Species
A species is one or more populations of individuals that can be interbreeding under natural conditions producing fertile offspring, and are reproductively isolated from other such populations
Speciation
the formation of a new species from existing species
If they can produce fertile viable offspring, they are from the same spe
Macroevolution
evolutionary changes that occur at the species level
Reproductive isolating Mechanisms
Any heritable feature of body, form, functioning, or behavior that prevents breeding between one or more genetically divergent populations
Pre -zygotic Isolating mechanisms: Behavioural
- behaviors that prevent other spp. from recognizing or selecting them for mating * ex. unique dancing of the male Arizona spider of leg shaking and palps waving is unrecognized by the female of another spp. Different bird calls)
Pre -zygotic Isolating mechanisms: Temporal
- Two species that live in the same habitat or the same niche but have different mating seasons due to varying reproductive cycles * - Because of different mating times different species are reproductively isolated even though they live in the same area
- ex. Blooming times – cacti = day and night blooming; irises = spring and summer blooming Species breed at different times. In North America, five frog species of the genus Rana differ in the time of their peak breeding activity
Pre -zygotic Isolating mechanisms: Ecological
- two species that live in the same general area but in different habitats
- due to different habitats they do not encounter one another to reproduce
- ex: The common garter snake is often found near water but the northwest garter snake prefers open meadows
Pre -zygotic Isolating mechanisms: Mechanical
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 their genitals do not fit together
Pre -zygotic Isolating mechanisms: Gametic Isolation
- if egg and sperm from 2 different species do happen to meet gametic isolation will ensure that a zygote doesn’t form
- gametes are incompatible in some way
- ex: sperm from one species is unable to survive in the female reproductive tract
- Ex. In coral reefs, many species with external fertilization release their gametes simultaneously, so trillions of eggs and sperm enter water at the same time → gametes of the same spp. recognize one another by molecular markers.
- 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
Post-zygotic isolating mechanisms: Hybrid breakdown
Hybrid forms but when these hybrids mate their offspring are weak and sterile
Post-zygotic isolating mechanisms: Hybrid Inviability
- The 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 goats often die
Post-zygotic isolating mechanisms: Hybrid Sterility
- Hybrid produced is sterile (cannot produce normal gametes)
- Ex: horse and donkey can create a mule but the mule cannot reproduce (it’s sterile)
Types of Speciation: Allopatric Speciation
the evolution of populations into separate spp. as a result of geographic isolation
(ex. isolation caused by rivers, mountain ranges, canyons, human construction of dams or highways, strong winds carrying a few seeds)
Types of Speciation: Adaptive radiation
An ancestorial species diversifies into a variety of differently adaptive species
Sympatric Speciation
the evolution of populations into separate spp. within the same geographic area (ex. two spp. of the grey tree, frogs have overlapping territories, but one spp. is a diploid (2n), and 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).
