Ectoparasites and host energetics: house martin bugs and house martin nestlings

Cimicids of Medical and Veterinary Importance

Members of the Cimicidae family are significant pests for mammals and birds, and they have attracted medical and veterinary interest. A number of recent studies have investigated bed bugs, due to their dramatic resurgence all over the world. Indeed, bed bugs are of significant public health and socioeconomic importance since they lead to financial burdens and dermatological complications and may have mental and psychological consequences. It is important to note that certain cimicids with a preference for specific hosts (birds and bats) use humans as an alternative host, and some cimicids have been reported to willingly feed on human blood. In addition, members of the Cimicidae family can lead to economic burdens and certain species are the vectors for pathogens responsible for diseases. Therefore, in this review, we aim to provide an update on the species within the Cimicidae family that have varying medical and veterinary impacts, including their distribution and their associated microorganisms. Various microbes have been documented in bed bugs and certain important pathogens have been experimentally documented to be passively transmitted by bed bugs, although no conclusive evidence has yet associated them with epidemiological outbreaks. Additionally, among the studied cimicids (bat bugs, chicken bugs, and swallow bugs), only the American swallow bug has been considered to be a vector of several arboviruses, although there is no proven evidence of transmission to humans or animals. Further studies are needed to elucidate the reason that certain species in the Cimicidae family cannot be biologically involved in transmission to humans or animals. Additional investigations are also required to better understand the roles of Cimicidae family members in the transmission of human pathogens in the field.

Experimental evidence of parasite-induced behavioural alterations modulated by food availability in wild capuchin monkeys

In disease dynamics, host behaviour can both determine the quantity of parasites a host is exposed to, and be a consequence of infection. Observational and experimental studies in non-human primates have consistently found that parasitic infections result in less movement and reduced foraging, which was interpreted as an adaptive response of the host to counter infection. Variation in host nutritional condition may add complexity to the infection-behaviour relationship, and its influence may shed light on its significance. To experimentally evaluate how host activity and social relationships are affected by the interaction of parasitism and nutrition, during two years we manipulated food availability by provisioning bananas, and helminth infections by applying antiparasitic drugs, in two groups of wild black capuchin monkeys (Sapajus nigritus) in Iguazú National Park, Argentina. We collected faecal samples to determine the intensity of helminthic infections, as well as data on behaviour and social proximity. Individuals with unmanipulated helminth burdens foraged less than dewormed individuals only when food provisioning was low. Resting time was increased when capuchins were highly provisioned, but it did not vary according to the antiparasitic treatment. Proximity associations to other group members were not affected by the antiparasitic treatment. This is the first experimental evidence of a modulating effect of food availability on the influence of helminth infection on activity in wild primates. The findings are more consistent with an impact on host behaviour due to the debilitating effect caused by parasites than with an adaptive response to help fight infections.

Host tolerance and resistance to parasitic nest flies differs between two wild bird species

Hosts have developed and evolved defense strategies to limit parasite damage. Hosts can reduce the damage that parasites cause by decreasing parasite fitness (resistance) or without affecting parasite fitness (tolerance). Because a parasite species can infect multiple host species, determining the effect of the parasite on these hosts and identifying host defense strategies can have important implications for multi-host-parasite dynamics.Over 2 years, we experimentally manipulated parasitic flies (Protocalliphora sialia) in the nests of tree swallows (Tachycineta bicolor) and eastern bluebirds (Sialia sialis). We then determined the effects of the parasites on the survival of nestlings and compared defense strategies between host species. We compared resistance between host species by quantifying parasite densities (number of parasites per gram of host) and measured nestling antibody levels as a mechanism of resistance. We quantified tolerance by determining the relationship between parasite density and nestling survival and blood loss by measuring hemoglobin levels (as a proxy of blood recovery) and nestling provisioning rates (as a proxy of parental compensation for resources lost to the parasite) as potential mechanisms of tolerance.For bluebirds, parasite density was twice as high as for swallows. Both host species were tolerant to the effects of P. sialia on nestling survival at their respective parasite loads but neither species were tolerant to the blood loss to the parasite. However, swallows were more resistant to P. sialia compared to bluebirds, which was likely related to the higher antibody-mediated immune response in swallow nestlings. Neither blood recovery nor parental compensation were mechanisms of tolerance.Overall, these results suggest that bluebirds and swallows are both tolerant of their respective parasite loads but swallows are more resistant to the parasites. These results demonstrate that different host species have evolved similar and different defenses against the same species of parasite.

