Paulina Meller is finishing her PhD at the University of Hamburg, Germany. She studies the evolutionary forces that generate diversity in plants. Paulina shares her recent work on the environmental factors that have given rise to diversity in geoxyles, plants with disproportionately high below-ground woody biomass.

Paulina Meller taking a break from digging in the Afromontane grasslands of Tundavala, Angola. Photo credit: Manfred Finckh (Twitter: @ManfredFinckh)

Personal links. Twitter | Webpage

Institute. Institute of Plant Science and Microbiology, University of Hamburg, Germany.

Academic life stage. PhD (but finishing soon!).

Major research themes. Patterns and drivers of diversity, with a research focus on tropical vegetation (and a personal interest in birds).

Current study system. I study geoxylic plants (geoxyles) in Afrotropical grasslands. Geoxyles have a low growth form and disproportionally high belowground woody biomass. Many geoxyles evolved from tree species in response to environmental changes that proceeded the Miocene. Emerging fire occurrences have been hypothesised as the evolutionary driver of geoxyles. Hundreds of geoxyle species exist in Africa, and there are more in other tropical grasslands. They can be so diverse and abundant that they form “underground forests”. The belowground storage organs and bud banks enable geoxyles to resprout again after environmental disturbances. Their abundance, diversity and resilience make geoxyles a key element of tropical grassy ecosystems.

Recent paper in JBI. Meller, P., Stellmes, M., Fidelis, A., & Finckh, M. (2022). Correlates of geoxyle diversity in Afrotropical grasslands. Journal of Biogeography, 49, 339–352. https://doi.org/10.1111/jbi.14305

Motivation behind this paper. Geoxyles have been mostly overlooked in studies on tropical grassy ecosystems, probably due to the fact they are hidden underground. Despite some very good studies on geoxyles in Southern Africa and the Cerrado in South America, the main narrative remains that they all evolved from trees in response to fire. However, this narrow focus neglects other environmental factors that might have shaped the evolution of geoxyles and their taxonomic diversity. As a result, the knowledge on geoxyles has been rather fragmentary and one-sided so far.

As part of my PhD, I was working on a geoxyle species list for Angola when a nice paper by Pausas et al. (2018)* came out, providing a framework to classify belowground plant structures. It was therefore an exciting opportunity to combine the species list with analyses on their ecology, belowground functionality, and taxonomic and biogeographical origin, linking the fragmented knowledge together to better characterise geoxyle evolution.

* https://doi.org/10.1111/nph.14982

Caloncoba suffruticosa (Achariaceae) resprouting and flowering shortly after fire. The belowground woody storage organs and bud banks are partly excavated, typically only the green parts and flowers are visible aboveground.

Key methodologies. Our recent paper is quite complex because we measured so many facets of geoxyle biology, which was necessary to understand how heterogeneous and diverse this group of plants is. Each facet of geoxyle biology required a different analysis. Our study is the first to integrate different kinds of data – from field-derived functional traits, over literature research on origins, to large scale spatial and environmental modelling – to show how the facets of geoxyle biology interlink with one another. We took the vivid discussion on the main drivers of geoxyle evolution – fire versus frost – as an incentive to test for correlations between belowground traits, spatial distribution, and environmental pressures. Strikingly, some species seem to be more fire dependent than others, and most geoxyles had a strong link to frost-prone sites. So both frost and fire are important evolutionary drivers.

Major results. It was important to show that the geoxylic life form is much more diverse, complex and heterogeneous than previously assumed. The focus so far has been on the species with close tree relatives, which is totally reasonable since they are the most striking geoxyles. But they make up less than 50% of the geoxyle pool studied so far. In order to better understand tropical grassy biomes, and manage these often-threatened ecosystems sensibly and sustainably, it is crucial to characterise the diversity in geoxyles. Another important point to me was to reconcile whether fire or frost is the one driver of geoxyle evolution. We showed that there is no single driver, as implicit in previous discussion on the overarching importance of fire. Although some geoxyles clearly evolved in response to fire, there are species that have evolved in response to dry season frost events, and likely some also evolved in response to edaphic conditions. By recognizing that geoxyles are diverse and heterogeneous, determining an ultimate evolutionary driver of their diversity becomes less important.

