What is it about?
We analysed the shell morphology of two species of planktonic Foraminifera from the Mediterranean Sapropel S5. At the time, the communieties were exposed to lethal stress levels, which led to local extinctions of the species. We find that both species react distinctively to that stress, but with different evolutionary patterns. The terminally stressed populations are clearly distinct from the unstressed populations.
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Why is it important?
The work helps to understand how evolution and adaptive evolution works already on the protist level. It thus improves our knowledge of evolution in the protist world, which is scarce at the moment.
Read the Original
This page is a summary of: Disruptive selection and bet-hedging in planktonic Foraminifera: shell morphology as predictor of extinctions, Frontiers in Ecology and Evolution, October 2014, Frontiers, DOI: 10.3389/fevo.2014.00064.
You can read the full text:
Morphology of Orbulina universa and Globorotalia scitula across local extinctions during Sapropel S5 (Eastern Mediterranean Sea, c.126-121 ka)
Extinction is a remarkably difficult phenomenon to study under natural conditions. This is because the outcome of stress exposure and associated fitness reduction is not known until the extinction occurs and it remains unclear whether there is any phenotypic reaction of the exposed population that can be used to predict its fate. Here we take advantage of the fossil record, where the ecological outcome of stress exposure is known. Specifically, we analyze shell morphology of planktonic Foraminifera in sediment samples from the Mediterranean, during an interval preceding local extinctions. In two species representing different plankton habitats, we observe shifts in trait state and decrease in variance in association with non-terminal stress, indicating stabilizing selection. At terminal stress levels, immediately before extinction, we observe increased growth asymmetry and trait variance, indicating disruptive selection and bet-hedging. The pre-extinction populations of both species show a combination of trait states and trait variance distinct from all populations exposed to non-terminal levels of stress. This finding indicates that the phenotypic history of a population may allow the detection of threshold levels of stress, likely to lead to extinction. It is thus an alternative to population dynamics in studying and monitoring natural population ecology.
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