Subtle short-term physiological costs of an experimental augmentation of fleas in wild Columbian ground squirrels

Parasites affect many aspects of host physiology and behavior, and thus are generally thought to negatively impact host fitness. However, changes in form of short-term parasite effects on host physiological markers have generally been overlooked in favor of fitness measures. Here, we studied flea (Oropsylla idahoensis and Oropsylla opisocroistis tuberculata) parasitism on a natural population of Columbian ground squirrels (Urocitellus columbianus) in Sheep River Provincial Park, AB, Canada. Fleas were experimentally added to adult female U. columbianus at physiologically demanding times, including birth, lactation and weaning of their young. The body mass of adult females, as well as their oxidative stress and immunity were recorded multiple times over the active season under flea-augmented and control conditions. We also measured the prevalence of an internal parasite (Trypanosoma otospermophili). Doubly labeled water (DLW) was intra-peritoneally injected at peak lactation to examine energy expenditure. Effects of parasites on oxidative stress were only observed after offspring were weaned. There was no direct effect of experimentally heightened flea prevalence on energy use. A short-term 24 h mass loss (-17 g) was detected briefly after parasite addition, likely due to U. columbianus preferentially allocating time for grooming. Our parasite augmentation did not strongly affect hosts and suggested that short-term physiological effects were unlikely to culminate in long-term fitness consequences. Columbian ground squirrels appear to rapidly manage parasite costs, probably through grooming.

Multiple stressors including contaminant exposure and parasite infection predict spleen mass and energy expenditure in breeding ring-billed gulls

Daily energy expenditure (DEE) in animals is influenced by many factors although the impact of stressors remains largely unknown. The objective of this study was to determine how multiple physiological stressors (parasite infection and contaminant exposure) and natural challenges (energy-demanding activities and weather conditions) may affect DEE in nesting ring-billed gulls (Larus delawarensis) exposed to high concentrations of persistent organic contaminants (POPs). Physical activity, temperature, gastrointestinal parasitic worm abundance, relative spleen mass, plasma thyroid hormone levels and liver concentrations of POPs were determined; field metabolic rate (FMR) was used as a measure of DEE. For females, FMR was best explained by the percent of time spent in nest-site attendance and exposure to temperatures below their lower critical limit (65% of variation); 32% was also explained by relative spleen mass. In males, FMR was best explained by the number of hours spent in nest site attendance and either relative spleen mass or liver concentrations of tetra-brominated diphenyl ethers (tetra-BDEs) (55% of variation). Relative spleen mass, as an important factor relating to FMR, was best explained by models with a combination of parasite abundance (Diplostomum for females and Eucoleus for males) in a negative relationship, and liver POP concentrations (p,p'-DDE for females and tetra-BDEs for males) in a positive relationship (34%, 55% of variation for females and males, respectively). This study demonstrates that immune activity may be an important factor affecting energy expenditure in ring-billed gulls, and that contaminants and parasite abundance may have both a direct and/or indirect influence on FMR.

Impacts of parasites in early life: contrasting effects on juvenile growth for different family members

Parasitism experienced early in ontogeny can have a major impact on host growth, development and future fitness, but whether siblings are affected equally by parasitism is poorly understood. In birds, hatching asynchrony induced by hormonal or behavioural mechanisms largely under parental control might predispose young to respond to infection in different ways. Here we show that parasites can have different consequences for offspring depending on their position in the family hierarchy. We experimentally treated European Shag (Phalacrocorax aristoteli) nestlings with the broad-spectrum anti-parasite drug ivermectin and compared their growth rates with nestlings from control broods. Average growth rates measured over the period of linear growth (10 days to 30 days of age) and survival did not differ for nestlings from treated and control broods. However, when considering individuals within broods, parasite treatment reversed the patterns of growth for individual family members: last-hatched nestlings grew significantly slower than their siblings in control nests but grew faster in treated nests. This was at the expense of their earlier-hatched brood-mates, who showed an overall growth rate reduction relative to last-hatched nestlings in treated nests. These results highlight the importance of exploring individual variation in the costs of infection and suggest that parasites could be a key factor modulating within-family dynamics, sibling competition and developmental trajectories from an early age.

