Testosterone, ticks and travels: a test of the immunocompetence-handicap hypothesis in free-ranging male sand lizards

Abstract

The immunocompetence^handicap hypothesis suggests that androgen-dependent male characters constitute honest signals of mate and/or rival quality because of the imposed costs through immune suppression associated with elevated testosterone levels. We demonstrate in a ¢eld experiment that male sand lizards (Lacerta agilis) exposed to elevated testosterone su¡ered from increased mass loss and tick load compared to control males. Although the ¢rst of these two results could be due to an elevated basal metabolic rate from increased plasma testosterone levels, the increased parasite load was statistically independent of the loss in body condition and is likely to be due to compromised immune function. Testosterone-treated males showed greater mobility than control males, and greater mobility resulted in higher mating success. Our experiment thus lends support to the immunocompetence^handicap hypothesis, suggesting that male testosterone levels have been moderated by balancing selection for reproductive success and sustained immune function.

Proximate determinants of telomere length in sand lizards ( Lacerta agilis )

“…This seems to suggest a life under relatively little stress from predation compared with males (but see Olsson 1994b). In contrast, male tail regeneration is compromised by a high growth rate, perhaps because of selection for rapid growth in males that have more size-constrained reproductive success (Olsson & Shine 1996), and large males have a highly conspicuous phenotype and a reproductive success constrained by mate acquisition and mobility (Olsson et al 2000). Thus, males 'in-the-fast-lane' would be predicted to become more stressed during the mating season-and that is exactly what we see (Olsson et al 2005).…”

“…We included the same variables for analyses in both sexes (snout-vent length (mm), tail regeneration (mm) and their interaction to look for size-dependent effects (expected particularly in males), number of observations as a proxy for exposure, number of ectoparasites as a proxy of health (Uller et al 2003) and age (years)). In males, we also included the sexlimited badge size, since this has been shown to be correlated with a number of fitness components in males (Olsson et al 2000). Predictors were backward-eliminated at p .…”

Factors affecting helminths community structure of the Egyptian lizardChalcides ocellatus(Forskal, 1775)

“…Ulter & Olsson (2003) showed that, under controlled laboratory conditions, prenatal exposure to high testosterone levels not only increased offspring growth rate, but also susceptibility to a common ectoparasite in the common lizard, Lacerta vivipara. Testosterone has been shown to have a negative impact on immune response in some vertebrates (Olsson et al, 2000;Peters, 2000;Casto et al, 2001;Hughes & Randolph, 2001). There are at least two potential pathways in which increased steroid levels can influence parasite load in free-ranging animals.…”

Costly parasite resistance: a genotype-dependent handicap in sand lizards?

“…Detailed husbandry, field methods and molecular protocols have been published elsewhere Olsson et al 2000) and we, therefore, only give a brief account of methods used. Males were captured by noose or by hand within a week of emergence from hibernation (ca first week in May), were blood sampled within 30 s of capturing, measured and weighed and, on the day following capture, anaesthetized and given a silastic implant (every second male received an empty control implant or one with a 4 mm crystalline testosterone column; Sigma product no.…”