Morphology, nuclear SNPs and mate selection reveal that COI barcoding overestimates species diversity in a Mediterranean freshwater amphipod by an order of magnitude

Population Genomics Reveals Small-Scale Metapopulation Structure of Two Strictly Aquatic Keystone Species in a Recently Restored Urban River System (Emscher, Germany)

Urbanization and the resulting modifications of freshwater ecosystems can play an important role in shaping metapopulation structure and dynamics of aquatic organisms. Ecological restoration aims at improving river ecosystems by reducing or removing anthropogenic stressors and habitat fragmentation, facilitating natural dispersal among population patches. However, the success of such ecological restoration measures is not guaranteed, and for many of the functionally important but smaller organisms, improved connectivity is difficult to assess. Here, genetic markers can help in assessing small-scale connectivity and in identifying persisting gene flow barriers. In this study used high-resolution genetic markers to study the metapopulation structure of two ecologically important amphipod species, Gammarus pulex and Gammarus fossarum, in the heavily urbanized Emscher catchment in Germany. This catchment was strongly degraded and polluted for over a century but has been restored over the past two decades. For both strictly aquatic species, we analyzed mitochondrial cytochrome c oxidase I (COI) gene sequences as well as nuclear genome-wide single nucleotide polymorphism (SNP) data. We detected strong metapopulation structure within both species, which was mainly driven by catchment affiliation, wastewater, large in-stream barriers, and recent recolonization of restored stream sections. However, population structure was not fully explained by these factors, indicating that eco-evolutionary factors such as priority effects, adaptation, or biotic interactions play a role in shaping the population structure. Furthermore, our data show a strong mito-nuclear discordance for both species with regard to detailed population structure and also the presence of possible cryptic species for G. pulex. Here, nuclear data indicate that the diverging mitochondrial lineages of G. pulex (Gp-C and Gp-E) represent only one species in this region. Our study shows how genetic markers can support the assessment of population connectivity and thus evaluate the success of ecological restoration.

Population genetic data (COI, ddRAD) of Sialislutaria (Insecta, Megaloptera) from the Emscher catchment (Germany)

Background

In urban river systems, fragmentation of habitats and in-stream dispersal barriers play a major role in shaping the population genetic structure of freshwater macroinvertebrate species. In small, fragmented populations, effects of genetic drift and inbreeding are enhanced, which can lead to increased population differentiation and genetic diversity loss. One formerly strongly degraded and fragmented stream system in a highly urbanised area is the Emscher catchment in North Rhine-Westphalia, Germany. Major restoration efforts have led to an improvement of water and habitat quality over the past 20 years also in the formerly polluted tributaries, for example, the Boye catchment. However, the analysis of the population structure of two different amphipod and isopod species has revealed that some populations are still strongly isolated, indicating persisting gene flow barriers. In contrast, the effects are expected to be less pronounced in merolimnic species, which have an adult winged life stage, such as the alderfly Sialislutaria (Linnaeus, 1758) . However, this species was much less abundant in the Boye catchment and not found in adjacent catchments (only 9 of 41 sampling sites), reducing the power of possible analyses.

New information

As no population genetic studies of S.lutaria have to our knowledge been published so far and genetic resources are generally scarce for this species, we generated and present here population genetic data for 70 S.lutaria specimens for the mitochondrial cytochrome c oxidase I (COI) gene and, more importantly, high resolution genomic single nucleotide polymorphism (SNP) data for 71 specimens, generated with double-digest restriction site-associated sequencing (ddRAD-seq). These data can be valuable for further studies, analysing the population genetic structure, dispersal pathways and potential gene flow barriers for S.lutaria on a larger geographic scale. Additional to presenting the data, we also give first insights in the population structure on a small geographic scale (area of approx. 15 km2). While the population differentiation was generally low, as expected on this small scale, we still found that gene flow was not equally strong between all populations, but that one population played a central role as a source and sink population, which cannot only be explained by the distance between populations.

Cryptic diversity begets challenges and opportunities in biodiversity research

How many species of life are there on Earth? This is a question that we want to know but cannot yet answer. Some scholars speculate that the number of species may reach 2.2 billion when considering cryptic diversity and that each morphology-based insect species may contain an average of 3.1 cryptic species. With nearly two million described species, such high estimates of cryptic diversity would suggest that cryptic species are widespread. The development of molecular species delimitation has led to the discovery of a large number of cryptic species, and cryptic biodiversity has gradually entered our field of vision and attracted more attention. This paper introduces the concept of cryptic species, how they evolve, and methods by which they may be discovered and confirmed, and provides theoretical and methodological guidance for the study of hidden species. A workflow of how to confirm cryptic species is provided. In addition, the importance and reliability of multi-evidence-based integrated taxonomy are reaffirmed as a way to better standardize decision-making processes. Special focus on cryptic diversity and increased funding for taxonomy is needed to ensure that cryptic species in hyperdiverse groups are discoverable and described. An increased focus on cryptic species in the future will naturally arise as more difficult groups are studied, and thereby, we may finally better understand the rules governing the evolution and maintenance of cryptic biodiversity.

