Fecundity of ant queens in relation to their age and the mode of

Insectes Sociaux, Paris
9
Masson, Paris, 1990
1990, Volume 37, n ~ 2, pp. 116-130
FECUNDITY OF ANT QUEENS IN RELATION
TO THEIR AGE AND THE MODE OF COLONY FOUNDING
L. KELLER (1) and L. PASSERA (2)
(1) Musde Zoologique, Palais de Rumine, CP 448, 1000 Lausanne 17, Switzerland
(2) Laboratoire d'Entomologie, Universitd Paul Sabatier, 118, route de Narbonne, F 31062
Toulouse Cedex, France, U.A. C.N.R.S. 303
Regu le 23 janvier 1989
Accept6 le 15 juin 1989
SUMMARY
The change over time in the fecundity and weight of queens was investigated in three
monogynous, i n d e p e n d e n t colony founding species, Lasius niger, Camponotus ligniperda
a n d C. herculaneus, and two polygynous dependent colony founding species, Plagiolepis
pygmaea and Iridomyrmex humilis. Queens of the three species founding independently
exhibited a similar p a t t e r n with a significant loss of weight between mating and the
emergence of the first workers. In contrast, weights of queens of the species employing
d e p e n d e n t colony founding remained m o r e stable. Fecundity of queens founding independently increased slowly with time whereas fecundity of queens founding dependently
reached the m a x i m u m level some weeks after the beginning of the first reproductive
season. These results are discussed in relation to some differences in the life history
(e.g., life-span) b e t w e e n queens utilizing i n d e p e n d e n t and d e p e n d e n t colony founding.
RESUME
Fdcondit6 des reines de fourmis en relation avec leur &ge
et le mode de fondation de la soci6t6
On a 6tud6 dans ce travail les variations en fonction du t e m p s de la f6condit6 et du
poids des reines fondatrices de trois esp6ces monogynes h fondation ind6pendante
(Lasius niger, Camponotus ligniperda, Camponotus herculeanus) et de deux esp6ces
polygynes h fondation d6pendante (Plagiolepis pygmaea et Iridomyrmex humilis). Les
reines fondatrices des trois esp6ces ~ fondation ind6pendante m o n t r e n t des similitudes
avec une p e r t e de poids significative entre le m o m e n t de l'accouplement et celui de
l'6mergence des premi6res ouvribres. A l'inverse, le poids des jeunes reines h fondation
d6pendante reste plus stable apr6s l'accouplement. La f6condit6 des reines fondant de
mani6re i n d d p e n d a n t e augmente lentement avec le temps, alors que celle des reines fond a n t de fagon d6pendante atteint son niveau maximal quelques semaines seulement
apr6s le d6but de la premi6re saison d'activit6. Ces r~sultats sont discut6s dans le cadre
des diff6rences ph6nologiques (comme p a r exemple l'esp6rance de vie) qui apparaissent
e n t r e les reines p r a t i q u a n t les deux types de fondation.
FECUNDITY OF A N T Q U E E N S
117
INTRODUCTION
A colony of social insects may have a single functional, i.e., egg-laying
queen (monogyny) or more than one queen (polygyny) WILSON, 1974;
HOLLDOBLER and WILSON, 1977). Monogynous species generally exhibit high
intercolonial aggression. In contrast intercolonial aggression is generally
lower in polygynous species (H/)LLDOBLER and WILSON, 1977; KELLER and
PASSERA, 1989a).
Monogynous species generally employ independent colony founding i.e.,
after the nuptial flight, newly mated queens excavate a cell and rear the
first brood in isolation without the help of workers. A few exceptions can be
mentioned such as army ants which reproduce by colony fission (FRANKS
and HOLLDOBLER,~987). In contrast, many polygynous species can not found
new colonies without the help of workers (dependent colony founding)
(KELLER, unpublished). In those species, young queens remain within the
mot he r nest after mating or they enter a foreign colony of the same species.
Foundation of new colonies generally occurs by budding or fission; a process in which one or several queens move out of t h e nest, accompanied by
workers and establish a new colony.
A question of great interest is the adaptive value of polygyny vs. monogyny in the context of the evolution of sociality. Several authors have discussed the advantages of dependant and independent colony founding in
relation to dispersal ability, probability, of successful colonization of a new
habitat (H6LLDOBLERand WILSON, 1977 ; ROSENGRENand PAMILO, 1983 ; KELLER,
1988a) and relative investment of energy that each type of colony founding
necessitates (KELLER and PASSERA, 1988). In the case of independent
colony founding, it is well known that queens have low fecundity during the
founding stage (see BRIAN, 1983). After the emergence of the first workers,
fecundity of queens regulary increases with time. This can be explained first,
by the fact that food input in the colony depends on the num ber of workers,
and second by the fact that the number of workers limits th~ quantity of
brood which can be raised in the colony. In contrast to species with independent colony founding, species with dependent colony founding have
young queens which are accompanied by a high num ber of workers immediately after mating. This raises the question of whether these queens rapidly
reach a high leveI of fecundity after mating or, by contrast, if the fecundity
of queens increases as a function of their age. To investigate this question,
which is important in assessing the adaptive benefits of independent vs.
dependent colony founding, we compared the change in the fecundity of
queens in relation to age in five species of ants, three exhibiting independent
colony founding and two employing dependent colony founding.
