Search for: All records

Spiders are unique in having a dual respiratory system with book lungs and tracheae, and most araneomorph spiders breathe simultaneously via book lungs and tracheae, or tracheae alone. The respiratory organs of spiders are diverse but relatively conserved within families. The small araneoid spiders of the symphytognathoid clade exhibit a remarkably high diversity of respiratory organs and arrangements, unparalleled by any other group of ecribellate orb weavers. In the present study, we explore and review the diversity of symphytognathoid respiratory organs. Using a phylogenetic comparative approach, we reconstruct the evolution of the respiratory system of symphytognathoids based on the most comprehensive phylogenetic frameworks to date. There are no less than 22 different respiratory system configurations in symphytognathoids. The phylogenetic reconstructions suggest that the anterior tracheal system evolved from fully developed book lungs and, conversely, reduced book lungs have originated independently at least twice from its homologous tracheal conformation. Our hypothesis suggests that structurally similar book lungs might have originated through different processes of tracheal transformation in different families. In symphytognathoids, the posterior tracheal system has either evolved into a highly branched and complex system or it is completely lost. No evident morphological or behavioral features satisfactorily explains the exceptional variation of the symphytognathoid respiratory organs.

 

Two new species of the genus Putaoa Hormiga and Tu, 2008 from southern China are described, Putaoa annulata n. sp. (♂♀) and Putaoa titanoverpa n. sp. (♂♀), for a total number of five described species in this genus. Detailed descriptions and illustrations of the two new species are provided. A map of collecting localities is also provided for all five Putaoa species. 

Abstract A prominent question in animal research is how the evolution of morphology and ecology interacts in the generation of phenotypic diversity. Spiders are some of the most abundant arthropod predators in terrestrial ecosystems and exhibit a diversity of foraging styles. It remains unclear how spider body size and proportions relate to foraging style, and if the use of webs as prey capture devices correlates with changes in body characteristics. Here, we present the most extensive data set to date of morphometric and ecological traits in spiders. We used this data set to estimate the change in spider body sizes and shapes over deep time and to test if and how spider phenotypes are correlated with their behavioral ecology. We found that phylogenetic variation of most traits best fitted an Ornstein–Uhlenbeck model, which is a model of stabilizing selection. A prominent exception was body length, whose evolutionary dynamics were best explained with a Brownian Motion (free trait diffusion) model. This was most expressed in the araneoid clade (ecribellate orb-weaving spiders and allies) that showed bimodal trends toward either miniaturization or gigantism. Only few traits differed significantly between ecological guilds, most prominently leg length and thickness, and although a multivariate framework found general differences in traits among ecological guilds, it was not possible to unequivocally associate a set of morphometric traits with the relative ecological mode. Long, thin legs have often evolved with aerial webs and a hanging (suspended) locomotion style, but this trend is not general. Eye size and fang length did not differ between ecological guilds, rejecting the hypothesis that webs reduce the need for visual cue recognition and prey immobilization. For the inference of the ecology of species with unknown behaviors, we propose not to use morphometric traits, but rather consult (micro-)morphological characters, such as the presence of certain podal structures. These results suggest that, in contrast to insects, the evolution of body proportions in spiders is unusually stabilized and ecological adaptations are dominantly realized by behavioral traits and extended phenotypes in this group of predators. This work demonstrates the power of combining recent advances in phylogenomics with trait-based approaches to better understand global functional diversity patterns through space and time. [Animal architecture; Arachnida; Araneae; extended phenotype; functional traits; macroevolution; stabilizing selection.] 

