Relationship between Climate Change and Cannibalistic Gastropod Behavior

Indirect effects of climate change altered the cannibalistic behaviour of shell-drilling gastropods in Antarctica during the Eocene

Gregory P. Dietl, Judith Nagel-Myers, and Richard B. Aronson

Summarized by Joseph Ferreira. Joey is a senior at the University of South Florida in Tampa. Joey is pursuing his B. S in geology and is planning on finding a job either in the hydrology or seismology field. He has aspirations of owning his own business one day providing geo surveying services to companies in need of them. In his free time, Joey enjoys playing guitar and hanging out with his friends and family.

What data were used? The samples in this study included nearly 2,000 Naticidae Falsilunatia gastropod (snail) shells that were preserved well enough to show bore holes made from the cannibal snails. These samples were from a time frame in the Eocene that experienced mass cooling event. These samples came from 108 different localities in Seymour Island, Antarctica.

Methods: The prediction made during the start of this study suggested that the cooling temperatures would result in a decrease in the cannibalistic behaviors of these gastropods; meaning,  the colder temperatures would make it more difficult for the mollusk to maintain a productive activity level. To test their hypothesis, each drill hole found on the gastropods (complete or incomplete) was counted and the frequency of cannibalism was found by dividing the number of drilled samples by the total number of specimens in the group. The scientists looked at how frequent the drilled holes were in the specimens and also the body size of each specimen. They connected these specimens to a time either before, during, or after the known cooling event. They then looked to see if there were any significant changes in the frequency of these cannibalistic drill holes.

Figure showing Seymour Island in Antarctica (image A) where the study took place along with (image B) a sample with a perfectly drilled hole and a sample with an incomplete drill hole from another Falsilunatia gastropod. Image C shows one of the cannibalistic snails from multiple angles.

Results: When comparing the number of attacked specimens from before, during, and after the cooling event that occurred nearly 41 million years ago, the frequency of cannibalistic tendencies did not decrease or increase, but they remained stagnant. There was a very slight increase in frequency, but this increase was not statistically significant, meaning the increase was not big enough to cause concern or to blame the temperature change. This result came was a surprise because the way that these naticids drill holes into their prey’s shell involves a chemical reaction to dissolve the carbonate shell. The cooling temperatures were thought to slow down this chemical reaction hence slowing down the rates of cannibalistic tendencies between these creatures. However, this was not the case, the rates of cannibal attacks remained steady during the cooling event.

Why is this study important?  This study is important because it gives us a better understanding of how climate change can potentially affect species’ behaviors and tendencies. Even though the Falsilunatia’s cannibalistic behaviors were not affected by the cooling temperatures, it still shows some insight on how not all creatures are drastically affected by cooling events. Understanding the correlation between climate change and species behavior can help us gauge what we will expect to see in different animals’ behaviors as today’s climate change is in full effect.

The big picture: This study was set out to find the relationship between an Eocene cooling event and the cannibalistic behaviors of Falsilunatia gastropods. Although finding no direct effect from the cooling temperatures, this is still an excellent example of how we can use the behaviors of ancient creatures and their response to global climate alterations to predict how today’s animals will respond to more recent climate change.

Citation: Dietl G.P., Nagel-Myers J., Aronson R.B., 2018 Indirect effects of climate change altered the cannibalistic behaviour of shell-drilling gastropods in Antarctica during the Eocene: Royal Society Open Science, v. 5, 181446. http://dx.doi.org/10.1098/rsos.181446

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A fossil-rich rock formation at the Cretaceous-Paleogene Boundary in Mississippi, USA indicates environmental changes before mass extinction

A fossiliferous spherule-rich bed at the Cretaceous–Paleogene (K–Pg) boundary in Mississippi, USA: Implications for the K–Pg mass extinction event in the Mississippi Embayment and Eastern Gulf Coastal Plain

James D.Witts, Neil H.Landman, Matthew P. Garb, Caitlin Boas, Ekaterina Larina, Remy Rovelli, Lucy E. Edwards, Robert M.Sherrell, J. KirkCochran

Summarized by Mckenna Dyjak. Mckenna Dyjak, who is an environmental science major with a minor in geology at the University of South Florida. She plans to go to graduate school for coastal geology; once she earns her degree, she plans on becoming a research professor at a university. Mckenna spends her free time playing the piano and going to the gym.

