California mice eat monarch butterflies
This newly discovered mouse-butterfly interaction suggests that western monarch decline could disrupt ecosystems in unanticipated ways

Date:
January 6, 2022
Source:
University of Utah
Summary:
At the largest winter monarch aggregation in central Mexico,
scientists have observed that rodents attack monarchs that fall
to the ground.

Biologists have now discovered that the western harvest mouse also
eats grounded monarchs. Documenting this new feeding behavior is
a reminder of little we know about the interactions that may be
lost as insect populations decline.



FULL STORY ========================================================================== Monarch butterflies possess a potent chemical armor. As caterpillars,
they eat plants filled with toxic cardenolides that build up in their
bodies and make them unpalatable to most -- but not all -- predators. In central Mexico, where the largest winter monarch aggregations occur,
scientists observed that rodents attack monarchs that fall to the
ground. In particular, the black-eared mouse (Peromyscus melanotis)
specializes in these bitter-tasting insects, eating as many as40 per
night.


==========================================================================
In a new study, University of Utah biologists found that mice at
California monarch overwintering sites can also consume monarch
butterflies. Working at one of the largest monarch aggregations outside
of Mexico, Pismo State Beach Monarch Butterfly Grove, the researchers discovered that the western harvest mouse (Reithrodontomys megalotis)
also ate the grounded monarchs. However, with the precipitous decline
in western monarch populations, this butterfly buffet may be in jeopardy.

The authors do not think that rodents are contributing to the western
monarch decline, nor that the monarchs are the only thing that mice
can eat. Rather, documenting this new feeding behavior is a reminder
of how little we know about the interactions that may be lost as insect populations decline.

"We are in an insect apocalypse right now. There are estimates that 40%
of studied invertebrate species are threatened and that over 70% of
flying insect biomass is already gone. This is devastating on its own
and is also going to have enormous impacts on the other organisms that
feed on insects," said Sara Weinstein, the postdoctoral researcher who
led the study.

"Western monarchs and other western butterflies need conservation
attention and part of that awareness-raising is illuminating the many
ways these animals are interconnected to other insects, birds, mammals,
as well as our human communities. This study helps us appreciate more
deeply how fewer butterflies means less food for other native animals"
said Emma Pelton, senior conservation biologist at the Xerces Society.

The study published in the journal Ecology on Dec. 12, 2021.

To study mouse-monarch interactions, the researchers first trapped
rodents in the grove in February 2020. The rodents were released, but
their feces were kept to screen for monarch DNA -- which they found in
one sample. This first survey occurred in late winter as monarchs were
leaving the aggregation and few remained for mice to munch. Weinstein
and colleagues intended to return the following fall during peak monarch season. However, after years of decline, the western monarch population crashed.

"At a site where 100,000 butterflies used to roost, in 2020 there
where were fewer than 200 monarchs. So, we had to change tactics,"
Weinstein said. "We tested whether rodents would feed on the butterflies
using captive-reared monarchs." Weinstein set up lab-reared monarch
carcasses under camera traps and captured footage of wild harvest
miceeating butterflies. She also caught a half dozen mice and offered
them monarchs. The mice ate monarchs, typically favoring the abdomen or
thorax, high-calorie parts with fewer toxins.

"Many rodent species are likely to have some resistance to cardenolides
in monarchs, due to genetic changes at the site where these toxins bind,"
said Weinstein. "The Pismo Grove is one of hundreds of western monarch aggregation sites, and it seems likely that, at least in the past, rodents throughout the western monarch range may have supplemented their winter
diets with monarchs.

If you can handle the cardenolides in a monarch, their bodies are full
of fat and offer a pretty good meal." This meal will be a lot harder
to find, as over 90% of western monarchs have disappeared in the last
40 years. The missing beauties will surely impact the ecosystem that
depends on them for food.

"When monarch numbers crashed last year and the project started to
go sideways, Sara cleverly rescued it by growing her own monarchs
and obtaining frozen ones from researchers," said Denise Dearing,
senior author of the study and Distinguished Professor of biology
at the U. "Her creative solution advanced our understanding of the
interactions between mice and monarchs, even during a time of limited
monarch numbers. It lays the groundwork for future research in this area." ========================================================================== Story Source: Materials provided by University_of_Utah. Original written
by Lisa Potter.

Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* Mice_eating_monarch_butterflies ========================================================================== Journal Reference:
1. Sara B. Weinstein, M. Denise Dearing. Harvest mice ( Reithrodontomys
megalotis) consume monarch butterflies ( Danaus plexippus
). Ecology, 2021; DOI: 10.1002/ecy.3607 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220106143714.htm

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