An alternative to killing? Treatment of reservoir hosts to control a vector and pathogen in a susceptible species

SUMMARYParasite-mediated apparent competition occurs when one species affects another through the action of a shared parasite. One way of controlling the parasite in the more susceptible host is to manage the reservoir host. Culling can cause issues in terms of ethics and biodiversity impacts, therefore we ask: can treating, as compared to culling, a wildlife host protect a target species from the shared parasite? We used Susceptible Infected Recovered (SIR) models parameterized for the tick-borne louping ill virus (LIV) system. Deer are the key hosts of the vector (Ixodes ricinus) that transmits LIV to red grouse Lagopus lagopus scoticus, causing high mortality. The model was run under scenarios of varying acaricide efficacy and deer densities. The model predicted that treating deer can increase grouse density through controlling ticks and LIV, if acaricide efficacies are high and deer densities low. Comparing deer treated with 70% acaricide efficacy with a 70% cull rate suggested that treatment may be more effective than culling if initial deer densities are high. Our results will help inform tick control policies, optimize the targeting of control methods and identify conditions where host management is most likely to succeed. Our approach is applicable to other host-vector-pathogen systems.

Condition- and parasite-dependent expression of a male-like trait in a female bird

In many species, females display brightly coloured and elaborate traits similar to those that males use in intra- and inter-sexual selection processes. These female characters are sometimes related to fitness, and might function as secondary sexual characteristics that have evolved through sexual selection. Here, we used descriptive data from 674 females in 10 populations and an experimental removal of Trichostrongylus tenuis parasites in four populations, to examine the effects of season, age, condition, and parasites on the size of supra-orbital combs displayed by female red grouse Lagopus lagopus scoticus . We found that comb size (i) was greater during the breeding than the non-breeding season, (ii) was greater in adult than in young females, (iii) was positively correlated with body condition, and (iv) negatively correlated with parasite abundance. Experimentally, we showed that comb size increased proportionally to the number of worms removed after parasite dosing. Our findings provide a better understanding of proximate mechanisms behind the expression of a male-like trait in females, and we discuss its possible function as a female ornament.

Burning management and carbon sequestration of upland heather moorland in the UK

The use of fire in land management has come under increasing scrutiny with regard to its potential effects on sustainability and climate change. Moorlands in the United Kingdom have traditionally used rotational burning of the heather (Calluna vulgaris) to improve the grazing and habitat, especially for grouse (Lagopus lagopus scoticus). However, these ecosystems overlie carbon-rich soils and concerns have been raised about the merits of this practice. In order to assess the impact of rotational burning on carbon balance, an investigation was undertaken on a grouse moor in the Yorkshire Dales, UK. This showed that the quantity of carbon stored above ground in heather biomass ranged from 600 to 1325 g C/m2 (typical for UK upland heaths). However, the national UK carbon inventory assumes 200 g C/m2, thereby appearing to underestimate considerably the importance of these habitats for carbon storage above ground. Analysis of 2 burns in subsequent years showed that 16 ± 4% and 24 ± 5% (± s.e.) of the above-ground material was consumed in the fires, resulting in the direct release of 103 ± 22 and 201 ± 62 g/m2 of carbon, respectively. Indirect carbon losses, which other studies have shown to be primarily due to erosion, were estimated to release another 5–21 g C/m2.year. The significance of other major greenhouse gas fluxes was assessed for the whole system using published parameters and models. We show that, over the burning cycle of 15–20 years, losses of carbon from burning are <10% of the total losses of carbon from the system, implying that careful burning management at this site does not have a major detrimental effect on the carbon budget, which for this moor lies within the range of an annual net loss of 34 g C/m2.year to a net uptake of 146 g C/m2.year.