Characteristics of methane and carbon dioxide in ice caves at a high-mountain glacier of China.

The exploration of the spatiotemporal distribution of greenhouse gas (GHG) exchange in the cryosphere (including ice sheet, glaciers, and permafrost) is important for understanding its future feedback to the atmosphere. Mountain glaciers and ice sheets may be potential sources of GHG emissions, but the magnitude and distribution of GHG emissions from glaciers and ice sheets remain unclear because observation data are lacking. In this study, in situ CH4 and CO2 and the mixing ratios of their carbon isotope signatures in the air inside an ice cave were measured, and CH4 and CO2 exchange in the meltwater of Laohugou glacier No. 12, a high-mountain glacier in an arid region of western China, was also analyzed and compared with the exchange in downstream rivers and a reservoir. The results indicated elevated CH4 mixing ratios (up to 5.7 ppm) and depleted CO2 (down to 168 ppm) in the ice cave, compared to ambient levels during field observations. The CH4 and CO2 fluxes in surface meltwater of the glacier were extremely low compared with their fluxes in rivers from the Tibetan Plateau (TP). CH4 and CO2 mixing ratios in the air inside the ice cave were mainly controlled by local meteorological conditions (air temperature, wind speed and direction) and meltwater runoff. The carbon isotopic compositions of CH4 and CO2 in the ice cave and terminus meltwater indicated δ13C-CH4 depletion compared to ambient air, suggesting an acetate fermentation pathway. The abundances of key genes for methanogenic archaea/genes encoding methyl coenzyme M reductase further indicated the production of CH4 by methanogenic archaea from the subglacial meltwater of high-mountain glaciers. The discovery of CH4 emissions from even small high-mountain glaciers indicates a more prevalent characteristic of glaciers to produce and release CH4 from the subglacial environment than previously believed. Nevertheless, further research is required to understand the relationship between this phenomenon and glacial dynamics in the third pole.

The behavioural costs of overcrowding for gregarious cave-dwelling bats.

Bats are known for their gregarious social behaviour, often congregating in caves and underground habitats, where they play a pivotal role in providing various ecosystem services. Studying bat behaviour remains an underexplored aspect of bat ecology and conservation despite its ecological importance. We explored the costs and impacts of overcrowding on bat social behaviour. This study examined variations in bat behavioural patterns between two distinct groups, aggregated and non-aggregated male Rousettus amplexicaudatus, within the Monfort Bat Cave Sanctuary on Mindanao Island, Philippines. We found significant variations in the incident frequencies of various bat behavioural activities, particularly aggression and movement, between these two groups. The increase in aggregation was closely related to negative social behaviour among bats. In contrast, sexual behaviour was significantly related to the positive behaviour of individual bats and was headed in less crowded areas. The disparities in bat behaviour with an apparent decline in bat social behaviour because of overcrowding, with more aggressive behaviours emerging, align with the 'behavioural sink' hypothesis. Our study underscores the importance of considering habitat quality and resource availability in the management and conservation of bat colonies, as these factors can reduce the occurrence of aggressive and negative social behaviours in colonies with high population density by providing alternative habitats.

Sexual dimorphism in subterranean amphipod crustaceans covaries with subterranean habitat type.

Sexual dimorphism can evolve in response to sex-specific selection pressures that vary across habitats. We studied sexual differences in subterranean amphipods Niphargus living in shallow subterranean habitats (close to the surface), cave streams (intermediate), and cave lakes (deepest and most isolated). These three habitats differ because at greater depths there is lower food availability, reduced predation, and weaker seasonality. Additionally, species near the surface have a near-even adult sex ratio (ASR), whereas species from cave lakes have a female-biased ASR. We hypothesized (a) a decrease in sexual dimorphism from shallow subterranean habitats to cave lake species because of weaker sexual selection derived from changes in the ASR and (b) an increase in female body size in cave lakes because of stronger fecundity selection on account of oligotrophy, reduced predation, and weaker seasonality. We measured body size and two sexually dimorphic abdominal appendages for all 31 species and several behaviours related to male competition (activity, risk-taking, exploration) for 12 species. Species with an equal ASR that live close to the surface exhibited sexual dimorphism in all three morphological traits, but not in behaviour. The body size of females increased from the surface to cave lakes, but no such trend was observed in males. In cave lake species, males and females differed neither morphologically nor behaviourally. Our results are consistent with the possibility that sexual and fecundity selection covary across the three habitats, which indirectly and directly, respectively, shape the degree of sexual dimorphism in Niphargus species.

