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Although the vibrant, waifish petals of the poppy may appear inviting to the casual observer, a closer look reveals a pricklier message: Stay away! To discourage plant eaters like insects and birds from biting into their leafy appendages, many plant species protect themselves with defense mechanisms, like tougher leaves, distasteful latex, and armor made of prickles. Developing these defense features is part of a plant’s natural growth throughout its lifetime. Some plants, however, are able to activate additional protection when faced with attacking herbivores. The authors of a recent PLOS ONE paper investigated these defense mechanisms in two species of poppy currently found in Hawaii, where natural herbivores have long been extinct. The authors’ results reveal that island poppies may have more “nettle” in the face of simulated adversity than previously predicted.
The authors chose two species of poppy for testing, Argemone glauca, a species native to Hawaii, and Argemone mexicana, a species originally hailing from the North American continent and a recent inhabitant of the Hawaiian islands. Both species come pre-equipped with permanent features that may function as defense strategies. However, permanent defenses are costly to maintain for a plant: They divert energy away from other functions, like reproduction and growth, and are therefore an energy investment for the plant. To combat the cost of maintaining a full suite of permanent defenses, some plants respond to attacks from plant eaters only when they occur by activating additional defenses, known as inducible defenses. Unlike defense features that develop throughout the course of a plant’s lifetime, also known as constitutive defenses, inducible defenses are not permanent, only prompted by specific need.
In this study, the researchers simulated the need for additional defenses by subjecting the two species to various “attacks” to see how the poppies would respond. Plants were assigned to one of four random treatment groups:
The researchers then allowed for two new leaves to grow to ensure that the plants had an adequate amount of time to respond.
Although neither species developed additional leaf toughness or produced more natural latex in response to treatments, both species exhibited increased prickle density on new leaves that grew after treatment. To evaluate prickle density, the authors harvested new leaves and counted all the new prickles on the surfaces of the leaves, excluding prickles found along the leaf edge. They also quantified the leaf area and performed statistical analyses to identify patterns in the various groups.
The authors found that Hawaiian native A. glauca responded more intensely to treatment by developing significantly more prickles than its continental North American counterpart, A. mexicana. The authors report that prickles for A. glauca were 20x more dense and 2.7x higher than A. mexicana.
Plant defenses are selected for over time due to snacking pressures from herbivores. On the Hawaii islands, however, natural herbivores of A. glauca, such as flightless ducks and beetles, are now extinct. The lack of natural predators for island plants has given rise to the idea that island plants have ‘gone soft’ over time. The authors consider A. glauca’s robust response to external attacks evidence that island plants may be better defended than previously thought.
Although it may be impossible to determine whether these island defenses have been selected for by herbivores of the past, no longer present, the inducibility of prickles in A. glauca and A. mexicana demonstrates that these poppies have the mettle to fight back against attackers and snackers.
For more on how herbivores and plants interact, check out this EveryONE blog post on snail mucus.
Citation: Hoan RP, Ormond RA, Barton KE (2014) Prickly Poppies Can Get Pricklier: Ontogenetic Patterns in the Induction of Physical Defense Traits. PLoS ONE 9(5): e96796. doi:10.1371/journal.pone.0096796
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The Black Death, a pandemic at its height in Europe during the mid-14th century, was a virulent killer. It was so effective that it wiped out approximately one third of Europe’s population. Recent studies have shown that the elderly and the sick were most susceptible. But was the Black Death a “smart” killer?
A recent PLOS ONE study indicates that the Black Death’s virulence might have affected genetic variation in the surviving human population by reducing frailty, resulting in less virulent subsequent outbreaks of the plague. By examining the differences in survival rates and mortality risks in both pre-Black Death and post-Black Death samples of a London population—in combination with other, extrinsic factors, like differences in diet between the two groups—the researcher found that in London, on average, people lived longer following the plague than they did before it, despite repeated plague outbreaks. In other words, in terms of genetic variation, the Black Death positively affected the health of the surviving population.
To uncover differences in the health of medieval Londoners, Dr. Sharon DeWitte of the University of South Carolina examined 464 pre-Black Death individuals from three cemeteries and 133 post-Black Death individuals from one. She chose a diverse range of samples for a comprehensive view of the population, including both the rich and the poor, and women and children, but targeted one geographic location: London.
The ages-at-death of the samples were determined by calculating best estimates—in statistics these are called point estimates—based on particular indicators of age found on the skeletons’ hip and skull bones. Individuals’ ages were then evaluated against those in the Anthropological Database of Odense University, a pre-existing database comprising the Smithsonian’s Terry Collection and prior age-at-death data from 17th-century Danish parish records.
After estimating how old these individuals were when they died and comparing the age indicators against the Odense reference tool, the author conducted statistical analyses on the data to examine what the ages-at-death could tell us about the proportion of pre- and post- Black Death medieval Londoners who lived to a ripe old age, as well as the likelihood of death.
