Who are you?

1. Who are you?

2. Homo sapiens

3. The speciesconcept Dr.S.N.Hegde Professor of Zoology University of Mysore Manasagangotri, Mysore - 570006 09448365799 malerhegde@yahoo.com

4. History of species • Aristotle used the words genus and species to mean generic and specific categories. Carolus Linnaeus (1707-1778) believed in the fixity of species.

5. Jean-Baptiste Lamarck 1744-1829

6. Charles Darwin 1809-1882

7. Alfred Wallace (1823-1913) • "species" are not homogeneous, fixed, permanent things; members of a species are all different, and over time species change. • Neodarwinian concept.

8. Theodosius Dobzhansky (January 24, 1900 - December 18, 1975) • A group of organisms capable of interbreeding and producing fertile offspring. • Wait for definition

9. Richard Dawkins defines two organisms as conspecific if and only if they have the same number of chromosomes and, for each chromosome, both organisms have the same number of nucleotides • Charles Sibley's ground-breaking DNA-DNA hybridisation studies in the 1970s leading to DNA sequencing techniques. • Species are identified on the basis of homology of DNA

10. Species used to be identified based on characters • Hybridization • Now based on chromosomes • Genes • DNA

11. Taxonomical hierarchy

12. Class Sub-class Order Suborder genus species

13. Kingdom Sub-Kingdom Phylum There are 10 levels above species Species forms fundamental unit of taxonomic hierarchy Sub-phylum Class Sub-class Order Sub-order Genus Species

14. What is a species? • Species is the basic unit of classification • Fundamental unit of evolution • Pre-Darwinian concept : Species are immutable productions specially created • Darwin – Species is a group of organisms differing from each other, and from other species of the same genus, in trifling respects

15. Definition Three perspectives Morphological Biological Evolutionary

16. I. Morphological • Assemblage of individuals with morphological features in common and separable from other such assemblages by correlated morphological discontinuities in a number of features – Davis and Heywood, 1963 • Basis, similarities and dissimilarities statistical correlations numerical or phenetic taxonomy • Ancient but Some times arbitrary

17. II. Biological • Species is a sexually interbreeding or potentially interbreeding group of individuals normally separated from other species by the absence of genetic exchange • Groups of interbreeding individuals with open genetic system among them selves but closed with others

18. Species is a group of interbreeding individuals which are able to produce fertile offspring up to any number of generations and unable to produce the hybrids with other such groups -Dobzhansky Th, 1940

19. Word interbreeding poses two problems • Do individuals in population in the same locality normally interbreed? • If they breed do the embryos develop and are the hybrid progeny viable and fertile? • If the answer is ‘No’ then the species are said to be reproductively isolated – true species • If the answer is ‘Yes’ then the species are called Incipient species – Incomplete species

20. Inability to cross breed, inability to fertilize, inability to produce hybrid, inability to produce viable offspring are negative attributes • Some people use positive approach – Recognition concept • A group of common fertilization system • Ability to transfer the genetic material between them

21. Applying biological species concept has allowed the taxonomists to identify similar appearing species • Eg. D.melanogaster,D.simulans : Sibling species

22. Taxonomists unify different groups in to a single species Eg. Song sparrows Passerella melodica =Polytypic species

23. III. Evolutionary (Cladistic) • An evolutionary species is a lineage (an ancestor dependent sequence of populations) evolving separately from others and with its own unitary evolutionary role and tendencies - Simpson,1961 • Species is not a static feature • Species an evolutionary entity

24. This also has limitation – separation of species which underwent significant change can be recognised. • Intermediates cannot be separated • Eg. Drosophila ananassae complex

25. Types of Species : Based on different parameters species are identified. Different authors have defined in different ways. • Typological species -A group of organisms in which individuals are members of the species if they sufficiently confirm to certain fixed properties - The clusters of variations or phenotypes within specimens, would differentiate the species. Holotypes and paratypes

26. a. This method was used as a "classical" method of determining species. • Similar to Linneaus theory. • Not clear whether different phenotypes do /do not always constitute different species (e.g: a 4-winged Drosophila born to a 2-winged mother is not a different species). • Species named in this manner are called morphospecies

27. Morphological species  : A population or group of populations that differs morphologically from other populations. Eg. Distinction between a chick and a duck- their bills and webbed feet are different. Species have been defined in this way from time immorial.

