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Great new literature review on the role of stress hormones in amphibian plasticity

 

    Over the past couple of weeks, we have spent a lot of time focusing on plasticity responses in amphibians to different environmental scenarios, covering everything from pond drying to predatory cues. I recently came across a great literature review that not only covers both of these studies, but also dives into the proximate hormonal mechanisms driving such cases of plasticity in amphibians (the author of the paper, Robert Denver, is actually the same person who did the studies on pond drying and spadefoot toads). The literature review goes through the main hormones of the neuroendocrine stress axis before discussing how these various hormones specifically affect development in amphibian larvae.

    One particular aspect that I found fascinating was the role of corticosterone in predatory response. We have already discussed some of the morphological effects caused by exposure to chemical cues given off by predators in class, but something that we did not discuss was immediate behavioral changes. Detecting a predatory chemical cue causes a response in the hypothalamo-pituitary-interrenal (HPI) neuroendocrine stress axis and a subsequent release of corticosterone. As a result, tadpoles will freeze in place to avoid detection, something referred to as behavioral inhibition. This response is reversed a few hours later as corticosterone levels start to drop. However, if tadpoles are chronically exposed to predators (as they very may well be in wetland environments) then corticosterone levels do not decline but start initiating morphological changes such as increased tail height, changes in tail color, and decreased relative body size that supposedly help them escape from predators. I find it fascinating that the same proximate mechanism (in this case, corticosterone) can enact such different results under different conditions, revealing that plasticity shows up even at the hormonal level. This is just one of the examples that Denver delves into, and I found the paper as a whole to be a great read, so I figured that I would share it here for the rest of the class if you have the time and are interested (see citation and link below).

 

Denver, R.J. 2021. Stress hormones mediate developmental plasticity in vertebrates with complex life cycles. Neurobiology of Stress 14. DOI: https://doi.org/10.1016/j.ynstr.2021.100301

Comments

  1. BenMarch 17, 2021 at 6:56 PM

    I find the ability to of the HPI to influence behavior *AND* morphological development also interesting. To think that the HPI might also affect the timing of life history events is another level of effect, too. The pleiotropy of endocrine signaling is something that I end up thinking about a lot in different contexts-- Does endocrine-mediated pleiotropy inhibit or facilitate the evolution of novel, adaptive organismal responses to their environment? I can see it how might work both ways.

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    Replies
    1. BenMarch 17, 2021 at 7:12 PM

      Also, the HPA (HPI equivalent in humans) affects fight or flight behavior in humans, but I thought this was mediated by catecholamines (epinephrine and norepinephrine) rather than cortisol. Do amphibians have these hormones or does cortisol perform this behavioral function in their stead?

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