Survivorship was estimated using the Kaplan-Meier Estimator, a function used to indicate a quantity based on known data; in this case the function evaluated how long people lived in a given time period (pre-Black Death or post-Black Death). The calculated differences were significant: In particular, the proportion of adults who lived beyond the age of 50 from the post-Black Death group was much greater than those from the pre-Black Death group.
In the pre-Black Death group, death was most likely to occur between the ages of 10 and 19, as seen above.
The Kaplan-Meier survival plot shows how the chances of survival, which decrease with age, differ for Pre-Black Death and Post-Black Death groups, as seen below.
As the survival plot indicates, post-Black Death Londoners lived longer than there Pre-Black Death predecessors.
Finally, Dr. DeWitte estimated the risk of mortality by applying the age data to the statistical model known as the Gompertz hazard, which shows the typical pattern of increased risk in mortality with age. She found that overall post-Black Death Londoners faced lower risks of mortality than their pre-Black Death counterparts.
To make long and complicated methodology short, these analyses indicate that post-Black Death Londoners appear to have lived longer than pre-Black Death Londoners. The author estimates that the general population of London enjoyed a period of about 200 years of improved survivorship, based on these results.
The virulent killer, the Black Death, may have helped select for a healthier London by influencing genetic variation, at least in the short term. However, to better understand the improved quality of life of post-Black Death London, the author suggests further study to disentangle two major factors: the selectivity of the Black Death, coupled with improvements in lifestyle for post-Black Death individuals. For example, the massive depopulation in Europe resulted in increased wages for workers and improvements to diet following the plague, which also likely improved health for medieval Londoners. By unraveling intrinsic, biological changes in genetic variation from outside extrinsic factors like improvements in diet, it may be possible to better understand the aftermath of one of the most devastating killers in infectious disease history.
The EveryONE blog has more on the medieval killer here.
Citation: DeWitte SN (2014) Mortality Risk and Survival in the Aftermath of the Medieval Black Death. PLoS ONE 9(5): e96513. doi:10.1371/journal.pone.0096513
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The pygmy blue whale, cousin to the more well-known Antarctic blue whale, has an enigmatic history. Pygmy blue whales dwell in vast expanses of the Indian and southern Pacific oceans, and are a highly mobile species. The species was identified in 1966—although it’s likely to have been confused with its cousin the “true” blue whale prior to 1966—so it’s only in recent years that we’ve been able to catch glimpses of these elusive cetaceans during their migrations to and from breeding and feeding grounds. The researchers of a recent PLOS ONE paper tested out a new method of tracking these whales: satellite telemetry (described below). Using this method, the researchers mapped the migration of pygmy blue whales as they moved from the coast of Australia to the waters of Indonesia. We caught up with author Virginia Andrews-Goff to get some additional details on what it’s like to track these tiny giants.
How did you become interested in pygmy blue whales, and how did you get involved in mapping their migratory movements?
This research was carried out by the Australian Marine Mammal Centre, a national research centre focused on understanding, protecting and conserving whales, dolphins, seals, and dugongs in the Australian region. The work we carry out aims to provide scientific research and advice that underpins Australia’s marine mammal conservation and policy initiatives. We, therefore, have a keen interest in all whales that migrate through Australian waters including pygmy blue, right and humpback whales.
Pygmy blue whales are of particular interest, however, as so little is known in regard to their movements and population status. Large scale movements of whales are particularly hard to study and what we do know about pygmy blue whales we have mainly learnt from examining whaling records. Fortunately, pygmy blue whales were targeted by the whaling industry for only a very short period of time in the late 1950s and early 1960s just prior to the IWC banning the hunting of all blue whales in 1966.
What are the challenges of better understanding whale migration in general?
Large-scale, long-term whale movements are challenging to study as it is impractical to do so by direct observation. Therefore, we need to use devices, such as satellite tags, that can be attached to the whale to provide real-time location information.
What is satellite telemetry and how did it enable your findings?
In this case, satellite telemetry refers to the use of a satellite-linked tag attached to the whale. This tag communicates with the Argos satellite system when the antenna breaks the surface of the water. A location can then be determined when multiple Argos satellites receive the tag’s transmissions. We then receive this location data in almost real time via the Argos website, which allows us to track the movement of the tagged whale.
Based on your tracking, you found that the pygmy blue whales traveled from the west coast of Australia north to breeding grounds in Indonesia. Can you give readers a sense of why they travel this route?
