Lecture 4- Fitness

Question 1

species

Answer 1

a population of reproducing organisms that is isolated from other populations (but there are multiple definitions)

Question 2

when can this definition of species not be used

Answer 2

• prokaryotes and eukaryotes that aren’t strictly sexual
  -with extinct organisms
  -with bacteria and archaea that have horizontal gene transfer

Question 3

where can species appear

Answer 3

-in a long-time lineage (e.g. humans/ chimps and our common ancestor)
-In space due to geographic isolation (e.g. animals on an island)
-Various genetic effects can play a role

Question 4

how can species be identified/ detected

Answer 4

by comparing populations using population genetics

Question 5

allopatric speciation

Answer 5

allo- other, patra- homeland
Not necessarily different selection pressures and adaptations in two zones, leading to speciation
-populations are geographically isolated
-e.g diff species of antelope squirrels on either side of the Grand Canyon

Question 6

what can occur when populations are isolated?

Answer 6

-directional selection
-disruptive selection
-stabilising selection

Question 7

genetic drift

Answer 7

-random effects causing major changes in small populations ( by chance only some individuals reproduce)
-in large randomly mating populations, large fluctuations are unlikely

Question 8

founder effects/ bottle necks

Answer 8

founder effect- type of genetic drift, loss of genetic variation (species evolved from a small group)
bottleneck- environment causes a small population

Question 9

sympatric speciation

Answer 9

• (sym = same, patra = homeland)
• Much debated in animals from a theoretical point of view, few examples (parasites, perhaps?)
• Plants can easily show these effects

Question 10

examples of speciations in progress

Answer 10

blackcap (breeds in central Europe, over-winters in Spain, and for the last 30 years in the UK)

Question 11

how do black caps show temporal isolation

Answer 11

-black caps have assortative mating where Spanish birds mare with Spanish birds and UK mate with UK which is a result of arrival time on breeding grounds
-strong signs of genetic and morphological differences in Spanish and UK populations
-rapid genetic change= raw material of speciation

Question 12

comparison of hooded crow and carrion crow

Answer 12

have different distributions (83 base differences)
can hybridise
81 in same genetic region

Question 13

why do plants show polyploid species

Answer 13

have greater genetic, physiological and developmental flexibility

Question 14

example of sympatric speciation in Shortcleuch Waters

Answer 14

-appearance of Mimulus peregrines in Scotland
-Mimulus peregrinus originated from interspecific hybrids: hybrids were triploids (three sets of chromosomes usually prevents meiosis)
-A genome duplication event occurred in one of these triploid hybrids (entire set of chromosomes was doubled, creating a hexaploid individual -with six sets of chromosomes)
-This duplication restored the ability of the plant to undergo meiosis effectively because it now had an even number of chromosome sets, allowing the usual pairing and separation of chromosomes during reproduction.
-The hexaploid individual could reproduce and create offspring, forming a new, self-sustaining population (new species)

Question 15

what genetic factors can lead to speciation

Answer 15

-sampling and statistical effects e.g. drift and bottlenecks

Question 16

is speciation an adaptation

Answer 16

no, it’s an event
-consequence of particular conditions which can involve the by-products of subsequent selection

Question 17

how long can speciation take

Answer 17

up to 5,000,000 years (Mean time taken to go from single eukaryotic population to two reproductively isolated populations)

Question 18

how many species are there?

Answer 18

-unknown
-estimated based on sampling
-massive unknown in the sea

Question 19

why are there so many insect species?

Answer 19

-unknown
-appearance has been linked to evolution of plants
-the evolution of the larval stage enables insects to exploit new niches
-evolution of flowering plants coincides with radiation of the butterflies
-changes in ecology means new niches

Question 20

isolating mechanisms

Answer 20

-lack of interbreeding
-mechanisms: adaptation and therefore selection
-selection may be involved indirectly or sometimes directly, but needs to be shown, not assumed

Question 21

what are the different prezygotic barriers

Answer 21

premating (habitat isolation, temporal isolation and behavioural isolation)
post-mating (mechanical isolation, gametic isolation)

Question 22

postzygotic barriers

Answer 22

-reduced hybrid viability, reduced hybrid fertility, hybrid breakdown (fertile hybrids but reproductive failure at F2 or afterward)

Question 23

hybrid zones

Answer 23

-regions where two distinct meet and interbreed as a consequence of gene flow (movement of genes between groups)

Question 24

fitness

Answer 24

the reproductive success of hybrids or parents

Question 25

hybrid zones: fusion

Answer 25

-lots of gene flow
-groups are highly infertile, no barriers to breeding
-lead to a single population

Question 26

hybrid zones: reinforcement of isolation

Answer 26

If there is moderate gene flow, but hybrids experience reduced fitness (e.g., they are sterile, weak, or poorly adapted to the environment), natural selection will act against hybridization
-more reproductive barriers (e.g. mating preferences to prevent producing unfit hybrids)
-push the groups further apart genetically and more isolation

Question 27

hybrid zones: stability

Answer 27

-If gene flow is limited and hybrids experience no significant fitness disadvantage, the hybrid zone can remain stable over time.
-This means that the two groups remain distinct but continue to produce hybrids in the overlap area. The hybrid zone persists because neither fusion nor complete reproductive isolation occurs.