Leaf drip tips are one of those features of tropical rain forests that always draws the eye. Walking through the forest during a hard rain, it just seems so obvious that drip tips- long narrow tips on the end of the leaves -must be associated with....drip. 
​

In a new paper published in New Phytologist, my collaborators and I explore drip tips in the larger context of traits associated with leaf wettability. Plants in tropical rain forests frequently get wet. Wet leaf surfaces are considered bad for plant function. For instance, wet leaves have long been associated with increasing pathogen establishment and growth, decreasing rates of photosynthesis, and leaching nutrients out of the leaf. Drip tips are thought to increase the rate at which leaves dry by funneling water off of the leaf surface. 

The problem with this idea is that no one can really find any evidence that it works.

We demonstrate that drip tips do not vary with rainfall, but rather with temperature. The warmer the forest, the higher the proportion of species with drip tips. In fact, we also demonstrate that leaf water repellency, a trait that describes the hydrophobicity of the leaf surface, also does not vary with rainfall. The most hydrophobic leaves appear to occur in cold and dry environments, rather than warm wet environments where it would be beneficial to be hydrophobic.

What does all this mean? One possibility is that wet environments simply do not impair plant function as much as we might imagine. A second possibility is that we are measuring the wrong traits. 

As far as drip tips are concerned, the best evidence I can find suggests that they may simply be a function of leaf development - the formation of a long central vein followed by expansion of the remainder of the leaf.

Maybe it's time to stop calling them drip tips...

Goldsmith, G.R., L.P. Bentley, A. Shenkin, N. Salinas-Revilla, B. Blonder, R.E. Martin, R. Castro-Ccossco, P. Chambi-Porroa, S. Diaz, B.J. Enquist, G.P. Asner, & Y. Malhi. In Press Variation in leaf wettability traits along a tropical montane elevation gradient. New Phytologist DOI: 10.1111/nph.14121​

​As part of a series of plant gas exchange measurements I have been making in collaboration with Rolf Siegwolf and Lucas Cernusak, we have estimated boundary layer conductance in the Walz gas exchange system that we are using. As a contribution for the common good, I thought I would make those estimates available.
 
The estimates are made for a Walz 3010GWK gas exchange chamber with and without their new elbow flange. We measured conductance to water vapor as the evaporative flux from a saturated piece of filter paper cut into the shape of a poplar leaf with different fan speeds. To do so, we cut two pieces of filter paper, made a thin slit in one, and inserted the thermocouple between the two pieces in the leaf cuvette.
 
The results show that the new flange makes an overwhelming difference in removing the boundary layer and increasing conductance. There are modest differences in leaf size, but this is largely due to the difficulty of keeping the smaller leaf saturated at high fan speeds. Overall, these estimates may be lower than those made in other systems, particularly in comparison to smaller leaf cuvettes, but the result is still a very low resistance.
 
If you have questions or would like access to the raw data, please do not hesitate to contact me. 

​I have not thought much about how I dry my hands, beyond knowing that doing so is important for hygiene.
 
A new paper in the Journal of Applied Microbiology demonstrates that not all methods are created equal. And the differences are not what you might expect. Rather, they have to do with the extent to which bacteria and viruses become airborne based on the method- paper towel, warm air dryer or jet air dryer –that you use. The authors demonstrate that the jet air dryer they use results in a much higher concentration of bacteria in the air than other methods. This bacteria persists up to 1 meter away from the dryer in the air for about 10-15 minutes. The paper has some notable and surprising issues with statistical replication (there is spatial and temporal autocorrelation in the data and t-tests are incorrectly applied) that detracts from its credibility, but the data largely speak for themselves.
 
The implication of the study is that it is not in our best public health interest to use jet air dryers given their potential for disease transmission. There is now a critical need for additional studies with added realism – does replacing paper towel with jet air dryers in an entire university increase disease transmission?
 
I was excited by the advent of jet air dryers, particularly given the ecological implications of using paper towel, but this will certainly warrant our attention on a hot crowded planet. 
 
Kimmitt PJ & KF Redway. 2016. Evaluation of the potential for virus dispersal during hand drying: a comparison of three methods. Journal of Applied Microbiology 120:478-486. 

One of the highlights of 2015 was the opportunity to spend a few days with students on National Geographic's student expedition to Costa Rica. I had so much fun - I think I learned more from the students than they did from me.

​​I am excited to be joining two trips to Ecuador again this summer as a guest expert. We'll be exploring the cloud forests near Mindo and the Páramo near Cotopaxi together and I am looking forward to it! 

The top podcasts in the science and medicine category on iTunes this week include Neil deGrasse Tyson's StarTalk Radio and Jim Harold's The Paranormal Podcast. You can find almost every other possible subject in between. So what makes someone tune in to listen to a podcast about climate change?

I consider this question in a review of a fantastic podcast called The Adaptors. The review is published in this week's Books et al. section of Science. 

Thanks to J. Catanoso, B. Anderegg and P. Lopes for comments on the review. 

I had definitely not heard of phylomemetics before reading Nick Matzke's recent paper on the evolution of anti-evolution policies in Science. The concept is simple and incredibly clever: use tools developed for studying evolutionary relationships in biology to study the transmission of culture (i.e. the phylogenetics of memes).  In this case, Matzke explores the relationships among anti-evolution legislation in the decade since the Kitzmiller v. Dover court case. 