Generally, whales migrate between productive feeding grounds (at high latitudes) in the summer to warmer breeding grounds (at low latitudes) during the winter. The exact reason for this general pattern is unclear, though quite a few theories exist, including to avoid predators, to assist the thermoregulatory ability of the calf, and to birth in relatively calm waters. Because of the timing of this migration, we believe these animals travel to Indonesian waters to calve. Usually it is assumed that whales fast outside of the summer when no longer located in the productive feeding grounds. Interestingly, these pygmy blue whales travel from productive feeding grounds off Western Australia to productive breeding grounds in Indonesia and therefore, probably have the opportunity to feed (and not fast) on the breeding grounds.
You’ve mentioned that pygmy blue whale migratory routes correspond with shipping routes. How does this interaction impact the whales?
Baleen whales (whales that use filters to feed instead of teeth) use sound for communication and to gain information about the environment they occupy. When pygmy blue whale movements correspond to shipping routes, there is potential for the noise generated by the ships to play some role in altering calling rates associated with social encounters and feeding.
Why is it important for us to better understand pygmy blue whale migration, and how does mapping their migratory movements help conservation efforts for this endangered animal?
Our coauthor, Trevor Branch, hypothesised in 2007 that pygmy blue whales occupying Australian waters traveled into Indonesian waters. However, prior to this study, we didn’t actually know that this was the case. As such, conservation efforts relevant to the pygmy blue whales that use Australian waters are required outside of Australian waters too. We can also now gain some understanding of risks within the pygmy blue whale migratory range, such as increased ambient noise from development, shipping, and fishing, and therefore assist in mitigating these risks.
What’s next for you and your research team?
A question mark still remains over the movements of the pygmy blue whales that utilise the Bonney Upwelling feeding grounds off southern Australia. Genetic evidence indicates mixing between the animals in the feeding areas of the Perth Canyon (the animals that were tagged in this study) and the Bonney Upwelling. This indicates the potential for individuals from the Bonney Upwelling to follow a similar migration route to those animals feeding in the Perth Canyon. However, it is also thought that Bonney Upwelling animals may utilise the subtropical convergence region south of Australia. We plan to collaborate on a research project that aims to tag the pygmy blue whales of the Bonney Upwelling and ascertain whether these animals move through the same areas and are therefore exposed to the same risks as the Perth Canyon animals.
Citation: Double MC, Andrews-Goff V, Jenner KCS, Jenner M-N, Laverick SM, et al. (2014) Migratory Movements of Pygmy Blue Whales (Balaenoptera musculus brevicauda) between Australia and Indonesia as Revealed by Satellite Telemetry. PLoS ONE 9(4): e93578. doi:10.1371/journal.pone.0093578
Image 1: IA19847 Blue pygmy whale
Photograph © Mike Double/Australian Antarctic Division
Image 2: IA19850 Blue pygmy whale
Photograph © Mike Double/Australian Antarctic Division
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Image 4: IA19851 Blue pygmy whale off Western Australian coast near Perth, Western Australia, Australia Photograph © Mike Double/Australian Antarctic Division
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Like PLOS ONE, the English language is rapidly taking over the world (we kid). In 2010, English clocked in at over 360 million native speakers, and it is the third-most-commonly used native language, right behind Mandarin Chinese and Spanish. While these languages spread, however, other indigenous languages decline at an accelerated pace. A fraction of these enigmatic languages belong to uncontacted indigenous groups of the Amazonian rainforest, groups of people in South America who have little to no interaction with societies beyond their own. Many of these groups choose to remain uncontacted by the rest of the world. Because of their isolation, not much is known about these languages beyond their existence.
The researchers of a recent PLOS ONE paper investigated one such language, that of the Carabayo people who live in the Colombian Amazon rainforest. Working with the relatively scarce historical data that exists for the Carabayo language—only 50 words have been recorded over time—the authors identified similarities between Carabayo and Yurí and Tikuna, two known languages of South America that constitute the current language family, Ticuna-Yurí. Based on the correspondences, the authors posit a possible genealogical connection between these languages.
Few resources were available to the authors in this endeavor. They analyzed historical wordlists collected during the last encounter with the Carabayo people in 1969—the only linguistic data available from this group— against wordlists for the Yurí language. In addition, they sought the expertise of a native speaker of Tikuna, a linguist trained in Tikuna’s many dialects. Using these resources, the authors broke down the Carabayo words into their foundational forms, starting with consonants and vowels. They then compared them to similarly deconstructed words in Yurí and Tikuna.
The examination involved the evaluation of similarities in the basic building blocks of these words: the number of times a specific sound (or phoneme) appeared; the composition and patterns of the smallest grammatical units of a word (a morpheme); and the meanings attached to these words. When patterns appeared between Carabayo and either Yurí or Tikuna, the authors considered whether or not the languages’ similarities constituted stronger correspondences. They also paid attention to the ways in which these words would have been used by the Carabayo when the lists were originally made many years ago.
