1/9/2013
Topic 5: Heterochrony & Scaling
What is Heterochrony?
What is Heterochrony?
Paedomorphosis
Peramorphosis
Allometry and Isometry
Important scaling relationships
A change in timing of
developmental events
relative to the ancestor
Descendent 1
A C D B E F G
2 important components
Descendent 2
A C D B F E G
Timing of appearance of
digits in a crocodile and an
ostrich
Which is ancestral?
Which is descendent?
___________________
___________________
___________
What is
Heterochrony?
What is Heterochrony?
Ancestor
A B C D E F G
What is Scaling?
heteros = different
chronos = time
Front limb developmental stages
Somite number =
developmental stage
Timing of front and hind
limb development
Number of Somites
20
40
60
Frog
Opposum
Key
Shrew
Front Limb
Turtle
Hind Limb
Chamaeleon
Rat
Crocodile
Pig
Salamander
Mud Puppy
Chicken
Ostrich
www.talkorigins.org
Richardson 1995
Lizard
Garden
Lizard
Deer
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Types of Heterochrony
________________
The retention of
juvenile characters
into adulthood
________________
The extension of
development to give
characters that are
“beyond” the adult
morphology
Paedomorphosis
Peramorphosis
Can characterize heterochrony
mathematically
Three parameters:
α – ________ of development
β – ________ of development
k – ________ of development
Shape
Types of Heterochrony
k
0
α
β
Proportion of
Developmental
Time
1
Photos © S Dalton, J Sevcik, H Hillewaert
Paedomorphosis
Types of Heterochrony - Paedomorphosis
Retention of juvenile characters can be accomplished by:
______________:
-k,
______________:
-β, moving up the offset time
the slowing down of development
______________: +α, delaying the onset time
The evolution of cephalochordates from a
urochordate-like ancestor
Urochordata
Deceleration
Hypomorphosis
Cephalochordata
Post-Displacement
Larva
Adult
Liem et al. Fig 1-4
Liem et al. 2001, Fig 2-10; C Arenz; N Hobgood
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Paedomorphosis
Salamanders have much paedomorphosis
Retention of ___________
Adult Ambystoma
Retention of ___________
Retention of ___________
Larval Ambystoma
Adult Axolotl
Photos © S Dalton, JP Clare
What human features are
paedomorphic?
Baboon Skull Ontogeny
Paedomorphosis
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Paedomorphosis
Types of Heterochrony - Peramorphosis
Primate Feet
Gibbon
Organutan
Human paedomorphic
features?
Over-development of structures:
______________: +k,
______________: +β, delaying the offset time
the speeding up of development
______________: -α, moving up the onset time
Human Hand
Acceleration
Chimp
Vertebrate Life Fig 24-10; www.seawayort.com
Gorilla
Human
Peramorphosis
____________ in
plesiosaurs
Ancestrally, there
are 3-5 phalanges
per digit
Plesiosaurs have
7-13 phalanges
per digit
Some
Derived
Antelope
Species
Photos © UMMZ, Univ. Michigan
What is scaling?
Peramorphosis
Typical
Antelope
Over-developed teeth
Under-developed horns
Over-developed
horns
AS Smith; Storrs 1993
Pre-Displacement
Liem et al. Fig 1-4
Peramorphosis
Hypermorphosis
Vampire Tetra
(Hydrolycus scomberoides)
Teeth grow to extreme
lengths
Often protrude through
dorsal surface of head
No other tetra has teeth
anywhere near this long
________________________
________________________
________________________
Differs from Heterochrony
Photos © MV da Costa, www.valleyanatomical.com
Typically within a species or
taxon
Not a comparison between
ancestor-descendent pairs
Can include multiple species
No real time/age axis
www.openlearn.ac.uk
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What is scaling?
Many important biological
processes are sizedependent
Do not simply change in
step with size
If hedgehog is modeled as
a cube:
How does surface area
increase with body
length?
How does volume
increase with body
length?
How about Area &
Volume?
www.openlearn.ac.uk
What is scaling?
____________________
____________________
____________________
____________________
Area
ororVolume
Area
Volume
600
500
400
300
200
100
0
0
1
2
3
4
5
6
7
8
9
60
70
Body Length
Length
600
Volume
Volume
500
400
300
200
100
0
0
www.openlearn.ac.uk
10
20
30
40
50
Area
Area
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The growth equation
600
Growth is modeled as an
exponential process
Area
ororVolume
Volume
Area
Cells divide exponentially
500
400
300
200
100
__________
Area
Volume
or Volume
Areaor
0
0
Log-transformation
linearizes this equation
log(y) = a + b(log(x))
1
2
3 4 5 6
Body Length
7
8
9
100
10
1
1
2
3 4 5 6 7 89
Body Length
Length
Isometry and Allometry
What is the slope of these
relationships?
Body length vs length
Body length vs area
Body length vs volume
Slope = ________
Slope = ________
Slope = ________
These expectations represent
_____________
As body length increases, the
other measures increase in
concert
Area or Volume
100
10
1
1
2
3 4 5 6 7 89
Body Length
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Isometry and Allometry
What if they increase faster or
slower than expected?
____________________ –
when a measure increases
faster than expected
(isometry)
____________________ –
when a measure increases
slower than expected
(isometry)
Area or Volume
100
Still have a positive
relationship
Increase is faster or slower
What body parts grow with positive allometry?
Negative allometry?
Vertebrate development occurs from anterior to posterior,
meaning that the anterior is always ahead of the posterior
10
1
Scaling in Human Ontogeny
1
2
3 4 5 6 7 89
Body Length
Moore 1983
Deer Antler Scaling
Surface Area to Volume Ratio
Are the antlers positively or negatively allometric relative to the
skull?
Antlers are used as weapons in intraspecific contests for mates
SA ∝ V2/3
Fish use cutaneous respiration
But as fish grows, SA decreases, so oxygen
from skin decreases
Gills develop and are used more and more
Surface Area
Sexual selection for ever larger horns
Size of horns is a measure of how
tough a male is
Volume
Photos © UMMZ, Univ. Michigan
Photo © www.advancedaquarist.com
Metabolic Rate and Body Size
Scaling of Bone Proportions
Mass ∝ Volume1
Metabolic Rate ∝ Mass3/4
Smaller mammals have
faster mass-specific
metabolic rate
Muscle Power ∝ PCSA
∝ Mass3/4
Metabolic rate may be
dependent on how much
power can be produced
How does the skeleton of an elephant compare
to that of a cat?
Why?
Metabolic Rate (W)
Body Mass (Kg)
Schmidt-Nielson 1984
Liem et al. Fig 5-25
1