Martin Schwentner

Cyclestheria hislopi (Crustacea: Branchiopoda): A group of morphologically cryptic species with origins in the Cretaceous

Cyclestheria hislopi is thought to be the only extant species of Cyclestherida. It is the sister taxon of all Cladocera and displays morphological characteristics intermediate of Spinicaudata and Cladocera. Using one mitochondrial (COI) and two nuclear (EF1α and 28S rRNA) markers, we tested the hypothesis that C. hislopi represents a single circumtropic species. South American (French Guiana), Asian (India, Indonesia, Singapore) and several Australian populations were included in our investigation. Phylogenetic and genetic distance analyses revealed remarkable intercontinental genetic differentiation (uncorrected p-distances COI>13%, EF1α>3% and 28S>4%). Each continent was found to have at least one distinct Cyclestheria species, with Australia boasting four distinct main lineages which may be attributed to two to three species. The divergence of these species (constituting crown group Cyclestherida) was, on the basis of phylogenetic analyses of COI and EF1α combined with molecular clock estimates using several fossil branchiopod calibration points or a COI substitution rate of 1.4% per million years, dated to the Cretaceous. This was when the South American lineage split from the Asian-Australian lineage, with the latter diverging further in the Paleogene. Todays circumtropic distribution of Cyclestheria may be best explained by a combination of Gondwana vicariance and later dispersal across Asia and Australia when the tectonic plates of the two continents drew closer in the early Miocene. The lack of morphological differentiation that has taken place in this taxon over such a long evolutionary period contrasts with the high level of differentiation and diversification observed in its sister taxon the Cladocera. Further insights into the evolution of Cyclestheria may help us to understand the evolutionary success of the Cladocera.

Phylogeny of Spinicaudata (Branchiopoda, Crustacea) based on three molecular markers--an Australian origin for Limnadopsis.

Taxonomy and phylogeny within the branchiopod taxon Spinicaudata are still controversial. We analyzed sequences of three gene fragments (28S rRNA, 16S rRNA and COI) from up to 41 species of the Cyzicidae, Limnadiidae and Leptestheriidae to infer their phylogenetic relationships, focusing in particular on species from Australia and their phylogenetic position within Spinicaudata. Four major monophyletic lineages could be distinguished: Limnadiidae, Leptestheriidae, Eocyzicus and all Cyzicidae except Eocyzicus. A clear genetic distinction between Australian and non-Australian Cyzicidae is well supported (i.e. Caenestheria and Caenestheriella species from Australia and Caenestheriella and Cyzicus species from Europe, Asia and North America). In the genera Eocyzicus and Eulimnadia the Australian species were closely related to those from other continents. The species of the Australian endemic genus Limnadopsis and Australian Limnadia species form a monophylum. This suggests that the origin of Limnadopsis lies in Australia and that Limnadia is not monophyletic.

Flying with the birds? Recent large-area dispersal of four Australian Limnadopsis species (Crustacea: Branchiopoda: Spinicaudata)

Temporary water bodies are important freshwater habitats in the arid zone of Australia. They harbor a distinct fauna and provide important feeding and breeding grounds for water birds. This paper assesses, on the basis of haplotype networks, analyses of molecular variation and relaxed molecular clock divergence time estimates, the phylogeographic history, and population structure of four common temporary water species of the Australian endemic clam shrimp taxon Limnadopsis in eastern and central Australia (an area of >1,350,000 km2). Mitochondrial cytochrome c oxidase subunit I sequences of 413 individuals and a subset of 63 nuclear internal transcribed spacer 2 sequences were analyzed. Genetic differentiation was observed between populations inhabiting southeastern and central Australia and those inhabiting the northern Lake Eyre Basin and Western Australia. However, over large parts of the study area and across river drainage systems in southeastern and central Australia (the Murray–Darling Basin, Bulloo River, and southern Lake Eyre Basin), no evidence of population subdivision was observed in any of the four Limnadopsis species. This indicates recent gene flow across an area of ∼800,000 km2. This finding contrasts with patterns observed in other Australian arid zone taxa, particularly freshwater species, whose populations are often structured according to drainage systems. The lack of genetic differentiation within the area in question may be linked to the huge number of highly nomadic water birds that potentially disperse the resting eggs of Limnadopsis among temporary water bodies. Genetically undifferentiated populations on a large geographic scale contrast starkly with findings for many other large branchiopods in other parts of the world, where pronounced genetic structure is often observed even in populations inhabiting pools separated by a few kilometers. Due to its divergent genetic lineages (up to 5.6% uncorrected p-distance) and the relaxed molecular clock divergence time estimates obtained, Limnadopsis parvispinus is assumed to have inhabited the Murray–Darling Basin continuously since the mid-Pliocene (∼4 million years ago). This means that suitable temporary water bodies would have existed in this area throughout the wet–dry cycles of the Pleistocene.

