Speciation and Reproductive Isolation Flashcards
(24 cards)
Perfection in adaptation?
Adaptation is rarely perfect
Pre-zygotic mechanisms for reproductive isolation
- Geographic Isolation (allopatric speciation)
- Gametic isolation
- Mechanical isolation
- temporal
- behavioral
- ecological preferences and mating isolation (apple maggot)
Mechanical isolation
- simply put, male “parts” don’t fit female “parts” (e.g. dragonflies, beetles, bush babies)
- flowering plants & specificity in their pollinators
temporal mechanisms for pre-zygotic isolation
inter-species differences in timing of reproduction
behavioral mechanisms for pre-zygotic isolation
mating rituals, displays, songs, etc.
post-zygotic mechanisms for reproductive isolation
- zygote mortality
- hybrid inviability
- hybrid sterility
- low hybrid fitness (survivorship)
3 Geographic Models of Speciation
- Allopatry
- Parapatry, “ring species”
- Sympatry
Sympatry
i.e. no geographic speciation
How do geographically isolated populations diverge?
- natural selection adjusts population to local environment
- genetic drift (mutations)
- founder effect
Other important effects of small population size
- Founder effect
- Bottleneck effect
examples: including Amish, cheetahs
Biological species concept
Species are groups of interbreeding natural populations that are reproductively isolated from other such groups
- Groups of populations that can exchange genes (actually or potentially)
- Produce fertile offspring
- Reproductively isolated from other such groups
- As long as two forms interbreed, they cannot diverge
- If two forms DO NOT interbreed, each can develop different adaptations
Pre-zygotic isolation
union of egg and sperm never occurs because gametes never encounter one another
Post-zygotic isolation
egg and sperm encounter one another but the zygote is either not viable or gives rise to individuals that cannot reproduce or that have very low fitness
Zygote
cell formed by the union of male (a sperm) and female (an ovum) sex cells. The zygote develops into the embryo following the instructions encoded in its genetic material, the DNA.
Allopatry
physical barrier separating species
Parapatry
“ring species” i.e. grass adapting to rivers with heavy metals whereas the grass in clean rivers don’t need to
Sympatry
i.e. no geographic separation - genetic polymorphism
How do geographically isolated populations diverge?
- natural selection adjusts population to local environment
- genetic drift (mutations, unpredictable allele fluctuations), is more prevalent in smaller populations
- founder effect
founder effect
when a few individuals from a larger population interbreed, results in a more limited gene pool (ex: the Amish population with heritable genetic conditions such as polydactyly, dwarfism, twins). The genetic variety in the original main population is preserved (new subpopulation has a different allele frequency than the original population!)
bottleneck effect
when a large population decreases in size (could be due to hunting, home environment getting destroyed, etc), resulting in a lack of genetic diversity (survivors of the bottleneck effect tend to lack genetic diversity themselves. Ex: the inbreeding among remaining Florida panthers results in more genetic disorders and birth defects)
hybrid inviability
occurs when gametes fuse, development progresses, but the offspring cannot survive to adulthood
hybrid sterility
when gametes fuse, development progresses, but the offspring cannot survive to adulthood
low hybrid fitness
when gametes fuse, development progresses, and offspring survive to adulthood and can reproduce, but have very low fitness in the wild
gametic isolation
a type of prezygotic barrier where the gametes (egg and sperm) come into contact, but no fertilization takes place (e.g. tubes sprouting from pollen grains)
