1987, V o l u m e 34, n ~ 1, p p . 28-43
QUEEN POLYMORPHISM IN A NON-PARASITIC L E P T O T H O R A X SPECIES
(HYMENOPTERA, FORMICIDAE)
J. H E I N Z E and A.
BUSCHINGER
Institut fi~r Zoologie, Fachbereich Biologie Technische Hochschule Darmstadt Schnittspahnstr. 3, D-6100 Darmstadt, FRG
Re~;t. Je 10 juillet 1986 Accept6 le 30 d 6 c e m b r e 1986
S U M M A R Y
Queen p o l y m o r p h i s m , the o c c u r r e n c e of several m o r p h o l o g i c a l l y d i s t i n c t f o r m s of r e p r o d u c t i v e f e m a l e s w i t h i n one species, h a s b e e n r e p o r t e d in several P o n e r i n a e , a n d i n some m o s t l y socially p a r a s i t i c F o r m i c i n a e a n d Myrmicinae. We r e p o r t h e r e the f i r s t r e c o r d of a q u e e n p o l y m o r p h i s m in a n o n - p a r a s i t i c l e p t o t h o r a c i n e species. Dealate g y n o m o r p h i c as well as i n t e r m o r p h i c a n d n e a r l y e r g a t o m o r p h i c s p e c i m e n s are f o u n d to b e t h e r e p r o d u c t i v e q u e e n s in several p o p u l a t i o n s of this species along St. L a w r e n c e River, Quebec, Canada. The species is f u n c t i o n a l l y m o n o g y n o u s , h a v i n g only one repro- ductive f e m a l e in e a c h colony, a n d o f t e n one o r several i n s e m i n a t e d b u t n o t egg-laying p o t e n t i a l queens. I n t e r m o r p h s m a y h a v e i d e n t i c a l offspring, o r p r o d u c e b o t h i n t e r m o r p h s a n d g y n o m o r p h s as y o u n g p o t e n t i a l queens. A genetical origin of t h i s q u e e n polymor- p h i s m , as i n Harpagoxenus sublaevis, is suggested. The species is r e l a t e d to Leptothorax muscorum (Nyl.), b u t n o t yet definitely identified. The q u e e n p o l y m o r p h i s m is described, t h e k n o w n r a n g e of t h e p h e n o m e n o n a n d p r e l i m i n a r y r e s u l t s of b r e e d i n g e x p e r i m e n t s are recorded.
Z U S A M M E N F A S S U N G
K6niginnenpolymorphismus bei einer nichtparasitischen Leptothorax-Art (Hymenoptera, Formicidae)
K S n i g i n n e n p o l y m o r p h i s m u s , das V o r k o m m e n m e h r e r e r m o r p h o l o g i s c h v e r s c h i e d e n e r F o r m e n v o n r e p r o d u k t i v e n W e i b c h e n i n n e r h a l b e i n e r Art, ist y o n einigen P o n e r i n e n sowie z u m e i s t s o z i a l p a r a s i t i s c h e n F o r m i c i n e n u n d M y r m i c i n e n b e k a n n t . Wir b e r i c h t e n h i e r fiber d a s e r s t e Beispiel v o n K t i n i g i n n e n p o l y m o r p h i s m u s bei e i n e r selbstSndigen L e p t o t h o r a c i n e n - A r t . Entfliigelte g y n o m o r p h e , i n t e r m o r p h e u n d n a h e z u e r g a t o m o r p h e Tiere sind als r e p r o d u k t i v e K/Sniginnen in einigen P o p u l a t i o n e n dieser Art e n t l a n g d e m St. L o r e n z s t r o m in Quebec, K a n a d a , zu finden. Die Art ist f u n k t i o n e l l m o n o g y n , h a t also n u r jeweils ein r e p r o d u k t i v e s W e i b c h e n i n j e d e m VoIk, dazu oft eine o d e r m e h r e r e b e g a t t e t e , a b e r n i c h t legende potentielle K6niginnen. Eine K/Snigin e i n e r b e s t i m m t e n
Q U E E N P O L Y M O R P H I S M I N L E P T O T H O R A X 29 Morphe kann gleichartige Nachkommen haben, eine andere Morphe, oder auch beide nebeneinander als potentielle Jungk/Sniginnen produzieren. Wir vermuten eine genetische Grundlage fiir den K/Sniginnenpolymorphismus dieser Art, wie bei Harpagoxenus sublaevis nachgewiesen. Die Art ist mit Leptothorax muscorum (Nyl.) verwandt, jedoch nicht endgtiltig determiniert. Der K/Sniginnenpolymorphismus wird beschrieben, seine bisher bekannte Verbreitung und vortSufige Ergebnisse yon Zuchtversuchen werden mitgeteilt.
I N T R O D U C T I O N
I n m o s t species of a n t s the q u e e n is easily d i s t i n g u i s h e d f r o m the w o r k e r caste b y its m o r p h o l o g y . I t h a s t h r e e ocelli, a t h o r a x w i t h c l e a r l y s e p a r a t e pro-, meso-, m e t a - a n d e p i n o t u m , a n d t w o p a i r s of wings w h i c h a r e shed a f t e r m a t i n g .
T h e w o r k e r on the o t h e r h a n d h a s no t r a c e s of wings, a n d its t h o r a x is m u c h s m a l l e r w i t h the sclerites widely fused. T h e ocelli a r e a b s e n t in m a n y species, p a r t i c u l a r l y in the M y r m i c i n a e .
S e v e r a l a n t species a r e k n o w n , h o w e v e r , w h e r e the q u e e n is ergatoid, i.e. w o r k e r l i k e , o r w h e r e a queen p o l y m o r p h i s m does occur, in t h a t t w o or m o r e m o r p h o l o g i c a l l y d i f f e r e n t f e m a l e f o r m s m a y f u n c t i o n as r e p r o d u c t i v e s . I n s u c h species it is s o m e t i m e s difficult to tell a p a r t q u e e n a n d w o r k e r by m o r p h o l o g y . BUSCHINGER & WINTER (1976) t h e r e f o r e h a v e p r o p o s e d to res- t r i c t t h e t e r m s " q u e e n " a n d " w o r k e r " to d e s i g n a t e the role, a n d t h u s c a s t e (MICHENER, 1974), of an individual, a n d to d e n o t e its m o r p h o l o g i c a l a s p e c t as g y n o m o r p h i c , i n t e r m o r p h i c , or e r g a t o m o r p h i c , i r r e s p e c t i v e of its function.
