Naturwissenschaften (2004) 91:182–185
DOI 10.1007/s00114-004-0514-z
SHORT COMMUNICATION
C. S. F. Mariano · J. H. C. Delabie · L. S. Ramos ·
S. Lacau · S. G. Pompolo
Dinoponera lucida Emery (Formicidae: Ponerinae):
the highest number of chromosomes known in Hymenoptera
Received: 22 July 2003 / Accepted: 8 February 2004 / Published online: 19 March 2004
Springer-Verlag 2004
Abstract We report the remarkable karyotype of Dinoponera lucida, a Brazilian endemic ponerine ant. Its
chromosome number is 2n=106, most of the chromosomes are acrocentric and of very small size, and the
karyotype formula is 88A+18M. A chromosome pair of
the AMt type is reported. This is the largest number of
chromosomes reported for the Hymenoptera order until
now.
Introduction
The ant genus Dinoponera belongs to a notable and
convergent group of Ponerinae in which there is no
distinguishable reproductive female and reproduction is
guaranteed by fertilized workers, called gamergates
(Peeters 1993, 1997; Monnin and Peeters 1998). It is
also remarkable because the species of this genus, all
restricted to South America, are amongst the largest ants
in the world (Kempf 1972; Paiva and Brand¼o 1995).
Belonging to the tribe Ponerini, it is phylogenetically
C. S. F. Mariano
P-G Entomologia, Universidade Federal de Viosa,
DBA, 36570-000 Viosa, MG, Brazil
C. S. F. Mariano · J. H. C. Delabie ()) · L. S. Ramos · S. Lacau
UPA Laboratrio de Mirmecologia,
ConvÞnio UESC-CEPEC,
CP 7, 45600–000 Itabuna, BA, Brazil
e-mail: [email protected]
Tel.: +33-73-2143254
Fax: +33-73-2143204
L. S. Ramos
CEIS Instituto de BiociÞncias, UNESP,
CP 199, 13506-900 Rio Claro, SP, Brazil
S. Lacau
Laboratoire d’Entomologie,
MNHN, 45 rue Buffon, 75005 Paris, France
S. G. Pompolo
Universidade Federal de Viosa,
DBG, 36570-000 Viosa, MG, Brazil
close to Pachycondyla (S. Lacau, personal observation).
These peculiarities have allowed interesting studies on the
chemistry (Oldham et al. 1994; Peeters et al. 1999),
behavior (Fowler 1985; Araffljo et al. 1990; Monnin
and Peeters 1998; Monnin et al. 2002), and ecology
(Fourcassi and Oliveira 2002) of several species of this
genus to be carried out.
In Brazil, Dinoponera lucida Emery is distributed in
fragments of Atlantic rain forest, from southern Bahia
through to the north of Esprito Santo, with isolated
populations in the State of Minas Gerais (Kempf 1972;
Paiva and Brand¼o 1995; Laboratrio de Mirmecologia
Collection). This ant was recently (and after the present
experiment) officially classified as endangered (Ministrio
do Meio Ambiente 2003) due to the poor conditions for
preservation of its populations. Nevertheless, and despite
its remarkable size, which makes it immediately recognizable in the field, no study on the ecology, behavior, or any
other aspect of the biology of this particular species has
been carried out.
The chromosome number is a valuable characteristic
of a taxon and is important information for taxonomic and
phylogenetic studies. Cytogenetic studies in the Hymenoptera order have indicated a variation in chromosome
number from 2n=2 to 2n=94. Both extremes are found
amongst the Formicidae, respectively in Myrmecia
croslandi Taylor (Myrmeciinae) (Crosland and Crozier
1986) (2n=2), and Nothomyrmecia macrops Clark
(Myrmeciinae) (Imai et al. 1990, 2002) plus Platythyrea
tricuspidata Emery (Ponerinae) (Imai et al. 1984a) (both
with 2n=94). In the other Hymenoptera, the chromosome
number is always intermediate between these values. Of
the 99 families in this order (Mason and Huber 1993),
cytogenetic information exists for 17. Besides the Formicidae, the highest reported numbers of chromosomes in
individual families were as follows: Vespidae: n=34
(Hoshiba et al. 1989); Andrenidae: 2n=6; Anthophoridae:
2n=46; Apidae: 2n=46; Braconidae: n=11; Chrysididae:
n=19; Colletidae: 2n=32; Eumenidae: 2n=24; Halictidae:
2n=32; Ichneumonidae: 2n=30; Megachilidae: n=16;
Pompilidae: 2n=30; Sphecidae: 2n=48 (Hoshiba and Imai
183
Table 1 Genera in the Ponerini
tribe for which cytogenetic
studies have been carried out
Genus
Number
of species
Variation in 2n
Anochetus
Centromyrmex
Cryptopone
Diacamma
Hypoponera
Leptogenys
Odontomachus
Odontoponera
Pachycondyla
10
1
3
6
8
14
8
2
38
2n=24, 28, 30, 34, 38
1,
2n=44
1
2n=12, 18, 28
2,
2n=14, 30, 36, 44, 66
1,
2n=24, 36, 38
3,
2n=26, 30, 32, 38, 46, 48, 52, 54
1,
2n=30, 32, 44
2,
2n=42, 46
1,
2n=12, 16, 18, 20, 22, 24, 26, 28, 30, 1,
34, 36, 38/40, 42, 48, 52, 76
2n=8, 12
3,
Ponera
5
Reference
2, 3, 4
5,
2,
4,
2,
3,
3
2,
6,
3,
5,
3,
4,
7, 8
4, 8
8
4, 8
8
3, 4, 5, 6, 7, 8, 9, 10
6, 7, 8, 11
References: 1 Imai et al. 1984a; 2 Tjan et al. 1985; 3 Imai et al. 1985; 4 Goi et al. 1981; 5 Imai et al.
