Follow me on Twitter @ KolmannMA!
We discuss in this latest New & Views articles the findings of a recent paper by Marianne Porter and colleagues, who studied how shark vertebral morphology aid in making for more efficient swimming. Sharks can alter the frequency by which they pass waves of motion down their body, which in turn changes how the cartilage in the spines of these animals behaves. The gradient mechanical properties from the intervertebral disks to the vertebrae themselves store and release elastic energy - meaning these sharks have a continuously-variable transmission. Sharks can shift from low-energy cruising to high-speed swimming almost instantaneously, a handy trick for catching prey over a reef or in the open ocean.
So our (Nate Lovejoy, Ken Welch, & Adam Summers) most recent paper, is about to be released in Proceedings of the Royal Society: Part B and it's getting a bit of press. So I'm giving ya'll the lowdown on what we found and why it's so interesting (before you hear elsewhere).
Here's the gist:
Freshwater stingrays are found in South American river basins and feed on a diverse array of prey. Many of these species specialize on a single kind of prey, be they fish, crustaceans, snails, or even aquatic insect larvae. But not all of these prey are created equal – some prey are harder, softer, or tougher than others. Insectivorous freshwater stingrays are the only elasmobranchs (sharks and rays) to feed on insects – which are difficult to eat and digest due to high amounts of chitin in their exoskeletons, a remarkably complex and tough material. Other vertebrates, namely mammals like shrews, bats, and tenrecs also eat insects and they use complex jaw motions – chewing – to shred chitin to allow digestive juices to breakdown prey. Stingrays can protrude their jaws away from their skull as well as protrude these jaws laterally, to the left or right. Using high-speed videography we determined that stingrays do actually chew their food – just like mammals. We also found that these stingrays lift their disk to suck prey underneath the body – thereby capturing food with their pectoral fin ‘limbs.’ This decoupling of behaviors, prey capture and prey processing, is reminiscent of what is seen in several major radiations of bony fishes where the oral jaws suck prey and jaws in the throat (pharyngeal jaws) crush prey.
Q. There are freshwater stingrays?
A: There are many! You can find freshwater stingrays in many tropical rivers – in North Australia, New Guinea, Thailand, and even West Africa, to name a few places. But the largest concentration of freshwater rays are found in South America – from Guyana and Venezuela in the north, through Brazil and Peru, and even down into Argentina and Uruguay. These rays (Potamotrygon) were originally marine, but invaded South America millions of years ago, back when the Andes hadn’t risen and the middle of the continent was filled by a shallow, slightly salty lagoon, called the Pebas Mega-Wetland (the best name for a big salty swamp that I can think of). They must have been successful, because now there’s over 30 species of freshwater rays in South America – all inhabiting freshwater.
Q. Why is chewing in rays important?
A: Some of these freshwater rays (potamotryonids: literally – ‘river rays’ in Greek) are unique in that they eat aquatic insect larvae – the juvenile phase of insects like dragonflies, beetles, and caddisflies, which live along the bottoms of rivers and ponds. Insect larvae are made of chitin – a tough substance like plastic that has to be sheared or shredded apart – that’s why stingrays chew, to tear chitin into bits. Aquatic insects are quite plentiful, but they are tough to eat – so stingrays that chew have found a means of eating a plentiful food option that they don’t have to compete with other animals to eat!
Q. I don’t understand why you think the comparison to goats is interesting. Why goats?
A: For a very long time, scientists thought that only mammals, like goats, could chew. Some of the earliest mammals fed on insects, and these sorts of critters were the land animals that ‘inherited the earth’ after the dinosaurs went extinct. Chewing is widely believed to have been a real important adaptation that helped mammals take advantage of new diets when they diversified some 60-70 million years ago. What we’re finding more recently is that other organisms that we wouldn’t have expected to be able to chew, are arguably doing the same thing as mammals – and they’re chewing because this behavior seems to be the best solution for eating tough substances like insects, grasses, and even bone. Now we know there are carp that chew. Lizards that chew, even some dinosaurs are hypothesized to have been chewers. But chewing has never been observed in sharks and stingrays, and we’re the first to find it.
