Social status regulates growth rate: Consequences for life-history strategies

Abstract

The life-history strategies of organisms are sculpted over evolutionary time by the relative prospects of present and future reproductive success. As a consequence, animals of many species show flexible behavioral responses to environmental and social change. Here we show that disruption of the habitat of a colony of African cichlid fish, Haplochromis burtoni (Gü nther) caused males to switch social status more frequently than animals kept in a stable environment. H. burtoni males can be either reproductively active, guarding a territory, or reproductively inactive (nonterritorial). Although on average 25-50% of the males are territorial in both the stable and unstable environments, during the 20-week study, nearly two-thirds of the animals became territorial for at least 1 week. Moreover, many fish changed social status several times. Surprisingly, the induced changes in social status caused changes in somatic growth. Nonterritorial males and animals ascending in social rank showed an increased growth rate whereas territorial males and animals descending in social rank slowed their growth rate or even shrank. Similar behavioral and physiological changes are caused by social change in animals kept in stable environmental conditions, although at a lower rate. This suggests that differential growth, in interaction with environmental conditions, is a central mechanism underlying the changes in social status. Such reversible phenotypic plasticity in a crucial life-history trait may have evolved to enable animals to shift resources from reproduction to growth or vice versa, depending on present and future reproductive prospects.

Social control of brain morphology in a eusocial mammal

“…For example, changes in the social environment trigger changes in reproductive status and alterations in neural morphology and neuropeptide gene expression in males of the species Astatotilapia burtoni (11)(12)(13)(14)(15). The behavioral and neural changes are reversible, as A. burtoni males may switch status both rapidly and repeatedly (46). Increases in immediateearly gene expression are observed in gonadotrophin-releasing hormone (GnRH) neurons within minutes of a relevant social stimulus, suggesting that this is a very early event in a molecular cascade presumably leading to longer-term changes (16).…”

Functional genomics of neural and behavioral plasticity

“…Changes in morphology, physiology, and behavior as they relate to survival and reproductive fitness have long been studied within the context of life history theory (Stearns, 1992) and the tradeoffs have been analyzed in much detail in a few select model systems (Zera and Harshman, 2001). As an example, consider the differential allocation of resources towards growth and reproduction in the African cichlid fish Astatotilapia (Haplochromis) burtoni (Hofmann et al, 1999): Reproductively active territorial males spend all their time and energy on territory maintenance and mate attraction (as well as sperm production), whereas nonreproductive males spend most of their time feeding and, as a result, show increased growth. Once a subordinate animal has grown sufficiently to challenge a territory owner, a rank reversal accompanied by a change in phenotype often occurs, as size is an important predictor of dominance.…”

Social and reproductive physiology and behavior of the Neotropical cichlid fish Cichlasoma dimerus under laboratory conditions

“…There are strong interactions between behavior, the endocrine and nervous systems that affect the interactions between an animal and its environment, including social interactions. For example, dominance status has been shown to control fertility (Fraley & Fernald, 1982;Abbot et al, 1998;Faulkes & Bennet, 2001), suppressing gonadal maturation in subordinate individuals (Barret et al, 1990), and also influence on neurogenesis (Kozorovitskiy & Gould, 2004), growth rate (Hofmann et al, 1999), and stress (Fox et al, 1997;Abbot et al, 2003). Although social regulation on several physiological processes is a well-established phenomenon, little is known about the mechanisms linking the social environment to physiological changes associated with dominance.…”