Wood and Rain

 As much as I love being outside, I also can't help, but sing the praises of the occasional rainy day spent curled up indoors. There's just something very cozy and comforting about sitting around with your friends, family, coworkers, or even just by yourself in a warm, dry box of artificial light, pushing out again the dreary shadow of the clouds. Days like this were some of the only ones, when I was in school, where I wasn't distracted at least once by the desire to go outside and explore. Having now worked several eight-hour fall days in the cold and rain as a field tech, I'm also pretty content as an adult to take shifts indoors when made necessary by the weather. 

While shifting breezes and churning clouds are, for us humans, usually taken as signs to seek shelter, there are plenty of organisms out there for whom rainy days are calls to do the opposite, to leave hiding places behind to do what must be done in the open. This is especially the case for amphibians and invertebrates that lose moisture easily through their skin. During dryer periods, these animals spend most of their time beneath moist leaf litter and rotten wood, where they can keep out of the sun. When it rains, they emerge to take advantage of shady conditions and moist air and surfaces to disperse, feed, or reproduce. Less mobile critters, like fungi and certain short-lived plants will also take advantage of the influx of water afforded by rain showers to quickly sprout and undergo the reproductive portion of their life cycles.

During the last month, we here in Connecticut have received a lot of rain, breaking a two-year pattern of summer drought. This has resulted in work interrupted by thunderstorms and made uncomfortable (to put it lightly) by high humidity and a baby boom of mosquitos. It’s also provided an excellent opportunity, however, to observe some of those fascinating critters that only really show themselves in the aftermath of fall and summer storms. As we welcome some much-needed clear skies and cooler temperatures in the first days of August, here are some highlights from a warm, wet July - beasts of the wood and rain, none of which are quite what they appear to be. 

Red-Spotted Newt:

Some of you are probably familiar with the creature in this photograph as one those adorable little salamanders which, along with baby toads and wood frogs, one must carefully avoid stepping on during a post-storm walk in the woods. You may have heard them referred to as red efts and may also have heard the name eastern or red-spotted newt used to describe the aquatic, olive green salamanders living in a local lake or pond. But did you know that these two, seemingly very different animals are actually members of the same species?

Okay, so I guess if you knew both of those names, you probably did. But for those who didn't - yeah, it's true! Red-spotted newts (Notophthalmus viridescens), like many salamanders, start their lives in an aquatic form known as a tadpole or larva. In their tadpole form, newts have feathery, external gills that allow them to breath underwater. Over the span of two to five months after hatching from their eggs, the tadpoles lose their gills and develop lungs and sturdy legs for breathing and walking on land. Eventually, they climb out of the water, becoming the bright red efts that we all know and love from our rainy-day hikes (CT DEEP 2016). 

This is the point where most terrestrial salamander species develop into sexually mature adults, spending the rest of their lives hidden underground or in moist leaf litter and only returning to the water to breed. Red-spotted newts do indeed spend a while in their terrestrial eft stage - typically between one and three years - but they are not sexually mature adults during this time. Rather, once their time on land is complete, efts will go through another period of metamorphosis in which they will retain their lungs and general body plan, but developed a flatter, more streamline shape, webbed toes, and a rudder-like tail. They will also change from bright red to olive green, with black-spotted, yellow bellies and small red spots on their backs. The now-adult newts will then return to the water, where they will breed and spend the rest of their lives (CT DEEP 2016).

So, why do newts do this? That is, if they are born in the water and are eventually going to breed and live out their adult lives in the water, why have an intervening stage where they spend a few years on land, not breeding, and exposing themselves to an early death by terrestrial predator? Well, first of all, it should be noted that efts actually have a pretty effective defense mechanism in the form of an awful tasting toxin secreted from their skin (Brodie Jr. 1968). Their bright red coloration is meant to warn would-be predators that they taste bad and is probably a part of the reason why they seem to be so confident in walking around in the open after storms, despite being so slow and perfectly bitesize. 

