An Ancient Hawaiian Moss

Sphagnum_palustre_030208a.jpg

The cloud forests of Kohala Mountain on the island of Hawai'i are home to a unique  botanical community. One plant in particular is quite special as it may be one of the most ancient clonal organisms in existence. Look down at your feet and you may find yourself surrounded by a species of moss known as Sphagnum palustre. Although this species enjoys a broad distribution throughout the northern hemisphere, its presence on this remote volcanic island is worth closer inspection. 

Hawai'i is rather depauperate in Sphagnum representatives and those that have managed to get to this archipelago are often restricted to growing in narrow habitable zones between 900 to 1,900 meters in elevation as these are the only spots that are cool and wet enough to support Sphagnum growth. Needless to say, successful colonization of the Hawaiian Islands by Sphagnum has been a rare event.  The fact that Sphagnum palustre was one of the few that did should not come as any surprise. What should surprise you, however, is how this particular species has managed to persist. 

Mounds of  S. palustre  in its native habitat. 

Mounds of S. palustre in its native habitat. 

Hawaiian moss aficionados have long noted that the entire population of Kohala's S. palustre mats never seem to produce a single female individual. Indeed, this moss is dioicous, meaning individuals are either male or female. As such, many have suspected that the mats of S. palustre growing on Kohala represented a single male individual that has been growing vegetatively ever since it arrived as a spore on the island. The question then becomes, how long has this S. palustre individual been on Kohala?

To answer that, researchers decided to take a look at its DNA. What they discovered was surprising in many ways. For starters, all plants were in fact males of a single individual. A rare genetic trait was found in the DNA of every population they sampled. This trait is so rare that the odds of it turning up in any number by sheer chance is infinitesimally small. What this means is that every S. palustre population found on Kohala is a clone of a single spore that landed on the mountain at some point in the distant past. Exactly how distant was the next question the team wanted to answer. 

A lush cloud forest on the slopes of Kohala.

A lush cloud forest on the slopes of Kohala.

The first clue to this mystery came from peat deposits found on the slopes of the mountain. Researchers found remains of S. palustre in peat deposits that were dated to somewhere around 24,000 years old. So, it would appear that S. palustre has been growing on Kohala since at least the late Pleistocene. But how long before that time did this moss arrive?

Again, DNA was the key to unlocking this mystery. By studying the rate at which mutations arise and fix themselves within the genetic code of this plant, they were able to estimate the average rate of mutation through time. By sampling different moss populations on Kohala, they could then use those estimates to figure out just how long each mat has been growing. Their estimates suggest that the ancestral male sport arrived on Hawai'i somewhere between 49,000 and 50,000 years ago and it has been cloning itself ever since. 

A large mat of  S. palustre

A large mat of S. palustre

As if that wasn't remarkable in and of itself, their thorough analysis of the genetic diversity within S. palustre revealed a remarkable amount of genetic diversity for a clonal organism. Though not all genetic mutations are beneficial, enough of them have managed to fix themselves into the DNA of the moss clones over thousands of years. The DNA of S. palustre is challenging long-held assumptions about genetic diversity of asexual organisms.

Of course, no conversation about Hawaiian botany would be complete without mention of invasive species. As one can expect at this point, Kohala's S. palustre populations are being crowded out by more aggressive vegetation introduced from elsewhere in the world. Unlike a lot of Hawaiian plants, however, the clonal habit of S. palustre puts a more nuanced twist to this story. 

Because Sphagnum is spongy yet durable, it has often been used as packing material. Packages stuffed with S. palustre from Kohala have been sent all over the island and because of this, S. palustre is now showing up en masse on other islands in the archipelago. Sadly, when it starts to grow in habitats that have never experienced the ecosystem engineering traits of a Sphagnum  moss, S. palustre gets pretty out of hand. It's not just packages that spread it either. All it takes is one sprig of the moss stuck on someone's boot to start a new colony elsewhere. The unique flora elsewhere in the Hawaiian archipelago have not evolved to compete with S. palustre and as a result, escaped populations are rapidly changing the ecology to the detriment of other endemic Hawaiian plants. 

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

Further Reading: [1] [2] 

The Mighty 'Ama'u

We tend to think of ferns as fragile plants, existing in the shaded, humid understories of forests. This could not be farther from the truth. Their lineage arose on this planet some 360 million years ago and has survived countless extinctions. In truth, they exhibit a staggering array of lifestyles, each with its own degree of adaptability. Take the Hawaiian tree fern, Sadleria cyatheoides for example.

