Immunocompetence and reproductive characteristics of Campbell’s dwarf hamster males selected for low and high humoral immune response on sheep red blood cells (SRBC): Testing the immunocompetence handicap hypothesis

Abstract

Characteristics of innate (nonspecific) and acquired T-cell immunity, resting metabolic rate, hormonal and reproductive status, morphological traits of maturation and aggressive behavior were studied in two sample groups of Campbell’s dwarf hamster males (Phodopus campbelli Thomas, 1905) selected in three generations for high and low humoral immune response to sheep red blood cells (SRBC). The groups of males with low and high immune responses (LIR and HIR, respectively) to SRBC did not differ statistically in the intensity of delayed-type hypersensitivity cutaneous response to phytohemagglutinin (T-cell immunity test), the activity of the peroxidase-endogenous hydrogen peroxide system of neutrophils (characteristic of the innate immunity state), the white blood cell counts, the resting metabolic rate, body weight, anogenital distance at the age two months, testosterone level in the blood before immunization and at the peak of secondary immune response to SRBC, or the blood cortisol level in response to social conflict (encountering). LIR males had a significantly higher background blood cortisol level and were less aggressive (reaction to the stranger male). The midventral sebaceous gland was less developed in them at the age of two months. We observed no differences in the time of first litter birth after uniting LIR and HIR males in pairs with intact females; however, females in pairs with LIR males had smaller numbers of pups in the litter. The results of comparison do not favor the immunocompetence handicap hypothesis, which assumes the existence of a trade-off between the immunocompetence and reproductive effort.