Uncommon Ground


Trait-climate evolution in Protea

Protea compacta

If you’re reading this post, you know that my colleagues and I have been studying Protea for more than a decade. A lot of our work has focused on documenting and understanding trait-environment associations. We’ve studied those associations both among populations within species (Protea repens: https://doi.org/10.1093/aob/mcv146), among populations within a small, closely related clade (Protea sect. Exsertae: https://doi.org/10.1111/j.1558-5646.2010.01131.x and https://doi.org/10.1111/j.1420-9101.2012.02548.x), and across the entire genus (https://doi.org/10.1086/680051). But all of those studies look at the relationship between the climate as it is now (as reflected in the South African Atlas of Agrohydrology and Climatology). They haven’t examined how traits have evolved in response to changes in climate.

Our latest paper, begins to address that shortcoming. We use the highly resolved phylogeny of Protea that Nora Mitchell constructed as part of her dissertation (http://darwin.eeb.uconn.edu/uncommon-ground/blog/2017/01/23/a-new-phylogeny-for-protea/ and https://doi.org/10.3732/ajb.1600227), and we reconstruct estimates of how traits changed over evolutionary time in concert (or not) with climates. Our reconstructions depend on particular models of evolutionary change, and we explore several alternatives. Here’s the abstract:

Evolutionary radiations are responsible for much of Earth’s diversity, yet the causes of these radiations are often elusive. Determining the relative roles of adaptation and geographic isolation in diversification is vital to understanding the causes of any radiation, and whether a radiation may be labeled as “adaptive” or not. Across many groups of plants, trait–climate relationships suggest that traits are an important indicator of how plants adapt to different climates. In particular, analyses of plant functional traits in global databases suggest that there is an “economics spectrum” along which combinations of functional traits covary along a fast–slow continuum. We examine evolutionary associations among traits and between trait and climate variables on a strongly supported phylogeny in the iconic plant genus Protea to identify correlated evolution of functional traits and the climatic-niches that species occupy. Results indicate that trait diversification in Protea has climate associations along two axes of variation: correlated evolution of plant size with temperature and leaf investment with rainfall. Evidence suggests that traits and climatic-niches evolve in similar ways, although some of these associations are inconsistent with global patterns on a broader phylogenetic scale. When combined with previous experimental work suggesting that trait–climate associations are adaptive in Protea, the results presented here suggest that trait diversification in this radiation is adaptive.

Mitchell, N., J.E. Carlson, and K.E. Holsinger.  2018.  Correlated evolution between climate and suites of traits along a fast–slow continuum in the radiation of Protea. Ecology and Evolution 8:1853–1866. doi: 10.1002/ece3.3773.

The origin of a bipolar moss (i.e., one that occurs in the far North and the far South)

One of the great pleasures of serving as an associate advisor on PhD committee is that sometimes you contribute enough to the analysis and interpretation of the data that you end up being a co-author on a paper. That’s why I have papers on New Zealand cicadas, deer mice, and tapeworms, among other things. Now I’ve added another group to my list – moss. Lily Lewis finished her PhD at UConn in the spring of 2015 working with Bernard Goffinet. I was a member of her committee, and now a chapter of her dissertation on which I was able to help has appeared in the American Journal of Botany.1 Here’s the title and abstract. You’ll find the DOI and a link to the paper below.

Resolving the northern hemisphere source region for the long-distance dispersal event that gave rise to the South American endemic dung moss Tetraplodon fuegianus.

PREMISE OF THE STUDY: American bipolar plant distributions characterize taxa at various taxonomic ranks but are most common in the bryophytes at infraspecific and infrageneric levels. A previous study on the bipolar disjunction in the dung moss genus Tetraplodon found that direct long-distance dispersal from North to South in the Miocene–Pleistocene accounted for the origin of the Southern American endemic Tetraplodon fuegianus, congruent with other molecular studies on bipolar bryophytes. The previous study, however, remained inconclusive regarding a specific northern hemisphere source region for the transequatorial dispersal event that gave rise to T. fuegianus.
METHODS: To estimate spatial genetic structure and phylogeographic relationships within the bipolar lineage of Tetraplodon, which includes T. fuegianus, we analyzed thousands of restriction-site-associated DNA (RADseq) loci and single nucleotide polymorphisms using Bayesian individual assignment and maximum likelihood and coalescent model based phylogenetic approaches.
KEY RESULTS: Northwestern North America is the most likely source of the recent ancestor to T. fuegianus.
CONCLUSIONS: Tetraplodon fuegianus, which marks the southernmost populations in the bipolar lineage of Tetraplodon, arose following a single long-distance dispersal event involving a T. mnioides lineage that is now rare in the northern hemisphere and potentially restricted to the Pacific Northwest of North America. Furthermore, gene flow between sympatric lineages of Tetraplodon mnioides in the northern hemisphere is limited, possibly due to high rates of selfing or reproductive isolation.

