Speciation

It occurs within populations and species.

It involves changes in gene frequencies, genetic drift, and phenotypic design for reproductive success. It occurs rapidly.

Microevolution

A group of taxa or species that share features from a common ancestor

Occurs among species and clades.

It involves speciation, extinction, and biogeography patterns. It occurs slowly.

Pattern; process

Macroevolution

Micro; macro

• Microevolution affects macroevolution by being the drive that creates new traits that ultimately affect speciation and extinction.
• Macroevolution affects microevolution by constraining the direction that microevolution can go on (i.e. dolphins can’t suddenly evolve to live without an internal skeleton while forming an external skeleton).

Selection; drift

Populations of the same species that differ when distantly localized. May produce subspecies or races that meet and hybridize in a hybrid zone.

Sibling species (aka: cryptic species) are species that resemble each other so closely that they cannot be distinguished by external morphology, but are reproductively isolated. D. melanogaster and D. simulans are nearly indistinguishable, but do not interbreed.

• Biological Species concept (BSC)
• Phylogenetic Species Concept (PSC)
• Ecological Species Concept (ESC)
• Morphospecies Concept (MSC)

• Separation
• Cohesion (both genetically and ecologically)
• Monophyly
• Distinguishability

Morphological, behavioural, genetic; also includes mechanisms that produced separation 9geographic or behavioural).

Population must be internally cohesive, both genetically (must interbreed) and ecologically (must actually or potentially occupy the same habitat at the same time). Ecological cohesion is necessary but not sufficient for genetic cohesion.

The organisms and populations within a species must share a single most recent common ancestor.

• Three levels:
• A diagnosable species trait
• Phenetic cluster traits
• Genetic cluster traits

A level of distinguishability as a criteria of species that defines a trait that is fixed or distinct from other species.

A level of distinguishability as a criteria of species that defines a trait that is useful when several are considered together so that trait values for species forming a cluster will have different values and little or no overlap so that they may be distinguished.

A level of distinguishability as a criteria of species that distinguishes morphologically identical species from one another with little or no overlap through the analysis of several different sequences of the genome.

The Biological Species Concept (BSC).

Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups (i.e. two individuals are of the same species if they can produce viable offspring with the opposite sex).

Uniformity

Genetic diversity

Two groups of organisms are exactly in the same habitat but refuse to interbreed.

• Prezygotic
• Postzygotic

• Prevents formation of the zygote
• Temporal habitat (i.e. mating at different times of year or day)
• Behavioural (i.e. have different mating behaviours and strategies)
• Mechanical (i.e. have incompatible reproductive organs between sexes)

Acts after zygote formation. Hybrids produced but have low fitness.

• Hybrid inviability
• Hybrid sterility
• Hybrid breakdown

A postzygotic reproductive isolating mechanism in which offspring do not live to adulthood.

A postzygotic reproductive isolating mechanism in which first generation gonads fail to develop properly (i.e. sterile).

A postzygotic reproductive isolating mechanism in which F2 individuals have reduced viability due to the accumulation of lethal complementary alleles.

When in the offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous (heterogametic) sex.

One sex may be absent, rare or sterile among F1 offspring of two animal races. Ligers (tiger x lion) have infertile males but fertile females.

The male hybrid offspring will be absent, rare, or sterile.

• Hybrids
• Asexual organisms
• Ring species

BSC defines species based on their sexual compatibility. However, some species of plant and fungi have somehow lost the ability to sexually reproduce … so you might find a “species” in which you have several strains of unique but very much related individuals that only reproduce asexually. According to BSC, you could not group these individuals into the same species because they do not interbreed, and yet they are practically the same species.

BSC defines species based o their sexual compatibility, and yet some distinct species may result in fertile hybrids, more commonly in plants.

Ring species may form a ring around some given natural habitat (for example, around Hudson’s Bay). Populations along the ring will interbreed with other populations along the gradient, but on occasion scientists will find that the species on the ends of the ring will not and cannot interbreed. Since BSC defines species as a group of individuals that can interbreed, this poses a challenge to defining these individuals as members of the same species.

It predicts that barriers to interspecies recombination for core genes are not shared by auxiliary genes. This means that we can focus on differences between core genes and ignore auxiliary genes when trying to determine if cryptic species are unique from one another.

Individual bacterial or viral genes composed of bits and pieces of very different origin (conflicts with BSC).

Core genes are involved in cell metabolism, are rarely transferred, and are divergent between taxa.

Auxiliary genes are involved in adapting to local conditions, including genes for pathogenicity, antibiotic resistance toxins, and novel metabolic functions. There are advantages to exchanging these.

• Genetic drift
• Natural selection
• Sexual selection

A monophyletic group composed of the ‘smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent’.

4

The ecological species concept involves defining a species based on a shared adaptation to acquire a particular set of resources (niche).

• It’s difficult to measure niche overlap between individuals.
• Also breaks down when different sexes or different morphs occupy different niches.

The morpho species concept defines as a species as those groups of organisms that show the same phenotype.

Doesn’t take into account sibling species which look the same but are reproductively isolated. Also doesn’t consider that a lot variation can be found within a species.

BSC

ESC

PSC

MSC

• Isolation (usually geographic, allopatric)
• Populations diverge (drift, natural selection, sexual selection)
• Secondary contact (either reinforcement which completes speciation, or resume gene-flow which is despeciation)

• Speciation sometimes happens in sympatry.
• Secondary contact isn’t necessary.
• There other possible outcomes besides just one or two species.

• Temporal
• Behavioral
• Habitat

Occupy same area but don’t interbreed because they mate at different times.

Courtship rituals can differ greatly between species, and females or males will only respond to the “right one”.

Different species can prefer different breeding grounds.

• Peripatry
• Parapatry

Occurs when a small peripheral population gets separated from a large central population.

Occurs when you have two populations that have adjacent geographic ranges with some contact.

• Dispersal
• Vicariance

Dispersal is the way in which allopatry can occur when a sub-set of a population expands into a separate range such as an island, moutaintop, or swamp.

It’s the splitting of a population into two populations by some geographic event (ex. Newly formed river or lake can split a population into two, or a new mountain range, a new valley, etc).

Ring species

• Polyploidy in plants
• Disruptive selection that selects for extremes over intermediates

No

When populations re-establish contact after a period of divergence, hybrids usually less fit than ’parental’ (pure) forms. If populations have become postzygotically isolated (low hybrid fitness) selection should now favour evolution of prezygotic isolating mechanisms. This reinforcement of parental forms is a necessary final step in speciation (according to Dobzhansky).