Ch. 23: Macroevolution
Speciation and Extinction
Adaptive Radiation
Developmental Genes
When the rate of speciation is greater than the rate of extinction, you get species growth (appearance of new species)
Certain influences can have a large impact on the survival of groups of organisms including:
Plate tectonics
Mass extinctions
Adaptive radiations
This is the theory that continents are part of great plates of Earth’s crust that float on the hot, underlying portion of the mantle
Continental drift is where movements in the mantle cause the continents to move slowly over time
More on this in a separate branch!
Continental drift results in:
Altered habitats
Climate change due to new location
The promotion of allopatric speciation on a grand scale
Causes extinction of species as well as new growth opportunities for organisms surviving a change
Defined as the elimination of a large number of species throughout Earth, and is the result of global environmental changes
5 mass extinctions have occurred within the past 500 million years resulting in the majority of species that ever lived to now be extinct
Consequences of Mass Extinctions:
It severely disrupts interactions in an ecological community.
It changes types of organisms in community affecting species interactions
Species go extinction meaning their evolutionary lineage is gone forever
It takes millions of years to recover the previous levels of diversity
It promotes adaptive radiation where new groups of organisms fill empty niches and diversify
Defined as a period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities
Typically happens in 1 of 3 ways:
- After a mass extinction
- When a group of organisms has a major evolutionary innovation (ex: seeds, armored body covering)
- When a group of organisms colonizes regions in which they face little competition from other species
Ex: After dinosaurs went extinct mammals greatly expanded in diversity and size to fill empty niches
Ex: After land plants developed adaptations like waxy leaf coats and stems to fight gravity, they were able to fill new niches
Ex: When plants colonized and diversified on land, it stimulated AR in insects that ate or pollinated plants
Factors that Promote Adaptive Radiation:
Mass extinctions
Major evolutionary innovations
Diversification of another group of organisms (which can provide new sources of food)
Migration to new locations where few competitor species exist
Genes that control the embryonic and post-embryonic development of an organism (influencing rate, timing, and spatial pattern of form)
These genes tend to be identical or very highly similar between species even when they are very distantly related as they are so important for their function
Changes in Developmental Genes Include:
Mutations, or Changes in Gene Sequences
Results from the process of duplication and divergence
The original gene still exists and functions allowing for survival, but the new copy is free to accumulate mutations and possibly even new function(s)
Changes in Gene Regulation
Gene regulation controls when, where, and how long a gene is expressed or allowed to function, so changing it can have significant effects
What does Macroevolution Tell Scientists?
Speciation has been affected by both small scale factors and large scale factors
New forms arise by the slight modification of existing forms
A structure gradually acquires a different role, called exaption
Can observe trends in the fossil record
The fossil record is documentation of the rise and fall of different groups of organisms over time
Based mostly on the sequence in which fossils accumulate in sedimentary rock layers called strata
This picture demonstrates an example using the Artemia Ubx gene
This gene promotes leg formation in the trunk of the body however mutation occurred in the nucleotide sequence resulting in a new gene (Drosophilia Ubx) that suppresses leg formation in the trunk
This picture demonstrates an example using threespine stickleback fish
Here the marine species have spines on the lower surface that is made of calcium. In lake species however, there are no spines because calcium is used for other purposes. The Pitx1 gene is the same for both species but the gene regulation is different. The marine species express it in the spine and mouth regions while lake species express it only in the mouth region.