Unexpected results and challenges. A particularly surprising finding was that many species in our study sites exhibit considerable belowground woody biomass. We had to include almost every species we looked at, and the more species we excavated, the longer grew our list of geoxyles. We therefore show that it is not sufficient to describe and understand an ecosystem by its visible, aboveground parts alone. Moreover, it was hard work to excavate all these over 100 different species, as some formed tubers big as a football in 1.2 m depth, others grew in particularly rocky ground. Our field assistant Segunda was a great help in this regard! Neither have I had so many blisters on my hands before, nor dirty finger nails, than during this campaign. But afterwards I lost some 5 kg and had hands as tough as a sailor’s.

Paulina in the field. This is a drone image of a geoxyle grassland near Chitembo, Bié province, in Central Angola. Geoxyles resprout and colour the landscape brightly at the end of the dry season, long before grasses or trees do.

Next steps. There are still so many open questions, but I would like to compare the geoxyle diversity hotspots of Africa (Miombo) and Brazil (Cerrado) more closely. Our Brazilian colleagues have done some amazing work on geoxyles, and often on different aspects to what we have done with African geoxyles. A combined, intercontinental analysis would fill many knowledge gaps and yield important new insights. For instance, whether similar families or genera produce geoxyles, thereby hinting at a phylogenetic predisposition to evolve this life form, or whether species and functional diversity are dependent on similar environmental factors on both continents.

If you could study any organism on Earth, what would it be? I don’t know if I am competent enough, but I would like to study big birds like the Southern Ground Hornbill (Bucorvus leadbeateri), or the Great Blue Turaco (Corythaeola cristata). I have seen both during my trips to Angola, and I love to see and hear them, they make me happy. There is something magic in waking up in the early morning to the bass sound of a foraging group of Ground Hornbills. They always look like the Blues Brothers on a stroll.

Anything else to add? Doing research in Angola is exciting and exhausting, beautiful and bizarre, endearing and endangering – but you come home the wiser and more experienced, and you will always be able to tell an interesting story. So even after 7 years of countless blisters, sunburns, malaria, and a barely survived crocodile attack I still enjoy digging in Angolan grasslands, and collaborating with our Angolan colleagues and friends.

Rodolfo is a PhD student at Monash University, Melbourne, Australia. He is a herpetologist with an interest in physiology and biogeography. Rodolfo shares his recent work on the ecophysiological strategies used by an Australian skink, Lampropholis guichenoti, to survive in diverse, variable climatic conditions.

Rodolfo on top of Cradle Mountain, Tasmania.

Personal. Twitter

Institute. School of Biological Sciences, Monash University, Melbourne, Australia.

Academic life stage. PhD student.

Major interests. Herpetology, Ecophysiology and Biogeography.

Current study system. I’m studying lizards. These amazing dry-skinned ectotherms depend on environmental temperatures to keep their own body temperature within suitable limits. They employ several strategies, such as thermoregulatory behaviour and tolerance to extreme temperatures, to cope with climatic variation. In my PhD, I’ve focused on an Australian genus, Lampropholis skinks, to study how the environment interacts with physiology, setting their distribution. Lampropholis skinks are small (1–4 g) and found all down the Australian east coast, spanning ~30 degrees of latitude, and must therefore cope with considerable climatic variation across their range. My work characterises the different ecophysiological strategies used by these skinks to cope with very different climatic regimes.

Recent paper in JBI. Anderson, R. O., Alton, L. A., White, C. R., & Chapple, D. G. Ecophysiology of a small ectotherm tracks environmental variation along an elevational cline. Journal of Biogeography. https://doi.org/10.1111/jbi.14311

The Garden-skink (Lampropholis guichenoti) foraging on the leaf litter. Photo by Jules Farquhar.

Motivation behind this work. The ecophysiology of species, that is, how organisms interact with their environment through their physiology, is key to understanding the limits of its geographic distribution. One species of Lampropholis (the Garden-skink, L. guichenoti) is found across different elevations in the Australian Alps, which are in the southern part of Australia. At the top of their distribution in the Alpine National Park (~1500 masl), in the state of Victoria, temperatures can go below zero and snow is present during the coldest months of the year. By contrast, in the lowlands, the climate is much hotter and drier. This huge disparity across an elevational gradient suggests that Garden skinks must have incredibly flexible physiological strategies. I wanted to know how the ecophysiology – which includes metabolism, thermal physiology, water balance, and locomotion – changes in response to climatic variation. Understanding how ecophysiology shifts across climatic gradients could help reveal how these small animals can inhabit contrasting environments, survive, and potentially expand their geographic range.