Effects of parasites on host energy expenditure: the resting metabolic rate stalemate

Detrimental effects of parasitism on host fitness are frequently attributed to parasite-associated perturbations to host energy budgets. It has therefore been widely hypothesized that energetic costs of infection may be manifest as changes in host resting metabolic rate (RMR). Attempts to quantify these effects have yielded contradictory results across host–parasite systems. We used a meta-analysis of the literature to test the effects of parasites on mass-specific (n = 22) and whole-body (n = 15) host RMR. Parasites resulted in a qualitative increase in host RMR in the majority of studies; however, the overall effect of parasites on host RMR was small and statistically nonsignificant. Additionally, substantial among-study variation in host RMR could not be explained by any of the tested covariates. We conclude that the lack of an overall effect of parasites on host metabolism reflects inconsistent directionality and varying magnitudes of parasite-associated effects across studies, rather than an absence of system-specific effects. We contend that a general understanding of parasite effects on host energetics may be best achieved through identifying mechanisms underlying among-system variance in parasite effects on host RMR and relating parasite-associated perturbations of host energy budgets to robust estimates of host fitness.

It costs to be clean and fit: energetics of comfort behavior in breeding-fasting penguins

BACKGROUND

Birds may allocate a significant part of time to comfort behavior (e.g., preening, stretching, shaking, etc.) in order to eliminate parasites, maintain plumage integrity, and possibly reduce muscular ankylosis. Understanding the adaptive value of comfort behavior would benefit from knowledge on the energy costs animals are willing to pay to maintain it, particularly under situations of energy constraints, e.g., during fasting. We determined time and energy devoted to comfort activities in freely breeding king penguins (Aptenodytes patagonicus), seabirds known to fast for up to one month during incubation shifts ashore.

METHODOLOGY/PRINCIPAL FINDINGS

A time budget was estimated from focal and scan sampling field observations and the energy cost of comfort activities was calculated from the associated increase in heart rate (HR) during comfort episodes, using previously determined equations relating HR to energy expenditure. We show that incubating birds spent 22% of their daily time budget in comfort behavior (with no differences between day and night) mainly devoted to preening (73%) and head/body shaking (16%). During comfort behavior, energy expenditure averaged 1.24 times resting metabolic rate (RMR) and the corresponding energy cost (i.e., energy expended in excess to RMR) was 58 kJ/hr. Energy expenditure varied greatly among various types of comfort behavior, ranging from 1.03 (yawning) to 1.78 (stretching) times RMR. Comfort behavior contributed 8.8-9.3% to total daily energy expenditure and 69.4-73.5% to energy expended daily for activity. About half of this energy was expended caring for plumage.

CONCLUSION/SIGNIFICANCE

This study is the first to estimate the contribution of comfort behavior to overall energy budget in a free-living animal. It shows that although breeding on a tight energy budget, king penguins devote a substantial amount of time and energy to comfort behavior. Such findings underline the importance of comfort behavior for the fitness of colonial seabirds.

Do fleas affect energy expenditure of their free-living hosts?

Background

Parasites can cause energetically costly behavioural and immunological responses which potentially can reduce host fitness. However, although most laboratory studies indicate that the metabolic rate of the host increases with parasite infestation, this has never been shown in free-living host populations. In fact, studies thus far have shown no effect of parasitism on field metabolic rate (FMR).

Methodology and Results

We tested the effect of parasites on the energy expenditure of a host by measuring FMR using doubly-labelled water in free-living Baluchistan gerbils (Gerbillus nanus) infested by naturally occurring fleas during winter, spring and summer. We showed for the first time that FMR of free-living G. nanus was significantly and positively correlated with parasite load in spring when parasite load was highest; this relationship approached significance in summer when parasite load was lowest but was insignificant in winter. Among seasons, winter FMRs were highest and summer FMRs were lowest in G. nanus.

