Biology 105 - Evolution Dr. Theodore Garland, Jr. 5 Nov. 2015:

1. Biology 105 - Evolution • Dr. Theodore Garland, Jr. • 5 Nov. 2015: • "Hybrid Zones, Character Displacement, Geographic Variation and Clines" Accompanies pages 467-469 and 65 in: Bergstrom, C. T., and L. A. Dugatkin. 2012. Evolution. W.W. Norton and Company.

2. Remember the Biological Species Concept (1) “Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.” (Mayr, 1942) This is the definition you are most likely to be familiar with.

3. Species 1 Species 2 Remember the Biological Species Concept (2) This definition implies that species are real, discrete entities.

4. Remember the Biological Species Concept (3) Evolutionarily, it defines a species as the smallest collection of individuals that evolve independently of others. Specifically, it states that species do not exchange genes with one another. No!

5. Hybrid Zones Geographically restricted areas between subspecies or species where hybrids are common May indicate:1) partially reproductively isolated populations that have come back into contact or2) speciation in progress (“parapatric speciation”)

6. Example of Hybrid Zone between western and eastern “subspecies” of the Northern Flicker Futuyma, 1998, p. 258

7. Cnemidophorus tigris Example of Hybrid Zone (newer generic name is Aspidoscelis) The genus Cnemidophorus includes several species, some of which have several subspecies.

8. Example of Hybrid Zone Stebbins, R. C. 1985. A field guide to western reptiles and amphibians. 2nd ed. Boston, Houghton Mifflin. Range map for six named subspecies of Cnemidophorus tigris. Two exhibit a narrow hybrid zone near AZ-NM border.

9. Example of Hybrid Zone Sampling across the hybrid zone reveals a steep transition in allele frequencies at loci that code for allozymes. Also termed “stepped clines.” Morphological traits show a similar pattern. Repeated cycles of climatic change seem to have caused cycles of contact vs. separation by unsuitable habitat. Forms on either side may be “subspecies,” “semispecies”or true species.

10. Example of a Hybrid Between two Species Dark-eyed Junco White-throated Sparrow Hybrid

11. Example of a hybrid between two species

12. Junco Sparrow Hybrid Song of hybrid is intermediate. Would it be attractive to neither or both “parental” species? This will have a huge effect on the potential for gene flow back into the parental species (introgression).

13. Character Displacement Originally, a pattern, in a narrow contact zone between two closely related species • the species are more different in sympatry (where they occur together) than in allopatry

14. Character Displacement in Galapagos Finches The best known case of character displacement occurs between the finches Geospiza fuliginosa and G. fortis. When they occur together, G. fuliginosa has a much narrower beak that G. fortis, and the former eats smaller seeds: the resource is partitioned. When found on separate islands, both species have beaks of intermediate size, and exploit a wider variety of seeds. These inter-population differences might have evolved in response to interspecific competition.

15. When a third species occurs with them, it has a much deeper beak Character Displacement in Galapagos Finches

16. Character Displacement in Stag Beetles Kawano, K. 2003. Character displacement in stag beetles (Coleoptera: Lucanidae). Annals of the Entomological Society of America 96:503-511. Abstract. I quantitatively analyzed male morphology of two closely related stag beetles species (Odontolabis mouhoti Hope and O. cuvera Parry) in 11 allopatric and two sympatric locations in the Asian tropics and subtropics. Across allopatric locations, body size and genitalia size nearly completely overlapped between O. mouhoti and O. cuvera, and body color was more similar between the two species in allopatric locations. In sympatric locations the differences between the two species in these characters were highly noticeable, genitalia size being most significant. The body color difference between the two species was most striking in sympatric locations. It is probable that the interaction between the two species induced character displacement in sympatry. Character displacement may enable species to maintain themselves as integrated units by minimizing interspecific competition and enhancing reproductive isolation.

