How Insects Got Where They Are!! Or Insect Evolution Pests, Plagues & Politics Lecture 4

Key Points Insect Evolution Evolution by Natural Selection –Survival of the Fittest –The 5 Principles How is Paleoentomology important? Evolutionary Timeframes Important events in insect evolution

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The true “ ladder ” of life DNA

Alfred Russell Wallace Charles Darwin Brit – 1913 Interests in Botany Entomology So. America SE Asia 1854 to 1862 Brit – 1882 Interests in Botany Entomology So. America 1831 to 1836

Charles Darwin –The Origin of Species “ I have called this principle, by which each slight variation, by which each slight variation, if useful, is preserved, by the term if useful, is preserved, by the term Natural Selection. ” Natural Selection. ”

Evolution via Natural Selection A theory independently derived by Wallace & Darwin. Simplistically summarized as: Survival of the Fittest –“ 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 for (in favor of) those organisms that are best suited to survive the change. against Selective pressure also selects against those organisms that are not able to “ cope ” with change.

Evolution by Natural Selection Evolution by Natural Selection works 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 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% –33% of total known species have fossil representatives Phylum Arthropoda (Class Insecta) –1% –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 Flash : oldest salvaged DNA is from an amber termite ca. 100 mya.

CT Scan of an amber Insect inclusion A 100 mya wasp. FYI

A North American Honey Bee Compression Fossil 14 mya Nevada FYI

Newest {Oldest} bee fossil Melittosphex burmensis 35 – 46 mya FYI

Hymenoptera Eocene FYI Coleoptera – Aquatic beetle Cretaceous

Phylogeny Phylogeny A 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 oldEarth – 4.5 billion years old Precambrian – 3.1 byaPrecambrian – 3.1 bya –Prokaryotes Cambrian – 600 myaCambrian – 600 mya –First abundant fossils (metazoans) Silurian – 425 myaSilurian – 425 mya –Invasion of land by arthropods

Events of Note Devonian – 400 myaDevonian – 400 mya –First true insects Carboniferous – 345 myaCarboniferous – 345 mya –First great radiation of insects Cretaceous – 135 myaCretaceous – 135 mya –Second great radiation of insects Tertiary- 63 myaTertiary- 63 mya –Dominance of the land by mammals, birds & insects Quaternary – 2 myaQuaternary – 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 ThysanuraThysanura –The bristle tails & silverfish CollembolaCollembola –The Springtails

From Annelid (worm) to “ Bug ” Thysanura Collembola

The development of wings The Pterygotes: 350 mya Primitively winged insects known as PALEOPTEROUS Simple wing articulation Seen today in the orders : Odonata Odonata = the dragonflies Ephemeroptera Ephemeroptera = the mayflies

Dragonfly - Odonata Mayfly - Ephemeroptera

The development of the wing flexion mechanism Neoptera Neoptera (new or “ modern ” wing) 300 mya Today this covers 97% of all extant species Snakefly Rhaphidioptera

Development of Complete Metamorphosis ( holometabolous ) ( holometabolous ) Ca. 290 mya (note: soon after the wing flexion mechanism) (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 –Lepidoptera with 120,000 species –Coleoptera –Coleoptera with 250,000 species –Hymenoptera –Hymenoptera with 89,000 species –Diptera –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 tiny twig on the enormously arborescent bush of life. ” --S.J. Gould, 1995

Key Points Insect Evolution Evolution by Natural Selection –Survival of the Fittest –The 5 Principles How is Paleoentomology important? Evolutionary Timeframes Important events in insect evolution