L. K E L L E R
118
MATERIALS
a n d L. P A S S E R A
AND
METHODS
The fecundity of queens w a s investigated in three rnonogynous species, Lasius niger,
Camponotus herculeanus, C. ligniperda (independent colony founding), and two polyg y n o u s species, Plagiolepis pygmaea and Iridomyrmex humilis (dependent colony founding) f o r the two first years of their life.
Monogynous species : L. niger is a monogynous species employing i n d e p e n d e n t colony
founding. Colony founding may occur either by haplometrosis (queens s t a r t a n e w
colony alone) o r by pleometrosis (several queens associate during founding) (WALoFF,
1957).
C. herculeanus and C. ligniperda are generally monogynous although some nests m a y
contain up to three queens (H6LLDOBLER, 1962). In these two species, colony founding
may also occur by haplometrosis or pleometrosis (H~iLLDOBLFR, 1962).
Polygynous species : Plagiolepis pygmaea is a polygynous species w i t h a m e a n o f
17 queens p e r colony (MERCIER et al., 1985). In s o u t h e r n France, we have n e v e r observed
queens founding new colonies claustrally. We therefore suspect that this m o d e of colony
founding is a b s e n t o r very rare in this species. New colonies probably result f r o m
b u d d i n g a n d new queens are added by adoption of newly-mated queens after the m a t i n g
flights occurring in mid-July.
L humilis is a polygynous ant (NEWELL, 1909; MARKIN, 1970; KELLER, 1988b). In this
species, w o r k e r s are sterile (MARKIN, 1970; BARTELS, 1988); there is usually no nuptial
flight by queens, mating occurs, in the nest (PASSERA and KELLER, 1987; PASSERA et al.,
1988b), and colony founding is accomplished by budding (N~VELL and BARBER, 1913;
MARKIN, 1970).
Experimental
procedure
Founding queens of L. niger were collected in June 1987 near Lausanne, Switzerland
and those of C. herculeanus and C. ligniperda were collected j u s t a f t e r their nuptial
flight in early July close to the Marchairuz pass in the Jura mountains, Switzerland.
Young queens of these three species were housed in small nests (see PASSERAet al., 1988a)
and were fed t h r e e times a week with honey and m e a l w o r m s as soon as the first w o r k e r s
emerged. The n u m b e r of eggs, larvae, pupae and workers was counted and the queens
weighed weekly for two years. All colonies of the three species were overwintered at
12 - 3~ C for t h r e e m o n t h s f r o m the beginning of December to the end of February.
There was high mortality in the three species. Only data from queens survivir~g to the end
of the e x p e r i m e n t w e r e considered, i.e., 9 in L. niger and C. herculeanus each and 7 in
C. ligniperda.
P. pygmaea colonies were collected near Toulouse, France, in early July before the
yearly m a t i n g flight. They contained laying queens and sexual pupae. The ants w e r e
kept in small nests (see PASSERA, 1969) and maintained in a rearing r o o m at 26.5 • 1~ C
during the experimental period and at 12 • 1~ C during overwintering. After the emergence of the sexuals, mating flights occurred in a large experimental cage in the laboratory. The newly- inseminated queens shed their wings and r e t u r n e d to the nests. At
this time, each queen was marked w i t h a spot of paint. As a result of the r e t u r n of
the newly m a t e d females, at the beginning of October, colonies contained b o t h young
queens less t h a n f o u r m o n t h s old and old queens collected f r o m the field, at least
16 m o n t h s old. These colonies overwintered until March of the following year. Then,
they w e r e split into 24 units containing one " y o u n g " queens now 9 m o n t h s old a n d
24 units containing one "old ~'' queen being at least 21 m o n t h s old. Each queen w a s
F E C U N D I T Y OF A N T Q U E E N S
119
n u r s e d by 23 _ 4 w o r k e r s . Since in this species the fecundity of individual queens is
related to weight (MERCIERet al., 1985) we selected queens w i t h similar w e i g h t : the
m e a n weight of the young queens was 0.810 • 0.019 m g while t h a t of the old queens was
0.808 • 0.017 mg. During t h e first days following of the beginning of the experiment,
the units were m o n i t o r e d daily in o r d e r to d e t e r m i n e w h e n the queens b e g a n to lay.
Later, eggs were removed a n d counted at 7, 14, 21, 28 a n d 35 days a f t e r t h e beginning of
the experiment. At the same time each queen and a r a n d o m sample of 10 eggs from
b o t h young and old queens were weighed.
Colonies of I. humilis were collected in December 1986 in Port-Leucate n e a r Perpignan
in s o u t h e r n France. They were reared in conditions similar to those described by PASSERA
et al. (1988a) ; the ants were m a i n t a i n e d at a c o n s t a n t t e m p e r a t u r e of 28 • 2~ C a n d fed
w i t h a n artificial diet (see KELLER et al. in press). U n d e r these conditions queenless u n i t s
r e a r winged queens and males (PASSERA et al., 1988b). Mating soon occurs (5.1 ~- 2.0 days)
a f t e r emergence (KELLERand PASSERA, 1988; PASSERA et al., 1988b). I m m e d i a t e l y a f t e r
m a t i n g a n d dealation, 10 newly-inseminated queens were weighed, then housed individually in experimental units consisting of 700 workers. At 15, 30 a n d 45 days a f t e r the
beginning of the experiment, each queen was weighed a n d subjected to a n oviposition
test (see KELLER, 1988a) : each queen was confined to a small vial containing a layer of
d a m p p l a s t e r for 14 h o u r s a n d the n u m b e r of eggs laid was counted w i t h the aid of a
dissecting microscope. To c o m p a r e the fecundity of newly-emerged queens to t h a t of old
queens, 12 old queens which were collected on 7 April 1987 at the same place as the o t h e r
colonies were s u b m i t t e d to the same procedure. The age of these latter queens w a s
u n k n o w n b u t it was close to one year since queens are p r o d u c e d yearly in late spring.