E r g a t o m o r p h i c o r m o r e o r less i n t e r m o r p h i c f e m a l e s as t h e only q u e e n m o r p h s a r e q u i t e f r e q u e n t in m o r e p r i m i t i v e a n t s u b f a m i l i e s , like the Cera- p a c h y i n a e a n d P o n e r i n a e (for a s u r v e y see HASKINS & WHELDEN, 1965). S u c h q u e e n s h a v e b e e n r e p o r t e d also f r o m several m y r m i c i n e ants, especially f r o m species of the M o n o m o r i u r n s a l o m o n i s - g r o u p (BOLTON, 1986). A q u e e n p o l y m o r p h i s m , h o w e v e r , w i t h several q u e e n m o r p h s w i t h i n one species, is a p p a r e n t l y r a r e . Occasionally i n t e r m o r p h s h a v e b e e n f o u n d in species w i t h g y n o m o r p h i c queens, like M y r m i c a rubra (BRIAN, 1955), L e p t o t h o r a x acer- v o r u m (BERNARD, 1948, 1951), L. gredleri (BusClJINGER, 1974 a), L. nylanderi (PLATEAUX, 1970), Harpagoxenus a m e r i c a n u s (BusCHINGER & ALLOWAY, 1977), a n d H. canadensis (BUSCHINGER & ALLOWAY, 1978). T h e s e e i t h e r lack a sper- m a t h e c a o r h a v e at least n o t b e e n f o u n d i n s e m i n a t e d a n d fertile (A.B., un- publ. results).
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 , i n t e r m o r p h i c , a n d / o r erga- t o m o r p h i c r e p r o d u c t i v e f e m a l e s h a s b e e n d e s c r i b e d in R h y t i d o p o n e r a metal- lica (HASKINS & WHELDEN, 1965; H/fLLOOBLER & HASKINS, 1977), a n d in Hypo- p o n e r a e d u a r d i (LE MASNE, 1953, 1956).
With t h e exception of t h e a f r o t r o p i c a l Monomorium rufulum, in w h i c h b o t h a p t e r o u s a n d alate emales a r e p r o d u c e d (BoLTo~, 1986), in the h i g h e r subfamilies, Myrrnicinae a n d Formicinae, q u e e n p o l y m o r p h i s m a p p e a r e d to be r e s t r i c t e d to c e r t a i n socially p a r a s i t i c species. I n the Formicinae, it w a s f o u n d in Polyergus rufescens (STITZ, 1939 a n d p e r s o n a l o b s e r v a t i o n s of A.B.), a n d in Aporomyrmex ampeloni (FABER, 1969). A m o n g t h e Myrmicinae, the guest ants of the genus Formicoxenus, living in nests of Formica a n d Myrmica species, a p p a r e n t l y all have p o l y m o r p h i c queens (FRANC(EUR et al., 1985), a n d in the s l a v e m a k i n g ant, Harpagoxenus sublaevis, a genetical origin of q u e e n p o l y m o r p h i s m has been d e m o n s t r a t e d (BUSCHINGER, 1978; WINTER BUSCHINGER, 1986). The m e a n i n g of q u e e n p o l y m o r p h i s m is n o t y e t under- stood. I n F o r m i c o x e n u s it m i g h t be a d a p t i v e in t h a t the w i n g e d queens a r e able to r e a c h a n d colonize d i s t a n t h o s t species nests, w h e r e a s the flightless ones are b e t t e r fit f o r the c o n t i n u o u s exploitation of the suitable h a b i t a t w h e r e t h e y were born, w i t h usually several closely n e i g h b o r i n g h o s t species nests. Queen p o l y m o r p h i s m t h u s m a y be kept in b a l a n c e b y t w o c o u n t e r a c t i n g selective forces. I n Harpagoxenus sublaevis, q u e e n p o l y m o r - p h i s m a p p a r e n t l y r e p r e s e n t s a side-effect of a genetically m e d i a t e d caste d e t e r m i n a t i o n (WINTER & BUSCHINGER, 1986).
Quite unexpectedly, therefore, we r e c e n t l y f o u n d a p o l y m o r p h i c queen caste in a non-parasitic Leptothorax species f r o m Quebec, Canada. The species in q u e s t i o n is close to, b u t certainly n o t i d e n t i c a l with, Leptothorax muscorum (Nyl.). The t a x o n o m y of the N o r t h A m e r i c a n species belonging to the s u b g e n u s Leptothorax s. str. ( = Mychothorax Ruzsky) is quite in confusion. A revision of the g r o u p a n d the identification of o u r taxon will be p r o v i d e d b y A. FRANCO~UR. We t h e r e f o r e r e f r a i n f r o m giving a definite n a m e yet, a n d will refer to it in the f u r t h e r text als Leptothorax species A.
M A T E R I A L A N D M E T H O D S
Complete colonies of Leptothorax sp. A and other related species were collected in early summer 1979 (BUSCHINCEg), 1983 (BUSCHINGER, FRANCO~UR, ALLOWAY, STUART), and 1985 (BUSCHINGER, H~It~zv.) in Quebec in several localities along St. Lawrence and Saguenay Rivers (fig. 1). The ants nest in dry, decaying sticks on flat, sunexposed rocks which are partly covered by lichens and shrubs. Some were also found in light coniferous forests, and a few colonies were collected underneath small pebbles.
A total of 237 colonies were gathered. Some of them were directly stored in 70 % ethanol, others were kept alive in artificial nests (BuscHINCER, 1974b) o v e r several breeding cycles.
To check the reproductive function o f intermorphic females about 100 of them were dissected as described by BUSCHINGER & ALLOWAY (1978).
Measurements of length and width of thorax etc., and classification of thoracic structures, wing vestiges and ocelli were done with a Wild M5 dissecting microscope.
About 200 queens and other females with sperrnatheca, inseminated or not, were exa- mined, though not all measurements could be taken from each female. Thoracic
QUEEN POLYMORPHISM IN LEPTOTHORAX 31
Selll - ills | H a ~ ~
- - -
f I
Fig. I. - - Map of s o u t h e r n Quebec. Collecting sites of Lepthorax species A a n d B are indicated. I n all sites b o t h species w e r e collected.
Abb. 1. - - K a r t e des siidlichen Quebec. Die F u n d o r t e ftir Species A und B sind angegeben.
