The birds and the bees and the microbes

Vannette et al. 2013. “Nectar bacteria, but not yeast, weaken a plant-pollinator mutualism”. Proceedings of the Royal Society B-Biological Sciences.

"When we try to pick out anything by itself, we find it hitched to everything else in the Universe."- John Muir

You can’t help but marvel at the complexity of ecology, at the intricacy and multiplicity of species interactions. But this complexity is also problematic. For many ecologists, it becomes necessary to focus on a single type of interaction, or on interactions limited to only a few species. But real ecological systems are hardly ever limited to a single important process. They might include competition, mutualism, facilitation, predation, environmental constraints and fluctuations, additive and interactive effects, nonlinearities, thresholds and emergent properties. Can knowledge of  omplexity emerge from simplicity? Can simplicity emerge from complexity? These are important and longstanding questions in ecology, the focus of some of our smartest minds. We may not have the answer yet, but if nothing else, it is helpful when experimental work in community ecology attempts to explore multiple interactions.

For example, some of the work from Tadashi Fukami’s lab is focused on how communities of microorganisms (yeast and bacteria species) assemble in Mimulus aurantiacus nectar. In the past, this work has focused particularly on priority effects and resource competition, which plays an important role in structuring these communities. While past work has suggested the importance of pollinators as a dispersal vector for microorganisms, fascinating new work suggests that microbial communities have important effects on pollinators and their mutualistic interactions with the host plant as well.

Vannette et al. (2013) focused on the effects of the two most abundant species in Mimulus nectar, Gluconobacter sp., an acid-producing bacteria, and Metschnikowia reukaufii, a yeast. They then looked at three related questions – how do nectar microbes affect nectar chemistry, how do they affect nectar removal by hummingbird pollinators, and how to they affect pollination success and seed set. Basically, do nectar microbes disrupt important mutualistic interactions between the plant and their pollinators, or are their effects neutral?

This is where the story becomes interesting. Both types of microbes altered nectar chemistry, but in different ways. The bacteria acidified the nectar (to ~ pH 2.0) far more than the yeast species, and tended to also reduce the sugar content of the nectar far more than the yeast. Hypothesizing that these changes could ultimately affect pollinator preference, the authors then filled artificial flowers with nectar containing either the bacteria, yeast, or no microbes. Half of these flowers were bagged to prevent hummingbird access. Compared to the bagged controls, flowers with bacteria-inoculated nectar had less nectar removed than either yeast-inoculated or sterile nectar. It appeared that nectar removal was related to the changes in chemistry driven by bacterial growth in the nectar. Finally,  the authors looked pollination success in relation to microbial inoculation. Flowers inoculated with bacteria did indeed have less pollination success (measured as the number of stigmas closed) and had decreased seed numbers. Microbial communities were not isolated from the ecology of the plant.

Perhaps none of this is that surprising – hummingbirds are intelligent and will preferentially feed, and pollinator choice is important for plant fitness. However, these bacteria and yeast species are specialized for growth in the hypertonic nectar environment and their continued presence in the ecosystem depends on dispersal from one flower to the next before their host flower dies. The transient nature of this nectar habitat suggests that obtaining a dispersal vector should be important. The fact that Gluconobacter alters nectar chemistry in a way which negatively affects their likelihood of movement to other patches suggests an interesting paradox and a complicated relationship between plants, their nectar microbes, and pollinators. Gluconobacter species growing in Mimulus flowers produce acidifying H+ ions and reduce sugar concentrations in nectar – this increases their likelihood of winning competitive interactions with other microbes in the nectar, which should select for the maintenance of acidifying, sugar-reducing characteristics. But on the other hand, these characteristics reduce the likelihood of being transported to new flowers and persisting in the metacommunity. Further, these pollinator-decreasing characteristics may result in selection by the Mimulus plants for nectar compounds that reduce microbial contamination. So understanding competitive interactions in microbial communities, or understanding pollinator-plant interactions, or understanding pollinator-microbial interactions on their own might be inadequate to understand the important ecological and evolutionary processes structuring the entire system.

Given that the question of simplicity vs. complexity is still so difficult and at least for me, uncertain, I would hesitate to draw a general conclusion about whether this is the kind of work all community ecologists should strive for. But it seems that recognizing ecological and evolutionary context is key, whether you work with Arabidopsis, microcosms, or tropical forests.

Travel the world with the Carnival of Evolution

The latest edition of the Carnival of Evolution, hosted by Lab Rat, is online. Take an evolutionary journey around the world.

Exploring biodiversity science: The BioDiverse Perspectives blog

A network of graduate students has started a new blog called 'BioDiverse Perspectives'. The purpose of this blog is to explore and compile seminal papers in biodiversity science.  In some ways this mode of knowledge gathering replaces existing 'Foundations of...' compilations of classic papers. Instead, this blog creates an ever-evolving dialogue about our understanding of the different dimensions of biodiversity. Check it out!

A different kind of ecological diversity: on sticking out in academia

This is a guest post from Sarah Hasnain, currently a PhD student in ecology at Queen's University. Sarah did her MSc at the University of Toronto with Brian Shuter on the interplay between environmental and evolutionary processes underlying thermal response in freshwater fish. Sarah was an office mate of mine for a while at the University of Toronto, and we had some interesting conversations about balancing cultural backgrounds and academia.

