally, we inferred a single, remarkable transition from aquatic to terrestrial habitats involving early evolution of the large and ecologically diverse lineage: the ancestor of the Halacaridae + Parasitengona clade was probably freshwater given our dataset, thus making terrestrial Parasitengona secondarily terrestrial. Overall, our results suggested a strong asymmetry in environmental transitions: the majority occurred from terrestrial to aquatic habitats. This asymmetry is probably linked to mites' biological properties and uneven biodiversity patterns across habitats rather than Earth's geological history. Since the land holds more acariform diversity than water habitats, a shift from the former is more likely than from the latter. We inferred the following relationships: alicid endeostigmatid + eriophyoid (Alycidae, (Nanorchestidae, (Nematalycidae, Eriophyoidea))) being sister group to the remaining Acariformes: (proteonematalycid Endeostigmata, alicorhagiid Endeostigmata, Trombidiformes, Oribatida (including Astigmata)). Trombidiform relationships had several novel rearrangements: (i) traditional Eupodina lacked support for the inclusion of Bdelloidea; (ii) Teneriffidae, traditionally placed among Anystina, was consistently recovered in a clade including Heterostigmata in Eleutherengona; (iii) several lineages, such as Adamystidae, Paratydeidae, Caeculidae and Erythracaridae, were recovered in a large clade along other Anystina and Eleutherengona, suggesting single origins of several fundamental character states, such as the reduction of the cheliceral fixed digit and development of the palpal thumb-claw complex.

Molecular phylogeny of marine mites (Acariformes: Halacaridae), the oldest radiation of extant secondarily marine animals.

The family Halacaridae comprises more than one thousand mostly marine or rarely freshwater species. Many are predacious, but among marine mites, some genera evolved the ability to feed on macroalgae. We inferred a time-calibrated phylogeny based on 18S rDNA, 28S rDNA, and Cytochrome oxidase I (5,143 nt aligned) and all non-monotypic halacarid subfamilies plus a representative outgroup set (72 taxa). The family Halacaridae was rendered as the sister-group of Parasitengona, diverging 321.5, 264.0-381.3 Ma and radiating 271.3, 221.7-324.2 Ma (median, HPD). Thus, marine mites represent the oldest known extant animal lineage that secondarily invaded the sea, with the marine turtles being the second oldest such lineage (crown group 212.3, 194.9-231.4 Ma). Two freshwater mite lineages, represented by Limnohalacarus (219.2, 165.9-274.6) and Porohalacarus (175.3, 118.5-233.1), were inferred mutually non-monophyletic, suggesting two independent invasions to freshwater. The conventional subfamily Rhombognathinae (macroalgae feeders) was not recovered as monophyletic, with Metarhombognathus-Rhombognathides, restricted to the Northern Hemisphere, originating 177.5, 134.8-223.3 Ma and diversifying 88.3, 32.7-152.3 Ma. This is congruent to a previous hypothesis of their northern origin prior to the opening of the Norwegian Sea (58 Ma). Our phylogeny indicates the need for reclassification of the traditional subfamilies and suggests that previous molecular results (e.g., Rhombognathus deeply nested in Copidognathinae) is an analytical artifact due to a chimeric sequence.

Two new species of Halacarus (Acari, Prostigmata) from Brazil.

The genus Halacarus is recorded from the Brazilian littoral for the first time. Two new species are described. Halacarus omului sp. nov., obtained from algae on the intertidal or immediate subtidal, is a member of the actenos species group and can be distinguished from most congeners by having fifth and sixth pairs of dorsal setae immediately adjacent to fourth and fifth pairs of gland pores, on same minute sclerite. Halacarus todaroi sp. nov. was obtained from sublittoral coarse sand and shell debris and can be distinguished from most congeners by lacking sexually dimorphic dorsal plates, the presence of the posterior dorsal plate, although it does not bear the fourth pair of gland pores, and the presence of ocular plates as a small platelet bearing the pore canaliculi. Further diagnoses are provided along with the species descriptions.

Horizontal transmission maintains host specificity and codiversification of symbionts in a brood parasitic host.

