Colony fitness and garden growth in the asexual fungus-growing ant Mycocepurus smithii (Attini, Formicidae)

Abstract

Nest-founding in the fungus-growing ant Mycocepurus smithii is typically by single queens (monogyny) and colonies transition to multiple queens (polygyny) as they grow larger. Here, we study the transition from monogyny to polygyny of M. smithii under lab conditions. We hypothesize that the worker-to-queen ratio affects colony growth, fungus-garden growth, and colony survival. Monogyne colonies with small gardens (0.1 g) had greater garden growth than polygyne colonies, suggesting that monogyny may be the superior strategy for small colonies after initial nest establishment. In monogyne colonies with small gardens and either 30, 60, or 90 workers, colonies with 60 workers produced the largest gardens, suggesting that an intermediate worker-to-queen ratio is optimal for monogyne colonies with small gardens. For monogyne colonies with larger gardens (0.45 g) and with either 6, 18, 60, or 90 workers, colonies with 60 or 90 workers had significantly greater garden growth than those with 6 or 18 workers. New daughter queens were produced only by colonies with a worker-to-queen ratio of 60 or 90, suggesting that only colonies with sufficient worker numbers and garden growth are stimulated to produce new queens. A single queen lays only 1.12 ± 0.06 (SE) eggs within 24 h, therefore, limiting growth of monogyne colonies. The transition from monogyny to polygyny through the addition of supernumary queens, as well as a worker-to-queen ratio of around 60, are, therefore, critical for colony growth and reproduction in M. smithii.