Nathalie Bacardi, Tudor Aniculaesei
The famous monarch butterfly, Danaus plexippus, has gotten its notoriety mostly from its impressive migratory patterns and iconic white, black and orange wings. Every year, millions of monarch butterflies migrate from southern Canada and northern United States to overwinter in Mexico. It is the only butterfly known to migrate in a two-way fashion similar to birds. A study conducted by Zhan et al (2014) investigated this great migratory phenomenon to locate the species origins and to see how the butterflies diverged from their ancestors. Its well known colouration was also studied.
Where does the journey begin?
Observing that the species D. plexippus are characteristically tropical and non-migratory, it had been hypothesized that populations from South and Central America were the ancestral source of North America D. plexippus populations. On the contrary, the genomic data gathered disproved this idea and instead showed that the monarch butterfly originated from an ancestral migratory population in North America. This suggests that other species, which are specific to Central and South America, must have diverged from them. When comparing genetic data from both migratory and non-migratory populations of North American against those of non-North American Populations, the populations in North American had significantly higher gene flow. This seems to support that non-North American populations must have evolved independently due to their isolation.
Migratory and non-migratory population show distinctions in wing shape and size, body mass and kinetic wing loading. Differences in their length of flight would then also be thought to be reflected by differences in essential muscle function. Studies on collagen type IV has shown divergence between migratory and non-migratory populations. It was seen that collagen IV alpha-1 and alpha-2 were down regulated in migratory butterflies, showing that flight efficiency has been naturally selected for long-distance flight. It was then found that active flight is almost 25 times more demanding in energy. These same migratory butterflies therefore also show lower metabolic rates. This increase in the efficiency of energy consumption seems to be a result of muscle performance during flight, because the difference was minimal when populations were not in flight.
Wing pigmentation— it attracts attention!
Studies have been done to determine the wing pigmentation of the monarch butterflies by sequencing genomes of wild type butterflies and the Hawaiian white ‘nivosus’ morphs. The myosin gene DPOG206617 has been found to be strongly associated with wing colour.
Knowing the origin of D. plexippus and having acquired its whole genome are key factors brought to light by Zhan and his team, which will aid in the conservation of this butterfly. The alarming decline in the monarch populations has been caused by deforestation, drought and precipitous drop-off in the number of milkweed host plants across North America. Though there has been a growth in awareness on the issue, environmental concerns still continue to rise, leaving us with the question of how long the Danaus plexippus population will survive.
Zhan, Shuai. “The Genetics Of Monarch Butterfly Migration And Warning Colouration”. Nature 514.7522 (2014): 317-321.
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