Fall Equinox

Note: This program first aired on September 28, 2013.

It’s fall in Maine. We’ve just passed the autumnal equinox, that point in the Earth’s orbit where, mathematically we can think of the spin axis of the Earth as a tangent line on the orbital ellipse. What this means in practice is everywhere on Earth has a day of 12 hours of daylight, 12 hours of darkness, more or less. After that, at least here at our middling  northern hemisphere latitude, the darkness increases dramatically, making the light sensitive among us go into mourning, and the snow lovers among us optimistic.

I recently received a weather alert on my phone, telling me that frost and freeze advisories had been suspended for northern Maine, as they had officially reached the end of the growing season there. The alert added that frost and freeze warnings would continue in my neck of the woods, coastal Maine, until the official end of the growing season here, noted as October 10, or earlier if we received a hard freeze before then. It made me wonder, what exactly is the growing season? How is it calculated and what does it really mean? How do we know the exact date when it ends?

Here in Maine, midway between the equator and the north pole, there are three components to growing plants, which when we talk about the growing season, is what we mean. We need light, water and we need warm enough temperatures. The light aspect is very predictable, at least in terms of day length. We know to within seconds how much time the sun will be above the horizon on any given day of the year. Temperature, however, is harder to predict. We can look at averages over time; the date of the first frost for a region, averaged over a period of years for example. I suspect that is where the October 10 deadline came from. Water is, for the most part, not a significant issue here, as we usually have plenty of it, with one major exception. In winter, there may be lots of water around, but it is frozen, and thus not available for use by living plants.

Information for farmers about the growing season is all about mitigating the effects of cold temperatures, really, unless you want very powerful grow lights, temperature is the only aspect of the growing season we can control, and only on a small scale at that. When it comes to light, 10 hours seems to be the magic number. Below that amount of daylight, plants can simply not fix enough of the sun’s energy to meet their metabolic needs and grow. They may be able to maintain, but not get any bigger, or reproduce. For that reason winter is a time of dormancy, a holding period that plants simply wait through. Here in Maine, our true non growing season runs from the beginning of November until the beginning of February, based on that magic 10 hours of light. Wild plants obey the same rules as their domesticated cousins, if my observations are correct. Trees lose their leaves, annual grasses and forbs die back to their under ground roots, or over winter as seeds. Even the hardy ever green trees are limited in their abilities to photosynthesize over the dark, cold winter months by low light, cold slowed metabolism, and lack of available liquid water.

We are tropical animals, living in a temperate climate. Even in the tropics there are patterns of growth and rest, wet and dry, exuberance and senescence. As the calendar rolls towards October 10th, the last day they will bother to warn us about a possible frost, or the beginning of November, when the daylight dips below the 10 hour mark and stays there for three whole months, take heart that this time of year plays a valuable role in the yearly cycle of plants, and people. Take this time to show your other, hidden colors; draw in and hunker down. The dark provides our excuse, our opportunity, finally, after the excitement of summer, to simply stay home and regroup. So don’t fight it. Look around you, are the trees in your yard, the weeds in your garden, or the ferns in the woods arguing with the solstice? Neither should you. Happy fall everyone.

References:

Interesting info from Maine’s own Johnny’s Seed company http://www.johnnyseeds.com/t-catalog_extras_vegetables.aspx

A frost free dates for my neck of the woods, from the National Climatic Data Center, featured on a gardening website: http://davesgarden.com/guides/freeze-frost-dates/index.php?q=04676&submit=Go

Fresh Water Mussels

Note: This program first aired on September 21, 2013.

This past weekend I spent a perfectly lovely day at Hirundo Wildlife Refuge. Just 10 miles from the University of Maine in Orono, this private refuge straddles Pushaw Stream and showcases forested wet lands, open sedge meadows and miles of canoeing and hiking trails enjoyable by all. I was there as a teaching assistant in a class studying fresh water ecology, and we looked at trees and unique shrubs particular to wetlands, canoed on the stream in 28 foot peace canoes, seined for fish, and hunted for elusive fresh water bryozoans. As surprised as I was to learn that there was such a thing as a fresh water bryozoan, I was even more surprised to learn how many different fresh water mussels there are, and how different they are than the ones we have in the ocean.

