ECR Feature: Kathryn (Katie) M. Everson on the diversification of Madagascar’s small montane mammals and reptiles

Katie is a postdoc at the University of Kentucky. She combines phylogenetics and phylogeography to understand species diversity and distributions. Katie shares her recent work on patterns of co-distributed genetic structure among 25 small-bodied animals (tenrecs, rodents, and reptiles) from Madagascar’s highland regions.

Name. Kathryn (Katie) M. Everson

Personal website.

Institute. University of Kentucky, Department of Biology

Academic life stage. Postdoc

Major research themes. I’m driven by three major questions: how many species exist in a given lineage (species delimitation), how are those species related (phylogenetics), and which landscape features have shaped their evolutionary history (phylogeography)? I think the best avenue for exploring these topics is to blend traditional museum-based systematics with genomic datasets.

Current study system. Most of my research is focused on Madagascar’s mammals. The island of Madagascar is a biodiversity hotspot and 100% of its native terrestrial mammals are found nowhere else on Earth. Even though Madagascar is well known among biologists, many of its species have not been described in the scientific literature, and researchers still don’t fully understand how and why the island’s biodiversity arose. Describing this biodiversity and its evolutionary history is urgently important as Madagascar’s forest habitats are quickly disappearing.

Recent paper in JBI. Everson, KM, Jansa, SA, Goodman, SM, Olson, LE. Montane regions shape patterns of diversification in small mammals and reptiles from Madagascar’s moist evergreen forest. Journal of Biogeography. 2020; 47: 2059– 2072.

Motivation for this work. This paper has been a long time in the making! The original idea came from my PhD advisor Dr. Link Olson (University of Alaska Museum) who studied Madagascar’s tenrecs, and his friend and colleague Dr. Sharon Jansa (University of Minnesota) who studied Madagascar’s native rodents. In the early 2000s, Link and Sharon had each been looking at some mitochondrial data from museum specimens when they realized that many species had very similar phylogeographic patterns. Specifically, when they looked at the eastern humid forest, they saw that many species are co-distributed and have a nearly identical population structure. This made them wonder if the same geological features could be driving population structure across multiple species. They teamed up with Dr. Steve Goodman (Field Museum and Association Vahatra), who brought a wealth of on-the-ground knowledge and experience in the eastern humid forest, and me, who brought the skillset for comparative phylogeographic analyses and a fresh perspective.

(left) Katie Everson checking pitfall traps in Madagascar’s moist evergreen forest near Betampona Reserve. (Photo credit: Link Olson) (right) Leaf-tailed geckos (genus Uroplatus) are endemic to Madagascar and occur broadly in the moist evergreen forests. (Photo credit: Katie Everson)

Key methodologies. This was a comparative phylogeographic study – we used genetic and geographic data from 25 species (13 tenrecs, 7 rodents, and 5 reptiles) to identify similarities in population structure. This approach assumes that if multiple species share the same phylogeographic break – say, across a river – then that river has probably been an important feature driving diversification. We were surprised to find that 24 out of our 25 species shared phylogeographic breaks between Madagascar’s highland regions, so we concluded that the highlands have played an important role in driving diversification on Madagascar. 

Any challenges? We ran into a few roadblocks while working on this paper, but we’re glad that we were ultimately able to overcome them all! One big challenge was dealing with ever-changing taxonomy in this biodiversity hotspot. While we were working on this research, several papers were published suggesting that at least 6 of our focal species should actually be split into multiple species. We debated whether we needed to remove those groups from our study, but in the end we decided to move forward and treat everything as a “species complex.” We also added a new analysis to test whether any of our other 19 species also contained hidden diversity (spoiler alert: they all did!).

Major results. We found that the Madagascan highlands have played an important role in structuring genetic diversity on Madagascar. This finding represents a new phylogeographic model for Madagascar that we hope will be used by future scientists as a jumping point to explore new hypotheses. We also identified 85 deeply divergent lineages that may represent new (i.e., unrecognized or cryptic) species, which corroborates other findings that Madagascar’s species-level biodiversity is vastly underestimated. On the whole, our work shows that Madagascar’s distinctive fauna is continuing to diversify, and it shows that the highlands might be a key to explaining how Madagascar became one of the world’s foremost biodiversity hotspots.

Shrew tenrecs (genus Microgale) are endemic to Madagascar. They featured prominently in this study. (Photo credit: Jonathan Fiely)

Nest steps. It would be interesting to add other species besides small-bodied vertebrates to see whether the Madagascan highlands have played an important role for diversification of other groups like lemurs, plants, or insects. It would also be great to collect a bigger genetic (or maybe even genomic?) dataset. With more data we would have the power to explore divergence times, patterns of gene flow, and other fine-scale aspects of demographic history. Finally, this study illuminated the presence of potential new species and pointed to important, previously unrecognized regions of microendemism. I think it will be important to follow up on these on a case-by-case basis.

If you could study any organism on Earth, what would it be? That’s a hard question! I love studying Madagascar’s mammals, but I know there are a lot of other groups that would be interesting to study too. One that comes to mind are the pangolins. They’re the most trafficked mammals in the world, they carry a coronavirus that is very similar to human COVID-19, and they have a really interesting distribution from Africa to the islands of Southeast Asia. Plus, they look like something from another planet – the way they walk is so funny!

Anything else to add? I want to emphasize that obtaining all of the samples for this research was an enormous collecting effort, both by my coauthors and by numerous Malagasy researchers over the last several decades. I feel very fortunate to have been able to work with these samples!

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