F u r t h e r m o r e , m o s t of t h e m were p r o b a b l y not older t h a n one year since ca. 9 0 %
of the queens are executed by workers in May j u s t before the t i m e of the p r o d u c t i o n
of new sexuals (KELLERet al., 1989).
Statistical analysis
All d a t a were found to be normally d i s t r i b u t e d according to the Kolmogornov test.
All m e a n s were therefore c o m p a r e d with the t-test.
RESULTS
Species using independent c o l o n y f o u n d i n g
The three species employing independent
colony founding exhibited a
similar:pattern
in the change in weight and fecundity.
Data are therefore
presen~ted together
for'thesespecies.
Egg:taying started rapidly after the
m a t i n g f l i g h t (table I). T h e f i r s t l a r v a e w e r e p r o d u c e d f i r s t i n L. niger t h e n
i n t h e t w o C a m p o n o t u s s p e c i e s (table I). S i m i l a r l y , p u p a t i o n o f t h e f i r s t
b r o o d a n d e m e r g e n c e o f t h e f i r s t w o r k e r s o c c u r r e d e a r l i e r i n L. niger t h a n
i n t h e t w o C a m p o n o t u s s p e c i e s . I n t h e t w o C a m p o n o t u s s p e c i e s , C. ligniperda
had the slower brood development, pupae and workers being observed ca.
o n e w e e k l a t t e r t h a n i n C. herculaneus.
L. K E L L E R and L. P A S S E R A
120
T a b l e I. - - F i r s t r e c o r d of w o r k e r s a n d e a c h b r o o d
exhibiting independent colony founding.
s t a g e in t h e c o l o n i e s o f s p e c i e s
T a b l e a u I. - - D a t e s d ' a p p a r i t i o n d e s o u v r i b r e s et d u c o u v a i n d a n s les c o l o n i e s d ' e s p 6 c e s
avec fondation ind6pendante.
Species
First eggs
First larvae
First pupae
First workers
Lasius niger
2.8 -- 1.7 d a y s
3rd week
4th week
5th week
Camponotus herculaneus
2.8 • 1.8 d a y s
4th week
5th week
7th week
Camponotus ligniperda
2.1 • 1.3 d a y s
4th week
6th week
8th w e e k
A : L niger
150
~
~
youngqueens
30 -* B : C. herculaneus
.....
-----0---
youngqueens
~
9
120
old queens
~176
30-
o
30-
0
0
1
0
30 84
2
3
4
5
6
7
Time s i n c e s t a r t of experiment ( w e e k s )
C : C. llgnlperda
~
g
9
i
1
9
i
2
9
i
9
,
3
4
Time s i n c e
9
,
9
5
start
,
6
of
-
,
7
,
,
8
,
,
9
-
,
10
experiment
young~ueens
old q u e e n s
9
...
8
.,~
~ 2O
N
S
~ ~ .
I
N
S. .
o
iE
7= lo
'
9
i
1
-
,
2
-
|
a
-
J
4
9
J
s
9
=
e
.
t
z
-
,
a
9
Timeslncestadofexpedment(weeks)
Fig. I. - - N o m b r e
=
o
9
,
lo
Fig. 1. - - M e a n s + S E n u t n b e r o f e g g s
p e r c o l o n y of (A) Lasius niger
(N = 9), (B) Camponotus herculeanus (N = 7) a n d (C) Camponotus
ligniperda (N = 7) d u r i n g t h e 60
days following mating flight (young
q u e e n s ) a n d 60 d a y s f o l l o w i n g overw i n t e r i n g (old q u e e n s ) .
Probabilities a r e g i v e n f o r t - t e s t s ; * =
P < 0.05; ** = P < 0.01; *** =
P < 0.001.
d'oeufs m o y e n (-- e r r e u r s t a n d a r d ) c o m p t 6 s darts d e s soci~t6s d e (A)
Lasius niger (N = 9), (B) Camponotus herculeanus (N = 7) et (C) Camponotus
ligniperda (N = 7) p e n d a n t les 60 j o u r s q u i s u i v e n t l e v o l n u p t i a l ( j e u n e s r e i n e s ) et
p e n d a n t les 60 j o u r s q u i s u i v e n t l ' h i b e r n a t i o n (vieilles r e i n e s ) . L e s p r o b a b i l i t 6 s
s e n t d o n n ~ e s a p r ~ s a p p l i c a t i o n d u t e s t de t ; * = P < 0,05; ** = P < 0,01; *** =
P < 0,001.
