1. Species concepts in biology
morphological species
phylogenetic species
biological species

2. Morphological species
the familiar “taxonomic” description based on sets of distinguishing characteristics
often works but can be misleading

3. Morphological species of horned lizards
from Futuyma (1998), p. 463

4. Morphological species
these morphologically similar meadowlarks sing different songs and do not interbreed: they are true species
Eastern meadowlark Sternella magna
Western meadowlark S. neglecta
photo from Shaw Creek Bird Supply
photo from USFWS

6. Morphological species
these allopatric warblers were previously classified as distinct species
but they freely interbreed
Audubon’s warbler
Myrtle warbler

7. Maps from USGS Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler

8. In the Rocky Mountains of British Columbia and Alberta, eastern boreal forest (white and black spruce) mixes with western montane forest (Douglas fir, Engelman’s spruce, and western white spruce)
Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler

9. Intergrades between myrtle and Audubon’s warblers result from interbreeding
They are now known as the Audubon’s and myrtle races of the yellow-rumped warbler
Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler

10. The phylogenetic species concept: species are monophyletic groups
[tips of the tree are individuals, letters are species, numbers are populations]

11. Application of the phylogenetic concept helped uncover cryptic species in the copepod Eurytemora affinis

12. And in African elephants

13. Biological species
“...groups of interbreeding populations that are reproductively isolated from other such groups...”
Ernst Mayr

14. Biological species the most widely accepted and useful species concept
problems:
useless for asexual organisms
sometimes difficult to test (e.g. allopatric species)

15. Biological species the most widely accepted and useful species concept
problems:
useless for asexual organisms
sometimes difficult to test (e.g. allopatric species)

16. Biological species
reproductive isolation: an objective criterion that is biologically significant
application of the concept has born a research program

17. Understanding speciation?
study the evolution of reproductive isolation

18. Reproductive isolating mechanisms
prezygotic mechanisms act prior to hybrid zygote formation
behavioral (mate choice)
gamete recognition
postzygotic mechanisms act on hybrid zygotes
hybrid inviability/sterility
ecological inferiority of hybrids

19. Prezygotic: behavioral isolation
courtship and mating behaviors diverge dramatically, even between closely related species
Hawaiian Drosophila do not interbreed: females reject courtship of heterospecific males

20. Mating behaviors can evolve rapidly
Drosophila heteroneura and D. silvestris are sister species, sympatric on Hawaii
from Freeman and Herron 2002
D. heteroneura has dumbbell-headed males that butt heads with other males to gain display territories on leks
D. silvestris has roundy-headed males that fight other males, Greco-Roman style, for territories

21. Behavioral isolation
mating calls of frogs and insects are species-specific
females recognize conspecific calls

22. Prezygotic isolation by gamete incompatibility
marine invertebrates and other organisms that lack mating behavior: species recognition occurs between egg and sperm

23. Sea urchin bindin: a gamete recognition protein involved in speciation
Bindin is an adhesive protein that binds sperm to the egg surface. Without this, fertilization does not occur.
Rapid change of bindin proteins creates barriers to fertilization between species.
Bindin
egg surface

24. Postzygotic reproductive isolation
hybrids are often inviable or sterile

25. Postzygotic reproductive isolation
hybrids are sometimes ecologically inferior
bird predation on hybrids creates abrupt boundaries between Heliconius color races