The stenoendemic cave-dwelling planarians (Platyhelminthes, Tricladida) of the Italian Alps and Apennines: Conservation issues

Inferring on Speleomantes Foraging Behavior from Gut Contents Examination

We here provide the first comprehensive analysis and discussion on prey consumed by the European cave salamanders of the genus Speleomantes. Our study stems from the need to shed light on the still unknown foraging behavior adopted by Speleomantes cave salamanders. Starting from the published datasets on gut contents from all Speleomantes species (including hybrids), we here discuss additional information (i.e., species ecology, lower taxonomic level), which were systematically omitted from those data sets. We analyzed a data set consisting of 17,630 records from 49 categories of consumed prey recognized from gut contents of 2060 adults and juveniles Speleomantes. Flying prey accounted for more than 58% of the prey items, while elongated crawling prey accounted for no more than 16% of the diet within a single population. Among the total recognized prey items, only three can be surely ascribed to the group of strictly-cave species (i.e., troglobites), meaning that European cave salamanders mostly forage in surface environment, and therefore represent one of the major drivers of allochthonous organic matter in subterranean environments. Some of the consumed prey seemed to be aquatic, allowing us to hypothesize whether Speleomantes are able to catch prey from a shallow body water. Furthermore, European cave salamanders possess the ability to prey upon taxa characterized by particular anti-predator defenses, while morphological constraints seem to be the most important limit to prey consumption. For each specific case, we provide insights and propose hypotheses concerning the foraging behavior that need to be tested to properly understand the foraging behavior of this cryptic salamanders.

Preliminary investigations of microplastic pollution in karst systems, from surface watercourses to cave waters

Microplastic pollution in different environments has increasingly been documented in detail in recent times, but it is still poorly studied in caves and karst aquifers. To deepen the knowledge of microplastic pollution, for karst environment protection and conservation purposes, we collected and investigated different water samples from a karst area of Italy, considering connected surface and cave waters. Microplastics were extracted from water samples by filtration and subjected to organic matter removal with 15% hydrogen peroxide solution. Microplastics on filters were counted and characterised (size, colour, shape) via visual identification under a microscope, with and without UV light, exploiting fluorescence given by fluorescent whitening additives contained in plastic materials. Finally, spectroscopic analyses were carried out on 10% of the microplastics observed on each filter. The concentration of microplastics in cave waters varied from 12 to 54 items/L, with a mean value of 28 items/L. In the surface water of a tributary, it was of 23 items/L, and in the downstream, it was 29 items/L. Fibres represented the most abundant shape (95.1%) in the karst system waters, and most microplastics (82.9%) were smaller than 1 mm. The majority of the microplastics were fluorescent under UV light (84.8%), and most fluorescent particles were transparent (46%). However, black microplastics (68%) were more common among the non-fluorescent ones. Polyethylene (51.7%) was the main type of microplastics found in the karst system waters. Our results show the presence of microplastics in karst systems and provide useful information for future research. Karst aquifers are open systems, subjected to possible contamination by surface pollutants. Microplastics in karst systems can be consumed by animals, damage ecosystems and contaminate water resources; surface karst areas and underground environments should therefore be monitored and protected, especially regarding the management of water resources. To further understand the sources and transport of microplastics within a karst system, analyses on a greater range of surface and subterranean waters throughout the world are required.

