Selection Across the Three-Dimensional Structure of Venom Proteins from North American Scolopendromorph Centipedes

Gene duplication followed by nucleotide differentiation is one of the simplest mechanisms to develop new functions for genes. However, the evolutionary processes underlying the divergence of multigene families remain controversial. We used multigene families found within the diversity of toxic proteins in centipede venom to test two hypotheses related to venom evolution: the two-speed mode of venom evolution and the rapid accumulation of variation in exposed residues (RAVER) model. The two-speed mode of venom evolution proposes that different types of selection impact ancient and younger venomous lineages with negative selection being the predominant form in ancient lineages and positive selection being the dominant form in younger lineages. The RAVER hypothesis proposes that, instead of different types of selection acting on different ages of venomous lineages, the different types of selection will selectively contribute to amino acid variation based on whether the residue is exposed to the solvent where it can potentially interact directly with toxin targets. This hypothesis parallels the longstanding understanding of protein evolution that suggests that residues found within the structural or active regions of the protein will be under negative or purifying selection, and residues that do not form part of these areas will be more prone to positive selection. To test these two hypotheses, we compared the venom of 26 centipedes from the order Scolopendromorpha from six currently recognized species from across North America using both transcriptomics and proteomics. We first estimated their phylogenetic relationships and uncovered paraphyly among the genus Scolopendra and evidence for cryptic diversity among currently recognized species. Using our phylogeny, we then characterized the diverse venom components from across the identified clades using a combination of transcriptomics and proteomics. We conducted selection-based analyses in the context of predicted three-dimensional properties of the venom proteins and found support for both hypotheses. Consistent with the two-speed hypothesis, we found a prevalence of negative selection across all proteins. Consistent with the RAVER hypothesis, we found evidence of positive selection on solvent-exposed residues, with structural and less-exposed residues showing stronger signal for negative selection. Through the use of phylogenetics, transcriptomics, proteomics, and selection-based analyses, we were able to describe the evolution of venom from an ancient venomous lineage and support principles of protein evolution that directly relate to multigene family evolution.

Genetic diversity varies with species traits and latitude in predatory soil arthropods (Myriapoda: Chilopoda)

Aim

To investigate the drivers of intra-specific genetic diversity in centipedes, a group of ancient predatory soil arthropods.

Location

Asia, Australasia and Europe.

Time Period

Present.

Major Taxa Studied

Centipedes (Class: Chilopoda).

Methods

We assembled a database of 1245 mitochondrial cytochrome c oxidase subunit I sequences representing 128 centipede species from all five orders of Chilopoda. This sequence dataset was used to estimate genetic diversity for centipede species and compare its distribution with estimates from other arthropod groups. We studied the variation in centipede genetic diversity with species traits and biogeography using a beta regression framework, controlling for the effect of shared evolutionary history within a family.

Results

A wide variation in genetic diversity across centipede species (0-0.1713) falls towards the higher end of values among arthropods. Overall, 27.57% of the variation in mitochondrial COI genetic diversity in centipedes was explained by a combination of predictors related to life history and biogeography. Genetic diversity decreased with body size and latitudinal position of sampled localities, was greater in species showing maternal care and increased with geographic distance among conspecifics.

Main Conclusions

Centipedes fall towards the higher end of genetic diversity among arthropods, which may be related to their long evolutionary history and low dispersal ability. In centipedes, the negative association of body size with genetic diversity may be mediated by its influence on local abundance or the influence of ecological strategy on long-term population history. Species with maternal care had higher genetic diversity, which goes against expectations and needs further scrutiny. Hemispheric differences in genetic diversity can be due to historic climatic stability and lower seasonality in the southern hemisphere. Overall, we find that despite the differences in mean genetic diversity among animals, similar processes related to life-history strategy and biogeography are associated with the variation within them.

