It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Saturday, February 20, 2021
A study with 1,600 dogs: More than 20 gene loci associated with canine hip dysplasia
Hip dysplasia is a developmental disorder common in most dog breeds, and its onset is affected by both hereditary and environmental factors.
Prior studies have identified dozens of genetic loci associated with hip dysplasia in various breeds. The relevance of the loci to disease susceptibility remains an open question. The previously identified loci were reinvestigated at the University of Helsinki, Finland, using a large independent cohort of 1,600 dogs representing ten breeds.
The individual genetic variants at the target loci were determined from blood samples. The standardized radiographic hip phenotypes as assessed by expert veterinarians were obtained from the Finnish Kennel Club.
"Key to the study was the opportunity to utilize the world's largest canine DNA bank maintained by Professor Hannes Lohi's research group. We validated the disease association of 21 loci from 14 chromosomes," says Professor Antti Iivanainen from Faculty of Veterinary Medicine, University of Helsinki, and continues: "Genes related to a protein modification process known as neddylation were overrepresented among the genes residing in the validated loci. This was an interesting new find."
Lea Mikkola, PhD, who wrote her doctoral thesis on the topic at the University of Helsinki, emphasizes that, genetically, hip dysplasia is a highly complex disease.
"A multitude of genes affect the development of the disease. There are marked differences in the genetic background of the disease between breeds, even if certain gene loci associated with it are the same."
In the future, the researchers want to pay closer attention to the loci now identified as relevant to uncover the actual genes underlying hip dysplasia and their variants.
"The findings do not boost disease diagnostics or dog breeding as such, but they can likely be used as part of broader risk profiles in the future. The identified loci also contain new candidate genes associated with hereditary hip dysplasia in humans, which may eventually improve humans' care. More hip dysplasia studies should be conducted, through increased international collaboration, with different dog breeds," notes Professor Hannes Lohi from the Faculty of Veterinary Medicine and the Faculty of Medicine.
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New piece of the puzzle increases understanding of speciation
Speciation is important because it increases biodiversity. A thesis from the University of Gothenburg examines the speciation process in multiple marine species where different populations of the same species might evolve into two completely new species.
When two populations of a species become isolated, their genes no longer intermix and over time, the two populations become increasingly different from each other. What is known as a reproduction barrier has then been formed because the two different populations no longer mate with each other even if they would meet again.
For a long time, researchers proposed that new species could be formed only if two populations were separated by a physical barrier over a very long period of time, for hundreds of thousands of generations or more.
New species can form without physical isolation
Today, there are many examples of species being formed without isolation, such as during ongoing genetic exchange. This exchange should prevent two populations to become different and so, understanding how reproductive barriers can still develop is an intriguing question for speciation researchers.
Samuel Perini, researcher at the Department of Marine Sciences and author of the new thesis, has studied what happens in species with populations that are genetically different and meet at a contact zone, a boundary area between the two populations.
"I have investigated reproductive barriers that exist between two different forms of Littorina saxatilis, an intertidal marine snail, and I have analyzed data on reproductive barriers found in several marine species around the mouth of the Baltic Sea," says Perini.
Surrounding marine environment plays a role
In a review of reproductive barriers in 23 different species, including cod, herring and plaice, Samuel Perini found large genetic differences between the Baltic Sea populations and the North Sea populations.
"These differences are maintained partly because the populations survive differently in different salinities and partly because their reproduction is separated in time or space, or both."
For the Littorina saxatilis snail, which is common in the Atlantic along the coasts of both Europe and North America, two different populations or ecotypes have formed under ongoing genetic exchange, according to previous research. One population is known as the "Crab" ecotype and the other population is known as the "Wave" ecotype.
Crab snails live in and are adapted to portions of the rocky shore with large stones and crabs, while Wave snails live on portions of the rocky shore with rock slabs exposed to waves. Crab snails and Wave snails meet at the boundary of these two habitats but genetic and phenotypic differences are still maintained between the two populations. Adaptations to the Crab and Wave habitat is strongly driven by natural selection and survival in the non-native environment is low. Hence, natural selection reduces genetic exchange between Crab and Wave snail populations because it decreases the opportunity for a Crab snail to survive and reproduce in the Wave habitat with a Wave snail of the opposite sex (and vice versa).
