[Leps-l] monarchs, reversal of orientation and overwintering temperatures

[MexicoDoug]

Chip,

Thanks for the links, it is part of an interesting study if you aren't 
squeamish about amputating Monarch antennae and watching carefully what 
happens!  If I can get a free copy of this complete paper it will be 
interesting to read ...  In the mean time, a free pdf is available here:

http://reppertlab.org/media/files/publications/natcomm2012.pdf

which seems to cover the same experiment except notably for the module 
of suspending some of the Monarchs in Texas, in an artificial fall 
condition during the migratory and overwintering period to fool the 
Monarchs into thinking they are still in Autumn ... effectively by 
swapping the Northern and Southern equinoxes' to give the Monarchs a 
form of Jet Lag that is undetectable by some senses.

The release point basically is at the same temperature after the 
seasonal swap, correct?  The artificial autumn condition created seems 
to be an average of around 61 degrees F, with limits of something like 
54 degrees F > temp > 68 F.

This seems then to be contrasted with a current estimate 36 degree F 
low (January) temperature in the Mexico State & Michoacan State 
overwintering region and another attempt to show that prolonged cooling 
of undetermined length to Monarchs already in diapause is a dependable 
way to orient the Monarchs northward even in short winters.

The provocative conclusion seems to be if the Monarchs can be given 
seasonal jet lag under the right conditions and not notice while they 
were in the lab --- that they gained a half season.  The suggestion 
that without experiencing the cold temperatures in their Oyamel woods 
that the Monarchs can be fooled.  It is interesting in the sense that 
it argues that this effectively says the Monarchs' "compass" is really 
only a 180 degree compass and I would infer is requiring diapause and 
all the biochemical/physiological reactions that accompany it to 
calibrate with hemisphere of the compass is "up".

As an amateur and conservationist, think it is a very constructive 
work, but a few more Monarchs need to be seasonally jet-lagged 
(sans-antennae amputees) to figure out the relationship between 
entering diapause, flip/flopping navigational 'compasses', and if it 
all plays out according to the hypothesis, precising for how long and 
at what temperature (not studied between 36 and 61 degrees F) in a 
predictive sense these Monarchs need to be exposed to go into diapause. 
  Unless of course, the study is saying that diapause is unrelated to 
the proposed N/S calibration/inversion observed in these laboratory 
Monarchs.  Right?

That's what I get from this, where the interesting diligence here, 
besides utilizing this "disappearance bearing" (As a layman this gives 
me discomfort since measurement of disoriented butterflies after 
initial release is being generalized, and not all individuals' bearings 
are being counted  which has the potential to introduce experimental 
bias - though I have no idea how it could be done better without GPS 
trackers or huge experiments with tags via something like Monarch 
Watch) is a laboratory attempt to control photo-period length; and the 
implication to conservation of the migration would seem to me not 
addressed since even under the most pessimistic scenarios, no one is 
saying that it will be 61 degrees at those elevations in the Monarchs' 
dominion of Oyamel woods.  But it does build on studies during a time 
much less had been determined about the 'compass', at that time which 
suspected but did not confirm this at least as far back as Herman, WS 
(1981)

http://www.biolbull.org/content/160/1/89.full.pdf

Best wishes
Doug





-----Original Message-----
From: Chip Taylor <chip at ku.edu>
To: Leps-l <Leps-l at mailman.yale.edu>
Sent: Thu, Feb 21, 2013 1:45 pm
Subject: [Leps-l] monarchs, reversal of orientation and overwintering 
temperatures

http://www.climatecentral.org/news/spring-chill-sends-monarchs-fluttering-north-15634

http://www.cell.com/current-biology/abstract/S0960-9822(13)00087-0

Coldness Triggers Northward Flight in Remigrant Monarch Butterflies

Current Biology, 21 February 2013
Copyright © 2013 Elsevier Ltd All rights reserved.
10.1016/j.cub.2013.01.052

Authors
Patrick A. Guerra
,
Steven M. Reppert
Summary
Each fall, eastern North American monarch
butterflies (Danaus plexippus) migrate from their
northern range to their overwintering grounds in
central Mexico [1,2,3]. Fall migrants are in
reproductive diapause, and they use a
time-compensated sun compass to navigate during
the long journey south [4,5,6]. Eye-sensed
directional cues from the daylight sky (e.g., the
horizontal or azimuthal position of the sun) are
integrated in the sun compass in the midbrain
central complex region [7,8]. Sun compass output
is time compensated by circadian clocks in the
antennae so that fall migrants can maintain a
fixed flight direction south [9,10]. In the
spring, the same migrants remigrate northward to
the southern United States to initiate the
northern leg of the migration cycle. Here we show
that spring remigrants also use an
antenna-dependent time-compensated sun compass to
direct their northward flight. Remarkably, fall
migrants prematurely exposed to
overwintering-like coldness reverse their flight
orientation to the north. The temperature
microenvironment at the overwintering site is
essential for successful completion of the
migration cycle, because without cold exposure,
aged migrants continue to orient south. Our
discovery that coldness triggers the northward
flight direction in spring remigrants solves one
of the long-standing mysteries of the monarch
migration.

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