An allen angegebenen P u n k t e n karnen beide Arten n e b e n e i n a n d e r vor.
s t r u c t u r e s w e r e classified following BUSCHIN6ER • WINTER (1975, f o r Harpagoxenus sublaevis), b u t a d a p t e d to t h e p a r t i c u l a r s i t u a t i o n in L. sp. A. Skeletal e l e m e n t s of t h e t h o r a x w e r e n a m e d according to WHEELER (1910). The following d i s c r i m i n a t i o n s w e r e m a d e (fig. 2, 3) :
0 : E r g a t o m o r p h , t h o r a x of n o r m a l " w o r k e r " , p r o m e s o n o t a l s u t u r e only slightly d e p r e s s e d , if at all.
1: I n t e r m o r p h , p r o m e s o n o t a l s u t u r e strongly d e p r e s s e d .
2 : I n t e r m o r p h , s c u t u m s e p a r a t e d f r o m pro- a n d m e t a n o t u m , the t r a n s s c u t a l s u t u r e n o t clearly visible in t h e light microscope.
3: I n t e r m o r p h , s c u t u m a n d scutellum s e p a r a t e d b y a deep suture. Traces o f p a r a p t e r a s o m e t i m e s p r e s e n t .
4 : G y n o m o r p h , t h o r a x of o r d i n a r y alate female.
D u e t o - t h e d a r k coloration of t h e h e a d in L. sp. A., ocellar s t r u c t u r e could n o t be classified by its p i g m e n t a t i o n . Only the relative s i z e of t h e ocelli w a s r e c o r d e d w i t h t h e following r a n k s : n o ocelli at all - m i n u t e d e p r e s s i o n s in t h e cuticle - small o c e l l i - large ocelli. The p o s i t i o n of w i n g vestiges, if p r e s e n t , was also recorded.
G y n o m o r p h i c females of L. sp. A h a d to b e told a p a r t f r o m t h e g y n o m o r p h s of a n o t h e r , s y m p a t r i c a l species, in which q u e e n p o l y m o r p h i s m a p p a r e n t l y does n o t exist, by
T L
~ ,
o , . . ... , - - ~
2
I m m
Fig. 2. - - A l i t r u n k o f e r g a t o m o r p h , c l a s s 2 i n t e r m o r p h a n d g y n o - m o r p h o f Leptothorax species A i n l a t e r a l v i e w . T L = L e n g t h o f t h o r a x .
Abb. 2. - - T h o r a x u n d S t i e l c h e n v o n E r g a t o m o r p h e , I n t e r m o r p h e d e r K l a s s e 2 u n d G y n o m o r p h e v o n Leptothorax species A i n S e i t e n - a n s i c h t . T L = Thoraxl~inge.
J
i:
Fig. 3. - - A l i t r u n k o f L. species A e r g a t o m o r p h (class 0), i n t e r m o r p h s ( c l a s s e s 1-3) a n d g y n o m o r p h ( c l a s s 4), d o r s a t v i e w . T w = w i d t h o f t h o r a x . I n t h e c l a s s 3 i n t e r m o r p h t h e a r r o w s i n d i c a t e t h e d i f f e r e n t s u t u r e s : A ~ p r o m e s o n o t a l , B = t r a n s s c u t a l , a n d C -- m e s o m e t a n o t a l s u t u r e s .
A b b . 3. - - T h o r a x u n d S t i e l c h e n y o n E r g a t o m o r p h e ( K l a s s e 0), I n t e r m o r p h e n ( K l a s s e n 1-3) u n d G y n o m o r p h e ( K l a s s e 4) v o n L. species A in D o r s a l a n s i c h t . T w = T h o r a x - b r e i t e . Die T h o r a x n ~ i h t e s i n d i n K l a s s e 3 d u r c h Pfeile v e r d e u t l i c h t : A : P r o m e - s o n o t a l n a h t , B : T r a n s s c u t a l n a h t , C : Mesometanotalnaht.
QUEEN P O L Y M O R P H I S M I N L E P T O T H O R A X 33 morphological critera like coloration, shape and length of epinotal spines, and shape of petiole and postpetiole. In addition,, isozyme studies were done on ultrathin Polyacryl- amide gels (0.2 mm), cast on polyester sheets (using the " flap "' technique, RADOLA, 1980).
pH-range was 4 to 8 and 3.5 to 9.5 (ampholines by Serva and LKB). Whole white pupae were crushed in 20 ~I of a solution containing 20 % glycerol and 2 % Bromthymol Blue, and applied to the gel surface. Gels were run for approximately 5,000 Volthours, not exceeding 1,500 V. Gels were stained with Coomassie Brilliant Blue R 250, or using standard histochemical stains (SHAw & PRASAD, 1970; HARRIS & HOPKINS0N, 1976, recipes slightly varied) for Isocitrate Dehydrogenase (IDH), Superoxide Dismutase (SOD), NAD dependent Malate Dehydrogenase (MDH), and others.
R E S U L T S
E v i d e n c e o f q u e e n p o l y m o r p h i s m w i t h i n Leptothorax sp. A.
C o l o n i e s o f t h i s s p e c i e s a r e u s u a l l y s m a l l w i t h o f t e n l e s s t h a n a d o z e n a n d r a r e l y u p t o 100 a d u l t i n d i v i d u a l s . T h u s , i t is q u i t e e a s y t o a s p i r a t e t h e m c o m p l e t e l y , a n d t o c h e c k t h e i r n a t u r a l c o m p o s i t i o n .
A m o n g a t o t a l o f 237 Leptothorax c o l o n i e s c o l l e c t e d i n t h e f i e l d w e f o u n d 144 c o l o n i e s h a v i n g a n i n t e r m o r p h i c q u e e n . D u r i n g t h e t i m e o f s a m - p l i n g t h e r e p r o d u c t i v e s w e r e e a s i l y r e c o g n i z e d b y t h e i r c o n s i d e r a b l y e x t e n d e d g a s t e r s . 38 c o l o n i e s w i t h a g y n o m o r p h i c d e a l a t e q u e e n e a c h , a p p a r e n t l y b e l o n g e d t o t h e s a m e s p e c i e s , Leptothorax sp. A. T h e i r w o r k e r s w e r e o f s i m i l a r s i z e a n d c o l o r a t i o n , a n d n o m o r p h o l o g i c a l d i f f e r e n c e s c o u l d b e f o u n d w i t h t h e a i d o f a d i s s e c t i n g m i c r o s c o p e . F i n a l l y , 55 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 s a p p a r e n t l y d i d b e l o n g t o a s e c o n d , l a r g e r s p e c i e s , w i t h d a r k e r c o l o r a t i o n i n 9 2 a n d g ~. I t w i l l b e r e f e r r e d t o a s Leptothorax sp. B. i n t h e f u r t h e r t e x t .
