I n s e c t e s Sociaux, Paris 1989, V o l u m e 36, n ~ 2, p p . 139-155
9 M a s s o n , P a r i s , 1989
QUEEN POLYMORPHISM IN LEPTOTHORAX SPEC.A:
ITS GENETIC AND ECOLOGICAL BACKGROUND (HYMENOPTERA : FORMICIDAE)
J . H E I N Z E ( 1 ) a n d A . B U S C H I N G E R
Inst. f. Zoologie, TH Darmstadt, Schnittspahnstrasse 3 D6100 Darmstadt, FRG
ReCu le 9 j u i n 1988 Accept6 le 1 '.'r d 6 c e m b r e 1988
S U M M A R Y
Queen p o l y m o r p h i s m in the n o n - p a r a s i t i c ant, Leptothorax spec. A, is m o s t p r o b a b l y genetically m e d i a t e d by a p a i r of alleles E/e. E s u p p r e s s e s the d e v e l o p m e n t of wings, thoracic s t r u c t u r e s a n d ocelli in female larvae. Only ee-larvae m a y grow to g y n o m o r p h i c , winged queens, EE- a n d Ee- larvae develop into i n t e r m o r p h i c , wingless queens. The frequency of i n t e r m o r p h i c q u e e n s varies widely in different h a b i t a t s . Whereas in h o m o g e n e o u s c o n i f e r o u s f o r e s t s t h r o u g h o u t s o u t h e r n a n d c e n t r a l Quebec the g y n o m o r p h is a b u n d a n t , in p a t c h i l y d i s t r i b u t e d rocky o u t c r o p s along the St. L a w r e n c e River inter- m o r p h i c q u e e n s p r e d o m i n a t e . We suggest a different dispersal success of the two m o r p h s in the various h a b i t a t s .
Z U S A M M E N F A S S U N G
K6niginnen-Polymorphismus bei keptothorax spec. A :
Genetischer und 6kologischer Hintergrund (Hymenoptera - Formicidae)
Der K / S n i g i n n e n p o l y m o r p h i s m u s d e r n i c h t - p a r a s i t i s c h e n Ameisena/'t Leptothorax spec. A w i r d genetisch, w a h r s c h e i n l i c h d u r c h ein Allelpaar E/e, k o n t r o l l i e r t . E u n t e r - dri.ickt dabei in w e i b l i c h e n L a r v e n die E n t w i c k l u n g von Flfigeln. Ocellen u n d Thorax- nShten, n u r ee-Larven k/Snnen zu geflfigelten, g y n o m o r p h e n Jungk/Sniginnen h e r a n w a c h s e n . EE- u n d Ee-K~iniginnen sind i m m e r i n t e r m o r p h . Die HSufigkeit i n t e r m o r p h e r K 6 n i g i n n e n im F r e i l a n d v a r i i e r t yon P o p u l a t i o n zu Population: in den h o m o g e n e n , lichten Nadel- w~ildern S/.id/und Z e n t r a l q u e b e c s iiberwiegt die G y n o m o r p h e , in i n s e l a r t i g beschr~inkten Biotopen, wie auf den Felsfl~ichen a m L o r e n z s t r o m , d o m i n i e r e n i n t e r m o r p h e Weibchen.
U n t e r s c h i e d l i c h e r E r f o l g d e r b e i d e n M o r p h e n in den v e r s c h i e d e n e n B i o t o p e n w i r d ange- n o m m e n .
(I) Present address: MCZ-Labs, Harvard-University, Cambridge, MA 02138, USA.
140 J. H E I N Z E and A. BUSCHINGER I N T R O D U C T I O N
T h e t y p i c a l a n t q u e e n is m o r p h o l o g i c a l l y distinct f r o m the w o r k e r . Queens (9 2) a r e g y n o m o r p h i c , t h e y u s u a l l y h a v e ocelli, t h e y h a v e wings, w h i c h a r e s h e d a f t e r m a t i n g , a n d t h e i r v o l u m i n o u s t h o r a x c o n s i s t s of indi- vidual sclerites. T h e w o r k e r s (~ ~), on the o t h e r hand, a r e e r g a t o m o r p h i c , t h e y n e v e r h a v e w i n g s a n d the t h o r a c i c sclerites a r e widely fused. I n the a n t s u b f a m i l y M y r m i c i n a e , e r g a t o m o r p h s u s u a l l y d o n ' t h a v e ocelli.
I n a n u m b e r of species, h o w e v e r , q u e e n s a r e r e g u l a r l y found, w h i c h a r e w o r k e r l i k e o r i n t e r m o r p h i c , i.e. s h o w i n g m o r p h o l o g i c a l l y f e a t u r e s i n t e r m e - diate b e t w e e n t h o s e of g y n o m o r p h s a n d e r g a t o m o r p h s . I n i n t e r m o r p h i c queens, w i n g s a n d ocelli a r e r e d u c e d a n d t h e i r t h o r a c i c s t r u c t u r e s a r e simplified.
I n t e r m o r p h i c a n d e r g a t o m o r p h i c q u e e n s a r e k n o w n f r o m several species of ants belonging to the m o r e p r i m i t i v e s u b f a m i l i e s P o n e r i n a e or Cerapa- chyinae. A m o n g t h e h i g h e r ants they o c c u r in s o m e social p a r a s i t i c species, s u c h as Polyergus ru[escens, Tetramorium ergatogyna, Harpagoxenus sub- laevis, the guest-ant genus Formicoxenus, Leptothorax wilsoni, a n d Aporo- myrmex ampeloni.
Queen p o l y m o r p h i s m , the coexistence of several m o r p h o l o g i c a l l y diffe- r e n t queens w i t h i n o n e species, in n o n - p a r a s i t i c h i g h e r a n t s os k n o w n only f r o m a couple of species. I n the l i t e r a t u r e , i n t e r m o r p h i c o r e r g a t o m o r p h i c q u e e n s a r e listed, e.g., for several Monomorium (BOLTON 1986, DO BOIS 1986), a n d two N o r t h A m e r i c a n species of the genus Leptothorax (FRANCOEUR 1986, HEINZE a n d BUSCHINGER 1987). R e c e n t l y we h a v e s t u d i e d t h e . m o r p h o l o g y of i n t e r m o r p h i c a n d g y n o m o r p h i c queens in one of the l a t t e r species. This n o n - p a r a s i t i c a n t b e l o n g s to the N o r t h A m e r i c a n Leptothorax " m u s c o r u m "
c o m p l e x (BROWN 1955) a n d is n o t yet f o r m a l l y described. T h e r e f o r e , we h e r e again r e f e r to it as Leptothorax spec. A.
L. spec. A is a c o m m o n a n t in the b o r e a l f o r e s t s of N o r t h e a s t America.
The f r e q u e n c y of colonies w i t h i n t e r m o r p h i c q u e e n s varies widely f r o m p o p u l a t i o n to p o p u l a t i o n . I n Quebec it r a n g e s f r o m a b o u t 15 % in G r a n d s J a r d i n s N a t i o n a l P a r k to o v e r 80 % in T a d o u s s a c .
Queen p o l y m o r p h i s m in a n t s h a s b e e n t h o r o u g h l y s t u d i e d only in t h e p a l a e a r c t i c s l a v e - m a k e r ant, Harpagoxenus sublaevis. H e r e the q u e e n m o r p h is m o s t p r o b a b l y genetically m e d i a t e d b y one single, diallelic locus (BuscHIN- GER 1975, 1978). T h e d o m i n a n t allele E s u p p r e s s e s the d e v e l o p m e n t of wings, t h o r a c i c sclerites a n d ocelli in larvae, w h i c h a r e epigenetically d e t e r m i n e d to b e c o m e q u e e n s . E E - - a n d E e - - q u e e n s always a r e i n t e r m o r p h i c . Only f r o m e e - b r o o d a r e g y n o m o r p h i c , w i n g e d f e m a l e s r e a r e d . I f a g y n o m o r p h m a t e s w i t h t h e s o n of a h o m o z y g o u s i n t e r m o r p h i c queen, the y o u n g q u e e n s in h e r o f f s p r i n g will be i n t e r m o r p h i c f e m a l e s (ee x E ~ Ee). The alleles do n o t a f f e c t t h e r e p r o d u c t i v e organs. I n t e r m o r p h s a n d g y n o m o r p h s b o t h
QUEEN POLYMORPHISM 141 h a v e eight o v a r i o l e s a n d a r e c e p t a c l e , t h e y b o t h m a t e a n d m a y b e c o m e f e r t i l e queens. E r g a t o m o r p h i c w o r k e r s u s u a l l y h a v e s i m p l i f i e d ovaries, c o n s i s t i n g of t w o to eight ovarioles, a n d l a c k i n g the r e c e p t a c l e (BusCHINGER a n d WINTER 1978). I n s o m e cases e r g a t o m o r p h i c w o r k e r s a n d i n t e r m o r p h i c q u e e n s c o u l d o n l y b e d i s t i n g u i s h e d b y dissection.
