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Patterns in Evolution
II. Morphological
A. Patterns
B. Developmental Trends in Morphological Patterns
2. Individualization
Evolution by duplication - individualization - specialization - reduction
Duplication - Specialization - Reduction.... and individualization at the
duplication stage allows for separate evolutionary pressures to act on these
replicated parts.
B. Developmental Trends in Morphological Patterns
3. Heterochrony
evolutionary change due to a change in the timing of developmental
events...two classic examples are:
Paedomorphosis - either a reduction of development rate, or a shorter
absolute development time; either way resulting in the attainment of
reproductive adulthood while juvenile characteristics are still present
Axolotl
B. Developmental Trends in Morphological Patterns
3. Heterochrony
evolutionary change due to a change in the timing of developmental
events...two classic examples are:
Peramorphosis - delayed maturity; reproduction at a disproportionately large
size
Patterns in Evolution
II. Morphological
A. Patterns
B. Developmental Trends in Morphological Patterns
4. Allometry
•Differential rates of growth of different body parts. This is a very
important mechanism of evolutionary change, because often homologous
traits simply differ in the relative size of their parts (bat wing, hand). Often,
body size, itself, is used as the standard against which allometric
increases in specific body parts are measured... y = bx^a. If a = 1, the body
dimensions change at the same rate (no allometry). if a > 1, then y
changes faster than x (positive allometry - leg length), and if a < 1, then
there is negative allometry. Obviously, allometric differences become more
pronounced as the organism increases in size... so large organisms and
small often have the most extreme proportions (Irish Elk).
•Got another example?
B. Developmental Trends in Morphological Patterns
4. Allometry
Patterns in Evolution
II. Morphological
A. Patterns
B. Developmental Trends in Morphological Patterns
5. Results: Evolutionary Trends
Developmental changes can be rather "easy" these are tweaks to a system. Allometric
differences, alone, can occur solely in response to
selection for different body sizes. This can produce
a very regular and progressive trend in morphology
over time, and within a group of closely related
organisms. This can occur in an Adaptive Radiation
- and these changes in morphology, though slight,
may have dramatic changes in the ecology of the
organism and may result in niche partitioning
among many similar species - like Darwin's
Finches, and the Cichlid fishes of lakes in Africa
(Malawi, Victoria, Tanganyika). Variant trait can be
used for a new purpose…
Patterns in Evolution
I. Phylogenetic
II. Morphological
III. Historical (later)
IV. Biogeographical
Patterns in Evolution
IV. Biogeographical
A. Darwin's Points
•1. The similarity and dissimilarity of faunas can't be completely explained
by correlations with environment. For instance, although the faunas of the
pampas and Australian grasslands are convergent in response to the
similar environment, they are composed of radically different organisms placentals vs. marsupials.
Patterns in Evolution
IV. Biogeographical
A. Darwin's Points
•2. Barriers to migration are critical to maintaining these different
communities.
Patterns in Evolution
IV. Biogeographical
A. Darwin's Points
•2. Barriers to migration are critical to maintaining these different
communities. (Pliocene = 5-1.75 mya) - Great Faunal Exchange
Patterns in Evolution
IV. Biogeographical
A. Darwin's Points
•3. Species on a continent are more closely related than those from
different continents, on average. Wallace's biogeographical realms
Patterns in Evolution
IV. Biogeographical
A. Darwin's Points
B. Alfred Russel Wallace. 1855. On the law that has regulated the introduction
of new species. Annals and Magazine of Natural History.
1. Large groups, such as classes and orders, are generally spread over the
whole earth, while smaller ones, such as families and genera, are frequently
confined to one portion, often to a very limited district.
Class: Aves
Family: Trochilidae
(Hummingbirds)
Archilochus spp.
Selasphorus spp.
B. Mechanisms
1. Dispersal: both range expansion over contiguous habitat, and 'jump'
dispersal across a barrier, or a 'stepping stone' model across an
archipelago
B. Mechanisms
2. Vicariance: a range is divided by separation of the habitat - tectonic
plate separation, new river, etc.
A
B
C
C. Patterns
1. Vicariance: phylogeny correlates with the division of land masses (or
other geographic or historical patterns)
LAND
PHYLOGENY
C. Patterns
1. Vicariance: monophyletic groups correlate with the division of land
masses (or other geographic or historical patterns)
Nelsen and Platnick, 1981
C. Patterns
1. Vicariance: monophyletic groups correlate with the division of land
masses (or other geographic or historical patterns)
Vicariance doesn't explain all
patterns, but it accounts for
the basic pattern.
Nelsen and Platnick, 1981
C. Patterns
2. Dispersal: Actually, you can't really falsify dispersal... because some
particular dispersal sequence could fit a phylogeny. So, you need to
falsify vicariance... and then assume dispersal.
C. Patterns
2. Dispersal: Actually, you can't really falsify dispersal... because some
particular dispersal sequence could fit a phylogeny. So, you need to
falsify vicariance... and then assume dispersal.
BUT... dispersal can also correlate with geographical history... in volcanic
archipelagoes that "produce" new islands over hotspots... phylogenies
that correlate with island age imply dispersal and speciation:
Island Age
Phylogeny
C. Patterns
2. Dispersal: Actually, you can't really falsify dispersal... because some
particular dispersal sequence could fit a phylogeny. So, you need to
falsify vicariance... and then assume dispersal.
BUT... dispersal can also correlate with geographical history... in volcanic
archipelagoes that "produce" new islands over hotspots... phylogenies
that correlate with island age imply dispersal and speciation.
ALSO... unbalanced communities are suggestive of dispersal; the
differential dispersal ability of different organisms creates "unbalanced"
communities.
1. Marine Archipelagoes lack frogs and large mammals.
2. Islands forms are often giant or dwarf species.