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International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 Contents lists available at ScienceDirect International Journal for Parasitology: Parasites and Wildlife Experimental manipulation reveals few subclinical impacts of a parasitecommunity in juvenile kangaroos Jemma Cripps a,b,⇑, Ian Beveridge b, Richard Ploeg b,1, Graeme Coulson aa Department of Zoology, The University of Melbourne, VIC 3010, Australiab Faculty of Veterinary Science, The University of Melbourne, Veterinary Clinical Centre, Werribee, VIC 3030, Australia Large mammalian herbivores are commonly infected with gastrointestinal helminths. In many host spe- Received 27 January 2014 cies, these helminths cause clinical disease and may trigger conspicuous mortality events. However, they Revised 15 March 2014 may also have subclinical impacts, reducing fitness as well as causing complex changes to host growth Accepted 28 March 2014 patterns and body condition. Theoretically, juveniles should experience significantly greater costs fromparasites, being immunologically naive and undergoing a significant growth phase. The aims of our studywere to quantify the subclinical effects of helminths in juvenile eastern grey kangaroos (Macropus gigan- teus), which commonly harbour large burdens of gastrointestinal nematodes and are susceptible to asso- ciated mass mortality during cold, wet conditions. We conducted a field experiment on a population of free-ranging kangaroos, removing nematodes from one group of juveniles using an anthelmintic treat- ment. We then compared growth parameters (body condition and growth rates) and haematological Macropus giganteus parameters of this group with an age-matched, parasitised (untreated) control group. Treated juvenile kangaroos had significantly higher levels of plasma protein (albumin) but, contrary to our predictions,showed negligible changes in all the other parameters measured. Our results suggest that juvenile kan-garoos are largely unaffected by their gastrointestinal helminth burdens, and may be able to compensatefor the costs of parasites.
! 2014 The Authors. Published by Elsevier Ltd. on behalf of Australian Society for Parasitology. This is an open access article under the CC BY-NC-ND license (
in livestock and wildlife often differ, due to the difficulties ofstudying natural host–parasite relationships and quantifying fit- Gastrointestinal helminths commonly infect mammalian herbi- ness consequences. In order to thoroughly investigate such effects, vores (Sykes, 1987). Helminth infections often have clinical experimental manipulation is imperative. Field experimentation impacts, causing disease and mortality (Holmes, 1987), but can allows the actual costs of parasites on hosts to be investigated rig- also cause what has been termed ‘subclinical' disease (Gunn and orously, eliminating many of the issues associated with extrapolat- Irvine, 2003), inducing more subtle effects in the host. Subclinical ing laboratory results onto free-living individuals or populations impacts are well known in livestock: reductions in appetite and (Seitz and Ratte, 1991). Studies of fitness consequences in the wild food absorption caused by helminth infections can decrease host typically focus on natural covariation between parasite load and fecundity and growth (Mejia et al., 1999), body condition fitness parameters, and so may be confounded by the inherent dif- (Loyacano et al., 2002) and alter metabolism (O'Kelly et al., ferences among individuals that can contribute to high parasite 1988). In contrast, the effects of parasitism on wildlife have burdens. Consequently, it is often unclear whether changes in fit- received far less attention, although there is mounting evidence ness parameters are due to heavy parasite burdens, or if these bur- that parasites can have similar negative impacts, reducing fitness dens result from other pre-existing factors related to fitness.
(Watson, 2013) as well as causing complex changes to host physi- Ecological host–parasite studies in wild animals have been mostly ology (Van Houtert and Sykes, 1996), behaviour (Scantlebury et al., based on correlations, although there have been some field exper- 2007) and population dynamics (Hudson et al., 1992a; Albon et al., iments in wild systems (e.g. Svalbard reindeer, Rangifer tarandus 2002; Stien et al., 2002). However, the types of impacts measured platyrhynchus (Stien et al., 2002), Soay sheep, Ovis aries (Gulland,1992) and red grouse Lagopus lagopus scoticus (Hudson et al.,1992b)).
⇑ Corresponding author at: Department of Zoology, The University of Melbourne, VIC 3010, Australia. Tel.: +61 3 8344 4862.
The subclinical effects of parasites can be extremely difficult to E-mail address: [email protected] (J. Cripps).
quantify in the wild. Ecologists tend to use body condition as an 1 Previous address: IDEXX Laboratories, Mount Waverley, VIC 3149, Australia.! 2014 The Authors. Published by Elsevier Ltd. on behalf of Australian Society for Parasitology.
