Episode 15: Exploring Collection-Based Research
In our last episode, we discussed the role of collection data for scientific investigation. In this episode, we explore the value of the research on museum specimens and artifacts themselves, focusing on the use of specimen examination and evolutionary hypotheses to better explain the natural world. To help us discuss this topic, we are pleased to be joined by Dr. Peter Makovicky, The Field Museum's own Curator of Dinosaurs and Chair of the Department of Geology. Phylogenies (a hypothesis of how life is related evolutionarily) are crucial for predicting the distribution of incompletely studied organismal characteristics ranging from the presence of venom in fishes, to feathers on dinosaurs, or how the anatomy of eyes change in the deep sea as a result of selective pressures. In other words, knowledge of the evolutionary relationships of life allows for effective predictions about the unstudied characteristics of species. Museum collections are a critical component of this work, from the initial collection of samples used to infer our hypotheses of how life is related (e.g., whole specimens, tissues used to extract DNA for genetic work) to our ability of accessing this material again to test and explore evolutionary hypotheses.
An example of the biological questions we can explore in this manner is tracing the evolution of venomous fishes. By looking at venomous fishes from an evolutionary perspective, we generated a much more accurate picture of fish venom evolution than was previously suggested using a strictly observational approach. To explore venom evolution, we began by taking a major stab at the fish tree of life by analyzing all suborders and known venomous groups of spiny-rayed (Acanthomorpha) fishes for the first time. Using the resulting family tree of fishes as a framework, we mapped the species that were known to be venomous on to this DNA-based tree. This provided an initial estimate of how many times venom evolved and allowed us to predict which fish species beyond the "knowns" should be venomous or could possibly be venomous. To test these predictions, we explored the museum collections and dissected scores of specimens to look at the detailed anatomy of fish venom glands and clarify how many times venom evolved on the fish tree of life. By working our way down the fish tree of life by comparing ever more distantly related fishes from the known venomous fishes, we could pinpoint the number of times venom evolved, the exact groups of fishes that are venomous, and revise the identity of venomous fishes. This type of research is occurring world wide based on the collections at The Field Museum, and similar institutions that house, maintain, and allow access to museum specimens for scientific research. This example is just one of the many stories surrounding research done at The Field Museum with collection-based research.
Piecing Together the Mysteries of the Fish Tree of Life
One of the primary reasons that we here at What the Fish? are fascinated with the evolutionary history of life on Earth is that it provides a context and scientific hypothesis from which we can further study the wonderful biodiversity of fishes. For example, if we have a working scientific hypothesis of how different species of clownfishes are related to one another, we can address questions surronding the number of times clownfishes have formed symbiotic relationships with anemones. But how do we build these evolutionary trees of fishes, such as the one seen below? Well there are various different kinds of scientific data that can be used to infer evolutionary relationships through time (e.g. variation in the sequence of DNA/genes, anatomical features, behavioral traits) that scientists around the world collect in order to support these hypotheses. Shared anatomical characteristics, such as the position of a spiny-rayed dorsal fin, may be indicative of common evolutionary ancestry, and scientists use this evidence to produce hypotheses regarding the evolution of life on Earth.
A Fish Can Be Encased in Armor?
Although they vary in size, morphology, and type (e.g., plates, scutes), many fishes have evolved thick armor-like scales that help protect them from their aquatic environment and potential predators. Many fishes that live in and around the bed of aquatic environments utilize armor to protect their bodies from loosing scales as they burrow and scrape along rough substrates and potentially rocky or jagged environments, such as catfishes and poachers. Other armored fishes may sacrifice mobility for a tank-like body that makes them nearly inedible to nearby predators. For example, the aptly named boxfishes have scales are hexagonal in shape and result in an armor that looks like a bee's honeycomb. The body armor of fishes are so effective that various scientists and researchers have been investigating the morphological properties of fish scales, such as those in bichirs, to aid with the development of stronger body armor for humans!
You Are What You Eat
Among fishes, the different types of food and the ways in which they are consumed are as incredibly varied as the fishes themselves. Some fishes are vegetarians, including the Piranha relative the Pacu, while others are ferocious carnivores, such as the African Tiger Fish. Fishes often have very specilized dentition and feeding structures depending on their source of food. For example, fishes that crush hard crustacean shells may have large boulder-like teeth. Filter feeding fishes, such as the Whale Shark seen below, have evolved fine filamentous structures to help sift through plankton. Overall, fishes eat almost anything you might find in an aquatic environment, and they do so efficiently!
In the deep, no one can hear you scream
The vast expanse of the seas is our destination, and uncontrollable terror is our goal. Join us as we descend into the madness that only total darkness can bring. The deep holds many secrets, and we shall share them with you...including inspirations for sea serpents (Oarfishes - including the photo here taken by our own Leo Smith), fierce predators that hide behind shimmering lights (Anglerfishes), and even the secrets to zombification (Pufferfishes). Caution, don't try zombification at home. Seriously, we don't recommend it. We hope you enjoy our special Halloween and spooky season podcast!