The Yurí language was first recorded in the 19th century, but it is thought to have become extinct since then. From these lists, five words stood out: in Carabayo, ao ‘father’, hono ‘boy’, hako ‘well!’, and a complex form containing both the Yurí word from warm, noré, and the Yurí word, t?au, which corresponds in English to ‘I’ or ‘my’. Given the evidence, the authors contend that the strongest link between Carabayo and Yurí is found in the correspondence of t?au. The study of other languages has indicated that first person pronouns are particularly resistant to “borrowing”, or the absorption of one language’s vocabulary into another. Therefore, the authors surmise it is unlikely in this instance that either of the languages absorbed t?au from the other, but that they share a genealogical link.
Similarly, the comparison of Carabayo words to words of the living language of Tikuna provided a high number of matches, including in Carabayo gudda ‘wait’ and gu ‘yes’. The matches especially exhibit sound correspondences of Carabayo g (or k) and the loss of the letter n in certain circumstances. Table 7 from the article shows the full results (click to enlarge):
Although it is possible that the Carabayo language represents a language that had not yet been documented until the time of 1969, the results of the researchers’ evaluation have led them to conclude that Carabayo more likely belongs to the language family of Ticuna-Yurí. The relationship of Carabayo to Yurí and Tikuna changes the structure of the Ticuna-Yurí family by placing Carabayo on the map as a member of that family. The Tikuna language, once considered to be the sole surviving member of the Ticuna-Yurí family, might now have a sibling, and the identity of a barely known language has become that much more defined.
For the authors, this research is a complicated endeavor. The desire to advance our knowledge and understanding of these precious languages must be balanced with the desires of the uncontacted indigenous groups, some of whom voluntarily choose to remain in isolation. As the authors themselves express, the continued study of these uncontacted languages seeks to engender an awareness in the larger community of the people who speak these languages, and to reiterate their right to be left to live their lives as they wish—in isolation.
Citation: Seifart F, Echeverri JA (2014) Evidence for the Identification of Carabayo, the Language of an Uncontacted People of the Colombian Amazon, as Belonging to the Tikuna-Yurí Linguistic Family. PLoS ONE 9(4): e94814. doi:10.1371/journal.pone.0094814
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Cancer, the transformation of normal cells into malignant tumor cells, reigns among diseases as one of the leading causes of death around the world. In 2012, cancer claimed 8.2 million lives, and numbers continue to increase each year. While our understanding of cancer is far from complete, we’ve been able to attribute some of the killer’s virulence to increased environmental risk: Increased pollutants and other environmental carcinogens, coupled with an average increase in tobacco and alcohol use and added to a concurrent decrease in daily exercise, cumulatively represent significant risk factors directly related to an increasingly modern world. Ironically, we humans also live a lot longer than we used to, which increases the disease’s chances of occurring.
However, we have identified far fewer examples of the disease in the archaeological record compared to its current frequency in the current population, which has led to the idea that cancer was much less widespread in antiquity. As a result, very little is known about its evolutionary history.
As part of a larger research project undertaken by the British Museum in the city of Amara West, Sudan, the authors of a PLOS ONE paper dug a little deeper into the dark, early history of cancer. Their subject of interest was an over 3,000 year-old skeleton of a young man from ancient Nubia, then part of Egypt, whose remains were excavated at this site, designated on the map below.
When the researchers uncovered skeleton 244-8, as he has been cataloged, they were presented with the difficulties of examining a less-than-complete body. Parts of the skeleton had been broken, highlighted as fragmentary in the image below. In addition, salt in the surrounding soil had slowly damaged the skull over time. The soft tissue of the over 3,000-year-old skeleton, was also long gone.
On top of these difficulties, damages to the body incurred over time, both before and after death, can look very similar to the eye. Cancer, in particular, is notoriously hard to diagnose in human remains; its similarities to other pathologies combined with natural damages sustained after burial made the researchers’ task of properly diagnosing skeleton 244-8 a complicated one. The earliest signs of cancer in bone are also only visible via methods like X-ray that allow us to visualize the inner parts of bone where the disease begins, which the naked eye cannot see.
The researchers assessed the condition of skeleton 244-8, using digital microscopes, scanning electron microscopes (SEM), and radiography (X-rays), and by examining the visual markers on the bone. They looked for evidence of sustained lesions, or damage on the bone, which they found on his vertebrae, ribs, sternum, pelvis, and other parts of the skeleton.
In the X-ray and photo image above of a rib, we can see the damage as noted by the arrows. The parts of the skeleton most affected by lesions were sections of the spine. The image below depicts an especially damaged thoracic vertebra.
The authors discussed four possible causes for the skeleton’s bone damage:
Although very similar, the visual markers on bone differ slightly depending on the malady causing the damage. We can see in the image below of the tibia that taphonomic damage caused by insects is slightly more uniform in shape than lesions caused by cancer, and the holes continue straight through to the other side of the affected bone.