T h e g e n o t y p e s E E , Ee, a n d ee h a v e s t r o n g influence on t h e r a t i o of w o r k e r s a n d y o u n g q u e e n s r e a r e d in t h e colonies. I n f o u r b r e e d i n g cycles, colonies of t h e m a t i n g t y p e s E E • E a n d ee • e p r o d u c e d a l m o s t e q u a l n u m b e r s of f e m a l e d e s c e n d a n t s , b u t the ~ 9 / g ~ r a t i o d i f f e r e d significantly.
I n total, 18.8 % of t h e h o m o z y g o u s E E - arid 60.3% of t h e e e - b r o o d b e c a m e y o u n g q u e e n s . Caste d e t e r m i n a t i o n in H. sublaevis is i n f l u e n c e d b y t h e E / e - s y s t e m in t w o ways: the E-allele slows d o w n the d e v e l o p m e n t of the b r o o d , a n d t h e i n h i b i t o r y c a p a c i t y of E E - q u e e n s is h i g h e r t h a n t h a t of ee- q u e e n s (WINTER a n d BUSCHINGER 1986).
Since in a b o u t 99 % of all colonies collected f r o m the field the q u e e n w a s an i n t e r m o r p h , t h e r e is a p p a r e n t l y a s t r o n g ecological a d v a n t a g e f o r wingless f e m a l e s . T w o f a c t o r s f a v o r i n t e r m o r p h i c queens. One is t h e h i g h e r w o r k e r - b i a s . T h e m o r e g ~ a r e r e a r e d in a colony of the s l a v e - m a k e r Harpagoxenus, the m o r e s u c c e s s f u l a r e the slave-raids. Second, host-species colonies o c c u r in highly v a r i a b l e densities, a n d s u i t a b l e sites w i t h h i g h p o p u l a t i o n densities a r e p a t c h i l y d i s t r i b u t e d . An i n t e r m o r p h i c y o u n g queen, thus, m a y h a v e a b e t t e r c h a n c e ~to find a h o s t n e s t f o r colony f o u n d a t i o n in the vicinity of h e r m o t h e r ' s n e s t t h a n an alate, g y n o m o r p h i c q u e e n w h o m i g h t d r i f t off into u n s u i t a b l e h a b i t a t s d u r i n g flight activity. W i n g e d f e m a l e s , on t h e o t h e r h a n d , m a y b e i m p o r t a n t f o r the i n f e s t a t i o n of n e w h o s t p o p u l a t i o n s (WINTER a n d BUSCHINGER 1986).
According to t h e s e a u t h o r s , the b e s t a d a p t e d colony type w o u l d b e Ee • E: Due to the c a s t e - d e t e r m i n i n g influence of E a n d e, these colonies p r o d u c e a r e a s o n a b l y high n u m b e r of g g f r o m EE-larvae, a n d also m a n y i n t e r m o r p h i c q u e e n s f r o m Ee-larvae. W h e n the old q u e e n dies a f t e r a b o u t 10 y e a r s the declining colony p r o d u c e s a v e r y high n u m b e r of" m a l e s w h i c h t h e n a r e w o r k e r - o f f s p r i n g . Since t h e w o r k e r s a r e p r e d o m i n a n t l y E E , t h e i r sons will .be..mostly....E ... Im..Ihe.._population .a .high .fraction of the y o u n g e r g a t o i d f e m a l e s will b e Ee ( o f f s p r i n g f r o m the q u e e n r i g h t Ee • E colonies), a n d also a high f r a c t i o n of the ~ ~ will b e E ( o f f s p r i n g f r o m q u e e n l e s s colonies w i t h laying E E - w o r k e r s ) . Most y o u n g colonies t h e n s h o u l d b e Ee • E, again, a n d the s y s t e m is b a l a n c e d .
A l m o s t n o t h i n g is k n o w n a b o u t the role of wingless queens in non- p a r a s i t i c species. BOLTON (1986) d e v e l o p e d the h y p o t h e s i s , t h a t in s e v e r a l species of Monomorium the loss of wings a n d o t h e r f e a t u r e s of the g y n o m o r p h in t h e q u e e n c a s t e is a s i d e - p r o d u c t of d e p e n d e n t colony f o u n d a t i o n via p o l y g y n y a n d b u d d i n g . The r i s k f o r a y o u n g q u e e n is f a r lower, if she r e m a i n s in h e r m o t h e r ' s colony a f t e r m a t i n g , b e c o m e s fertile there, a n d
142 J. H E I N Z E a n d A. B U S C H I N G E R
f o u n d s a n e w c o l o n y b y c o l o n y f i s s i o n o r b u d d i n g , t h a n d u r i n g i n d e p e n d e n t c o l o n y f o u n d a t i o n . I f r e s o u r c e s a r e r e s t r i c t e d , as o n r o c k y i s l a n d s o r i n d e s e r t s , c o l o n i e s s h o u l d p r e f e r to i n v e s t e n e r g y i n t o w i n g l e s s f e m a l e s w i t h a s t a t i o n a r y s e x u a l b e h a v i o r , w h o a r e h i g h l y s u c c e s s f u l i n c o l o n y f o u n d a t i o n . S i m i l a r l y , c e r t a i n F o r m i c a s p e c i e s , w h o s e q u e e n s a r e c l u m s y f l i e r s a n d r e t u r n t o t h e i r m o t h e r s ' n e s t s , s e e m to h a v e a d v a n t a g e s i n p a t c h i l y d i s t r i b u t e d h a b i t a t s (RoSENOREN a n d PAMILO 1983).
D u r i n g t h e p a s t f e w y e a r s w e h a v e e x t e n s i v e l y s t u d i e d t h e b i o l o g y of L e p t o t h o r a x s p e c . A f r o m v a r i o u s p o p u l a t i o n s i n N e w E n g l a n d . W e h e r e r e p o r t r e s u l t s o f e x p e r i m e n t s d e s i g n e d t o a s c e r t a i n w h e t h e r t h e q u e e n poly- m o r p h i s m of L e p t o t h o r a x s p e c . A is g e n e t i c a l l y m e d i a t e d , s i m i l a r to t h a t of H a r p a g o x e n u s s u b l a e v i s , a n d d i s c u s s t h e e c o l o g i c a l b a c k g r o u n d of q u e e n p o l y m o r p h i s m i n t h i s s p e c i e s .
M A T E R I A L A N D M E T H O D S
Complete colonies of Leptothorax spec. A and related species of the myrmicine tribe Leptothoracini were collected in 1979, 1983, 1985, 1987 and 1988 in Quebec, especially along Saguenay River and St. Lawrence River, and in New England. Laboratory colonies
. .
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Fig. 1. - - Thorax of an ergatomorphic worker, an intermorphic queen and a gynomorpnic queen of Leptothorax spec. A (from left to right). The development of thoracic sutures in intermorphic females varies widely. The picture shows a female with a nearly intermediate morphology. Pictures were taken by A. Maiazza, using the scanning electron microscope of the FB Geologie, TH Darmstadt.
Abb. 1 . - Thorax einer ergatomorphen Arbeiterin, emer intermorphen und einer gyno- morphen K6nigin von Leptothorax spec. A (yon links nach rechts). Die Thorax- struktur intermorpher Weibchen ist recht variabel, dargestellt ist eine Intermorphe mit intermedi~irer Thoraxentwicklung. REM-Aufnahmen dutch A. Maiazza, FB Geologie, TH Darmstadt.
