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Pregnancy Timeline by SemestersDevelopmental TimelineFertilizationFirst TrimesterSecond TrimesterThird TrimesterFirst Thin Layer of Skin AppearsEnd of Embryonic PeriodEnd of Embryonic PeriodFemale Reproductive SystemBeginning Cerebral HemispheresA Four Chambered HeartFirst Detectable Brain WavesThe Appearance of SomitesBasic Brain Structure in PlaceHeartbeat can be detectedHeartbeat can be detectedFinger and toe prints appearFinger and toe prints appearFetal sexual organs visibleBrown fat surrounds lymphatic systemBone marrow starts making blood cellsBone marrow starts making blood cellsInner Ear Bones HardenSensory brain waves begin to activateSensory brain waves begin to activateFetal liver is producing blood cellsBrain convolutions beginBrain convolutions beginImmune system beginningWhite fat begins to be madeHead may position into pelvisWhite fat begins to be madePeriod of rapid brain growthFull TermHead may position into pelvisImmune system beginningLungs begin to produce surfactant
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Perception of constant stress is passed on...

For decades science has shown environmental stress experienced in one generation induces change in the biochemistry affecting the next generation. But how ecological conditions stimulate such responses — with differing results in multiple species — is perplexing.

Researchers at The University of Texas at Arlington now provide the first evidence that stable environments — even with consistent predator threat — generate non-genetic "trans-generational responses" onto their next generation.

"In times of rapid change, organisms with a long reproductive cycle (like mammals) can perceive ecological conditions as unstable and evolve a "transgenerational response" — to improve species survival.

"Organisms that mature in days (like water fleas) can not perceive such changes and progressively improve only their own fitness."

Matthew Walsh, Assistant Biology Professor, The University of Texas at Arlington, and leader of the study.

Walsh's team used the interplay of fish and their prey, water fleas, to demonstrate the ecological conditions needed for a "trans-generational response." 

Populations of water fleas that experience consistently intense predation respond by programming future generations to develop 10 percent faster to enhance their species' survival.

However, parent water fleas that experience variable predator threat responded by accelerating their own maturation — and did not pass on "trans-generational responses" to their next generation.

Findings were published in the Proceedings of the Royal Society B1.

The study builds on a previous work by Walsh which demonstrates that one generation can speed up its own maturation in response to a predator threat — or speed up the maturation of its offspring, but not both at the same time.

His paper "Predator-induced phenotypic plasticity within-and across-generations: A Challenge for theory?" was published in the Proceedings of the Royal Society B2 and forms part of an ongoing study of how organisms alter traits across generations.

Morteza Khaledi, dean of the UTA College of Science, commended Walsh on his continued efforts to bridge ecology and evolution: "This research provides key information on evolutionary response to environmental threats and aligns with the university's Strategic Plan 2020: under the theme of Global Environmental Impact. These responses are widespread across many species, and a better understanding of these mechanisms helps us all."

Abstract1: Local adaptation in transgenerational responses to predators
Environmental signals can induce phenotypic changes that span multiple generations. Along with phenotypic responses that occur during development (i.e. ‘within-generation’ plasticity), such ‘transgenerational plasticity’ (TGP) has been documented in a diverse array of taxa spanning many environmental perturbations. New theory predicts that temporal stability is a key driver of the evolution of TGP. We tested this prediction using natural populations of zooplankton from lakes in Connecticut that span a large gradient in the temporal dynamics of predator-induced mortality. We reared more than 120 clones of Daphnia ambigua from nine lakes for multiple generations in the presence/absence of predator cues. We found that temporal variation in mortality selects for within-generation plasticity while consistently strong (or weak) mortality selects for increased TGP. Such results provide us the first evidence for local adaptation in TGP and argue that divergent ecological conditions select for phenotypic responses within and across generations.

Walsh was accompanied on this study by Stephan Munch of the National Marine Fisheries Service; David Post of Yale University's Ecology and Evolutionary Biology Department; and Todd Castoe, Julian Holmes, Michelle Packer, Kelsey Biles and Melissa Walsh, all from UTA.

Abstract2: Predator-induced phenotypic plasticity within- and across-generations: a challenge for theory?

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.

The research was supported through UTA's Research Enhancement Program.

About The University of Texas at Arlington
The University of Texas at Arlington is a Carnegie "highest research activity" institution of more than 50,000 students in campus-based and online degree programs and is the second-largest institution in The University of Texas System. The Chronicle of Higher Education ranked UTA as one of the 20 fastest-growing public research universities in the nation in 2014. U.S. News & World Report ranks UTA fifth in the nation for undergraduate diversity. The University is a Hispanic-Serving Institution and is ranked as the top four-year college in Texas for veterans on Military Times' 2016 Best for Vets list. Visit http://www.uta.edu to learn more, and find UTA rankings and recognition at http://www.uta.edu/uta/about/rankings.php.

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Mar 7, 2016   Fetal Timeline   Maternal Timeline   News   News Archive   

The "helmet" head of this water flea is an adaptation protecting it from fish.
Image Credit: Dr. Jan Michels // Christian Albrecht University of Kiel, Institute of Zoology // Kiel, Germany - Specimen: Daphnia atkinsoni (Water Flea) -Technique: Confocal laser scanning microscopy




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