Incomplete lineage sorting and ancient admixture, and speciation without morphological change in ghost-worm cryptic species

Circumtropical distribution and cryptic species of the meiofaunal enteropneust Meioglossus (Harrimaniidae, Hemichordata)

Hemichordata has always played a central role in evolutionary studies of Chordata due to their close phylogenetic affinity and shared morphological characteristics. Hemichordates had no meiofaunal representatives until the surprising discovery of a microscopic, paedomorphic enteropneust Meioglossus psammophilus (Harrimaniidae, Hemichordata) from the Caribbean in 2012. No additional species have been described since, questioning the broader distribution and significance of this genus. However, being less than a millimeter long and superficially resembling an early juvenile acorn worm, Meioglossus may easily be overlooked in both macrofauna and meiofauna surveys. We here present the discovery of 11 additional populations of Meioglossus from shallow subtropical and tropical coralline sands of the Caribbean Sea, Red Sea, Indian Ocean, and East China Sea. These geographically separated populations show identical morphology but differ genetically. Our phylogenetic reconstructions include four gene markers and support the monophyly of Meioglossus. Species delineation analyses revealed eight new cryptic species, which we herein describe using DNA taxonomy. This study reveals a broad circumtropical distribution, supporting the validity and ecological importance of this enigmatic meiobenthic genus. The high cryptic diversity and apparent morphological stasis of Meioglossus may exemplify a potentially common evolutionary 'dead-end' scenario, where groups with highly miniaturized and simplified body plan lose their ability to diversify morphologically.

Understanding natural selection and similarity: Convergent, parallel and repeated evolution

Parallel and convergent evolution offer some of the most compelling evidence for the significance of natural selection in evolution, as the emergence of similar adaptive solutions is unlikely to occur by random chance alone. However, these terms are often employed inconsistently, leading to misinterpretation and confusion, and recently proposed definitions have unintentionally diminished the emphasis on the evolution of similar adaptive solutions. Here, I examine various conceptual frameworks and definitions related to parallel and convergent evolution and propose a consolidated framework that enhances our comprehension of these evolutionary patterns. The primary aim of this framework is to harmonize the concepts of parallel and convergent evolution together with natural selection and the idea of similarity. Both concepts involve the evolution of similar adaptive solutions as a result of environmental challenges. The distinction lies in ancestral phenotypes. Parallel evolution takes place when the ancestral phenotypes (before selection) of the lineages are similar. Convergent evolution happens when the lineages have distinct ancestral phenotypes (before selection). Because an ancestral-based distinction will inevitably lead to cases where uncertainty in the distinction may arise, the framework includes a general term, repeated evolution, which can be used as a term applying to the evolution of similar phenotypes and genotypes as well as similar responses to environmental pressures. Based on the argument that genetic similarity may frequently arise without selection, the framework posits that the similarity of genetic sequences is not of great interest unless linked to the actions of natural selection or to the origins (mutation, standing genetic variation, gene flow) and locations of the similar sequences.

nRCFV: a new, dataset-size-independent metric to quantify compositional heterogeneity in nucleotide and amino acid datasets

MOTIVATION

Compositional heterogeneity-when the proportions of nucleotides and amino acids are not broadly similar across the dataset-is a cause of a great number of phylogenetic artefacts. Whilst a variety of methods can identify it post-hoc, few metrics exist to quantify compositional heterogeneity prior to the computationally intensive task of phylogenetic tree reconstruction. Here we assess the efficacy of one such existing, widely used, metric: Relative Composition Frequency Variability (RCFV), using both real and simulated data.

RESULTS

Our results show that RCFV can be biased by sequence length, the number of taxa, and the number of possible character states within the dataset. However, we also find that missing data does not appear to have an appreciable effect on RCFV. We discuss the theory behind this, the consequences of this for the future of the usage of the RCFV value and propose a new metric, nRCFV, which accounts for these biases. Alongside this, we present a new software that calculates both RCFV and nRCFV, called nRCFV_Reader.

AVAILABILITY AND IMPLEMENTATION

nRCFV has been implemented in RCFV_Reader, available at: https://github.com/JFFleming/RCFV_Reader . Both our simulation and real data are available at Datadryad: https://doi.org/10.5061/dryad.wpzgmsbpn .

