A new species of fungus-growing ant and its implications for attine phylogeny (Hymenoptera: Formicidae).

6 Pages·1999·0.19 MB·English

by  Lattke, J. E.

Systematic Entomology (1999) 24, 1-6
A new species of fungus-growing ant and its
implications for attine phylogeny (Hymenoptera:
Formicidae)
JOHN LATTKE
E. institute de Zoologia Agricola, Universidad Central de Venezuela, Venezuela
Abstract. Aptewstigma megacephala, a new species ofattine ant, is described from
PeruandColombia. Itis diagnosedbythefollowingcombinationofworkercharacters:
flattened compound eyes partially wrapped around conical tubercles, mesonotal
denticles and erect rigid pilosity on the head, mesosoma and gaster. It is thought to
be a basal species in relation to the rest ofAptewstigma. Phylogenetic relationships
among basal genera ofthe tribe Attini are discussed.
Introduction initially were considered a different genus. Subsequent work
revealed them to be a basal Apterostigma with an unusual
The Attini is a tribe of mostly Neotropical ants characterized combination of characters that provide clues for the basal
by fungus-growing habits. They apparently constitute a phylogeny ofthe Attini.
monophyletic groupas evidencedbythisuniquehabit, andthe
larvalmorphology (Schultz&Meier, 1995),althoughthefungi
themselvesarepolyphyletic(Chapela, 1994).Attineshavebeen Materials and methods
the object of many studies, but most of the work has been
limited to groups ofimmediate economic importance such as
Atta and Acromyrmex, leaving the other genera in relative Measurements and indices
obscurity. This dearth of information covers not only their
ecology, but their taxonomic status as well, consequently HL, Head length. The maximum straight-line distance from
making most of them difficult to identify. It is commonly the posterior cephalic margin to the anteriorclypeal margin
agreedamongmyrmecologiststhataconfusing situationexists with the head in full dorsal (frontal) view.
in the nature ofthe genera as they presently exist in the tribe, HW, Headwidth.Themaximumstraight-linedistancebetween
and that the relationships between these groups are unclear. the lateral cephalic margins, excluding the ocular
Kusnezov (1964) delimitedMyrmicocrypta, Aptewstigma and prominences. Taken in the same plane ofview as HL.
Mycocepurus as a group called Palaeoattini within Attini. He LW, Frontal lobe width. The maximum straight-line distance
argued for their more primitive status as compared with the between the external margins ofthe frontal lobes. Taken in
rest ofattines because ofthe characteristics oftheir nests and the same plane ofview as HL.
fungus gardens, fungal substrate, worker monomorphism and ML, Mandibular length. The maximum straight-line distance
behaviour (Kusnezov, 1955). At least some ofhis conclusions between the outer mandibularbase to the mandibular apex.
have found support in studies of attine phylogeny based on Taken in the same plane ofview as HL.
larval morphology (Schultz & Meier, 1995). Their results SL, Scape length. The maximum straight-line distance ofthe
corroborate the monophyly of the tribe, but render the first antennal segment measuredfrom the basal constriction
genusMyrmicocrypta paraphyletic.Myrmicocrypta buenzUi to the scape apex. This was taken in an oblique posterior
apparently conserves the greatest number of ancestral attine cephalic view sincethefrontallobescovertheantennalbase
characters. It forms a basal trichotomy, along with the clade in frontal view.
formed by Mycocepurus and Apterostigma and the rest of CI, Cephalic index: HW/HL.
the Attini. SI, Scape index: SL/HW.
Duringthe course ofgatheringmaterial forarevision ofthe
genusApterostigma (Lattke, 1997), specimens werefoundthat
Collections
Correspondence: John E. Lattke, Department of Entomology,
University of California, One Shields Avenue, Davis, CA 95616, CPDC, Laboratorio de Mirmecologia, Centre de Pesquisas do
U.S.A. E-mail:[email protected] Cacau, Itabuna, Bahia, Brazil.
