Speciation Evolution creates (and destroys) new species, but … Macroevolution 5/9/2019 Speciation Evolution creates (and destroys) new species, but … What is a species? Its not as straightforward a question as most believe. G. Podgorski, Biol. 1010

Macroevolution 5/9/2019 What is a Species? The definition we’ll use is this: A species is a group of individuals capable of interbreeding to produce fertile offspring. G. Podgorski, Biol. 1010

How Many Species Are There? Macroevolution 5/9/2019 How Many Species Are There? We don’t know. About 2 million species have been described. Estimates of existing species number range from 4 million to 100 million (with 10-15 million being a more commonly considered upper estimate). G. Podgorski, Biol. 1010

How did this diversity of life come to be? Macroevolution 5/9/2019 How did this diversity of life come to be? Speciation is an event that produces two or more separate species from an original species. Species = basic unit Continuous lineage - information passed through genes Speciation - rise of new species G. Podgorski, Biol. 1010

The key to speciation is reproductive isolation of populations. Macroevolution 5/9/2019 How Do Species Arise? The key to speciation is reproductive isolation of populations. There are extrinsic and intrinsic reproductive isolating mechanisms. Geographic isolation is the primary extrinsic reproductive isolating mechanism. G. Podgorski, Biol. 1010

Geographic isolation is the primary extrinsic isolating mechanism. Macroevolution 5/9/2019 Geographic Isolation Geographic isolation is the physical separation of members of a population. Geographic isolation is the primary extrinsic isolating mechanism. G. Podgorski, Biol. 1010

Allopatric Speciation Allopatric (different home lands) speciation occurs when geographic isolation creates a reproductive barrier (an extrinsic mechanism). Once a populations have been separated, Natural Selection cause the two new Populations to genetically Diverge.

Allopatric Speciation Macroevolution 5/9/2019 Allopatric Speciation Harris’ antelope squirrel White-tailed antelope squirrel Two species of ground squirrel are postulated to have descended from a common ancestral population that was separated by formation of the Grand Canyon. G. Podgorski, Biol. 1010

Sympatric Speciation Sympatric speciation occurs when a reproductive barrier is created by something other than geographic isolation (intrinsic mechanisms). Intrinsic mechanisms involve changes to organisms that prevent interbreeding. There are many different causes for intrinsic speciation.

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation Macroevolution 5/9/2019 Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation (different habits within an overlapping range) G. Podgorski, Biol. 1010

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation Macroevolution 5/9/2019 Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species. G. Podgorski, Biol. 1010

Behavioral Isolation Mechanisms Macroevolution 5/9/2019 Behavioral Isolation Mechanisms Courtship rituals, like these, are critical for mating within a species, but ineffective for attracting members of other species. G. Podgorski, Biol. 1010

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation Macroevolution 5/9/2019 Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation G. Podgorski, Biol. 1010

Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation Macroevolution 5/9/2019 Many Intrinsic Reproductive Isolating Mechanisms Drive Speciation G. Podgorski, Biol. 1010

Hybrid Infertility Was the reeson for Cloning Mules Macroevolution 5/9/2019 Hybrid Infertility Was the reeson for Cloning Mules G. Podgorski, Biol. 1010

Speciation Occurs at Widely Differing Rates Macroevolution 5/9/2019 Speciation Occurs at Widely Differing Rates A slow rate of speciation evidenced by a living horseshoe crab (13 extant species) and a 300 million year-old fossil species A rapid rate of speciation evidenced by Galapagos finches which have diversified into 13 species within the last 100,000 years. G. Podgorski, Biol. 1010

Speciation Dynamics - Gradualism or Punctuated Equilibrium? Macroevolution 5/9/2019 Speciation Dynamics - Gradualism or Punctuated Equilibrium? Gradualism states that speciation Occurs at a regular gradual rate. Punctuated equilibrium states that organisms evolved in a relatively short period of time. Short bursts. Scientists still argue over this one! G. Podgorski, Biol. 1010

Macroevolution 5/9/2019 G. Podgorski, Biol. 1010

A typical “lifetime” for a species is about 1 million years. Macroevolution 5/9/2019 Species Come and Go Best estimates from the fossil record indicate that greater than 99% of species that have exited are now extinct. A typical “lifetime” for a species is about 1 million years. G. Podgorski, Biol. 1010

Classifying Life’s Rich Diversity Macroevolution 5/9/2019 Classifying Life’s Rich Diversity Why bother? An intrinsic reason is that modern classification systems tell who’s related to whom and how we all came to be. G. Podgorski, Biol. 1010

Classifying Life’s Rich Diversity Macroevolution 5/9/2019 Classifying Life’s Rich Diversity Why bother? A practical reason is that if we want to preserve an environment compatible with human life, we’d better know what’s out there. G. Podgorski, Biol. 1010

The Linnaean Hierarchical Classification System Macroevolution 5/9/2019 The Linnaean Hierarchical Classification System G. Podgorski, Biol. 1010

How Do We Classify Organisms? Macroevolution 5/9/2019 How Do We Classify Organisms? Ideally, classification is based on establishing the evolutionary relationships between organisms. The evolutionary relationship between organisms is their phylogeny. Cladistics is the method of classification based on establishing phylogenies (i.e. getting at evolutionary relationships. Cladistics proceeds by comparing shared ancestral and shared derived characters between sets of organisms. G. Podgorski, Biol. 1010

Macroevolution Cladistics 5/9/2019 A phylogeny (cladogram) for vertebrates. each node indicates a common ancestor The greater the number of derived characters shared by a pair of organisms, the closer their degree of relationship. The closer the degree of relationship, the closer the most recent common ancestor. G. Podgorski, Biol. 1010

Macroevolution It’s Critical (and often difficult) To Distinguish Homology from Analogy 5/9/2019 Homologous structures, like the bat wing and gorilla arm, are similar because they are derived by modification of a shared ancestral structure. Homology is the key to establishing phylogenies. G. Podgorski, Biol. 1010

Another Set of Analogies Created by Convergent Evolution Macroevolution Another Set of Analogies Created by Convergent Evolution 5/9/2019 Ocotillo of the US southwest Allauidia of Madagascar G. Podgorski, Biol. 1010

Macroevolution Results of Cladistic Analyses Sometimes Run Counter to Classical Classification Schemes 5/9/2019 Which pair is more closely related? A lizard/crocodile or bird/crocodile? Cladistic analysis indicates that the bird/crocodile pair is more closely related. G. Podgorski, Biol. 1010

DNA Hybridization: uses DNA similarity between species Macroevolution 5/9/2019 DNA Hybridization: uses DNA similarity between species G. Podgorski, Biol. 1010

Macroevolution 5/9/2019 G. Podgorski, Biol. 1010

Which species are the closest living relatives of modern humans? Macroevolution 5/9/2019 Which species are the closest living relatives of modern humans? Humans Gorillas Chimpanzees Chimpanzees Bonobos Bonobos Gorillas Orangutans Orangutans Humans 14 15-30 MYA MYA The pre-molecular view was that the great apes (chimpanzees, gorillas and orangutans) formed a clade separate from humans, and that humans diverged from the apes at least 15-30 MYA. Mitochondrial DNA, most nuclear DNA-encoded genes, and DNA/DNA hybridization all show that bonobos and chimpanzees are related more closely to humans than either are to gorillas. G. Podgorski, Biol. 1010