The Economist - USA (2022-05-14)

The Economist May 14th 2022 Science & technology 75

terium  which  causes  stubborn  infections
in  people  with  cystic  fibrosis.  Theysus­
pected it was leading the body to mountan
ineffective  type­2  response  against  itand
wanted to know how it was doing this.
To explore the matter, they grew labora­
tory cultures of the sorts of epithelialcells
that  line  human  airways  and  monitored
their  gene­expression  profiles  when ex­
posed to LasB, a toxic enzyme producedby
the  bacterium.  They  found  that  LasBacti­
vated signalling pathways which drovethe
epithelial  cells  to  make  a  protein  called
amphiregulin.  This  forms  the  basisofa
thick mucus that excels at ensnaringpara­
sitic  worms.  It  also  recruits  immunecells
called  eosinophils,  which  are  adept at
attacking multicellular parasites. 

A type-2 error
That  finding  alone  is  interesting,  because
it  helps  explain  why  cystic­fibrosis pa­
tients  with  bacterial  infections  oftende­
velop  copious  mucus  in  their  lungs,even
though  this  does  nothing  to  counterthe
bacteria.  More  intriguing,  though, was
what happened when the researcherstried
growing  P. aeruginosaon  samples  ofthis
mucus.  So  long  as  LasB  was  present,the
bacteria did not merely thrive, but actually
consumed the mucus. Not only is P. aerugi-
nosatricking  the  immune  system  intoan
inappropriate  response,  it  is  also  feeding
on  the  result.  And  to  make  things  worse
still, Dr Medzhitov also discovered thatall
this immune manipulation makes thesur­
rounding tissues prone to allergy.
Allergic reactions are, essentially,exag­
gerated and inappropriate type­2 immune
responses. The researchers thereforewon­
dered whether the reactions being created
by LasB could cause lasting allergiestode­
velop.  To  find  out,  they  sprayed  micein­
fected  with  P. aeruginosawith  egg­white
protein (often used as an experimentalal­
lergen)  on  the  first  and  seventh  daysofa
four­week  experiment.  As  a  control,they
did  the  same  with  some  mice  genetically
engineered  to  lack  the  ability  to  produce
amphiregulin when exposed to LasB.
They  theorised  that,  in  the  absenceof
worms,  the  inflamed  epithelial  tissuesin
normal  mice  might  instead  identifythe
egg­white  protein  as  an  intruder.  Thisis
exactly  what  happened.  When  injected
with a small amount of egg­white protein
two  and  three  weeks  after  the  start  ofthe
experiment,  the  normal  mice  showeda
strong  allergic  response  to  it.  In  contrast,
the amphiregulin­free mice showed little.
These discoveries, fascinating in andof
themselves, also pave the way for newap­
proaches  to  treating  infections  in those
with  cystic  fibrosis.  Moreover,  if  onebug
has thus evolved a way to milk the immune
system,  the  chances  are  good  that  others
have done so too. Thus alerted, researchers
will be on the lookout for similar cases.n

Animalbehaviour

Buzz off!

I

ntheanimalkingdom,mimicsarea

dimea dozen.Stickinsectspretendtobe

twigs. Hawk­moth caterpillars resemble

venomoussnakes.Edibleheliconidbutter­

flies disguise themselveswiththe wing

patterns of noxious ones, and noxious

onescopyeachothertomakeiteasierfor

predatorstolearnwhatnottoeat.

Alltheseexamples,though,arevisual.

Auditorymimicryisrarer.But,ashede­

scribesinCurrentBiology, DaniloRussoof

theUniversityofNaplesFedericoIIthinks

hehasfounda novelcaseofit.Somebats,

hebelieves,mimicangrybees,waspsand

hornetsinordertoscareawayowlsthat

mightotherwiseeatthem.

DrRussofirstnoticedthepropensityof

greater mouse­eared bats to buzz a few

yearsago,whenhewascollectingthemin

mistnetstostudytheirecology.Thenoise

struckhimassimilartothesoundofhor­

netsthatinhabitedtheareaofsouthernIt­

aly hewasworkingin. Thatled himto

wonderwhetherbatbuzzingwasa formof

mimicrywhichhelpeditspractitionersto

scareoffwould­bepredators.

Totestthisidea,heandLeonardoAncil­

lotto,acolleagueatFederico II,firstre­

corded the buzzing that captured bats

madewhenhandled.Then,havingdonned

suitable protective clothing, they em­

barkedonthemoredangeroustaskofre­

cording thebuzzingmade,enmasse, by

four different  species  of  hymenoptera:

Europeanpaper  wasps;  buff­tailed  bum­

blebees;European  hornets;  and  domestic

honeybees. Computer  analysis  revealed

thatchiropteran and hymenopteran buzz­

eswere,indeed, similar. 

Forthenext part of their experiment Dr

RussoandDrAncillotto recruited the ser­

vicesof 16 captive  owls—eight  barn  and

eight tawny. Both  of  these  species  are

knowntohunt bats. 

Theresearchers  put  the  owls,  one  at  a

time, in an enclosure  equipped  with

branchesforthem  to  perch  on,  and  also

twoboxeswith  holes  in  them.  The  boxes

resembledthesorts of cavities in trees that

owlswouldexplore  in  the  wild  for  food.

Theyplaceda loudspeaker  alongside  one

oftheboxesand, after the birds had settled

in,broadcastthrough it five seconds of un­

interrupted bat  buzzing  and  a  similar

amountofinsect buzzing three times in a

row for each noise.  As  a  control,  they

broadcast in like  manner  several  non­

buzzingsounds made by bats. 

Duringthebroadcasts (which occurred

in random order)  and  for  five  minutes

thereafter,they videoed the owls. The vid­

eoswerethenanalysed, by an independent

observer,without  benefit  of  their  sound­

tracks. The results  were  unequivocal.

Whentheyheard both the bat buzzings and

thehornetbuzzings the owls moved as far

fromthespeakers as they could manage. In

contrast, when  the  non­buzzing  bat

soundswereplayed, they crept closer. 

DrRussoand Dr Ancillotto believe this

isthefirstreported case of a mammal us­

ingacousticmimicry to scare away a pred­

ator.Theystrongly suspect, however, that

itisnotunique. Anecdotes suggest several

birdsandalso  small  mammals,  such  as

dormice—particularly  species  that  dwell

intreesand,like  dormice,  in  rock  cavi­

ties—makebuzzing noises when their hid­

ey­holesaredisturbed.  This  has  not  yet

been documented  formally  as  acoustic

mimicry.But,given the propensity for ven­

omousbuzzing  insects  to  dwell  in  those

sortsofplaces  too,  and  also  the  fear  that

theseinsectsgenerate in other species, hu­

manbeingsincluded, Dr Russo thinks this

maywellbewhat is going on. He therefore

predictsthatwhen  these  other  buzzes  are

recorded and analysed  the  results  will

showthatacoustic mimicryby vertebrates

ofstinginginsects isfarmore widespread

thancurrently realised.n

Bats mimic bees, wasps and hornets to frighten owls

Batty, but it works