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Aelys HumphreysAssociate Professor

Research

I use a combined experimental and phylogenetic approach to study how biodiversity evolves and is distributed globally. I’m interested in how people perceive and classify biodiversity and how the patterns apparent to humans relate to the patterns generated by evolution. I’m also interested in the extent to which geographic patterns of biodiversity are caused and can be predicted by climate, as well as how plants adapt to different climates. The specific questions I address in my research span quite a diverse set of topics but most of my work is on plants, tends to be at the macro scale and centres on phylogenies.

 

Ongoing projects

 

Evolution of cold tolerance

Over 200 years ago, Alexander von Humboldt famously noted that plant distribution patterns correlate with climate. His legacy lives on, and still today temperature is considered to be one of the strongest determinants of plant distribution patterns globally. This is particularly true for cold temperatures because the physiology required to tolerate cold and freezing temperatures is complex and is assumed to be difficult to evolve. Indeed, this assumption provides the basis for one of the main explanations for the uneven distribution of biodiversity on Earth, being highest in the tropics and decreasing toward the poles, that the tropics are more diverse because only a subset of Earth’s biota has evolved the physiology to survive at higher latitudes. Yet, around half of all seed plant families have temperate species. These species are scattered phylogenetically, suggesting multiple, independent transitions from the tropics to the temperate zone, in turn suggesting that evolving cold tolerance may not be so difficult afterall. In addition, experimental work and evidence from invasive species suggest that cold tolerance can evolve relatively quickly. Our research addresses this controversy by studying the frequency and mechanisms of cold tolerance evolution in angiosperms. An earlier project showed that southern temperate grasses (Danthonioideae, Poaceae) have evolved most of their cold tolerance recently and can tolerate more severe freezing temperatures than would be predicted from the extent of their current distribution. These findings suggest that cold temperature is not a good predictor of the distribution of danthonioid grasses (see Humphreys and Linder 2013). More recently, I performed a macro-level study on how both cold and heat tolerances vary globally and show that: 1) Plant cold tolerances are more variable overall and show steeper latitudinal gradients than heat tolerances; 2) Phylogeny, geography and the local climate are all needed to explain variation in both cold and heat tolerances but cold tolerances are best explained by evolutionary history (phylogeny) and heat tolerances by biogeographic processes (spatial distance). See Lancaster and Humphreys, 2020.

Current projects include:

1) The macroevolution and biogeography of cold tolerance in cool season grasses (Pooideae, Poaceae)

2) The effect of geothermal warming on cold tolerance, winter survival ability and phenology of grasses. See a DEEP insights blog post on this.

3) Pre-adaptations to cold tolerance in northern temperate angiosperms

Funded by the Bolin Centre for Climate Research and Stockholm University (DEEP).

*See a recent DEEP insights blog post on fieldwork on Iceland: Don't walk on the grass - do some science on it!

*New study on how both cold and heat tolerances of plants vary globally published together with Lesley Lancaster: Global variation in the thermal tolerances of plants (PNAS, 2020).

 

 
How do plants adapt to freezing winters and how are these adaptations affected by geothermal warming? Above: Stockholm University campus in a blizzard (February 2018). Below: Hengill, a geothermally heated valley on Iceland in summer (photo: Jan-Niklas Nuppenau 2017).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Extinction of biodiversity

Extinction is a natural process that has shaped life on Earth throughout its evolutionary history. Remarkably, it is estimated that of all organisms that have ever lived, less that 1% is alive today. Extinction has several facets. Most species termination is the result of “background extinction”, the spontaneous replacement of one species with another. “Mass extinction” events are important because of their broad geographic and taxonomic devastation, leading to new selection regimes for survivors. “Modern extinction” (extinction events that have occurred in recent centuries) and “extinction threat” are of concern because they are thought largely to be the result of human activities. It is very hard to compare these facets of extinction because the data underlying our understanding of each is so different.

In this context, we are studying whether current diversification rates can predict threat levels for a clade. However, clade choice is known to affect inferences of diversification but it is not so straightforward to know a priori what clades to study separately. Independently evolving clades above the level of species (higher Evolutionarily Significant Units; see Humphreys and Barraclough 2014) provide hypotheses of how speciation and extinction processes are shared and decoupled among clades. We are exploring their usefulness for linking evolutionary extinction with current threat.

