Camel Crickets and the Dust Seeds of Parasitic Plants

A common way for plants to disperse their seeds is to entice animals to eat their seed-bearing fruits – a strategy known as endozoochory. Undigested seeds have the potential to travel long distances in the belly of an animal, and when they are finally deposited, a bit of fertilizer joins them. Discussions surrounding this method of seed dispersal usually have birds and mammals playing the starring roles – vertebrates, in other words. But what about invertebrates like insects? Do they have a role to play in transporting seeds within themselves?

Certain insects are absolutely important in the dispersal of seeds, particularly ants. But ants aren’t known to eat fruits and then poop out seeds. Instead they carry seeds to new locations, and some of these seeds go on to grow into new plants. In certain cases there is an elaisome attached to the seed, which is a nutritious treat that ants are particularly interested in eating. Elaisomes or arils have also been known to attract other insects like wasps and crickets, which may then become agents of seed dispersal. But endozoochory in insects, at first, seems unlikely. How would seeds survive not being crushed by an insect’s mandibles or otherwise destroyed in the digestion process?

camel crickets eating fruits of parasitic plants (via New Phytologist)

While observing parasitic plants in Japan, Kenji Suetsugu wanted to know how their seeds were dispersed. Many parasitic plants rely on wind dispersal, thus their seeds are minuscule, dust-like, and often winged. However, the seeds of the plants Suetsugu was observing, while tiny, were housed in fleshy fruits that don’t split open when ripe (i.e. indehiscent). This isn’t particularly unusual as other species of parasitic plants are known to have similar fruits, and Suetsugu was aware of studies that found rodents to be potential seed disperers for one species, birds to be dispersers of another, and even one instance of beetle endozoochory in a parasitic plant with fleshy, indehiscent fruit. With this in mind, he set out to identify the seed dispersers in his study.

Suetsugu observed three achlorophyllous, holoparisitic plants – Yoania amagiensis, Monotropastrum humile, and Phacellanthus tubiflorus. While their lifestyles are similar, they are not at all closely related and represent three different families (Orchidaceae,  Ericaceae, and Orobanchaceae respectively). All of these plants grow very low to the ground in deep shade below the canopy of trees. Air movement is at a minimum at their level, so seed dispersal by wind is not likely to be very effective. Using remote cameras, Suetsugu captured dozens of hours of footage and found camel crickets and ground beetles to be the main consumers of the fruits, with camel crickets being “the most voracious of the invertebrates.” This lead to the next question – did the feces of the fruit-eating camel crickets and ground beetles contain viable seeds?

Monotropastrum humile via wikimedia commons

After collecting a number of fecal pellets from the insects, Suetsugu determined that the seeds of all three species were “not robust enough to withstand mastication by the mandibles of the ground beetles.” On the other hand, the seeds passed through the camel crickets unscathed. A seed viability test confirmed that they were viable. Camel crickets were dispersing intact seeds of all three parasitic plants via their poop. The minuscule size of the seeds as well as their tough seed coat (compared to wind dispersed seeds of similar species) allowed for safe passage through the digestive system of this common ground insect.

In a later study, Suetsugu observed another mycoheterotrophic orchid, Yoania japonica, and also found camel crickets to be a common consumer of its fleshy, indehiscent fruits. Viable seeds were again found in the insect’s frass and were observed germinating in their natural habitat. Seutsugu noted that all of the fruits in his studies consumed by camel crickets are white or translucent, easily accessible to ground dwelling insects, and give off a fermented scent to which insects like camel crickets are known to be attracted. Camel crickets also spend their time foraging in areas suitable for the growth of these plants. All of this suggests co-evolutionary adaptations that have led to camel cricket-mediated seed dispersal.