Discussion

The lack of parasite effect on FMR in winter could be related to the fact that FMR rates were highest among seasons. In this season, thermoregulatory costs are high which may indicate that less energy could be allocated to defend against parasites or to compensate for other costly activities. The question about the cost of parasitism in nature is now one of the major themes in ecological physiology. Our study supports the hypothesis that parasites can elevate FMR of their hosts, at least under certain conditions. However, the effect is complex and factors such as season and parasite load are involved.

Immunity and fitness in a wild population of Eurasian kestrels Falco tinnunculus

The immune system of vertebrates consists of several components that partly interact and complement each other. Therefore, the assessment of the overall effectiveness of immune defence requires the simultaneous measurement of different immune components. In this study, we investigated intraspecific variability of innate [i.e. natural antibodies (NAb) and complement] and acquired (i.e. leucocyte profiles) immunity and its relationship with fitness correlates (i.e. blood parasite load and reproductive success in adults and body mass and survival until fledging in nestlings) in the Eurasian kestrel Falco tinnunculus. Immunity differed between nestlings and adults and also between adult males and females. Adult kestrels with higher levels of complement were less parasitised by Haemoproteus, and males with higher values of NAbs showed a higher reproductive success. In nestlings, the H/L ratio was negatively related to body mass. Survival until fledging was predicted by all measured immunological variables of nestlings as well as by their fathers' level of complement. This is the first time that innate immunity is linked to survival in a wild bird. Thus, intraspecific variation in different components of immunity predicts variation in fitness prospects in kestrels, which highlights the importance of measuring innate immune components together with components of the acquired immunity in studies assessing the effectiveness of the immune system in wild animals.

Health of Antarctic birds: a review of their parasites, pathogens and diseases

Antarctic birds are not beyond the effects of parasites or pathogens. However, potential ecological consequences of wide-spread infections for bird populations in Antarctica have received little attention. In this paper, we review the information published about disease and parasites, and their effects on Antarctic birds. The information on host species, parasites and pathogens, and geographic regions is incomplete and data on ecological effects on the populations, including how birds respond to pathogens and parasites, are almost inexistent. We conclude that more research is needed to establish general patterns of spatial and temporal variation in pathogens and parasites, and to determine how such patterns could influence hosts. This information is crucial to limit the spread of outbreaks and may aid in the decision-making process should they occur.

Do food availability, parasitism, and stress have synergistic effects on red colobus populations living in forest fragments?

Identifying factors that influence animal density is a fundamental goal in ecology that has taken on new importance with the need to develop informed management plans. This is particularly the case for primates as the tropical forest that supports many species is being rapidly converted. We use a system of forest fragments adjacent to Kibale National Park, Uganda, to examine if food availability and parasite infections have synergistic affects on red colobus (Piliocolobus tephrosceles) abundance. Given that the size of primate populations can often respond slowly to environmental changes, we also examined how these factors influenced cortisol levels. To meet these objectives, we monitored gastrointestinal parasites, evaluated fecal cortisol levels, and determined changes in food availability by conducting complete tree inventories in eight fragments in 2000 and 2003. Red colobus populations declined by an average of 21% among the fragments; however, population change ranged from a 25% increase to a 57% decline. The cumulative basal area of food trees declined by an average of 29.5%; however, forest change was highly variable (a 2% gain to a 71% decline). We found that nematode prevalence averaged 58% among fragments (range 29-83%). The change in colobus population size was correlated both with food availability and a number of indices of parasite infections. A path analysis suggests that change in food availability has a strong direct effect on population size, but it also has an indirect effect via parasite infections.