Microplastic pollution calls for urgent investigations in stygobiont habitats: A case study from Classical karst.

Microplastic pollution in karst systems is still poorly studied, despite the presence of protected species and habitats, and important water reserves. Vulnerable key species hosted in these habitats could consume or assimilate microplastics, which can irreversibly damage management efforts, and thus ecosystems functionality. This can be particularly true for subterranean water habitats where microplastic pollution effects on wildlife management programs are not considered. The aim of this study is to provide a case study from the Classical Karst Region, which hosts peculiar habitats and key species protected at European level, such as the olm Proteus anguinus. As this area has been deeply exploited and modified over time, and is adjacent to highways, roads and railways, which could contribute to pollution within the karst system, threatening the ecosystems, it provides a perfect model system. In this study we collected and investigated water and sediment samples from aquatic environments of surface and subterranean habitats hosting several subterranean environment-adapted organisms. Examined particles were counted and characterized by size, color and shape via visual identification under a microscope, with and without UV light. Furthermore, spectroscopic analyses were carried out in order to identify microplastics typology. Microplastics were found in all examined habitats. In water, microplastics concentration ranged from 37 to 86 items/L, in sediments from 776 to 2064 items/kg. Fibre-shape was the main present, followed by fragments and beads, suggesting multiple sources of pollution, especially textile products. Most of the particles were fluorescent under UV light and were mainly transparent, while not-fluorescent ones were especially black, blue or brown. Samples contained especially polyesters and copolymers. These results highlight intense MP pollution in karst areas, with significant impacts on water quality, and potential effects on subterranean environment-dwelling species. We stress the importance of monitoring pollution in these critical environments for biodiversity and habitat conservation: monitoring in karst areas must become a priority for habitat and species protection, and water resources management, improving analyses on a larger number of aquatic surface and subterranean habitats.

Integrative taxonomy reveals first record of Loxoscelesrufescens (Dufour, 1820) (Araneae, Sicariidae) in the Philippines.

Background: The spider family Sicariidae Keyserling, 1880 represented by the synanthropic Mediterranean recluse spider, Loxoscelesrufescens (Dufour, 1820), is reported in the Philippines for the first time, based on morphological and molecular data. The introduced spider was observed in a small cave (Kamantigue Cave) in Lobo, Batangas Province. Considering the medical importance of this spider, the proximity of its habitat to human habitation and tourist sites poses a potential public health concern. New information: This study reports on the first record of the family Sicariidae in the Philippines and the fourth recorded occurrence of L.rufescens in Southeast Asia.

Discriminating organic carbon from endokarstic moonmilk-type deposits by LIBS. The case of a natural carbonated Martian analogue.

Moonmilk-type deposits exemplify carbonated Martian analogues existing in the subsurface of Earth, an endokarstic speleothem with a possible biochemical origin composed principally by carbonates, mainly huntite and dolomite. In this work, samples of moonmilk located in Nerja Cave (southern Spain) have been studied by LIBS with the aim of identifying carbon of biogenic origin by establishing a relationship between a molecular emission indicator, CN signal, and the organic carbon content. The characterization of this kind of carbonate deposit with a multiple mineralogical composition has been completed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction techniques for qualitative and semi-quantitative analysis. The information attained from LIBS regarding energy thresholds and time-resolved kinetics of CN emissions provides useful insight into the identification of different molecular emitters, namely organic and inorganic CN, depending on the laser irradiance and time settings conditions. These promising results are of application in the search and identification of biosignatures in upcoming planetary missions with astrobiological purposes.

Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave.

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces - the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11-6653 by Bq m-3 and 10-89,020 Bq m-3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process - convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Connecting molecular biomarkers, mineralogical composition, and microbial diversity from Mars analog lava tubes.

