Resource predictability and host specificity in fleas: the effect of host body mass

Abstract

Ecological specialization is hypothesized to result from the exploitation of predictable resource bases. For parasitic organisms, one prediction is that parasites of large-bodied host species, which tend to be long-lived, should specialize on these hosts, whereas parasites of small host species, which represent more ephemeral and less predictable resources, should become generalists. We tested this prediction by quantifying the association between the level of host specificity of fleas and the mean body mass of their mammalian hosts, using published data from 2 large, distinct geographical regions (South Africa and northern North America). In general, we found supporting evidence that flea host specificity, measured either as the number of host species exploited or their taxonomic distinctness, became more pronounced with increasing host body mass. There were, however, some discrepancies among the results depending on the different measures of host specificity, the geographical region studied, or whether we used the raw values or phylogenetically independent contrasts. These are discussed with respect to other forces acting on the evolution of host specificity in parasites, as well as in the context of the regions' contrasting evolutionary histories. Overall, though, our findings indicate that the exploitation of large-bodied, and therefore long-lived, host species has promoted specialization in fleas, most likely because these hosts represent predictable resources.

Determinants of Host Specificity and Comments on Attachment Site Specificity of Tetraphyllidean Cestodes Infecting Rajid Skates from the Northwest Atlantic

“…respectively) range between 1 and 5; parasites exhibiting the greatest degree of specificity will tend toward 1. The variance in taxonomic distinctness (VarS TD ) was not calculated because not a single tetraphyllidean species was recovered from more than 2 host species as adults, a requirement for calculations of VarS TD (Poulin and Mouillot, 2003;Krasnov et al, 2006). Molecular data have shown that the distribution of immature Pseudanthobothrium hanseni and P. purtoni specimens mirrors that of adults (mature specimens) (Randhawa et al, 2007); therefore, data for both immature and mature Pseudanthobothrium specimens were used to measure the degree of specificity of these parasites using the aforementioned indices.…”

Reconsidering the Specialist-Generalist Paradigm in Niche Breadth Dynamics: Resource Gradient Selection by Canada Lynx and Bobcat

“…Species with narrow niches, “specialists”, are presumably favoured during periods of environmental stability or homogeneity, whereas those with broad niches, “generalists”, likely are favoured during environmental instability or heterogeneity [5], [6]. It is noteworthy that the evolution of specialists and generalists also may implicate a variety of more specific considerations such as efficiency of food source use [7], [8] or intensity of biotic interactions (e.g. competition and mate choice; [3]), which can affect population density and environmental carrying capacity of the species.…”

Host allometry influences the evolution of parasite host-generalism: theory and meta-analysis

“…For trophically transmitted parasites, the model predictions were more complicated, suggesting that this correlation could be positive or negative, depending on model assumptions and the value of other parameters. Interestingly, previous verbal models for host range evolution have suggested the correlation between host-generalism and host body size should work in the opposite direction, with high host specificity evolving when hosts are large-bodied [27], supposedly because large-bodied species are longer-lived, and thus are more predictable in their availability. However, the predictability of a resource (in this case, the host) depends on the probability of the agent encountering that resource [48], which is determined not by resource lifespan but by abundance.…”

“…Most work on this relationship, however, has been host-centric. Few studies have considered the question from the parasite perspective; that is, are parasites that infect large-bodied hosts also generalists infecting a wide range of hosts [24,25,27]? There are, however, several reasons to suspect that host body size might influence a parasite's host diversity.…”

“…host body sizecontinuous (here, maximum length of fish host)specialist Monogenean parasites tend to be found on large-bodied fish hosts [24–26]. variance in phylogenetic diversity of host species infected by fleas is negatively correlated with mean host body size [27]. …”