A new species of Otostigmus (Chilopoda, Scolopendromorpha, Scolopendridae) from China, with remarks on the phylogenetic relationships of Otostigmuspolitus Karsch, 1881

Through a combination of morphological and DNA data, a new scolopendrid centipede from southern and southwestern China was revealed: O.tricarinatussp. nov. The species belong to the politus group but has three sharp tergal keels. Validation of phylogenetic status was performed through molecular analysis of the cytochrome c oxidase subunit I (COI), 16S rRNA, and 28S rRNA sequences from 16 Otostigmus species. Otostigmustricarinatussp. nov. was found to be two populations and varied in the number of spines on the ultimate prefemur, the sutures on a sternite, and a pore-free median longitudinal strip in the pore field. The Yunnan-Guizhou plateau population of O.tricarinatussp. nov. was sister to the clade O.polituspolitus + O.politusyunnanensis + Guangxi population of O.tricarinatussp. nov. with strong support from both BI (bayesian inference) and ML (maximum likelihood) analyses (PP = 1, BS = 97%).

Nguyen, Thinh T. Do, Binh T.T. Tran. Species diversity and distribution of large centipedes (Chilopoda: Scolopendromorpha) from the biosphere reserve of the western Nghe An Province, Vietnam

A total of 12 scolopendromorph species from five genera and three families were recorded in three different habitats (wooden forest, mixed timber-bamboo forest, and bamboo forest) and at three elevation ranges (>1,000 m, 700–1,000 m, and <700 m) from the biosphere reserve of the western Nghe An Province. Eleven species were recorded for the first time in the area. Scolopendridae is the most diverse family with nine species. The number of species was highest at elevation <700 m (9 species), and lowest at 700–1,000 m (4). By habitat distribution, the bamboo forest had the lowest number of species (3). 

Patients with centipede bites presenting to a university hospital in Bangkok: a 10-year retrospective study

INTRODUCTION

Centipede envenomation occurs commonly in tropical and subtropical countries. In most cases, centipede envenomation causes benign clinical manifestations. Serious complications are reported occasionally. Clinical studies regarding centipede envenomation are limited to case reports and case series. This study aimed to determine the prevalence and clinical characteristics of centipede bites in Bangkok, Thailand.

METHODS

This was a retrospective medical record review study. We included patients who were clearly envenomated by a centipede presenting to the emergency department of a tertiary university hospital in Bangkok from January 1, 2006, to December 31, 2015. Data were collected on demographics, details of the exposure, signs, symptoms, treatment, and complications of envenomation.

RESULTS

A total of 245 cases were included. The prevalence of centipede bite was 0.0367%. The majority were female (56.7%). The median age was 34.6 years (range: 1 month to 90 years). The number of envenomations was highest from October through December. Feet (38.3%) and hands (19.1%) were the parts of the body most often envenomated. Local effects were common with 99.5% of patients having localized pain and 87% having local swelling at the bite site. In terms of systemic effects, urticarial rash (5.7%) and fever (4.1%) were most frequently observed. Twelve cases (5%) had clinical pictures compatible with anaphylaxis. For pain management, all patients who had pain received analgesic drugs, while 29.7% were injected with local anesthesia. Antibiotics, antihistamines, and steroids were prescribed in 53.9%, 20.4%, and 10.2% of cases, respectively. No deaths occurred in this study.

CONCLUSIONS

Even though the location of our hospital is in a metropolitan city in Thailand, there were centipede bites every month, especially during the last three months of each year. Nearly all patients had local effects. In contrast, serious complications such as anaphylaxis and systemic infection only occurred occasionally.

