Chapter 24 terms/concepts Flashcards
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 groups
Hybrid(s)
Offspring that results from the mating of individuals from two different species or from two true-breeding varieties of the same species.
Speciation
An evolutionary process in which one species splits into two or more species
Reproductive Isolation
The existence of biological factors that impede members of two species from producing viable, fertile offspring
Prezygotic mechanisms (barriers)
Prevent mating or fertilization
Postzygotic mechanisms (barriers)
prevent zygote development or reproduction
Strengths and Weaknesses (limitations) of the biological species concept
Strength: directs our attention to a way by which speciation can occur: by evolution of reproductive isolation
Limitation: The number of species to which this concept can be usefully applied is limited (no fossils, or prokaryotes)
Morphological species concept (what is it, and strengths and weaknesses?)
Definition: distinguishes a species by body shape and other structural features.
Strength: can be applied to both asexual and sexual organisms, and it can be useful even without information on the extent of gene flow
Weakness: it relies on subjective criteria; researchers may disagree on which structures distinguish a species
Ecological species concept (definition, strengths and weaknesses)
Definition: defines a species in terms of its ecological niche, the sum of how members of the species interact with nonliving and living parts of the environment
strength: Accommodates both asexual as well as sexual species, and emphasizes the role of disruptive natural selection
weakness: Too many decisions on how much difference between individuals is too much variation
Habitat isolation
Animals who live in different habitats within the same area may never encounter each other (prezygotic)
Temporal isolation
Mating time differences between species (prezygotic)
Behavioral isolation
courtship rituals that attract mates and other behaviors unique to a species (prezygotic)
Mechanical isolation
morphological characteristics are not viable for reproduction (prezygotic)
Gametic isolation
sperm cannot fertilize egg (prezygotic)
Reduced hybrid viability
genes of different parent species may interact in ways that impair hybrid’s development (postzygotic)
Reduced hybrid fertility
if parent chromosomes differ in number or structure, meiosis in hybrids may fail to produce normal gametes (postzygotic)
Hybrid breakdown
first gen hybrids are viable and fertile, but when they mate with parent species or each other, the next-gen are feeble and sterile (postzygotic)
Allopatric speciation
species are geographically isolated from one another
Sympatric speciation
a subset of a population forms a new species without geographic separation
Polypoidy
When a species originates by an accident during cell division that results in extra sets of chromosomes
Autopolyploid
An individual that has more than two chromosome sets that are all derived from a single species
Hybrid zone
a region in which members of different species meet and mate with one another
Reinforcement
1st possible outcome concerning hybrid zones and formation of hybrid species - hybrid species is weak and unfit, and natural selection selects for prezygotic factors that eliminate the hybrids between the two species, thus reinforcing the reproductive barriers
Fusion
the 2nd outcome for hybrid zones is when gene flow is increasingly strong between two species that the zone deteriorates, and the two (once) separate species now converge as their gene pools become increasingly similar due to cross-breeding
