Reprint From: J. Bomba.v nat. Hist. Soc. Vo l. 100 (2&3). December 2003
CONTRIBUTIONS TO THE BIOLOGY OF THE QUEENLESS PONERINE ANT DIACAMMA CEYLONENSE EMERY (FORMJCJDAE)
Sy Vedham Karpakakunjaram. Padmini Nair. Thrcsiamma Varghese. George Royappa. Milind Kolatkar and Raghavcndra Gadagkar CONTRIBUTIONS TO THE BIOLOGY OF THE QUEENLESS PONE~ ANT DIACAMMA CEYLONENSE EMERY (FORMICIDAE) (Withfrve text-figures)
1 1 1 VEDHAM KARPAKAKUNJARAM , PADMININAIR , THRESIAMMA VARGHESE', GEORGE ROYAPPA , 2 1 2 3 MILIND KOLATKAR AND RAGHAVENDRA GADAGKAR • •
Key words: Diacamma ceylonense, queenless ant, Ponerinae, Formicidae, Hymenoptera
All ants are generally classified as highly eusocial. However, there are some I 00 species of ants belonging to the morphologically primitive subfamily Ponerinae, which lack a morphologically differentiated quet(n. One or a small number of mated workers (gamergates) function as queens, i.e. they produce male as well as female offspring. Such ant species are of great interest as they provide unique opportunities to understand the causes and consequences of queenlessness. This is the first report ofa long-term field study we have initiated on a large population of the queenless ponerine ant, Diacamma ceylonense Emery, on the campus of the Indian Institute of Science, Bangalore. Data are provided on the numbers of colonies present during a 213-week period, from which the probable time of colonisation of the site by D. ceylonense is suggested. Twenty-six entire colonies were excavated to study the adult and brood composition. While some colonies did not appear to have a gamergate at the time of excavation, others had only one gamergate per colony. Only the gamergate was mated and had well developed ovaries, while all the workers were unmated and had undeveloped ovaries. Excavated colonies had an average of230 adult females, 2 males and 80 items of brood. The gamergates were indistinguishable from their workers in body size but there was significant variation in the size of workers between colonies. On an average, colonies employed 24% of their workers outside the nest for foraging and other duties. The relative constancy of this proportion permits estimation of total colony size by merely estimating the number of extranidal workers and thus without having to excavate the nests. In the five colonies studied, foragers spent an average of 9 to 23 days of their lives in performing foraging duties. Most foragers remained faithful to one or a narrow range of compass directions, although such directional preferences ofall of them put together permitted colonies to exploit resources in all directions.
INTRODUCTION In this scale of social evolution, all ants are generally classified as highly eusocial (HOlldobler Eusocial insects are defined as those and Wilson 1990, Bourke and Franks 1995). insects whose colony members exhibit overlap of However, some 100 species of ants, belonging to generations, cooperative brood care and the morphologically primitive subfamily reproductive caste differentiation into a queen Ponerinae, lack a morphologically distinguishable caste and a worker caste. Highly eusocial species queen. Their colonies consist only of workers (in are those in which the queen and worker castes addition to males of course), one or a few ofwhom are morphologically differentiated (Wilson 1971 ). are mated and take on the function of queens, i.e. production of male and female offspring. These 'Centre for Ecological Sciences, Indian Institute of Science, mated, reproducing workers are termed gamergates Bangalore 560 012, Karnataka, India. (Peeters 1991 ). Queenless ants are ofgreat interest 2Evolutionary and Organismal Biology Unit, for several reasons: (I) They provide an Jawaharlal Nehru Centre for Advanced Scientific opportunity to understand the conditions under Research, Jakkur, Bangalore 560 064, Karnataka, India. which the queen caste may be lost. (2) In the 'Email: [email protected] absence of winged queens, new colonies have to
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY. 100(2&3), AUG.-DEC. 2003 533 BIOLOGY OF THE QUEENLESS PONERINE ANT
