It has been a quite a while since I updated this blog, but that’s the life of an Assistant Professor I guess! Good news though, my colleagues and I at SHSU and Lone Star College University Park were recently awarded a National Science Foundation grant to study perspectives of late high school students and teachers and early community college students on the geosciences. Our program, Geoscience Exposure and Training in Texas (GET TX), will run for three years and has four main components:
1) Visits to high school STEM classrooms to demonstrate the interdisciplinary nature of the Geosciences
2) Open-house events at SHSU and LSC-UP with professional scientists as guest speakers to highlight career opportunities
3) Teacher workshops to provide teachers with region specific examples of the applicability of geoscience topics and how they can be incorporated into their classrooms
4) A 12-day summer bridge program for students held at SHSU that includes an $800 stipend with room and board
We are actively recruiting participants for each component from the broader southeast Texas region. If you are interested in participating please send me an email at firstname.lastname@example.org
More details about the grant can be found https://www.shsu.edu/academics/environmental-and-geosciences/get-tx/index
Lifespan and growth of Astarte borealis (Bivalvia) from Kandalaksha Gulf, White Sea, Russia
David K. Moss, Donna Surge, and Vadim Khaitov
What we did:
We were interested in understanding lifespans and growth rates of the polar bivalve Astarte borealis from a small population in the White Sea, Russia (67° N, 32° E). Bivalves record growth lines in their shells that are similar to the rings of trees. However, bivalves complicate things a bit, because they can record growth lines at several different periodicities: daily, tidal, fortnightly, monthly, and annual. Therefore, you cannot cut a shell in half a count everything that is there. Oxygen isotopes though can be used to distinguish annual from non-annual growth lines. This is because the ratio of 18O/16O is partially dependent on temperature. A. borealis like many other clams makes its shell out of aragonite (CaCO3) and faithfully records the ratio of 18O/16O. Essentially, clam shells act like thermometers that keep a record of temperature while the organism was growing. Using this information, we can go back and understand at what time of the year different growth lines formed. When we did this with A. borealis we found that it records an annual growth line (dark line in Fig1 below) in the late summer.
In bivalves, annual growth lines represent a time of significantly slowed growth. They can result from a number of things but most often, they have to do with temperature stress or reproduction. In the White Sea, summer temperatures do not reach the known thermal maximum for A. borealis so we rule that out as a cause. Instead, my co-authors and I suggest that the summer shutdown might be a time of reproduction in this species. More work is need to confirm our hypothesis.
Knowing which lines were annual allowed us to determine the lifespan and growth rate of A. borealis from the studied population. Though we had a small sample (n=18), we found that A. borealis is both slow growing and long-lived (oldest individual was 48 years).
Fig 1. Top image: individual of A. borealis. Dashed line shows axis of maximum growth along which specimen was cut. Bottom image: polished cross-section of individual above captured using a light microscope; red arrows indicate annual growth lines.
Why is it important?
Before our study, only one studied had used oxygen isotopes to determine the lifespan of A. borealis. In that study, which looked at individuals from extreme northern Greenland (Torres et al. 2011), the authors found individuals up to 150 years old! Most other studies looking at lifespans of this species relied on ridges on the external surface of the shell, which can be misleading. Because A. borealis is so long-lived, it might be a potentially important archive of past climate conditions at high latitudes. In other words, they can act as thermometers before human records.
Our study in the White Sea is part of a larger one that looks at how the growth strategy (i.e., when do they form annual lines) vary on the planet today and what happens to that strategy when Earth’s climate changes. This information can inform us about what might happen to this, and other species, in the near future. We are currently examining this species from the Baltic Sea and closely related species from the Atlantic Coast of the United States.
Link to paper here: https://link.springer.com/article/10.1007/s00300-018-2290-9
Please email me (email@example.com) if you would like access to the pdf version.
Ooooh that smell
Can't you smell that smell
Ooooh that smell
The smell of death surrounds you” – Lynyrd Skynyrd, That smell
Wet dog. The bottom of a dumpster on a summer day. A decomposing fish. Old socks. A touch of salt water. What smells like a combination of all those? Two year old, once frozen but now partially defrosted clams. It is probably not what Lynyrd Skynrd was referring to but the smell of death filled the Paleo lab at UNC last week.
