Adriana Uscanga is a PhD candidate at the University of Oregon in the US. She is an ecologist interested in unveiling the evolutionary drivers shaping biodiversity distribution in tropical mountains. Here, Adriana shares her recent work on evaluating colonization routes of newly emerged high-elevation habitats.

Adriana Uscanga is a PhD candidate at the University of Oregon.

Personal links. Twitter | GitHub | Orcid

Institute. University of Oregon

Academic life stage. PhD candidate

Major research themes. Tropical Mountain Ecosystems; Landscape Ecology; Geospatial Science; Agroecology; Climate Change; Cartography and Data Visualization

Here, I am collecting pitfall traps in an alpine grassland at the top of the mountain Ajusco, Mexico.

Current study system. My research focuses on the study of tropical landscapes, especially mountains. Tropical mountains exhibit outstanding climatic and ecosystem diversity in short distances, making them fascinating study systems. I am interested in understanding what shapes biodiversity and ecosystem functions in these landscapes. Currently, I am studying the ecological and socioeconomic processes and consequences of agriculture expansion and intensification in Mexican tropical montane forests. In so doing, I use theories and methods from Landscape and Forest Ecology, Geospatial Science, and Political Ecology to understand the complex relationships between forest ecosystem functions and services, food production, and climate change in these beautiful landscapes.

Recent JBI paper. Uscanga, A., López, H., Piñero, D., Emerson, B.C., Mastretta-Yanes, A. (2021) Evaluating species origins within tropical sky-islands arthropod communities. Journal of Biogeography, 48(9): 2199-2210 https://doi.org/10.1111/jbi.14144

Alpine grasslands at sunset. Fir forest is visible further below. The difference in elevation between these two ecosystems in the Transmexican Volcanic Belt ranges between 600 to 800 m.

Motivation behind this paper. This study sought to understand how biodiversity is structured along the Transmexican Volcanic Belt, a long tropical mountain range that crosses Mexico from West to East. Previous studies had suggested that animal and plant communities in the Eastern (E) mountains differed from those distributed in the Western mountains, as if biodiversity was structured in two groups, divided in the middle of the mountain range. Although this pattern came repeatedly in the literature, studies that would explicitly test it were lacking. Our main motivation was to test this pattern with a spatially explicit study and to assess whether this pattern varied in ecosystems at different elevations. This last objective would provide information about how new habitats are colonized.

Fir forest viewed from the understory.

Key methodologies. To test whether biodiversity along the Transmexican Volcanic Belt is structured in two groups (a Western and an Eastern group), we sampled arthropods in two ecosystems, alpine grasslands (at around 3,900 m in elevation) and fir forests (at around 3,200 m in elevation), at seven mountains using pitfall traps. We selected all spiders and beetles we found in the traps, classified them in morphotypes, and sequenced a region of the mtDNA COI gene from each individual. In this way, we were able to use classic population genetics methods for studying whole communities. Besides assessing richness and diversity within and among mountains, we used a neutral model to test the W-E groupings. We were also interested in addressing whether the W-E spatial pattern was present in different ecosystems. Thus, we compared grassland and forest communities.  

Unexpected challenges. We faced several challenges in this research. First, we realized that lists or inventories of arthropod communities at these sites are rare. In many cases, species have not been described yet. Because of this, we had to use morphotypes and operational taxonomic units instead of species. Second, doing fieldwork was fun but very challenging. Alpine grasslands are at very high elevations, and we had to hike all the way up the top of these mountains to set up the traps and then again to collect them a week after (no wonder why so many species have not been described yet!). An unexpected outcome was the striking difference we found between grasslands and forests communities within single mountains. Throughout the project, we were mainly focused on the W-E structure story, and the difference between ecosystems turned up to be just as − or even more − interesting in the end.

Alpine grassland and fir forest in the Western mountains of the Transmexican Volcanic Belt.

Major results. Two main results were drawn from this research. First, the difference between W and E communities is larger than expected if only present-day distance among mountains is considered. This pattern is probably related to the geologic history of this mountain range. Second, we found that communities from different mountains, but the same ecosystem, share more species among them than those within a single mountain but different ecosystems. This pattern was more common among lower elevation ecosystems (forests) than higher elevations (grasslands). Our results suggest that the long-distance colonization from similar ecosystems may be a more common pattern than the colonization of new habitats from lower elevations within the same mountain. Also, geologic history and ancient communities leave a strong trace on diversity structure despite recent processes of migration and connectivity. Our results contribute to broadening the understanding of how different factors like geology and climate shape biodiversity.

