Going Gray

Note: This program first aired on July 30, 2016.

This week’s show originated as a question from my nephew. He was wondering why hair turns gray. I have thought of that myself, as I sport a head full of white hairs, which started losing color far ahead of the curve early in my 20s. And the answer to the question is of course, complicated and partially unknown.

To start we have to look at where hair, and fur color comes from. Hair is made of several layers of a structural protein called keratin (the same thing your finger nails are made of). It grows from collection of cells, which some sources refer to as a mini-organ, called a follicle. The skin of most mammals is studded with hair follicles, it is a defining characteristic of the group. The color of hair is controlled by cells around the follicle called melanocytes, who’s job unsurprisingly is to generate a pigment called melanin. Melanin gives hair its color, by being injected into the filamentous protein we call hair, as it grows. The variety of hair colors we see in mammalian  animals is determined by the mix and balance of different types of melanins, broadly speaking, eumelanins are black and brown, and phaeomelanins are lighter, reds and yellows.

Human hair has three develpmental stages: anagen or growth phase, which lasts for years,  catagen or transitional phase, as the hair transitions from active growth to being shed, and telogen, a quiescent phase that ends with the hair fiber being shed. While we look mainly at what is going on with the hair itself, these phases represent dramatic differences in the functioning of the hair follicle. As the hair is growing in anagen, the melanocytes are pumping melanin into the hair fiber. When the follicle enters catagen, the first thing that happens is the melanocytes stop melanin production and undergo apoptosis, which is programmed cell death. Individual melanocytes then only get to produce melanin for a single strand of hair. Hair pigmentation shuts off in the transitional phase of hair growth, and if it doesn’t turn back on when the cycle starts over, the resulting hair that grows will be colorless, or white.

Now I said that not only does the melanocyte stop producing pigment, it actually dies, and in order for the next hair that grows to have pigment a new melanocyte has to form. And that is where the root of all this going gray as a normal part of aging happens. The new melanocytes arise from stem cells, melanocyte stem cells, which can mature into a pigment producing cell when needed. These stem cells continually divide and create more stem cells, so there is always a supply on hand when the hair follicle returns to the anagen active growth phase. The current thinking is that mammals go gray as they age because stem cells start to lose their integrity the older they are. The older you are the more damaged the cells in the melanocyte stem cell reservoir are, so the chances of a functional stem cell being able to mature into a pigment producing cell go down. The more times cells divide, the more chances there are for errors in transcription, the copying of genetic information. That is why age impacts cellular health, in general, the older a cell is, the more times it has divided. Cells only have so many times they can divide, before the telomere mechanisms inhibit further cell division and the cell effectively is put out to pasture. When we get very old, we don’t have any melanocyte stem cells left. Normal aging (which really means the changing of our cellular DNA, or shortening of our telomeres, that occurs during cell division) results in this decrease in stem cells, but cellular stress in the form of mutagens that damage DNA can as well, things like Xrays and UV light.

Many questions remain about this going gray business. The diversity of pattens of human graying is thought to be genetic but we don’t know why, and are there implications for other stem cells in the body, do all your stem cells function the same way? Why do dogs go gray around their muzzles but not other parts of their bodies? Why do some mammals not go gray at all? Many questions, fewer answers, but that is actually a good thing. If we had all the answers there would be nothing left to do. So please, keep your questions coming.

 

References:

http://www.iflscience.com/health-and-medicine/why-does-hair-change-colour-and-turn-grey/

http://www.livescience.com/3670-roots-gray-hair-cellular-stress.html

More than you ever wanted to know about hair: https://repositorium.sdum.uminho.pt/bitstream/1822/15299/1/2010%20Biology%20of%20Human%20Hair%20Know%20Your%20Hair.pdf

http://genetics.thetech.org/original_news/news15

Caterpillars, Food Webs and Doug Tallamy

Note: This program first aired July 23, 2016.

Ecosystems are like salad bars, you fill your plate with lots of leafy greens and then sprinkle lesser amounts of more concentrated food items on top (nuts, olives, bacon bits). Ecosystems have a similar food or trophic structure, at the bottom are the primary producers, the plants and other photosynthetic organisms, as you move up at each level there are fewer and fewer non plant individuals ( herbivores, omnivores and carnivores).