This is an open access article under the CC BY-NC-ND license (
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J. Cripps et al. / International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 indicator of an animal's health and reproductive potential. Body the pouch, young will exit permanently at around 320 days condition essentially reflects available energy reserves (Green, (Poole, 1975). Toward the end of pouch life, juveniles begin to for- 2001): an animal in good condition is assumed to have more age on the pasture and are exposed to the infective stages of nem- reserves than one in poor condition (Schulte-Hostedde et al., atodes. Juveniles will continue to associate with and suckle from 2005). Energy reserves can be quantified directly by measuring their mothers until over 18 months of age (Poole, 1975). The year fat stores (e.g. amount of back or kidney fat (Riney, 1955)) or following permanent pouch exit is the most critical for juvenile non-invasively using mass/size ratio indices of body condition, kangaroos, as they must undergo substantial growth. During this which attempt to determine the size of energy stores after correct- period, the average monthly weight gain is 1.4 kg for males and ing for structural body size (Schulte-Hostedde et al., 2005). Alter- 0.9 kg for females (Poole et al., 1982). To sustain this growth, juve- natively, haematological and serum biochemical parameters can niles have around 1.8 times the energy requirement of mature, be used to assess an animal's health. Although less commonly used non-lactating females (Munn and Dawson, 2004). In addition, dur- in ecological studies of wildlife, haematological parameters may ing this period of growth, individuals are immunologically naive provide more sensitive information on the immediate physiologi- (Arundel et al., 1990), and become infected by gastrointestinal par- cal status of a host (Milner et al., 2003; Budischak et al., 2012). That asites. Individual variability in body size increases following per- is because parasite infections can alter haematological parameters manent pouch exit (Poole et al., 1982), suggesting that growth directly through haematophagy (blood-feeding) and indirectly rate is a plastic trait that can be influenced by external factors.
through activation of host immunity in response to infection or We examined the effect of concomitant infection with multiple by limiting the digestion and absorption of essential nutrients, parasites on the growth, body condition and blood chemistry of such as protein (Colditz, 2008). Red blood cell counts, haemoglobin one cohort of free-ranging juvenile eastern grey kangaroos, by and plasma protein concentrations can all be used to assess an ani- manipulating parasite loads. We removed gastrointestinal para- mal's health and condition, and have been directly linked to perfor- sites from a group of juveniles using an oral anthelmintic and then mance and reproductive success (Moore and Hopkins, 2009). The compared them with control individuals, with the expectation that combined application of both haematological and body condition control juveniles would show subclinical effects. We predicted that indices may therefore provide greater insight into the subclinical due to an increased availability of nutrients and energy resources, effects of parasite communities on a host.
treated juveniles would have a greater growth rate and mass gain, Juvenile mortality is commonly increased by infection (Schmidt and would increase their body condition relative to controls. We et al., 1979), however evidence from livestock suggests that this also predicted that there would be changes in haematological age-class can also experience considerable subclinical effects such parameters, with decreases in red blood cell counts, haemoglobin as reductions in body weight (Chiejina and Sewell, 1974), growth concentration and haematocrit in control juveniles. Similarly, we (Loyacano et al., 2002) and appetite (Kyriazakis et al., 1998).
expected that serum biochemistry would indicate subclinical Despite the evidence from livestock hosts, it is unclear to what effects, with decreased levels of total protein and albumin, and degree subclinical effects occur in juveniles of wildlife species. The- increases in levels of globulin.
oretically, juveniles should experience significant costs wheninfected with parasites due to the nutritional deficits they causeand the costs of mounting an immune response (Colditz, 2008), 2. Materials and methods and these effects should be particularly marked during earlygrowth and development. Such effects are important to compre- hend as it is well established that conditions early in life can havesignificant implications for survival and reproductive success as an This study was conducted at the Anglesea Golf Club (38"240S, adult (Metcalfe and Monaghan, 2001).
