The Odonata of Bioko, Republic of Equatorial Guinea, with the description of fan-shaped setae on early instar Libellulidae larvae

10 Pages·2001·2.1 MB·English

by  Brooks, S J

Odonatologica30(1): 29-38 March I, 2001
The Odonataof Bioko, Republic of Equatorial
Guinea, with the description of fan-shaped setae
on early instar Libellulidae larvae
S.J. Brooks and K.A. Jackson
Department ofEntomology,The Natural History Museum, Cromwell Road,
London, SW7 5BD, United Kingdom
Received July 7, 2000 /Reviewed and AcceptedAugust 31, 2000
A checklist of48 spp. recorded from the island of Bioko (3°30’N 8°40’E),
based on historical records compiledby Dr ElliotPinhey and augmentedby a
collection made in March-April 1999, is presented, togetherwith notes on the
distribution ofthe spp. onthe island. The Odonata fauna apparently comprises2
elements,an uplandfauna which includes 6 spp. that only occur above 500 m,
and alowlandfauna of 17 spp., noneofwhich occurs above 500 m. Afurther 13
spp. have been found in both lowland and uplandsites. There are insufficient
publisheddata ontheremaining 13 spp.to assign them to either ofthese faunistic
elements. In addition,uniquefan-shaped setaeon the dorsumofthe head,thorax
and abdomen ofearly instar libellulid larvae are described. These setae arethought
tobe mechano-receptorsthatare held above the sediment to detect the presence
ofprey and current flow while thelarva remains buried.
INTRODUCTION
BiokoisasmallwestAfricanislandsituatedabout40km offthecoastofCameroon
intheGulfofGuinea(3°30’N8°40’E).Theislandwas formerly knownasFernando
Pooandnow forms partof theRepublic ofEquatorial Guinea, togetherwith Rio
Munionthemainlandandthemoresoutherly islandofAnnobon.Biokocovers an
area ofabout2000km2and is about72 km North-to-Southand 35 km West-to-
East.Thereare threevolcanoes,Basile (3011 m)intheNorth,andCalderdeLuba
(2261 m) andBiao(2001 m) intheSouth.Mostofthehumanpopulation lives in
the littorallowlands below500 m in theNorth oftheisland. Here much ofthe
forestissecondary, orhasbeenreplaced bycocoaplantations andotheragricultural
crops.Above500mandintheSouth, whichis largely inaccessibleexcept by foot,
are extensive tracts ofprimary tropical rain forest. Biokois one ofthe wettest
30 S.J. Brooks & K.A. Jackson
places on earth.Annualrainfall, whichcanexceed 14m (DE TERAN, 1962) is
seasonal, mostly falling between July and November. There are 247 rivers and
streamsontheisland,ofwhichabout58%flowduringthe dryseason(McCALLet
al.,1998).Becausetheislandis sosteep,mostoftheserivers arefast flowing even
inthecoastal lowlands.Average annualcoastal temperaturesareabout25°C.
Bioko supports a rich biota with some endemic species. The island has a
significant levelofspecies endemism, running atabout 1-3%inthose groupsso
farstudied,including birds, reptiles, amphibians andfish(JONES, 1994). Partof
theisland hasbeen designated as aUNESCO World Heritage Conservation Site.
The dragonflies of Bioko havebeen relatively well-studied, and the faunawas
most recently reviewed by PINHEY (1971; 1974), although he never actually
visited the island himself. PINHEY (1974) listed 42 species with provisional
records for an additional four species. These records were based mainly on
collectionsmade by W. Hartwig, who lived on theisland from 1957-1963,and
from two expeditions to Bioko, one in 1900-1902by LeonardoFea (MARTIN,
1908) and the other by W.H.T. Tams in 1932(LONGFIELD, 1936).Of the 42
species recorded, six were describedfrom theislandandthought to beendemic.
However, recent taxonomicrevisions and further collections from theAfrican
mainlandhaveshownthat infact noneoftheBiokoanodonatespecies isrestricted
totheisland(VICK, 1999).Theonly endemictaxon nowrecognised is Chlorocypha
cancellatainsulana,asubspecies ofC.cancellatawhichis widespread inequatorial
AfricasouthwardstoZaire(PINHEY.1974).