Matzke studied the text of more than 65 bills introduced to erode the teaching of evolution in classrooms. However, the most striking aspect of his results from my perspective are the implications for teaching students about global climate change. In essence, he finds that the introduction of a policy in Louisiana in 2006 is the origin of a much broader change in legislation, in that it now simultaneously targets evolution, human cloning and global warming. By including human cloning and global warming, the authors can deflect the idea that the reason to not teach evolution is founded solely on religious principles, which has been found to be unconstitutional. This should serve as a warning for science educators of all shapes and sizes. 

It is not surprising that the anti-evolution movement  continues to evolve. It is ironic that the tools developed to study evolution might contribute to the movement's undoing. 

Paper has its limits. For instance, a paper field guide: 

-Can only include so much information before it is no longer a field guide and instead a desk reference.

-Can only have the information organized in one way, with one or two indices at the rear to guide the user to the information they are looking for.

-Can only be updated when the author and publisher choose to release a new edition.

-Can only be published and distributed in one, or at most two, languages at a time.

This week in the Books et al. section of Science, I explore some of the incredible opportunities for re-imagining how we construct field guides made possible by the advent of mobile technology. I do so through the lens of the fantastic new field guide Map of Life, one of the most impressive efforts to provide on-demand access to biodiversity information. This is the first time that Science has reviewed a mobile application; there is no doubt in my mind that this will not be the last time.

The review is by no means exhaustive in exploring all of the important considerations that go into making these applications and I am looking forward to many interesting discussions as we push these ideas forward.

My thanks to Walter Jetz and Rob Guralnick for providing additional information on Map of Life and to a host of colleagues including Ken Feeley, Brian Enquist, Jens-Christian Svenning, and Chelsea Little for feedback on the review.

Goldsmith, G.R. 2015. The field guide, rebooted. Science 349: 594.

For the last two years, I have been fortunate to collaborate with Brian Enquist and the folks in the Botanical Information and Ecology Network (BIEN) to try and bring their incredible database on plant species distributions to a broader audience by means of a mobile application, which has affectionately become known as Plant-O-Matic. The application matches your location with detailed information on plant species distributions in the Americas to provide you with a list of all the species expected to occur within 100 sq. km. You can access additional information on each species, as well as conditionally search, sort and filter the information. Plant-O-Matic can be downloaded for free from the Apple Store.  

For those of you interested in the finer details, there have been some delays in the review process (ironically, this relates to my previous post). Please find below an abstract of the manuscript currently in review and do not hesitate to contact me if you wish to have a complete copy.  

In the past 12 months, I have been asked by editors from 18 different journals to peer review 22 different manuscripts. This is clearly not sustainable. 

I recognize that I am not alone in this experience and I offer no great solutions; my approach has been to review a manuscript for every manuscript that I author or co-author.

However, beginning with the article we published last year in Ecosphere, I have adopted one new habit. I am writing and mailing a thank you note to every handling editor that I work with, regardless of their decision. If I receive 22 manuscripts a year, I can only imagine the thankless job of an editor. 

I am a co-author on a new paper that is in press at Global Change Biology. The paper explores how landscape level patterns in precipitation and soil drive differences in the carbon cycle of lowland Amazon forests. I'll write more on this soon, but in the interim, you can check out the layperson's abstract and access the full text through the link at the bottom: 

Understanding the relationship between photosynthesis, net primary productivity and growth in forest ecosystems is key to understanding how these ecosystems will respond to global anthropogenic change, yet the linkages among these components are rarely explored in detail. We provide the first comprehensive description of the productivity, respiration and carbon allocation of contrasting lowland Amazonian forests spanning gradients in seasonal water deficit and soil fertility. Using the largest dataset assembled to date, ten sites in three countries all studied with a standardized methodology, we find that (i) gross primary productivity (GPP) has a simple relationship with seasonal water deficit, but that (ii) site-to-site variations in GPP have little power in explaining site-to-site spatial variations in net primary productivity (NPP) or growth because of concomitant changes in carbon use efficiency (CUE), and conversely, the woody growth rate of a tropical forest is a very poor proxy for its productivity. Instead, (iii) spatial patterns of biomass are much more driven by patterns of residence times (i.e. tree mortality rates) than by spatial variation in productivity or tree growth. Current theory and models of tropical forest carbon cycling under projected scenarios of global atmospheric change can benefit from advancing beyond a focus on GPP. By improving our understanding of poorly understood processes such as CUE, NPP allocation and biomass turnover times, we can provide more complete and mechanistic approaches to linking climate and tropical forest carbon cycling.


Malhi, Y. C.E. Doughty, G.R. Goldsmith, D.B. Metcalfe, C.A.J. Girardin, T.R. Marthews, J. del Aguila-Pasquel, L.E.O.C. Aragão, A. Araujo-Murakami, P. Brando, A.C.L. da Costa, J.E. Silva-Espejo, F.F. Amézquita, D.R. Galbraith, C.A. Quesada, W. Rocha, N. Salinas-Revilla, D. Silvério, P. Meir & O.L. Phillips. 2015. The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests. Global Change Biology DOI: 10.1111/gcb.12859