A secreted antibacterial neuropeptide shapes the microbiome of Hydra

Colonization of body epithelial surfaces with a highly specific microbial community is a fundamental feature of all animals, yet the underlying mechanisms by which these communities are selected and maintained are not well understood. Here, we show that sensory and ganglion neurons in the ectodermal epithelium of the model organism hydra (a member of the animal phylum Cnidaria) secrete neuropeptides with antibacterial activity that may shape the microbiome on the body surface. In particular, a specific neuropeptide, which we call NDA-1, contributes to the reduction of Gram-positive bacteria during early development and thus to a spatial distribution of the main colonizer, the Gram-negative Curvibacter sp., along the body axis. Our findings warrant further research to test whether neuropeptides secreted by nerve cells contribute to the spatial structure of microbial communities in other organisms.Certain neuropeptides, in addition to their neuromodulatory functions, display antibacterial activities of unclear significance. Here, the authors show that a secreted neuropeptide modulates the distribution of bacterial communities on the body surface during development of the model organism Hydra.

A new genus and species of large limnadiid clam shrimp from Australia (Spinicaudata: Limnadiidae)

A large limnadiid, here described as Australimnadia gigantea n. gen., n. sp., is shown to be different from all known Australian Eulimnadia, Paralimnadia, and Limnadopsis, though somewhat similar to the widespread Holarctic species Limnadia lenticularis. It differs from this species in many features, including having the caudal filaments inserted at the 10th spine in the telsonic spine row, numerous long plumose setae on the caudal furca, the common occurrence of males and in the detailed surface morphology of the egg. The morphological uniqueness of A. gigantea is supported molecularly. Australimnadia gigantea is sparsely distributed in northern and eastern Australia.

Spinicaudata (Branchiopoda: Diplostraca) in Australia’s arid zone: unparalleled diversity at regional scales and within water bodies

Multispecies spinicaudatan assemblages, where several species co-occur simultaneously within the same water body, are relatively rarely observed. In part, this can be due to taxonomic impediments and the presence of cryptic species. Several recent studies on Australian Spinicaudata revealed much higher species diversities than previously known for this continent. Herein we summarize the results of three years of extensive sampling within eastern and central Australia, including 232 sampling events from 205 water bodies, and present new genetic data on Eulimnadia and Paralimnadia. Species were delimited following an evolutionary systematics framework using mitochondrial and nuclear markers to identify reproductively isolated species (biological species). Our conservative approach suggests 55 species occurring within central and eastern Australia, which raises the number to about 70 species Australia wide: one third of the known global spinicaudatan diversity. The central Paroo River catchment exhibited the largest spinicaudatan diversity ever observed on a regional scale with 31 species recorded on just approximately 60 km2. Diversities within water bodies are exceptionally high: half of the water bodies feature two or more species, with up to seven species and up to four congeners co-occurring simultaneously. Such diversities within water bodies have never been observed before for Spinicaudata. When a water body was sampled multiple times or when sediment samples were artificially incubated, the total species count was further increased (up to eight species). Nevertheless, most species are mutually exclusive, suggesting competition and/or restrictive habitat requirements are responsible for shaping spinicaudatan communities.

