BG21

Question 1

what is the morphospace distributions of phenotype due to?

Answer 1

1. adaptive constrain: the morph wont work so does not proliferate/occur in nature.
2. developmental constraint: it cannot be made, there are not mutations which will produce the phenotype.

Question 2

snail geometrical diversity examples

Answer 2

turritella to stomatella

Question 3

who attempted to model snail shell geometry mathmatically, and how

Answer 3

1960 - David Raup
from this any kind of shell could be generated by changing the degree of overlap of three paramaters
- W (width)
- T (translation: how fat every turn you move a coil down)
- D (distance) when generating the curve from the centre.

• few parameters can ploy all variation seen acros snail shell taxonomic groups

Question 4

what does David raups model assume

Answer 4

helical spiral is logarithmically growing from the aperture.

Question 5

what could be seen on david raups model

Answer 5

regions of morphospace not occupied by
shells
adaptive?
developmental?

Question 6

Who was Gary Vermeij

what did he argue

Answer 6

bind man knows 50,000 shells by touch

• argued shell form is primarily the result of adaptive constraints
• arms race beetween mollusc and predator - losely coiled shells = no defence.

** but adaptive constaints werent neccessarily the only factor that limit distribution

Question 7

How to study developmental constraints

Answer 7

1. examine patterns of phenotypic or genetic varaince and co-variance.
2. phenotypic engineering
3. computational modelling of development.

Question 8

Describe digit loss in salamanders

Answer 8

ancestral salamander = 5 toes
many species only have 4
toe loss has evolved independtly atleast 6 times

Question 9

first toe loss in salamanders

why might this be the case?

Answer 9

always the 4th or 5th is lost first
- identified by association with underlying wrist carpels.

• seems odd to be adaptive? as it less toes is adaptive why not lose 2/3?
  could be developmental, intrinsic tendancy to lose 4/5 first due to way they are built

Question 10

salamander toe loss extremes

Answer 10

S. lacertina = 4 toes
A. tridactylum = 3 toes
A. means = 2 toes
A. pholeter = 1 toe

Question 11

what does sequence of loss tend to be in salamanders

Answer 11

4/5-> 1/2 ->.3

Question 12

what should we be able to show if toe loss in salamanders is a developmental constraint

Answer 12

that the order in which we lose digits is not adaptive but due to consequence of inhibiting growth of the limb meaning different digts are therefore formed frist and last

Question 13

testing developmental constraint of toe loss

Answer 13

inhibit growth in the foot by treating with colchicine = cell proliferation inhibitr
= amputate axolotl limb and treat with colocichine prior to regeneration
- resuls in small foot missing digits 4/5

Question 14

mimicing the sequential pattern of toe loss in axolotl

Answer 14

shh is a promoter of growth in the limb
potential to mimic loss of digits in evolution by inhibiting shh activity in the limb bud, using cyclopamine.
- when applied to axolotl at different stages we can see sequential pattern of digit loss mimiced. consistent as seen in evolution.

Question 15

Hemiergis lizard toe loss

Answer 15

little australian genus of lizard
several spp. have lost toes
middle 3 and 4 are preserved
edge digits 1 2 and 5 are lsot.

Question 16

correlation of shh expression and digit loss

Answer 16

reduction in shh expression is correlated with loss of digits.
earlier expression of shh stops the fewer digits are formed

** not a manipulative experiment so other limb factors such as bmp may also be reduced here.

Question 17

salamander digit loss, adaptive or developmental?

Answer 17

reductions in distal foot size or digit no. may be adaptive.
precise seq of digit loss (4,5->1 or 2->3) is not adaptive and is visible in patterns of variation.

Question 18

pleiotropy

Answer 18

multiple phenotypic effects of genes in development.

- reflects structure of developental pathways.

Question 19

what are developmental modules

Answer 19

visible patterns of phenotypic or genetic co-varaition in traits.

Question 20

testosterone signalling in mammals

Answer 20

are a development module
- mutations in the pathway show this
XY homoxzygous for testosterone null receptor are phenotypically female
XY homo for 5-alpha-reductase (metabolises testosterone) null mutations are hermaphrodites.

Question 21

mammal molar sizes

Answer 21

varies according to the food they eat
carnivores = assymetrically size molars
m1 > m2> m3
- changes in size are proportional = gradient of relative molar size.
herbivores = even sized molars
m1 = m2 =m3
** therefore pandaa nd sutralian water mouse each have molars that look like their trophic group rather than their phylogenetic group

Question 22

how are molars formed

developmental constriant?

Answer 22

in succession fro enamal knots
each knot inhibits formation of its neighbours via signalling molecules = module

• thought perhaps this developmental mechanism constrains size of teeth in evo.

Question 23

Model: adjacent knots inhibit growth

Answer 23

grow mouse gfp-expressing knots in a petri dish and seperate surgically
seperated m2 and m3 grow larger relative to m1.

• model appears to account for variation in development

Question 24

molar patterns in herbivores

Answer 24

three even sized moalrs
or big m2,
smaller m2 and really small m1
large m2 and no m1
but no other combos (large m2 and small m1 etc)
the molar inhibitory cascade is a developmental constrain on evolution.

Question 25

computational model of tooth formation

Answer 25

• An initial grid of 7 epithelial cells arranged in a hexagon and two layers of underlying mesenchymal cells.
• The grid grows by cell division and folds owing to forces arising from cells. 10 parameters control how these cells physically interact; adherence, repulsion etc.
• A set of coupled differential equations governs gene product interactions in each cell.
When the model is run for 10k time steps it grows tricuspid teeth.

Question 26

computational model for seal teeth

Answer 26

popualtions of lake lagoda appear to have variable teeth.
normally 4 cusps, but these can have as few as 3 or as many as 5
- if use model and change parameters these popualtions can be reproduced

Question 27

why are developmental constraints important to note?

Answer 27

tells us what variation is available for NS
- with knowledge of possible forms could predict evoltuion
for example in diseases like influenza
or animals on the cusp of extinction like coral reefs.