Phylogeny
Image Credit- https://static.scientificamerican.com/sciam/cache/file/28CB4623-8A4B-4DBA-9708866CCA9FECE8_source.png
What is Phylogeny?
"The evolutionary history of a kind of organism."
-Merriam Webster's Dictionary(18)
Monarch Ancestry
Phylogeny of Monarchs
Image Credit- https://doi-org.lopes.idm.oclc.org/10.1038/nature13812
Kingdom- Animalia
Phylum- Arthropoda
Class- Insecta
Order- Lepidoptera
Family- Nymphalidae
Genus- Danaus
Species- Plexippus
This phylogenetic tree is a hypothesis of the relationships between Monarchs and their closest relatives. Generated through the careful analysis of Monarch genotypic and phenotypic traits, Zahn and colleagues attempted to trace the lineage of monarchs in order to learn about the evolution of migration (14). In the hypothesized phylogenetic tree above, the closest hypothesized ancestor was placed in genus danainae (14).
Evolution Of Migration In Butterflies
There are Monarch butterfly species all over the world! Why do some populations migrate and some not(13)?
The Isolation of a population leads to genetic drift.
image credit- https://media.springernature.com/lw685/springer-static/image/art%3A10.1038%2Fnature13812/MediaObjects/41586_2014_Article_BFnature13812_Fig5_ESM.jpg?as=webp
Monarch population locations worldwide!! Population drift occurs faster as population size decreases(6).
Only Monarch populations colored sea green in the image above are migratory. North American populations are unique, however, even among these populations not all migrate. South Florida contains non-migratory populations(14).
Genetic differences! (14)
Divergent selection has led to migratory populations having major differences in key genes:
Collagen IV alpha-1 Gene
Migratory populations have lower levels of collagen IV alpha-1 gene expression.
This gene is responsible for "flight muscle formation and function" (14).
Having this gene allows monarchs to decrease in oxygen intake and increase in flight endurance.
The Collagen IV alpha-1 gene was also associated with a decrease in the metabolism of migratory butterflies, allowing them to fly longer distances.
Image Credit- https://doi-org.lopes.idm.oclc.org/10.1038/nature13812
Phylogenetic tree showing the divergence of the Collagen IV alpha- 1 gene among populations.
CRY Gene
This gene allows migratory monarchs to sense the earth's magnetic field.
Without the sun, migratory monarch populations are able to continue using the south to north magnetic pole (14).
Kettin Gene
Kettin is a flight muscle formation gene.
Migratory Monarchs expressing this gene have increased longevity in flight distances and are able to make the 3000 mile long migration(14).
Ancestry of the Monarch Migration!
Image Credit- https://doi-org.lopes.idm.oclc.org/10.1038/nature13812
Comparing the genetics of Migratory verses non-migratory populations the above phylogram was created. Here, the phenotypic and genotypic differences were taken into account(14).