But as for answering the main part of our question - why newts would evolve a terrestrial stage instead of just staying in the water for their whole lives - we should remember that evolution is never a goal-oriented process. Whether or not a particular trait makes it to the next generation depends not on the straightforwardness of its contribution to a more complex trait in the future, but on whether it helps, or at least does not hinder, the survival of the individuals that have it right now. The eft stage helps newts because it allows them to disperse widely across the land and colonize new bodies of water (Gill 1978; Takahashi and Parris 2008). The tadpole stage does not have lungs and so cannot breathe on land, while the adult stage has sacrificed terrestrial mobility for aquatic mobility. In situations where the quality of a body of water has declined, neither would be able to effectively leave and find a new home. The efts, however, will often travel widely during their time on land, allowing them to eventually colonize new and better habitats. Newts that have an eft stage are thus more likely to survive and thrive in the long term because their young are less likely to be killed due to the sudden decline of an isolated, aquatic habitat. 

Of course, the newts could theoretically evolve so that the terrestrial stage acts as both a dispersal stage and a breeding stage. As I've already mentioned, this is the case in many other salamander species. But that's not the niche that these particular newts are using, and no matter the criticisms of judgey humans, it seems to be working out pretty well for them - the red spotted newt is one of the most wide-ranging salamanders in North America.

Ghost Pipe:

Like the red eft, the ghost pipe (Monotropa uniflora) is a wide-ranging, forest dweller most likely to be seen in the aftermath of summer rain, when they suddenly rise from the leaflitter like zombies from the grave. If you are like me, you probably always assumed that they were some kind of fungus - both their coloration and behavior match up with other members of that group, after all - but that assumption is incorrect. The ghost pipe is actually a plant in the family Ericaceae, the same family as blueberries. It looks so different from most other plants because it is a non-photosynthetic, myco-heterotroph. Thats that a lot of jargon, so let's break it down piece by piece. 

Many readers will already be familiar with photosynthesis as the process by which plants convert sunlight and carbon dioxide into food. Energy from the sun is captured by pigments in the leaves of the plant and, though a series of chemical reactions, is stored in the form of stable, sugar compounds. These sugars are broken down during a process called cellular respiration and their stored energy is used to power varies physiological processes. A non-photosynthetic plant, then, is a plant that is not capable of producing its own food through photosynthesis. The ghost pipe is bright white because it does not perform photosynthesis and so lacks chlorophyll, the main pigment that plants use to capture energy from the sun and the source of their green color. 

Photosynthetic plants and algae form the base of almost every food chain on the planet, the point at which energy from the sun enters an ecosystem. Organisms that are able to make their own food from the physical environment are called autotrophs, while organisms that cannot make their own food, and so must somehow get it from other organisms (whether dead or alive), are called heterotrophs. A heterotrophic plant, then, is a plant that gets its food from other organisms rather than via photosynthesis. 

So how do ghost pipes get their food? Well, this is actually where fungi come back into our story. When you see a mushroom growing in the woods, what you are looking at is called a fruiting body. It isn't actually the main part of the fungus' body, but is more like an apple on a tree - that is, a structure used for reproduction. The "tree" part of the fungus, called the mycelium, is underground in the form of a network of thin, strands called hypha. The mycelium grows outwards through the soil in all directions, searching out patches of dead organic matter which it breaks down for nutrients. Fungal mycelium can be quite large and so are capable of obtaining certain nutrients that are spread out widely through the soil, but the sugars they get from breaking down organic matter tend to be of either a low quality or require a lot of resources to digest. To get around this, some fungi have formed mutualistic relationships with plants (Stephenson 2010). These fungi, known as mycorrhizae, form linkages with plant roots, which they use to swap nutrients and water for sugars produced by the plants. Both plant and fungus benefit from this relationship, with the fungus getting high quality sugars and the plant getting nutrients that it wouldn't necessarily be able to obtain with its own limited root system. One fungus will often connect with the roots of several induvial plants and there is even evidence that plants use the fungal network to communicate with each other (Johnson and Gilbert 2015)!

All ghost pipes are hooked up into this mycorrhizal fungal network, but they turn what is typically a mutually beneficial relationship on its head. Instead of giving the fungus sugar molecules, which it cannot produce on its own, the ghost pipe somehow convinces the fungus to give it sugar from the other plants in the network (Bjorkman 1960). Nobody is really sure how the ghost pipe does this. Maybe it gives the fungus something else is return for the sugars that we aren't aware of or maybe it manipulates the system with some clever chemistry. We don't know. What we do know is that the ghost pipe is not alone in using this strategy, but is just one of over 400 species of mycoheterotrophic plants documented as of the early nineties (Leake 1994). Some of these are rare or possible even extinct, but many others, including the ghost pipe and the beech drop, are pretty common (Merckx et al. 2009). That something so tiny and so common could contain so much intriguing mystery and complexity is part of the reason why Montropa are some of my favorite plants - ghosts indeed. 