C o n s p e c i f i t y o f t h e 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 s a n d t h e s i m i l a r o n e s w i t h g y n o m o r p h i c q u e e n s is b e t t e r d e m o n s t r a t e d b y e l e v e n c o l o n i e s a m o n g t h e 144 w i t h i n t e r m o r p h i c q u e e n s w h i c h e i t h e r i n a d d i t i o n c o n t a i n e d s e v e r a l n o n f e r t i l e g y n o m o r p h s , o r i n t e r m o r p h a n d g y n o m o r p h p u p a e , w h i c h a p p a r e n t l y w e r e o f f s p r i n g o f t h e i n t e r m o r p h i c q u e e n s . N o c o l o n i e s , h o w e v e r , w e r e f o u n d w i t h g y n o m o r p h i c q u e e n a n d e x c l u s i v e l y i n t e r m o r p h i c o f f s p r i n g . I n l a b o r a t o r y c u l t u r e s e v e r a l c o l o n i e s w e r e p r o d u c i n g f e m a l e o f f s p r i n g o v e r u p t o s e v e n s u b s e q u e n t b r e e d i n g c y c l e s ( a r t i f i c i a l l y s h o r t e n e d a n n u a l c y c l e s , s e e BUSCHIN6ER, 1974 b). I n a l l t h e s e e x p e r i m e n t s t h e o f f s p r i n g o f a c o l o n y , a n d t h u s i t s q u e e n , w a s i d e n t i c a l in a l l b r e e d i n g c y c l e s :
- - O n e colony, collected in June, 1983, at Baie-St.-Catherine, with intermorphic queen and interrnorph and g:cnomorph pupae, was producing ergatomorphs, intermorphs and gynomorphs during four subsequent breeding cycles.
- - A colony with intermorphic queen, collected June, 1983, at La Baie, produced ergatomorphs and exclusively intermorphic young queens in seven breeding cycles.
A colony with gynomorphic queen (species A), collected June, 1983, in the Laurentides Park, over seven breeding cycles had always gynomorphic offspring together with ergatomorphs.
The s a m e c o n s t a n c y in the c o m p o s i t i o n of the o f f s p r i n g could be o b s e r v e d in all colonies collected in s u m m e r , 1985, a n d k e p t in captivity d u r i n g t w o l a b o r a t o r y b r e e d i n g cycles.
These o b s e r v a t i o n s clearly d e m o n s t r a t e t h a t the p r o d u c t i o n of gyno- m o r p h s a n d / o r i n t e r m o r p h s is n o t due to l a b o r a t o r y c o n d i t i o n s o r e n v i r o n m e n t a l influences.
Like several o t h e r l e p t o t h o r a c i n e species (BuscHINGER et al., 1980), the i n t e r m o r p h i c y o u n g females exhibit a sexual calling b e h a v i o r w h e n r e a d y to mate. W i t h the gaster s o m e w h a t erect a n d the stinger e x t r u d e d they offer a sexual p h e r o m o n e f r o m the p o i s o n gland, w h i c h a t t r a c t s a n d stimulates the alate males f o r copulation. Alate g y n o m o r p h s of species. A exhibit an identical behavior, a n d male o f f s p r i n g of i n t e r m o r p h i c queens is a t t r a c t e d b o t h b y calling i n t e r m o r p h s a n d g y n o m o r p h s . Mating o c c u r s in laboratory.
conditions. Thus, " c r o s s b r e e d i n g " of sexual o f f s p r i n g of g y n o m o r p h s and i n t e r m o r p h s was possible.
I n c o n t r o l e x p e r i m e n t s we o b s e r v e d t h a t s p e c i e s ,4- $ $ were m u c h less a t t r a c t e d b y s p e c i e s B p o i s o n gland secretion t h a n by the secretion of s p e c i e s A p o i s o n glands. E u r o p e a n L. m u s c o r u m (Nyl.) females also have a sexual calling b e h a v i o r (BuscHInGER & ALLOWAV, 1978), b u t s p e c i e s A- ~ again do n o t r e a c t to t h e i r p h e r o m o n e .
| I
|
I
i
I
~ c = = n
I 1
I I
I I
! l F a J
I , l 9 I I
Fig. 4 . - Schematic and simplified pattern of iso- enzymes of nonspecific esterases in different Leptothorax species. Samples were applied near the cathode; pH-gradient is 4 to 8. Black bands indicate greater enzyme activity. Dotted bands correspond to allozymes on one locus in each species (see text). From left to right : L. species A., L. species B, L. acervorum, L. muscorum from Europe.
Abb. 4. u Vereinfachtes Schema der Isoenzyme un- spezifischer Esterasen verschiedener Lepthorax- Arten. Die Proben wurden nahe der Kathode aufgetragen; pH-Gradient 4 bis 8. Schwarze Banden zeigen stiirkere Enzymaktivit~t an. Ge- rasterte Banden entsprechen verschiedenen Allo- zymen eines Locus innerhalb einer Art (vgl.
Text). Yon links nach rechts: L. species A, L.
species B, L. acerv~um, L. muscorum aus Europa.
Q U E E N P O L Y M O R P H I S M I N L E P T O T H O R A X 35 Finally, p r e l i m i n a r y r e s u l t s of e l e c t r o p h o r e t i c studies also reveal t h a t species A s h o u l d r e p r e s e n t a g o o d species w i t h p o l y m o r p h i c q u e e n caste.
- - E s t e r a s e I E F yields f o u r to five m a j o r b a n d s in L. species A, in species B, a n d in E u r o p e a n L. a c e r v o r u m a n d m u s c o r u m (fig. 4), w h i c h s e e m to be species-specific a n d quite i n v a r i a b l e in all p o p u l a t i o n s s t u d i e d (37 colonies of L. sp. A f r o m 10 d i f f e r e n t sites, 11 colonies of sp. B f r o m 7 sites, a n d a b o u t 8 colonies each of L. a c e r v o r u m a n d L. m u s c o r u m f r o m sites n e a r N u r e m b e r g , Bavaria, a n d N y e h u s e n in S o u t h e r n Sweden). No d i f f e r e n c e w a s f o u n d b e t w e e n species A colonies w i t h i n t e r m o r p h i c o r g y n o m o r p h i c q u e e n s (8 colonies w i t h only g y n o m o r p h s , 5 w i t h b o t h g y n o m o r p h a n d i n t e r m o r p h offspring, a n d 24 w i t h only i n t e r m o r p h s ) .
