Unravelling causality from correlations: revealing the impacts of endemic ectoparasites on a protected species (tuatara)

Your infections are what you eat: How host ecology shapes the helminth parasite communities of lizards

Understanding how parasite communities are assembled, and the factors that influence their richness, can improve our knowledge of parasite-host interactions and help to predict the spread of infectious diseases. Previous comparative analyses have found significant influences of host ecology and life history, but focused on a few select host taxa. Host diet and habitat use play key roles in the acquisition of parasitic helminths as many are trophically transmitted, making these attributes potentially key indicators of infection risk. Given the paucity of comparative studies with non-piscine, non-avian or non-mammalian hosts, it is critical to examine the degree to which host ecology influences parasite communities in other host taxa in order to identify common drivers. We examined helminth diversity in over 350 species of lizards in relation to their body mass, ecology (diet and habitat use) and life history (clutch size, and ovo- or viviparity) using previously published data. Overall, lizard species with herbivorous diets harboured fewer types of helminths (especially larval stages), with similar results for traits that were ultimately strongly associated with diet (host mass and habitat use). Large hosts tended to be herbivores with few helminth types, whereas species utilizing arboreal habitats typically consumed some animal matter and hosted more helminths. Understanding how host ecology and life history are related to their parasite assemblages has significant implications for the risk of acquiring novel parasites. Our results indicate an overwhelming influence of host diet such that many helminths may be relatively easily acquired by hosts in new ranges, or through dietary shifts.

Tick parasitism in the Mediterranean spur-thighed tortoise in the Maamora forest, Morocco

Macroparasites in general, and ectoparasites in particular, have the potential to regulate host population dynamics. In this context, this study addresses the tick parasitism traits of the Mediterranean spur-thighed tortoise (Testudo graeca) in the core area of its distribution range (northwestern Morocco, Maamora). It was discovered that 92.5% of the tortoises were parasitized by ticks in spring, with an infestation intensity and an abundance of 6.7 and 6.2 tick/tortoise, respectively. The observed parasitization rates were among the highest reported worldwide for T. graeca, which could relate to density-depended effects driving host-parasite interactions. The main tick species that parasitized the tortoises were Hyalomma aegyptium (95.6% of the ticks and in the 100% of the parasitized tortoises), Hy. marginatum, Hy. excavatum and Hy. scupense. Individual predictors for the tortoises, such as age, sex and the interaction between body condition and sex, were significantly related to tick abundance. Age-related behavioural differences might favour a higher host-tick effective contact in adults than in juveniles. The fact that males are more active in spring - the breeding season - might explain the observed male-bias in tick abundance and may also be responsible for the negative effect of male body condition on tick infestation rate in contrast to females. Given the potential role played by parasites as regards modulating population dynamics, our results suggest that ticks should be taken into account in the conservation and management programmes of this tortoise species.

Parasite load and MHC diversity in undisturbed and agriculturally modified habitats of the ornate dragon lizard

Major histocompatibility complex (MHC) gene polymorphism is thought to be driven by host-parasite co-evolution, but the evidence for an association between the selective pressure from parasites and the number of MHC alleles segregating in a population is scarce and inconsistent. Here, we characterized MHC class I polymorphism in a lizard whose habitat preferences (rock outcrops) lead to the formation of well-defined and stable populations. We investigated the association between the load of ticks, which were used as a proxy for the load of pathogens they transmit, and MHC class I polymorphism across populations in two types of habitat: undisturbed reserves and agricultural land. We hypothesized that the association would be positive across undisturbed reserve populations, but across fragmented agricultural land populations, the relationship would be distorted by the loss of MHC variation due to drift. After controlling for habitat, MHC diversity was not associated with tick number, and the habitats did not differ in this respect. Neither did we detect a difference between habitats in the relationship between MHC and neutral diversity, which was positive across all populations. However, there was extensive variation in the number of MHC alleles per individual, and we found that tick number was positively associated with the average number of alleles carried by lizards across reserve populations, but not across populations from disturbed agricultural land. Our results thus indicate that local differences in selection from parasites may contribute to MHC copy number variation within species, but habitat degradation can distort this relationship.

Weight watching in burrows: variation in body condition in pygmy bluetongue lizards

The pygmy bluetongue lizard, Tiliqua adelaidensis, is an endangered scincid lizard that occurs in remnants of natural grasslands in the mid-north of South Australia. We assessed the factors affecting body condition of male and female lizards, using body size residuals as an index, over five sampling years. We included sex, phenotypic (patterned or plain morphs), temporal (sampling year and activity period within year), and climatic factors in our analyses. The results indicated that sampling year and activity period within the year were the two most important factors influencing variation in body condition of both male and female lizards over the period of the study. There were similar trends when we considered males and females separately. However, when prepartum and postpartum females were analysed separately, sampling year did not affect their body condition. None of the analyses showed any significant effect of phenotype on body condition. Winter–spring rainfall was positively correlated with body condition of females in the prepartum period, but showed no significant effect on mean body condition of any other grouping of adult lizards, nor a consistent direction of correlation among the different subsets of adult lizards that we considered. The substantial annual variations in the body condition of lizards, although of uncertain cause, provide important information for conservation managers who monitor persisting populations of this endangered species.