Scrambled Egg Slime Mold:

Speaking of organisms that people often mistake for fungi, I hope you will allow me the pleasure of introducing you to the scrabbled egg slime mold (Fuligo septica). There are a couple of other names by which this particular critter goes, but they aren't especially flattering, and I prefer this one for its goofiness and the emphasis it puts on the slime mold's striking yellow color. Spotting a slime mold on the side of a dead tree on or on a log, it's easy to assume that it is just another kinda-gross-looking, kinda-beautiful mushroom and indeed, as the name suggests, scientists thought for many years that they were closely related to the molds that you find on bread loafs and bathroom grout. Weirdly enough though, it turns out that slime molds are much more similar to giant amoebas than mushrooms. 

Yes, that does mean that they move!

Slime molds begin life as microscopic, single cells before eventually developing into plasmodia, often as the result of two of the single cells fusing together. A plasmodium is an undivided mass of cytoplasm (the viscus fluid in a cell) which lacks a cell wall and contains multiple nuclei. A plasmodium grows as its nuclei divide and multiply and, in the case of the scrambled egg slime, can reach up to 8 inches in diameter. During both their single celled and plasmodium life stages, slime molds feed mostly on bacteria and are capable of moving around to find food. They do this by pushing their cytoplasm forward in the direction that they want to go and pulling it up in the direction that they are moving away from. The process is slow, but can be seen quite clearly with the use of a time lapse camera. Slime molds require moisture to survive and, in its absence, are capable of going dormant for long periods in hardened forms known as sclerotia. These can then turn back into plasmodia with the return of rain, allowing some slime molds to survive even in extreme environments, such as deserts (Stephenson 2010). 

Eventually, the slime mold stops its roaming and enters the final, reproductive stage of its life cycle. During this stage, the plasmodium sprouts fruiting bodies that produce spores. As you may remember from my post on horsetails, spores share with seeds the purpose of dispersal, but produce young that are clones on the parent, rather than unique genetic individuals. Slime mold spores are typically dispersed by the wind and, if they land in a suitable environment, they become the single celled amoeba-like critters that started our story with (Stephenson 2010).

I found this particular slime mold on a dead tree in the woods, but scrambled egg slimes are actually pretty common and can often be found crawling over the mulch in an urban planter box or tree well in the aftermath of a good storm. So, take a good look at the photo, and next time you see something like it, you can impress your friends with the knowledge that it is not a mushroom, but a giant amoeba. 

Sources:

Bjorkman, E. R. I. K. (1960). Monotropa hypopitys L.-an epiparasite on tree roots. Physiologia Plantarum, 13(2), 308-27.

Brodie Jr, E. D. (1968). Investigations on the skin toxin of the red-spotted newt, Notophthalmus viridescens viridescens. American Midland Naturalist, 276-280.

Conant, R. & Conant, I. H. (1975). A field guide to reptiles and amphibians of eastern and central North America, second edition. Houghton Mifflin Company Boston. 

Connecticut Department of Energy and Environmental Protection (October 11, 2016). Red-spotted newt. Wildlife Fact Sheets. https://portal.ct.gov/DEEP/Wildlife/Fact-Sheets/Red-Spotted-Newt#:~:text=Their%20life%20cycle%20is%20one,adults%20which%20retain%20their%20lungs.    

Gill, D. E. (1978). The metapopulation ecology of the red‐spotted newt, Notophthalmus viridescens (Rafinesque). Ecological monographs, 48(2), 145-166.

Johnson, D., & Gilbert, L. (2015). Interplant signalling through hyphal networks. New Phytologist, 205(4), 1448-1453.

Leake, J. R. (1994). The biology of myco‐heterotrophic (‘saprophytic’) plants. New Phytologist, 127(2), 171-216.

Merckx, V., Bidartondo, M. I., & Hynson, N. A. (2009). Myco-heterotrophy: when fungi host plants. Annals of Botany, 104(7), 1255-1261.

Stephenson, S. L. (2010). The kingdom fungi: the biology of mushrooms, molds, and lichens. Timber Press, Inc. 

Takahashi, M. K., & Parris, M. J. (2008). Life cycle polyphenism as a factor affecting ecological divergence within Notophthalmus viridescens. Oecologia, 158, 23-34.