Next steps for this research. The next step in this research, led by Dr. Mastretta-Yanes, is to explore entire arthropod communities using metabarcoding data to sequence thousands of specimens from hundreds of pitfall traps and examine diversity patterns in multiple hierarchical levels (haplotype, putative species and supra-specific levels). With this high-resolution data, we are examining the role of neutral processes in promoting differentiation not only among mountains but also within a single mountain. With this analytical framework, we will assess if dispersal limitations within and between mountains can act as a source of local-scale genetic differentiation in tropical mountains, which may translate to species-level diversification over time.

Pitfall trap in alpine grassland (left), specimen from the family Curculionidae (middle) and specimen from the family Linyphiidae (right). We made our own traps using plastic cups, brown paint, alcohol, and glycerine. We selected all beetles and spiders that fell in the traps and took photos of every specimen we classified and sequenced. Sequences and photos are available through BoldSystems.

If you could study any organism on Earth, what would it be? I love elephants, octopuses, ferns, and magnolia trees. Actually, I’m fascinated by many organisms, but I always find myself studying processes and interactions more than single units or organisms. I really feel passionate about studying interactions among living beings and between these and their environment.

Anything else to add? I was first involved in this research because of my interest in learning population genetics and phylogeography. Tropical mountains happened to be the system model, but they were not my main focus. With time, as I developed my research further, I got more interested in tropical mountains as a study system. They are so fascinating! They are also under a lot of stress due to deforestation and climate change. Now, I keep working on tropical mountains but with a different focus. I study patterns of forest loss, their effects on ecosystems and people, and their interactions with climate change. Science and curiosity can take you on so many different paths!

Cindy Paquette is a PhD student at the University of Quebec in Canada. She is an aquatic ecologist interested in the impact of climate change and human activities on lake aquatic environments. Here, Cindy shares her recent work on how zooplankton are structured at different spatial scales.

Cindy Paquette collecting zooplankton in Lac Croche (Station de Biologie des Laurentides, University of Montreal), QC – Canada.

Personal links. Research Gate

Institute. University of Quebec at Montreal, Department of Biological Sciences; McGill University, Department of Biology

Academic life stage. PhD student

Major research themes. I am a Biology student specializing in aquatic ecology, more specifically at the level of planktonic communities. I am interested in the consequences of climate change and human activities in the Anthropocene on lake aquatic environments. Currently, I am working on a project to evaluate how zooplankton communities relate to overall lake health as well as watershed factors like land use and cover type.

Current study system. I work on freshwater zooplankton. Zooplankton compose the heterotrophic planktonic group that feeds on the main energy mobilizers (phytoplankton and bacteria) in pelagic lake food webs. As primary consumers, zooplankton are in turn, the food supply for macroinvertebrate and fish predators, and thus a critical trophic link in the upward transfer of energy. Changes in zooplankton communities can thus be essential to lake ecosystem functioning given their central food web position, mediating bottom-up and top-down energy transfers. Moreover, zooplankton are also sensitive to anthropogenic impacts, being good integrators and indicators of water quality.

Recent JBI paper. Paquette, C., Gregory-Eaves, I. and Beisner, B.E. (2021), Multi-scale biodiversity analyses identify the importance of continental watersheds in shaping lake zooplankton biogeography. Journal of Biogeography, 48(9): 2298-2311. https://doi.org/10.1111/jbi.14153

Zooplankton collected in Fox Valley (SK) showed red pigmentation (left) while specimens from Lac Augustin (Qc) had green pigmentation (right).

Motivation behind this paper. Worldwide, Canada has the greatest number of and surface area covered by lakes. Lakes are thus an integral part of Canadian culture and global water sustainability. However, we do not have a complete picture of Canadian lakes’ health because evaluation of lakes is handled differently by each province, including to what degree they are affected by human activities. Nor do we know how they are likely to change with future climate change, again because the evaluation of lakes is handled regionally by provinces. My research was part of a network called LakePulse (LakePulse.ca), created to answer these questions by evaluating over 650 lakes across Canada in a consistent way with a wide variety of ecological parameters. My main motivation behind this paper was to explore dispersal-related processes behind zooplankton biogeographical patterns, with the objective to determine how zooplankton taxonomic and functional composition are structured at different spatial scales (e.g. Canadian ecozones or continental drainage basins) across one of the largest and freshwater-rich countries in the world.

