Download Lecture 2 - The evolution of arthropods (handout)

The evolution of arthropods,
including insects
(EE, pp. 9-21)
"Don’t accept the chauvinistic!
tradition that labels our era the!
age of mammals. This is the age!
of arthropods. They outnumber!
us by any criterion – by species,!
by individuals, by prospects for!
evolutionary continuation."!
!
Stephen Jay Gould (1988)
Geological
clock with
events and
periods
First life -
single
cell
prokaryotes
- appear
4000 MYA
7.2
Present
Cambrian Explosion 542 mya
Plankton
!
Bacteria
!
Bluegreen
algae
3,500 mya
No life
~ 4.6 billion years ago = Earth formed
Animation showing Earth's palaeogeographic
reconstruction beginning from early Cambrian period.
(540 MYA)
http://commons.wikimedia.org/wiki/File:TectonicReconstructionGlobal.gif
Andrew Parker
The Burgess Shale
http://commonfossilsofoklahoma.snomnh.ou.edu/cambrian-communities
Reconstruction of a Cambrian
marine community
http://commonfossilsofoklahoma.snomnh.ou.edu/cambrian-communities
Cambrian Period
In Texas
!
Texas laid under a shallow
sea during the
Cambrian Period.
Land lying to the
northwest contained
sediments comprising
mostly sands that were
carried into the sea. Other
sediments, such as
limestones and
dolostones were
deposited further out to
sea. Fossils of sponges,
gastropods, trilobites,
bivalves and bryozoans are
found within those
deposits.
Lobopods
Appeared in the Cambrian ‘explosion’
!
Featured: antennae, annular (ring-like) body
segmentations, soft fleshy limbs with claws
!
Ancestor of velvet worms (Onycophora) and
water-bears (Tardigrada)
Insect classification
Based on:
!
!
•Morphology
•Molecular Data
Goal: Group species together into their
correct evolutionary relationships
Dynamic, still changing and improving
as we learn more.
Homology vs. Homoplasy
Homology: When body parts look alike because they are derived
from a common ancestor (e.g., bee wings and fly wings).
Homoplasy: When body parts look alike because of convergent
evolution (e.g., bird wings and bat wings).
Sister groups: groups of the same taxonomic rank resulting from
the splitting of an ancestral lineage
In the top figure, insects and
myriapods are sister groups.
In the bottom figure, insects and
crustaceans are sister groups.
Phylogenetic
relationships among
arthropods are still
being debated.
Dunn et al. (2008; Nature 452: 745-749)
Classification categories
broad
Kingdom:
!
!
!
!
!
!
narrow
Phylum:
Class:
Order:
Family:
Genus:
Species:
Classification categories: humans
broad
Kingdom: Animalia
!
!
Phylum: Chordata
Class: Mammalia
!
Order: Primates
!
Family: Homindae
!
Genus: Homo
!
narrow
Species: sapiens
Superclass: Tetrapoda
Classification categories: fire ants
broad
Kingdom: Animalia
!
!
Phylum: Arthropoda
!
!
Class: Insecta
Order: Hymenoptera
!
!
narrow
Family: Formicidae
Genus: Solenopsis
Species: invicta
Superclass: Hexapoda
4) What traits define Arthropods?
a) chitinous cuticle
b) segmented paired legs
c) body segments grouped into tegmata
d) all of the above
e) none of the above
Arthropod key features
• Chitinous cuticle
(exoskeleton)
!
• Segmental paired legs
!
• Body segments group into
tagmata (usually 2 or 3)
Phylum: Arthropoda
Subphylum (or superclass) Myriopoda
Class: Chilopoda
(centipedes)
Class: Paurapoda
Class: Diplopoda
(millipedes)
Class: Symphyla
Phylum: Arthropoda
Subphylum Trilobita
(Trilobites, extinct)
Subphylum or superclass Chelicerata
Class: Metostomata
(horseshoe crabs)
Class: Arachnida
(spiders, scorpions,
ticks, mites)
Phylum: Arthropoda
Subphylum (or s.c.)
Pycnogonida
(sea spiders)
Subphylum or superclass Cructacea
Class: Brachiopoda
Class: Malacostraca
(crabs, shrimp,
lobsters)
Phylum: Arthropoda
Superclass: Hexapoda
Class: Insecta
Class: Collembola
Class: Diplura
Class: Protura
Evolution of insects
Insects evolved on land.
!
The earliest known
ancestor of insects:
(Kalbarriab rimmellae)
!
This fossil form was found
in 1990 in a 420 million
year old sandstone deposit
in Australia.
!
Although it has more
legged segments than an
insect, many of its features
are very insect-like.
Recorded History
First humans
CARBONIFEROUS
Insect ancestor
First Terrestrial
Arthropods
Neopterans
(new wings)
Carboniferous
CARBONIFEROUS
Palaeopterans
(old wings)
Neopterans
(new wings)
Giant radiation
(diversification)
CARBONIFEROUS
Carboniferous
Palaeopterans
(old wings)
CARBONIFEROUS
Complete
Metamorphosis
Benefits:
!
Great way to spend the winter
!
Larva and adults eat different food
(don’t compete)
!
Larva evolve into eating machines
!
Adult stage for reproduction
Hemimetabola: insect orders with
incomplete metamorphosis
Adult
Example: aphids, grasshoppers
fourth instar
first instar
second instar
third instar
Holometabola: insect orders with
complete metamorphosis
Examples: beetles, flies,
butterflies, moths
Flowering plants (angiosperms)
CARBONIFEROUS
Flowering plants (angiosperms)
CARBONIFEROUS
Important evolutionary events
• Neopteran wings
!
• Holometabolous development
(aka complete metamorphosis)
!
• Diversification of Flowering Plants