Louse Loads Research Articles

A passive fish sampling method is representative for size but selective for parasite load

Fish capture in industrial aquaculture is both necessary (i.e., for transfer, monitoring and harvesting) and difficult. The most logistically feasible methods rely heavily on crowding, a process that is detrimental to fish welfare and production outcomes. Jump nets, which rely on passive capture via jumping behaviour, present a welfare-friendly alternative. But reliance on behaviour means capture is not guaranteed, and limited knowledge of their capture rate and sampling biases means they are not yet used to their full potential. Here, in sea-cages stocked with Atlantic salmon Salmo salar, we investigated how capture rate varied with net size, position, and time of day, and if salmon caught via jump net were representative of the sea-cage population. A comparison of jumping rates into surface rings (without nets) indicated that larger jump nets will catch more fish. Capture rate was highest in rings positioned in the centre of cages, and during the morning and evening. Jump nets sampled representatively for fish size but caught salmon with marginally lower condition (<2% difference) and with three times higher parasitic salmon louse (Lepeophtheirus salmonis) loads than fish caught using lift nets. Our results indicate that jump nets can be used as a size-representative sampling tool and to target lice infected salmon for treatment.

Louse‐induced mortality thresholds in Atlantic salmon of wild‐origin

AbstractWild salmonid fish are faced with the challenge of infections from the ectoparasitic salmon louse, which thus dictates the management of salmon aquaculture in areas where farms and wild populations co‐exist. The mortality risk of wild Atlantic salmon is used as an indicator of threat levels when monitoring wild populations, and therefore the aim of this study was to robustly investigate the effect of infection intensity on probability of mortality in salmon of wild origin. To assess critical infection levels, recently‐smoltified Atlantic salmon were infected with intensities ranging from 0 to 2.5 lice g−1 and exposed to a 48‐h simulated migration. The first mortalities occurred when preadults appeared and ceased as lice became adults. Infection intensity negatively affected mortality probability and survival time, whereas the simulated migration had no influence on the probability of mortality. Individual‐level effects of infection on host mortality is difficult to quantify in the field; however, the correlation between louse load and mortality probability obtained in this study can facilitate indirect estimates of mortality risk of wild salmon populations and contribute to conservation efforts associated with this parasite.

The Number of Louse Eggs on Wild Japanese Macaques (Macaca fuscata) Varies with Age, but Not with Sex or Season

During grooming, primates remove harmful ectoparasites, such as ticks and lice, and there is direct evidence for a health benefit of tick removal. Grooming behaviors differ among primates with respect to age and sex. Moreover, the number of ectoparasite may exhibit seasonal variation. Therefore the number of ectoparasites on a host may vary with effects, host age and sex, and season. However, these effects have not been a focus of louse infestation studies of primates. Grooming in Japanese macaques is related to sex and age, with developmental changes in behavior corresponding to the timing of tooth eruption. Moreover, behavioral data for Japanese macaques suggest that lice load may differ with the season. Thus, we examined whether the number of louse eggs varies according to host macaque sex, age, and season, and whether it changes in response to tooth eruption. We counted unhatched and hatched eggs attached to the hair on six 1-cm2 areas on the left wrist skin of culled macaques, using a stereoscopic microscope. We sampled five winter coats and three summer coats for each age class: infant, juvenile, adolescent, and adult. The number of unhatched and hatched eggs was related to age, but not to sex and season. There were significant differences in the number of unhatched eggs between infants and adults, juveniles and adults, and adolescents and adults. There were also significant differences in the number of hatched eggs between infants and adults, juveniles and adults, adolescents and adults. Tooth eruption did not influence the number of louse eggs. These results suggest that researchers should consider the age of host animals when assessing the relationship between grooming and ectoparasites.

One step at a time in investigating relationships between self-directed behaviours and parasitological, social and environmental variables.

