MARTIN, LB; HOTCHKISS, AK; WEIL, ZM; NELSON, RJ; The Ohio State University; The Ohio State University; The Ohio State University; The Ohio State University: Fitness costs of induced immune activity in Siberian hamsters
The vertebrate immune system is costly to use and develop, but the extent to which the induction of immune activity affects fitness (a proxy for survival costs) remains unspecified. Three days after birth, we induced immune activity in neonatal male and female Siberian hamsters (Phodopus sungorus) with lipopolysaccharide (LPS), a fever-inducing component of gram-negative bacteria, and compared i) the progression of puberty, ii) the strength of immune defenses, and iii) reproductive behavior and output of animals (once they had reached adulthood) to saline-challenged control hamsters. Both groups consisted of siblings randomly chosen from litters. After weaning (18 days old), all animals were housed singly, fed ad libitum, and kept on a 16:8 hour light:dark cycle until maturation was complete. LPS-challenges reduced the body temperatures of neonates (both males and females) and slowed gonad growth of juveniles (males only) compared to saline controls. Peripubertal body mass however was not different between groups. Once animals mature, immune defenses (delayed-type hypersensitivity (DTH), wound healing, and antibody production), as well as reproductive behavior and reproductive organ mass of males and reproductive output of females will be determined. If short-term costs of immune activity have long-term consequences for fitness, then these measures will be reduced in LPS-challenged hamsters relative to controls. Further, we will compare androgen and estrogen concentrations between groups throughout maturation to determine whether the costs of immune activity are mediated by steroid hormones. Finally, we will determine whether the costs of immune activity span generations by comparing the reproductive output and strength of immune defenses of offspring (post-weaning) from LPS and saline-challenged parents.
