A new paper was just published on coprophagy in a cave salamander involving collaborators from the New Jersey Institute of Technology, The Nature Conservancy, San Antonio Zoo, and U.S. Fish & Wildlife Service.
Soares D, Adams R, Hammond S, Slay ME, Fenolio DB, Niemiller ML. 2017. Evolution of coprophagy and nutrient absorption in a cave salamander. Subterranean Biology 24: 1–9.
The transition from carnivory to omnivory is poorly understood. The ability to feed at more than one trophic level theoretically increases an animal’s fitness in a novel environment. Because of the absence of light and photosynthesis, most subterranean ecosystems are characterized by very few trophic levels, such that food scarcity is a challenge in many subterranean habitats. One strategy against starvation is to expand diet breadth. Grotto Salamanders (Eurycea spelaea (Stejneger, 1892)) are known to ingest bat guano deliberately, challenging the general understanding that salamanders are strictly carnivorous. Here we tested the hypothesis that grotto salamanders have broadened their diet related to cave adaptation and found that, although coprophagous behavior is present, salamanders are unable to acquire sufficient nutrition from bat guano alone. Our results suggest that the coprophagic behavior has emerged prior to physiological or gut biome adaptations.
A paper on the morphological evolution of amblyopsid cavefishes was recently published in the journal Copeia. The full citation and abstract are below.
Armbruster JW, Niemiller ML, & Hart PB. 2016. Morphological evolution of the cave-, spring- and swampfishes of the family Amblyopsidae (Percopsiformes). Copeia 104: 763–777.
The Amblyopsidae is a small family of fishes from North America in which most of the species occur in caves. Despite considerable interest and study by biologists, a comprehensive morphological phylogenetic analysis of the family has not been conducted to date. We examined the skeletal morphology of all six genera and recognized species, which included 66 characters. The resulting phylogeny was compared to morphological- and molecular-based phylogenies of previous studies. Results showed a progression of cave adaptation that was significantly different from previous phylogenetic studies. Amblyopsidae was supported by 34 synapomorphies of the skeleton, but relationships within the Amblyopsidae were comparatively weak. The relationships of amblyopsids are likely influenced by morphological convergence as well as changes in the timing of development of some characters. Heterochrony is most visible in the unfused bones of the dorsal portion of the skull. The sister group to Amblyopsidae is Aphredoderidae (pirate perches), and the main character that supports this relationship is the presence of a unique set of upper jaw bones termed here lateromaxillae. This relationship is also supported by an anterior position of the vent, which is used for expelling gametes in Aphredoderus and for moving eggs to the gill chamber in Amblyopsis. It is more likely that Amblyopsis is the only branchial brooding amblyopsid and all other species likely exhibit transbranchioral spawning.
A paper on the vertebrate fauna found in caves of east Tennessee was recently published in the journal Journal of Cave and Karst Studies. The full citation and abstract are below.
Niemiller ML, Zigler KS, Stephen CDR, Carter ET, Paterson AT, Taylor SJ, & Engel AS. 2016. Vertebrate fauna in caves of eastern Tennessee within the Appalachians karst region, USA. Journal of Cave and Karst Studies 78: 1–24.