FECUNDITY OF ANT QUEENS
121
Queen fecundity and brood composition
I n the t h r e e species, the n u m b e r of eggs p e r c o l o n y r e g u l a r l y i n c r e a s e d
a f t e r c o l o n y f o u n d i n g (fig. 1). The m a x i m u m n u m b e r of eggs w e r e r e c o r d e d
at w e e k 6 in L. niger, at w e e k 7 in C. herculanteus a n d at w e e k 3 in C. ligniperda. A f t e r h a v i n g r e a c h e d this m a x i m u m , egg n u m b e r d e c r e a s e d in the
t h r e e species a n d no m o r e eggs w e r e r e c o r d e d in the colonies f r o m w e e k s 15, 9
a n d 10 o n w a r d s f o r L. niger, C. herculaneus a n d C. ligniperda, r e s p e c t i v e l y .
The a b s e n c e of eggs in the colonies r e s u l t e d f r o m the c e s s a t i o n of egg laying
by queens until after overwintering.
C o m p o s i t i o n of the colonies a f t e r o v e r w i n t e r i n g is given in table II.
All colonies of the t h r e e species c o n t a i n e d no eggs a n d no p u p a e . The n u m b e r
of l a r v a e a n d w o r k e r s w a s s i m i l a r in the t w o s p e c i e s of Camponotus ( t - t e s t ,
NS). I n L. niger t h e n u m b e r of l a r v a e a n d w o r k e r s w a s f a r g r e a t e r ( t - t e s t ;
P < 0.001 f o r b o t h l a r v a e a n d w o r k e r s ) t h a n in t h e t w o species of Camponotus. A f t e r o v e r w i n t e r i n g , queens r a p i d l y s t a r t e d to lay eggs in the t h r e e
species (fig. 1); the n u m b e r of eggs p e r colony r e g u l a r l y i n c r e a s e d in the
t h r e e s p e c i e s a n d the m a x i m u m n u m b e r of eggs w e r e r e c o r d e d in the censuses p e r f o r m e d at weeks 4, 4 a n d 5 f o r L. niger, C. herculaneus a n d C.
ligniperda, r e s p e c t i v e l y . In the t h r e e species, the n u m b e r of eggs p e r colony
was h i g h e r in the censuses p e r f o r m e d a f t e r o v e r w i n t e r i n g t h a n in the corresp o n d i n g ones p e r f o r m e d a f t e r n u p t i a l flight (fig. 1). The d i f f e r e n c e was signif i c a n t f o r all c o m p a r i s o n s e x c e p t one in L. niger a n d C. herculaneus. In C.
ligniperda, the n u m b e r of eggs was also a l w a y s h i g h e r a f t e r o v e r w i n t e r i n g ,
b u t the d i f f e r e n c e was significant only for t h r e e censuses.
Weight of queens
A f t e r n u p t i a l flight, queens of the t h r e e s p e c i e s e x p e r i e n c e d a d r a s t i c
a n d c o n t i n u o u s loss of w e i g h t up to the t i m e of e m e r g e n c e of the first
w o r k e r s (fig. 2). W e i g h t d e c r e a s e d f r o m 27.6 • 2.6 mg to 15.1 - 3.2 mg
( m e a n __ S D ; p a i r e d t - t e s t ; P < 0.001; d e c r e a s e 45 %), 118.6 +- 26.0 to
76.3 4- 24.0 (P < 0.001; d e c r e a s e 36 %) a n d 164.6 --- 24.8 to "139.0 4- 17.1
(P < 0.001 ; d e c r e a s e 16 %) in L. niger, C. herculaneus and C. ligniperda, resTable II. - - Composition of the colonies after overwintering.
Tableau II. - - Composition des colonies apr6s l'hibernation.
Species
Number
of eggs
Number
of larvae
Number
of pupae
Number
of workers
Lasius niger
0
38.4 • 14.7
0
23.5 • 4.3
Camponotus herculaneus
0
5.3 -
3.8
0
3.5 • 1.0
Camponotus ligniperda
0
7.1 •
2.8
0
3.5 - 4.3
L. K E L L E R
122
A : L niger
---.--I=---.
401
9
J
9**
9.
***
***
a n d L. P A S S E R A
~-
old queens
.,
...
----D---
B : C. hercdeneus
young queetls
young queens
o/d queens
160.
NS
INS
140.
~'
z
*"
~' 1 ~ .
z
~ 19o80-
0
1
2
3
4
5
6
7
8
T i m e since start of experiment ( w e e k s )
----o---
C : C. ~gniperda
-----B-,,--
9
0
1
2
3
4
S
6
7
T i m e since start of experiment
8
9
10
(weeks)
young queens
old queens
190
NS
NS
"
"
T
T
NS
~ 170.
Fig. 2. --Means • SE weight of (A)
Lasius niger (N -- 9), (B) Camponotus herculeanus (N = 7) and (C)
Camponotus ligniperda (N = 7)
140 queens during the 60 days following
130mating flight (young queens) and
60 days following overwintering (old
120
. = - , - , . = . , . , . , . , . , . r
queens). Probabilities are given as
O
1 2 3 4 5 6 7 6 9 1 0
~ m e since start of oxpedmont (weeks)
in fig. 1.
