Evolution of Geospiza Fortis

• Chapter 22 is about the theory of evolution, evidence of evolutionary change, and the molecular processes that underlie evolution

The Theory of Evolution

• Evolution: heritable alteration in population or species traits from one generation to the next.
• Microevolution: changes to a single gene within a population over time
• Macroevolution: leads to the formation of new species or groups of species

Species and Population

• Species: related organisms sharing a distinctive common characteristic.
• Sexually reproducing species members can interbreed, producing viable, fertile offspring
• Population: members of the same species, likely to interact, with potential to interbreed

History of Evolutionary Thought

• Empirical thought relies on observation to form an idea/hypothesis
• Around the 1600s, empirical thought encouraged scholars to look for cause/effect relationships
• Mid to late 1600s: John Ray initiated the study of the common world
• He developed an early classification system and the modern species concept
• Carolus Linnaeus furthered Ray's work:
• Neither Ray nor Linnaeus suggested that evolutionary change promotes new species

Later Scientists

• Late 1700s saw some European scientists starting to suggest that life forms aren't fixed
• George Buffon stated that life forms change with time
• Jean-Baptiste Lamarck noted animal similarity, but also change.
• He thought living things evolve toward human perfection.
• He suggested inheritance of acquired characteristics, like giraffe necks

Uniformitarianism Hypothesis

• From geology, slow geological processes lead to big changes
• The earth is far older than 6,000 years
• Thomas Malthus: populations produce more offspring than can survive/reproduce

Charles Darwin

• British naturalist born in 1809
• Darwin's theory was influenced by other areas of study including geology, economics, and the voyage of the Beagle

Voyage of the Beagle (1831-1836)

• Darwin's ideas came from personal observation
• He noticed distinctive traits that allowed species to exploit their environments
• Galapagos Island finches had similarities but with specialized feeding strategies

Darwin's Finches Diet and Beak Types

• Ground finches crushed seeds. The large ground finch (Geospiza magnirostris) beak crushes large seeds. The medium ground finch (G. fortis), and small fround finch (G. fuliginosa) eat small seeds
• The Vegetarian finch (Platyspiza crassirostris) crushes buds
• Tree finches grasp insects such as the large tree finch (Camarynchus psittacula), medium tree finch (Camarhynchus pauper), and small tree finch (Camarhynchus parvulus)
• Tree and warbler finches have probing features for insects such as Mangrove finch (Cactospiza heliobates), Woodpecker finch (Camarhynchus pallidus) and Warbler finch (Certhidea olivacea)
• Cactus finches probe fruits and take out seeds such as cactus finch (G. conirostris) and (G. scandens)
• Darwin formulated evolution theory by the mid-1840s.
• He then studied barnacles for several years
• 1856: Darwin started writing his book
• 1858: Alfred Wallace sent Darwin his unpublished manuscript proposing similar ideas.
• Darwin and Wallace published their papers together.
• 1859: Darwin published "On the Origin of Species" with observational support

Decent with Modification

• Evolution is based on variation within a given species
• Traits are heritable, passed down from parents to offspring. The genetic basis was still unknown
• Natural selection:
• More offspring are produced than can survive. There's competition for limited resources
• Individuals that have better traits flourish and reproduce.

Natural Selection on Bird Beak Size Example

• A small population of birds migrates from the South American mainland to a distant island because of readily available seeds to eat
• Birds produce many variable offspring with differences in beak size from random genetic mutations
• In the island environment, with limited seed resource, only offspring with larger beaks survive
• Succeeding generations tend to have larger beaks
• Over generations, this adaptation to food changes and creates new species with larger beaks and other traits

The Grants' Research

• The Grants studied Galapagos finches on Daphne Major, an undisturbed, isolated habitat
• They compared parents' and offspring's beak sizes for many years
• Larger beaks meant higher survival during droughts
• The year following a drought showed increased average beak sizes
• The Grant's hypothesis was dry conditions produce larger seeds. This results in larger beaks for the next generations of Geospiza fortis.