In host-symbiont systems, interspecific transmissions create opportunities for host switches, potentially leading to cophylogenetic incongruence. In contrast, conspecific transmissions often result in high host specificity and congruent cophylogenies. In most bird-feather mite systems, conspecific transmission is considered dominant, while interspecific transmission is supposedly rare. However, while mites typically maintain high host specificity, incongruent cophylogenies are common. To explain this conundrum, we quantify the magnitude of conspecific vs. interspecific transmission in the brood parasitic shiny cowbird (Molothrus bonariensis). M. bonariensis lacks parental care, allowing the assessment of the role of horizontal transmission alone in maintaining host specificity. We found that despite frequent interspecific interactions via foster parental care, mite species dispersing via conspecific horizontal contacts are three times more likely to colonize M. bonariensis than mites transmitted vertically via foster parents. The results highlight the previously underappreciated rate of transmission via horizontal contacts in maintaining host specificity on a microevolutionary scale. On a macroevolutionary scale, however, host switches were estimated to have occurred as frequently as codivergences. This suggests that macroevolutionary patterns resulting from rare events cannot be easily generalized from short-term evolutionary trends.

Ecological changes have driven biotic exchanges across the Indian Ocean.

The Indian Ocean has a complex geological history that has drawn the attention of naturalists for almost a century now. Due to its tectonic history, many geological elements and processes have been evoked to explain the exchange of species between landmasses. Here, we revisited previous studies on twenty-three taxa to investigate trends across time since the Gondwana breakup. We investigated these datasets by applying a time-calibrated Bayesian framework to them and reconstructing their ancestral ranges. We conclude that ecological transformations have presented opportunities for the establishment of migrants. The role of donating and receiving migrants has shifted several times according to these transformations. Time-specific trends show weak evidence for the stepping-stones commonly suggested as physical routes between landmasses. However, before its collision with Asia, India may have served as an intermediary for such exchanges.

Phylogenetic position of the acariform mites: sensitivity to homology assessment under total evidence.

BACKGROUND: Mites (Acari) have traditionally been treated as monophyletic, albeit composed of two major lineages: Acariformes and Parasitiformes. Yet recent studies based on morphology, molecular data, or combinations thereof, have increasingly drawn their monophyly into question. Furthermore, the usually basal (molecular) position of one or both mite lineages among the chelicerates is in conflict to their morphology, and to the widely accepted view that mites are close relatives of Ricinulei. RESULTS: The phylogenetic position of the acariform mites is examined through employing SSU, partial LSU sequences, and morphology from 91 chelicerate extant terminals (forty Acariformes). In a static homology framework, molecular sequences were aligned using their secondary structure as guide, whereby regions of ambiguous alignment were discarded, and pre-aligned sequences analyzed under parsimony and different mixed models in a Bayesian inference. Parsimony and Bayesian analyses led to trees largely congruent concerning infra-ordinal, well-supported branches, but with low support for inter-ordinal relationships. An exception is Solifugae + Acariformes (P. P = 100%, J. = 0.91). In a dynamic homology framework, two analyses were run: a standard POY analysis and an analysis constrained by secondary structure. Both analyses led to largely congruent trees; supporting a (Palpigradi (Solifugae Acariformes)) clade and Ricinulei as sister group of Tetrapulmonata with the topology (Ricinulei (Amblypygi (Uropygi Araneae))). Combined analysis with two different morphological data matrices were run in order to evaluate the impact of constraining the analysis on the recovered topology when employing secondary structure as a guide for homology establishment. The constrained combined analysis yielded two topologies similar to the exclusively molecular analysis for both morphological matrices, except for the recovery of Pedipalpi instead of the (Uropygi Araneae) clade. The standard (direct optimization) POY analysis, however, led to the recovery of trees differing in the absence of the otherwise well-supported group Solifugae + Acariformes. CONCLUSIONS: Previous studies combining ribosomal sequences and morphology often recovered topologies similar to purely morphological analyses of Chelicerata. The apparent stability of certain clades not recovered here, like Haplocnemata and Acari, is regarded as a byproduct of the way the molecular homology was previously established using the instrumentalist approach implemented in POY. Constraining the analysis by a priori homology assessment is defended here as a way of maintaining the severity of the test when adding new data to the analysis. Although the strength of the method advocated here is keeping phylogenetic information from regions usually discarded in an exclusively static homology framework; it still has the inconvenience of being uninformative on the effect of alignment ambiguity on resampling methods of clade support estimation. Finally, putative morphological apomorphies of Solifugae + Acariformes are the reduction of the proximal cheliceral podomere, medial abutting of the leg coxae, loss of sperm nuclear membrane, and presence of differentiated germinative and secretory regions in the testis delivering their products into a common lumen.