Lanzarote (Canary Islands, Spain) is one of the best terrestrial analogs to Martian volcanology. Particularly, Lanzarote lava tubes may offer access to recognizably preserved chemical and morphological biosignatures valuable for astrobiology. By combining microbiological, mineralogical, and organic geochemistry tools, an in-depth characterization of speleothems and associated microbial communities in lava tubes of Lanzarote is provided. The aim is to untangle the underlying factors influencing microbial colonization in Earth's subsurface to gain insight into the possibility of similar subsurface microbial habitats on Mars and to identify biosignatures preserved in lava tubes unequivocally. The microbial communities with relevant representativeness comprise chemoorganotrophic, halophiles, and/or halotolerant bacteria that have evolved as a result of the surrounding oceanic environmental conditions. Many of these bacteria have a fundamental role in reshaping cave deposits due to their carbonatogenic ability, leaving behind an organic record that can provide evidence of past or present life. Based on functional profiling, we infer that Crossiella is involved in fluorapatite precipitation via urea hydrolysis and propose its Ca-rich precipitates as compelling biosignatures valuable for astrobiology. In this sense, analytical pyrolysis, stable isotope analysis, and chemometrics were conducted to characterize the complex organic fraction preserved in the speleothems and find relationships among organic families, microbial taxa, and precipitated minerals. We relate organic compounds with subsurface microbial taxa, showing that organic families drive the microbiota of Lanzarote lava tubes. Our data indicate that bacterial communities are important contributors to biomarker records in volcanic-hosted speleothems. Within them, the lipid fraction primarily consists of low molecular weight n-alkanes, α-alkenes, and branched-alkenes, providing further evidence that microorganisms serve as the origin of organic matter in these formations. The ongoing research in Lanzarote's lava tubes will help develop protocols, routines, and predictive models that could provide guidance on choosing locations and methodologies for searching potential biosignatures on Mars.

Bridging Place-Based Astrobiology Education with Genomics, Including Descriptions of Three Novel Bacterial Species Isolated from Mars Analog Sites of Cultural Relevance.

Democratizing genomic data science, including bioinformatics, can diversify the STEM workforce and may, in turn, bring new perspectives into the space sciences. In this respect, the development of education and research programs that bridge genome science with "place" and world-views specific to a given region are valuable for Indigenous students and educators. Through a multi-institutional collaboration, we developed an ongoing education program and model that includes Illumina and Oxford Nanopore sequencing, free bioinformatic platforms, and teacher training workshops to address our research and education goals through a place-based science education lens. High school students and researchers cultivated, sequenced, assembled, and annotated the genomes of 13 bacteria from Mars analog sites with cultural relevance, 10 of which were novel species. Students, teachers, and community members assisted with the discovery of new, potentially chemolithotrophic bacteria relevant to astrobiology. This joint education-research program also led to the discovery of species from Mars analog sites capable of producing N-acyl homoserine lactones, which are quorum-sensing molecules used in bacterial communication. Whole genome sequencing was completed in high school classrooms, and connected students to funded space research, increased research output, and provided culturally relevant, place-based science education, with participants naming three novel species described here. Students at St. Andrew's School (Honolulu, Hawai'i) proposed the name Bradyrhizobium prioritasuperba for the type strain, BL16AT, of the new species (DSM 112479T = NCTC 14602T). The nonprofit organization Kauluakalana proposed the name Brenneria ulupoensis for the type strain, K61T, of the new species (DSM 116657T = LMG = 33184T), and Hawai'i Baptist Academy students proposed the name Paraflavitalea speifideiaquila for the type strain, BL16ET, of the new species (DSM 112478T = NCTC 14603T).

Characteristics of submerged and partially submerged caves (habitat type 8330) in Romania.

Underwater sea caves form a relatively under-examined habitat type within the marine regions of Europe, although they provide unique physical conditions such as reduced light and wave energy, in addition to reduced temperature amplitude. This study aimed at revealing the characteristics of submerged cavities on the southern Romanian continental shelf where six protected areas exist. We used high-resolution bathymetry data and side-scan sonar imaging to identify limestone outcrops where cavities would be most probable to form and then performed visual observation during SCUBA diving activities. We found that submerged cavities appear in all marine-protected areas and their neighboring unprotected areas from the shore to ~20-m depth mostly in the form of caverns, niches, and overhangs that meet the physical requirements of the habitat type 8330 as defined by the European Commission. We propose that habitat type 8330 should be listed in the Natura 2000 Standard Data Forms of the protected areas where it is missing, and we also propose that some protected areas should be expanded to include important areas with the occurrence of this habitat type. Finally, we note here for the first time the occurrence of Movile-type karst and an associated sulfidic water spring on the southern shore of Lake Techirghiol, similar to the region near Mangalia where it was first described in the literature. Although our finding prompts for a more detailed study, it indicates the existence of an underground ecosystem similar to that from the well-studied Movile Cave, but isolated by a distance of over 20 km.

A New Species of Spelaeometra Polhemus & Ferreira, 2018 (Hemiptera: Heteroptera: Hydrometridae) from a Hotspot of Troglobites in Brazil, Serra do Ramalho Karst Area.

