Genetics and Evolution IB 201 06 Lecture 12 Species and Speciation SPECIES All cultures early and modern group organisms based on similarities and differences in 1 morphology 2 behavior 3 ecology 4 reproductive compatibility Species are the units of biodiversity they are the basis of our classification systems Thus we are interested in grouping organisms based on evolutionary history The tree of life is the result of millions of speciation events over time I What is a species A Most usable definitions converge on two major principles B Differences among species concepts arise because C General criteria of species concept 1 II Species concepts A Evolutionary pattern based concepts taxonomic phylogenetic 1 Darwinian species concept Wallace 1865 Darwin 1859 Criterion Problem 2 Morphological species Cronquist 1978 Criterion Problems 3 Phylogenetic species Cracraft 1989 Criterion 2 Problems B Evolutionary process based concepts biological 4 Biological Species concept Mayr 1963 also known as the Isolation concept Criterion Problems 5 Mate Recognition Paterson 1985 Criterion 3 Problems Additional References Futuyma D J 2005 Evolution Sinauer Sunderland Mass Cracraft J 1989 Speciation and its ontology the empirical consequences of alternative species concepts for understanding patterns and processes of differentiation pp 28 37 55 59 In Otte D and J A Endler Speciation and Its Consequences Sinauer Sunderland MA Cronquist A 1978 Once again what is a species Belstville Symp Agricult Res 2 3 20 Hey J 2001 The mind of the species problem Trends in Ecology and Evolution 16 326 329 Harrison R G 1998 Linking evolutionary pattern and process the relevance of species concepts for the study of speciation pp 19 31 In Endless Forms Species and Speciation Eds Howard D J and S H Berlocher Oxford University Press NY and Oxford Howard D J and S H Berlocher 1998 Endless Forms Species and Speciation Oxford University Press NY and Oxford Mayr E 1963 Animal Species and Evolution Harvard University Press Cambridge MA Mayr E and P D Ashlock 1991 Principles of Systematic Zoology 2nd Edition McGraw Hill NY Chap 5 pp 86 109 Speciation and taxonomic decisions Paterson H E H 1985 The recognition concept of species In Vrba E S ed Species and Speciation pp 21 29 Transvaal Museum Monograph No 4 Transvaal Museum Pretoria Templeton A R 1989 The meaning of species and speciation a genetic perspective In Otte D and J A Endler Speciation and Its Consequences pp 3 27 Sinauer Sunderland MA 4 SPECIATION The process of how species evolve I General Species as taxa Nonetheless species are real entities living in interbreeding populations and communities in time and space they are real taxa which often exhibit greater or lesser amounts of variation These subdivisions of a species into different populations assumed to be actually or potentially interbreeding are known variably as subspecies races varieties etc Such a subdivided species is known as a polytypic or polymorphic species The subdivisions are useful only as a means of categorizing the amount of variability within a species and do not necessarily represent incipient species The species as groups of interbreeding populations cannot accommodate asexual organisms Species as a category A species is also a rank in the Linnaean hierarchy e g phylum class order family genus species The species rank includes all forms of organisms that have been described and given names including asexual species Maintenance of species A species is maintained via gene flow exchange of genes between interbreeding neighboring populations Species are isolated physically and or biologically Species isolating mechanisms refer to the biological properties of the organism that prevent them from interbreeding Isolating mechanisms are especially relevant to sympatric species that overlap in the same area and therefore whose populations are exposed to the potential of interbreeding Because most interbreeding between animal species often leads to inviable sterile or inferior offspring species isolating mechanisms maintain the unity of a species II How do new species form In spite of the fact that a species has unifying mechanisms such as gene flow it nonetheless can give rise to new descendent forms Speciation is distinct from phyletic evolution anagenesis speciation leads to multiplication of species from a single parental species phyletic evolution leads to changes over time generations of a single species Speciation is ultimately dependent on 1 2 3 4 5 Premating mechanisms Postmating mechanisms A Modes of Speciation 1 Allopatric speciation Traditional allopatric Problem 2 Sympatric speciation Problems 3 Parapatric speciation Problem 6 4 Peripatric 5 Allochronic Problem B Stages in Speciation Process Speciation takes place in basically 3 stages 1 2 3 Additional References SHoward D J and S H Berlocher 1998 Endless Forms Species and Speciation Oxford University Press NY and Oxford Otte D and J A Endler 1989 Speciation and Its Consequences Sinauer Sunderland MA 7
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