Age at weaning, immunocompetence and ectoparasite performance in a precocial desert rodent

Abstract

We studied the effects of early weaning on immunocompetence and parasite resistance in a precocial rodent Acomys cahirinus. We hypothesized that if parasite resistance is energetically expensive and nutritional and immunological support from mothers are necessary for the long-term health of offspring, then early weaned animals would be immunologically weaker and less able to defend themselves against parasites than later weaned animals. We weaned pups at 14, 21 or 28 days after birth and assessed their immunocompetence and resistance against fleas Parapulex chephrenis when they attained adulthood. Immunocompetence was assessed using leukocyte concentration (LC) and a phytohaemagglutinin injection assay (PHA test). To estimate resistance against fleas, we measured performance of fleas via the number of produced eggs and duration of development and resistance to starvation of the flea offspring. We found a significant positive effect of weaning age on the PHA response but not on LC. The effect of age at weaning on flea egg production was manifested in male but not female hosts, with egg production being higher if a host was weaned at 14 than at 28 days. Weaning age of the host did not affect either duration of development or resistance to starvation of fleas produced by mothers fed on these hosts. We conclude that even in relatively precocial mammals, weaning age is an important indicator of future immunological responses and the ability of an animal to resist parasite infestations. Hosts weaned at an earlier age make easier, less-resistant targets for parasite infestations than hosts weaned later in life. KEY WORDS: Fleas, PHA response, Weaning, Spiny mouse INTRODUCTIONIt is well known that resistance against parasites is often energetically expensive and a number of studies have investigated the potential trade-offs between resistance and other energetically demanding processes (Sheldon and Verhulst, 1996;Lochmiller and Deerenberg, 2000;Rigby et al., 2002;Sandland and Minchella, 2003; but see Klasing, 1998;Hasselquist and Nilsson, 2012 trade-off may be particularly noticeable in energy-limited organisms, or young animals facing elevated energetic demands associated with growth (Ricklefs and Wikelski, 2002;. While the exact cost of resistance remains difficult to quantify, it is increasingly clear that from a life-history perspective, maintenance and upregulation of immune function may suffer in the face of a limited energy supply (Lochmiller and Deerenberg, 2000;Pilorz et al., 2005;French et al., 2009).Reproductive choices concerning weaning time in mammals are likely to have a great effect on a number of life-history parameters. Evolutionarily, mammalian mothers face a conflict: lactation is wellknown to be energetically demanding and it delays future reproductive events; however, early weaning may place nursing offspring at greater risk for restricted growth or increased susceptibility to pathogens or parasites (Grindstaff et al., 2003;Grindstaff, 2008). Mothers absorb some of the energetic costs plac...

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