Key methodologies. As part of the LakePulse network, we sampled 664 lakes across Canada over the course of three years, covering 12 ecozones and six continental drainage basins. For the first time, taxonomic and functional zooplankton biogeographical patterns were analysed at the pan-Canadian scale. Using the lens of traits (e.g. body size, feeding mode, habitat) permitted a common currency across a wide range of community taxonomic lists, by which to examine how Canadian lake plankton communities respond to and influence their environment and its functioning. We explored the role of spatial extent using a combination of zooplankton composition and diversity, including spatial or β-diversity. β-diversity compares species composition among lakes or regions and is a useful tool in conservation and biodiversity management as it enables identifying species or lakes critical for regional diversity maintenance. The combination of metrics and diversity dimensions we used revealed novel spatial patterns across Canadian lakes, especially at the continental drainage basin spatial scale.

Unexpected challenges. Sampling 664 lakes over the course of three summers was a great challenge. I participated in all three field campaigns (2017-2018-2019) and thus had the opportunity to sample personally over one hundred lakes across Canada. Field teams faced multiple challenges, from difficult lake access to bear encounters. More than 100 different variables were sampled at each lake, with many samples having to remain sufficiently cold or frozen while the field crews travelled to a new lake each day. We are very grateful to the landowners, including several First Nations, who made this sampling possible. This intensive field campaign taught me many skills and allowed me to meet incredible people across the country, all connected by the desire to protect Canada’s freshwaters and especially its lakes.

Mauro de Toledo performing zooplankton sampling in Alberta (Canada).

Major results. Our major finding was that zooplankton species and trait composition were best structured at the larger scale defined by continental watershed basins than at the regional scale of Canadian ecozones. We were expecting to find a latitudinal pattern in zooplankton diversity, with greater diversity in the south because of higher solar radiation levels, as had been observed in at least one other study. Surprisingly, we found an overall longitudinal pattern in local diversity, with eastern Canada showing greater diversity, and little latitudinal pattern. Our results pointed to the importance of physical barriers in species dispersal as the main diversity turnover seemed to occur at the Rocky Mountains, with diversity increasing when moving to the east as species accumulated across the country. Our results also showed that country-wide taxonomic β-diversity varied more than functional β-diversity, indicating real compositional shifts in species.

Next steps for this research. Our next step is to relate the spatial biogeographical patterns observed in this study to environmental factors in and around each lake. In addition to zooplankton community data, we also collected data on water quality (physical, chemical and biological variables), lake morphometry, human land use, and land cover type in each lake’s watershed. By relating these data, our goal will be to determine which local lake variables are most critical for zooplankton diversity across Canada. Going even further, we will also compare our contemporary crustacean zooplankton assemblages collected from the top sediments in each lake to pre-industrial assemblages that have accumulated in the sediments by analysing sub-fossil zooplankton remains from sediment cores. This will allow us to evaluate to what degree zooplankton communities have changed during the course of the Anthropocene.

Some lakes were particularly scenic to sample, like Chaunigan Lake, BC (Canada).

If you could study any organism on Earth, what would it be? I really enjoy working with plankton as they are plentiful and relatively easily studied as well as being charismatic in their own way. However, I also really enjoy being in the mountains. I would love to combine these passions and study zooplankton communities in alpine regions. Alpine lakes are unique in that they are particularly vulnerable to climate change, and are thus great systems to estimate how freshwater lakes will continue to change in the future.

Anything else to add? Plankton are great indicators of lake food web functioning, but they are also great because there are so many little-known fun facts about them to share at parties (post-pandemic, of course). In addition to zooplankton, one of my main passions is rock climbing. Rock can be formed in many ways, including by accumulating sediments containing the bodies of dead plankton throughout millions of years. Thus, in some places like the Sister Cliffs (UK) or Saint-Alban (Canada), the sedimentary rock forms cliffs where climbers can explore this unique rock type. I love the fun fact that it is possible to climb on plankton! 

