Ch. 22: Speciation

cline

A pattern of smooth variation in a characteristic along a geographical gradient.

host race

A population of insects that may be reproductively isolated from other populations of the same species as a consequence of their adaptation to feed on a specific host plant species.

hybrid invariability

A postzygotic reproductive isolating mechanism in which a hybrid individual has a low probability of survival to reproductive age.

hybrid sterility

A postzygotic reproductive isolating mechanism in which hybrid offspring cannot form functional gametes.

hybrid breakdown

A postzygotic reproductive isolating mechanism in which hybrids are capable of reproducing, but their offspring have either reduced fertility or reduced viability.

mechanical isolation

A prezygotic reproductive isolating mechanism caused by differences in the structure of reproductive organs or other body parts.

gametic isolation

A prezygotic reproductive isolating mechanism caused by incompatibility between the sperm of one species and the eggs of another; may prevent fertilization.

temporal isolation

A prezygotic reproductive isolating mechanism in which species live in the same habitat but breed at different times of day or different times of year.

ecological isolation

A prezygotic reproductive isolating mechanism in which species that live in the same geographical region occupy different habitats.

behavioral isolation

A prezygotic reproductive isolating mechanism in which two species do not mate because of differences in courtship behavior; also known as ethological isolation.

postzygotic isolating mechanisms

A reproductive isolating mechanism that acts after zygote formation.

prezygotic isolating mechanisms

A reproductive isolating mechanism that acts before the production of a zygote, or fertilized egg.

ring species

A species with a geographical distribution that forms a ring around uninhabitable terrain.

subspecies

A taxonomic subdivision of a species.

parapatric speciation

Speciation between populations with adjacent geographical distributions.

sympatric speciation

Speciation that occurs without the geographical isolation of populations.

morphological species concept

The concept that all individuals of a species share measurable traits that distinguish them from individuals of other species.

polyploidy

The condition of having one or more extra copies of the entire haploid complement of chromosomes.

biological species concept

The definition of species based on the ability of populations to interbreed and produce fertile offspring.

reinforcement

The enhancement of reproductive isolation that had begun to develop while populations were geographically separated.

allopatric speciation

The evolution of reproductive isolating mechanisms between two populations that are geographically separated.

autopolyploidy

The genetic condition of having more than two sets of chromosomes from the same parent species.

allopolyploidy

The genetic condition of having two or more complete sets of chromosomes from different parent species.

speciation

The process of species formation.

species cluster

A group of closely related species recently descended from a common ancestor.

hybrid zones

A geographical area where the hybrid offspring of two divergent populations or species are common.

reproductive isolating mechanism

A biological characteristic that prevents the gene pools of two species from mixing.

phylogenetic species concept

A concept that seeks to delineate species as the smallest aggregate population that can be united by shared derived characters.

unreduced gametes

A gamete that contains the same number of chromosomes as a somatic cell.