Based on the shape, size, and appearance of the lesions under X-ray, the authors surmised that the man suffered from metastatic cancer, originating in the man’s organs. However, since no soft tissue was preserved over time, it is nearly impossible to ascertain the exact location of skeleton 244-8’s primary tumor, which would have affected soft tissue like his organs.
Considering the decay caused by time, salt, and insects, the researchers were able to ascertain quite a lot about skeleton 244-8 based on their examinations of the skeleton. In addition to diagnosing him with metastatic cancer, researchers suggest that skeleton 244-8 was a young man between the ages of 25 to 35 who belonged to a middle-class Nubian family at the time of his death, based on the context of his burial.
With increasing advances in the technology used to examine subjects like skeleton 244-8, the inner secrets and pathologies held in places like the inside of bone become less of a mystery. With further study, we’ll be able to understand a little more about the environmental risk factors of skeleton 244-8’s own world: for instance, the possible use of fires in poorly ventilated mudbrick houses, or possible infectious diseases spread by parasites. By taking a closer look at human remains like skeleton 244-8, it may eventually be possible to see the effects of a disease not only of our time, but of considerable antiquity.
Citation: Binder M, Roberts C, Spencer N, Antoine D, Cartwright C (2014) On the Antiquity of Cancer: Evidence for Metastatic Carcinoma in a Young Man from Ancient Nubia (c. 1200BC). PLoS ONE 9(3): e90924. doi:10.1371/journal.pone.0090924
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With more than 7.1 billion people living across the globe, cities house more than 50% of the world’s population. The United Nations Population Fund projects that by 2030 more than 5 billion people will live in cities across the world. The Global Heath Observatory, a program run by the World Health Organization, predicts that by 2050, 7 out of 10 people will live in cities, compared to 2 of 10 just 100 years ago.
Recently, researchers developed what is called “urban scaling theory” to mathematically explain how modern cities behave in predictable ways, despite their unprecedented growth. Recent work in urban scaling research considers cities “social reactors”. In other words, the bigger the city, the more people and more opportunity for social interaction. Think for a moment about the social interactions that occur just on the block outside of your local coffee shop; now multiply those interactions by millions. Cities magnify the number of interactions, increasing both social and economic productivity and, ultimately, encouraging their own growth.
The authors of a recent PLOS ONE paper sought to determine whether ancient cities “behaved” in predictable patterns similar to their modern counterparts. To do so, they developed mathematical models and tested them on archaeological settlements across the Pre-Hispanic Basin of Mexico (BOM, approximated by the red square in the figure below). Based on their findings, they suggest that the principles of settlement organization, which dictate city growth, were very much the same then as they are now, and may be consistent over time.
To test their predictions, the researchers analyzed archaeological data from over 1,500 sites in the BOM, previously surveyed in the 60s and 70s by researchers from the University of Michigan and Penn State.
Using low-altitude aerial photographs and primary survey reports from the original surveyors, the researchers organized the following data from approximately 4,000 sites: the settled area, the average density of potsherds—broken pieces of ceramic material—within it, the count and total surface area of domestic architectural mounds, the settlement type, the estimated population, and the time period.
The researchers were interested in examining areas of the BOM that enabled social interaction between residents, so they excluded site types that did not allow social interaction, for example, isolated ceremonial centers, quarries, and salt mounds. They then grouped the remaining 1,500 sites into both chronological groups and size groups. For chronological grouping, each site was assigned to one of four time periods: the Formative period (1150 B.C.E.–150 B.C.E.), the Classic period (150 B.C.E.–650 C.E.), the Toltec period (650–1200 C.E.), and the Aztec period (1200-1519 C.E.). By the Aztec period, the area had developed from amorphous rural settlements to booming metropolises comprising over 200,000 people.
For site grouping, settlements greater than 5,000 people were categorized differently than smaller settlements. In the figure above, panel B denotes settlements dating to the Formative period (1150 B.C.E.–150 B.C.E.), and panel C, settlements dating to the Aztec period (1200-1519 C.E.).
After separating the data into both chronological groups and size groups, the researchers applied their mathematical models and tested their predictions about urban growth in the settlements of the BOM. One aspect of city development assessed by the researchers was the evolution of defined networks of roads and canals in growing cities. Because roads act as conduits, directly influencing social interaction—much like the roads leading to the aforementioned coffee shop—growing cities develop increasingly defined networks to connect social hubs to one another.
