Evolution and development

Question 1

Ernest Haeckel 1834-1919

Answer 1

• best known for his recapitualisation theory or ‘Haeckel’s biogenetic law’
• an individual organism’s biological development, or ontogeny, parallels and summarises its species’ evolutionary development, or phylogeny
• ontogeny recapitulates phylogeny

Question 2

In Haeckel’s scheme, animals advance to new levels by adding stages to existing embryonic development

Answer 2

in reality:
there are stages that related embryos do share
-all vertebrate embryos pass through a stage that are embryonic gill slits

Question 3

An evo devo approach

Answer 3

• understand the origins of variation
• arrival of the fittest
• gain a mechanistic understanding of evolutionary divergence in phenotypes

Question 4

Evo devo revealed that…

Answer 4

the same genes underlie the body plans of a diversity of organisms
-eg. eyes rely on genes such as opsonins, pax and otx that first evolved in a primitive ancestor that gave rise to all animals with eyes

Question 5

Opsonins

Answer 5

• detect light in animals
• but are present in modern organisms that don’t have eyes - such as archaea, fungi, green algae, protists
• members of the opsin family act as ion pumps, sensory molecules, light-gated ion channels, and circadian-rhythm regulators

Question 6

Modes of developmental change:

Answer 6

Pedomorphosis - the retention by adults of traits previously seen only in juveniles Peramorphosis: Heterochronic change in which the juvenile of a derived organism resembles an adult of the ancestor

Question 7

Heterochrony

Answer 7

• a developmental change in the timing of events

- changes lead to difference in size and shape

Question 8

Heterochrony happens through two main courses:

Answer 8

• a change in offset or onset of developmental events
• a change in the rate of a developmental event
• acceleration (faster)
• neoteny (slower)

Question 9

Peramorphosis-

Answer 9

species mature past adulthood and take on unseen traits

Question 10

Why change ontogeny?

Answer 10

• likely an adaptive reason
• probably much easier than adding a new structure
• some stages of ancestral ontogeny may have an adaptive phenotype
• allometry- the relationship between size and shape may be difficult to change

Question 11

Dollo’s law of irreversibility

Answer 11

1893 Louis Dollo

• states that evolution is not reversible
• a structure or organ that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms

eg. pelagization in Antarctic Icefish

Question 12

Antarctic notothenioids

Answer 12

-absence ancestral swim bladder
-secondary pelagcism by pedomorphism
-pedomorphic characters:
delayed and reduced skeletal ossification, reduction of the notochord, reduced no of teeth, reduction of pterygoid process
-i.e. lighter

Question 13

what mechanisms underline reductions in bone>

Answer 13

• collagen genes which play important role in bone development had altered expression
• heterochronic shift
• Col2a1 - early cartilage development
• Col10a1 - early cartilage marker
• Col1a1-late cartilage development

Question 14

Vestigial traits

Answer 14

-genetically determined structures that have lost most or all of their ancestral function
-e.g. snakes with legs
derived snakes are completely limbless
primitive snakes have pelvis girdles and femurs

Question 15

snakes have lost their limbs through changes in..

Answer 15

HOX expression and reduced Shh expression