Known in Hawai'i as the 'Ama'u, this tree fern is one of the first species to colonize the barren lava flows that make the Big Island so famous. This is an incredibly harsh landscape and many challenges must be overcome in order to persist. This does not seem to be an issue for the 'Ama'u. It is just as much at home in these water-starved habitats as it is in wetter forests. It is easily the most successful species in this genus, having colonized every island in the archipelago.

Much of its success has to due with a part of its life cycle that is much less obvious to us - the gametophyte stage. The tree fern we see is only half of the story. It is the spore-producing phase conveniently referred to as the sporophyte. When a spore finds a suitable site for germination, it grows into the other half of the life cycle, the gametophyte. This minute structure looks like a tiny green heart and it houses the reproductive organs of the plant. When water is present, male gametophytes release their flagellated sperm, which swim around until they find a female gametophyte to fertilize. Once fertilized, the resulting embryos will then grow into a new tree fern and start the cycle anew.

What sets the 'Ama'u apart from its rarer cousins is the fact that its gametophyte appears to be quite capable of both outcrossing and self-fertilization. Outcrossing, of course, promotes genetic diversity, however, the ability to self-fertilize means that a new plant can grow from only a single spore. This is super advantageous when it comes to colonizing new habitats. Its cousins seem to lack this ability to self-fertilize successfully, restricting them to more localized areas. Taken together, I think it's safe to say that the 'Ama'u is one tough cookie. 

Photo Credits: [1] [2]

Further Reading: [1] [2]

 

The Amazing Radiation of Hawaii's Lobeliads

Hawai'i is home to so many interesting species of plants, many of which are found nowhere else in the world. One group, however, stands out among the rest in that it represents the largest plant radiation not just in Hawai'i but on any island archipelago in the world!

I am of course talking about the Hawaiian lobelioids. We are familiar with species found on North America, which include the lovely cardinal flower (Lobelia cardinalis) and the great blue lobelia (Lobelia siphilitica), but the 6 genera that comprise the Hawaiian radiation are something quite different altogether.

Numbering roughly 125 species in total (and many extinct species as well), it was long thought that they were the result of at least 3 separate invasions. Thanks to recent DNA analysis, it is now believed that all 6 genera are the result of one single invasion by a lobelia-like ancestor. This may seem ridiculous but, when you consider the fact that this invasion happened back when Gardner Pinnacles and French Frigate Shoals were actual islands and none of the extant islands were even in existence, then you can kind of grasp the time scales involved that produced such a drastic and varied radiation.

Sadly, like countless Hawaiian endemics, the invasion of the human species has spelled disaster. Hawaiian endemics are declining at an alarming rate. Introduced pigs and rats eat seeds, devour seedlings, and even go as far as to chew right through the stems of adult plants. To make matters worse, many species evolved to a specific suite of pollinators. Take the genus Clermontia for example. The flowers of these species are evolved for pollination by the island's endemic honey creepers. Due to avian malaria and other human impacts, many honey creepers are endangered and some have already gone extinct. Without their pollinators, many of these lobelioids are doomed to slow extinction if they haven't disappeared already. For some, what few populations remain are now fenced off and have to be hand pollinated. As I have said all too often, the future of this great radiation of plants is uncertain.

Photo Credits: Oakapples (http://bit.ly/OjOqhU), Forest and Kim Starr (http://bit.ly/1miCAA5), Dave Janas

Further Reading:

http://bit.ly/2aIviF5

http://bit.ly/2bh9Dpv

http://bit.ly/2b4i5dV

Brother of Hibiscus

Islands are known for their interesting flora and fauna. Until humans came on the scene, colonization events by different species on different islands were probably rare events, with long stretches of time in between. Because of this, islands are interesting experiments in evolution, often having endemic species found nowhere else in the world. Hawai'i was once home to many different kinds of endemic species. One such group are the Hibiscadelphus.

As you may have gathered by the name, Hibiscadelphus is a relative of hibiscus. The Latin name means "brother of Hibiscus." Unlike the widely splayed flowers of their relatives, Hibiscadelphus flowers never fully open. Instead, they form a tubular structure with a curved lower lip. The genus consists of 7 species. Four of these have gone completely extinct, two are only maintained in cultivation, and the remainder is barely holding on. There have been attempts to reestablish some species into other portions of their range but due to hybridization, these attempts were ceased. In my opinion this is a shame. In this case, a hybrid is better than losing both parental species and it would still be uniquely Hawaiian.