Fig. 2. w Poids moyens (• erreur standard) des reines de (A) Lasius niger (N = 9), (B)
Camponotus herculeanus (N = 7) et (C) Camponotus ligniperda (N -- 7) pendant
les 60 jours qui suivent le vol nuptial (jeunes reines) et pendant les 60 jours qui
suivent l'hibernation (vieilles reines). Les probabilit6s sent calcul6es comme dans
la fig. 1.
p e c t i v e l y . A f t e r t h e t i m e of e m e r g e n c e of the f i r s t w o r k e r s , t h e w e i g h t of
q u e e n s of t h e t h r e e species i n c r e a s e d u p to a v a l u e s l i g h t l y h i g h e r t h a n t h a t
f o u n d at t h e t i m e of m a t i n g flight. W e i g h t of q u e e n s d e c r e a s e d s l i g h t l y
d u r i n g t h e t i m e of o v e r w i n t e r i n g , b u t i n c r e a s e d a g a i n a f t e r o v e r w i n t e r i n g .
Species u s i n g d e p e n d e n t colony f o u n d i n g
Plagiolepis pygmaea
A f t e r t r a n s f e r r i n g c o l o n i e s f r o m the r o o m w h e r e t h e y o v e r w i n t e r e d to
t h e r e a r i n g r o o m , q u e e n m o r t a l i t y w a s 12.5 % (N = 24) f o r y o u n g q u e e n s
a n d 25 % (N = 24) f o r old q u e e n s . H o w e v e r , this d i f f e r e n c e w a s n o t signif i c a n t 0r 2 = 1.23).
Y o u n g q u e e n s (N = 21) laid t h e f i r s t eggs 6.1 ___ 0.6 d a y s a f t e r overw i n t e r i n g , w h e r e a s old q u e e n s (N = 18) l a i d ca. t w o days l a t e r (7.9 • 0.6
F E C U N D I T Y OF A N T Q U E E N S
123
days; P (0.01).
Eggs l a i d b y t h e y o u n g q u e e n s w e r e s i g n i f i c a n t l y h e a v i e r
(12.0 ~ 0.04 lxg) t h a n t h e o n e s l a i d b y the old q u e e n s (10.8 - 0.01 ~ g ; P
0.01).
F e c u n d i t y of y o u n g q u e e n s w a s v e r y s i m i l a r to t h a t of old q u e e n s e x c e p t
a t w e e k s 1 a n d 5 w h e r e y o u n g q u e e n s h a d a h i g h e r f e c u n d i t y (fig. 3A).
Overall, t h e m e a n , n u m b e r of eggs p e r c o l o n y r e c o r d e d d u r i n g t h e 5 c e n s u s e s
w a s 31.4 ___ 29.0 f o r y o u n g q u e e n s a n d 17.8 - 16.7 f o r o l d q u e e n s (t = 1.71 ;
NS). I n t h i s species, f e c u n d i t y of q u e e n s is d e p e n d e n t o n t h e n u m b e r of
n u r s e s (PAssERA, 1972). S i n c e i n o u r e x p e r i m e n t s , t h e n u m b e r of w o r k e r s
p e r c o l o n y w a s low (23 ~ 4), this e x p l a i n s t h e r e l a t i v e l y l o w f e c u n d i t y of
q u e e n s c o m p a r e d to t h a t of t h e o n e o b s e r v e d i n c o l o n i e s n u r s e d b y a h i g h
n u m b e r of w o r k e r s (PAsSERA, 1972).
W e i g h t of old q u e e n s w a s n o t s i g n i f i c a n t l y d i f f e r e n t of t h a t of y o u n g
q u e e n s e x c e p t a t w e e k 2 (fig. 4A).
I r i d o m y r m e x humilis
D u r i n g t h e 45 days of t h e e x p e r i m e n t , t h e f e c u n d i t y of y o u n g q u e e n s
(N = 10) w a s s i m i l a r to t h a t of the o l d o n e s (N=~ 12) (fig. 3B) a n d t h e t o t a l
n u m b e r of eggs laid b y y o u n g q u e e n s a n d old q u e e n s w a s s i m i l a r (11.9 ___ 8.1,
r e s p e c t i v l y ; NS).
I n c o n t r a s t , y o u n g q u e e n s w e i g h e d less t h a n t h e old ones, this d i f f e r e n c e
b e i n g s i g n i f i s a n t f o r all w e e k s (fig. 4B).
12-
A : P. pygmao=
B : I. humitis
NS
.-.-o--9
young queens
8 -
ok[ queens
7 -
N,S;
NS
young queens
9
o(d queens
10-
teS
o
6 84
IE
4
6
0
4'
Z
2"
1
0
0
;
" ~-
~
-~-
T i m e I l n c e start of experiment ( w e e k s )
;
-
:
0
,
Time since start o f experiment (weeks)
Fig. 3. - - (A) Means -----SE number of eggs per colony of Plagiolepis pygmaea containing
young queens less than 9 months old (White squares, N = 21) and old queens being
one year older (black squares, N = 18). (B) Means -----SE fecundity of Iridomyrmex
humilis newly mated queens (white squares, N = 10) and old queens about one
year old (black squares, N --- 12). Probabilities are given as in figure 1.
Fig. 3. - - (A) Nombre d'~eufs moyen ( - erreur +standard) compt6s dans des soci6t6s de
Plagiolepis pygmaea contenant une jeune reine 5g6e de moins de 9 mois (carr6s
blancs, N = 21) et une vieille reine ~g6e d'au moins u n an (carr6s noirs, N = 18).