1999 Blackwell Science Ltd
2 John E. Lattke
UNCB, Institute de Ciencias Naturales, UniversidadNacional
de Colombia, Santafe de Bogota, Colombia.
MCZC, MuseumofComparativeZoology,HarvardUniversity,
Cambridge, Massachussetts, U.S.A.
MIZA, MuseodelInstitutedeZoologiaAgricola,Universidad
Central de Venezuela, Maracay, Aragua, Venezuela.
Phylogenetic relations
In an effort to gain an idea of the possible relationships of
Apterostigma megacephala with other basal Attini, selected
species from several genera were compared: Apterostigma
auriculatum, A. dentigerum, A. cf. pilosum, A. urichii;
Blepharidattabrasiliensis;Mycocepurusgoeldii,M. smithi,M.
tardus;Myrmicocrypta buenzlii', Sericomyrmexamabilis, S. cf.
saussurei, S. zacapanus, S. sp. 1, S. sp. 2. Blepharidatta, a
&
nonattine and putative sister group to Attini (Schulz Meier,
1995) was included for determining character polarities. The
following characters were used to determine relationships.
1. Anterior strip ofsmooth and shiny integument on clypeus:
(0) absent; (1) present.
Table1.Characterstate matrix for selected generaofAttini.
A new species offungus-growing ant 3
Fig.3.Anteromedian clypeal area and inner posterior mandibular
comers. Median clypeal setavisible as themostrobusthairpresent.
antennal fossae, ocularprominences and most ofdorsomedian
Fig.2.Dorsal view of head of Apterostigma megacephala. depression. Scapes transversely rugose, base strongly bent,
Bar=1.0mm. with rigid decumbent hairs. Antennal fossae relatively large,
reniform. Dorsal mandibular surface striate, smooth and shiny
alongchewingborderanddistad;chewingborderwith8widely
spaced teeth, apical tooth largest. Palpal formula: 3:1 or 3:2.
Manu, 13-17/02/92, R. Combra, D. Quintero leg. Worker In situ count. Transverse carina lacking on cervical area;
deposited in CPDC. (2) COLOMBIA, Meta, Parque Natural pronotum withmedianlongitudinal carina, laterally with more
Nacional La Macarena, IX-90, M.T. Barreto leg. Worker or less parallel rugulae. Lateral margins of propleura and
depositedinUNCB. (3)PERU, MadredeDios, ManuReserve pronotumevenlycurved,withoutdenticleorangle.Mesonotum
Zone, Pakitza Station. X-88. J. Tobin leg. Worker deposited with 4 denticles, anterior pair longer than posterior; neither
in MIZA.
promesonotal suture nor metanotal sulcus evident.
Worker. Measurements,holotype(UNCB-CPDCparatypes): Anepistemumwithlowrugae, dorsoposteriorlyboundby brief
HL 1.69 (1.70-1.64); HW 1.44 (1.51-1.46); LW 0.90 (0.94- carina; mesopleuron with short ventral carina at mesosomal
0.91); ML 0.90 (1.06-1.02); SL 1.47 (1.64-1.54); LM 2.49 constriction. Rugae on mesosoma not as broad and coarse as
(2.51-2.47) mm. CI 0.85 (0.89-0.89); SI 1.02 (1.09-1.05). on head; sculpture finer with sparse rugulae. Mesometanotum
Head in frontal view subquadrate, anterior clypeal border without well defined longitudinal carinae. Mesosoma laterally
broadly convex, medially bluntly angulate or with blunt short with relatively straight anterior pronotal margin; margins of
denticle (Fig. 3); sides slightly diverging posterad, posteriorpronotumandmesonotumformconvexityinterrupted
posterolaterallyconvexandwithstraightposteromedianborder. by mesonotaldenticles. Metanotumconcave; dorsal propodeal
Clypeus anteriorly with narrow, longitadinal band of smooth face very broadly convex, almost straight, abouttwice as long
and shiny integument, remainder opaque, rugose; prominent asdeclivitousface.Propodealdorsumwith2posteriordenticles;
mediansetausuallypresentonanterioredge,thickerandlonger base of each propodeal denticle joined to inferior propodeal
than surrounding hairs (Fig. 3). Clypeus medially with carinae lobe by vertical carina. Mesopleuron with low anteriorly
forming Y-shapedridge, eachposteriorarm stems from below projecting ventral lobe, just dorsad of mesocoxa. Pronotal-
frontal lobe, with anterior arm extending to posterior edge of mesopleural suture distinct, terminating dorsally at brief lobe
shiny strip. Clypeus posterolaterally boundby ridge extending overlapping mesothoracic spiracle; small tubercle present at
from frontal lobe, separating it from antennal fossae; each apparent dorsal end of metapleura. Metapleura and lateral
ridge then extends posterad, bordering antennal fossa laterally propodeal faces with finely granulose sculpturing, no rugae.
