Elucidating stygofaunal trophic web interactions via isotopic ecology

© 2019 Saccò et al. Subterranean ecosystems host highly adapted aquatic invertebrate biota which play a key role in sustaining groundwater ecological functioning and hydrological dynamics. However, functional biodiversity studies in groundwater environments, the main source of unfrozen freshwater on Earth, are scarce, probably due to the cryptic nature of the systems. To address this, we investigate groundwater trophic ecology via stable isotope analysis, employing δ13C and δ15N in bulk tissues, and amino acids. Specimens were collected from a shallow calcrete aquifer in the arid Yilgarn region of Western Australia: a well-known hotspot for stygofaunal biodiversity. Sampling campaigns were carried out during dry (low rainfall: LR) and the wet (high rainfall: HR) periods. δ13C values indicate that most of the stygofauna shifted towards more 13C-depleted carbon sources under HR, suggesting a preference for fresher organic matter. Conversion of δ15N values in glutamic acid and phenylalanine to a trophic index showed broadly stable trophic levels with organisms clustering as low-level secondary consumers. However, mixing models indicate that HR conditions trigger changes in dietary preferences, with increasing predation of amphipods by beetle larvae. Overall, stygofauna showed a tendency towards opportunistic and omnivorous habits- typical of an ecologically tolerant community-shaped by bottom-up controls linked with changes in carbon flows. This study provides baseline biochemical and ecological data for stygofaunal trophic interactions in calcretes. Further studies on the carbon inputs and taxaspecific physiology will help refine the interpretation of the energy flows shaping biodiversity in groundwaters. This will aid understanding of groundwater ecosystem functioning and allow modelling of the impact of future climate change factors such as aridification

Refining trophic dynamics through multi-factor Bayesian mixing models: A case study of subterranean beetles

© 2020 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd Food web dynamics are vital in shaping the functional ecology of ecosystems. However, trophic ecology is still in its infancy in groundwater ecosystems due to the cryptic nature of these environments. To unravel trophic interactions between subterranean biota, we applied an interdisciplinary Bayesian mixing model design (multi-factor BMM) based on the integration of faunal C and N bulk tissue stable isotope data (d13C and d15N) with radiocarbon data (?14C), and prior information from metagenomic analyses. We further compared outcomes from multi-factor BMM with a conventional isotope double proxy mixing model (SIA BMM), triple proxy (d13C, d15N, and ?14C, multi-proxy BMM), and double proxy combined with DNA prior information (SIA + DNA BMM) designs. Three species of subterranean beetles (Paroster macrosturtensis, Paroster mesosturtensis, and Paroster microsturtensis) and their main prey items Chiltoniidae amphipods (AM1: Scutachiltonia axfordi and AM2: Yilgarniella sturtensis), cyclopoids and harpacticoids from a calcrete in Western Australia were targeted. Diet estimations from stable isotope only models (SIA BMM) indicated homogeneous patterns with modest preferences for amphipods as prey items. Multi-proxy BMM suggested increased—and species-specific—predatory pressures on amphipods coupled with high rates of scavenging/predation on sister species. SIA + DNA BMM showed marked preferences for amphipods AM1 and AM2, and reduced interspecific scavenging/predation on Paroster species. Multi-factorial BMM revealed the most precise estimations (lower overall SD and very marginal beetles' interspecific interactions), indicating consistent preferences for amphipods AM1 in all the beetles' diets. Incorporation of genetic priors allowed crucial refining of the feeding preferences, while integration of more expensive radiocarbon data as a third proxy (when combined with genetic data) produced more precise outcomes but close dietary reconstruction to that from SIA + DNA BMM. Further multidisciplinary modeling from other groundwater environments will help elucidate the potential behind these designs and bring light to the feeding ecology of one the most vital ecosystems worldwide

Measuring proper motions of isolated neutron stars with Chandra

The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray sources. We took advantage of this capability to constrain the proper motion of RX J0806.4-4123 and RX J0420.0-5022, two X-ray bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper, we present results from a preliminary analysis from which we derive 2 sigma upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4-4123 and RX J0420.0-5022 respectively. We use these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably consistent with those of 'normal' pulsars. Their distribution on the sky and, for those having accurate proper motion vectors, their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the earth.Comment: 8 pages, 3 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zan

Differential transcriptomic responses to heat stress in surface and subterranean diving beetles

Subterranean habitats are generally very stable environments, and as such evolutionary transitions of organisms from surface to subterranean lifestyles may cause considerable shifts in physiology, particularly with respect to thermal tolerance. In this study we compared responses to heat shock at the molecular level in a geographically widespread, surface-dwelling water beetle to a congeneric subterranean species restricted to a single aquifer (Dytiscidae: Hydroporinae). The obligate subterranean beetle Paroster macrosturtensis is known to have a lower thermal tolerance compared to surface lineages (CTmax 38 °C cf. 42–46 °C), but the genetic basis of this physiological diference has not been characterized. We experimentally manipulated the thermal environment of 24 individuals to demonstrate that both species can mount a heat shock response at high temperatures (35 °C), as determined by comparative transcriptomics. However, genes involved in these responses difer between species and a far greater number were diferentially expressed in the surface taxon, suggesting it can mount a more robust heat shock response; these data may underpin its higher thermal tolerance compared to subterranean relatives. In contrast, the subterranean species examined not only diferentially expressed fewer genes in response to increasing temperatures, but also in the presence of the experimental setup employed here alone. Our results suggest P. macrosturtensis may be comparatively poorly equipped to respond to both thermally induced stress and environmental disturbances more broadly. The molecular fndings presented here have conservation implications for P. macrosturtensis and contribute to a growing narrative concerning weakened thermal tolerances in obligate subterranean organisms at the molecular level.Perry G. Beasley-Hall, Terry Bertozzi, Tessa M. Bradford, Charles S. P. Foster, Karl Jones, Simon M.Tierney, William F. Humphreys, Andrew D.Austin, Steven J. B. Coope