Size matters
The size of the intertidal marine snail is important for adaptation to the different environments. Large snails are selected for in environments where there are crabs, and small snails are favoured in environments exposed to waves.
"My studies show that the size of intertidal marine snails is important not only for survival but also for mating. I show in my thesis that mating is more common between snails of similar sizes and that small males have more matings. Both of these factors help to counteract gene exchange between the large Crab snails and the smaller Wave snails when they meet both inside and outside the contact zones."
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Contact:
Samuel Perini, Department of Marine Sciences, University of Gothenburg +46 (0)31-786 20 47, +46 (0)766-18 20 47, samuel.perini@gu.se
The dissertation's title: Reproductive isolation at contact zones
After describing a unique behaviour in the Small-banded Kukri Snake (Oligodon fasciolatus) last September, two new studies, also led by Henrik Bringsøe, are now reporting the same gruesome feeding strategy in another two species: the Taiwanese Kukri Snake (Oligodon formosanus) and the Ocellated Kukri Snake (Oligodon ocellatus). In their research across Asia, the scientists also observed and contemplated other rare behaviours in kukri snakes.
CAPTION
An Ocellated Kukri Snake (Vietnam) first pierced this poisonous Asian common toad and buried its head deeply into the abdomen of the amphibian, as it was probably eating the organs. However, as seen in the photo, the kukri snake proceeded to swallow the toad whole.
CREDIT
James Holden
The closely related three species of snakes within the genus Oligodon have evolved an unusual behaviour where they pierce the abdomens of the amphibians, tear off their organs and swallow them one by one, keeping the prey alive for up to a few hours. Given that these species have also been recorded to feed in a more typical way: by swallowing their prey whole, the scientists find it likely that the alternative strategy has evolved specifically in their species group, in order to be able to eat larger animals. The latest findings are also published in the peer-reviewed, open-access scholarly journal Herpetozoa.
One of the new studies reports about two instances from Hong Kong, where Taiwanese Kukri Snakes were observed to disembowel Painted Burrowing Frogs (Kaloula pulchra). In one of the cases, the snake had cut open the belly of the frog and inserted its head into the frog's abdomen. Further, the reptile was seen to repeatedly rotate its body longitudinally in a "performance" also known as "death rolls". In the other case, reported in the study, the organs of the frog had been forced out of its abdomen. The researchers also provide video recordings of these unique behaviours.
"We believe that the purpose of these death rolls was to tear out organs to be subsequently swallowed," comments Bringsøe.
Meanwhile, the study mentions a new observation of one of the studied snake species (the Small-banded Kukri Snake, Oligodon fasciolatus), however preferring to swallow its Painted Burrowing Frog whole, after doing the same "death rolls", which led the scientists to think that it is the size of the prey that determines how exactly the snake would go about its dinner. The researchers also add that in both cases, the snake would eventually swallow its prey's remains.
The second newly published research paper studies a third species: the Ocellated Kukri Snake, which was observed to eat the toxic Asian Black-spotted Toad (Duttaphrynus melanostictus) in Vietnam. Initially, the snake was seen to have buried its large head eyes-deep into the amphibian's abdomen. Eventually, though, the snake swallowed the toad whole despite its toxicity, providing further evidence that kukri snakes are in fact resistant to the cardiac glycoside toxins of the toads.
"We hope that future observations may uncover additional aspects of the fascinating feeding habits of kukri snakes though we may indeed call them gruesome!" says Bringsøe.