Yoania japonica via wikimedia commons

Insect endozoochory may be an uncommon phenomenon, but perhaps it’s not as rare as we once presumed. As mentioned above, an instance of endozoochory by a beetle has been reported, as has one by a species of cockroach. Certainly the most well known example involves the wetas of New Zealand, which are large, flightless insects in the same order as grasshoppers and crickets and sometimes referred to as “invertebrate mice.” New Zealand lacks native ground-dwelling mammals, and wetas appear to have taken on the seed dispersal role that such mammals often play.

Where seeds are small enough and seed coats tough enough, insects have the potential to be agents of seed dispersal via ingestion. Further investigation will reveal additional instances where this is the case. Of course, effective seed dispersal means seeds must ultimately find themselves in locations suitable for germination in numbers that maintain healthy populations, which for the dust seeds of parasitic plants is quite specific since they require a host organism to root into. Thus, effective seed dispersal in these scenarios is also worth a more detailed look.

Further Reading:

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For more stories of seed dispersal check out the first issue of my new zine, Dispersal Stories.

Out Now! Dispersal Stories #1

Before I started this blog, I had spent 16 years publishing zines at a steady clip and sending them to all corners of the world through the mail. I had never really meant to abandon zines altogether, and in some ways, putting all my writing efforts into a blog felt a little like a betrayal. My intention had always been to one day put together another zine. Now, six and a half years later, I’m happy to report that day has come.

Rather than bring an old zine back from the grave, I decided to make a new zine. Thus, Dispersal Stories #1. It’s quite a bit different from zines I’ve made in the past, which were generally more personal and, I guess, ranty. In fact, Dispersal Stories is very much like this blog, largely because it is mostly made up of writing that originally appeared here, but also because its main focus (for now) is plants. What sets it apart is that, unlike this blog, it zeroes in on a specific aspect of plants. As the title suggests, it’s all about dispersal. For much of their life, plants are essentially sessile. Once they are rooted in place, they rarely go anywhere else. But as seeds, spores, or some other sort of propagule they are actually able to move around quite a bit. The world is their oyster. What’s happening during this period of their lives is the focus of Dispersal Stories.

But why do a zine about this? Apart from just wanting to do another zine after all these years, my hope is that Dispersal Stories will be the start of a much more ambitious project. A book perhaps. My interest in dispersal was born out of my interest in weeds, and there is so much that I would like to learn and share about both of these subjects – so much so that the blog just doesn’t really cut it. So, I’m expanding the Awkward Botany empire. First a zine, then a book, then … who knows? I’m an oyster! (Or something like that.)

Dispersal Stories #1 is available in our etsy shop, or you can contact me here and we can work something out. While you’re at it, check out our new sticker.

If you love looking at plants and learning their names, then you probably enjoy doing it any chance you get. Usually it’s an activity you do while walking, but who says you can’t botanize while riding a bike? This sticker is inspired by a friend who once said that while mountain biking you get to “see three times as many flowers in half the time!” Stick it on your bike or in some other prominent location to remind yourself and others that we can botanize anytime anywhere.

Your purchase of one or both of these items helps support what we do. You can also support us by buying us a ko-fi or putting money in our donorbox. Sharing these posts also helps us out. If you get a copy of the zine, let us know what you think by sending us an email, a message on twitter or facebook, or by leaving a comment below. As always, thanks for reading.

Related Posts:

Pine Cones Are Like Hangars for Pine Tree Seeds

Over the past year I’ve written about the making of pine tar and the drinking of pine needle tea. But why stop there? Pines are a fascinating group of plants, worthy of myriad more posts, and so my exploration into the genus continues with pine cones and the seeds they bear.