I n a d d i t i o n to these i n v a r i a b l e b a n d s in all f o u r species a set of v a r i a b l e b a n d s w a s f o u n d ; one a l w a y s a p p e a r s in single (haploid) m a l e p u p a e , one or t w o in f e m a l e p u p a e , a n d one to t h r e e in w h o l e colonies. These b a n d s a p p a r e n t l y r e p r e s e n t allozymes of one locus. T h e b a n d s (four in L. sp. A, f o u r in L. sp. B, t w o in L. a c e r v o r u m a n d L. m u s c o r u m ) in e a c h s p e c i e s h a v e a d i f f e r e n t p I . No interspecific h e t e r o z y g o t e s h a v e b e e n found.
- - I s o c i t r a t e d e h y d r o g e n a s e (IDH) p a t t e r n s a r e v e r y s i m i l a r in the m a j o r b a n d s in L. sp. A, L. a c e r v o r u m a n d L. rnuscorum. Only f o r L. sp. B a d i f f e r e n t p a t t e r n w a s f o u n d (fig. 5).
|
m
m m m
|
m
m m m
i II d! II. I
I II I( II I
Fig. 5. - - S c h e m a t i c p a t t e r n of IDH (black a n d w h i t e bands) a n d SOD (dotted bands) isoenzymes. Ap- plication p o i n t is indicated b y t h e d o t t e d line.
F r o m left to right : L. species A, L. species B, L.
acervorum, L. muscorum.
Abb. 5. - - S c h e m a d e r I s o e n z y m m u s t e r von IDH (schwarze u n d weiBe Benden) u n d von SOD (gerasterte Banden). Die u n t e r b r o c h e n e Linie gibt d e n A u f t r a g u n g s p u n k t an. Von links n a c h r e c h t s : L. species A, L. species B, L. acervorum, L. m u s c o r u m .
I n S u p e r o x i d e d i s m u t a s e (SOD) ( = T e t r a z o l i u m o x i d a s e ) a n d o t h e r e n z y m e s ( n o t i l l u s t r a t e d ) c l e a r s p e c i e s d i f f e r e n c e s w e r e n o t y e t o b s e r v e d . F u r t h e r i n v e s t i g a t i o n s w i l l b e d o n e .
T h e s e r e s u l t s s t r o n g l y s u p p o r t a s e p a r a t e s p e c i f i c r a n k o f species A, a n d a l s o p r o v e c o n s p e c i f i t y o f 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 s p e c i m e n s o f t h i s t a x o n .
Analysis of queen polymorphism in Leptothorax sp. A.
Figures 2 and 3 i l l u s t r a t e t h e t h o r a c i c s t r u c t u r e s o f e r g a t o m o r p h s , i n t e r - m o r p h s a n d g y n o m o r p h s o f L. sp. A. T h e e r g a t o m o r p h c o r r e s p o n d s t o t h e u s u a l " w o r k e r " o f o t h e r L e p t o t h o r a x (s. str.) s p e c i e s . T h e i n t e r m o r p h s e x h i b i t t h o r a c i c s t r u c t u r e s g r a d u a l l y c h a n g i n g f r o m c l a s s 1 t o 3 i n t o t h e f u l l y d e v e l o p e d p t e r o t h o r a x o f t h e g y n o m o r p h ( c l a s s 4).
S o m e m e a s u r e m e n t s w e r e d o n e t o d e m o n s t r a t e t h e m o r p h o l o g i c a l l y i n t e r m e d i a t e a p p e a r a n c e o f t h e i n t e r m o r p h i c q u e e n s . S p e c i e s B g y n o m o r p h s w e r e i n c l u d e d t o s h o w t h e i r s i z e d i f f e r e n c e s i n c o m p a r i s o n w i t h species A (table I).
I n t e r m o r p h i c q u e e n s i n g e n e r a l h a v e a t h o r a x l e n g t h (TL) b e t w e e n t h a t o f e r g a t o m o r p h s a n d g y n o m o r p h s , w i t h m e a n v a l u e s (0.93 m m ) c l o s e r t o t h o s e o f e r g a t o m o r p h s (0.88 r a m ) t h a n t o g y n o m o r p h s (1.01 r a m ) . T h e i r
Table I. - - Thorax length and width of ergatomorphs, intermorphs and gynomorphs of Leptothorax species A, and gynom0rphs of L. species B, in mm. Differences of TL/
TW indices in class 1-4 specimens are statistically significant (U-test).
Tabelle I. - - ThoraxlSnge und - breite yon Ergatomorphen, Intermorphen und Gynomor- phen yon Leptothorax species A, sowie Gynomorphen yon L. species B, in mm.
Die Unterschiede der TL/TW-Indices von Exemplaren der Klassen 1-4 sind sta- tistisch signifikant (U-Test).
Thorax length Thorax width Thorax length n specimens
min-mean-max min-mean-max . . . checked
Thorax width L. species A
Ergatomorphs (0) Int. class 1 Int. class 2 Int. class 3 Gynomorphs (4)
0.83 - 0.89 - 0.96 0.27 - 0.30 - 0.36 ca. 3.00 30
n . s .
0.93 0.31 2.98 35
< 0.01
0.84 - 0.93 - 1.05 0.27 - 0.33 - 0.39 2.87 57
< 0.01
0.93 0.35 2.58 15
< 0.01
0.87 - 1.01 - 1.19 0.38 - 0.46 - 0.53 2.19 42
L. species B n.s.
Gynomorphs (4) 0.94 - 1.12 - 1.24 0.45 - 0.53 - 0.62 2.09 61
Q U E E N P O L Y M O R P H I S M I N L E P T O T H O R A X :37 Table II. - - Correlation between the development of thorax a n d ocelti,in intermorphic
females of Leptothorax species A.
Tabelle II. - - Korrelation zwischen der AusprSgung von Thorax u n d Ocellen ,bei inter- morphen Weibchen yon Leptothorax species A.
Thorax class
n and size of ocelli 1 2 3
2 minute 4 % m
3 minute 12.5 % 10.5 %
2 minute, I medium 37.5 % 13.0 % 6.0%
3 medium 46.0 % 76.5 % 94.0 %
n intermorphs 48 85 17
checked
t h o r a x w i d t h (TW) is e v e n m o r e l i k e t h a t o f e r g a t o m o r p h s (erg. 0.30, i n t . 0.31-0.35, g y n . 0.46 m m ) . T h u s , t h e l o w e r i n t e r m o r p h s o f c l a s s 2 a n d 1 h a v e q u i t e a n a r r o w t h o r a x w i t h a n i n d e x T L / T W o f 2.87 a n d 2.98 r e s p e c t i v e l y , c l o s e t o t h a t o f e r g a t o m o r p h s (3.00). I n t e r m o r p h s o f c l a s s 3 a r e i n t e r m e d i a t e w i t h a T L / T W i n d e x o f 2.58 as c o m p a r e d t o g y n o m o r p h s w i t h 2.19.
