Shifting Paradigms of the Evolution of Cave Life

The unique morphology of cave animals has interested biologists at least since the time of Lamarck. After a number of non-adaptive explanations for the morphology of cave animals, especially with respect to eye and pigment loss, a neo-Darwinian explanation, emphasizing constructive morphological changes rather than losses, was put forward by Barr, Christiansen, and Poulson in the 1960’s. Emphasizing convergent evolution (troglomorphy), this paradigm has recently been challenged, with evidence of divergent selection and the widespread occurrence of morphologically similar species in other subterranean habitats, including ones with abundant food and relatively strong environmental fluctuations. An emerging paradigm emphasizes the central role of darkness in convergent evolution, and the role of habitat size and interspecific competition in divergent evolution of subterranean species.Sprememba paradigme o evoluciji jamskega življenjaEdinstvena morfologija jamskih živali, predvsem v povezavi z izgubo oči in pigmenta, je zanimala biologe že od časa Lamarcka. Kasneje so bile predstavljene tudi druge, t.im. neodarvinistične razlage, s poudarkom na konstruktivnih morfoloških spremembah namesto izgubah, povzete s strani Barra, Christiansena in Poulsona v 60. letih 20. stoletja. Z novejšimi raziskavami o divergentni selekciji in razširjeni prisotnosti morfološko podobnih vrst v drugih podzemeljskih habitatih, vključno s tistimi, kjer je veliko hrane in z relativno velikimi okoljskimi nihanji, se je zamajala paradigma, temelječa na konvergentni evoluciji (troglomorfija). Novo nastajajoča paradigma poudarja osrednjo vlogo teme v konvergentni evoluciji, ter vlogo velikosti habitata in medvrstne kompeticije v divergentni evoluciji podzemeljskih vrst

Organic Carbon in Shallow Subterranean Habitats

subterranean habitatsOrganic carbon is likely to be a limiting factor in shallow subterranean habitats (SSHs). Data on dissolved organic carbon (DOC) in three SSHs are reviewed: (1) hypotelminorheic and associated seepage springs (Nanos Mountain, Slovenia), (2) hyporheic zones (Rhône River, France and seepage streams on Nanos Mountain, Slovenia), and (3) epikarst (China, Slovenia, and USA). Hypotelminorheic habitats are superficial groundwater sites less than 1 m below the surface that exit from seepage springs. Hyporheic habitats are the underflow of streams and rivers. Epikarst is the uppermost zone of karst with extensive small cavities and channels. Nanos hypotelminorheic sites that harbored stygobiotic species had organic carbon values averaging 3.4 mg C L−1, and temporal variability was high. For hypoheic sites in the Rhône River basin and on Nanos Mountain, mean values ranged from 1.4 to 3.5 mg C L−1. In the more extensively studied Rhône River basin sites, temporal variability was low. Epikarst DOC ranged from 0.70 to 1.10 mg C L−1 in three caves in China (Shihua Cave), Slovenia (Postojna Planina Cave System) and United States (Organ Cave, West Virginia). These results suggest that organic carbon in aquatic SSHs is lowest in epikarst.Keywords: dissolved organic carbon, epikarst, hyporheic, hypotelminorheic, seepage spring.DOI: 10.3986/ac.v42i2.60

Climate, abiotic factors, and the evolution of subterranean life

Climate, and more generally the physical conditions in caves and other subterranean habitats have a profound influence on the biota. At longer time scale (centuries), climate change can force and/or isolate species in subterranean habitats. Not only Pleistocene climate changes, but earlier ones as well, suchas the Messinian salinity crisis were important in this regard. While many speleobiologists assume that caves are nearly constant environmentally and withscarce organic carbon, this is not the case, especially in non-cave subterranean habitats. Many shal­low subterranean habitats, suchas epikarst, seepage springs, and talus harbor highly modified organisms, ones without eyes and pigment and withelongated appendages. Yet these habi­tats are highly variable withrespect to temperature and other environmental factors, and often have highlevels of organic carbon. Overall, the role of these shallow subterranean habitats in the evolution and biogeography of subterranean species may be crucial. On smaller spatial scales, environmental differences, suchas differences in chemistry of epikarst water, may be im­portant in allowing large numbers of species to coexist

What Does the Distribution of Stygobiotic Copepoda (Crustacea) Tell Us About Their Age?

