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      Metabolic responses to long-term food deprivation in subterranean and surface amphipods

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      Subterranean Biology

      Pensoft Publishers

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          Abstract

          A long-standing hypothesis in subterranean biology posits that organisms living in poor resource subsurface habitats can withstand long periods of bioenergetic shortages due to an innate reduced metabolic rate when compared to their epigean counterparts. However, previous studies have proposed that caves with ample energy resources may not evolve organisms with reduced metabolic rate. The equivocal nature of previous findings suggests that there is a need to compare food deprivation responses of subterranean and surface species in order to elucidate whether there are widespread adaptations to low energy systems in subterranean taxa. The purpose of the study was to examine patterns in basal metabolism and the effects of food deprivation in closely related subterranean- and epigean- amphipods, Stygobromus pecki and Synurella sp. from central and east Texas, USA, respectively. Basal metabolic rates (measured as O2 consumption) differed between species, with S. pecki having substantially lower rates than Synurella. Individuals of both species were food deprived for a pre-determined time interval and changes in total body protein, lipids, and carbohydrates were measured throughout food deprivation experiments. Stygobromus pecki had larger initial energy stores than Synurella and were more conservative in the use of energetic reserves over a prolonged period of food deprivation. Thus, it appears that although S. pecki are currently found in shallow phreatic and spring opening environments, they have maintained more efficient metabolic adaptations to deal with prolonged periods of food deprivation.

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          Most cited references 24

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          Evolution in caves: Darwin's 'wrecks of ancient life' in the molecular era.

          Cave animals have historically attracted the attention of evolutionary biologists because of their bizarre 'regressive' characters and convergent evolution. However, understanding of their biogeographic and evolutionary history, including mechanisms of speciation, has remained elusive. In the last decade, molecular data have been obtained for subterranean taxa and their surface relatives, which have allowed some of the classical debates on the evolution of cave fauna to be revisited. Here, we review some of the major studies, focusing on the contribution of phylogeography in the following areas: biogeographic history and the relative roles of dispersal and vicariance, colonization history, cryptic species diversity and modes of speciation of cave animals. We further consider the limitations of current research and prospects for the future. Phylogeographic studies have confirmed that cave species are often cryptic, with highly restricted distributions, but have also shown that their divergence and potential speciation may occur despite the presence of gene flow from surface populations. Significantly, phylogeographic studies have provided evidence for speciation and adaptive evolution within the confines of cave environments, questioning the assumption that cave species evolved directly from surface ancestors. Recent technical developments involving 'next generation' DNA sequencing and theoretical developments in coalescent and population modelling are likely to revolutionize the field further, particularly in the study of speciation and the genetic basis of adaptation and convergent evolution within subterranean habitats. In summary, phylogeographic studies have provided an unprecedented insight into the evolution of these unique fauna, and the future of the field should be inspiring and data rich. © 2010 Blackwell Publishing Ltd.
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            Adaptation and Natural Selection in Caves

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              The influence of resource subsidies on cave invertebrates: results from an ecosystem-level manipulation experiment

              Spatial resource subsidies can greatly affect the composition and dynamics of recipient communities. Caves are especially tractable for studying spatial subsidies because primary productivity is absent. Here, we performed an ecosystem-level manipulation experiment to test the direct influence of detrital subsidies on community structure in terrestrial cave ecosystems. After performing baseline censuses of invertebrates, we removed all organic material from 12 caves and constructed exclusion boxes to prevent natural resource inputs. Next, we stocked each cave with standardized quantities of two major natural subsidies to caves: leaves (leaf packs) and carcasses (commercially supplied rodents), and measured the invertebrate colonization and utilization of these resources for 23 months. Over the course of the experiment, 102 morphospecies were observed. Diplopods and collembolans were most abundant on leaf packs, and dipteran larvae and collembolans were most abundant on the rats. On average, caves receiving either treatment did not differ in species richness, but abundance was significantly higher in rat caves over both the duration of the experiment and the temporal "life" of the individual resources, which were restocked upon exhaustion. Post-manipulation invertebrate communities differed predictably depending on the type of subsidy introduced. Over the course of the experiment, caves that received the same subsidy clustered together based on community composition. In addition, the invertebrate community utilizing the resource changed over the duration of the two-year experiment, and evidence of succession (i.e., directional change) was observed. Results from this study demonstrate how allochthonous resources can drive the community dynamics of terrestrial invertebrates in cave ecosystems and highlight the need for consideration of the surface environment when managing and protecting these unique habitats.
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                Author and article information

                Journal
                Subterranean Biology
                SB
                Pensoft Publishers
                1314-2615
                1768-1448
                January 13 2020
                January 13 2020
                : 33
                : 1-15
                Article
                10.3897/subtbiol.33.48483
                © 2020

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