Why is Madagascar special? The extraordinarily slow evolution of pelican spiders (Araneae, Archaeidae)

Burma Terrane Amber Fauna Shows Connections to Gondwana and Transported Gondwanan Lineages to the Northern Hemisphere (Araneae: Palpimanoidea)

Burmese amber is a significant source of fossils that documents the mid-Cretaceous biota. This deposit was formed around 99 Ma on the Burma Terrane, which broke away from Gondwana and later collided with Asia, although the timing is disputed. Palpimanoidea is a dispersal-limited group that was a dominant element of the Mesozoic spider fauna, and has an extensive fossil record, particularly from Burmese amber. Using morphological and molecular data, evolutionary relationships of living and fossil Palpimanoidea are examined. Divergence dating with fossils as terminal tips shows timing of diversification is contemporaneous with continental breakup.Ancestral range estimations show widespread ancestral ranges that divide into lineages that inherit different Pangean fragments, consistent with vicariance. Our results suggest that the Burmese amber fauna has ties to Gondwana due to a historical connection in the Early Cretaceous, and that the Burma Terrane facilitated biotic exchange by transporting lineages from Gondwana into the Holarctic in the Cretaceous.

Micro-Computed Tomography Reveals a Remarkable Twin Intromittent Organ in Spiders – A Novelty for Arachnids With Direct Sperm Transfer

The modification of male pedipalps into secondary sexual intromittent organs is one of the hallmark characteristics of spiders, yet understanding the development and evolution of male genitalia across the order remains a challenging prospect. The embolus – the sclerite bearing the efferent spermatic duct or spermophor, and used to deliver sperm directly to the female genitalia during copulation – has always been considered the single unambiguously homologous palpal sclerite shared by all spider species, fundamental to the bauplan of the order and to the evolution and functional morphology of spider reproductive systems. Indeed, after two centuries of comparative research on spider reproduction, the presence of a single spermophor and embolus on each of a male spider’s two pedipalps remains a central tenet of evolutionary arachnology. Our findings challenge this premise, and reveal a remarkable twin intromittent organ sperm transfer system in a lineage of Australian palpimanoid spiders, characterized by a bifurcate spermophor and the presence of two efferent ducts leading to a pair of embolic sclerites on each pedipalp. This is the first time such a remarkable conformation has been observed in any group of arachnids with direct sperm transfer, complicating our understanding of palpal sclerite homologies, and challenging ideas about the evolution of spider genitalia.

Another Laurasian connection in the Early Eocene of India: Myrmecarchaea spiders (Araneae, Archaeidae)

The first fossil Archaeidae in Cambay amber from India, of Eocene age, is documented. The inclusion is a spider exuvium and is placed as Myrmecarchaea based on the presence of elongated legs, a slightly elongated pedicel with lateral spurs, and a diastema between coxae III and IV that is similar to M.antecessor from Oise amber. The previous occurrences of the genus are from Baltic and Oise amber, both of Eocene age. Because most spiders, including Archaeidae, only molt as juveniles, the exuvium does not have adult features nor have distinct species-specific features, and a new taxon is not erected. This new record further extends the distribution of the family and genus to India 50-52 million years ago. Myrmecarchaea in Indian Cambay amber provides additional evidence that India in the Early Eocene had affinities with the Palearctic mainland rather than showing Gondwanan insularity.

New specimens from Mid-Cretaceous Myanmar amber illuminate the phylogenetic placement of Lagonomegopidae (Arachnida: Araneae)

New lagonomegopid spiders are described from Mid-Cretaceous Myanmar (Burmese) amber. Two new genera and species based on single specimens, Scopomegops fax gen. & sp. nov. and Hiatomegops spinalis gen. & sp. nov. are described. Two specimens belonging to Lineaburmops beigeli are further described. Additionally, after re-examining the holotype of Odontomegops titan, a detailed description of its basal ventral abdomen is added here. A phylogenetic analysis was performed to investigate the phylogenetic placement of Lagonomegopidae. A matrix of 79 morphological characters, scored for six lagonomegopid taxa and 26 non-lagonomegopid taxa, was analysed through parsimony and Bayesian phylogenetic inference. Our results recover extant Palpimanoidea as a monophyletic group and partly suggest that Lagonomegopidae is the sister-group to extant Palpimanoidea. The external sexual organs, retrolateral tibial apophysis on the male palp and tracheal spiracle in lagonomegopids are discussed.