Geographic distribution of stygobionts is often used to estimate age of a group by assuming vicariant speciation with little or no subsequent dispersal. We investigated the utility of using distributional data for Slovenian stygobiotic copepods by assuming that dispersal is a way to measure age of a species. We list some species of Copepoda that, on the basis of their range and frequency of occupancy within their range, should be older. Body size is not predictor either of range or frequency of occupancy

Fifty Years of the Hypotelminorheic: What Have We Learned?

Originally described by Meštrov in 1962, hypotelminorheic habitats are superficial subterranean drainages, typically less than a meter or so in depth, that emerge at small seepage springs. These are persistent wet spots, typically with blackened leaves in small depressions. There may be no flow during dry periods, but the underlying clay retains water above. They share the landscape with other small bodies of water (močila in Slovenian), not necessarily connected with groundwater. Hypotelminorheic habitats (mezišča in Slovenian) usually harbor a fauna dominated by species adapted to subterranean life, characteristically without eyes or pigment. The basic chemistry and hydrology of the habitat is described as are the basic faunal elements. The habitat is placed in a more general context by reviewing how species invade the habitat, their morphology, and their possible connection to deeper subterranean habitats

High-density speckle contrast optical tomography (SCOT) for three dimensional tomographic imaging of the small animal brain

High-density speckle contrast optical tomography (SCOT) utilizing tens of thousands of source-detector pairs, was developed for in vivo imaging of blood flow in small animals. The reduction in cerebral blood flow (CBF) due to local ischemic stroke in a mouse brain was transcanially imaged and reconstructed in three dimensions. The reconstructed volume was then compared with corresponding magnetic resonance images demonstrating that the volume of reduced CBF agrees with the infarct zone at twenty-four hours.Peer ReviewedPostprint (author's final draft

Morphological Differences Among Eyeless Amphipods in the Genus Stygobromus Dwelling in Different Subterranean Habitats

The amphipod genus Stygobromus occurs in a variety of subterranean habitats in North America, including caves, phreatic (groundwater) lakes, and superficial subterranean habitats (seeps and epikarst). The habitats share the absence of light but differ in other features, such as pore size of the habitat, available food, and degree of seasonality. Measurements of body size, antennal size, and antennal segment number of type specimens were compared for 56 species occurring in the eastern United States. Except for differences in body size, differences among species in the four different habitats were not significant. Body size was related to relative pore size of the habitat, e.g., epikarst, with the smallest spaces, had the smallest species. However, in all habitats, there was one very large species (\u3e 15mm); these enigmatic species apparently occupy a distinct ecological niche, perhaps being more predatory. Differences in relative antennal size showed no significant differences among habitats, and differences in number of antennal segments were marginally significant (P = 0.06) among habitat types and not in the predicted pattern. Differences among habitats in seasonality and available food seemed to be a minor part of the selective environment; absence of light seemed to be a major part of the selective environment

High-density speckle contrast optical tomography of cerebral blood flow response to functional stimuli in the rodent brain

Noninvasive, three-dimensional, and longitudinal imaging of cerebral blood flow (CBF) in small animal models and ultimately in humans has implications for fundamental research and clinical applications. It enables the study of phenomena such as brain development and learning and the effects of pathologies, with a clear vision for translation to humans. Speckle contrast optical tomography (SCOT) is an emerging optical method that aims to achieve this goal by directly measuring three-dimensional blood flow maps in deep tissue with a relatively inexpensive and simple system. High-density SCOT is developed to follow CBF changes in response to somatosensory cortex stimulation. Measurements are carried out through the intact skull on the rat brain. SCOT is able to follow individual trials in each brain hemisphere, where signal averaging resulted in comparable, cortical images to those of functional magnetic resonance images in spatial extent, location, and depth. Sham stimuli are utilized to demonstrate that the observed response is indeed due to local changes in the brain induced by forepaw stimulation. In developing and demonstrating the method, algorithms and analysis methods are developed. The results pave the way for longitudinal, nondestructive imaging in preclinical rodent models that can readily be translated to the human brain.This project was funded by Fundació CELLEX Barcelona, Ministerio de Economía y Competitividad/FEDER (PHOTODEMENTIA, DPI2015-64358-C2-1-R), Instituto de Salud Carlos III/FEDER (MEDPHOTAGE, DTS16/00087), the “Severo Ochoa” Program for Centers of Excellence in R\&D (SEV-2015-0522), the Obra Social “la Caixa” Foundation (LlumMedBcn), AGAUR-Generalitat (2017 SGR 1380), LASERLAB-EUROPE IV, and “Fundació La Marató TV3.