andjoining rugae on cephalic dorsumjustbelow level ofeye. Propodeal spiracle prominent, opening directed obliquely
Frontallobesrelativelymassiveandsubtriangular, withbluntly laterally. Dorsal propodeal surface forms slightly elevated
roundedapex, very shortanteriormargin, very broadlyconvex rectangular surface bordered anterad by transverse carina and
lateral margin and approximately straight posterior margin; laterallyby longimdinalcarinae thatendposteradatpropodeal
dorsalsurfacewithcoarselongitudinallyarchingrugae.Frontal denticles. Convex propodeal lobes present. Petiole slightly
carinae extending posterad only to upper level of eyes, pedunculate, node broadly convex, its posterolateral margins
afterwards joining 2 posteromedian swellings that meet at angulate and pointing obliquely posterad; low anteroventral
midline to enclose dorsomedian cephalic depression. lobe present. Petiolar and postpetiolar dorsum rugulose.
Compoundeyeon subcornealtubercle, inlateralviewforming Postpetiole laterally with convex anterodorsal mjirgin; ventral
ellipsecurved around anteriorhalfoftubercle; ommatidia flat, marginstraight,boundateachendbyraisedtriangularmargins;
separatedfromoneanother. Occipitallobes short, subquadrate, dorsalsurfacewithposterolateralridgeendinginroundedlobe.
joined by posterodorsal low transverse ridge. Cephalic First gastral segment with anterodorsal lobe, a continuous
sculpturing opaque, coarsely rugose except finely granulose extension of gastral sculpturing partially overlapping
1999 Blackwell ScienceLtd,SystematicEntomology, 24, 1-6
4 John E. Lattke
Fig.4.Helciumandanterodorsalgastral areaofApterostigmaauriculatum andMyrmicocryptabuenzUi. a, dorsal viewinA.auriculatum;b, lateral
viewinA. auriculatum; c, dorsal view inM. buenzlii; d, lateralviewinM. buenzUi. he = helcium. lo = anterodorsal lobe.
constriction ofhelcium dorsally (Fig.4), apex bluntly pointed probably safe to assume that this species is monomorphic,
and base with modest but well-defined transverse concavity. given the small variation in measurements of the studied
Posterodorsalmarginofpostpetiolecoversmostoflobe. Gaster specimens and the basal position of the group within Attini.
laterallysubglobulose,dorsalmarginevenlyconvexandventral Only more derived attines, such asAcromyrmex andAtta, are
margin sharply convex; tergum of gastral segment I with polymorphic.
rugulae forming almost areolate pattern, sternum with rugulae Etymology. The species name is derived from the Greek
alongposteromedianarea, fading outtowardsbase; low lateral
words for large, mega, and head, kephale. It alludes to the
longitudinalcarinaepresentontergum.Procoxaemostlysmooth
prominent head.
exceptforlowrugulaetowards apex, norugulae onmeso- and
metacoxae. Apex of metacoxa with a sulcus along each side
of insertion of trochemter, each sulcus divided into rounded Discussion
cells. Body without pubescence except on antennal flagella,
protibiae and tarsi. Hairs on mesosoma rigid and frequently The results of the phylogenetic analysis are shown in Fig. 5.
capitate, those on gaster slender and subdecumbent; head with The attine ingroup is divided into a clade formed by
sparsedepressedhairs;vertexandocciputwitherecttosuberect Mycocepurus, Myrmicocrypta and Apterostigma, while
rigidhairs. Bodybrown, mandibularmasticatoryborderblack. Sericomyrmex is positioned as a sister group to them.
