The Southern Appalachian Mountains are a biodiversity hotspot, especially for plethodontid salamanders. While the ranges of some salamander species are well understood, much less is known about how environmental parameters affect their diversity and abundance. To investigate these patterns, we conducted repeated nighttime visual encounter surveys along 128 transects measuring 25 x 4 m spanning 500–2,000 m elevation across western North Carolina and eastern Tennessee during the summer of 2024. Using single-species N-mixture models (spAbundance R package), we estimated the abundances of the five most common species encountered accounting for imperfect detection: Desmognathus orestes, Eurycea wilderae, Plethodon cylindraceus, P. montanus, and P. yonahlossee. We hypothesized that study species would exhibit patterns of abundance predicted by the center-periphery hypothesis where abundance is highest in the center of a species' geographic or elevational range. All species abundance exhibited hump-shaped elevation curves, peaking at different elevations, with abundance decreasing above and below their respective optima. While elevation taken in isolation supports the center-periphery hypothesis, interacting environmental factors create complex abundance patterns the hypothesis cannot explain. Proximity to streams consistently increased abundance, but its effect weakened at higher elevations. Their abundance is shaped by interacting climatic and topographic gradients, with peak densities in cool, moist mid-elevation zones. Humidity had the strongest influence on surface activity and, thus, detection rates. Temperature and precipitation influence on detection was less. Given their high abundance, salamanders likely play a disproportionately large and underappreciated role in Appalachian Forest ecosystems. This study provides the first abundance estimates for these species in this region, setting a baseline for future surveys to understand changes in distribution over time.
In this study, we evaluated the effect of land-use change on the taxonomic and functional diversity of the lizard communities of the Valley of Mexico. Taxonomic alpha diversity was calculated with Hill numbers, while taxonomic beta diversity was estimated through the turnover and nesting components. For functional diversity, we evaluated richness, evenness, and divergence, and identified functional groups of lizard communities. Our records showed that 18 lizard species inhabit the nine land-use types, of which oyamel forest (OF) had the highest taxonomic diversity. Anthropized areas (AA) and agricultural cropland (AG) showed less taxonomic dissimilarity compared to other types of land use, of which nestedness was the most important component. Oak forest (OKF) and OF have high functional richness and functional divergence, but low evenness, indicating niche similarities among species of the different land-use types and therefore greater competition for available resources. In addition, we found that the land-use type with the highest degree of anthropization and expansion in the study area, AA, has a less functional richness and functional group than forest cover like pine forest, oak forest, pine-oak forest, and other types of land use. The most abundant species in the Valley of Mexico are those considered as generalists, which are able to cope with the ongoing land-use change in this part of the country.
Caudal autotomy in lizards is an important defense mechanism that involves cutting and shedding the tail to distract a threatening predator. This phenomenon has not been previously studied in the genus Phymaturus and rarely in Liolaemus. A large sample of individuals from almost all described species of Phymaturus (n = 896) revealed that this genus exhibits autotomy considerably less frequently than its sister genus Liolaemus (12.3% versus 42.9%), and that the cutting site is located more posteriorly in the tail (55.4% versus 26.9% of an intact tail). In the Phymaturus palluma group, the cutting frequency is even lower and the cutting site is more posterior than in Liolaemus (frequency of 10.4% and cutting site at 68%). In congruence with these differences in the tail cut site between Phymaturus and Liolaemus, we found that the first autotomy vertebra is located further back in the former (and further back in species of the palluma group compared to those of the patagonicus group). In many species, autotomy is even lost, or its frequency is so low that it becomes difficult to detect. We found that in some species where autotomy has not been reported, there are still vertebrae with fracture planes. We also found that Liolaemus has more caudal vertebrae than Phymaturus, perhaps explaining the long tails in some Liolaemus groups. However, no relationship was found between the species' body size and the frequency of autotomy. The tails of Phymaturus are not major fat deposits like those of Liolaemus, and cutting them would not result in a significant energetic loss. Rather, the tails of Phymaturus lizards are more aligned to increase stability and balance on slopes and to be used defensively when they take refuge in cracks. In any case, these possible explanations are mere hypotheses that should be tested with new studies.
Most anguilloid eels inhabit the deep ocean and exhibit a wide range of deep-sea specializations, including caudal and dorsolateral bioluminescence in the Pelican Eel, Eurypharynx pelecanoides, and swallower eels, Saccopharynx spp. The type of bioluminescence exhibited by these eels has been uncertain, and the anatomy of the bioluminescent organ in E. pelecanoides has never been described. Here we seek to describe the bioluminescent organs in this group and use an updated phylogeny to discuss the evolution of bioluminescence and other specializations within the Anguilloidei. We examined publicly available footage of live eels, used gross and histological examination of bioluminescent organs in museum specimens, and conducted a phylogenetic analysis using public and newly generated mitogenomic DNA-sequence data. We determined that bioluminescence in E. pelecanoides and Saccopharynx spp. is intrinsic. We also identified extensive blood sinuses in the caudal bioluminescent organ of S. lavenbergi and a specialized caudal bioluminescent organ in E. pelecanoides with putative photocytes ventrally and in dorsolateral grooves underlain by skeletal muscle that may support flashing or blinking. The dorsolateral grooves lateral to the dorsal fin of E. pelecanoides and S. lavenbergi may support bioluminescence and have a structure involving muscular opening. Our phylogeny is largely consistent with other studies, supports recognition of three superfamilies (Anguilloidea, Moringuoidea, and Saccopharyngoidea), and allows discussion of the diverse range of morphology and ecology in anguilloids.
In addition to lateral undulation, oarfishes (Regalecus spp.) swim by passing unidirectional or counter-propagating waves along the elongated dorsal fin. Such ribbon-finned swimming evolved independently in several groups of teleosts, such as the gymnotiform knifefishes, which have an elongated anal fin. Studies of ribbon-finned swimming in knifefishes led to an interest in the biomimetic potential of this type of propulsion. We studied the anatomy of the dorsal-fin rays, their skeletal supports, and their muscles as well as photographs and videos to describe the functional morphology of ribbon-finned swimming in oarfishes. In contrast to the typical acanthomorph condition, two pterygiophores symmetrically support each ovoid-shaped distal radial and its associated dorsal-fin ray. Each distal radial has a ball-and-socket connection with its supporting proximal-middle radials, and this allows the fin ray to rotate. Unlike the other Lampridiformes, such as Lampris, the dorsal-fin rays of Regalecus are smooth, unbranched, and unsegmented (monolithic). The musculoskeletal system is complex. The three bilateral muscles (inclinator, erector, and depressor muscles) have four bilateral insertions on the radials and fin ray. The muscles originate on the fascia as well as on the two proximal-middle radials that support each distal radial. We term a complete dorsal pterygiophore with its associated fin ray and muscles to be a musculoskeletal unit; there are hundreds of these units in the dorsal fin of an oarfish (e.g., 401 units in one specimen we studied). During ribbon-finned swimming, each dorsal-fin ray can rotate 360° at the ball-and-socket joint for the distal radial, mimicking a range of motion like that of a mechanical joystick. The presence and importance of the rotational capability of the dorsal-fin rays may inform interpretations of other teleosts that use ribbon-finned swimming and offer new biomimetic inspiration for aquatic robots.
