Intestinal parasites impact host health, survival and reproductive success
and therefore exert selective pressures on hosts' ecology and behavior. Thus,
characterizing and comparing the parasitic fauna of different wildlife hosts
sharing the same habitat can provide insights into the mechanisms underlying
variation in parasitism, as well as the role of parasites as possible
conservation threats. Several host traits have been proposed to generate
differences in parasite diversity among different host species, including
phylogeny, host body mass, host longevity, diet, and differences in ranging
and social behavior. Here, we provide an overview of intestinal helminths and
protozoa detected by fecal microscopy in six sympatric lemur species in
Kirindy Forest, western Madagascar. The described patterns indicate that host
phylogeny and diet may play an important role in shaping intestinal parasite
assemblages in this system, as the closely related, omnivorous cheirogaleids
showed the strongest overlap in parasite communities. No indication was found
for an effect of body mass or longevity on parasite species richness.
Regarding the effect of sociality, the two group-living lemur species,
Parasites affect host survival and reproduction and thus constitute an important selective force shaping host physiology, ecology and behavior (Coltman et al., 1999; Nunn and Altizer, 2006; Wood and Johnson, 2015). Specifically, intestinal helminths and protozoa may cause reduced energy uptake, pathological damage and decrease their hosts' reproductive success (Hudson et al., 1992, 1998; Delahay et al., 1995; Hillegass et al., 2010). In addition, they impact the host's immune system and alter gut microbial communities (Kreisinger et al., 2015; Reynolds et al., 2015), potentially increasing host susceptibility to bacteria or viruses (Cox, 2001; Ezenwa and Jolles, 2015).
Thus, natural selection should favor mechanisms that reduce exploitation by parasites, whereas parasites evolve mechanisms to circumvent these defense strategies and to secure their ecological niches in this evolutionary arms race. As a consequence, considerable differences in parasite species richness may be generated between different host species. Understanding the factors contributing to this variation in parasite diversity is relevant for fundamental questions in ecology (Poulin, 2004) as well as for species conservation (Kamiya et al., 2014). Host switching, intra-host speciation and loss of parasites over evolutionary time are the principal mechanisms involved, which can be influenced by host ecological characteristics like body size, longevity, diet, substrate use and social organization (Poulin, 2004). Furthermore, parasites may co-speciate with their hosts so that common ancestry is an additional important determinant of shared parasite communities between related species (Poulin, 2004). However, empirical support for the role of these factors is mixed and their relative importance is not well understood (Poulin, 2004; Kamiya et al., 2014; Morand, 2015). We therefore first discuss these factors in more detail.
First, because hosts are regarded as insular habitats for their parasites, it has been proposed that larger-bodied hosts provide more ecological niches for parasites and should therefore harbor a richer parasitic fauna (Kuris et al., 1980; Poulin, 1995; Gregory et al., 1996). Evidence for a correlation between host body size and intestinal parasite species richness has, for example, been found in tropical freshwater fish (Guégan et al., 1992) and ungulates (Ezenwa et al., 2006). In several meta-analyses across mammals, however, body mass was only a significant predictor of parasite richness if host phylogeny was not controlled for (Poulin, 2004). Likewise, in a meta-analysis across primates, body mass was only positively correlated with parasite richness in non-phylogenetic models (Vitone et al., 2004). Therefore, it appears that larger bodied mammals do harbor richer parasitic faunas, but this pattern may be explained mainly by inheritance of ancestral parasites through phylogeny (Poulin, 2004).
Second, longer-lived hosts may experience more transmission events throughout their lifetime and are therefore expected to harbor more parasite species (Morand and Harvey, 2000). However, if parasites contribute to host mortality, a negative association between parasite species richness and longevity seems more likely (Cooper et al., 2012). Additionally, longevity is often positively correlated with host body size, making it difficult to distinguish between these two factors (Poulin, 2004). Controlling for host body mass, Morand and Harvey (2000) found a negative correlation between longevity and parasite species richness across mammals. The same pattern was found in ungulates (Ezenwa et al., 2006; Cooper et al., 2012), whereas no association between longevity and parasite species richness was found in carnivores and primates (Cooper et al., 2012). Thus, evidence for a positive association between longevity and parasite species richness is weak and it seems more likely that parasite-induced mortality has selected for short life histories and fast reproduction in some taxa (Cooper et al., 2012).
