Introduction
The major climatic factor influencing ecological systems in the Neotropics is seasonal variation between dry and rainy periods. Changes in the amount of rain and in duration of the rainy period can affect patterns of infection spread and persistence (see Altizer et al., Reference Altizer, Dobson, Hosseini, Hudson, Pascual and Rohani2006). Therefore, parasitic interactions involving Neotropical species are expected to change over time in response to periodic variation in rainfall, which can, in turn, result in seasonal patterns of infection. Lizards are ectotherms, thus adjusting their activity patterns and behaviours according to environmental conditions (e.g. Hatano et al., Reference Hatano, Vrcibradic, Galdino, Cunha-Barros, Rocha and Van Sluys2001; Filogonio et al., Reference Filogonio, Del Lama, Machado, Drumond, Zanon, Mezzetti and Galdino2010), and so patterns of helminth infection can be expected to vary seasonally as well, reflecting the behavioural adjustments of these hosts (Ribas et al., Reference Ribas, Rocha, Teixeira-Filho and Vicente1995; Vrcibradic et al., Reference Vrcibradic, Rocha, Ribas and Vicente1999; Pereira et al., Reference Pereira, Sousa and Lima2012; Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014).
Lizards are important components of the life cycle of many species of helminths, serving as definitive or intermediate hosts (e.g. Ávila & Silva, Reference Ávila and Silva2010). The helminth fauna that parasitizes lizards is diverse and with varied patterns of infection. In this sense, helminth richness can vary geographically among populations (Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014; Galdino et al., Reference Galdino, Ávila, Bezerra, Passos, Melo and Zanchi-Silva2014), and changes in the composition of component communities can be unrelated to geographical distance among populations (Bezerra et al., Reference Bezerra, Pinheiro, Melo, Zanchi-Silva, Queiroz, Anjos, Harris and Borges-Nojosa2016). Additionally, some studies have shown divergent results when considering whether infection rates and parasite loads of helminths vary between sexes, or whether parasite load is related to host body size. Hence, information is still needed for a more complete understanding of the epidemiological and ecological patterns of helminth infection in lizards.
The genus Tropidurus is speciose, with 30 species (Uetz & Hošek, Reference Uetz and Hošek2016). The genus harbours a rich helminth fauna with nearly 30 different parasite species and with component communities hosting from 3 to 21 species (Ávila & Silva, Reference Ávila and Silva2010; Anjos et al., Reference Anjos, Ávila, Ribeiro, Almeida and Silva2012). Recently, there have been efforts to uncover the diversity and patterns of helminth infection of species of Tropidurus (e.g. Tropidurus itambere, Ávila et al., Reference Ávila, Cardoso, Oda and Silva2011; T. hygomi and T. psammonastes, Lambertz et al., Reference Lambertz, Kohlsdorf, Perry, Ávila and Silva2012; T. spinulosus, Lunaschi et al., Reference Lunaschi, Lamas and Drago2012; T. torquatus, Pereira et al., Reference Pereira, Sousa and Lima2012; T. oreadicus, Santos et al., Reference Santos, Melo, Nazaré, Furtado and Giese2013; T. hispidus and T. semitaeniatus, Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014); however, parasitological data are missing for approximately 60% of the species of the genus.
The occurrence of the lizard T. montanus is restricted to the rocky outcrop formations of the mountaintop habitats of the Serra do Espinhaço (Espinhaço mountain range) in South America (Rodrigues, Reference Rodrigues1987). To the best of our knowledge, information on parasitism of this species by helminths is lacking. The aim of the present study was to describe the helminth species composition and infection levels in the Neotropical lizard T. montanus, relative to seasonality, host sex and size.
Materials and methods
We conducted the study in the rocky outcrop formation at c.1460 m above mean sea level in the Serra da Piedade (Piedade mountain range; 19°49′S; 43°40′W), a branch of the Espinhaço Range, in the state of Minas Gerais, Brazil. High-elevation open habitats of the mountains from eastern Brazil (which include the Espinhaço Range and related branches) are considered as isolated insular environments that play a role in biogeographical processes of plant and animal species (Chaves et al., Reference Chaves, Freitas, Vasconcelos and Santos2015, Neves et al., Reference Neves, Barbieri, Pacheco, Resende, Braga, Azevedo, Fernandes and Fernandes2016). The mean annual temperature is 21°C and the mean annual rainfall averages 1650 mm. The region experiences a marked distinction between rainy (from October to March) and dry (from April to September) periods (Alvares et al., Reference Alvares, Stape, Sentelhas, Moraes and Sparovek2014).
