This document discusses different concepts of what defines a biological species, including historical, modern, and problematic concepts. It outlines the biological species concept, which defines a species as a group of interbreeding natural populations reproductively isolated from other such groups. However, it notes there are issues with this concept, as reproductive isolation evolves gradually and does not always correspond with morphological or genetic differences between forms. Other concepts discussed include the evolutionary species concept and problems identifying species without evidence of interbreeding.

1. Species Concepts and Speciation Mark McGinley Associate Professor Honors College and Department of Biological Sciences Texas Tech University

2. Species Concepts Defining “a species” is not as simple as you might hope There are many different “species concepts”.

3. Historical Species Concepts Typological Species Concept species are a 'type' of organism Lineaeus " Species are as many as were created in the beginning by the Infinite. “ Systema Naturae , 10th ed. (1758) establishes a catalog of 4,162 "types"

4. Historical Species Concepts Nominalistic Species Concept : a name given for convenience Darwin " I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other.... “ philosophical Essentialism Only individuals exist, not universal classes.

5. Historial/Modern Species Concepts Morphospecies Concept Species traditionally have been described and identified on the basis of morphological criteria According to this concept, species are “groups of individuals that are morphologically similar and clearly distinguishable from individuals of other groups”

6. Modern Species Concepts Biological Species Concept a reproductively isolated population Mayr " Species are groups of interbreeding natural populations that are reproductively isolated from other such groups. " Historically, the most widely used concept among ecologists

7. Biological Species Concept- Key Concepts " Interbreeding : => a genetic unit species are gene pools : a coadapted gene complex Members of the same species resemble each other because they have common ancestors

8. Biological Species Concept- Key Concepts " Natural Populations " => an ecological unit

9. Biological Species Concept- Key Concepts " Reproductively isolated " => a reproductive unit Reproductive Isolating Mechanisms features that prevent mating outside the species Species Recognition Mechanisms features that allow recognition of potential mates

10. Premating or prezygotic mechanisms Ecological or habitat isolation Seasonal or temporal isolation Sexual or ethological isolation Mechanical isolation Isolation by different pollinators Gametic isolation

11. Habitat Isolation- Geese

12. Seasonal Isolation- Frogs

13. Behavioral Isolation- Crabs

14. Mechanical Isolation- Insects

15. Postmating or post-zygotic mechanisms Hybrid inviability Hybrid sterility F1 fails to produce viable gametes Hybrid breakdown F2s or backcrosses have reduced viability

16. Hybrid sterility- Mule

17. Reproductive Isolation Summary

18. Identifying Species Using the Biological Species Concept Biological Species Concept suggests a research program that will allow scientists to identify species using this concept the mark of a good theory

19. Identifying Species Using the Biological Species Concept (1) Experiment: test cross A and B interbreed, but neither with C => A & B are conspecific C is a separate species

20. Identifying Species Using the Biological Species Concept (2) Field observations : a " species gap" exists Populations maintain identity when sympatric (occuring in the same place) & synchronic (occuring at the same time)

21. Odocoileus hemionus Mule Deer

22. Odocoileus virginianus White-tailed Deer

23. Odocoileus Distribution

24. Variation in Morphology

25. Variation in Behavior O. hemionus O. virginianus

26. Lacewings Chrysoperla plorabunda

27. Lightening Bugs Lampyridae: Hemiptera: Insecta

28. Firefly Flashing Patterns

29. Identifying Species Using the Biological Species Concept (3) Inference : forms 'look different' Many new species are described from single 'skin & skull' or small series. Most commonly used criterion: inference is often weak.

30. Morphological Differences

31. Geographic Variation in Weasels Mustela erminea

32. Feloid ( Panthera ) and Canoid ( Canis)

33. Identifying Species Using the Biological Species Concept 4) Genetic studies indicate no gene flow between forms - fixation for alternative alleles - distinct DNA sequences - distinct karyotypes

34. Evolutionary Species Concept an evolving lineage " An evolutionary species is a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate. " Historically, the most popular concept among paleontologists . Used extensively in comparative biology & phylogenetic systematics

35. Evolutionary Species Concept (1) " Lineage ": an ancestor-descendent series genealogy is crucial: members of a species have a common ancestor Research program of paleontology is inferrence of genealogy Pelycodus an early Eocene Primate

36. Evolutionary Species Concept (2) " Identity ": a biologically distinct entity Includes concepts associated with Biological Species, the Biological Species Concept is the broadest general case of the Evolutionary Species Concept [ i.e. , a biological species is an evolutionary species at a partcular point in time]

37. Evolutionary Species Concept (3) " Tendencies & Fate ": a species is a historical entity Species have an origin (by cladogenesis = ' splitting ' of lineages) undergo evolution (by anagenesis = change within lineages) disappear (by extinction = termination of lineage).

38. Other Species Concepts Phylogenetic Species Concept Recognition Species Concept Cohesion Species Concept Ecological Species Concept Internodal Species Concept Why so many species concepts???

39. Problems with the Biological Species Concept (1) Reproductive isolation is a &quot;typological criterion&quot; (an either / or rule). Does one successful hybridization invalidate species distinction? Extent & consequences of hybridization may vary: < 4% of Alberta deer show hybrid ancestry, including F1 s (Hughes & Carr 1993) > 50% in West Texas (Ballinger et al . 1996): no F1 s

40. Problems with the Biological Species Concept (2) Reproductive isolation evolves gradually: species distinctions somewhat arbitrary Rassenkreis (''race circle'): a geographically convergent series of species adjacent forms are reproductively compatible & morphologically similar ends of circle are reproductively isolated & morphologically distinct

41. Ensatina - salamanders

42. Ring species in Gulls ( Larus )

43. Problems with the Biological Species Concept Reproductive isolation arises without morphological differentiation: Sibling species are morphologically identical species pairs

44. Tree Creepers Sibling Species

45. Sibling Species Empidonax flycatchers

46. Problems with the Biological Species Concept (3) Reproductive criterion does not work well with asexual species. parthenogenesis is common in plants Plant species hybridize widely outside 'species' boundary:

47. Hybridization Raphanus radish X Brassica cabbage => “ Raphanobrassica &quot; (radish leaves & cabbage root )

48. Problems with the Biological Species Concept (4) Genetic differences may not indicate reproductive isolation or morphological divergence . Fixed allelic differences may indicate local adaptation or genetic drift.

49. Problems with the Biological Species Concept (5) What to do with paleospecies (extinct or fossil species)? fragmentary ecological evidence : only by inference

50. Problems with the Biological Species Concept Are dinosaurs ? 'hot-blooded', 'maternal', ‘ colorful' fragmentary physical evidence