Q U E E N P O L Y M O R P H I S M 143 were k e p t for several artificial b r e e d i n g cycles as d e s c r i b e d by BUSCHINGER (1974). Since Leptothorax spec. A shows a s t a t i o n a r y sexual calling b e h a v i o r ( " L o c k s t e r z e l n " , BUSCmr~- GER 1968), it was easy to m a t e sexuals of defined origin in the l a b o r a t o r y .
Females a n d w o r k e r s w e r e dissected a c c o r d i n g to t h e m e t h o d d e s c r i b e d b y BUSCmN- 6ER a n d ALLOWAY (1978).
Conspecifity of colonies f r o m d i f f e r e n t h a b i t a t s was p r o v e n u s i n g karyological t e c h n i q u e s (IMAI et al. 1977) a n d enzyme gel electrophoresis, as m o r p h o l o g i c a l f e a t u r e s vary widely in t h i s g r o u p of Leptothorax.
Esterase, MDH a n d o t h e r enzymes were s e p a r a t e d b y isoelectric focusing of c r u d e p u p a l h o m o g e n a t e s in u l t r a t h i n p o l y a c r y l a m i d e gels (HEINZE a n d BUSCHINGER 1988).
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Fig. 2 . - Collecting sites of Leptothorax spec. A. N u m b e r s c o r r e s p o n d to t h o s e given in t a b l e I. I n u n n u m b e r e d sites less t h a n t h r e e q u e e n r i g h t colonies each h a v e b e e n collected. Dots w i t h a q u e s t i o n m a r k i n d i c a t e collecting sites of colonies of w h o s e conspecifity we are n o t yet s u r e ( O n t a r i o a n d Mt. Desert Island, Me.).
Abb. 2 . - F u n d p u n k t e yon Leptothorax spec. A. Die N u m m e r n e n t s p r e c h e n d e n e n in Tabelle I. Weitere Fundstellen, a n d e n e n w e n i g e r als drei Kolonien m i t K6nigin g e s a m m e l t w e r d e n k o n n t e n , sind o h n e N u m m e r eingezeichnet. Fragezeichen (in O n t a r i o u n d Mt. Desert Island, Me.) s t e h e n ftir Kolonien z w e i f e l h a f t e r Artzugeh6:
rigkeit.
144 A H E I N Z E and A. B U S C H I N G E R
R E S U L T S
Leptothorax spec. A h a s a q u e e n - p o l y m o r p h i s m w i t h g y n o m o r p h i c (G 9 9) a n d i n t e r m o r p h i c f e m a l e s (I 9 9 ) , w h i c h b o t h m a y b e f u l l y f e r t i l e q u e e n s i n t h e f i e l d . I n t e r m o r p h s d i f f e r f r o m e r g a t o m o r p h i c w o r k e r s i n t h e p r e s e n c e o f a t l e a s t o n e m i n u t e o c e l l u s a n d i n m o s t c a s e s o f s o m e m o r e o r l e s s d i s t i n c t t h o r a c i c s u t u r e s (fig. 1). I n c o n t r a s t t o e r g a t o m o r p h s a n d o c c a s i o n a l i n t e r g r a d e s b e t w e e n 9 9 a n d g ~ i n o t h e r s p e c i e s o f Leptothorax, I 9 9 o f L. spec. A a l w a y s h a v e a f u l l y d e v e l o p e d s p e r m a t h e c a .
T h e f r e q u e n c y o f q u e e n m o r p h s v a r i e s W i d e l y i n t h e f i e l d (table 1).
Table I. - - Frequency of colonies with gynomorphie females in different populations.
Biotopes are characterized by the letters A to D.
A : patchy, rocky outcrops, sparsely overgrown with lichen, American laurel, blue- berries, few bushes and young trees, surrounded by dense thickets or forests.
B : extended, though patchy, rocky areas, surrounded by light coniferous forests.
C: homogeneous, light forests, mostly pines or spruces.
D: open homogeneous shrub forests with young or dwarfed birches and alders.
The geographical location of the populations is indicated in fig. 2. Site 21, Mr.
Monadnock in New Hampshire, is not shown on the map.
Tabelle I. - - H~iufigkeit von Kolonien mit gynomorphen 9 2 in verschiedenen Popula- tionen. Biotope sind dutch die Buchstaben A bis D charakterisiert.
A : isolierte, yon Flechten, Katmia, Blaubeeren, einigen Biischen und jungen B~iumen sp~irlich bewachsene FelsflSchen inmitten dichterer Gebiische oder W~ilder.
B : ausgedehnte, isolierte Felsfl~ichen in lichteren Nadelw~,ildern.
C : homogene, lichte W~ilder, meist Kiefern oder Fichten.
D : offene Gebiische mit jungen oder zwergwiichsigen Birken und Eden.
Die Lage der verschiedenen Populationen ist Fig. 2 zu entnehmen. Fundpunkt 21, Mt. Monadnock in New Hampshire, ist nicht eingezeichnet.
Population Biotope n col. % G 9 2
1 Matagami A 14 7
2 Tadoussac A 145 18
3 Lac La Haie, B 5 20
4 Cap ~t l'Orignal A 4 25
5 Baie Sainte-Catherine A 3 33
6 Sacrd-Cceur du Saguenay C 3 33
7 Grandes-Bergeronnes A 6 33
8 Les Escoumins C 3 33
9 RiviSre Romaine A 9 33
10 Shawinigan A 3 33
11 Rivi~re Cran B 11 36
12 La Baie A 35 40
13 Rivi~re Vermilion B 5 40
14 Saint-Fdlix de Dalquier A 5 40
15 Saint-Simeon C 24 54
16 Lac du Sablon B 7 57
17 Cadillac B 6 66
18 Rouyn-Noranda B 7 71
19 route 109, km 170 C 9 78
20 Grands Jardins C 28 88
21 Mount Monadnock, N.H. D 34 97
QUEEN POLYMORPHISM 145 I n p a t c h i l y d i s t r i b u t e d areas, like on the r o c k y o u t c r o p s along t h e St.
L a w r e n c e R i v e r in T a d o u s s a c or in M a t a g a m i , I 2 2 b y f a r o u t n u m b e r g y n o m o r p h s . G 2 2 a r e a b u n d a n t in h o m o g e n e o u s h a b i t a t s , light c o n i f e r o u s f o r e s t s s u c h as in St. S i m d o n or G r a n d s J a r d i n s , o r o p e n s c r u b b y f o r e s t s s u c h as on Mt. M o n a d n o c k .
53 colonies of Leptothorax spec. A f r o m d i f f e r e n t p o p u l a t i o n s w e r e k e p t in the l a b o r a t o r y f o r u p to ten b r e e d i n g cycles ( a b o u t five y e a r s ) , w h e r e they r e g u l a r l y p r o d u c e d sexual o f f s p r i n g a n d w o r k e r s . The m o r p h s of the f e m a l e sexuals r e m a i n e d c o n s t a n t in e a c h colony t h r o u g h o u t this time. I n a d d i t i o n to m a l e s a n d e r g o t o m 0 r p h i c w o r k e r s ,
9 g y n o m o r p h i c q u e e n s p r o d u c e d only g y n o m o r p h i c offspring, 4 g y n o m o r p h i c q u e e n s p r o d u c e d only i n t e r m o r p h s ,
8 i n t e r m o r p h i c q u e e n s p r o d u c e d b o t h m o r p h s , a n d
32 i n t e r m o r p h i c q u e e n s p r o d u c e d only i n t e r m o r p h i c females.
No g y n o m o r p h p r o d u c e d b o t h m o r p h s , a n d no i n t e r m o r p h p r o d u c e d only g y n o m o r p h i c offspring.
T h e s e o b s e r v a t i o n s i n d i c a t e a genetic influence on m o r p h d e t e r m i n a t i o n , s i m i l a r to t h a t in Harpagaxenus sublaevis, w i t h a d o m i n a n t allele E a f f e c t i n g tile d e v e l o p m e n t of ocelli, wings a n d t h o r a c i c s t r u c t u r e s in the f e m a l e b r o o d . According to this h y p o t h e s i s , g y n o m o r p h s s h o u l d a l w a y s b e ee.