1977; 6 Imai and Kubota 1972; 7 Imai 1969; 8 Imai et al. 1984b; 9 Mariano et al. 2001; 10 Mariano et
al. 1999; 11 Hauschteck-Jungen and Jungen 1983
1993); Aphelinidae: 2n=22 (Baldanza et al. 1999); Eulophidae: 2n=14; and Pteromalidae: 2n=12 (Silva 2001).
In the Ponerini tribe, the karyotypes of species from 10
of the 24 known genera have already been studied, their
chromosome number being determined in some species of
Anochetus, Centromyrmex, Cryptopone, Diacamma, Hypoponera, Leptogenys, Odontomachus, Odontoponera,
Pachycondyla and Ponera (Table 1). Their diploid
chromosome numbers vary between 2n=12–94 (see references in Table 1).
Methods
Three colonies of D. lucida were collected in the reserve of the
CEPLAC experimental station at Barrolndia, Belmonte, Bahia
State, Brazil (CEPLAC/CEPEC/EGREB, 16080 S 39150 W) in
October 2002. The nests were taken in an area of native vegetation
(primary forest) from an aggregated population. The colonies were
kept at the Laboratrio de Mirmecologia, at a temperature of
approximately 27C, and fed with small grasshoppers.
Seventeen slides were prepared from pharate larvae using Imai
et al.’s (1988) protocol, then stained with Giemsa. The metaphases
were photographed using an Olympus BX60 microscope equipped
with camera. The chromosome morphology was determined according to Imai (1991).
Fig. 1 Mitotic metaphase spread of Dinoponera lucida, using
Giemsa staining. 2n=106. Arrowheads indicate the pair of large
AMt chromosomes with their heterochromatic short arms and a
large heterochromatin block at their long arm ends. Bar = 5 mm
Results and discussion
Analyses of the slides showed that the diploid karyotype
of D. lucida is 2n=106 (Fig. 1). Most of the chromosomes
were acrocentric (A) and of very small size (making its
detailed study rather difficult). This compares with many
other Ponerini whose chromosome numbers vary between
2n=8–76 (Table 1). The karyotype formula is 88A+18M.
Among the A chromosomes, a pair of the AMt type is
larger than the rest and is characterized by having a
heterochromatic short arm and a large heterochromatin
block at the end of a long arm (Fig. 2). According to Imai
(1991), this kind of chromosome may result from centric
fission and heterochromatine addition. Such chromosomes have already been observed, albeit rarely, in ants
(Imai 1991).
Fig. 2 Chromosomal morphology in Dinoponera lucida, characterized by using Imai’s (1991) procedures
The N. macrops karyotype, with 2n=94, has small
almost acrocentric chromosomes (Imai et al. 1990), while
the karyotype of P. tricuspidata, with the same number of
chromosomes, was not figured, nor was its formula
precisely established (Imai et al. 1984a). One of the most
important conclusions of the study by Imai et al. (1988)
184
was that the increase in the chromosome number in
several eukaryote groups is generally linked to a reduction
in its average size. Preliminary results of recent studies on
a group of the Neotropical Pachycondyla suggest that this
rule is especially true for the Ponerini tribe as a whole.
These observations on D. lucida cytogenetics are of
importance for the understanding of its evolutionary
biology, as well as of the tribe’s taxonomy and evolution.
The monophyletic Ponerini can be considered as the best
defined tribe of the whole Ponerinae subfamily, which is
certainly paraphyletic (Bolton and Brown 2002; Ward and
Brady 2003). The genus Pachycondyla has been reported
from early Tertiary (Rust and Andersen 1999) and this ant
lineage is particularly ancient. Interestingly, all the ant
species for which a high chromosome number has been
recorded belong to genera in subfamilies seen as “primitive” (see discussion of this term in Schultz 2000; Ward
and Brady 2003): Myrmeciinae (Myrmecia, Nothomyrmecia; Imai et al. 1990, 1994) and Ponerinae (Platythyrea;
Imai et al. 1984a, and several Ponerini as shown in
Table 1). Although it is difficult to draw conclusions
about the origin of high chromosome numbers in ants, and
since the ancestral number is assumed to be low (Imai et
al. 1994), we can expect that such species have experienced an early radiation, since a high number of chromosomal events would probably be required in order to
reach their modern karyotype structure.
Acknowledgements The authors acknowledge CNPq for the grant
concession to three of them, Anderson Fernandes and Lucileide S.
Ramos for technical support, and Nathalie Hites and Jonathan D.
Majer for kindly reviewing the English manuscript. The authors
declare that the present experiment complies with the current laws
of Brazil.
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