The fossil record of spiders revisited: implications for calibrating trees and evidence for a major faunal turnover since the Mesozoic

Studies in evolutionary biology and biogeography increasingly rely on the estimation of dated phylogenetic trees using molecular clocks. In turn, the calibration of such clocks is critically dependent on external evidence (i.e. fossils) anchoring the ages of particular nodes to known absolute ages. In recent years, a plethora of new fossil spiders, especially from the Mesozoic, have been described, while the number of studies presenting dated spider phylogenies based on fossil calibrations increased sharply. We critically evaluate 44 of these studies, which collectively employed 67 unique fossils in 180 calibrations. Approximately 54% of these calibrations are problematic, particularly regarding unsupported assignment of fossils to extant clades (44%) and crown (rather than stem) dating (9%). Most of these cases result from an assumed equivalence between taxonomic placement of fossils and their phylogenetic position. To overcome this limitation, we extensively review the literature on fossil spiders, with a special focus on putative synapomorphies and the phylogenetic placement of fossil species with regard to their importance for calibrating higher taxa (families and above) in the spider tree of life. We provide a curated list including 41 key fossils intended to be a basis for future estimations of dated spider phylogenies. In a second step, we use a revised set of 23 calibrations to estimate a new dated spider tree of life based on transcriptomic data. The revised placement of key fossils and the new calibrated tree are used to resolve a long-standing debate in spider evolution - we tested whether there has been a major turnover in the spider fauna between the Mesozoic and Cenozoic. At least 17 (out of 117) extant families have been recorded from the Cretaceous, implying that at least 41 spider lineages in the family level or above crossed the Cretaeous-Paleogene (K-Pg) boundary. The putative phylogenetic affinities of families known only from the Mesozoic suggest that at least seven Cretaceous families appear to have no close living relatives and might represent extinct lineages. There is no unambiguous fossil evidence of the retrolateral tibial apophysis clade (RTA-clade) in the Mesozoic, although molecular clock analyses estimated the major lineages within this clade to be at least ∼100 million years old. Our review of the fossil record supports a major turnover showing that the spider faunas in the Mesozoic and the Cenozoic are very distinct at high taxonomic levels, with the Mesozoic dominated by Palpimanoidea and Synspermiata, while the Cenozoic is dominated by Araneoidea and RTA-clade spiders.

Comparative phylogeography of oceanic archipelagos: Hotspots for inferences of evolutionary process

Remote island archipelagos offer superb opportunities to study the evolution of community assembly because of their relatively young and simple communities where speciation contributes to the origin and evolution of community structure. There is great potential for common phylogeographic patterns among remote archipelagos that originate through hotspot volcanism, particularly when the islands formed are spatially isolated and linearly arranged. The progression rule is characterized by a phylogeographic concordance between island age and lineage age in a species radiation. Progression is most likely to arise when a species radiation begins on an older island before the emergence of younger islands of a hotspot archipelago. In the simplest form of progression, colonization of younger islands as they emerge and offer appropriate habitat, is coincident with cladogenesis. In this paper, we review recent discoveries of the progression rule on seven hotspot archipelagos. We then discuss advantages that progression offers to the study of community assembly, and insights that community dynamics may offer toward understanding the evolution of progression. We describe results from two compelling cases of progression where the mosaic genome may offer insights into contrasting demographic histories that shed light on mechanisms of speciation and progression on remote archipelagos.

Tip-dated phylogeny of whirligig beetles reveals ancient lineage surviving on Madagascar

The temporal origin of Madagascar's extraordinary endemic diversity is debated. A preference for Cenozoic dispersal origins has replaced the classical view of Mesozoic vicariance in the wake of molecular dating. However, evidence of ancient origins is mounting from arthropod groups. Using phylogenetic 'tip-dating' analysis with fossils, we show that a whirligig beetle species, Heterogyrus milloti, inhabiting forest streams in southeastern Madagascar is the last survivor of a once dominant and widespread Mesozoic group. With a Late Triassic to Early Jurassic origin (226-187 Ma) it is the hitherto oldest dated endemic lineage of animal or plant on Madagascar. Island biotas' sensitivity to extinction is well known, but islands can also provide refuge from continental extinction. Heterogyrus milloti is an irreplaceable link to the freshwater biota of the Mesozoic and serves as a reminder of what may be lost without critical conservation efforts on Madagascar.