In another study, together with collaborators at the Royal Botanic Gardens, Kew, I am looking at modern extinction in seed plants (defined as having occurred since the publication of Linnaeus’ Species plantarum) to see whether what is known from modern extinction in animals is true also for plants. For example, is modern extinction in plants elevated in rate compared to background rates? Is it exceptionally high on isolated oceanic islands? See recent findings from this work here (Humphreys et al. 2019). We recently extended this work to test whether our knowledge on plant extinction may be biased by inequalities in our  knowledge of global plant diversity, using the grasses of Madagascar and the British Isles as an example (we found that it probably is; see Vorontsova et al. 2020).

*Some media coverage of our study on plant extinction:

Plant extinction 'bad news for all species' (BBC)
‘Frightening’ number of plant extinctions found in global survey (The Guardian)
World’s largest plant survey reveals alarming extinction rate (Nature News)
Twice as many plants have gone extinct than birds, mammals, and amphibians combined (Science Magazine)
All växtutrotning i världen kartlagd för första gången (SVT)
Arter dör ut i allt snabbare takt (Forskning och Framsteg)
Las plantas se están extinguiendo a un ritmo nunca visto antes (El País)

Funded by the Swedish Research Council Formas.

*See a DEEP insights blog post on plant extinctions: Hundratals växtarter har redan utrotats.

 

How can we know what clades to study separately in macroevolutionary inferences of diversification dynamics? Independently evolving clades above the level of species (higher Evolutionarily Significant Units, ESUs) are hypotheses of how speciation and extinction process are shared among clades (from Humphreys et al. 2016). And see a MEE blog post related to this article: "Conifers for Christmas: Evolution above the level of species".

 

Life history evolution

Being an annual plant is an extreme strategy for surviving in a harsh environment: all faith is placed in the next generation while the current generation dies shortly after flowering and seed set. Classic ideas about life history evolution in angiosperms suggest that it is labile, that annuals are derived and favoured in habitats where the probability of surviving as an adult plant is low (e.g. the annual life history strategy is commonly referred to as a drought avoidance strategy). Some studies have found support for these ideas, while others have not, and our knowledge of the circumstances under which annuals evolve and their current geographic and phylogenetic distribution is poor. To provide a more complete picture of the occurrence of annuals, and as a springboard for future studies, we are compiling an overview of their phylogenetic and geographic distribution.

Grasses (Poaceae) are one of the families with the most species of annuals. Preliminary results of more detailed analyses in grasses suggest that 1) life history evolution is not so labile, 2) temperature may be more important for understanding current distribution patterns of annuals than currently appreciated and 3) annuals are more widespread than perennials.

 

Nailwort (Draba verna). This tiny annual sets seed early in spring – in Stockholm it can be seen fruiting even before first leaf flush! – and pretty much completes its life cycle at freezing temperatures. It invests almost nothing in vegetative structures and almost everything into reproduction. Before onset of summer, flowering is already over and the adult plant is senescing (as in photo, taken in May 2018). This is fascinating because one classic idea about annuals is that they need warm temperatures to be able to complete their life cycles quickly.

 

Current group members

 

Dr. Marian Schubert (postdoc)
Jan-Niklas Nuppenau (PhD student, since May 2017)
Laura Schat (PhD student, since August 2018)
Maja Edlund (PhD student, since January 2019, main supervisor: Gitte Petersen)
Sanne Welin (MSc student, since April 2020)
Ruben Cousins Westerberg (MSc student, since April 2020)

 

"The Humps", 2020 (L-R): Elsa Höglund, Lovisa Thilén, Jan-Niklas Nuppenau, Marian Schubert, Aelys Humphreys, Sanne Welin, Laura Schat, Ruben Cousins Westerberg

 

Previous group members and supervised students

Dr. Kent Kainulainen (postdoctoral researcher, 2018)

Elsa Höglund (MSc, Stockholm Univeristy, 2020)
Lovisa Thilén (MSc, Stockholm University, 2020)
Nikos Minadakis (MSc, Stockholm University, 2019)
Sylvia Pal Stolsmo (MSc, Norwegian University of Life Sciences, 2019; co-supervised with Siri Fjellheim)
John MacDonagh (MRes, Imperial College London, 2015)
Leah Callender-Crowe (MSc, Imperial College London, 2014)
David Alsop (MSc, Imperial College London, 2014)
Karolina Jerrå (MSc, Stockholm University, 2014)
Beatriz Lopez (MRes, 2011, Imperial College London)
Melissa Marr (MRes, 2011, Imperial College London)

