Download Survival of the Fittest - Oregon State Horticulture

Pests, Plagues & Politics
Lecture 4
How Insects Got Where They Are!!
Or
Insect Evolution
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
• Brit.
• 1823 – 1913
• Interests in
• Botany
• Entomology
• So. America
• SE Asia
• 1854 to 1862
Charles Darwin
• 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 suited
to survive the change.
Selective pressure also selects against those organisms
that are not able to “cope” with change.
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.
• 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.
FYI
CT Scan of an amber
Insect inclusion
A 100 mya wasp.
FYI
A North American Honey Bee
Compression
Fossil
14 mya
Nevada
Newest {Oldest} bee fossil
Melittosphex burmensis
FYI
35 – 46 mya
FYI
Coleoptera – Aquatic beetle
Hymenoptera
Cretaceous
Eocene
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 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
Snakefly
Rhaphidioptera
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 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