What data were used? A fossil and spherule-rich rock formation in Union County, Mississippi exposed by construction. The formation contains the Cretaceous-Paleogene (K-Pg) boundary, which marks the end of the Cretaceous and the beginning of the Paleogene, estimated at ~66 million years ago. This boundary is characterized by a thin layer of sediment with high levels of iridium which is uncommon in Earth’s crust, because it is almost exclusively from extraterrestrial sources.  The K-Pg boundary is associated with a mass extinction: a significant, widespread increase in extinction (ending of a lineage) of multiple species over a short amount of geologic time. The iridium indicates that the extinction was likely caused by an extraterrestrial impact; the spherules found support this idea as well, as spherules are formed from ejecta after an impact. 

Stratigraphic (ordered) section of the rock formation showing the rock units, type of
sedimentology (sand, silt, clay), and fossil type. The K-Pg boundary is marked by the horizontal
dashed line. The black arrows point to calcareous nannofossils and the white arrows point to
dinoflagellate cysts.

Methods: The fossils present in the rock formation were identified and compiled into a complete list. In order to find out the composition of the rock formation. 14 sediment samples were collected; these samples were used to construct a biostratigraphic analysis: corresponding relative rock ages of different rock layers to the fossils found within them. The mineral composition and grain size were determined to construct this analysis. The mineral composition (mineral percentages present) of the sediment samples were determined by using a Scanning Electron Microscope (SEM) and a Diffractometer (type of X-ray). The grain size analysis of the sediment samples was determined by using a sieve (mesh strainer) to sort into different sizes. The Carbon-13 levels of the sediment samples were analyzed: Carbon-13 can be used to determine the amount of plants that were present at the time.The data collected was used to construct the stratigraphic section shown in the figure below.

Results: There was a significant decrease in the amount of micro and macro fossils present. Along with the decrease of fossils there was a positive shift of Carbon-13. The positive shift of Carbon-13 indicates that there was an increase in plant matter buried in the rock record. Sedimentary structures such as weak cross-bedding and laminations (indicates flowing water and fluctuating energy levels) An important layer was analyzed: 15–30 cm thick muddy, poorly sorted sand containing abundant spherules (sphere pieces) that were likely a product of  the Chicxulub impact event.

Why is this study important? The findings suggest that there was a quick, local change in sediment supply and possibly sea level due to the significant variation in facies (body of sediment), fossil changes, and different geochemical data that coincided with the extinction event. 

Big Picture: This study helps us understand how different areas were affected locally before the mass extinction event, which can help us understand how recovery from mass extinctions take place. 

Citation: Witts, James, et al. “A Fossiliferous Spherule-Rich Bed at the Cretaceous-Paleogene (K-Pg) Boundary in Mississippi, USA: Implications for the K-Pg Mass Extinction Event in the MS Embayment and Eastern Gulf Coastal Plain.” 2018, doi:10.31223/osf.io/qgaj

Recently excavated human skulls provide insight into human migration from Southeast Asia to Australia

Somewhere beyond the sea: Human cranial remains from the Lesser Sunda Islands (Alor Island, Indonesia) provide insights on Late Pleistocene peopling of Island Southeast Asia

Sofía C. Samper Carro, Felicity Gilbert, David Bulbeck, Sue O’Connor, Julien Louys, Nigel Spooner, Danielle Questiaux, Lee Arnold, Gilbert Price, Rachel Wood, Mahirta

Summarized by: Lisette E. Melendez. Lisette Melendez is a geology major and astronomy minor at The University of South Florida. She is currently a junior, but has her sights set on going to graduate school for planetary Geology. She loves rocks, space, and everything pink.

What data were used? Newly excavated human remains from three test pits in Tron Bon Lei
(Wallacean Islands, Indonesia) are being compared to human remains from Asia and Australia to test for similarities. Other elements that were found in the excavation include shellfish, fish remains, and fish hooks were used to characterize the living environment.

Methods: This study used dating of various elements and observation of skull traits to estimate ages of the cranial remains. The first element studied was the amount of carbon- 14 in the specimen because carbon-14 can date items up to approximately 50,000 years old. Uranium and Thorium are both elements that are preserved in fossilized teeth and those elements were also measured to reinforce the reliability of the age estimates from carbon. Physical traits of the skull fragments were analyzed to estimate the age and sex of the samples. Age estimation was based on how worn down the teeth were and degree of cranial suture closure (tissues that fuse together as you get older).

The human remains recovered from Tron Bon Lei (Wallacean Islands, Indonesia).

