To delay once or twice: the effect of hypobiosis and free-living stages on the stability of host–parasite interactions

Abstract

The life cycle of many endoparasites can be delayed by free-living infective stages and a developmental arrestment in the host referred to as hypobiosis. We investigated the effects of hypobiosis and its interaction with delay in the free-living stages on host-parasite population dynamics by expanding a previous attempt by Dobson & Hudson. When the parasite life cycle does not include free-living stages, hypobiosis destabilizes the host-parasite interactions, irrespective of the assumptions about the regulation of the host population dynamics. Interestingly, the destabilizing effect varies in a nonlinear way with the duration of hypobiosis, the maximal effect being expected for three to five months delay. When the parasite life cycle involves free-living stages, hypobiosis of short or intermediate duration increases the destabilizing effect of the first time delay. However, hypobiosis of a duration of five months or more can stabilize interactions, irrespective of the regulation of the host population dynamics. Overall, we confirmed that hypobiosis is an unusual time delay as it can stabilize a two-way interaction. Contrary to the previous conclusions, such an atypical effect does not require self-regulation of the host population, but instead depends on the existence of free-living stages.

Climate change and infectious disease: helminthological challenges to farmed ruminants in temperate regions

“…Alterations of the hypobiotic period may therefore be expected. Gaba and Gourbiere (2008) demonstrated that, if the timing of the arrest of development were to change as a result of climate change, the consequences for parasite populations are highly unpredictable.…”

“…Interestingly, Langrova and Janskova (2004) suggested that the proportion of larvae arresting may also depend on the effects of these environmental cues on the hosts. Gaba and Gourbiere (2008) showed that the duration of hypobiosis is crucial to the success and stability of parasite populations. Alterations of the hypobiotic period may therefore be expected.…”

Implications of between-isolate variation for climate change impact modelling of Haemonchus contortus populations

“…The authors concluded that "there was limited evidence for adaptations to temperate 169 climatic conditions". However, under untreated conditions (fresh L3) significantly higher arrest rates 170 and longer pre-patent periods were observed in the Swedish isolate, which would act to stabilise 171 populations in the absence of free-living stages (Gaba and Gourbière, 2008), as is common during 172 the Swedish winter, and one could argue that this is evidence of local adaptation. Therefore, the 173 potential for the degree of local adaptation to vary from trait to trait should be addressed when 174 extrapolating knowledge and models to different regions, for example by conducting additional 175 validation to ensure the response of local populations of parasites is captured by model predictions.…”

Competition, virulence, host body mass and the diversification of macro-parasites

“…Combining these probabilities with the partition of residents among hosts, which typically follows a negative binomial distribution (see [31] for a meta-review of field values), one can derive the average number of residents a mutant individual is expected to interact with Sðm; rÞ ¼ PðmÞ PðrÞ…”

“…Accordingly, we have no clear understanding of the influence of the specificities of the parasite lifestyle on the conditions and rates of competitive speciation. Parasite populations typically live in a fragmented environment as they are associated with host individuals, and their distribution among hosts is well known to be highly aggregated ( [30,31] for reviews). Intuitively, fragmentation is expected to influence the level of competitive interactions and this should be further modulated by the level of aggregation.…”