Third, many helminths with complex life cycles are transmitted via ingestion of intermediate hosts (Guégan and Kennedy, 1993; Vitone et al., 2004). Host diet should therefore have a strong impact on parasite communities. Carnivorous and insectivorous mammals are expected to harbor more indirectly transmitted parasites relative to herbivorous species. In a study across primates, no support for this pattern was found, however (Vitone et al., 2004). Until now, diet as a predictor of parasite richness has been examined in too few comparative studies to allow drawing general conclusions across taxa (Kamiya et al., 2014).
Fourth, ranging behavior can influence exposure to fecal-orally transmitted parasites by mediating contact with feces (Freeland, 1980; Hart, 1990). More intensive ranging should lead to an increased probability of contact with fecally contaminated substrates, and indeed ranging intensity correlates with helminth richness in African ungulates (Ezenwa, 2004) and primates (Nunn and Dokey, 2006). Likewise, in carnivores, rodents and lagomorphs home range size was found to correlate negatively with helminth richness (Bordes et al., 2009), lending support to the fecal exposure hypothesis. In this context, arboreality has also been evoked as a parasite avoidance strategy, limiting contact with infectious parasite stages present in soil (Nunn et al., 2003; Loudon and Sauther, 2013). However, the only comparative study we are aware of that explicitly tested the influence of this behavioral trait on parasite species richness failed to find a significant effect (Nunn et al., 2003). Therefore, this hypothesis needs additional testing in future studies.
Finally, epidemiological theory predicts that transmission of parasites increases with animal density and, thus, represents one of the major disadvantages of gregariousness (Alexander, 1974; Anderson and May, 1982; Anderson et al., 1986; McCallum et al., 2001). Consequently, gregarious hosts should harbor more parasites than solitary species, and species richness should increase with group size. Indeed, an association of gregariousness with parasite diversity has been found in fish (Ranta, 1992), and gregarious African ungulates display both an increase in parasite prevalence and infection intensity as compared to solitary species (Ezenwa, 2004). Furthermore, a significant relationship between host density and parasite species richness has been found across primates (Nunn et al., 2003). However, a meta-analysis including a wide range of host species from mammals to insects revealed that effect sizes of group size on parasite species richness are generally low, except for animals living in large aggregations (Rifkin et al., 2012). In summary, there is overall support for an association between parasite risk and a gregarious lifestyle, but this relationship varies considerably across taxa (Rifkin et al., 2012).
Characteristics of six lemur species inhabiting Kirindy Forest, Madagascar.
Here, we examine the intestinal parasite communities of six sympatric lemur species in Kirindy Forest, western Madagascar. To our knowledge, this is the first systematic study comparing intestinal parasite communities of more than two sympatric lemur species. Although the number of studies investigating lemur parasitism has recently increased (e.g., Clough, 2010; Rasambainarivo et al., 2013; Larsen et al., 2016), knowledge on the parasitic fauna of these threatened primates still remains comparatively limited. The host species studied here share the same habitat and are thus theoretically exposed to the same set of parasites, but they differ in their degree of phylogenetic relatedness, body mass, life histories, diet and social organization, as detailed in Table 1. Thus, variation in patterns of parasitism can be expected based on the hypotheses outlined above.
Four of the species studied (
All four cheirogaleid species are omnivores, consuming fruit, plant exudates
and invertebrates in varying proportions; Coquerel's dwarf lemurs
additionally prey on small vertebrates (Dammhahn and Kappeler, 2014). All
cheirogaleids forage solitarily but show differences in their degree of
association with conspecifics. The two mouse lemur species
(
The other two lemur species examined here, red-fronted lemurs
(Lemuridae:
The largest lemurs inhabiting Kirindy Forest, Verreaux's sifakas, are strictly diurnal. They are herbivorous, feeding mainly on leaves, but incorporate flowers and fruit into their diet based on seasonal availability (Norscia et al., 2006). Being vertical clingers and leapers, they rarely descend to the ground and do not drink from waterholes, but rather they rely entirely on the water content of their diet and on dew present on trees (Kappeler and Fichtel, 2012). Sifakas are characterized by a slower life history than members of Lemuridae (Richard et al., 1991).
Here, we report intestinal parasite richness and patterns of prevalence for these six lemur species as determined by fecal microscopy. Regarding animal diet, we expected omnivores to harbor more parasite species which can be transmitted via intermediate hosts than herbivores. We predicted that the two group-living lemur species would harbor more directly transmitted intestinal parasite species than those with a less cohesive social system, due to more opportunities for transmission events. Because Kirindy Forest is subject to pronounced seasonality, we also compared seasonal variation in parasite prevalence for the three species with the largest sample size, controlling for animal sex. We expected prevalence to be higher during the wet season than during the dry season because of better conditions for parasite survival in the environment during these months.
