Macroevolution Topic 10

The evolution of species

Evolution is a process that occurs at two scales

How do we define a species?

The origin of a species

How do new species form?

What needs to happen for organisms to be consideered as two different speices

Macroevolution- formation of new speices

• occurs as microevolutionary changes accumulate across often many generations, can a also be quickly

The accumulation of changes in microevolution

The mechanisms of microevolution are also all mechanisms of macroevolution

A species is a port of biological classification

Species: related organisms that maintain distinct set of traits in nature (the biggest gene pool possible under natural conditions)

• subspecies: some different traits, not enough to warrant different “species”

• ecotypes: genetically distinct populations

Species concepts- are used to dinstinguish one species from another

There are many species concepts, different groups of organisms pose different challenges for describing species

• extinct organisms (fossils)

• sexual vs. asexual reproduction

• high or low instaspecific variation

• sexual dimorphisms

• others

The morphological species concept: unique species based on physical characteristics

Pros

• can be applied to asexually reproducing species

• can be applied to extant and extinct species

Cons

• variation within species

• similarity across species

• cryptic species

• sexual dimorphism

The ecological species concept: unique species based on ecological niche

The ecological niche is the unique set of habitat resources and its influence on the environment

Pros

• can be applied to asexually reproducing species

• can be applied to extant and extinct species

Cons

• variation within species

• niches can be difficult to define

The phylogenetic species concept: unique species based on shared common ancestor

Ancestry commonly based on analysis of molecular data (most often DNA sequences)

Pros

• can be applied to asexually reproducing species

• can be applied to extant and extinct species

Cons (limitations)

• variation within a species (subspecies, different populations)

The biological species concept: unique species based on potential to interbreed

Species must be able to produce viable, fertile offspring—focuses on reproductive isolation

Pros

• easy to define

• easy to measure

Cons

• cannot be applied asexually reproducing species

• cannot be applied to extinct species

Different species concepts may provide different “answers”

Morphological & Biological concepts identified 6 subspecies

In 1980 only 6 male Dusky sparrows remained

Morphologically, penninsulae is the closest, so the two subspecies were interbred to save genetic diversity

However, phylogenetically dusky was closer to macgillivraii and martitima

Microevolution, any form changes in frequency of traits in a population

• mutations

• natural selection

• nonrandom mating

• drift

• gene flow

How does speciation happen?

Mutation, natural selection, nonrandom mating, genetic drift, —-interbreeding— mutation, natural selection, non-random mating, genetic drift

Gene flow= interbreeding, which limits gene flow and R.I.M.s (incomplete)

Speciation requires microevolution and reproductive isolation; What are the reproductive isolation mechanisms?

Barries prevent individuals from producing fertile offspring

Barries can be either, pre-zygotic which prevents zygote formation, or post-zygotic, which prevents development of viable, fertile offspring after zygote formation

How does progression work?

Reproductive isolating mechanisms: 8 types

Pre-zygotic

• habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation

• habitat isolation is due to geographical behavior, due to habitat choice preventing contact

• temporal isolation is when species reproduce at different types, (could be times of days or times of the year)

• behavioral isolation are traits associated with mate choice (sexual selection), e.g., songs, mating dance, other forms of assessment

• mechanical isolation is when morphological features prevent successful mating

• gametic isolation is when mating occurs but gametes fail to unite, fertilization is unsuccessful

Post zygotic

• reduces hybrid viability, reduced hybrid fertility, hybrid breakdown

• reduced hybrid viability (hybrid inviability) when mating and fertilization occur but there is impaired embryonic development, or impaired survival in the environment

• reduced hybrid fertility (hybrid sterility) interspecies hybrid is viable but it is sterile

• hybrid breakdown is the first round of interspecies hybrids (F1s) are viable and fertile, but subsequent hybrid generations (F2, F3, etc.) have decreased fitness

  • this means hybrids may always exist but they will never dominate the population/gene pool