Lecture 2: Phylogeny & Invasion Flashcards
Arthropods are the __ assemblage of invertebrates
LARGEST
how are all members of arthropods similar
- -jointed legs
- external articulated skeleton
- -compound eyes
- -distinct head
classification & phylogenies look at ___ & ____ to infer evolutionary association + HOWEVER WITH INSECTS
similarities and differences
–when we do this with insects there’s a problem
phylogeny solutions for insects:
1) arthropods have several origins
2) arthropods have a single origin
1) arthropods have several origins:
why is this considered to be possibility
Sidnie Manton - a comparitie anatomist - believed that the similarities in the arthropods were due to constraints imposed by a rigid exoskeleton. So used differences!
2) arthropods have a single origin: why is this considered to be possibility
Monophyly : Cladists - believe that similarities in the arthropods are the best traits to use
how do we know which solution is correct?
ultimately boils down to whether insects are TRULY uniramous (one pair of appendages per segment)
crustacean limbs are
biramous
are modern insects uniramous?
YES
if their legs were never branched then _____ is correct
non - monophyly
monophyly? YES SUPPORTS:
- 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
developmental genetics of insects:
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)
monophyly? NOT SUPPORTIVE
mtDNA: insects more similar to crustacean, BUT
Collembolan branded off before insects
So where did insects come from?!
- looks like insects arose from a crustacean-like ancestor (NOT a worm)
- this ancestor invaded the land about 500Mya
Possible ancestor of insects which invaded land
an animal called a Euthycarcinoid
how did the ancestor of insects invade the land?
- animal had to solve a host of physical and physiological problems
- did this by moving through a BRIDGING HABITAT
bridging habitat:
- graded series of environments from aquatic - terrestrial
- in these bridging habitats we find transition species today
problems invasive land species had to face
- water loss
- respiring in air
- reproduction & fertilisation
- support
problems invasive land species had to face: Water loss
- 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
problems invasive land species had to face: respiring in air
- how this was solved is a mystery
- insects have a unique system - TACHEA
problems invasive land species had to face: Reproduction + fertilisation
- internal fertilisation (not all insects have copulation though)
- spermatophores - evolved in the sea (lobsters have them)
problems invasive land species had to face: Support
- select for small size
- insects have a very stable gait (tripod shape, 3 points)
why are marginal bridging habitats not good for fossils
no hard evidence
insects were the ___ animals to colonise land, at same time as plants
first
-being 1st was important for their success
