Biology 3201 Unit 4 Ecology Ch. 21 - Adaptation and Speciation
Speciation Speciation: the formation of a new species Biological species: a group of organisms able to interbreed and produce fertile offspring. Ex. Horses and donkeys are separate species. They are able to interbreed but the offspring produced are not fertile
How to species form? There are generally two pathways in which species are formed: 1. Transformation: the formation of a species because of a series of accumulated changes over time. One species changes into another in this way 2. Divergence: the formation of species from a parent species
Speciation Speciation occurs when two groups in a population become isolated from each other The separation is caused by one or more BARRIERS.
Barriers that cause speciation Geographical barriers: When a population becomes divided by a geographic boundary such as a canyon, river, etc. This prevents interbreeding. Over time natural selection causes genetic differences to become so large two species form. Ex. Giraffes that have become separated by mountains will eventually develop into separate species. Biological barriers: barriers that keep species reproductively isolated; may be pre-zygotes barriers or post-zygotic barriers
Pre-zygotic barriers These are known as pre-fertilization barriers that impede mating or prevent fertilization Behavioral isolation: bird songs, courtship rituals, pheromones, etc. are all species specific and prevent fertilization Temporal isolation: these are often timing barriers. Several species mate at different times during the year and as such are not able to mate. Habitat isolation: some species live in the same area but have different habitats; ex. North American Garter snakes, one species prefers open areas while the other prefers water
Pre-zygotic barriers Mechanical isolation: some species are anatomically incompatible thus not allowing them to exchange sperm and egg Ex. The genitals on certain species of insect work only on a lock-key system. If the lock does not fit the key, no fertilization can occur. Gametic isolation: sometimes the gametes from species do not even meet. This prevents fertilization Ex. Sea urchins release their eggs into the water, but chemicals on the surface of the eggs prevent sperm from a different species from fertilizing them.
Post-zygotic barriers These are barriers that prevent a zygote from developing into a fertile offspring Hybrid invariability: incompatibility of the two species may cause the zygote to stop embryonic development Ex. Embryos of sheep/goats do not survive Hybrid sterility: the production of an organism, but it is sterile Ex. Horse + donkey = mule (sterile) Hybrid breakdown: sometimes the first generation of offspring are viable, but subsequent generations are either sterile or wheat (cotton plants)
Adaptive Radiation Adaptive radiation: the diversifying of an ancestral species into a variety of species. This usually occurs after a novel characteristic has evolved or there is a mass extinction Ex. The finches of the Galapagos islands evolved from one common ancestor.
Divergent evolution Divergent evolution: where species that were once similar to an ancestral species diverge to become different species Adaptive radiation is an example of divergent evolution.
Convergent evolution Convergent evolution: evolution where two completely unrelated species have similar traits Ex. Birds and bees have wings (similar trait) Each species develops the same traits because they adapt to the same type of environmental conditions. The species DO NOT come from a common ancestor
Coevolution This is evolution where two species change together where each species responds to the changes in the other Ex. Milkweed plants and Monarch butterflies. The milkweed plant has toxins in their leaves. Monarch butterflies eat the leaves and absorb the toxins making them toxic. Most birds avoid Monarch butterflies for this purpose.
The pace of evolution How fast does evolution occur? There are two theories/models that explain how fast evolution occurs. Both examine the fossil record 1. Gradualism 2. Punctuated equilibrium
Gradualism A model that says change occurs slowly and steadily before and after a divergence Proposed by Darwin Fossils show a slow and repeated change through the fossil record
Gradualism
Punctuated equilibrium A model proposed by Gould and Eldridge A model that proposes evolution happens in "spurts" The model says that species undergo long periods of "stasis" where they remain unchanged, followed by short periods of very rapid change (spurts) The changes are usually brought about by sudden environmental changes such as volcanoes, earthquakes, etc. Species previously disadvantaged could now be advantaged and new species could develop quickly
Punctuated equilibrium
Gradualism vs punctuated equilibrium
The origins of life Many theories exist that try to explain the origin and development of life on Earth. The following theories will be considered: 1. Chemical evolution 2. Panspermia 3. Gaia hypothesis 4. Heterotroph hypothesis 5. Symbiogenesis (Symbiotic theory) 6. Intelligent design
Chemical evolution A theory of evolution created by Oparin-Haldane They said that organic molecules (the building blocks of life) could develop from inorganic compounds present on the surface of the early earth The early earth had an atmosphere that consisted of no oxygen, but plenty of hydrogen, ammonia, methane, and water vapor (inorganic molecules) These gases condensed and formed a "primordial soup" Energy from lightning and UV radiation caused organic molecules to develop from the inorganic molecules in the soup Over time, the organic molecules combined to become an early life form
Chemical evolution - Miller-Urey Two scientists who designed an experiment to prove Oparin-Haldane's theory: They combined methane, ammonia, water vapor, and hydrogen in a flask and exposed the gases to an energy source simulating lightning The liquid inside the flask changed color and when examined contained several organic compounds including amino acids
Panspermia theory A theory that suggests life began "elsewhere" in the universe and "migrated" to our planet For example, it is believed that life originated from bacterial cells elsewhere and travelled from outer space to earth on meteorites.
Gaia hypothesis Theory put forth by James Lovelock Idea that Earth is a "superorganism" called "Gaia" The Earth has systems that keep a balance between temperature and atmosphere After life originated on earth, Gaia came "alive" and began to regulate earth systems The systems help provide an environment where life could exist and survive
Heterotroph hypothesis Theory put forth by Oparin; said first "cells" on earth had to be heterotrophs that eventually developed into autotrophs Primordial soup existed of organic molecules The environment was oxygen poor Heterotrophs such as anaerobic bacteria fed on the organic molecules The heterotrophs began to release carbon dioxide into the atmosphere.
Heterotroph hypothesis The heterotrophs developed into autotrophs and began using the carbon dioxide The autotrophs bean to release oxygen into the atmosphere This made the atmosphere oxygen rich that could now support life
Symbiogenesis Put forth by Lynn Margulis Theory that attempts to explain the development of mitochondria and chloroplasts as organelles that appear in eukaryotic cells Chloroplasts and mitochondria have their own DNA and come from the symbiosis (working together) of prokaryotic cells
Symbiogenesis - how it happened 1. An anaerobic bacterium ate but did not digest an aerobic bacterium (called a guest bacterium) 2. The guest provided oxygen to the bacterium. The guest bacterium eventually became a mitochondrial 3. Other bacteria ate photosynthesizing bacteria. The photosynthesizing bacteria became chloroplasts
Intelligent design A theory that suggests life and mechanisms of life are too complex to have evolved by chance Believed that the generation and evolution of life must have been directed by some unidentified supernatural intelligence