The Beech Aphid Poop-Eater

Interactions between organisms are what got me into ecology. After all, no living thing operates in a vacuum. I recently had an experience that reminded me of this on a recent hike with some friends. We stumbled across a strange black growth on the limb of a beech tree. It was like a crusty black stalagmite on the branch. Luckily, my friend Kristen happened to be there. Her expertise in plant/fungal interactions was exactly what this moment called for. What we had found was one of the most unique fungi I have seen in a long time. What's more, it only lives on American beech trees (Fagus grandifolia).  

The fungus in question is a type of sooty mold known scientifically as Scorias spongiosa. I'm not sure if it has a widely used common name but at least one source I referenced lovingly referred to it as "the beech aphid poop-eater." Though that name doesn't come close to rolling off the tongue, it nonetheless describes the life cycle of this bizarre fungus quite accurately. 

A  Scorias spongiosa  colony changing from its asexual phase (beige) to its sexual phase (black)

A Scorias spongiosa colony changing from its asexual phase (beige) to its sexual phase (black)

We begin with an aphid called the beech blight aphid (Grylloprociphilus imbricator). It is not the insect responsible for beech bark disease but it is specific to American beech. These aphids are gregarious little creatures and large populations can quickly accumulate on beech trees. They secrete a white woolly substance, making them quite easy to spot. Like all aphids, they feed on sap and poop out mass quantities of honeydew (sugary aphid poop) in the process. 

A colony of beech blight aphids

A colony of beech blight aphids

It is this honeydew that the sooty mold feeds on. Spores that manage to land on the accumulation of aphid poop begin to grow fungal hyphae. At first, the fungus takes on a beige coloration. Gradually it forms a tangled mass of fungal tissues. It is important to note that it is not a parasite on the beech tree whatsoever.  S. spongiosa simply feeds on the sugary beech blight aphid poop. The reason S. spongiosa can grow into such a large formation has to do with the colonial nature of the beech blight aphid. The more aphid poop that accumulates, the lager S. spongiosa will grow.

By mid summer, some S. spongiosa resemble large sponges on the branches and trunks of beech trees. At this point they are producing asexual spores. Later in the year, the fungus switches over to producing sexual spores. This shift also causes the fungal mass to produce more melanin, which gives it its black coloration. It also becomes much more durable, meaning there is a good chance of finding this fungus outside of the growing season. 

Patches of  Scorias spongiosa  covering the bark of a beech tree

Patches of Scorias spongiosa covering the bark of a beech tree

What amazes me the most is that this fungus will only ever be found on American beech trees. The reason for this is because it feeds only on the poop of the beech blight aphid, which, as its common name suggests, feeds only on beech trees. This is but one example of the myriad ecological interactions that makeup life on this planet. It is also a reminder that single species conservation efforts forget most of what makes a species special. 

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]

Herbarium Biases

Humans carry countless biases with them wherever they go. Even the logical mind of a scientist is no stranger to prejudice. Identifying such biases in the way we do science is key to improving the discipline and, as computing power and access to big data increases, we are gaining a better understanding of just how prevalent our biases really are. A recent study that looked at herbarium collections around the world aims to do just that.

With herbaria closing shop around the globe, the need to digitize collections has never been more urgent. Although more and more collections are finding their way into digital libraries, a vast majority of herbarium collections risk being lost forever. This alone represents a major bias. Such organismal science has sadly been scoffed at in recent decades. Still, enough collections have been entered into databases that interesting patterns are starting to emerge. A team of researchers recently took a closer look at roughly 5 million digitized floras representing the most complete digital floras from Australia, South Africa, and New England.

In doing so, the team was able to find some startling biases in these collections. They broke them down into a handful of categories with the hope that botanists and ecologists can start to improve on these gaps over the coming decades. Although the floras they examined by no means represent anything close to a complete picture of our floristic understanding of the world, they nonetheless mirror issues that are sure to crop up no matter where collections have been made.