We thank Norscia and Palagi for their insightful commentary on our article ‘Scratch that itch: revisiting links between self-directed behaviour and parasitological, social and environmental factors in a free-ranging primate’ [1]. We welcome such discussion because we think, as the authors themselves point out at the end of their commentary, that research needs to continue in this area. In general, we agree that different stressors may act at different time frames in triggering self-directed behaviours. As rightly pointed out by Norscia and Palagi, our analysis did not take into account the different time frames that would allow for separating the effects of acute and chronic stressors on self-directed behaviours. At the level of a behavioural observation of 15 min, we instead investigated whether the occurrence of scratching and self-grooming was linked to various factors such as lice load, social activities, neighbours in proximity and environmental conditions, together and/or separately. Our study was correlational and we, therefore, avoided claims of causality, although we did address potential causal mechanisms in the discussion. That said, we would nonetheless like to respond to several points made by Norscia and Palagi. First, one of the main points of our study was to highlight biases in the investigation of certain research hypotheses, such as those involving self-directed behaviours. Studies in primatology have often, if perhaps inadvertently, assumed that the primary drivers of self-directed behaviour (SDB) are social, with parasite or abiotic factors being secondary. Norscia and Palagi nonetheless state that ‘(…) the association between self-directed behaviours, and particularly scratching, with social, environmental and parasitological factors can be considered as more than just a hypothesis. Once established that the different factors are not alternative and that their relationship with scratching has been demonstrated, it is worth focusing on the role that each factor can have in …

Scratch that itch: revisiting links between self-directed behaviour and parasitological, social and environmental factors in a free-ranging primate.

Different hypotheses explain variation in the occurrence of self-directed behaviour such as scratching and self-grooming: a parasite hypothesis linked with ectoparasite load, an environmental hypothesis linked with seasonal conditions and a social hypothesis linked with social factors. These hypotheses are not mutually exclusive but are often considered separately. Here, we revisited these hypotheses together in female Japanese macaques (Macaca fuscata fuscata) of Kōjima islet, Japan. We input occurrences of scratching and self-grooming during focal observations in models combining parasitological (lice load), social (dominance rank, social grooming, aggression received and proximity), and environmental (rainfall, temperature and season) variables. Using an information-theory approach, we simultaneously compared the explanatory value of models against each other using variation in Akaike's information criterion and Akaike's weights. We found that evidence for models with lice load, with or without environmental–social parameters, was stronger than that for other models. In these models, scratching was positively associated with lice load and social grooming whereas self-grooming was negatively associated with lice load and positively associated with social grooming, dominance rank and number of female neighbours. This study indicates that the study animals scratch primarily because of an immune/stimulus itch, possibly triggered by ectoparasite bites/movements. It also confirms that self-grooming could act as a displacement activity in the case of social uncertainty. We advocate that biological hypotheses be more broadly considered even when investigating social processes, as one does not exclude the other.

Relationships between beak condition, preening behavior and ectoparasite infestation levels in laying hens

The effects of beak condition on ectoparasite populations and preening in laying hens were investigated. Beak-trimmed and beak-intact caged Hy-Line W-36 hens were infested with either chicken body lice or northern fowl mites using a 2 × 2 factorial design with 4 replicate cages (each containing 2 hens)/treatment: 1) BTL (beak-trimmed lice-infested); 2) BTM (beak-trimmed mite-infested); 3) BIL (beak-intact lice-infested); and 4) BIM (beak-intact mite-infested). Mite scores and lice numbers were estimated weekly. Hens were video recorded the wk before infestation and at wk 6 and 9 post-infestation. Time spent preening on 6 body areas and in total were analyzed using a repeated measures ANOVA. There was a wk × beak condition interaction for lice loads, with BTL harboring approximately 17 times more lice than BIL from wk 7 to 10 post-infestation (P < 0.0001). Beak condition affected mite loads (P < 0.0001), with BTM having a higher mite score (3.8 ± 0.26) than BIM (1.4 ± 0.26). At peak infestation, BTL spent more total time preening (P = 0.02, s ± SE: 232.1 ± 37.6) than prior to infestation (33.9 ± 37.6) and directed their preening behavior towards the vent. In contrast, BIL (73.9 ± 37.6), BTM (9.4 ± 1.6), and BIM (8.6 ± 1.6) did not increase total time spent preening over pre-infestation levels (103.6 ± 37.6, 5.8 ± 1.6, 6.7 ± 1.6 respectively), although BTM did redirect their preening behavior toward the vent. This study confirmed previous studies showing that an intact beak is important for reducing ectoparasite infestations. Preening behavior increased in response to lice infestation, but only in beak-trimmed hens; preening behavior and louse load were correlated at peak infestation. In contrast, mite infestation did not lead to increased preening, and there was no correlation between preening and mite load. However, both lice- and mite-infested hens directed preening behavior predominantly towards the vent where these parasites are typically found.