Q. Why don’t other stingrays eat insects?
A: Well, we think that to chew on insects you need really flexible jaws. Most stingrays have these, although some of the rays I’ve studied previously, ones that eat mollusks have very rigid jaws. So those clam-eating stingrays probably can’t chew, just crush. Freshwater rays have particularly kinetic, or mobile jaws – the jaws of all rays are extended away from the skull during feeding by two cartilages, the hyomandibulae. But what makes freshwater rays so unique is that they have an extra joint that runs between the hyomandibulae and the jaws – making their jaws extra flexible. But maybe the answer to why more stingrays don’t eat insects in that because there just aren’t that many aquatic insects in the oceans – so only freshwater rays have had the opportunity!
Q. Why would anything eat an insect anyway?
A: Insect larvae are packed with nutritious fats that they’re saving prior to metamorphosing – when these insects change from generally flightless juveniles to volant (flying) adults. All these fat stores are very nutritious and freshwater stingrays sure seem to love them! When I was conducting my experiments, the rays would ignore other foods if I dropped insects into the tanks – even though they took more of an effort to eat!
02/09/2016 - I'm excited to say that I have passed my PhD final examination and I will be starting my post-doc at Friday Harbor Labs in just a few weeks!
Stay tuned for more updates... there are several things cooking in the meantime!
10/07/2016 - Still recovering from the shock, elation, and honor at being awarded the American Elasmobranch Society (AES) Gruber Award at this year's Joint Meeting of Ichthyologists and Herpetologists in New Orleans.
I've had some really tremendous influences and mentors along the way, and I in particular thank my coauthors, Nate Lovejoy, Adam Summers, & Ken Welch for their support and advice along the way. Couldn't have done it without these gentlemen scientists.
Sonja Fordham (Shark Advocates) - is credited for snapping this photo of me with past winner Chris Mull and sawfish whisperer, Dana Bethea! Great seeing you two again!
04/07/2016 - The International Congress of Vertebrate Morphology was a whirlwind of activity and I barely could keep up with all the sorts of cutting edge science taking place!
Particularly fascinating with Mason Dean et' al's symposium on biomaterials research - such absolutely awesome stuff! Highlights were biomimetic composites that simulate nacre and glass sponge spicules 3D printed at Harvard by my collaborator James Weaver!
In case you didn't get a chance to see it, check out my poster to the right on the evolution of insectivory in freshwater rays - a curious story of a 'lower' vertebrate which effectively chews tough prey like aquatic insect larvae. Insect larvae are widespread in tropical and temperate freshwater systems - but are a dietary niche that has remained out of reach for most elasmobranchs (sharks and rays) until now.
16/06/2016 - The folks at Experiment.com contacted me regarding creating a project for crowd-sourcing through their Shark Research Challenge, during Shark Week.
Please visit my research page there and consider donating (we're about 20% there after a week!) or share widely among your friends and family.
I'm trying to determine just how widely among the freshwater rays complex feeding behaviors, like chewing, are distributed and how these behaviors correlate with their dietary ecology and morphology.
Maybe most importantly for the casual reader, I've written several 'LabNotes' for this project which introduces you to the freshwater ray 'phenomena' - why they're so interesting, where they come from, and how my research is answering these sorts of questions (and generating more questions, too).
Alternatively, check out my blog post on Southern Fried Science, too! If anything - it's a fun read!
01/06/2016 - Our JEB paper, 'Morphology does not predict performance' was chosen by the UToronto Scarborough Biology Dept as the best student paper of 2016! Nice way to enter into the summer stretch towards dissertation defense!
Thanks to my coauthors, Nate Lovejoy, Mason Dean, Adam Summers, and Stephanie Crofts!
My undergraduate research assistant, Swara Shah - also one best undergraduate student research project for her research with me on bullnose ray feeding biomechanics!