The first major category is that of spatial or geographic bias. This occurs whenever specimens are collected at a higher frequency in one place over another. There are likely many reasons for this - ease of access, proximity to research institutions, just to name a few. The team found that herbarium collections tended to occur in the same areas through time. What's more, they tended to occur more often near roads with a surprising 50% of specimens collected within 2 km of a roadside. This can result in a highly skewed perspective of the kind of taxa represented in a region. Roadside vegetation is comprised of species capable of dealing with runoff, soil compaction, and pollution, and is likely depauperate of taxa less able to handle such conditions. They also found a elevational bias, with a majority of specimens having been collected below 500 meters. 

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

The second major category is that of temporal bias. This occurs whenever specimens are collected more frequently during certain parts of the year over others. The team found that collections disproportionately occurred during spring and summer months. As anyone who hikes can tell you, there is a lot of variation among plant communities from season to season and any good collection should sample a location multiple times a year. In addition to seasonal biases, the team also found extreme biases in terms of history. Collections in South Africa and Australia started to rise shortly after World War II and peaked in the 1980's and 1990's respectively. Compare this to New England where peak collections occurred nearly 100 years prior. If we are to track long term trends and changes in the flora of various regions, collections need to occur far more regularly. Obviously institutions have shied away from such investigations in recent decades. Only public interest and funding can reverse such trends, hopefully not before it is too late.

The third major bias they found is that of trait bias. This occurs whenever a collector specifically aims for species with a certain life history characteristic (annual vs. perennial, woody vs. herbacious) as well as species of conservation concern. Indeed, the team found that perennial species were over-represented in most herbarium collections. Also, gramminoids dominated herbarium collections in Australia and South Africa whereas herbs and trees were over-represented in New England. Another interesting pattern that emerged is that short plants had higher representation in harbaria than taller species. Obviously this has a lot to do with ease of collection.

Another pattern that emerged which is of conservation concern is that threatened or endangered species are severely under-represented in herbarium collections. Although care must be taken to not over-collect species whose numbers are dwindling, their lack of representation in herbarium collections can seriously hinder conservation efforts. Such under-represenation can lead to erroneous estimations of species abundances and distributions. It can also hinder our understanding of plant community dynamics.

The fourth major bias is that of phylogenetic bias. Certain clades are more sought after than others. This leads to a disproportionate amount of showy or valuable species turning up in herbaria around the globe. It also leads to an over-representation of potentially "useful" plant species in terms of things like medicines or dyes. This leaves a large portion of regional floras under-sampled. This in turn exacerbates issues relating to our understanding of plant community dynamics and the change in plant abundance and distribution through time.

Finally, the fifth major bias is that of collector bias. This pattern stems from the fact that in all the regions sampled for this study, a majority of the collections were made by only a handful of individuals. This means that all of these collections are the products of the habits and preferences of these collectors. Some collectors may favor sampling the entire flora of a region whereas others may favor certain clades over others. Similarly, some collectors may favor plants with interesting physiologies whereas other may favor plants with peculiar life-histories such as carnivores or succulents.

The use and importance of herbaria has changed a lot over the last two centuries. Whereas they largely started out as a tool for taxonomists, the utility of herbarium collections has since expanded into areas that were never thought possible. With the advent of new technologies, who knows what the future holds. Of course, this means nothing if interest and support for herbarium collections continues to decline. Their utility in the context of research and conservation cannot be understated. We need herbaria now more than ever. Understanding biases is a great step towards improving the discipline. We must aim to improve collections in these so-called cold spots and to avoid as many biases as possible in doing so.

Photo Credits: Wikimedia Commons

Further Reading: [1]

 

On Orchids and Fungi

It is no secret that orchids absolutely need fungi. Fungi not only initiate germination of their nearly microscopic seeds, the mycorrhizal relationships they form supplies the fuel needed for seedling development. These mycorrhizal fungi also continue to keep adult orchids alive throughout their lifetime. In other words, without mycorrhizal fungi there are no orchids. Preserving orchids goes far beyond preserving the plant. Despite the importance of these below-ground partners, the requirements of many mycorrhizal fungi are poorly understood.