A few days ago I received a shipment of clams from the Virginia Institute of Marine Science (VIMS, www.vims.edu) via FedEx (you can ship almost anything in the mail). Among many other things, VIMS conducts surveys of marine creatures living on the seafloor. A few times a year a research vessel goes out and dredges the sea bottom at various areas along the Atlantic Coast. The data collected from these cruises are used to inform the public, industry, and policy makers about the status of many economically important marine animals. Researchers like myself use these samples for scientific studies. My work at UNC examines the consequences of environmental change on the bivalve Astarte and I was fortunate enough to receive 100+ individuals from a series of dredges from Massachusetts to southern Virginia.
A look inside the styrofoam container the in which the clams were shipped. Note the camouflage lunch box. The number of everyday items scientists use always amuses me. I think most people assume we are using fancy, expensive equipment but most of the time it is stuff that can be purchased at your local Wal-Mart.
So what do you do with a bunch of stinky, old clams? Science! Step one, scoop out the goop. Not the technical term, but for my work I am interested in growth increments preserved in the shell so thankfully the squishy stuff (which is the smelly part) can be discarded. Most of it is easily scrapped out using a scalpel but for the sticky bits, a soft toothbrush does the trick. I’ll admit, before I started working with clams I kind of thought they were rather simplistic and boring animals. However, this is not the case. Clams, like us, have a rather complex organ system. In the diagram of clam anatomy below you’ll notice that we share many of the same organs as clams (e.g., heart, kidney, stomach, anus [yes, everything poops]), but also that there are a few differences (e.g., gills, siphon). Though they have an organ called a foot, clams cannot walk. However, the foot, which is a muscular like organ, does help them burrow into the sediment and sometimes avoid predators (watch this cool video https://www.youtube.com/watch?v=_KVFDfv6R2M).
A diagram of internal clam anatomy. Taken from here http://what-when-how.com/animal-life/class-bivalvia//, but I doubt that is the original source.
What I refer to as the “goop” is actually the organs of the clam, which are contained in the visceral mass. The adductor muscles actively close the shell. The foot helps the clam burrow into the seafloor. It is hard to see all of the organs if the clam is not prepped for dissection.
Both values of several individuals after the goop has been cleaned out. Note this toothbrush is used for lab purposes only.
Step two. What have we got? First a sidetrack. My master’s thesis at the University of Oklahoma dealt with phylogenetic (evolutionary) relationships of a group of trilobites (Moss and Westrop 2014). Determining phylogenetic relationships requires detailed taxonomic study so I spent an inordinate amount of time staring at and taking pictures of trilobites, and trying to reconcile minute differences to identify the species I was working with. One day, my advisor said to me “all you need to know for this project, you learned in kindergarten.” Of course, that is an oversimplification, but in some ways, he was right. At its most basic level, my project was one of those spot the differences activities they give children to keep them entertained at IHOP. Except I was not using crayons. Google image search trilobites real quick if you are not familiar with them and you will see that they are an incredibly diverse group with lots of different shapes and features. If you are doing taxonomic work on trilobites, you have a lot to work with. Now google image search clams. One of my Ph.D. committee members, Jim Brower, liked to refer to clams as amoeboid shaped objects. Honestly, it is not a bad description. After not doing any real taxonomic in my PhD work, I thought I was done with it. Life lesson, you never know when or how skills you have acquired will come in handy.
Taxonomy, the science of naming organisms, is an old discipline. Carl Linnaeus is the so-called “father of taxonomy” and the birth of taxonomy is usually credited to his Systema Naturae in 1735. With this publication, Linnaeus became one of the first scientists to consistently use a hierarchical system of classification in naming organisms. Most high school biology students are required to memorize Linnaeus’ classification, but I think most people forget shortly after. Kingdom, phylum, class, order, family, genus species. Linnaean taxonomy also gives a binomial nomenclature for naming organisms in which every organism is identified by a genus and species name. When written, these are always either italicized or underlined and the genus is always capitalized. When first encountered in a scientific publication an author is typically included in parentheses with the year it was first described. For example Haliaeetus leucocephalus (Linnaeus, 1766) is scientific name for the bald eagle. One more time just for fun. Kingdom, phylum, class, order, family, genus, species.
