RESUMEN
Nutrient sensitive insulin-like peptides (ILPs) have profound effects on invertebrate metabolism, nutrient storage, fertility and aging. Many insects transcribe ILPs in specialized neurosecretory cells at changing levels correlated with life history. However, the major site of insect metabolism and nutrient storage is not the brain, but rather the fat body, where functions of ILP expression are rarely studied and poorly understood. Fat body is analogous to mammalian liver and adipose tissue, with nutrient stores that often correlate with behavior. We used the honey bee (Apis mellifera), an insect with complex behavior, to test whether ILP genes in fat body respond to experimentally induced changes of behavioral physiology. Honey bee fat body influences endocrine state and behavior by secreting the yolk protein precursor vitellogenin (Vg), which suppresses lipophilic juvenile hormone and social foraging behavior. In a two-factorial experiment, we used RNA interference (RNAi)-mediated vg gene knockdown and amino acid nutrient enrichment of hemolymph (blood) to perturb this regulatory module. We document factor-specific changes in fat body ilp1 and ilp2 mRNA, the bee's ILP-encoding genes, and confirm that our protocol affects social behavior. We show that ilp1 and ilp2 are regulated independently and differently and diverge in their specific expression-localization between fat body oenocyte and trophocyte cells. Insect ilp functions may be better understood by broadening research to account for expression in fat body and not only brain.
Asunto(s)
Abejas/genética , Abejas/fisiología , Conducta Animal/fisiología , Cuerpo Adiposo/metabolismo , Genes de Insecto/genética , Insulina/genética , Conducta Social , Albúminas/metabolismo , Aminoácidos/farmacología , Animales , Abejas/efectos de los fármacos , Conducta Animal/efectos de los fármacos , Cuerpo Adiposo/citología , Cuerpo Adiposo/efectos de los fármacos , Técnica del Anticuerpo Fluorescente , Regulación de la Expresión Génica/efectos de los fármacos , Hemolinfa/efectos de los fármacos , Hemolinfa/metabolismo , Miel , Insulina/metabolismo , Hormonas Juveniles/metabolismo , Modelos Biológicos , ARN Mensajero/genética , ARN Mensajero/metabolismo , Reproducibilidad de los Resultados , Volumetría , Vitelogeninas/genética , Vitelogeninas/metabolismoRESUMEN
Variation in endocrine pathways can be a major mechanism underlying life-history evolution. Yet it is unclear whether this insight, derived primarily from solitary species, explains the origins of complex life-history traits in highly social taxa. Thus, we here document and study variation in social life-history syndromes of female fecundity, behavior, and life span in selectively bred honeybee (Apis mellifera) strains. Associated variation in endocrine signaling was uncovered by RNA interference (RNAi) silencing of the juvenile hormone (JH) suppressor gene vitellogenin. High versus low endocrine reactivity in response to vitellogenin knockdown consistently correlated with rapid social behavioral ontogeny and short life span versus slow social behavioral ontogeny and long life span. Variation in JH reactivity, furthermore, was a function of variation in fecundity (ovary size and follicle development). A JH-mediated pleiotropy of female life-history traits, including fecundity, behavior, and life span, characterizes the distantly related solitary insect Drosophila. For the first time, we document a similar regulatory principle in a highly social species where most females are alloparental helpers (workers) that seldom reproduce. We conclude that variation in endocrine pathways of solitary origin can underlie variation and evolvability of complex social life-history traits.