Longevity of kings and queens and first time of production of fertile progeny in dampwood termite (Isoptera; Termopsidae; Zootermopsis) colonies with different reproductive structures

Abstract

Summary 1.We report age-specific survivorship of founding kings and queens and colony age of first production of fertile progeny (alates) of two cohorts, containing 52 and 42 complete colonies, respectively, in the primitive dampwood termite Zootermopsis nevadensis ssp. nevadensis . 2. Longevity of kings and queens was determined and compared in various experimental manipulations of reproductive structure of incipient colonies (removal of king or queen or both vs. unmanipulated pairs as controls) performed one year after pairing. Life span of reproductives was also evaluated in circumstances of interactions between young colonies, a treatment inspired by field observations of natural nest spacing and intraspecific competition between young dampwood termite colonies. 3. In our first experimental series, founding pairs survived 2-7 years ( x = 4·5 ± 0·3 SE) after pairing. Kings lived significantly longer ( x = 4·7 ± 0·3 years after pairing; range 2·2-7·3 years) in treatments initiated as pairs than when left as the remaining founder in the queen removal treatment ( x = 3·2 ± 0·6 years after pairing; range 1·5-5·3 years), even though one or more female replacement reproductives differentiated within several months after queen loss. Queen life span in the absence of kings averaged 4·9 ± 0·4 years (range 3·6-6·3 years) after pairing, not significantly different from the life span of queens living with kings. There was no significant difference between king and queen life spans in non-interaction treatments in our first experiment. Results from the second experimental series (35 colonies) are presented to date. 4. Survival of pairs until death of one mate was significantly shorter in interaction treatments compared with control colonies, suggesting that intraspecific competition between young colonies may create opportunities for replacement reproductives. 5. The first alates were produced between 1·8 and 6·5 years after pairing in our first experimental series, and between 2·4 and 5 years, to date, in the second experiment. 6. Ecological and evolutionary correlates of long life span in social insect reproductives and other animals are discussed.

Nonrelatives inherit colony resources in a primitive termite

“…Although the motivation to attack reproductives could be dampened by potential reductions in egg-laying rates at a critical period of colony growth and risks of injury to the attackers, workers from either colony in an interaction have a better chance at inheriting the resources of the nest if at least one primary reproductive from the opposing colony dies. Also, surviving primaries in colonies that participated in an interaction do not live as long as founding reproductives in isolated control colonies (31). Thus, opportunities to inherit a colony will typically arise faster in merged colonies than in isolated families even if both primaries from one colony initially survive an interaction.…”

“…In this manner, workers can replace kings and/or queens killed during interactions between colonies, giving helper offspring early opportunities to inherit the colony resources [''Accelerated Inheritance'' (25), parallel results are described in the more derived kalotermitid Cryptotermes secundus Hill (38)]. Zootermopsis kings and queens in isolated colonies tend to live for many years (31). These intraspecific interactions that occur naturally within a limited resource and cause death of young parents are significant in creating opportunities for workers to differentiate into replacement reproductives and inherit colonies.…”

“…Neighboring Zootermopsis colonies encounter each other as they grow, leading to interactions between colonies that can result in deaths of the king and queen from either or both colonies. Surviving members form a larger merged colony (25,31). This merging behavior is intriguing because neighboring colonies are typically unrelated (32).…”

“…We grew colonies from unrelated pairs of alates, and staged interactions between pairs of similarly sized complete colonies, simulating natural meetings between neighboring families (25,31). We recorded which kings and queens were killed when colonies met, and collected new replacement reproductives and alates as they differentiated in the merged colony.…”

Evolution of eusociality and the soldier caste in termites: Influence of intraspecific competition and accelerated inheritance

“…The inheritance hypothesis, productively applied to the evolution of altruistic behavior in other social groups, was logically extended to termites, supported by the fact that philopatric reproduction is common through helper differentiation into secondary (replacement or supplementary) reproductives on death or senescence of established reproductives (4,17,26). An apparent problem with this application to termites, however, is that founding kings and queens are long-lived in captivity and in some field colonies (31), even in relatively primitive taxa (32), suggesting that early orphaning of helpers (or originally, nonhelpers) and thus opportunities for inheritance might be rare in the young families that must have characterized the evolutionary transition to termite eusociality (23). Founder life spans may have been shorter in prototermites than in modern groups (4), but timing of inheritance opportunities would be important if parents survived past the time their first offspring could reach sexual maturity and if remaining in the natal nest resulted in progeny delaying or forgoing direct reproduction.…”