UNIT 2 DAY 8 - SPECIATION Flashcards
Speciation
new species arising from ancestral species
Darwin’s theory of natural selection had fallen into disregarded by the early 20th century
- field biologists, the one who best understood adaptations in nature, favoured neo-lamarckian theories of species origins
-lab centrered biologists favoured single-step, macromutational theories
1930s natural selection was back
- fisher showed that natural selection worked perfectly with mendelian genes
evolutionary synthesis
- fusion of Darwin and Mendel’s theories
- brought natural selection back to centre of evolution
biological species concept
- emphasised species nature as evolving populations rather than as static types
- species are interbreeding populations that are reproductively isolated from other populationsn
evolutionary biologists agreed that natural selection drives evolution (1940s)
- by accumulating many smal, favourable genetics variants over time each generated by random mutation, natural selection slowly and gradually alters a species in ways that adapt to its environment
- environment with competing species and physical conditions `
microevolution
evolutionary change within a species or small group of organism, especially over a short period of time
macroevolution
large-scale evolutionary changes that take place over long-periods of time
reproductive isolation
- the inability of a species to breed successfully with related species due to geographical, behavioural, physiological or genetic barriers or differences
geographic isolation
isolation between populations due to physical barriers
how new species arise
- how does a new species acquire its own, distinct set of traits
- how does it become reproductively isolated from other species
- are the answers to the first 2 questions related?
Species
is a population (or a set of populations) with a distinct constellation of traits (grand Fact #1) that fit it to a particular ecological niche (Grand Fact #3). it remains distinct because it is reproductively isolated from other populations, breeding only with its own kind
how does a new species acquire its own, distinct set of traits
- Darwin’s answer to the first question as his principle of divergence of character
- natural selection, he argued, drives the descendants of an original species into ever-divergent niches because the most divergent forms suffer the least competition
- gaps between species, makes them distinct
how does it become reproductively isolated from other species?
- Mayr assumed that populations are somehow physically isolated as they diverge - either geographically or by habitat choice –> else they would interbreed and merge back into one
- Darwin expected diverging populations to lose the ability to interbreed even if they come back into contact
reinforcement
- process by which selection can strengthen reproductive barriers
- selection will favour individuals who mate within their own population because they will avoid having unfit hybrids and over time, stronger and stronger pre-mating reproductive barriers will evolve, yielding 2 distinct species
allopatric speciation
the process of speciation that occurs with geographic isolation
allopatry
occurs in separate, non-overlapping geographic areas
sympathy
occurring in the same geographic area
prezygotic barriers
prevent mating or fertilisation between species
temporal isolation (prezygotic)
mating or flowering occurs at different seasons or times of day
habitat isolation (prezygotic)
populations live in different habitats and do not meet
behavioural isolation (prezygotic)
there is little or no sexual attraction between species
mechanical isolation (prezygotic)
structural differences in genitalia or flowers prevent copulation or pollen transfer
gametic isolation (prezygotic)
male and/or female gametes die before uniting or fail to unite