More than one-fifth of the documented caves in the United States occur in Tennessee. The obligate subterranean biota of Tennessee is rich and diverse, with 200 troglobionts reported from over 660 caves. Fifty troglobionts are known from just 75 of the 1,469 caves in the Appalachian Valley and Ridge physiographic province of eastern Tennessee. Tennessee’s Valley and Ridge has been under-sampled relative to other karst areas in the state, limiting our knowledge of cave and karst species diversity and distributions and compromising our ability to identify habitats and species potentially at risk from anthropogenic threats, such as urban sprawl near the metropolitan area of Knoxville. Knowledge of nontroglobiontic species inhabiting caves, including vertebrates, is particularly sparse in this region. Although caves have long been recognized as critical habitats for several bat species, the importance of caves for other vertebrate taxa has received less attention. Caves are important habitats for many other nontroglobiontic vertebrates and should be considered in the management and conservation of these species. Our decade-long study bioinventoried 56 caves in 15 counties and begins to address knowledge gaps in distributions and cave use by vertebrates in the Valley and Ridge and adjacent Blue Ridge Mountains of eastern Tennessee within the Appalachians karst region. In addition, we conducted a thorough review of the literature and museum databases for additional species-occurrence records in those provinces of eastern Tennessee. From these sources, we present an annotated list of 54 vertebrate taxa, including 8 fishes, 19 amphibians (8 anurans and 11 salamanders), 6 reptiles, 3 birds, and 18 mammals. Three species are included on the IUCN Red List of Threatened Species, while six species are at risk of extinction based on NatureServe conservation rank criteria. Ten bat species are known from 109 caves in 24 eastern Tennessee counties. Our bioinventories documented five bat species in 39 caves, including new records of the federally endangered Gray Bat (Myotis grisescens). We observed visible evidence of white-nose syndrome caused by the fungal pathogen Pseudogymnoascus destructans at four caves in Blount, Roane, and Union counties. We documented two new localities of the only troglobiontic vertebrate in the Valley and Ridge, the Berry Cave Salamander (Gyrinophilus gulolineatus). Despite these efforts, significant sampling gaps remain—only 7.7% of known caves in the Valley and Ridge and Blue Ridge Mountains of eastern Tennessee have records of vertebrate-species occurrence. Moreover, few caves in eastern Tennessee have experienced repeated, comprehensive bioinventories, with the exception of periodic surveys of hibernating bats at selected caves. Future bioinventory efforts should incorporate multiple visits to individual caves, if possible, and more efforts should focus on these understudied areas of eastern Tennessee.
A paper on the life history and demography of a population of the Big Mouth Cave Salamander (Gyrinophilus palleucus necturoides) was recently published in the journal Copeia. The full citation and abstract are below.
Niemiller ML, Glorioso BM, Fenolio DB, Reynolds RG, Taylor SJ, & Miller BT. 2016. Growth, survival, longevity, and population size of the Big Mouth Cave Salamander (Gyrinophilus palleucus necturoides) from the type locality in Grundy County, Tennessee, USA. Copeia 104: 35-41.
Salamander species that live entirely in subterranean habitats have evolved adaptations that allow them to cope with perpetual darkness and limited energy resources. We conducted a 26-month mark–recapture study to better understand the individual growth and demography of a population of the Big Mouth Cave Salamander (Gyrinophilus palleucus necturoides). We employed a growth model to estimate growth rates, age at sexual maturity, and longevity, and an open population model to estimate population size, density, detectability, and survival rates. Furthermore, we examined cover use and evidence of potential predation. Individuals probably reach sexual maturity in 3–5 years and live at least nine years. Survival rates were generally high (.75%) but declined during the study. More than 30% of captured salamanders had regenerating tails or tail damage, which presumably represent predation attempts by conspecifics or crayfishes. Most salamanders (.90%) were found under cover (e.g., rocks, trash, decaying plant material). Based on 11 surveys during the study, population size estimates ranged from 21 to 104 individuals in the ca. 710 m2 study area. Previous surveys indicated that this population experienced a significant decline from the early 1970s through the 1990s, perhaps related to silvicultural and agricultural practices. However, our data suggest that this population has either recovered or stabilized during the past 20 years. Differences in relative abundance between early surveys and our survey could be associated with differences in survey methods or sampling conditions rather than an increase in population size. Regardless, our study demonstrates that this population is larger than previously thought and is in no immediate risk of extirpation, though it does appear to exhibit higher rates of predation than expected for a species believed to be an apex predator of subterranean food webs.
My coauthor Steve Taylor and my paper on the conservation status and biogeography of subterranean Bactrurus amphipods was recently published in the journal Subterranean Biology. The full citation and abstract are below.
Taylor SJ, & Niemiller ML. 2016. Biogeography and conservation assessment of Bactrurus groundwater amphipods (Crangonyctidae) in the central and eastern United States. Subterranean Biology 17: 1–29.
