Maternally-derived anti-helminth antibodies predict offspring survival in a wild mammal

The transfer of antibodies from mother to offspring provides crucial protection against infection to offspring during early life. However, few studies have tested the consequences of variation in maternal antibody transfer for offspring fitness in the wild. Further, separating out the immunoprotective effects of antibodies from their association with nutritional resources provided by the mother is difficult. Here, we measured plasma levels of total and parasite-specific antibody levels in neonatal (<10 days old) wild Soay sheep over 25 years to quantify variation in maternal antibody transfer and test its association with offspring survival. Maternal antibody transfer was predicted by maternal age and previous antibody responses, and was consistent within mothers across years. Neonatal total IgG antibody levels were positively related to early growth, suggesting they reflected nutritional transfer. Neonatal parasite-specific IgG levels positively predicted first year offspring survival, independent of lamb weight, total IgG levels and subsequent lamb parasite-specific antibody levels. This relationship was in part mediated via an indirect negative association with parasite burden. We show that among-female variation in maternal transfer of immunity can have long-term effects on offspring growth, parasite burden and fitness in the wild, and is likely to impact naturally-occurring host and parasite dynamics.

Methods
This data was collected as part of the long term individual based study on the Soay sheep of St Kilda in Scotland.