Lecture 4

Question 1

the biological species concept

Answer 1

can be considered equal to a group of organisms capable of producing fertile offspring

Question 2

A more practical definition of species

Answer 2

a group of organisms which can and usually do interbreed to produce fertile offspring

Question 3

Ring species

Answer 3

two end populations are reproductively isolated from one another but indirectly connected by a continuous chain of reproducing populations

its debatable how to classify such populations

Question 4

the morphological species concept

Answer 4

defines a species by morphological characteristics, applies to both sexual and asexual organisms
mainly the species concept for extinct species where other info isn’t available

subjective criteria

Question 5

cryptic species

Answer 5

species that are reproductively isolates so are separate biological species but morphologically similar

it may not have been initially recognised that they were separate species in term of the biological species concept

Question 6

speciation

Answer 6

the formation of a new species

the source of biodiversity

a focal point of evolutionary theory

above the microevolutionary level of allele frequencies in populations

Question 7

Macroevolution

Answer 7

evolutionary change above the species level

Question 8

Allopatric speciation

Answer 8

gene flow is interrupted or reduced when a population is divided by an environmental barrier

two populations become isolated from each other over time and differences form

Question 9

Sympatric speciation

Answer 9

speciation takes place in geographically overlapping populations
e.g due to reproductive barriers

Question 10

Reproductive isolation

Answer 10

reproductive isolation is the existence of reproductive barriers that stop two species from interbreeding to produce viable and fertile offspring

Question 11

Hybrids

Answer 11

are the offspring of crosses between different species

they occasionally occur and can be infertile or occasionally fertile

Question 12

two main biological mechanisms of reproductive isolation

Answer 12

pre zygotic barriers- before fertilisation
postzygotic barriers- after fertilisation

Question 13

Three prezygotic barriers

Answer 13

impeding different species from attempting to mate

preventing the successful completion of mating

hindering fertilisation if mating is successful

Question 14

impeding different species from attempting to mate

Answer 14

habitat isolation in different habitats

temporal isolation in time

behavioural isolation by different behaviours

Question 15

preventing successful completion of mating

Answer 15

mechanical isolation that prevents mating

Question 16

hindering fertilisation if mating is successful

Answer 16

gametic isolation

Question 17

Habitat isolation

Answer 17

two species encounter each other rarely or not at all as they occupy different habitats even though not isolated by physical barriers

Question 18

temporal isolation

Answer 18

species that breed at different times of the day, different seasons or different years cannot interbreed

Question 19

behavioural isolation

Answer 19

courtship rituals and other behaviours are unique to a species

Question 20

mechanical isolation

Answer 20

morphological differences can prevent successful mating

Question 21

gametic isolation

Answer 21

sperm of one species may not be able to fertilise egg of another

Question 22

Postzygotic barriers

Answer 22

block hybrid survival and reproduction

Question 23

three types of post zygotic barriers

Answer 23

reducing hybrid survival reduced- hybrid viability

reducing hybrid mating success
-reduced hybrid fertility in 1st generation

reducing ongoing hybrid mating success - hybrid breakdown 2nd generation

Question 24

reduce hybrid viability

Answer 24

genes of the different parent species may combine to impair the hybrids development or health

Question 25

reduced hybrid fertility

Answer 25

even if hybrids are healthy they may be sterile

Question 26

hybrid breakdown

Answer 26

some first generation hybrids are fertile but when they breed with other species or with either parent species, offspring of the second generation are feeble or sterile

Question 27

Hybrid zones

Answer 27

hybrids can occur when the reproductive barriers between species are incomplete

a hybrid zone is a region in which members of different species mate and produce hybrids

hybrid zones can tell us about mechanisms of reproductive isolation

a barrier to gene flow forms and the OG pop splits into two populations partially reproductively isolated but retain a hybrid zone

Question 28

there are three possible long term outcomes of hybrid zones

Answer 28

reinforcement
fusion
stability

Question 29

Reinforcement

Answer 29

differences increase until hybrids are no longer formed
-hybrids become less viable or fertile
over time the rates of hybridisation decreases
-finally the 2 species do not produce hybrids
-pre-zygotic mechanisms appear

Question 30

fusion

Answer 30

barriers weaken until there’s one species
-fusion of populations can occur if there is continues substantial gene flow in a hybrid zone
-reproductive barriers weaken and 2 species fuse into one

Question 31

stability

Answer 31

hybrids continue to be produced
-a hybrid zone may be stable over a long period of time, if some gene flow continues to occur
-usually involves only a small overlap between populations preventing fusion or reinforcement