DOI: 10.3732/ajb.1700144

Climate change and Pelargonium in South Africa

For more than a decade my colleagues Margaret Rubega and Bob Wyss have co-taught a course to graduate students in science and engineering and undergraduates in Journalism.1 The purpose of the course is to help science students improve their skills in working with journalists and to help journalist increase their skills in interviewing scientists and developing stories from those interviews. One of the projects in this fall’s edition of the course was for the journalism students to interview one of the science graduate students and produce a short video describing the student’s research. Daniela Doncel interviewed Tanisha Williams, a PhD student in EEB whom I co-advise with Carl Schlichting. In addition to interviewing Tanisha, Daniela also interviewed Cindi Jones and me. She assembled a video that explains Tanisha’s work very well. I think Daniela did a very nice job of weaving the disparate interviews into a compelling story, and I think the video looks very good (even though it has me in it). I hope that you agree.


AIBS Emerging Public Policy Leadership Award

The American Institute of Biological Sciences works to ensure that the public, legislators, and others have access to the best scientific information available, especially in the fields of environmental and organismal biology. In addition to individual members, more than 100 professional societies are organizational members. One of the most interesting programs AIBS offers is its Emerging Public Policy Leadership Award. Here is the text of an e-mail I recently received announcing this year’s award.

Each year, the American Institute of Biological Sciences (AIBS) recognizes graduate students in the biological sciences who have demonstrated initiative and leadership in science policy. Recipients obtain first-hand experience at the interface of science and public policy.Winners receive:

  • A trip to Washington, DC, to participate in the AIBS Congressional Visits Day, an annual event that brings scientists to the nation’s capital to advocate for federal investment in the biological sciences, with a primary focus on the National Science Foundation. The event will be held on April 17-18, 2018. Domestic travel and hotel expenses will be paid for the winners.
  • Policy and communications training, including information on the legislative process and trends in federal science funding.
  • Meetings with congressional policymakers to discuss the importance of federal investment in the biological sciences.
  • A one-year AIBS membership, including a subscription to the journal BioScience and a copy of “Communicating Science: A Primer for Working with the Media.”
    The 2018 award is open to U.S. citizens and U.S. permanent residents enrolled in a graduate degree program in the biological sciences, science education, or a closely allied field. Applicants should have a demonstrated interest in and commitment to science policy and/or science education policy.

Applications are due by 11:59 PM Eastern Time on 9 January 2017. The application can be downloaded at http://www.aibs.org/public-policy/eppla.html.

Plants, People, and the Mother City

Tanisha Williams, Fulbright 2015-2016, South Africa, at Boulders Beach visiting the penguins.

Some of you know that Carl Schlichting and I co-advise Tanisha Williams. If you know that, you almost certainly know that Tanisha spent the 2015-2016 academic year as a Fulbright Fellow in South Africa. She was based at the Cape Peninsula University of Technology, and she used her time not only to collect seeds of Pelargonium and establish experimental gardens at Kirstenbosch Botanical Garden and Rhodes University but also to work with two non-profit environmental organizations. She posted an article about her experience on the blog of the Fulbright Student Program. Here’s an excerpt to whet your appetite:

Among the many experiences I had, I must say the residents from the Khayelitsha township have taken a special place in my heart. This is where I taught girls and young women math, science, computer tutoring, life skills, and female empowerment through a community center program. It was such an impactful experience, as these girls are growing up in a community with high rates of unemployment, violence, and other socioeconomic issues. It was empowering for me to see the curiosity and determination these girls had for learning and changing their community. They thought I was there to teach them from my own experiences being raised in a comparable situation and now working on my doctorate as a scientist, but I know I was the one that gained the most from our time together. I learned what it truly means to have hope and persevere. These lessons, along with the ecological and evolutionary insights from my academic research, will be ones that I always remember.

Announcing the BioOne Career Center

BioOne logos
BioOne is a collaboration between libraries and non-profit scholarly publishers in organismal and environmental life sciences. It was founded in 1999 to help publishers obtain the revenue they need to support their publishing program while ensuring affordable access to scholarly journals for libraries and their patrons. I am proud to have served as Chair of the BioOne Board of Directors since 2000.