We were inBiokoto conduct anenvironmentalimpact assessment onbehalfof
theWorld Health Organisation African Programme for Onchocerciasis Control
(WHO/APOC).Thevisitwas madebetween23Marchand9April1999and,although
itwas relatively short, wewereableto collectOdonatafrommanymoresites than
hadbeenvisitedby previous Odonatacollectorsto theisland.Thepurposeof this
paperis to update thechecklistofOdonatarecordedfrom Biokoandto provide a
more detailed account ofthedistributionofOdonataaround theisland than has
been possible before. In addition, we take this opportunity to describe some
extraordinary fan-shaped structures that we foundon the dorsumofearly instar
libellulidlarvae collectedduringour fieldwork.
METHODS
Adult dragonfliesweresampled usingastandard butterflynet.Adult dragonfliescanbe difficult
andtime-consumingto collect so, in order tooptimise speciesrepresentation,upto six specimens
ofeach taxonrecognisablydifferent in the field were collected at each samplinglocality. Special
efforts were made to sample pairs in tandem so that females could be associated with males.
Samplescollected in this mannerare not quantitativebut give a good indication ofthe distribution
ofadult Odonata (BROOKS, 1989). Odonata larvae were sampled from fast-flowingrivers by
standard kick-sampling (ENVIRONMENT AGENCY, 1997). At each sampling station 20 ten-
-second subsamples were taken across the stream channel. Slow-flowing sections and standing
Odonata of Republicof EquatorialAfrica 31
water were sampled by
sweeping amongst vegetation.
Samples werecollected using
a 250pm mesh net and were
sorted within a few hours of
collection sospecimens were
alive and very small larvae
were easy to locate as they
moved around the sortingtray.
To estimate the distribution
of Odonata onBioko a total
of 17 localities was sampled
mostly in the northern half
oftheisland (Fig. 1), Mostof
the sites sampled had similar
physical characteristics,being
relatively fast-flowing
streams dominated by riffle
sections, below 500 m in
altitude. Samples were taken
from both open, sunny
sections and tree-shaded
reaches. Odonata were also Fig. 1. The island of Bioko,EquatorialGuinea, showingmajor
sampled from slow-flowing rivers and towns, and the three volcanic peaks. The numbers
and standing water sites, but indicate the sampling localities: (1) Rio Edda;- (2)Rio Lada;-
these were few on the island (3) Rio Musola (this river was sampled throughout its length
because of the steep topo- from upstream ofMusola villageto the river mouth; - (4) Rio
graphy. One site at about 600 Apu;- (5)Malabo; - (6)Rio Matadores;- (7)RioSampaca; - (8)
m, and two at about 1500 m Rio Tiberones-Uruabella;- (9)RioTimbabe; - (10) Rio Cope;-
waneriendaiclsaotiosnamopflethdetoinpflruoevnidcee (R1i1o)SRaioboG;-arc(i1a5;)-Ba(1s2il)d;R-iab(1a6)ReRsieorvIolaird;y-i;(1-3)(1R7)ioRRioumTae;o.- (14)
of altitudeon dragonfly dis-
tribution,but few high altitude sites wereaccessible.
Adult Odonata were identified using an unpublishedkey to the Odonata ofCameroon (VICK,
1996) andidentifications wereconfirmed by reference to the Odonata collections atThe Natural
History Museum,London. Odonata larvae wereidentified to family or genus withreference to
DEJOUX et al. (1981), ASKEW(1988) and CHELMICK (1998).
CHECKLIST OF ODONATA RECORDED FROM BIOKO
Approximately 260 adultspecimens werecollected,representing 24 species. A
listoftheseandtheirdistribution,togetherwithalistofalltheOdonatarecorded
fromtheislandinthepast,ispresented below.Inaddition,47larvaewerecollected.
These were identifiedas Protoneuridae, Pseudagrion, Chlorocypha, Sapho,
Paragomphus, TetratheminaeandOrthetrum.We also collected 10specimens of
early instarlibellulidlarvae fromRioMusolaupstream ofMusolavillage.
Numbers refer to localities marked on map (Fig. 1). Records from P1NHEY (1974) are
indicated with p, other records are fromthe present study. Speciesmarked * were notpreviously
recorded from Bioko.
