Ultimate mechanisms of age-biased flea parasitism

Abstract

Mechanisms that cause nonrandom patterns of parasite distribution among host individuals may influence the population and evolutionary dynamics of both parasites and hosts, but are still poorly understood. We studied whether survival, reproduction, and behavioral responses of fleas (Xenopsylla conformis) changed with the age of their rodent hosts (Meriones crassus), experimentally disentangling two possible mechanisms: (a) differential survival and/or fitness reward of parasites due to host age, and (b) active parasite choice of a host of a particular age. To explore the first mechanism, we raised fleas on rodents of two age groups and assessed flea survival as well as the quantity and quality of their offspring. To explore the second mechanism, three groups of fleas that differed in their previous feeding experience (no experience, experience on juvenile or experience on adult rodents) were given an opportunity to choose between juvenile and adult rodents in a Y-maze. Fleas raised on juvenile rodents had higher survival and had more offspring that emerged earlier than fleas raised on adults. However, fleas did not show any innate preference for juvenile rodents, nor were they able to learn to choose them. In contrast to our predictions, based on a single previous exposure, fleas learned to choose adult rodents. The results suggest that two mechanisms-differential survival and fitness reward of fleas, and associative learning by them-affect patterns of flea distribution between juvenile and adult rodents. The former increases whereas the latter reduces flea densities on juvenile rodents. The ability of fleas to learn to choose adult but not juvenile hosts may be due to: (a) a stronger stimulus from adults, (b) a higher profitability of adults in terms of predictability and abundance, or (c) the evolutionary importance of recognizing adult but not juvenile hosts as representatives of the species.

Host sex and age typically explain variation in parasitism of rock ptarmigan: implications for identifying determinants of exposure and susceptibility

“…Alternatively, parasites may preferentially parasitize a particular age class: adults may provide more resources and higher fitness to infecting parasites, or may produce a more intense stimulus to infective stages of parasites (e.g. fleas actively selecting adult over juvenile potential hosts in experiments, Hawlena et al 2007).…”

Strong Host-Feeding Preferences of the Vector Triatoma infestans Modified by Vector Density: Implications for the Epidemiology of Chagas Disease

“…Examples of innate (genetically determined) host-feeding preferences are few, and convincing evidence with both experimental and field support is scarce [1],[3]. Fleas ( Xenopsylla conformis ) do not have an innate preference but can discriminate between juvenile and adult hosts, and derive a higher reproductive reward when feeding on juvenile hosts [4]. In Lutzomyia longipalpis sandflies, host size was the main determinant of host-feeding choices among a human, a dog and a chicken exposed simultaneously to laboratory-reared sandflies [5], and its feeding success on chickens was density-dependent [6].…”

Sex ratio in flea infrapopulations: number of fleas, host gender and host age do not have an effect

“…Furthermore, this explanation is valid only if fleas are able to distinguish between host individuals belonging to different genders and age cohorts. According to experimental studies, this appears to be the case (Mears et al 2002 ;Hawlena et al 2007).…”