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Research papers:
Bringsøe H, Suthanthangjai M, Suthanthangjai W, Lodder J, Komanasin N (2021) Gruesome twosome kukri rippers: Oligodon formosanus (Günther, 1872) and O. fasciolatus (Günther, 1864) eat Kaloula pulchra Gray, 1831 either by eviscerating or swallowing whole. Herpetozoa 34: 49-55. https://doi.org/10.3897/herpetozoa.34.e62688
Bringsøe H, Holden J (2021) Yet another kukri snake piercing an anuran abdomen: Oligodon ocellatus (Morice, 1875) eats Duttaphrynus melanostictus (Schneider, 1799) in Vietnam. Herpetozoa 34: 57-59. https://doi.org/10.3897/herpetozoa.34.e62689
VIDEO
CAPTION
A Taiwanese Kukri Snake with its head buried deep into the abdomen of a Painted Burrowing Frog. During the initial immobility of both individuals, the frog moves its long fourth toe of the left hind foot up and down 21 times. During the subsequent active struggle, the snake makes three rotations ("death rolls"), first two counterclockwise, then one clockwise.
CREDIT
Jonathan Rotbart
CAPTION
A Taiwanese Kukri Snake has cut open the abdomen of a Painted Burrowing Frog and has extracted several organs which it is biting and chewing. The video shows the snake in the process of swallowing. The observation took place in Hong Kong.
CREDIT
Vince Natteri
New revelations of tiger genomes
Tiger genomes reveal signatures of population bottlenecks, recent divergence between subspecies, local adaptation, and ongoing impacts of fragmentation
Genetic variation is like money in the bank: the more you have, the better your chances of survival in the future. Population bottlenecks decrease genetic variation, especially in endangered species. An individual's genome comprises the events that have impacted genetic variation over time, and relatively recent sequencing technologies allow us to read and interpret genetic variation across the genome. Although tigers have received significant conservation attention, little is known about their evolutionary history and genomic variation. This is especially true for Indian tigers, and with 70% of the world's tigers living in India, such understanding is critical to tiger conservation.
A team of researchers from the National Centre for Biological Sciences (NCBS), Stanford University, and zoological parks and NGOs across the world recently completed a three-year project to gain insights into genomic variation in tigers and the processes that have sculpted it. The work, just published in Molecular Biology and Evolution, reiterates that tiger subspecies are genetically distinct and reveals that although Indian tigers have the highest total genetic variation, some individuals are inbred. Simulations based on the genomic data suggest relatively recent divergences between subspecies, and intense population bottlenecks. Analyses also indicate adaptation to cold environments in Russian far east tigers, and potential selection on body size in Sumatran tigers.
The team sequenced whole genomes from 65 individual tigers from four subspecies, with a specific aim to enhance genomes from wild tigers in different habitats in India. They used these data to conduct a variety of population genomic analyses that quantify genetic variability, and investigate the partitioning of genetic variation, possible impacts of inbreeding and founder events, demographic history (including population divergence) and possible signatures of local adaptation.
They found that total genomic variation in Indian tigers was higher than in other subspecies. However, several individual tigers in India had low variation, suggesting possible inbreeding and founding bottlenecks. Tigers from northeast India were the most divergent/different from other populations in India. "Given our results, it is important to understand why some Bengal tigers appear inbred and what the consequences of this are," says Anubhab Khan, co-first author, NCBS.
The history of tiger populations from across their current range shows recent divergences between tiger subspecies, within the last 20,000 years, which is concordant with a transition from glacial to interglacial climate change and increasing human impacts across Asia. These findings are in sharp contrast to an earlier study by ShuJin Luo and others in 2018 that suggested much older divergence times. The recent divergence between populations will need to be investigated further with expanded datasets and analyses of more tiger genomes.
The data and analyses also suggest strong bottlenecks in all tiger populations, highlighting the importance of population size decline on the erosion of genetic variation. "Most studies focusing on species of conservation concern use limited numbers of specimens to try to gain understanding into how genomic variation is partitioned. It is clear from our work here, and a growing number of other studies, that it is crucial to increase our sampling efforts and use caution when interpreting results from limited sample sizes," comments Ellie Armstrong, co-first and co-corresponding author, Stanford University.