Marcos Vinicius Dantas-Queiroz is a PhD from the São Paulo State University in Brazil. He is a botanist interested in linking microevolutionary processes to macroevolutionary patterns. Here, Marcos shares his recent work on the phylogeography of ancient neotropical mountains.

Personal links. Personal website | Twitter

Marcos Vinicius Dantas-Queiroz during lab work.

Institute. São Paulo State University (Rio Claro campus), Department of Ecology

Academic life stage. PhD

Major research themes. Plant Evolution | Phylogeography | Bioinformatics | Biogeography | Ecology

Current study system. I’m currently studying one of the most biodiverse ecosystems of the world: the campos rupestres, a unique vegetation with more than 2,000 endemic plant species mainly found in Eastern Brazil. The campos rupestres is composed of xerophytic vegetation, dominated by herbaceous and shrubby species well-adapted to harsh conditions since most of the soils in the area are shallow and well-drained with intense solar radiation and a striking daily temperature variation. Under a phylogeographic approach, I’m trying to unveil the evolutionary dynamics that generated such an amazing biota.

Recent JBI paper. Dantas-Queiroz, M.V.; Cacossi, T.C.; Leal, B.S.S.; Chaves, C.J.N.; Vasconcelos, T.N.; Versieux, L.M. & Palma-Silva, C. 2021. Underlying microevolutionary processes parallel macroevolutionary patterns in ancient neotropical mountains. Journal of Biogeography, 48(9): 2312-2327 doi.org/10.1111/jbi.14154

The vegetation known as campos rupestres is mainly found in Eastern Brazil. This picture is from Rio de Contas, in Chapada Diamantina, Bahia, Brazil.

Motivation behind this paper. How can one link the microevolutionary processes that generate macroevolutionary patterns? Visualizing the effects of microevolutionary processes in already diverged lineages may be challenging. Still, it might be possible to observe these first steps of speciation in extant species with structured populations. Thus, we selected a species widely distributed but endemic to the campos rupestres, the bromeliad Vriesea oligantha, as a model system to investigate how its populations are structured and which factors probably generated this pattern. With this approach, we provided insights into how the macroevolutionary patterns of this vegetation originated.

Key methodologies. Our paper relies mainly on two analyses: ecological niche modeling and population genetic simulation models using Approximate Bayesian Computing (ABC). We hypothesized that past climatic fluctuations strongly interfered with the population dynamics of this bromeliad. We tested for demographic expansion with genetic markers and, with niche modeling, for suitable areas over time. By uniting the two approaches, we found that both corroborate an expansion scenario in the past. We were able to demonstrate that, in fact, the climatic fluctuations of the last thousands of years, mainly during the Last Glacial Maximum, had a great role in the population dynamics of this species and is possibly a strong evolutionary driver for the entire community.

The bromeliad Vriesea oligantha, the model of my study. This species is endemic but widespread in the Espinhaço, an Eastern South American mountain range.

Unexpected challenges. An inherent problem of bromeliads is the low level of polymorphism in their genetic markers. So, revealing the genetic structure and demographic patterns of V. oligantha was challenging. Using “classical” demographic analyses (e.g., Tajimas’s D, Fu’s F), we could not get much information. Fortunately, with more robust and computationally more intensive analyses, such as the ABC simulations we performed, we untangled the population history of V. oligantha, demonstrating that even with Sanger sequencing technology, it is possible to have positive insights when elucidating the natural history of tropical species.

Major results. We showed that microevolutionary processes are a proxy for understanding macroevolutionary patterns. In our paper, we suggest that continuous cycles of climate changes in the Pleistocene might be key factors for understanding evolutionary responses (speciation, extinction, migration and adaptation) due to the continuous cycles of connectivity and disconnection amongst populations. Considering the assumption that population differentiation is the primary mechanism of speciation, the concordant pattern between V. oligantha population divergence and the biogeography of the Eastern Brazilian mountains generated powerful insights into how climatic variables and limited gene flow might have shaped early stages of macroevolutionary patterns in the region.

An overview of the Espinhaço Range. The peak on the left is known as Pico das Almas (Bahia), one of the highest points of the Espinhaço (1958 m).

Next steps for this research. Our next step is to incorporate more organisms into a comparative phylogeographic approach. Thus, additional evidence using distinct organisms with independent evolutionary histories and divergent ecological traits could provide contrasting examples of how microevolutionary processes act and translate into the current biogeographic patterns of tropical montane biotas.