The genus Astarte was first named in the 1800s (Schumacher 1817) and now contains over 30 accepted species (www.marinespecies.org). Its’ taxonomy is rather complicated and there are many differing scientific opinions on species differences. The first few sentences of most papers I read included the world difficult. In the world of taxonomy, there are splitters and there are lumpers. Splitters like to create many species based on small variations, whereas lumpers tend to create fewer. Most Astarte workers appear to have been splitters as some of the differences between species are incredibly minute. Complicating the matter further, there can be a good deal of shape variation within a single population! I was hoping to get A. borealis from the VIMS cruises to compare to another study from the White Sea (Moss et al in prep). After losing much sleep, (though admittedly part of that was due to having an 11-month-old son) I determined that I got not only A. borealis, but also A. subaequilatera, and A. castena. This is exciting because it will allow me to establish a latitudinal gradient from NC to NY in lifespan and growth rate of three modern species of Astarte. I can then turn to a time in the fossil record when temperatures were much warmer and potentially understand what might happen to these (and other) clams as Earth continues to warm. But first, I need to cut, polish, image, and conduct isotopic analyses on these shells (for another post).
From left to right: Astarte subaequilatera, Astarte castena, and Astarte borealis.
The smell of science, however unpleasant, is only temporary. The goop has been properly disposed of and counters cleaned and disinfected. For a day, the paleo lab was lemon fresh. Now it is back to nitrile gloves and burnt plastic. Ooooh that smell.
Moss DK, Surge D, Khaitov V, Lifespan and growth of Astarte borealis (Bivalvia) from Kandalaksha Gulf, White Sea, Russia. To be submitted to Polar Biology (October, 2017).
Moss DK, Westrop SR (2014) Systematics of some Late Ordovician encrinurine trilobites from Laurentian North America. J Paleontol 88:1095–1119. doi: 10.1666/13-159
Schumacher C (1817) Essai d’un nouveau systeme des habitations des vers testaces. Copenhagen
On my homepage, I describe myself as a paleontologist, and while that is technically true via my training, I wear a few other “hats” as well. One of them is sclerochronology, which is “the study of periodic features in the skeletal portions of marine organisms” (Jones 1983). Huh?
Ok let’s back up a bit here. I am sitting in my office at UNC looking out the window (as I often do) at a very large Oak tree. UNC is the oldest public university in the United States. It was chartered in 1789 and began admitting students in 1795 (unc.edu). If you have never been, the campus is quite beautiful and fits almost perfectly the image of what some might call southern charm. Thanks to large expanses of red clay throughout the state, most of the buildings on campus are made from red bricks and many have large, white columns dawning their entries. The university has done a great job landscaping and has had the foresight to preserve as many trees as possible. Some of these trees are quite large, especially the one outside my window. I have not measured, but I’d guess it must be over 60 feet tall and the base of the trunk is at least 4 feet in diameter. So how old is this magnificent oak tree? Did it sprout during the colonial days of the university? How do we find the answer? Cut it in down! Why? Because, as you might already know, trees produce rings as they grow. Since the tree is alive, we could count up the number of rings and subtract that from the current year to determine its birthday. Ok, let’s fire up the chainsaw…wait, I think the university (and my wife) might have some reservations not only about losing this tree, but also my lumberjack skills.
http://web.utk.edu/~grissino/treering-gallery1.htm - go here to learn much more about dendrochronology and see some really neat images.
Believe it or not, there is an entire field of science dedicated to studying tree rings. It is called dendrochronology (Dendron=tree, chronos=time, logos=study of). The term sclerochronology is derived from the word dendrochronology. Instead of studying trees, sclerochronologists study the hard parts of marine organisms like corals, clams, and oysters. It turns out that like trees, these organisms produce growth increments (we use the term increment instead of ring) throughout their lifespans.
From (Buick and Ivany 2004). The long-lived (>100 years) fossil bivalve Cucullaea raea from Seymour Island, Antarctica. Cutting the shell in half reveals annual growth increments that are used to determine lifespan and growth rate. Each couplet of a light and dark increment represents on year of growth.