Phylogeography and cohesion species delimitation of California endemic trapdoor spiders within the Aptostichus icenoglei sibling species complex (Araneae: Mygalomorphae: Euctenizidae)

Species delimitation is an imperative first step toward understanding Earth's biodiversity, yet what constitutes a species and the relative importance of the various processes by which new species arise continue to be debatable. Species delimitation in spiders has traditionally used morphological characters; however, certain mygalomorph spiders exhibit morphological homogeneity despite long periods of population-level isolation, absence of gene flow, and consequent high degrees of molecular divergence. Studies have shown strong geographic structuring and significant genetic divergence among several species complexes within the trapdoor spider genus Aptostichus, most of which are restricted to the California Floristic Province (CAFP) biodiversity hotspot. Specifically, the Aptostichus icenoglei complex, which comprises the three sibling species, A. barackobamai, A. isabella, and A. icenoglei, exhibits evidence of cryptic mitochondrial DNA diversity throughout their ranges in Northern, Central, and Southern California. Our study aimed to explicitly test species hypotheses within this assemblage by implementing a cohesion species-based approach. We used genomic-scale data (ultraconserved elements, UCEs) to first evaluate genetic exchangeability and then assessed ecological interchangeability of genetic lineages. Biogeographical analysis was used to assess the likelihood of dispersal versus vicariance events that may have influenced speciation pattern and process across the CAFP's complex geologic and topographic landscape. Considering the lack of congruence across data types and analyses, we take a more conservative approach by retaining species boundaries within A. icenoglei.

Cost-saving population genomic investigation of Daphnia longispina complex resting eggs using whole-genome amplification and pre-sequencing screening

Resting stages of aquatic organisms that accumulate in the sediment over time are an exceptional resource that allows direct insights into past populations and addressing evolutionary questions. This is of particular interest in taxa that face relatively new environmental challenges, e.g., climate change and eutrophication, such as the Daphnia longispina species complex, a keystone zooplankton group in European freshwater ecosystems. However, genomic analysis might be challenging as DNA yield from many of these resting stages can be low and the material degraded. To reliably allow the resequencing of single Daphnia resting eggs from different sediment layers and characterize genomic changes through time, we performed whole-genome amplification to obtain DNA amounts suitable for genome resequencing and tested multiple protocols involving egg isolation, whole-genome amplification kits, and library preparation. A pre-sequencing contamination screening was developed, consisting of amplifying mitochondrial Daphnia and bacterial markers, to quickly assess and exclude possibly contaminated samples. In total, we successfully amplified and sequenced nine genomes from Daphnia resting eggs that could be identified as Daphnia longispina species. We analyzed the genome coverage and heterozygosity of these samples to optimize this method for future projects involving population genomic investigation of the resting egg bank.

Ramisyllis kingghidorahi n. sp., a new branching annelid from Japan

Among over 20,000 species of Annelida, only two branching species with a highly modified body-pattern are known until now: the Syllidae Syllis ramosa McIntosh, 1879, and Ramisyllis multicaudata Glasby et al. (Zoological Journal of the Linnean Society, 164, 481–497, 2012). Both have unusual ramified bodies with one head and multiple branches and live inside the canals of host sponges. Using an integrative approach (combining morphology, internal anatomy, ecology, phylogeny, genetic divergence, and the complete mitochondrial genome), we describe a new branching species from Japan, Ramisyllis kingghidorahi n. sp., inhabiting an undescribed species of Petrosia (Porifera: Demospongiae) from shallow waters. We compare the new species with its closest relative, R. multicaudata; emend the diagnosis of Ramisyllis; and discuss previous reports of S. ramosa. This study suggests a much higher diversity of branching syllids than currently known. Finally, we discuss possible explanations for the feeding behaviour in the new species in relation to its highly ciliated wall of the digestive tubes (especially at the distal branches and anus), and provide a hypothesis for the evolution of branching body patterns as the result of an adaptation to the host sponge labyrinthic canal system.

Pervasive admixture and the spread of a large-lipped form in a cichlid fish radiation