114"100E) in southern Victoria, Australia, in 2012. The golf course Most wildlife hosts harbour complex parasite communities covers an area of 73 ha and contains open, grassy fairways domi- (Bordes and Morand, 2011), and kangaroos (Marsupialia: Macropo- nated by couch grass (Cynodon dactylon), separated by patches of didae) are known to support more species of parasites than any woodland and shrubland (Inwood et al., 2008). The course is bor- other group of mammals (Beveridge and Chilton, 2001). The east- dered by native heathy woodland to the north and west; kangaroos ern grey kangaroo (Macropus giganteus) carries a diverse fauna of move freely between the course and native vegetation, as well as gastrointestinal nematode parasites in its complex, sacculated through residential properties in the south and east. Population forestomach (Beveridge and Arundel, 1979), with most species surveys (following Inwood et al., 2008) at the time of the study showing seasonal fluctuations, peaking in the winter months showed that the population density of kangaroos at the site was (Arundel et al., 1990). Most of these gastrointestinal nematodes approximately 2.0/ha (Cripps and Coulson, unpublished data).
are directly transmitted via ingestion (Sykes, 1987). Adult kanga- Potential predators at the site include the red fox (Vulpes vulpes) roos do not appear to develop immunity to most of these nema- and domestic dogs (Canis lupus familiaris).
tode species (Arundel et al., 1979), and juveniles are susceptible Post-mortem examinations of three juveniles found dead at the to gastrointestinal parasitism, primarily from high burdens (400– study site during 2010–2011, using standard methods (Beveridge 1500) of the intestinal trichostrongylid nematode Globocephaloides and Arundel, 1979), revealed a diverse gastrointestinal parasite trifidospicularis Juveniles can experience high mortality, coupled community. The stomach contained the strongyle nematodes with declining haematocrit and plasma protein concentrations, in Rugopharynx macropodis (intensity 8240–69,000 per kangaroo), their first winter post-weaning between 14 and 20 months of age Rugopharynx rosemariae (500, n = 1) and Pharyngostrongylus kappa (Arundel et al., 1990). Populations of eastern grey kangaroos can (500–10,000). The small intestine contained G. trifidospicularis reach high densities, and individuals are gregarious, forming (31–73), levels well below those known to cause clinical impacts mixed-sex, open-membership groups to forage and rest (Coulson, (Arundel et al., 1990). The large intestine contained two oxyuroid 2009), conditions that favour helminth parasite transmission nematodes, Macropoxyuris brevigularis (40–3450) and Macropoxyu- (Altizer et al., 2003).
ris longigularis (500–1050), and one strongyle nematode species Eastern grey kangaroos are capable of breeding throughout the Macropostrongyloides baylisi (50–9000). The bile ducts of two juve- year, but most births occur between September and March, during niles had the cestode Progamotaenia festiva. Examination of seven the austral spring/summer months (Poole, 1983). Following a short adults from the site revealed a further ten helminth species: Labio- gestation period and then an extended period of development in simplex kungi, Labiosimplex bipapillosus, Cloacina pelops, Cloacina Author's personal copy
J. Cripps et al. / International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 herceus, Cloacina hermes, Cloacina selene, Cloacina artemis, Cloacina of 77 days, range 68–114 days) and final body measurements were expansa, Cloacina obtusa, and Alocostoma clelandi in the stomach collected. In total, each individual was captured three times.
(Cripps, unpublished data). Coinfection levels ranged from 5 to 8helminth species in juveniles kangaroos, and a further 3–5 species 2.3. Faecal egg counts in adults (Cripps, unpublished data). Total worm counts in juve-niles (12,870–79,853) and adults (1844–84,017) were well within To determine the efficacy of the parasite treatment, egg counts the range recorded for eastern grey kangaroos (Arundel et al., were conducted on faecal samples collected within 33 days of first 1990; Beveridge and Arundel, 1979). Ectoparasites (lice, ticks) capture. Samples were collected again at 40–90 days post-treat- were not recorded as eastern grey kangaroos have relatively few ment, prior to the second re-treatment period. At this point, it is ectoparasites (Beveridge and Arundel, 1979).
possible that many of the nematodes were larval stages and thuswere not reflected in the faecal egg counts. Faecal samples were 2.2. Animal capture and treatment collected in 2 h blocks at dawn and dusk, as this is when kangaroosare actively foraging and defaecation rates are greatest (Johnson Juvenile kangaroos (n = 42) were first captured in March and et al., 1987). Marked juveniles were observed until they defaecat- April 2012. Due to their habituation to humans, kangaroos at this ed, and observers collected faecal samples immediately after they site tolerate close approach on foot. Juveniles were identified pri- were deposited. It was not possible to collect samples from every marily based on their size, but also on whether they were closely individual, so faecal samples were collected for a subset of juve- associated with an adult female. Juveniles were captured using niles in each group. Samples were collected from 13 juveniles (5 either an extendable pole syringe (1.4 m, 2.4 m or 3.6 m long) treated, 8 controls) days 12–33 post-treatment, and from 20 juve- (King et al., 2011), or by an injection arrow fired from a band-pow- niles (9 treated, 11 controls) days 40–90 post-treatment. Samples ered gun (Para-medic; Wildvet, Melbourne, Victoria, Australia).
