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Lab postdoctoral researcher Lars Iversen and his partner Mette Bendixen just had their research on sand featured in Nature and the New York Times – Lars’ guest post follows below.

Mette and I had a commentary article out in Nature last week. Here we argue that there is an urgent need for a global agenda for sand. The paper is promoted via globalsand.org which we plan to develop into a global hub for future research on sand shortage.

Rapid urbanization and global population growth have fueled the demand for sand and gravel, with between 32 and 50 billion tons extracted globally each year, and both consumption and prices are expected to rise further. Consequently, we are now starting to exhaust a resource that many people often consider infinite.

In the article we discuss how research must adopt a holistic approach, not only focusing on issues such as the amount of sediment held back in reservoirs, and the effects of changing riverine water and sediment flux in a warming climate, but also take into account the sediment removed through sand mining. New technologies are, at last, enabling us to see the realistic goal of a global sediment monitoring network: what is required now is the political will and finance to put this in place. Furthermore, the full range of anthropogenic impacts on the world’s rivers, and their potentially nonlinear interactions, must be incorporated into estimates of global sediment fluxes. The issue of sand scarcity cannot be studied in geographical isolation as it has worldwide implications and the reality and size of the problem must be acknowledged, and action taken, on a global stage. In a rapidly changing world, we cannot afford blind spots.

Although the paper is targeting a general audience it has sparked several promising ideas for future research on sand mining in the world big rivers.

Mette is highlighting our paper in the most recent Nature podcast, starting at 10:48.

Bendixen M., Best J., Hackney C., & Iversen L.L. (2019): Time is running out for sand. Nature. DOI: 10.1038/d41586-019-02042-4. https://www.nature.com/articles/d41586-019-02042-4

Melting Greenland Is Awash in Sand. New York Times (Jul 1 2019) – https://www.nytimes.com/interactive/2019/07/01/climate/greenland-glacier-melting-sand.html

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Lab postdoc Dr. Luiza Aparecido has been busy in Yasuní measuring photosynthesis rates on many of the common canopy-dominant species, but the work has been more challenging than expected.

Everything has been going well with our side of experiments, which focus on understanding how vein architecture affects photosynthetic responses to leaf damage. Above our student Emily is severing leaves with a razor blade; below, Luiza uses our LI-6800 gas analyzer to measure photosynthesis.

Nature has been providing the challenges.

The rains have been more frequent and intense than normal, limiting when we can collect branches from the forest. Fortunately we’re doing all the measurements under a roof, so this only slow us down a bit.

We have had a few hitchhikers come along to interfere with lab operations, like this grasshopper investigating the gas exchange system’s cuvette.

We have also had some more serious flow rate issues with the instrument. Luiza took it apart to see what was going on, and found, very surprisingly, a spider web in one of the air intakes for the system.

With a bit more nudging, she also found the spider – now that both have been evicted, the system is running much better and the results are a little more trustworthy.

But the most surprising problem we have had is a Baird’s tapir. This adult female has become quite accustomed to humans near the field station, and has been regularly making friendly visits to Luiza during her work. Unfortunately our cut branches often look like a good lunch, so Luiza has had to persuade her to leave on more than a few occasions.

We’ve been lucky to enjoy all of these beautiful challenges, and are now halfway through the field work for this project. More to come soon!

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Benjamin Blonder by Benjamin Blonder - 3w ago

Off to the Amazon – two weeks ago Dr. Luiza Aparecido and I headed to eastern Ecuador to start a new ecophysiology project.

We are working with Dr. Renato Valencia, his student Emily Guevara, botanist Pablo Alvia, and Dr. Rafael Cárdenas (all at the Pontificia Universidad Católica del Ecuador) to better understand tradeoffs underlying herbivory in diverse tropical forest canopies.

The journey to our field site was a small adventure, taking us through cities, forests, farms, oil concessions, and some beautiful forests.

Fortunately our gas analyzer did not sink in the Rio Napo on a canoe crossing, so all is well in the field – more stories to come soon!

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Undergraduate researcher Sabrina Woo just accepted two prestigious awards here at ASU – a ‘true grit’ award, and a ‘student of the year’ award. They are both well-deserved. Sabrina joined us a year ago, and has done a great job working in both the desert and in the wet lab, while also taking good care of her job and family. She’s off to another research program for the summer, and we look forward to having her back in the autumn. Congratulations, Sabrina!

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This week Carolyn Flower defended her masters thesis, titled “Food Plant Biogeography of the Sonoran Desert”. She is the lab’s first ASU student to graduate.

Carolyn’s work focused on human impacts on plant dispersal and biogeography, as seen through the lens of food uses. She has shown that in the Sonoran Desert, many edible species (like this cactus, Echinocereus engelmannii) may be found in places today because of the actions of past human groups who have lived on these landscapes. It is very exciting work and I hope we will have it published soon.

Carolyn is off to a great job with the Arizona Game and Fish Department in a few weeks. We’ll be sad to lose her from the lab, but wish her well on her new adventures!

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Benjamin Blonder by Benjamin Blonder - 3M ago

A few weeks ago our lab participated in ASU’s Open Door outreach event, sharing our research with families and children throughout the region. Here are a few photos of our team in action!

Our biggest draw was our leaf tensiometer, which we use for studying the mechanical properties of plants (like force to tear). We brought branches of a range of desert and campus species for people to experiment with. More than a few leaves were sacrificed for the cause.