Key methodologies. This study comprised three parts. Firstly, I went to the field to collect the skinks, either by hand or by mealworm fishing. I went to four different sites, ranging from the lowlands (near the sea level) up to 1500 masl. Secondly, caught skinks were brought to the lab at Monash University, Melbourne, so I could quantify several ecophysiological traits (e.g., thermal tolerances, water loss, metabolism). Finally, I used the ecophysiological data to develop mechanistic models (NicheMapR) to predict the physiology and behaviour of the skinks in the field. This integrative approach provided interesting insights about the role of behaviour in the survival of these animals, especially in the cold highlands. I found that thermal physiology, metabolism, and rates of water loss, follow the demands of different climates. Skinks in the highlands are more cold tolerant and have a more efficient metabolism. In the drier and warmer lowlands, the skinks have to save their body water content, but they can reach higher locomotor performance. Finally, behavioural thermoregulation can maintain body temperature above freezing conditions and increase the activity time of skinks.

View of the Alpine National Park, Victoria. Garden skinks (Lampropholis guichenoti) can be found to altitudes of up to ~1500 m, where temperatures drop to below zero.

Garden skinks (Lampropholis guichenoti) were collected in dry woodlands across the elevational gradient in the Alpine National Park.

Major results. We demonstrated how an integrative approach can be very fruitful for biogeographical research. We showed that physiology as a whole is affected by climate, going beyond approaches that solely analyse thermal physiology. The environment is complex, and multiple interactions occur between the physical world and organisms. In the same study, we showed that in response to low temperatures, skinks increase their metabolic rate and energy efficiency, and elevate their cold tolerance. In dry and hot environments, skinks have to avoid water loss to prevent dehydration, but they have fewer fitness costs. Therefore, thermal physiology, metabolism and water balance are flexibly modulated to shape the fundamental niche of these skinks. Our work demonstrates that understanding the interaction between physiology and climate is key to understanding how organisms can survive in different types of environments, and hence the processes shaping their geographic distribution.

Unexpected challenges. The fieldwork was certainly the hardest challenge in this project. My field assistants and I had to actively search for the lizards for several days in areas with hard access. The fieldwork was also carried out in late summer/early Autumn, when the temperatures in the highlands drop dramatically at night. In a few instances, we had to refuge in emergency huts to spend the night in the field. Fortunately, all of us survived and we found a sufficient number of skinks for my experiments.

One of the emergency huts where people can find refuge during bad weather conditions. In one of our field works to the Alpine National Park, we spent a night in a similar hut to shelter from the wind and freezing temperatures.

Next steps. A crucial next step would be to disentangle the contributions of plasticity versus adaptation to the ecophysiological changes across elevation in the Garden skinks. To do that, a common garden experiment would be necessary. This would provide a more powerful inference about the fundamental niche and its role in shaping the distribution of these ectothermic animals.

If you could study any organism on Earth, what would it be? It would have to be the Maned Wolf (Chrysocyon brachyurus), or Lobo-Guará in Portuguese, because this extraordinary animal is perhaps the most beautiful mammal in the world, but is sadly a near threatened species. The savannah-like Cerrado in Brazil, where the Maned Wolf lives, is also endangered and deserves more attention from the general public and scientific community.

Rowan J. Schley is a postdoc at the University of Exeter and the University of Edinburgh. He is particularly interested in using genomic approaches to study diversity in tropical ecosystems. Rowan shares his recent work on the diversification of the pantropical tree genus, Pterocarpus, and the relative roles of biome-switching and long-distance dispersal.

Rowan with Wallace’s Flying Frog (Rhacophorus nigropalmatus).

Personal links. ResearchGate | Twitter | Website | ORCID | GoogleScholar

Institute. University of Exeter & University of Edinburgh

Academic life stage. Postdoc

Major research themes. I am particularly interested in asking questions about speciation, hybridisation, diversification, biogeography and genome evolution to understand the superlative diversity of the tropics.

Current study system. I work on tropical trees, which as a whole are relatively understudied despite their incredible diversity. As an example, one hectare of the Ecuadorian Amazon may contain more tree species than the entirety of Europe (>600 species). It is critically important to understand how this diversity was assembled, both to further our understanding of how species diversify and because tree species are the basis of many tropical ecosystems. In particular, the genus, Pterocarpus (Fabaceae/Leguminosae), is an excellent study system for understanding tropical tree diversification and biogeography because it is ecologically diverse, exhibits multiple dispersal phenotypes and is found across the tropics.