New records of species of Saemundssonia (Insecta: Phthiraptera: Philopteridae) infesting breeding terns in the Arabian Peninsula, with notes on their phylogeny and ecology.

Six species of terns, which breed on the Arabian Peninsula, were examined for head chewing lice of the genus Saemundssonia in four different islands around the coasts of Saudi Arabia, both in the Red Sea and in the Arabian Gulf. Four louse species were collected: Saemundssonia laticaudata, Saemundssonia melanocephalus, Saemundssonia meridiana and Saemundssonia sternae, of which three are recorded for the first time from this region. Also, we record three new host-louse associations for the world-Saemundssonia laticaudata and Saemundssonia sternae from white-cheeked terns and Saemundssonia melanocephalus from Saunders's terns-including a host-switch event of Saemundssonia laticaudata on white-cheeked terns in the Karan Island population. Gene bank data for the COI gene from seven species of Saemundssonia that infest marine birds were used to propose evolutionary trees using two different statistical methods: maximum parsimony (MP) and neighbour joining (NJ). The result indicated that the tree which was produced by NJ is likely to be more accurate as it appeared more compatible with hosts' phylogeny. The trees indicate relationships between tern Saemundssonia and congeneric species from other marine birds, especially from gulls. An ANOVA was also conducted to test the mean parasite load for each tern species studied, and results indicate that there is a relation between louse loads and colonization behaviour of the hosts. Data from lice examined and illustrations of lice and their hosts are also included.

Population levels of Phthiraptera on Greylag Goose, Anser anser (L.)

The present study was performed to record the mean monthly prevalence, intensity of infestation, sample mean abundance and frequency distribution pattern of one phthirapteran species infesting of A. anseris. Ten birds were examined every month. Infested birds were deloused. The bird was placed in a polythene bag containing a wool of cotton soaked in chloroform (head protruded out to allow breathing). After 10 minutes, the bird's feathers were ruffled on a white plastic sheet placed below. The head was examined separately. The louse load was transferred to 70% alcohol and separated stage wise and sex wise. A total of 339 specimens of A. anseris were recovered from 66 infested hosts. Male-female ratio was 1: 1.8. Prevalence of Anaticola anseris was 55% (n=120). The sample mean abundance was 2.38 lice/bird. Variance to mean ratio exceeded unity (10.70). The index of discrepancy (D) was 0.75 and the value of exponent of negative binomial (k) remained 0.334.The observed and expected frequencies did not differ significantly (χ2= 13.33, df= 15, p=0.05). The prevalence of A. anseris on Indian greylag goose was high but its intensity remained quite low. The distribution pattern of A. anseris conformed the negative binomial model.The temperature, photoperiod and heat index exhibited significant positive correlations with the prevalence of A. anseris.

Colonial seabird’s paralytic perfume slows lice down: An opportunity for parasite-mediated selection?