be necessarily founded by walking gamergates, Diacamma cey/onense Emery, which is which must result in a rather unusual population abundantly distributed in and around Bangalore. genetic structure. (3) They can be used as model There iS a large population of D. ceylonense in systems to understand how one or a small number the so-called Jubilee Garden in the campus of the of individuals can establish and maintain Indian Institute of Science, Bangalore (13° 00' N reproductive monopoly among a group of 77° 32' E). Such an easily accessible population identical, or nearly identical, individuals. This is a facilitates observation of colonies in their natural problem that has been extensively investigated habitats. Most previous work on Diacamma, and with bees and wasps (see Gadagkar 2001 and indeed on most ponerine ants, has been largely references therein) but because queenlessness restricted to observ11tion in artificial nests in the in ponerine ants is evolutionarily derived from laboratory, ofants removed far from their natural the queenright condition (Baroni Urbani et al. habitat. 1992), a new perspective is expected from a study For all these reasons, we have initiated a of these ants. long-term study of the population of In this context, the genus Diacamma D. cey/onense in the Jubilee Garden ofthe Indian represents a most fascinating example. In Institute of Science, Bangalore. This is the first Diacamma, all females eclose with a pair of club report of this ongoing study. like thoracic appendages called gemmae. The gamergate mutilates all workers who eclose after MATERIAL AND METHODS her, by clipping their gemmae. Such mutilation results in poorly understood neurological changes This study was conducted in the Jubilee in the victims, making them incapable of sexual Garden, Indian Institute of Science, Bangalore. calling and mating. This unique mechanism by The site is a plantation of Acacia auriculiformis, which the gamergate maintains her reproductive with a few individuals of Po/yalthia longifolia, monopoly seems to have a built-in mechanism to Tamarindus indica and Ficus sp. The area (about ensure that a colony does not necessarily die if two hectares) was divided into 60 line transects. its gamergate dies. Mutilated workers do not Initially, an extensive search was conducted to mutilate others so that, upon the death of a locate the nests of D. ceylonense. All nests were gamergate, the next individual to eclose retains marked with sequentially numbered aluminium her gemmae, mutilates all those that eclose after tags and the tree nearest to each nest was marked her and takes over as the next gamergate of the with red paint. Every Monday, the nests were colony (Fukumoto et al. 1989, Peeters and monitored for activity and for the occurrence of Higashi 1989). While this description fits all other males. Nests that appeared to be abandoned were species of Diacamma examined so far, there does checked by inserting a stick inside the nest appear to be an exception. There is at least one entrance and waiting for the appearance of species in which the gamergate seems to be workers. In addition, such nests were also capable of maintaining reproductive monopoly monitored for activity during the subsequent 4-5 without mutilating her workers. This species, weeks, before confirming them as abandoned. On which was first found at the foot of the Nilgiri the first Monday and Tuesday of every month, hills, and mistakenly identified as Diacamma the entire study site was searched systematically vagans Smith (Peeters et al. 1992), is yet to be to record any newly initiated nests. Data thus described. We therefore refer to it here as obtained, during 213 weeks, on the numbers of Diacamma sp. from Nilgiri. Diacamma sp. from nests, numbers of newly initiated nests, Nilgiri is morphologically very similar to abandoned nests and number of males, were