Spelaeometra Polhemus & Ferreira, 2018 (Hemiptera: Heteroptera: Hydrometridae) is a monotypic and troglobitic genus, recently described based on material collected in the state of Minas Gerais, Brazil. From specimens collected in the Gruna do Enfurnado Cave in the Serra do Ramalho karst area, municipality of Coribe, state of Bahia, Brazil, we describe Spelaeometra hypogea Cordeiro & Moreira, sp. nov. and compare it with Spelaeometra gruta Polhemus & Ferreira, 2018. The new species is diagnosed by the general body color being pale-yellow to light-brown; antennal segments I and II being subequal in length; the reduced gular lobe, not covering any labial segment; the male proctiger without apical projections; and the male paramere with convex dorsal margin after the curvature, with a narrow hook-like apex.

Design and optimization of an improved qPCR assay for the detection of Histoplasma capsulatum.

Background: This study aimed at improving a real-time polymerase-chain-reaction (qPCR) assay for the detection of Histoplasma capsulatum, a fungal pathogen that can cause severe respiratory infections in humans, in clinical and soil samples. Methods: Primer and probes were in-silico designed, in-silico and in-vitro evaluated including clinical biopsy materials and finally subjected to a real-world application with collected soil samples. Results: Applying the qPCR assay with liver and lung biopsies from 71 patients each, including 59 patients infected with human immunodeficiency virus (HIV), as well as with Sabouraud (SAB) agar culture as the diagnostic reference standard, diagnostic accuracy of the qPCR assay of 100% (5/5) sensitivity and 96% (63/66) specificity for liver samples and 100% (4/4) sensitivity and 94% (63/67) specificity for the lung samples was recorded. When applying the assay with soil samples from caves near of Presidente Figueiredo city, Amazonas, Brazil, one sample from the Maroaga cave was confirmed as positive. Conclusions: The improved qPCR assessed in this study was successful in detecting H. capsulatum with high efficiency and accuracy in in-vitro evaluation, including the identification of the target pathogen in both clinical and environmental samples.

A New Species of Bryaxis (Coleoptera: Staphylinidae: Pselaphinae) from Mount Etna (Sicily, Italy) and Notes on Its Ecology and Distribution.

A new species of the subfamily Pselaphinae (Coleoptera: Staphylinidae) has been discovered on Mount Etna (Sicily, Italy) and is described herein as Bryaxis aetnensis sp. nov. The new species is closely associated with the Bryaxis difficilis group, a highly homogeneous group of species living in the regions of Sicily and Sardinia. Diagnostic features and distribution of Sicilian species of this group are treated and illustrated herein. Bryaxis aetnensis sp. nov. exhibits similarities to B. marinae but can be distinguished by the darker color, longer antennal scape and terminal palpomere, and in the aedeagus morphology. The distribution of B. aetnensis sp. nov. spans a wide altitudinal range, demonstrating a remarkable climatic tolerance across the slopes and diverse habitats of Mount Etna. This broad tolerance reflects the species' probable high ecological plasticity, which may also contribute to the observed morphological variability among individuals from different sampling sites. The significance of this new discovery on Mount Etna highlights the need to intensify sampling efforts in the region. Strengthening protection for these unexplored environments is crucial, and it also aids in unraveling biogeographic questions about the fauna inhabiting the area. As a relatively young volcanic environment, species colonization has occurred recently, making it an intriguing subject of investigation.

A Hansel & Gretel breadcrumb-style dynamically deployed communication network paradigm using mesh topology for planetary subsurface exploration.

We introduce a dynamically deployed communication network (DDCN) paradigm using mesh topology in support of a distributed robotic multi-agent approach for the autonomous exploration of subsurface environments, i.e., caves, lava tube caves, lakes, and oceans, etc. The DDCN, comprising wireless communication beacons autonomously deployed via a rover or submersible in a Hansel & Gretel-inspired breadcrumb style, allows for the longest and most robust communication link between subterranean robotic agent(s) within, e.g., a lave tube cave or a subsurface ocean, and associated surface-borne robotic agent(s). Moreover, we briefly touch on the development of a robotic testbed and wired/wireless communication beacons in support of such astrobiological surface/subsurface exploration scenarios. Candidate lava tube caves have been identified on the Moon and Mars, raising possibilities for planetary exploration, astrobiology, habitat construction for future astronauts, and potential mining operations. Subterranean caverns, and in particular relatively deep lava tube caves, provide a possible refuge for life under otherwise challenging planetary surface conditions, and, as such, are of prime astrobiological relevance. Lava tube caves or other subsurface environments may also be suitable habitats for astronauts and subsequent human settlement but are yet to be explored in part due to difficulties ensuring continued communication with a robotic probe inside these environments. Moreover, the existence of subsurface oceans on ocean worlds, such as Europa, Enceladus, and Titan, has been backed by varying levels of evidence since the 1980s, though there has been no confirmation, i.e., direct observation, thus far. Such environments are also shielded from radiation, and, in combination with the hypothesized presence of water, are additional candidate environments for finding extant or fossilized life. The DDCN paradigm introduced herein directly addresses NASA's Space Technology Grand Challenges - "All Access Mobility" by enabling the most unconstrained exploration of subsurface environments through a dynamic communication network which ensures transmission of data from and possibly commands to the subsurface robotic probe. 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

