Whereas terminological recommendations require authors to use mean intensity or mean abundance to quantify parasites in a sample of hosts, awkward statistical limitations also force them to use either the median or the geometric mean of these measures when making comparisons across different samples. Here, we propose to reconsider this inconsistent practice by giving priority to biological realism in the interpretation of different statistical descriptors and choosing the statistical tools appropriate to our decisions. Prevalence, mean intensity, and indices of parasite distribution (such as median intensity) are suitable descriptors to quantify parasites in a sample of hosts. These measures have different biological interpretations and need different statistical methods to be compared between samples.

/pdf/quantifying-parasites-in-samples-of-hosts-3mbxkolxq1.pdf

Quantifying parasites in samples of hosts

I tested three assumptions of the Hamilton and Zuk hypothesis (1982), which suggests that the extravagant male plumage of many bird species allows females to choose mates that are resistant to the parasites exploiting the host population at a given time. By choosing such males as mates, females will rear offspring carrying the genes for resistance. I tested three necessary conditions for the Hamilton and Zuk model: (1) whether parasites affect the fitness of their hosts; (2) whether there is heritable variation in parasite resistance, and (3) whether the expression of the sexual ornament varies with parasite burden. The haematophagous mite Ornithonyssus bursa (Macronyssidae, Gamasida) sucks blood from their Barn Swallow (Hirundo rustica) hosts. Experimental manipulation of mite loads and partial cross-fostering experiments on Barn Swallows, where half of the nestlings in the brood were exchanged with nestlings from another nest, shows that parasite burdens and origin, but not rearing conditions, of Bam Swallow nestlings, affected their adult tarsus length and maximum body weight shortly before fledging. Mite loads of adult Barn Swallows at spring arrival were more similar to mite loads of their own offspring, whether reared in their own or in foster nests inoculated with mites, than to loads of foster offspring. Parent Barn Swallows with long tail ornaments had offspring with smaller mite loads in the partial cross-fostering experiments. The amount of increase in male tail ornaments from one year to another was negatively related to experimentally manipulated mite loads of Barn Swallow nests during the preceding breeding season. In conclusion, the three assumptions of the hypothesis were supported by the experimental tests.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1558-5646.1990.tb03804.x

Effects of a haematophagous mite on the barn swallow (hirundo rustica): a test of the hamilton and zuk hypothesis.

Although some parasites have obvious pathogenic effects, others appear to have subtle, indirect effects that are poorly understood, particularly in natural populations. Indirect effects may result from parasites altering host metabolic rate and hence host energy needs, yet no experimental studies have shown this to be the case for non-laboratory hosts. We report the results of a long-term field experiment designed to test the impact of parasites on host energetics. We measured the energetics of feral rock doves (Columba livia) with populations of feather-feeding lice, traditionally considered to have little or no effect on host fitness. The lice reduced feather mass leading to increased thermal conductance and metabolic rate, as well as a steady reduction in host body mass over the course of the nine-month study. Our results demonstrate that even classically `benign' parasites such as feather lice can reduce host condition through the accumulation of subtle energetic costs over time. We argue that experimental manipulations are a prerequisite for documenting such effects.

Experimental Demonstration of the Energetic Cost of Parasitism in Free-Ranging Hosts