T h e i r sons t h e r e f o r e , should c a r r y the allele e. I n t e r m o r p h i c f e m a l e s , h o w e v e r , m a y b e Ee a n d E E , a n d m o r p h o l o g i c a l l y t h e r e is no d i f f e r e n c e b e t w e e n f e m a l e s of the l a t t e r genotypes. The sons of i n t e r m o r p h i c q u e e n s t h e r e f o r e m a y b e E or e. C r o s s - b r e e d i n g e x p e r i m e n t s of m a t i n g t y p e s 2, 4 5 a n d 6 (table III) t h u s m a y lead to d i f f e r e n t results. If, e.g., an i n t e r m o r - phic f e m a l e of u n k n o w n g e n o t y p e m a t e s w i t h the son of an i n t e r m o r p h i c queen, f o u r d i f f e r e n t m a t i n g types a r e possible: E E • E, E E • e, Ee X E a n d Ee • e.
B y choice of m a l e s a n d f e m a l e s f r o m c e r t a i n p o p u l a t i o n s w e d e v i s e d o u r e x p e r i m e n t s in a w a y t h a t one of the p o s s i b l e m a t i n g t y p e s b e c a m e m o r e p r o b a b l e t h a n o t h e r s .
I f b o t h the m o r p h of the q u e e n a n d t h a t of h e r d a u g h t e r s a r e k n o w n , in s o m e cases the h y p o t h e t i c a l m a t i n g type c a n be deduced. I t s h o u l d b e ee X e in colonies w i t h a g3/nomorphic queen, w h o p r o d u c e s g y n o m o r - phic f e m a l e s only,
ee • E in colonies w i t h a g y n o m o r p h i c queen, w h o p r o d u c e s inter- m o r p h i c o f f s p r i n g , a n d
Ee X e in colonies w i t h an i n t e r m o r p h i c queen, w h o p r o d u c e s b o t h g y n o m o r p h i c a n d i n t e r m o r p h i c females.
T h e s o l u t i o n s of the c u b i c e~tuation.
p3 ( E E X E) + p2q ( E E X e) + pq2 (ee X E) + 2p2q ( E e X E) + 2pq2 (Ee • e) + q3 (ee X e) = 1.
(where p a n d q a r e the f r e q u e n c i e s of the alleles E a n d e) w i t h t h e
146 J. H E I N Z E and A. BUSCHINGER
o b s e r v e d f r e q u e n c i e s of colonies w i t h k n o w n m a t i n g type in the e x t e n s i v e l y s t u d i e d p o p u l a t i o n of T a d o u s s a c give e s t i m a t e d values f o r p a n d q (table II).
W i t h r e s p e c t to t h e q u e e n m o r p h , t h e p o p u l a t i o n s e e m s n o t to b e in a H a r d y - W e i n b e r g e q u i l i b r i u m ; allele-frequencies v a r y w i d e l y a c c o r d i n g to t h e d a t a set u s e d as b a s i s f o r the evaluation. F r e q u e n c i e s of p = 0.85 a n d q = 0.15 s e e m to b e c l o s e s t to t h e o b s e r v e d c o n d i t i o n s in the field.
Thus, m o s t of t h e i n t e r m o r p h i c f e m a l e s in the p o p u l a t i o n of T a d o u s s a c s h o u l d b e h o m o z y g o u s , E E . Males, p r o d u c e d b y t h e m , s h o u l d c a r r y t h e allele E. T h e s e m a l e s w e r e u s e d in c r o s s - b r e e d i n g e x p e r i m e n t s of t y p e 2, 4, a n d 6 (table III). I n t e r m o r p h i c females, m a t e d in e x p e r i m e n t s 5 a n d 6, also w e r e r e a r e d in colonies f r o m p o p u l a t i o n s , in w h i c h i n t e r m o r p h s f a r o u t n u m b e r e d g y n o m o r p h i c queens. T h e i n t e r m o r p h i c f e m a l e s u s e d in bree- ding e x p e r i m e n t s 3 a n d 4, w e r e e i t h e r o f f s p r i n g of a g y n o m o r p h i c q u e e n o r of an i n t e r m o r p h i c female, w h o p r o d u c e d b o t h f e m a l e m o r p h s . I n b o t h cases, i n t e r m o r p h i c f e m a l e s s h o u l d b e h e t e r o z y g o u s : Ee. T h e h y p o t h e s i s p r e s u p p o s e s , h o w e v e r , t h a t colonies a r e m o n o g y n o u s a n d t h a t q u e e n s m a t e only once. I n p r e v i o u s studies we h a v e d e m o n s t r a t e d b y dissection func- tional m o n o g y n y in Leptothorax spec. A; in e a c h colony only one single f e m a l e is fertile. O t h e r females, t h o u g h o f t e n i n s e m i n a t e d , r e m a i n sterile ([-IEINZE a n d BUSCHINGER, 1987). I n the l a b o r a t o r y , y o u n g f e m a l e s s t o p p e d sexual calling b e h a v i o r a f t e r one successful c o p u l a t i o n w i t h a male. Electro- p h o r e t i c a l s t u d i e s gave f u r t h e r evidence f o r single m a t i n g in the field.
E s t e r a s e 7 is v a r i a b l e in m o s t species of the s u b g e n u s Leptothorax s. str., a n d in L. spec. A at least f o u r d i f f e r e n t a l l o z y m e s can be s e p a r a t e d b y isoelectric f o c u s i n g (HEINZE 1987). We s c r e e n e d Est-7 p a t t e r n s in five to ten p u p a e e a c h f r o m 36 colonies, all collected f r o m the p o p u l a t i o n in T a d o u s s a c . T h e a l l o z y m e s w e r e f o u n d in m o s t p o s s i b l e h e t e r o z y g o u s a n d h o m o z y g o u s c o m b i n a t i o n s .
Multiple m a t i n g in s o m e cases s h o u l d r e s u l t in m o r e t h a n t w o d i f f e r e n t a l l o z y m e c o m b i n a t i o n s p e r colony, e.g. AB X C/D - , AC, BC, AD, CD.
We n e v e r f o u n d m o r e t h a n t w o d i f f e r e n t p a t t e r n s p e r colony. T h e ' f r e q u e n c y of h o m o z y g o u s g e n o t y p e s a p p a r e n t l y is s o m e w h a t i n c r e a s e d ; all p u p a e in 11 of 36 colonies s h o w e d the s a m e single b a n d , suggesting a h o m o z y g o u s geno- t y p e t h r o u g h o u t the colony. T h e results, h o w e v e r , do n o t indicate s t r o n g i n b r e e d i n g in the p o p u l a t i o n in T a d o u s s a c .
Out of 175 2 ~, m a t e d w i t h ~ 3 in the l a b o r a t o r y , 68 h a v e p r o d u c e d f e m a l e sexual o f f s p r i n g f o r three, four, or even five b r e e d i n g cycles.
W h i t h the e x c e p t i o n of one colony, w h e r e in a d d i t i o n to 47 g g a n d 38 g y n o m o r p h i c 2 2 f o u r wingless ~ ~ w e r e r e a r e d , all g y n o m o r p h i c queens, m a t e d w i t h t h e s o n of a g y n o m o r p h , p r o d u c e d g y n o m o r p h i c o f f s p r i n g (ee X e --~ ee, # 1 in table III). I n t e r m o r p h i c 2 2 a r o s e in c r o s s - b r e e d i n g s of g y n o m o r p h i c 2 2 w i t h the sons of i n t e r m o r p h i c q u e e n s (ee • E --* Ee,
# 2, in table III). B o t h m o r p h s w e r e p r o d u c e d b y h e t e r o z y g o u s i n t e r m o r p h i c
Q U E E N P O L Y M O R P H I S M 147 Table II. - - Estimated frequencies p and q of the hypothetica alleles E and e in the Tadoussac population, based on observed frequencies of different colony types in the field. The colony types used as the basis for the calculation were ee x e - - colonies (gynomorphic queens producing gynomorphic offspring only) in 1, Ee x e - - colonies (intermorphic queens producing both morphs) in 2, and the ratio of ee x E and ee • e - - colonies in 3.
