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Chapter 17
Speciation –Development of
new species
Species
• Species is a Latin word meaning
“kind”. It refers to a particular
kind of organism.
• The biological species concept is
used to define characteristics
particular to one kind of animal.
Ernst Mayr
• He phrased it this way “Species are
groups of interbreeding natural
populations that are reproductively
isolated from other such groups.”
• Differences in phenotype do not
disqualify some members
• As long as the form is the same, the
physiology and behavior allow them to
interbreed and produce fertile
offspring, then they are considered a
species.
Mayr continued
• The other qualification for membership
is the ability to contribute to the gene
pool.
• Mayr’s definition does not apply to
asexual creatures (as they do not have
an extensive gene pool – each offspring
being a clone of the parent), but it does
help classify sexually reproducing
organisms.
Gene Flow
• Gene flow is the movement of
alleles into and out of populations
by emigration (entering) or
immigration (leaving).
• This helps maintain a reservoir of
alleles.
Genetic Divergence
• If a physical barrier prevents
mingling of genes between
populations or subpopulations,
then each will become
evolutionarily different.
• This is referred to as genetic
divergence.
• This way, genetic differences will
arise in the gene pools of
separated populations; mutations,
natural selection, and genetic drift
will be free to operate.
• Mostly, speciation occurs by
divergence.
Reproductive Isolation
• This is any heritable body form,
function, or behavior that prevents
breeding between one or more
genetically divergent populations.
• Includes behavioral, temporal,
mechanical, and ecological
isolation.
Behavioral Isolation
• Differences in behavior are
barriers to gene flow.
• A certain species has reproductive
rituals that may not be recognized
by similar species, but are
definitely recognized by members
of the same species.
Temporal Isolation
• Members of two closely related
species could breed together, but
their reproductive times are too
different.
• For example, “some species of insects
seek mates for only a few hours of the day
or night, and related species do so at
different times”
Mechanical Isolation
• Incompatibility between body
parts of potential mates or
pollinators.
Ecological Isolation
• In seasonal habitats, two populations
are adapted to different
microenvironments of one habitat.
• “Two sympatric species of ladybirds in Japan,
Epilachna nipponica feed on thistles and E.
yasutomii feed on blue cohosh. Each species also
mates exclusively on its host plant, which acts as
a microhabitat.”
Allopatric Speciation
• Some type of barrier prevents gene
flow between populations or
subpopulations of a species.
• Reproductive isolating methods
will arise in each group after the
separations.
• Even if the groups are reunited,
they will not breed together again.
Archipelagos are island chains that are a
far distance from a continent.
• For example – Galapagos Islands.
Finches from the mainland moved to
one of the islands and became
separated from the group.
• Later some of their descendents moved
to a different island in the chain. The
moves kept occurring until all of the
islands were inhabited with finches.
• Each move led to evolutionary changes
among the finches of each island. Each
group had to evolve to the climate changes,
differing foods, etc…of the island it was
inhabiting.
• Therefore, each island has a different finch
that came from a main group of finches.
Sympatric Speciation
• Species within the home range of
an existing species may form into
new species without a physical
barrier.
• Example – cichlids are fish in
African volcanic lakes.
• Nine to eleven species of cichlids
are coexisting in one lake.
• They could not have evolved
because of separation – they are all
in one lake and have never been
separated.
Cichlids
• Polyploidy may be the answer.
– It is a change in chromosome number.
• Offspring will inherit three or
more of each type of chromosome
from their parent.
• Changes come when the
chromosomes separate
improperly.
• Most polyploid organisms have
problems, but in rare cases it can
lead to sympatric speciation.
Parapatric Speciation
• Neighboring populations can
become distinct new species while
maintaining a common border.
• Interbreeding between the two
species will produce a new hybrid
species.
• The Baltimore Oriole (a bird) has a
range that overlaps with the
Bullock’s Oriole.
• The two species are similar
enough to reproduce and produce
fertile offspring.
• Their offspring is a new species.
Orioles
•
Baltimore
Oriole
• Bullock’s Oriole
Extinction
• The irrevocable
loss of one
species.
• Example – the
loss of the dodo
bird
Mass Extinction
• Loss of several
species at once
due to a
catastrophic
event. The loss of
dinosaurs could
be considered
mass extinction.
Works Cited
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http://hcgs.unh.edu/cichlid/fish.jpg
perso.orange.fr/.../drax/dronte.htm
http://www.birdsasart.com/Baltimore-Oriole.jpg
http://www3.nbnet.nb.ca/maryspt/observ/oriole1.jpg
http://www.geologyrocks.co.uk/tutorials/isolation_new_species
http://evolution.berkeley.edu/evolibrary/article/history_12