I studied the effect of the parasitic haematophagous tropical fowl mite (Or- nithonyssus bursa, Macronyssidae, Gamasida) on the reproduction of the Barn Swallow (Hirundo rustica, Hirundinidae, Passeriformes). Barn Swallows regularly reuse old nests, but avoid old nests with mites as demonstrated by experimental manipulation of mite loads. An equally large proportion of nests was infected with mites in experimental colonies, where all old Barn Swallow nests were removed, as in control colonies without such removal. Furthermore, the estimated number of mites per nest did not differ between experimental colonies, where all old nests were removed, and control colonies. These results suggest that new nests are not primarily infected from old nests harboring large mite populations. Mite population density per nest after fledging was significantly positively related to mite pop- ulation density on adult Barn Swallows upon arrival at the breeding site in early spring the same year. Mate choice may significantly affect levels of ectoparasitism, if parasite loads of nests originate from inoculates provided by adult Barn Swallows. In order to mimic the effects of choice of a mate with few or many mites, respectively, I manipulated mite loads of newly built first clutch nests during the egg-laying period of Barn Swallows by either spraying nests with a pyrethrin solution or introducing an inoculate of 50 mites, or nests were simply kept as controls. Addition of mites to nests decreased reproductive success of the birds measured in terms of number of independent fledglings of first clutches and in terms of clutch size, brood size, and number of independent fledglings of second clutches. Barn Swallow nestlings in nests with mites had lower body mass but similar body size compared with nestlings in sprayed nests. Incubation periods were longer and nestling periods shorter for nests with added mites. Interclutch intervals were significantly shorter in the group of sprayed nests, mainly because more such nests were reused for second clutches and because adult swallows suffered less from mite infestations. Slightly fewer Barn Swallows had second clutches during the same breeding season if their nests held many mites. Fitness of adult Barn Swallows is thus directly related to their own mite infection level and that of their mate.

Effects of Parasitism by a Haematophagous Mite on Reproduction in the Barn Swallow

Fleas are one of the most interesting and fascinating taxa of ectoparasites All species in this relatively small order are obligatory haematophagous (blood-feeding) parasites of higher vertebrates This book examines how functional, ecological and evolutionary patterns and processes of host-parasite relationships are realized in this particular system As such it provides an in-depth case study of a host-parasite system, demonstrating how fleas can be used as a model taxon for testing ecological and evolutionary hypotheses The book moves from basic descriptive aspects, to functional issues and finally to evolutionary explanations It extracts several general principles that apply equally well to other host-parasite systems, so it appeals not only to flea biologists but also to 'mainstream' parasitologists and ecologists

/pdf/functional-and-evolutionary-ecology-of-fleas-a-model-for-19fffslv18.pdf

Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology

https://www.tandfonline.com/doi/pdf/10.1080/03078698.1983.9673804

A method for the quantitative collection of ectoparasites from birds

. The role of the louse Trinoton anserinum (F) as an intermediate host of Sarconema eurycerca (Wehr) was investigated in swans. 8.3% of healthy swans carried one to twelve lice per bird, dispersed contagiously. Injured and lead-poisoned swans were more heavily infected.



The mouthparts appear designed to penetrate the hosts' skin; the mandibles are robust and asymmetric, and the maxillae have a serrated intercutting surface. 22% fed exclusively on blood and 33% on both blood and feather. All life-cycle stages fed upon blood and the barbs and barbules from down feathers; hooklets from contour feathers were only found in adults. 9% of lice were infected with developing nematode larvae in the head, thorax or abdomen.



Lice labelled with Technetium 99 m moved towards the scapulas and the wings. Lice were found to be highly active and were mobile.

The louse Trinoton anserinum (Amblycera: Phthiraptera), an intermediate host of Sarconema eurycerca (Filarioidea: Nematoda), a heartworm of swans

. 1. Mallophaga and Acari were collected from 324 reed buntings (Emberiza schoeniclus (Linnaeus)) captured in a communal winter roost between October 1980 and March 1981.



2. Frequency distributions of one of the mallophagan species, (Philopterus docophorulus (Zlotorzycka)), of the aggregated Mallophaga, and of the aggregated Acari, conform well with a negative binomial model. The remaining three mallophagan species collected were not present in sufficient numbers to describe a frequency distribution.



3. The ratio of nymphs to adults in the mallophagan community increased significantly in the second half of the roosting period (January–March) indicating the onset of increased reproductive activity.

J. A. Fowler

Papers

A method for the quantitative collection of ectoparasites from birds

The louse Trinoton anserinum (Amblycera: Phthiraptera), an intermediate host of Sarconema eurycerca (Filarioidea: Nematoda), a heartworm of swans

Population dynamics of Mallophaga and Acari on reed buntings occupying a communal winter roost

Non-haematophagous ectoparasite populations of Procellariiform birds in Shetland, Scotland

Seasonal Variation In The Infestation Of Blackbirds By Fleas