15/04/2016 - I was interviewed regarding the talk I gave at the 2016 SICB meeting in Portland OR on how stingrays feed on tough and stiff biomaterials. So how do they do it? Well, not to give away too much, rays feeding on tough prey have incredibly flexible, many-jointed (kinetic) jaws that help them "chew" prey like insect larvae and crustaceans. Rays that specialize on stiff prey like mollusks, on the other hand, use a drastically different strategy - fusing their jaws and teeth into a single, solid crushing platform. The diversity of feeding modes in stingrays is impressive given their low species richness (# of species). I thank the writer, Kaitlyn Lowder, for doing such a great job!
07/04/2016 - My BIOC99 (Seminar in Biomechanics and Comparative Phylogenetic Methods) presented their work as posters to our lab group today - and did a fantastic job. Swara presented work she did with another student of mine, Henil Patel, on scaling of feeding performance in bullnose rays (Myliobatis freminvillei). The highlight of this study is that these animals have comparable performance to other durophagous rays, but it is driven by efficient force transfer rather than increases in gross muscle morphology, as we documented in related cownose rays. Moreover, a sesamoid-tendon complex in these animals keeps pace with muscle growth and jaw leverage in order to offset internal tendon stresses during biting.
Amy & Ereny discussed their findings on functional redundancy and morphological diversity in the jaws of dasyatoid stingrays (below). They found that not only is morphology redundant when its comes to function (i.e. there are diverse shapes, but only several functional outcomes), but performance in these rays increases at a greater rate than one expects across the phylogeny of these animals. Incidentally, freshwater stingrays occupy a comparably huge area of morphospace compared to other rays.
07/01/2016 - Made an early departure from the Society for Integrative and Comparative Biology meeting in Portland, OR. It was a great time, and I got to witness some great science. Good times meeting old friends, and new - but most importantly I got to see my students get their first taste of a professional conference. Swara and Henil did a fantastic job presenting their research! You can see a photo of their poster to the left and the slide from my presentation on prey materials and their influence on stingray feeding morphology (below).
Our new paper featured in Journal of Experimental Biology went live - here's an FAQ about what we found and why it's interesting!
Q. What is the most important point of the paper?
A: The jaws of hard prey crushing stingrays have really different shapes. Despite this no shape is better than any other at smashing hard prey. There are many types of hammers and they all perform equally well. This is unusual because we expect to see performance differences when there are large differences in shape. Consider for comparison the beaks of Galapagos finches - different shapes are better for dealing with different types of seeds.
Q. How hard can a stingray bite?
A: Very, very hard...a cownose ray just 2 feet across can generate more than 110 pounds of force. A big eagle ray could generate over 1000 pounds.
Q. Why did you use models of prey items?
A: Nature is messy. Using models reduces the “noise” from natural variation. We used 3D printed shells that were identical in shape and structure to live shells. These faux shells broke in the same manner as live shells. This suggests that shape was not very important in predicting when any shell would be destroyed… but what the shells are made of… well that was pretty important!
Q. If shape is not important why does it vary?
A: Shape CAN be important, if it artificially inflates the size of the prey. Prey can act larger by having large spines or knobs or ridges. Predators must then be large enough to swallow the whole prey, including the spines. Spines discourage smaller predators, and large predators if the spines are venomous or sharp.
Q. Are there any of these stingrays near where I live?
A: Most of these rays are tropical, with cownose and bullnose rays occurring as far North as Delaware Bay in the United States. In the Caribbean, Florida, and the Bahamas you can find spotted eagle rays (Aetobatus). But other types of eagle rays (Aetomylaeus) are found only in the Indo-Pacific, alongside the other three stingrays.
Q. Is crushing hard prey common?
A: There are many critters that crush hard prey, hyenas, for example. All are very specialized, with particular teeth, jaws, and big muscles. That sort of suggests a common evolutionary theme that molds these creatures along similar processes. Interestingly, there are several, unrelated hard-prey crushing stingrays, despite their having a cartilaginous skeleton.
