Searching for Species at the Edge of the World

Latitude: -63 20.091 Longitude: -53 12.789

One of the most longstanding questions in biology is “why are there so many species?”. In fact, I strongly suspect most biologists are primarily motivated by this essential question once you take all the fancy words out. Charles Darwin answered this question in part with his theory of evolution but in doing so raised many more. Of particular interest to those of us currently onboard the RVIB Nathaniel B. Palmer is where are there so many species? Or, more formally, how is biodiversity distributed across space? One interesting trend in particular that has emerged is that, generally, the most species rich areas tend to be near the equator, with biodiversity dropping off as you move farther away toward the poles. This phenomenon is known as the latitudinal diversity gradient, or LDG for short. Scientists have known about the LDG for a long time, but we still don’t understand exactly what causes it. One theory is that environments are more unstable at extreme latitudes, with cycles of glaciation leading to higher rates of extinction, and therefore fewer species. Others think that the higher temperatures near the equator create faster generation times and mutation rates, resulting in higher rates of diversification, and therefore more species.

Given the LDG one might expect Antarctica to be relatively species poor, however this is far from the case. In fact, there are some groups of animals, especially among marine invertebrates, that appear to follow the opposite trend, with more species the farther away from the equator they are. ~20% of all sea spider species, for example, are found in Antarctica. One of the trickiest things about studying the LDG is that it assumes we have a complete record of global biodiversity, when in fact ~80% of species remain undiscovered. Much of this undiscovered diversity is found in places that are very hard for humans to reach, such as Antarctica and the deep sea. Indeed, species are constantly being found in these environments making them some of the most active regions in the world for the discovery of new species. Antarctica in particular also has a large percentage of endemic species, that is species that are found nowhere else in the world, due to its unique environment as well as a circumpolar current that keeps it isolated from the rest of the world’s oceans.

All these factors make Antarctica an extremely unique and interesting environment to study, especially if you are as interested in broad patterns of species diversity and evolution as I am. But before I can start the really fun work of exploring big ideas like the LDG I need to get a better idea of how many species there are in the first place. How can we say polar regions have fewer species when we have only just started looking for them? This is one of the reasons collection trips like this one is so important, discovering new samples from all across the animal tree of life will help us chip away at the ignorance surrounding one of the most enigmatic environments on the planet. As I write this, we are currently approaching our very first sampling site, a tiny strip of land off the very tip of the Antarctic peninsula. We will begin sampling around 0600 ship time, and since I am on the night shift (lucky me!) I will be on deck to start processing our first haul. After more than two months of quarantining and weeks at sea I am extremely excited to be one the privileged few that is able to perform the important work of exploring and documenting the unique organisms that inhabit one of the most extreme (by human standards at least) and rapidly changing environments on the planet.

Kyle David
Ph.D. student in the Halanych Lab
Auburn University