So what good are growth increments preserved in the shell of a clam? In other words, who cares? Well, it turns out that much like trees, the variations in increment widths and values of oxygen isotopes from the shell material (for a post at a later date) can tell us a lot about past temperatures. This is extremely useful because the longest continual instrumental temperature record “only” goes back to 1659 (https://www.metoffice.gov.uk/hadobs/hadcet/). Thankfully, clams and other marine organisms can help us extend climate records much deeper into the past. Because of its long lifespan, one of the most widely used clam species in sclerochronology is Arctica islandica (often called the ocean quahog or northern quahog). We have known for a few decades now that off the Atlantic coast of the United States individuals of A. islandica can live over 200 years. Think about that the next time you eat clam chowder! A 200 year old clam…now that rubbery texture makes sense! A group of scientists from Bangor University in the United Kingdom was well aware of this and decided to use A. islandica for climate studies in Iceland, where the species is also abundant. To their surprise, they found an individual that was 507 years old! Affectionately referred to as “Ming” (because it was alive during the Ming dynasty), the individual was at the time the record holder for maximum reported lifespan of any non-colonial animal (this honor may now go to a deep sea oyster Wisshak et al. (2009)). Unfortunately, Ming was alive when it was collected so the scientists accidentally killed the oldest animal on the planet. Oops! Their so-called “mistake” caught some negative attention from the media. However, because A. islandica grows extremely slow, it is very hard to distinguish between a 200 and a 500-year-old clam based on size and their mistake is forgivable. Never fear though, the statistics of maxima tell us that with more sampling, we would likely find an older individual.
“Ming” a 507 year-old clam found off the coast of Iceland (https://www.usatoday.com/story/tech/2013/11/15/newser-worlds-oldest-animal/3574863/)
I am a paleontologist. Why do I also wear a sclerochronology hat? My research interests lie in understanding how the so-called “pageant of life” has unfolded throughout Earth’s history. Typically, when we study evolution in the fossil record we look at changes in morphology (size and shape) over time. One way to bring about dramatic changes in morphology, is to change life history parameters such as growth rate and lifespan –though in most animals these are hard to measure. Clams were one of the earliest marine organisms with hard parts and have been on the planet for around 540 million years. We know a good deal about the lifespans and growth rates of modern clams, but almost nothing about those from the fossil record. This is a completely untapped field of research. Using sclerochronological techniques applied to modern and fossil clams some of the questions I hope to answer include: what controls lifespan (see Moss et al. (2016) and Moss et al. (2017)); what are the biological consequences of environmental change (my postdoc work at UNC); is lifespan a trait that passed from ancestor to descendant; what is the pattern of lifespans and growth rates in clams (and their relatives) across the Phanerozoic (540 million years ago until now).
Buick DP, Ivany LC (2004) 100 years in the dark: Extreme longevity of Eocene bivalves from Antarctica. Geology 32:921–924. doi: 10.1130/g20796.1
Jones DS (1983) Sclerochronology : Reading the record of the the Molluscan Shell: Annual growth increments in the shells of bivalve molluscs record marine climatic changes and reveal surprising longevity. Am Sci 71:384–391.
Moss DK, Ivany LC, Judd EJ, et al (2016) Lifespan, growth rate, and body size across latitude in marine bivalvia, with implications for Phanerozoic evolution. Proc R Soc B. doi: 10.1098/rspb.2016.1364
Moss DK, Ivany LC, Silver RB, et al (2017) High-latitude settings promote extreme longevity in fossil marine bivalves. Paleobiology 43:365–382. doi: 10.1017/pab.2017.5
Wisshak M, López Correa M, Gofas S, et al (2009) Shell architecture, element composition, and stable isotope signature of the giant deep-sea oyster Neopycnodonte zibrowii sp. n. from the NE Atlantic. Deep Res Part I Oceanogr Res Pap 56:374–407. doi: 10.1016/j.dsr.2008.10.002
David Moss. Paleontologist.
While most of my blog posts will relate to my research, from time to time I plan to write about something completely unrelated. I like to tell stories to communicate scientific ideas. Hopefully they will be entertaining as well as informative.