Genomes of tigers in the Russian far east suggest adaptation to the cold, while those of Sumatran tigers suggest selection based on body size. Co-senior author Elizabeth Hadly of Stanford University says, "The tiger is an excellent example of the myriad historic events that sculpt species' genomic diversity and points to the importance of understanding this diversity as we attempt to stave off extinction of our most precious species on Earth. While some populations demonstrate the importance of adaptation to local conditions, other evidence suggests that particular populations may suffer the effects of climatic change in the Anthropocene." Such information will be critical to the success of genetic rescue efforts, which should take local adaptation into consideration.
'I have worked on Indian tiger genetic variation for over a decade and always wondered how they compared to other wild tigers. Our study reveals that while the total variation in Indian tiger genomes is high, they have also been dramatically shaped by population bottlenecks. The genomic variation of Indian tigers continues to be shaped by the ongoing loss of connectivity. Population management and conservation action must incorporate information on genetic variation. I hope doing so will help India maintain the gains in tiger conservation achieved so far,' says Uma Ramakrishnan, co-senior and co-corresponding author, NCBS.
Despite being one of the world's most charismatic species, tigers face uncertain futures primarily due to habitat fragmentation, human-wildlife conflict and poaching. As global tiger populations decline, so does their genetic diversity. But until now it's been unclear how the animals' dwindling numbers are affecting them at the genetic level.
To find out, researchers at Stanford University, the National Centre for Biological Sciences, India, and various zoological parks and NGOs sequenced 65 genomes from four of the surviving tiger subspecies. Their findings confirmed that strong genetic differences exist between different tiger subspecies but showed, surprisingly, that these differences emerged relatively recently, as Earth underwent a major climatic shift and our own species grew increasingly dominant.
The research, detailed in a new paper published this week in the journal Molecular Biology and Evolution, shows how genomics can help guide conservation efforts toward wild tigers and other species, said study co-leader Elizabeth Hadly, the Paul S. and Billie Achilles Professor in Environmental Biology in the School of Humanities and Sciences.
"The increasing dominance of humans across the world means that our understanding of which attributes of species and populations are best suited to the Anthropocene becomes ever more important," said Hadly, referring to the proposed geological epoch marked by significant human impact on the environment.
"Some populations are well adapted to a future dominated by humans and our new climates and others are not, so any type of management of species should be informed by what we can glean from their genomes," added Hadly, who is also a senior fellow at the Stanford Woods Institute for the Environment. "Conservation genomics is far from a perfect science, but this tiger study hints at the power of adequate sampling across both the species range and its genome."
The study reveals that the world's existing tiger subspecies began exhibiting signs of dramatic and recent contractions starting only around 20,000 years ago - a period that coincided with both the global transition out of the Pleistocene Ice Age and the rise of human dominance in Asia. Each subspecies of tiger the team studied showed unique genomic signatures as a consequence of their increasing isolation from one another.
For example, local environmental genomic adaptation to cold temperatures was found in the Siberian (or Amur) tigers, the northernmost tigers found in the Russian Far East. These adaptations were absent in the other tiger subpopulations studied. Tigers from Sumatra, meanwhile, showed evidence of adaptations for body size regulation, which could help explain their overall smaller size. Despite these adaptations, tigers from these populations have low genetic diversity, suggesting that if populations continue to decline, genetic rescue may need to be considered.
One form that rescue might take is through the mating of different tiger subspecies together as a way of increasing their genetic diversity and protecting against the ill effects of inbreeding. Inbreeding occurs when populations are so small and isolated from other populations that related individuals breed with each other. Over time, this leads to lower genomic diversity and to the emergence of recessive diseases, physical deformities and fertility problems that often result in behavioral, health and population declines. Although increasing genetic diversity is one goal, another might be to select for inherited traits that confer higher survival in a changing world.
Even Bengal tigers from India, which comprise about 70 percent of the world's wild tigers and exhibit relatively high genomic diversity compared to other subspecies, showed signs of inbreeding in some populations, the study concluded.
"Some Bengal tiger populations are essentially small islands surrounded by an inhospitable sea of humanity. These tigers cannot disperse and so have only their close relatives to choose as mates," Hadly said.
