Transcript ENVI 30 Environmental Issues

I.
Macroevolution
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Major innovations  separation at higher
taxonomic levels
Exaptation
A.
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Existing feature modified to perform novel function
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Some plasticity in biological structures
Ex: Bird feathers evolved from reptile scales
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Ex: Development of bird wings from reptiles forelimbs not
designed for flight
May have provided insulation for primitive birds
Preadaptation for flight
Ex: Middle ear bones in mammals evolved from jaw
bones in reptiles
Does not imply that structures developed in anticipation
of future use
I.
Macroevolution
B.
Developmental Rate and Timing
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Some evolutionary modifications result from
minor genetic changes
Heterochrony
May affect regulatory genes
Ex: Allometric growth – Changes in relative
growth rates of body parts during development
Prolonged
juvenile
period
Fig. 25.21
I.
Macroevolution
B.
Developmental Rate and Timing
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Paedomorphosis – Retention of juvenile
characteristics in adults
Fig. 25.22
I.
Macroevolution
C.
Changes in Spatial Pattern
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Some genes control spatial organization of
body parts
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Ex: Homeotic genes regulate organism’s bauplan
Hox genes provide positional information in
animal embryos
Purple:
HoxC6 expression
(limbless regions)
Fig. 25.23
I.
Macroevolution
C.
Changes in Spatial Pattern
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Regulatory changes may affect gene
expression without changes in gene sequence
Fig. 25.25
I.
Macroevolution
D.
Directionality
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Macroevolution not goal-oriented
Fig.
25.27
II.
Phylogeny and Systematics
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Evolutionary processes reflected in
organismal phylogeny
Genealogies often represented as
phylogenetic trees that reflect
relationships among species
Systematics deals with classification of
taxa according to evolutionary history
Fig. 26.4