Primate evolution: Completing the timetree of life for all of our closest relatives
The order ‘”Primates” includes over 450 species of monkeys, lemurs, lorises, and galagos, in addition to our closest relatives, the seven species of great apes.
From 400-pound gorillas to minute mouse lemurs (Microcebus) that can weigh a single ounce, primates showcase incredible diversity.
They also display remarkable behaviors. For example, chimpanzees use sticks to fish for termites, while orangutans use leaves as gloves to handle spiky durian fruits.
Building a timetree for primates
Despite extensive studies on their diversity, primate evolutionary history remains incompletely understood.
There is no comprehensive molecular phylogenetic tree summarizing the relationships and timing of all primates.
Existing efforts include a timetree for just over 200 species, and a synthetic timetree, derived from over 4,000 studies, that covers only about 300 primate species. This leaves a significant portion of the primate evolutionary tree unresolved.
Why complete evolutionary trees matter
Timed evolutionary trees are essential for understanding biodiversity and evolutionary history.
These phylogenetic trees, also called timetrees, provide insights into when species emerged and how they relate to one another. Their importance extends beyond curiosity.
Timetrees form the foundation for:
- Taxonomy and species identification: they help identify and catalog new species.
- Evolutionary studies: researchers analyze rates of evolution and factors like climate change or geological events that influence species development.
- Biogeography and historical ecology: timetrees reveal spatial and ecological patterns in species distributions.
- Conservation: as biodiversity declines, timetrees highlight conservation priorities and assess preservation efforts.
Simply put, phylogenies are critical tools for understanding the past, present, and future of species.
Rarity of complete phylogenies
Considering their value, one might assume that complete phylogenies are common. However, they remain rare. The NCBI taxonomy database holds molecular sequences for nearly 500,000 species.
In contrast, The TimeTree of Life, the largest timed phylogeny database, includes only about 150,000 species. Most published phylogenies focus on smaller groups of organisms, averaging just 25 species.
These smaller phylogenies prioritize precision within limited taxonomic groups. However, to construct a complete tree of life, researchers must merge these smaller efforts.
New path to build complete primate timetrees
While complete timetrees are uncommon, the resources to build them already exist. Untimed phylogenies, which outnumber timed ones, hold significant potential.
By adding a few calibrations, researchers can transform these untimed trees into useful components of larger timetrees.
Additionally, molecular data for many species exist in public repositories like NCBI GenBank, where DNA sequences are freely available.
This abundance of untapped data offers an opportunity to construct comprehensive evolutionary trees. Researchers have developed a supertree-building method to maximize these resources.
Their approach involves:
- Collecting published, timed phylogenies of species.
- Searching for untimed phylogenies and adding calibrations to estimate timing.
- Assembling new alignments using molecular data from repositories.
- Combining all of the above to produce a complete, synthetic timetree.
Most complete primate timetree to date
Using this method, researchers from Temple University have successfully constructed a new synthetic supertree of 455 primate species, covering 98% of primates listed in NCBI taxonomy.
This achievement adds 55 species previously absent from the TimeTree of Life. The new primate timetree represents the most complete depiction of primate evolutionary relationships to date.
Insights on primate evolution
This effort proves that incomplete knowledge of evolutionary history can be addressed with existing data. Complete timetrees not only provide evolutionary context but also enable researchers to test new hypotheses.
For instance, in this study, the researchers explored whether the diversity of primate clades resulted from faster speciation rates in some lineages or simply from the passage of time.
The findings revealed that major primate groups shared similar speciation rates. Therefore, older lineages accumulated more species over time.
This analysis highlights the utility of large, complete timetrees. Without accurate dates and species counts, such conclusions would be unreliable.
Completing the tree of life
The new primate timetree demonstrates that filling gaps in evolutionary history is achievable. The tools and data exist, but collaboration and synthesis remain key.
As researchers continue to combine molecular sequences, untimed phylogenies, and calibrated studies, the dream of a complete TimeTree of Life grows closer to reality.
Complete timetrees have far-reaching impacts. They guide taxonomic studies, reveal evolutionary trends, and can strengthen conservation efforts during the ongoing biodiversity crisis.
This research offers a blueprint for future projects that aim to build complete evolutionary trees.
Ultimately, understanding primate evolution helps us appreciate the rich diversity of life on Earth – from the tiniest mouse lemur to the powerful gorilla – and the intricate history that shaped it all.
The study is published in the journal Frontiers in Bioinformatics.
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