Researchers from the Smithsonian Environmental Research Center have recently shone some light on the needs of these fungi. Their findings highlight an important concept in ecology - conservation of the system, not just the organism. Their results clearly indicate that orchid conservation requires old, intact forests.

Their experiment was beautifully designed. They added seeds and host fungi to dozens of plots in both young (50 - 70 years old) and old (120-150 years old) forests. They continued to monitor the progress of the seeds over a period of 4 years. Orchid seeds only germinated in plots where their host fungi were added. This, of course, was not very surprising.

The most interesting data they collected was data on fungal performance. As it turns out, the host fungi displayed a marked preference for older forests. In fact, the fungi were 12 times more abundant in these plots. They were even growing in areas where the researchers had not added them. What's more, fungal species were more diverse in older forests.

The researchers also noted that host fungi grew better and were more diverse in plots where rotting wood was added. This is because many mycorrhizal fungi are primarily wood decomposers. Nutrients from the decomposition of this wood are then channeled to growing orchids (as well as countless other plant species) in return for carbohydrates from photosynthesis. It is a wonderful system that functions at its best in mature forests.

This research highlights the need to protect and preserve old growth forests more than ever. Replanting forests is wonderful but it may be centuries before these forests can ever support such a diversity of life. Also, this stands as a stark reminder of the importance of soil conservation. Less obvious to most is the importance of decomposition. Without dead plant material, such fungal communities would have nothing to eat. Clearing a forest of dead wood can be just as detrimental in the long run as clearing it of living trees.

Research like this is made possible by the support of organizations such as the Native North American Orchid Conservation Center. Head on over to www.indefenseofplants.com/shop and pick up an In Defense of Plants sticker. Part of the proceeds are donated to this wonderful organization, which helps support research such as this! As this research highlights: What is good for orchids is good for the ecosystem.

Further Reading:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2012.05468.x/abstract;jsessionid=3385C965FF5BA4CB83290005DFD47FD1.f01t02

Cyclamen

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There is something about flowers with reflexed petals that I find quite appealing. That is probably why I have always had a soft spot for Cyclamen. These interesting little plants are quite popular as horticultural specimens due to their relative hardiness. A lush individual can really brighten up a room. As with any common house plant, I am always eager to learn about their ecology. A quick search for Cyclamen in the literature turns up some interesting facts. 

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Cyclamen are native to Europe, the Mediterranean Basin, Iran, with a single species native to Somalia. There are approximately 23 different species and a decent amount of revisions regarding where they fit taxonomically. The latest that I am aware of has placed this genus in a subfamily within Primulaceae. Though they seem to grow well in a lot of different habitats, most species appear to be at home growing along mountainsides in stable scree slopes. Each plant grows from a true tuber, which allows them energy stores for re-sprouting after a dry season dormancy. 

The flowers are adapted for buzz pollination, not unlike tomatoes and their relatives. However, some researchers have noted that for some species, buzz pollination is a rare event. Instead, many non-specialist pollinators are the most frequent visitors. Some have taken this as a sign that certain species of Cyclamen have lost their original pollinator for an unknown reason. 

Throughout their range, many species have been severely depleted due to over-collection for the horticulture trade. As such, a handful of species are considered quite endangered. Luckily, there are many organizations out there that are cultivating these species on a large scale to take pressure off of wild populations. There may be hope after all. However, some climate change projections put other species at risk of loosing the habitats that sustain them. This is especially true for montane species. Only time will tell. 

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Photo Credit: Wikimedia Commons

Further Reading:

http://www.sciencedirect.com/science/article/pii/S0367253006000211

http://www.biomedcentral.com/1471-2148/6/72

http://www.amjbot.org/content/87/9/1325.full

http://www.cyclamen.org/indexCS.html

Tillandsias and Ants

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Tillandsias are all the rage. Their relative ease of care has found them included in seemingly every terrarium sold these days - often in very inappropriate circumstances that result in their death. There is no denying that these epiphytic relatives of the pineapple are unique and beautiful plants but I would argue that their ecology is probably the coolest aspect about them. I am particularly fond of the bulbous species because of their relationship with ants. 