Fresh water mussels! Who knew? As some one who specializes in the marine environment, moonlights with terrestrial botany and occasionally goes a little nuts over aquatic insects, I didn’t. We have lots of mussels in the ocean of course, mainly the ones we eat, blue mussels Mytilus edulis, and their deep water cousins, Modiolus modiolus, the big sub tidal horse mussel. Compared to these, fresh water mussels are mussels in name only. Taxonomically fresh and salt water mussels are both in the class Bivalvia, a group of Molluscs that has a common trait of having two shells. They then split off into two separate subclasses; the salt water mussels fall in the evolutionary line that also includes scallops and oysters. Freshwater mussels are out alone in their own subclass, whats called a monophyletic group; they are the only type of organism on that branch of the tree of life.

Unlike marine mussels which live as epifauna, strongly adhered to hard surfaces by anchors called byssal threads, freshwater mussels are infauna, they live buried in the sediment more like clams. Their relatively short siphons and weak feet ensure that while they are in the sediment, they cannot go deep into the substrate and will be found near the surface of the bottom. Like most bivalves marine or fresh, fresh water mussels make a living filtering organic matter out of the water. These food items can be algae, bacteria, or detritus. They have an inhalant siphon and an exhalant siphon (sort of like us, except in mussels the inhalant and the exhalant apertures are located directly next to one another, think about that for a minute.). To eat, which they do continuously, they suck water in and it flows over their large gills, which perform the dual function of not only absorbing oxygen from the water but also filtering out bits of food, and just about anything from the water. Food items that don’t agree with their palates are trapped in mucus and ejected before they can be digested. I had no idea that filter feeders could do this. All this time I was under the impression that they ate indiscriminately, and thus were always a net bonus for water quality. Little did I know that they can reject food, which in regions with the invasive Zebra mussel, is actually creating a water quality issue as the Zebra mussels preferentially eat planktonic algae but spit out cyanobacteria, leading to a large change in the planktonic composition in these lakes and waterways.

Besides living it the mud or sand, and not having byssal threads, the biggest difference between marine and fresh water mussels is reproductive strategy. Marine mussels simply release their sperm and eggs into the water column, employing fully external fertilization. If the sperm and eggs meet in the water column, free floating larvae are formed, which go through several stages of development as plankton before they settle out as what we would recognize as tiny little mussels. Fresh water mussels don’t leave it so much to chance. Males release sperm into the water but the females then capture that sperm with their incurrent siphon (think about that for a minute), it simply comes in with everything else they filter out of the water. The females fertilize the eggs internally and hold the eggs in special pouches on the gills for a period of days to months depending on species. When the larvae are big enough the female expels them into the water. Here is where it gets really interesting. The larvae have to find a fish, and not just any fish, to act as a host for days or months, again by species. If they find their proper fish, and there are many strategies for doing so, including stringy mucus lures meant to attract unsuspecting fish, the larvae attach themselves to the fish, either to its skin and fins or in its gills, again, depending on the species. They grow and develop and actually get encysted in the fish’s tissue, apparently at no cost to the fish, though at least one reference refers to the relationship as parasitic, which implies harm. At the end of their period of fishy development, they drop off and if they are really lucky, they drop off into appropriate sediment substrate, and don’t get eaten by a hungry predator.

So all this time, this has been going on in fresh water streams and rivers, and ponds all over the state, and I had no idea. I feel like some one just told me about another planet in our solar system. Somewhere I knew, in a dimly lit corner of my head, about the existence of what I thought of as fresh water “clams”, from a child hood of fresh water swimming, but it was a part of my brain I never funneled any light or energy to. Its nice to know that surprises exist, and not just on the frontiers of science, but right in your own back yard.  Seek them out, you will be glad you did.

References:

Hirundo’s website: http://www.hirundomaine.org/

Maine’s info page about threatened fresh water mussels
http://www.maine.gov/ifw/wildlife/species/invertebrates/freshwater_mussels.html

Nice site from Virginia Department of Game and Inland fisheries: http://www.dgif.virginia.gov/wildlife/freshwater-mussels.asp

The American Museum of Natural History has an extensive website about the freshwater mussels of the New York and New Jersey area, many of which are the same ones we have here in Maine http://www.amnh.org/our-research/center-for-biodiversity-conservation/research/species-based-research/invertebrate-conservation/freshwater-mussels

NOAA document on zebra mussels and blue green algae (cyanobacteria) and changes to Great Lakes aquatic ecosystems
http://www.publicaffairs.noaa.gov/pr96/mar96/noaa96-11.html

Frass Happens

Note: This program first aired on September 14, 2013.