Strong Small-Scale Differentiation but No Cryptic Species Within the Two Isopod Species Asellus aquaticus and Proasellus coxalis in a Restored Urban River System (Emscher, Germany)

Worldwide, humans have strongly altered river networks. Key changes resulted in modified hydromorphology, poor habitat quality and availability, migration barriers, and pollution. Restoration measures aim at mitigating anthropogenic stressors and at restoring connectivity, but the biological success of these measures is not guaranteed. Analyzing genetic diversity and metapopulation structure of target species in the river network with genetic markers can help to understand recolonization processes and to identify persisting gene flow barriers. Here, we studied the population genetic structure of the two pollution-tolerant detritivorous isopod species, Asellus aquaticus and Proasellus coxalis, in the former heavily degraded and polluted, but now mostly restored Emscher catchment in Germany. For both species, we analyzed mitochondrial cytochrome c oxidase I (COI) gene sequences and nuclear genome-wide single nucleotide polymorphism (SNP) data. Surprisingly, we found a strong metapopulation structure for both species with several isolated populations on a small-scale of few kilometers, but a still high genetic diversity, especially in the COI gene. For both taxa, potentially cryptic species are known, but our SNP data showed that the mitochondrial lineages represent only one species, each, in the study area. This highlights the importance of integrating high-resolution nuclear markers into species identification because species diversity may otherwise be overestimated. While we could identify some migration barriers and find indications for passive dispersal by birds or humans, these factors could not fully explain the local metapopulation structure, suggesting that also other drivers, such as isolation by adaptation, priority effects, or biotic interactions, play a role in shaping the population genetic structure.

Molecular diversity of Diplura in southern High Appalachian leaf litter

The fauna of Diplura, the two-pronged bristletails (Hexapoda), of the southern Appalachians has received little focused systematic attention. Existing literature suggests the fauna to comprise around a dozen species. Based on a broader DNA barcode-based survey of high elevation litter arthropods in the region, we suggest the fauna to be much richer, with automated species delimitation methods hypothesising as many as 35 species, most highly restricted to single or closely proximate localities. Such a result should not be very surprising for such small, flightless arthropods, although it remains to be seen if other markers or morphology support such high diversity. The region still remains sparsely sampled for these more cryptic elements of the arthropod fauna and much larger numbers of species undoubtedly remain to be discovered.

A new species of Orchomenella (Amphipoda, Tryphosidae) described from hydrothermal vent in the Okinawa Trough, Northwest Pacific

A new species of the family Tryphosidae, Orchomenellacompressasp. nov., is described from hydrothermal vents in the Okinawa Trough. This is the first known Orchomenella species found in vent fields. Important morphological characters that differentiate O.compressasp. nov. from its congeners are the absence of eyes, the compressed distal three articles of gnathopod 2, the shape of the posterior margin of epimerons 2 and 3, and the number of dorsal spines on the telson. The genetic divergence of the analyzed COI gene clearly supports this new taxon.

Integrative taxonomic revision of the genera Nesticella and Howaia in Japan with the description of five new species (Araneae, Nesticidae, Nesticellini)

The Japanese species of the genera Nesticella Lehtinen & Saaristo, 1980 and Howaia Lehtinen & Saaristo, 1980 (Araneae, Nesticidae, Nesticellini) are revised using an integrative taxonomic approach. Their morphology, phylogenetic position within the genera, assignment to species groups, and distribution in mainland Japan and the Ryukyu islands are discussed herein. A phylogenetic and species delimitation analysis was conducted to confirm the boundaries between the putative species that were initially discriminated based on external and genital morphology. As a result of the present study, six species of Nesticella and three species of Howaia are proposed for the fauna of Japan based on the combined results of morphology and molecular analyses. Male and female of the previously known species H.mogera (Yaginuma, 1972), N.brevipes (Yaginuma, 1970), and N.okinawaensis (Yaginuma, 1979) are redescribed and illustrated using type specimens or specimens collected at the type locality. Nesticellaterrestris (Yaginuma, 1970) is resurrected as a valid species and distinguished from the closely related N.brevipes based on morphological and molecular evidence. The male of N.terrestris is described for the first time. We herein describe three new species of Nesticella and two new species of Howaia from different islands in the Ryukyu Archipelago, southwest Japan: N.insulanasp. nov. (♂, ♀) from Yonaguni-jima Island, N.occultasp. nov. (♀) from Ishigaki-jima Island, N.silvicolasp. nov. (♂, ♀) from Yakushima Island, H.albasp. nov. (♂, ♀) from Miyako-jima Island and H.subterraneasp. nov. (♀) from Okinoerabu-jima Island. Nesticellaoccultasp. nov., H.albasp. nov. and H.subterraneasp. nov. dwell exclusively in caves and show extensive morphological adaptation to subterranean life.