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Adap%ve Radia%on Adap%ve Radia%on •  The forma%on of many new species from a single progenitor •  Usually associated with opening up of new ecological niche •  Species vary adap%vely to exploit the niche •  Founder effects have been proposed to assist the rapid forma%on of new species Adap%ve radia%ons in Vertebrates •  Honeycreepers on Hawaiian islands •  Cichlid fishes in great African lakes •  Finches on the Galapagos Islands Background •  Finches collected by Darwin on visit of Beagle to Galapagos Islands •  Not ini%ally prominent in Darwin’s work but later a paradigm of species origin •  13 species endemic to Galapagos (1000km from Ecuador) •  Differ par%cularly 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 monophyle%c group that underwent adap%ve radia%on on coloniza%on of the Galapagos •  DF probably originated on South American mainland among the subfamily Emberizinae. 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 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 for;s ; 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 vegeta@on Small ground finch: Geospiza fuliginosa Small tree finch: Camarhynchus parvulus Medium ground finch: Geospiza for;s 1976 – 77 severe drought. Decline in the produc%on of the seeds that are the dietary mainstay of Geospiza for;s, the medium ground finch. Drought Popula%on decline from 1400 to 200 on the %ny Galapagos island of Daphne Major. Species has become completely specialised (adapted) to one food source Boag & Grant Science 214:82, 1981 Sharp-­‐ beaked ground finch: Geospiza difficilis a.k.a. Vampire finch Cactus ground finch: Geospiza scandens Large ground finch: Geospiza magnirostris MHC based study of DF •  MHC= Major Histocompa%bility Complex •  Large amount of ancient MHC polymorphism present in DF •  Much of the polymorphism predates arrival on Galapagos (16-­‐18 alleles) •  Coloniza%on must have begun with a sizable (>30 individuals) flock. 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
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 con%nent 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 ea%ng Insect ea%ng Hawai’ian Honeycreepers •  Probably descended from finch-­‐like seed-­‐
ea%ng ancestor •  Radiated adap%ng to new food sources and habitats •  Gene%c 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 Cichilds are distributed throughout the World Africa is the centre of cichlid biodiversity East African Lakes Victoria Tanganyika Malawi 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 rim 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 Cichlids have adapted to different ecological niches within the lakes •  Species co-­‐exist without being in direct compe%%on •  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 selec%on) •  Cichlid species have also evolved different reproduc%ve strategies –  isolates the groups and reinforces specia%on –  mouth brooding •  Many colour morphs exist Mouth Brooding Protects the young Tanganyika Very similar-­‐looking species in different lakes occupy similar ecological niches. BUT are only distantly related Morphological similarity has liqle correla%on with evolu%onary relatedness. Malawi Evolu%onary Rela%onships •  Lake Tanganyika has the smallest number of species, but the greatest evolu%onary diversity (longest %me) •  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 Cichlids – summary •  There has been a huge radia%on 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 evolu%onary rela%ves •  Specia%on has followed similar trends in each of the lakes independently •  Lake Victoria’s cichlid popula%on is under threat from the introduced perch species. •  The destruc%on of the cichlid popula%ons is in turn threatening the en%re ecosystem of the lake.