While many studies investigating endangered species using genomics sequences from a single or just a few individuals, this work reiterates that individuals are not likely to be representative of a population or species status. Further work investigating the consequences of potential inbreeding and diversity declines across the subspecies are needed.
"As genomics has become available to conservation, it is apparent that collaborative studies to investigate the diversity within species are critical," said study first author Ellie Armstrong, a Stanford PhD student in Hadly's lab. "Inferences made from single genomes, while excellent additions to our knowledge of diversity in general, cannot be extrapolated to entire species, especially when using captive animals to infer adaptation to complex habitat change."
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Other Stanford co-authors on the study, titled "Recent Evolutionary History of Tigers Highlights Contrasting Roles of Genetic Drift and Selection," include former postdoctoral scholars Ryan Taylor and Stefan Prost; PhD students Jonathan Kang and Sergio Redondo; Gregory Barsh, professor of genetics and pediatrics, emeritus; Dmitri Petrov, professor of biology; and Christopher Kaelin, staff geneticist.
Magnetic attraction: Breakthrough test for malaria
After nearly a decade of research, a new test that detects the magnetic properties of malaria-infected blood could soon be used to help eliminate the mosquito-borne disease.
Dr Stephan Karl, a Senior Research Fellow in Malaria and Vector Biology at James Cook University's Australian Institute of Tropical Health and Medicine, has led an international study to field-test a new tool in the fight to eliminate the disease, which had 229 million reported cases in 2019.
"Malaria is easily treated but it is actually hard to diagnose, and because of that there can be over-treatment, which we have seen can lead to the spread of drug-resistant malaria," Dr Karl said.
"Improving malaria diagnosis, especially through the development of practical methods for resource-limited places, is important and timely."
The international team including the University of Augsburg's Professor Istvan Kezsmarki, with the PNG Institute of Medical Research and the Burnet Institute, developed and tested the method called rotating-crystal magneto-optical detection (RMOD).
Dr Karl said malaria parasites break down blood in such a way that heme molecules in the blood assemble themselves into organic crystallites containing magnetic iron, which is detected by the RMOD method.
"I've studied the magnetic properties of malaria infected blood since 2006, and we engaged with Professor Kezsmarki's team in 2013 to demonstrate the sensitivity of this test using human malaria parasites," Dr Karl said.
Professor Kezsmarki said the success of the field study, which involved nearly 1000 suspected malaria patients in a high-transmission area of Papua New Guinea, was an exciting breakthrough.
"After years of in-lab optimisation of the device, in collaboration with Dr Karl we demonstrated the great potential of RMOD in fast and reliable malaria field tests performed in Papua New-Guinea," Prof Kezsmarki said.
"We showed that RMOD performs well in comparison to the most reliable existing method," he said.
"It's very promising, as RMOD testing can be conducted after a short training session and provides test results within 10 minutes. From a funding perspective the cost is very low since no expensive reagents are used," said Dr Karl.
He said the team aimed to refine the prototype device so that, eventually, performing a test would be as simple as pushing a button.
"There are other hurdles to overcome too, at the moment the RMOD has difficulty discriminating between current and previous malaria infections and we are working on a solution for this," said Dr Karl.
Cone snail venom shows potential for treating severe malaria
Study finds anti-adhesion drugs may hold the key to treating malaria, COVID-19, aids and other emerging diseases
Severe forms of malaria such as Plasmodium falciparum may be deadly even after treatment with current parasite-killing drugs. This is due to persistent cyto-adhesion of infected erythrocytes even though existing parasites within the red blood cells are dead. As vaccines for malaria have proved less than moderately effective, and to treat these severe cases of P. falciparum malaria, new avenues are urgently needed. Latest estimates indicate that more than 500 million cases of malaria and more than 400,000 deaths are reported worldwide each year. Anti-adhesion drugs may hold the key to significantly improving survival rates.
suggests that these conotoxins could potentially treat malaria. The study provides important leads toward the development of novel and cost-effective anti-adhesion or blockade-therapy pharmaceuticals aimed at counteracting the pathology of severe malaria.
