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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.

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.

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.

Yee Wah Lau, Frank R. Stokvis, Yukimitsu Imahara and James D. Reimer

Stoloniferan octocorals (Cnidaria: Anthozoa: Octocorallia: Alcyonacea) are a relatively unexplored fauna in the Ryukyus (southern Japan), known to be a tropical marine region of high biodiversity and endemism of species. Specimens of stoloniferous octocorals were collected during fieldwork along the coasts of two islands (Okinawa and Iriomote) in the Okinawa Prefecture. Despite their phenotypic polyp variation, this study shows their morphological and molecular uniqueness, leading to the description of a new genus with a single species: Hanabira yukibana, gen. nov., sp. nov. They are placed within the Clavulariidae and form a sister clade basally to the genus Knopia Alderslade & McFadden, 2007 and species of Clavularia Blainville, 1830. The polyps of this new species show morphological variation in both shape and sclerite density, but there is conformity in the typical overall petal shaped tentacles, which have fused pinnules (pseudopinnules). Depending on the densities of their sclerites and their photosynthetic endosymbiotic algae (zooxanthellae) of the family Symbiodiniaceae, there is a characteristic sheen present in the tentacles. Moreover, the zooxanthellae hosted by our specimens form a clear, small-scale biogeographic pattern; all H. yukibana specimens from Okinawa Island contained zooxanthellae of the genus Cladocopium Lajeunesse & H.J. Jeong, 2018 (= former Symbiodinium ‘Clade C’) and all specimens from Iriomote Island hosted zooxanthellae of the genus Durusdinium LaJeunesse, 2018 (= former Symbiodinium ‘Clade D’). These results show the potential for variation among the Symbiodiniaceae floras within octocorals, something that has not yet been investigated for the large majority of zooxanthellate octocoral species.

Neil Cumberlidge and Savel R. Daniels

Edited by R. Vonk

Surveys of the freshwater crabs of two islands in the Gulf of Guinea, Central Africa, allowed a revision of the taxonomy of two little-known island endemic species, based for the first time on adult males: Potamonautes margaritarius (A. Milne-Edwards, 1869) from São Tomé, and of P. principe Cumberlidge, Clark and Baillie, 2002, from Príncipe (Brachyura; Potamonautidae). A new species of Potamonautes from southern São Tomé (Potamonautes saotome sp. nov.) is also described that is genetically distinct and has a clearly separate geographic distribution from P. margaritarius from northern São Tomé. The new species from southern São Tomé can be recognized by a suite of characters of the carapace, thoracic sternum, and gonopods. The taxonomy of P. margaritarius (A. Milne-Edwards, 1869) is stabilized by selecting a neotype from northern São Tomé. Potamonautes principe from Príncipe is the most distinct of the three taxa, with a more swollen carapace that has smooth anterolateral margins, and a shorter, straighter male first gonopod. All three taxa are morphologically distinct species that have also been clearly distinguished as evolutionarily separate lineages by mtDNA analysis and haplotyping in an earlier study. Previous phylogenetic evidence supports two separate island colonization events at different times in the past from different ancestral populations, one to São Tomé and another to Príncipe that resulted in the establishment of the endemic freshwater crab faunas of these two islands.

Sharon E. Kessler, Ute Radespiel, Alida I. F. Hasiniaina, Leanne T. Nash and Elke Zimmermann

Edited by V. Nijman

Frequent kin-biased coalitionary behaviour is a hallmark of mammalian social complexity. Furthermore, selection to understand complex social dynamics is believed to underlie the co-evolution of social complexity and large brains. Vocalisations have been shown to be an important mechanism with which large-brained mammals living in complex social groups recognise and recruit kin for coalitionary support during agonistic conflicts. We test whether kin recognition via agonistic calls occurs in a small-brained solitary foraging primate living in a dispersed social network, the grey mouse lemur (Microcebus murinus, Miller JF, 1777). As mouse lemurs are frequent models for ancestral solitary foraging mammals, this study examines whether kin recognition via agonistic calls could be the foundation from which more complex, kin-based coalitionary behaviour evolved. We test whether female wild mouse lemurs in Ankarafantsika National Park, Madagascar, react differently to agonistic calls from kin and nonkin and to calls from familiar and unfamiliar individuals during playback experiments. Subjects showed no significant differences in reactions to the different stimuli; thus they did not react differently based upon kinship or familiarity. Results suggest that this solitary foraging species does not use agonistic calls to recognise kin and monitor agonistic interactions involving kin, unlike several species of Old World monkeys and hyenas. Thus, kin recognition via agonistic calls may have evolved independently in these lineages in parallel with greater social complexity and frequent coalitionary behaviour.

Alejandro Sánchez-Chardi, Marian García-Pando, Eudald Pujol-Buxó, Maria A. Sans-Fuentes, María José López-Fuster and Francesc Muñoz-Muñoz

Edited by A. Ivanović

Island populations of terrestrial mammals often undergo extensive behavioural and morphological changes when separated from mainland populations. Within small mammals these changes have been mainly reported in rodents but were poorly assessed in soricomorphs. In this study we compared mandible morphology and body condition between mainland and island populations of the greater white-toothed shrew, Crocidura russula. The results indicated that island specimens were bigger and heavier than the mainland counterpart, and they showed changes in mandible shape that were associated with higher mechanical potentials. We suggest that these changes might be the result of the interaction of two main factors taking place in the island population: ecological release (i.e. the decrease of predation and interspecific competition), and consequently the increase of intraspecific competition. While the increase in size and body condition in island shrews could be a direct result from reduced predation and interspecific competition, the changes in mandible shape and the increase of both mechanical potential and sexual dimorphism could have arisen indirectly as a response to stronger intraspecific competition.