Complex determination of queen body size in the queen size dimorphic ant Leptothorax rugatulus (Formicidae : Hymenoptera)

In order to understand the evolution of natural variability, and polymorphi sms in particular, it is essential to study proximate causes. Our study is the first work on ants to determine formally the heritability of quantitati ve traits in a quantitative genetic framework. We investigated the causes o f queen size dimorphism of the ant Leptothorax rugatulus and derive from th e results a possible scenario for its evolutionary maintenance. Mother size was highly predictive of daughter size in field colonies. This finding cou ld be repeated under constant laboratory conditions. Data suggested that ma ternal effects via egg size are not the cause for the transmission of body size. In colonies with coexisting large and small mother queens, daughter s ize did not correlate with mother size, and in an additional experiment we found a negative effect of queen number on daughter size. The integration o f these various results suggests a high transmissibility of body size from generation to generation. However, social (queen) influences also affect da ughter size, especially in the case of mixed colonies. This complex determi nation fits well with an adaptive adjustment of queen size to alternative r eproductive strategies.