Chapter 24 Flashcards
speciation
the origin of new species, is at the focal point of evolutionary theory
-evolutionary theory must explain how new species originate and how populations evolve
microevolution
consists of changes in allele frequency in a population over time
macroevolution
refers to broad patterns of evolutionary change above the species level
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
reproductive isolation
the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
hybrids
offspring of crosses between different species
prezygotic barriers
and 3 ways it occurs by
block fertilization from occurring by
- impeding different species from attempting to mate
- preventing the successful completion of mating
- hindering fertilization if mating is successful
habitat isolation:
two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
temporal isolation
species that breed at different times of the day, different seasons, or different years cannot mix their gametes
behavioral isolation
courtship rituals and other behaviors unique to a species are effective barriers
mechanical isolation
morphological differences can prevent successful mating
different sexual organs
gametic isolation
sperm of one species may not be able to fertilize eggs of another species
postzygotic barriers
3 preventions
prevent they hybrid zygote from developing into a viable, fertile adult:
- reduced hybrid viability
- reduced hybrid fertility
- hybrid breakdown
reduced hybrid viability
genes of the different parent species may interact and impair the hybrid’s development
ex) a mule
reduced hybrid fertility
even if hybrids are vigorous, they may be sterile
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
the biological species concept cannot be applied to _____ or ______ organisms
- fossils
- asexual organisms
the biological species concept emphasizes ________
absence of gene flow
morphological species concept
defines a species by structural features
-applies to sexual and asexual species but relies on subjective criteria
ecological species 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
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
in what two ways can speciation occur?
- allopatric speciation
- sympatric speciation
allopatric speciation
gene flow is interrupted or reduced when a population is divided into geographic isolated subpopulations
- a population forms a new species while geographically isolated from its parent population
- -ex) the flightless cormorant of the galapagos likely originated from a flying species on the mainland
true or false:
a definition of barrier depends on the ability of a population to disperse
true!
ex) a canyon may create a barrier for small rodents, but not birds, coyotes, or pollen
separate populations may evolve independently through what three things
- mutation
- natural selection
- genetic drift
reproductive isolation may arise as a result of ______
genetic divergence
genetic divergence
the process in which two or more populations of an ancestral species accumulate independent genetic changes (mutations) through time, often after the populations have become reproductively isolated for some period of time. This means that the populations of species live independently of each other long enough that they can no longer produce offspring that can survive.
true or false:
Regions with many geographic barriers typically have more species than do regions with fewer barriers
true
sympatric speciation
speciation takes place in geographically overlapping populations
polyploidy
the presence of extra sets of chromosomes due to accidents during cell division
true or false:
polyploidy is more common in animals than plants
false: polyploidy is more common in plants than animals
what can result from the appearance of new ecological niches
sympatric speciation
sexual selection can drive _____
sympatric speciation
in allopatric speciation, geographic isolation restricts _____
gene flow between populations
in isolated populations, reproductive isolation may arise by ____,____, or ______
- natural selection
- genetic drift
- sexual selection
true or false:
in sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species
true
sympatric speciation can result from ____, _____, or _____
polyploidy, natural selection, or sexual selection
hybrid zone
a region in which members of different species mate and produce hybrids
hybrids often have reduced ____ compared with parent species
fitness
when closely related species meet in a hybrid zone, there are three possible outcomes
- reinforcement
- fusion
- stability
reinforcement
barriers occurs when hybrids are less fit than the parent species
-over time, the rate of hybridization decreases
if hybrids are fit as parents, there can be substantial _____ between species
gene flow
Fusion….
if gene flow is great enough, the parent species can _______
fuse into a single species
Stability….
True or false:
extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone
true
broad patterns in speciation can be studied using what three things
- fossil record
- morphological data
- molecular data
the fossil record includes examples of species that ______, ______, and then______
- appear suddenly
- persist essentially unchanged for some time
- apparently disappear
puncuated equilibrium
describe periods of apparent stasis punctuated by sudden change
-contrasts with a model of gradual change in a species’ existence
true or false:
speciation may require the change of only a single allele
false
-may require EITHER change in only a single allele or many alleles
macroevolution
the cumulative effect of many speciation and extinction events
