SPECIES CONCEPTS Dr M C John Milton PG

SPECIES CONCEPTS Dr. M. C. John Milton PG & Research Department of Advanced Zoology and Biotechnology Loyola College (Autonomous), Chennai 600 034 drjohnmilton@gmail. com drmilton@loyolacollege. edu 1

Species concept q Cuvier (1829) assemblage descended from common parents q Darwin (1859) could not define q Thompson (1937) individuals distinguished by irreducible properties and connected by descent and genetic relationship. q Dobszhansky (1937) single systematic category withstood all changes in nomenclature q Huxley (1942) geographically definable group, interbreed, fertile with related groups q Zimmermann (1948) species are considered similar on superficial observation q Borgmeier (1963) species as natural phenomenon and biological unit based on objective facts. 2

Typological species concept q Diversity of universe is because of limited number of ‘Univesals’ q If 2 individuals are sufficiently different they are different species q Variation is irrelevant q Essentialism – species can be recognised by their essential characters q Colour, size, habitat etc. , (morphological species concept) 3

criticism q Sexual dimorphism, age difference, polymorphism and other forms of individual variation –no use for caterpillar and butterfly classification q It is helpless in sibling species – good genetic species but lack conspicuous morphological differences 5

Nominalistic species concept q q Popular in France in 18 th century - Occam Nature produces individuals nothing more Species are man made and mental concepts Species have no actual existence in nature it is to refer great numbers collectively. 6

criticism q Species are products of evolution not man made q Misinterprets similarity and relationship q Members of species are similar because of common heritage they are nor called species because they are similar 8

Biological species concept q q q Introduced by Mayr 1750 Species has three separate functions Reproductive community Ecological unit Genetic unit 9

Problems of biological species concept q q q Apomictic or asexual groups Sibling and cryptic species Gradual speciation Rings of races Hybrid complexes 12

Evolutionary species concept q It is applicable to apomictic and fossil lineages q Species is a single lineage of ancestral descendant population of oranisms which maintains its own evolutionary tendencies and historical fate 13

Recognition species concept q Species is the most inclusive population of individual biparental organisms which share a common fertilization system. q Fertilization includes all aspects of an organisms biology q Organisms recognise each other as mates or passive q This doesn’t include barriers to gene flow after fertilization – hybrid sterility, inviability 18

Kinds of species q Sibling species : closely related, morphologically identical but reproductively isolated. q Sympatric species : occupying same geographical area q Allopatric species : inhabit completely different geographical areas. q Continental Species : living on large land masses. q Insular species : living on isolated islands owe their fauna to dispersal methods. q Tropicopolitan or pantropical species : found throughout tropics 33

q Montane species : occur at high elevations. q Morphogeographical species : known from Linnaean times to present q Agamospecies : consists of uniparental organisms – reproduce parthenogenitically. q Panmictic species : species in which each sex is produced by diff. individual (dioecious) or species in which 2 sexes are produced by same individual (Monoecious) 34

q Apomictic species : no mixing of gametes between different individuals – unisexual- producing ova others reproduce completely by budding or fission. q Parapatric species : whose ranges are adjacent due to competition. q Contemporaneous species : occur at same time level. They indicate number of lines or lineages occuring at any particular time. 35

q Polytypic species : consist 2 or more subspecies q Monotypic species : no sub species q paleontological species : fossils q Philapatric species : do not show any tendency to extend their range. q Incipient species : geographical subspecies which become isolated will be distinct 36

q Morphospecies : morphological similarity regardless of other considerations. q Form species : fossil objects not identifiable 37