Mute swan population helps explain longstanding evolutionary question

To: Birding Aus <>
Subject: Mute swan population helps explain longstanding evolutionary question
From: knightl <>
Date: Wed, 25 Jan 2006 17:33:52 +1000

Public release date: 24-Jan-2006
Mute swan population helps explain longstanding evolutionary question

In an important new study forthcoming from The American Naturalist,
biologists from the University of Oxford tracked a colony of mute swans for more than two decades to explore a longstanding evolutionary question: whether the number of eggs laid by a female bird – known as "clutch size" – changes in accordance with natural selection.

"Extensive debate in the literature…was first focused on the question: Why does a population's average clutch size differ from the most
productive clutch size?" said researcher Ann Charmantier. "Gradually
the debate switched to an evolutionary point of view with a second,
related question: Why is clutch size not evolving despite significant
heritability and directional selection?"

Many long-term studies of avian clutch size have looked for--but not
seen-- an increase in the number of eggs laid. However, this 25-year
study of the selection, inheritance, and evolution in the mute swan
population of Abbotsbury, England, yielded data on clutch size
consistent with the direction predicted by evolutionary theory.

"In this study population, clutch size shows a clear response to
selection, providing us with a clear illustration of microevolutionary process on a small timescale," explain the researchers.

The researchers hypothesize that a recent relaxation of food
constraints and an increase in protection from predators may have
helped enable the swans to evolve towards a new, larger clutch size.


Since its inception in 1867, The American Naturalist has maintained its position as one of the world's most renowned, peer-reviewed
publications in ecology, evolution, and population and integrative
biology research.  AN emphasizes sophisticated methodologies and
innovative theoretical syntheses--all in an effort to advance the
knowledge of organic evolution and other broad biological principles.

Charmantier, Ann, Christoper Perrins, Robin H. McCleery, and Ben C.
Sheldon. "Evolutionary response to selection on clutch size in a
long-term study of the mute swan," The American Naturalist 167:2.
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