Tabelle II. - - Anteile p und q der hypothetischen Allele E und e in der Population Tadoussac, berechnet aus den beobachteten Hiiufigkeiten verschiedener Koloniety- pen im Freiland. Grundlage der Berechnung waren ee • e - - Kolonien (gynomorphe K6nigin, die gynomorphe Jungweibchen produziert) in 1, Ee x e - - Kolonien (intermorphe K6nigin produziert beide Morphen) in 2 und das VerhSltnis yon ee x E zu ee x e - - Kolonien in 3.
Frequencies of different colony types Estimated
1 2
EE x E 0.18 / 0.61
EE • e 0.14 i 0.61 0.11 0.94
Ee x E 0.28 0.22
Ee • e 0.21 0.04
ee x E 0.11 0.02
ee • e 0.08 0.00
pE 0.57 0.85
qe 0.43 0.15
3 0.02 0.05 0.18 0.11 0.25 0.14 0.39 0.27 0.73
Observed
?
? 0.85
? 0.04 0.03 0.08
?
?
q u e e n s , w h i c h h a d b e e n m a t e d w i t h a n e - m a l e ( E e • e -~ E e + e e ,
# 3 i n table I I I ) .
I n c r o s s - b r e e d i n g e x p e r i m e n t s o f t h e t y p e s 4, 5, a n d 6, w i t h t h e e x c e p t i o n o f t w o G * ~ in o n e c o l o n y , o n l y i n t e r m o r p h s w e r e r e a r e d as f e m a l e s e x u a I o f f s p r i n g .
I n m o s t m a t i n g s , t h e c o l o n i e s o f m a l e s a n d f e m a l e s c a m e f r o m d i f f e r e n t p o p u l a t i o n s . A f t e r m a t i n g w i t h m a l e s f r o m T a d o u s s a c , e.g., G ~ 2 f r o m p o p u l a t i o n s w i t h a h i g h f r e q u e n c y o f g y n o m o r p h s r e a r e d i n t e r m o r p h s as.
d i d G ~ ~ f r o m T a d o u s s a c .
O n e a d d i t i o n a l e x p e r i m e n t p r o v i d e s f u r t h e r e v i d e n c e f o r a g e n e t i c c o n t r o l o f q u e e n p o l y m o r p h i s m . I n all p o p u l a t i o n s k n o w n Lepto- thorax spec. A l i v e s s y m p a t r i c a l l y w i t h a s e c o n d u n d e s c r i b e d s p e c i e s , L e p t o t h o r a x spec. B. B o t h t a x a a r e e a s i l y d i s t i n g u i s h e d b y k a r y o - t y p e , c o l o n y s t r u c t u r e , a n d M D H - o r I D H - i s o z y m e s (HEINZE a n d BUSCHINGER 1987, HEINZE 1987), a n d a l s o d i f f e r m o r p h o l o g i c a l l y . I n all o f 222 c o l o n i e s : o f L. spec. B t h e q u e e n w a s g y n o m o r p h i c . I n t h e field, h y b r i d s a p p a r e n t l y a r e v e r y r a r e . I s o l a t i o n is g u a r a n t e e d b y d i f f e r e n t t i m e s o f d a y o f s e x u a l a c t i v i t y . I n t h e l a b o r a t o r y , h o w e v e r , w e s u c c e s s f u l l y m a t e d a g y n o m o r p h i c f e m a l e o f spec. B w i t h a s o n o f a n i n t e r m o r p h i c spec. A - f e m a l e . I n f o u r b r e e d i n g c y c l e s , t h e g y n o m o r p h i c spec. B - f e m a l e p r o d u c e d w o r k e r s a n d y o u n g q u e e n s : all 17 f e m a l e s e x u a l s w e r e i n t e r m o r p h s . All h y b r i d I ~ 9 h a d six o v a r i o l e s a n d a r e c e p t a c l e . H y b r i d i z a t i o n h a s b e e n v e r i f i e d b y c o m p a - r i s o n o f M D H - p a t t e r n s a n d b y p r e p a r a t i o n o f c h r o m o s o m e s f r o m t h e b r a i n s . o f f e m a l e p r e p u p a e . H y b r i d s s h o w M D H - i s o z y m e s f r o m b o t h p a r e n t a ~
148 J. H E I N Z E and A. B U S C H I N G E R
Table III. - - Queen morphs obtained in the crossbreeding experiments with Leptothora.~
spec. A. G2 2 and I 2 2 are gynomorphic and intermorphic females, G$ ~ and I ~ 3 males produced by gynomorphic or intermorphic queens, respectively. The most probable genotypes of the parents (see text) are underlined.
Tabelle III. M Ergebnisse der Kreuzungsexperimente mit Leptothorax spec. A. G9 2 und I 2 9 steht dabei ftir gynomorpbe bzw. intermorphe Weibchen, G 8 ~ und 13 3 sind M~innchen, die yon gynomorphen bzw. intermorphen Weibchen produziert wurden.
Der wahrscheinlichste Genotyp der Kreuzung ist jeweils unterstrichen (vergl. Text).
# Mated Possible Female morphs
sexuals genotype Expected Observed n. col.
ser. 1 G9 • ee • e G9 9 108 G9 2 4 I 2 9" 10
ser. 2 G9 • 13 ee • E I 2 2 0 G2 9 210 I 2 2 20
ee • e G 2 2
ser. 3 19 x G 3 Ee x e G9 2 + I 2 2 46 G 9 2 229 I 9 2 11
ser. 4 I 9 x I 3 Ee • E I 2 9 0 G 2 9 393 I 9 9 11
Ee x e G 9 9 + I 2 2
ser. 5 I 9 x G 3 EE x e I 9 9 0 G2 9 10 12 2 1
Ee • e G 9 9 + I 9 2
ser. 6 12 X I 3 EE x E I 9 2 2 G9 9 228 I 2 2 8
EE x e 1 2 2
Ee • I 2 2
Ee • e G 2 9 + I 2 2
* The four 19 2 were reared in one single colony.
s p e c i e s . W h e r e a s L e p t o t h o r a x spec. A t y p i c a l l y h a s 2 n = 30 c h r o m o s o m e s a n d spec. B 2 n = 36, w e c o u n t e d 60 o r m o r e c h r o m o s o m e s i n m e t a p h a s e p l a t e s of t h e h y b r i d .
I n c r o s s - b r e e d i n g s of t h e m a t i n g t y p e E e X e, # 3 i n table III, b o t h m o r p h s s h o u l d b e p r o d u c e d i n e q u a l n u m b e r s . R a t i o s of I Q 9 a n d G 9 9 i n o u r e x p e r i m e n t s , h o w e v e r , d i f f e r w i d e l y f r o m a l : l - s e g r e g a t i o n . T h e y v a r y f r o m c o l o n y t o c o l o n y a n d r a n g e f r o m 0 G 9 9 / 1 2 I 9 9 to 14 G 9 9 / 7 I 9 9 ,(table I V ) . A s i m i l a r v a r i a b i l i t y of r a t i o s w a s also o b s e r v e d i n c o l o n i e s
~ r o m t h e field. T h e r e t h e p r o d u c t i o n of G 9 2 n o t o n l y d i f f e r s b e t w e e n c o l o n i e s , b u t a l s o w i t h i n a s i n g l e c o l o n y f r o m y e a r to y e a r . I n all, m o s t c o l o n i e s p r o d u c e d m o r e 19 9 t h a n G 9 9.