Recent paper in JBI. Schley R. J., Qin, M., Vatanparast, M., Malakasi, P., de la Estrella, M., Lewis G. P., Klitgård, B. (2022) ‘Pantropical diversification of padauk trees and relatives was influenced by biome-switching and long-distance dispersal’. Journal of Biogeography. https://doi.org/10.1111/jbi.14310

(left) Pterocarpus rohrii sensu lato; (right) Pterocarpus angolensis © Gwilym P. Lewis

Main motivation. Many plant groups are found pantropically, and there has been much debate about how such distributions arise. The prevailing narrative was that of vicariance, where the splitting of continental landmasses led to isolation of populations on different continents, and therefore, different evolutionary trajectories. However, time-calibrated molecular phylogenies have shifted this paradigm for many groups, and now, dispersal is believed to have led to the pantropical distributions of many tropical tree species. This is because the estimated divergences between many plant groups post-date continental splitting, and because long-distance dispersal is well known in plants. The macroevolutionary consequences of dispersal can be influenced by phenotypes which promote dispersal at ecological scales, as shown by work on the Podocarpaceae (Klaus & Matzke, 2020) and Annonaceae (Onstein et al., 2019). This work showed that dispersal traits influenced the distribution, diversity and ecology of these plant groups, inspiring us to ask similar questions in Pterocarpus.

Key methodologies. To test how seed dispersal phenotypes influenced Pterocarpus’ biogeographical history we first inferred a ‘dated’ phylogenetic tree. This helped us understand the evolutionary relationships between Pterocarpus species in a temporal context. We built this tree based on DNA sequence datacollected from RBG Kew’s herbarium, and used fossils to calibrate the tree to understand when speciation events happened within Pterocarpus. We then performed biogeographical analyses to test whether the dispersal phenotypes of Pterocarpus species influenced the evolutionary history and geographical distribution of the group. For example, dispersal phenotypes which facilitate long-distance dispersal by water (e.g., floating fruits) may lead to very broad species distributions, whereas other phenotypes may restrict species distributions. We tested the influence of these traits on geographical range evolution as well as on adaptation to different biomes, and we assessed how many shifts between biomes occurred across Pterocarpus’ evolutionary history.

Challenges. A major challenge was to find a method which allowed us to ‘date’ our phylogenetic tree from the vast amount of next-generation sequencing data we collected. This was pretty hard because most of the methods which we can use to date phylogenetic trees were designed to use much smaller datasets (e.g., only one or a few genes), but we used more than 300 genes in our phylogenetic analyses. Because of this, we decided to use a method which was designed for dating phylogenetic trees built with entire genomes (i.e., even more data than we used in this study) called ‘MCMCtree’ (Yang et al., 2007). We were also particularly fortunate in the case of Pterocarpus, because there has been much genetic work done on closely related groups, and so we could leverage existing, smaller datasets to do a corroborative analysis using older methods, and ensure that our MCMCtree analyses were accurate.

Major results. We found that there were two evolutionary lineages within Pterocarpus – one of which diversified in the Neotropics, and the other in the Palaeotropics. These groups diverged during the Miocene (~12 Ma), and most of the species diversification in Pterocarpus occurred during this epoch. Interestingly, we found that seed dispersal phenotypes had little significant effect on contemporary distributions, but that dispersal did have a significant effect. This suggests that random, rare ‘sweepstakes dispersal’ influenced Pterocarpus’ distribution. It was also apparent that biome-switching mostly occurred into rainforests and savannas. These environments are prone to disturbance and so experience high turnover of plant species, facilitating colonisation from other biomes. Biome switching was also likely promoted by Miocene climate change, such as the aridification of Africa. Overall, our results suggest that rare long-distance dispersal, coupled with climate change and speciation in different biomes, likely explain the wide distributions of many pantropical tree genera.

Next steps. I’d love to investigate the ‘weirdest’ Pterocarpus of all – P. dubius. This looks very different to other Pterocarpus species, its phylogenetic position is different when inferred with plastid vs nuclear genes, and it was previously circumscribed in a separate genus as Etaballia dubia. It would be great to unpick these peculiarities using plastid genomes and by investigating phylogenetic incongruence, because it seems that this odd placement may result from chloroplast capture following ancient hybridisation. In addition, Klitgård et al. will be circumscribing new taxa within the P. rohrii species complex and publishing IUCN red list assessments for threatened Pterocarpus species.

Rio Tiputini in Yasuní National park, Ecuador.