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That's right, there are upwards of 13 species of bulbous Tillandsia that offer up housing for ants. If you look closely at the leaves of these species, you will notice that they roll up to form tubes that lead down into the bulb. The space between the leaves is a hollow chamber, a perfect microclimate for ants to nest. In many habitats, the Tillandsia offer better housing than the surrounding environment. One would be surprised at how many ants can fit in there too. Colonies containing anywhere between 100 - 300 individuals are not unheard of. 

The rewards for the plant are obvious. Ants provide nutrients as well as protection. In return the ants get a relatively safe and dry place to live. Ant houses have been recorded in roughly 13 different species, many of which are some of the most commonly sold Tillandsias on the market like T. baileyi, T. balbisiana, T. bulbosa, and T. caput-medusae. If this doesn't make your hanging glass Tillandsia orb even cooler then I don't know what will.

Photo Credits: scott.zona (http://bit.ly/16kZ1RR) and Alex Popovkin (http://bit.ly/1BXMEUH)

Further Reading:

http://www.jstor.org/stable/2483400?seq=1#page_scan_tab_contents

http://www.geraceresearchcentre.com/pdfs/2ndBotany/7_Eshbaugh_2ndBotany.pdf

Slippery When Wet

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Pitcher plants in the genus Nepenthes have been getting a lot of attention in the literature as of late. Not only have researchers discovered the use of ultraviolet pigments around the rims of their pitchers, it has also been noted that the pitchers of many species aren't as slippery as we think they are. Indeed, scientists have noted that prey capture is at its highest only when the pitchers are wet. This seems counterintuitive. Why would a plant species that relies on the digestion of insects for most of its nitrogen and phosphorus needs produce insect traps that are only effective at certain times? After all, it takes a lot of energy for these plants to produce pitchers, which give little to nothing back in the way of photosynthesis. 

The answer to this peculiar conundrum may lie in the types of insects these plants are capturing. Ants are ubiquitous throughout the world. Their gregarious and exploratory nature has provided ample selection pressures for much of the plant kingdom. They are particularly well known for their military-esque raiding parties. It is this behavior that researchers have looked at in order to explain the intermittent effectiveness of Nepenthes pitchers. 

A recent study that looked at Nepenthes rafflesiana found that ants made up 65% of the prey captured, especially on pitchers produced up in the canopy. What's more, younger pitchers produced closer to the ground were found to be much more slippery (containing more waxy cells) than those produced farther up on the plant. When the pitchers of this species were kept wet, prey capture consisted mostly of individual insects such as flies. However, when allowed to dry between wettings, the researchers found that prey capture, specifically ants, increased dramatically. How is this possible?

It all goes back to the way in which ants forage. A colony sends out scouts in all directions. Once a scout finds food, it lays down a pheromone trail that other ants will follow. It is believed that this is the very behavior that Nepenthes are relying on. The traps produce nectar as a lure for their insect prey. As the traps dry up, the nectar becomes concentrated. Ants find this sugary treat irresistible. However, if the pitcher were to be slippery at all times, it is likely that most ant scouts would be killed before they could ever report back to the colony. By reducing the slippery waxes, especially around the rim of the trap, the Nepenthes are giving the ants a chance to "spread the news" about this new food source. Because these plants grow in tropical regions, humidity and precipitation can fluctuate wildly throughout a 24 hour period. If the scouting party returns at a time in which the pitchers are wet then the plant stands to capture far more ants than it did if it had only caught the scout. 