32 S.J. Brooks & K.A.Jackson
Protoneuridae Localities
Chlorocnemis nigripes Selys, 1886 3;7; 8P; 15
*Elattoneura balli Kimmins, 1938 2; 3;4; 6;7; 10; 11; 13; 14; 15
Coenagrionidae
Agriocnemis maclachlani Selys, 1877 3P; 6; 14
Ceriagrion glabrum (Burmeister, 1839) 6;12P; 16p
Enallagma buchholzi Pinhey, 1971 16p
Pseudagrion angelicum Fraser, 1947 12P
Pseudagrion epiphonematicumKarsch, 1891 no locality citedp
Pseudagrionkersteni (Gerstaecker, 1869) no locality citedp
Pseudagrion melanicterum Selys, 1876 3; 4;6; 7 ; 8; 9; 10; 11; 13; 14; 15; 16
*Pseudagrion serrulatum Karsch, 1839 16; 17
Pseudagrion sjostedti Forster, 1906 12P
Chlorocyphidae
Africocypha lacuselephantum (Karsch, 1899) I6P
Chlorocypha cancellata (Selys, 1879) 2; 3;4; 9; 10; 13; 14; 16p
Chlorocypha curta (Hagen, 1853) no locality citedp
*Chlorocypha cyanifrons (Selys, 1873) 15
*Chlorocypha rubida (Hagen, 1853) 3; 4;6
Calopterygidae
Sapho orichalcea McLachlan, 1869 3;4;7; 15
Umma longistigma (Selys, 1869) 4
Umma mesostigma (Selys, 1879) 8P; 15; 16; 17
Umma purpurea Pinhey, 1961 8P
Gomphidae
Paragomphus abnormis Karsch, 1890 16p
Paragomphus sp. indet. (larva) 3; 4; 13
Aeshnidae
Acanthagyna cylindrata (Karsch, 1891) 5
Anax imperatorLeach, 1815 3; 12p; 13
Hemianax ephippiger (Burmeister, 1839) nolocality citedp
Corduliidae
Macromia aeneothorax (Nunney, 1895) 16p; 17
Libellulidae
Acisoma trifidumKirby, 1889 3P; I2P
Allorhizucha klingi Karsch, 1890 3; 4; 14; 15; 16p
Brachythemis leucosticta (Burmeister, 1839) no locality citedp
Chalcostephia flavifrons Kirby, 1889 no locality citedp
Crocothemis erythraea (Brulle, 1832) no locality citedp
Diplacodes lefebvrei (Rambur, 1842) 12p
Hadrothemis camarensis (Kirby, 1889) 5P
Orthetrum africanum (Selys, 1887) 5P
Orthetrum austeni (Kirby, 1900) 12; I6P
Orthetrum chrysostigma (Burmeister, 1839) no localitycitedp
Orthetrum guineenseRis 1910 no localitycitedp
Orthetrum juliaKirby, 1900 3; 4; 6; 7; 8;9;10; 11; 12; 14; 15; 16p; 17
Palpopleura lucia (Drury, 1773) 3P; 5P; 8; 12; 16p
Pantala flavescens (Fabricius, 1798) 12
Thermochoria equivocata Kirby, 1889 no localitycitedp
*Tholymis tillarga (Fabricius, 1798) 12
Odonata of Republic ofEquatorialAfrica 33
*Trapezostigma basilaris (Palisot deBeauvois, 1805) 12
Trithemis aconita Lieftinck, 1969 1; 3;4; 6;7;8;9; 11; 14
Trithemis arteriosa (Burmeister, 1839) nolocalitycitedp
Trithemis dichroa Karsch, 1893 3P; 7; 9; 16p
Trithemis furva Karsch, 1899 5P
Trithemis hartwigi Pinhey, 1970 16p
Trithemis nuptialisKarsch, 1894 nolocalitycitedp
DESCRIPTIONOFFAN-SHAPEDSETAE
INEARLYINSTARLIBELLULIDAELARVAE
The early instarlibellulidlarvae were found tohave extraordinary fan-shaped
setae,mountedontuberclesandarranged inpairs onthe dorsumofthehead,thorax
andabdomen(Figs2a-c). Thesesetae areabsentfromlaterinstarlibellulidlarvae.