The energetic grooming costs imposed by a parasitic mite (Spinturnix myoti) upon its bat host (Myotis myotis)

Parasites often exert severe negative effects upon their host's fitness. Natural selection has therefore prompted the evolution of anti-parasite mechanisms such as grooming. Grooming is efficient at reducing parasitic loads in both birds and mammals, but the energetic costs it entails have not been properly quantified. We measured both the energetic metabolism and behaviour of greater mouse-eared bats submitted to three different parasite loads (no, 20 and 40 mites) during whole daily cycles. Mites greatly affected their time and energy budgets. They caused increased grooming activity, reduced the overall time devoted to resting and provoked a dramatic shortening of resting bout duration. Correspondingly, the bats' overall metabolism (oxygen consumption) increased drastically with parasite intensity and, during the course of experiments, the bats lost more weight when infested with 40 rather than 20 or no parasites. The short-term energetic constraints induced by anti-parasite grooming are probably associated with long-term detrimental effects such as a decrease in survival and overall reproductive value.

Physiological and haematological consequences of a novel parasite on the red-rumped swallow Hirundo daurica

Parasite virulence has been hypothesised to increase with the degree of host sociality because highly social hosts have a greater probability of encountering horizontal transmission of parasites and experiencing infections with multiple strains of the same parasites than do solitary hosts. As compared with the defences of closely related social host species, we predicted that solitary hosts should have relatively weak defences against parasites, thus being relatively more affected when parasitised by a novel parasite. We tested this prediction by either experimentally infesting 12 nests of the solitarily nesting red-rumped swallow Hirundo daurica with 50 individuals of the generalist martin bug Oeciacus hirundinis or by fumigation of nine nests. Nestlings 13 days old from the parasite addition group experienced increased mortality, attained lower body mass and tended to have shorter tarsi compared to nestlings from fumigated nests. Surprisingly, nestlings from the parasite addition group had higher packed cell volume (cellular fraction of blood) and lower levels of heat shock proteins (HSP60) than nestlings from the fumigation group. A measure of immunocompetence was not significantly affected by treatment, but its magnitude was positively related to packed cell volume and negatively related to level of HSP60. Solitary hosts like the red-rumped swallow have weak immune responses and low levels of heat shock proteins when infested with ectoparasites while highly social hosts have strong immune responses and high levels of heat shock proteins when infested. These findings partially support the hypothesis that potential host species with weak defences are more susceptible to infection and the deleterious effects of evolving parasites than potential hosts with strong defences.

Genetic and environmental components of phenotypic variation in immune response and body size of a colonial bird, Delichon urbica (the house martin)

Directional selection for parasite resistance is often intense in highly social host species. Using a partial cross-fostering experiment we studied environmental and genetic variation in immune response and morphology in a highly colonial bird species, the house martin (Delichon urbica). We manipulated intensity of infestation of house martin nests by the haematophagous parasitic house martin bug Oeciacus hirundinis either by spraying nests with a weak pesticide or by inoculating them with 50 bugs. Parasitism significantly affected tarsus length, T cell response, immunoglobulin and leucocyte concentrations. We found evidence of strong environmental effects on nestling body mass, body condition, wing length and tarsus length, and evidence of significant additive genetic variance for wing length and haematocrit. We found significant environmental variance, but no significant additive genetic variance in immune response parameters such as T cell response to the antigenic phytohemagglutinin, immunoglobulins, and relative and absolute numbers of leucocytes. Environmental variances were generally greater than additive genetic variances, and the low heritabilities of phenotypic traits were mainly a consequence of large environmental variances and small additive genetic variances. Hence, highly social bird species such as the house martin, which are subject to intense selection by parasites, have a limited scope for immediate microevolutionary response to selection because of low heritabilities, but also a limited scope for long-term response to selection because evolvability as indicated by small additive genetic coefficients of variation is weak.