were maintained at 4 "C and analysed within 24 h. The number Both methods injected the hind limb musculature with Zoletil# of eggs per gram (epg) was determined by a modified McMaster 100 (100 mg/mL of 50:50 tiletamine hydrochloride – zolazepam technique using 2 g of faeces mixed with 60 mL of saturated hydrochloride mixture; Virbac Animal Health Pty Ltd, Milperra, sodium nitrate solution (Redox Pty Ltd, Minto, New South Wales, New South Wales, Australia) at a dose of approximately 5 mg/kg Australia). An aliquot of 0.5 mL of homogenised filtrate was trans- ferred into a Whitlock Universal counting chamber then examined To identify individuals, they were fitted with a unique combina- under a microscope at 100! magnification. Only typical strongylid tion of coloured, reflective ear tags (Leader, Craigieburn, Victoria, eggs were counted, with each egg representing 60 epg of faeces.
Australia). Standard body measurements (Poole et al., 1982) werecollected using a retractable tape measure and Vernier calipers.
2.4. Blood collection and analysis Leg, pes (foot) and arm lengths were measured to the nearestmm; body mass was measured to the nearest 0.1 kg using 25-kg During the second recapture, blood samples were also collected spring scales (Salter, Melbourne, Victoria, Australia).
from the lateral caudal vein. Blood for haematology was trans- The approximate date of birth of each individual was calculated ferred into 2 mL vacutainers containing EDTA, and for serum anal- from the mean of three estimates based on leg, foot and arm mea- ysis into 5 mL vacutainers containing gel for serum separation but surements at the first capture using growth tables provided by no additives. Vials were immediately placed in a cooler and taken Poole et al. (1982). In some cases, one measurement gave an esti- back to the field base, where blood for serum analysis was centri- mate that was >2 months apart from the other two. If this fuged for 15 min. Blood smears were also prepared on glass slides occurred, birthdate was calculated using the mean of the other within 4 h of collection. Sera and whole blood samples were refrig- two estimates. Only individuals born after 1 August 2010 were erated until transport to a commercial, NATA-accredited, diagnos- included in the final analysis to ensure that they were 621 months tic veterinary laboratory (IDEXX Laboratories, Mount Waverley, of age and therefore encountering nematode larvae for the first Victoria, Australia). The time between blood collection and deliv- time over the winter months of June – August 2012.
ery to the lab was <24 h. Whole blood was analysed for the number Individuals were randomly allocated to either a control (n = 20) of red blood cells, the haemoglobin concentration and haematocrit.
or a treatment (n = 22) group, stratified by sex to ensure equal Assessment of haematologic values was performed using a Sysmex numbers of males and females in each group. Treated individuals XT-2000i haematology analyzer (Sysmex Corportaion, Kobe, were given an oral dose of albendazole (Alben# for sheep, lambs Japan). Serum chemistry profiles were obtained with an Olympus and goats, 19 g/L, Virbac Animal Health Pty Ltd, Milperra, New AU 400 analyzer (Olympus Diagnostics, Hamburg, Germany) and South Wales, Australia) at a rate of 3.8 mg/kg body mass (Cripps included total protein, albumin and globulin.
et al., 2013), while control individuals were left untreated. No oralcontrol was administered to untreated individuals to avoid indi- 2.5. Statistical analysis rectly affecting the gastrointestinal fauna. A number of juvenilesdisappeared (either died or dispersed) during the study, so only Logistic regression was used to analyse the effects of sex and 15 controls (8 male, 7 female) and 12 treatment (8 male, 4 female) treatment on the disappearance rate of individuals throughout kangaroos were included in the analysis. The average age of these the study. Faecal egg count reduction calculations were made individuals at first capture was 14.5 months (range 11– according to Wood et al. (1995) using the Excel plug-in ‘Reso' 19.5 months).
