genomes to ecosystems lecture 3- evolution and natural selection

Question 1

what is does pattern mean?

Answer 1

the change we see in the fossil record overtime. infer evolutionary relationships between different fossil organisms and their living descendants.

assumption that all organisms, extinct or extant are in some way related

Question 2

what is the process?

Answer 2

natural selection and ecological opportunity.

eg ecological opportunity in the shallow equatorial tethys ocean, abundant marine food sources in the shallows

Question 3

what is Mutationalism?

Answer 3

Species emerge in large jumps
Also ‘saltationism’
Hugo de Vries 1900

Question 4

what is Orthogenesis?

Answer 4

Directional force driving evolution
Evolution is non-reticulate
Various proponents

Question 5

what is Theistic evolution?

Answer 5

Divine creation
God generating beneficial mutations
Asa Grey and others

Question 6

what is Scalae Naturae?

Answer 6

A solid march towards ‘perfection’
Slime moulds at the bottom, us at the top

Question 7

what is catastrophism?

Answer 7

Series catastrophic events defines the fossil record
Georges Cuvier (1812)

Question 8

what is Lamarckianism?

Answer 8

Individuals loose characters they don’t require
Acquired traits are heritable
JB Lamarck (1809)

Question 9

what happens when Mendel meets Darwin?

Answer 9

Mendel studies inheritance of seven phenotypic traits

Developed two key ‘rules’ of inheritance 1) law of segregation (gametes), 2) law of independent assortment (prophase 1). Described genes as ‘factors’

Darwin posited that a portion of inter-individual variation must be heritable
Darwin developed ‘pangensisis’ theory of evolution involving ‘gemmules’ which were produced by all tissues. Pangenesis had a Lamarckian twist

Question 10

what is Darwins big idea?

Answer 10

On the Origin of Species’ published 1859
Broad support among scientists (scientific naturalism)
Skepticism from the church and the establishment (natural theologists)
The result of 30 years of careful natural observation and synthesis

Question 11

what is darwins theory in a nutshell on natural selection?

Answer 11

Individuals in a population vary significantly from one another and much of this variation is heritable
Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their heritable traits to future generations, which produces the process of natural selection

This slowly effected process results in populations changing to adapt to their environments, and ultimately, these variations accumulate over time to form new species

Question 12

why does population size stay the same?

Answer 12

Every species is fertile enough that if all offspring survived to reproduce, the population would grow

Despite periodic fluctuations, populations remain roughly the same size

Resources such as food are limited and are relatively stable over time

Question 13

how does selection act on phenotype?

Answer 13

A hypothetical population of organisms

‘Trait’ is the phenotype under selection (e.g. tail length)

Variation in trait values might be normally distributed without selection

Question 14

what is Selection type 1 – Stabilizing or ‘purifying’ selection (when the graph reaches a high peak in the centre)

Answer 14

Selection against extreme trait values

Phenotypic variation lost from population

Mean trait value stays the same

Question 15

what is selection type 2- directional selection (when the value of a trait moves direction but the graph remains the same shape)

Answer 15

Mean trait value moves in response to the direction and intensity of the selection

Question 16

what is Selection type 3 – Disruptive Selection (when the peaks are high on either sides but have a dip in the middle where it peaked previously)

Answer 16

Selection against mean trait

The result is a multimodel trait distribution

Question 17

what is sexual selection?

Answer 17

Darwin noted that some characteristics in sexually dimorphic species could not readily be explained by natural selection.

Question 18

what is intrasexual selection?

Answer 18

Intrasexual selection, or competition between members of the same sex (usually males) for access to mates (accepted immediately)

Question 19

what is intersexual selection?

Answer 19

Intersexual selection, where members of one sex (usually females) choose members of the opposite sex (ridiculed for 80 years!)

Question 20

how is heritability used to predict evolutionary change?

Answer 20

The essence of the modern synthesis is that selection due to environmental pressures can be propagated via heritability through evolutionary time

Question 21

what is the breeders equation?

Answer 21

R = h2 x S The greater the heritability of a trait, the faster a species can respond to selective pressure

Question 22

what does each letter stand for in the breeders equation?

Answer 22

R = the evolutionary response - change in phenotype between generations
h2 = selection differential - change in phenotype due to selection
S = heritability - transmissibility of phenotype

Question 23

how is the h2 value calculated?

Answer 23

the heritability (h2) of any given trait is the ratio of the genetic variation to total phenotypic variation
h2 = VG / VP

Variability against the same genetic background = phenotyic plasticity

Question 24

how do we use heritability to predict evolutionary change?

Answer 24

A way of directly measuring heritability is to look at how well trait values correlate between generations
strong heritability= a high gradient and weak= low gradient