Adaptive radiations have proven important for understanding the mechanisms and processes underlying biological diversity. The convergence of form and function, as well as admixture and adaptive introgression, are common in adaptive radiations. However, distinguishing between these two scenarios remains a challenge for evolutionary research. The Midas cichlid species complex (Amphilophus spp.) is a prime example of adaptive radiation, with phenotypic diversification occurring at various stages of genetic differentiation. One species, A. labiatus, has large fleshy lips, is associated with rocky lake substrates, and occurs patchily within Lakes Nicaragua and Managua. By contrast, the similar, but thin-lipped, congener, A. citrinellus, is more common and widespread. We investigated the evolutionary history of the large-lipped form, specifically regarding whether the trait has evolved independently in both lakes from ancestral thin-lipped populations, or via dispersal and/or admixture events. We collected samples from distinct locations in both lakes, and assessed differences in morphology and ecology. Using RAD-seq, we genotyped thousands of SNPs to measure population structure and divergence, demographic history, and admixture. We found significant between-species differences in ecology and morphology, local intraspecific differences in body shape and trophic traits, but only limited intraspecific variation in lip shape. Despite clear ecological differences, our genomic approach uncovered pervasive admixture between the species and low genomic differentiation, with species within lakes being genetically more similar than species between lakes. Taken together, our results suggest a single origin of large-lips, followed by pervasive admixture and adaptive introgression, with morphology being driven by local ecological opportunities, despite ongoing gene-flow.

The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses

Fungi are rich in complexes of cryptic species that need a combination of different approaches to be delimited, including genomic information. Beauveria (Cordycipitaceae, Hypocreales) is a well-known genus of entomopathogenic fungi, used as a biocontrol agent. In this study we present a polyphasic taxonomy regarding two widely distributed complexes of Beauveria: B. asiatica and B. bassiana s.lat. Some of the genetic groups as previously detected within both taxa were either confirmed or fused using population genomics. High levels of divergence were found between two clades in B. asiatica and among three clades in B. bassiana, supporting their subdivision as distinct species. Morphological examination focusing on the width and the length of phialides and conidia showed no difference among the clades within B. bassiana while conidial length was significantly different among clades within B. asiatica. The secondary metabolite profiles obtained by liquid chromatography-mass spectrometry (LC-MS) allowed a distinction between B. asiatica and B. bassiana, but not between the clades therein. Based on these genomic, morphological, chemical data, we proposed a clade of B. asiatica as a new species, named B. thailandica, and two clades of B. bassiana to respectively represent B. namnaoensis and B. neobassiana spp. nov. Such closely related but divergent species with different host ranges have potential to elucidate the evolution of host specificity, with potential biocontrol application. Citation: Kobmoo N, Arnamnart N, Pootakham W, et al. 2021. The integrative taxonomy of Beauveria asiatica and B. bassiana species complexes with whole-genome sequencing, morphometric and chemical analyses. Persoonia 47: 136-150. https://doi.org/10.3767/persoonia.2021.47.04.

Conservation Genomics of Wild Red Sage (Salvia miltiorrhiza) and Its Endangered Relatives in China: Population Structure and Interspecific Relationships Revealed From 2b-RAD Data

Red sage (Salvia miltiorrhiza) is a widely used medicinal plant for treatment of cardiovascular and cerebrovascular diseases. Because of excessive excavation by huge market demand and habitat loss by human activities, the wild population resources of S. miltiorrhiza have reduced drastically in recent years. Meanwhile, population status of two closely related species S. bowleyana and S. paramiltiorrhiza were in a trend of decreasing due to their potential replacement of S. miltiorrhiza. Particularly, S. paramiltiorrhiza was threatened and endemic to a small region in eastern China. However, to date there has been no conservation genetic research reported for wild S. miltiorrhiza population and its endangered relatives. Assess the wild germplasm diversity for S. miltiorrhiza and its related species would provide fundamental genetic background for cultivation and molecular breeding of this medicinally important species. In the present study, we investigated the genetic diversity, population structure, and intra/inter-specific differentiation of S. miltiorrhiza and above two relatives using 2b-RAD genome-wide genotyping method. By investigating 81 individuals of S. miltiorrhiza, 55 individuals of S. bowleyana and 15 individuals of S. paramiltiorrhiza from 23 locations in China, we obtained 23,928 SNPs in total. A comparatively high genetic diversity was observed in S. miltiorrhiza (π = 0.0788, H e = 0.0783 ± 0.0007). The observed and expected heterozygosity in populations of these three species ranged from 0.0297 to 0.1481 and 0.0251 to 0.831, respectively. Two major lineage groups were detected in the examined S. miltiorrhiza populations. The results indicated that Dabie Mountain as a genetic diversity center of S. miltiorrhiza and possible complex inter-specific genetic exchange/hybridization occurred between S. miltiorrhiza and the two relatives. We suggest that strategic conservation and germplasm preservation should be considered not only for wild populations of S. miltiorrhiza, but also for its related S. bowleyana and S. paramiltiorrhiza.