If you could study any organism on Earth, what would it be? To study the extraordinary diversity of any tropical taxon is a dream come true. I have a particular love for working on tropical trees and understanding the evolution of diversity through that lens. That said, as a naturalist I am interested in a broad range of questions across the tree of life, and I have also been lucky enough to work on orchids and cichlid fishes. I would love the opportunity to further understand speciation in diverse coral reef taxa (e.g., Acanthurid fishes, Scarid fishes, Scleractinian corals), phenotypically diverse and strange plant groups (e.g., mangroves and Nepenthes pitcher plants) or in an island radiation like Scalesia. That’s the great thing about the tropics – there is so much to study, not to mention so much to conserve!

Anything else you would like to share? Pterocarpus species are valuable timber trees under immense pressure from logging. They are known as ‘rosewoods’ and ‘bloodwoods’, among many other common names. These names refer to the sought-after red colour of their wood, and to the red sap that is exuded when their trunks are cut. There is a short BBC film called ‘Trees that bleed’ that documents the poaching of rosewoodtrees in West Africa – it is really worth a watch! https://www.youtube.com/watch?v=G_GmLPPNbGc

Maria Guerrina is a postdoc at the Università degli Studi di Genova in Italy. She is a plant biologist interested in the evolution of endemic biota. Here, Maria shares her recent work on the post-glacial contraction of an Alpine endemic species.

Maria Guerrina during fieldwork in the South-western European Alps.

Personal links. Research Gate

Institute. Dipartimento di Scienze della terra, dell’ambiente e della vita (DISTAV) – Università degli Studi di Genova.

Academic life stage. Postdoc

Major research themes. Endemic species, conservation, glacial refugia, climate change, reproductive biology, alpine flora, phylogeography.

Current study system. My study species is Berardia subacaulis Vill., the only living species belonging to a monospecific genus endemic to the South-western European Alps. This cold-adapted species is a relic of the Tertiary paleo flora (~24 mya), which almost went completely extinct during Late Quaternary climatic oscillations. Being such an “ancient” species makes it interesting and necessary to understand how past climatic changes affected the demographic history of this species. By doing so, we can make more reliable predictions on how it will respond to future pressures.

Maria out in the field collecting leaves of B. subacaulis.

Recent JBI paper. Guerrina M, Theodoridis S, Minuto L, Conti E,Casazza G (2022) First evidence of post-glacial contraction of Alpine endemics: insights from Berardia subacaulis in the European Alps. Journal of Biogeography. 49 (1): 79-93 https://doi.org/10.1111/jbi.14282

Motivation behind this paper. This study sought to understand the possible responses of plants to the Late Quaternary dynamics (i: post-glacial expansion; ii: post-glacial contraction; and iii: long-term stability). The study is located in the South-western European Alps (SW Alps). This area was less affected by the glaciations than the rest of the Alps because of the Mediterranean Sea influence. Given the proximity of the SW Alps to the Mediterranean and Alpine climates, the region is characterized by high local climatic variability and topographic heterogeneity, which promoted a variety of phylogeographical patterns in the biota. Until today, two common hypotheses have been proposed: post-glacial expansion or long-term stability (mainly by altitudinal shift). However, an interesting pattern never yet detected is the expansion of cold-adapted species during glaciation due to the limited extent of the glacial sheet in the area, followed by a population contraction after glaciation.

A blooming individual of B. subacaulis. It is possible to see the secondary presentation of pollen on the stigma in the central open flowers.

Key methodologies. Our paper relies on species distribution models (SDMs) throughout the last 28 Ky and genome-wide sequences (genotyping-by-sequencing; GBS) to estimate current spatial structure patterns from genetic diversity. Because B. subacaulis grows only on specific calcareous substrates, we added substrate information into the in SDMs to report the presence/absence of this suitable substrate, based on the global lithological map dataset (GLiM). Integrating the results of the two independent approaches (SDMs and GBS) allowed us to test several demographic models under an Approximate Bayesian Computation framework.

Unexpected challenges. One of the biggest challenges we faced was field sampling. Berardia subacaulis grows on very steep scree, and this kind of habitat did not make sampling easy! Because of it, before starting the sampling, I went shopping for comfortable boots for walking on scree – the clerk looked at me strangely! The sampling season began with two outings of about eight hours of hiking each before we managed to find the plant (I’m glad I got proper boots!). Funny thing, I was with a colleague, and none of us had ever seen the plant before. But it was really nice to find some populations following herbarium information from the end of the 19th century.

Achenes of B. subacaulis.

