The accessory glands of the female genital tract in Aeshna juncea (L.) and A. grandis (L.) (Anisoptera: Aeshnidae)

2005·3 MB·English

by  Åbro, A

Odonatologica34(2):103-110 JuneI,2005
Theaccessory glandsof thefemalegenital tract
inAeshna juncea(L.) andA. grandis(L.)
(Anisoptera: Aeshnidae)
A.Åbro
Division ofAnatomy,DepartmentsofBiomedicine,UniversityofBergen,Jonas Liesvei91,
N-5009Bergen,Norway
ReceivedJune11,2004/RevisedandAcceptedDecember2,2004
Themicro-anatomyofthe $ accessory glandsinadult A. junceaand A. grandisis
similarbutthesizeoftheA. grandisglandsisclearlylargerthan that ofA.juncea.The
secretorycellsconstituteasimplecolumnarepitheliumsurroundingacuticle-lined lu-
men.The glandularepitheliumisprovidedwith apeculiarsystemof deep,narrow,
intercellular cryptsbordered with microvillar cell membranes. Lipidsreleased tothe
cryptlumenarepresumablyforcedinto thecentralglandlumenby contractions ofthe
muscularnetworkattachedtotheoutsideofthegland.Theefferentductofeach gland
that openstothedistalpartofthevaginahasacomplicatedmuscularapparatus,prob-
ablyservingasapump.The secretedsubstancesaccumulate in thecentralglandcavity
mainlyduringthepre-reproductivephase,whichthedragonfliesspendawayfromwater.
The secretioncontains substanceswithwax-likeproperties andbecomes darkened by
osmication. Secretorycellsappeartopossessalimited lifespan;scatteredcellsinproc-
essofdyingoccuralready duringtheearlyreproductivephase.Inthelatereproductive
phasemostoftheglandularepitheliumpresentsadisintegratedappearance.Thereisno
cell renewal intheglandinthecourseofadultlife. The patternofcell deathindicatesa
decompositionbyapoptosis.Besidescontributingtoinvestmentoftheeggs,theglands
presumablyintervene alsoinotheraspectsofthereproductiveprocesses.
INTRODUCTION
Inthedragonfly Aeshnajuncea(L.),apairofconspicuous accessory glandsmake
upanintegral partofthefemalegenital tracttogether withsperm-storingorgans
(ABRO, 2004a).However, theseglandsdonotseemtohavereceivedanyparticular
attentionfromformerworkers concernedwith dragonflyanatomy(TILLYARD,
1917;WHEDON, 1919;WINKELMANN, 1973).Theaimofthepresentstudy
hasbeentoprovide furtherinformationon thestructure andfunctionof thesene-
glected glands.
104 A.Abro
Preliminaryobservations havedisclosedthatthefemaleaccessory glandsofOdo-
natamightvaryconsiderably betweendifferentspecies. Thetwo aeshnidspecies A.
junceaandA. grandis arepresumed tobecloselyrelated. Theaccessory glandsof
bothwereexaminedinordertorevealany dissimilaritiesintheirmicro-anatomy.
MATERIALANDMETHODS
Ovipositingfemales ofAeshnajuncea(L.)andA. grandis(L.)werecapturedatabreedingsitenear
Bergen,westernNorway. Also,atclearingsin surroundingwoodland,afew specimenswerecollected
duringtheirpre-reproductivephaseintheearlyflight season(lateJune- early July).Mostspecimens
werefixed immediatelyinthefieldbyinjectingcoldfixativeintotheposteriorabdomenwith afinehy-
podermicneedle. The femalegenitaltractwasnextdissected inalargervolumeofthesamefixative.As
acontrol,freshtissuesofsomespecimens, anaesthetized incarbon dioxide,weredissected.
Thefixative wasmadeup of3% glutaraldehydein0.2 M cacodylatebuffer (pH 7,3)with0.17 M
sucroseadded;postfixationtookplaceina 1%solution ofosmiumtetroxide inthesamebuffer.Speci-
mensweredehydratedthroughagradedseries ofethanolandclearedinpropyleneoxide,embedded in
epoxyresin,and sectionedwithadiamondknife. Semi-thinplasticsectionsforlightmicroscopy,from
material processed for electron microscopy, were stained
in a 1%solution oftoluidine blue. Ultrathin sections for
electron microscopywerecontrasted with uranyl acetate
andleadcitrate.