Results: The dating measurements of these Wallacean specimens suggest that the skeletons were buried around 11.5 to 13 thousand years ago, at the end of the Pleistocene Epoch. They are smaller than any of the other cranial remains from Indonesia, Australia, and New Guinea, but the small size of these remains are similar in size to Holocene- age remains, supporting the model that southeastern Indonesian populations were isolated.

Why is this study important? This study helps us unravel the environment of southeast Asia and understand living conditions thousands of years ago.

The big picture: This study shows that the Wallacean islands may be an example of island dwarfing, suggesting that these populations may have been relatively isolated, at least up to the late Pleistocene. Island dwarfing typically occurs when there is a scarce amount of resources on an island, which was only exacerbated by the genetic isolation that occurred on this island.

Citation: Samper Carro, S. C. et al. Somewhere beyond the sea: Human cranial remains from the LesserSunda Islands (Alor Island, Indonesia) provide insights on Late Pleistocene peopling of Island Southeast Asia. J. Hum. Evol. 134, 102638 (2019). Online.

Using glacial erratics to study nautiloids in eastern New York

Nautiloid cephalopods from the Rickard Hill facies of the Saugerties Member of the Schoharie Formation, eastern New York, USA (late Emsian, Devonian): A case study in taphonomy 

Martin A. Becker, Harry M. Maisch IV, Rebecca A. Chamberlain, John A. Chamberlain Jr., Christi G. Kline, and Clint F. Mautz

Summarized by Leighanne Haverlin. Leighanne Haverlin is a geology major at the University of South Florida. She will graduate in December of 2019 and plans to enter the workforce in the field of environmental consulting, coastal geology, or geophysics. After some time working, she hopes to further her education and earn a master’s of science in one of the fields previously mentioned. In her free time, she enjoys running, kayaking, and listening to music. 

What data were used? Glacial fragments containing Nautiloid cephalopods found in the Rickard Hill facies (RHf; facies refer to a certain group of rocks that share the same characteristics) of Lower New York and northern New Jersey were compared to outcrops from the Helderberg Mountains near Clarksville, New York. 

Methods: This study used petrographic thin sections (microscope analysis of the rock) along with hand samples to look at chemical and physical erosion to determine depositional environment (the environments in which rocks were formed in) and lifestyle of nautiloids, animals closely related to the octopus today. 129 specimens in glacial fragments from the RHf were examined. 

Results: By studying the nautiloid assemblages, the study determined that the depositional environment was an inner shelf reef. The glacial erratics (rock that is different than the surrounding rock where it lies) that were found in the Lower Hudson Valley of New York were similar to the rock found in the Helderberg Mountains of New York which are approximately 200 km to the north. The erratics contain nautiloid fossils with coiled and orthoconic (long and narrow) shapes. They were physically and chemically weathered when the Laurentide Ice Sheet, the major ice sheet that covered much of northern North American approximately 20,00 years ago) moved. The nautiloid fossils that were found were determined to be assembled after their death in an area that sustained living organisms. This deposition occurred during a sea level regression (a sea level drop). The RHf glacial fragments featured jointed bedding that is also present in the outcrop in Clarksville, NY. For 5,000 years, the nautiloids were eroded during the movement of the ice sheet and experienced dissolution (meaning they and the rock they were contained in began to dissolve over time) which exposed and preserved structures. The study determined that the depositional environment was an inner shelf reef that harvested great biodiversity (a high number of species of animals). To confirm this hypothesis, it was argued that it is uncommon for dead organisms (especially nautiloids) to drift very far distances after death because the shells would sink to the sea floor. It was determined that juvenile nautiloids lived in a different depositional environment than adults, which explains the large size of the nautiloids in the RHf. The nautiloids were continually buried and unburied due to storm events and sea level change. This same hypothesis was used to understand the fossil assemblages of the Wadleigh Formation in Alaska, the Cherry Valley Limestone in NY, and the Trebotov Chotec Limestone in the Czech Republic

Nautiloid casts from RHf glacial erratics. Both orthoconic (long and narrow) and coiled forms are depicted in the image.

Why is this study important? Prior to this study, no research had been conducted that explained the conditions that resulted in the large numbers and sizes of both coiled and long and narrow (orthoconic) nautiloid cephalopods. This study provided evidence that indicates that much of what we thought we understood of cephalopod ecology (where an animal lives and how it interacts with other animals) and preservation needs to be revised. This was also the first study that used glacial erratics and principles of sequence stratigraphy to address the lives of an assemblage of nautiloids which makes this study unique. 