Major results. For the first time, we provide empirical evidence of post-glacial demographic contraction and a recent split between the two genetic groups for an endemic plant in the European Alps during the Late Quaternary. The pattern observed might be due to several factors. First, the SW Alps were characterized by greater availability of ice-free terrain during the Last Glacial Maximum (LGM) because of the Mediterranean Sea mitigation that maintained temperatures some degrees higher than in the rest of the Alps. Second, the SW Alps were characterized by relatively high precipitation, which, combined with the ice-free areas, might have allowed B. subacaulis to persist or even expand in most climatically suitable areas at high altitudes during the LGM.

Next steps for this research. Several hypotheses explaining patterns of endemism have been explicitly tested at the global scale, raising questions about the persistence of biodiversity during the present era of changing climate. However, these hypotheses have never been tested at local scales, and the SW Alps are an interesting place to test them. The next step in this research is to explore the environmental drivers promoting endemic richness distribution in the SW Alps.

Typical habitat of B. subacaulis, growing on steep calcareous scree.

If you could study any organism on Earth, what would it be? Plants, I cannot change my study organism! In particular, I would like to study any rare and endemic plants with peculiarities, such as blooming every 40 years or growing in almost inaccessible places.

Katie Nigro is a PhD candidate at the Colorado State University in the USA. She is an ecologist interested in plant distributions and their responses to impacts. Here, Katie shares her recent work on the effects of wildfire and beetle outbreaks on the range expansion of trembling aspen.

Katie Nigro in the field, after a day of searching for aspen seedlings.

Personal links. Twitter

Institute. Colorado State University

Academic life stage. PhD (4th year)

Major research themes. Disturbance impacts on vegetation recovery and plant species range shifts.

Current study system. I work in the montane and subalpine forests of Colorado and currently am focused on two tree species – trembling aspen and ponderosa pine. This system is experiencing rapid change via the increased frequency of large, severe wildfires, bark beetle outbreaks, and drought. Studying aspen and ponderosa simultaneously is super interesting because they both exhibit different responses to disturbances and thus are likely to face very different futures. In our recently published paper, we focus on aspen, which is great at repopulating after disturbance but needs a lot of water, whereas, in an ongoing study for my PhD, we are focusing on ponderosa pine, which is not as prolific a reproducer but is extremely drought tolerant.

A spruce-fir forest in the study area (Colorado, USA) with extensive canopy mortality due to spruce beetle outbreaks.

Recent JBI paper. Nigro, K. M., Rocca, M. E., Battaglia, M. A., Coop, J. D., & Redmond, M. D. (2022). Wildfire catalyzes upward range expansion of trembling aspen in southern Rocky Mountain beetle-killed forests. Journal of Biogeography 49(1), 201– 214 https://doi.org/10.1111/jbi.14302.

Motivation behind this paper. Until a decade or so ago, it was commonly thought that trembling aspen trees almost always reproduce asexually (by resprouting from their roots) and that sexual reproduction (aspen trees growing from seed) was extremely rare, occurring only under the perfect combination of soil and climate conditions. However, researchers have recently been stumbling upon aspen seedlings (from seed) more and more, especially in burned areas. Many of these seedling sightings have been far away from adult aspen, which led us to think that disturbance could facilitate aspen’s migration to cooler areas in response to climate warming. Tree migrations are usually projected to lag behind climate change because trees are long-lived and can’t just get up and walk to cooler sites, which leaves them vulnerable. We wanted to see if disturbances like fire and bark beetle outbreaks could promote faster migrations for tree species like aspen.

A severely burned area in the West Fork Fire Complex of 2013, Colorado, USA – where the study was located.

Key methodologies. This project hinged on two key methods – the first was figuring out what the upper elevational limit of aspen was in the study area via aerial imagery, and the second was to go out and survey areas above that upper elevational limit to see if signs of upward migration were occurring in fire and bark beetle impacted sites. Figuring out the local elevational limits of aspen’s distribution was novel for our study area and highlighted the fact that species elevations are highly localized and do not follow a strict minimum and maximum elevation profile for a given latitude. In addition, focusing the surveys on just those elevations above the local maximum allowed us to uncover patterns of range expansion at the same time as documenting post-disturbance forest recovery.

Katie conducting field surveys looking for aspen and characterizing site conditions.

Unexpected challenges. One surprising thing was the rarity of aspen seedlings overall. I was amazed that we did not find any aspen seedlings in sites that were beetle-killed but not burned. I expected less in beetle-killed sites than burned sites, given the documented benefit of bare soil for aspen seedling establishment. However, due to increased light availability, I still expected to find some seedlings in the beetle-killed forests. In general, the rarity of seedlings on the landscape (even in burned areas) was definitely a mental challenge at the beginning of the field season – we surveyed 25 plots before encountering an aspen seedling. You can imagine the adrenaline rush I felt when my field technician finally yelled over, “I think I found one!” 