By the time that I was nine years old, I already knew that I wanted to do something in science. By the time I was eleven, my grandparents had patiently explained that in order to be a research scientist, I need to complete something called a PhD. And by thirteen, after brief flirtations with physics (which seemed cool at the time, and still is), mathematics, and history, I had decided to pursue a career as an ecologist.

My family supported me in my goal of being a scientist, even though they didn't  know what an ecologist was. And as an undergraduate in Canada’s largest, most multicultural city, I didn’t stand out from my fellow classmates, who similarly came from all over the globe. And yet surprisingly, in addition to the usual student woes about finding scholarships, funding and the right academic advisors, the fact that I am a Pakistani female (and until recently a Hijabi) always seemed to play a role in how people responded to my goals. I continue to be asked to explain my career choice and my passion for science on a  regular basis by colleagues, faculty members and visiting scientists  which was and continues to be emotionally exhausting. For example, a senior faculty member followed me to the lab that I worked in as an undergraduate research student, to confirm that I actually worked there. People always came to my posters at conference poster sessions, but a number of them wantied to tell me that they are very glad to have someone “like you” here. One of the determining factors for which PhD labs I wanted to be in was that during the interview, at no point did the potential supervisor asks what made someone from my cultural, ethnic and religious background decide to pursue ecological research. This actually knocked a few labs out of the running.

I understand that my career choice is interesting, considering that ecology is not a field that has historically attracted many Pakistani women. And it’s undeniable that these comments and questions are about people wanting to be open and accepting and welcoming to me. But I can’t help but feel that the constant questions about my background insinuate, probably unintentionally, that my ethnic, religious and cultural affiliations are more interesting than my research. As an ecologist belonging to a minority group, these questions can have the opposite effect – instead of feeling accepted by their interest, I feel like I am constantly justifying my existence in this field. I imagine that for many minority ecologists, the underlying message is that they don't belong here.

Of course I don’t represent all minority, or Pakistani female ecologists. Probably some individuals would appreciate this interest in their background. But others, like myself, may not. Regardless of ethnic, cultural or religious affiliations, ecology is not the expected career choice in North American society. Why is someone like me interested in ecology? Because I like it. Just like everyone else here. 

Understanding modern human society through the lens of evolution

Book review of Edmund Russell’s ‘Evolutionary History’

We often think about the ways in which evolution has shaped this world, from the amazing diversity of cichlid fishes in the African Great Lakes, to Australian marsupials that seem to replicate strategies that placental mammals have evolved elsewhere (e.g., Tasmanian tiger and the North American wolf). We even look at our own bodies or behaviors to find evolution’s imprint –why do I have a non-functional appendix attached to my intestine? However, we seldom look to important events in human history to examine the effects of evolution, yet, according to Edmund Russell, human history can be better understood through evolution –like my appendix.

Russell is advocating for a new field of inquiry within the study of human history –namely, evolutionary history. When I first read the book jacket, I must admit that I was skeptical. However, this book makes the compelling case that historians gain a much fuller understanding past events by including evolution. Russell’s main claim is that modern civilization is the product of an evolution revolution. Even Russell’s unremarkable dog “Riley, like all dogs, is a testament to the extraordinary power of human beings to shape the evolution of other species”. While citing dogs may seem like a trivial example, it was coevolution that shaped this relationship. Wolves that were less aggressive and less fearful, which tend to be more puppy-like, found benefits by associating with human groups. Human groups that tolerated the presence of these wolves were likely alerted to approaching threats. Even the fact that dogs bark is a product of this relationship. This evolution revolution can similarly explain the domestication of other animals and plants, and ultimately produces the necessary conditions for permanent large settlements.

An important and intriguing underlying theme of this book is that these evolutionary revolutions are not often the product of conscious effort. We are used to the narrative that highlights humans as selecting individuals and driving the evolution towards some goal. But this would require early peoples knowing what they wanted in the end, having a specific goal. In the dog example, do we really think that early humans thought ‘hey, I would like a poodle’? No, the reality is that canines and human changed with one another producing a mutually beneficial outcome. Even the domestication of many of the earliest crop species likely resulted from lazy and sloppy humans. Lazy because humans probably harvested the easiest, most accessible fruits and seeds –selecting for bigger, easily removed fruits that ripened at the same time. Sloppy because seeds were discarded around settlements. Then that laziness again means we looked to those nearby plants for harvesting. Thus evolution has continually informed the development of human civilization and produced the much of the cultural norms today.

While modern cultures may consciously drive evolution through selective breeding and genetic engineering, we are immersed in an evolving world. Diseases that are resistant to drugs, pest that are immune to pesticides, and commercial fish that are now smaller and reproduce earlier are examples of important evolutionary changes that affect human activities and economics. Russell provides evidence that evolution is in part responsible for the industrial revolution, due to some varieties of cotton evolving particular features.

Taken all together, Russell admirably succeeds in his goal of convincing the reader that evolution has influenced much of human civilization. Moreover, his intended audience of historians should be re-assessing previous explanations of important human events by asking the basic question: how has evolutionary change influenced major changes in human history.

Edmund Russell. 2011. Evolutionary History. Cambridge University Press.