(B) F6condit6 moyenne (• erreur standard) de reines nouvellement f6cond6es
d'Iridomyrmex humilis (carr6s blancs, N = 10) et de reines vieilles ~g6es d'environ u n an (carr6s noirs, N = 12). Les probabilit6s sont calcul6es comme dans
la figure 1.
L. K E L L E R and L. P A S S E R A
124
1.3-
A : P. pygmaea
----o--
NS
4.0-
young queens
'9
01d queens
NS
B : I. humilis
young queens
..
9
old queens
NS
3.6 ~
L2-
A
ca 3.4 ~
E
g
J=
3.2 ~
3.0 ~
2.8 ~
1 . 0 84
ze~
0.9
9
i
1
-
~
2
,
=
3
-
=
,
4
=
5
9
,
2.4
6
Time since start of experiment (weeks)
Time since start of experiment (weeks)
Fig. 4. - - Means + SE weights of: (A) Plagiolepis pygmaea young queens less than 9
months old white squares, N = 21) and old queens being one year older (black
squares, N = 18).' (B) Iridomyrmex humilis newly mated queens (white squares,
N = 10) and old queens about one year old (black squares, N = 12). Probabilities
are given as in figure 1.
Fig. 4. - - Poids moyens (-- erreur standard) de : (A) jeunes reines de Plagiolepis pygmaea
-~g6es de moins de 9 mois (carr6s blancs, N = 21) et de vieilles reines fig6es d'au
moins un an (carr~s noirs, N = 18). (B) reines d'Iridomyrmex humilis nouvellement
f6cond6es (carr6s blancs, N = 10) et de vieilles reines fig6es d'environ un an (carr6s
noirs, N = 12). Les probabilit6s sent calcuMes comme dans la figure 1.
DISCUSSION
For queens of the three species with independent colony founding, the
number of eggs laid increased regularly during the first weeks after the
mating flight and then decreased when the first larvae hatched. This pause
in e g g - l a y i n g d u r i n g t h e g r o w t h o f t h e f i r s t b r o o d is w e l l - k n o w n in i n d e p e n d e n t c o l o n y f o u n d i n g a n t s ; it h a s b e e n o b s e r v e d b y POLDI (1963) in Tetram o r i u m caespitum, MARKIN et al. (1972) in Solenopsis invicta ONOYAMA (1981)
in M e s s o r aciculatus a n d KITAMURA (1984) i n Formica (Serviformica), japonica.
T h i s d e c r e a s e i n e g g n u m b e r m a y r e s u l t e i t h e r f r o m o o p h a g y of eggs b y
larvae and/or pheromonal inhibition of queen fecundity by larvae.
A f t e r o v e r w i n t e r i n g , t h e p a t t e r n w a s s i m i l a r to t h e f o u n d i n g s t a g e w i t h
a r a p i d i n c r e a s e i n egg n u m b e r f o l l o w e d b y a d e c r e a s e . H o w e v e r , in a l l
t h r e e s p e c i e s , t h e n u m b e r o f eggs i n t h e c o l o n y i n c r e a s e d a t a f a s t e r r a t e
and reached a higher number after overwintering than just after mating.
S i m i l a r r e s u l t s h a v e b e e n f o u n d in o t h e r s p e c i e s w i t h i n d e p e n d e n t c o l o n y
f o u n d i n g ; i n M y r m i c a rubra (BRIAN, 1957), O d o n t o m a c h u s h a e m a t o d e s
(COLOMBEL, 1970), Solenopsis invicta (MARKIN et al., 1973; LOFGREN et al.,
1981), Messor ebeninus (TOHMr 1975) a n d M. barbarus (CERDAN a n d DELYE,
1987), f e c u n d i t y o f q u e e n s w a s f o u n d to i n c r e a s e a s a f u n c t i o n o f t h e i r age
a n d a g e o f t h e c o l o n y . S i m i l a r l y , in Leptothorax nylanderi t h e r e is a cons-
FECUNDITY OF ANT QUEENS
125
tant increase in the n u m b e r of larvae p r e s e n t during the first 7 years of colony life (PLATEAUX, 1986). All these data are in a g r e e m e n t w i t h histological
a n d a n a t o m i c a l observations on queens of Camponotus lateralis (PALMA-VALLr
a n d D~LXE, 1981) showing that the n u m b e r of follicles p e r o v a r y increased
with the age of the queen f r o m 2 to 8 in young queens (1 to 3 years old) to
over 20 in old queens (5 to 6 years old).
Generally speaking, this increase of queen fecundity and b r o o d quantity
in colonies as a function of queen and colony age is linked to the exponential
g r o w t h of the colonies during the first years of t h e i r life (see BRIAN, 1965 and
ELMES, 1965 a n d ELMES, 1973). Fecundity of queens is p r o b a b l y d e p e n d e n t on
the n u m b e r of w o r k e r s which can feed t h e m and care for the brood. In this
respect, it is w o r t h w h i l e to m e n t i o n the higher increase of egg n u m b e r / c o l o n y
a f t e r o v e r w i n t e r i n g (as c o m p a r e d to the time a f t e r the m a t i n g flight) in L.
niger t h a n in t h e ' two Camponotus. This higher increase p r o b a b l y resulted
f r o m the higher n u m b e r of w o r k e r s in the L. niger at the end of overwintering.
