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Key PointsInsect Evolution
• Evolution by Natural Selection– Survival of the Fittest– The 5 Principles
• How is Paleoentomology important?• Evolutionary Timeframes• Important events in insect evolution
Alfred Russell Wallace Charles Darwin• Brit.• 1823 – 1913• Interests in
• Botany• Entomology
• So. America• SE Asia
• 1854 to 1862
• Brit.• 1809 – 1882• Interests in
• Botany• Entomology
• So. America• 1831 to 1836
Charles Darwin
• 1859– The Origin of Species
“I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection.”
Evolution via Natural Selection• A theory independently derived by Wallace
& Darwin.• Simplistically summarized as:
– “Survival of the Fittest” by the English philosopher Herbert Spencer
• Survival = placement of your genes into the next generation
• Fittest = your ability to get your genes into the next generation
Selective Pressure
Forces (usually environmental change) that select
for (in favor of) those organisms that are best suitedto survive the change.
Selective pressure also selects against those organismsthat are not able to “cope” with change.
Evolution by Natural Selectionworks on the principle of differential reproduction
• Natality - more individuals are born into a generation than will survive and reproduce.
• Variability - there is variation between individuals in any given population.
• Survivorship - individuals with certain characters have a better chance of surviving and passing along their genes
Natural Selection, cont.
• Heritability – at least some of the characteristics responsible
for differential reproduction are genetically mediated.
• Time – enormous spans of time are involved in
evolutionary change.
Insect Evolution
• Bugs do not make particularly good fossils• Phylum Cordata (vertebrates)
– 33% of total known species have fossil representatives
• Phylum Arthropoda (Class Insecta)– 1% of total species have a fossil record
Paleoentomology
• The study of prehistoric insects• Best preserved insect fossils are from ambers• How many orders of insects?
– Extant = 27– Extinct adds another 55!
Flash: oldest salvaged DNA is from an amber termite ca. 100 mya.
PhylogenyA family tree
• A phylogeny is based largely on morphological & structural similarities between groups.
• And while the fossil record is far from complete, it can be used to trace the outlines of insect evolution
Evolutionary Time Frames
• Micro-evolution - changes in populations that happen in a time scale of decades.
• Speciation - changes over a longer time frame that result in the appearance of new species - hundreds of thousands of years
• Macro-evolution - major changes in phylogenetic patterns over long time scales and broad geographical areas.
Events of Note
• Earth – 4.5 billion years old• Precambrian – 3.1 bya
– Prokaryotes• Cambrian – 600 mya
– First abundant fossils (metazoans)• Silurian – 425 mya
– Invasion of land by arthropods
Events of Note
• Devonian – 400 mya– First true insects
• Carboniferous – 345 mya– First great radiation of insects
• Cretaceous – 135 mya– Second great radiation of insects
• Tertiary - 63 mya– Dominance of the land by mammals, birds & insects
• Quaternary – 2 mya– First Homo
Insect Evolution
• Insects (as a group = taxon)– Evolved from the Annelids (the worms)– Ca. 400 mya
• Most primitive (oldest) Insect orders– The APTERYGOTES, wingless– Devonian, ca. 400 mya
• Thysanura–The bristle tails & silverfish
• Collembola–The Springtails
The development of wings
The Pterygotes: 350 mya
Primitively winged insects known as PALEOPTEROUS
Simple wing articulation
Seen today in the orders:
Odonata = the dragonflies
Ephemeroptera = the mayflies
The development of the wing flexion mechanism
Neoptera (new or “modern” wing)
300 mya
Today this covers 97% of all extant species
SnakeflyRhaphidioptera
Development of Complete Metamorphosis (holometabolous)
Ca. 290 mya (note: soon after the wing flexion mechanism)
Benefits: utilize favorable aspects of different habitats for different life stages.
Insect Evolution
• Most advanced insect orders– Lepidoptera with 120,000 species– Coleoptera with 250,000 species– Hymenoptera with 89,000 species– Diptera with 78,000 species
The BIG Four [in review]
• Origin of insects 400 mya• Wings [paleopterous] 350 mya• Wing flexion [neopterous] 300 mya• Complete metamorphosis 290 mya
“Humans are not the end result of predictable evolutionary progress, but rather a fortuitous cosmic afterthought, a tinytwig on the enormouslyarborescent bushof life.”--S.J. Gould, 1995
Key PointsInsect Evolution
• Evolution by Natural Selection– Survival of the Fittest– The 5 Principles
• How is Paleoentomology important?• Evolutionary Timeframes• Important events in insect evolution