Jillian Morris featured some of my batoid-related research interests over at Sharks4Kids! In case you haven't heard, Sharks4Kids teaches young people about ocean life, especially elasmobranchs, in order to inspire the next generation of shark advocates through education, outreach and adventure.
Bit of departmental recognition for graduate students here, one of which was me and my buddy Derrick!
There's been a lot of controversy about the collection of the Moustached Kingfisher, an infrequently-collected species from Guadalcanal in the Solomon Islands (https://en.wikipedia.org/wiki/Guadalcanal).
I'll leave the story to the news article, but when the collecting scientist, Dr. Filardi of the American Museum of Natural History wrote an op-ed to defend his collection of the animal, he was lambasted for being a "murderer" amongst other things. I tried to explain why collections are still absolutely necessary in today's world and some of my comments are featured in this great summary article by Audubon:
The time is nigh... I begin my lengthy roadtrip from UToronto to Academy of Natural Sciences (ANSP) to grab specimens and then onward to Cambridge MA to start my research position at the Wyss
Institute at Harvard University. I'm incredibly humbled to have been given this opportunity.
I will be ct scanning dozens of species of stingrays. There are two over-arching goals here, (1) to generate a dataset for my last doctoral dissertation chapter on morphological evolution of the feeding apparatus in marine and freshwater stingrays and (2) gather more data for Mason Dean and James Weaver's project on the mechanics of tessellated cartilage. I'm stoked.
That big brown floppy thing in the photo is a torpedo ray, just fyi!
If you missed my talk @ AES/JMIH 2015 - you can see a sampling of the slides below. Turns out asymmetrical jaw protrusion is a pretty common behavioral condition of prey capture in Potamotrygon. Why? Well we're not sure yet - but maybe it has something to do with shearing insect prey.
Kolmann, M.A. & Lovejoy, N.R. Feeding kinematics of the ocellate freshwater stingray, Potamotrygon motoro. American Elasmobranch Society. July 2015. Reno, NV.
and be sure to contact Lisa Whitenack for information regarding our study on the functional morphospace of shark teeth since the Permian(!):
Whitenack, L.B. & Kolmann, M.A. Integrative Chondrichthyan Paleobiology: The Present is the Key to the Past. American Elasmobranch Society. July 2015. Reno, NV.
Great news - our paper on the scaling of bite force generation in cownose rays for the Journal of Anatomy has been accepted! Check out my ResearchGate profile soon for a copy!
How "hard" can a stingray bite? Think you know?
(and by "hard" I mean "forcefully")
Happy Cinco de Mayo! See below for slides from my presentation at the Interdisciplinary Approaches to Fish Skeletal Biology in Tavira, Portugal <http://iafsb.org/>!
I had a great time and met some fantastic people. Not to mention the fish markets were great for specimens (Engraulis and Torpedo, nice!) My talk focused on our meager understanding of how durophagous stingrays use mineralized teeth, stress-dissipating struts, and massive muscles to process prey like shellfish. I found that jaw shape has no effect on crushing performance and muscle morphology is the primary contributor to positive gains in feeding performance in these wild critters!
Kolmann, M.A., Summers, A.P., Lovejoy, N.R. Development and decoupling of form and function in the tooth plate modules of durophagous stingrays. Interdisciplinary Approaches in Fish Skeletal
Biology. March 2015. Tavira, Portugal.
Been a little while on updates - unless you've been following me on Twitter @KolmannMA.
The ROM expedition to the Marowijne and Corantijne Rivers was a success, as was my own expedition to the Lower Demerara, to survey estuarine and freshwater fishes.
Not only did my collaborators and I collect ~115 spp in 44 families, including stingrays for my thesis - but in Suriname we re-discovered a species from it's type locality that hasn't been seen in over 60 years, a banded knifefish (Gymnotus anguillaris).
So what does this mean exactly? Well, when a new species is discovered and described, several specimens are put aside as "types" - holotypes and paratrypes - and are distributed between several museums. These type specimens embody what is that species - a voucher that is available for reexamination, sort of like a entry in a glossary (but an exceedingly dead fish). With the advent of modern molecular methods in systematics, fresh tissue is needed to provide a biochemical "type" specimen (along with the preserved specimen being a morphological type), what we call a tissue voucher.
