62 
Psyche 
[Vol. 95 
weeks later, often show the presence of a new inseminated egg- 
laying queen. But the process of the regulation is different than in /. 
humilis: the replacement queens does not originate from a new rear- 
ing of sexual larvae. Rather they were probably surviving foun- 
dresses remaining in the societies after the pleometrotic colony 
founding, which leads the authors to hypothesize that these societies 
were functionally monogynous. 
The second case of regulation exists in Cataglyphis cursor. The 
mechanism is again completely different than in I. humilis. In the 
laboratory, workers in queenless societies lay arrhenotokous eggs 
which develop into males and thelitokous eggs which develop into 
queens (Cagniant, 1976). After mating, which occurs near the nest at 
ground level (Cagniant, 1976), queens return to their society. By this 
mechanism, societies display the ability to replace the mated queen 
when she is experimentally removed in field colonies (Lenoir et al., 
1986). 
The third case of queen replacement is found in Monomorium 
pharaonis which displays a similar mechanism as in the Argentine 
ant; namely when societies are dequeened, males and winged queens 
are produced and mate within the nest (Peacock and Baxter, 1949; 
Petersen-Braun, 1975). 
Hence, M. pharaonis is the only species which displays a similar 
mode of queen replacement as the one described in I. humilis. Such 
a mechanism involves three factors: 
— Mating must occur within the nest or in the immediate vicinity. 
This condition involves a polygynous colony structure as occurs in 
both M. pharaonis and I. humilis. Several pairs of closely related 
species are known, one being monogynous and the other polygy- 
nous, e.g., Myrmica ruginodis, macrogyna and microgyna (Brian 
and Brian, 1955), Pseudomyrmex ferruginea and P. venefica (Jan- 
zen, 1973), Lasius niger and L. sakagamii (Yamauchi et al., 1981). In 
these three pairs, the first species is monogynous and queens mate 
outside the nest during a nuptial flight, whereas the second species is 
polygynous and queens often mate within the nest. In monogynous 
species, mating within the nest is probably selected against because 
the deleterious effect of inbreeding (Bruckner, 1980; Brian, 1983). 
On the contrary, in polygynous species in which sexuals are pro- 
duced by several queens, e.g., I. humilis (Keller, unpublished data), 
mating within the nest is possible without a high degree of 
inbreeding. 
