Antihypertensives and Horseshoe Crabs

Adult Horseshoe Crab on Railing

Last time I wrote about something not pertaining to interdisciplinary studies, I wrote about American Horseshoe Crabs. You can read more there about the little interesting facts about them, because in this post I want to focus on the results of my recently finished study. While in my first study I examined the effects of Prozac and how it affected horseshoe crab behavior, this time I looked at how two antihypertensive drugs affected them similarly (poster link is here). Besides the difference in drugs between my two studies, these two also differ in the age of the crabs used. In my first study I used adult horseshoe crabs from New England, the size of your face (but still smaller than those from Delaware and especially Florida!). While in my second study, I used baby juvenile horseshoe crabs, barely the size of your pinky nail. Consequently, the variety of behaviors I could look at are more limited when compared to the first study.

In the experiment this time around, I focused mainly on measuring movement in these crabs. While not necessarily having the most pizazz of measurable behaviors (like having rats push a button for sugar), it does allow us to speculate about more concretely about how effects of drugs can affect their overall likelihood of survival. For example, in Peters et al. (2017) found that chronic exposure to Prozac increased the risk for predation (being eaten as prey) in a estuarine crab. While they may have used an actual predator (which helps verify their hypothesis more), the changes in movement patterns and intensity also contribute greatly to animal survival in the wild.

Baby Juvenile Horseshoe Crabs.
Baby Juvenile Horseshoe Crabs. Photo Credit: Wayne Parry – Associated Press (https://m.washingtontimes.com/news/2014/sep/27/rutgers-lab-churning-out-baby-horseshoe-crabs/)

While the consequences of these pharmaceutical compounds we have become reliant upon may sound scary, it isn’t all bad news. There are studies were no effects are found, or that a certain species tends to be pretty resilient–like the horseshoe crab and its ‘resistance’ to mercury and cadmium (compared against other animals; Botton, 2000). In the same vein, my experiment found similar results to that of Botton–that horseshoe crabs are hardy critters. When I looked at their [a] linear velocity (sum of all movement), [b] angular velocity (sum of all turning, expressed in degrees), and their [c] rhythmic behaviors (when they moved, like circadian rhythm stuff), there were no effects. While I may have not obtained statistically significant effects–the ambition every scientist distantly and intensely longs for–my results do also suggest that these two pharmaceuticals may not be all that harmful to baby juvenile horseshoe crabs!

Now I am presupposing that these two antihypertensives, propranolol and valsartan, could never cause any harm to horseshoe crabs of any age. While I hope for that to be the case, it is not necessarily so. Although exposure for 11 weeks with second-instar Horseshoe crabs may not prove to be harmful now, what if someone replicates this experiment (as is part of the scientific method), and they get statistically significant results? Or maybe instead, they opt to administer for an even longer chronic exposure than mine, while also starting from egg fertilization. While the results I found merely suggest, with statistical ‘backing’, that these drugs are not necessarily harmful in this pretty specific manner, it doesn’t preclude or exclude the necessity for more research to be done–for there will always need to be more research done.

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