Pines are conifers and, more broadly, gymnosperms. They are distinct from angiosperms (i.e. flowering plants), with the most obvious distinction being that they don’t make flowers. Since they are flowerless, they are also fruitless, as fruits are seed-bearing structures formed from the ovary or ovaries of flowering plants. Pines do make seeds though, and, as in angiosperms, pollen is transported from a “male” organ to a “female” organ in order for seeds to form. Rather than being housed in a fruit, the seeds are essentially left out in the open, which is why the term “naked seeds” is frequently used in reference to gymnosperms.

seed cone of Scots pine (Pinus sylvestris ‘Glauca Nana’)

In the case of pines and other conifers, the seeds may be naked, but they’re not necessarily homeless. They have the protection of cones, which is where the female reproductive organs are located. Male, pollen cones are separate structures and are smaller and less persistent than the cones that house the seeds. A cone, also known as a strobilus, is a modified branch. A series of scales grow in a spiral formation along the length of the branch, giving the cone its shape. On the inside of these scales is where the seeds form, two per scale. First they are egg cells, and then, after pollination and a period of maturation, they become seeds. The scales protect them throughout the process and then release them when the time is right.

With more than 120 species in the genus Pinus, there is great diversity in the size, shape, and appearance of pine cones. While at first glance they don’t appear all that different from one another, the cones of each species have unique characteristics that can help one identify the pine they fell from without ever having to see the tree. Pine cones are also distinct from the cones of other conifers. For one, pine cones take at least two or, in some cases, three years to reach maturity, whereas the cones of other conifers develop viable seeds in a single year. Pine cones are also known to remain on the tree for several years even after the seeds are mature – in some species up to 10 years or more – and they don’t always part with their seeds easily. Lodgepole pines (Pinus contorta) require high temperatures to melt the resin that holds their scales closed, the cones of jack pine (P. banksiana) generally only open in the presence of fire, and the seeds of whitebark pine (P. albicaulis) are extracted with the aid of birds (like Clark’s nutcracker) and other animals.

immature seed cone of lodgepole pine (Pinus contorta)

Every pine cone is special in its own right, but some stand out in particular. The largest and heaviest pine cones are found on Coulter pine (P. coulteri), measuring up to 15 inches long and weighing as much as 11 pounds with scales that come to a sharp point. It’s understandable why the falling cones of this species are frequently referred to as widowmakers. Longer cones, but perhaps less dangerous, are found on sugar pine (P. lambertiana). The tallest trees in the genus, the cones of sugar pine consistently reach 10 to 20 inches long and sometimes longer.

Pine tree seeds are a food source for numerous animals, including humans. Most are so small they aren’t worth bothering with, however, several species have seeds that are quite large and worth harvesting. Most commercially grown pine nuts come from stone pine (P. pinea) and Korean pine (P. koraiensis). In North America, a wild source for pine nuts is found in the pinyon pines, which have a long history of being harvested and eaten by humans.

immature seed cone of ponderosa pine (Pinus ponderosa)

The seeds of many pines come equipped with little wings called samaras, which aid them in their dispersal. Upon maturity, pine cone scales open and release the seeds. Like little airplanes leaving the hangar, the seeds take flight. Wind dispersal is not an effective means of dispersal for all pines though. A study published in Oikos found that seeds weighing more than 90 milligrams are not dispersed as well by wind as lighter seeds are. When it comes to long distance dispersal, heavier seeds are more dependent on animals like birds and rodents, and some pines rely exclusively on their services. The author of the study, Craig Benkman, notes that “bird-dispersed pines have proportionately thinner seed coats than wind-dispersed pines,” which he points out in reference to Japanese stone pine (P. pumila) and limber pine (P. flexilis), whose seeds weigh around 90 milligrams yet rely mostly on birds for dispersal. Benkman suspects that the seeds of these two species “would probably weigh over 100 milligrams if they had seed coats of comparable thickness as wind-dispersed seeds.”

Whitebark pine, as mentioned above, holds tightly to its seeds. Hungry animals must pry them out, which they do. Pine seeds are highly nutritious and supplement the diets of a wide range of wildlife. Some of the animals that eat the seeds also cache them for later. Clark’s nutcrackers are particularly diligent hoarders, harvesting thousands more seeds than they can possibly consume and depositing them in small numbers in locations suitable for sprouting.