RESULTS
Fromthegrossanatomyofthefemalegenital
tractitisscarcely possible todistinguishbetween
AeshnajunceaandA. grandis, exceptfortheac-
cessory glands which in A. grandis are clearly
larger thanthose of A. juncea. However,their
micro-anatomy issimilar.Thepaired accessory
glandsoftheAeshnafemalearesituatedventral-
ly in the ninthand tenthabdominalsegments.
Infreshmaterialthelength ofeach gland from
the ductproximally to thetip ofthetailmeas-
ures, for A. grandisintherange2.9-4.0mm,for Fig. 1.Aeshnajuncea:distalregionof
A.juncea 1.9-2.7mm. the adultfemale genitaltractshowing
theposteriorlysituatedaccessoryglands
Thepositioninsituoftheaccessory glandsof (Agl); lateral (left)and dorsal (right)
A. junceahasbeendrawn in outlinefromsev- views. Based ondissections ofseveral
eral dissectionsoftheadultfemalegenitaltract specimens,fixedandstoredin buffered
(Fig. 1).Insomeindividualsthetwoglands are glutaraldehydesolution. Surrounding
ofuneven size. musculature and nerves are omitted.
G: position of theeighthabdominal
Each gland isflattenedwithfoldsand clefts. 8
ganglion;od: oviduct;rs; seminal re-
Whensectionedtheyappearlobulatedandmade ceptaclewith accessory sacs; v;vaginal
up of microscopic subunitsrecognized as sac- canal;7-10;abdominal segments.[Scale
bar2.0mm].
Accessory glandsinAeshnafemalegenitaltract 105
cularout-pocketings calledacinioralveoli(Fig. 2). Thegland unitsare formedby
asinglelayer ofcolumnarepithelial cellsthatsurroundacentrallumen, linedwith
athincuticlethatisnot incontact withthecellapices, givingrise to asubcuticular
space(Figs3,4).Thecentralglandularcavityexhibitsnarrowbranchesandis con-
nectedto ashortefferentductopening to thedistalpartofthevagina. Thecavity
system, carrying theglandularsecretion, is initsentirety cuticle-lined.Thefemale
accessory glandsofaeshniddragonfliesareofectodermalorigin,having developed
by invagination of theintegument.
Infresh material,thegland cavity containsagranulated substancedispersed in
a liquid. Fixed glands exhibit an osmiophilic content. Components ofthe secre-
tionindicatewax-like properties. Electronmicrographs show afinegranular pre-
Figs2-4.Thefemaleaccessorygland:(2)Aeshnajuncea:theglandwiththeefferentductcutoffnear
its outlettothe vagina(brokenline),tr,remainingtrachealtrees.Tissue fixedin bufferedglutaralde-
hydesolution;unstained whole-mount incacodylatebuffer.Viewedintransmittedlight,brightfield.
[Scalebar400pm]; —(3)A.juncea:view ofaglandlobule;pre-reproductivephase.Thelumen(L)
containsexpelledsecretion.Notedeepintercellular cryptswithsecretedmaterial,(arrows), ac:glan-
dular acinus;bl:basal lamina;c:liningcuticle;E:glandularepithelium.Toluidine blue.[Scalebar25
pm);- (4)A.grandis:partofgland(reproductivephase)showingtwomusclefibres(mu)connected
with acommoninsertion tothe basallamina (bl)betweenadjacentacini, c:cuticle;E:glandularepi-
thelium;L: lumen.Toluidine blue.[Scalebar25pm).
106 A.Abro
cipitate onthecuticle(Fig.5).
Thecolumnargland epithelium, mostly withovoidnuclei,rests onaprominent
basallamina.Inelectronmicrographsthecellsexhibitanapical surfacewithsmall,
intermittent, poorly-developed microvilli.Themicrovillarborderextendsintodeep
intercellularcrypts, linedbymicrovillarcellmembranes(Fig. 5)reaching close to
thebasalplasmamembrane.Inearly adultlife,theglandular epithelialcellscontain
Fig,5.Aeshnajuncea:finestructureofthe glandularepithelium;pre-reproductivephase.Surveyviewof
theepitheliumwith itsintercellularcrypts(cr)linedwithmicrovilli,fromthesamespecimenasinFig.3.