Fig. 2a-c. Early instar libellulidlarvae
with fan-shaped dorsal setae; (a)Lateral
view of larva (body length 2.96 mm)
with median dorsal spines on abdomen;
paired fan-shaped setae on dorsum of
thorax; spineonposteriorangle ofhead;
andreduced fan-shaped setaeondorsum
of head; - (b) Dorsal view of smaller
larva (body length 1.36mm) with paired
fan-shapedsetaeon dorsum ofabdomen,
thorax andhead; - (c) Caudo-lateral view
of same larva.
34 S.J. Brooks & K.A. Jackson
Basedonthe arrangementofthe fan-shaped setae,the larvaecouldbeplaced in
fourgroups. On theheads ofthe two largest larvae (headwidth 0.79-1.18mm;
bodylength 1.61-2.96mm)were asingle spiniformseta onaprominenttubercle at
theposterior angle, fourpairs of postero-dorsal fan-shaped setae,andtwo pairs of
robust,narrow antero-dorsalsetae.They alsohadlarge,recurved mid-dorsalspines
on abdominal segments5-9 anda vestigial mid-dorsalspine on segment4. One
intermediate-sizedlarva(headwidth0.54mm;bodylength 1.64mm)hadsix pairs
offan-shaped setae onthehead(fourpairsposteriorly andtwo pairsanteriorly)and
paired sub-dorsal fan-shaped setae on abdominal segments 6-9. All three large
larvaehadalarge lateralspineonabdominalsegment9andshort, slendersetaeon
themid-dorsalspines. Six small larvae(head width0.45-0.46mm; body length
0.93-1.36mm) each had four pairs of fan-shaped setae on the head (two pairs
posteriorly and two pairs anteriorly), paired sub-dorsal fan-shaped setae on
abdominalsegments 6-9, and a small narrow seta positioned mid-dorsally on
segment 10. Nofan-shaped setae werepresent on thesmallest larva(head width
0.43mm;body length 0.93mm). Allthelarvae, withtheexception ofthesmallest,
hadapair ofsub-dorsalfan-shaped setae on eachthoracic segment.All thelarvae
had3-5robustspines onthedorsumofthefemora,andthesix smallerlarvaealso
hadasimilarnumberofspines inarow onthedorsumof themid-andhind-tibiae.
The fan-shaped setae (Figs 3a-b) (macrotrichia) had a finely crenellatedapical
marginandshallowcorrugations onthesurface.They appearedtobehollowinternally
butthiscavity was sealedand didnot extendintothebody ofthelarva. They were
attachedto a tubercle rising from the body surface by a ‘ball-and-socket’ joint.
DISCUSSION
SETATION OFEARLY INSTAR LIBELLULID LARVAE
Wewere unabletoidentify theearlyinstarlibellulidlarvaetogenus- orspecies-
level; however,Allorhizuchaklingi, Orthetrumjulia and Trithemisaconita were
theonly libellulidsrecordedas adultsfromtheRioMusolawherethelarvaewere
collected. The three largest larvae differedmorphologically from the six small
larvaewhichsuggests thatthey mayhavebelonged to differenttaxa.
However, itis also possible that thelarvaerepresented differentdevelopmental
stagesofthe sametaxon. The fan-shaped setae appearto be unique, suggesting a
taxonomic affinity between the specimens, although adaptive convergencecould
also account forthissimilarity. Thedistributionofthesetae ontheheadofall the
larvaeis similar.Thetwo pairs ofnarrow anteriorhead setae inthelargest larvae
were in the same position as the two anterior pairs offan-shaped setae in the
intermediate-sizedlarva. This suggests they were homologousbut have become
reduced in size,perhaps because functionally they are no longer important. Fan-
-shaped setae have neverbeen recorded inany late-instarOdonata larvae which
Odonata ofRepublic of EquatorialAfrica 35
implies thatatsomestage
inthelarvaldevelopment
they are lost. If all the
larvae are of the same
taxon,theabdominalfan-
-shaped setae,which are
only present on the
smallest class oflarvae,
mustbereplaced by long
spines in the larger
larvae.Thereis acircular
area betweenthe baseof
the abdominal fan-
-shapedsetaefromwhich
the mid-dorsal spines
may develop in later
instars.
