Mediation of vertebrate life historiesviainsulin‐like growth factor‐1

Abstract

Life-history traits describe parameters associated with growth, size, survival, and reproduction. Life-history variation is a hallmark of biological diversity, yet researchers commonly observe that one of the major axes of life-history variation after controlling for body size involves trade-offs among growth, reproduction, and longevity. This persistent pattern of covariation among these specific traits has engendered a search for shared mechanisms that could constrain or facilitate production of variation in life-history strategies. Endocrine traits are one candidate mechanism that may underlie the integration of life history and other phenotypic traits. However, the vast majority of this research has been on the effects of steroid hormones such as glucocorticoids and androgens on life-history trade-offs. Here we propose an expansion of the focus on glucocorticoids and gonadal hormones and review the potential role of insulin-like growth factor-1 (IGF-1) in shaping the adaptive integration of multiple life-history traits. IGF-1 is a polypeptide metabolic hormone largely produced by the liver. We summarize a vast array of research demonstrating that IGF-1 levels are susceptible to environmental variation and that IGF-1 can have potent stimulatory effects on somatic growth and reproduction but decrease lifespan. We review the few studies in natural populations that have measured plasma IGF-1 concentrations and its associations with life-history traits or other characteristics of the organism or its environment. We focus on two case studies that found support for the hypothesis that IGF-1 mediates adaptive divergence in suites of life-history traits in response to varying ecological conditions or artificial selection. We also examine what we view as potentially fruitful avenues of research on this topic, which until now has been rarely investigated by evolutionary ecologists. We discuss how IGF-1 may facilitate adaptive plasticity in life-history strategies in response to early environmental conditions and also how selection on loci controlling IGF-1 signaling may mediate population divergence and eventual speciation. After consideration of the interactions among androgens, glucocorticoids, and IGF-1 we suggest that IGF-1 be considered a suitable candidate mechanism for mediating life-history traits. Finally, we discuss what we can learn about IGF-1 from studies in free-ranging animals. The voluminous literature in laboratory and domesticated animals documenting relationships among IGF-1, growth, reproduction, and lifespan demonstrates the potential for a number of new research questions to be asked in free-ranging animals. Examining how IGF-1 mediates life-history traits in free-ranging animals could lead to great insight into the mechanisms that influence life-history variation.

Insulin-like growth factor-1 is associated with life-history variation across Mammalia

“…The nature of the relationship between hormones and the traits they influence as they evolve has important consequences for whether the vertebrate neuroendocrine system constrains or facilitates evolutionary change [9][10][11]36,37]. Owing to their pleiotropic effects, hormones can promote phenotypic integration [9,38], but could also constrain the rate of evolutionary change if rspb.royalsocietypublishing.org Proc.…”

“…Within mammalian species, increased plasma IGF-1 concentrations are associated with increased growth, rapid development and increased reproduction, but reduced lifespan (reviewed in [11]). We show that similar patterns hold across diverse mammalian species.…”

“…IGF-1 may also influence mammalian life-history traits by mobilizing energy reserves or macronutrient stores [17], thereby mediating the energetic burden of lactation or other forms of parental care [18,19]. Although steroid hormones (glucocorticoids and androgens) may also affect life-history traits, IGF-1 could in some cases act as an intermediary mechanism [11].…”

“…Based on results from previous intraspecific studies [11,20], we predicted that species with high plasma IGF-1 concentrations would exhibit fast life histories. Although mammalian species at the altricial end of the altricial-precocial continuum may Figure 1.…”

Expression of genes involved in the embryo–maternal interaction in the early-pregnant canine uterus

“…By interacting mainly with the IGF1R (Wang & Chard 1999), both IGF1 and IGF2 are mitogenic factors whose uterine expression is regulated Embryo-maternal interaction in the dog by steroidogenic hormones (De Cock et al 2002, Bhatti et al 2007, Dantzer & Swanson 2012. They possess differentiation properties capable of influencing embryonic development, as shown, e.g., in humans and ruminants (Wathes et al 1998, Irwin et al 1999, Kim et al 2008.…”