Biology 2

Name the types of reproductive isolation mechanisms

Prezygotic Barriers

Postzygotic Barriers

What’s a prezygotic barrier?

Impedes mating and prevents fertilization between different species

What’s a postzygotic barrier?

prevents different species from producing healthy or fertile offspring

What are the different types of prezygotic barriers? (list)

• Habitat Isolation

• Behavioral Isolation

• Temporal Isolation

• Mechanical Isolation

• Gametic Isolation

What are the different types of postzygotic barriers? (list)

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

Habitat Isolation

In the same region but separated by different microhabitats

Garter Snakes are found in one region. However, the aquatic species of garter snakes prefer to stay in water and rarely encounter terrestrial species of garter snakes, preventing them from reproducing. This is an example of what?

Habitat isolation

Behavioral Isolation

incompatible mating behaviors or signals

Male fireflies have specific flashing patterns to appeal to female fireflies. Certain species have unique flashing patterns. Female fireflies only recognize and respond to the exact flash pattern of their own species. This is an example of what?

Behavior Isolation

Temporal Isolation

different timing of mating seasons

Western skunks mate in the summer to the early fall. Eastern skunks mate in the late winter to early spring. Due to their different mating seasons, they are unable to mate with one another. This is an example of what?

Temporal Isolation

Mechanical Isolation

incompatibility of reproductive structures

Some floral structures have specific shapes, sizes, or orientations that restrict pollen transfer to certain pollinators or prevent cross-pollination between different plant species. This is an example of what?

Mechanical Isolation

Gametic Isolation

incompatible recognition proteins on sperm & egg preventing fertilization

Sea urchins release gametes in the open water during their mating season. If sperm and eggs from different species meet in the water, the specialized surface proteins fail to recognize the foreign eggs, preventing the sperm from fusing. This is an example of what?

Gametic Isolation

Reduced Hybrid Viability

puny offspring or offspring that don’t develop to maturity

Reduced Hybrid Fertility

viable offspring that are sterile or have reduced fertility

When sheep and goats mate, they can form a zygote, but the hybrid embryos fail to develop fully and die during early development before birth. This is an example of what?

Reduced Hybrid Viability/Hybrid Inviability

When Horses and donkeys mate, their chromosomes fail to line up properly due to their gene loci being vastly different. This results in the uneven splitting of chromosomes during anaphase, which leads to offspring being infertile. This is an example of what?

Reduced Hybrid Fertility/Hybrid Sterility

Hybrid Breakdown

The first generation offspring are viable and fertile, but second and third generation of offspring die out.

Crossing certain strains of cultivated rice (such as specific Asian rice varieties) produces a healthy, fully fertile F₁ generation. However, when these F₁ hybrids interbreed, the resulting F₂ generation exhibits widespread sterility and reduced growth

Hybrid Breakdown

How do reproductive barriers arise

Speciation

• first fragmentation of gene pool of a species, preventing gene exchange/flow

• then genetic divergence in daughter gene pools, independent changes leading to speciation

What are the modes of speciation

• Allopatric Speciation

• Sympatric Speciation

• Parapatric Speciation

Allopatric Speciation

geographic/physical barrier splits range into geographically isolated gene pools

In the formation of the Isthmus of Panama, a strip of land separated the Pacific and Atlantic Ocean. In the process, the organisms in the ocean were separated as well. This is an example of what?

Allopatric speciation

Populations at extremities of range are reproductively isolated, however gene flow still occurs between adjacent populations.

Ring Species

Small separated groups of species that live on the edges of the main population’s geographic range. Often occurs on archipelagoes islands.

Peripheral Isolates

Name some traits about peripheral isolates

• extreme genotypes on edge that are different from main population

• small population which means high chance of genetic drift

• encounter of different selective factors from main mother range

Adaptive Radiation

evolution of many diversly adapted species from one common ancestor

Darwin observed finches on the archipelagoes islands whose beaks were different to accommodate to various food sources, such as thicker beaks for finches who needed to crack nut shells, and thinner beaks for finches who caught insects. This is an example of what?

Adaptive radiation

Sympatric Speciation

reproductive isolation without geographical isolation

Polyploidy (an extra set of chromosomes) during cell division in plants prevents them from producing fertile offspring with the parent population. This is an example of what?

Sympatric Speciation

Autopolyploidy

multiple chromosome sets from the same species (ex. due to error in cell division)

Allopolyploidy

multiple chromosome sets from different species which results in hybrid species

Autopolyploidy

Allopolyploidy

Population of insects that are reproductively isolated from other populations of the SAME species as a consequence of their adaptation to feed on a specific host plant.

Host Race

Hawthorn maggot flies feed and mate on hawthorn, which was their main source of food in the region. When apples were introduced to the region, some flies would begin feeding and mating on apples instead, which led their offspring to do the same. Those are now referred to as apple maggot flies. Due to some flies mating on hawthorn and some mating on apples, the populations became reproductively isolated.

Host race

Host fruit fidelity

behavior where an insects mate on the same species of fruit from which it developed

Parapatric Speciation

similar to allopatric speciation because it occurs in adjacent ranges but has sharp changes in environment as its boundaries instead of a physical barrier. It is also less common.

Phylogeny

1) evolutionary history of a group of organisms

2) diagram of the family tree that shows genetic linkages between ancestors and descendants

3) depicts cladogenesis clades

Taxon

any classable group must be monophyletic

Monophyly

includes most recent common ancestor and all of its descendants

Paraphyly

includes most recent common ancestors and most/some of its descendants

Polyphyly

does NOT include common ancestor

Phylogeny reconstruction utilizes evidence through…

fossils and recent species

Some flaws of using fossils as evidence are…

• fossil records are incomplete

  • only hard structure preserved, soft structures (like genetic info) are rarely preserved

• unconformities in the earth; fossils from missing periods lost

Some flaws of using recent species as evidence are…

• we look for similarities between species but not all similarities are useful for phylogenic reconstruction

Homologous characters

similarities/shared characters due to descent from a common ancestor

Analogous characters

similarities/shared characteristics due to similar functions but NOT from sharing a common ancestor

Convergent evolution

independent development of evolutionary traits

The wings of birds, bats, and insects are an example of what?

convergent evolution

Synapomorphy

shared derived characters

shows evidence of a recent relationship

Symplesiomorphy

shared ancestral characters

shows evidence of a distant relationship

Autapomorphy

unique trait to a single species

This is an example of what?

Synapomorphy

This is an example of what?

Symplesiomorphy

node based taxon

group defined by the last common ancestor

stem based taxon

group defined by a branch on a phylogenic tree

crown group

includes all living organisms as well as organisms that went extinct IN the clade/lineage

Earth assumedly formed how many years ago

4.6 billion years

Old atmosphere traits

• hydrogen sulfide, ammonia, methane, hydrogen cyanide, carbon dioxide, and water

• no ozone layer, high UV

• reducing atmosphere

Modern atmosphere traits

• 21% O2

• oxidizing atmosphere

What did the Stanley miller and Harold Urey experiment prove?

Demonstrated that the basic building blocks, amino acids, nitrogen bases, etc., can form outside of life

Initially the earliest forms were ______ based

RNA

imprint fossils

remains of organisms are gone but the imprint of it still remains in the earth

trace fossils

not the organisms itself put proof of its activity

petrification

an organism that has completely turned into stone through a slow geological process

amber

Tree resin traps an organism, which then hardens and undergoes a chemical transformation

What is an example of a synamorphy

carnassial teeth in dogs, cats, bears, etc.

What is an example of a symplesiomorphy

Hair on mammals

Four limbs in vertebrates

Pentadactyly in vertebrates