BioOne’s primary service is to provide BioOne Complete, a database of 207 journals including many open access titles. As the title of this post suggests, BioOne is now offering a new service, the BioOne Career Center. Anyone looking for an opportunity can create a free account, set up a job aloer, and post their CV. Employers can post jobs on the site for free until the end of October (you’ll find the necessary code in the announcement), and posting for internships, volunteer opportunities, and conferences will always be free. We hope that the BioOne Career Center will become a valuable resource.

A crack in creation

In August, 2012 a paper entitled “A Programmable Dual-RNA–Guided DNA Endonuclease in Adaptive Bacterial Immunity” appeared in Science (doi: 10.1126/science.1225829). I probably saw the title in the table of contents of the August 17th issue and skipped right by. Bacterial immunity isn’t a topic a pay a lot of attention to. OK. Let’s be honest. I don’t pay any attention to bacterial immunity.

Not too long after that paper appeared, I started hearing about something called CRISPR-Cas9. I didn’t know what it was or what it might be useful for, only that a lot of people who were interested in molecular genetics were paying attention to it, especially those who were interested in using molecular tools to edit genomes of complex, multicellular organisms. I started to see newspaper and magazine articles talking about how this new technology would revolutionize biology and medicine in the same way that the discovery and use of restriction endonucleases had revolutionized them in the mid-1970s.

Some of the most ambitious projections suggested that we could be entering an era of designer genes in which gene therapy might be used not only to modify or replace genes that lead to diseases like sickle cell anemia, but in which it might be used to enhance “normal” functions. Not too long after that I started hearing about biologists who realized that CRISPR-Cas9 could be used to build gene drives that might be used to control pest populations. A lot of people began worrying about the ethical issues associated with use of CRISPR-Cas9 (e.g., doi: 10.1093/bmb/ldx002).

In June, two pioneers in the work leading to development of CRISPR-Cas9 published a book outlining the history of the work and exploring some of the ethical implications. I am a little less than halfway through A crack in creation, but so far I have found it very readable and informative. Reading this book is the only reason I know about the Science paper from 2012. Only now, 5 years later, am I taking the time to learn about this new technology. I had an inkling of its power and utility before I started reading, and I was (am still am) uneasy about some potential applications. Since so much of the basic science is very distant from my expertise and experience, I can’t judge the historical accuracy of the story Douda and Sternberg tell, but they seem generous in giving credit to other scientists who made contributions and very aware that their creative insights depended on previous work by many other people. That makes me think that if there are inaccuracies in the story, they are inadvertant and unintentional.

If you’ve been waiting for a good time to learn more about CRISPR-Cas9, your wait is over. Click on the image above, go to Amazon, and buy yourself a copy of A crack in creation or check it out from your library. You won’t be disappointed.

(In case you’re wondering, I don’t know either of the authors, and I won’t get any Amazon affilliate credits if you buy the book from Amazon. I’m endorsing the book only because I’ve found it very informative. It’s also written very clearly, clearly enough that I think your non-biologist friends and relatives would find it interesting and informative, too.)

Using weather to predict growth of forest trees

Last January I mentioned that I co-authored a paper that appeared on bioRxiv in which we combined tree ring and growth increment data to predict growth from weather and biophysical data. The paper has now appeared in Ecosphere, an open acces journal from the Ecological Society of America. Here’s the abstract. You’ll find the full citation below.

Fusing tree-ring and forest inventory data to infer influences on tree growth

Better understanding and prediction of tree growth is important because of the many ecosystem services provided by forests and the uncertainty surrounding how forests will respond to anthropogenic climate change. With the ultimate goal of improving models of forest dynamics, here we construct a statistical model that combines complementary data sources, tree-ring and forest inventory data. A Bayesian hierarchical model was used to gain inference on the effects of many factors on tree growth—individual tree size, climate, biophysical conditions, stand-level competitive environment, tree-level canopy status, and forest management treatments—using both diameter at breast height (dbh) and tree-ring data. The model consists of two multiple regression models, one each for the two data sources, linked via a constant of proportionality between coefficients that are found in parallel in the two regressions. This model was applied to a data set of ~130 increment cores and ~500 repeat measurements of dbh at a single site in the Jemez Mountains of north-central New Mexico, USA. The tree-ring data serve as the only source of information on how annual growth responds to climate variation, whereas both data types inform non-climatic effects on growth. Inferences from the model included positive effects on growth of seasonal precipitation, wetness index, and height ratio, and negative effects of dbh, seasonal temperature, southerly aspect and radiation, and plot basal area. Climatic effects inferred by the model were confirmed by a dendroclimatic analysis. Combining the two data sources substantially reduced uncertainty about non-climate fixed effects on radial increments. This demonstrates that forest inventory data measured on many trees, combined with tree-ring data developed for a small number of trees, can be used to quantify and parse multiple influences on absolute tree growth. We highlight the kinds of research questions that can be addressed by combining the high-resolution information on climate effects contained in tree rings with the rich tree- and stand-level information found in forest inventories, including projection of tree growth under future climate scenarios, carbon accounting, and investigation of management actions aimed at increasing forest resilience.