The trophic niche of subterranean populations of Speleomantes italicus

The determination of a species trophic niche can clarify its functional role within a food web and how prey resources are used in relation with the spatial and temporal variability of environmental conditions. This information may result particularly useful for the implementation of conservation plans of endangered species having a cryptic behaviour or living in places difficult to be surveyed. Here we present the first long-term study on the trophic niche of the Italian cave salamander Speleomantes italicus, a strictly protected facultative cave species that seasonally exploits surface environments (e.g., forested areas) as well as both natural and artificial subterranean environments. We analysed the diet variation of six populations of S. italicus inhabiting natural caves, surveyed 24 times in a full year. During the surveys, all sampled individuals were subjected to stomach flushing and the ingested prey were identified and enumerated; furthermore, salamanders' body condition was also evaluated. The results of the analyses provided the first comprehensive, year-round assessment of the diet for a Speleomantes species. Remarkable divergences in terms of trophic niche and body condition were observed between the studied populations. We found a discrepancy in the foraging activity of the populations located in different areas; specifically, the individuals that experienced sub-optimal microclimatic conditions poorly performed in foraging. Furthermore, we found temporal and spatial variability in the body condition of individuals. Our study highlighted a remarkably high spatial and temporal divergence in the trophic habits of conspecific populations, a feature that may represent one of the major factors promoting the variability of multiple population traits.

Thermal acclimation and metabolic scaling of a groundwater asellid in the climate change scenario

Metabolic rate has long been used in animal adaptation and performance studies, and individual oxygen consumption is used as proxy of metabolic rate. Stygofauna are organisms adapted to groundwater with presumably lower metabolic rates than their surface relatives. How stygofauna will cope with global temperature increase remains unpredictable. We studied the thermal acclimation and metabolic scaling with body mass of a stygobitic crustacean, Proasellus lusitanicus, in the climate change scenario. We measured oxygen consumption rates in a thermal ramp-up experiment over four assay temperatures and tested two hypotheses: (i) P. lusitanicus exhibits narrow thermal plasticity, inadequate for coping with a fast-increasing thermal regime; and (ii) oxygen consumption rates scale with the body mass by a factor close to 0.75, as commonly observed in other animals. Our results show that P. lusitanicus has low thermal plasticity in a fast-increasing thermal regime. Our data also suggest that oxygen consumption rates of this species do not follow mass-dependent scaling, potentially representing a new trait of metabolic optimization in groundwater habitats, which are often limited in food and oxygen. Species with limited dispersal capacities and rigid metabolic guilds face extinction risk due to climate change and omitting groundwater ecosystems from climate change agendas emphasizes the unprotected status of stygofauna.

Mapping global conservation priorities and habitat vulnerabilities for cave-dwelling bats in a changing world

Research and media attention is disproportionately focused on taxa and ecosystems perceived as charismatic, while other equally diverse systems such as caves and subterranean ecosystems are often neglected in biodiversity assessments and prioritisations. Highlighting the urgent need for protection, an especially large fraction of cave endemic species may be undescribed. Yet these more challenging systems are also vulnerable, with karsts for example losing a considerable proportion of their area each year. Bats are keystone to cave ecosystems making them potential surrogates to understand cave diversity patterns and identify conservation priorities. On a global scale, almost half (48 %) of known bat species use caves for parts of their life histories, with 32 % endemic to a single country, and 15 % currently threatened. We combined global analysis of cave bats from the IUCN spatial data with site-specific analysis of 1930 bat caves from 46 countries to develop global priorities for the conservation of the most vulnerable subterranean ecosystems. Globally, 28 % of caves showed high bat diversity and were highly threatened. The highest regional concentration of conservation priority caves was in the Palearctic and tropical regions (except the Afrotropical, which requires more intensive cave data sampling). Our results further highlight the importance of prioritising bat caves by incorporating locally collected data and optimising parameter selection (i.e., appropriate landscape features and threats). Finally, to protect and conserve these ecosystems it is crucial that we use frameworks such as this to identify priorities in species and habitat-level and map vulnerable underground habitats with the highest biodiversity and distinctiveness.

