Sara Lewis: The loves and lies of fireflies

69,215 views ・ 2014-07-01

TED


Please double-click on the English subtitles below to play the video.

00:12
As a scientist, and also as a human being,
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I've been trying to make myself
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susceptible to wonder.
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I think Jason Webley last night called it
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"conspiring to be part of the magic."
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So it's fortunate that my career as a biologist
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lets me dive deeply into the lives
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of some truly wondrous creatures
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that share our planet:
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fireflies.
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Now, for many of you, I know that fireflies
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might conjure up some really great memories:
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childhood, summertime,
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even other TED Talks.
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Maybe something like this.
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My seduction into the world of fireflies
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began when I was back in graduate school.
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One evening, I was sitting out in my backyard
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in North Carolina,
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and suddenly, these silent sparks
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rose up all around me,
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and I began to wonder:
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How do these creatures make light,
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and what's with all this flashing?
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Are they talking to one another?
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And what happens after the lights go out?
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I've been lucky enough to answer
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some of these questions
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as I've explored this nocturnal world.
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Now if you've ever seen
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or even heard about fireflies,
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then you'll know how magically they can transform
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our everyday landscape into something
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ethereal and otherworldly,
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and this happens around the globe,
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like this hillside in the Smoky Mountains
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that I saw transformed into a living cascade of light
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by the eerie glows of these blue ghost fireflies,
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or a roadside river that I visited in Japan
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as it was giving birth to the slow, floating flashes
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of these Genji fireflies,
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or in Malaysia, the mangrove trees
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that I watched blossom nightly
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not with flowers
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but with the lights of a thousand — (Bleep! Bleep!) — fireflies,
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all blinking together
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in stunning synchrony.
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These luminous landscapes
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still fill me with wonder,
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and they keep me connected to the magic
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of the natural world.
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And I find it amazing that they're created
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by these tiny insects.
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In person, fireflies are charming.
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They're charismatic.
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They've been celebrated in art
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and in poetry for centuries.
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As I've traveled around the world,
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I've met many thoughtful people
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who have told me that God put fireflies on Earth
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for humans to enjoy.
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Other creatures can enjoy them too.
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I think these graceful insects are truly miraculous
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because they so beautifully illuminate
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the creative improvisation of evolution.
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They've been shaped by two powerful
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evolutionary forces:
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natural selection, the struggle for survival,
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and sexual selection,
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the struggle for reproductive opportunity.
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As a firefly junkie, the past 20 years
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have been quite an exciting ride.
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Together with my students at Tufts University
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and other colleagues,
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we've made lots of new discoveries about fireflies:
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their courtship and sex lives,
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their treachery and murder.
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So today I'd like to share with you
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just a couple of tales that we've brought back
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from our collective adventures
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into this hidden world.
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Fireflies belong to a very beautiful
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and diverse group of insects, the beetles.
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Worldwide, there are more than 2,000 firefly species,
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and these have evolved remarkably diverse
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courtship signals,
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that is, different ways to find and attract mates.
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Around 150 million years ago,
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the very first fireflies probably looked like this.
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They flew during the daytime
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and they didn't light up.
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Instead, males used their fantastic antennae
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to sniff out perfumes given off by their females.
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In other fireflies, it's only the females who light up.
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They are attractively plump and wingless,
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so every night, they climb up onto perches
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and they glow brightly for hours
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to attract their flying but unlit males.
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In still other fireflies, both sexes
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use quick, bright flashes to find their mates.
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Here in North America,
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we have more than 100 different kinds of firefly
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that have the remarkable ability to shine energy
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out from their bodies
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in the form of light.
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How do they do that?
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It seems totally magical,
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but these bioluminescent signals
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arise from carefully orchestrated chemical reactions
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that happen inside the firefly lantern.
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The main star is an enzyme called luciferase,
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which in the course of evolution
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has figured out a way to wrap its tiny arms
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around an even smaller molecule called luciferin,
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in the process getting it so excited
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that it actually gives off light.
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Incredible.
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But how could these bright lights
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have benefited some proto-firefly?
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To answer this question, we need to flip back
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in the family album to some baby pictures.
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Fireflies completely reinvent their bodies as they grow.
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They spend the vast majority of their lifetime,
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up to two years,
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in this larval form.
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Their main goal here, like my teenagers,
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is to eat and grow.
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And firefly light first originated
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in these juveniles.
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Every single firefly larva can light up,
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even when their adults can't.
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But what's the point
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to being so conspicuous?
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Well, we know that these juveniles
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make nasty-tasting chemicals
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that help them survive their extended childhood,
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so we think these lights first evolved as a warning,
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a neon sign that says, "Toxic! Stay away!"
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to any would-be predators.
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It took many millions of years
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before these bright lights
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evolved into a smart communication tool
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that could be used not just to ward off potential predators
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but to bring in potential mates.