A f i r s t c e n s u s o f g ~ i n c o l o n i e s o f d e f i n e d g e n o t y p e s u g g e s t s a n i n f l u e n c e o f t h e a l l e l e s E / e o n c a s t e - d e t e r m i n a t i o n i n Leptothorax spec. A, l i k e i n H. sublaevis, t h o u g h w e a k e r . I n c o l o n i e s of t h e h y p o t h e t i c a l m a t i n g - t y p e E E X E d u r i n g t h r e e b r e e d i n g - c y c l e s , 20.9 p e r c e n t of t h e f e m a l e b r o o d e c l o s e d t o s e x u a l s , c o m p a r e d to 44.1 p e r c e n t i n t h e ee • e - - c o l o n i e s . Off- s p r i n g w e r e c o u n t e d o n l y i n c o l o n i e s t h a t w e r e s t i l l q u e e n r i g h t a f t e r t h e t h i r d b r e e d i n g - c y c l e (table V). D i f f e r e n c e s i n b r o o d p r o d u c t i o n a r e h i g h l y s i g n i - f i c a n t (p < 0.001, G-test).
R e c e n t l y w e h a v e s h o w n (HEINZE a n d BUSCHINER 1987) t h a t G 9 9 a r e s i g n i f i c a n t l y l a r g e r t h a n I 9 9 . T o a s s e s s a n i n f l u e n c e of t h e h y p o t h e t i c a l a l l e l e s E / e o n w o r k e r s a n d m a l e s , t h o r a x l e n g t h of i n d i v i d u a l s p r o d u c e d
Table IV. - - P r o d u c t i o n of Tabelle IV. - - P r o d u k t i o n
K r e u z u n g s s c h e m a s Ee
QUEEN POLYMORPHISM 149
i n t e r m o r p h i c a n d g y n o m o r p h i c 9 2 in Ee x e - - colonies.
yon i n t e r m o r p h e n u n d g y n o m o r p h e n 2 2 in Kolonien des X e .
Colony G 2 9 I 2 2 g g ratio G 2 2 t ( I 2 9 + G 2 9 )
.~ 11 8 27 190 0.23
:~ 46 2 67 252 0.03
:g: 51 4 69 196 0.05
:~ 64 0 7 33 020
97 0 I 9 0.00
--~ 107 14 7 19 0.67
# 111 I 1 2 0.50
r 125 12 I0 11 0.55
r 194 4 23 24 0.15
# 202 0 12 59 0.00
# 213 1 5 6 0.17
total 46 229 801 0.17
Table V. - - Ratio of 2 2 / ~ ~ p r o d u c e d in the o f f s p r i n g of EE X E - - a n d ee x e - - colonies.
Differences b e t w e e n 2 2 / ~ ~ ratios are significant, p < 0.001, 2 • 2 test of i n d e p e n d e n c e (G-Test).
Tabelle V. - - ProduktionsverhSltnis ~ 2 / g ~ in d e r N a c h k o m m e n s c h a f t von E E • E - - u n d ee • e - - Kolonien.
Die U n t e r s c h i e d e im P r o d u k t i o n s v e r h S l t n i s sind n a c h d e m G-Test signifikant (p < 0.001).
Colony Hypothetical m a t i n g type 2 ~ ~ ~ % 2 2
# 98 ee • e
99 ee • e
-~ 114 ee • e
115 ee X e
r 118 ee • e
# 195. ee X e
8 E E •
# 16 EE • E
# 18 EE • E
total
total
42 47 47.2
10 14 41.7
40 27 59.7
23 31 42.6
19 54 26.0
30 35 46.1
164 208 44.1
45 116 27.9
18 124 12.7
19 70 21.3
82 310 20.9
e i t h e r b y a g y n o m o r p h i c o r a n i n t e r m o r p h i c m o t h e r w a s m e a s u r e d (table VI).
S o n s o f a g y n o m o r p h i c q u e e n a r e s i g n i f i c a n t l y l a r g e r t h a n s o n s o f i n t e r - m o r p h i c f e m a l e s , a n d t h e s a m e t e n d e n c y w a s f o u n d i n ~ ~ f r o m m o s t p o p u l a t i o n s . D i f f e r e n c e s i n w o r k e r s i z e a r e q u i t e s m a l l a n d d a t a w e r e n o t n o r m a l l y d i s t r i b u t e d . C o l o n i e s w i t h g y n o m o r p h i c q u e e n u s u a l l y h a d a n u m b e r o f v e r y s m a l l w o r k e r s , w h o s o m e t i m e s w e r e e v e n s m a l l e r t h a n s m a l l e s t w o r k e r s i n c o l o n i e s w i t h i n t e r m o r p h i c q u e e n . T h e a v e r a g e g i n G 2 - - c o l o n i e s , h o w e v e r , a r e l a r g e r t h a n a v e r a g e ~ ~ i n c o l o n i e s w i t h I 9 9 .
150 J. H E I N Z E a n d A. B U S C H I N G E R
Table VI. i T h o r a x length (TL) of 9 9 , 8 8 , a n d ~ g of Leptothorax spec. A f r o m colonies w i t h g y n o m o r p h i c or i n t e r m o r p h i c queen.
Significance of d i f f e r e n c e s in t h o r a x size w e r e usually t e s t e d w i t h t- a n d U-test.
Since TL of w o r k e r s in m o s t p o p u l a t i o n s was n o t n o r m a l l y d i s t r i b u t e d , t h e t e s t by S m i r n o f f - K o l m o g o r o f f w a s applied in t h e s e cases.
Tabelle V I . - Thoraxl~inge ( T L ) y o n ~ 9 , 8 8 u n d ~ ~ Kolonien von Leptothorax spec. A m i t g y n o m o r p h e r bzw. i n t e r m o r p h e r K6nigin.
Auf Signifikanz d e r U n t e r s c h i e d e in d e r Thoraxl~inge w u r d e m i t t- u n d U-Test geprtift, i m Falle d e r g ~ auch m i t d e m Test fiir nicht normal-verteilte Werte n a c h S m i r n o f f - K o l m o g o r o f f .
Colonies w i t h Colonies w i t h Difference
g y n o m o r p h i c q u e e n i n t e r m o r p h i c queen
TL [ m m ] n TL [ m m ] [ m m ]
Q Q 42 1.01 + / - - 0.04 !07 0.93 + / - - 0.09 0.08 p < 0.01
( d a t a f r o m all p o p u l a t i o n s in Quebec)
8 8 86 1.41 + / - - 0.10 221 1.30 + / - - 0.10 0.1l p < 0.01
( d a t a f r o m l a b o r a t o r y b r e d males)
~ 89 0.90 + / - - 0.05 120 0.89 + / - - 0.04 0.01 n.s.
(data f r o m Tadoussac)
~ 91 0.89 + / - - 0.05 120 0.86 - h / - - 0.04 0.03 p < 0.01
( d a t a f r o m La Bale)
g 92 0.94 + / - - 0.05 109 0.88 + / - - 0.07 0.06 p < 0.01
(data f r o m A s h u a p m u s h u a n : colonies f r o m Rivi6re Cran and Rivi6re Vermilion)
~ 89 0.89 + / - - 0.05 66 0.87 + / - - 0.05 0.02 p < 0.01
(data f r o m Saint F61ix de Dalquier)
~ 36 0.91 + / - - 0.04 81 0.87 + / - - 0.04 0.04 p < 0.01
( d a t a f r o m G r a n d e s B e r g e r o n n e s )
D i s s e c t i o n d a t a s h o w t h a t ~ ~ f r o m c o l o n i e s w i t h i n t e r m o r p h i c f e m a l e s m o r e o f t e n h a d o v a r i e s w i t h t h r e e , f o u r f i v e a n d s i x o v a r i o l e s t h a n d o g f r o m c o l o n i e s w i t h G Q 2 ( t a b l e V I I ) .
Table VII. - - Percentage of w o r k e r s w i t h i ovarioles in different colony types. The m o s t p r o b a b l e genotype of w o r k e r s is indicated. Data are f r o m colonies collected in the field a n d kept f o r four b r e e d i n g cycles in the laboratory.
Differences in the f r e q u e n c i e s of w o r k e r s w i t h m o r e than two ovarioles are significant (p ~ 0.01), if colonies w i t h i n t e r m o r p h i c queen are c o m p a r e d to t h o s e with g y n o m o r p h i c queen (G-Test).
Tabelle VII. - - H~iufigkeit von 9 Q m i t i Ovariolen in den v e r s c h i e d e n e n Kolonietypen.