Kirindy Forest is located at approximately 44
All necessary research permits were obtained from the respective Malagasy and German authorities (Ministère des Eaux et Forêts of Madagascar; Commission ad hoc Flore et Faune (CAFF) of Madagascar; Centre National de Formation, d'Etudes et de Recherche en Environnement et Foresterie (CNFEREF); The Federal Agency for Nature Conservation of Germany). Regarding animal welfare, we followed the “Code of Best Practices for Field Primatology” of the International Primatological Society.
Fecal samples from six lemur species were collected in Kirindy Forest from 2006
to 2014 by various researchers. Fecal samples from cheirogaleids were
taken during animal handling or from traps following capture in Sherman or
Tomahawk live traps from 2010 to 2014 (Hämäläinen et al., 2015b;
Rakotoniaina et al., 2016). Fecal samples from
Fecal samples were stored in 10 % formalin until analysis. All fecal samples were processed using a modification of the formalin-ethyl acetate sedimentation technique, as described in Clough (2010). This technique is commonly used to recover helminth eggs from formalin-fixed fecal samples of wild primates (Muehlenbein and Watts, 2010; Pebsworth et al., 2012) and results in the sedimentation of eggs, larvae and protozoa on the bottom of the test tube during centrifugation (Ash and Orihel, 1987). Parasite stages were microscopically identified to genus level, if possible, based on morphological criteria following the key in Irwin and Raharison (2009). Seasonal prevalence was calculated as the number of individuals infected with a certain parasite, based on the microscopic results of all available samples per individual from that season.
To assess seasonal differences in prevalence, we constructed generalized
linear mixed models (GLMMs) with binomial error structure and logit link
function for the most prevalent parasites (i.e., with total prevalence across
years and seasons
Parasite morphotypes detected in six lemur species in Kirindy Forest, Madagascar. Morphotypes with a prevalence of more than 20 % are printed in bold. Morphotypes found in less than 1 % of all samples from a given species are not reported.
n.a.: morphotype cannot be identified to the family level;
Parasite morphotype sharing network of six sympatric lemur species at Kirindy Forest, Madagascar. Node size corresponds to the number of parasite morphotypes detected in a species, while line width reflects the number of shared morphotypes.
Sixteen unique helminth egg morphotypes and three different protozoan
morphotypes were detected in lemur fecal samples. A summary of all
morphotypes detected per host species is presented in Table 2. To exclude
spurious parasites, we only report morphotypes that were present in more
than 1 % of samples from a given species.
In all four cheirogaleids, the most prevalent parasites were
Seasonal prevalence for
Sex also influenced prevalence patterns in
Seasonal prevalence of intestinal parasites for three sympatric lemur species at Kirindy Forest, Madagascar, for the year 2013.
Results of GLMMs testing the influence of sex and season on the most
prevalent parasite infections in
Characterizing and comparing the parasitic fauna of different wildlife hosts sharing the same habitat can provide insights into the mechanisms underlying variation in parasitism, as well as the role of parasites as possible conservation threats. Here, we provide information on the intestinal parasite communities of six of the eight sympatric lemur species which co-occur in Kirindy Forest, Madagascar. These host species represent three lemur families and include the smallest extant primate species, which is endemic to this area.
We detected a total of 16 different intestinal parasite morphotypes based on
fecal microscopy. The most intensively sampled host species, the gray mouse
lemur (
It has to be kept in mind that sample size was very limited for
The observed infection patterns indicate that, in addition to phylogeny,
host diet may play a role in shaping parasite assemblages in this system. As
expected, more indirectly transmitted parasites occurred in the omnivorous
cheirogaleids as compared to the two herbivorous species. All cheirogaleids
studied here supplement their diet with insects. While the exact life cycles
and transmission pathways of lemur parasites are unknown (Irwin and
Raharison, 2009), evidence from similar parasites of domestic species
suggests that insects serve as intermediate hosts for two of the most
prevalent parasites in cheirogaleids, namely
Only 2 of 10 parasites harbored by the mainly frugivorous
We found no indication for host body mass, longevity or social system as a
determinant of intestinal parasite richness in this community. Contrary to
the hypotheses that parasite richness should increase with host body mass
and age, one of the smallest and shortest-lived species,
While both Vitone et al. (2004) and Nunn et al. (2003) report a positive association between animal density and parasite richness, we found no clear pattern regarding the influence of social system on infection patterns. Contrary to our prediction, cheirogaleids, which live solitarily or in dispersed social systems, did not harbor fewer directly transmitted parasites than the two group-living species in terms of species diversity. However, prevalence of directly transmitted parasites was lower in cheirogaleids than in the two group-living species.
