Outcomes of Evolution

Selection acts on Variation Genetic variation Directional Disruptive Stabilizing

Directional Selection Favors one of the extreme variations of a trait Can lead to rapid evolution of a population

Disruptive Selection Favors both extreme variations of a trait Eventually results in no intermediate forms of the trait Leads to the evolution of two new species

Stabilizing Selection Favors average individuals Reduces variation in a population

SPECIATION The evolution of a new species from previously existing species Isolating Mechanisms lead to speciation

Crash Course: Speciation https://www.youtube.com/watch?v=2oKlKmrbLoU&list=PL3EED4C1D684D3ADF&index=15

What can lead to speciation? Geographic Isolation A new species can evolve when a population has been GEOGRAPHICALLY ISOLATED. Physical barriers divide a population

Reproductive Isolation Occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring Genetic information becomes too different (mutations) Behaviors become too different (mating seasons)

On the Origin of Species Darwin did not publish his ideas on evolution until 1859. He published On the Origin of Species by Means of Natural Selection

Darwin’s ideas have been updated Genes are responsible for inherited traits.

Darwin’s ideas have been updated Isolation leads to species formation. Isolation: the condition in which two populations of the same species cannot breed with one another. Populations of the same species living in different locations tend to evolve differently. http://williamcalvin.com/bk3/img/kaibab.gif

Kaibab Squirrel Aberts Squirrel

Species: Group of organisms that are genetically similar and can produce fertile offspring.

13: Processes and outcomes of evolution Challenge: How do evolutionary processes lead to changes in biodiversity? Vocab: Adaptations Macroevolution Microevolution Speciation

#1 Microevolution refers to the evolution of very small organisms, such as bacteria. FALSE Microevolution is evolution on a small scale that changes the gene pool of a population or species

Microevolution Results in changes in the frequency of alleles (like we saw in the mice in activity 12) Four main factors: Mutations Natural selection Genetic drift Gene flow

#2 The evolutionary fitness of an organism is related to its physical strength or size. FALSE Evolutionary fitness is related to the probability of survival and reproduction

#3 Adaptations result only from natural selection. TRUE Adaptations are inherited characteristics that favor survival or reproduction and are the result of natural selection

Adaptations Inherited traits that increase an organism’s fitness (survival and rate of reproduction) Results from natural selection Organisms cannot CHOOSE to adapt Organisms don’t adapt out of NEED. Either they have traits that will help them survive, or they die! INDIVIDUAL organisms cannot adapt in their lifetime

#4 Geographic Isolation results from either changes in the land or migration of a group of organisms to a distant location. TRUE Geographic Isolation can occur when rivers or canyons form, or if a population moves far away from others of the same species.

#5 When gene flow continues between two populations, they are likely to remain the same biological species. TRUE When populations share a common gene pool they exchange genes through sexual reproduction and share any genetic changes

#6 The evolution of many species from one ancestral species is proposed as a mechanism for the evolution of the 13 species of Galapagos finches. TRUE Scientists think that the different species of finches evolved from a small population that was blown off course from mainland South America

Speciation If enough small changes accumulate in a population (microevolution), this could lead to speciation (macroevolution) Occurs most often when gene flow is restricted or cut off Examples: adaptive radiation of Darwin’s finches changes in birds seen in the computer simulation

#7 Until human populations grew and began to change the environment, there were very few extinctions. FALSE Extinctions have occurred throughout earth’s history for many reasons, including disease and natural disasters. Human activities have increased the rate of extinctions

#8 Macroevolution refers to any evolutionary changes at or above the species level. TRUE Macroevolution includes speciation and extinction, which change earth’s biodiversity. Most species that have lived on earth are now extinct, perhaps as high as 99%

Activity 10: What is a Species? Challenge: How do new species separate from existing species? Page 472 -- Introduction

Background Information- pg 473 The biological species concept is a method of defining a species based on whether the organisms can breed with each other in nature to produce fertile offspring. Gene flow results from this interbreeding, as genes move between populations Members of the same species share a common group of genes called a gene pool This method of classification does not always fit: (species that reproduce asexually, some plants that can crossbreed, extinct fossil organisms)

Part A: Procedure Claims about the process of species separation: Early means they are still one species or have just begun separation. Mid means they are separating. Late means they are at the end of separation, they are most likely two species.

Part A: Procedure Read the examples from the textbook, pages 475-479 Complete a chart for each of your assigned examples Species Separation Example number/ organism name Claim Evidence to support the claim Reasoning

Ex. 1: Red and Purple Sea Urchins Species Separation Example number/ organism name Example 1: Red and purple sea urchins Claim Late Evidence to support the claim Eggs can only be fertilized in a lab, embryos do not survive Reasoning Even though eggs can be artificially fertilized, the offspring don’t survive, so there is no exchange of genes or a common gene pool. They have most likely split into two different species

Procedures Example #1 as a class Group 1– examples 4, 5, 8

Part A: Procedure Dogs and wolves Midas cichlid Red sea urchins Horses Orchids Copper resistant/tolerant monkeyflowers Eastern/Great Plains frogs Northern & California Spotted owls Blue & red Cichlids green lacewings Dogs and wolves Arrow cichlid Purple sea urchins Donkeys Orchids

Part B: Procedure Steps 13-15 (Scientific Groupings) Analysis questions 2 & 3

Procedure Step 15– Reproductive Barriers Behavioral Isolation- different mating signals/rituals Meadowlarks, fireflies, blue/red cichlids Habitat Isolation- same area, different habitat Garter snakes, insects Temporal Isolation- different breeding times Lacewings, orchids Mechanical Isolation- physically incompatible Flowering plants, damselflies Gametic Isolation- sperm and eggs can’t interact Purple/White Sea urchins Hybrid Sterility- offspring are infertile Horses/donkeys Reduced Hybrid Viability- offspring don’t live long Frogs Geographical Isolation- live in different locations Lions/tigers, squirrels

So what happens next? Reproductive barriers prevent gene flow between populations Mutations and adaptations that evolve in one population can’t be shared with the other if there is no gene flow Over time, populations can become so genetically different that they are no longer the same species (speciation)

Analysis Question 2 Explain how geographic isolation can lead to speciation. If two populations do not meet in nature, than there is no gene flow between the populations. There genes will continue to mutate and evolve separately, since the populations will have different gene pools.

Analysis Question 3 Lions and tigers do not overlap in range and do not breed in nature. In captivity, a male lion may mate with a female tiger and produce offspring. Although more rare, a male tiger may also mate with a female lion to produce offspring. In both cases, the male offspring are sterile, while the females might or might not be fertile. Explain where lions and tigers are on the speciation continuum, according to the biological species concept. Support your answer with evidence and reasoning. Very late in the process of speciation, but not totally separate, since male offspring are infertile but females might still be able to produce offspring of their own.

Human Species DNA evidence suggests that modern humans (Homo sapiens) could interbreed with Homo neanderthalis There is newly discovered evidence of another human ancestor, “Denisova” that might have bred with humans as well One current hypothesis is that all three species evolved from Homo heidelbergensis along parallel paths at the same time. Denisovans and Neanderthals went extinct. Homo sapiens survived.