Queen. Unknown. Apterostigma megacephala has a sister group relationship to
the othermembers ofits genus. Thefungus antgenerastudied
Male. Unknown.
here arejoined by three synapomorphies: (1) development of
Remarks. F. Fernandez has supplied additional data about a smooth and shiny anterior clypeal margin; (2) presence of
the locality for the Colombian specimen: 'primary forest lateral carinae along the gastral dorsum; (3) presence of
between Ri'os Duda and Guayabero, some kilometres west of mesonotal denticles. But in some groups at least one ofthese
the town La Macarena, 350m.' The collection data for all charactershasbeenlost. Thegradualdevelopmentofadistinct
specimens indicate this species is found in lowland mesic smooth and shiny strip of cuticle along the anterior clypeal
forests. Although only four workers have been found, it is border can be traced through these groups. Blepharidatta
© 1999 Blackwell ScienceLtd, SystematicEntomology, 24, 1-6
A new species offungus-growing ant 5
Blepharidana
visible in the A. megacephala specimens studied. Dissection
ofthetypeswasprecludedduetoeachbeingauniquespecimen
• Mycocepurus foreachcollection.Neverthelessthebasalandmedianstructure
of the lobe corresponds well to the state in the remaining
Apterostigma (Fig.4a,b), and is unlike the other ants studied
Apterostigma
(Fig.4c,d). In the other attines dissection was not necessary,
as pressingdown on the gasterofrelaxed specimens permitted
A.megacephala viewing of the anterior edge of the first gastral tergite. An
additional synapomorphy, considered belatedly, is the reduced
palpalformulaofA. megacephalaandotherApterostigma.The
. Myrmicocrypta primitive number in Attini is 4:2 except in two Acromyrmex
socialparasitesandinApterostigma,whereitis3:2(T. Schultz,
Sericomyrmex personal communication; Kusnezov, 1951, 1954). A sister
.
group relationship betweenA. megacephala and the two other
Fig.5. Strict consensus tree computed from three trees oflength 11, Apterostigma clades is argued on the basis of these four
CI = 0.73 andRI = 0.63. characters.
Someapomorphies separating allotherknownApterostigma
from A. megacephala are: (1) complete loss of the median
brasiliensis possesses an anterior lamella, but it is opaque, clypeal seta; (2) loss of distinct mesonotal teeth, represented
while Mycocepurus has a distinct, though usually bytwolongitudinal carinae, which occasionally areraisedinto
inconspicuous, lamella. Some species have traces of shine blunt triangles in a few species ofthe auriculatum group; (3)
though, and it is very obvious in M. tardus where it is presence of a transverse carina on the cervical area; (4) loss
partially smooth and shiny. Apterostigma, disregarding A. of lateral denticles on the pronotum, sometimes apparently
megacepahala, can be divided into two clades: one in which represented as avery inconspicuous swelling on each humeral
the smooth and shiny strip is present, thepilosum group, and side; (5) tendency toward loss of the propodeal denticles,
one in which the strip has been lost, the auriculatum group which are conserved in a few species of the auriculatum
(Lattke, 1997).Thepresenceoflateralcarinaealongthegastral group; (6) loss ofthe posterolateral ridges ofthe clypeus; (7)
transformationoferectandrigidcorporalhairsintoflexousand
dorsum is shared by all these attines exceptMyrmicocrypta.
curved, decumbenthairs. AutoapomorphiesofA. megacephala
All attines considered here have denticles on the mesonotum,
withtheexceptionofApterostigma, inwhichprobablevestiges include: (1) the reduced ommatidiaofthe compoundeyes; (2)
thedevelopmentofspatulateendsonsomeoftheerectcorporal
of these can be seen in the prominent triangular lobes of the
hairs; (3) the angulate lobes on the posterolateral petiolar and
mesonotal carinae found in a few species of the auriculatum
postpetiolar margins. In A. megacephala the median clypeal
group (Lattke, 1997), yetthey are retainedinA. megacephala. seta may occasionally be indistinct.