Deciphering the evolutionary relationships of Chelicerata (arachnids, horseshoe crabs, and allied taxa) has proven notoriously difficult, due to their ancient rapid radiation and the incidence of elevated evolutionary rates in several lineages. Although conflicting hypotheses prevail in morphological and molecular data sets alike, the monophyly of Arachnida is nearly universally accepted, despite historical lack of support in molecular data sets. Some phylotranscriptomic analyses have recovered arachnid monophyly, but these did not sample all living orders, whereas analyses including all orders have failed to recover Arachnida. To understand this conflict, we assembled a data set of 506 high-quality genomes and transcriptomes, sampling all living orders of Chelicerata with high occupancy and rigorous approaches to orthology inference. Our analyses consistently recovered the nested placement of horseshoe crabs within a paraphyletic Arachnida. This result was insensitive to variation in evolutionary rates of genes, complexity of the substitution models, and alternative algorithmic approaches to species tree inference. Investigation of sources of systematic bias showed that genes and sites that recover arachnid monophyly are enriched in noise and exhibit low information content. To test the impact of morphological data, we generated a 514-taxon morphological data matrix of extant and fossil Chelicerata, analyzed in tandem with the molecular matrix. Combined analyses recovered the clade Merostomata (the marine orders Xiphosura, Eurypterida, and Chasmataspidida), but merostomates appeared nested within Arachnida. Our results suggest that morphological convergence resulting from adaptations to life in terrestrial habitats has driven the historical perception of arachnid monophyly, paralleling the history of numerous other invertebrate terrestrial groups. 

The Opiliones family Neopilionidae is restricted to the terranes of the former temperate Gondwana: South America, Africa, Australia, New Caledonia and New Zealand. Despite decades of morphological study of this unique fauna, it has been difficult reconciling the classic species of the group (some described over a century ago) with recent cladistic morphological work and previous molecular work. Here we attempted to investigate the pattern and timing of diversification of Neopilionidae by sampling across the distribution range of the family and sequencing three markers commonly used in Sanger-based approaches (18S rRNA, 28S rRNA and cytochrome-c oxidase subunit I). We recovered a well-supported and stable clade including Ballarra (an Australian ballarrine) and the Enantiobuninae from South America, Australia, New Caledonia and New Zealand, but excluding Vibone (a ballarrine from South Africa). We further found a division between West and East Gondwana, with the South American Thrasychirus/Thrasychiroides always being sister group to an Australian–Zealandian (i.e. Australia + New Zealand + New Caledonia) clade. Resolution of the Australian–Zealandian taxa was analysis-dependent, but some analyses found Martensopsalis, from New Caledonia, as the sister group to an Australian–New Zealand clade. Likewise, the species from New Zealand formed a clade in some analyses, but Mangatangi often came out as a separate lineage from the remaining species. However, the Australian taxa never constituted a monophyletic group, with Ballarra always segregating from the remaining Australian species, which in turn constituted 1–3 clades, depending on the analysis. Our results identify several generic inconsistencies, including the possibility of Thrasychiroides nested within Thrasychirus, Forsteropsalis being paraphyletic with respect to Pantopsalis, and multiple lineages of Megalopsalis in Australia. In addition, the New Zealand Megalopsalis need generic reassignment: Megalopsalis triascuta will require its own genus and M. turneri is here transferred to Forsteropsalis, as Forsteropsalis turneri (Marples, 1944), comb. nov. 

We address the phylogenetic relationships of pimoid spiders (Pimoidae) using a standard target-gene approach with an extensive taxonomic sample, which includes representatives of the four currently recognized pimoid genera, 26 linyphiid genera, a sample of Physoglenidae, Cyatholipidae and one Tetragnathidae species. We test the monophyly of Pimoidae and Linyphiidae and explore the biogeographic history of the group. Nanoa Hormiga, Buckle and Scharff, 2005 and Pimoa Chamberlin & Ivie, 1943 form a clade which is the sister group of a lineage that includes all Linyphiidae, Weintrauboa Hormiga, 2003 and Putaoa Hormiga and Tu, 2008. Weintrauboa, Putaoa, Pecado and Stemonyphantes form a clade (Stemonyphantinae) sister to all remaining linyphiids. We use the resulting optimal molecular phylogenetic tree to assess hypotheses on the male palp sclerite homologies of pimoids and linyphiids. Pimoidae is redelimited to only include Pimoa and Nanoa. We formalize the transfer from Pimoidae of the genera Weintrauboa and Putaoa to Linyphiidae, re-circumscribe the linyphiid subfamily Stemonyphantinae, and offer revised morphological diagnoses for Pimoidae and Linyphiidae.