patterns in evolution ii. morphological a. patterns

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)

Nelsen and Platnick, 1981

Vicariance doesn't explain all patterns, but it accounts for the basic pattern.

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.