Yoyo-bang: a risk-aversion investment strategy by a perennial insect society

Abstract

In 1978, Oster and Wilson proposed a bang-bang investment strategy for social insects in which colony size at maturity amplifies colony reproduction. In this paper, the investment strategies of the monogyne form of the fire ant, Solenopsis invicta, were compared to the predictions of the bang-bang model. Demographic census data, collected on fire ant mounds excavated every month during the years 1985 and 1988, revealed that colony reproduction was independent of colony size (~50,000 to ~250,000 workers). Why were mature S. invicta colonies up to five times larger than they needed to be to reproduce an annual batch of sexual offspring? To address this question, Oster and Wilson's bang-bang model was modified to a "yoyo-bang" investment strategy for perennial societies. In the yoyo-bang model, excess workers are a disposable reserve - a buffer - that can oscillate up or down depending on resource availability without adversely affecting annual reproductive cycles. The yoyo-bang model links colony size, colony survival and lifetime reproductive fitness.

Extraordinary starvation resistance in Temnothorax rugatulus (Hymenoptera, Formicidae) colonies: Demography and adaptive behavior

“…This finding is in contrast to the major assumption of the "fasting endurance" hypothesis for Bergman's rule (Kaspari and Vargo, 1995) and the yoyo-bang hypothesis (Cassill, 2002). The brood emerged as the single most important factor for colony survival, and it appears that workers and super-numerous queens of T. rugatulus can not be efficiently sacrificed to keep the reminder of the colony alive under the experimental circumstances.…”

“…Resources in "regular" workers (Brian, 1983;Amdam et al, 2003) may also serve to ensure against seasonal food shortages and consequently seasonality has been suggested to be a major determinant of worker number or colony size (Kaspari and Vargo, 1995;Cassill, 2002). A number of storage proteins have been isolated from ants (Wheeler and Martínez, 1995;Martínez et al, 2000).…”

Impact of worker longevity and other endogenous factors on colony size in the fire ant, Solenopsis invicta

“…(2) Colony growth occurs as a mated-queen produces hundreds, thousands or sometimes millions of sterile offspring-the number depends on species. (3) Colony maturity occurs when colony size reaches a set point (in the fire ant, that set point is *50,000 workers, Cassill, 2002). At this point, and each spring thereafter, the mated-queen produces fertile offspring that disperse, mate and found their own colonies.…”

“…comm.). Assuming that queens continue to produce fertile offspring as they age, factors that extend a queen's longevity will increase her lifetime fitness- (Cole and Wiernasz, 2000;Cassill, 2002Cassill, , 2006.…”

“…Typically, fertile offspring are produced by mated-queens during the spring when food is abundant and weather is agreeable. In the fire ant, Solenopsis invicta, colony maturity is reached within approximately 2 years when the number of sterile offspring, the workers, reaches about 50,000 (Cassill, 2002). Oster and Wilson (1978) postulated a 'bang-bang' model linking colony size to a queen's annual fitness (measured as the number of fertile offspring produced per year).…”