Polyhydroxybutyrate-producing cyanobacteria from lampenflora: The case study of the “Stiffe” caves in Italy

This study aimed to estimate the green formation lampenflora of “Stiffe” caves in order to evaluate their suitability as an isolation source of cyanobacteria useful for the production of polyhydroxyalkanoates (PHAs). The cave system was chosen as the sampling site due to its touristic use and the presence of high-impact illuminations. The biofilms and the mats of the illuminated walls were sampled. Samples were investigated by 16S rRNA gene analysis and culturable cyanobacteria isolation. The isolated strains were then screened for the production of PHAs under typical culturing and nutritional starvation. Cultures were checked for PHA accumulation, poly-β-hydroxybutyrate (PHB) presence (infrared spectroscopy), and pigment production. The 16S rRNA gene metabarcoding. Highlighted a considerable extent of the pressure exerted by anthropogenic activities. However, the isolation yielded eleven cyanobacteria isolates with good PHA (mainly PHB)-producing abilities and interesting pigment production rates (chlorophyll a and carotenoids). Under normal conditions (BG11₀), the accumulation abilities ranged from 266 to 1,152 ng mg dry biomass^–1. The optimization of bioprocesses through nutritional starvation resulted in a 2.5-fold increase. Fourier transform infrared (FTIR) studies established the occurrence of PHB within PHAs extracted by cyanobacteria isolates. The comparison of results with standard strains underlined good production rates. For C2 and C8 strains, PHA accumulation rates under starvation were higher than Azospirillum brasilense and similar to Synechocystis cf. salina 192. This study broadened the knowledge of the microbial communities of mats and biofilms on the lightened walls of the caves. These findings suggested that these structures, which are common in tourist caves, could be used to isolate valuable strains before remediation measures are adopted.

Collecting eco-evolutionary data in the dark: Impediments to subterranean research and how to overcome them

Caves and other subterranean habitats fulfill the requirements of experimental model systems to address general questions in ecology and evolution. Yet, the harsh working conditions of these environments and the uniqueness of the subterranean organisms have challenged most attempts to pursuit standardized research.Two main obstacles have synergistically hampered previous attempts. First, there is a habitat impediment related to the objective difficulties of exploring subterranean habitats and our inability to access the network of fissures that represents the elective habitat for the so-called "cave species." Second, there is a biological impediment illustrated by the rarity of most subterranean species and their low physiological tolerance, often limiting sample size and complicating laboratory experiments.We explore the advantages and disadvantages of four general experimental setups (in situ, quasi in situ, ex situ, and in silico) in the light of habitat and biological impediments. We also discuss the potential of indirect approaches to research. Furthermore, using bibliometric data, we provide a quantitative overview of the model organisms that scientists have exploited in the study of subterranean life.Our over-arching goal is to promote caves as model systems where one can perform standardized scientific research. This is important not only to achieve an in-depth understanding of the functioning of subterranean ecosystems but also to fully exploit their long-discussed potential in addressing general scientific questions with implications beyond the boundaries of this discipline.

Planarians, a Neglected Component of Biodiversity in Groundwaters

Underground waters are still one of the most important sources of drinking water for the planet. Moreover, the fauna that inhabits these waters is still little known, even if it could be used as an effective bioindicator. Among cave invertebrates, planarians are strongly suited to be used as a study model to understand adaptations and trophic web features. Here, we show a systematic literature review that aims to investigate the studies done so far on groundwater-dwelling planarians. The research was done using Google Scholar and Web of Science databases. Using the key words “Planarian cave” and “Flatworm Cave” we found 2273 papers that our selection reduced to only 48, providing 113 usable observations on 107 different species of planarians from both groundwaters and springs. Among the most interesting results, it emerged that planarians are at the top of the food chain in two thirds of the reported caves, and in both groundwaters and springs they show a high variability of morphological adaptations to subterranean environments. This is a first attempt to review the phylogeny of the groundwater-dwelling planarias, focusing on the online literature. The paucity of information underlines that scarce attention has been dedicated to these animals. Further revisions, including old papers and books, not available online will be necessary.

Switching from mesopredator to apex predator: how do responses vary in amphibians adapted to cave living?