534 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY. 100(2&3), AUG.-DEC. 2003 BIOLOGY OF THE QUEENLESS PONERINE ANT analysed in relation to abiotic factors such as observations and continuing throughout the maximum and minimum temperatures and total period of observation. All extranidal behaviours rainfall using the Kendall's correlation coefficient. visible to the observer, positioned near the nest Climatic data were obtained from the India mound, were recorded. The 852 hours of data Meteorological Station, Bangalore. As there was a thus colle.cted, were used to compute the number monotonic increase in the number of nests during the of extranidal ants active per day, the number of first 120 weeks ofstudy, a linear regression model was days for which different ants were active, and fitted to these data which was then used to predict the the rate per hour at which they performed probable time of colonisation of Jubilee Garden by extranidal activities. When the ants left the Diacamma ceylonense. vicinity of the nest mound, the compass direction Twenty-six colonies with all individuals and in which they· departed was recorded in eight brood were collected from within the Indian discrete directions namely North, Northeast, East, Institute of Science campus, but outside the Southeast, South, Southwest, West and Jubilee Garden. Nest characteristics such as height Northwest. When the foragers returned, what of the mound, number of brood chambers, depth they brought back (food, building material or of the nest and commensals encountered, were nothing) was noted. The proportion of successful recorded for all these nests. Head width and and unsuccessful trips made by foragers who alitrunk length of all individuals were measured in had made at least three trips were then computed 21 of these colonies. Data on head width and and compared. A successful trip was defined as alitrunk length were subjected to one-way analysis the act of returning to the nest with either food or of variance to partition variance within and building material. An unsuccessful foraging trip between colonies. In the nine colonies that had a was one in which the ants returned with neither gamergate, one-sample t-tests were performed to food nor building material. Data on foraging compare each gamergate with her workers. In 15 directions of all active foragers were subjected of these 21 colonies (including the nine that had a to Rayleigh's test (Batschelet 1981) of gamergate ), the numbers of mature eggs, width randomness to determine the degree of and length of proximal oocytes and the presence randomness in the foraging paths, both for (or absence) of sperm in the spermatheca, were individual ants as well as for colonies as a whole. recorded for all individuals by dissecting their Another eleven colonies were excavated in gaster. an attempt to predict the colony size from the Five other colonies were chosen for numbers of ants engaged in extranidal tasks. Over observation of the extranidal behaviours. Four a period of three days, all ants seen outside the of these colonies were observed for four weeks nest were marked. At least two persons spent 3 each while one was observed for 55 weeks. Each hours and 30 minutes each, per day (30 minutes at observation session was of 4-hour duration and the beginning of every hour from 0600 hrs-1800 was conducted either in the morning (0600 to hrs) for three consecutive days, marking the ants. 1000 hrs), midday (1000 to 1400 hrs) or afternoon Pilot experiments had indicated that this effort (1400 to 1800 hrs). One each of the morning, was more than adequate to mark all extranidal ants. midday and afternoon sessions were completed On the fourth day the nest was excavated to in each week, thus yielding 12 hours of data per determine the colony size (these nests were then week, per nest. All new workers seen outside the used for other experiments not reported here) so nest were uniquely marked with quick-drying that the relationship between the number of coloured paint on the thorax or abdomen, starting extranidal ants and the total colony size could be two weeks before the commencement of ascertained.
JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 535 BIOLOGY OF THE QUEENLESS PONERINE ANT
