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.

Sensory evolution in a cavefish radiation: patterns of neuromast distribution and associated behaviour in Sinocyclocheilus (Cypriniformes: Cyprinidae)

The genus Sinocyclocheilus, comprising a large radiation of freshwater cavefishes, are well known for their presence of regressive features (e.g. variable eye reduction). Fewer constructive features are known, such as the expansion of the lateral line system (LLS), which is involved in detecting water movements. The precise relationship between LLS expansion and cave adaptation is not well understood. Here, we examine morphology and LLS-mediated behaviour in Sinocyclocheilus species characterized by broad variation in eye size, habitat and geographical distribution. Using live-staining techniques and automated behavioural analyses, we examined 26 Sinocyclocheilus species and quantified neuromast organ number, density and asymmetry within a phylogenetic context. We then examined how these morphological features may relate to wall-following, an established cave-associated behaviour mediated by the lateral line. We show that most species demonstrated laterality (i.e. asymmetry) in neuromast organs on the head, often biased to the right. We also found that wall-following behaviour was distinctive, particularly among eyeless species. Patterns of variation in LLS appear to correlate with the degree of eye loss, as well as geographical distribution. This work reveals that constructive LLS evolution is convergent across distant cavefish taxa and may mediate asymmetric behavioural features that enable survival in stark subterranean microenvironments.

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 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.

The rise of Astyanax cavefish

Numerous animals have invaded subterranean caverns and evolved remarkably similar features. These features include loss of vision and pigmentation, and gains in nonvisual sensation. This broad convergence echoes smaller-scale convergence, in which members of the same species repeatedly evolve the same cave-associated phenotypes. The blind Mexican tetra of the Sierra de El Abra region of northeastern Mexico has a complex origin, having recurrently colonized subterranean environments through numerous invasions of surface-dwelling fish. These colonizations likely occurred ∼1-5 MYa. Despite evidence of historical and contemporary gene flow between cave and surface forms, the cave-associated phenotype appears to remain quite stable in nature. This model system has provided insight to the mechanisms of phenotypic regression, the genetic basis for constructive trait evolution, and the origin of behavioral novelties. Here, we document the rise of this model system from its discovery by a Mexican surveyor in 1936, to a powerful system for cave biology and contemporary genetic research. The recently sequenced genome provides exciting opportunities for future research, and will help resolve several long-standing biological problems. Developmental Dynamics 244:1031-1038, 2015. © 2015 Wiley Periodicals, Inc.