Non-Biodiversity

Adaptation & Speciation 3

  1. Explain the fundamental “paradox of sex” and the main hypotheses about why sexual reproduction is common in nature despite its many costs

Overall: The paradox of sex is that sexual reproduction is riskier, and has more disadvantages than asexual reproduction. 

Asexual produce 2x more offspring & are easier.

Theories of why sexual reproduction is more common.

  • Sexual reproduction increases genetic diversity, which increases:

The likelihood of a species to produce offspring that can survive in various conditions.

The speed of reshuffling genes

Red Queen - More offspring will help fight against evolving pathogens and parasites. 

Mullers Ratchet - With asexual reproduction, harmful mutations will persist over time(increasing genetic load). Sexual reproduction will have those mutations purged from natural selection. 

  1. Explain how differing reproductive strategies in males and females can result in differing selective pressures. 

Overall: Males have a lot of sperm, so they focus on quantity of offspring not quality. Females have a few eggs, so they focus on quality of offspring not quality. 

From this, males produce better in environments where selection favors mating opportunities. Whatever features allow for more mating opportunities will typically persist through generations. 

Intrasexual Selection in Males(competition)

Females will produce better in environments that select for better quality care for their offspring. Whatever features allow for better quality offspring in these environments will persist for generations.

Intersexual Selection in Females(choice)

These differences lead to sexual dimorphism, the differences between males and females. 

All of the above is typical, but the reverse can happen. 

More

  1. Evaluate the relationship between the operational sex ratio and the direction and intensity of sexual selection

OSR: Sexually Active Males / Sexually Active Females

Higher OSR -> Male-Biased OSR: more competition among males

Sexual Selection acts strongly on males leading to more traits that improve matability (combat, attractiveness). Intrasexual Selection in Males and Intersexual Selection in females,Lower OSR -> Female Biased OSR: competition among females for mates. Males choose, leading to sexual selection acting on females more. Intrasexual Selection in females and intersexual selection for males. 

X-Gender Biased OSR-> more competition between x, increased intrasexual selection and sexual selection acts primarily on them. Intersexual selection acts on Y-Gender. 

Higher OSR -> increased intensity of sexual selection & dimorphism. 

  1. Describe how sexual dimorphism can result from sexual selection

Sexual Selection is when certain traits evolve and develop in order to reproduce. These traits involve being better competitively and being more attractive. These traits often are different from the traits of the opposite sex, therefore sexual dimorphism exists. 

  1. Explain the circumstances that can lead to intersexual selection (mate choice) and intrasexual selection (mating competition)

Intrasexual Selection is when members of one sex compete against one another, which happens when OSR is biased(typically to males).

Intersexual Selection is when members of one sex choose of the sex, and it’s when OSR is biased towards the opposite sex. 

  1. Describe the process by which sexual selection can take place after mating

There is sperm competition, so sexual selection favors what sperm gets to fertilize. Females can play a part in this too. 

  1. Explain how sexual conflict can lead to antagonistic coevolution

Sexual Conflict - when female and male reproductive interests do not align. 

Antagonistic Coevolution - when a sex evolves a trait to counteract the sexual conflict between them in order to reproduce.

Conflict Happens(lets say males benefit more from reproducing more, and females don’t) —> One Sex evolves trait —> Other Sex evolves countertrait first sex trait → cycle.

Senescence: (Aging) The process of gradual deterioration & decline in function that occurs with age. 

Metapopulation: A group of separate populations of the same species that interact through occasional migration or gene flow. 

Types of Speciation(when two populations cannot procreate)

Allopatric Speciation: When there is a geographic barrier that divides a population and over time they evolve differently to the point that they are two different species

Peripatric Speciation: When a small section gets isolated from the population, and then the same as allopatric speciation. More rapid evolution because it is a littler subset which will be less representative of the population

  • Vicariance: the formation of geographic barriers that

separate a population

  • Colonization & Dispersion: 

Paripatric Speciation: When neighboring populations are unable to mate to do differences in neighboring conditions, but they are able to interact with each other. 

Sympatric Speciation: When new species evolve in a population that is not geographically isolated. 



Gametic Incompatibility - Sperm & Egg from different species fail to meet.

Prezygotic vs Postzygotic Reproductive Barriers

Prezygotic - before fertilization ex.(mating behavior or timing)

  • Pre-mating and post-maring before fertilization

Postzygotic - after fertilization ex.(sterile offspring)

Hybrids

Reinforcement & Fusion are opposites

Reinforcement is when natural selection strengthens reproductive barriers, reducing hybrid formation. Reinforcement - Reduce

Fusion is when natural selection weakens the barriers, allowing for more hybrid formation. Fusion - Free

Zones

Primary Hybrid Zone -> When populations are initially diverging(still in contact), and typically during parapatric speciation, there is a hybrid zone of gradual genetic drift.