Land plants are the primary producers of terrestrial ecosystems, doing the work of capturing the sun’s energy on dry ground, they are the lettuce on the salad bar of the forest. And it turns out there are bacon bits here in the forest as well, in the form of caterpillars. As herbivores these organisms are able to transfer the energy that plants capture from the sun to higher trophic levels in the forest food web. That is what I learned listening to a talk from University of Delaware entomologist Doug Tallamy when he came to Maine to speak earlier this summer.

Tallamy’s work looks at the relationship between the primary producers, insects and the upper trophic levels, mainly birds. And what he has discovered has profound implications for the way we manage the landscapes directly under our control. It turns out that if you want birds around, particularly migratory song birds, you need insects, specifically caterpillars. These birds migrate thousands of miles to northern North America to breed, because of the plentiful food sources here. 

Caterpillars, which are made up of fat and protein, are very nutrient dense and make up a huge proportion of that food for many of these birds. Tallamy recalled watching a pair of birds feeding their young, calculating that the nest of young birds were fed hundreds of caterpillars a day, thousands over the two week period they spent in the nest. And here is where it gets interesting, because if you want caterpillars around, caterpillars being the larval stage of lepidoptreans, the butterflies and moths, you need plants, because caterpillars eat plants.

But not just any plants, caterpillars generally eat specific plants, plants they have a long evolutionary relationships with. Plants do everything they can to not be eaten, evolving elaborate chemical warfare against hungry insects. Insects do everything they can to evolve physiologic means of evading the plant defenses, in an ever escalating evolutionary game, the relationship between the eater and the “eat-ee” gets more and more specific. We have all heard about the monarch butterfly and its host plant common milkweed, but many lepidopterans have this level of specificity with their target food source. Others are less specific and play the field, having relationships with plants in more than one genus. And plants are not monogamous, as the “prey species” in this relationship, they have many different insects trying to eat them, and can play host to tens to hundreds of different kinds of caterpillars. 

What Tallamy and his lab have quantified is the number of different lepidopteran species (in the form of the caterpillars—which are the stage in which these insects do the majority of their primary production energy transfer) various genera of plants support. The results are astonishing. In my area, native tree genera like willow (Salix) and oak (Quercus) can support between 300 and 350 different types of caterpillars!  Other native tree genera support nearly that many. The corallary to this is that nonnative trees and shrubs, frequently planted as part of “normal” landscaping, support virtually no caterpillars, because no native insects have evolved ways to evade these plants’ defenses. None. Insects are the animal that is responsible for transferring the majority of primary productivity from plants to the rest of the terrestrial food web. Birds, reptiles, amphibians, spiders, and rodents all rely on caterpillars as a food source. So if you don’t have plants that support insects, you don’t have anything else in the food web either.  Biodiversity is our life support system, and what I learned from Doug Tallamy is that it starts from the ground up, in an elegant and fundamental relationship between those that eat and those that are eaten.

References:

Doug Tallamy’s book on native plant landscaping in the suburban environment: http://www.bringingnaturehome.net/

Download the data from Doug Tallamy’s studies here: http://udel.edu/~dtallamy/host/

One of Doug’s popular science articles (slightly dated) but with interesting stats: https://www.americanforests.org/magazine/article/backyard-biodiversity/

 Our local native plant advocacy group, Wild Seed Project, has lists of appropriate native plants (to Maine) for different environmental conditions: http://wildseedproject.net/using-natives-in-the-landscape-a-comprehensive-plant-list/

The native plant finder at the National Wildlife Federation site: http://www.nwf.org/nativeplants-beta/About (its a beta version--still a little buggy, no pun intended, for example, when I searched my zip code some high scoring trees did not appear, but when I searched them individually they showed up in my zip code…)

Nutritional info on caterpillars: http://healthland.time.com/2013/08/21/why-eating-bugs-is-good-for-you-its-about-the-nutrients/slide/caterpillar/

Want to eat some bugs yourself? Here’s a list of internet resources: https://edibug.wordpress.com/where-to-get-bugs/

Bumble Bees Part 2: Life History

Note: This program first aired on July 9, 2016. 