Take, for example, the figure below, which displays both a city in an early stage (panel A) and later (panel B) of growth:
Panel A shows the early, or Amorphous Settlement Model, displaying a small settlement easily accessible to the individual via walking, and thus negating the necessity for clearly defined networks of roads. Panel B, on the other hand, shows the Networked Settlement Model, an infrastructure-dense area where networks are clearly defined to accommodate the increased size of the city and density of the residents. Larger cities analyzed by the authors, like Teotihuacan of the Classic period and Tenochtitlán of the Aztec period, epitomize the Networked Settlement Model with its organized network of roads and canals. The findings from the BOM echo the earlier-stated notion that, like their modern counterparts, ancient cities may have acted as “social reactors”, in part by facilitating an increasingly defined network of roads, themselves directly influencing the ability of residents to socially interact.
Scientists use urban scaling theory to show that population and social phenomena follow distinct, mathematical patterns over time. By developing mathematical models to predict measurable changes in city growth, these researchers applied the same patterns to ancient cities and concluded that the development of settlements over time in the BOM seem analogous to those observed in modern cities. Researchers predict that the same mathematical models could be reformatted to estimate population size of ancient cities, as well as to develop measures for calculating socio-economic output like the production of art and public monuments based on the relationship size between settlement size and division of labor. Although there is still much to be solved through the equations of urban scaling theory, the consistency of city growth over time has implications for both the past and the present.
Citation: Ortman SG, Cabaniss AHF, Sturm JO, Bettencourt LMA (2014) The Pre-History of Urban Scaling. PLoS ONE 9(2): e87902. doi:10.1371/journal.pone.0087902
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Although seaweed is the dominant habitat-forming organism along temperate coastlines, one of the major macroalgae of Australia, Phyllospora comosa, has disappeared over the last forty years from the urban shores around Sydney, Australia. Human activity is likely related to the degradation of these habitats in urbanized areas: During the 1970s and 1980s, humans discharged large amounts of sewage from nearby cities along surrounding coasts. Unfortunately, despite significant improvements in water quality around Sydney since, Phyllospora has not returned. To test whether Phyllospora can ever be restored in reefs where it was once abundant, authors of a recent PLOS ONE paper transplanted Phyllospora into two reefs in the Sydney area. In this interview, corresponding author Dr. Alexandra Campbell from the University of New South Wales elaborates on the group’s research and the impact of these ‘missing underwater forests’:
You’ve said that “seaweeds are the ‘trees’ of the ocean”. Can you tell us a little more about your study organism, Phyllospora, and explain its importance for coastal ecosystems around Australia?
Phyllospora comosa (known locally as ‘crayweed’) grows up to 2.5 m in length and forms dense, shallow forests along the south-eastern coastline of Australia, from near Port Macquarie in New South Wales, around Tasmania to Robe in South Australia. Individuals appear to persist on reefs for around 2 years and are reproductive year round.
How do these ecosystems change with the reduction of seaweed forests?
Large, canopy-forming macroalgae provide structural complexity, food and habitat for coastal marine ecosystems and other marine organisms. When these habitat-formers decline or disappear, the ecosystem loses its complexity, biodiversity decreases and many ecosystem services are also lost. Losing large seaweeds from temperate reefs has analogous ecosystem-level implications to losing corals from tropical reefs.
We’re interested in learning more about how you got involved in this research. Can you tell us how you became interested in studying Phyllospora?
For my doctorate, I studied how changing environmental conditions may disrupt relationships between seaweeds and microorganisms – which are abundant and ubiquitous in marine environments – potentially leading to climate-mediated diseases. During my PhD, my colleagues (Coleman et al.) published a paper describing the disappearance of crayweed from the urbanised coastline of Sydney and hypothesised that the cause was the high volume, low treatment, near shore sewage outfalls that used to flow directly on to some beaches and bays in the city. I wondered whether this pollution may have disrupted the relationship between Crayweed and its microbial associates and that’s how I got involved in the project.
Why is the loss of canopy-forming macroalgae difficult to study retrospectively and how has this informed your current study?
Once an organism has disappeared from an ecosystem, it can be difficult to piece together the processes that caused its demise, particularly if the disappearance occurred several decades ago and the ecosystem state shifted dramatically as a consequence. In our study, we hypothesized that poor water quality might have caused the decline of Phyllospora. There have been significant improvements in water quality in the region since the decline, but the species and ecosystems they used to support have failed to recover. To test whether the water quality has improved enough to allow recolonisation of this seaweed, we transplanted the seaweed back onto reefs where it was once abundant. The survival rates of transplanted seaweed were very good, suggesting that with a little help, this species may be able to recolonize Sydney’s reefs.
What were some of the difficulties you faced while conducting your research?
Moving hundreds of large seaweeds many kilometres from donor populations to the restoration sites was a big job. Thankfully, we received a great deal of help from many volunteers from the local community – mostly divers, with an interest in conserving and restoring the marine ecosystems they visit recreationally and value as a natural resource.
You’ve talked about Phyllospora ‘recruitment’ at one recipient site. Can you explain in greater detail what a ‘recruit’ is and how this is important for the success of a restoration site?
