Lecture 2- Evolution, adaptation and speciation

Question 1

What are some of the questions in evolution?

Answer 1

• why is there such extraordinary diversity of life?
• how did such diversity come about?
• the answers depend on where the diversity of interest lies between or within species
• diversity of adaptations and the number of species
• diversity between species= what explains the diversity in skin colour between species
• diversity within species= like in humans from dark to light
• nothing in biology makes sense without evolution

Question 2

How is breeding domesticated animals an example of evolutionary process?

Answer 2

• picking some animals to breed while excluding others changes the attributes of the entire population
• artificial selection (acts as natural selection would)
• this way we get different breeds of dogs

Question 3

Can selection for some traits also select for other traits?

Answer 3

• yes
• eg. selection for high-speed running is associated with the evolution of relatively stiff, brittle limb bones (whippets)
• eg. selection for fighting leads to the evolution of limb bones with relatively high resistance to failure

Question 4

What are the premises of evolution of adaptation by natural selection?

Answer 4

1. there is variation in the trait within a population (eg. visual activity: some people see well, some do not)
2. the trait is heritable (otherwise the process of evolution by natural selection cannot occur)
3. more individuals are born than can possibly survive (otherwise no selection)

Question 5

What is evolution?

Answer 5

-change in trait frequency over generation (evolution is not only change!)

Question 6

What is natural selection?

Answer 6

• the mechanism of evolution
• differential mortality and/or fecundity between individuals with different traits
• it is a numbers game

Question 7

How would you describe what evolution is to someone?

Answer 7

• divide the process in two
• evolution is change, change in the frequency of a particular trait (gene) in a population over generations and natural selection is the agent of this change

Question 8

What is this?

Answer 8

• Observation 1: potential increase in population size
• Observation 2: typically population size remains stable
• Deduction 1: this means that there must be a struggle for existence among individuals (since the populations size remains approximately the same over time despite having fecund females)
• Observation 3: heritable variation in organisms (like produces like, children resemble their parents)
• Deduction 2: from this we deduce that there must be a differential survival for different individuals (ie. natural selection), the surviving individuals may have common characteristics

Question 9

What happened between generation n and n+x?

Answer 9

• change in trait frequency from generation n to generation n+x
• the green may be a disadvantage, perhaps makes the butterfly more conspicuous to predators, or lower fecundity
• or else the red butterflies have lower mortality for some reason or an increase in fecundity
• the colour trait (adaptation) determines the difference in mortality or fecundity

Question 10

What is the example of evolution of adaptation by natural selection? (the classic one)

Answer 10

• industrial melanism and the peppered moth
• pre-industrial revolution 99% of the moths are of the “wild” colouring that allows them to blend in with the environment, 1% are melanic (dark)
• post-industrial revolution the countryside is covered in soot, the melanic moths now make up 95% of the population and the wild ones only 5%
• result of the melanic form being at an advantage and having lower mortality

Question 11

What does selection act on? Also look at an example of how natural selection works (numbers).

Answer 11

-selection acts on trait associate with mortality and fecundity

Question 12

What is the unit of selection?

Answer 12

• inidividuals
• differential survival and reproductive output in individuals
• however there is also the issue that the phenotype and genotype are destroyed at meiosis so technically the unit of selection would be genes

Question 13

Why are species not the units of selection?

Answer 13

• competition occurs between individuals only
• differential species mortality and/or survivorship unlikely

Question 14

Why are groups not the units of selection?

Answer 14

• groups comprise selfish individuals
• differential group mortality and/or survivorship unlikely
• empirical studies of individual behaviour

Question 15

What is the reproductive success in great tits (example for the unit of selection and parent/offspring concflict)?

Answer 15

• females lay between 8 and 9 eggs in a clutch (why not more or less?) -experiments have demonstrated:
• parents cannot feed larger broods, chicks in large broods tend to be lighter than those in smaller broods
• heavier chicks survive better than lighter chicks
• there is an optimum brood size, which maximises the number of surviving young without costing the parents unnecessary effort

= selection at individual level

= results in population stability

Question 16

What is the nutrient transfer in the mammalian uterus (example for the unit of selection and parent/offspring conflict)?

Answer 16

• mothers increase their production of insulin (causes cells to remove glucose from blood) during pregnancy, you’d expect a decrease in insulin in order to provide sugar to the foetus
• the foetus produces extremely high levels of a hormone (hPL) that counteracts insulin, so the net result is no alteration of blood glucose concentration
• the escalation of opposing hormones seems to serve no purpose, but is an expected result of a parent/offspring conflict since from the embryo’s perspective it wants to get as much sugar as possible while the mother wants to give enough but not too much so she has a future opportunity to reproduce again

=selection at the level of genes

Question 17

Is speciation natural selection?

Answer 17

-it is not natural selection but it does involve natural selection

Question 18

What are species?

Answer 18

• species are groups of actual or potentially interbreeding natural populations which are reproductively isolated from other such groups
• but there are two exceptions:
  1. asexual organisms: is each clone a different species?
  2. inter-species hybridisation: not common among animals but frequent among plants and fungi, how much gene flow between populations can the biological species concept tolerate to retain its meaning?

Question 19

What are the two principal processes of speciation?

Answer 19

1: Genetic separation: splitting one gene pool into two or more largely separated gene pools
2: Phenotypic differentiation: diversification of one biological form into two or more phenotypically different forms =these processes proceed via allopatric (geographic separations) or sympatric (not necessarily geographic) separations

Question 20

What is allopatric speciation?

Answer 20

• starts when populations become geographically isolated, eventually cannot interbreed
• eg. Darwin’s finches

Question 21

What is sympatric speciation?

Answer 21

• populations not completely isolated
• group in the population that for some reason does not interbreed with the rest of the population
• eg. host shifts in phytophagous insects

Question 22

What is the example of allopatric speciation?

Answer 22

• Darwin’s finches:
• Galápagos islands never connected to mainland
• small groups of birds colonised one island -other island subsequently colonised
• populations initially isolated and specialised according to local conditions
• natural selection acting on the populations, advantages would differ depending on the particular traits of the environment

Question 23

What is the example of sympatric speciation?

Answer 23

• Rhagoletis, host shifts in phytophagous insectes
• typically lay eggs in hawthorns but were discovered in apples in 1864
• females prefer to lay in fruit from which they originally emerged -males mate on fruit from which they emerged
• an oviposition “mistake” can thus lead to speciation, even in sympatry
• there are genetic differences between flies emerging from apples vs hawthorns

Question 24

What is the issue with “ring species”

Answer 24

• Herring gull is different to the Lesser black backed gull and these do not interbreed
• however, the lesser black backed gull interbreeds with Heuglin’s gull, which then interbreeds with Vega herring gull which in turn interbreeds with American herring gull and that one interbreeds with the Herring gull
• thus there is gene flow from the Lesser black-backed gull to the Herring gull, are they still separate species?