RESULTS AND DISCUSSION Table 2: Co-inhabitants observed in Diacamma ceylonense nests Diacamma ceylonense nests were found Commensal No. of nests in which to occur quite commonly in the study area. The observed nests are subterranean, with a distinct mound at Cockroaches 12 the entry of the nest. The mounds are often Crickets 11 decorated with dry twigs, leaves, insect and spider Pseudoscorpions 9 exuviae, and occasionally, bird feathers. Moffett Bagworms 3 Grubs (1985) observed that these decorations are used Earthw6rms to harvest dewdrops, which the ants drink in the lsopods 14 mornings. The excavated nests contained 230.5 Other ant species 1 ±108.6 adult female ants, 2.3 ±5.3 males, 18.5 ±19.4 eggs, 22.6±18. 7 larvae and 40.0 ±36.6 pupae. The yet complete. Of the 15 colonies used for nests were 63.9 ± 20.6 cm deep under the ground dissection, 9 had one gamergate each, while the with 4 .1 ± 1.2 brood chambers and the mounds remaining 6 colonies did not have a gamergate. were 3.2 ±4.1 cm above the ground (Table 1). The number of mature eggs in the gamergates Males were usually found in the first chamber, ranged from 0-24 with amean of8.78 ±10.28 eggs. closest to the entrance. The next 2-3 chambers None of the workers had developed ovaries and had brood and the last chamber at the bottom none of them were mated in any of the colonies, contained refuse. We often found cockroaches, including those without a gamergate (Table I). isopods, crickets, pseudoscorpions, bagworms, Thus D. ceylonense colonies are monogynous grubs, earthworms and a few other ant species in and recent molecular studies suggest that they the nests; we presume that these were commensals are also monoandrous but with some serial (Table 2). Nine out of the twenty-one colonies polygyny (gamergate turnover) (Gopinath 2002). excavated, seemed to lack a gamergate; the For both head width and alitrunk length, possibility that the gamergate was lost during there was a significant added variance between excavation seems unlikely but cannot, of course, colonies. In the case of head width, this added be entirely ruled out. The remaining 12 colonies variance between colonies was significantly invariably had only one gamergate each. In two higher than the variance within colonies, while in nests, one or two individuals other than the the case of alitrunk length, this variance was gamergate also had gemmae, but only on one side significantly less than the variance within of their thorax; perhaps their mutilation was not colonies (Table 3). Variance between colonies is
Table 3: One-way analysis of variance of head width and alitrunk length of individuals of Diacamma ceylonense from 21 colonies
Source OF SS MS F p
Head widtha Among colonies 20 1811.07 90.55 791.42 0.001 Within colonies 4731 541.31 0.11 Total 4751 2352.38
Alitrunk lengthb Among colonies 20 1151.20 57.96 94.61 0.001 Within Colonies 4683 2849.00 0.61 Total 4703 4000.19
8Variance between colonies significantly higher than variance within colonies t>variance between colonies significantly lesser than variance within colonies
536 JOURNAL. BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003
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±0.38 ±0.38
±0.39 ±0.39
±0.14 ±0.14
±0.04 ±0.04
±0.21 ±0.21
±0.29 ±0.29 ±0.25 ±0.25
±0.05 ±0.05
were were
1.4 1.4
proximal proximal
Length Length
(mm) (mm)
oocyte oocyte
1.31 1.31
1.33 1.33
1.27 1.27
1.03 1.03
0.25 0.25
0.73 0.73
0.95 0.95
0.98 0.98
found found
which which
were were
±0.04 ±0.04
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±0.13 ±0.13
±0.03 ±0.03
±0.06 ±0.06
proximal proximal
(mm) (mm)
oocyte oocyte
Width Width
those those
0.4 0.4
-
0.38 0.38
0.63 0.63
0.29 0.29
0.43 0.43
0.37 0.37 0.46 0.46
0.31 0.31
0.43 0.43
dissected dissected
of of
eggs eggs
0 0
3 3
0 0
8.8 8.8
0 0
0 0
13 13
16 16
23 23
24 24
±10.3 ±10.3
mature mature
No. No.
eggs" eggs"
ceylonense ceylonense
bmature bmature
3 3
gamergates gamergates
±0.10 ±0.10
±0.14 ±0.14
±0.16 ±0.16
±0.14 ±0.14
±0.15 ±0.15
±0.16 ±0.16
±0.14. ±0.14.
±0.16 ±0.16 ±0.23 ±0.23
±0.15 ±0.15
±0.16 ±0.16
±0.17 ±0.17
±0.14 ±0.14
±0.16 ±0.16
±0.17 ±0.17
±0.20 ±0.20
±0.21 ±0.21
±0.13 ±0.13
±0.14 ±0.14
±0.17 ±0.17
