Diffusible iodine-based contrast-enhanced computed tomography (diceCT) : an emerging tool for rapid, high-resolution, 3-D imaging of metazoan soft tissues.

Morphologists have historically had to rely on destructive procedures to visualize the three-dimensional (3-D) anatomy of animals. More recently, however, non-destructive techniques have come to the forefront. These include X-ray computed tomography (CT), which has been used most commonly to examine the mineralized, hard-tissue anatomy of living and fossil metazoans. One relatively new and potentially transformative aspect of current CT-based research is the use of chemical agents to render visible, and differentiate between, soft-tissue structures in X-ray images. Specifically, iodine has emerged as one of the most widely used of these contrast agents among animal morphologists due to its ease of handling, cost effectiveness, and differential affinities for major types of soft tissues. The rapid adoption of iodine-based contrast agents has resulted in a proliferation of distinct specimen preparations and scanning parameter choices, as well as an increasing variety of imaging hardware and software preferences. Here we provide a critical review of the recent contributions to iodine-based, contrast-enhanced CT research to enable researchers just beginning to employ contrast enhancement to make sense of this complex new landscape of methodologies. We provide a detailed summary of recent case studies, assess factors that govern success at each step of the specimen storage, preparation, and imaging processes, and make recommendations for standardizing both techniques and reporting practices. Finally, we discuss potential cutting-edge applications of diffusible iodine-based contrast-enhanced computed tomography (diceCT) and the issues that must still be overcome to facilitate the broader adoption of diceCT going forward

Functional morphology and evolution of the feeding apparatus of blindsnakes (Serpentes: Scolecophidia)

Most recent phylogenetic analyses of snakes have recognized two major clades within Serpentes: Alethinophidia and Scolecophidia. Alethinophidians feed predominantly on relatively large vertebrate prey, which they transport into and through the mouth via reciprocating ratcheting movements of the toothed palatopterygoid jaw arches. In contrast, scolecophidians are small-prey specialists, feeding almost exclusively on small arthropods. In addition, these diminutive, fossorial snakes lack many of the key morphological features which underlie the feeding mechanisms of alethinophidians, such as toothed palatopterygoid jaw arches and a distensible lower jaw. However, the functional significance of these morphological differences has remained poorly understood because there have been no detailed descriptions of feeding behavior in Scolecophidia. I used magnified high-speed videography, videofluoroscopy, and standard histological and gross morphological preparations to study the functional morphology of the feeding apparatus in representatives of two families of Scolecophidia, Leptotyphlopidae and Typhlopidae. In Leptotyphlops (Leptotyphlopidae), a mandibular raking mechanism is used to capture, ingest and transport prey. In this mechanism, the toothed anterior portions of the mandibular rami are rotated medially about the intramandibular joints in a bilaterally synchronous fashion. In contrast, Typhlops and Rhinotyphlops (Typhlopidae) feed via a maxillary raking mechanism, in which asynchronous rotations of the toothed maxillae are used to drag prey into and through the mouth. Both mandibular raking and maxillary raking involve exceptionally rapid (3–5 Hz) movements of the tooth-bearing elements of the jaws, thereby facilitating the ingestion of large numbers of small prey within relatively brief periods of time

Burrowing in blindsnakes: a preliminary analysis of burrowing forces and consequences for the evolution of morphology

International audienceBurrowing is a common behavior in vertebrates. An underground life-style offers many advantages but also poses important challenges including the high energetic cost of burrowing. Scolecophidians are a group of morphologically derived subterranean snakes that show great diversity in form and function. Although it has been suggested that leptotyphlopids and anomalepidids mostly use existing underground passageways, typhlopids are thought to create their own burrows. However, the mechanisms used to create burrows and the associated forces that animals may be able to generate remain unknown. Here, we provide the first data on push forces in scolecophidians and compare them with those in some burrowing alethinophidian snakes. Our results show that typhlopids are capable of generating higher forces for a given size than other snakes. The observed differences are not due to variation in body diameter or length, suggesting fundamental differences in the mechanics of burrowing or the way in which axial muscles are used. Qualitative observations of skull and vertebral shape suggest that the higher forces exerted by typhlopids may have impacted the evolution of their anatomy. Our results provide the basis for future studies exploring the diversity of form and function in this fascinating group of animals. Quantitative comparisons of the cranial and vertebral shape in addition to collecting functional and ecological data on a wider array of species would be particularly important to test the patterns described here