Since this banded knifefish was discovered (like many species) before the genesis of molecular phylogenetics (methods of determining evolutionary relationships from patterns of DNA) researchers lacked any record of its genetic distinctiveness. Now we have a record of this fish, from a molecular standpoint - and this has allowed us to determine exactly which species of knifefish this particular fish is related to - and how they have dispersed themselves across the Guianas.
This last March I led a sort of hybrid expedition/fisheries dependent survey of the Lower Demerara and its estuary, funded by Rufford Foundation. We went fishing with locals, intent on determining which fishes were being caught for local consumption and export - especially what species of sharks and rays were being harvested. So we get to analyze not just the local biodiversity, but also the "ecology" of the fishermen... with some interesting results. The highlight of the trip for me is catching the long-snout stingray Dasyatis geijskesi... a little known component of the ichthyofauna (fish diversity) in Guiana Shield estuaries. I'm hoping to start a project with the University of Guyana on understanding the reproductive biology of this stingray, which seems (anecdotally) to be strange, rather slow for a dasyatid.
Had a great time at Cano Palma Biological Station with a group of stellar students: http://www.coterc.org/cantildeo-palma-overview.html
Cano Palma is a field station organized by the Canadian Organization For Tropical Education and Rainforest Conservation (COTERC). The station generates baseline survey data for shorebird migrations, turtle nesting, snake demography, caiman populations, and mammal diversity in addition to being a base for visiting scientists pursuing their own research year-round. The station has hosted the Lovejoy Lab's Tropical Biodiversity course for two years now and the area features an interesting array of fishes - from characids to poeciliids!
All fishes are being identified and taken to the Royal Ontario Museum where they will be some of the first records of the fish fauna inhabiting northeastern coastal Costa Rica - in fact, we may have a new species or two, which is pretty exciting!
We caught some great fishes and overall, had ourselves a time! But I miss my station people...
**Update** and we got featured in the University news!:
some of the photos below courtesy of Patrick Traynor
Got back from SICB 2015 (http://www.sicb.org/meetings/2015/) and caught up with my FHL friends and collaborators! It was a hell of a meeting - accelerometers, suction-feeding, and ballistic tongue projection - oh my... For those of you who may have missed it - here's a poster of the work I did at FHL and presented at SICB in West Palm Beach.
Just a few photos of me filming Potamotrygon motoro feeding using high-speed videography - we're trying to figure out how these animals use de-coupled (loosely-connected skeletal structures) to feed on complex prey!
Donald Taphorn and I just received a grant through the Rufford Foundation to study freshwater and estuarine fish biodiversity in the Demerara River, Guyana!
We will be working with local fishermen and recruiting a local University of Guyana student to catalog commonly-caught fish species as well as document fish in the Demerara, probably the most
extensive scientific survey in this river for a hundred years! Hopefully we'll catch more Potamotrygon too!
Back to Friday Harbor to continue my research on shell mechanical properties and how durophagous (animals that eat shelled prey) stingrays crush mollusks!
Here's a Nucella snail about to be crushed using replica Aetomylaeus (Indo-Pacific eagle ray) jaws made from ct scanned cross-sections and milled from solid aluminum!
More photos below! Skates (Rajidae), snailfish (Liparidae), sunsets, lighthouses, varnish clams (Nuttalia), 3D printers and mechanical loading frames (MTS Corp).
Got finished with Adam Summer's Functional Morphology of Fishes course (I highly recommend):
And I already miss Friday Harbor! Not only did I learn how to identify a whole series of fish families new to me, being a temperate/tropical United States coastline person, like cottids and embiotocids - but I learned a ton of new stuff! Reconstructing ct scans, rendering images in 3D CAD software, 3D programmable milling (stingray jaws out of aluminum!), and 3D printing - one hell of a class!