Intraplasmiclipidispreservedassphericalglobulesstainedblack,presumablyowingtoconstituentsof
unsaturated fattyacids.Inthecryptlumen,accumulations ofexocytosedlipids(whiteasterisks),as:ac-
cumulated secretion;bl:basallamina;C:cuticle;L: glandularcavitywithsecretion;mu:musclefascicle;
n:epithelialnucleus; si:subcuticular lumen.[Scalebar 10pm].Inset:Enlargementshowingmicrovillar
borders. Eachvillusholdsatubuleofsmoothendoplasmicreticulum (arrows),[Scalebar5pm].
Accessory glandsinAeshnafemale genitaltract 107
Figs 6-7.Aeshnajuncea: (6)Electron micrographofstrongly vacuolated glandularepithelium;re-
productivephase.Some intraplasmaticdarkened lipidsarestill present. Intheglandcavity thereis
someresidual secretion(L).bl: basallamina;c:cuticle;n:epithelialnucleus;v:vacuole. [Scalebar20
pm]; —(7)Theefferentduct,transverselycut,displayingtissuecoatsaroundthefolded,cuticle-lined
lumen (L).Theborder between theepitheloidcells(E)and themusculartunic (mu)isindicated by
asterisks, bl: basallamina;C:cuticle;fc:fatcell;mf: musclefibres;ne:corticalnervoustissue.[Scale
bar20pm],— Inset:Enlargementshowingcuticularintimanext tosomeresidual secretioninthe
duct lumen(L).[Scalebar5pm].
108 A.Abro
organized arraysofgranularandsmoothendoplasmic reticulum,Golgicomplexes,
numerous mitochondriaand membrane-boundlipidinclusions (Fig. 5). Tubular
elementsofagranularendoplasmic reticulumcanbeseenextending intothemicro-
villialmostto thetip(Fig. 5, inset). Minorlipidinclusionsgather intheglandular
cytoplasm nearthecrypts; large lipid depositscanbe seeninthe nearbycrypt lu-
men(Fig. 5).Secretedlipidinthecryptsandalsointhesubcuticularspaceislikely
to traversethecuticleandaccumulateinthemaincavity.
Surrounding theglandularunitsare muscularfascicles, forming anetworkwith
insertionsonthebasallaminabetweenadjacent acini(Fig. 4).In addition,adven-
Figs8-9. Aeshnajuncea:electron micrographs:(8)The wall ofthe efferentduct showingepitheloid
cellswithcytoskeleton(cs)andglycogendeposits(g).Cellapicesfurnishedwithmicrovilli (mv)against
cuticle(C); eachvilluscontainsatubuleofsmoothendoplasmicreticulum. Theborderbetween epi-
theloid andmuscular (mu)layersisindicatedbyasterisks, bl:basal lamina;N:nucleus ofepitheloid
cell;ne:corticalnervetissue.[Scalebar5pm]; —(9)Thewalloftheefferent ductshowingpartofa
muscle fibrewithnerveterminals(openarrows). Withinthe axonterminals(ax)areseennumerous
small (synaptic?) vesicles. F:muscle fibril;Z:muscularZ-band. [Scalebar 2pm].
Accessory glandsinAeshnafemalegenitaltract 109
titiouscellscarry tracheoles.Differences occur in thehistological appearanceof
glands fromvariousindividuals, depending onwhetherthey are captured during
pre-reproductive orreproductive phase. Secreted substances seem to accumulate
inthecentralglandularlumenmainly duringthepre-reproductive phaseofadult
life.Inearlyreproductive phase, glandularcellsoffunctionaldeclinecouldberec-
ognized as localatrophy. Lateronthereoccurs cytoplasmic vacuolation(Fig. 6)
and/orchromatincondensationofscatterednucleiin theglandularparenchyma,
indicativeof dying by apoptosis. Thepresenceof apoptoticcells ischaracterized
bynucleiandcytoplasm brokenupintoseveralcompactfragmentsandanumber
of smallmembrane-boundglobules.