Results, published in the Journal of Proteomics, expand the pharmacological reach of conotoxins/ conopeptides by revealing their ability to disrupt protein-protein and protein-polysaccharide interactions that directly contribute to the disease. Similarly, mitigation of emerging diseases like AIDS and COVID-19 also could benefit from conotoxins as potential inhibitors of protein-protein interactions as treatment. Venom peptides from cone snails has the potential to treat countless diseases using blockage therapies.
"Molecular stability, small size, solubility, intravenous delivery, and no immunogenic response make conotoxins excellent blockade-therapy candidates," said Andrew V. Oleinikov, Ph.D., corresponding author and a professor of biomedical science, FAU's Schmidt College of Medicine. "Conotoxins have been vigorously studied for decades as molecular probes and drug leads targeting the central nervous systems. They also should be explored for novel applications aimed to thwart amiss cellular responses or foil host parasite interactions through their binding with endogenous and exogenous proteins. Further investigation is likely to yield breakthroughs in fields continuously toiling for more efficient therapeutic approaches such as cancer, autoimmune diseases, novel emerging viral diseases as well as malaria where venom-based peptidic natural products can be put into practice."
The disruption of protein-protein interactions by conotoxins is an extension of their well known inhibitory action in many ion channels and receptors. Disabling prey by specifically modulating their central nervous system is a ruling principle in the mode of action of venoms.
CAPTION
Conus nux, a species of sea snail
CREDIT
Fred Pflueger, Ph.D.
"Among the more than 850 species of cone snails there are hundreds of thousands of diverse venom exopeptides that have been selected throughout several million years of evolution to capture their prey and deter predators," said Frank Marí, Ph.D., corresponding author and senior advisor for biochemical sciences at the National Institute of Standards and Technology. "They do so by targeting several surface proteins present in target excitable cells. This immense biomolecular library of conopeptides can be explored for potential use as therapeutic leads against persistent and emerging diseases affecting non-excitable systems."
For the study, researchers used high-throughput assays to study Conus nux collected off the Pacific coast of Costa Rica. They revealed the in vitro capacity of cone snail venom to disrupt protein-protein and protein-polysaccharide interactions that directly contribute to pathology of P. falciparum malaria. They determined that six fractions from the venom inhibit the adhesion of recombinant P. falciparum erythrocyte membrane protein 1 (PfEMP-1) domains to their corresponding receptors, which express on the endothelial microvasculature and the placenta.
The results are noteworthy as each of these six venom fractions, which contain a mostly single or a very limited set of peptides, affected binding of domains with different receptor specificity to their corresponding receptors, which are proteins (CD36 and ICAM-1), and polysaccharide. This activity profile suggests that the peptides in these conotoxin fractions either bind to common structural elements in the different PfEMP1 domains, or that a few different peptides in the fraction may interact efficiently (concentration of each is lower proportionally to the complexity) with different domains.
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Study co-authors are Alberto Padilla, Ph.D., first author and a former graduate student, FAU's Schmidt College of Medicine; Sanaz Dovell, Ph.D., a former student in FAU's Charles E. Schmidt College of Science; Olga Chesnokov, Ph.D., research associate, FAU's Schmidt College of Medicine; aand Mickelene Hoggard, Ph.D., Chemical Sciences Division, National Institute of Standards and Technology.
This research is supported in part by the National Institute of Allergy and Infectious Diseases (grants R21A137721 and R01AI092120) awarded to Oleinikov.
About the Charles E. Schmidt College of Medicine:
FAU's Charles E. Schmidt College of Medicine is one of approximately 155 accredited medical schools in the U.S. The college was launched in 2010, when the Florida Board of Governors made a landmark decision authorizing FAU to award the M.D. degree. After receiving approval from the Florida legislature and the governor, it became the 134th allopathic medical school in North America. With more than 70 full and part-time faculty and more than 1,300 affiliate faculty, the college matriculates 64 medical students each year and has been nationally recognized for its innovative curriculum. To further FAU's commitment to increase much needed medical residency positions in Palm Beach County and to ensure that the region will continue to have an adequate and well-trained physician workforce, the FAU Charles E. Schmidt College of Medicine Consortium for Graduate Medical Education (GME) was formed in fall 2011 with five leading hospitals in Palm Beach County. The Consortium currently has five Accreditation Council for Graduate Medical Education (ACGME) accredited residencies including internal medicine, surgery, emergency medicine, psychiatry, and neurology.