Major results. We found that wildfire has the capacity to accelerate migrations for trembling aspen and likely other wind-dispersed, shade-intolerant tree species, thereby allowing them to catch up with climate changes that have already occurred. Interestingly, another widespread disturbance agent, bark beetles, did not facilitate the same expansion of aspen’s upward elevational limit as fire did. This reveals that tree species migrations will be differentially impacted by the increasing frequency and severity of disturbances in the coming decades. Importantly, we found that aspen regeneration not only depended on wildfire, but was also significantly impacted by local site conditions. Therefore, range shifts are unlikely to progress uniformly upwards in elevation, but rather will occur quite heterogeneously across the landscape.  

A burned aspen tree with abundant resprouts at its base, this is an example of aspen’s asexual mode of reproduction

Next steps for this research. Now that we have documented upward elevational shifts in a shade-intolerant wind dispersed species due to wildfire, I am looking into other tree species prominent in the western United States to see how disturbances and life history traits may impact their range margins. I am also investigating the potential for certain populations of trees to be better adapted to future climates than others. In the case where a species is unable to migrate fast enough, we can use this information to reforest disturbed areas with individuals that will be more resistant to future climate changes.

If you could study any organism on Earth, what would it be? I think I would still stick with plants – they’re generally agreeable, so resilient, and will sit still for hours on end while you measure anything and everything about them.

An aspen seedling found at a burned site, growing out from under a downed log. This is an example of sexual reproduction.

Anything else to add? I think I must shoutout once more to all the wonderful people that helped me collect field data for this project. The final data reflected in the paper is the result of steep, grueling off-trail hikes through snow, streams, and around downed logs, running from thunderstorms (more than once) and just generally sacrificing the comforts of home for the sake of science – I couldn’t have done it without the help of some seriously tough and adventurous folks.

Jeronymo Dalapicolla is a postdoc at the Instituto Tecnológico Vale in Brazil. He is an evolutionary biologist interested in the impact of landscape features on evolutionary processes. Here, Jeronymo shares his recent work on the influence of different forest associations in the genetic variation of two sympatric species of spiny rats in the Western Amazon.

Jeronymo in a boat on Guamá River, Brazil.

Personal links. Twitter | Instagram | Research Gate

Institute. Instituto Tecnológico Vale (Belém, Brazil)

Academic life stage. Postdoc

Major research themes. Phylogenomics, Landscape Genetics, Conservation Genetics, and Statistical Phylogeography of Neotropical Mammals and Plants.

Current study system. Proechimys is a genus with more than 20 species of spiny rats (rodents closely related to capybaras and cavies) distributed throughout the Amazon basin. Given its distribution, this genus is an excellent model to study the evolutionary processes that generated current Amazonian biodiversity patterns. Furthermore, there is an unusual fact: the high rate of sympatry and syntopy between species of Proechimys. Usually, different species in the same Neotropical rodent genus show parapatric or allopatric distributions, with rare cases of sympatry. However, up to five species of Proechimys can be sampled in the same area, sometimes even in the same trapline! Which makes this genus more intriguing to study how species can use the landscape/habitat.

Jeronymo installing traps to collect rodent samples during fieldwork for his PhD.

Recent JBI paper. Dalapicolla, J.; Prado, J. R.; Percequillo, A. R.; Knowles, L. L. Functional connectivity in sympatric spiny rats reflects different dimensions of Amazonian forest-association. J. Biogeography, 48(12): 3196-3209 https://doi.org/10.1111/jbi.14281

Motivation behind this paper. I was greatly influenced by the work of Latin and North American mammalogists. One of these works was performed by James Patton’s group (UC Berkeley) using sympatric species of Proechimys and mitochondrial DNA (mtDNA) to test how gene flow occurs between river banks in the Amazon (Matocq et al. 2000: https://doi.org/10.1111/j.0014-3820.2000.tb00574.x). In general, their results confirmed an established premise for the species inhabiting seasonal floodplain forests where this habitat works as linear corridors to dispersal along the river. In contrast, in inland areas (non-flooded forests), species should present more restrictive dispersal patterns. However, Patton’s group also found some peculiar results, with some species not entirely fitting this premise. So, our goal using genomic data was to effectively test whether habitat preference impacts levels of gene flow and genetic diversity patterns. Also, we aimed to clarify why some of the previous results based on mtDNA did not fit in the general premise for seasonal floodplain forests.