Even large seeds that naturally fall from their cones have a chance to be dispersed further. As the seeds become concentrated at the base of the tree, ground-foraging rodents gather them up and cache them in another location, which Benkman refers to as secondary seed dispersal.

Particularly in pine species with wind dispersed seeds, what the weather is like helps determine when the hangar door will open to release the flying seeds. When it is wet and rainy, the scales of pine cones close up. The seeds wouldn’t get very far in the rain anyway, so why bother? When warm, dry conditions return, the scales open back up and the seeds are free to fly again. You can even watch this in action in the comfort of your own home by following the instructions layed out in this “seasonal science project.”

immature seed cones of limber pine (Pinus flexilis)

mature seed cones of limber pine (Pinus flexilis)

Further Reading:

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Photos of pine cones were taken at Idaho Botanical Garden in Boise, Idaho

A Few Snags Near Ketchum and Stanley

A couple of weeks ago, Sierra and I were in Ketchum, Idaho taking a much needed mid-October vacation. The weather was great, and the fall color was incredible, so heading out on multiple hikes was a no-brainer. On our hikes, I found myself increasingly drawn to all of the snags. Forested areas like those found in the Sawtooth National Forest are bound to have a significant amount of standing dead trees. After all, trees don’t live forever; just like any other living being, they die – some of old age, some of disease or lightning strike or any number of other reasons. But death for a tree does not spell the end of its life giving powers. In the case of snags, it’s really just the beginning.

Death might come quick for a tree, but its rate of decomposition is slow. Fungi move in to begin the process and are joined by myriad insects, mosses, lichens, and bacteria. The insects provide food for birds, like woodpeckers and sapsuckers who hammer out holes in the standing trunk. As primary cavity nesters, they also nest in some of these holes. Secondary cavity nesters make a home in these holes as well. This includes a whole suite of birds, mammals, amphibians, and reptiles. Without the habitat provided by snags, many of these animals would disappear from the forest.

Eventually snags fall, and as the rotting continues, so does the dead tree’s contribution to new life. It’s at this point that snags become nurse logs or nurse stumps, providing habitat and nutrients for all sorts of plants, fungi, and other organisms.

Unfortunately I can’t bring a you a complete representation of the many snags of Sawtooth National Forest. You’ll have to visit sometime to see them all for yourself. Instead, what follows is a small sampling of a few of the snags we saw near Ketchum and Stanley.

new cavities in new snag

old cavities in old snag

knobby snag with lichens

lone snag on hillside

double-trunked snag

fallen snag

snags are more alive than you might think

just look at those cavities

For more snag and nurse log fun, check out the following episodes of Boise Biophilia:

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This will be the last post for a few weeks as I will be taking a break to finish working on a related project. I hope to be back sometime in December with more posts, as well as the unveiling of what I have been working on. In the meantime, you can stay updated by following Awkward Botany on Twitter or Facebook.

From Cut Flower to Noxious Weed – The Story of Baby’s Breath

One of the most ubiquitous plants in cut flower arrangements hails from the steppes of Turkey and neighboring countries in Europe and Asia. It’s a perennial plant with a deep taproot and a globe-shaped, multi-branched inflorescence loaded with tiny white flowers. In full bloom it looks like a small cloud hovering above the ground. It’s airy appearance earns it the common name baby’s breath, and the attractive and durable nature of its flowers and flower stalks, both fresh and dried, have made it a staple in the floral industry. Sadly, additional traits have led to it becoming a troublesome weed outside of its native range.

baby’s breath (Gypsophila paniculata) via wikimedia commons

Gypsophila paniculata is in the family Caryophyllaceae – sharing this distinction with other cut flowers like carnations and pinks, as well as other weeds like chickweed and soapwort. At maturity and in full bloom, baby’s breath might reach three to four feet tall; however, its thick taproot extends deep into the ground as much as four times its height. Its leaves are unremarkable and sparse, found mostly towards the base of the plant and sometimes with a blue or purplish hue. The flowers are numerous and small, have a sweet scent to them (though not appreciated by everyone), and are pure white (sometimes light purple or pink).