(Cameron, 2003). Analysis of the effects of treatment on kangaroo Juvenile kangaroos were recaptured between May and June faecal egg counts was carried out using Genstat, Version 10 (VSN 2012 to re-administer the anthelmintic to the treated group and International Ltd., Hemel Hempstead, UK). Faecal egg counts were to collect body measurements from both groups. The interval of log (1 + epg) transformed to meet the assumptions of normality re-treatment was based on the estimated pre-patent period of and analysed using restricted maximum-likelihood analyses infection (approximately 3 months) in eastern grey kangaroos (REML), with time and treatment as fixed factors, and kangaroo (Cripps et al., 2013). Individuals were recaptured in a similar order identity as a random factor to account for repeated measures.
to their initial captures; the average time between first and second Differences in body mass and leg lengths of juveniles in the capture was 77 days (range 69–91). Individuals were recaptured treated and control groups at the initial capture were tested using again between July and September 2012 (mean recapture interval independent sample t-tests. The Scaled Mass Index (Peig and

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J. Cripps et al. / International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 Green, 2009) was used to measure body condition. This index over-comes several drawbacks of other indices, many of which fail toaccount for the changing relationship between mass and lengthas growth occurs. Following Peig and Green's procedure (2009),the most strongly correlated body measurement with body mass(on a log–log scale) was determined. Initially each sex was testedseparately, but there was no difference in the strength of the cor-relations so sexes were pooled. Both leg and arm length were morehighly correlated with body mass (leg: r = 0.92, P < 0.01; arm:r = 0.91, P < 0.01) than pes length (r = 0.81, P < 0.01), so we choseleg length as the length (Li) value for each individual. The popula-tion mean (L0) was calculated separately for each of the three cap- ture periods. The Scaled Mass Index of body condition was thencalculated as Mi(L0/Li)bSMA, where Mi is the body mass of the indi- vidual and bSMA is the standardised major axis regression slopeof the lnMi " lnLi plot (Peig and Green, 2009).
To assess the effect of treatment across the three capture peri- ods, repeated measure ANOVAs were performed to determine dif-ferences in body mass, leg length and the Scaled Mass Index. The Fig. 1. Mean faecal egg counts for control and anthelmintic-treated juvenile eastern main factor was treatment (albendazole administered or untreated grey kangaroos in two periods post-capture (12–33 days) and initial treatment (40–90 days) at the Anglesea Golf Club, Victoria, Australia, from March to May 2012.
control), and the repeated factor was captures. Mauchly's test of Bars indicate standard errors. It was not always possible to sample each individual sphericity indicated that the assumption of sphericity was violated in each period; numbers on columns indicate sample size for each time period.
in all cases (body mass: v22 = 9.86, P = 0.007; leg: v22 = 10.93, P = 0.004; body condition: v22 = 13.97, P = 0.001), so a Greenhouse– Geisser correction was used. Analysis of the effect of treatment on in the faecal flotations. Eimeria oocysts were present in some sam- haematological and serum biochemical parameters was carried out ples but at very low numbers.
using independent sample t-tests or Mann–Whitney U tests in the Body mass of control and treated juvenile kangaroos did not dif- cases where data were non-normal.
fer at the time of first capture, (t25 = 0.19, P = 0.85), nor did skeletal Power analyses were performed for each growth and blood size, measured as leg length (t25 = 0.01, P = 0.99). Mass gain was parameter, using G*Power (Erdfelder et al., 1996). The magnitude explained by time (F1.49,37.39 = 21.22, P < 0.001) but not treatment of effects for most of the parameters we tested is rarely reported (F1,25 = 0.04, P = 0.84), and there was no interaction between the in the literature. The magnitude of body mass effects reported for two (F1.49,37.39 = 0.44, P = 0.59). There was also no significant effect livestock hosts are extremely variable. When compared to parasi- of treatment on the growth of leg length (F1,25 = 0.08, P = 0.93).
tised controls, unparasitised heifers gained approximately 18% Instead, time explained leg growth (F1.46,36.61 = 71.39, P < 0.001), more weight (Mejia et al., 1999), whereas in sheep, the difference and there were no interactions between time and treatment ranged from 74% (McLeod and Wolff, 1968) to 81% (Anderson et al., (F1.46,36.61 = 0.24, P = 0.72). The body condition of individual juve- 1980). Consequently, we used both 20% and 80% differences nile kangaroos increased during the study (F1.39,34.69 = 21.60, between the treatment and control groups as the effect sizes in P < 0.001; Table 1) but there was no effect of treatment these calculations.