There was a striking difference in intestinal parasite diversity between the
two group-living species. As mentioned above,
We investigated the influence of season and sex on infection status with the
most prevalent parasites in a subset of three species, for which a
sufficient sample size was available. We found statistically significant
effects of season on infection patterns in
All parasites that showed a significant seasonal difference in prevalence
(
Furthermore, both
Here, we have provided an overview of intestinal helminths and protozoa detected by fecal microscopy in six sympatric lemur species, which is a first step towards exploring the parasitic fauna of these animals from a community ecology and evolutionary perspective. The described patterns indicate that host phylogeny and diet may play an important role in shaping intestinal parasite assemblages in this system, whereas no indication was found for an effect of body mass or longevity. Regarding the effect of sociality, group-living lemurs harbored directly transmitted parasites at higher prevalence than solitary foragers but not at higher diversity. Effects of season and sex on parasite prevalence confirm the results of previous studies, with higher prevalence in the energetically demanding dry season and a male bias in parasitism.
Despite these important insights, many gaps in our knowledge still remain,
e.g., regarding delimitation of cryptic species with the same egg morphotype,
parasite life cycles, pathogenic potential and fitness consequences. While
sampling of
Madagascar is considered a hotspot of biodiversity and lemurs are regarded as the most threatened group of mammals globally, due to intense habitat destruction and human encroachment (Schwitzer et al., 2014). However, information on lemur parasites still remains limited despite their potential relevance for lemur conservation. To date, the pathogenic potential of lemur parasites can only be inferred from related, better studied parasites of domestic animals. For many species, the exact life cycles and location of the different parasite stages within the host remain unknown (Irwin and Raharison, 2009). Necropsies of wild lemurs have been conducted only rarely, as animals are rarely found dead, e.g., due to high predation pressure. Nonetheless, there is a need to identify which parasites can be potentially more harmful than others to evaluate their impact on fitness and their conservation relevance.
Studying natural variation in parasitism may also shed light on which lemur
species may be most at risk of acquiring introduced parasites. For example,
the zoonotic protozoan parasite
Despite the remaining gaps in our knowledge, this long-term field study continues to provide the unique opportunity of studying host–parasite relationships in a natural setting. For example, repeated sampling of individuals over their life span allows addressing questions related to immunosenescence and fitness outcomes. Hämäläinen et al. (2015b) were able to show a within-individual decline in parasite infections of aging gray mouse lemurs, for example, indicating acquired immunity by older animals rather than immunosenescence. Finally, comparison of the parasitic faunas of the same species assemblages in multiple study areas, which differ for example in the amount of anthropogenic disturbance, can shed light on the impact of environmental factors on animal health and fitness. This information is crucial to assess the coping capacity of populations in light of increasing habitat disturbance and climate change.
All raw data have been stored in the data bank of the Behavioral Ecology and Sociobiology Unit of the German Primate Center and are available upon request.
We thank the team of the Kirindy field station, especially Rodin Rasoloarison and Léonard Razafimanantsoa, and the Malagasy Ministère de l'Environnement et des Eaux et Forêts, the Département Biologie Animale de l'Université d'Antananarivo, and the Centre National de Formation, d'Etudes et de Recherche en Environnement et Foresterie for supporting and authorizing our long-term research in Kirindy. Tiana Andrianjanahary, Mamy Razafindrasamba and Jean-Pierre Ratolojanahary assisted in animal capture and sample collection. The authors thank the technicians at the Institut Pasteur of Madagascar for analyzing a part of the samples and Josué H. Rakotoniaina, Eva Pechouskova and Cornelia Kraus for sharing unpublished data. Peter M. Kappeler is particularly grateful to Franz-Josef Kaup for decades of shared passionate disgust of ticks and wishes “Allzeit Glück auf!” for his retirement. This research was funded by the Deutsche Forschungsgemeinschaft (Ka 1082/29-1) and the German Primate Center and has profited from discussions in the research group “Sociality and Health in Primates” (FOR 2136). Edited by: K. Mätz-Rensing Reviewed by: one anonymous referee