Spiny rat (Proechimys sp.) collected on non-flooded forests close to the Madeira River, Rondônia, Brazil (Photo by J. L. Souza).

Key methodologies. Comparative studies on phylogeography and landscape genetics with mammals usually employ phylogenetically distant species living in the same area to look for similar patterns of diversification. The particularity of our study was to use closely related species (all in the same genus) living in the same area but showing differences in habitat preferences. Another key for our study was to use mixed models to analyse isolation-by-resistance. By doing it, we were able to control for spatial autocorrelation and for pairwise comparisons effect to improve the models’ explanations. Moreover, I consider that the landscape variables we generated representing characteristics of different habitats are also new insights going further than classical temperature and precipitation variables typically used in evolutionary studies in the Amazon region.

Unexpected challenges. Using genomic data may be commonplace for most researchers from the Global North. However, it is still challenging and expensive for researchers from Brazil like me (and other countries in the Global South). Studies involving genomics in Amazonian mammals are still scarce. As I mentioned above, this work was motivated by Matocq’s study, and we thought we would confirm their results and explain some results that did not fit the initial premise on habitat preferences. However, by using more data and increasing the scale, we were surprised that we didn’t corroborate the previous results. Indeed, we demonstrated that habitat preferences assumptions might sometimes oversimplify the real world and might not be the primary driver explaining genetic and diversity patterns.

Putumayo-Içá River in Amazonas, Brazil (Photo: R. Recorder).

Major results. Biologists have been highly dedicated to explaining the diversity patterns of species, especially in mega-diverse regions, such as Amazon. These explanations typically use hypotheses about major historical events (e.g., climate change, mountains uplift, river as barriers) to explain current diversity. Researchers often look for concordance of patterns in different species to indicate the existence of a unique or generalizable factor to explain the diversity. Our study shows that premises like “species from seasonal floodplain forests have low structure and high gene flow” are not completely accurate for the entire biota, which can bring important conservation implications. So, understanding the relationship between ecology and how different species use the landscape can be more important in explaining diversity patterns in some instances than historical events. In addition, in this study, we applied modern analytical methods that can be used in other studies – with all scripts, data, and examples available as supplementary material (Dryad; GitHub).

Next steps for this research. We still have lots of work to do with this rodent group and the Amazon. Our research group is focused on unravelling the patterns of diversity of small Amazonian mammals to promote a better understanding of the evolution of the Amazonian region to provide key information for the conservation of this biome. Specifically, about the Proechimys, we are working on the species delimitation for the genus and the taxonomic rearrangements using morphological data. We hope to share these results as soon as possible.

Boat on Putumayo-Içá River during a scientific expedition in Amazonas, Brazil (2015) to collect material for the Zoology Museum of Universidade de São Paulo during my PhD (Photo: I. Prates).

If you could study any organism on Earth, what would it be? It’s funny how our expectations change, right? When I was an undergrad student, I dreamed about studying Marine Biology, especially turtles and cetaceans. Today I don’t see myself studying any marine organisms – I’m not a good swimmer! Although I love living close to the ocean, it was another expectation that didn’t work! Considering terrestrial organisms, I have a fascination for big cats and would love to study them, preferably in the field.

Anything else to add? Although I like working in the molecular biology laboratory, I have three passions in Biology. The first is fieldwork, data collection, and contact with nature, which always brings insights and important research questions. My second passion is museums and scientific collections. I spent a good part of my academic life managing regional mammal collections in Brazil and a lot of my Ph.D. time in collections gathering data. My research wouldn’t be possible without these institutions, so I have to thank them so much! My third passion is teaching. I started teaching in elementary and high school more than ten years ago, and now I teach graduate courses at the Vale Institute of Technology. I love to share what I’ve learned with other people – it’s a rewarding job! I’m known among my colleagues and friends for the tutorials and “how-to-do” scripts that I like to create, explaining in detail all the steps of analyses or software’s use. I always get emails asking if I have a tutorial or material about some analysis and if I could help solve some issues. I understand that the knowledge I gained from my professors is my heritage, and using it to help others is wonderful. Sharing knowledge is probably my most precious legacy for future generations.

Sunset in Solimões River during the scientific expedition to Putumayo-Içá River, Amazonas, Brazil (2015) (Photo: R. Recoder).