The Apterostigma + Mycocepurus + Myrmicocrypta clade
It is concluded thatApterostigma megacephala represents a
is supported by the loss of the lateral pronotal denticles or basal species in the Apterostigma clade. The objective ofthis
angles, and perhaps by the development of the posterolateral discussion has been to place this new ant within the 'lower'
clypeal ridge. This ridge stretches from the base ofthe frontal attines, and does not pretend to address the phylogenetic
carinaeandextendsposteradalongthelateralcephalicdorsum. relationships of all attine genera. That will have to await an
Such a structure is lacking in B. brasiliensis and its absence in-depth study ofthe entire tribe.
in Apterostigma, other thanA. megacephala, is interpreted as
a loss.
Acknowledgements
Apterostigma megacephala shares the following synapo-
morphies with the rest of Apterostigma: (1) each compound Credit goes to Stefan Cover (MCZC) forpointing out this ant
eyeispartiallyortotallymounteduponatubercle; (2)presence aspossiblyrepresentinganewgenus,JacquesDelabie(CPDC)
ofa posteriorcephalic ridge or lamella thatjoins the occipital and Fernando Fernandez (Instituto Humboldt) for loaning
lobes; (3) an anterodorsal lobe that partially overlaps the additional specimens for study, and PhilipWard forcomments
helcium of the first gastral tergite. The ocular tubercle is far on the manuscript. Ted Schultz (Smithsonian Institution)
more developed inA. megacephala, being larger than the eye supplied specimens of M. buenzlii and provided thoughtful
itself, whereas in otherApterostigma the eye is always larger. comments on this manuscript. Financial support for this
The posterior cephalic ridge is interpreted as homologous to research came from the Fundacion Polar, Caracas, and the
theposteriorneckcharacteristicofotherApterostigma. Inmost Consejo de Desarollo Cientifico y Humanistico of the
Apterostigma it is quite developed, forming alamellarprocess Universidad Central de Venezuela.
that completely fuses laterally with the occipital lobes, and
forms with them a single structure. The separation between
References
the lobes and the ridge is still evident inA. megacephala.
Theanterodorsalgastrallobecanonlybe seeninits entirety Chapela,I.,Rehner, S.,Schultz,T. &Mueller, U. (1994)Evolutionary
by removing the postpetiolar tergite. Unfortunately only the history of the symbiosis between fungus-growing ants and their
basal and median portions ofthe anterodorsal gastral lobe are fungi. Science, 266, 1691-1694.
© 1999Blackwell ScienceLtd, SystematicEntomology, 24, 1-6
6 John E. Lattke
Kusnezov, N. (1951) Los segmentos palpales en hormigas. Folia Lattke, J. (1997) Revision del Genero Apterostigma Mayr
Universitaria, Cochabamba, 5, 62-70. (Hymenoptera: Formicidae).ArquivosdeZoologia, 35, 121-221.
Kusnezov, N. (1954) Phyletische Bedeutung der Maxillar- und Schultz,T. &Meier,R. (1995)Aphylogeneticanalysisofthefungus-
LabialtasterderAmeisen. ZoologischeAnzeiger, 53, 28-38. growing ants based on morphological characters of the larvae.
Kusnezov, N. (1955) Evoluciondelas hormigas. Dusenia, 6, 1-34. SystematicEntomology, 20, 337-370.
Kusnezov, N. (1964) Zoogeografia de las hormigas en Sudamerica.
ActaZoologica Lilloana, 19, 25-186. Accepted27 November 1997
© 1999 Blackwell Science Ltd, SystematicEntomology, 24, 1-6