Abstract

The effective detection of both prey and predators is pivotal for the survival of mesopredators. However, the condition of being a mesopredator is strongly context dependent. Here we focus on two aquatic caudate species that have colonised caves: the Pyrenean newt (Calotriton asper) and the olm (Proteus anguinus). The former maintains both surface and subterranean populations, while only cave-adapted populations of the latter exist. Both species are apex predators in underground waterbodies, while the Pyrenean newt is a mesopredator in surface waterbodies. Shifting to a higher level of the trophic web through colonising caves may promote the loss of anti-predator response against surface apex predators, and an increase in the ability to detect prey. To test these two non-exclusive hypotheses, we integrated classical behavioural characterisations with a novel approach: the assessment of lateralisation (i.e. preference for one body side exposure). Behavioural experiments were performed using laboratory-reared individuals. We performed 684 trials on 39 Pyrenean newts and eight olms. Under darkness and light conditions, we tested how exposure to different chemical cues (predatory fish, prey and unknown scent) affected individuals’ activity and lateralisation. Both cave and surface Pyrenean newts responded to predator cues, while olms did not. In Pyrenean newts, predator cues reduced the time spent in movement and time spent in lateralisation associated with hunting. Our results show that predator recognition is maintained in a species where recently separated populations inhabit environments lacking of higher predators, while such behaviour tends to be lost in populations with longer history of adaptation.

Significance statement

Predator recognition can be maintained in animals adapted to predator free habitats, but varies with their history of adaptation. Species that are not at the apex of the food web can become top predators if they colonise subterranean environments. We compared the behavioural responses of the olm, a strictly cave species with a long underground evolutionary history, and of the Pyrenean newt, a facultative cave species that also has stream-dwelling populations. Moreover, we integrated a classical behavioural characterisation, such as movement detection, with a novel approach: the assessment of lateralisation. While olms do not respond to external predators scent, cave-dwelling newts still recognise it. This clearly indicates that predator recognition is still maintained in species that have colonised predator-free environments more recently.

A preliminary survey of the abundance, diversity and distribution of terrestrial macroinvertebrates of Gcwihaba cave, northwest Botswana

Inventories of cave species and in-depth understanding of cave ecosystems are essential for informing conservation approaches for the unique and vulnerable cave fauna. Gcwihaba cave is the largest cave in Botswana but its ecology is poorly understood. This study set out to provide the first quantitative survey of the cave’s terrestrial macroinvertebrates. Macroinvertebrates were collected from sample sites at 10 m intervals into the cave from the cave entrance. At each site, macroinvertebrates on the cave floor were collected by quadrat sampling while macroinvertebrate from cave walls were collected by visual opportunistic searches. Moisture content, pH and electrical conductivity of the cave floor substrate were measured at each site to examine the influence of the floor properties on the distribution of macroinvertebrates on the cave floor. Twelve species in 10 families and 8 orders of terrestrial macroinvertebrates were collected. The occurrence of taxa varied across the sites, with most taxa occurring in the light and twilight sectors of the cave (within 30 m), whereas the dark sector (beyond 30 m) was dominated by cave cockroaches (Gyna sp.). The abundance of the cave cockroaches, darkling beetles (Tenebrionidae, Tenebrio sp.) and cave wasps (Sphecidae) positively correlated with floor substrate of high moisture content and high electrical conductivity, which became increasingly common with distance into the cave. The abundance of other taxa from the cave floor positively correlated with a floor substrate of high pH and low moisture, which was common near the cave entrance.

Do Chinese cavefish show intraspecific variability in morphological traits?

Cavefishes represent one of the most bizarre and intriguing life forms inhabiting groundwater environments. One-third of the known cavefishes worldwide is endemic to China, and almost half of those belongs to a single genus, Sinocyclocheilus (Cypriniformes: Cyprinidae). Analyzing the morphometrics of three Sinocyclocheilus species, we aimed to assess whether variability among conspecific populations exists. We predict that populations inhabiting different subterranean habitats (shallow vs. deep) show divergences in specific morphological traits to better cope with the local ecological conditions. Our results showed that the populations showing bigger eyes and reduced humpback were those occurring close to the cave entrance (habitats with light and high food availability), while specimens with smaller eyes and increased humpback were collected from deeper groundwater areas (habitats laying in darkness with food scarcity). This explorative study paves the way for further researches aiming to collect novel data on Chinese cavefishes and highlights the usefulness of these species in evolutionary studies.

