Journal of Morphology最新文献

The sense of touch (mechanoreception) in snakes is not widely appreciated despite emerging evidence of tactile specialisation among sea snakes. This is partly due to the challenges in quantifying small (< 1 mm) and numerous scale mechanoreceptors concentrated on the head. By using a novel application of gel-based 3D profilometry (GelSight scanner) in combination with histology and scanning electron microscopy, we comprehensively quantified the morphology and distribution of scale mechanoreceptors in the olive-headed sea snake, Hydrophis major (Hydrophiinae), for the first time. H. major is one of the few predators to eat eel-tailed catfishes (Plotosidae), which have venomous spines that they lock into erect positions during defence. We discovered that in addition to the radially symmetrical smooth, dome-shaped mechanoreceptors typically found in sea snakes, H. major has asymmetrical, peak-shaped mechanoreceptors that are significantly larger but rarer. Smooth domes are distributed in decreasing density antero-posteriorly on the head with the highest densities on the snout and labial scales. Asymmetrical peaks are rarer; they are detected only on the dorsal and lateral sides of the head, are most dense behind the eye, and their associated dermal papilla (that contains mechanosensitive cells) is spatially offset from the stiff peak. Based on their morphology and distribution, we suggest functional differences in mechanosensory modalities: (1) smooth domes for direct touch used in prey handling to avoid dangerous spines of catfish prey, and (2) asymmetrical peaks that create a lever system capable of amplifying directional water flow. The latter might allow H. major to detect the C-start escape response of free-swimming catfish and/or enhance kinaesthesia for the snake's perception of self-motion during foraging and predatory strikes, but physiological studies are needed to investigate these functional hypotheses further.

The respiratory organs of water-breathing ectotherms (WBEs), typically in the form of gills, extract oxygen from the water. The size and shape of respiratory organs are vital to the efficiency of oxygen diffusion and often unique to each species. Oxygen concentrations in water are < 1%, far lower than in the atmosphere, so WBEs have evolved gill morphologies that maximize their oxygen uptake but are also shaped by their life history and the environment. Gill surface area is related to the body mass of an individual, scaling as a power-law function whose exponent, based on theory and empirical evidence, generally lies between 0.6 and 0.9. However, nearly all estimates of gill surface area are based on 2-dimensional rather than 3-dimensional measurements, assuming that gill thickness is negligible and unimportant to respiration in accord with the physics of oxygen diffusion. This study aimed to develop methods to measure gills in three dimensions and then convert 2-dimensional gill surface area to the 3-dimensional gill surface area. The body mass and gill surface area scaling relationship was then determined for two decapod crustaceans with contrasting life histories: the Caribbean Spiny Lobster (Panulirus argus) and the Caribbean King Crab (Maguimithrax spinosissimus). We found a positive relationship between gill lamellae thickness and body mass for both species, which could be beneficial or detrimental to larger, oxygen-limited WBEs depending on the balance between oxygen diffusion through the additional surface area and the dynamics of oxygen diffusion into a larger volume. The 2-dimensional scaling exponent between gill surface area and body mass was 0.626 for lobsters and 0.779 for crabs, compared to their 3-dimensional scaling exponents (0.809 and 0.702, respectively). These are the first 2D and 3D body mass and gill surface area scaling exponents determined for these species and will set the basis for future physiological research.

Some of the most extensively studied phenotypic adaptations in reef fish pertain to trophic diversification. Within the Pomacentridae family, a strong correlation between head morphology and diet has been identified. The relationship between structures involved in food detection (eyes) and capture (mouth) has been demonstrated, prompting the question of whether pharyngeal jaws vary in an integrated manner with the eyes and mouth to detect, capture, and process food according to different trophic guilds. In this study, morphometric analyses were applied to X-rays of the 24 damselfishes of the eastern Pacific. A comprehensive database of dietary items for all species was constructed. The species were grouped according to their diet in trophic groups, which were tested on the morphometric data to determine ecomorphological groups. Six ecomorphological groups were determined: three benthic feeders, one benthopelagic, and two pelagic. Phylogenetic (phy) and nonphylogenetic (n-phy) modulatory analyses were conducted on the entire sample, three broad ecomorphological categories (phy-benthic, pelagic, pelagic–benthopelagic; n-phy, benthic, benthopelagic, pelagic), and the six specific ecomorphological groups (n-phy). Four modularity hypotheses were tested: three modules, the eye (E), mouth (M), and pharyngeal jaws (PJ), and two modules, PJ&E versus M, M&PJ versus E, and M&E versus PJ. Across all groupings, the hypothesis of three distinct modules was most strongly supported, followed by PJ&E versus M, with M&E versus PJ being the least supported. These findings suggest that the eye and mouth are more functionally decoupled than the pharyngeal jaws. It was evident that these structures exhibit a greater decoupling in benthic species than in benthopelagic and pelagic species. Our results indicate that different trophic groups show different levels of decoupling and integration in structures to detect, capture, and process food, and that, despite operating within a relatively narrow range of ecomorphological variation, damselfishes display a remarkable array of ecomorphological combinations.