Each flower produces just a few seeds that are black, kidney-shaped, and minuscule. Many of them drop from their fruits and land near their parent plant, but some are retained within their little capsules as the flower stalk dries and becomes brittle. Eventually a stiff breeze knocks the entire inflorescence loose and sends it tumbling across the ground. Its rounded shape makes it an effective tumbleweed, as the remaining seeds are shaken free and scattered far and wide.

baby’s breath flowers close up (via wikimedia commons)

Being a tumbleweed gives it an advantage when it comes to dispersing itself and establishing in new locations, but this is not the only trait that makes baby’s breath a successful weed. Its substantial taproot, tolerance to drought and a variety of soil conditions, and proclivity to grow along roadsides, in ditches, and abandoned fields also make it a formidable opponent. Mowing the plant down does little to stop it, as it grows right back from the crown. Best bets for control are repeated chemical treatments or digging out the top portion of the taproots. Luckily its seeds are fairly short-lived in the soil, so vigilant removal of seedlings and not allowing the plant to reproduce can help keep it in check. Baby’s breath doesn’t persist in regularly disturbed soil, so it’s generally not a problem in locations that are often cultivated like agricultural fields and gardens.

The first introductions of baby’s breath to North America occurred in the 1800’s. It was planted as an ornamental, but it wasn’t long before reports of its weedy nature were being made. One source lists Manitoba in 1887 as the location and year of the first report. It is now found growing wild across North America and is featured in the noxious weed lists in a few states, including Washington and California. It has been a particular problem on sand dunes in northwest Michigan, where it has been so successful in establishing itself that surveys have reported that 80% of all vegetation in certain areas is composed of baby’s breath.

baby’s breath in the wild (via wikimedia commons)

Invading sand dune habitats is particularly problematic because extensive stands of such a deep-rooted plant can over-stabilize the soil in an ecosystem adapted to regular wind disturbance. Plants native to the sand dunes can be negatively affected by the lack of soil movement. One species of particular concern is Pitcher’s thistle (Cirsium pitcheri), a federally threatened plant native to sand dunes along the upper Great Lakes. Much of the research on the invasive nature of baby’s breath and its removal comes from research being done in this region.

Among numerous concerns that invasive plants raise are the affects they can have on pollinator activity. Will introduced plants draw pollinators away from native plants or in some other way limit their reproductive success? Or might they help increase the number of pollinators in the area, which in turn could benefit native plants (something known as the magnet species effect)? The flowers of baby’s breath rarely self-pollinate; they require insect visitors to help move their pollen and are highly attractive to pollinating insects. A study published in the International Journal of Plant Sciences found that sand dune sites invaded by baby’s breath attracted significantly more pollinators compared to uninvaded sites, yet this did not result in more pollinator visits to Pitcher’s thistle. According to the researchers, “a reduction in pollinator visitation does not directly translate to a reduction in reproductive success,” but the findings are still a concern when it comes to the future of this threatened thistle.

Perhaps it’s no surprise that a plant commonly found in flower arrangements is also an invasive species, as so many of the plants we’ve grown for our own pleasure or use have gone on to cause problems in areas where they’ve been introduced. However, could the demand for this flower actually be a new business opportunity? Noxious weed flower bouquets anyone?

Related Posts:

Eating Weeds: Chicory

Over the course of human history, plant species once esteemed or considered useful have been recategorized into something less desirable. For one reason or another, plants fall out of favor or wear out their welcome, and, in come cases, are found to be downright obnoxious, ultimately losing their place in our yards and gardens. The particularly troublesome ones are branded as weeds, and put on our “do not plant” lists. These plants are not only unfavored, they’re despised. But being distinguished as a weed doesn’t necessary negate a plant’s usefulness. It’s likely that the plant still has some redeeming characteristics. We’ve just chosen instead to pay more attention its less redeeming ones.