If you could study any organism on Earth, what would it be? I’m a Brazilian botanist, so I am privileged to have been born and grew up in a tropical country. However, In 2018 I had the opportunity to visit the Pacific West Coast, where I fell in love with the Sequoia forests, a sacred place for any biophile. Thus, if I could study a single organism, that would be the amazing Sequoia trees! I would like to understand its complete evolutionary history while also working with conservation policies and strategies to save this species and the astonishing landscapes where it lives.

Kevin Ma is a postdoc at Rhodes University. He is a biogeographer with an interest in marine organisms and their spatial structure. Kevin shares his recent work on the distribution of the invasive mussel, Mytilus galloprovincialis, in South Africa.

Kevin, sampling mussels during low tide.

Links. Twitter | GoogleScholar | Webpage

Institute. Rhodes University, South Africa

Academic life stage. Postdoc

Research themes. Spatial scales; Range shifts; Larval Ecology; Biological invasions; Early detection; Monitoring

Current study system. Native to the Mediterranean Sea, the mussel Mytilus galloprovincialis has been introduced to every continent except Antarctica. This highly invasive species has massive ecological consequences in southern Africa that range from outcompeting other species for space to driving increased abundances of endangered African oystercatchers. Its invasion of southern Africa continues to be one of our focal model systems to understanding marine biogeography, species interactions, and invasions. Moreover, as a relatively well-studied species, it is an ideal model species to look at long-term changes to better understand patterns of biological invasions, especially as it spreads from one biogeographic region to another.

Recent paper in JBI. Ma KCK, Gusha MNC, Zardi GI, Nicastro KR, Monsinjon JR, McQuaid CD. 2021. Biogeographic drivers of distribution and abundance in an alien ecosystem engineer: Transboundary range expansion, barriers to spread, and spatial structure. Journal of Biogeography. https://doi.org/10.1111/jbi.14124​

Motivation behind this paper. We were initially motivated to identify the contemporary warm range-edge of Mytilus galloprovincialis in southern Africa that might have shifted since their original invasion. Unexpectedly, our surveys revealed that its distributional limits had not changed substantially for the past decade or so. In fact, the warm range-edge has remained relatively stable at the transitional zone between two bioregions. We then wanted to know how this invader had interacted with biogeographic boundaries over the course of its invasion history in southern Africa. Consequently, the geographic scope of the study expanded by 1000s of km to encompass much of the southern African coastline that have been invaded by this mussel. Opportunistically, we were on the lookout for any new alien species (for early detection purposes) and any significant distributional changes of other established invasive species. In particular, we noted that another invasive mussel, Semimytilus algosus, an invader from Chile, has been spreading in the region, so this was reported in another study (Ma et al. 2020, in African Journal of Marine Science).

A patch of mussels, which consisted of both the invasive and native species

Methodologies. In addition to extracting occurrence records from the literature, we sampled an invasive mussel across 1000s of kilometres of the South African coastline to understand how its range had shifted over decadal timescales and assess spatial structure in abundance. Determining whether there are patterns in abundance across space can be challenging, because it depends on the scale of observation and the ecological processes operating at those scales. For example, the importance of wave action may be obvious at small scales, but hidden by biogeographic effects at larger scales. This can lead to contrasting patterns of deterministic versus stochastic abundance depending on the spatial scale sampled. We borrowed a technique that is commonly used on temporal datasets to examine heterogeneity in mussel abundance across space: wavelet analysis. By decomposing abundance values into different scales, wavelet analysis helped us identify the scales that exhibited significant structure in abundance, allowing us to speculate on the ecological processes most likely to explain these scale-dependent patterns.

Unexpected outcomes. Although the dominant mussels on rocky intertidal shores of southern Africa are the invasive Mytilus galloprovincialis and the native Perna perna, we also encountered another invasive mussel, Semimytilus algosus. Right away, we realised that S. algosus has extended its range since its distribution South Africa was last surveyed in 2010. In light of this unexpected information, we compiled all available historic and contemporary records of S. algosus to reconstruct its invasion history, first, for its invasion of South Africa (Ma et al. 2020 in African Journal of Marine Science) and, later, of Namibia and Angola (Ma et al. 2020 in PLoS ONE).

Exposed rocky shore at low tide.