Specialised setae,
restricted to early instar
odonatelarvae, havebeen
describedfrom anumber
of Odonata families in-
cluding Coenagrioni-
dae, Libellulidae, Gom-
phidae and Corduliidae
(see CORBET, 1999,for
areview).Thesesetaeare
generally consideredto
be mechano-receptors
thataidthelarvatodetect
prey.Inmost cases these Fig. 3a-b. Early instarlibellulidlarva: (a) Fan-shapedsetaeon
setaearespiniform,butin dabodrsoumminaolfsheegamde;n-ts(b6)aPnadire7d. fan-shaped setae on dorsum of
Cordulegaster insignis,
which lives in flowing water, the setae are flattened, stiff and fan-shaped
(VERSCHUREN, 1989).In C. insignis thesemodifiedsetae are located only on
those anteriorparts of thebody that are exposed to the water when the larva is
resting, partly buried inthesediment.Although themodifiedsetae ofC. insignis
arevery muchsmallerandmorenumerousthanthosedescribedinthispaper,they
are similar in shape and this suggests that they may have a similar function.
Unfortunately, we did not observe the microhabitatoccupied by theearly instar
libellulidlarvae,butperhaps they lieburiedjustbelowthesurfaceofthe sediment
withthetallfan-shaped setaeprotruding abovethesubstrateto detectthemovements
36 S.J. Brooks &K.A. Jackson
ofpreyandcurrent flow.Laterinstarlarvae may migratefromthishabitatanduse
visual stimulito detectprey and so nolonger haveneedofthesemodifiedsetae.
DISTRIBUTION OF ODONATA IN BIOKO
Of the42 species previously recordedfrom Bioko, 19 were found during this
study, togetherwithanadditionalsix species whichhadnot beenlistedpreviously.
Relatively littleofthe island had been surveyed for dragonflies inthe past and
PINHEY (1974) lists species collectedfromjust six localities:Malabo(as Santa
Isabel),FincaFrauendorf(close toBasupii andRio Tiburones-Uruabela), Luba(as
SanCarlos), RioMusola, Moca, andRiaba(as ParadorConcepcion). During this
study all these localities were visited, as well as additional sites. Unfortunately,
therewas notimeto visitthesouthernpartoftheislandsincethiswasnotaccessible
by road.Much ofthe forest in the Southis still pristine and for this reason it is
possible thatotherspecies ofOdonatamayoccur therebutnot elsewhereonBioko.
Theseresultsbeg twoquestions. Whywere so manyof thepreviouslyrecorded
species notrediscoveredduringthepresentstudy?Whyweresomany(24%) ofthe
dragonfliescollectedduringthisstudy recordedforthefirsttime?Theanswers to
both questions are probably themarked seasonality of someOdonata species.
Thefamily withthelowestrepresentation ofpreviously recordedspecies inthe
present collection were Libellulidae.Twenty-one libellulidspecies had been
recordedfromtheislandinthepast,butonly sevenofthesewere foundthis time,
plus afurthertwo species thathad not beenfoundon Bioko before.Theprobable
explanation is that most ofthe libellulidspecies recorded from Bioko breed in
standing water. Very fewstanding water sites wereavailableforbreedingodonates
in Bioko during late-Marchand early-April 1999. The largest ofthese was the
reservoironRioRumaaboveRiaba,whichwasconstructedafterPINHEY’s,(1974)
account was published. Wefoundsix libellulidspecies atthissitein 1999,including
Trapezostigma basilarisand Tholymis tillarga whichhadnot beenrecorded from
theislandbefore, although PINHEY (1974) predictedthateventually they would
bediscovered.We collectedmostoftheotherlibellulidsby pools andslow-flowing
sections ofrivers elsewhere on theisland. The only exceptions were Orthetrum
julia which was ubiquitous andAllorhizuchaklingi whichwas restrictedto fast-
-flowingrifflesectionsofcertainstreams.
Duringthebeginning ofApril1999rainbecamemorefrequent, fdlingnumerous
puddles and pools on roads and tracks. These rapidly attracted territorial male
libellulids.Itseemslikely thatduringtherainy season theabundanceanddiversity
oflibellulidsonBiokoincreases asthenumberofstanding waterbiotopes increases.
Such temporary biotopes probably do not support these species yearround on
Bioko, suggesting that many ofthelibellulidsspend the dryseason onmainland
Africaand migrateto theislandduringtherainy season.