Der w a h r s c h e i n l i c h s t e Genotyp d e r A r b e i t e r i n n e n ist angegeben. Pr~ipariert w u r d e n n u r ~ g aus Freilandkolonien, die fiir vier Brutzyklen im L a b o r gehalten w o r d e n waren.
Der U n t e r s c h i e d z w i s c h e n d e r H~iufgikeit yon A r b e i t e r i n n e n m i t m e h r als zwei Ovariolen in Kolonien m i t g y n o m o r p h e r K6nigin u n d Kolonien m i t i n t e r m o r p h e r K6nigin ist gesichert (p < 0.01, G-Test).
Colony type Genotype ~vorkers w i t h i ovarioles [%]
Q u e e n / o f f s p r i n g n i = 2 3 4 5 6
I Q ~ I Q Q E E 412 88.6 2.7 3.2 1.9 3.6
GQ ~ IQ Q Ee 118 92.5 2.5 4.2 0.8 - -
][Q ~ GQ Q + - ~ Q Q E e / e e 27 88.8 7.4 3.7 - - - -
G Q --~ G Q Q ee 98 97.0 1.5 1.5 - - - -
QUEEN POLYMORPHISM 151 D I S C U S S I O N
Leptothorax spec. A is an u n u s u a l ant, b e i n g one of the f e w non- p a r a s i t i c species of h i g h e r a n t s w i t h several m o r p h o l o g i c a l l y d i f f e r e n t t y p e s of queens. As in t h e s l a v e - m a k i n g l e p t o t h o r a c i n e Harpagoxenus sublaevis, q u e e n m o r p h s in L. spec. A a r e m o s t p r o b a b l y genetically d e t e r m i n e d . O u r c r o s s - b r e e d i n g r e s u l t s can be e x p l a i n e d b y the a s s u m p t i o n of a single locus w i t h t w o alleles E / e . E s u p p r e s s e s the d e v e l o p m e n t of t h o r a c i c s t r u c t u r e s , wings a n d ocelli in f e m a l e l a r v a e p r e d e t e r m i n e d to b e c o m e queens. Gyno- m o r p h s a l w a y s a r e h o m o z y g o u s , ee, while i n t e r m o r p h s a r e E E a n d Ee.
According to o u r one-locus-hypothesis, in colonies of the m a t i n g - t y p e Ee X e b o t h m o r p h s of q u e e n s s h o u l d b e r e a r e d in e q u a l a m o u n t s . I n t h e s e colonies, h o w e v e r , the p e r c e n t a g e of r e a r e d g y n o m o r p h s varies widely, a n d in total b y f a r m o r e i n t e r m o r p h s a r e p r o d u c e d .
We c a n n o t exclude the p o s s i b i l i t y t h a t t w o or m o r e loci c o n t r o l q u e e n m o r p h s . M o r e loci m i g h t b e t t e r explain the s e g r e g a t i o n of G9 9 a n d I 2 2 in c r o s s - b r e e d i n g e x p e r i m e n t s of the t y p e Ee • e. If, e.g., a two-loci hypo- thesis is c o n s i d e r e d , in s o m e colonies only 25 % g y n o m o r p h i c o f f s p r i n g is expected, if g y n o m o r p h s a r e h o m o z y g o u s in t w o recessive alleles; if q u e e n m o r p h s a r e d e t e r m i n e d b y t h r e e loci, s o m e of the colonies s h o u l d p r o d u c e 12.5% g y n o m o r p h s a n d 87.5% i n t e r m o r p h s . A m o d e l w i t h g y n o m o r p h s which a r e h e t e r o z y g o u s in b o t h loci, c o m p a r a b l e to the c a s t e - d e t e r m i n a t i n g s y s t e m p r o p o s e d f o r stingless b e e s (KERR, 1950), w o u l d not explain w h y g y n o m o r p h i c queens p r o d u c e a l m o s t exclusively either i n t e r m o r p h i c or g y n o m o r p h i c offspring, b u t r a r e l y b o t h m o r p h s .
If, h o w e v e r , e x t e r n a l f a c t o r s m i g h t influence a genetically m e d i a t e d m o r p h d e t e r m i n a t i o n , as t h e y a p p a r e n t l y do in c a s t e - d e t e r m i n a t i o n in Meli- pona (KERR a n d N~EI.SEN, 1966; KERR et al., 1966), o u r r e s u l t s can b e e x p l a i n e d w i t h the E / e - h y p o t h e s i s .
i n Harpagoxenus sublaevis, in ee X e - - colonies i n t e r m o r p h i c f e m a l e s w e r e r e g u l a r l y r e a r e d , too, suggesting, t h a t s o m e ee-larvae m a y d e v e l o p into i n t e r m o r p h i c f e m a l e s (BusCHINGER 1978). T h e r a t i o of g y n o m o r p h i c vs.
i n t e r m o r p h i c f e m a l e s in Ee • e - - colonies of Leptothorax spec. A m a y be b i a s e d b y t h e s a m e effect, a n d the f o u r i n t e r m o r p h s w h o w e r e r e a r e d in one of o u r ee X e - - colonies m i g h t b e e e - i n t e r m o r p h s , too.
Though, following o u r a s s u m p t i o n , a m a j o r p a r t of t h e I ~ 2 in c o l o n i e s of series 3 s h o u l d be of the g e n o t y p e ee, only f e w ee-I2 2 w e r e p r o d u c e d in colonies of g r o u p 1. W i n t e r a n d BUSCHINGER (1986) h a v e s h o w n t h a t inter- m o r p h i c q u e e n s of Harpagoxenus sublaevis h a v e a s t r o n g e r i n h i b i t o r y in- fluence on l a r v a e t h a n do g y n o m o r p h s . I n colonies of the m a t i n g t y p e E E • e f a r less i n t e r m o r p h i c f e m a l e s a n d m o r e ~ ~ w e r e p r o d u c e d t h a n in colonies of the t y p e ee • E. The b r o o d in b o t h cases w a s of t h e s a m e h e t e r o z y g o u s genotype, Ee, b u t the m o r p h of the queen differed. This
152 J. H E I N Z E and A. BUSCHINGER
s t r o n g e r i n h i b i t o r y c a p a c i t y of 12 ~ m i g h t n o t only explain the h i g h e r w o r k e r - b i a s in colonies w i t h i n t e r m o r p h i c q u e e n s (see below), b u t also the diffe- r e n c e s in the f r e q u e n c y of e e - i n t e r m o r p h s . I n t w o or t h r e e field colonies t h a t w e r e r e c e n t l y collected, we f o u n d g y n o m o r p h i c q u e e n s a c c o m p a n i e d b y s e v e n o r m o r e gynomo/-phic f e m a l e s a n d one or t w o i n t e r m o r p h s . T h e s e 19 9 p e r h a p s w e r e h o m o z y g o u s , ee.
The s t r o n g e r i n h i b i t o r y i n f l u e n c e of H. sublaevis i n t e r m o r p h s on l a r v a e is t h o u g h t to b e o n e of the r e a s o n s f o r t h e d i f f e r e n c e b e t w e e n the p r o d u c t i o n of f e m a l e c a s t e s b y G9 ~ a n d I I ~. I n L. spec. A, first r e s u l t s i n d i c a t e a s i m i l a r shift t o w a r d s h i g h e r w o r k e r r a t i o s in E E X E - - colonies of this n o n p a r a s i t i c species. H o w m i g h t the c a s t e - d e t e r m i n a t i o n be a f f e c t e d b y the g e n o t y p e s of b r o o d a n d q u e e n ? As dissections of ~ g f r o m d i f f e r e n t colony t y p e s h a v e shown, w o r k e r s p r o d u c e d b y a g y n o m o r p h i c m o t h e r a r e less likely to h a v e m o r e t h a n t w o ovarioles t h a n w o r k e r s r e a r e d b y an i n t e r m o r p h . I n s o m e cases, e i t h e r t h e allele E in the l a r v a o r the i n h i b i t i n g influence of t h e i n t e r m o r p h i c q u e e n m i g h t n o t only p r e v e n t the develop- m e n t of wings, t h o r a c i c s u t u r e s , a n d ocelli, b u t of a r e c e p t a c l e a n d the ovaries, too. A larva, epigenetically p r e d e t e r m i n e d to develop to a y o u n g i n t e r m o r p h , thus m i g h t b e c o m e a w o r k e r w i t h six or less ovarioles. ~ ~ of H. sublaevis r e g u l a r l y h a v e 5, 6, or 7 ovarioles, a n d the i n t e r m o r p h s h a v e 7 o r 8 (BusCHINGER a n d WINTER 1978). I n the closely r e l a t e d H. canadensis, a species t h a t h a s only g y n o m o r p h i c q u e e n s , w o r k e r s have 2, 3, or 4 o v a r i o l e s (BuscHINCER a n d ALLOWAY, 1978).
