Chapter 17-4 Patterns of Evolution

Macroevolution Large-scale evolutionary patterns and processes that occur over long periods of time. There are 6 important patterns of macroevolution. Macro: ft, micro:inches

1. Extinction More than 99% of all species that have ever lived are now extinct!!! Usually, species gradually become extinct in ways that are caused by natural selection. Several times in Earth’s history, mass extinctions wiped out entire ecosystems. 1) Competition for resources, some adapt and survive to environment, some dont 2) Example picture: huge asteroid impact wiped out dinosaurs and other organisms. Dust and water vapor thrown into air, global climate change. Cleared way for modern mammals and birds. 3) Left habitats open and provided opportunities for those organisms that survived. Researchers looked for a single, major cause for this but now think mass extinctions were caused by several factors.

What effects have mass extinctions had on the history of life? Mass extinctions have: provided ecological opportunities for organisms that survived resulted in bursts of evolution that produced many new species

2. Adaptive Radiation (divergent evolution) A single species (or small group of species) evolves into several different forms that live in different ways. Small scale example: In the adaptive radiation of Darwin's finches, more than a dozen species evolved from a single species. Ex: Darwin’s finches, more than a dozen species evolved from a single species

Large scale example: The disappearance of dinosaurs resulted in the adaptive radiation of mammals. 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.

3. Convergent Evolution Different organisms undergo adaptive radiation in different places/times but in similar environments. Convergent Evolution: The process by which unrelated organisms come to resemble one another. Example: shark (fish), penguins (birds), and dolphins (mammals) A dolphin’s fluke and a fish’s tail fin are analogous structures (body parts of organisms that do not have common evolutionary origins but are similar in function). Streamlined body and various appendages that enable it to move quickly through water (analogous structures)

Cactus! Euphorbia

4. Coevolution Sometimes organisms that are closely connected to one another by ecological interactions evolve together. Coevolution: The process by which two species evolve in response to changes in each other over time. As an outstanding example of this, take the case of Darwin’s orchid, pictured right. When Charles Darwin first encountered this species (Angraecum sesquipetale), he predicted that a moth species would be discovered as its sole pollinator – that green tube that drops down to the ground in the picture is where the moth would stick its proboscis to get to the nectar. Darwin’s prediction was completely right: in 1902, Xanthopan morganii praedicta was discovered. Its proboscis was the longest in the insect world, it was also endemic to Madagascar and was observed pollinating the orchid. How did Darwin know this moth would exist? The fact is that, as I said already, flowers are structured around their insect pollinators and both flower and pollinator need each other to survive, hence the mutualism. Some flowers are more specific than others, orchids being the more extreme cases of this.

5. Punctuated Equilibrium Darwin felt that biological change was slow and steady, an idea known as gradualism. Punctuated equilibrium is a pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. Ex: horseshoe crabs have changed little since the time they first appeared in the fossil record

Evolution has often proceeded at different rates for different organisms at different times during the history of life on Earth.

6. Developmental Genes and Body Plans Biologists perform experiments with gene expression by turning genes on or off in embryological development and looking at the results. Small changes in the activity of control genes can affect many other genes to produce large changes in adult animals.

Changes in gene expression may explain how these differences evolved. For example, if a gene called “wingless” is turned on in an insect body segment, that segment grows no wings. Changes in gene expression may explain how these differences evolved. 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.

What are the 6 important patterns of macroevolution? extinction adaptive radiation convergent evolution coevolution punctuated equilibrium changes in developmental genes