(F1,25 = 0.01, P = 0.91) nor any interaction between treatment and All other statistical analyses were carried out using SPSS Ver- time (F1.39,34.69 = 0.32, P = 0.65). With the estimated 80% effect size, sion 21 (IBM Corporation, Armonk, New York, USA). The assump- power was high for leg measurements (>0.8, Table 1) and moderate tions of parametric statistic analyses (normality and equality of for body mass and body condition (0.3–0.8, Table 1). With the esti- variances) were tested for all sets of data. Normality was assessed mated 20% effect size, power was low (<0.3, Table 1) for all of the using the Kolmogorov–Smirnov statistic with a > 0.05, and Levene's test for homogeneity of variances was used to test equal- Serum albumin levels were 8% higher in treated juveniles than ity of variances, with a > 0.05. We did not apply sequential Bonfer- in controls, and this difference was significant (P = 0.01, Table 2).
roni adjustments on the basis that we report power analyses for all While there were no significant differences in the concentrations our tests, and had already selected a subset of blood and growth of total protein, globulin or haemoglobin, the red cell count or parameters for analysis (Moran, 2003).
the haematocrit, all of these parameters showed trends in the pre-dicted directions, with lower levels in the parasitised juveniles.
Power was high for all the blood parameters (>0.8, Table 2) for both 20% and 80% effect sizes.
The overall disappearance rate of juveniles from the beginning to the end of the experiment was 39%. Neither treatment(b = "1.12, v21 = 2.30, P = 0.13) nor kangaroo sex (b = 0.21, Contrary to our predictions, experimental removal of parasites v21 = 0.08, P = 0.77) accounted for variation in disappearance.
in juvenile kangaroos had no effect on their body condition, mass Mean (±SE) faecal egg counts of treated kangaroos (36 ± 24 epg) gain or limb growth. Juvenile kangaroos treated with anthelmintics were much lower than for control kangaroos (885 ± 251 epg, had significantly higher albumin levels than control juveniles, but F1,25.6 = 19.23, P < 0.001; Fig. 1) 12–33 days following treatment, showed no differences in any other blood parameters. There was resulting in a 99% reduction in faecal egg counts. There was no dif- no evidence of parasite-induced mortality at our site, and the dis- ference in the faecal egg counts within each group in either time appearance rate of juveniles (39%) was comparable to that seen in period (F1,3.1 = 2.41, P = 0.22). However, there was a significant another eastern grey kangaroo population subject to predation by interaction between time and treatment (F1,3.4 = 32.36, P = 0.007), red foxes (Banks et al., 2000). Our results suggest that juvenile such that faecal egg counts in the treated group increased more eastern grey kangaroos are largely unaffected by gastrointestinal than those in the control group. No cestode eggs were detected parasitism in populations where burdens of G. trifidospicularis are Author's personal copy
J. Cripps et al. / International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 Table 1Repeated measures ANOVA of treatment effects on selected ecological growth parameters for control and anthelmintic-treated juvenile eastern grey kangaroos at the AngleseaGolf Club, Victoria, Australia, from May to September 2012. The summaries show the sample size (n), the mean (±SE) increase (first to final capture) and the P-value for eachgroup. The statistical power of this experiment to detect a significant difference between treatment and control groups was calculated for effect sizes of 20% and 80%.
Body condition (scaled mass index) Table 2Summary of the sample size (n), mean (±SE) (at the final capture) and test statistics of selected serum chemistry and haematological parameters for control and anthelmintic-treated juvenile eastern grey kangaroos at the Anglesea Golf Club, Victoria, Australia, from May to September 2012. The statistical power of this experiment to detect a significantdifference between treatment and control groups was calculated for effect sizes of 20% and 80%.