Major results. Our recent paper clearly demonstrates that marine invasions along the South African coastline do not spread constantly over time and that biogeographic boundaries influence the rate of colonisation over decadal timescales. We hope that this contribution will help us better understand how marine biogeography drives (and hinders) the spread of biological invasions, especially the saltatory spread of alien ecosystem engineers. In addition, structure in the abundance of an invasive mussel was detected at multiple ranges of spatial scales, namely, scales of 120­–160 kilometres and of 400–990 kilometres. By identifying these dominant spatial scales, we hope that this will bring us one step closer to understanding large-scale ecological processes that together determine mussel abundance. Although the processes themselves are not exactly known to us, detecting structure at these two ranges of scales indicate that such processes are operating on mussel abundance at both intra-bioregional (scales of 120–160 km) and inter-biogeographical scales (scales of 400–900 km).

Next steps. At present, we would like to take a closer look at the range-edge dynamics of mussels by examining long-term changes in abundance and variation in endolithic infestation between range edge to centre populations.

If you could study any organism on Earth, what would it be? In addition to studying intertidal species, I also have a life-long fascination with ascidians (Tunicata: Ascidiacea). And, if I could, I would certainly like to study deep sea ascidians, especially macrophagous/carnivorous species. I imagine that there is more to know about their ecology, biogeography, taxonomy, and physiology. With the advent of ROVs, new records of deep-sea ascidians are being collected and documented, probably because specimens were damaged in the past when they were collected via dredging. Excitingly, new species are still being described in infrequently sampled regions of the world.

Anything else to add? It would be remiss not to mention the wealth of ecological data (in this case records of Mytilus galloprovincialis) that can be found in student theses. These records accounted for a substantial proportion of the historical dataset we used to reconstruct the geographic spread of this invader. Often student theses contain valuable details (e.g., dates, localities) that were not necessarily mentioned in the corresponding journal articles.

Morning view of rocky shores after a very early rise

Joshua Hallas is a PhD student at the University of Nevada in the USA. He is an evolutionary biologist interested in how environmental variation and natural histories mediate population structure, local adaptation, and genetic differentiation through time. Here, Joshua shares his recent work on the population genetics of the Western terrestrial garter snake.

Joshua Hallas during field collecting in Namibia, Africa.

Personal links. Personal website | Twitter

Institute. University of Nevada, Reno; Department of Biology and Graduate Program in Ecology, Evolution, and Conservation Biology

Academic life stage. PhD student

Major research themes. My research interests mainly focus on incorporating phylogenomic and population genomic techniques to understand how environmental variation and natural histories mediate population structure, local adaptation, and genetic differentiation through time.

Queets River at Olympic National Park.

Current study system. Thamnophis (garter snakes) are an ecologically and morphologically diverse group of North American colubrids (“harmless snakes”). For decades, this group has been used as a model to better understand numerous ecological and evolutionary processes (e.g., behaviour, coevolution, feeding ecology). Among Thamnophis, the western terrestrial garter snake (T. elegans) is one of the most ecologically variable and well-studied species in the genus whose range encompasses much of western North American. Even though T. elegans is primarily associated with aquatic habitat types, the species occupies a broad array of environments that include coastal rainforests, alpine communities, and high deserts, which makes it ideal to examine the influence of landscapes on genetic differentiation.

Recent JBI paper. Hallas, J.M., Parchman, T.L. and Feldman, C.R., 2021. The influence of history, geography and environment on patterns of diversification in the western terrestrial garter snake. Journal of Biogeography, 48(9): 2226-2245 https://doi.org/10.1111/jbi.14146

Thamnophis sirtalis at Olympic National Park – Queets River.

Motivation behind this paper. I have always been captivated by the landscapes and species richness of western North America. The region, which includes the California Floristic Province (a biodiversity hotspot), has a complex geological history that includes ancient marine embayments, multiple mountain ranges, volcanic activity, and has been repeatedly subjected to glacial cycles. Moreover, it comprises a variety of environments that may also play a role in patterns of differentiation. Biogeographic studies of herpetofauna throughout this region have recovered highly congruent patterns of differentiation associated with these features (e.g., Central Valley and Sacramento – San Joaquin River Delta). We decided to take advantage of the vast distribution and pronounced ecological diversity of T. elegans to test previous biogeographic hypotheses focused on western North America. We also took this opportunity to re-examine phylogenetic estimates surrounding the subspecies that comprise T. elegans.

