1. Speciation

2. “It is really laughable to see what different ideas are prominent in various naturalists’ minds, when they speak of ‘species’. It all comes, I believe, from trying to define the indefinable”.
Charles Darwin

3. What is a species?

4. Using the BSC
"a species is an array of populations which are actually or potentially interbreeding, and which are reproductively isolated from other such arrays under natural conditions."
(Ernst Mayr)
Reproductive isolation is the failure of populations to interbreed or to form viable or fertile hybrids
Speciation = generation of a reproductive isolating mechanism

5. Figure 24.4 Reproductive barriers
Prezygotic barriers
Postzygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Individuals of
different
species
Mating
attempt
Viable,
fertile
offspring
Fertilization
(a)
(c)
(e)
(f)
(g)
(h)
(i)
(l)
(d)
(j)
(b)
Figure 24.4 Reproductive barriers
(k)

6. Fig. 24-4a
Prezygotic barriers
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Individuals of
different
species
Mating
attempt
(a)
(c)
(e)
(f)
(d)
Figure 24.4 Reproductive barriers
(b)

7. Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown
Fig. 24-4i
Prezygotic barriers
Postzygotic barriers
Gametic Isolation
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Viable,
fertile
offspring
Fertilization
(g)
(h)
(i)
(l)
(j)
Figure 24.4 Reproductive barriers
(k)

8. Speciation is often gradual, so we expect to see some “gray areas” (are they different species or not?)

9. Speciation is often gradual, so we expect to see some “gray areas” (are they different species or not?)
Canis latrans
Canis lycaon
Canis lupus

10. Speciation is often gradual, so we expect to see some “gray areas” (are they different species or not?)
Canis latrans
Canis lycaon
Canis lupus
Canis Soup

11. The BSC can only apply to a small portion of life

12. The PSC
the smallest set of organisms that share a common ancestor and can be distinguished from other such sets. Or
the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent
(Cracraft 1983)
Speciation = cladogenesis

13. Figure 16.4a Elephant diversity
(a) In West Africa, elephants that live in forest habitats (left) have morphological characteristics that distinguish them from savanna-dwelling elephants (right) from west, central, and east Africa.

14. Figure 16.4b Elephant diversity
(b) This evolutionary tree indicates that forest-dwelling elephants are a distinct phylogenetic species.

15. Eastern and Western Northern Flickers
Morphological differences evolved in allopatry
Differences don’t function as premating RIM’s (they hybridize in the Great Plains)
Don’t seem to be any postmating RIM’s (hybrids fit and reproduce)

16. Moore et al., 1991, Mol. Biol. Evol. 8(3):327-344

17. Types of speciation
Anagenesis—draw it

18. Types of speciation
Anagenesis—draw it
Cladogenesis—draw it

19. Types of speciation Anagenesis—draw it Cladogenesis—draw it
Reticulate speciation—draw it

20. Bold = species thought to have formed as hybrids
Red arrows = mtDNA source
Koblmüller et al. BMC Evolutionary Biology 2007 7:7  
doi: /

21. 3 hybrid species of sunflower that thrive where the parental species cannot