The big picture: This study used a new method of using glacial erratics and principles of stratigraphy to determine the lifestyle of a species. Nautiloid adults and juveniles are not found in the same depositional environment. The glacial erratics that do not belong to the RHf show similar assemblages of nautiloids which can be analyzed using the same method. Overall, the study brought in a new method of studying taphonomy which could be used in future studies.   

Citation: Becker, M.A, Maisch, H.M., Chamberlain, R.A., Chamberlain, J.A., Kline, C.G. and Mautz, C.F.., 2018, Nautiloid cephalopods from the Rickard Hill facies of the Saugerties Member of the Schoharie Formation, eastern New York, USA (late Emsian, Devonian): A case study in taphonomy : Palaeontologia Electronica, 21.3.42. https://doi.org/10.26879/896

How much ice does Antarctica lose during warm times in Earth’s history?

Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials
David J. Wilson, Rachel A. Bertram, Emma F. Needham, Tina van de Flierdt, Kevin J. Welsh, Robert M. McKay, Anannya Mazumder, Christina R. Riesselman, Francisco J. Jiminez-Espejo, Carlota Escutia
Summarized by Time Scavengers collaborator Adriane Lam

Figure 1. An elevation map of Antarctica with a) the major regions labeled and b) a zoomed-in view of East Antarctica. The location of the sediment core (named U1361A) is denoted by the pale yellow dot. Image from Wilson et al. (2019).

Brief Summary: Today, sea level rise due to increasing global average temperatures is a huge threat to low-lying, coastal, and island communities. Sea level is rising, in part, from ice that is melting on Antarctica and Greenland. To understand how much sea level may rise in the near future, scientists look to the geologic past, when global temperatures were much warmer than today or close to the temperatures predicted for the coming decades. In this study, scientists looked at how much ice was lost from the Wilkes Subglacial Basin of East Antarctica during a time when global average temperatures were about 2 degrees Celsius warmer than pre-industrial values. They find that during these warmer periods, called interglacials, there was significant ice that melted from East Antarctica, and contributed to sea level rises. Thus, in the future, the ice melting from East Antarctica will contribute more to sea level rise than we previously thought.

Data used and Methods: Sediment from a deep-sea core drilled from the continental margin of East Antarctica was used in this study (Figure 1). From this sediment core, the authors analyzed the different types of sediment contained within the core through time. From the changes in sediments, the scientists could tell how much erosion was occurring. They also looked at the neodymium (Nd) isotopes from the sediments. Nd isotopes are a good way to also trace where the sediments in the core were coming from, so the scientists could determine not only how much erosion was taking place within East Antarctica, but where the eroded sediment was coming from. Increased erosion and a shift in the Nd isotope records indicate increased glacial melt and ice retreat on East Antarctica, thus the authors could tell through geologic time when and approximately how much the ice melted.

Results: Over the past 800,000 years, Earth’s climate has oscillated between cooler (glacial) and warmer (interglacial) periods (read more about this on our CO2 page). During some interglacial periods (times when the climate was warmer), the scientists found that the East Antarctic Ice Sheet began to erode the rock on which it sits and melted significantly. This led to increased sea levels within a world that was less warm than today.

Why is this study important? This study places new approximations on how much melting from East Antarctica could occur in a warming world, and how much that could raise sea level. Climate scientists think that if all the ice on East Antarctica were to melt, it would lead to approximately 53 meters of sea level rise globally! With the data from this study, it will provide new constraints on melting ice in a warming world, which will be incorporated into climate models of the future climate. This data will be given to policymakers to help us best prepare and mitigate the consequences of climate change.

Citation: Wilson, D. J., Bertram, R. A., Needham, E. F., van de Flierdt, T., Welsh, K. J., McKay, R. M., Mazumder, A., Riesselman, C. R., Jimenez-Espejo, F. J., and Escutia, C., 2019. Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials. Nature 561, 383-386.

 

Bone disease found in an early amniote from the Permian

Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote
Yara Haridy, Florian Witzmann, Patrick Asbach, Robert R. Reisz
Summarized by Time Scavenger collaborator Jen Bauer

Brief Summary: This study examined bone remodeling (how the bone fixes itself after disease or other events) in an amniote (animals such as birds, reptiles, and mammals) from the early Permian (289 million years ago). Through detailed measurements and 3D internal and external modeling of the bone the authors determined that this animal suffered from a metabolic bone disease similar to Paget’s disease in humans. This is the oldest evidence of  viral infection in the fossil record!