Phyllospora reproduces sexually, with gametes from male individuals fertilizing gametes from females, forming zygotes, which then attach themselves to the bottom (usually not very far from their parents) and grow into juvenile algae which we call ‘recruits’. In the context of restoration, the high level of recruitment (i.e. successful reproduction) we observed at our transplant site is very encouraging because it creates the possibility for the establishment of a self-sustaining population of Phyllospora at this site for the first time in many decades.
Why do seaweed forests receive less attention than other marine ecosystems, for example mangroves or coral reefs?
Most people don’t think about seaweeds very often. When they do, it’s usually because the sight, touch or smell of seaweed on the beach is annoying or offensive. Even the name “seaweed” conjures negative imagery so perhaps it’s a PR issue! Arguably, macroalgae have traditionally received less attention from marine ecologists than other marine ecosystems as well, with much more attention and funding going to coral reef research. With global patterns of declines of temperate, habitat-forming macroalgae, this needs to change and our understanding of the processes that affect seaweed populations needs to grow.
What would a successful restoration of underwater kelp forests mean for the ecosystem and for the local population?
It’s our hope that, by restoring habitat-forming macroalgae like Phyllospora, we will also enhance populations of other organisms that rely on this species for food or shelter. Detecting such follow-on benefits of our seaweed restoration program is the focus of ongoing research and our initial results are very encouraging.
You’ve mentioned that larger scale restoration would be a sound way of combating the grazing (herbivory) you saw. What is the next step forward for you?
Enhanced grazing may be another mechanism by which Phyllospora disappeared from these reefs (or perhaps why it’s failed to recover). The impacts of grazing we observed were site-specific, so further investigations in to why one place was so severely impacted by herbivores while the other was not, are needed. Our first step towards resolving this is to establish more numerous restoration patches of different sizes to see whether we can satiate the herbivores and whether smaller patches are more susceptible to grazing than larger patches.
For more PLOS ONE articles about the ‘trees of the ocean’, check out the way seaweed and coral interact in “Seaweed-Coral Interactions: Variance in Seaweed Allelopathy, Coral Susceptibility, and Potential Effects on Coral Resilience” and how ocean currents influence seaweed community organization in “The Footprint of Continental-Scale Ocean Currents on the Biogeography of Seaweeds”.
Citation: Campbell AH, Marzinelli EM, Vergés A, Coleman MA, Steinberg PD (2014) Towards Restoration of Missing Underwater Forests. PLoS ONE 9(1): e84106. doi:10.1371/journal.pone.0084106
Image: Adriana Vergés, co-author
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From the 9th to the mid-14th century, the region of Angkor in modern-day northern Cambodia was the capital of Khmer Empire and the largest preindustrial city in the world. Home to possibly more than three quarters of a million people, several different urban plans and reservoir systems, and impressive monuments like the temple of Angkor Wat (pictured from a bird’s-eye-view above), Angkor was the core of the Khmer Empire, which dominated Southeast Asia by the 11th century CE. Like many modern, booming cities, Angkor was fed by water sourced from another city.
Mahendraparvata, a hill-top site in the mountain range of Phnom Kulen, is significant as the birthplace of the Khmer Kingdom and as the seat of Angkor’s water supply. In 802 CE, Jayavarman II proclaimed himself the universal king of the Angkor region on the top Mahendraparvata. Jayavarma’s ascension to power marked the unification of the Angkor region and the foundation of the Khmer Empire.
Until recently, however, little was known about the urban settlement of Mahendraparvata; a dense forest canopy obscures a great deal of the area’s archaeological landscape. To determine the extent of land use around Mahendraparvata, the authors of a recent PLOS ONE paper examined soil core samples taken from one of the Phnom Kulen region’s reservoirs.
As Angkor’s source of water, Phnom Kulen’s archaeological landscape is littered with hydraulic structures, like dams, dykes, and reservoirs (points A, B, and E on the remote sensing digital image shown below), meant to store and direct Angkor’s water sources strategically. The researchers focused on an ancient reservoir upstream of the main river running north to south, now a swamp, to find evidence of intensive land use.
Core samples taken from the sediment of this ancient reservoir, point F on the image above, provided the researchers with chronological layers of earth containing organic materials, like wood, pollens, and spores, which could be assessed using radiocarbon dating.
By analyzing the sediment cores, researchers found that the reservoir was likely in use for about 400 years. Although the age of the reservoir itself remains inconclusive, sediment samples suggest that the valley was flooded in the mid-to-late 8th century CE, around the time Jayavarman II unified the area.
The authors found that medium-to-coarse sand deposition in the sediment samples beginning in the mid-9th century points to the presence of continual soil erosion, either from the surrounding hills or from the dyke itself, likely caused by deforestation in the area. By analyzing samples from the late 11th century, the authors found that the last and largest episode of erosion occurred, a possible result of intensive land use.
