1986] Rissing, Johnson, & Pollock— Acromyrmex 183 
dramatically from the close relatedness of cofoundresses in primi- 
tively eusocial wasps (Pfennig et al. 1983 and included references). 
Given the normally claustral method of colony foundation in ants, 
relatedness to potential cofoundresses should be unimportant in this 
essentially mutualistic process (Rissing and Pollock 1986). Colony 
foundation in leaf-cutters (including A. versicolor ), however, is not 
claustral; foundresses forage (references cited above). This presents 
an opportunity to extend and examine the dynamics of the mutual- 
istic process of colony foundation by unrelated females. Work in 
this area is currently planned. 
Summary 
Queens of the desert leaf-cutter ant, Acromyrmex versicolor 
exhibit distinct habitat choice during colony foundation; almost all 
natal nests are located directly under the canopy edge of large trees. 
Soil temperatures in these sites are conducive to queen survivorship 
during the first several days of colony initiation while those in open 
areas between trees are high enough to result in queen death. This 
habitat choice results in clumping of many natal nests under indi- 
vidual trees implying strong natal colony competition. Indeed, as 
with several other ant species exhibiting such competition, starting 
colonies are frequently pleometrotic; 82.5% of all queens excavated 
were from such multiple foundress associations. As with other 
pleometrotic ant species, mating aggregations of A. versicolor are 
small and localized, and relatedness appears unimportant in a 
queen’s decision to enter a foundress association. 
Acknowledgments 
G. E. Walsberg provided advice regarding queen temperature tol- 
erance tests. 
Literature Cited 
Bartz, S. H. and B. Holldobler 
1982. Colony founding in Myrmecocystus mimicus Wheeler (Hymenoptera: 
Formicidae) and the evolution of foundress associations. Behav. Ecol. 
Sociobiol. 10 : 137-147. 
Chapman, J. A. 
1957. A further consideration of summit ant swarms. Canadian Entomol. 89 : 
389-395. 