What data were used? The authors were exploring two fused (pathological or abnormal) and one normal vertebra. Vertebrae are the interlocking bones that make up your spinal column. They were able to identify both specimens as being caudal vertebraes (vertebrae of the tail area) of a varanopid animal. For comparison, the authors also examined several other non-pathological caudal vertebrae of a similar animal for comparison to this abnormal specimen. 

Varanopids are an extinct group of amniotes (animals that have a membrane around their embryos) that looked similar to extant (still alive) monitor lizards. The veranopids were alive from the late Carboniferous to the late Middle Permian (~300-260 million years ago). 

Figure 1. External feature of the diseased varanopid vertebrae (specimen number MB.R.5931). (a) Generalized diagram with normal vertebrae in blue and the pathological (diseased) vertebrae in orange. (b-f) different views of the specimen. Abbreviations: as, articular surface; fz, fusion zone; gn, growth nodule; hp, haemapophyses; irg, irregular groove; ivf, intervertebral foramen; na, neural arch; nc, neural canal; ntc, notochordal canal; poz, postzygapophysis fused; vph, ventral processes of haemapophyses. Refer to Figure 2 in paper as this is a direct capture but with a more technical caption. Scale bar = 5 mm.

Methods: Measurements of the specimens were done using ImageJ, a freely available imaging editing program that can be used for a variety of projects. The idea was to measure different thickness of the bones. There is bone repair due to the disease and the author’s were quantifying the difference in the diseased bone compared to the thicknesses of normal (non-diseased) bones. Specimens were also CT scanned at the Museum für Naturkunde Berlin and the models were visualized and analyzed in Volume Graphics Studio MAX 2.2. Computed Tomography (CT) allows for scientists to look inside the bones without cutting them into pieces, making it a non-destructive visualization technique. This is particularly helpful for looking at any internal bone structure and any possible abnormalities in the external or internal structure. 

Results: The pathological (diseased) specimen is two vertebral centra completely fused together, with no trace of a previous suture between the bones. The internal bone structure is slightly different. The notochordal canal (where the notochord resides) is uniform where there is some tapering the non-pathological specimens. The micro-CT scans reveal the outer cortex of the vertebrae has been dramatically altered through bone remodeling and growth causing features to be thickened and misshapen.

Why is this study important? The oldest recorded case of Paget disease of bone (PBD)-like alteration was in a Late Jurassic (~150 million years ago) vertebrate of a dinosaur, so this new find pushes the interpretation back to the Permian (~290 million years ago) – a shift of 140 million years back! The other major finding is about how this disease affects animals. Certain organisms are susceptible to certain diseases more than others. This bone disease has been found in primates (including humans), extant (living) dogs, lizards and snakes, and a dinosaur. The new finding in a varanopid furthers the spread across the tree of life, meaning that the disease must have evolved in early amniotes before the split between the split of synapsids (mammals) and diapsids (reptiles and birds). 

Evolutionary history of groups that have recorded evidence of the disease. Modified from figure 5 of the paper.

Citation: Haridy Y, Witzmann F, Asbach P, Reisz RR (2019) Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote. PLoS ONE 14(8): e0219662. https://doi.org/10.1371/journal.pone.0219662

New fossil from China changes much of what we know about early echinoderm evolution

A new stemmed echinoderm from the Furongian of China and the origin of Glyptocystitida (Blastozoa, Echinodermata)
S. Zamora, C.D. Sumrall, X-J. Zhu, and B. Lefebvre
Summarized by Time Scavengers contributor, Sarah Sheffield

What data were used? A single, beautifully preserved echinoderm (relatives of sea stars and sea urchins) fossil from South China, named Sanducystis sinensis. Rhombiferans are extinct types of echinoderms with diamond shaped plates.

Sanducystis sinensis, a new rhombiferan echinoderm fossil from China tells us a lot about the evolution of echinoderms from an important time in Earth’s history, the late Cambrian (~500-480 million years ago).

Methods: The new rhombiferan fossil was examined for all preserved features on its body; these features were ‘coded’ as characters for an evolutionary analysis. An example of a character: Does this have a stem? Yes=0; No=1. These characters were also used to code multiple other species of rhombiferan echinoderms. The reason for this was to figure out to what Sanducystis sinensis was most closely related. Computer programs, like PAUP*, take all of the characters coded and determine evolutionary relationships, based on the shared similarities between the species used in the analysis.

