Mechanisms for reproductive isolation

Question 1

breeding at different times of the year (3)

Answer 1

• two species showing hibernation and aestivation would never have the chance to mate.
• these seasonal differences are temporal isolation factors
• diurnal and nocturnal animals cannot mate because of temporal isolation factors associated with their behaviour

Question 2

species-specific courtship behaviour (2)

Answer 2

• the different courtship behaviours of animal species create powerful pre-zygotic reproductive barriers, which isolate apparent similar species
• many animal species have specific complex behaviour and courtship displays that attract the opposite sex of that species only, and each stage of the courtship depends on the response of the partner

Question 3

plant adaptation to different pollinators (2)

Answer 3

• some plants species anre adapted to be pollinated only by specific pollinator animal species
• since pollinators have specialised diets, this also ensures that only pollen from the same species is used to fertilise the ova

Question 4

habitat isolation (4)

Answer 4

• when two species live in different habitats, they will meet very seldom, if at all
• habitat isolation also affects parasites which are confined to the body of their host
• habitat isolation can be a pre-zygotic barrier that hinders species from interbredding
• this principle applies to all living organisms, including plants

Question 5

mechanical isolation (prevention of fertilisation)

Answer 5

• mating pairs may not be able to reproduce if their genitals are not compatible
• evolution has led to increasingly complex genital organs in organisms, which cause mechanical isolation between species
• mechanical isolation in plants is related to the adaptation and co-evolution of each species in the attraction of a specific pollinator so that pollen is not transferred to other species

Question 6

infertile offspring in cross-species hybrids

Answer 6

this is a post-zygotic barrier. if a sperm cell from one species fertilised an egg cell of another species, then post-zygotic barriers will prevent the hybrid zygote from developing into a fertile adult.

Question 7

reduced hybrid viability

Answer 7

the hybrid is not viable, the embryo will be aborted

Question 8

reduced hybrid fertility

Answer 8

two different species mate and produce living offspring. the offspring are most often sterile and cannot produce new offspring

Question 9

hybrid breakdown

Answer 9

sometimes two different species interbreed and produce hybrids that are viable and fertile. however, the next generation is often sterile