In water fleas, from ScienceDaily:
Current theory says similar conditions will favor phenotype changes within and across generations of organisms. Walsh’s experiment, which involved about 25 lineages of Daphnia, contradicts that thought.
“The surprising aspect of our research is, they couldn’t do both,” said Walsh, who is lead author on a paper published in Proceedings of the Royal Society B. “They could either do something that strengthens their own fitness and their own survival or they could do something to strengthen the fitness and survival of future generations. What we’re trying to find now is what makes these responses happen.”
“Dr. Walsh’s research suggests that environmental cues experienced by one generation can affect growth and maturation of future generations in ways that are not explained by current theory,” she said. “This elegant study highlights the need for the use of similar experiments to test important biological theories with direct implications for how organisms are affected by changes in their environment.”
Here’s the abstract:
Much work has shown that the environment can induce non-genetic changes in phenotype that span multiple generations. Theory predicts that predictable environmental variation selects for both increased within- and across-generation responses. Yet, to the best of our knowledge, there are no empirical tests of this prediction. We explored the relationship between within- versus across-generation plasticity by evaluating the influence of predator cues on the life-history traits of Daphnia ambigua. We measured the duration of predator-induced transgenerational effects, determined when transgenerational responses are induced, and quantified the cues that activate transgenerational plasticity. We show that predator exposure during embryonic development causes earlier maturation and increased reproductive output. Such effects are detectable two generations removed from predator exposure and are similar in magnitude in response to exposure to cues emitted by injured conspecifics. Moreover, all experimental contexts and traits yielded a negative correlation between within- versus across-generation responses. That is, responses to predator cues within- and across-generations were opposite in sign and magnitude. Although many models address transgenerational plasticity, none of them explain this apparent negative relationship between within- and across-generation plasticities. Our results highlight the need to refine the theory of transgenerational plasticity. (paywall)
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