I’ve been noticing lately, and maybe you have been too, what seems like an awful lot of insect frass around. Frass on my porch, my roof, my adirondack chairs. Put up a tent or a tarp, and as long as it is underneath some trees, it will be covered with the stuff. What this tells me is that there are a lot of insects in the trees, specifically, larval insects, and they are apparently doing a lot of eating. Frass is indeed linked to food, because frass, my friends, is insect poo. Just like you and me, the more they eat, the more they excrete.

Summer is the time of the insect, the warm temperatures bring plentiful food sources, and insects have evolved to take full advantage of this brief window. The insect life cycle is a fascinating one; I, for one, can’t stop thinking about how cool it is. There are three main paths to becoming an adult insect. The first is simple metamorphism, and it has a couple of sub categories. Of those, the first is gradual metamorphism (also called paurometabolous (small or slight change) metamorphism). The egg is laid by an adult, and what hatches out of the egg is essentially a tiny little adult, that eats and grows and molts its exoskeleton and grows some more, molting and growing until it gets big enough to be sexually reproductive and is considered and adult. This is the M.O. of grass hoppers, for example. The other form of simple metamorphosis is incomplete or hemimetabolous (half change) metamorphism. An egg is laid by an adult insect, and out of the egg hatches a juvenile stage that looks different than the adult. In this immature stage they are called nymphs or naiads and are aquatic. This nymph eats and grows, molting its exoskeleton, until its last molt, when what comes out is not another nymph but an adult insect. Dragon flies grow this way.

The second category is complete metamorphism also called homometabolous (whole change) metamorphisman. An adult lays an egg, from which hatches a larvae, (caterpillar, grub etc) which grows through several different stages, called instars, molting an exoskeleton or outer skin as it passes from one instar to the next. Then the larvae turns into a pupa, the stage of true metamorphosis, during which the cells of the insects body completely rearrange themselves. It is often referred to as a resting stage in the literature, but the insect is only appearing to rest. Inside there is a major transformation going on. This is the cocoon stage of the butterfly, as an example. From the pupa emerges the adult, totally and utterly reconfigured from the larvae.

Complete metamorphism is by far the most popular means of insect growth, found in approximately 10 times as many species as incomplete metamorphism. There are some distinct advantages to having such wide variation in the different stages of growth, and the first is division of labor. Ken Kaufman in his guide to insects refers to each stage of the insect as having a different job, and the analogy is a good one. The egg has it the easiest, it simply has to incubate. The larvae are “eating machines”, their job is to get as much nutrition as they can because the metamorphosis that occurs in the pupa stage is so incredibly hard and energy consuming. The adults may or may not eat, but their main job is to reproduce. Typically the larvae also live in different habitats than the adults (sometimes really different habitats, for example the larvae of black flies and mosquitos are totally aquatic, they live under water). This can reduce intergenerational competition for resources, always a good thing.

So it is larvae in the trees that is making all that frass, larvae doing all the work of eating, for many of these caterpillars turn into moths and butterflies that don’t eat at all. It’s a division of labor so stark it is hard to imagine. Its also perfectly synched to the rhythm of nature, those caterpillars, grown fat on summer’s greenery, will pupate and spend the long winter slowly rearranging their cells, preparing to emerge in the spring as new beings. It makes me feel crass and ill fitted in comparison. As the days grow shorter, we would do well follow their example, respecting the season and using what it offers, a break from the frenetic frass making of summer, to renew and reorganize ourselves as well.

References:

www.bugguide.net The definitive internet insect resource, email in your photos to get identifications from an online community of bug nerds.

Ken Kaufman’s Field Guide to Insects of North America 2007 Houghton Mifflin, I love this book, it (like all Kaufman guides) uses actual photographs, but at the same time manages not to be too creepy.

Freeman, Quillin, Allison Biological Science 5th ed. 2014, Pearson
Most any modern biology textbook will give you some good basic information about Arthropods

Nice site from the West Virginia University Extention service, clarifying  different types of metamorphosis,
http://www.caf.wvu.edu/~forage/insect_m_morph.htm

Frog and Snake Aren't Friends

Note: This program first aired on August 31, 2013.

Frogs and snakes are not known to be friends. Folktales from many parts of the world document this fact repeatedly. In fact frogs and snakes are on such unfriendly terms that snakes often eat frogs, and very occasionally frogs eat snakes as well.