Chicory is a good example of a plant like this. At one point in time, Cichorium intybus had a more prominent place in our gardens, right alongside dandelions in fact. European colonizers first introduced chicory to North America in the late 1700’s. Its leaves were harvested for use as a salad green and its roots were used to make a coffee additive or substitute. Before that, cultivation of chicory for these and other purposes had been going on across Europe for thousands of years, and it still goes on today to a certain extent. Along with other chicory varieties, a red-leafed form known as radicchio and a close cousin known as endive (Chicorium endivia) are grown as specialty crops, occassionally finding their way into our fanciest of salads.

Radicchio di Chioggia (Cichorium intybus var. foliosum) is a cultivated variety of chicory. (via wikimedia commons)

Chicory’s tough, adaptable nature and proclivity to escape cultivation have helped it become widespread, making itself at home in natural areas as well as urban and rural settings. Its perennial life history helps make it a fixture in the landscape. It sends down a long, sturdy taproot and settles in for the long haul. It tolerates dry, compacted soils with poor fertility and doesn’t shy away from roadside soils frequently scoured with salts. It’s as though it was designed to be a city weed.

Unlike many other perennial weeds, chicory doesn’t spread vegetatively. It starts its life as a seed, blown in from a nearby plant. After sprouting, it forms a dandelion-esque rosette of leaves during its first year. Wiry, branched stems rise up from the rosette in following years, reaching heights of anywhere from about a foot to 5 or 6 feet. When broken, leaves, stems, and roots ooze a milky sap. Abundant flowers form along the gangly stems. Like other plants in the aster family, each flower head is composed of multiple flowers. Chicory flower heads are all ray flowers, lacking the disc flowers found in the center of other plants in this family. The petals are a brilliant blue – sometimes pink or white. Individual flowers last less than a day and are largely pollinated by bees. The fruits lack the large pappus found on dandelions and other close relatives, but the seeds are still dispersed readily with the help of wind, animals, and human activity.

chicory (Cichorium intybus) via wikimedia commons

The most commonly consumed portions of chicory are its leaves and roots. Its flowers and flower buds are also edible. Young leaves and blanched leaves are favored because they are the least bitter. Excluding the leaves from light by burying or covering them up keeps them pale and reduces their bitter flavor. This is standard practice in the commercial production of certain chicory varieties. The taproots of chicory are dried, roasted, and ground for use as a coffee substitute. They are also harvested commercially for use as a natural sweetener due to their high concentration of inulin.

my puny chicory root

I harvested a single puny chicory root in order to make tea. On my bike ride to work there is a small, sad patch of chicory growing in the shade of large trees along the bike path. I was only able to pull one plant up by the roots. The others snapped off at the base. So, I took my tiny root, dried and roasted it in the oven, and ground it up in a coffee grinder. I followed instructions for roasting found on this website, but there are many other sources out there. I had just enough to make one small cup of tea, which reminded me of dandelion root teas I have had. Sierra found it to be very bitter, and I agreed but still enjoyed it. I figure that wild plants, especially those growing in stressful conditions like mine was, are likely to be more bitter and strong tasting compared to coddled, cultivated ones found in a garden.

roasted chicory root

roasted and ground chicory root

When I find a larger patch of feral chicory, I hope to try one of several recipes included in Luigi Ballerini’s book, A Feast of Weeds, as well as other recipes out there. I’ll be sure to let you know how it goes.

Are you curious to know how chicory became such a successful weed in North America? Check out this report in Ecology and Evolution to learn about the genetic explanation behind chicory’s success.

Seed Dispersal by Way of Tree Climbing Goats

Goats are surprisingly good climbers. Given the opportunity, they’ll climb just about anything, including each other. So what’s stopping them from climbing a tree, especially if there is something up there they can eat? And so they do. Tree climbing goats are such a fascinating sight, they even have their own calendar. But the story doesn’t end there. The goats find food in the trees, entertaining humans as they go; meanwhile, the trees have a reliable partner in the goats, who inadvertently help disperse the tree’s seeds.