Evidence of Evolutionary Changes

• Fossil records
• Biogeography
• Convergent evolution
• Selective breeding
• Homologies including anatomical, developmental, or molecular

Fossil Records

• Compared by age, fossils show evolutionary change from oldest to youngest

Fishapod

• Also known as Tiktaalik roseae
• It represents a evolutionary step contributing to the evolution of tetrapods.
• Transitional form links earlier and later life forms
• Features included:
  • Broad skull
  • Flexible neck
  • Eyes on the top
  • Primitive wrist and 5-fingered
  • Could peek above water to find food

Horse Evolution

• Is an interesting example of adaptation to changing environments
• Adaptive changes are shown in the fossil record through size, foot anatomy and tooth morphology
• These changes resulted from natural selection as climates shifted globally
• Large, dense forests were replaced by grassland
• This meant horses needed to be faster and have tougher teeth

Biogeography

• This is the study of the geographical distribution of extinct and modern species
• Isolated landmasses and island groups had their own distinct plant and animal groups
• Species are endemic, existing nowhere else
• Island fox evolved from mainland gray fox

Evolution of Major Animal Groups and Landmasses

• Evolution correlates to landmass changes on Earth.
• The first mammals arose 225 million years ago with Australia connected to other land
• Placental mammals appear about 80 million years ago when Australia separated
• Australia did not have large, terrestrial placental mammals

Convergent Evolution

• This is where similar characteristics emerge in species from different lineages in the same environments.
• Examples include giant anteaters and echidnas both having snots and tongues for eating ants
• Other examples include:
• Aerial rootlets for climbing in English ivy and Wintercreeper.
• Antifreeze proteins in very cold water fish

Selective Breeding

• This uses programs designed to change domestic species characteristics.
• It is referred to as artificial selection
• Pigeon breeding influenced Darwin
• In natural selection, nature chooses; in artificial selection, breeders choose
• Breeds are only possible through genetic variation, favoring desirable phenotypes
• Examples include dog breeds, Brassica plants, and corn

Homology

• Fundamental similarity due to common descent
• Categories of homology
• Anatomical
• Developmental
• Molecular

Anatomical Homology

• The same bone sets exist in modern vertebrate limbs, which have changed through selection
• Homologous structures are from a common ancestor
• Vestigial structures are anatomical with no function, but resemble structures in presumed ancestors
• Ear wiggling muscles are an example

Developmental Homology

• Species that are sharply different as adults, can be very similar as embryos
• Gill ridges in human embryos show common traits with aquatic animals with gills
• Human embryos also have long bony tails

Molecular Homology

• Shared cell similarities at a molecular level illustrates a common origin.
• DNA is used by all life
• Certain biochemical process routes are conserved through nearly all species

Homologous genes

• These are two genes from the same ancestral source
• Orthologs exist within separate species

Gene structure

• Homologous genes display the molecular details of evolutionary change because they contain sequences with mutations

Paralogs

• Homologous genes within a specific species
• Gene duplication results in multigene families
• Two paralogs exist in a single-organism genome
• An example is globin genes for specialized function, with expression changing per tissue and time

New Genes in Eukaryotes

• They have evolved through exon shuffling. During exon shuffling, exons and introns flanking the genes are inserted into the genes to create a protein strand
• This process can alter traits and be affected by natural selection mechanisms of crossover or transposable elements

Horizontal Gene Transfer

• Genetic material exchange between species
• Surprisingly very common
• Can involve transfer
• From prokaryotes to eukaryotes
• From eukaryotes to prokaryotes
• Between prokaryotes
• Between eukaryotes
• Widespread among bacteria

Evolution at the Genomic Level

• Affects genome through changes to both structure and number
• There are shared properties with the three major chromosomes between apes and human
• Differences include the fact humans have 1 large chromosome 2, while apes have 2.
• Chromosome #3 shows differences from the orangutans with the inversion.

Explore the adaptation of Geospiza fortis, a Galapagos finch. This study examines the relationship between environmental dryness, seed dimensions, and beak sizes across generations. Animations demonstrate natural selection in action. All rights reserved by McGraw-Hill.