17-4 Patterns of Evolution

I. Extinction

Macroevolution - large-scale evolutionary patterns & processes that occur over long periods of time.

Six important topics in macroevolution are: extinction adaptive radiation convergent evolution coevolution punctuated equilibrium changes in developmental genes

Over 99% of all species that have ever lived are now extinct Mass extinctions have: provided ecological opportunities for organisms that survived resulted in bursts of evolution that produced many new species

II. Adaptive radiation

Adaptive radiation - the process of a single species or a small group of species evolves into several different forms that live in different ways.

Adaptive Radiation of Mammals Artiodactyls Cetaceans Perissodactyls Tubulidentates Hyracoids Sirenians Proboscideans This diagram shows part of the adaptive radiation of mammals, emphasizing current hypotheses about how a group of ancestral mammals diversified over millions of years into several related living orders. Note that the dotted lines and question marks in this diagram indicate a combination of gaps in the fossil record and uncertainties about the timing of evolutionary branching. Ancestral Mammals Copyright Pearson Prentice Hall

The evolution mammals is an example of adaptive radiation b/c many species of mammals evolved from one ancestral species

III. Convergent evolution

Convergent Evolution- process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Ex: the similar nature of the flight/wings of insects, birds, pterosaurs (flying reptiles that are now extinct), and bats.

IV. coevolution

Ex: Predator/prey and parasite/host Coevolution- A process that takes place with two species evolve in response to each other as time passes. Ex: Predator/prey and parasite/host Some Central American Acacia species have hollow thorns and pores at the bases of their leaves that secrete nectar (see image at right). These hollow thorns are the exclusive nest-site of some species of ant that drink the nectar. But the ants are not just taking advantage of the plant—they also defend their acacia plant against herbivores. berkeley.edu

v. Punctuated equlibrium

Gradualism- evolutionary change is slow and steady Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent. Copyright Pearson Prentice Hall

Punctuated equilibrium- a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent. Copyright Pearson Prentice Hall

vi. Developmental genes & body plans

Scientist believe changes in genes for growth and differentiation during embryological development could produce changes in body shape and size. Small changes in the activity of control genes can affect many other genes to produce large changes in adult animals. Small changes in the timing of cell differentiation and gene expression can make the difference between long legs and short ones. Copyright Pearson Prentice Hall

Evolution of Wings in Insects Ancient Insect Two Types of Modern Insects Some ancient insects, such as the mayfly nymph (top), had winglike structures on many body segments. Modern insects have only four wings or two wings. Changes in the expression of developmental genes may explain how these differences evolved. Copyright Pearson Prentice Hall