Larval amphibian growth and development under varying density: are parasitized individuals poor competitors?

Abstract

Population density and infection with parasites often are important factors affecting the growth and development of individuals. How these factors co-occur and interact in nature should have important consequences for individual fitness and higher-order phenomena, such as population dynamics of hosts and their interactions with other species. However, few studies have examined the joint effects of density and parasitism on host growth and development. We examined the co-influences of rearing density and parasitism, by the trematode Echinostoma trivolvis, on the growth and development of larval frogs, Rana (=Lithobates) pipiens. We also examined the potential role of parasite-mediated intraspecific competition by observing how unparasitized individuals performed when housed with other unparasitized tadpoles, versus housing with a combination of unparasitized and parasitized hosts. Mean mass and mean developmental stage were reduced under high rearing densities. The presence of parasitized conspecifics had no significant effect, but there was a significant interaction of density and parasitism presence on host mass, due to the fact that parasitized conspecifics grew poorly at high densities. Unparasitized individuals reared with parasitized and unparasitized conspecifics fared no better than unparasitized individuals reared only with one another. This result indicates that infected hosts compete as much as uninfected hosts for resources, even though infected individuals have reduced mass under high-density conditions. Resource acquisition and resource allocation are different processes, and parasitism, if it only affects the latter, might not have a discernible impact on competitive interactions.

Parasitism in a community context: Trait-mediated interactions with competition and predation

“…Tadpoles had higher survival at low density and in the absence of parasitism, consistent with most previous studies of echinostomes in tadpoles (Fried et al 1997, Schotthoefer et al 2003, Belden 2006, Holland et al 2007, Rohr et al 2008a, though not all studies have found tadpole mortality due to infection (Koprivnikar et al 2008, Orlofske et al 2009). Also as predicted, high tadpole density led to delayed development and slower growth rates, and tadpoles responded to competition and predation by increasing and decreasing their activity levels, respectively.…”

“…However, the echinostome-infected snail had no significant effect on mass at metamorphosis. These two results together imply slower growth rates with parasitism, likely because antiparasite responses were costly or because echinostome infection caused direct sub-lethal effects on growth (Fried et al 1997, Koprivnikar et al 2008. This reduction of growth with echinostome exposure was probably not driven by selective mortality of larger tadpoles, because smaller tadpoles are generally less tolerant of echinostome infection (Schotthoefer et al 2003, Holland et al 2007, or by thinning due to parasite-induced mortality, which should reduce competition and accelerate growth (Peacor and Werner 2001).…”

“…Based on the analogy between predation and parasitism, we predicted that antiparasite responses would be stronger at low tadpole density, as has been shown consistently for antipredator responses (Relyea 2004). Based on previous studies, we predicted that E. trivolvis infection would decrease tadpole survival (Fried et al 1997, Schotthoefer et al 2003, Belden 2006, Holland et al 2007), and we predicted that, like predators, parasites would decrease tadpole growth and development (Relyea 2007), though previous studies of E. trivolvis in tadpoles have not always found significant effects on these factors (Belden 2006, Koprivnikar et al 2008, Orlofske et al 2009.…”

Infectious personalities: behavioural syndromes and disease risk in larval amphibians

“…Cercariae were obtained as previously detailed [31] after local collection of aquatic gastropods that serve as first intermediate hosts (Stagnicola elodes here), and were identified based on the presence of 43 collar spines [32]. Cercariae of Echinoparyphium spp.…”

Moderate Echinostoma trivolvis Infection Has No Effects on Physiology and Fitness-Related Traits of Larval Pickerel Frogs (Rana palustris)

“…However, macroparasites are often highly aggregated in nature, with a few individual hosts harboring high infections while the majority of the host population possesses much lower parasite burdens (Shaw et al, 1998). This aggregation of parasites likely occurs in populations of tadpoles, but the effects of more common, modest levels of infection on growth, development, and competitive ability have only recently been investigated (Koprivnikar et al, 2008) and require additional examination. Furthermore, seasonal timing of infection associated with amphibian life histories should also be addressed (Schotthoefer et al, 2003).…”