Lecture 7

Question 1

What is the morphospecies concept?

Answer 1

• morphologically distinct populations
• just as in humans, there are small physical differences among individual animals, but need to look closely
• they share many distinctive phenotypic characteristics

Question 2

What are species according to the morphospecies concept?

Answer 2

• they are discrete groups of organisms, defined by unique reliable morphological characters that separate them from other species”

BUT

• this is a simple concept, but some species are diverse in morphology, or cryptic (differences are not morphological

Question 3

What is the biological species concept?

Answer 3

• reproductive isolation between populations (they don’t breed and don’t produce viable, fertile offspring)
• species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups” (Ernst Mayr, 1942)

ex. many different species of Anolis lizards on different Caribbean islands

Question 4

What are the limitations of the biological species concept?

Answer 4

• cannot be applied to fossils or asexual organisms (including all prokaryotes)

Question 5

What is the phylogenetic species?

Answer 5

• smallest monophyletic group on the phylogenetic tree
• smallest diagnosable group of species that evolved from a single ancestral population (monophyletic), and acquired new features (synapomorphies) diagnostic for each species (need a PHYLOGENY)

Question 6

What is the ecological species concept?

Answer 6

• resources exploited
• range of environmental tolerances

Question 7

What are the advantages and disadvantages of biological species concept?

Answer 7

advantage: reproductive isolation = evolutionary independence

disadvantage: not applicable to asexual or fossil species; difficult to assess if populations do not overlap geographically

Question 8

What are the advantages and disadvantages of morphospecies concept?

Answer 8

advantages: widely applicable

disadvantages: subjective (researchers often disagree about how much or what kinds of morphological distinction indicate speciation); misidentifies polymorphic species; misses cryptic species

Question 9

What are the advantages and disadvantages of ecological species concept?

Answer 9

advantages: applicable to asexual species

disadvantages: different species may have similar ecological roles

note: ecological species may look very similar (CRYPTIC species), but have strong and different ecological niches that keep them isolated in nature

Question 10

What are the advantages and disadvantages of phylogenetic species concept?

Answer 10

advantages: widely applicable; based on testable criteria

disadvantages: relatively few well-estimated phylogenies are currently available

Question 11

What are the 2 speciation model

Answer 11

• allopatric speciation
• sympatric speciation

*in both cases of speciation, the isolated groups diverge enough genetically over time to become 2 separate species

Question 12

explain allopatric speciation

Answer 12

• a species is split into separate geographically separated groups, either by dispersal of individuals or by vicariance (barriers arise between population) like new rivers, mountains, glaciation, climatic changes

Question 13

explain sympatric speciation

Answer 13

• a species diverges into 2 groups within the same geographical area where they could meet and mate. Organisms in the same lake may diverge, or food preferences change, … (less common?)

Question 14

Review example of key breeding barrier (fruit scent) in flies

Answer 14

concepts of speciation may overlap:
A. Some researchers consider two fly populations as cryptic species

B. Because the breeding barrier involves different food preferences and different fruiting times for hawthorns and apples – this is also the 4th speciation mode: ECOLOGICAL SPECIATION

C. Also an example of disruptive
selection, since selection favours the two extremes, separate fruit scents (apples vs Hawthorn), but when both scents are mixed, neither species is strongly attracted to it

Question 15

review sympatric speciation in lakes

Answer 15

• Lakes can be considered “Islands in reverse”, same isolation is possible. BC example of stickleback fish pairs
• Several coastal lakes have 2 morphospecies of sticklebacks, derived from 2 invasions of lakes due to sea-level changes that allowed invasion by the ancestral marine form
• Different lakes have evolved such pairs independently!
• In the wild, the limnetic and benthic forms behave differently, and prefer to mate with the same morphotypes, (Assortative mating) keeping the two body types separate.

Question 16

what are the 2 types of mechanism that reproductive isolation can be divided into?

Answer 16

• prezygotic barriers and postzygotic barriers

Question 17

explain prezygotic barriers

Answer 17

• prevents sperm from fertilizing the egg

Question 18

give enample of prezygotic gametic barriers

Answer 18

gametic isolation
- only sperm from the same species is able to successfully fertilize the egg (biochemical barrier)

• this is important in species with external fertilization

ex. sea urchins

Question 19

What are postzygotic barriers?

Answer 19

• follow successful fertilization but reduce hybrid viability or fitness

Question 20

What is an example of postzygotic barriers

Answer 20

• fertilization happens, and zygote formed
• hybrids have reduced viability or sterility

ex. hybrid embryos of leopard frogs and wood frogs don’t develop and die

• reduced hybrid fertility

ex. mules are unable to produce eggs or sperms due to problems with meiosis; still viable and very strong