Topic 5 - Biol 213

Mountain Lion Eye Color Practice Problem

If a mountain lion population has only 1 eye color allele (A_light), eye color is likely not evolving due to either drift or selection because there is no genetic variation to act upon

Tree Height Selection Practice Problem

Trees that are too short cannot compete for sunlight, while trees that are too tall break in the wind, meaning stabilizing selection favors intermediate height

Speciation

Simply the evolutionary process by which one original species splits over time to become two distinct species

Species Concepts

morphological, phlyogenetic, Biological and more

Morphological Species Concept

A concept defining a species as a group of individuals that share distinct morphological (physical) characteristics in common

Morphological Species Concept (Pros)

It applies easily to both sexual and asexual species, is simple to understand, and represents how most species have historically been classified

Morphological Species Concept (Cons)

It relies heavily on subjective criteria, and fails when dealing with convergent evolution, cryptic species, or high phenotypic variation within a single species

Phylogenetic Species Concept

A concept defining a species as a group of related individuals that form a clade and share a certain pre-determined degree of genetic relatedness

Phylogenetic Species Concept (Pros)

It applies to both sexual and asexual species, utilizes multiple data types (including molecular/DNA sequences), and is highly precise and objective

Phylogenetic Species Concept (Cons)

It can be very expensive and time-consuming to analyze, and a high degree of genetic relation doesn't necessarily reflect the organism's physical biology

Biological Species Concept

A concept defining a species as a group of individuals that can mate and produce viable, fertile offspring, but are reproductively isolated from other groups

Biological Species Concept (Pros)

It is experimentally testable, objective, and directly takes into account the actual reproductive biology of the organisms

Biological Species Concept (Cons)

It cannot be applied to fossil records and is entirely non-applicable to organisms that reproduce asexually

Reproductive Isolation

The existence of biological barriers that prevent individuals of different species from producing viable, fertile offspring

Pre-zygotic Isolation Barriers

Barriers that act before fertilization by making mating physically impossible or by preventing successful fertilization if mating does occur

Post-zygotic Isolation Barriers

Barriers that act after a zygote forms by ensuring the hybrid offspring are either completely non-viable or completely sterile

Reduced Hybrid Viability

A post-zygotic barrier where the offspring of two genetically distinct populations fail to survive or develop properly during their life cycle

Reduced Hybrid Fertility

A post-zygotic barrier where hybrid offspring are born perfectly healthy but are completely sterile or have severely reduced fertility (e.g., mules)

Hybrid Breakdown

A post-zygotic barrier where the first generation of hybrids is healthy and fertile, but their descendants accumulate severe health defects and the lineage becomes inviable

Two-Group Frog Breeding Practice Problem

Two identical-looking frog groups living in the same lake might be prevented from breeding by pre-zygotic barriers like temporal isolation (different breeding times) or behavioral isolation (different mating calls)

General Mechanism of Speciation

Occurs when populations become isolated with no gene flow, allowing mutations, genetic drift, and natural selection to differentiate them independently over time

Allopatric Speciation

The formation of a new species that occurs because a physical geographic barrier divides a population, entirely cutting off gene flow

Sympatric Speciation

The formation of a new species that occurs without any physical geographic barrier, taking place while populations inhabit overlapping ranges

Sympatry by Habitat Differentiation

Sympatric speciation driven by populations occupying the same geographical range but developing separate ecological niches (e.g., apple maggot flies preferring apples vs. hawthorns)

Polyploidy and Speciation

An unintentional doubling of chromosome numbers due to a mistake in meiosis

Polyploidy Reproductive Isolation Mechanism

When a haploid gamete and a diploid gamete mate, they form a triploid zygote whose homologous chromosomes cannot line up properly during meiosis, resulting in sterile gametes with uneven chromosomes

What evolutionary mechanism(s) cause(s) isolated populations to diverge over time?

Mutation, drift, and natural selection (Isolated populations without gene flow accumulate differences via these three mechanisms).

True or false: Polyploidy can immediately cause reproductive isolation.

True (Chromosomal doubling prevents proper pairing in meiosis during cross-mating, instantly creating a reproductive barrier).

Sympatric speciation differs from allopatric speciation because:

It does not require a physical barrier (Occurs in overlapping geographic ranges, unlike allopatric speciation).

True or false: The morphological species concept can be applied to both sexual and asexual organisms.

True (It groups organisms by shared physical traits rather than interbreeding capability).

Which of the following is a prezygotic reproductive barrier?

Behavioural isolation (Prevents mating or fertilization before a zygote can form).

Which species concept generally cannot be applied to fossil organisms?

Biological species concept (Relies on observing interbreeding and producing fertile offspring, which cannot be tested in fossils).

Two populations of squirrels become separated when a river changes course. Over thousands of generations, mutations, natural selection, and genetic drift cause them to diverge until they can no longer interbreed. This is an example of:

Allopatric speciation (Speciation driven by geographic separation by a physical barrier).

Two species of frogs live in the same pond. One breeds in March while the other breeds in June. What reproductive barrier is at play here?

Temporal isolation (Species reproduce at different times, seasons, or years).

Gametic Isolation

A prezygotic barrier where the sperm of one species is unable to fertilize the eggs of another species.

Mechanical Isolation

A prezygotic barrier where structural/morphological differences prevent successful mating or pollen transfer.

Temporal Isolation

A prezygotic barrier where species breed or flower at different times of the day, different seasons, or different years.

Habitat Isolation

A prezygotic barrier where two species occupy different habitats within the same general area and rarely or never encounter one another.

Two insect populations live in the same forest. One feeds exclusively on oak trees and mates there, while the other feeds and mates only on maple trees. Very little interbreeding occurs. Which of the statements is true?

These populations are isolated by habitat isolation, and may eventually become different species (Different host plant preferences create spatial separation within the same general area).

A researcher finds that two populations differ genetically, morphologically, and behaviourally. However, when individuals are brought together in captivity, they mate readily and produce healthy, fertile offspring. Under the biological species concept, the best conclusion is:

They are likely the same species (The biological species concept defines species based on the ability to interbreed and produce viable, fertile offspring).