[Immunocompetence and reproductive characteristics of male Campbell dwarf hamsters selected for low and high humoral immune response to SRBC: testing the immunocompetence handicap hypothesis].

Abstract

We selected Campbell dwarf hamsters (Phodopus campbelli Thomas, 1905) for low and high humoral immune response to the sheep red blood cells (SRBC) challenge in three generations (P, F1, F2). Non-specific innate immunity and acquired T-cell immunity, resting metabolic rate, testosterone, and cortisole hormone levels, reproductive characteristics, including maturation related morphological traits, and aggressive behavior were studied within sets of males:with low (LI) and high (HI) immune response to SRBC. We found no difference between LI and HI males in cutaneous response to injection of phytohemagglutinin, (DTH test for T-cell immunity), in activity of Peroxidase - Endogenous Hydrogen Peroxide System of Neutrophils , in the white blood count, in resting metabolic rate, in body mass and ano-genital distance at the age of two months, in the blood level of testosterone before and after recurrent immunization by SRBC and in the blood level of cortisole in response to the social stressor (10 min encounter in the neutral arena). At that, LI males had significantly higher basal level of blood cortisole, were less aggressive in response to stranger male and had smaller testosterone-dependent mid-ventral specific skin gland at the age of two months. Males of two groups did not differ in the initial mating success with intact young females (time since pair formation until first litter born), although females of LI males born fewer number of pups. In fact, our results do not support the Handicap Immunocompetence Hypothesis (Folstad, Karter, 1999) which is based on the assumption of trade-off between immunocompetence and reproductive effort.