chapter 7 Flashcards
how is evolution both cont and discrete and why is this?
evolution is a cont process which produces discrete groups of plants and animals which are separated by appearance and behaviour gaps
this is because of speciation
what is the morphological species concept?
its used to explain what a species is, as in a species is a group of individuals which resemble each other more than members of other groups
what are the limitations of morphological species concept?
sexually dimorphic species can have males and females which appear v diff leading them to be misclassified as diff species
variation within an interbreeding group can exist
ex. humans are the same species but have diff hair, eye, skin colour
some distinct cryptic species can look almost identical
why are cryptic forms considering diff species?
despite coexisting in same locations they never exchange genes/don’t hybridize
what is biological species concept?
it refers to an interbreeding natural pop which are reproductively isolated from other such interbreeding natural pops
what is reproductive isolation?
other species have traits/diffs in appearance, behaviour, physiology, which prevents successful interbreeding
what are some reasons species might not interbreed?
diff flowering/mating seasons habitat isolation/not encountering e/o diff pollinators diff mating displays/pheromones biologically isolating barriers like sterile offsprings
what are the limits to biological species concept?
can’t test reproductive compatibility of extinct species
some organisms don’t reproduce sexually, unsure if asexual organisms can form discrete clusters
what are sister species?
sister species are species that are each other’s closest relatives and are often seperated by geographical barriers
how do sister species form?
sister species descend from a common ancestor
they then somehow get geographically isolated, adapt to their separate environments and eventually diverge so much that they become reproductively isolated to on another
this can be due to diff sexual selection by female, changes in genomes which cause hybrids to die prematurely or be sterile
theory of geographic speciation?
idea that geographic isolation is the first step to origin of species/speciation
theory of pop genetics?
its difficult to split a single pop into 2 genetically isolated parts w/o isolation as they will retain the opportunity to interbreed
what’s the first prediction of speciation and how is it supported?
if speciation depends on geographical isolation then there must’ve been many opportunities for species to experience this in the past (cuz there are a lot of species)
this is supported by the fact that throughout earth’s history mountains ranges rise, glaciers spread, deserts form, continents drift, droughts divide forests into separate grasslands
why do oceanic islands create the most speciation?
long-distance dispersal can also cause sexual isolation
on oceanic islands individuals can move b/w neighbouring islands and each time they do they become geographically isolated which reates a new change for speciation
what’s the second prediction of speciation
since speciation involves physically separating a pop to create diff species, most recently formed species shld be in diff but nearby areas
this prediction is fulfilled as many sister species are close but divided by geographic barriers
what is most often found to be the cause of sexual isolation in lab experiments?
mating discrimination, although its unknown how pops are able to discriminate
the third prediction of speciation?
geographic speciation shld still be occuring in nature
final speciation prediction?
reproductive isolation b/w reproductive isolated pops shld increased as a function of time
this is supported when drosophila were investigated it was found that reproductive isolation increased w/ time
how is it possible to tell if two species arose in same place?
habitat islands, small patches of terrain (ex. oceanic islands, tiny lakes) which are too small to contain geographic barriers can be investigated
if closely related species exist it can be conceded they formed sympatrically since the possibility of geographic isolation is small
what causes sympatric speciation?
there are two common forms which cause sympatric speciation
allopolyploid speciation and polyploid speciation
what is polypoid speciation?
speciation which arises from doubling all chromos in a single species in a autoploidy process which results in new species which can mate w/ other autopolyploids but not parental species
what is allopolyploid speciation?
speciation starts w/ hybridization of 2 species which have diff number chromos
the chromos are doubled so even if there are diff number it all successfully pairs up and produces a fertile hybrid
what is necessary for either type of polyploid speciation?
formation + union of egg and sperm w/ abnormally high chromos must occur in 2 successive gens
why are polyploidy common in plants but rare in animals?
the reasoning polyploidy is rare in animals cld be because of its x/y sex determination disruption or the inability of animals to self fertilize