A Q fever outbreak among visitors to a natural cave, Bizkaia, Spain, December 2020 to October 2021.

We describe a large Q fever outbreak reported in Spain, including 108 cases, 53 with pneumonia and 27 requiring hospitalisations. The first cases were detected in February 2021 among rock climbers visiting a cave in Bizkaia, and the last case was detected in October 2021. Most cases were notified after the Easter holiday (April-May 2021). More males (63.9%) than females (36.1%) were infected (median ages: 42 (1-68) and 39 years (6-61), respectively). We detected Coxiella burnetii by PCR in faecal, dust and/or aerosol samples taken inside the cave in March 2021, and in dust and aerosol samples collected between March 2021 and February 2023. Coxiella burnetii from dust samples were cultured on Vero cells, showing viability for 24 months. Based on serological and genotyping data, goats sheltering in the cave were the most likely source of infection. The cave was closed on 29 April 2021, movements of goats and sheep in the area were restricted (March-July 2021), and the animals were vaccinated in October 2021. Investigation of Q fever outbreaks requires a multidisciplinary One Health approach as these outbreaks can occur in unexpected places like natural sites where animals are present.

Impact of limestone caves and seawater intrusion on coastal aquifer of middle Andaman.

Seawater intrusion has become a common problem in coastal and island aquifers with the rise in climate change that greatly affects the majority of developing countries. The island hydrology is very complex and associated with a unique set of environmental characteristics with the dynamic interaction of groundwater, surface water, and seawater. Further, Sea level rise, erratic rainfall, and over-extraction of groundwater triggered salt-water intrusion. A study on seawater intrusion and the effect of limestone caves on groundwater was carried out in middle Andaman using a combination of ionic ratios of major ions. A total of 24 samples and a reference sample from the sea were collected and analysed using ICP, spectrophotometer, and flame photometer. A combination of 10 ionic ratios Cl/HCO3, Ca/(HCO3 + SO4), (Ca + Mg)/Cl, Ca/Mg, Ca/Na, Cl/(SO4 + HCO3), Ca/SO4, K/Cl, Mg/Cl, and SO4/Cl was used to assess the dissolution of limestone minerals and the level of saltwater intrusion into groundwater. The geospatial method was used to extract and combine all the hydrogeochemical parameters and ionic ratios in the GIS platform. Durov plot was used for the interpretation of groundwater chemistry and the identification of natural processes controlling the hydrogeochemistry of the area. The dominance of Ca-HCO3 and Na-HCO3 was confirmed in 48% and 24% of the sample respectively. The equiline graph of chloride with other major ions showed the enrichment of alkali and alkaline earth metal salt in groundwater. Schoeller's diagram depicted the dominance of Cl, Ca, and the sum of CO3 and HCO3 in seawater near Mayabunder. The lower concentration of Na with respect to Cl (64%) and Ca (100%) showed the presence of a reverse ion exchange process. Further, the correlation matrix showed a strong relationship between Cl, K, Ca, and Na. The analysis of X-ray diffraction of the rock samples confirmed the presence of limestones such as Aragonite, Calcite, Chlorite, Chromite, Dolomite, Magnetite, and Pyrite in the study area. The integration of ionic ratios showed moderately affected and slightly affected saline regions in 44% and 54% of the region respectively. Finally, the role of tectonic activities and active lineaments connected to the sea was found to play a major role in the intrusion of seawater where interconnected faults created an opening for surface water to recharge groundwater leading to the deep aquifer.

Three new species of cave-adapted pseudoscorpions (Pseudoscorpiones, Chthoniidae) from eastern Yunnan, China.