The effects of conflict role and intensity on preschoolers’ expectations about peer conflict

Using a puppet procedure depicting hypothetical conflict involving the participant and a peer, 96 preschoolers’ (48 boys and 48 girls; M 1/4 5.14 years, SD 1/4 0.78 years) expectations about peer conflict were assessed as a function of their role in the conflict (i.e., initiator of or responder to initial provocation) and the intensity level of the conflict. Initiators of conflict expected less conflict escalation and subsequent problems with the same peer from the conflict than did responders, particularly following low-intensity conflict. Findings also indicated that, for low-intensity but not high-intensity conflict, girls expected the same peer to provoke them during a subsequent interaction more often than did boys. Results provide further support for assessing preschoolers’ understanding of conflict and are consistent with previous work demonstrating a self-serving bias in young children’s perceptions and reports of their conflicts with other children. Moreover, findings are discussed in terms of their implications for the development of peer relations.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Subterranean fauna of Christmas Island: habitats and salient features

A review is presented of the history of subterranean fauna exploration, the nature of the subterranean environments of Christmas Island and the biogeographical significance of members of the subterranean and springdependent species. The island, which has probably been emergent since the mid-Miocene, has a basalt core largely covered by Tertiary carbonates which have undergone intense karstification owing to the high rainfall on tropical forest, and through mixing corrosion as relative sea level changed and marine terraces formed as a result of tectonic uplift of the island. As a result, surface water is largely absent and drainage is largely as submarine groundwater discharge, however, there is a perched underground stream tapped for water on the plateau and some spring discharge on lower terraces where basalt intercepts the carbonate surface. Together these provide a range of subterranean habitats including terrestrial, freshwater streams and anchialine systems, in addition to springs and spring rills. Terrestrial caves shelter glossy swiftlets that support a rich guano-based community. Sediment banks and the tree root mats spreading over them support a community, thus far not rich, but containing troglobitic species, including the cockroach Metanocticola (Blattodea), scorpion (Ischnuridae), pseudoscorpions (Chthoniidae), microwhipscorpion (Hubbardiidae), spiders (from families Symphytognathidae; Trochanteriidae; Ochyroceratidae; Oonopidae; ?Desidae) and a variety of oniscoid isopods. As expected on an isolated seamount, it supports a procaridiid-type anchialine fauna characterised by an endemic species of Procaris (Procarididae). Unexpectedly, it is the only seamount supporting, in addition, representatives of a remipede-type anchialine fauna, namely Humphreysella (formerly Danielopolina) (Myodocopa: Thaumatocyprididae) and Halosbaena (Thermosbaenacea). In addition, the anchialine system supports the only known extant population of Microceratina (Podocopida: Cytheruridae). The freshwater subterranean stream and spring outlets support an extraordinary diversity of Darwinulidae (Ostracoda). A number of invasive species of fish have been introduced to freshwater areas and if established in springs could have a detrimental impact of stygiofauna and potentially invade anchialine waters. Direct anthropogenic impacts on caves is low owing to minimal caving activity on the island but the most sensitive to trampling are root mats and sediment banks in some caves, and especially guano piles, the disturbance to which could extend to glossy swiftlet colonies. Indirect impacts on fauna may occur owing to changes to the spring discharges as a result of water abstraction which could also impinge on the anchialine system by changing the hydrodynamic relationships between freshwater outflow and seawater, and through contaminants arising from land or sea.William F. Humphrey

Troglobitic millipedes (Diplopoda: Paradoxosomatidae) from semi-arid Cape Range, Western Australia: systematics and biology

Paradoxosomatid millipedes are an important component of the rich troglobitic fauna of the semi-arid tropical Cape Range, Western Australia. They are found in at least 55 of the 282 caves known from Cape Range covering >500 km2. The millipedes occur in dense populations only in areas of high relative humidity and organic carbon content. They appear to be opportunistic and are able to grow and breed rapidly on the intermittently available patches of organic matter washed into the caves by unpredictable rainfall. A new genus of paradoxosomatid millipedes (Stygiochiropus, gen. nov.), comprising three species (S. communis, sp. nov., S. sympatricus, sp. nov., and S. isolatus, sp. nov.) is described from the caves. A key is provided for males, but females cannot be identified. The only widespread species (S. communis) separates into three provinces between which there are many fixed allelic differences, as determined by allozyme electrophoresis. Although these genetic provinces are separated by deep gorges that cut through the cavernous limestone into the underlying non-cavernous strata, the millipede populations cannot be separated using morphological criteria. The affinities of the millipedes are unknown, but they are part of a rich community of troglobites (>26 species) of which many species have affinities with the northern wet tropical forest fauna, rather than with the current semi-arid fauna.W. F. Humphreys and W. A. Shea