Download Adaptive Radiation Adaptive Radiation

10/16/12
Adaptive Radiation
Adaptive Radiation
•  The formation of many new species from a
single progenitor
•  Usually associated with opening up of new
ecological niche
•  Species vary adaptively to exploit the
niche
•  Founder effects have been proposed to
assist the rapid formation of new species
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Adaptive radiations in Vertebrates
•  Honeycreepers on Hawaiian islands
•  Cichlid fishes in great African lakes
•  Finches on the Galapagos Islands
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Background
•  Finches collected by Darwin on visit of
Beagle to Galapagos Islands
•  Not initially prominent in Darwin’s work but
later a paradigm of species origin
•  13 species endemic to Galapagos
(1000km from Ecuador)
•  Differ particularly in habitat, feeding and
morphology (beak)
Background cont.
•  Geological evidence indicates that the current
Galapagos Islands are up to 4MY old but that
islands were present for >20MY
•  Darwin’s Finches (DF) may be a monophyletic
group that underwent adaptive radiation on
colonization of the Galapagos
•  DF probably originated on South American
mainland among the subfamily Emberizinae.
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3 Lineages of Darwin’s finches
•  Ground finches (6 species)
–  Geopsiza; Seed eaters
•  Tree finches (6 species)
–  Camarhynchus; Insect eaters
–  Platyspiza Vegetarian finch
•  Warbler-like finch (1 species)
–  Certhidea; insect eater
Cactus finches
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Above: Darwin's own sketches of Galápagos finches. From Darwin's
Journal of Researches:
1.Large ground finch Geospiza magnirostris; seed eater
2.Medium ground finch Geospiza fortis ; seed eater
3.Small tree finch Camarhynchus parvulus ; insect eater
4.Warbler finch Certhidea olivacea ; insect eater
Galapagos islands: Many Arid regions,
cactus and scrub vegetation
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Small ground finch: Geospiza fuliginosa
Small tree finch: Camarhynchus parvulus
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Medium ground
finch:
Geospiza fortis
1976 – 77 severe drought.
Decline in the production of the seeds that are the dietary
mainstay of Geospiza fortis, the medium ground finch.
Drought
Population decline from
1400 to 200 on the tiny
Galapagos island of
Daphne Major.
Species has become
completely specialised
(adapted) to one food
source
Boag & Grant Science 214:82, 1981
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Sharpbeaked
ground
finch:
Geospiza
difficilis
a.k.a.
Vampire
finch
Cactus ground finch: Geospiza scandens
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Large ground finch:
Geospiza
magnirostris
MHC based study of DF
•  MHC= Major Histocompatibility Complex
•  Large amount of ancient MHC polymorphism
present in DF
•  Much of the polymorphism predates arrival on
Galapagos (16-18 alleles)
•  Colonization must have begun with a sizable
(>30 individuals) flock.
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From an initial founder
population from South
America, these finches have
radiated out into 13 species.
Similar in body size and colour,
but highly differentiated in size
and shape of beak. Each has
adapted to a different food
source
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Darwin’s Finches in the
Galápagos Islands
From an initial founder
population from South
America, these finches have
radiated out into 13 species.
Many are similar in body size
and colour, but highly
differentiated in size and shape
of beak. Each has adapted to a
different food source
Hawai’i – 4000km from nearest
continent
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Endemic species in Hawai’i
Group
% endemic
Mosses
46
Ferns
70
Angiosperms
91
Gymnosperms 91
Arthropods
99
Birds
81
Endemic birds
Hawai’ian Honeycreepers
Finch
like
Nectar
eating
Insect eating
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Hawai’ian Honeycreepers
•  Probably descended from finch-like seedeating ancestor
•  Radiated adapting to new food sources
and habitats
•  Genetic divergence indicates that founders
arrived 3.5 – 8 mya
•  29-33 species and 14 more fossil species
Cichlid fish species of the
Great African Lakes
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Cichilds are distributed throughout
the World
Africa is the centre of
cichlid biodiversity
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East African
Lakes
Victoria
Tanganyika
Malawi
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Cichlid Species in the East African
Lakes
•  Lake Victoria
–  Formed 250,000-750,000 years ago
–  Saucer-shaped (shallow) & size of Ireland
–  500+ species of cichlids
•  Tanganyika & Malawi
–  Deep - fill rift between tectonic plates
•  Malawi
–  4 million years old
–  500-700 species
•  Tanganyika
–  9-12 million years old
–  200-250 species
Cichlids possess two sets of jaws
Mouth jaws
Throat jaws
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Cichlids have adapted to different
ecological niches within the lakes
•  Species co-exist without being in direct competition
•  The sets of jaws are adapted (“fine-tuned”) to different
food sources
–  algae scrapers –eat algae off rocks
–  insect pickers –pluck larvae from between rocks
–  scale eaters –scrape scales off other cichlids (who
eventually become wary: c.f. frequency dependent
selection)
•  Cichlid species have also evolved different
reproductive strategies
–  isolates the groups and reinforces speciation
–  mouth brooding
•  Many colour morphs exist
Mouth Brooding
Protects the young
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Tanganyika
Malawi
Very similar-looking species
in different lakes occupy
similar ecological niches.
BUT are only distantly related
Morphological similarity has
little correlation with
evolutionary relatedness.
Evolutionary Relationships
•  Lake Tanganyika has
the smallest number of
species, but the
greatest evolutionary
diversity (longest time)
•  In Lake Malawi and in
Lake Victoria, any of
the species within the
lake is more closely
related to other species
of the same lake than
to species from another
lake
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Cichlids – summary
•  There has been a huge radiation of cichlid species
over the last few million years
•  Different lakes in Africa contain similar-looking
species that have adapted to similar ecological
niches, but that are not close evolutionary relatives
•  Speciation has followed similar trends in each of
the lakes independently
•  Lake Victoria’s cichlid population is under threat
from the introduced perch species.
•  The destruction of the cichlid populations is in turn
threatening the entire ecosystem of the lake.
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