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Monarch butterflies (Danaus plexippus) occur
in temperate and tropical zones throughout the world including temperate
N. America and tropical S. Florida and Hawaii. After hatching from
eggs, monarchs pass through several larval stages and pupate before
emerging as adults. Monarchs develop faster in warmer temperatures
and slower in cooler temperatures and thermal stress has been shown
to affect monarch size and survival. We investigated how thermal
stress affected monarchs from eastern and western migratory and
S. Florida resident populations to explore potential differences
in the way each population responded to hot and cold stress. Groups
of siblings were raised from multiple females from each population
in controlled environment chambers under cold (19°C) moderate
(26°C) and hot (33°C) temperatures. We measured larval pupal
and adult survival pupal and adult mass and development time to
pupation and eclosion. Monarchs from different populations varied
in their responses to thermal stress. For example S. Florida monarchs
developed the fastest in the hot and medium treatment but not in
the cold treatment. Results showed significant effects of population
and temperature treatment on survival development time and pupal
and adult mass.
Monarch butterflies (Danaus plexippus) can
be found in temperate and tropical regions around the world. In
the United States the Rocky Mountains divide eastern and western
populations which annually migrate to the California coast and Mexico
to overwinter. The S. Florida population does not migrate and breeds
year round. Little research has been done to examine potential differences
between the monarch populations. These butterflies have been commercially
reared and shipped all over the country to be released at social
and festive occasions creating much concern over the potential ecological
impacts of this industry. Past research using monarchs from single
populations has shown that temperature stress affects larval development.
Cold temperatures slow growth rates and heat accelerates growth
and increases mortality. In this study we are trying to answer the
following questions:
1. How does thermal stress affect monarch survival development time
and pupal mass?
2. Do populations differ in their response to thermal stress?
3. Is there a genetic basis to temperature responses as indicated
by family-level effects?
Offspring from 5-12 females per population were taken
from Eastern Western and S. Florida monarchs and placed in plastic
containers on their hatch date. Each female’s offspring were
divided equally among three temperature treatments with 10-12 larvae
per treatment. Temperatures regimes were established within three
controlled environment chambers set to 19°C (cold) 26°C
(medium) and 33°C (hot). Survival was recorded as the number
of monarchs alive at days 3, 6, 9, pupation, and eclosion. After
all larvae had pupated in a container the pupae were all numbered
and weighed. Adults were held at room temperature for 24 hours after
eclosion and were then weighed. Development time was determined
by comparing the hatch date to the pupation date and eclosion date
for each individual.
-Populations responded differently to thermal stress
-Survival for all populations was highest in the medium treatment
and western monarchs had lower survival compared with Florida and
eastern monarchs (figure 1).
-Monarchs developed fastest in the hot
None given
We thank Leslie Real and John Lucchesi for use of the Biology Department
greenhouse and incubator. Nick Vitone, Katy Cook, and Zack Bauman
provided assistance with collecting wild female monarchs and conducting
the experiment. The Farrey family assisted in collecting monarchs
from S. Florida. We thank the SURE summer research program at Emory
University for supporting this research. This material is based
upon work supported by the Howard Hughes Medical Institute under
Grant No. 52003727 .
None given
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