Selection for chemical signals in birds could be influenced by parasitism as has been previously suggested for visual and acoustic displays. Crested auklets (Aethia cristatella), colonial seabirds from Alaska and Siberia, offer an example of how this might occur. Crested auklets secrete lipids in plumage, possibly as an indicator of status and attractiveness. Prominent among these secretions are aldehydes, which are noticeable as a pungent citrus-like odour. Octanal and hexanal, the most abundant aldehydes in the plumage of crested auklets, are potent invertebrate repellents, reported from the chemical defenses of heteropteran insects. These aldehydes occur at high concentrations within specialized secretory structures. Experiments presented here show that these compounds can paralyse lice. Lice obtained from auklets were paralysed or killed within seconds after exposure to volatiles from nicks in the integument of a crested auklet. Chemical analysis demonstrated the presence of aldehydes in the area of integument used for this experiment. Lice exposed to control tissues in the same manner were not affected. A synthetic blend of crested auklet odourant constituents caused a sequence of impaired behaviours in auklet lice comparable to the effects of neuroactive insecticides. The time until onset of effects was dependent on dose, suggesting that the rate of molecular diffusion into louse spiracles was the explanatory factor. Impairment was evident even at very low concentrations that can occur in crested auklet plumage during winter. The same aqueous emulsions were present in both experimental and control treatments but lice in controls experiments were not affected. Crested auklets inhabit crowded social neighbourhoods with larger social groups, closer interindividual spacing and higher rates of contact than sympatric least auklets (Aethia pusilla). This could help to explain why crested auklets can have higher louse abundances. Lice are spread through direct contact between hosts and louse-infected mates could transmit lice to offspring. Large differences in the louse loads on crested auklet fledglings suggest differences in the parental transmission of lice to offspring.

Experimental evidence for costs due to chewing lice in the European bee-eater (Merops apiaster)

Animals frequently host organisms on their surface which can be beneficial, have no effect or a negative effect on their host. Ectoparasites, by definition, are those which incur costs to their host, but these costs may vary. Examples of avian ectoparasites are chewing lice which feed exclusively on dead feather or skin material; therefore, costs to their bird hosts are generally considered small. Theoretically, many possible proximate effects exist, like loss of tissue or food, infected bites, transmission of microparasitic diseases or reduced body insulation due to loss of feathers, which may ultimately also have fitness consequences. Here, we experimentally examined a possible negative impact of 2 feather-eating louse species (Meropoecus meropis and Brueelia apiastri) on male and female European bee-eaters (Merops apiaster) by removing or increasing louse loads and comparing their impact to a control group (lice removed and immediately returned) after 1 month. A negative effect of chewing lice was found on body mass and sedimentation rate and to a lesser extent on haematocrit levels. Males and females lost more weight when bearing heavy louse loads, and were more susceptible to infestations as indicated by the higher sedimentation rate. Our results further suggest differences in sex-specific susceptibility.

Ringing Procedure Can Reduce the Burden of Feather Lice in Barn SwallowsHirundo rustica

Chewing lice (Insecta: Phthiraptera) are the most widespread obligate ectoparasites living in the plumage of birds. Lice have to cope with unusual mechanical effects during ringing, and they could fall off their hosts. We assumed that trapping birds in nets, taking measurements and estimating condition could reduce their louse burdens. Lousiness affects life expectancy and reproductive success, so if ringing causes remarkable louse loss, the fitness of ringed birds could be altered. Lice are usually collected at ringing sites, and ringing precedes parasite sampling. This may therefore lead to an underestimation of louse prevalence and intensity. Here we tested whether ringing reduces the louse burden. We allocated Barn Swallows Hirundo rustica in the breeding season to two experimental groups — the birds were subject to either a standard ringing procedure (recording biometry, fat and other condition scores, feather hole counts), or a reduced one (only feather hole counts). We used feather holes (traces of louse chewing) as a measure of louse loads. Holes were recounted after a month. Significantly more new holes appeared in the reduced ringing procedure group, indicating tat the usual ringing procedures effectively reduce louse loads. We believe this is the first evidence that bird ringing affects ectoparasite infestations.

The effect of sea lice (Lepeophtheirus salmonis) on juvenile pink salmon (Oncorhynchus gorbuscha) swimming endurance

The swimming endurance of naturally and experimentally infected juvenile pink salmon ( Oncorhynchus gorbuscha ) was measured to determine the effects of sea lice ( Lepeophtheirus salmonis ). Salmon naturally infected with adult male and preadult stage lice did not appear to have a reduced swim performance, but when experimentally infected with adult female lice, juvenile salmon showed a reduced ability to swim compared with uninfected control fish, and this effect increased with lice load. A reduced swimming endurance is not only likely to influence predation risk for salmon, but may have other ecological implications, such as slower seaward migration.

Is Melanin a Defense Against Feather-Feeding Lice?