I n table I I w e t r i e d t o e v a l u a t e w h e t h e r a c o r r e l a t i o n e x i s t s b e t w e e n t h e d e v e l o p m e n t o f t h o r a x a n d o c e l l i i n i n t e r m o r p h i c q u e e n s . E r g a t o m o r p h s i n t h i s s p e c i e s g r o u p u s u a l l y h a v e n o t r a c e s o f o c e l l i o n t h e i r h e a d s , w h e r e a s i n g y n o m o r p h s t h r e e w e l l d e v e l o p e d , f u l l s i z e d o c e l l i a r e p r e s e n t . C l e a r l y t h e n u m b e r a n d s i z e o f o c e l l i a r e g r o w i n g i n c o r r e l a t i o n w i t h t h e t h o r a c i c c l a s s o f t h e s p e c i m e n s . W i n g v e s t i g e s o f d i f f e r e n t size a l s o m a y b e p r e s e n t in i n t e r m o r p h i c q u e e n s , a n d , l i k e t h e o c e l l i , t h e y a r e p r e f e r a b l y f o u n d in h i g h e r
c l a s s i n t e r m o r p h s (table III).
Table III. - - Size and localization of wing vestiges in intermorphic females of Leptothorax species A.
Tabelle III. - - G r ~ e und Lage von Fliigelrudimenten bei intermorphen Weibchen von Leptothorax species A.
Thorax class
Wing vestiges 1 2 3
none 58.0 % 36.0 % 5.5 %
front 19.0 % 45.0 % 50.0 %
hind 17.0 % 6.0 % - -
2 pairs 6.0 % 9.0 % 11.0 %
Wing stumps
front - - 3.0 % 28.0 %
hind . . . .
2 pairs - - 1.0 % 5.5 %
n intermorphs checked 52 98 18
I n t h e i r e x t e r n a l m o r p h o l o g y a n d size t h e i n t e r m o r p h i c q u e e n s , t h u s , r e p r e s e n t t r u e i n t e r m e d i a t e s b e t w e e n t h e e r g a t o m o r p h a n d t h e g y n o m o r p h . D i s s e c t i o n s o f r e p r e s e n t a t i v e n u m b e r s of s p e c i m e n s w e r e c a r r i e d o u t in o r d e r to c h e c k t h e r e p r o d u c t i v e o r g a n s a n d to c o m p a r e t h e m w i t h t h o s e of g y n o m o r p h s .
T h e r e s u l t s c l e a r l y d e m o n s t r a t e d t h a t all i n t e r m o r p h s h a d fully d e v e l o p e d o v a r i e s w i t h 2 • 3 ovarioles a n d a s p e r m a t h e c a , w i t h o u t a n y visible d i f f e r e n c e to t h o s e of g y n o m o r p h s . T h e r e p r o d u c t i v e organs, thus, h a v e t h e size a n d s h a p e w h i c h is t p i c a l f o r r e p r o d u c t i v e f e m a l e s of the genus. E r g a t o m o r p h s , o n the c o n t r a r y , n e v e r h a d a s p e r m a t h e c a , a n d t h e i r o v a r i e s u s u a l l y c o n s i s t e d of 2, r a r e l y u p to 5 ovarioles, as is also f r e q u e n t in o t h e r L e p t o t h o r a x pecies.
Evidence of functional monogyny in Leptothorax sp. A.
I n a b o u t 25 % of the colonies collected we f o u n d m o r e t h a n one, a n d u p to five f e m a l e s , e i t h e r i n t e r m o r p h i c o r g y n o m o r p h i c ones o r b o t h t o g e t h e r . D i s s e c t i o n i n g of all f e m a l e s of s u c h colonies r e v e a l e d t h a t in all' cases only o n e of t h e m w a s egg-laying, w h e r e a s t h e o t h e r s also h a d t h e i r r e c e p t a c l e s filled w i t h s p e r m , b u t t h e i r ovarioles w e r e s h o r t a n d t r a n s p a r e n t like in virgin f e m a l e s . No y o l k d e p o s i t i o n could be seen in t h e i r oocytes.
One remarkable sample apparently consisted of two colonies which had been nesting in close vicinity, and thus were unfortunately aspirated together, which resulted in fighting among the ants. However, the sample contained two fully fertile intermorphs (the queens of the two colonies), nine inseminated but sterile intermorphs, and one gynomorph in the same reproductive state. So, in one of the original colonies, a poten- tially fertile gynomorph had been living alongside an intermorphic queen.
T h e " p o t e n t i a l queens " c e r t a i n l y w e r e living in t h e colonies, p r e s u m a b l y t h e i r m o t h e r colonies, at least since the p r e v i o u s s u m m e r , since d u r i n g the t i m e of collecting the n e w sexual b r o o d h a d n o t y e t r e a c h e d the a d u l t instar.
S u c h a p r e s e n c e of i n s e m i n a t e d p o t e n t i a l queens alongside of only o n e t r u l y fertile q u e e n w a s t e r m e d f u n c t i o n a l m o n o g y n y (PARDI, 1940, 1946 ; BUSEHINGER, 1968). I t is a f r e q u e n t p h e n o m e n o n in the guest a n t genus F o r m i c o x e n u s (FRANC(EUR et al., 1985), b u t also o c c u r s in L e p t o t h o r a x grettleri M a y r (BuscHINGER, 1968), a close relative of L. m u s c o r u m .
Range of Leptothorax species A and frequency of intermorphic queens in different populations
I n t h e m a p (fig. 1) the localities a r e i n d i c a t e d w h e r e w e h a v e collected colonies of L. sp. A. (L. sp. B w a s f o u n d in all these sites, too). S u p p o s e d l y its a c t u a l r a n g e is m u c h l a r g e r t h a n is p r e s e n t l y k n o w n , h o w e v e r , in s o m e a r e a s w h e r e we h a v e collected, the species is a p p a r e n t l y lacking. Thus, in quite d e n s e a n d d a r k m i x e d a n d c o n i f e r o u s f o r e s t s in the G a s p e p e n i n s u l a (not i n d i c a t e d in t h e m a p ) , we only f o u n d Lepthorax sp. B. I n a c o r n a n d h i c k o r y f o r e s t s n e a r M o n t r e a l (Mont Rigaud) w i t h h a b i t a t s a p p a r e n t l y s u i t a b l e f o r
QUEEN POLYMORPHISM IN L E P T O T H O R A X 39 L. sp. A, o n l y Myrafant species w e r e collected, a n d no species of the s u b g e n u s Lepthorax a t all. N u m e r o u s Leptothorax colonies w e r e s a m p l e d b y o n e of us (A.B.) n e a r R o u y n - N o r a n d a in n o r t h e r n Quebec, a r o u n d Mississauga, Ontario, a n d f a r t h e r to the W e s t including the C a n a d i a n a n d A m e r i c a n R o c k y Mokm- tains. W i t h the e x c e p t i o n of one i n t e r m o r p h i c f e m a l e in a n e s t quite s u r e l y b e l o n g i n g to L. sp. A f r o m Sioux N a r r o w s ( O n t a r i o ; the site is n o t i n d i c a t e d on t h e m a p ) , no o t h e r i n t e r m o r p h i c f e m a l e s w e r e f o u n d in these places, b u t w h e t h e r o r n o t o n e of the f o r m s o b s e r v e d t h e r e is identical w i t h L. sp. A c a n n o t y e t b e d e t e r m i n e d .