±0.14 ±0.14
All All
length
(mm) (mm)
Alitrunk Alitrunk
4.51 4.51
4.14 4.14
3.91 3.91
4.10 4.10
4.29 4.29
3.97 3.97
4.25 4.25 4.32 4.32
4.20 4.20 4.26 4.26
4.32 4.32 4.06 4.06
4.15 4.15
4.07±0.18 4.07±0.18
4.18 4.18
4.14 4.14 4.28 4.28
4.10 4.10
4.23 4.23 4.54 4.54 4.21 4.21
4.16 4.16
(n=4703) (n=4703)
Diacamma Diacamma
colonies; colonies;
in in
3 3
some some
±0.03 ±0.03
±0.05 ±0.05
±0.09 ±0.09
±4.29 ±4.29
±0.07 ±0.07 ±0.08 ±0.08
±0.07 ±0.07 ±0.08 ±0.08
±0.05 ±0.05
±0.05 ±0.05
±0.06 ±0.06 ±0.08 ±0.08
±0.06 ±0.06
±0.08 ±0.08 ±0.06 ±0.06
±0.08 ±0.08
±0.07 ±0.07
±0.05 ±0.05 ±0.07 ±0.07
±0.07 ±0.07
±0.08 ±0.08
±4.28 ±4.28
gamergate; gamergate;
in in
Head Head
width
(mm) (mm)
1.99 1.99
2.29 2.29
2.06 2.06
2.00 2.00
2.02 2.02
2.02 2.02 2.02 2.02
2.26 2.26
2.00 2.00 2.07 2.07
2.10 2.10
2.06 2.06
2.06 2.06 2.00 2.00
2.03 2.03
2.01 2.01
2.06 2.06
2.06 2.06
2.04 2.04
2.03 2.03
2.04 2.04 2.05 2.05
(n=4751) (n=4751)
individuals individuals
without without
the the
5 5
3 3
5 5
4 4
3 3
5 5
3 3
2 2
5 5 4 4
2 2 5 5
4 4
5 5
4 4
4 4
3 3
5 5
7 7 6 6
4.1 4.1
4 4
2 2
of of
4 4
4 4
±1.2 ±1.2
brood brood
No.of No.of
chambers chambers
°Colony °Colony
measurements measurements
5 5
0 0
0 0
6 6
5 5 5
0 0
0 0
0 0
0 0
0 0
0 0
0 0
3.2 3.2
0 0
0 0
0 0
8 8
0 0
0 0
5 5
0 0
8 8
7 7 3
Height Height
of of
(cm) (cm)
mound mound
length length
10 10
10 10
10 10
10 10
±4.1 ±4.1
counted; counted;
measurements measurements
nest nest
not not
alitrunk alitrunk
50 50
50 50
55 55
50 50
75 75 50 50
65 65
65 65
60 60
65 65
80 80 70 70
50 50
85 85
50 50
60 60
60 60
63.9 63.9
65 65
65 65 60 60
60 60
45 45 70 70 65 65
40 40
of of
Depth Depth
(cm) (cm)
150 150
±20.6 ±20.6
body body
and and
dEggs dEggs
and and
3 3
0 0
0 0
0 0
0 0
11 11
15 15
15 15
15 15
12 12 78 78
18 18
30 30
35 35
45 45
75 75
38 38 23 23
53 53
55 55
40.0 40.0
64 64
49 49
No.of No.of
pupae pupae
110 110
103 103
130 130
±36.6 ±36.6
width width
done; done;
head head
1 1
0 0
8 8
9 9
0 0
0 0
0 0
not not
11 11
11 11
13 13
13 13
51 51
23 23
51 51
10 10
55 55 29 29
20 20
31 31
26 26
21 21
36 36
66 66 64 34 34
33 33
35 35
22.6 22.6
larvae larvae
No.of No.of
±18.7 ±18.7
for for
composition composition
d d
d d
0 0
8 8
3 3
0 0
0 0 0 0 0 0
0 0
0 0
0 0
9 9
used used
11 11
11 11
No.of No.of
14 14
18.5 18.5
36 36
33 33
28 28
eggs eggs 42 42
24 24
35 35
66 66
33 33
44 44
46 46
±19.4 ±19.4
Colony Colony
not not
1: 1:
measurements measurements
0 0
0 0
1 1
0 0 1 1
0 0
1 1
8 8
3 3
0 0
0 0
0 0
0 0
0 0 0 0
0 0
0 0 0 0
0 0 0 0
0 0
0 0 0 0
2.3 2.3
No.of No.of
10 10
males males
13 13
22 22
±5.3 ±5.3
were were
Table Table
cBody cBody
9 9
9 9
8 8
8 8
8 8
8 8
6 6
18° 18°
91 91
45
No.of No.of
females females
184c 184c
341 341 158 158
140
138
161 161
131 131
292c 292c
180° 180°
499
319 319 250 250
237c 237c
269 269
22oc 22oc 420
230.5 230.5
297 297
262c 262c
286 286
293 293
312 200
251 251
duct; duct;
±108.6 ±108.6
individuals individuals
spermatheca. spermatheca.
the the
main main
1 1
D-1 D-1 14 14
13 13
19 19
12 12
18 18
17 17
10 10
16 16
15 15 5 5
3 3
2 2
11 11
7 7 6 6
D-3 D-3
9 9
8 8 D-4 D-4
22 22
4 4
21 21
20 20
D-2 D-2
code code
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of of
the the
the the
in in
9% 9%
of of
to to
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Up Up
Date Date
18.01.95 18.01.95
15.11.94 15.11.94
13.07.95 13.07.95 24.02.94 24.02.94
collection collection
MEAN MEAN 16.06.95 16.06.95 25.01.94 25.01.94
28.07.94 28.07.94
17.05.95 17.05.95 25.11.93 25.11.93
28.06.94 28.06.94 1509.95 1509.95
13.09.95 13.09.95 24.05.94 24.05.94
27.04.94 27.04.94
28.09.94 28.09.94
31.03.94 31.03.94
31.08.94 31.08.94
23.08.94 23.08.94 25.07.95 25.07.95 07.02.95 07.02.95
27.10.95 27.10.95 06.12.94 06.12.94
sperms sperms
27.10.94 27.10.94
05.04.95 05.04.95
08.03.95 08.03.95 8
to to
23.08.95 23.08.95
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200 likely to have a genetic basis and variance within (a) colonies, a nutritional basis. As expected from (/) fil 150 the fact that the gamergate is simply an unmutilated c: worker, in 17 out of 18 tests (9 colonies, each tested
