Connie Rojas Speciation Lesson Plan

Content: How do new species arise? Geographic barriers, dispersal, and genetic drift can increase the genetic differences between populations and contribute to their reproductive isolation, which can lead to speciation, or the origin of new species. Objectives: Students will analyze the four most commonly used definitions of species and evaluate their strengths and limitations. They will understand the four modes of speciation and how geographic barriers, dispersal, and genetic drift promote speciation. Lastly, they will apply what they learn and read primary literature on speciation, and identify the mode of speciation that was observed and how scientists determined speciation had indeed occurred. Assessment questions: Pre-class In what ways do organisms differ? [short answer] What is a species? [1-2 sentence short answer] What are the limitations to each species definition? [group work] Which species concept represents this scenario best? [2 question multiple choice quiz] During-Class Draw a concept map that relates the four modes of speciation to each other and to the concepts of reproductive isolation, gene flow, genetic drift, genetic divergence, natural selection, migration and competition [group work] Come up with multiple examples of a pre-zygotic or post-zygotic reproductive isolation mechanism [group work] Post-Class Find journal article on speciation and i) identify the mode of speciation that was investigated, ii) explain what methods the authors used to study speciation and iii) summarize the evidence authors used to support their claim that speciation had occurred [short essay; group work] What we would already know:

● Genetic variation refers to differences in DNA sequences. ● Molecular evolution is a change in DNA or amino acid sequences over time. ● Migration (i.e. gene flow), mutation, genetic drift, and non-random mating and

how they promote evolution. ● There is an immense diversity of life forms on Earth. ● How to formulate hypotheses and predictions, and relate evidence to hypothesis.

Connie Rojas Speciation Lesson Plan

Activities [Pre-Class] Establishing a Problem There is immense diversity of life on Earth

Here I would ask students: In what ways do these organisms differ? I would want them write down that these organisms differ in their morphology, physiology, metabolisms, diets, size, lifespans, coloration, social structures, and behavior, among other things. I would also ask the rhetorical question: But how do new species arise? Before we answer that, we must first define what a species is. Model a New Concept What is a species? I can ask students to write down their initial thoughts on what makes a species a species. What do members of the same species have in common? What do members of closely related species have in common? Defining and recognizing a species has been a controversial issue for a long time. Here is why…

Connie Rojas Speciation Lesson Plan

There are 4 main definitions of a species: Evolutionary species concept / phylogenetic species concept: species are groups of populations that share a common ancestry and a common fate, at least until the species itself bifurcates to form a new descendant species. A species is the smallest monophyletic group distinguished by a shared derived character.

Here, each branch in the phylogenetic tree is a unique species. Phenetic species concept / morphospecies concept: species are clusters of phenotypically similar individuals and populations.

Here, these mice look very similar and actually, all belong to the same family (Crecitadae)

Connie Rojas Speciation Lesson Plan

Biological species concept: species are groups of actually or potentially interbreeding populations that are reproductively isolated from other groups.

Here, African and Asian elephants can potentially interbreed, but they live locations that are far apart from each other and thus, they are considered different species. Ecological species concept: species are groups of populations that have similar ecological requirements and nutritional needs. Members of the same species occupy the same niche. Species are ecologically different.

Here, these two mosquitos represent different species because they are active at different times of the day, and prefer different breeding grounds, among other things.

Connie Rojas Speciation Lesson Plan

Coach However, what are the limitations? I would ask students to communicate with their groups outside of class [via email, video chat, in person meetings] to work together and fill out the following table and upload it to Google Drive or Outlook Powerpoint. Species Concept Limitations Evolutionary ● need to obtain sequenced data

● it is rarely possible to reconstruct with certainty the past evolutionary pathway

● have to constantly revise because species bifurcate

Phenetic ● Not useful for asexual organisms that look similar ● Some species might be morphologically

indistinguishable but are indeed different species ● Some species can look similar because of convergent

evolution but are not the same species ● Some species have multiple phenotypes (phenotypic

plasticity) Biological ● depends on observing the mating behavior and

interbreeding patterns of animals in their natural environments

● not applicable to fossils of organisms that lived in the past or to asexual organisms

Ecological ● Niches are difficult to define completely ● Niches are dynamic and species can change their diet

if a resource becomes scarce or they change location ● Members of same species can have more than one

niche. ● Sibling species can have the same niche4

Take home: this is why it’s hard to single out one of these concepts as the best concept. Coach Summative assessment: short 2 question quiz Many bacteria cannot be cultured in the laboratory and are impossible to observe in nature. Thus, scientists rely on DNA sequences and similarity among DNA sequences to classify bacteria into species. This represents the ___________ species concept.

a. Biological b. Ecological c. Evolutionary d. Morphological e. Physiological

Connie Rojas Speciation Lesson Plan

There are over 220 wasp species in the genus Polistes and they exhibit very distinct morphologies:

This represents the _________ species concept.

a. Biological b. Ecological c. Evolutionary d. Morphological e. Physiological

I can make these questions more challenging by including more detail in my descriptions and having these match more than 1 species concept. Activities [During-Class] Model a New Concept How do new species arise? Overview of the four modes of speciation Mode of speciation

Brief definition

Allopatry / allopatric

Populations are geographically isolated from one another and acquire enough genetic differences to diverge into distinct populations.