O u r o b s e r v a t i o n s suggest t h a t r e p r o d u c t i v e o r g a n s develop d u r i n g a n e a r l i e r stage of o n t o g e n y t h a n e x t e r n a l s t r u c t u r e s . I f a f e m a l e of L. spec. A h a s wings, she u s u a l l y h a s the t h o r a c i c s t r u c t u r e of a gynomorpl~. I f she h a s a t least slightly i m p r e s s e d p r o m e s o n o t a l s u t u r e s , she r e g u l a r l y has ocelli, too.
I f t h e r e a r e ocelli, in all cases t h e r e is also a receptacle. 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 Myrmica (BRIAN, 1955), Leptothorax nylanderi (PLATEAUX, 1970), a n d Harpagoxenus sublaevis (WINTER a n d BUSCHINGER 1986).
I f o u r single-locus-hypothesis, o r a n y o t h e r h y p o t h e s i s w i t h several loci, is a p p l i e d to calculate allele f r e q u e n c i e s in the T a d o u s s a c p o p u l a t i o n , in s o m e m a t i n g types, especially ee • e, o b s e r v e d a n d e x p e c t e d f r e q u e n c i e s d i f f e r significantly (table II). T h e r e a r e too m a n y g y n o m o r p h i c f e m a l e s w h o p r o d u c e g y n o m o r p h i c offspring," c o m p a r e d to those w h o r e a r inter- m o r p h s . W i t h r e s p e c t to q u e e n p o l y m o r p h i s m the p o p u l a t i o n a p p a r e n t l y is n o t in a H a r d y - W e i n b e r g e q u i l i b r i u m . E l e c t r o p h o r e t i c a l studies on e s t e r a s e v a r i a b i l i t y do n o t give c l e a r e v i d e n c e f o r i n b r e e d i n g t h a t w o u l d explain this a s y m m e t r y .
I n t w o species of Pogonomyrmex, DAVIDSON (1982) o b s e r v e d m a t i n g prefe- rences: large f e m a l e s m a t e d d i s p r o p o r t i o n a l l y w i t h large males. In Lepto- thorax spec. A G Q ~ a n d e-~ ~ a r e significantly l a r g e r t h a n 1 9 ~ a n d E-~ ~.
I n the l a b o r a t o r y , m a l e s i n d i s c r i m i n a n t l y seize f e m a l e s a n d a t t e m p t to
QUEEN POLYMORPHISM 153 m a t e , b u t f e m a l e s quite o f t e n actively resist c o p u l a t i o n b y a t t a c k i n g t h e male. Size p r e f e r e n c e s in m a t i n g , s i m i l a r to the r e l a t i o n s in Pogonomyrmex, m i g h t lead to h i g h e r f r e q u e n c i e s of h o m o z y g o u s m a t i n g types.
G y n o m o r p h s a n d i n t e r m o r p h s of Leptothorax spec. A h a v e b e e n col- lected in a b o u t t w e n t y d i f f e r e n t p o p u l a t i o n s t h r o u g h o u t Q u e b e c a n d N e w England. T h e f r e q u e n c i e s of g y n o m o r p h s s e e m to b e c o r r e l a t e d w i t h c h a r a c t e r s of the biotope. I n open, h o m o g e n e o u s forests, as in St. S i m 6 o n , in G r a n d s J a r d i n s , or on Mt. M o n a d n o c k , g y n o m o r p h s b y f a r o u t n u m b e r i n t e r m o r p h i c females. I n p a t c h i l y d i s t r i b u t e d suitable areas, as in M a t a g a m i or T a d o u s s a c , m o r e t h a n 80 p e r c e n t of queens a r e i n t e r m o r p h i c . S t u d i e s o n colony s t r u c t u r e in Leptothorax (HEINZE and BUSCHINGER, in press.) s u g g e s t , t h a t s o m e y o u n g f e m a l e s of L. spec. A, especially 19 9, r e t u r n into t h e i r m o t h e r s ' colonies a f t e r m a t i n g . T h e r e they stay w i t h o u t b e c o m i n g fertile (functional m o n o g y n y ) ; n e w colonies p e r h a p s a r e f o u n d e d b y b u d d i n g in spring. E v i d e n c e h a s b e e n f o u n d f o r solitary colony f o u n d a t i o n e s p e c i a l l y b y G9 9. I n t e r m o r p h i c f e m a l e s s h o w a s t a t i o n a r y sexual calling b e h a v i o r a n d m o s t p r o b a b l y s t a r t sexual d i s p l a y in the i m m e d i a t e vicinity of the n e s t . G y n o m o r p h s , on the o t h e r h a n d , fly f o r several m e t e r s b e f o r e s t a r t i n g sexual calling. The h a b i t a t s w i t h high f r e q u e n c i e s of i n t e r m o r p h i c f e m a l e s h a v e a size of only several 10 to 100 s q u a r e m e t e r s , they a r e w i n d exposed, a n d they a r e s u r r o u n d e d b y a r e a s u n s u i t a b l e for colony f o u n d a t i o n : the sea, as on the r o c k y o u t c r o p s in T a d o u s s a c a n d G r a n d e s B e r g e r o n n e s , or d e n s e thickets, f o r e s t s or spruce-bogs, like M a t a g a m i . A g y n o m o r p h m i g h t fre- q u e n t l y d r i f t off d u r i n g sexual flight b e h a v i o r , a n d thus h a v e a l o w e r c h a n c e f o r s u c c e s s f u l colony f o u n d a t i o n in p a t c h y biotopes. T h e d e n s i t y of available n e s t i n g sites is quite high on the o u t c r o p s in T a d o u s s a c o r M a t a g a m i . R o t t e n b r a n c h e s , p a r t l y c o v e r e d by lichens a n d s h a d o w e d b y A m e r i c a n laurel a n d o t h e r p l a n t s of the h e a t h e r family, p r o v i d e p r e f o r m e d cavities w i t h the p r o p e r a m o u n t of insolation for Leptothorax ants to n e s t in.
I n T a d o u s s a c , we collected five a n d m o r e colonies f r o m one s q u a r e m e t e r . Colony f o u n d a t i o n b y b u d d i n g m i g h t be highly successful here."
On t h e o t h e r hand, in t h e light c o n i f e r o u s f o r e s t s in G r a n d s J a r d i n s o r St. Sim6on, c o m p a r a b l e n e s t i n g sites a r e quite r a r e a n d colonies of L. spec. A are f a r less a b u n d a n t . B u d d i n g p e r h a p s b e c o m e s m o r e difficult in t h e s e h a b i t a t s , a n d a winged g y n o m o r p h m i g h t have a b e t t e r c h a n c e to find a suitable place f o r colony f o u n d a t i o n t h a n a wingless i n t e r m o r p h .
G y n o m o r p h i c f e m a l e s also p l a y an i m p o r t a n t role in the colonization o f n e w h a b i t a t s t h a t a r e i n a c c e s s i b l e t o i n t e r m o r p h s . I n one r o c k y a r e a in La Bale, a p p a r e n t l y the ideal b i o t o p e f o r i n t e r m o r p h i c f e m a l e s , all six colo- nies c o n t a i n e d a g y n o m o r p h i c q u e e n (unpubl. res.).
R e c e n t o b s e r v a t i o n s in the field indicate, t h a t q u e e n p o l y m o r p h i s m is not as r a r e in the h i g h e r a n t s as w a s p r e v i o u s l y t h o u g h t . I n the g e n u s
