Above: Fat-tailed Dwarf Lemurs. Image courtesy of Duke Lemur Center.  

In the words of DreamWorks’ King Julian, welcome to Madagascar! 

With swaths of lush tropical rainforests along the eastern coast, mosaics of rolling grasslands and patchy woodlands across the plateau, deciduous forests and mangroves on the western coast, and regions of succulent woodlands and spiny bush in the arid south, it’s no wonder that Madagascar accounts for 5% of the world's biodiversity. 

However, as with most biodiversity hotspots around the globe, Madagascar is currently threatened by anthropogenic, or human-based, activity. Climate change and deforestation are degrading these unique habitats and devastating the long-established ecosystems they contain. As these challenges threaten species and habitats across the globe, scientists and conservations must work to allocate finite resources to the regions in need. 

Thus, conservationists face an urgent task: identifying vulnerable regions where habitats are shrinking, populations are experiencing declining genetic health or sustained decreases in size, and ecological stressors are intensifying.

How can we accomplish this? The answer may lie in the field of phylogenetics. 

What is Phylogenetics?

Phylogenetics is the study of the evolutionary history of life on Earth and the genetic relationships between organisms. Researchers use phylogenetic trees to map out how scientists believe organisms diverged from one another over evolutionary time to form distinct species. In the context of Madagascar, where most species are endemic, or native exclusively to the region, deep evolutionary relationships between species strengthen the argument for protecting the habitat in which they developed.  

Above: Components of a phylogenetic tree. Image courtesy of Khan Academy.  

The Yoder Lab

The Yoder Lab at Duke University has dedicated decades of research toward unraveling the rich biological complexity of the island through the lens of integrative evolutionary genomics. The lab, headed by Dr. Anne Yoder, focuses on the cryptic history behind Madagascar’s iconic lemurs, exploring everything from the bacteria that inhabit their guts to the adaptations that enable them to thrive in diverse environments. “[Our work is] all about Madagascar [and] explor[ing] the evolutionary history there and protecting that history,” Dr. Yoder said. 

In 2019, the Yoder Lab published a study on the threatened lemur genus Cheirogaleus (dwarf lemurs), whose four sub-clades occupy diverse geographic regions throughout Madagascar. Dwarf lemurs are unique even amidst the vibrantly diverse backdrop of Madagascar’s lemurs: they’re the only genus to truly hibernate during the winter. Sampling four individuals from each sub-clade—C. Medius, C. major, C. crossleyi, and C. sibreei—Dr. Yoder’s team set out to conduct high-quality genotypic analyses of each. The team hoped to validate the current classification of Cheirogaleus and better understand how these clades evolved over time. 

What began as a study exploring the separation of Cheirogaleus into four distinct clades quickly expanded into something more complex. While 99.4% of the genome aligned with previously established phylogenetic relationships, the remaining 0.6% revealed discordance. As Dr. Yoder explained, lead author Dr. Williams “became almost obsessive over it [the discordance]... manually curating annotations of the genome to figure out what each individual part did.”

Through her analysis, Dr. Williams found that millions of years ago, some individuals in the diverging clades C. major and C. sibreei interbred with C. medius, transferring parts of the genome before they diverged completely. Over time, they continued to breed within their own clades, but certain parts of the other species’ genome remained in the population. Upon closer inspection, the team observed several transcription factor genes related to hibernation in these introgressed, or mixed-genome, regions. This finding was especially interesting, as C. medius and C. sibreei are known as “super-hibernators,” remaining in this state for up to seven months of the year. Though Dr. Yoder noted that “correlation does not necessarily mean causation,” this finding “surely has the appearance… [of a connection].” 

In the greater context of conservation, the findings presented by Dr. Williams, Dr. Yoder, and the rest of the Yoder Lab demonstrate the applicability of comparative conservation genomics in identifying vulnerable populations. Additionally, the presence of hibernation genes in “genetically mixed” regions may indicate a possible means by which organisms adapt and evolve. Through this research, the Yoder Lab highlights the importance of adding genomic analysis to conservationists' toolkits, helping us work towards preserving the vibrant biodiversity of our natural world.