A worker bee, temporarily interrupted from foraging.

I’ve been spending a lot of time lately thinking about bumble bees, watching which flowering plants they visit and which they don’t, looking at them trying to discern one species from the next, and learning when they like to fly and when they don’t. I’ve volunteered to survey bumble bees for the Maine Bumble Bee Atlas project and the learning curve has been steep. The entomologists who direct the project are evidence of the fact that the rabbit hole you can go down when you open your eyes and start to see the insect world all around you has no bottom. Arthropods are the most successful phylum of animals on the planet, and there is no shortage of wonder to be pursued in their diversity. For me it seems bumble bees may just be the beginning.

One place to start is with their life history. I’ve kept honey bees on and off for a few years and thought that bumble bees worked the same way, albeit on a smaller scale. I was wrong. Bumble bees, like honey bees are true eusocial insects, meaning they live in colonies that have castes of workers with behavioral specialization, communal care of brood, overlapping generations, and reproduction limited to a few specific individuals (often a single queen and specially raised males). Bumble bees live this eusocial life in a way very different from the European honey bees many of us bee keepers are familiar with.

Bumble bee colonies over winter as queens, the large, mated reproductively active females that are raised and mated the fall before. When the weather turns cool these individuals search out an overwintering spot, in leaf litter at the edge of the forest. These are well fed bees, having been raised on the bountiful nectar and pollen from the late season golden rods and asters. These queens emerge in the spring and are the stock from which the new colonies form. The only bumble bees that survive the winter are the queens, colonies do not over winter, workers do not over winter. Only single bees do, prepared to start a brand new colony of their own the next year.

So those first really big bees you see flying in the spring are the over wintered queens. They emerge and look for a spot in which to nest, a spot that will house their  modest colonies for the summer. Old rodent burrows are especially good spots, as apparently are the seat cushions of the old abandoned cars in the woods you see frequently in Maine as early 20^th century farmsteads are reclaimed by forest. Once a queen finds a good nest cavity, she lays the first of her eggs (remember she mated the fall before, so she has all the sperm she needs to lay fertilized eggs), She incubates them herself by generating heat shivering, and feeds the larva nectar and pollen when they hatch. One bee foraging to feed several hungry babies though does not quite cut it, so the first round of bees that are produced by the queen are quite small. These are the first worker bees you will see in the spring, they look stunted, and quite literally they are—nutritionally they got enough to survive but not really thrive. Once there are more workers in the colony, the subsequent larvae get fed better, and the resulting bees are bigger. This pattern continues throughout the summer, the queen lays eggs, staying in the nest once there are enough worker bees to do the foraging, the workers out in the field collecting the nectar and pollen needed to sustain the hive. Workers live around 25 days, and a typical hive has between 50-100 bees when up and running during the summer.

At the end of the summer, two different kinds of bees get produced by the hive. The first are males—these come from unfertilized eggs. They have one purpose only, that next year’s queens can get fertilized before hibernating. The others are the new queens. The last batch of worker bee eggs that are laid become the queens for next year. Theoretically the hive is at its highest capacity at the end of the summer, the land is covered with golden rod and asters and thus there is plenty of forage, and many workers able to feed these up and coming queens. Once these very large nascent queens emerge, they mate with the males which also unsurprisingly emerge at the same time. As fall progresses on, the old queen, the founder of the colony, dies. Her daughters, the worker bees, all die. Her sons, the males, all die. The only bumble bees that don’t die are the new queens, well fed and stocked with sperm, ready to over winter in the leaf litter until the process starts over again in the spring.

It’s a pretty remarkable process, and something to consider when you clean up your yard in the fall. Do the bumble bees a favor, leave those leaves where they are until the spring, in doing so you create safe space for the potential bumble bees of the future.

References:

On eusocial insects:  https://www.amentsoc.org/insects/glossary/terms/eusocial 

The Maine Bumble Bee Atlas project: https://ac41277bd54735c2b85336aff6fdfbfd153fcee3.googledrive.com/host/0B985dSJVRA1maGtVekhDUkJjYWM/

Maine Bumble Bee Atlas

Note: This program first aired on July 2, 2016.