The p a t t e r n exhibited by the d e p e n d e n t founding species P. pygmaea
and I. humilis c o n t r a s t s sharply w i t h that found in the i n d e p e n d e n t founding
species. I. hurnilis queens r e a c h e d very early, i.e., less t h a n two weeks a f t e r
emergence, t h e i r m a x i m a l fecundity. Similarly; fecundity, of young P.
pygmaea queens, only a few m o n t h old, was at least equivalent, if not higher,
t h a n t h a t of queens one y e a r older. These data suggest t h a t in c o n t r a s t to
the queens with independent colony founding, newly-mated queens of species
utilizing d e p e n d e n t colony founding are able to r e a c h their m a x i m a l rate of
egg o u t p u t w h e n they are very young : a few weeks old for I. humilis, and a
few m o n t h s old for P. pygmaea. However, the scarcity of r e s e a r c h conducted
on the fecundity of young dependently founding queens p r e v e n t s generalisation. EDWARDS (1987) obtained different results in Monomorium pharaonis.
Fecundity of young queens was far inferior to that of older queens. Similarly,
young queens of Myrmica rubra are less fecund t h a n older ones (BRIAN, 1988).
However, it is necessary to m e n t i o n that queens of these two species p r e s e n t
s o m e pecularities ; Monomorium pharaonis queens exhibit a life-cycle clearly
s e p a r a t e d into three distinct periods characterized b y a change in t h e i r inhibitory p o w e r over sexual production. Fecundity of queens m a y t h e r e f o r e dep e n d on this cycle. Gynes of Myrmica rubra m a y either found new colonies
i n d e p e n d e n t l y by non claustral colony founding or join an incipient nest (G.W.
ELMES p e t s . com.). This species m a y therefore not be a typical dependent
colony founding species.
Queens of species with i n d e p e n d e n t a n d , d e p e n d e n t colony founding
also differed drastically in weight change Over time. During the first weeks
of colony founding p r i o r to the emergence of the first w o r k e r s , there was a
significant d r o p in weight for queens founding independently. This drop
resulted f r o m the c a t a b o l i s m of the flight muscles a n d large fat reserves that
gynes a c c u m u l a t e d p r i o r to nuptial flight. At s w a r m i n g , fat content repre-
126
L. KELLER and L. PASSERA
sents 51, 43 a n d 46 % of the dry weight of gynes of L. niger, C. herculaneus
a n d C. ligniperda, respectively (KELLER and PASSERA, 1989b). These fat
r e s e r v e s p r o v i d e the energy needed b y queens to feed themselves a n d
the first b r o o d until the first w o r k e r s s t a r t foraging. I n contrast, queens of
P. pygmaea a n d I. humilis did not lose weight during the first period of their
r e p r o d u c t i v e activity. This can be explained b y the fact that soon a f t e r
mating, these queens are i m m e d i a t e l y fed b y w o r k e r s . I n this respect, it
should be m e n t i o n e d that gynes founding d e p e n d e n t l y do not a c c u m u l a t e
large a m o u n t s of fat p r i o r to m a t i n g (KELLER and PASSERA, 1989 b). For
example, fat constitutes only 25 % of dry weight of m a t u r e gynes of I.
humilis (KELLER a n d PASSERA,1988 ; KELLER and PASSERA, 1989 b).
The weights of queens of species founding i n d e p e n d e n t l y increased
r a p i d l y a f t e r the e m e r g e n c e of the first w o r k e r s . At the t i m e of overwintering,
t h e i r weight was similar to that at the t i m e of the nuptial flight. Dissection
of queens s h o w e d that this increase in weight r e s u l t e d at least partially f r o m
the d e v e l o p m e n t of the ovaries a n d storage of n e w fat reserves (KELLER and
PASSERA,u n p u b l i s h e d data). After overwintering, the weight of queens f u r t h e r
increased, b u t at a slow rate, being p r o b a b l y due m o s t l y to o v a r y development.
Young queens of I. humilis w e r e significantly lighter t h a n old ones. In
I. humilis, fecundity of queens is linked to their weight, heavier queens having
a higher f e c u n d i t y (KELLER, 1988b). ,Our results t h e r e f o r e seem c o n t r a d i c t o r y
since old queens w e r e heavier but h a d similar fecundity to young ones. One
possible e x p l a n a t i o n is that l a b o r a t o r y conditions m a y have influenced the
process of fat accumulation. Young queens which u n d e r w e g t all of their
m a t u r a t i o n in the l a b o r a t o r y m a y have had less o p p o r t u n i t y to accum u l a t e fat reserves in c o m p a r i s o n to the old queens which w e r e collected
in the field. I n P. pygmaea, there was only little difference b e t w e e n young
a n d old q u e e n s b o t h for weight and fecundity.
Considering the r e p r o d u c t i v e potentiality of the queens m u s t take into
a c c o u n t t h e i r life-span. Queens of L. niger have been o b s e r v e d to live m o r e
t h a n 28 y e a r s (KUTTERand STUMPER, 1969). One colony of Camponotus ligniperda w a s still alive a f t e r 7 years of o b s e r v a t i o n (KELLER u n p u b l i s h e d data).
