Transcript slides - Royal Oak Schools

SPECIATION

formation of a new species
BIOLOGICAL SPECIES CONCEPT

population or group of populations
whose members have the potential to
interbreed with one another to produce
viable, fertile offspring, but who cannot
produce viable, fertile offspring with
members of other species
REPRODUCTIVE BARRIERS

impede 2 species from producing viable,
fertile hybrids
PREZYGOTIC

impede mating or hinder fertilization of egg
HABITAT
--different  rare  no chance
habitats
encounters
to mate
 BEHAVIORAL
--signals and unique behaviors used to attract
mates
--Ex. fireflies
--Ex. meadowlarks

PREZYGOTIC (cont.)
TEMPORAL
--breed during different times of day, seasons,
or years
 MECHANICAL
--anatomically incompatible
--Ex. Flowering plants pollinated by insects or
other animals
 GAMETIC
--gametes don’t fuse to form zygote
--sperm may not be able to survive in female
internal environment or specific molecules on
coat of egg may prevent fusion

POSTZYGOTIC
successful fertilization, but hybrid zygote
doesn’t develop into a viable, fertile adult
 REDUCED HYBRID VARIABILITY
--developing zygote may abort at some
embryonic stage
 REDUCED HYBRID FERTILITY
--sterile offspring; meiosis doesn’t produce
gametes
--Ex. horse + donkey  mule
 HYBRID BREAKDOWN
--1st generation hybrids are viable and fertile,
but successive generations are sterile or feeble

MODES OF SPECIATION

ALLOPATRIC
--allos = other
--patria = homeland
--speciation takes place in populations
with geographically separate ranges
--gene flow is interrupted due to this
separation
MODES OF SPECIATION
SYMPATRIC
--sym = together
--patria = homeland
--speciation takes place in geographically
overlapping populations
1. polyploid plants = result from accident in cell
division
2. allopolyploid = contribution of 2 different
species to polyploid hybrid
3. animals = best example is L. Victoria ciclids
--fish have exploited food sources and other
resources differently
--nonrandom mating

Limitations of the BSC
no way to check interbreeding of extinct
species
 like fossils, which use morphological
characteristics to distinguish species,
existing species are classified based
primarily on their appearance
 cannot be applied to organisms that
reproduce asexually

OTHER SPECIES CONCEPTS
MORPHOLOGICAL
 appearance
ECOLOGICAL
based on ecological niche (set of resources
used by a species)
 Ex. parasite defined by adaptations to host
PLURALISTIC
 factors important to identifying species vary
GENEALOGICAL
 species is set of organisms with unique
genetic history
(DNA, RNA, protein sequencing is basis)

islands are living laboratories for the
study of speciation
--flurries of allopatric speciation occur
when groups stray
 adaptive radiation = evolution of many
diversely adapted species from a
common ancestor

Gradualism
traditional evolutionary trees have gradual
branching pattern
--big changes occur by the accumulation of
many small ones
--however, gradual transitions are rarely seen
in fossil forms
--new forms appear suddenly
--lack of connecting fossils confused Darwin
 gaps can be partially explained by applying
the allopatric model of speciation

Punctuated equilibrium
species diverge in spurts of rapid change
(long periods of stasis punctuated by
episodes of speciation)
 “sudden” may be thousands of years in
evolutionary time
 paleontologists base theories almost entirely
on external anatomy and skeletons
(changes in internal anatomy, physiology,
and behavior cannot be observed)

Speciation

exists on the boundary between
microevolution (change in allele
frequency) and macroevolution
(cumulative change over millions of
speciation events)
Most evolutionary novelties
are modified versions of older
structures
examples of complex structures
evolving in increments
 complex eyes of various types evolved
from simpler ones
 exaptation = feature evolves in one
context, but becomes co-opted for
another function
Ex. light, honey-combed bones of birds

“Evolution is like modifying a
machine while it’s running.”
Karl Liem
 interface between evolutionary biology
and how organisms develop is termed
“evo-devo”
 many examples of slight genetic
divergences leading to major
morphological differences
Growth & development
allometric growth = progression of
proportions through development
 heterochrony = evolutionary change in the
rate or timing of developmental events
 paedomorphosis = reproductive
development accelerates compared to somatic
development, resulting in the mature stage of
the organism retaining body features that
were juvenile structures
 homeotic genes = control placement and
spatial organization of body parts
