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31 Cards in this Set

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Define the biological species concept
Biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations.
Distinguish between prezygotic and postzygotic reproductive barriers.
Prezygotic: prevent mating or fertilization between different species, preventing the successful completion of mating and hindering fertilization if mating is successful.

Postzygotic: prevent the hybrid zygote from developing into a viable, fertile adult
Describe five prezygotic reproductive barriers and give an example of each.
-Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers (snakes)

-Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes (skunks)

-Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers (blue footed boobies)

-Mechanical isolation: Morphological differences can prevent successful mating (snails)

-Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species (sea urchins)
Explain a possible cause for hybrid breakdown.
The amount of recessive alleles present in the next generation
Explain how hybrid breakdown maintains separate species even if fertilization occurs.
Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile.
Describe some limitations of the biological species concept.
fossils and asexual organisms (including all prokaryotes)
Ecological species concept
The concept views a species in terms of its ecological niche. It applies to sexual and asexual species and emphasizes the role of disruptive selection
Phylogenetic species concept
The concept defines a species as the smallest group of individuals on a phylogenetic tree. It applies to sexual and asexual species, but it can be difficult to determine the degree of difference required for separate species
Morphological species concept
The concept defines a species by structural features. It applies to sexual and asexual species but relies on subjective criteria.
Distinguish between allopatric and sympatric speciation.
Allopatric speciation: gene flow is interrupted when a population is divided into geographically isolated subpopulations. For example, a mountain range or lake divides a population. In contrast, sympatric speciation occurs in populations that live in the same geographic area, and gene flow is reduced by such factors as polyploidy, habitat differentiation, and sexual selection. Sympatric speciation is much less common than allopatric speciation
Define allopatric speciation. Describe the mechanisms that may lead to genetic divergence of isolated gene pools.
geographic isolation causes an interruption in gene flow. Once the population has become isolated, mutations, natural selection and genetic drift alter allele frequency.
Explain how reproductive barriers evolve. Describe an example of the evolution of a prezygotic barrier and the evolution of a postzygotic barrier.
Reproductive barriers evolve in many diverse ways. The bottleneck effect, the founder effect, polyploidy, and allopatric/sympatric speciation all contribute to the evolution of reproductive barriers. A prezygotic barrier may evolve from any of the isolating factors (habitat, temporal, behavior). A postzygotic barrier may evolve from reduced hybrid aviability, reduced hybrid fertility or hybrid breakdown
Define sympatric speciation and explain how polyploidy can cause reproductive isolation.
improper cell division that results in extra sets of chromosomes. A mutant condition called polyploidy. This means that new species will appear.
Distinguish between autopolyploid and an allopolyploid speciation and describe examples of each.
Polyploids can be distinguished into two groups:

Autopolyploid:An organism that has more than two chromosome sets, all derived from a single species

Allopolyploid: A polyploid hybrid resulting from contributions by two different species. Most are sterile.
Explain how habitat differentiation has led to sympatric speciation in North American maggot flies.
The maggot fly’s original habitat was the native hawthorn tree, but some populations colonized apple trees that had been introduced by European settlers. As apples mature more quickly than hawthorn fruit, natural selection has favored apple-feeding flies with rapid development. These apple-feeding populations now show temporal isolation from the hawthorn-feeding, providing a prezygotic restriction to geneflow between the two populations.
Explain how sexual selection has led to sympatric adaptive radiation in the cichlids of Lake Victoria. Explain how the process of speciation may be reversing, due to pollution in this lake.
One has a blue back, and the other has a red tinged back. They are both closely related sympatric species. This mate choice by coloration is the main reproductive barrier that normally keeps the gene pool of these two species separate. In natural light, females of each species mated only with males of their own species. However, this process of speciation may be reversible. In poor light (due to pollution) females of each species may mate indiscriminately with males of both species. These matings are viable and fertile.
Define the term ‘hybrid zone’. Describe the three outcomes for hybrid zones over time.
A region where different species mate and produce hybrids with reduced fertility.
1-Strengthening of reproductive barrier-Able to reproduce, not viable offspring, rate of hybridization decreases.

2.Weakening of reproductive barrier- Fusion of species into a single one, hybrids become as fit as parents then continue to mate

3.Stability- continued formation of hybrids
Describe examples that illustrate rapid and gradual speciation events.
In a punctuated, or rapid, pattern, new species change most as they branch from a parent species and then change little for the rest of their existence. The wild sunflower is an example of this.
In gradual speciation, other species diverge from one another much more gradually over time. Ex: humans.
Explain how a small number of genetic changes may lead to speciation in plants and animals.
The cumulative effect of many speciation and extinction events
Punctuated Equilibrium
describes periods of apparent stasis punctuated by sudden change
Speciation can be studied using
the fossil record, morphological data, or molecular data
Sympatric speciation can result from
polyploidy, natural selection or sexual selection
Reduced hybrid fertility
Even if hybrids are vigorous, they may be sterile
Reduced hybrid viability
Genes of the different parent species may interact and impair the hybrid’s development
Hybrid breakdown
Some first-generation hybrids are fertile, but when they mate with another species or with either parent species, offspring of the next generation are feeble or sterile
Reproductive isolation
The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
the offspring of crosses between different species
refers to evolutionary change above the species level
consists of adaptations that evolve within a population, confined to one gene pool
the origin of new species, is at the focal point of evolutionary theory