Three new cave-adapted chthoniid pseudoscorpions from four karst caves of Yunnan Province (China) are described, including detailed diagnosis and illustrations: Tyrannochthoniuscalvatussp. nov. from an unnamed cave and Dongtianfu Cave (Fuyuan County), T.capitosp. nov. from Xianren Cave (Xichou County), and Lagynochthoniusdaidaiensissp. nov. from Daidai Cave (Qiubei County). All three species are endemic to Yunnan. Tyrannochthoniuscalvatussp. nov., lacking the carapaceal antero-median setae and having intercalary teeth on the movable chelal finger only, is a peculiar chthoniid species.

A multidisciplinary approach to the comparison of three contrasting treatments on both lampenflora community and underlying rock surface.

Removing lampenflora, phototrophic organisms developing on rock surfaces in tourist cavities due to the artificial lighting, is a challenge for sustainable and appropriate long-term management of caves. Photosynthetic-based biofilms usually cause rock biodeterioration and an ecological imbalance in cave ecosystems. In this work, a detailed investigation of the effects of the 3 most commonly used lampenflora cleaning operations (NaClO, H2O2 and UVC) was carried out in Pertosa-Auletta Cave (Italy). The application of NaClO showed good disinfection capability over extended periods of time without causing any appreciable rock deterioration. The H2O2 treatment showed to be corrosive for the rock surfaces covered with vermiculation deposits. The chemical alteration of organic and inorganic compounds by H2O2 did not remove biomass, favoring biofilm recovery after three months of treatment. Both NaClO and H2O2 treatments were effective at removing photoautotrophs, although the bacterial phyla Proteobacteria and Bacteroidetes as well as Apicomplexa and Cercozoa among the Eukaryotes, were found to be resistant to these treatments. The UVC treatments did not show any noticeable effect on the biofilms.

Genomic Comparisons Reveal Selection Pressure and Functional Variation Between Nutritional Endosymbionts of Cave-Adapted and Epigean Hawaiian Planthoppers.

Planthoppers in the family Cixiidae (Hemiptera: Auchenorrhyncha: Fulgoromorpha) harbor a diverse set of obligate bacterial endosymbionts that provision essential amino acids and vitamins that are missing from their plant-sap diet. "Candidatus Sulcia muelleri" and "Ca. Vidania fulgoroidea" have been associated with cixiid planthoppers since their origin within the Auchenorrhyncha, whereas "Ca. Purcelliella pentastirinorum" is a more recent endosymbiotic acquisition. Hawaiian cixiid planthoppers occupy diverse habitats including lava tube caves and shrubby surface landscapes, which offer different nutritional resources and environmental constraints. Genomic studies have focused on understanding the nutritional provisioning roles of cixiid endosymbionts more broadly, yet it is still unclear how selection pressures on endosymbiont genes might differ between cixiid host species inhabiting such diverse landscapes, or how variation in selection might impact symbiont evolution. In this study, we sequenced the genomes of Sulcia, Vidania, and Purcelliella isolated from both surface and cave-adapted planthopper hosts from the genus Oliarus. We found that nutritional biosynthesis genes were conserved in Sulcia and Vidania genomes in inter- and intra-host species comparisons. In contrast, Purcelliella genomes retain different essential nutritional biosynthesis genes between surface- and cave-adapted planthopper species. Finally, we see the variation in selection pressures on symbiont genes both within and between host species, suggesting that strong coevolution between host and endosymbiont is associated with different patterns of molecular evolution on a fine scale that may be associated with the host diet.

Cavefishes in Chronobiological Research: A Narrative Review.

Cavefish are vertebrates living in extreme subterranean environments with no light, temperature changes, and limited food. Circadian rhythms in these fish are suppressed in natural habitats. However, they can be found in artificial light-dark cycles and other zeitgebers. The molecular circadian clock has its peculiarities in cavefish. In Astyanax mexicanus, the core clock mechanism is tonically repressed in the caves due to the overactivation of the light input pathway. A lack of functional light input pathway but rather the entrainment of circadian genes' expression by scheduled feeding were revealed in more ancient Phreatichthys andruzzii. Different evolutionarily determined irregularities in the functioning of molecular circadian oscillators can be expected in other cavefish. The unique property of some species is the existence of surface and cave forms. Along with the ease of maintenance and breeding, it made cavefish a promising model for chronobiological studies. At the same time, a divergence of the circadian system between cavefish populations requires the strain of origin to be indicated in further research.