Results: Sanducystis sinensis falls within a large group of rhombiferan echinoderms called “Glyptocystitida” (similar to how humans are a large group of mammals). It’s an important find, as its place within the evolutionary tree of life is representative of a type of transitional fossil between a group of early rhombiferans that lack specialized breathing apparati and a group of more advanced, or derived, rhombiferans.

Why is this study important? This study paints a more complete story of how rhombiferans evolved through the Cambrian. It was not clear how the transition from rhombiferans without specialized breathing apparati gave rise to the more derived forms that we saw after the late Cambrian. This new find, Sanducystis sinensis, helps us to understand how that transition happened.

Big picture: Rocks from the late Cambrian (~500-480 million years ago) are very rare worldwide; this, of course, means that there are also very few fossils from this time as well. The late Cambrian is a very important time in Earth’s history, however, so finding fossils preserved from this time is critical towards understanding the evolution of life. Fossil finds, such as Sanducystis sinensis, have the potential to completely change what we currently know about how and when different groups of organisms on Earth evolved.

Citation: Zamora, S., Sumrall, C.D., Zhu, X-J., Lefebvre, B., 2016, A new stemmed echinoderm from the Furongian of China and the origin of Glyptocystitida (Blastozoa, Echinodermata): Geological Magazine, p. 1-11.

Microplastics Alter Plankton Poop

Microplastics alter feeding selectivity and faecal density in the copepod, Calanus helgolandicus

Rachel L. Coppock, Tamara S. Galloway, Matthew Cole, Elaine S. Fileman, Ana M. Queirós, & Penelope K. Lindeque

Summarized by Adriane Lam

The Problem: There is a growing body of research that shows that microplastics, tiny (1um-5 mm) pieces of plastics, have made their way into the deepest reaches of our oceans and are being ingested by marine life. Microplastics ingested by animals have been shown to cause adverse health effects to them, but as consumers of marine animals, these same microplastics are making their way into our diets. As yet, we do not know the exact ways in which microplastics can affect human health on longer time scales.

Zooplankton, which are small animals and protists that float in the water column and feed on primary-producing phytoplankton, are an important link between phytoplankton and other, larger animals. Zooplankton make up the base of the food chain, and are the main food source of marine mammals such as blue whales.

Different species of copepods.
Different species of copepods.

One type of zooplankton is especially common in our oceans today. Copepods are marine crustaceans that are found in nearly every freshwater and saltwater habitat. In addition to being an important food source, copepod poop is an important part of the biological pump. In other words, these animals’ poop transports atmospheric carbon dioxide (which is trapped in organic matter, or fixed carbon) to the seafloor, where it is stored in seafloor sediments.  The poop also provides important nutrients to other animals that live within or on top of these sediments. Copepods have been shown to ingest microplastics in the wild. The ingestion of microplastics by copepods may alter the way in which these animals select their food. And of course, if microplastics are being ingested, they are also being exported to the seafloor in fecal pellets. This study was designed to look at how microplastics alter how copepods choose their food and how the ingested plastic materials affect the sinking rate of copepod poop.

Methods: In this study, the scientists grew three species of microalgae (all that copepods like to feast on) in the lab and spiked it with different types of microplastics. The microplastics included things such as nylon, which is commonly found in clothing, especially active wear, and polyethylene, which is the most commonly-used plastic in the world (it is used to make shopping bags, shampoo bottles, and toys, to name a few uses).

The microalgae with microplastics was then fed to the copepods back in the lab, where the amount of microplastics ingested. The fecal pellets from the copepods were then collected and rinsed over a screen. To determine if microplastics contained in the poop affected the sinking rate of the pellets, the scientists dropped the pellets into cylinders filled with filtered seawater. They marked where the pellet was in the cylinder every 40 mm. To determine how different each pellet sank with microplastics, the scientists also measured the rate at which copepod poop without microplastics fell through the water column. When the poop reached the bottom of the cylinders, they were taken out and examined under a microscope. This way, the scientists could count the number of plastic pieces in each pellet.

Results: The scientists found that copepods preferentially liked to eat microplastics in a smaller size range (10-20 um), with a preference for the polyethylene over nylon fibers. When the copepods were exposed to microplastics, they preferentially did not eat as much algae. In addition, the copepods shifted their preference for one species of algae over others. Nylon fibers impeded ingestion of algae that was a similar size and shape to the microplastics. The scientists think the copepods associated algae of similar size and shape with microplastics, and thus avoided eating that algae species in an attempt to avoid plastic consumption.