We also brought along some microscopes to examine the branching patterns of leaf veins using some of our research samples for ongoing desert studies – these were a big hit as well!

Thanks to all our dedicated lab members for committing their weekend to communicating the excitement of what we do to the public – and thanks to postdoc Dr. Pierre Gaüzère for the photographs.

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This week was the ASU School of Life Sciences’ annual undergraduate research symposium. Last year, my first at ASU, I attended the event and was surprised by the limited amount of field ecological research being showcased. This year, thanks to a lot of dedicated mentoring effort by lab members Courtenay Ray and Dr. Luiza Aparecido, we were able to send six students and five ecology research projects to the symposium.

I’m proud of all the students’ hard work – the presentations were the culmination of months of effort, and represent waypoints along a journey to what will hopefully become student-led papers and undergraduate theses.

This week we are back to the lab – more chemistry to do, more soils to pick through, more data to analyze – and I am excited to see where all this work goes. We have a great team to do the work with.

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(Written by lab postdoc Lars Iversen)

In nature, males’ eager attempts to mate with females can be so extreme that they will harm females. Such negative impact of mating interactions has been shown to promote the emergence of new species. This week, in Proceedings B, we publish a study exploring an alternative scenario in which female diversification brings the coevolutionary chase to the end.

In a seminal PNAS paper from 2002 Sergey Gavrilets and David Waxman outlined several regimes in which sexual conflict would maintain population polymorphism and thereby stop population divergence. Under these alternative scenarios, negative frequency-dependent sexual conflict acts as a conservative pullback force that prevents population divergence by maintaining rare male and female morphs in local populations rather than resulting in evolutionary escalation. However, it is largely unknown if such stabilizing selection occur in natural populations and this is what we set out to show in this study.


The front leg of a male diving beetle Graphoderus zonatus. Dense clusters of tiny hairs form a number of suctions cups which the male uses to attached to the back of the female during mating. © Aslak Kappel Hansen

Diving beetles are one of the few well documented examples of speciation via sexual conflicts. In many diving beetles, males are equipped with suction cups on their front legs. They use these suction cups to attach on the elytra of females during mating. This grasping ability has become so effective that females can be harmed under high mating pressure. As a consequence, some females have developed a rough elytra reducing the male adhesive ability. As a counteradaptation males have evolved their suction cups to increase adhesive power on rougher elytra structures. These male/female counteradaptations have been described as an arms race causing speciation in diving beetles.


A male of the diving beetle Graphoderus zonatus and the two female morphs with or without granulated elytra. The species has been trapped in an evolutionary standstill due to mating conflicts between males and females. Left: © Niels Sloth/Biopix. Right: © Johannes Bergsten.

Here we study a species in which the female is known to be polymorphic. In the diving beetle Graphoderus zonatus females are present in two morphs, one with a smooth elytra and one with a granulated elytra. We wanted to test if this polymorphism was an ongoing speciation event or if the females was captured in a polymorphic state due to sexual conflict (as described by Gavrilets and Waxman). The work consisted of two field campaigns, one in 2016 and one in 2017, where we collected beetles from 29 boreal lakes in Sweden.

The first important finding in our study is that males have diversified in correlation with the females. The variation in male suction cup morphology was divided into two distinct clusters. Within populations the proportion of these clusters were closely correlated to the proportion of female morphs. The match between male and female morphs within G. zonatus is identical to what we see between species in the family. Males adapted to a smooth elytra structure have a few rather large suction cups optimized to attach to a smooth surface. In contrast, males adapted to rough elytra structures have a high density of very small suction cups. This all suggest that there indeed is correlated traits between the sexes.


Correlation between male and female sexual traits in Graphoderus zonatus. Left: Two separated morphological clusters of males based on variation in male protarsal discs (the inserts depict examples from each group). Right: Positive relationship between the proportion of females with granulated elytra and males with Group 2 disc-traits in the 29 sampled populations.

The second important finding is the presence of assortative mating and negative frequency-dependent selection between the male and female morphs. By collecting copulating beetles, we did show that there was assortative mating (and thereby genetic correlation) between male and female trait pairs. The presence of negative frequency-dependent selection was inferred indirectly as a morph “pullback force” within population dynamics. We had historical trait data in seven of our study sites. From these we could see that populations move towards a state where both smooth and granulated females are equally abundant and thereby minimizing the mating pressure on a specific female type. These repeated measurements also confirmed the outcome in Gavrilets and Waxman’s model, that populations maintain polymorphism through time.


Evolutionary dynamics of male and female morph frequencies in Graphoderus zonatus polymorphism. Left: Change in the proportion of male and female morphs from 1990s (red) to 2017 (blue) in seven populations. The dotted line depicts a saturated morph correlation. Right: Distance from observed proportions of male and female morphs to the 0.5/0.5 equilibrium point in the 1990s (red) and 2017 (blue). The average distance to the predicted equilibrium point decreased during the study period, consistent with equal fitness of all morphs, frequency-dependent sexual conflict selection and assortative mating maintaining both male and female morphs locally.

In many ways this study points to some remaining and outstanding questions under which circumstances sexual conflicts do and do not promote speciation. Hopefully, there will be follow up work on these beetles exploring aspects such as the genetic architecture of this polymorphism and if sexual antagonism arises under specific conditions breaking the evolutionary limbo these beetles are currently kept in.

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Lab postdoc Lars Iversen and his wife Mette Bendixen have just written up a nice piece entitled “One couple, two cities: How to handle an international career move” for Nature Careers. Have a read at the journal!

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