In butterfly battle of sexes, males deploy 'chastity belts' but females
fight back

Date:
September 3, 2020
Source:
Florida Museum of Natural History
Summary:
Some male butterflies seal their mate's genitalia with a waxy
'chastity belt' to prevent future liaisons. But female butterflies
can fight back.

Could this sexual one-upmanship ultimately result in new species?


FULL STORY ==========================================================================
Some male butterflies go to extreme lengths to ensure their paternity -
- sealing their mate's genitalia with a waxy "chastity belt" to prevent
future liaisons. But female butterflies can fight back by evolving
larger or more complex organs that are tougher to plug. Males, in turn, counterattack by fastening on even more fantastic structures with winglike projections, slippery scales or pointy hooks.


==========================================================================
It's a battle that pits male and female reproductive interests against
one another, with the losing sex evolving adaptations to thwart the
winner's strategies.

Could this sexual one-upmanship ultimately result in new species? It's a longstanding hypothesis and one that would help explain how butterflies
became so diverse. But it has proven difficult to test.

Ana Paula dos Santos de Carvalho, a doctoral student in the Kawahara
Lab at the Florida Museum of Natural History, tackled the question in
a study of mating plugs in brush-footed butterflies. She traced the
trait's evolution and analyzed the rate at which new species appeared
across the Acraeini tribe, a group of about 300 species. Unexpectedly,
lineages with and without mating plugs evolved at the same rate,
suggesting other factors such as habitat may be responsible for driving
the insects' diversity.

"I was expecting to see an association between plugs and new species
appearing faster, but my work suggested there was no link at all,"
Carvalho said. "Other studies had proposed a connection between sexual
conflict and diversity, so these results came as a surprise." Found in
about 1% of butterfly species, external mating plugs, also known as
sphragis, can resemble a scab or a blob of petroleum jelly in some
species while others take astonishingly architectural forms.

But they all serve the same purpose: enforcing female monogamy. Because a female butterfly fertilizes the majority of her eggs with sperm from her
last partner, males have a vested interest in blocking rivals. Females, however, stand to benefit by mating with more than one male. Another
partner may provide higher-quality sperm, and multiple mating events can increase the genetic diversity of offspring. Plus, females get a health
boost from the nutrients included in males' sperm packets.

To help guarantee their own successors, males in plug-producing
species omit the courtship behavior that often precedes mating in other butterflies.

Instead, "males pursue the females, grab them midair and drag them to
the ground," Carvalho said. After depositing their sperm, males excrete
a pre- molded mating plug, which hardens on the female's abdomen.

Plugs may indirectly constrain males as well. Making a mating plug is
an expensive investment of time and resources, potentially limiting how
many females a male can inseminate, she said.

Whether females can remove the plug requires further study, but in her fieldwork and museum specimen analysis, Carvalho noted the structures
were often partially broken or missing in species with smaller, more
delicate plugs.

In species with large, complex plugs, she usually found the structures
intact and rarely encountered a female without one -- a sign that males
may be "winning." But Carvalho's study revealed some female victories
as well. In the evolutionary family tree she constructed for Acraeini butterflies, she found evidence that mating plugs originated once across
the tribe and were subsequently lost in some species, suggesting a
successful female counteroffensive. Wide variations in the shape and
size of female genitalia also hint at attempts to render mating plugs ineffective.

"Butterflies and moths continue to surprise us," said study co-author
Akito Kawahara, curator at the Florida Museum's McGuire Center for
Lepidoptera and Biodiversity. "This study suggests we still have a lot
to learn about what drives insect diversity and the role sexual conflict
plays in evolution."

========================================================================== Story Source: Materials provided by
Florida_Museum_of_Natural_History. Original written by Halle Marchese
and Natalie van Hoose. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ana Paula S Carvalho, Ryan A St Laurent, Emmanuel F A Toussaint,
Caroline
Storer, Kelly M Dexter, Kwaku Aduse-Poku, Akito Y Kawahara. Is
Sexual Conflict a Driver of Speciation? A Case Study With a
Tribe of Brush- footed Butterflies. Systematic Biology, 2020;
DOI: 10.1093/sysbio/syaa070 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200903155503.htm

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