AbstractThe adaptive basis of plumage color has received much attention, including the finding that color can reveal information about parasite loads to potential mates. A related possibility, that color may be a direct defense against parasites, has received less attention. Melanin makes feathers tough and more resistant to wear and tear. Melanin may also make feathers more difficult for feather-feeding parasites to eat. We explored the role of melanin as a possible ectoparasite defense using Rock Pigeons (Columba livia) and their feather-feeding lice (Insecta: Phthiraptera). Rock Pigeons are an ideal species for such work because of the extreme variation in the feathers of different color morphs, ranging from melanin-rich black to melanin-free white individuals. We tested the effect of melanin on lice in several ways. First, we compared the natural louse loads of free-ranging pigeons to see whether the more melanistic color morphs had fewer lice. We also did laboratory assays in which we measured the survival and reproductive success of pigeon lice forced to feed on feathers with different amounts of melanin, and we compared the quantities of feather material consumed by these lice. Finally, we tested the habitat and feeding preferences of lice exposed to feathers with different amounts of melanin. None of our tests revealed any effect of melanin on lice. We conclude that melanin is not, at least in Rock Pigeons, a defense against feather lice.¿Es la Melanina una Defensa Contra los Piojos que se Alimentan de Plumas?

IS MELANIN A DEFENSE AGAINST FEATHER-FEEDING LICE?

Abstract The adaptive basis of plumage color has received much attention, including the finding that color can reveal information about parasite loads to potential mates. A related possibility, that color may be a direct defense against parasites, has received less attention. Melanin makes feathers tough and more resistant to wear and tear. Melanin may also make feathers more difficult for feather-feeding parasites to eat. We explored the role of melanin as a possible ectoparasite defense using Rock Pigeons (Columba livia) and their feather-feeding lice (Insecta: Phthiraptera). Rock Pigeons are an ideal species for such work because of the extreme variation in the feathers of different color morphs, ranging from melanin-rich black to melanin-free white individuals. We tested the effect of melanin on lice in several ways. First, we compared the natural louse loads of free-ranging pigeons to see whether the more melanistic color morphs had fewer lice. We also did laboratory assays in which we measured the s...

Age-dependent health status and song characteristics in the barn swallow

Bird song has been hypothesized to evolve, partly, to signal health status of males, and song features should therefore correlate with parasite load. Immune function, parasitism, and secondary sexual characters can, however, differ between age classes, and any apparent relationship between song and parasite loads can be the result of systematic age effects. We tested for an age-dependent relationship between sexually selected characters and measures of parasitism in a Spanish population of the barn swallow Hirundo rustica. A comparison across age classes revealed that chewing lice load, song duration, mean peak amplitude frequency of songs, and tail length differed significantly between yearlings and adults. In a longitudinal analysis, we found significant evidence for mean peak amplitude frequency of songs, tail length and chewing louse parasitism, and a nonsignificant tendency for song duration to change with age of an individual. We found a significant association between song duration and chewing louse load and between hematocrit and peak amplitude frequency of the rattle, the typical harsh terminal syllable. In tests for associations between song traits and health status, while controlling for age, age and chewing louse load were independently related to song duration. We found a significant relationship between pairing success and song duration, implying that females may use this song trait in their choice of parasite-free males. Although the song of the barn swallow may provide information about both male age and parasite resistance, signaling of health status appears to be independent of age effects, in accordance with the theory of parasite-mediated sexual selection, suggesting that male signals can be used as reliable indicators of parasitism.

Path coefficient analysis of correlation between breeding cycles of the common myna Acridotheres tristis (Passeriformes: Sturnidae) and its phthirapteran ectoparasites.