Although y o u n g colonies of C. tigniperda m a y occasionally c o n t a i n several
queens (H/:iLLDOBLER, 1962), we have never found m o r e t h a n one queen in
m a t u r e colonies (KELLER u n p u b l i s h e d data), suggesting t h a t the queen of the
a b o v e m e n t i o n n e d colony has been alive for m o r e t h a n 7 years. While we
should r e m a i n cautious because m o s t data c o m e f r o m l a b o r a t o r y observations, a s u r v e y of the literature seems to indicate t h a t long life-spans of
m a t e d queens m a y be a c o m m o n feature of m o n o g y n o u s i n d e p e n d e n t founding
species. The survivorships of queens was at 1east 5/6 years in Camponotus
lateralis (PALMA VALLI and DgLYE, 1981), 5/6 years in several Myrmecia
(HASKINS a n d HASKINS, 1980), 10 years in Ectatomma quadridens (D. FRESNEAU
FECUNDITY OF ANT QUEENS
127
a n d J.P. LACHAUD, pers. com.), 9 years in Ectatomma ruidum (HASKINS and
HASKINS, 1980), Messor semirufus (ToHM~ and TOHM~, 1978) a n d Lasius alienus
(JANET, 1904), 10 years in Apnaenogaster picea (HASKINS, 1960), 11 years in
Camponotus perthensis (HASKINS a n d HASKINS, 1980), 12.5 years in Rhytidoponera purpurea (HASKINS and HASKINS, 1980), 11 to 20 years in several Leptothorax species (PLATEAUX, 1986), 17/18 years in Stenamma westwoudi
(DoNISTHORPE, 1936), 20 years in Crematogaster scuteUaris (J. CASEVITZWEULERSSE, com. pers.) a n d at least 22.5 years in Lasius flavus (PRESCOTY,
1973). Similarly, physiological studies by d e t e r m i n i n g s p e r m depletion in
~spermatheca gave an a p p r o x i m a t i o n of 6/7 y e a r s f o r the m e a n life span of
.queens in the m o n o g y n o u s f o r m of Solenopsis invicta (TSCHINKEL, 1987).
The life-spans of queens f r o m polygynous d e p e n d e n t colony founding
species s e e m to ~be shorter. Queens have b e e n e s t i m a t e d to live less than
o n e y e a r in Monomorium pharaonis (PEACOK a n d BAXTER, 1950; PETERSENBRAUM, 1975), 4.5 years in Odontomachus haematodes (HASKINS a n d HASKINS,
1980), and p r o b a b l y less t h a n 2 years in Wasmania auropunctata (P. ULLOAo
CHACON a n d D. CHERIX, pets. com.). According to ELMES (1980) it is very difficult to m a i n t a i n Myrmica queens in the l a b o r a t o r y for m o r e t h a n one
season. E m p i r i c a l data suggest that in the field, the queens of Myrmica
sulcinodis m a y live 4/5 years (ELMES, 1987). The life-span of m o s t queens
of. I. humilis is less than one year, resulting f r o m a m a s s i v e regicide that
o c c u r s each y e a r at the beginning of the r e p r o d u c t i v e season (KELLER et a!.,
1989). No data are presently available concerning the life-span of P.
pygmaea queens but it should be recalled t h a t in the e x p e r i m e n t r e p o r t e d
here the m o r t a l i t y was e s t i m a t e d at 25 % for old queens at the end of overwintering. I t is reasonable to i n t e r p r e t these d a t a as the result of a rather
short life-span of queens in this species.
Thus, a m a j o r difference in the life history of queens using d e p e n d e n t
a n d i n d e p e n d e n t colony founding m a y be a s h o r t e r life s p a n a s h o r t e r delay
in reaching m a x i m u m egg-output for the f o r m e r . F u r t h e r m o r e , since the
u l t i m a t e factors influencing the fitness of queens is not the n u m b e r of
w o r k e r s , b u t the n u m b e r of sexuals produced, it should be m e n t i o n e d that
queens of species with i n d e p e n d e n t colony founding have a chance to produce sexuals only w h e n the colony is m a t u r e , i.e., only a f t e r several years
(see O s t e r and WILSON, 1978), w h e r e a s queens e m p l o y i n g d e p e n d e n t colony
founding m a y p r o d u c e sexuals w h e n they are young, e.g., less t h a n one y e a r
in I. humilis (KELLERand PASSERA,u n p u b l i s h e d data).
Finally, NONACS (1988) developed a series of kin selection models in which
in investigated factors which m a y f a v o r polygyny in eusocial H y m e n o p t e r a .
Polygyny was found to be favored by s h o r t e r life-span of queens. Our
review on the litterature of life-span of queens of m o n o g y n o u s vs. polygynous
species s e e m s to s u p p o r t the models of NONACS. However, as m e n t i o n e d by
L. K E L L E R
128
NONACS h i m s e l f ,
it is n o t p o s s i b l e
a n d L. P A S S E R A
to determine
whether
short-lived
queen~.
favor polygyny or, alternatively, if polygyny selects for short-lived queens.
ACKNOWLEDGMENTS.
Our special thanks are due to E. L. VARGO and two anonymous:
r e f e r e e s for helpful criticisms and for English language editing.
-
-
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