Citizen science is a growing movement in this country. I’ve talked about it before on the show, describing the Signs of the Seasons program that uses the observations of amateur naturalists to document the phenological patterns of seasonal events, like when the red maple trees are in bloom, when various sea weeds become reproductive and when the first wood frogs are heard. The timing of those events results from environmental cues, particularly temperature, and thus changes in the timing of those key seasonal milestones could reflect and inform our understanding of how the environment is responding to climate change.

Another citizen science initiative underway here in Maine is the Maine Bumble Bee Atlas, a project designed to use trained volunteers to survey bumblebee populations throughout the state. Like the Butterfly and Dragonfly surveys before it, the goal of the Bumble Bee Atlas project is to document the abundance, diversity and distribution of bumblebees in Maine, in the absence of any good baseline data. Because we lack baseline data, we don’t really know what bees are here or how many of them there are. Historic records point to 17 different species of bumblebees in the state, but those historic records are incomplete. And while there have been documented declines in bumblebee populations in other parts of the country, we don’t know if that has happened here. At its simplest, the project will establish a baseline of understanding with data from all over the state, collected over a 5 year period, that will allow scientists to have a high degree of confidence that what is out there has truly been sampled, and that the data set really reflects the diversity distribution and abundance. You get enough people collecting enough data in enough places, you stand a high probability of having enough overlap to get good coverage. Citizen science is based on this premise, it accomplishes through the use of knowledgeable volunteers what it never could relying only on professional field biologists. There are plenty of us willing and interested volunteers, and not enough field biologists to generate this massive, multi year data set.

I recently attended the one day training session in preparation for participating in this year’s sampling season, and learned that volunteering is a great way to get education. I learned a lot I didn’t know about bumblebees, it was very exciting for a super nerd like myself. Bumblebees are of course of interest because of their ecological role as native pollinators of flowering plants. Something like 90% of angiosperm species rely at least in part on some form of animal pollination. Here in Maine there are many different insect species that perform this pollination job. The Lepidoptera (butterflies and moths), ants, beetles, wasps and hornets (especially the wasp and hornet queens), flies, bee flies (which are bee parasites), and bees. We have over 250 species of native bees in Maine, most of which are solitary bees, only 17 of which are bumble bees. Relative to other states this is actually a pretty low number of bee species. The boxes of honey bees you see on blue berry barrens in late spring are native to Europe, and are used commercially for agricultural pollination because their colonies grow large quickly, providing thousands of foraging (and thus pollinating) individuals in each colony.

It can’t be stressed enough the role these pollinators play in terrestrial ecosystems. Plants and insects have evolved over millions of years to rely on one another, and declines in pollinating insects result in declines in vegetation. Plants are the source of all of our energy, they are the means by which energy from the sun becomes useful to us biologically. In both ecological and agricultural systems, without mechanisms of pollination, you will see declines.

Next week we’ll look more closely at the specifics of bumble bee natural history, and learn how their lifestyle makes them unique among those 250+ species of native bees in Maine.

References:

Listing of citizen science opportunities throughout New England (not sure how up to date: http://newengland.stewardshipnetwork.org/citizen-science)

The Maine Bumble Bee Atlas home page: https://ac41277bd54735c2b85336aff6fdfbfd153fcee3.googledrive.com/host/0B985dSJVRA1maGtVekhDUkJjYWM/

The Maine Bumble Bee Atlas blog: http://www.maine.gov/wordpress/bumblebeeatlas/

The Maine Bumble Bee Atlas on Facebook (current and great photos!) https://www.facebook.com/MaineBumblebeeAtlas/

If you are curious, the Maine Butterfly Survey site: https://2d042df5ce2f94779d5a6c1b6c47d612202b3787.googledrive.com/host/0B985dSJVRA1mWm43NXVQWEhmVGM/

And the Maine Damselfly and Dragonfly Survey site: https://bad7c31b56f9e6bfcd572114fde5c911ee02ad88.googledrive.com/host/0B985dSJVRA1mbUNxVms3ejBSa1E/