Chapter 24 Flashcards
Darwin discovered
plants and animals in the galapagos island that didn’t exist anywhere else on earth.
Speciation
the origin of new species, is the focal point of evolutionary theory
Microevolution
consists of changes in genetic alleles frequency in a population over time.
Macroevolution
refers to broad patterns of evolutionary change above the species level.
- origin of new groups
- cumulative effect of many speciation and extinction time
Species Latin word
“kind” or “appearance”
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 members with another population.
Reproductive Isolation
is the existence of another biological factors (barriers) that impede 2 species from producing viable, fertile offspring.
Hybrids
are the offspring of crosses between different species
- a sterile mule ( a hybrid product of horse+ donkey)
pre or post zygotic barriers
Reproductive isolation can be classified by whether
factors act before or after fertilization
Prezygotic barriers
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
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 & other behaviors
unique to a species are effective barriers to mating
mechanical isolation
Morphological/anatomical differences prevent successful completion of mating
Gametic Isolation:
Sperm of 1 species may not be able to fertilize eggs of another species
Postzygotic barriers
prevent the hybrid zygote from developing into a viable, fertile adult
Reduced hybrid viability:
Genes of the different parent species may interact and impair the hybrid’s development or survival in its environment
-Hybrid offspring don’t complete development or if they do, are “frail”
Reduced hybrid fertility:
Even if hybrids are vigorous, they may be sterile.
Ex. a robust mule still can’t mate with a donkey or horse
Hybrid breakdown
Some 1st generation hybrids are fertile, but when they mate with each other or with either parent species, offspring of the next generation are feeble
or sterile
Limitations of the Biological Species Concept
It emphasizes absence of gene flow. However, gene flow (transfer of genes/alleles from 1 population to another) can occur between distinct species
- Ex. Brown/grizzly bears & polar bears can mate to produce “grolar bears”
Morphological species concept
defines a species by structural features
Ecological species concept
views a species in terms of its ecological niche (sum of how members of the species interact with the nonliving & living parts of their environment)
Phylogenetic species concept
defines a species as the smallest group of individuals on a phylogenetic tree
Speciation can take place with or without geographic separation
-Allopatric speciation
- Sympatric speciation
allopatric speciation
gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
barrier
depends on the ability of a population to disperse
Separate populations may evolve independently through
DNA mutation, natural selection & genetic drift
mosquitofish
have evolved reproductive isolation as a result of selection under different levels of predation
sympatric speciation
speciation takes place in
geographically overlapping populations
Habitat differentiation
Sympatric speciation can also result from
the appearance of new ecological niches
Polyploidy
autopolyploid & allopolyploid
Sexual selection
Ex. Lake Victoria (East Africa) mate choice based on male
coloration in cichlid fish which serves as a reproductive barrier
Polyploidy is the
presence of extra sets of chromosomes due to accidents/mistakes that occur during cell division
-common in plants than in animals
Many important crops
oats, cotton, potatoes, tobacco, and wheat) are polyploids