Rebekka Eriksen Ween (Bachelor student, 2019, Norwegian University of Life Sciences; co-supervised with Siri Fjellheim)
Lovisa Thilén (Kandidat, 2018, Stockholm University)
Luana Bourgeaud (BSc, 2015, Imperial College London)
Thomas Sinclair (BSc, 2015, Imperial College London)
Mircea Sofonea (Summer student 2011, Imperial College London; co-supervised with Tim Barraclough)
Stefan Roffler (Summer student 2010, University of Zurich; co-supervised with Peter Linder)

 

Main collaborators

Maria Vorontsova, Royal Botanic Gardens, Kew
Siri Fjellheim, Norwegian University of Life Sciences
Lesley Lancaster, University of Aberdeen
Gudrun Kadereit, Johannes Gutenberg University Mainz
Nancy Garwood, Southern Illinois University
Kurt Neubig, Southern Illinois University
Tim Barraclough, University of Oxford
Catarina Rydin, Stockholm University
Johan Ehrlén, Stockholm University

 

Selected publications

Lancaster, LT & AM Humphreys. 2020. Global variation in the thermal tolerances of plants. Proc Nat Acad Sci USA 117:13580-13587.

Vorontsova, MS, PP Lowry II, SR Andriambololonera, L Wilmé, A Rasolohery, R Govaerts, SZ Ficinski & AM Humphreys. 2020. Inequality in plant diversity knowledge and unrecorded plant extinctions: An example from the grasses of Madagascar. Plants People Planet xx:1-16

Humphreys, AM, R Govaerts, SZ Ficinski, E Nic Lughadha & MS Vorontsova. 2019. Global dataset shows geography and life form predict modern plant extinction and rediscovery. Nature Ecol Evol 3:1043-1047

Abrahamczyk, S, M Kessler, D Hanley, DN Karger, MPJ Muller, AC Knauer, F Keller, M Schwerdtfeger & AM Humphreys. 2017. Pollinator adaptation and the evolution of floral nectar sugar composition. J Evol Biol 30:112-127

Humphreys, AM, Rydin, C, Jønsson, KA, Alsop, D, Callender-Crowe, LM & Barraclough, TG. 2016. Detecting evolutionarily significant units above the species level using the Generalised Mixed Yule Coalescent methodMEE 7:1366-1375

Barraclough, TG & Humphreys, AM. 2015. The evolutionary reality of species and higher taxa in plants: a survey of post-modern opinion and evidenceNew Phytol 207:291-296

Humphreys, AM & TG Barraclough. 2014. The evolutionary reality of higher taxa. Proc B 281:1471-2954

Humphreys, AM & HP Linder. 2013. Evidence for recent evolution of cold tolerance in grasses suggests current distribution is not limited by (low) temperatureNew Phytol 198:1261-1273

Humphreys, AM, A Antonelli, MD Pirie & HP Linder. 2011. Ecology and evolution of the diaspore "burial syndrome". Evolution 65:1163-1180.

Humphreys, AM & HP Linder. 2009. Concept versus data in delimitation of plant genera. Taxon 58:1054-1074

For a complete publication list see Google Scholar Citations or ResearchGate.

 

 
 

Teaching

• Evolution of biodiversity, Vetenskaplighet och evolutionärt tänkande 5 hp (Grundkurs BL2020) (2017-)

• Speciation and adaptive radiation, Biodiversity 7.5 hp (Masterkurs BL8001) (2017- )

• Plant diversity and evolution - a global perspective 15 hp (Masterkurs BL7032) (VT 2017); *Kursansvarig

• Phylogenetics and tree thinking, Evolutionary biology 15 hp (Kandidatkurs BL5026) (2015- )

• Angiospermer, Organismernas mångfald och fylogeni 15 hp (Grundkurs BL2013) (HT 2016)

 

Projects

If you are interested in working on these topics (at Master's, PhD or postdoc level), please contact me. There may be opportunities to get involved and I am always keen to talk about ideas and overlapping interests. Please note that all job opportunities via SU will be posted here.