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Driven now by sexual selection,
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some adult fireflies
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like this proud male
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evolved a shiny new glow-in-the-dark lantern
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that would let them take courtship
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to a whole new level.
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These adults only live a few weeks,
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and now they're single-mindedly focused on sex,
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that is, on propelling their genes
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into the next firefly generation.
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So we can follow this male out into the field
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as he joins hundreds of other males
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who are all showing off their new courtship signals.
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It's amazing to think that the luminous displays
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we admire
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here and in fact everywhere around the world
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are actually the silent love songs
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of male fireflies.
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They're flying and flashing their hearts out.
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I still find it very romantic.
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But meanwhile, where are all the females?
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Well, they're lounging down below
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surveying their options.
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They have plenty of males to choose from,
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and these females turn out to be very picky.
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When a female sees a flash
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from an especially attractive male,
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she'll aim her lantern in his direction,
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and give him a flash back.
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It's her "come hither" sign.
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So he flies closer and he flashes again.
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If she still likes him,
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they'll strike up a conversation.
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These creatures speak their love
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in the language of light.
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So what exactly do these females consider sexy?
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We decided to conduct some firefly opinion polls
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to find out.
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When we tested females using blinking LED lights,
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we discovered they prefer males
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who give longer-lasting flashes.
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(Laughter) (Applause)
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I know you're wondering,
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what gives these males their sex appeal?
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Now we get to see what happens
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when the lights go out.
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The first thing we discovered
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is that once a male and female hook up like this,
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they stay together all night long,
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and when we looked inside
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to see what might be happening,
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we discovered a surprising new twist
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to firefly sex.
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While they're mating,
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the male is busy giving the female
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not just his sperm
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but also a nutrient-filled package
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called a nuptial gift.
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We can zoom in to look more closely
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inside this mating pair.
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We can actually see the gift —
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it's shown here in red —
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as it's being passed from the male to the female.
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What makes this gift so valuable
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is that it's packed with protein
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that the female will use to provision her eggs.
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So females are keeping their eyes on this prize
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as they size up potential mates.
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We discovered that females use male flash signals
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to try to predict which males
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have the biggest gifts to offer,
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because this bling helps the female lay more eggs
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and ultimately launch more of her own offspring
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into the next generation.
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So it's not all sweetness and light.
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Firefly romance is risky.
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For the most part, these adult fireflies
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don't get eaten because like their juveniles
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they can manufacture toxins that are repellent
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to birds and other insectivores,
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but somewhere along the line,
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one particular group of fireflies
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somehow lost the metabolic machinery
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needed to make their own protective toxins.
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This evolutionary flaw,
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which was discovered by my colleague Tom Eisner,
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has driven these fireflies
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to take their bright lights out into the night
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with treacherous intent.
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Dubbed "femme fatales"
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by Jim Lloyd, another colleague,
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these females have figured out how to target
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the males of other firefly species.
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So the hunt begins with the predator —
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she's shown here in the lower left —
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where she's sitting quietly
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and eavesdropping on the courtship conversation
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of her intended prey,
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and here's how it might go.
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First the prey male flashes, "Do you love me?"
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His own female responds, "Maybe."
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So then he flashes again.
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But this time, the predator sneaks in a reply
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that cleverly mimics exactly what the other female just said.
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She's not looking for love: she's looking for toxins.
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If she's good, she can lure this male close enough
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to reach out and grab him,
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and he's not just a light snack.
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Over the next hour, she slowly
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exsanguinates this male
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leaving behind just some gory remains.
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Unable to make their own toxins,
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these females resort to drinking the blood
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of other fireflies to get these protective chemicals.
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So a firefly vampire,
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brought to you by natural selection.
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We still have a lot to learn about fireflies,
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but it looks like many stories will remain untold,
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because around the world, firefly populations
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are blinking out.
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The main culprit: habitat loss.
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Pretty much everywhere, the fields and forests,
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the mangroves and meadows that fireflies need to survive,
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are giving way to development and to sprawl.
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Here's another problem: we've conquered darkness,
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but in the process, we spill so much extra light out into the night
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that it disrupts the lives of other creatures,
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and fireflies are especially sensitive to light pollution
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because it obscures the signals
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that they use to find their mates.
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Do we really need fireflies?
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After all, they're just one tiny bit
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of Earth's biodiversity.
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Yet every time a species is lost,
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it's like extinguishing a room full of candles
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one by one.
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You might not notice
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when the first few flames flicker out,
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but in the end, you're left sitting in darkness.
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As we work together to craft a planetary future,
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I hope we can find a way
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to keep these bright lights shining.
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Thank you.
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(Applause)
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