17. Character Displacement in Stag Beetles Body length Fig. 3. Top: Body length of O. mouhoti and O. cuvera at allopatric and sympatric sites. (The 5% reliable range of mean of each population is shown by a rectangular box.) Bottom: Genitalia length of O. mouhoti and O. cuvera at allopatric and sympatric sites. (The 5% reliable range of the mean of each population is shown by a rectangular box.) Genitalia length Kawano 2003

18. Allopatric Sympatric Fig. 2. Top: Relationship between body length and genitalia length of O. mouhoti in eastern Thailand and O. cuvera in Assam where each is allopatric from the other. (Note that the dimensions of the two species overlap with each other.) Bottom: Relationship between body length and genitalia length of O. mouhoti and O. cuvera at a sympatric location (northern Thailand-I). (Note that the dimensions of the two species are far apart, without any overlap.) Character Displacement in Stag Beetles • Fig. 1. Geographic distribution of allopatric and sympatric sites for O. mouhoti and O. cuvera, where sampling for this study was successful. Kawano 2003

19. Character Displacement in Stag Beetles Fig. 4. Top: Male O. cuvera (above) and O. mouhoti (below) at allopatric sites (O. cuvera from Assam and O. mouhoti from eastern Thailand). Bottom: The same species at a sympatric location (northern Thailand-I). Shown are three males on the right and a female on the left, at each locality for each species. Genitalia of males are shown immediately below the body. There is a great difference between the two species in body size, genitalia length, and elytral color pattern at the sympatric site.

20. Ring Species “a chain of interbreeding populations, the ends of which overlap but do not interbreed”

21. Ring species:Ensatina in California See Bergstrom & Dugatkin, 2012, pages 467-469

22. Ensatina spread from north to south, around the valley See Bergstrom & Dugatkin, 2012, pages 467-469

23.    Neighboring forms can interbreed See Bergstrom & Dugatkin, 2012, pages 467-469

24. … but the forms at the south end are so different that they cannot!

25. Wake, D. B. 1997. Incipient species formation in salamanders of the Ensatina complex. Proceedings of the National Academy of Sciences USA 94:7761-7767.

26. Geographic Variation = within-species variation in thephenotype or genotype that shows geographic pattern virtually all characters show geographic variation useful for testing various evolutionary hypotheses important for understanding adaptation and speciation

27. Geographic Variation “... the foundation of most evolutionary theory rests upon inferences drawn from geographic variation or upon the verification of predictions made about it.” Gould, S. J., and R. F. Johnston. 1972. Geographic variation. Annual Review of Ecology and Systematics 3:457-498.

28. Subspecies Geographic Races can be called Subspecies Elaphe obsoleta obsoleta Elaphe o. bairdi Elaphe o. quadrivittata Elaphe o. lindheimeri Elaphe o. rossalleni Elaphe o. spiloides

29. Subspecies Some Subspecies of the Black Rat Snake Elaphe obsoleta obsoleta Elaphe o. bairdi Elaphe o. quadrivittata Elaphe o.lindheimeri Elaphe o.rossalleni

30. Subspecies Subspecies (or species) may be named after people, e.g., E. Ross Allen, a herpetologist in Florida (1908-1981) Elaphe o.rossalleni

31. Subspecies However, Subspecies that have been recognized based on color patterns, scale counts, etc., do not necessarily correspond to patterns of genetic variation (e.g., allozymes, microsatellite loci, mitochondrial DNA). Example: Burbrink, F. T., R. Lawson, and J. B. Slowinski. 2000.Mitochondrial DNA phylogeography of the polytypic North American rat snake (Elaphe obsoleta): a critique of the subspecies concept. Evolution 54:2107-2118.

32. Subspecies They sampled from throughout the geographic range.

33. Subspecies Abstract. … Mitochondrial DNA analysis of the polytypic snake, Elaphe obsoleta, yields well-supported clades that do not conform to any of the currently accepted subspecies. … Thus, the subspecies of E. obsoleta do not represent distinct genetic lineages.

