Transcript Speciation & Macroevolution

Speciation & Macroevolution
Packet #30
Reproductive Isolating
Mechanisms
 Restriction of gene flow between
species.
Reproductive Isolating Mechanisms
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
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
 Due to molecular and chemical differences
Postzygotic Barriers
 Definition
 Reproductive isolating mechanisms that prevent gene flow
after fertilization has taken place
 Hybrid Inviability
 Death of interspecific embryos during development.
 Hybrid Sterility
 Prevents interspecific hybrids that survive adulthood from
reproducing successfully
 Hybrid Breakdown
 Prevents offspring of hybrids that survive to adulthood and
successfully reproduce, from reproducing beyond one or a
few generations.
Speciation
 The evolution of a new species from an
ancestral population
 More likely to occur when the population is
small.
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
Sympatric Speciation
 The genetic divergence of multiple populations (from a
single parent species) inhabiting the same geographic
region
 Plants
 Results from allopolyploidy
 Polyploid individual (one with more than two sets of
chromosomes) is a hybrid derived from two species
 Kew primroses and hemp nettles
 Animals
 How it occurs remain to be determined
 Fruit maggot flies and cichlids
Pace of Evolution
 Punctuated Equilibrium
 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.
Macroevolution
 Definition
 Large-scale phenotypic changes in populations
that warrant their placement (species) in
taxonomic groups at the species level and higher.
(new taxons)
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.
 Novelties may originate from preadaptation.
 Structures that originally fulfilled one role but changed in a way that
was adaptive for a different role.
 Feathers
 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
Macroevolution III
 Adaptive Radiation
 Process of diversification of an ancestral species into many
new species.
 Extinction
 Death of a species
 Adaptive zones 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