How Insects Got Where They Are!!

Or

Insect Evolution

Pests, Plagues & PoliticsLecture 4

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

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The true “ladder” of life

DNA

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 selectfor (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.

CT Scan of an amber Insect inclusion

A 100 mya wasp.

FYI

A North American Honey Bee

CompressionFossil14 myaNevada

FYI

Newest {Oldest} bee fossilMelittosphex burmensis 35 – 46 mya

FYI

HymenopteraEocene

FYI

Coleoptera – Aquatic beetleCretaceous

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

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 = the dragonflies

Ephemeroptera = the mayflies

Dragonfly - Odonata

Mayfly - Ephemeroptera

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