The out-of-India hypothesis: evidence from an ancient centipede genus, Rhysida (Chilopoda: Scolopendromorpha) from the Oriental Region, and systematics of Indian species

The Oriental Region has been a focus of biogeographical research for more than two centuries. We examined systematics and biogeography of the centipede genus Rhysida in this region. A robust species hypothesis for the Indian subcontinental and Southeast Asian Rhysida clade uses molecular, morphological and distribution data. Twelve species are recognized in two monophyletic species complexes, eight belonging to the Rhysida immarginata and four to the Rhysida longipes species complex. They include Rhysida aspinosa, Rhysida crassispina, R. immarginata, R. longipes and seven new species, five of which are formally named in this paper: Rhysida ikhalama, Rhysida konda, Rhysida lewisi, Rhysida pazhuthara and Rhysida sada The nine Rhysida species are documented taxonomically and their morphological variation is reviewed. An integrative systematic approach reveals that diversity of Rhysida in the Indian subcontinent has been underestimated. Both species complexes started to diversify in the Early to Late Cretaceous in the Indian subcontinent. The out-of-India hypothesis is supported in both clades, because Southeast Asian species are nested in Indian subcontinental clades. Historical biogeographical analyses suggest two independent post-collision dispersal events, one in the immarginata clade and another where R. longipes expanded its range into Southeast Asia.

Evolutionary biogeography of the centipede genus Ethmostigmus from Peninsular India: testing an ancient vicariance hypothesis for Old World tropical diversity

BACKGROUND

Understanding the relative influence of vicariance and dispersal in shaping Old World tropical biodiversity remains a challenge. We aimed to infer the roles of these alternative biogeographic processes using a species time-tree for the centipede genus Ethmostigmus from the Old World tropics. Additionally, we explored fine-scale biogeographic patterns for an endemic radiation of Ethmostigmus from the peninsular Indian Plate (PIP), an area with complex geological and climatic history.

RESULTS

Divergence time estimates suggest that Ethmostigmus began diversifying in the Late Cretaceous, 99 (± 25) million years ago (Ma), its early biogeographic history shaped by vicariance. Members of Ethmostigmus in PIP form a monophyletic group that underwent endemic radiation in the Late Cretaceous, 72 (± 25) Ma. In contrast, a new species of Ethmostigmus from north-east India formed a clade with African/Australian species. Fine-scale biogeographic analyses in PIP predict that Indian Ethmostigmus had an ancestor in southern-central parts of the Western Ghats. This was followed by four independent dispersal events from the southern-central Western Ghats to the Eastern Ghats, and between different parts of the Western Ghats in the Cenozoic.

CONCLUSIONS

Our results are consistent with Gondwanan break-up driving the early evolutionary history of the genus Ethmostigmus. Multiple dispersal events coinciding with geo-climatic events throughout the Cenozoic shaped diversification in PIP. Ethmostigmus species in PIP are restricted to wet forests and have retained that niche throughout their diversification.

Molecular phylogeny and systematics of the centipede genus Ethmostigmus Pocock (Chilopoda : Scolopendromorpha) from peninsular India

Integrative taxonomy assesses the congruence between different lines of evidence for delimiting species, such as morphological, molecular or ecological data. Herein molecular phylogenetics is used to test monophyly and determine the phylogenetic position of the Old World tropical centipede genus Ethmostigmus Pocock, 1898, and to define species boundaries for Ethmostigmus in peninsular India. A phylogeny of the family Scolopendridae based on DNA sequence data for three markers from 427 specimens sampling in all major lineages (144 individuals generated in this study) recovers Ethmostigmus as a monophyletic group, but relationships among the genera in its subfamily Otostigminae are poorly supported. Two species delimitation methods for DNA sequence data and phylogeny are integrated with morphology and geographic data to propose a well-supported species hypothesis for Ethmostigmus on the peninsular Indian plate. Five species of Ethmostigmus are recognised in peninsular India, of which E. coonooranus Chamberlin, 1920 and three new species, namely, E. agasthyamalaiensis, sp. nov., E. sahyadrensis, sp. nov. and E. praveeni, sp. nov., occur in the Western Ghats, a biodiversity hotspot. The lesser-known Eastern Ghats harbour one species, E. tristis (Meinert, 1886), which has been nearly unreported for 130 years. This study highlights the value of an integrative approach to systematics, especially in underexplored, high biodiversity regions and where morphological variation is limited among closely related species.