Peripatry / peripatric

A few individuals from a mainland population disperse to a new location remote from the original population and evolve separately.

Connie Rojas Speciation Lesson Plan

Parapatry / parapatric

Populations diverge in the absence of a geographic barrier because they experience different selective conditions.

Sympatry / sympatric

Populations diverge into new species while in the same location due to selective pressures and competition.

Modes of speciation in more detail: ALLOPATRY Populations become geographically separated from each other and cannot exchange genetic information (i.e. no gene flow) --> time allows for different mutations to become fixed in the two separated populations --> populations become reproductively isolated from each other and diverge into new species. Example: separation of continents during the late Pleistocence lead to the divergence of two populations of Camelids and the eventual origin of camels, llamas, and vicunas.

Connie Rojas Speciation Lesson Plan

PERIPATRY A few individuals from a mainland population disperse to a new location remote from the original population --> change accumulates faster in these smaller populations due to genetic drift, distinct environmental pressures, and natural selection --> genetic divergence of the island population from the mainland one --> speciation. Example: These varied Hawaiian plants, known as the "silversword alliance", are all descended from a common ancestral tarweed that arrived on the islands 5 million years ago from North America, and adapted to new niches in the archipelago.

Connie Rojas Speciation Lesson Plan

PARAPATRY Adjacent populations of individuals experience different selective conditions --> natural selection drives differences between the two populations--> two populations evolve phenotypic and genotypic variability and gene flow is reduced -->become new species. Example: a population of grasses (Anthoxanthum odoratum) live in soils contaminated with heavy metals and are now tolerant of heavy metals. Neighboring plants that don't live in polluted soil have not undergone selection for this trait. The two plants have evolved different flowering times which is reducing gene flow between the two populations. These two populations are on their way to becoming distinct species.

SYMPATRY Two populations occurs in the same place and experience gene flow (exchange genetic material) → natural selection acts to counteract gene flow (hybrid individuals do not survive to reproduce OR resource competition/resource partitioning separates the populations geographically--> become new species. Example: Ancestors of apple maggot flies (center) used to lay their eggs only on hawthorns (left), but when domestic apples were introduced (right), they started laying eggs in there too. Hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating with other apple flies. This means gene flow is reduced and these two groups are on their way to become new species.

Connie Rojas Speciation Lesson Plan

Coach Summative assessment: draw a concept map that relates the four modes of speciation to each other and to the concepts of reproductive isolation, gene flow, genetic drift, genetic divergence, natural selection, migration, and competition. I would have students draw their concept maps on Microsoft OneNote and then have each group edit/add on to another group’s concept map. Model a New Concept / Coach Mechanisms of Reproductive Isolation Reproductive isolation is key for the speciation and the origin of new species. I would assign each group one reproductive isolation mechanism, ask them to come up with multiple examples from one category and enter this information in the table that will be shared via Microsoft OneNote. We would then go over the complete table as a class.

Mechanism Definition Example Prezygotic: prevent fertilization from taking place Behavioral two populations are capable of

interbreeding, but don't breed because of differences in their courtship rituals

Gametic sperm and ova of the two different species are chemically incompatible (membrane sperm and egg proteins cannot recognize each other), and will not join to form a zygote

Mechanical Morphological differences between species prevent breeding

Temporal Species differences in their periods of sexual activity or breeding seasons prevent them from breeding

Ecological Two species differ in their habitat preferences which lowers their probability of mating

Postzygotic: prevent fertilized egg from developing into a fertile individual

Hybrid inviability Zygote dies early in embryogenesis or shortly after birth

Hybrid infertility Hybrids survive but are sterile

A second part of this task can ask groups to relate these mechanisms to one of the four modes of speciation.

Connie Rojas Speciation Lesson Plan

Activities [Post-Class] Fade In your groups, please search for a journal article on speciation. Article must be an original research paper published in the last 10 years [2009-2019]. Please share the article with me, and once approved, write a short two-three paragraph synthesis in which you mention:

● the mode of speciation that was investigated ● the study system and location ● the methods/ how scientist determined speciation had indeed occurred ● the evidence used to support claim that speciation had occurred ● if you were convinced by their claims and evidence