Question

1.Describe the basic process of metamorphosis and give three examples from three different phyla of the varied forms of metamorphosis in the animal kingdom.

2.Animals typically show either radial or bilateral symmetry. Explain what this means and discuss how this affects their ecology and behavior.

3.Only a few groups of animals have conquered land throughout evolutionary history. Identify these groups and describe some of the challenges associated with life on land as opposed to life in water. Given the challenges, what advantages are there to living on land?

4.With over one million species described, arthropods are the most diverse group of animals. In the space below, briefly describe at least three reasons that make arthropods such a successful group of animals.

Answer 1

1. Metamorphosis is the transition in overall body pattern that occurs during the life history of some animals following birth or hatching. In general, cells in the different parts of a multicellular organism all have the same genes, although only some of these genes are expressed (translated into proteins) in any given cell. At the molecular level, highly regulated temporal and spatial changes in gene expression cause metamorphosis in all animals. Metamorphosis is iodothyronine-induced and an ancestral feature of all chordates.

Insects:

metamorphosis, insects are classified as Ametabola, Hemimetabola, or Holometabola. The Ametabola do not undergo metamorphosis. During development, these insects increase in size but do not undergo distinct changes in form. In general, the Ametabola do not have wings. both hemimetabolous and holometabolous insects have significant morphological and behavioral differences between larval and adult forms,  In the Hemimetabola, a form called the nymph hatches from the egg. Nymphs lack wings, but have compound eyes and otherwise resemble the adult form, except they are smaller. In Holometabola the larva develops into a pupa inside a cocoon. The pupa is often considered a resting stage and can often survive in unfavorable environments. Eventually, the pupa metamorphoses into an adult.

Amphibians: Metamorphosis differs in the many different amphibian species. In frog development, the eggs hatch and give rise to tadpoles, small aquatic larvae that have external gills, and are mainly vegetarian. As the tadpole grows, internal gills and limbs form. Several significant changes occur during metamorphosis into the adult, including the growth of largemouth and tongue, loss of gills, the formation of lungs, growth of the front legs, and resorption of the tail. Numerous biochemical changes accompany these morphological changes, such as synthesis of a new visual pigment in the eyes and a new oxygen-binding hemoglobin protein in the blood. The adult is mainly insectivorous and partly terrestrial.

Fish:

Some fish, both bony fish (Osteichthyes) and jawless fish (Agnatha) undergo metamorphosis. Fish metamorphosis is typically under strong control by the thyroid hormone. Examples among the non-bony fish include the lamprey. Among the bony fish, mechanisms are varied. The salmon is diadromous, meaning that it changes from a freshwater to a saltwater lifestyle.

2.  Organisms with radial symmetry show a repeating pattern around a central axis such that they can be separated into several identical pieces when cutting through the central point.

Organisms with bilateral symmetry contain a single plane of symmetry, the sagittal plane, which divides the organism into two roughly mirror-image left and right halves – approximate reflectional symmetry.

Radial symmetry is advantageous to sedentary organisms because sensory receptors are evenly distributed around the body. For sessile (sedentary) organisms, radial symmetry is useful because the animal can just "sit down" and grab food or detect threats from all directions.

On the other hand, In invertebrates with bilateral symmetry, sense organs and nerves tend to be concentrated in front of their body. Such invertebrates can respond better to the environmental stimulus. Invertebrates having bilateral symmetry have segmented bodies. In the course of evolution, these segments evolved to become specialized cells and organs. Such specialized cells are able to perform specific functions. Segmentation also helps an organism to increase its body size without the use of much genetic material. This happens as a result of the repetition of similar cells in the segments.

3.  Vertebrates appear to have evolved from chordates in the near-shore seawater (SW) or brackish water, where rivers flow into the ocean. Thus, the earliest vertebrates likely had an excellent ability to swim against water currents (Romer, 1968). It is thought that primitive armored fishes once entered inland freshwaters (FWs) in the early Devonian period of the Paleozoic era and flourished there.