28. This concept is much criticised because - genetically distinct populations may look very similar or, contrarily, large morphological differences sometimes exist between very closely-related populations. But most species known have been described solely from morphology.

29. Biological / Isolation species : • Potentially interbreeding populations. • Useful for - living examples of higher taxa like mammals, fish, and birds. • Problematic for organisms that do not reproduce sexually. • The results of breeding experiments done in artificial conditions may or may not reflect what happens in nature. • Difficult to gauge whether or not the results of such experiments are meaningful in reference to natural populations.

30. Biological / reproductive species : • Two organisms that are able to reproduce naturally to produce fertile offspring. • Organisms that can reproduce but almost always make infertile hybrids, such as a mule (female horse crossed with a donkey) or hinny (female donkey crossed with horse), are not considered to be the same species.

31. Recognition species : based on shared reproductive systems, including mating behavior - introduced by Hugh E. H. Paterson.

32. Mate-recognition species :A group of organisms that are known to recognize one another as potential mates - Like the isolation species concept, it applies only to organisms that reproduce sexually. Unlike isolation species concept, it focuses specifically on pre-mating reproductive isolation.

33. Evolutionary / Darwinian species :A group of organisms that shares an ancestor; a lineage that maintains its integrity with respect to other lineages through both time and space. -At some point in the progress of such a group, some members may diverge from the main population and evolve into a subspecies, a process that eventually will lead to the formation of a new full species if isolation (geographical or ecological) is maintained.

34. Phylogenetic/Cladistic :Definition same as evolutionary species. Differs from it in that the parent species goes extinct taxonomically when a new species evolves, the mother and daughter populations now forming two new species. -Subspecies as such are not recognized here.

35. Ecological species :A set of organisms adapted to a particular set of resources, called a niche, in the environment. • -According to this concept, populations form discrete phenetic clusters, because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters.

36. Genetic species : based on similarity of DNA of individuals or populations. • Techniques to compare similarity of DNA include DNA-DNA hybridization, and genetic fingerprinting.

37. Phenetic species :based on phenotypes • Microspecies :Species that reproduce without meiosis or fertilization so that each generation is genetically identical to the previous generation - apomixis. • Cohesion species :Mate-recognition species - Concept to allow for post-mating isolation mechanisms; no matter whether populations can hybridize successfully

38. 14. Evolutionarily Significant Unit (ESU) : • ESU is a population of organisms that is considered distinct for purposes of conservation. • Often referred to as a species or a wildlife species, • An ESU also has several possible definitions, which coincide with definitions of species

39. These definitions often coincide, Overlap and the differences between them are more a matter of emphasis than of outright contradiction. • Species concepts proposed are not entirely objective, or can be applied in all cases without resorting to judgment.

40. Thus the basis for definition of species is morphological difference, genetic difference, cross fertility or reproductive isolation etc. • Certain species do not reproduce sexually, for such species these definitions do not hold good • Given the complexity of life, some have argued that such an objective definition is in all likelihood impossible.

41. Group of interbreeding individuals which are able to exchange their genetic material between each other and exhibit discernible differences in their morphology, genetic makeup and other life activities with other such groups • Words like open and closed genetic systems can also be used

42. Implications of the assignment of species status • Identity or distinguishability of the species or groups • Taxonomic relationship and evolutionary relationships • Genetic relationship and hybridization • Synonimization – different names for the same species – some times this is called lumping • Same name for two species – splitting • Understanding commonalities

43. Species are identified, • Morphologically • Anatomically • Karyotypically • Cross breeding-isolation • Genetically – DNA analysis

44. The outcome • Many populations regarded as separate species earlier are now considered to be a single taxon, • Many formerly grouped populations have been split, • Taxonomic level (species, genus, family, etc.) can be synonymized or split, • Taxonomic revisions have been made, • Taxonomic heirarchy is further extended eg. Species groups, Sub groups, Species complexes, Species, • There are also heirarchy below species - Sub species, Demes etc

45. THANK YOU