The subterranean amphipod genus Bactrurus (Amphipoda: Crangonyctidae) is comprised of eight species that occur in groundwater habitats in karst and glacial deposits of the central and eastern United States. We reexamine the distribution, biogeography, and conservation status of Bactrurus in light of new species distribution records and divergence time estimates in the genus from a recent molecular study. In particular, we discuss hypotheses regarding the distribution and dispersal of B. mucronatus and B. brachycaudus into previously glaciated regions of the Central Lowlands. We also conducted the first IUCN Red List conservation assessments and reassessed global NatureServe conservation ranks for each species. We identified 17 threats associated with increased extinction risk that vary in source, scope, and severity among species, with groundwater pollution being the most significant threat to all species. Our conservation assessments indicate that five of the eight species are at an elevated risk of extinction under IUCN Red List or NatureServe criteria, with one species (B. cellulanus) already extinct. However, none of the eight species are considered threatened or endangered by any state or federal agency. Significant knowledge gaps regarding the life history, ecology, and demography of each species exist. Given results of our conservation assessments and available information on threats to populations, we offer recommendations for conservation, management, and future research for each species.
My coauthors Daphne Soares, Dennis Higgs and I have a chapter titled “Hearing in cavefishes” in the recently published book “Fish Hearing and Bioacoustics – An Anthology in Honor of Arthur N. Popper and Richard R. Fay.” The volume is edited by Joe Sisneros and honors the scientific contributions of Art Popper and Richard Fay.
The full citation and abstract of the chapter are included below. The chapter and book can be downloaded from the Springer website here.
Soares D, Niemiller ML, & Higgs DM. Hearing in cavefishes. Pp. 187–195 in: Fish Hearing and Bioacoustics – An Anthology in Honor of Arthur N. Popper and Richard R. Fay (Sisneros JA, ed). Springer.
Caves and associated subterranean habitats represent some of the harshest environments on Earth, yet many organisms, including fishes, have colonized and thrive in these habitats despite the complete absence of light, and other abiotic and biotic constraints. Over 170 species of fishes are considered obligate subterranean inhabitants (stygobionts) that exhibit some degree of troglomorphy, including degeneration of eyes and reduction in pigmentation. To compensate for lack of vision, many species have evolved constructive changes to non-visual sensory modalities. In this chapter we review hearing in cavefishes, with particular emphasize on our own studies on amblyopsid cavefishes. Hearing in cavefishes has not been well studied to date, as hearing ability has only been examined in four species. Two species show no differences in hearing ability relative to their surface relatives, while the other two species (family Amblyopsidae) exhibit regression in the form of reduced hearing range and reduction in hair cell densities on sensory epithelia. In addition to reviewing our current knowledge on cavefish hearing, we offer suggestions for future avenues of research on cavefish hearing and discuss the influence of Popper and Fay on the field of cavefish bioacoustics.
A paper comparing the life history and ecology of cave and surface populations of the Western Slimy Salamander (Plethodon albagula) in Texas was recently published in the journal Herpetological Conservation and Biology. The full citation and abstract are below.
Taylor SJ, Krejca JK, Niemiller ML, Dreslik MJ, & Phillips CA. Life history and demographic differences between cave and surface populations of the western slimy salamander, Plethodon albagula (Caudata: Plethodontidae), in central Texas. Herpetological Conservation and Biology 10: 740–752.
The Western Slimy Salamander (Plethodon albagula) in central Texas is known from both surface and cave environments. Threshold species, such as P. albagula, may be excellent candidates to study potential differences in life history traits during the evolutionary transition from surface into subterranean habitats. We conducted a 29-mo mark-recapture study of a surface and a cave population in Bell County, Texas, USA, to determine whether these populations differed in body size, growth rate, age at sexual maturity, and life span. We employed a growth model to estimate growth rate, age at sexual maturity, and life span, and an open population model to estimate population size, density, catchability, and survival rates. Salamanders were smaller on average and reached a smaller maximum size in the surface population compared to the cave population, which was skewed toward larger, older individuals. Growth trajectories were similar between populations, but the cave population reached sexual maturity faster (0.9–1.4 y) than the surface population (1.5–2.2 y). Survival rates were similar between populations. Although population size estimates were 10 times higher for the surface compared to the cave population, densities were similar between sites suggesting that habitat availability alone could explain population size differences. Plethodon albagula exhibits plasticity in growth, body size, and development, which may be adaptive and a function of extreme variation in surface environmental conditions. Subterranean habitats may be important for the long-term persistence of local populations, which may persist for years in subterranean habitats.