The researchers suggest that deforestation, as evidenced by soil erosion, implies that “settlement on Mahendraparvata was not only spatially extensive but temporally enduring.” In other words, the estimated extent of deforestation by continual sand deposits from the mid-9th century to the late-11th century in core samples indicates that Mahendraparvata was home to a large and thriving urban network in need of resources.
However, an increase in pollen spores dated to the 11th century, followed by the establishment of swamp forests in the early to mid-12th century in the reservoir, reflects that, by this time, the reservoir had fallen out of use, perhaps linked to changes in water management throughout the broader area, and possible population decline nearby. According to mid-16th century samples, the swamp flora around this time appears to have developed into the swamp flora seen today in the ruins of Mahendraparvata.
For some 400 years, the Phnom Kulen mountains acted as the main source of water for the Angkor region. The change of water management practices in the Phnom Kulen region has implications for the water supply to Angkor itself. In sum, by examining core samples drawn from one of Phnom Kulen’s ancient reservoirs, authors were able to explore an archaeological landscape that is still largely hidden and a history still mainly obscured by time. The potential link between the rise and fall of urban life in the Angkor region and the use of reservoirs the one used in this study helps to unearth a little bit more about the the Khmer Kingdom and the marked environmental impact of Mahendraparvata.
Citation: Penny D, Chevance J-B, Tang D, De Greef S (2014) The Environmental Impact of Cambodia’s Ancient City of Mahendraparvata (Phnom Kulen). PLoS ONE 9(1): e84252. doi:10.1371/journal.pone.0084252
Image 2: journal.pone.0084252
Image 3: journal.pone.0084252
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Imagine a world where sight is limited by the extreme scattering of photons and smell is ineffective due to lethargic diffusion of molecules slowed by the density of water. In these conditions both sight and smell are limited. These conditions characterize, among other things, the ocean, where large sea mammals rely mostly on sound to communicate. The speed of sound is four times greater in water than in air at sea level. Male humpback whales have been observed communicating via ever-changing patterns of vocalization, which scientists have termed ‘song’. These whales compose their songs for the purposes of breeding, learning new songs as they come in contact with fellow crooners. Exactly how and when humpback whales learn these songs, however, remains a larger mystery.
Humpback whale song is identifiable because of its intricate pattern of structure. Songs are composed of multiple sounds types, for example, as these researchers suggest, ‘ascending cry,’ ‘moan,’ and ‘purr’. When units come together to form a pattern, these units form a phrase. Phrases repeated become a theme, and themes sung in a particular order compose a song. Researchers recorded these compositions by deploying radio-linked sonobuoys, which transmit underwater sound, and then digitized the recordings.
Here is an example of song recorded off the coast of New Caledonia in 2010:
Recordings, like the one above, reveal a possible link between three distinct breeding populations (marked D, E, and F on the map below) off the shores of eastern Australia and the island to the east of New Caledonia with a shared feeding ground in Antarctica (Area V).
In early 2010, the researchers identified four songs near Antarctica that matched themes from eastern Australia in 2009. By July, 2010, all four songs were then also identified in the group from New Caledonia. The themes recognized in New Caledonia in 2010 were entirely different than the themes of 2009, suggesting a movement of new songs eastward from eastern Australia to New Caledonia.
Consequently, the shared feeding grounds in Antarctica used by both the eastern Australia and New Caledonia groups in early 2010 may be the point at which these populations’ songs diverged.
By capturing sonobuoy recordings near feeding grounds off the Balleny Islands, researchers recorded the first instances of humpback whale song in Area V of Antarctica.
In addition, the inclusion of feeding grounds into the dynamic pattern of humpback whale song sharing helps shed new light on overall patterns of song learning and transmission from one breeding group to another.
Sound recording off the Balleny Islands near Antarctica, however, is challenging, and the sample of whale singers from this area remains relatively small. Regardless, the song documented here suggests Antarctica (Area V) as an emerging location for future study, and highlights the importance of feeding grounds in the transmission of humpback whale song. Through a better understanding of how and where these dynamic compositions radiate across the Southern Ocean, we can begin to understand humpback whale population connectivity and one of the best examples of non-human, large-scale learning demonstrated throughout the Southern Hemisphere.
Citation: Garland EC, Gedamke J, Rekdahl ML, Noad MJ, Garrigue C, et al. (2013) Humpback Whale Song on the Southern Ocean Feeding Grounds: Implications for Cultural Transmission. PLoS ONE 8(11): e79422. doi:10.1371/journal.pone.0079422
Images and Acoustic Files:
Acoustic File: doi:10.1371/journal.pone.0079422
Image 2: doi:10.1371/journal.pone.0079422
Image 3: doi:10.1371/journal.pone.0079422