About Florida Atlantic University:
Florida Atlantic University, established in 1961, officially opened its doors in 1964 as the fifth public university in Florida. Today, the University serves more than 30,000 undergraduate and graduate students across six campuses located along the southeast Florida coast. In recent years, the University has doubled its research expenditures and outpaced its peers in student achievement rates. Through the coexistence of access and excellence, FAU embodies an innovative model where traditional achievement gaps vanish. FAU is designated a Hispanic-serving institution, ranked as a top public university by U.S. News & World Report and a High Research Activity institution by the Carnegie Foundation for the Advancement of Teaching. For more information, visit http://www.fau.edu.
New UCF study examines leeches for role in major disease of sea turtles in Florida
The disease fibropapillomatosis causes sea turtles to develop tumors on their bodies, which can limit their health and mobility
ORLANDO, Feb. 18, 2021 - University of Central Florida researchers are homing in on the cause of a major disease of sea turtles, with some of their latest findings implicating saltwater leeches as a possible factor.
The disease, known as fibropapillomatosis, or FP, causes sea turtles to develop tumors on their bodies, which can limit their mobility and also their health by interfering with their ability to catch and eat prey.
While the cause of FP isn't known, saltwater leeches have been suspected to play a role due to their frequent presence on areas of sea turtles where FP tumors often develop, such as on their eyes, mouths and flippers.
The results, which were published recently in the journal Diseases of Aquatic Organisms, are the first evidence of a significant association between leeches and the disease in sea turtles, according to the researchers.
"Florida is one of the areas most heavily impacted by FP," says Anna Savage, an associate professor in UCF's Department of Biology and study co-author. "Over the past three decades, approximately half of the green turtle juveniles encountered in the Indian River Lagoon have FP tumors, which is one of the highest rates documented," she says.
Sea turtle health is important because the ancient marine reptiles contribute to healthy oceans and coastlines by grazing and maintaining sea grass beds.
All sea turtles are categorized as threatened or endangered because of threats from pollution, coastal development and fishing, in addition to infectious diseases.
Central Florida's Atlantic coastline hosts about one-third of all green turtle nests in the state and is one of the most important nesting areas in the world for loggerheads.
Knowing if leeches play a role in the disease transmission can help researchers better understand and predict its spread, as well as inform conservation actions, such as leech removal in sea turtle rehabilitation centers.
The Process
The study's lead author and a recent undergraduate alumna of UCF's Biology Department, Leah Rittenburg, spearheaded the research and was responsible for the genetic analyses.
To find out a possible connection between leeches and FP, the researchers documented the presence of leeches on green and loggerhead turtles captured from the Indian River Lagoon and also used genetic analyses to determine if leeches collected from the turtles contained chelonid alphaherpesvirus 5, or ChHV5, the virus most likely responsible for disease development in an individual turtle.
"Our historical data, collected by the UCF Marine Turtle Research Group between 2006 and 2018, revealed that leech parasitism was significantly associated with FP in green turtles but not in loggerhead turtles," Rittenburg says.
"For the genetic analysis, about one-fifth of the leeches we collected were positive for ChHV5, and one leech species trended towards coming from FP-positive turtles, further supporting the hypothesis that leeches may act as ChHV5 transmitters," she says.
Now that the researchers have demonstrated a relationship between FP and leeches, they want to evaluate more specifically if leeches transmit the turtle herpesvirus, which would provide stronger evidence that the virus in an underlying cause of FP.
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Study co-authors were Jake R. Kelley, a master's student in UCF's Department of Biology, and Kate L. Mansfield, an associate professor in UCF's Department of Biology and director of the UCF Marine Turtle Research Group.
The research was funded by grants from UCF's Office of Undergraduate Research and by a Florida Sea Turtle License Plate grant.
