Speciation Flashcards
behavioural isolation
Prezygotic
- behaviours that prevent other spp. from recognizing or selecting them for mating
ex. unique dancing of male Arizona spider of leg shaking and palps waving is unrecognized by female of another spp. Different bird calls)
temporal (timing) isolation
Prezygotic
- Two species in the same habitat, different mating seasons, reproductive isolation due to timing mismatches.
ex. Blooming times – cacti = day and night blooming; irises = spring and summer blooming
ecological / habitat isolation
Prezygotic
- two species that live in same general area but in different habitats
- due to different habitats they do not encounter one another to reproduce
ex: common garter snake is often found near water but northwest garter snake prefers open meadows
mechanical isolation
Prezygotic
- structural differences in reproductive organs that prevent fertilization.
- Cannot fertilize because they are anatomically incompatible
Ex: genitals of some insects operate like lock and key so if different species attempt to mate there genitals do not fit together
gametic isolation
Prezygotic
- if egg and sperm from 2 different species meet gametic isolation,the zygote won’t form
- gametes are incompatible in some way
ex: sperm from one species is unable to survive in female reproductive tract
Ex. In plants, trillions of different pollen are carried by wind or pollinators, but the stigma will not produce a pollen tube unless it recognizes pollen
Hybrid inviability
Postzygotic
- development of hybrid zygote stops in early development and it dies before birth
- Hybrid inviability is usually due to genetic incompatibility which prevents normal mitosis
Ex hybrid embryos of sheep and goat often die
Hybrid Sterility
Postzygotic
- Hybrid produced is sterile (cannot produce normal gametes)
Ex: horse and donkey can create a mule but mule cannot reproduce (its sterile)
Hybrid breakdown
Postzygotic
- Hybrid forms but when these hybrids mate their offspring are weak and sterile
allopatric speciation
allopatric speciation: the evolution of populations into separate spp. as a result of geographic isolation
- Occurs when populations are separated by a geographical barrier and diverge genetically.
ex. isolation caused by rivers, mountain ranges, canyon, human construction of dams or highways, strong winds carry a few seeds
sympatric speciation
sympatric speciation: the evolution of populations into separate spp. within the same geographic area
- Occurs when populations that live in the same habitat diverge genetically and become reproductively isolated.
ex. two spp. of grey tree frog have overlapping territories, but one spp. is a diploid (2n), the other is a tetraploid (4n) → duplication of identical genes meant they are still adapted to similar environments, but new genetic differences led to reproductive isolation.
Divergent evolution
as populations adapt, they become less and less alike.
Convergent evolution
When 2 or more species become increasingly similar in phenotypes due to experiencing similar selective pressures (similar environments)
Gradualism
- views evolutionary change as slow and steady, before and after a divergence
- Problem with the theory – expect to have transitional forms fossils, however many distinct species appear suddenly & followed by very little change.
- Accepted explanation – incomplete fossil record, intermediate forms may not have been preserved
- Changes go slow and steady, like horses evolving steadily.
Punctuated Equilibrium
- views evolutionary history as long periods of stasis, or equilibrium, that are interrupted by periods of seperation
- Evolution jumps fast, like trilobites (animal) suddenly changing in a rush
How humans impact evolution - examples
- Wilderness to cropland = Changing habitats for farming.
- Tourism development = Altering environments for visitors.
- Urban growth = Transforming landscapes for cities and roads.