213 weeks. Males were few in number but (/) were recorded 538 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 BIOLOGY OF THE QUEENLESS PONERINE ANT J!l en Q) c i 0 ~ E z:::> -150 t i t -50 0 50 100 150 200 250 300 -113 -85 Week -99 Fig. 2: Number of active nests from the 120-week data was used to fit a linear regression model which was extrapolated backwards using the slope and its 95% confidence intervals, to estimate the probable time of colonisation of Jubilee Garden by Diacamma ceylonense Diacamma cey/onense workers are extranidal tasks like nest cleaning and shifting of individual, diurnal foragers with directional fidelity materials around the nest increased soon after within a narrow range of directions (as seen from rainfall. On finding an item of prey, the forager our observations given below). Their major food paralysed it by stinging and returned with it to consisted of termites, although bugs, the nest quickly and in a short, more linear path cockroaches, grasshoppers, crickets, spiders and as compared to the often long-winding path it other species of ants were also observed being had followed during its outward journey. When a brought to the nest on some occasions. Prey, termite nest or trail was discovered, the successful however large, was never retrieved in groups, but forager made repeated trips to the same source. there was some cooperation among the workers The mean number of active individuals seen near the nest to manoeuvre it through the nest outside the nest during any 4-hour observation entrance. Foraging continued for most of the day session varied from about 6 to 32 and the mean on colder days, but was restricted to the mornings foraging life span of workers ranged from 9 to 23 and evenings only, on warmer days. Foraging was days (Table 4). Foraging was the most frequently suspended during heavy rains although some performed extranidal activity. In four out of five Table 4: Number of active animals per observation session, and foraging life span in five colonies Nests No. of sessions & No. of active animals/session• Foraging life span in days No. of days observed Mean ±SD (Range) Mean ±SD (Range) 071 165 sessions; 385 days 6.7 ±3.6 (1-17) 23.3 ±22.2 (1-154) 025 12 sessions; 26 days 17.2 ±2.2 (11-21) 13.2 ±10.2 (2-26) 056 12 sessions; 27 days 32.3 ±8.0 (22-51) 9.0 ±7.6 (2-27) 0117 12 sessions; 26 days 12.9 ±3.7 (5-18) 12.9 ±8.7 (2-26) 0134 12 sessions; 23 days 16.2 ±5.5 (4-22) 15.5 ±6.1 (2-23) •1 session = 4 hours JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 539 BIOLOGY OF THE QUEENLESS PONERINE ANT 63 121 62 902 179 0.75 94 824 95 J'5 0.5 ! ta. 12 0.25 0 Colony71 Colony25, Colony56 Colony 117 Colony134 Fig. 3: Proportions of successful (shaded bars) and unsuccessful (blank bars) trips made by foragers in five colonies (numbers above bars are the numbers of successful/unsuccessful trips) colonies (Fig. 3; Mann Whitney U test; Colony individual foragers were non-random with respect 71, 56 and 134atp<0.001, and Colony 117 atp<0.05), to the directions in which they made foraging trips, the number of successful foraging trips was but that the colony as a whole (with all its foragers significantly less than the number ofunsuccessful put together) was random in this regard. In each trips In one colony (Fig. 3, Colony 25), foragers colony, even the most random forager was less were somewhat more successful in retrieving prey so than the colony as a whole (according to items, but the number of successful and Rayleigh's test of randomness, p<0.05, see Fig. unsuccessful trips did not differ significantly from 5). The mechanism by which the foragers achieve each other (Mann Whitney U test, p>0.05). such collective randomness, in spite of individual Foragers who had made at least three trips were non-randomness, remains to be investigated. used for this analysis. The proportions of Experiments in which all the ants seen successful and unsuccessful trips were computed outside the nests· were marked before nest for each worker and then averaged across workers excavation demonstrate that the number of ants in each colony. seen outside the nest is a reasonably constant Many foragers seemed to be faithful to proportion of the total colony (24.39% ±9.63%) certain foraging directions (Fig. 4), although the (Table 5). This information can be used to colony itself seemed to have foragers covering approximately infer colony size without all dire~t!!