notagimmickjustamimic

[notagimmickjustamimic]

There are many things vertebrates have been known to do — run, fly, climb, or camouflage... but shrinking is not one of these. How is it then that marine iguanas (Amblyrhynchus cristatus) on the rocky shores of the Galapagos Islands can physically decrease the size of their bodies as adults and then grow it back? Why do they do it?

To answer the latter question, we must consider their location. These iguanas live in an archipelago off the coast of Ecuador in the Equatorial Pacific Ocean. The region experiences climate phenomena known as El Niño and La Niña; The first brings in much warm water than average and very little nutrients while the second performs the opposite, occurring every 3-7 years. El Niño particularly poses a challenge to these reptiles as the green and red algae they usually feed on die and are replaced by unpalatable brown algae. In the past, climate conditions in 1983 wiped about 60% of the marine iguana population while in 1998 the losses were as high as 90%. It's thought that with the warming climate, El Niño events may become intensified. Starving iguana must conserve their energy in order to survive. One way of doing this is to shrink.

Researchers aren't quite sure how this works. What they do believe is that entire bone must be getting absorbed as individuals have been observed to shrink as much as 20% (much greater than can be explained by weight or tissue loss)! They've also been drawing comparisons to how bone density decreases in response to low activity and high stress in the case of those who've developed osteoporosis or weightless astronauts that lived in space for long periods. The difference here is that iguanas are actually able to recover their bone. Strange, isn't it?

Sources:

Wikelski, M. and C. Thom. “Marine iguanas shrink to survive El Niño.” Brief Communications. vol. 403, 2000, p. 37.

Video: https://www.youtube.com/watch?v=un2_TgSWq1c

NOAA's website: https://www.climate.gov/news-features/blogs/enso/has-climate-change-already-affected-enso

Marine iguanas have a fascinating adaptation yet to be fully understood by science. It should encourage researchers to look out for other unconventional ways in which organisms might respond to the impacts of climate change. Learning more about their physiology might even help us to better understand the mechanics of bone disease and how to better treat it.

Stay tuned for more marine musings 🐙

[notagimmickjustamimic]

If you've ever pondered an octopus, you've probably scratched your head over just how it is they're able to match their environment so quickly and accurately. Its almost magical to watch a cephalopod in action change not only the color of their skin but at times even the texture as well. How is that?

CHROMATOPHORES!

(Well the color part anyway. Texture is different.)

"Chromatophores" are pigmented organs controlled by rapid nerve impulses to radial muscles. They come in colors of brown, red, orange, and yellow (but not every one of these is present in all species). When the eyes send visual information to the brain, the brain will send signals through the nervous system that stimulate the radial muscles connected to these colorful "sacs" to shorten.

Doing so affects the skin's appearance as the way the incoming light reflects the color changes. Pigments may be large or small, deep or shallow, smooth or rough and be layered on top of one another creating different effects depending on what is revealed. They are generally less dense in squids while the opposite is true for octopi, and that density can vary across different regions of its body.

In many species these organs are used for camouflage since it can render predators unable to discern its outline among the rest of the terrain, but its also been observed to have social or signalling utility as well. Fascinatingly, as showcased in the GIF above, some cuttlefish have been seen to "flash" colors at prey in order to entrance them. The common octopus also employs a similar strategy, which has been called the "Passing Cloud". "Deimatic" displays on the other hand are signals to predators in which many cephalopods will make themselves wider and larger while creating dark rings against a pale backdrop. Between those of the same species, signals may communicate mating intention or fighting capabilities.

Source:

Messenger, J.B. “Cephalopod Chromatophores: Neurobiology and Natural History.” Biological Reviews. vol. 76, 2001, pp. 473-528.

Chromatophores are are incredibly nuanced. They can be used in a variety of contexts and in complex ways that have still yet to be understood. They have the potential to teach a lot about nonhuman communication — exchanges of meaning beyond language.

Stay tuned for more marine musings 🐙