Bio Ch. 14

Phylogenetic Species Concept

A definition of species as the smallest group of individuals that shares a common ancestor, forming one branch on the free of life.

Ecological Species Concept

A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

Morphological Species Concept

A definition of species in terms of measurable anatomical criteria.

Hybrid Zones

A geographic region in which members of different species meet and mate, producing at least some hybrid offspring.

Species

A group whose members possess similar anatomical characteristics and have the ability to interbreed and produce viable, fertile offspring.

Prezygotic Barriers

A reproductive barrier that impedes mating between species or hinders fertilization if mating between two species is attempted. Includes temporal, habitat, behavioral, mechanical, and gametic isolation.

Postzygotic Barriers

A reproductive barrier that prevents hybrid zygotes produced by two different species from developing into viable, fertile adults. Includes reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.

Hybrids

An offspring of parents of two different species or of two different varieties of one species; an offspring of two parents that differ in one or more inherited traits; an individual that is heterozygous for one or more pairs of genes.

Polyploid

An organism that has more than two complete sets of chromosomes as a result of an accident of cell division.

Females of Galápagos finch Geospiza difficilis respond to the songs of males from their island but ignore songs of males from other islands. How would you interpret these findings?

Behavioral barriers to reproduction have begun to develop in these allopatric (geographically separated) finch populations.

Why might hybrid zones be called "natural laboratories" in which to study speciation?

By studying the fate of hybrids over time, scientists can directly observe factors that cause (or fail to cause) reproductive isolation.

Biological Species Concept

Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such populations.

In allopatric speciation, geographic isolation leads to speciation.

Geographically separated from other populations, a small population may become genetically unique as its gene pool is changed by natural selection, mutation, or genetic drift.

Two closely related fish live in the same lake, but one feeds along the shoreline and the other is a bottom feeder in deep water. This is an example of _______ isolation, which is a_______ reproductive barrier.

Habitat... Prezygotic

Hybrid zones provide opportunities to study reproductive isolation.

Hybrid zones are regions in which populations of different species overlap and produce at least some hybrid offspring. Over time, reinforcement may strengthen barriers to reproduction, or fusion may reverse the speciation process as gene flow between species increase. In stable hybrid zones, a limited number of hybrid offspring continue to be produced.

Why are errors in mitosis or meiosis a necessary part of speciation by hybridization between two pairs?

If a hybrid has a single copy of the chromosomes from two species, homologous pairs cannot join and separate during meiosis to produce gametes. Errors in mitosis or meiosis must somehow duplicate chromosomes so that there is a diploid number of each set and normal gametes can form.

How does the punctuated equilibrium model account for the relative rarity of transitional fossils linking newer species to older ones?

If speciation takes place in a relatively short time or in a small isolated population, the transition of one species to another may be difficult to find in the fossil record.

Punctuated Equilibria

In the fossil record, long periods in which a species undergoes little or no morphological change (equilibria), interrupted (punctuated) by relatively brief periods of sudden.

Sympatric speciation takes place without geographic isolation.

Many plant species have evolved by polyploidy, duplication of the chromosome number due to errors in cell division. Habitat differentiation and sexual selection, usually involving mate choice, can lead to sympatric (and allopatric) speciation.

The origin of most plant species can be traced to polyploid speciation.

Many plants, including food plants such as bread wheat, are the result of hybridization and polyploidy.

How does microevolution differ from speciation?

Microevolution involves evolutionary changes within a population; speciation occurs when a population changes enough that it diverges from its parent species and becomes a new species.

The Origin of Species

Natural selection, which adapts a population to its environment, and other processes may lead to speciation, the origin of new species.

Adaptive Radiation

Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill new or vacant ecological roles in their communities.

Isolated islands are often showcases of speciation

Repeated isolation, speciation, and recolonization events on isolated island chains have led to adaptive radiations of species, many of which are found nowhere else in the world.

Reproductive barriers can evolve as populations diverge.

Researchers have documented the beginning of reproductive isolation in fruit fly populations adapting to different food sources and have identified a gene for flower color involved in the pollinator choice that helps separate monkey flower species.

Why was it important for researchers to establish that cichlid color sensitivity is heritable?

Sensitivity to red is the phenotypic trait that allows P. nyererei females to chose P. nyererei males as mates, ensuring reproductive isolation.

Geographic Barriers

Several geologic processes can isolate populations; mountain ranges, small lakes, canyons, rivers, etc... or continental drift.

The origins of species is the source of biological diversity.

Speciation, the process by which one species splits into two or more species, accounts for both the unity and diversity of life.

Reproductive barriers keep species separate

Such barriers isolate a species' gene pool and prevent interbreeding.

There are several ways to define a species.

The biological species concept holds that a species is a group of populations whose members can interbreed and produce fertile offspring with each other but not with members of other species. This concept emphasizes reproductive isolation. Most organisms are classified based on observable traits; the morphological species concept.

Explain why isolated island chains provide opportunities for adaptive radiations.

The chance colonization of an island often presents a species with new resources and an absence of predators. Through natural selection acting on existing variation, the colonizing population becomes adapted to its new habitat and may evolve into a new species. Subsequent colonizations of nearby islands would provide additional opportunities for adaptation and genetic drift, which could lead to further speciations.

Geologic evidence indicates that the Isthmus of Panama gradually closed about 3 million years ago. Genetic analyses indicate that the various species of snapping shrimp originated from 9 to 3 million years ago, with the species pairs that live in deepest water diverging first. How would you interpret these data?

The deeper species would have been separated into two isolated populations first, which enabled them to diverge into new species first.

Speciation

The evolution of a new species.

Reproductive Isolation

The existence of biological factors (barriers) that impede members of two species from producing viable, fertile hybrids.

Allopatric Speciation

The formation of new species in populations that are geographically isolated from one another.

Sympatric Speciation

The formation of new species in populations that live in the same geographic area.

Which species concepts could you apply to both asexual and sexual species? Explain.

The morphological, ecological, and phylogenetic species concepts could all be used because they do not rely on the criterion of reproductive isolation.

Speciation can occur rapidly or slowly.

The punctuated equilibria model, which state that species change most as they arise from an ancestral species and then change relatively little for the rest of their existence, draws on the fossil record. Other species appear to have evolved more gradually. The time interval between speciation events varies from a few thousand years to tens of millions of years.

Lake Victoria is a living laboratory for studying speciation.

Through the rapid adaptive radiation of cichlids, researchers have gained insight into speciation via sexual selection.

Can we observe speciation occurring?

Yes