Total protein (g/L) Red blood cells (!1012/L) Haemoglobin (g/L) Haematocrit (L/L) * Denotes a significant difference between groups.
low, despite carrying high burdens of other gastrointestinal hel- Arundel et al., 1990), perhaps explaining why we observed only minth species.
an 8% difference in albumin levels between the two groups of Defence against parasites incurs a cost, which may lead to juveniles. The nematode M. baylisi may also feed on blood resources being partitioned into immune response rather than (Arundel et al., 1990), however clinical impacts have never been growth (Zuk and Stoehr, 2002). As resources are limited, animals confirmed. Larvae of a third species, R. rosemariae, can cause undergoing rapid growth must partition and prioritize them severe lesions on the gastric mucosa, yet hosts can carry large appropriately (partitioning framework; Coop and Kyriazakis, burdens without any obvious effects on health (Beveridge and 1999). Accordingly, a growing animal encountering parasites for Presidente, 1978). As in all eastern grey kangaroo populations, the first time would be expected to prioritise immunity over helminth coinfection was ubiquitous in kangaroos at our site, growth (Coop and Kyriazakis, 1999). We therefore predicted that and juveniles were infected with between 5 and 8 different hel- untreated (control) juvenile kangaroos, which were encountering minth species (post-mortem data, Cripps, unpublished data).
nematode parasite larvae for the first time, would have a reduced However, due to the inability to morphologically distinguish the allocation to growth and energy reserves, and this would be eggs of the various taxa in the faeces, it was impossible to deter- reflected in their blood parameters. Field experiments such as ours mine which combination of species were present in any individual are rare in wildlife hosts, but have mostly shown significant sub- in our study at any one time, and therefore hypoalbuminaemia clinical effects on hosts (e.g. Hillegass et al., 2010; Stien et al., could not be attributed to any helminth species in particular.
2002). It was therefore surprising that the removal of parasites Severe blood loss should also reduce concentrations of haemoglo- had little effect on growth or the haematological variables exam- bin and total protein, and lower the haematocrit, but we found no ined, particularly as the faecal egg counts were high in the parasi- differences in any of these despite our high statistical power. We tised kangaroos. However, when compared to untreated controls, are confident our experimental study would have detected even anthelmintic-treated juveniles tended to gain more weight, and small changes in any of the other blood parameters. Alternatively, tended to have a longer leg and pes. Although not significant, the the hypoalbuminaemia we observed could have resulted from power analysis suggests that perhaps with larger sample sizes, reduced food intake and consequent malnutrition, which is a com- greater impacts of parasitism in juvenile grey kangaroos might mon cause of reduced albumin synthesis (Rothschild et al., 1972).
have be seen. If individuals were investing extra energy and nutri- Voluntary reductions in food intake are common during parasitic ents in several areas at once (such as both skeletal and muscular infections in livestock (Holmes, 1987; Kyriazakis et al., 1998), but growth), it may have made it difficult to detect changes in each whether parasite-infected kangaroos also exhibit anorexia is parameter alone (Munger and Karasov, 1989), leading to low unknown. Our study demonstrates that when levels of G. trifido- spicularis are low, kangaroo hosts are able to tolerate their hel- Haematological parameters can be altered by parasites directly minth community and exhibit few subclinical effects from through haematophagy (blood-feeding) and indirectly by limiting the digestion and absorption of essential nutrients, such as amino Increasing resource acquisition may be pivotal in allowing hosts acids and protein (Colditz, 2008). Lowered albumin levels in kanga- to reduce the potential costs of parasitism. Livestock hosts on high- roos could be directly caused by blood loss and/or inflammation in protein diets show reduced pathophysiological responses to para- the gastrointestinal tract (Rothschild et al., 1988; Arundel et al., sitism (reviewed by Van Houtert and Sykes, 1996). For example, 1990). In juvenile eastern grey kangaroos, heavy infections of G.
infected sheep maintained on high protein diets increase their live trifidospicularis have been associated with severe anaemia and clin- weight gain by around 85% compared with control sheep (Van ical disease (Arundel et al., 1990; I. Beveridge pers. obs), although Houtert et al., 1995). Similarly, juvenile kangaroos could compen- burdens (from post-mortems) at our site were more than five sate for the costs of parasitism by using high-quality resources that times lower than levels known to cause disease (400–1500, offset nutrient and resource depletion. The best predictors of body Author's personal copy
J. Cripps et al. / International Journal for Parasitology: Parasites and Wildlife 3 (2014) 88–94 condition in free-ranging kangaroos are the biomass and quality of Arundel, J., Beveridge, I., Presidente, P., 1979. Parasites and pathological findings in forage (Shepherd, 1987; Moss and Croft, 2009), and juvenile kanga- enclosed and free-ranging populations of Macropus rufus (Demarest)(Marsupialia) at Menindee, New South Wales. Wildl. Res. 6, 361–379.
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