In ectotherms/etcoconforms (?cold-blooded? organisms), body temperature is set by the temperature in the environment. Ecotherms have a growth curve that is a peaked function of temperature: it is low when temperature is low, rising to an peak at an optimal temperature for growth, and then falling as temperature continues to increase. In work preliminary to this grant, we discovered that in sheepshead minnow, a small fish that is found from Florida to Connecticut, if mothers were raised at a temperature that was different from their optimal temperature for 30 days, then their offspring had a growth curve that peaked at a temperature closer to the one that the mother experienced rather than the mother?s optimal temperature. This phenomenon is called Trans-Generational Plasticity (TGP). With this grant, we explored additional aspects of TGP, using long-term experiments that involved multiple generations of sheepshead minnows. We discovered the following. First, sheepshead from different geographic locations responded had different levels of TGP, and that these levels of TGP are related to the predictability of the environment. This experiment was the first quantitative empirical test for the evolution of TGP. Second, TGP persists into the grand-offspring generation, although its strength weakens. This suggests that TGP is the result of a non-genetic modification of DNA (an epigenetic effect) rather than a consequence of mothers provisioning offspring differently. Third, we discovered that the blue coloration that male sheepshead minnows develop as they mature is an honest signal of their ability to reproduce. This signal can be used by females when selecting mates and by males defending their territories (that is, not to attack another male who shows little sign of reproductive development). Fourth, we showed that both males and females contribute to TGP but that the female contribution is greater than the male contribution. Finally, we are continuing (with the support of the Pew Foundation) a 5 generation experiment in which fish are experiencing a continually increasing temperature (as would occur in a warming ocean), to test the hypothesis that TGP will entrain with the increasing temperature. Our results have direct impact for understanding how organisms will respond to a changing climate. In particular, we have shown that sheepshead minnow have the ability to rapidly modify their temperature-growth curve, which allows some amount of resilience in the face of a changing environment. Our project involved the efforts of two post-doctoral colleagues, two graduate students, one technician, and about a dozen undergraduates. The post-doctoral colleagues are now employed as Assistant Professor of Biology at Kalamazoo College and as Staff Scientist, Korean Environmental Institute. One of the graduate students completed the PhD and is now staff scientist at the Maryland Department of Natural Resources; the other should complete the PhD in 2019. The technician went on to do a MSc degree in Ecology and Evolutionary Biology. The undergraduate assistants followed a wide variety of post-BSc trajectories, including graduate school and non-academic employment in both the private and public sectors. Last Modified: 07/07/2017 Submitted by: Marc S Mangel