Green plants in starling nests: effects on nestlings

European starlings, Sturnus vulgaris, intermingle fresh herbs, especially species rich in volatile compounds, with their otherwise dry nest material. In this field study we investigated whether these herbs reduce ectoparasites and thereby protect nestlings (the nest protection hypothesis). We also considered whether volatile compounds in herbs improve the condition of nestlings (the drug hypothesis). As measures of condition we used body mass, haematocrit levels and immunological parameters. We replaced 148 natural starling nests with artificial ones: half contained herbs and half (controls) contained grass. The ectoparasite loads (mites, lice, fleas) in herb and control nests were indistinguishable. However, nestlings in herb nests weighed more and had higher haematocrit levels at fledging than nestlings in control nests. Fledging success was similar in herb and control nests, but more yearlings from herb nests were identified in the colony the year after hatching. The response of the immune system when challenged with phytohaemagglutinin did not differ in nestlings from herb and control nests. Nestlings from herb nests had more basophils and fewer lymphocytes in their blood than those from control nests, while the eosinophil and heterophil counts did not differ. We conclude that herbs do not reduce the number of ectoparasites, but they improve the condition of nestlings, perhaps by stimulating elements of the immune system that help them to cope better with the harmful activities of ectoparasites. Copyright 2000 The Association for the Study of Animal Behaviour.

Begging behaviour and its energetic cost in great spotted cuckoo and magpie host chicks

Begging is one of the main factors governing food delivery to chicks by adult birds and it is of great importance in studies of biological communication theory. Many theoretical models have been proposed to explain the evolution of this noisy and conspicuous behaviour, all of which assume that begging activity is energetically costly. We show that both great spotted cuckoo (Clamator glandarius) brood-parasitic chicks and magpie (Pica pica) host chicks ceased to beg after ingesting enough food, and that great spotted cuckoo chicks emitted more begging calls and begged for much longer than did magpie chicks. Using the doubly labelled water method to measure the daily energy expenditure of begging and nonbegging chicks in the laboratory, we show that begging behaviour consumes only a small quantity of oxygen compared with other avian activities usually assumed to be energetically costly.

Growth, nutrition, and blow fly parasitism in nestling Pied Flycatchers

The nutritional status of the host may play a major role in mediating the detrimental effects of parasites. We performed an experiment with the aim of determining whether increased food availability can compensate for the effects of ectoparasites on growth during the late nestling period, final size, and survival until fledging of Pied Flycatcher (Ficedula hypoleuca) nestlings. Nests were provided with supplementary food, treated with insecticide, given both treatments, or given neither treatment (control). Differences in the number of blood-sucking, ectoparasitic blow fly larvae (Protocalliphora azurea) occurred between treated nests. Nestlings in the group given supplementary food and with low numbers of parasites grew faster and had a higher haematocrit value than those in groups that were fumigated and given supplementary food, with nestlings from control nests attaining the lowest values. Nestling measurements did not differ between fumigated and food-supplemented groups. Although the final sizes attained did not differ among nestlings from the different experimental groups, there was a significant difference in the rates of increase in size among groups. Nestlings in nests fumigated and provided with extra food were (nonsignificantly) smaller and leaner than nestlings from the other groups at the beginning of the experiment, but were slightly larger and heavier (again nonsignificantly) at the end of the experiment. Thus, their growth was faster than that of the other groups. The results are discussed, highlighting problems related to the function linking intensity of parasit ism to host fitness and variation in external (climate, food) conditions.

The effects of an ectoparasite on reproductive success in the great tit: a 3-year experimental study

The effects of ectoparasites on host reproductive success have been studied in a variety of bird species. Most of these studies concern either colonial or hole-nesting birds, which have been suspected of being particularly susceptible to parasites because of their social habits and (or) reuse of old nests. The effects of a horizontally transmitted flea, Ceratophyllus gallinae, on the reproductive success of hole-nesting great tits,Parus major, were experimentally studied over 3 years. Leaving nests in nest boxes in the intervals between breeding seasons does not result in a significant increase in parasite abundance in comparison with nest boxes cleaned between seasons. Flea abundance was reduced by spraying random nests with an insecticide during host egg laying. There were no significant effects of ectoparasite removal on clutch size, number of fledged young, hatching success, or fledging success in any of the 3 years, although a significant interaction between year and treatment in nestling body mass was observed. Thus, in 1 of the 3 years, body mass of nestlings in the sprayed boxes was, on average, significantly greater than that of controls. There was also a negative correlation between flea abundance and mean body mass of the brood. In addition, nestlings produced in flea-free boxes had a significantly higher probability of recruiting locally than nestlings from control nests. The effects of ectoparasites seem to vary over time and also among host populations, which implies that the effects of parasites may interact with other environmental factors.