lecture 18- speciation Flashcards
speciation
single ancestral species becomes two or more descendant species
what is a species
most resolved level of organization for how we classify the organisms in the world around us
evidence about species: species identification does not differ between cultures/peoples
evidence about species: animals can recognize different species
evidence about species: identification of statistical clusters
how many species exist on earth?
1.2 million now
biological species concept
reproductively isolated
reproductive barriers: prezygotic isolation
before the formation of the zygote
act to prevent or limit mating from even occurring (before a hybrid is produced)
reproductive barriers
features of organisms (or their ecology) that prevent or limit their ability to produce viable and fertile offspring with another species
reproductive barriers: postzygotic isolation
after the formation of the zygote
reduce the likelihood that a hybrid offspring will survive or itself reproduce after mating has occurred
5 examples of the reproductive barriers in prezygotic isolation
ecological: separated in space
temporal: separated in time
sexual/behavioral: separated by preference
mechanical: mating cannot physically occur (snails left vs right curl)
gametic incompatibility: eggs and sperm cannot combine (marine animals)
5 examples of prezygotic reproductive barriers: behavioral isolation
usually involves variation in male mating rituals or signals, and female recognition and preference for species-specific displays
caused by differences in behavioral
preferences, and most often these include mating rituals or signals.
These barriers may be substantial – as in the case of humans and
chimpanzees, our closest relatives – or subtle – as in the case of song
differences between closely related crickets
5 examples of prezygotic reproductive barriers: gametic incompatibility
corals and urchins
occurs when the egg and sperm themselves
are not compatible. This is common in broadcast spawners, that is
organisms that eject gametes into the water column, with the hope
that they will encounter each other (but do not fertilize if they meet a
gamete from another species)
postzygotic isolation: hybrid inviability
the offspring does not survive or is impaired in some way
postzygotic isolation: hybrid sterility
the offspring may be perfectly viable (horse plus donkey equal mule) but is infertile. often this is the case when there are chromosomal differences between the parents (so meiosis cant work properly)