Lecture 2: Evolution by natural selection

Question 1

Reproductive isolation

Answer 1

In sexually reproducing organisms: a group of interbreeding organisms not normally able to interbreed with other such groups

Question 2

Premating isolation

Answer 2

1) Ecological or seasonal isolation – individuals do not meet
2) Behavioural isolation – individuals meet but do not attempt to mate 3) Mechanical isolation – attempts at mating are unsuccessful

Question 3

Post mating isolation

Answer 3

1) Gametic incompatibility – gametes die before fertilisation
2) Non-viable hybrids – offspring are non-viable or have reduced viability

Question 4

Morphology species concept

Answer 4

The nature of evolution (the development of species from other species) inevitably causes problems with classification

• Originally Darwin suggested that species could be distinguished on morphological grounds – a certain level of difference could be explained as varieties, races and forms, but at some point there was a divide between distinct species.
• However, there are often discrete and discontinuous morphological differences within the same species

Question 5

Cladistic Species Concept

Answer 5

Species are branches in a lineage, with some variation in morphology found along a branch (within a species) without a new branch actually being formed.

Question 6

Linnaean nomenclature

Answer 6

Taxonomy – the science of naming and classifying species

• The system we use today is the Linnaean system, devised by Carl von Linne (Carolus Linnaeus) (1707-1778)
• Very popular hierarchical classification system
• Before Linnaeus no agreed system – scientific descriptions of plants varied with botanist and locations
• e.g. Common ground cherry: Physalis amno ramosissime ramis angulosis glabris foliis dentoserratis

Question 7

Early development life

Answer 7

Life developed around 3.5 billion years ago (Precambrian) • For around 2 billion years bacteria were the only life forms
• 1500 million years ago Eukaryotic cells developed, and then multi-cellular organisms
• 545 million years ago hard-bodied organisms • 500 million years ago first invertebrates (fish) • 430 million years ago bacteria on land
• 420 million years ago first land animals

Question 8

More on early development life

Answer 8

350 mya amphibians and insects
• 350 mya ferns – first plant with roots • 300 mya winged insects
• 280 mya beetles
• 200 mya crocodiles
• 200 mya mammals
• 65 mya KT boundary, rise of mammals • 20 mya hominid lines evolve

Question 9

Evolution and natural selection- 5 key propositions

Answer 9

1. Individuals are not identical; they vary to some extent
2. Some of this variation is inheritable; individuals share the characteristics of their ancestors
3. All populations have the potential to reproduce to an infinite size, but reproduction is never maximal – some reproduce less, some die before reproducing
4. Different ancestors leave different numbers of descendants; implications for inheritance of characteristics.
5. The number of descendants depends on the interactions between the individual’s properties and its environment.

Question 10

More on natural selection

Answer 10

An individual will survive, reproduce and leave descendants in some environments and not in others, and therefore pass on characteristics to the same extent
• This is a way of ‘selecting’ the most suitable individuals for a given environment (‘Natural Selection’) although the term ‘selection’ implies a goal – the process is actually much more random
• A current species is therefore the results of the successful breeding of millions of generations of individuals, with the most successful (best suited) individuals passing on their most useful characteristics

Question 11

Each species

Answer 11

Each species is a legacy of past environmental conditions (abaptation rather than adaptation)
• This legacy constrains future evolution (e.g. koala bears can only survive on Eucalyptus foliage).
• Most species that have existed have become extinct, and the majority of those currently in existence will become extinct.
• Abaptation = both advantage and constraint

Question 12

Dipodomys

Answer 12

Found in the W/SW of America, highly adapted to arid environments
• Small seed-eating rodents, with the ability to obtain moisture from dry seeds during digestion
• Kidneys adapted to obtain most of the moisture that would be expelled in urine
• Moisture exhaled in breathing is recaptured in specialised nasal cavities, and they do not sweat or pant
• Block their burrows during the day and only come out at night • Do not drink water, even in captivity