ECOSYSTEM MANAGEMENT AND MOOSE: CREATING A COHERENT CONCEPT WITH FUNCTIONAL MANAGEMENT STRATEGIES

Ecosystem management is a popular but poorly defined concept in conservation biology. Current vague, non-operational definitions provoke criticism of the concept and undermine credibility of its associated principles. We propose a definition of ecosystem management that emphasizes essential qualities of the concept rather than its accidental associations or properties, and that explains functional and operational attributes of ecosystem management rather than its descriptive characteristics. Based on these criteria, we offer a definition of ecosystem management as “a pattern of prescribed, goal-oriented environmental manipulations that: (1) treat a specified ecological system of identifiable boundaries as the fundamental unit to be managed; (2) has, as its desired outcome, the achievement of a state or collection of states in the ecosystem such that historical components, structure, function, products, and services of the ecosystem persist within biologically normal ranges and with normal rates of change; (3) uses naturally occurring, landscapescale processes as the primary means of management; and (4) determines management objectives through cooperative decision-making of individuals and groups who reside in, administer, and/or have vested interests in the state of the ecosystem”. Achieving workable ecosystem management is currently hindered by the lack of a unified vision and system of values for ecosystems, the absence of permanent inter-agency bodies with authority to manage ecosystems across multiple jurisdictions, and the lack of administrative mechanisms for the translation of ecosystem research findings into ecosystem management policies. We propose strategies to overcome these obstacles and examine moose (Alces alces) as an example of a species that is both important to ecosystem management and may benefit from it

The relationship between head shape, head musculature and bite force in caecilians (Amphibia: Gymnophiona)

ABSTRACT Caecilians are enigmatic limbless amphibians that, with a few exceptions, all have an at least partly burrowing lifestyle. Although it has been suggested that caecilian evolution resulted in sturdy and compact skulls as an adaptation to their head-first burrowing habits, no relationship between skull shape and burrowing performance has been demonstrated to date. However, the unique dual jaw-closing mechanism and the osteological variability of their temporal region suggest a potential relationship between skull shape and feeding mechanics. Here, we explored the relationships between skull shape, head musculature and in vivo bite forces. Although there is a correlation between bite force and external head shape, no relationship between bite force and skull shape could be detected. Whereas our data suggest that muscles are the principal drivers of variation in bite force, the shape of the skull is constrained by factors other than demands for bite force generation. However, a strong covariation between the cranium and mandible exists. Moreover, both cranium and mandible shape covary with jaw muscle architecture. Caecilians show a gradient between species with a long retroarticular process associated with a large and pennate-fibered m. interhyoideus posterior and species with a short process but long and parallel-fibered jaw adductors. Our results demonstrate the complexity of the relationship between form and function of this jaw system. Further studies that focus on factors such as gape distance or jaw velocity will be needed in order to fully understand the evolution of feeding mechanics in caecilians.</jats:p

Is vertebral shape variability in caecilians (Amphibia: Gymnophiona) constrained by forces experienced during burrowing?

ABSTRACT Caecilians are predominantly burrowing, elongate, limbless amphibians that have been relatively poorly studied. Although it has been suggested that the sturdy and compact skulls of caecilians are an adaptation to their head-first burrowing habits, no clear relationship between skull shape and burrowing performance appears to exist. However, the external forces encountered during burrowing are transmitted by the skull to the vertebral column, and, as such, may impact vertebral shape. Additionally, the muscles that generate the burrowing forces attach onto the vertebral column and consequently may impact vertebral shape that way as well. Here, we explored the relationships between vertebral shape and maximal in vivo push forces in 13 species of caecilian amphibians. Our results show that the shape of the two most anterior vertebrae, as well as the shape of the vertebrae at 90% of the total body length, is not correlated with peak push forces. Conversely, the shape of the third vertebrae, and the vertebrae at 20% and 60% of the total body length, does show a relationship to push forces measured in vivo. Whether these relationships are indirect (external forces constraining shape variation) or direct (muscle forces constraining shape variation) remains unclear and will require quantitative studies of the axial musculature. Importantly, our data suggest that mid-body vertebrae may potentially be used as proxies to infer burrowing capacity in fossil representatives.</jats:p