A review of the Madagascan pelican spiders of the genera Eriauchenius O. Pickard-Cambridge, 1881 and Madagascarchaea gen. n. (Araneae, Archaeidae)

An endemic genus of Madagascan spiders (Araneae, Archaeidae, Eriauchenius) is revised. All 20 species of Eriauchenius are described and keyed, of which 14 are new species: Eriauchenius andriamanelosp. n., Eriauchenius andrianampoinimerinasp. n., Eriauchenius goodmanisp. n., Eriauchenius harveyisp. n., Eriauchenius lukemacaulayisp. n., Eriauchenius milajaneaesp. n., Eriauchenius millotisp. n., Eriauchenius rafohysp. n., Eriauchenius ranavalonasp. n., Eriauchenius rangitasp. n., Eriauchenius rixisp. n., Eriauchenius samasp. n., Eriauchenius wunderlichisp. n., Eriauchenius zirafysp. n. Additionally, six species of the new genus Madagascarchaeagen. n. are described and keyed, of which four are new species: Madagascarchaea fohysp. n., Madagascarchaea lotzisp. n., Madagascarchaea moramorasp. n., Madagascarchaea rabesahalasp. n. Diagnostic characters for the Madagascan and African genera are described, and based on these characters and previous phylogenetic analyses the following species transfers are proposed: Eriauchenius cornutus (Lotz, 2003) to Afrarchaea; Afrarchaea fisheri (Lotz, 2003) and Afrarchaea mahariraensis (Lotz, 2003) to Eriauchenius. Finally, we propose that the distribution of Afrarchaea be restricted to South Africa. While several Madagascan specimens have previously been identified as Afrarchaea godfreyi (Hewitt, 1919), we argue that these are likely misidentifications that should instead be Eriauchenius.

Multilocus phylogenetic and geospatial analyses illuminate diversification patterns and the biogeographic history of Malagasy endemic plated lizards (Gerrhosauridae: Zonosaurinae)

Although numerous studies have attempted to find single unifying mechanisms for generating Madagascar's unique flora and fauna, little consensus has been reached regarding the relative importance of climatic, geologic and ecological processes as catalysts of diversification of the region's unique biota. Rather, recent work has shown that both biological and physical drivers of diversification are best analysed in a case-by-case setting with attention focused on the ecological and life-history requirements of the specific phylogenetic lineage under investigation. Here, we utilize a comprehensive analytical approach to examine evolutionary drivers and elucidate the biogeographic history of Malagasy plated lizards (Zonosaurinae). Data from three genes are combined with fossil information to construct time-calibrated species trees for zonosaurines and their African relatives, which are used to test alternative diversification hypotheses. Methods are utilized for explicitly incorporating phylogenetic uncertainty into downstream analyses. Species distribution models are created for 14 of 19 currently recognized species, which are then used to estimate spatial patterns of species richness and endemicity. Spatially explicit analyses are employed to correlate patterns of diversity with both topographic heterogeneity and climatic stability through geologic time. We then use inferred geographic ranges to estimate the biogeographic history of zonosaurines within each of Madagascar's major biomes. Results suggest constant Neogene and Quaternary speciation with divergence from the African most recent common ancestor ~30 million years ago when oceanic currents and African rivers facilitated dispersal. Spatial patterns of diversity appear concentrated along coastal regions of northern and southern Madagascar. We find no relationship between either topographic heterogeneity or climatic stability and patterns of diversity. Ancestral state reconstructions suggest that western dry forests were important centres of origin with recent invasion into spiny and rain forest. These data highlight the power of combining multilocus phylogenetic and spatially explicit analyses for testing alternative diversification hypotheses within Madagascar's unique biota and more generally, particularly as applied to phylogenetically and biologically constrained systems.