Preserved specimen of Thamnophis elegans from the Herpetology collection at the California Academy of Sciences.

Key methodologies. We used a reduced representation double-digest RADseq (ddRADseq) approach. This technique allowed us to generate copious amounts of sequence data needed to characterize fine-scale spatial structure among and within each subspecies.  Employing both population genetic and phylogenetic methods, we were able to investigate patterns of variation at multiple spatial scales and levels of differentiation. In conjunction with phylogenetic and ancestral area reconstruction analyses, we used EEMS (estimated effective migration surface) and genetic-environment association analyses (GEA). The EEMS analysis allowed us to test if geological features coincided with estimated areas of low migration, and the GEA was used to identify signatures of natural selection to environmental variables.

Prepping Namanazours jordani for following graduate student Jonathan Deboer – Namibia, Africa.

Unexpected challenges. An unexpected challenged that we encountered was incorporating multiple complex stories into a single cohesive biogeographic conclusion. This was mainly a result of having among and within subspecies datasets. Our analyses among subspecies gave great insight into dispersal and patterns of diversification. Unfortunately, we were only able to conduct within subspecies analyses for T. e. elegans and T. e. terrestris because we lacked the sampling for T. e. vagrans. Nevertheless, our population genetic analyses of T. e. elegans and T. e. terrestris allowed us to better understand the roles of both isolation-by-distance and population fragmentation driving genetic differentiation. This also meant we had differing explanations for the biogeographic patterns we observed in these two subspecies. Even though this complicated the writing process, I think it made our study more fulfilling and impactful.

Canopy from Redwood State and National Parks.

Major results. We recovered both broad and fine-scale geographic patterns in T. elegans associated with biogeographic features across western North America. For example, Central Valley, marine embayments, and Sacramento – San Joaquin River Delta, and possibly the Snake River Plain or Wyoming Basin are breaks and potential barriers to gene flow. We also detected non-neutral patterns of genetic variation associated with environmental variation (especially mean annual temperature, isothermality, total annual precipitation) in our GEA analyses for T. e. elegans and T. e. terrestris. This suggests that differentiation of these subspecies is jointly shaped by landscape features and environmental variables. Surprisingly, we also recovered signatures of possible admixture between T. e. elegans and T. e. terrestris where their ranges intersect in northwestern California. Conversely, we found no evidence between T. e. elegans and T. e. vagrans, even though their ranges intersect along northeastern California and southern Oregon. Our findings greatly improve the understanding of diversification across multiple spatial scales throughout western North America.

Photo of Thamnophis elegans terrestris from San Mateo county California (photo by Robert Hansen).

Next steps for this research. Some questions I would like to explore further would focus on the biogeographic patterns in T. e. vagrans, which has the largest range of the three subspecies. Our current analyses suggest some interesting patterns that divide the subspecies into two clades that represent the Pacific Northwest and the arid Southwest. Finer-scale work on T. e. vagrans would also fill in a knowledge gap regarding the influence of features like the Rocky Mountains, Colorado Plateau, and Columbia Plateau on patterns of diversification. The admixture we recovered between T. e. elegans and T. e. terrestris also warrants further investigation. However, increased genomic and specimen sampling would be needed to understand the genomic consequences of admixture.

Photo of Thamnophis elegans vagrans (photo by Robert Hansen).

If you could study any organism on Earth, what would it be? I thoroughly enjoy using garter snakes (Thamnophis) to investigate evolutionary questions. This group of organisms has been very influential in my research career and my interest in reptiles. They were one of the most common species I would catch in my youth, and it’s been a joy to work with them in a more academic and professional setting.

Educational outreach event at the University of Nevada Reno Natural History Museum.  Showing the arboreal ability of my Morelia spilota.

Anything else to add? Much of my enthusiasm for the natural world was fostered during family trips to California National Parks. Also, probably why I started collecting Junior Ranger badges. However, during these trips, my father would encourage my siblings and I to explore the outdoors. I was not only captivated by the overwhelming landscapes but also the ecological and evolutionary patterns I would observe. These experiences helped me develop my aspirations of conducting scientific research and learned the value of asking questions. This is why I am very passionate about scientific outreach and hands-on learning. I believe curiosity can’t be taught, and that it could only be nurtured. It is up to current researchers to help encourage future generations to continue to ask questions.