The stygofaunal family of Bathynellidae, is an excellent group to study the processes that shape diversity and distribution, since they have unknown surface or marine relatives, high level of endemism, and limited dispersal abilities. Recent research on Bathynellidae in Western Australia (Pilbara) has uncovered new taxa with unexpected distributions and phylogenetic relationships, but the biogeographical processes that drive their diversification on the continent are still unclear. By exploring the diversity, distribution, and divergence time of Bathynellidae in a setting such as the perched and isolated aquifers of the Cleaverville Formation in the north of the De Grey River catchment (Pilbara), we aim to test the hypothesis that vicariance has shaped the distribution of this family, specifically if one or multiple vicariant events were involved. We analysed the specimens collected from perched water in different plateaus of the Cleaverville Formation, combining morphological and molecular data from mitochondrial and nuclear genes. We described two new species and genera (Anguillanella callawaensis gen. et sp. nov. and Muccanella cundalinensis gen. et sp. nov.), and two additional taxa are recognised using morphology and/or Automatic Barcode Gap Discovery and Poisson Tree Processes species delimitation methods. New genera and species result restricted to isolate perched aquifers on single plateaus and their distributions, phylogenetic relationships, and divergence time estimates support multiple vicariant events and ancient allopatric speciation.
Giulia Perina, Ana I. Camacho, Joel Huey, Pierre Horwitz and Annette Koenders
Tomáš Němec and Michal Horsák
Shell formation is the main defensive strategy against predation for the majority of snails. Therefore, various predators have had to develop a variety of techniques how to overcome this barrier. As shells can persist in a calcium-rich environment for a long time, specific external or internal traces on shells left by predators indicate whether and who killed the snail. Based on litter samples collected at 30 sites of five different habitat types, the intensity and type of predation were assessed. The minimal predation rate varied between 0.0 and 21%, with an average of 8%. The highest rate was observed at limestone steppes, on average 15%. Beetles were found to be the most common predators of snails; however, predation by snails was more common in calcareous fens. Predation by some vertebrates and dipteran flies was also recognised. To test the role of mouth barriers as a means to reduce predation by carabid beetles that break the shell from an aperture, we analysed the predation rate separately on adult and juvenile shells using 24 populations of the steppe snail Granaria frumentum (Draparnaud, 1801). As expected, carabid beetles chiefly preferred juveniles compared to adult shells (Wilcoxon test, p < 0.001). On the contrary, the parasitoid fly Pherbellia limbata (Meigen, 1830) and Drilus beetles preferred adults. We found that predation by carabid beetles positively increased with prey abundance (R2 = 42.8%, p = 0.021), while no relation was observed for the parasitoid (p = 0.703), likely due to their feeding specialisation.
Maliheh Pirayesh Shirazinejad, Mansour Aliabadian and Omid Mirshamsi
The white wagtail (Motacilla alba) species complex with its distinctive plumage in separate geographical areas can serve as a model to test evolutionary hypotheses. Its extensive variety in plumage, despite the genetic similarity between taxa, and the evolutionary events connected to this variety are poorly understood. Therefore we sampled in the breeding range of the white wagtail: 338 individuals were analyzed from 74 areas in the Palearctic and Mediterranean. We studied the white wagtail complex based on two mitochondrial DNA markers to make inferences about the evolutionary history. Our phylogenetic trees highlight mtDNA sequences (ND2, CR), and one nuclear marker (CHD1Z), which partly correspond to earlier described clades: the northern Palearctic (clade N); eastern and central Asia (clade SE); south-western Asia west to the British Isles (clade SW); and Morocco (clade M). The divergence of all clades occurred during the Pleistocene. We also used ecological niche modelling for three genetic lineages (excluding clade M); results showed congruence between niche and phylogenetic divergence in these clades. The results of the white wagtail ancestral area reconstruction showed the influence of dispersal on the distribution and divergence of this complex species. The most important vicariance event for the white wagtail complex may have been caused by the Gobi and Taklamakan deserts. We conclude that the ancestral area of the white wagtail complex was probably in the Mediterranean, with its geography having a considerable effect on speciation processes.
