Chapter 18 Flashcards
Speciation and Microevolution
Speciation
The process of species formation
Morphological Species Concent
The concept that all individuals of a species share measurable traits that distinguish them from individuals of other species. Has practical applications in identifying extinct/fossilized species and external traits of organisms. Can present problems, some individuals of a single species look drastically different.
Biological Species Concept
The definition of species based on the ability of populations to interbreed and produce fertile offspring. If, under natural conditions, the offspring is fertile, they belong to the same species. Emphasizes genetic cohesiveness and genetic distinctness.
Phylogenetic Species Concept
Using morphological and genetic sequence data, scientists reconstruct the evolutionary tree. Then they define a phylogenetic species as a cluster of populations that emerge from the same small branch. Can be applied to any group of organisms, including species long extinct, as asexual species.
Subspecies
Phenotypic variation based on geographical separation. If two different geographical distributions meet, an intermediate phenotype will emerge.
Ring Species
A species with a geographic distribution that forms a ring around uninhabitable terrain. They can exchange genetic material directly, but gene flow between distant populations occurs only through intermediary populations.
Clinal Variation
A smooth pattern of variants across a geographical gradient. Gene flow between adjacent populations that are adapting to slightly different conditions. Very little genetic material exchange between opposite ends of a cline.
Reproductive isolating mechanisms
A biological characteristic that prevents the gene pools of two species from mixing.
Hybrid
An organism produced by a mating between parents of different species or subspecies.
Prezygotic Isolating Mechanisms
A reproductive isolating mechanism that acts prior to the production of a zygote, or fertilized egg. Include:
Ecological Isolation, species live in different habitats.
Temporal Isolation, species breed at different times.
Behavioural isolation, species cannot communicate.
Mechanical Isolation, species cannot physically mate.
Gametic Isolation, species have nonmatching receptors on gametes.
Postzygotic Mechanisms
Hybrid Inviability, hybrid offspring do not complete development.
Hybrid Sterility, hybrid offspring cannot produce gametes.
Hybrid Breakdown, hybrid offspring have reduced survival or fertility.
Allopatric Speciation
Allo: Different, Patria: homeland. The evolution of reproductive isolating mechanisms between two populations that are geographically separated. Two stages, the separation, and then the accumulation of genetic differences causing reproductive isolation. Most common mode of speciation in large animals.
Secondary Contact
Contact after a period of geographical isolation. Provides a test of whether genes in the population have diverged.
Species Fusion
Merger of two populations into one after the establishment of secondary contact.
Hybrid Zones
A geographic area where the hybrid offspring of two divergent populations or species are common.
Reinforcement
The enhancement of reproductive isolation that had begun to develop while populations were geographically separated.
Sympatric Speciation
Sym: together. Speciation that occurs without the geographic isolation of populations.
Host Race
A population of insects that may be reproductively isolated from other populations of the same species as a consequence of adaptation to feed on a specific host plant species.
Polyploidy
The condition of having one or more extra copies of the entire haploid complement of chromosomes. Can lead to speciation due to the large-scale genetic changes may prevent polyploid individuals from breeding with individuals of the parent species.
Autopolyploidy
The genetic condition of having more than two sets of chromosomes from the same parent species. Often results when gametes spontaneously receive the same number of chromosomes as a somatic cell.
Unreduced Gametes
A gamete that contains the same number of chromosomes as a somatic cell
Allopolyploidy
Two closely related species hybridize and subsequently form polyploid offspring. If the hybrid’s chromosome number is doubled, the chromosome complement of the gametes is also doubled, producing homologous chromosomes that can pair during meiosis. The hybrid can then produce polyploid gametes and, through self-fertilization or fertilization with other doubled hybrids, establish a population of a new polyploid species.