Evans, M. E. K., D. A. Falk, A. Arizpe, T. L. Swetnam, F. Babst, and K. E. Holsinger. 2017. Fusing tree-ring and forest inventory data to infer influences on tree growth. Ecosphere 8(7):e01889. doi: 10.1002/ecs2.1889

Lecture notes in population genetics – final version from Spring 2017

I’ve finally had time to clean and post the final version of lecture notes from my graduate course in population genetics last spring. The individual lectures have been since I revised them for class, meaning that the last set of them was available in late April. You will find links to the individual lecture notes at http://darwin.eeb.uconn.edu/uncommon-ground/eeb348/notes/. If you’re interested in a particular topic in population genetics and I have a lecture that covers the topic, that’s probably where you’ll want to go.

If you want a single-volume reference to population genetics (including some old notes that I no longer maintain), you’ll find a PDF (5.89MB, 322 pages) at Figshare (doi: 10.6084/m9.figshare.100687.v2). If you want to print the PDF, I recommend that you print it on a double-sided printer. You can then put the pages in a binder and flip through them as if it were a bound book.

If you use LaTeX (and you’re a glutton for punishment), the LaTeX source and EPS files (for figures) is available in a Github repository (https://kholsinger.github.io/Lecture-Notes-in-Population-Genetics/).

These notes are released under a Creative Commons Attribution-ShareAlike license (http://creativecommons.org/licenses/by-sa/4.0/). I hope you find them useful. If you find errors in them, please let me know.

Causes of genetic differentiation in Protea repens

American Journal of Botany Volume 104, Number 5. May 2017.

Protea repens is the most widespread member of the genus. It was one of the focal species in our recently completed Dimensions of Biodiversity project. Part of the project involved genotyping-by-sequencing analyses of 663 individuals from 19 populations spanning most of the geographical range of the species. We summarize results of those analyses in a paper that just appeared in advance of the May issue (cover photo featured above) of the American Journal of Botany. Here’s the abstract. You’ll find the citation and a link at the bottom.

PREMISE OF THE STUDY: The Cape Floristic Region (CFR) of South Africa is renowned for its botanical diversity, but the evolutionary origins of this diversity remain controversial. Both neutral and adaptive processes have been implicated in driving diversification, but population-level studies of plants in the CFR are rare. Here, we investigate the limits to gene flow and potential environmental drivers of selection in Protea repens L. (Proteaceae L.), a widespread CFR species.
METHODS: We sampled 19 populations across the range of P. repens and used genotyping by sequencing to identify 2066 polymorphic loci in 663 individuals. We used a Bayesian FST outlier analysis to identify single-nucleotide polymorphisms (SNPs) marking genomic regions that may be under selection; we used those SNPs to identify potential drivers of selection and excluded them from analyses of gene flow and genetic structure.
RESULTS: A pattern of isolation by distance suggested limited gene flow between nearby populations. The populations of P. repens fell naturally into two or three groupings, which corresponded to an east-west split. Differences in rainfall seasonality contributed to diversification in highly divergent loci, as do barriers to gene flow that have been identified in other species.
CONCLUSIONS: The strong pattern of isolation by distance is in contrast to the findings in the only other widespread species in the CFR that has been similarly studied, while the effects of rainfall seasonality are consistent with well-known patterns. Assessing the generality of these results will require investigations of other CFR species.

Prunier, R., M. Akman, C.T. Kremer, N. Aitken, A. Chuah, J. Borevitz, and K. E. Holsinger. Isolation by distance and isolation by environment contribute to population differentiation in Protea repens (Proteaceae L.), a widespread South African species. American Journal of Botany doi: 10.3732/ajb.1600232