Why are Hibiscadelphus so rare? Well, humans have a sad history when it comes to colonizing islands. They bring with them a multitude of invasive species at a rate in which the local flora and fauna cannot adapt. They change the land through cultivation and development as well as by subduing natural fire regimes. Also, they wipe out keystone species, which causes a ripple effect throughout the environment. Hibiscadelphus have faced all of these threats and more. Pigs and rats eat their seeds, their habitats have been turned over for the ever-increasing human population, fires have been stopped, and some of their pollinators, the endemic honeycreepers, have also been driven to extinction thanks to avian pox and malaria. Sadly, this is a story that repeats itself time and time again all over the world. For now, the future of Hibiscadelphus is rather bleak.

Photo Credit: David Eickhoff

Further Reading:

http://bit.ly/2ao84X1

http://bit.ly/2aEfpkn

The Curious Case of Hawaii's Endemic Orchids

Orchids and Hawai'i are nearly synonymous. It may come as a surprise then to learn that only three species of orchid are native to this lush archipelago. In fact, there are more non-native species of orchids growing in Hawai'i than there are native. Like much of Hawai'i's endemic flora and fauna, these three distantly related orchid species find themselves on the brink of extinction. How and why only three species of orchid came to call Hawai'i home is a great mystery and it is one that conservationists are struggling to understand before it is too late. 

Orchids produce the smallest seeds of any plants. These dust-like propagules can travel far and wide on the slightest breeze. If any plants were to make it to one of the worlds most remote island chains my bet would be on the orchids. Alas, until settlers arrived, Hawai'i was home to only three - the Hawaiian bog orchid (Platanthera holochila), the Hawai'i jewel-orchid (Anoectochilus sandvicensis), and the Hawai'i widelip orchid (Liparis hawaiensis). The ancestors of these plants must have traveled quite a distance to get to these islands. The Hawaiian bog orchid, for instance, can trace its ancestry back to a related species of Platanthera native to the Aleutian Islands whereas the other two likely blew in from Asia. 

These three species were once found in a variety of locations. Today, however, all of that has changed. Populations of each of Hawai'i's endemic orchids are declining at a rapid rate. In fact, the Hawaiian bog orchid is considered one of the most endangered orchids in the world. The causes of their decline is what one would expect from an island species - habitat destruction, the introduction and subsequent spread of invasive species, and just poor land management in general. It is strange though that so many orchid species from elsewhere in the world are thriving as their endemic cousins are declining. 

Though the exact reasons for this remain uncertain, some of it has to do with another invader - honeybees. Honeybees are native to Europe and are generalists in their foraging abilities. Until bees were were brought to Hawai'i, many introduced orchid species behaved themselves. There simply wasn't anything around to pollinate them. Once honeybees came onto the scene, a few of these introduced species such as the bamboo orchid (Arundina graminifolia) were suddenly able to reproduce. The tropical climate made the land ripe for the taking. But this is only part of the picture. There is another, more interesting conundrum that remains to be solved. 

Orchids absolutely require mycorrhizal fungi to germinate and grow. Why is it then that introduced orchids seem to be doing so much better than the Hawaiian endemics? Good question. Some orchids can be very specific about the fungi they will partner with whereas others are not. It could be that all of the introduced orchids that are naturalizing are generalists whereas the endemics are specialists. It could also be that the endemics simply can't handle the altered disturbance regimes brought on by modern society.

The real reason is probably some combination of these and many more but the fact of the matter remains, Hawai'i's native orchids are in trouble. Since they are not nearly as showy as other orchids they are rather overlooked. This is a shame because if they are lost from their native range, they are gone from the world forever. Luckily there are people out there like Dr. Nicole Hynson of the University of Hawai'i and Dr. Larry Zettler of Illinois College who are working to understand, propagate, and conserve these unique species. 

Photo Credits: University of Hawai'i Museum (http://bit.ly/1K8pjKC), Arkive (http://bit.ly/20kxg17), and G. Daida (http://bit.ly/1K8phCw

Further Reading:
http://bit.ly/1PKOV0C

http://s.si.edu/1QRn0el

http://s.si.edu/1Rjwd1g

http://s.si.edu/1W8bGMb

http://www2.hawaii.edu/~nhynson/Hynson_Lab/Welcome.html

http://www.ic.edu/LarryZettler