On the o t h e r hand, in s o m e localities along St. L a w r e n c e River, L. sp. A is b y f a r the m o s t c o m m o n Leptothorax species. Thus, we f o u n d 126 colonies of L. sp. A, 20 of L. sp. B, a n d 8 colonies of Harpagoxenus canadensis, in the c o m p a r a t i v e l y open, r o c k y a r e a s a r o u n d T a d o u s s a c .
T h e f r e q u e n c i e s of L. sp. A colonies w i 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 q u e e n s a p p a r e n t l y v a r y in d i f f e r e n t localities (table IV). P o p u l a t i o n s w i t h a p a r t i c u l a r l y h i g h p e r c e n t a g e of colonies w i t h i n t e r m o r p h i c queens w e r e m a i n l y f o u n d a l o n g the s h o r e s of St. L a w r e n c e a n d S a g u e n a y Rivers, w h e r e a s t h e g y n o m o r p h i c queens a p p a r e n t l y d o m i n a t e in s o m e d i s t a n c e f r o m the shores, e.g. in the L a u r e n t i d e s Park.
D I S C U S S I O N
T h e Leptothorax species t r e a t e d in this p a p e r a n d p r o v i s i o n a l l y n a m e d L. sp. A c l e a r l y r e p r e s e n t s a good species, living in s y m p a t r y w i t h at least one r e l a t e d species (L. sp. B) f r o m w h i c h it is told a p a r t b y m o r p h o l o g i c a l a n d b i o c h e m i c a l m e a n s . A c o m p a r a t i v e l y high n u m e r of s u b s p e c i e s a n d v a r i e t i e s of Lepthorax canadensis P r o v a n c h e r h a v e b e e n d e s c r i b e d f r o m N o r t h A m e r i c a (CREIGHTON, 1950). All these f o r m s l a t e r on w e r e s y n o n y m i z e d u n d e r L.
muscorum (Nyl.) b y BROWN (1955), w h i c h s u r e l y does n o t m a t c h t h e a c t u a l situation. A s y s t e m a t i c a l revision of all the g r o u p is u r g e n t l y needed. Due to a p p a r e n t l y w i d e l y o v e r l a p p i n g m o r p h o l o g i c a l c h a r a c t e r s , a b i o s y s t e m a t i c a l a p p r o a c h u s i n g b e h a v i o r a l studies (sexual b e h a v i o r a n d p h e r o m o n e s ) , karyo- logical a n d b i o c h e m i c a l cues will be m o s t p r o m i s i n g .
W i t h i n o u r L. sp. A we could d e m o n s t r a t e a q u e e n p o l y m o r p h i s m in t h a t the r e p r o d u c t i v e f u n c t i o n m a y b e t a k e n o v e r b y i n t e r m o r p h i c s p e c i m e n s m o r p h o l o g i c a l l y s t a n d i n g in b e t w e e n t h e u s u a l d e a l a t e f e m a l e a n d the w o r k e r ( e r g : t t o m o r p h ) , as well as b y n o r m a l d e a l a t e f e m a l e s .
So-called i n t e r c a s t e s h a v e b e e n f r e q u e n t l y r e p o r t e d to o c c u r in m a n y Leptothorax ( s u b g e n u s Leptothorax s e n s u SMITH, 1950 = Mychothorax Ruz- sky) species, h o w e v e r , L. sp. A is the f i r s t e x e m p l e w h e r e a fully r e p r o d u c t i v e function, i.e. p r e s e n c e of a s p e r m a t h e c a full of s p e r m a n d egg-laying, of such i n t e r m o r p h s h a s b e e n d e m o n s t r a t e d in a n i n d e p e n d e n t t e p t o t h o r a c i n e .
W i t h i n t h i s t r i b e , q u e e n p o l y m o r p h i s m o c c u r s r e g u l a r l y i n m o s t ( p e r h a p s a l l ?) s p e c i e s of t h e g u e s t a n t g e n u s Formicoxenus (FRANCO~UR et al., 1985), i n c l u d i n g t h e f o r m e r Leptothorax diversipilosus a n d L. provancheri (BusCHINaER, 1979 ; BUSCnINCER et al, 1980), a n d i n t h e E u r o p e a n s l a v e m a k e r
a n t , Harpagoxenus sublaevis (BusCHINGER, 1978; WINTER • BUSCHINGER,
1986). T h e f r e q u e n c y of g y n o m o r p h i c q u e e n s i n t h e l a t t e r is v e r y low, w i t h a b o u t 1 % o f f i e l d c o l o n i e s h a v i n g a d e a l a t e q u e e n , w h e r e a s a l l o t h e r s h a v e e r g a t o m o r p h i c o r s l i g h t l y i n t e r m o r p h i c o n e s . I n Formicoxenus t h e f r e q u e n c y o f g y n o m o r p h i c q u e e n s v a r i e s , d e p e n d e n t u p o n t h e s p e c i e s , b u t is u s u a l l y h i g h e r t h a n i n Harpagoxenus. I n F. nitidulus, e.g., a b o u t 20 % of t h e c o l o n i e s h a v e a g y n o m o r p h i c q u e e n .
