Body size, not age, predicts parasite load in Clark’s Spiny Lizards (Sceloporus clarkii)

Abstract

Determining the factors that influence parasite load is a fundamental goal of parasitology. Body size often influences parasite load in reptiles, but it is unclear whether higher levels of parasitism are a result of greater surface area of individuals (a function of size) or of longer periods of exposure to parasites (a function of age). Using skeletochronology in a wild population of Clark’s Spiny Lizards (Sceloporus clarkii Baird and Girard, 1852), we tested the hypotheses that (i) larger individuals have higher parasite loads due to increased surface area available for colonization by parasites and their vectors and that (ii) older individuals have higher parasite loads because they have had longer exposure to parasites and their vectors. Males harboured more ectoparasites than females. Males and females differed in how body size influenced chigger (Acari: Trombiculidae) load; larger males harboured more chiggers than smaller males, but this was not the case in females. Age did not affect ectoparasite load in either sex. These results emphasize the importance of disentangling the effects of size and age in models of parasitism to gain a clearer understanding of intraspecific variation in parasite load.

Phenological and intrinsic predictors of mite and haemacoccidian infection dynamics in a Mediterranean community of lizards

“…Olsson and Shine, 1996 ). However, Watkins and Blouin-Demers ( 2019 ) found that body size, but not age indirectly estimated by skeletochronology, predicted mite load in Sceloporus clarkii . In our study, A. erythrurus was infected by blood parasites only in individuals with an estimated age older than 300 days.…”

High tolerance of two parasites in ornate tree lizards reduces the fitness costs of parasitism

“…This association between parasite load and body size is consistent with previous observations in lizards (Schall, 1996; Garrido & Pérez‐Mellado, 2013; Halliday et al ., 2014) and fish (Lo, Morand & Galzin, 1998). Larger hosts may harbour more parasites because they have more surface area for attachment or entry, are easier to detect by parasites and their vectors, or because larger hosts are older and have had a longer time to accumulate parasites (Ruby & Dunham, 1984; Lo et al ., 1998; Blackenhorn, 2000; Watkins & Blouin‐Demers, 2019). Considering that blood‐feeding mite larvae and haemoparasitic Plasmodium infection did not decrease survival rates or growth rates of ornate tree lizard hosts, we posit that likely mechanisms are that older and larger hosts have more time to accumulate a higher parasite load, are easier to detect by parasites, or provide more space for attachment.…”

“…We fixed slides in methanol for one minute and then stained them with Wright–Gemsia stain. To assess Plasmodium infection load, we examined 5000 red blood cells under a light microscope at 400x magnification and counted the number of infected red blood cells (Halliday et al ., 2014; Watkins & Blouin‐Demers, 2019). We used the number of infected red blood cells (per 5000 cells) as an index of Plasmodium parasite load.…”

“…We used mite infection load as the response variable and body size (SVL), sex and day of the year (quadratic) as fixed effects. We included body size because larger individuals harbour more parasites in related lizard species in our study area (Halliday et al ., 2014; Watkins & Blouin‐Demers, 2019) and we included sex because male lizards often harbour more parasites than females (Klukowski & Nelson, 2001; Halliday et al ., 2014). We used a quadratic effect for day of the year because environmental temperatures increase in the spring and decline once the summer monsoons start in mid‐summer; a quadratic effect fit the data significantly better than a linear effect (log‐likelihood ratio test, χ 2 = 76.30, P < 0.0001).…”

Scaling species interactions: implications for community ecology and biological scaling theory

“…Smaller organisms in warmed environments should not only have altered rates of metabolism, growth, and reproduction, but also experience changes in the number/abundance of predators or parasites exploiting them, as expected from the size spectra for predation and parasitism documented in this review (see Section 3). Such spectra may even apply within species (see e.g., [155,[294][295][296][297][298][299]) and thus may be pertinent for intraspecific changes in body size caused by temperature changes. Furthermore, temperaturecaused shifts in body size may change prey/host preferences by size-selective predators, herbivores, and parasites [60-64, 200, 214, 215, 300-303].…”