P.sennae

[evoluhol at magnum.wpe.com]

> Dear Friends;
> I am a naturalist living in Western NC, and have spent many yrs studying
> the natural world around me. I have read in the Audubon's Butterflies by
> Pyle that many species emigrate Northward in the Fall, but few make it
> South again as the Monarch (D. plexippus) (sp?). Among these is P.
> sennae. I have seen P. sennae drifting South in NC and Ga, and have seen
> them doing so in th Mountains this year. It would seem to me that it
> would make no sense to go North in the Fall, reproduce, and have your
> progeny die of the cold. Where is the selective advantage? Would closer
> observation show that they do indeed return South to reproduce, and no
> one has seen it due to a more scattered migration than the Monarch? This
> question has troubled me for years.
> 

In answer to this question -- I submit the following from my book
"BUTTERFLIES AROUND YOU."  as it is copyrighted( © David W. Bouton) one
may print a copy of this for their own use, but it cannot be reprinted
from here for distribution.

This is from the pages on Polygonia interrigationis, the question mark
butterfly:

 
Rarely are they seen in large numbers in one spot, but they are found
around woodlands all over the USA east of the Rocky Mountains, except
frigid northern Maine and tropical Florida.  It is one of the ³angle
wings,² a group of butterflies found around the world in warm temperate
zones, all others having only a ³comma² not a ³question mark² on the
underside.
     Sometimes the question comes up, ³Why would a butterfly population
spread to the north every year and then die out there when winter comes?²
as this one does in most years.
     Two things bring this about.  Though we enjoy butterflies because of
their colorful wings, and the wings help in escape and finding mates,
their main purpose is to disperse the species -- spread it around --
colonize greater and greater areas, put eggs in new places.  Once in a
while some may survive and establish the butterfly in new localities.  As
with most butterfly and moth eggs, only .005 of 1% survive to become
butterflies. Winter is one of the editing factors for this species.
     ³But, why does it come north year after year only to be killed by
winter?²  Though in our experience there is relative constancy to the
weather and the seasons, it is only temporary.  Through the centuries, the
northeast has been the bottom of an ocean, steamy tropics, and frequently,
even as recently as only 15,000 years ago, under two miles of ice.  Though
many butterflies cannot survive our present winter in any stage -- two
things can happen if some fly north every year.  The first is mutation. 
The constant editing process of evolution may result in genetic change,
and as such could create the ability of a few individuals to survive the
winter.  The second is, in the centuries to come, it quite naturally will
be tropical here again and the butterfly will be able to survive here when
that warmer era comes -- or to repopulate here after the next ice age
drives it away and then retreats.


Dave Bouton