Latitude: -66 03.5875 Longitude: -66 16.3921
I must confess to having an ulterior motive when I agreed to come on this research cruise. I wanted to fall in love. Not with a dashing sea captain or mermaiden but with a study organism. Having jumped around, studying animals from frogs to sea slugs, I’ve often felt envious of my colleagues who seem completely committed to just one group of animals, publishing paper after paper monogamously. I won’t say I’m willing to put a ring on it just yet, but I am intrigued enough by a certain group of animals that I’ve encountered on the cruise that I’m willing to write about them for my blog post. In between the vibrant starfish and majestic octopods there was a certain little group of crustaceans that caught my eye. I’m talking, of course, about amphipods. Amphipods are a group of small (1-340mm) laterally compressed crustaceans with around 10,000 species, most of which are marine (NOT to be confused with isopods which are loathsome, longitudinally compressed crustaceans often known as “God’s mistake”). They’re not always super appealing to look at (though see below for some stunning exceptions) but they do have a lot of interesting qualities that intersect in unique ways that I think could help answer some really neat questions.
In my last blog post I talked about the latitudinal biodiversity gradient, the tendency for there to be more species closer to the equator. Amphipods are one group that do not follow this rule, in fact the number of species appears to increase with latitude. I’ve seen more amphipod species in the few weeks I’ve been in the Antarctic than I’ve seen in four years living in South Florida and the Galapagos. Another feature of Antarctic amphipods that’s shared with a lot of marine invertebrates at high latitudes is polar gigantism, which is exactly what is sounds like, marine invertebrates in polar regions are generally much larger than their warmer water cousins. The reasons for polar gigantism are still not very well understood but may correspond with the abundance of oxygen, food, and elements used in shell-building at the poles. However, it may also have something to do with an absence of predators, or the more efficient heat exchange that comes with larger body sizes. A third attribute that may also tie in with the first two is polyploidy, when organisms have multiple copies of all their DNA. Polyploidy often occurs before lots of new species appear, flowering plants, bony fishes, and even all vertebrates (including you!) have had polyploidy at some point in our evolutionary history. Another thing that can happen after a polyploidy event is an increase in body size. For example, tropical clawed frogs, who are polyploid, are more than twice the size of their closest non-polyploid relative, the western clawed frog. Finally, polyploids are more likely to occur near the poles. The reasons for this are also not known but there is some evidence to suggest that polyploids possess greater environmental resilience and adaptive potential than non-polyploids. Another possibility is that cold temperatures actually create polyploids through errors in cell division, or perhaps polyploids are simply forced toward more extreme ranges due to competition from non-polyploids. To my knowledge there is only one Antarctic amphipod currently known to be polyploid, named Charcotia obesa, but given how understudied they are I suspect there may be more.
In conclusion, I think Antarctic amphipods are a really cool system that offer a lot of neat opportunities to explore latitudinal biodiversity gradients, polar gigantism, polyploidy, and more as well has how all these different phenomena intersect. I hope I’ve done a good job convincing you of how cool these little bugs are (though not so much so that you go out and answer all the questions before I get a chance to) but if you’re still not convinced, check out some of the cool pictures below!
Ph.D. Student in the Halanych Lab