Stochastic effects associated with resting egg banks lead to genetically differentiated active populations in large branchiopods from temporary water bodies

For Branchiopoda (Crustacea) and other taxa with resting egg banks, genetic differentiation among populations has been commonly observed at small geographic scales. This has been explained by a combination of priority effects and local adaptation. However, stochastic effects associated with hatching from resting egg banks may distort estimates of genetic differentiation. Herein we assessed the genetic composition and differentiation of subsequent active populations of two spinicaudatan species within a temporary water body in eastern Australia by sequencing mitochondrial cytochrome c oxidase subunit I and compared it to the differentiation among populations. Furthermore, a simulation was performed in which the genetic differentiation between active populations derived from resting egg banks of identical genetic composition was assessed. Genetic differentiation between subsequent active populations of the same water body was significant and of similar magnitude as among neighboring populations, all simulated active populations were significantly differentiated from each other. Stochastic effects associated with hatching from resting egg banks combined with genetic drift can lead to significantly differentiated active populations, even if the genetic composition of their resting egg banks was identical. As a consequence, genetic differentiation among populations may often be overestimated due to stochastic effects, which in turn may result in underestimations of gene flow.

Molecular and morphological delimitation of Australian Triops species (Crustacea: Branchiopoda: Notostraca)—large diversity and little morphological differentiation

Australia has a very rich and diverse large branchiopod fauna with approximately 140 described or provisionally delimited species, but only one species of Triops, Triops australiensis (Spencer and Hall 1895), is currently recognized. Previous studies identified extensive genetic diversity within T. australiensis that suggested the presence of cryptic species. Herein, we employed an integrative approach to taxonomy to delimit putative species, integrating COI and EF1α sequence data and morphological data. Putative species were initially delimited based on COI by two computational approaches (GMYC and ABGD). The results were interpreted in the light of several species concepts, with particular emphasis on reproductive isolation. Twenty to 27 genetic lineages were delimited. Of these, up to 26 represent species following an evolutionary or phylogenetic species concept. Eighteen are biological species, though reproductive isolation could not be unambiguously established for allopatric species or species without known males. The level of co-occurrences was exceptionally high for Triops, with up to three syntopic and six sympatric species. Species delimitation was impeded by extensive overlap between intraspecific variability and interspecific variation in the genetic as well as morphological datasets. Without prior delimitation of putative species via COI, morphological delimitation would have been impossible. A potential explanation for the morphological variability is the retention of ancestral polymorphisms over long periods of time and across multiple speciation events without subsequent differentiation.

Evolution, classification, and global diversity of large Branchiopoda

We introduce this Branchiopoda Special Issue of the Journal of Crustacean Biology, providing a brief outline of the 13 research papers presented at the 8 th International Crustacean Congress in Frankfurt, Germany, August 2014. We also discuss the current status and direction of research on the large branchiopod crustaceans.

Phylogeny and species diversity of Tasmanian mountain shrimps and their relatives (Crustacea, Anaspidesidae)

Anaspidacea is an enigmatic taxon within Malacostraca with uncertain phylogenetic affinities. One of the four families within Anaspidacea, the Anaspidesidae (representing in most respects the plesiomorphic conditions of the entire taxon), is endemic to Tasmania and shows a remarkable geographical and vertical distribution. Eleven species in three genera (Allanaspides, Anaspides and Paranaspides) are recognized to date, occurring in freshwater habitats such as lakes, rivers, streams, tarns and also in caves. We present the most detailed analyses to date of the phylogeny of Anaspidesidae including all eleven species based on molecular data (COI, 16S and 28S). In addition, the genetic differentiation within the morphologically recognized species is studied and a dating of speciation is given using a molecular clock approach (based on mt‐DNA only). A special focus is on the multiple instances of immigration into the subterranean habitat. Most of the morphologically delineated species are recognized by molecular data. Significantly, however, in at least two cases, the molecular data suggest more species than so far described, but further molecular sampling from a wider range of localities is required. Our molecular divergence estimates suggest the anaspidesids are younger than previously thought. Rather than having Eocene origins, our results suggest Early Miocene origins with primary diversification in Miocene and Pliocene. Entry into subterranean habitats appears to have occurred in the Pleistocene rather than Tertiary. Thus, rather than being a defensive response to rising temperatures in the Tertiary, entry into caves in the Pleistocene may represent opportunistic expansion into new habitats created by the action of glacial meltwaters on existing karst formations. As a result, environmental changes during the Pleistocene appear to have prompted ecological expansion of Anaspides by “opening” new subterranean habitats leading to increased diversification in the group.