I witnessed this very event, that being a snake eating a frog, behind a road side rest area bathroom on Rt. 9 in Beddington Maine. Yes nature can happen anywhere, even somewhere as unglamorous as behind the rest stop, in the gravel. The snake was a common garter snake, Thamnophis sirtalis. These snakes are the most abundant reptiles in Maine and are found in a wide variety of habitats, including water, they swim quite well. As ectotherms you will find them sunning themselves to regulate their body temperature, as they cannot internally generate enough heat to support a high enough metabolism to be active. In the winter they hibernate in groups. This time of year the females are giving birth to live young. Some sources state that up to 80% of the common garter snake’s diet is earth worms, but they eat a wide variety of prey depending on availability, prey that can include frogs, leeches, slugs, rodents, small birds, fish, insects and molluscs. Generally they eat size appropriate prey, the bigger the snake, the larger the prey they can consume. At one point in my life I came up with a rule for eating, one I think is pretty reasonable, and I have followed it, for the most part, ever since. That rule is: don’t eat anything bigger than your head, and it works for me. Snakes don’t follow that rule, to a pretty astonishing degree. And snakes can’t take bites, they don’t have the proper dentation, nor appendages with which to gain leverage. They have to swallow whatever the catch whole (and usually alive). In order to do this they have to make their heads a great deal bigger, which is accomplished by unlatching their jaws, and having very stretchy skin, which allows their mouths to expand around their prey. Even while their skin expands to accommodate the prey, the muscles of their throat strongly pulse and move the prey towards the stomach, completing the swallow. I don’t often think of snakes as having strong muscles, but when I saw the snake pick the frog up off the ground and slither away with it, I gained a new appreciation for just how robust these creatures are.

The frog in question was a pickerel frog, Rana palustris. They are wide spread in Maine, and after reproducing in wet areas in the spring, they disperse into fields, meadows and damp woods for the summer.

The scene I came upon was this: the snake was biting the frog’s ankle, having not swallowed any part of the frog yet. The frog, for its part, was just laying there, seemingly paralyzed. It looked to me like one good kick and it would be free, but I probably underestimate the power of the snake’s bite strength. The snake kept chomping away on the ankle, apparently trying to maneuver the frog’s foot deeper into its mouth, so its throat muscles could start helping pull the frog in, in this initial phase it was all about the snake’s mouth, and whatever progress it could make with its incurved teeth and biting action. As we watched, and at this point, quite a crowd had gathered, the snake reared up and dragged the frog a few feet away, the frog all the while passively submitting. An occasional twitch or light kick, and its breathing were all we had to tell us it was alive. By the time we left, the snake had managed to swallow one of the frog’s legs up to the hip, and even though I know that snakes can eat prey much larger than one would expect, I still had my doubts.

Watching this I had what I suspect was a typical reaction; I wondered if I should try to intervene and “save” the frog, especially right at the beginning when the snake just had it by the ankle. I thought about how terrible it must be to be eaten alive, to be fully conscious (as conscious as a frog gets) while being slowly swallowed, your head and face the last to be part of you to be drawn in. I realized though that it while it is easy to sympathize with the frog, the snake, even though it is the predator in this case, is no less vulnerable. It was going to take some time for the snake to actually swallow that frog, time when the snake was completely defenseless and would be easy prey. All manner of larger vertebrates, from hawks and owls, to foxes and raccoons, would be happy to munch on a garter snake who’s biting teeth were otherwise occupied. I began to feel real empathy for this snake, who, by simply eating, as we all must eat, was exposing itself to danger with no real means of defending itself, a true vulnerability. We often say that life isn’t fair, but maybe that isn’t true. Maybe life is completely fair, and when we see the balance of nature so dramatically illustrated, the frog losing its life, the snake endangering its life to eat the frog, we have to admit that. We’re the ones that don’t play fair, but we should remember, in the long run, nature wins, every time.

References:

If you Google “ Frog and Snake” folk tales you will get lots of stuff. This is a nice one from Timor:
http://www.ling.hawaii.edu/ldtc/languages/tetum/Little%20Frog%20and%20Little%20Snake.html

The standard reference for us Mainers, and useful throughout the northeast: Maine Amphibians and Reptiles, Mac Hunter, Aram Calhoun and Mark McCollough, University of Maine Press

From Northern State University in Aberdeen South Dakota:  http://www3.northern.edu/natsource/REPTILES/Garter1.htm

Terrific series of photos of a garter snake eating a large green frog: http://www.flickr.com/photos/steve_byland/467564987/