Lecture 2: Phylogeny & Invasion

Question 1

Arthropods are the __ assemblage of invertebrates

Answer 1

LARGEST

Question 2

how are all members of arthropods similar

Answer 2

• -jointed legs
• • external articulated skeleton
• -compound eyes
• -distinct head

Question 3

classification & phylogenies look at ___ & ____ to infer evolutionary association + HOWEVER WITH INSECTS

Answer 3

similarities and differences

–when we do this with insects there’s a problem

Question 4

phylogeny solutions for insects:

Answer 4

1) arthropods have several origins

2) arthropods have a single origin

Question 5

1) arthropods have several origins:

why is this considered to be possibility

Answer 5

Sidnie Manton - a comparitie anatomist - believed that the similarities in the arthropods were due to constraints imposed by a rigid exoskeleton. So used differences!

Question 6

2) arthropods have a single origin: why is this considered to be possibility

Answer 6

Monophyly : Cladists - believe that similarities in the arthropods are the best traits to use

Question 7

how do we know which solution is correct?

Answer 7

ultimately boils down to whether insects are TRULY uniramous (one pair of appendages per segment)

Question 8

crustacean limbs are

Answer 8

biramous

Question 9

are modern insects uniramous?

Answer 9

YES

Question 10

if their legs were never branched then _____ is correct

Answer 10

non - monophyly

Question 11

monophyly? YES SUPPORTS:

Answer 11

• Russian fossils (evidence ancient may have been biramous)
• Neuroanatomy (brain & visual system wiring of insects is VERY similar to crustacea, & very dissimilar to worms)
• Developmental genetics
• mtDNA: insects more similar to crustacea

Question 12

developmental genetics of insects:

Answer 12

Distal-less determines limb branching (Insects & crustacea have the gene but it is
regulated differently.
Uniramous condition is determined by regulation of the same gene that causes biramous condition)

Question 13

monophyly? NOT SUPPORTIVE

Answer 13

mtDNA: insects more similar to crustacean, BUT

Collembolan branded off before insects

Question 14

So where did insects come from?!

Answer 14

• looks like insects arose from a crustacean-like ancestor (NOT a worm)
• this ancestor invaded the land about 500Mya

Question 15

Possible ancestor of insects which invaded land

Answer 15

an animal called a Euthycarcinoid

Question 16

how did the ancestor of insects invade the land?

Answer 16

• animal had to solve a host of physical and physiological problems
• did this by moving through a BRIDGING HABITAT

Question 17

bridging habitat:

Answer 17

• graded series of environments from aquatic - terrestrial

- in these bridging habitats we find transition species today

Question 18

problems invasive land species had to face

Answer 18

• water loss
• respiring in air
• reproduction & fertilisation
• support

Question 19

problems invasive land species had to face: Water loss

Answer 19

• water loss ( and osmoregulation) because of its small size (high SA:V)
• probably solved with cuticle
• however a waxy cuticle probably initially evolved to prevent entrapment in water film

Question 20

problems invasive land species had to face: respiring in air

Answer 20

• how this was solved is a mystery

- insects have a unique system - TACHEA

Question 21

problems invasive land species had to face: Reproduction + fertilisation

Answer 21

• internal fertilisation (not all insects have copulation though)
• spermatophores - evolved in the sea (lobsters have them)

Question 22

problems invasive land species had to face: Support

Answer 22

• select for small size

- insects have a very stable gait (tripod shape, 3 points)

Question 23

why are marginal bridging habitats not good for fossils

Answer 23

no hard evidence

Question 24

insects were the ___ animals to colonise land, at same time as plants

Answer 24

first

-being 1st was important for their success

Question 25

the first insects:

Answer 25

Apterygotes

Question 26

what did the first insects live off

Answer 26

they had chewing mouthparts and probably lived on plant material

Question 27

first insects: diverse communities were everywhere and for __M year nothing much changed

Answer 27

60

- then came 3 key innovations in a VERY short space of time

Question 28

3 key innovations of insects:

Answer 28

• evolution of wings
  -evolution of wing-folding mechanisms
  -holometabolism
  (beetles have all 3, most successful insects group )
  – no evidence as all happened in carboniferous

Question 29

___mya first insects?

Answer 29

400-500 mya