Dr Tim Shank
Dr. Tim Shank is an evolutionary biologist at the Woods Hole Oceanographic Institution in Massachusetts. Those who know him will tell you that he's a true explorer. Dr. Shank travels the world exploring the ocean floor to learn what animals live there, and how the animals found at hydrothermal vents are are to their unique environment.
Dr Shank and his students find seafloor animals by using sophisticated tools such as the deep-sea sumbersibles Alvin and ABE (see the slideshow). They also employ state-of-the-art molecular techniques to determine the genetic make-up of animals they collect (see the slideshow).
What is evolutionary biology?
Simply put, evolutionary biology is the study of how living things have changed over time. Evolutionary biologists look at variation within and between species and try to figure out how and why it came about. Take shrimp, for example. Deep-sea shrimp look basically like most other shrimp except for one rather obvious difference. Deep-sea shrimp have no eyestalks, and therefore no eyes. Why? How did this variation between shrimp species come about? Is this an adaptation to unique environmental conditions? Was it living in the darkness of the deep-sea that allowed these shrimp to "lose" their eyestalk (i.e., through mutation and selection), because it was no longer needed? Perhaps it's the other way around: maybe all shrimp were eyeless until shallow-water shrimp, adapting to light in the water, slowly over generations developed eyestalks and eyes? By the way, deep-sea shrimp are not exactly 'eyeless' - they actually have a photoreceptor on their back and appear to be able to detect infrared light. But that's another story.
The deep-sea mussel
Bathymodiolus thermophilus.
Deep-sea mussels and clams offer another evolutionary puzzle. Most mussels feed by filtering food particles from the water. However, the deep-sea mussel Bathymodiolus thermophilus has an another feeding strategy: in its gills it hosts bacteria that produce sugars chemosynthetically; the mussel feeds off these sugars. What's really fascinating is that — depending on environmental conditions — these mussels can use either feeding strategy (filter feeding and feeding off sugars produced by symbiotic bacteria). Deep-sea clams (like Calyptogena magnifica) on the other hand, host chemosynthetic bacteria but do not filter feed. Did this species of clam "lose" the ability to filter feed because there was little to filter from the deep seawater?
Answering such questions about variation and adaption requires us to understand that Earth's history is constantly changing. Over millions and millions of years, Earth's tectonic plates have moved, oceans and continents have rearranged, climate patterns have shifted, catastrophic events such as collisions with asteroids have occurred. All these environmental changes — and others — affect the living organisms on this planet. Many many species have gone extinct, opening up new territory for those remaining. Others became isolated by barriers such as mountains, islands or oceans, and over time, adapted to their specific environment, changing enough from their ancestors to be considered a new species. Understanding the adaptions of animals, plants (and microbes!) to their environment is a multi-step process requiring a variety of skills.
How to study deep-sea evolutionary biology?
Exploration & Collection
The study of evolution is the study of changes in traits of living organisms over many, many generations. To study changes in organisms over time, we first need to find organisms and observe differences (i.e., variation) between individuals. But finding animals in the deep sea is far from trivial. In fact, the majority of the deep ocean is still unexplored. It was only as recently as 1977 that hydrothermal vent ecosystems were discovered. Since then, scientists have discovered over 600 new species in these environments!
Working in the extreme environment of the deep-sea is tremendously challenging. Think of how difficult it would be to look for something underwater over a mile down, in total darkness, in near-freezing seawater and under crushing pressure. Fortunately, advances in deep-sea technology are enabling us to reach otherwise inaccessible areas.
Identification
Once deep-sea animals have been located on the seafloor, the next task is to identify the species concerned and document where it was found. In the deep sea, we are only just beginning to catalog seafloor life. So it can be a challenge to determine whether an animal is a new species or a member of a previously-described species. The scientists in Dr. Shank's lab use molecular genetic techniques to identify species and to see how animals from different regions are related to one another. Mussels, for example, are found at most hydrothermal vent sites, and molecular genetics can tell us if they are the same species or different species with different adaptations to local conditions.
Identifying what drives evolution of particular traits
Many things can cause organisms to change over time, including changes in the environment. To understand how environmental changes may have caused organisms to adapt, we need to understand not only how the animal functions within its environment, but also how that environment may have changed through time. For example, if an animal has a larval stage that is moved by ocean currents, could changes in these currents enable the animal to colonize new areas? Could changes in the vent fluid chemistry at a site affect the distribution of animals found there, favoring new species that can survive different temperatures and different levels of sulfide? These are the kinds of questions that Dr. Shank and his lab colleagues are investigating.
Deep-sea bio-regions
Map showing locations of
known hydrothermal vent
fields worldwide (red dots).
Click here for a slideshow
about the different biogeographic
provinces that distinguish
different groups of vent fields.
At this time, only a small percentage of the ocean floor has been explored. Dr. Shank and other scientists are working hard to reach new areas of seafloor to find and catalog animals living there. Even still, there are enough observations and collections made to identify six distinct regions on the ocean floor, or biogeographic provinces. See this slideshow for more information about biogeographic provinces. For more information on the general topic of deep-sea biogeography, read Dr. Shank's article "The Evolutionary Puzzle of Seafloor Life", published in the Oceanus magazine.
It is certainly an exciting time to be a deep-ocean explorer!