34. Burbrink et al., 2000 The Subspecies do not seem to represent separate evolutionary lineages. Elaphe obsoleta obsoleta We have had convergent evolution of the black coloration in three different lineages.

35. Subspecies Abstract. … Instead, the evidence points to three well-supported mitochondrial DNA clades confined to particular geographic areas in the eastern United States. This research underscores the potential problems of recognizing subspecies based on one or a few characters.

36. Burbrink et al. 2000, Fig. 5 Evolutionary lineages (clades) seem to have dispersed from southern “Pleistocene refugia” following glacial retreat.

37. Subspecies: an extreme example Distribution of Southern Pocket Gopher (Thomomys umbrinus). These fossorial rodents create extensive burrows, from which they rarely emerge. 215 subspecies are recognized in the southwestern U.S. and northern Mexico. They vary widely in pelage color, often matching the local soil type. Only certain soils are suitable for burrows, so the ranges are highly disjunct. www.mun.ca/biology/scarr/

38. Clines Cline = gradual change of characters(s) along environmental gradient, i.e., in some sort of ordered fashion, rather than just a patchwork like the snakes

39. Bergmann's (1847) Rule: • Within a genus of endothermic vertebrates, the larger species are found in cooler environments. • Mayr (1956, 1963) restricted Bergmann’s rule to variation within species. • Often examined by relating body size to latitude because as you move away from the equator temperature is generally lower. Examples of Clines

40. Bergmann's (1847) Rule in the short-tailed weasel (Mustela erminea): skull length is significantly positive correlated with latitude and negatively correlated with temperature Examples of Clines

41. Bergmann's (1847) Rule among species of penguins: Examples of Clines Stansfield, 1977

42. Recent paper:Ashton, K. G., M. C. Tracy, and A. de Queiroz. 2000. Is Bergmann's rule valid for mammals? American Naturalist 156:390-415. Examples of Clines

43. Ashton et al. (2000) examined the relationship between size and latitude as well as between size and temperature within species of mammals. • 78 of 110 species reported a positive correlation between body size and latitude(G = 18.96, df = 1, P << 0.001). • Of species that showed a significant relationship between size and latitude, 43 of 57 reported a positive association (P << 0.001). • 48 of 64 species showed a negative correlation between size & environmental temperature (P << 0.001). • Of species that showed a significant correlation between size and temperature, 31 of 38 showed a negative correlation (P << 0.001). Examples of Clines

44. Allen's Rule: extremities shorter where colder Examples of Clines Stansfield, 1977

45. Allen's Rule: extremities shorter where colder Examples of Clines Strickberger, 2000

46. These sorts of patterns are thought to indicate the past action of natural selection and hence adaptation to environmental factors. However, direct environmental effects can mimic these! Example:Weaver, M. E., and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50:710-713. Examples of Clines

47. Can mimic some classic clines! • Weaver, M. E., and D. L. Ingram. 1969.Morphological changes in swine associated withenvironmental temperature. Ecology 50:710-713. Direct Environmental Effects

48. Weaver, M. E., and D. L. Ingram. 1969. Morphological changes in swine associated with environmental temperature. Ecology 50:710-713. Direct Environmental Effects

49. Weaver, M. E., and D. L. Ingram. 1969.Morphological changes in swine associated withenvironmental temperature. Ecology 50:710-713. Take-home message:Be cautious about any data on clines or on other forms of geographic variation that do not pertain to organisms reared under common conditions -- the variation may not reflect genetic differences!And, as we discussed previously, you also need to be somewhat cautious about differences among species that were not raised under common-garden conditions. Direct Environmental Effects

50. Gloger's Rule: birds and mammals are darker in more humid environments (Hengeveld 1990) • Sometimes stated as: darker in color towards warmer climates at lower altitudes or lower latitudes, and lighter in color towards colder climates at higher altitudes or higher latitudes. Examples of Clines