>ps. Rayleigh's test of randomness necessarily having to excavate nests. Besides confirms that in all five colonies studied, helping to avoid unnecessary excavation of nests, 540 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 BIOLOGY OF THE QUEENLESS PONERINE ANT 100 Table 5: Colony size and percentage of extranidal ants 60 Colony No. of 60 Colony Percentage Colony 71 code extranidal size of foragers 40 n=96; T=1830; ants marked 20 I I.___ DC28 69 457 15.10 0 _ I DC29 89 376 23.67 100 DC30 135 593 22.77 60 DC31 23 192 11.98 60 DC42 23 121 19.00 Colony25 DC47 47 40 n=28; T=265; 145 32.41 DC52 47 271 17.34 20 DC53 24 137 17.51 0 11 ____ _ I DC64 60 145 41.38 100 ~ DC65 39 103 37.86 Q) 60 Cl DC66 12 41 29.26 I!! 60 $2 Colony 56 Mean ±SD 51.6 ±35.9 234.6 ±171.6 24.39 ±9.63 40 n=65; cQ) T=231; e 20 the proportion of foragers is in itself a useful 8?. 0 I 1. ____ _ parameter in many kinds of studies (see for e.g. 100 Andre et al. 2001, Gopinath 2002). Investigations to determine intra-colony genetic relatedness 60 using microsatellite markers, population genetic 60 Colony 117 structure using both nuclear and mitochondrial 40 n=23; T=94; markers and the mechanism of mutilation of the gemmae are in progress and would form the 20 1 ______subjects of future publications. 0 100 I ACKNOWLEDGEMENTS 60 60 We thank the Ministry of Environment and Colony 134 40 Forests, Department of Science and Technology, n=19; T=66; Council for Scientific and Industrial Research, 20 I ______Department of Biotechnology, Government of 0 India I1 2 3 4 5 6 7 8 and the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, for Number of directions foraged financial assistance, and several student trainees n = number of foragers observed and visitors, including Karthik, Nutan, Sumana, T = total number of trips observed Vidya, Yuvana, Andre, J.-B. and Ravi Kumar for help with marking ants in the field, for various Fig. 4: Frequency distribution of numbers of foragers experiments. who foraged in different numbers of direction We also thank Christian Peeters for in five colonies helpful comments on an early draft of this paper. JOURNAL, BOMBAY NATURAL HISTORY SOCIETY, 100(2&3), AUG.-DEC. 2003 541 BIOLOGY OF THE QUEENLESS PONERlNE ANT N (a) (b) (c) i 239 15 ...... >. 68 c: 271 332 0 13 0 0 (.) ~104 166 ~2 206 (n=96; r=0.13) (r=1.03) (r=0.36) lO N 06 32 c>. 0 21 2 0 9 0 (.) 25 (n=28;~ r=0.59) (r-1.03) (r=0.59) 25 ID lO . . >. c 30 24 0 ~1 ~1 0 .. u 30 16 . . 53 1 (n=65; r=0.11) (r-1.03) (r=0.36) 26 ,.._ ~9 19 ~ 26 10 - 3 8 1 (n=23; r=0.48) (r=1.03) (r=0.82) 6 (") "'" 6 >. 7 c 2 0 0 16 0 u 5 ~9 (n=19; r=0.23) (r-1.03) n = no. of foragers for the colony as a whole; r = randomness Bars are proportions of number of trips made by forager(s) in different directions. Values beside each bar indicate the number of trips made by one or more foragers (in a) and one forager (in b and c). Fig. 5: Foraging direction for (a) colony as a whole, (b) the most non-random forager and (c) for the relatively most random forager, in the five colonies studied. 542 JOURNAL, BOMBAY NATURAL HISTORY SOCIETY. 100(2&3), AUG.-DEC. 2003 BIOLOGY OF THE QUEENLESS PONERINE ANT REFERENCES ANDRE, J.-B., C. PEETERS & C. Doi.IMS (2001): Serial ant, Diacamma. Ph.D. thesis, Indian Institute of polygyny and colony genetic structure in the Science, Bangalore. monogynous queenless ant Diacamma cyaneiventre. HOLLDOBLER, B. & E.O. WILSON (l 990): The Ants. Behav. Ecol. Sociobiol. 50: 72-80. Harvard University Press, Cambridge, Massachusetts. BARONI URBANI, C., B. BOLTON & P.S. WARD (1992): The MOFFETT, M.W. (1985): An Indian Ant's Novel Method internal phylogeny of ants (Hymenoptera: for Obtaining Water. National Geographic Research Fonnicidae). Syst. Entomol. 17: 301-329. (Winter): 146-149. BATSCHELET, E. (1981): Circular Statistics in Biology. PEETERS; C. 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