Vladimir Nabokov vindicated – about butterflies

Polyommatus icarus 5

Polyommatus blue: Image via Wikipedia

Vladimir Nabokov (yes, he of Lolita fame) lived in Cambridge, Massachusets from 1942 to 1948 and while teaching at Wellesley he was curator of lepidoptery at Harvard University’s Museum of Comparative Zoology. His career in entomology was almost as distinguished – but not as lucrative – as his career in literature. In his spare time he composed chess problems. But his work in all these fields was characterised by his “love of detail and contemplation and symmetry”.

In 1945 he published a theory of butterfly evolution claiming that butterflies came to the New World in five waves of migration, through Asia across the Bering Strait into Alaska and then southward through North and then South America (much as humans migrated). Other butterfly experts scoffed at the idea. Nabokov’s theory was not taken seriously until after his death in 1977. Then, in the past decade, gene-sequencing technology finds that Nabokov was right all along and ironically during his life  “Nabokov never accepted that genetics or the counting of chromosomes could be a valid way to distinguish species of insects, and relied on the traditional (for lepidopterists) microscopic comparison of their genitalia”.

Now his theory stands vindicated by work  reported in a new paper in the Proceedings B of the Royal Society:

Phylogeny and palaeoecology of Polyommatus blue butterflies show Beringia was a climate-regulated gateway to the New World by Roger Vila, Charles D. Bell, Richard Macniven, Benjamin Goldman-Huertas, Richard H. Ree, Charles R. Marshall, Zsolt Bálint, Kurt Johnson, Dubi Benyamini and Naomi E. Pierce  doi:10.1098/rspb.2010.2213 Proc. R. Soc. B

Abstract: ….. By integrating molecular phylogeny, historical biogeography and palaeoecology, we test a bold hypothesis proposed by Vladimir Nabokov regarding the origin of Neotropical Polyommatus blue butterflies, and show that Beringia has served as a biological corridor for the dispersal of these insects from Asia into the New World. We present a novel method to estimate ancestral temperature tolerances using distribution range limits of extant organisms, and find that climatic conditions in Beringia acted as a decisive filter in determining which taxa crossed into the New World during five separate invasions over the past 11 Myr. Our results reveal a marked effect of the Miocene–Pleistocene global cooling, and demonstrate that palaeoclimatic conditions left a strong signal on the ecology of present-day taxa in the New World. …..

From Neatorama:

There were several plausible hypotheses for how the butterflies might have evolved. They might have evolved in the Amazon, with the rising Andes fragmenting their populations. If that were true, the species would be closely related to one another.

But that is not what Dr. Pierce found. Instead, she and her colleagues found that the New World species shared a common ancestor that lived about 10 million years ago. But many New World species were more closely related to Old World butterflies than to their neighbors. Dr. Pierce and her colleagues concluded that five waves of butterflies came from Asia to the New World — just as Nabokov had speculated.

“By God, he got every one right,” Dr. Pierce said. “I couldn’t get over it — I was blown away.”

Dr. Pierce and her colleagues also investigated Nabokov’s idea that the butterflies had come over the Bering Strait. The land surrounding the strait was relatively warm 10 million years ago, and has been chilling steadily ever since. Dr. Pierce and her colleagues found that the first lineage of Polyommatus blues that made the journey could survive a temperature range that matched the Bering climate of 10 million years ago. The lineages that came later are more cold-hardy, each with a temperature range matching the falling temperatures.


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