The streams close to the type locality ofParagomphus moka (= P. abnormis)
Odonata of Republicof EquatorialAfrica 37
were visited but no adults ofthe species were seen. However, the species was
previously recordedbetweenNovemberandFebruary (PINHEY, 1974) suggesting
thatadults may beseasonal inoccurrence. Morepuzzling was thefailureto find
Africocypha lacuselephantum duringthisstudy sincewevisitedtheupperreaches
ofRioIladyi, andit was here that Hartwig collectedlarge numbers on 11 March
1963(PINHEY, 1974).
Thefailureofprevious collectorstofindElattoneuraballiis surprisingsincewe
found thespecies to be abundant andalmost ubiquitous on the island’s lowland
streams.The species is fairly cryptic, being slender, darkcolouredand generally
fliesin deep shadebut, nevertheless, wasnotdifficulttocollect.Perhaps thespecies
has colonisedtheisland sincethelastintensivedragonfly collectionswere made
in theearly 1960s.Similarly, Chlorocypha rubidawascommononseveralstreams
including Rio Musola which was one ofHartwig’s collecting localities, but he
failedtofindit.
Since most of the lowland rivers were physically fairly uniform they each
supported asimilardragonfly fauna.However,therewas someevidenceofbiotope
segregation since Ceriagrion glabrum, Agriocnemis maclachlani, Palpopleura
lucia, TrithemisdichroaandAnax imperator wererestrictedto pooled andslow-
-flowing biotopes. Chlorocnemis nigripes andElattoneuraballi(both Protoneuri-
dae)were most commonintheshadedstretchesof streams.
Thetwo streams sampledabove 1500mnearMocasupported animpoverished
suite of species including Umma mesostigma, Pseudagrion serrulatum and
Macromialieftincki thatwere not foundatany ofthe sites sampled below500 m.
Enallagma buchholzi,Africocypha lacuselephantum andTrithemishartwigi,which
were not recorded during thepresentstudy, mayalsoberestrictedtothehighlands
around Moca(PINHEY, 1974).Paragomphus abnormis has only certainly been
recorded on Biokofrom Moca (as P. moka by PINHEY, 1974), butin this study
larvae ofan unidentifiedspecies of Paragomphus were found in three streams
below 500 m, so the species may be more widespread on the island. PINHEY
(1974) recorded Trithemis dichroa, Chlorocypha cancellata andAllorhizucha
klingi fromstreamsaroundMoca butall three species were collected on lowland
streams duringthis study. Umma mesostigma occurred atthehigh altitudesites,
andalsoatBasile, asiteatintermediatealtitude(600m). Thiswas theonly locality
at whichChlorocypha cyanifrons was found.
Theseresultsindicatethatelementsofthedragonfly faunaofBiokooccupy two
distinctaltitudinalzones. Six species wererestrictedtolocalitiesabove500m, 17
species occuronly atsitesbelow500mand 13 species were found atallaltitudes.
AlltheOdonata species knownfromBiokoalso occuron theAfricanmainlandin
Cameroon(VICK, 1996; 1999).However, otherodonatespecies may beawaiting
discovery in thesouthern partoftheisland.
38 S.J, Brooks & K.A.Jackson
ACKNOWLEDGEMENTS
We take this opportunity to thank MrGRAHAM VICK(Basingstoke, UK) and Mr DAVID
CHELMICK (Haywards Heath, UK) for allowing us to refer to their unpublished keys to the
Odonata fauna ofCameroon and for sharing their knowledgeofthe Odonata ofthis region. Our
fieldwork on Bioko was funded by World Health Organisation African Programme for
Onchocerciasis Control (WHO/APOC) and wethank DrA. SEKETELI(WHO/APOC) and NOTE
for permission to publishthis note. We also thank Dr ROLF MEYER (OCP, Kara, Togo), Dr
JORDI MAS (University ofBarcelona, Spain) and Dr ANACLETO SIMA (Ministry of Health,
Malabo,Bioko) whose local knowledge ofBioko made the field work possible. In addition, we
thank Mr MICHAELWHITEHEAD (OxfordBrookes University, UK) for assistance in sorting
the macro-invertebrate samples and Ms EDITH KAPINOS for carryingout a literature survey.
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