Speciation & Macroevolution Packet #61 Chapter #24 11/12/2018 12:01 PM

Introduction Species Biological Species Concept The concept of distinct kinds of organisms. Derived from Latin meaning “kind” Biological Species Concept Introduced by Ernst Mayr in 1942 Species consists of one ore more populations whose members interbreed in nature to produce fertile offspring and do not interbreed with members of a different species Problem Applies to sexually reproducing organisms Sometimes, there is successful interbreeding 11/12/2018 12:01 PM

Introduction II Evolutionary Species Concept Aka Phylogenetic Species Concept In order to be declared as a separate species, a population must have undergone “evolution” long enough for statistically significant differences in diagnostic traits to emerge. Not all species have been studied at this level If totally embraced, the number of species would probably double Why? The increase would occur because many closely related populations that are classified as subspecies or varieties under the biological species concept would fit the requirements of separate species under the evolutionary species concept. 11/12/2018 12:01 PM

REPRODUCTIVE BARRIERS & SPECIATION 11/12/2018

Reproductive Barriers Restrict of gene flow between species. Possible “evolutionary” mechanism that explain how the millions of species originated from ancestral species and the rates of evolutionary change 11/12/2018 12:01 PM

REPRODUCTIVE ISOLATING MECHANISMS Prezygotic Barriers REPRODUCTIVE ISOLATING MECHANISMS 11/12/2018 12:01 PM

Prezygotic Barriers Reproductive isolating mechanisms that prevent fertilization from taking place 11/12/2018 12:01 PM

Prezygotic Barriers Reproductive isolating mechanisms that prevent fertilization from taking place Temporal Isolation Two species reproducing at different times of the day, season or year Habitat Isolation Two closely related species that live and breed in different habitats in the same geographic area 11/12/2018 12:01 PM

Prezygotic Barriers II Behavioral Isolation Distinctive courtship behaviors prevent mating between species Mechanical Isolation Incompatible structural differences in reproductive organs of similar species Gametic Isolation Gametes of different species are incompatible Egg and sperm cannot unite Due to molecular and chemical differences 11/12/2018 12:01 PM

Figure 24.4 11/12/2018 12:01 PM

REPRODUCTIVE ISOLATING MECHANISMS Postzygotic Barriers REPRODUCTIVE ISOLATING MECHANISMS 11/12/2018 12:01 PM

Postzygotic Barriers Definition Reproductive isolating mechanisms that prevent gene flow after fertilization has taken place Generally, the embryo of an interspecific hybrid, the result of mating between different animal species, spontaneously aborts. 11/12/2018 12:01 PM

Postzygotic Barriers II Hybrid Inviability Death of interspecific embryos during development. Eggs of bullfrog fertilized with sperm of leopard frog Hybrid Sterility Prevents interspecific hybrids that survive adulthood from reproducing successfully Problems occurring during meiosis Common in parents that have different chromosome numbers Offspring of female horse (2n = 64) with male donkey (2n = 62) Offspring is sterile with ploidy of 2n = 63 11/12/2018 12:01 PM

Postzygotic Barriers III Hybrid Breakdown Prevents offspring of hybrids that survive to adulthood and successfully reproduce, from reproducing beyond one or a few generations. 11/12/2018 12:01 PM

Post zygotic Barriers Postzygotic Barriers Hybrid Inviability Death during development Hybrid Sterility Surviving hybrids cannot are sterile Hybrid Breakdown Hybrids that are able to reproduce are only able to sustain a few generations 11/12/2018

SPECIATION 11/12/2018 12:01 PM

Speciation The “evolution” of a new species from an ancestral population More likely to occur when the population is small. There are two types Allopatric speciation Sympatric speciation 11/12/2018 12:01 PM

Allopatric Speciation One population becoming geographically isolated from the rest of the species Eventually leading to divergent evolution Death valley pupfish Kaibab squirrels Porto Santo rabbits 11/12/2018 12:01 PM

Sympatric Speciation New species “evolves” within the same geographic region Divergence of two or more populations, from a single parent species in the same geographic region, occurs when reproductive isolating mechanisms evolve. Common in plant species 11/12/2018 12:01 PM

Sympatric Speciation II Plants Results from allopolyploidy Polyploid individual (organisms in possession of more than two sets of chromosomes) is a hybrid derived from two species Reproductive isolation occurs when polylpoidy organism arise from diploid (2n) parents Autopolyploid Multiple sets of chromosomes from single species Allopolyploid Multiple sets of chromosomes from two or more species Much more common in nature Extremely rare in animals As many as 80% of flowering species are polyploids Provides mechanism for rapid speciation Kew primroses and hemp nettles 11/12/2018 12:01 PM

Sympatric Speciation III For allopolyploids to be established as a new species, selective pressures cause one of three outcomes New species may not compete successfully with species already established May assume new role in the environment and co-exist with both parental species New species may successful compete with either or both parental species Traits confer greater fitness 11/12/2018 12:01 PM

Sympatric Speciation III Animals How sympatric speciation occurs—remains to be determined Fruit maggot flies and cichlids Homework What are some of the hypotheses proposed by scientists? 11/12/2018 12:01 PM

RATE OF “EVOLUTIONARY” CHANGE 11/12/2018 12:01 PM

Theories Punctuated Equilibrium Gradualism Evolution of species that occur in spurts Short periods of active speciation are interspread with long periods of stasis. Gradualism Populations diverge slowly from one another by the accumulation of adaptive characteristics within a population. 11/12/2018 12:01 PM

MACROEVOLUTION 11/12/2018 12:01 PM

Macroevolution I Definition Large-scale phenotypic changes in populations that warrant their placement (species) in taxonomic groups at the species level and higher. (new taxons) 11/12/2018 12:01 PM

Macroevolution II Appearance of evolutionary novelties may be due to changes that occurred during development Changes in regulatory genes could cause structural changes in the organism. Allometric Growth Varied different rates of growth for different parts of the body Result in a change in the overall shape of an organism Paedomorphosis Retention of juvenile characteristics in the adult Occurs to changes in the timing of development Adult axolotl salamanders with external gills and tail fins 11/12/2018 12:01 PM

Macroevolution III Preadaptation Variations in structures that were pre-existing Development of homologous structure Structures that originally fulfilled one role but changed in a way that was adaptive for a different role. Feathers 11/12/2018 12:01 PM

Macroevolution IV Adaptive Radiation Extinction Process of diversification of an ancestral species into many new species. Species taking advantage of adaptive zone(s), ecological opportunities, that were not used by their predecessors. Extinction Death of a species Adaptive zones once occupied become vacant Background extinction Continuous low level extinction of species Mass extinction Extinction of numerous and higher taxonomic groups in both terrestrial and marine environments 11/12/2018 12:01 PM

Macroevolution Preadaptation Adaptive Radiation Macroevolution Extinction 11/12/2018

REVIEW 11/12/2018