Theefferentductofthegland isbuiltupofconcentrictissuecoatsaroundacuti-
cle-lined,folded-uplumen.Thecuticleisratherthick,fibrousandwithanelectron-
densecuticularintima(Fig. 7). Beneaththecuticleisasimplelayeroftallepitheloid
cells, bordering amusculartunic(Fig. 8). Theepitheloid cellshaveinterdigitated
lateralborders anda foldedapical membranewith microvilli, eachcontaining a
tubuleofsmoothendoplasmic reticulum(Fig. 8).Inthecellsareintraplasmatic de-
posits ofglycogenandlarge,branchedbundlesofcloselyspaced parallel microtu-
bulesandinterspersed microfilamentsthatrunfromthecellbase upward through
thecell body to end atthe apex, apparentlyserving as cytoskeleton (Fig. 8).The
layer ofmusclefibresappearsthickestaroundtheproximalpartof theduct. Mus-
clefibresandepitheloid cellsarecloselyattachedwithoutabasallaminainbetween
butthereis aborderoftightly-woven texture withsomeshortbranching fingers
ontheepitheloid side oftheborder(Fig. 7). Musclefibresare seen concentrated
nearest to the epitheloid layer. A corticalsheathofnerve tissue canbe seen close
to thebasallamina:axons accompanied along theircourse by neuroglial cells and
alsoneuromuscularjunctions(Figs 7-9).Outsidethemusculartunicis anirregular
investmentoffatcellsandtracheolarcells(Fig. 7).
DISCUSSION
Theaccessory glandsofthefemalegenitaltractaretypicalexocrineglandsandare
presumed tohavemultiple functionsinthereproductive processes(ABRO, 2004a).
Theglands are thought to secrete the bulkoftheir production early inadult life
andstore itinthecentralcavity;laterthey secrete continuously atalowrate. Un-
dercertainconditionstheymight bestimulatedto secrete larger volumesoftheir
products. However, thereare no morphological criteriaby whichitis possible to
determinewhetheragivengland isstimulated.Thebranching cavitysystem ofthe
gland anditsefferentductcarry thesecretionto thedistal vaginalcanal. Thelip-
idsarepredominantly releasedto theintercellularcrypts byexocytosis. Fromthere
they arelikely tobesqueezed outtothesubcuticularspaceandthenthrough pores
in thecuticleto thecommongland lumenby contractions ofthemuscularreticu-
lumsurrounding theglandularlobules/aciniandthemuscularapparatusoftheef-
110 A.Abro
ferentduct.Blackening ofthesecretionby osmiumfixativesindicatesthepresence
ofunsaturatedlipids. TheAeshnaglandsexhibitseveral morphological featuresin
commonwith theegg-waxing glands ofixodid ticks (BOOTH, 1989).Thus they
possess similarcrypt systems in their glandularepithelia, thecells ofwhichbear
microvillicontaining tubularelementsofsmoothendoplasmic reticulum.Smooth
reticulumisknown tobeinvolvedinlipid metabolism(FAWCETT, 1981).Theef-
ferentductsofA.juncea andA. grandisglands exhibitstructuralsimilarityto that
ofthe damselflyPyrrhosoma nymphula(ABRO,2004b)butareofgreater size, so
thateachinvesting tissuecontainmorecellularelements.Themanynerveterminals
to themusclefibres, apparentlywithpolyneural innervation, indicateanintricate
nervous control.Theductprobably functionsasapump(ABRO, 2004b). Likethe
glandular epithelialcells, theepitheloid cellsoftheefferentductare provided with
microvillicontaining tubulesof smooth endoplasmic reticulum, whichindicates
thatbothcelltypesareof commonorigin.
Theaveragelongevity oftheadultAeshnafemaleisnotknownbutwillcertainly
not extendbeyond afewweeks. As to the activity ofthegland, thepresentstudy
indicatesthatmostoftheproduced substancesaccumulateintheglandularlumen
duringthepre-reproductive phase,whichthe dragonfliesspend away fromthewa-
ter.Secretory gland cells seemtopossessalimitedlife spanofafewdays, followed
byafunctionalandstructuraldecline.Thusdecompositionofscatteredsinglecells
in the gland parenchyma startsearly in thereproductive phase. Thisbecomes an
accelerating trendinthecourse ofthereproductive phase. Inthelatereproductive
phasemostofthegland exhibitsdisintegratingtissues.Renewalofsecretorycellsin
theadultgland appearsnotto occur.Theshortadultlifetimepresumably doesnot
need proliferation ofundifferentiatedrenewalcells. Degradation withintheglan-
dularepithelium appearstoaffectindividualcells ratherthantractsofcontiguous
cells dying spontaneously by apoptosis. CelldeathintheAeshnaaccessory glands
lookslikeastochasticprocess withdifferentprobabilities of dying.
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