• What are Darwin's finches?

• When Darwin fist came to the Galapagos islands back in the 1800’s he noted that there existed a variety of finches that all seemed to be derived from a common ancestor

• He had no way to test this hypothesis at the time but conjectured that a common finch flock may have been blown several hundred miles off coarse from the South American Mainland

• This flock would then have subsequently populated and diversified on the Galapagos Islands

http://www.rit.edu/~rhrsbi/GalapagosPages/Map.html

• This process of modification over time to fill a variety of niches is adaptive radiation

Put another way…

• It is “the emergence of numerous species from a common ancestor introduced into a new environment, presenting a diversity of new opportunities and problems”

– Campbell, Biology

• This happens in instances when there exist unrealized opportunities in a new environment.

• Over time once rare characteristics are emphasized and beneficial. This s divergent or directional selection depending on the circumstance

Divergent evolution

• Traits with similar internal structure are called homologous traits

• When homologous features become used for different purposes - are no longer analogous - the process is called divergent evolution, the splitting of a family tree in different directions. 

ADAPTIVE RADIATION – AN EXAMPLE OF DIVERGENT EVOLUTION

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://evolution.berkeley.edu/evolibrary/home.php

http://www.vanderbilt.edu/AnS/english/Clayton/Galapago_finches.gif

Convergent evolution

• When unrelated groups have analogous but nonhomologous features (wings in birds and butterflies, fins in squids and seals), the process is called convergent evolution (sometimes parallel evolution) - similar needs produce similar structures, even if they're based on different architecture.   Both support the concepts of evolutionary change by selection.

• Due to similar selection pressures that are consistent over long periods of time, unrelated organisms (or distantly related ones) acquire similar traits to deal with those similar pressures.

Convergent evolution

• ANATOMY– HOMOLOGOUS STRUCTURES– ANALOGOUS STRUCTURES

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://evolution.berkeley.edu/evolibrary/home.php

The following is taken from…

• http://www.pbs.org/wgbh/evolution/library/01/6/l_016_01.html

(and adapted by Mr.R)

• Peter and Rosemary Grant, spent part of each year since 1973 in a tent on a tiny, barren volcanic island in the Galapagos.

• They caught, weighed, measured, and identified hundreds of small birds and record their diets ever year.

• “In their natural laboratory, the 100-acre island called Daphne Major, the Grants and their assistants watched the struggle for survival among individuals in two species of small birds called Darwin's finches.”

http://www.math.umd.edu/~wwa/zgalapagos/dadwebsite2/images/692islaseymour.jpg

• “The struggle is mainly about food -- different types of seeds -- and the availability of that food is dramatically influenced by year-to-year weather changes.”

“For the finches, body size and the size and shape of their beaks are traits that vary in adapting to environmental niches or changes in those niches. Body and beak variation occurs randomly.”

http://www.rit.edu/~rhrsbi/GalapagosPages/DarwinFinch2.html

http://www.rit.edu/~rhrsbi/GalapagosPages/DarwinFinch.html

• “The birds with the best-suited bodies and beaks for the particular environment survive and pass along the successful adaptation from one generation to another through natural selection.”

http://www.perey-anthropology.net/AestheticRealism/large-ground-finch.jpg

What the Grants Witnessed

“Natural selection at its most powerful winnowed certain finches harshly during a severe drought in 1977. That year, the vegetation withered. Seeds of all kinds were scarce. The small, soft ones were quickly exhausted by the birds, leaving mainly large, tough seeds that the finches normally ignore. Under these drastically changing conditions, the struggle to survive favored the larger birds with deep, strong beaks for opening the hard seeds.”

“Smaller finches with less-powerful beaks perished.”

http://www.shock-therapy.org/reaper.jpg

“The big-beaked finches just happened to be the ones favored by the particular set of conditions Nature imposed that year.”

YEAH!

Life is GOOD!

http://www.mun.ca/biology/scarr/Adaptation_in_Darwins_Finches.html

• “The Grants found that the offspring of the birds that survived the 1977 drought tended to be larger, with bigger beaks. So the adaptation to a changed environment led to a larger-beaked finch population in the following generation.”

“Adaptation can go either way, of course. As the Grants later found, unusually rainy weather in 1984-85 resulted in more small, soft seeds on the menu and fewer of the large, tough ones.”

Long Live the

KING!!!!

“Sure enough, the birds best adapted to eat those seeds because of their smaller beaks were the ones that survived and produced the most offspring.”

http://fig.cox.miami.edu/~cmallery/150/unity/c7.1.23.finches.jpg

Examples of Adaptive Radiation