Supramedullary neurons (SMNs) were described almost 150 years ago as large, unipolar cells whose somata are located on the dorsal aspect of the medulla oblongata and spinal cord in adults of teleost fishes. SMNs are either aligned in a single, median longitudinal row, generally extending over the rostral third of the spinal cord, or clustered over the medulla oblongata and rostral spinal cord. We add to the list of species that have SMNs and provide the first description of a novel distribution of SMNs along most of the spinal cord in the oyster toadfish (Opsanus tau) and sea raven (Hemitripterus americanus). The number of SMNs ranges from 27 in the Atlantic butterfish (Peprilus triacanthus) to 3712 in the oyster toadfish (Opsanus tau), and soma diameter ranges from an average of 23 µm in the Atlantic butterfish to 232 µm in the Southern pufferfish (Sphoeroides nephelus). SMNs could not be identified in 11 species, including seven freshwater fishes. We discuss factors that may affect the presence/absence of SMNs including age, length of time in captivity, and habitat salinity. Proposed functions of SMNs include neurosecretion and mucous secretion, and we suggest approaches that may aid in the discovery of the role of these fascinating neurons.

Lizards represent the closest amniotes to mammals able to regenerate many tissues, therefore are useful models for studies of mammalian regeneration. Tail regeneration occurs by stem cells but tissue dedifferentiation may also be involved. When injury damages numerous tissues they may undergo dedifferentiation (re-programming). This was indicated especially in muscles and connectives of the tail 7–10 days postamputation. The transcriptome of regenerating tail and limb from the lizard Podarcis muralis detected upregulation of spalt-like genes (sall 1–4), known to be involved in re-programming. Here, immunolocalization of the sall4 protein and 5BrdU-labeled cells (proliferating) was conducted. A variable number of 5BrdU and sall4-positive cells are detected among stump connective tissues, injured muscles, and dermis. Labeling for sall4 is cytoplasmic and also nuclear, and it is also noted in cytoplasmic muscle fragments. The latter likely derived from the fragmentation of injured muscles in both tail and limb stumps at 7–16 days postamputation. Occasional, isolated sall4-labeled cells are rarely detected in the blastema, and none in the wound epidermis or regenerating spinal cord and muscles. The present study indicates that cell dedifferentiation occurs during early stages of tail and limb amputation in lizards, contributing with activated stem cells to their regeneration or scarring.

New World Blackbirds (Icteridae) are a diverse group of Neotropical passerines and an important component of the continental radiation of nine-primaried songbirds (Emberizoidea). Icterids and other emberizoids are chiefly omnivorous, but with variable predilection for invertebrates, fruits, and seeds. The icterids also exhibit a peculiar “gaping” behavior, whereby they insert their beaks into soil, fruits or bark and then open them inside the substrate. Cowbirds (Molothrus) stand out among the icterids for not being gapers and, with the exception of the Giant Cowbird, for a marked tendency towards a granivorous diet. To explore the signal of trophic ecology in the lower jaw of icterids and other emberizoids, we applied three-dimensional geometric morphometrics on Microcomputed tomography data and phylogenetic comparative methods. Phylomorphospaces were constructed and possible correlates with diet, gaping, and evolutionary allometry were assessed through phylogenetic ANOVA. Convergence between seed-eater species was also estimated by recently developed measures (Ct1). Results show a significant signal of trophic ecology in the mandible, with seed-eater species occupying a narrow domain of morphospace, partially overwhelming the signal of evolutionary allometry. The cowbird Molothrus ater stands out for clearly diverging from most icterids, showing significant convergence with other seed-eater emberizoids. Mandibular morphology, often neglected in avian ecomorphological studies, is informative of the trophic ecology of these birds.

An enigmatic salamander species Protohynobius puxiongensis was named 25 years ago but since then has been disputed as a genus and species of its own or a species in the genus Pseudohynobius. Here, we provide a detailed anatomical account for P. puxiongensis based on micro-CT scans of five specimens, including one larva, one subadult and three adults. For the first time we reveal anatomical details in the braincase, hyobranchium and the postcranial skeleton. Our comparative study with species of Pseudohynobius and Liua clarified previous disputes over the anatomy of the skull, and confirmed that the internasal bone is an intraspecific variation that is present in several hynobiid species. Our study found that P. puxiongensis possesses fundamental morphological features that distinguish this enigmatic salamander from all species in the genus Pseudohynobius; therefore, the results of our study provide evidence to reject the combination of “Pseudohynobius puxiongensis”, and support Protohynobius as the valid generic name for the species in question for the purpose of the Principle of Priority. The extensive morphological disparities between Protohynobius and Pseudohynobius identified herein combined with their relatively short genetic distances recognized by previous studies indicate that these hynobiids have had a high evolutionary rate that may be associated with the intense orogenies around the eastern edge of the Qinghai-Tibetan Plateau during the Neogene.