Secondary Hybrid Zone -> Previously separated populations come back into contact with each other, and fuse, allowing for interbreeding. 

Defining Species Methods

Morphological Traits -

Benefits - easily observed

Drawbacks - members of the same species can be morphologically distinct, and members of different species can be morphologically similar(cryptic species)

Biological Species Concept - based on if they can produce fertile, viable offspring

Benefits - objective criterion, and reveals a lot about evolution

Drawbacks - not easily observed, don't work for asexual species, and hybrid species make it difficult. 

Macroevolution 2


  1. Appreciate what the fossil record offers the study of evolution; especially what is unique to the fossil record (the past is the key to the present).

The fossil record is the best direct evidence of old life on Earth, because it is the only evidence where you can see the changes. 

  1. Transitional forms seen in the fossil record provide evidence of descent with modification.

Transitional forms are forms with evidence of both ancestral and derived species, therefore showing evidence of evolution, or descent with modification. The transitional forms are species, not half of one or another, but evidence of the ancestral and derived species.

  1. What is the overall pattern of marine diversity through time and how (what data) is this curve generated?

Generally, marine diversity increases over time, and it is shown through the Saposki Curve.

Sapkoksi Curve

  1. It starts with a slow, steady rise throughout the Cambrian Period after the Cambrian Explosion (~541 mya), when most major animal groups first appeared. During the Ordovician Period (~485–444 mya), diversity rose sharply in the Great Ordovician Biodiversification Event before dropping during the End-Ordovician Mass Extinction, the first of the Big Five. Through the Silurian and Devonian, diversity recovered and leveled off, forming a long plateau during the Paleozoic Era. Then, the Permian Extinction (~252 mya), the largest mass extinction in Earth’s history, wiped out around 90–96% of marine species, causing a massive crash in diversity. In the Mesozoic Era, diversity rebounded rapidly during the Mesozoic Marine Revolution, driven by new predator-prey dynamics and modern marine groups. After the End-Cretaceous Extinction (~66 mya), diversity continued to rise steeply throughout the Cenozoic Era, reaching the highest levels of marine biodiversity observed today.

  2. Appreciate biases and limitations of the fossil record.

Not all organisms fossil, and some fossil better than others. Harder ones typically get saved more. Temporal bias(time bias): certain time periods are studies more 

  1. Know the relationship between Standing Diversity, Origination, and Extinction.

Standing Diversity is the amount of a given species at a given time, origination is the increase of the species, and extinction is the decrease of the species. So if origination> extinction, standing diversity is increasing, and if origination<extinction, standing diversity is decreasing. 

  1. What is adaptive radiation and give an example or two.

Adaptive Radiation - The rapid diversification of species into many new species, adapting to a new niche. Usually happens when a new habitat opens up, or after a mass extinction. Darwin’s finches are a great example, so are Anolis lizards. 

  1. Explain the difference between background and mass extinction.

Background Extinction is the normal extinction rate of humanity. Mass extinction is caused by a catastrophic event.

  1. Know what kinds of phenomena caused the P-T and K-Pg mass extinctions.

P-T extinction (Permian Extinction) was caused by volcanic eruptions, leading to increased CO2 and methane. Ocean acidification from this kills marine life. 

K-Pg extinction (Dinosaur Extinction) was caused by an asteroid impact, which caused global cooling, killing the non-avian dinosaurs.


  1. The fossil record can be a source of information about the tempo and mode of evolutionary change.

The fossil record reveals both the tempo (rate) and mode (pattern) of evolutionary change over time. It shows whether evolution occurred gradually or in rapid bursts (punctuated equilibrium), and whether species evolved by transformation (anagenesis) or branching (cladogenesis). By preserving sequences of organisms through time, fossils provide direct evidence for how and how fast evolution has occurred.

Anagenesis: Evolutionary change within a single lineage where one species gradually transforms into another without branching — the original species no longer exists once the new one forms. (Straight Line)

Cladogenesis: Evolutionary change that involves the splitting of one lineage into two or more new species, increasing overall biodiversity — this is branching evolution. (Branch)

  1. Be able to read and interpret time by morphology plots.

If morphology is changing steadily, then anagenesis is happening. If it isn’t changing, then stasis is happening, and if  long periods of stasis are rapidly stopped, then it is punctuated equilibrium(cladogenesis).

  1. The fossil record shows both gradual change as well as a pattern of stasis and punctuated change, the latter being more common.

Because of this, we can assume most species go through long periods of stasis, then rapid evolution. 

  1. Understand why stasis is interesting and what might cause it.

It challenges the idea that evolution is constant. There are many reasons to why it could happen: 

  • Natural Selection could favor the current form.

  • Genetic Constraints

  • Constant habitat

  1. Understand and explain the theory of Punctuated Equilibrium.

Punctuated Equilibrium is the idea that evolutionary change happens in rapid bursts, associated with speciation events, followed by long periods of stasis (little or no change).