Miguel A. Meca, Pilar Drake and Daniel Martin
The polychaete Oxydromus okupa lives in association with the bivalves Scrobicularia plana and Macomopsis pellucida in the intertidal of Río San Pedro (CI = Cádiz Intertidal) and adjacent to CHipiona (CH) harbour, and in the subtidal of the Bay of Cádiz (CS = Cádiz Subtidal). We analyse these populations morphometrically, ecologically (including infestation characteristics) and genetically (intertidal populations, 16S and ITS-1 genes). We consider “host”, “environment” and the combined “host and environment” as possible factors of interpopulation variability. Morphometry revealed three well-defined clusters for CI, CH and CS, showing intergroup phenotypic differences ranging from 35 to 50%. Hosts shell lengths ranged between 26 and 36 mm for S. plana and 20 and 28 mm for M. pellucida. The infestation of small M. pellucida by juvenile O. okupa suggests they show an active size segregation behaviour. The intertidal seems to be less favourable (infestation rate <25% vs. up to 65% in the subtidal), and did not show recent bottleneck events. Overall, CI and CH were genetically homogeneous, but showed a significant divergence (one dominant haplotype in each host species), suggesting host shift as being a soft barrier to gene flow. Most characters related with host-entering varied among populations, suggesting symbiotic behaviour to play a key role in reducing panmixia and leading to the initial phases of a speciation process in sympatric symbiotic populations. Polyxeny and symbiotic behaviour in O. okupa seem thus to be underlying mechanisms contributing to its great phenotypic variety, marked ecological differences, and genetic divergence.
Giacinta Angela Stocchino, Ronald Sluys, Abdel Halim Harrath, Lamjed Mansour and Renata Manconi
Invasions of alien species form one of the major threats to global biodiversity. Among planarian flatworms many species are known to be invasive, in several cases strongly affecting local ecosystems. Therefore, a detailed knowledge on the biology of an invasive species is of utmost importance for understanding the process of invasion, the cause of its success, and the subsequent ecological impact on native species. This paper provides new information on the biology of introduced populations of the freshwater flatworm Girardia tigrina (Girard, 1850) from Europe. This species is a native of the Nearctic Region that was accidentally introduced into Europe in the 1920s. Since then, numerous records across the European continent bear witness of the invasiveness of this species, although only a few studies focused on the biology of the introduced populations. We report on the morphology of sexualized individuals from a fissiparous Italian population, representing the second record of spontaneous sexualization of fissiparous individuals in this species. A detailed morphological account of the reproductive apparatus of these ex-fissiparous animals is presented. Our results increased the number of morphological groups previously recognized for European populations of G. tigrina, thus corroborating the hypothesis on multiple independent introductions to this continent. Karyological results obtained from our fissiparous Italian individuals revealed a constant diploid chromosome complement of sixteen chromosomes. Further, we document the marked intraspecific variation in several morphological features of this species.
Cessa Rauch, Bert W. Hoeksema, Bambang Hermanto and Charles H.J.M. Fransen
Most marine palaemonid shrimp species live in symbiosis with invertebrates of various phyla. These associations range from weak epibiosis to obligatory endosymbiosis and from restricted commensalism to semi-parasitism. On coral reefs, such symbiotic shrimps can contribute to the associated biodiversity of reef corals. Among the host taxa, mushroom corals (Cnidaria: Anthozoa: Fungiidae) are known to harbour various groups of symbionts, including shrimps. Some but not all of these associated species are host-specific. Because data on the host specificity of shrimps on mushroom corals are scarce, shrimp species of the genus Periclimenes were collected from mushroom corals during fieldwork in Lembeh Strait, North Sulawesi, Indonesia. Using molecular (COI barcoding gene) and morphological methods, three species of Periclimenes were identified: P. diversipes, P. watamuae and a species new to science, P. subcorallum sp. nov., described herein. Their host specificity was variable, with eight, three and two fungiid host records, respectively. It is concluded that shrimp species of the genus Periclimenes show much overlap in their host choice and that particular morphological traits in the host species appear to play a more important role than phylogenetic affinities within the host group.
Gerrit Potkamp and Charles H.J.M. Fransen
Over the last century, a large body of literature emerged on mechanisms driving speciation. Most of the research into these questions focussed on terrestrial systems, while research in marine systems lagged behind. Here, we review the population genetic mechanisms and geographic context of 33 potential cases of speciation with gene flow in the marine realm, using six criteria inferred from theoretical models of speciation. Speciation with gene flow occurs in a wide range of marine taxa. Single traits, which induce assortative mating and are subjected to disruptive selection, such as differences in host-associations in invertebrates or colour pattern in tropical fish, are potentially responsible for a decrease in gene flow and may be driving divergence in the majority of cases. However, much remains unknown, and with the current knowledge, the frequency of ecological speciation with gene flow in marine systems remains difficult to estimate. Standardized, generally applicable statistical methods, explicitly testing different hypotheses of speciation, are, going forward, required to confidently infer speciation with gene flow.