Cave Communities: From the Surface Border to the Deep Darkness

The discipline of subterranean biology has provided us incredible information on the diversity, ecology and evolution of species living in different typologies of subterranean habitats. However, a general lack of information on the relationships between cave species still exists, leaving uncertainty regarding the dynamics that hold together cave communities and the roles of specific organisms (from the least to the most adapted species) for the community, as well as the entire ecosystem. This Special Issue aims to stimulate and gather studies which are focusing on cave communities belonging to all different typologies of subterranean habitats, with the overarching goal to corroborate the key role of the subterranean biology in ecological and evolutionary studies.

Do Salamanders Limit the Abundance of Groundwater Invertebrates in Subterranean Habitats?

Several species of surface salamanders exploit underground environments; in Europe, one of the most common is the fire salamander (Salamandra salamandra). In this study, we investigated if fire salamander larvae occurring in groundwater habitats can affect the abundance of some cave-adapted species. We analyzed the data of abundance of three target taxa (genera Niphargus (Amphipoda; Niphargidae), Monolistra (Isopoda; Sphaeromatidae) and Dendrocoelum (Tricladida; Dedrocoelidae)) collected in 386 surveys performed on 117 sites (pools and distinct subterranean stream sectors), within 17 natural and 24 artificial subterranean habitats, between 2012 and 2019. Generalized linear mixed models were used to assess the relationship between target taxa abundance, fire salamander larvae occurrence, and environmental features. The presence of salamander larvae negatively affected the abundance of all the target taxa. Monolistra abundance was positively related with the distance from the cave entrance of the sites and by their surface. Our study revealed that surface salamanders may have a negative effect on the abundance of cave-adapted animals, and highlited the importance of further investigations on the diet and on the top-down effects of salamanders on the subterranean communities.

Cave morphology, microclimate and abundance of five cave predators from the Monte Albo (Sardinia, Italy)

Background

Systematic data collection on species and their exploited environments is of key importance for conservation studies. Within the less-known environments, the subterranean ones are neither easy to be studied, nor to be explored. Subterranean environments house a wide number of specialised organisms, many of which show high sensitivity to habitat alteration. Despite the undeniable importance to monitor the status of the subterranean biodiversity, standardised methodologies to record biotic and abiotic data in these environments are still not fully adopted, impeding therefore the creation of comparable datasets useful for monitoring the ecological condition in the subterranean environments and for conservation assessment of related species.

New information

In this work we describe a methodology allowing the collection of standardised abiotic and biotic data in subterranean environments. To show this, we created a large dataset including information on environmental features (morphology and microclimate) and abundance of five predators (one salamander, three spiders and one snail) occurring in seven caves of the Monte Albo (Sardinia, Italy), an important biodiversity hotspot. We performed 77 surveys on 5,748 m² of subterranean environments througout a year, recording 1,695 observations of the five cave predators. The fine-scale data collection adopted in our methodology allowed us to record detailed information related to both morphology and microclimate of the cave inner environment. Furthermore, this method allows us to account for species-imperfect detection when recording presence/abundance data.

Morphometrics of eight Chinese cavefish species

Chinese cavefishes are a bizarre and interesting vertebrate taxa, but one with relatively little research. China holds the highest global cavefish diversity, accounting for about one-third of known species. Sinocyclocheilus is the largest genus of cavefishes in the world and is endemic to the south of China. The distribution of Sinocyclocheilus species is very narrow, and sometimes they inhabit just a single cave; this feature increases the vulnerability to extinction. With this study we provide the first comprehensive dataset related to the morphometrics of eight Sinocyclocheilus species. In addition to enhancing our knowledge on these poorly known species we aim to provide a dataset useful for future comparative analyses aiming to better understand the adaptive ability of cavefishes.