Louse population fluctuates seasonally. Several factors have been held responsible for the summer buildup of population of avian lice (Marshall A.G. 1981: The Ecology of Ectoparasitic Insects. Academic Press, London, 445 pp). It has been suspected that the breeding time of two haematophagous louse species (Ricinus picturatus and Menacanthus sp.) might be controlled by the reproductive hormones of the host bird, the orange crowned warbler (Vermivora cellata) (Foster M.S. 1969: Ecology 50: 315–323). Furthermore, testosterone implants gave rise to an increase in number of two haematophagous lice (Machaerilaemus malleus and Myrsidea rustica) on barn swallows (Hirudo rustica) (Saino N., Moller A.P., Bolzern A.M. 1995: Behav. Ecol. 6: 397–404). The present studies were undertaken to record the degree of synchronisation between the breeding cycles of a semidomestic passerine bird, the common myna Acridotheres tristis (L.) and its phthirapteran ectoparasites. Out of four phthirapteran species known to occur on Indian common myna, three species (Menacanthus eurysternus Burmeister, 1838, Brueelia sp. and Sturnidoecus bannoo Ansari, 1955) were taken into consideration in the present studies. Ten infested birds (both sexes) were weighed and deloused by lethal fumigation (Marshall 1981, op. cit.) every month during May 2000 to April 2001. The entire louse load was transferred to 70% ethanol and separated species-wise and sex-wise under stereozoom trinocular microscope. Total number of adult females of each species was specifically recorded. Feathers of the bird were plucked carefully from each region of body and placed in a glass jar. The bird was dissected in physiological saline to take out the gonads. The latter were cleaned, gently pressed between the folds of paper and weighed. Each feather was examined individually under the stereozoom trinocular microscope to record the number of fresh (unhatched) eggs of each louse species. Total number of live eggs of each louse species recorded from any bird was divided by total number of adult females of that species (subsequently averaged) to obtain the “egg index” in particular month. To derive the idea about the degree of synchronisation between breeding cycles of the host bird and its lice, an analysis of correlation between mean monthly live egg indices and mean monthly gonadal weights (in mg/100g of body weight) was taken into consideration (Fig. 1). The degree of correlation between live egg indices and mean monthly temperature as well as mean monthly photoperiod (averaged value of daily light hours) was also recorded. However, the values of Pearson’s coefficient of correlation (Table 1) give absolute measure of the extent of relationship between two variables (first and second), ignoring the effect of other variables (third, fourth ...) that may affect the first (dependent) variable. 200

Experimental Test of the Importance of Preen Oil in Rock Doves (Columba Livia)

Abstract Most species of birds have a uropygial gland, also known as a preen gland, which produces oil that birds spread through their plumage when preening. The plumage of waterfowl deprived of uropygial oil becomes brittle and is subject to breakage. For other groups of birds, however, the importance of preen oil remains unclear. Previous workers have argued that preen oil may serve little or no function in Columbiforms (pigeons and doves). We tested that assertion by removing uropygial glands from Rock Doves (Columba livia) and assessing their plumage condition after several months. The results of that experiment showed significant degradation of plumage in the absence of oil. Our results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl. We tested one possible function of preen oil—that it has insecticidal properties and that reduction in plumage condition on birds without glands is due to an increase in ectoparasites. We tested that hypothesis for feather-feeding lice (Phthiraptera:Ischnocera) using both in vitro and in vivo experiments. Lice raised in an incubator died more rapidly on feathers with preen oil than on feathers without oil, which suggests that preen oil may help combat lice. However, removal of the preen gland from captive birds had no significant effect on louse loads over the course of a four-month experiment. Although the results of our in vivo experiments suggest that preen oil may not be an important defense against lice, further experiments are needed. We also consider the possibility that preen oil may protect birds against other plumage-degrading organisms, such as bacteria and fungi.

Using observed load distributions with a simple model to analyse the epidemiology of sea lice (Lepeophtheirus salmonis) on sea trout (Salmo trutta).

Sea lice are ectoparasites of salmonids that have been associated with the recent decline in sea trout numbers in north-west Europe. Observed patterns of louse load distribution between sea trout in the seas surrounding the UK, Ireland and Norway and a simple model have been used to analyse the epidemiology of lice. Loads are aggregated and deviate strongly from the Poisson distribution, although less than is observed with many other parasites. The louse numbers on fish from offshore sites are slightly less variable than for fish from coastal sites with comparable mean loads. Analysis of louse development stages and sexes shows that selection between hosts by sea lice plays a limited role. If host selection is absent, then associated poor condition would be caused by, not the cause of, high louse burdens; however the absence of such selection is not proved. Scenarios with infection that is patchy in space and time best generate the aggregated load patterns observed; these patches accord with observed swarms of copepodids. Prevalence patterns may indicate the movement of trout between environments. Control of copepodids in infection 'hot spots', either directly or through control of louse egg production in their catchment, may reduce louse loads on wild sea trout and, in particular, extreme and damaging loads.

