BG21 Flashcards
what is the morphospace distributions of phenotype due to?
- adaptive constrain: the morph wont work so does not proliferate/occur in nature.
- developmental constraint: it cannot be made, there are not mutations which will produce the phenotype.
snail geometrical diversity examples
turritella to stomatella
who attempted to model snail shell geometry mathmatically, and how
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
what does David raups model assume
helical spiral is logarithmically growing from the aperture.
what could be seen on david raups model
regions of morphospace not occupied by
shells
adaptive?
developmental?
Who was Gary Vermeij
what did he argue
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
How to study developmental constraints
- examine patterns of phenotypic or genetic varaince and co-variance.
- phenotypic engineering
- computational modelling of development.
Describe digit loss in salamanders
ancestral salamander = 5 toes
many species only have 4
toe loss has evolved independtly atleast 6 times
first toe loss in salamanders
why might this be the case?
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
salamander toe loss extremes
S. lacertina = 4 toes
A. tridactylum = 3 toes
A. means = 2 toes
A. pholeter = 1 toe
what does sequence of loss tend to be in salamanders
4/5-> 1/2 ->.3
what should we be able to show if toe loss in salamanders is a developmental constraint
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
testing developmental constraint of toe loss
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
mimicing the sequential pattern of toe loss in axolotl
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.
Hemiergis lizard toe loss
little australian genus of lizard
several spp. have lost toes
middle 3 and 4 are preserved
edge digits 1 2 and 5 are lsot.
correlation of shh expression and digit loss
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.
salamander digit loss, adaptive or developmental?
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.
pleiotropy
multiple phenotypic effects of genes in development.
- reflects structure of developental pathways.
what are developmental modules
visible patterns of phenotypic or genetic co-varaition in traits.
testosterone signalling in mammals
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.
mammal molar sizes
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
how are molars formed
developmental constriant?
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.
Model: adjacent knots inhibit growth
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
molar patterns in herbivores
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.
computational model of tooth formation
• 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.
computational model for seal teeth
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
why are developmental constraints important to note?
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.