Meeting Abstract
Mounting an immunological response is energetically demanding and necessarily redirects allocation of resources towards immune system activation and away from other processes, such as reproduction. Repeated exposure to pathogens may impose long-term costs. Here we induced an immunological energetic challenge by giving three lipopolysaccharide (LPS) injections to probe for potential trade-offs between immunity and sperm viability following repeated immune challenges. LPS induces a reversible inflammatory acute phase response that can result in impaired testicular steroidogenesis and compromised sperm membrane integrity by disruption of spermatogenesis. Our study species, a wild-caught captive population of house sparrows (Passer domesticus), is a highly social species that engages in extra-pair copulations with intra- and inter sexual selection pressures for high-quality sperm. In birds, the number of sperm ejaculated and sperm fertilizing ability are influential for sperm competition in the wild. We measured sperm concentration and straight-line velocity at 4 time points for each of the 3 LPS injections: pre-injection and 24 hours, 48 hours, and 14 days post-injection. The 24- and 48-hour sperm samples would represent possible effects of fever on sperm stored in the testes, while the 14-day sperm sample indicates an influence on end stage spermatogenesis. The results will inform whether repeated immune challenges can readily induce a trade-off in resource allocation, and at what time point sperm quality is affected in house sparrows.