Images of the contaminated copepod poop. Image a contains nylon fibers, image b contains polyethylene spheres, and image c contains polyethylene spheres.

The study confirmed that fecal pellets that contained both polyethylene and nylon particles were slower to sink through the water column. There was a difference in sinking rates between poop that contained more polyethylene, a denser microplastic, compared to nylon, a less dense material.

Why is this study important? This study is one of several that highlight the ways in which plastics are negatively affecting our food chain in the marine realm. The reduced sinking rate of fecal pellets may also affect the rate at which carbon dioxde, a major greenhouse gas, can be removed from the atmosphere through photosynthesizing algae who are then eaten by zooplankton. If fecal pellets are left to float for longer, there is also a higher potential of the microplastics being re-ingested by other zooplankton through coprophagy (ingestion of fecal pellets). On long and short timescales, the decreased export of poop and fixed carbon dioxide to the seafloor may have large consequences, as plastic within poop could keep more carbon from being exported and stored on the seafloor.

Citation: Coppock, R. L., Galloway, T. S., Cole, M., Fileman, E. S., Queirós, A. M., and Lindeque, P. K., 2019. Microplastics alter feeding selectivity and faecal density in the copepod, Calanus helgolandicus. Science of the Total Environment 687, 780-789. Online.

Amazon Tree Mortality

Figure 1. Examples of dead and alive trees monitored in the Central Amazon.

Amazonian rainforest tree mortality driven by climate and functional traits

Izabela Aleixo, Darren Norris, Lia Hemeric, Antenor Barbosa, Eduardo Prata, Flávia Costa, & Lourens Poorter

The Problem: Climate scientists are constantly learning and sharing new details about climate change and its possible effects in the future. However, many of the impacts of climate change have already surfaced and revealed the fragility of our ecosystems. Recently, scientists have observed increasing tree mortality in tropical forests, which are some of the most biodiverse and ecologically important places in the world. Could tree mortality be another consequence of climate change–one that’s happening right now? This study by Aleixo and others (2019) explores this possible connection between modern climate change and downfall of tropical forests.

What data were used? This study uses monthly climate and tree mortality records along with about 50 years of observational data in the Amazon rainforest. Climate data include precipitation, temperature, and humidity. Tree mortality data is categorized by specific traits such as wood density (soft or hard), successional position (when a species colonizes a new area), and leaf phenology (deciduous or evergreen).

Figure 2. a–d, Variation in tree mortality (a), precipitation (b), temperature (c) and humidity (d). When analysing the variation in mortality within years, we found that 19% of all deaths occurred in January (analysis of variance, d.f. = 11; P < 0.001). Interestingly, January is one of the wettest months of the year, suggesting that waterlogged soils and storms may enhance mortality. Monthly values (circles), averages (black lines) and 95% confidence intervals (dashed grey lines) over the study period (1965–2016) are shown.

Methods: Aleixo and others (2019) tracked global climate and tree mortality in an area of the Amazon rainforest monthly for one year. They looked for increased tree mortality that aligned with variations in the climate data. They also examined tree mortality of different species traits during significant climate events in the past 50 years. These events include climate anomalies like El Niño or La Niña (click here to learn more about these).

Results: This study found that Amazon tree mortality is driven by climate, but the relationship is complex. For example, droughts can lead to immediate or slow tree death, depending on the mechanisms at play. Additionally, if a tree has harder wood, it is less likely to die during a drought. Aleixo and others (2019) also found that weather events like low rainfall or high temperatures can either immediately enhance tree mortality or cause increased mortality up to two years later. Similar outcomes are associated with years where El Niño or La Niña are particularly extreme. Various species traits may protect trees from dying under certain weather or climate events, but no single Amazon species is completely safe from the effects of climate change.

Why is this study important? As our climate continues to change and weather events become more extreme, the future of our forests remains uncertain. Even the most biodiverse and ecologically robust regions in the world are susceptible to the effects of climate change. This study provides a modern framework for us to understand those effects. From this, scientists can refine dynamic global vegetation models that predict how forests will respond to climate variability in the future.

Citation: Aleixo, I., D. Norris, L. Hemerik, A. Barbosa, E. Prata, F. Costa, and L. Poorter (2019), Amazonian rainforest tree mortality driven by climate and functional traits, Nature Climate Change, 9(5), 384-388, doi:10.1038/s41558-019-0458-0.

