Terrestrial Locomotion in American Eels (Anguilla rostrata): How Substrate and Incline Affect Movement Patterns.

Fishes overcome a variety of challenges in order to invade the terrestrial environment. Terrestrial invasions by fish occur over a variety of environmental contexts. In order to advance their bodies on land, fishes capable of terrestrial excursions tend to use one of three different types of locomotor modes: axial-based, appendage-based, or axial-appendage-based.

Body shape transformation along a shared axis of anatomical evolution in labyrinth fishes (Anabantoidei).

Major morphological transformations, such as the evolution of elongate body shape in vertebrates, punctuate evolutionary history. A fundamental step in understanding the processes that give rise to such transformations is identification of the underlying anatomical changes. But as we demonstrate in this study, important insights can also be gained by comparing these changes to those that occur in ancestral and closely related lineages.

How temperature-induced variation in musculoskeletal anatomy affects escape performance and survival of zebrafish (Danio rerio).

Fishes are particularly sensitive to the effects of environmental conditions during early development, which can significantly impact adult morphology, performance, and survival. Previous research has highlighted the sensitivity of fishes to the effects of temperature during early development on vertebral number and muscle composition, which are both important determinants of an individual's swimming performance. In this study, we investigated the effect of developmental temperature on vertebral and muscle variation, and the subsequent effect of any variation on burst swimming performance in zebrafish (Danio rerio).

Linking vertebral number to performance of aquatic escape responses in the axolotl (Ambystoma mexicanum).

Environmental conditions during early development in ectothermic vertebrates can lead to variation in vertebral number among individuals of the same species. It is often seen that individuals of a species raised at cooler temperatures have more vertebrae than individuals raised at warmer temperatures, although the functional consequences of this variation in vertebral number on swimming performance are relatively unclear. To investigate this relationship, we tested how vertebral number in axolotls (Ambystoma mexicanum) affected performance of aquatic escape responses (C-starts).

Locomotion in elongate fishes: A contact sport.

Despite the physical differences between water and air, a number of fish lineages are known to make terrestrial excursions on land. Many of these fishes exhibit an elongate body plan. Elongation of the body can occur in several ways, the most common of which is increasing the number of vertebrae in one or both regions of the axial skeleton--precaudal and/or caudal.

Differential occupation of axial morphospace.

The postcranial system is composed of the axial and appendicular skeletons. The axial skeleton, which consists of serially repeating segments commonly known as vertebrae, protects and provides leverage for movement of the body. Across the vertebral column, much numerical and morphological diversity can be observed, which is associated with axial regionalization.

A revised metric for quantifying body shape in vertebrates.

Vertebrates exhibit tremendous diversity in body shape, though quantifying this variation has been challenging. In the past, researchers have used simplified metrics that either describe overall shape but reveal little about its anatomical basis or that characterize only a subset of the morphological features that contribute to shape variation. Here, we present a revised metric of body shape, the vertebrate shape index (VSI), which combines the four primary morphological components that lead to shape diversity in vertebrates: head shape, length of the second major body axis (depth or width), and shape of the precaudal and caudal regions of the vertebral column.

Effects of precaudal elongation on visceral topography in a basal clade of ray-finned fishes.

Elongate body forms have evolved numerous times independently within Vertebrata. Such body forms have evolved in large part via changes to the vertebral column, either through addition or lengthening of vertebrae. Previous studies have shown that body elongation in fishes has evolved most frequently through the addition of caudal vertebrae.

Zebrafish mnx1 controls cell fate choice in the developing endocrine pancreas.

The vertebrate endocrine pancreas has the crucial function of maintaining blood sugar homeostasis. This role is dependent upon the development and maintenance of pancreatic islets comprising appropriate ratios of hormone-producing cells. In all vertebrate models studied, an initial precursor population of Pdx1-expressing endoderm cells gives rise to separate endocrine and exocrine cell lineages.

Axial elongation in fishes: using morphological approaches to elucidate developmental mechanisms in studying body shape.

One of the most notable features in looking across fishes is their diversity of body shape and size. Extant actinopterygian fishes range in shape from nearly spheroidal in pufferfishes to extremely elongate in snipe eels with nearly every shape in-between. One extreme along the body-shape continuum is a highly elongate form, which has evolved multiple times independently in Actinopterygii.

Elongation of the body in eels.

The shape of the body affects how organisms move, where they live, and how they feed. One body plan that has long engaged the interest of both evolutionary biologists and functional morphologists is axial elongation. There is a growing interest in the correlates and evolution of elongation within different terrestrial and aquatic vertebrate clades.

Cyp26 enzymes function in endoderm to regulate pancreatic field size.

The control of organ size and position relies, at least in part, upon appropriate regulation of the signals that specify organ progenitor fields. Pancreatic cell fates are specified by retinoic acid (RA), and proper size and localization of the pancreatic field are dependent on tight control of RA signaling. Here we show that the RA-degrading Cyp26 enzymes play a critical role in defining the normal anterior limit of the pancreatic field.

Origin of the zebrafish endocrine and exocrine pancreas.

Here, we report a detailed fate map of the zebrafish pancreas at the early gastrula stage of development (6 hours postfertilization; hpf). We show that, at this stage, both pancreas and liver progenitors are symmetrically localized in two broad domains relative to the dorsal organizer. We demonstrate that the dorsal and ventral pancreatic buds can derive from common progenitor pools at 6 hpf, but often derive from independent populations.

Convergent evolution of the head retraction escape response in elongate fishes and amphibians.

Aquatic escape responses have typically been described as C-starts. However, another aquatic escape response, head retraction, occurs in several elongate species, but has never been studied in detail. The goals of this study are to describe the head retraction escape response in a phylogenetically diverse sample of species, to trace the evolution of head retraction in anamniote vertebrates, and to correlate key morphological traits with escape response behavior.