Savage received her doctorate in ecology and evolutionary biology from Cornell University. She is a member of UCF's Genomics and Bioinformatics Cluster and joined UCF's Department of Biology, part of UCF's College of Sciences, in 2015.
IMAGE: THIS DIAGRAM ILLUSTRATES THE LONGFIN DAMSELFISH-MYSID RELATIONSHIP, WHERE THE NICHE CREATED BY THE TERRITORIAL ALGAE FARMING LONGFIN DAMSELFISH PROVIDES A PROTECTIVE REFUGE TO MYSIDS, LEADING TO INCREASED SURVIVAL. IN TURN,... view more
CREDIT: ILLUSTRATION BY ROHAN BROOKER
Throughout nature, there are instances of animals aiding one another and living together in mutually beneficial relationships that have helped shape the world's landscapes and biodiversity.
These domesticator-domesticate relationships form when one species provides multigenerational support to another species in exchange for a resource or service that benefits both species. An example of this type of relationship is how early humans domesticated gray wolves. The wolves were attracted to the human encampments, which provided them with protection and resources, and the wolves, in turn, helped the humans increase their hunting proficiency.
One area of the world where these mutually beneficial relationships could be examined further, however, is underwater.
A new study involving researchers from the University of Delaware looked at how a mutually beneficial relationship formed in the waters of Belize. Researchers discovered that longfin damselfish aggressively defend algal farms on which they feed, which provides a protective refuge for planktonic mysid shrimps, which in turn excrete nutrients onto the farms, enriching the algae on which the damselfish feed.
The paper was recently published in Nature Communications. Rohan Brooker, a former post-doctoral researcher at UD, served as the lead author and Danielle Dixson, associate professor in University of Delaware's School of Marine Science and Policy in the College of Earth, Ocean and Environment, served as one of the co-authors on the study.
The research was conducted in the field on the shallow reef habitat surrounding the Smithsonian's Carrie Bow Cay Research Station in Belize from January through April of 2018, however the idea and initial data was conducted when Brooker was a post-doctoral researcher in Dixson's lab and continued through his post-doctoral position at the University of Saskatchewan, Canada.
Aggressive fish
Dixson said that longfin damselfish are known to aggressively defend the algal farms that they consider to be their turf, and while they aren't a very big fish, they are tenaciously territorial.
"They will come after you if you go into their territory," said Dixson. "They'll try and bite you, and they'll try to scare everything away. They're really aggressive even though they're not very big. So they create this bubble that they protect, and one of the things that they don't bother chasing off are these mysids."
Mysids are tiny, clear planktonic crustaceans that live together by the hundreds in cloud-like structures. Using the damselfish as a kind of fence or a security system for their area, the mysids that lived within the damselfish farms were attacked less often than mysids that lived outside of the farms.
In return for this protection, the mysids provide a benefit to the damselfish by excreting nutrients onto the algae that the damselfish eat.
The damselfish that hosted the mysids in their communities exhibited a better body condition than those fish who did not host mysids in their communities.
To determine the effect of mysids on longfin damselfish body condition, the researchers looked at the hepatosomatic index (HSI), which can reflect the health or stored energy of a fish's liver and can indicate the relationship between the diet and physical condition of the damselfish. They compared the HSI of the fish who lived with the mysids to those who lived without the mysids and found that those fish living with the mysids had a higher HSI than those who had no mysids on their alga farms.
This could be for several reasons. For instance, within the mysid-associated farms, the algal composition was significantly different than those farms without mysids. Mysid-associated farms contained a significantly higher proportion of brown algae, which increases the structural complexity of damselfish farms and can serve as a catalyst for the growth of palatable turf-algae, the preferred food source for the damselfish.
Dixson said that it was interesting to see this relationship form in a natural environment and could lead to more studies looking at domesticator-domesticate relationships in the wild.
"We know that domesticator-domesticate relationships happen in nature," said Dixson. "But this is the first example we have found of this type of relationship underwater. Maybe this paper could spark other people to examine different commensal pathways or mutualistic behaviors that we see as potentially being something similar to this."