INFLUENCE OF BILL SHAPE ON ECTOPARASITE LOAD IN WESTERN SCRUB-JAYS

Populations of the Western Scrub-Jay (Aphelocoma californica) have bills specialized for feeding in their respective habitats. Populations in oak habitat have hooked bills, whereas those in pinyon habitat have pointed bills with a reduced maxillary overhang. Work on other bird species shows that the bill overhang is essential for efficient preening to control ectoparasites. Given the importance of this overhang, we predicted that louse-infested jays with pointed bills would have higher louse loads than those with hooked bills. We compared the number of lice on 65 pointed-billed (4 infested) and 105 hooked-billed (17 infested) birds. Despite their lower incidence of louse infestation, pointed-billed birds had significantly more lice than hooked-billed birds, supporting our prediction. While pointed bills enhance feeding in pinyon habitat, our results suggest that they may incur a cost of reduced preening efficiency. Evolution of bill shape has traditionally been interpreted mainly in terms of foraging. Our results suggest that selection for efficient preening may also play an important role. Influencia de la Forma del Pico en la Carga de Ectoparásitos en Aphelocoma californica Resumen. Los individuos de distintas poblaciones de Aphelocoma californica tienen picos especializados para alimentarse en sus hábitats respectivos. Las poblaciones de hábitats con robles se caracterizan por picos ganchudos, mientras que las de hábitats con piñones tienen picos puntiagudos, con el gancho de la punta de la maxila reducido. Estudios en otras especies de aves han mostrado que el gancho del pico es esencial para acicalarse eficientemente y así controlar los ectoparásitos. Dada la importancia de este gancho, predijimos que los individuos de A. californica de pico puntiagudo infestados con piojos de pluma tendrían una mayor carga de ectoparásitos que aquellos de pico ganchudo. Comparamos el número de piojos entre 65 individuos de pico puntiagudo (4 infestados) y 105 de pico ganchudo (17 infestados). A pesar de la baja incidencia de infestación por piojos, las aves de pico puntiagudo presentaron significativamente más piojos que las de picho ganchudo, apoyando nuestra predicción. Aunque los picos puntiagudos benefician la alimentación en hábitats de piñones, nuestros resultados sugieren que podrían representar un costo reduciendo la eficiencia de acicalamiento. Por lo general, la evolución de la forma del pico ha sido interpretada tradicionalmente en términos del forrajeo, pero nuestros resultados sugieren que la selección para acicalarse eficientemente también podría tener un papel importante.

Reciprocal Natural Selection on Host-Parasite Phenotypes.

Coevolution is evolution in one species in response to selection imposed by a second species, followed by evolution in the second species in response to reciprocal selection imposed by the first species. Although reciprocal selection is a prerequisite of coevolution, it has seldom been documented in natural populations. We examined the feasibility of reciprocal selection in a simple host-parasite system consisting of feral pigeons (Columba livia) and their Ischnoceran feather lice (Phthiraptera: Insecta). We tested for a selective effect of parasites on hosts with experimentally altered defenses and for a selective effect of host defense on a component of parasite escape. Previous work indicates that pigeons control lice through efficient preening, while lice escape from preening using complex avoidance behavior. Our results show that feral pigeons with impaired preening, owing to slight bill deformities, have higher louse loads than pigeons with normal bills. We use a controlled experiment to show that high louse loads reduce the survival of pigeons, suggesting that lice select for efficient preening and against bill deformities. In a reciprocal experiment, we demonstrate that preening with a normal bill selects for small body size in lice, which may facilitate their escape from preening. The results of this study verify a crucial element of coevolutionary theory by identifying likely targets of reciprocal phenotypic selection between host and parasite.