2.5 million specimens don't collect themselves!
The Field Museum's Division of Fishes houses approximately 2.5 million specimens of fish, including whole specimens in alcohol, skeletal specimens, tissue samples, and cleared and stained material. That is a lot of fishes! But the fishes did not just arrive overnight; scientists and researchers have been adding to the collection at The Field Museum since 1894.
Museum collections serve as records of the natural world, as well as critical resources for scientists wanting to study the biodiversity of the planet. The fishes collection has grown through continued fieldwork by ichthyologists that use a vast array of tools and strategies for sampling living and extinct fishes from around the world. Tune into our podcast this week with a special paleoichthyological guest, Sarah Gibson of the University of Kansas. Listen to us as we discuss the many different ways we collect fishes in the field.
The allure of sharks
Sharks, and cartilaginous fishes in general, have long mesmerized scientists and the public alike. They are fascinating creatures! Fossil remains indicate that sharks have been evolving on this planet for well over 400 million years. They have been described in popular culture as "perfect killing machines," and it is hard to argue with their abilities to hunt and secure prey of all shapes and sizes. Be it the incredible filter-feeding of the immense Whale and Basking sharks or the pure power and incredible bite of the Great White Shark, few organisms in nature portray an aura of such efficiency. Sharks are among the earliest known jawed-vertebrate lineages, and since their initial evolution, they have wasted no time in putting those jaws to work. After 400 million years they still remain some of the oceans most incredible predators with no signs of slowing down.
Sharks are venomous and bioluminescent?
However, there are more to sharks then just teeth! A number of lineages have independently evolved venom, including the horn sharks and angel sharks. The horn sharks release venom out of spines that stick out from each of their dorsal fins, making them an unattractive meal for even larger predatory fishes. The spines of the dorsal fins in some squaliform (or dogfish sharks) are also known to be venomous, including species within the lanternsharks. Sharks have also independently evolved bioluminescence, the ability to generate and emit light, as they have invaded the deep sea. These include predominantly deep-sea taxa, such as the lanternsharks and the bizarre Cookie Cutter Shark that sucks on to prey and rips off hunks of flesh before speeding away. These deep-sea sharks all use bioluminescence to hide from potential prey items, to avoid being eaten themselves, and for communication.
For most fishes, reproduction involves eggs and milting, which is like crop-dusting with sex cells (aka gametes). The vast majority of fishes are oviparous, which means they lay eggs that are fertilized and develop outside the mother's body. In these situations, males typically milt, which is the release and spreading of their gametes, onto the eggs that have been deposited in the environment. In ovoviviparous fishes, the eggs develop inside the body of the mother, and male gametes have to be passed into the females’ body through specialized structures, such as claspers (modified pelvic fins) in sharks or gonopodiums (modified anal fins) in guppies. Live birth (viviparity) has also evolved in a number of lineages of fishes, including sharks, guppies, and rockfishes. In viviparous fishes, the young develop within the mothers’ body.
Male, female, or both?
While most fishes have separate sexes, a number of lineages are simultaneous or sex-switching hermaphrodites. Some fishes, such as clownfishes, can change their sex once during their lifetimes either from female to male, or male to female depending on environmental and/or behavior scenarios. A small number of fish species are simultaneous hermaphrodites capable of producing both male and female gametes at the same time (e.g., lancetfish, some species of moray eels as seen above). Scientific studies have identified that at least some of these species (e.g., the mangrove killifish Kryptolebias marmoratus) are capable of self-fertilization!
How does a fish make light?
Bioluminescence, the production and emission of light from a living creature, is widespread among different groups of marine fishes (e.g., anglerfishes, flashlight fishes, dragonfishes). Most organisms produce light through a chemical reaction between luciferin (a small molecule) and oxygen. The enzyme luciferase speeds up this reaction, resulting in the production of light. But unlike the incandescent lightbulbs in your home, this light gives off almost no heat. Some fish species have the ability to produce the chemical compounds necessary for bioluminescence themselves (such as lanternfishes), while others rely on symbiotic bacteria to create and generate light (including the beloved anglerfish in our logo).
Why would a fish want to make light?
The majority of bioluminescent fishes are found in the deep sea. Below 1,000 meters there is no visible sunlight in the ocean. As a result, many organisms that live below this depth have evolved bioluminescent structures, and fishes use this light in a variety of ways. Some fishes use light for camouflage, specifically counterillumination. This is where the fish emits light around its belly to match any light coming from overhead, making it invisible to predators looking upwards for shadows in the water column. Others use light to attract and catch prey, such as the beckoning luminescent lure of the anglerfish. Fishes will even use light for communication in order to recognize each other in the darkness of the deep or to communicate with potential breeding partners.