Eigenmann in the early 1900s surveyed the fishes of Guyana, but only in two places - the Essequibo and the Potaro rivers. His lists of fish and their species descriptions are some of the
most accurate for this entire region of the Guiana Shield, a region of uplifted Precambrian rock that inspired Sir Arthur Conan Doyle to write the Lost World. We didn't find any dinosaurs,
but every time we come to Guyana we find new species!
This time in Guyana, myself, Donald Taphorn, Hernan Lopez-Fernandez, Jon Armbruster and others surveyed the Potaro, Kuribrong, and Amaila rivers for a potentially threatened fish new to science,
Characidium amaila, a strange crenuchid (Crenuchidae) fish from the lower Amaila River. We not only found the fish, but we also are the first biologists since 2004 (and before
that, 1904) to find and sample the sister taxa to the armored catfishes (Loricariidae) - Lithogenes villosus! This strange little fish is unarmored, unlike it's relatives and uses
its suckermouth to attach to rocks in high-flow rapids (rheophilic). Always a pleasure to work with World Wildlife Fund in this beautiful country.
Greetings from the Ucayali, Peru!
We're outside of the Pacaya-Samiria Biological Reserve sampling for knifefishes (Gymnotiformes)... these fishes produce an electric signal (EOD) through a modified muscle-structure called an electric organ (EO). Knifefishes use this signal (a wave or pulse) to navigate their environment, communicate with other knifefishes, and in the case of the electric eel (Electrophorus) actually shock predators and prey! We're trying to examine the genomic basis of electric signal differentiation between the sexes by recording the EOD from different species of knifefishes and analyzing the patterns of gene expression in EO tissue.
World Wildlife Fund Guianas (WWF) contacted the Royal Ontario Museum (ROM) to help them survey fish biodiversity (as part of a larger, multi-taxon biodiversity survey or BAT) in the Lower
Rupununi river basin in Guyana. Hernan Lopez-Fernandez (Curator of Fishes at the ROM) sent me to Guyana with his mentor, Dr. Donald Taphorn to work with WWF. What an experience!
Guyana is such a beautiful place - full of fishes and other interesting critters. A growing concern there is the expansion of artisanal gold mining along the rivers - which lead to
erosion and leaching of mercury into the water system - harmful for local wildlife and native peoples alike. With pressure from the rest of the world for cheaper gold, miners are moving
into the pristine interior of Guyana's waterways to strip mine the area. We found a remarkable array of fishes and other wildlife, now cataloged at the ROM, with some new species awaiting
description. More photos can be found under the Fieldwork tab. I wonder if I can add anymore acronyms to this paragraph...
New things to come now that I have secured independent funding for investigating the functional and evolutionary ramifications of cranial muscle evolution and jaw suspension in chondrichthyans. Expect to see how potamotrygonid stingrays (Family Potamotrygonidae) and allies can help us understand how molecular evolution, physiological redundancy and functional modularity has taken us vertebrates from our jawless ancestors to our shiny, toothed gnathostome heritage!
Also, look forward to new information on how stingrays have evolved to fill niches, new ecological roles and may be converging on similar morphological strategies... another example of freshwater fish and adaptive radiation?
12/21/2012 - UPDATE:
Check out the new updates in the Research section as I finally get the opportunity to start publishing my MSc work and start geeking out about my dissertation potential!
Changes to the About Me and Lab sections as well!
Stay tuned, lots of changes coming up - especially my new crowd-sourcing section!
Teaching in Costa Rica to commence in February! Back to the Tropics!
07/30/2012 - UPDATE:
Well, I'm now officially a Master of Science! Starting my PhD at UToronto in the Lovejoy lab on neotropical fish diversity, biogeography and speciation!
On to Potamotrygonidae!
Summer - UPDATE:
Getting ready to defend the MSc, couple last minute revelations about Rhinoptera, but maintaining sanity with field work in the Bahamas (Andros), the Florida Keys (pictured), and the Lost Coast of FLA (Steinhatchee fish fry, here we come!).
Come see my talk at the Joint Meeting of Ichthyologists & Herpetologists (AES/ASIH) in Vancouver this year!