But these early tetrapods had to develop more than a new way to walk - their entire skeletons had to change to support more weight, as the water supports mass in a way that air simply doesn't. Each vertebra had to become stronger for support. Ribs and vertebrae changed shape and evolved for extra support and to better distribute weight. Skulls disconnected, and necks evolved to allow better mobility of the head and to absorb the shock of walking. Bones were lost and shifted, streamlining the limbs and creating the five-digit pattern that is still reflected in our own hands and feet. Joints articulated for movement and rotated forward to allow four-legged crawling. Overall, it took a long 30 million years or so to develop a body plan fit for walking on land.

At the same time, these cumbersome wanna-be land-dwellers faced another obstacle: the air itself. With gills adept at drawing oxygen from water, early tetrapods were ill-equipped to breathing air. While many think that early tetrapods transformed their gills into lungs, this actually isn't true - instead, it was the fish's digestive system that adapted to form lungs. The first tetrapods to leave the water breathed by swallowing air and absorbing oxygen in their gut. Over time, a special pocket formed, allowing for better gas exchange. In many fish, a similar structure - called a swim bladder - exists which allows them to adjust buoyancy in the water, and thus many have hypothesized that tetrapod lungs are co-opted swim bladders. In fact, exactly when tetrapods developed lungs are unclear.

The prototetrapods that moved onto the land were faced with two major challenges: gravity (or the loss of the natural buoyancy provided by the watery habitat) and desiccation. Concerning the gravity issue, they have developed circulatory systems with a powerful heart to pump out the blood throughout the body against gravitational force, resulting in high arterial pressures in mammals and birds. We found that hormones that increase blood pressure and cardiac performance, including Ang II, vasopressin/vasotocin, and endothelin, play critical roles in the circulatory system of these tetrapods.

These crucial adaptations to tetrapod skeletons and anatomy allowed them to conquer the world above the waves. Without their evolutionary ingenuity, a diverse set of animals, including all mammals, would not be where they are today. Yet still, we barely understand the ecological settings that drove these early animals out of the sea.

4. Arthropods are the most diverse group of animals. It is certainly no accident that insects are the most abundant and most diverse group of organisms on earth. They have maintained a position of ecological pre-eminence for over 400 million years.

Exoskeleton

Unlike vertebrates, an insect's supporting skeleton is located on the outside of its body. This exoskeleton is a marvelous structure that not only gives shape and support to the body's soft tissues, but also provides protection from attack or injury, minimizes the loss of body fluids in both arid and freshwater environments, and assures mechanical advantage to muscles for strength and agility in movement.  

Small Size

In general, insects are marvels of miniaturization. Most species are between 2 and 20 mm (0.1 - 1.0 inch) in length, although they range in size from giant moths that would nearly cover your computer screen to tiny parasitic wasps that could hide inside the period at the end of this sentence. small size is the minimal resources needed for survival and reproduction. A crumb is a feast; a dewdrop quenches thirst; a pebble provides shade. In some cases, food requirements are so modest that an insect may live on a single plant or animal for its entire life and never exhaust its food supply.

Flight

Insects are the only invertebrates that can fly. Judging from the fossil record, they acquired this ability about 300 million years ago -- nearly 100 million years before the advent of the first flying reptiles. The flight gave these insects a highly effective mode of escape from predators that roamed the prehistoric landscape.

Metamorphosis

Most insects undergo significant developmental changes as they grow from immatures to adults. These changes, collectively known as metamorphosis, may involve physical, biochemical, and/or behavioral alterations that promote survival, dispersal, and reproduction of the species.

Adaptability

A combination of large and diverse populations, high reproductive potential, and relatively short life cycles, has equipped most insects with the genetic resources to adapt quickly in the face of a changing environment. Their record of achievement is impressive: they were among the first creatures to invade the arid expanses of dry land and exploit green plants as a source of food, they were the first animals to use flight as an escape from predators, and they were the first organisms to develop a complex social hierarchy with the division of labor and cooperative care of the young.