This is what is referred to as batch capture. The plants may be hedging their bets towards occasional higher nutrient input than constant low input. This is bolstered by the differences between pitchers produced at different points on the plant. Lower pitchers, especially on younger plants are far more waxy and thus are constantly slippery. This allows constant prey capture to fuel rapid growth into the canopy. Upper pitchers on older individuals want to maximize their yields via this batch capture method and therefore produce fewer waxy cells, relying on a humid climate to do the work for them. It is likely that this is a form of tradeoff which benefits different life cycle stages for the plant. 

Photo Credit: Andrea Schieber (http://bit.ly/1xUsGJk)

Further Reading:

http://rspb.royalsocietypublishing.org/content/282/1801/20142675

Sandfood

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Pholisma is yet another amazing genus of parasitic plants. Endemic to the southwestern United States and Mexico, these peculiar members of the borage family tap into the roots of a variety of plant species. They do not photosynthesize and therefore obtain all the nutrients they need from their hosts. Oddly enough, researchers have found that most of their water needs are met by absorbing dew through the stomata on their highly reduced, scale-like leaves. Water is then stored in their highly succulent stems. Throughout their limited range, Pholisma are critically imperiled. Development and agriculture have already eliminated many populations. To add insult to injury, the dunes in which most extant populations are found are owned by the BLM and are open to heavy off-road ATV traffic, which will likely push them to the brink of extinction if nothing is done to limit such recreational use. Unless people speak up about protecting these plants and their habitats, they could disappear for good.

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Photo Credits: [1] [2] [3]

Further Reading: [1] [2]

Noble Rhubarb

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The Himalayas. If there was ever a natural wonder worthy of the title "epic" it would certainly be these towering peaks. Home to some of the tallest points on our planet, these ragged peaks are best known for the near insurmountable challenges faced by adventurers from all around the world. Considering their elevation, it would seem that permanent life simply isn't possible on these mountains. However, this could not be further from the truth. Among sprawling shrubs and diminutive herbs towers one of the most peculiar plants known to the world. To make things more interesting, it is a relative of rhubarb, a denizen of gardens and pies throughout much more hospitable climates. 

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Meet the noble rhubarb, Rheum nobile. Growing at elevations between 13,000 and 15,000 feet (4000–4800 m), this species is quite deserving of its noble status. Plants growing at such elevations face some serious challenges. Temperatures regularly drop well below freezing and there is no shortage of damaging UV radiation. As with most alpine zones, a majority of plants cope with these conditions by growing prostrate over the ground and taking what little refuge they can find behind rocks. Not Rheum nobile. This member of the buckwheat family can grow to heights of 6 feet, making it easily the tallest plant around for miles. 

The most striking feature of this plant is the large spire of translucent bracts. These modified leaves contain no chlorophyll and thus do not serve as centers for photosynthesis. Instead, these structures are there to protect and warm the plant. Tucked behind the bracts are the flowers. If they were to be exposed to the elements, they would either freeze or be fried by UV radiation. Instead, these ghostly bracts contain specialized pigments that filter out damaging UV wavelengths while at the same time creating a favorable microclimate for the flowers and seeds to develop. In essence, the plant grows its own greenhouse.

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As a result, temperatures within the plant can be as much as 10 degrees warmer than the ambient temperatures outside. At such elevations, this is a real boost to its reproductive efforts. Even more of a challenge is the fact that at this elevation, pollinators are often in short supply. Plants have to do what they can to get their attention. Not only does Rheum nobile offer a visual cue that is in stark contrast to its bleak surroundings, it also goes about attracting pollinators chemically as well.

Rheum nobile has struck up a mutualistic relationship with fungus gnats living at these altitudes. The plant produces a single chemical compound that attracts the female fungus gnats. The females lay their eggs in the developing seeds of the plant but, in return, pollinate far more flowers than they can parasitize. These organisms have managed to strike a balance in these mountains. In return for pollination, the fungus gnats have a warm place to raise their young that is sheltered from the damaging UV radiation outside. 