Piotr Gąsiorek, Daniel Stec, Witold Morek and Łukasz Michalczyk
Isohypsibioidea are most likely the most basally branching evolutionary lineage of eutardigrades. Despite being second largest eutardigrade order, phylogenetic relationships and systematics within this group remain largely unresolved. Broad taxon sampling, especially within one of the most speciose tardigrade genera, Isohypsibius Thulin, 1928, and application of both comparative morphological methods (light contrast and scanning electron microscopy imaging of external morphology and buccal apparatuses) and phylogenetic framework (18S + 28S rRNA sequences) resulted in the most comprehensive study devoted to this order so far. Two new families are erected from the currently recognised family Isohypsibiidae: Doryphoribiidae fam. nov., comprising all aquatic isohypsibioids and some terrestrial isohypsibioid taxa equipped with the ventral lamina; and Halobiotidae fam. nov., secondarily marine eutardigrades with unique adaptations to sea environment. We also split Isohypsibius into four genera to accommodate phylogenetic, morphological and ecological variation within the genus: terrestrial Isohypsibius s.s. (Isohypsibiidae), with smooth or sculptured cuticle but without gibbosities; terrestrial Dianea gen. nov. (Isohypsibiidae), with small and pointy gibbosities; terrestrial Ursulinius gen. nov. (Isohypsibiidae), with large and rounded gibbosities; and aquatic Grevenius gen. nov. (Doryphoribiidae fam. nov.), typically with rough cuticle and claws with branches of very similar heigths. Claw morphology is reviewed and, for the first time, shown to encompass a number of morphotypes that correlate with clades recovered in the molecular analysis. The anatomy of pharynx and cuticle are also shown to be of high value in distinguishing supraspecific taxa in Isohypsibioidea. Taxonomy of all isohypsibioid families and genera is discussed, with special emphasis on the newly erected entities. Finally, a dychotomous diagnostic key to all currently recognised isohypsibioid families and genera is provided.
Bernhard A. Huber and Anne Chao
Ratio-like approaches for estimating global species richness have been criticised for their unjustified extrapolation from regional to global patterns. Here we explore the use of cumulative percentages of ‘new’ (i.e., not formally described) species over large geographic areas (‘megatransects’) as a means to overcome this problem. In addition, we take into account undetected species and illustrate these combined methods by applying them to a family of spiders (Pholcidae) that currently contains some 1,700 described species. The raw global cumulative percentage of new species (‘new’ as of the end of 2008, when 1,001 species were formally described) is 75.1%, and is relatively constant across large biogeographic regions. Undetected species are estimated using the Chao2 estimator based on species incidence data (date by species and locality by species matrices). The estimated percentage of new species based on the date by species matrices is 76.0% with an estimated standard error (s.e.) of 2.6%. This leads to an estimated global species richness of about 4,200 with a 95% confidence interval of (3,300, 5,000). The corresponding values based on locality by species matrices are 84.2% (s.e. 3.0%) and 6,300 with a 95% confidence interval of (4,000, 8,600). Our results suggest that the currently known 1,700 species of Pholcidae may represent no more than about 25–40% of the total species richness. The impact of further biasing factors like geography, species size and distribution, cryptic species, and model assumptions needs to be explored.
Antonio Archidona-Yuste, Carolina Cantalapiedra-Navarrete, Pablo Castillo and Juan E. Palomares-Rius
The genus Longidorus constitutes a large group of approximately 170 species of plant-ectoparasitic nematodes that are polyphagous and distributed almost worldwide. Some of the species of this genus are vectors of plant viruses. Species discrimination in Longidorus is difficult because the morphology is very conservative, and morphometric characters often overlap, leading to potential misidentification. Integrative taxonomy, based on the combination of molecular analyses with morphology, is a useful and necessary approach in Longidorus species identification. In Spain from 2014 to 2017, we conducted nematode surveys among cultivated and wild plants, from which we identified 13 populations of Longidorus, two of which appeared to represent new species and are described herein as L. iliturgiensis sp. nov. and L. pacensis sp. nov., and 11 populations belonging to eight known species: L. africanus, L. baeticus, L. carpetanensis, L. fasciatus, L. nevesi, L. cf. olegi, L. pini, and L. vallensis. Three species are new geographical records for Spain (L. nevesi, L. cf. olegi, and L. africanus). We report molecular data for L. nevesi, L. cf. olegi, L. carpetanensis and L. pini for the first time. Additionally, we describe the males of L. pini and the juveniles of L. cf. olegi.