In general, goats don’t need to climb trees to find food. Goats aren’t known to be picky eaters, and there is usually plenty for them to eat at ground level. However, in arid climates where food can become limited, ascending trees to eat foliage and fruits is a matter of survival. This is the case in southwestern Morocco, where goats can be found in the tops of argan trees every autumn gorging on the fruits of this desert tree.

goats in Argania spinosa via wikimedia commons

Argan (Argania spinosa) is a relatively short tree with a sprawling canopy and thorny branches. It is the only species in its genus and is endemic to parts of Morocco and neighboring Algeria. The tree is economically important to the area due to the oil-rich seeds found within its bitter fruits. Argan oil has a variety of culinary uses and is also used medicinally and in cosmetics. To get to the oil, goats are often employed in harvesting the fruits. The goats retrieve the fruits from the tops of the trees and consume their fleshy outer layer. The hard, seed-containing pits are expelled, collected, and cracked open to get to the seeds.

This is where a team of researchers from Europe come in. There has been some confusion as to how the pits are expelled, with some reports claiming that they pass through the goats digestive track and are deposited in their manure. This is a common way for the seeds of many other plant species to be dispersed, and is carried out not only by goats and other ruminants, but also by a wide variety of mammals, as well as birds and even reptiles. However, considering the average size of the pits (22 mm long x 15 mm wide), the researchers thought this to be unlikely.

fruits of Argania spinosa via wikimedia commons

Others reported that the seeds were spat out in the goats’ cud while they ruminated. Goats, like other ruminants, have stomachs composed of multiple compartments, the first of which being the rumen. Partially digested food, known as cud, is sent back into the mouth from the rumen for further chewing and may be spat out or swallowed again. Goats are known to ruminate in the same location that they defecate, which results in confusion as to when and how certain seeds, like those of the argan tree, are deposited.

By feeding various fruits to a group of goats, the researchers were able to test the hypothesis that seeds could be regurgitated and spat from the cud and that this is a viable method of seed dispersal. The researchers reported that larger seeds were more commonly spat out than smaller seeds, but that “almost any seed could be ejected during, mastication, spat from the cud, digested, or defecated.” The viability of spat out seeds was tested, and over 70% of them were found to be viable.

pits and seeds of Argania spinosa via wikimedia commons

This discovery suggests that seed dispersal via spitting by ruminants could be a common occurrence – possibly far more common than previously considered. The researchers postulate that studies that have only considered seeds dispersed in manure “may have underestimated an important fraction of the total number of dispersed seeds” and that the seeds spat from the cud likely represent different species from those commonly dispersed in dung. In addition, the seeds of some species don’t survive the digestive tract of ruminants, so “spitting from the cud may represent their only, or at least their main, dispersal mechanism.”

This study surrounding the argan trees was followed up by the same group of researchers with a literature review that was published last month. The review looked into all available studies that mentioned seed dispersal via regurgitation by ruminants. While they considered over 1000 papers, only 40 published studies were found to be relevant for the review. From these studies, they determined that the seeds of 48 plant species (representing 21 different families) are dispersed by being spat from a ruminant’s cud, and that most of these plant species are trees and shrubs whose fruits contain large seeds. Also of note is that ruminants across the globe are doing this – representatives from 18 different genera were mentioned in the studies.

ruminating goat via wikimedia commons

The researchers conclude that this is a “neglected” mechanism of seed dispersal. It’s difficult to observe, and in many cases it hasn’t even been considered. Like so many other animals, ruminants can disperse seeds in a variety of ways. Seeds can attach to their fur and be transported wherever they go. They can pass through their digestive track and end up in their dung, potentially far from where they were first consumed. And, as presented here, they can be spat out during rumination. Investigations involving all of these mechanisms and the different plant species involved will allow us to see, in a much clearer way, the role that ruminants play in the dispersal of seeds.