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3] [4] [5]

The Holoparasitic Mistletoes

Flowers of   Tristerix aphyllu s

Flowers of Tristerix aphyllus

The order collectively referred to as mistletoes is incredibly diverse. They range in size from rather large trees down to little more than a couple leaves, barely recognizable on their hosts. Even more unique are the mistletoes that have foregone much of what we would readily recognize as an actual plant. These parasitic plants have adopted an endophytic lifecycle, living their entire lives within the vascular tissues of their host plants, only visible to observers when in flower. 

Tristerix aphyllus is one such species. Its hosts are cacti in the genus Echinopsis (formerly Trichocereus) native to Columbia and Chile. Being an endophyte, the majority of this mistletoe lives as a mycelial-like network of filaments that wrap around the vascular tissues of the host cactus. The only part of the mistletoe that ever emerges are the flowers. They come in both red and yellow forms. What may appear to be lovely cactus covered in red flowers are actually the flowers of Tristerix. Strangely enough, the occasional small leaf is produced on the flowering branches. Though there is chlorophyll in the leaf, researchers believe that they perform little if any photosynthesis.

Fruiting   Tristerix aphyllu s

Fruiting Tristerix aphyllus

This is not a parasitic relationship that is unique to cacti either. Africa has its own endoparasitic mistletoe as well. However, as we have discussed before, Africa does not have any native cacti (http://on.fb.me/1zPbac7). Instead, through convergent evolution, plants in the genus Euphorbia have followed similar adaptive trajectories. As such, at least one species of African mistletoe has followed suit.

Flowers of   Viscum minimum

Flowers of Viscum minimum

A species known scientifically as Viscum minimum finds the cactus-like Euphorbia horrida and E. polygona to its liking. Like Tristerix, Viscum minimum is endoparasitic, living entirely within the tissues of its Euphorbia host until it decides to flower. It too produces brightly colored berries that aid in its dispersal to a new host. 

The main seed dispersers are birds. After consumption, a bird either regurgitates the embryo or passes it out the other end. If that bird happens to be sitting on a host cactus or Euphorbia, the embryo will grow into a seedling that quickly taps into its new host and begins its internal parasitic life. It will not be seen again until it flowers.

Viscum minimum  beginning to set seed.

Viscum minimum beginning to set seed.

Photo Credit: [1] [2] [3] [4]


Further Reading: [1] [2] [3] [4]

 

A North American Cycad and its Butterfly

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Most of us here in North America probably know cycads mainly from those encountered in botanical gardens or as the occasional houseplant. However, if you want to see a cycad growing in the wild, you don't have to leave North America to do so. One must only travel to parts of Georgia and Florida where the coontie can be found growing in well drained sandy soils. 

Known scientifically as Zamia integrifolia, the coontie is definitely your typical cycad, just on a smaller scale. Plants are either male or female and, like all gymnosperms, they produce cones. Here in the United States, the coontie is considered near threatened. Decades of habitat destruction and poaching have caused serious declines in wild populations. This has come at a great cost to at least one other organism as well.

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Thought to be extinct for over 20 years, a butterfly known as the atala (Eumaeus atala) require this lovely little cycad to complete their lifecycle. Like all cycads, the coontie produces a toxin known as "cycasin." Just as monarchs become rather distasteful to predators by feeding on milkweeds during their larval stage, so too do the larvae of the atala. The brightly contrasting colors of both the caterpillars and the adults let potential predators know that messing with them isn't going to be a pleasant experience. The reason for its decline in the wild is due to the loss of the coontie. 

Rediscovered only recently, populations of this lovely butterfly are starting to rebound. Caterpillars of the atala are voracious eaters and a small group of them can quickly strip a coontie of its foliage. For this reason, large populations of coontie are needed to support a viable breeding population of the atala. The coontie is becoming a popular choice for landscaping, especially in suburban areas of southeastern Florida, which is good news for the atala. As more and more people plant coonties on their property, more and more caterpillars are finding food to eat. This just goes to show you the benefits of planting natives!

An atala caterpillar

An atala caterpillar

Photo Credit: [1] [2] [3]

Further Reading: [1] [2] [3]