Figure 3. Comparisons of the ratios of annual mortality for different functional groups of species, calculated using two classes of wood density (that is, the mortality of soft-wooded species (0.30–0.69 g cm−3) divided by the mortality of hard-wooded species (0.70–1.10 g cm−3)), successional position (that is, the mortality of pioneer species divided by the mortality of late species) and deciduousness (that is, the mortality of evergreen species divided by the mortality of deciduous species) over 52 years and during 5 years of highest peak mortality (the 1982, 1992 and 2016 El Niño droughts, the 1999 La Niña wet year and the 2005 NAO drought). The black line shows where the ratio is equal to 1 (that is, the mortality rate of the two classes is the same). The results of a Pearson’s chi-squared test are shown. Asterisks indicate a significant result (P ≤ 0.05). Annual mortality rates were higher for pioneers compared with late-successional species, for soft compared with hardwood species, and for evergreen compared with deciduous species. When the mortality rates of the functional groups were compared between normal and extreme years, pioneers experienced much higher mortality rates than climax species in the two El Niño and La Niña years. Soft-wooded species experienced much higher mortality rates than hard-wooded species in the El Niño 1982 year. Evergreens experienced much higher mortality rates than deciduous species in the NAO year.

New Evolutionary Understanding of Horseshoe Crabs

A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error
Jesús A. Ballesteros and Prashant P. Sharma
Summarized by Maggie Limbeck

What data were used? Data were collected from whole genome sequence projects and RNA sequence libraries for all 53 organisms included in this study. Because there are four living species of horseshoe crabs and many living representatives of arachnids (spiders, scorpions, ticks) genetic data was able to be used as opposed to morphologic (shape and form) data. Organisms from Pancrustacea (crabs, lobsters, etc.) and Myriapoda (centipedes and millipedes) were used as outgroup organisms, organisms that are included in the analysis because they are part of the larger group that all of these animals fit into (Arthropoda) but have been determined to not be closely related to the organisms that they cared about in this study.

Methods: Several different methods were used in this study to estimate the evolutionary relationships between horseshoe crabs and arachnids. By using multiple different phylogenetic methods (different calculations and models to estimate relationships between organisms) these researchers had several different results to compare and determine what relationships always showed up in the analyses. In addition to all of these different methods that were used, two different scenarios were tested in each method. The researchers wanted to be able to run their data and see what results they got, but also test the existing hypothesis that horseshoe crabs are sister taxa to land-based arachnids.

One of the trees that was reported from one of the many phylogenetic analyses that were completed using this data set. The orange color represents the horseshoe crabs in this study and you can see that the orange is surrounded by green branches which represent arachnids. The boxes that are present on the branches of the trees are representative of different analyses and data sets that were used to return this particular tree and support that these relationships have in other analyses that were run. The stars on the tree show relationships that were well supported in all analyses.
Results: The vast majority of the phylogenetic trees that were produced in these different analyses showed that horseshoe crabs are “nested” or included in the group Arachnida and are sister taxa to Ricinulei (hooded tick spiders). The only analyses that returned results different from this, were those that were forced to keep horseshoe crabs as sister taxa to the land-based arachnids, but those trees had very low statistical support of being accurate.

Why is this study important? This study is particularly cool because it highlights interesting problems associated with using genetic data versus morphologic data and problems with understanding evolution in groups that diversified quickly. Chelicerates (the group of Arthropods that have pincers like spiders, scorpions, horseshoe crabs) diversified quickly, live in both aquatic and terrestrial settings, and have many features like venom, that all appeared in a short time frame geologically. By gaining a better understanding of the relationships between the members of Chelicerata and Arachnida researchers can start to look at the rates at which these features developed and the timing of becoming a largely land-based group. This is also an important study because it has demonstrated that relationships we thought were true for horseshoe crabs and arachnids for a long time may not actually be the case.

The big picture: The research done in this study really highlights the major differences in relationships that can be demonstrated depending on whether you are using morphological data or genetic data. This study found that by using genetic data for 53 different, but related organisms, that horseshoe crabs belong within the group Arachnida rather than a sister taxa to the group. It’s also really cool that this study was able to demonstrate evolutionary relationships that are contrary to what have long been believed to be true.

Citation:
Jesús A Ballesteros, Prashant P Sharma; A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error, Systematic Biology, syz011, https://doi.org/10.1093/sysbio/syz011