Evaluating the boundaries of marine biogeographic regions of the Southwestern Atlantic using halacarid mites (Halacaridae), meiobenthic organisms with a low dispersal potential.

AIM: We evaluated traditional biogeographic boundaries of coastal marine regions in Southwestern Atlantic using DNA sequence data from common, rocky-shore inhabiting, marine mites of the genera Agauopsis and Rhombognathus, family Halacaridae. METHODS: We investigated geographic population genetic structure using CO1 gene sequences, estimated divergence times using a multigene dataset and absolute time-calibrated molecular clock analyses, and performed environmental niche modeling (ENM) of common marine mite species. RESULTS: Agauopsis legionium has a shallow history (2.01 Ma) with four geographically differentiated groups. Two of them corresponded to the traditional Amazonian and Northeastern ecoregions, but the boundary between the two other groups was inferred at the Abrolhos Plateau, not Cabo Frio. Rhombognathus levigatoides s. lat. was represented by two cryptic species that diverged 7.22 (multilocus data) or 10.01 Ma (CO1-only analyses), with their boundary, again at the Abrolhos Plateau. ENM showed that A. legionium has suitable habitats scattered along the coast, while the two R. levigatoides cryptic species differ considerably in their niches, especially in parameters related to upwelling. This indicates that genetic isolation associated with the Abrolhos Plateau occurred in both lineages, but for the R. levigatoides species complex, ecological niche specialization was also an important factor. MAIN CONCLUSIONS: Our study suggests that the major biogeographic boundary in the Southwestern Atlantic lies not at Cabo Frio but at the Abrolhos Plateau. There two biogeographically relevant factors meet (a) changes in current directions (which limit dispersal) and (b) abrupt changes in environmental parameters associated with the South Atlantic Central Waters (SACW) upwelling (offering distinct ecological niches). We suggest that our result represents a general biogeographic pattern because a barrier at the Abrolhos Plateau was found previously for the fish genus Macrodon (phylogeographic data), prosobranch mollusks, ascidians, and reef fishes (community-level data).

The complex evolutionary history and phylogeography of Caridina typus (Crustacea: Decapoda): long-distance dispersal and cryptic allopatric species.

The evolutionary history of the old, diverse freshwater shrimp genus Caridina is still poorly understood, despite its vast distribution - from Africa to Polynesia. Here, we used nuclear and mitochondrial DNA to infer the phylogeographic and evolutionary history of C. typus, which is one of only four species distributed across the entire range of the genus. Despite this species' potential for high levels of gene flow, questions have been raised regarding its phylogeographic structure and taxonomic status. We identified three distinct lineages that likely diverged in the Miocene. Molecular dating and ancestral range reconstructions are congruent with C. typus' early dispersal to Africa, possibly mediated by the Miocene Indian Ocean Equatorial Jet, followed by back dispersal to Australasia after the Jet's closure. Furthermore, several different species delimitation methods indicate each lineage represents a distinct (cryptic) species, contradicting current morphospecies delimitation of a single C. typus taxon. The evolutionary history of C. typus lineages is complex, in which ancient oceanic current systems and (currently unrecognised) speciation events preceded secondary sympatry of these cryptic species.

Two new species of Rhombognathus (Halacaridae, Trombidiformes) from a Mangrove in the northern littoral zone of São Paulo State (Brazil).

Two species belonging to the algivorous genus Rhombognathus are described from algae associated to mangrove trees. Rhombognathus aribus sp. nov. is similar to R. major Bartsch, 2005, but may be set apart by the lacking of the third pair of dorsal setae on Ocular plates, adjunct setae on Posterior Epimeral plates, absence of ventral setae on basifemura III-IV and presence of ventromedial bipectinate setae on tibiae II of all individuals and on tibiae III of most of them. Rhombognathus picinguabensis sp. nov. shares the leg chaetotaxy and shape of the lateral claws with R. parvulus Viets, 1939. The latter species, however, can be easily separated from the former due the fusion of all dorsal plates in a single dorsal shield.