I n Leptothorax sp. A, g y n o m o r p h i c q u e e n s a p p a r e n t l y a r e e v e n m o r e f r e q u e n t (table IV), b u t h i g h l y d e p e n d e n t u p o n t h e c o l l e c t i n g s i t e s . T h u s , i n a l a r g e p o p u l a t i o n n e a r T a d o u s s a c o n l y 14 of 94 c o l o n i e s s t u d i e d ( = 15 %), d i d c o n t a i n a d e a l a t e f e m a l e , a n d o n l y 10 of t h e m w e r e t h e c o l o n y q u e e n s , t h e r e m a i n i n g 4 c o l o n i e s h a v i n g i n t e r m o r p h i c q u e e n s a n d a d e a l a t e g y n o - m o r p h e a c h i n a d d i t i o n . I n t h e L a u r e n t i d e s P a r k , o n t h e c o n t r a r y , t h e r e w e r e Table IV. - - Frequency (%) of Leptothorax species A colonies with gynomorphic females
in different collecting sites.
Tabelle IV. - - HSufigkeit (%) von V61kern von Leptothorax species A mit gynomorphen Weibchen an verschiedenen Fundorten.
No i n m a p Situated near to N colonies Colonies with
(fig. 1) checked gynomorphic
females
n %
1 Bagotville / La Bale 35 14 40
2 Laurentides Nat. Park 11 9 82
3 St. Sim6on 7 3 43
4 Baie Ste. Catherine 3 1 - -
5 Sacr6 Coeur du Saguenay 3 1
6 Tadoussac 9a 14 15
7 Grandes Bergeronnes 6 2 33
8 Les Escoumins 3 1 - -
9 Baie Comeau 4 0 --
10 Sept41es 3 0 - -
11 Magpie I 0 - -
12 Riviere Romaine 9 3 33
I3 Ste. Monique du Lac 2 I - -
St. Jean
14 Cacouna 2 0 - -
15 Cap-h-l'-Original 4 1 25
16 Bic 1 1 --
QUEEN POLYMORPHISM IN L E P T O T H O R A X 41 g y n o m o r p h i c queens in 9 of 11 colonies (80 %). Most p r o b a b l y the q u e e n p o l y r n o r p h i s m of this species is genetically m e d i a t e d as in Harpagoxenus sublaevis, w h i c h will be t e s t e d b y b r e e d i n g e x p e r i m e n t s .
A s e c o n d i n t e r e s t i n g f e a t u r e of L. sp. A is its f u n c t i o n a l m o n o g y n y . T h e p r e s e n c e of s e v e r a l i n s e m i n a t e d b u t n o t egg-laying f e m a l e s alongside always only one fully fertile s p e c i m e n in a colony, is c o m m o n again in m o s t , if n o t all, Forrnicoxenus species (FRANCO~UR et al., 1985), b u t it is definitely lacking in the s t r i c t l y m o n o g y n o u s Harpagoxenus subIaevis (BusCHINGER, 1966;
BUSCHINGER & WINTER, 1978). Up till p r e s e n t a f u n c t i o n a l m o n o g y n y , a m o n g the Leptothoracini, has only b e e n f o u n d in one o t h e r i n d e p e n d e n t species, L. gredleri M a y r (BusCHINGER, 1968), which, h o w e v e r , h a s g y n o m o r p h i c q u e e n s only.
T h e a d a p t i v e value of b o t h f u n c t i o n a l m o n o g y n y a n d q u e e n p o l y m o r - p h i s m is u n k n o w n yet. W e m a y s p e c u l a t e t h a t y o u n g f e m a l e s , a f t e r m a t i n g n e a r t h e m o t h e r nest, m a y r e t u r n to it, a n d p e r h a p s t a k e o v e r the q u e e n role w h e n the old queen e v e n t u a l l y dies. T h e c h a n c e to b e c o m e a r e p r o d u c - tive b y this w a y m a y be s i m i l a r to t h a t of successfully f o u n d i n g an o w n colony.
Q u e e n p o l y m o r p h i s m in Formicoxenus w a s d i s c u s s e d as p o s s i b l y a d a p t i v e in c o r r e s p o n d e n c e to life in the p a t c h i l y d i s t r i b u t e d colonies of t h e h o s t species (see i n t r o d u c t i o n ) . I n Leptothorax sp. A, w h i c h is i n d e p e n d e n t , we suggest a s i m i l a r explanation. Along the s h o r e s of St. L a w r e n c e a n d S a g u e n a y Rivers, w h e r e i n t e r m o r p h i c queens a r e p a r t i c u l a r l y f r e q u e n t , this species lives in r o c k y a r e a s w i t h a light to s p a r s e v e g e t a t i o n of c o n i f e r o u s trees a n d s h r u b s , I n s o l a t i o n t h e r e is m u c h m o r e i n t e n s e t h a n in the s u r r o u n d i n g dense f o r e s t areas, w h i c h a r e n o t i n h a b i t e d b y L. sp. A. The r o u n d e d , r o c k y out- crops, h o w e v e r , u s u a l l y h a v e a v e r y r e s t r i c t e d a r e a of several 100 to s e v e r a l 1000 m 2, w i t h o f t e n s o m e k i l o m e t r e s b e t w e e n s u c h places. T h e r e f o r e , it m i g h t b e m o r e a d v a n t a g e o u s f o r a young, i n s e m i n a t e d female, to r e m a i n in the a r e a w h e r e she w a s born, t h a n r i s k i n g to drift, d u r i n g h e r s w a r m i n g flight, into a n u n i n h a b i t a b l e area. A gene f o r flightless f e m a l e s t h e r e should h a v e a selective a d v a n t a g e . This gene m a y b e c a r r i e d to n e w sites w i t h s p e r m s t o r e d in the r e c e p t a c l e s of alate f e m a l e s . I t s f r e q u e n c y m a y v a r y w i t h the d i f f e r e n t sizes of h a b i t a t s , a n d in f a c t w e f o u n d m u c h less i n t e r m o r p h i c queens in quite extended, s a n d y c o n i f e r o u s forests, e.g., in the L a u r e n t i d e s P a r k (table IV).
Presently, h o w e v e r , these i n t e r p r e t a t i o n s m u s t r e m a i n speculative.
W i t h field a n d l a b o r a t o r y studies b e i n g c o n t i n u e d we h o p e to find o u t c o n v i n c i n g explanations.
A C K N O W L E D G E M E N T S . - - We are grateful to Pr. A. I:;RANC(EUR Of the Universit6 du Qu6bec
~t Chicoutimi for his support of our field studies, for providing laboratory facilities, and for having lent us a dissecting microscope during a trip to Gaspe and Tadoussac. Pr. P.
DAnCKER and Dr. C. BECKERS (TH Darmstadt) have kindly provided us with the equipment
f o r e l e c t r o p h o r e s i s . The w o r k in Canada w a s s u p p o r t e d by g r a n t s of t h e D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t a n d o f t h e N a t u r a l Sciences a n d Engineering R e s e a r c h Council o f Canada to A. BUSCmNCER.
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