Sampling of lizards took place during the rainy (December 2012) and dry months (June to August 2013). Lizards were sampled by performing visual encounter surveys throughout the period of activity of the species, and captured by noose or by shooting rubber bands. Captured lizards were killed by lethal injection of sodium thiopental, measured for body size (snout-to-vent length) with a Vernier caliper (nearest 0.1 mm), fixed and preserved following standard procedures, and deposited in the herpetological collection of the Museu de Ciências Naturais of Pontifícia Universidade Católica de Minas Gerais (MCNR 4893–4934; 5114–5145; 5159–5174), Belo Horizonte, Brazil.
Post-mortem examinations of the body cavity, digestive tract, liver and lungs were undertaken using a stereomicroscope. Nematodes were cleared with Aman's lactophenol (Andrade, Reference Andrade2000) and analysed using a computerized system for image analysis LAS 5.0 (Leica Application Suite), adapted to a DM 2500-Leica microscope with a differential interference contrast system (Leica, Wetzlar, Germany). All the parasitological terms used followed Bush et al. (Reference Bush, Lafferty, Lotz and Shostak1997). Worms were deposited in the helminthological collection of the Instituto de Biociências de Botucatu, Universidade Estadual Paulista (species batches: CHIBB 7861; CHIBB 7862; CHIBB 7863), Botucatu, Brazil.
Differences between the sexes in overall helminth prevalence were tested by using the binomial test for each of the periods (rainy and dry). The binomial test was also used to test for differences in prevalence between the two periods, considering all individuals in a period regardless of sex. To evaluate the effects of period (dry and rainy) and sex on the overall intensity of helminth infection we used a two-way analysis of variance (ANOVA). Effects of body size on intensity of infection were evaluated for the helminth species with higher prevalence by conducting a Generalized Linear Mixed Models analysis considering each individual as a random effect variable. In addition, we used a one-factor permutation test to evaluate the effect of period on infection intensity of the more prevalent helminth species (Hothorn et al., Reference Hothorn, Hornik, van de Wiel and Zeileis2008).
Results
The helminth component community of T. montanus (n = 80) was found to be composed of three species: Parapharyngodon alvarengai Freitas, 1957 (Pharyngodonidae) (prevalence = 59%; mean intensity of infection = 5.6 ± 5.1), found in both large and small intestines; Physaloptera sp. Rudolphi, 1819 (Physalopteridae) (prevalence = 12%; mean intensity of infection = 4.9 ± 8.2), found in the larval stage in the stomach and large intestine, and Strongyluris oscari Travassos, 1923 (Heterakidae) (prevalence = 44%; mean intensity of infection = 6.0 ± 7.2) found in lungs, large and small intestines. Therefore, P. alvarengai and S. oscari were the most prevalent nematodes found parasitizing individual lizards. Of the total of 80 lizards sampled, 64 were parasitized by at least one species, resulting in an overall prevalence of 80%. Regarding infracommunities, 64% of lizards were parasitized by a single parasite species, while 30% of the hosts were parasitized by two and 6% by three species. Nematode abundance averaged 7.4 ± 6.3. The intensities of infection by P. alvarengai and by S. oscari were not related to host body size (P = 0.07, n = 52 and P = 0.60, n = 50, respectively).
We sampled 17 males and 20 females of T. montanus in the rainy period and 21 males and 22 females in the dry period. In the dry period, 95% of males and 100% of females were found to harbour helminths, with no difference in overall prevalence between the sexes (P = 0.98). During the rainy period, 70% of males and 50% of females were found to be parasitized and there was no difference in prevalence between males and females for the rainy period (P = 0.34). The population of T. montanus had higher overall prevalence during the dry period (97%) than during the rainy period (59%) (P < 0.001). The overall intensity of helminth infection did not differ between seasons or between sexes (two-way ANOVA: F = 0.03, P = 0.85). The intensity of infection by P. alvarengai and S. oscari did not vary between dry and rainy periods (one-factor permutation test, Z = 1.52, P = 0.14 and Z = −1.18, P = 0.26, respectively).
Discussion
The nematode community parasitizing T. montanus was composed of three species. Of these, the nematode P. alvarengai (Pharyngodonidae) is known to infect other lizard species, including Ameiva ameiva (Padilha & Duarte, Reference Padilha and Duarte1979), Trachylepis atlantica (Ávila & Silva, Reference Ávila and Silva2010), Hemidactylus agrius (Anjos et al., Reference Anjos, Bezerra, Passos, Zanchi and Galdino2011), Urosaurus auriculatus (Goldberg & Bursey, Reference Goldberg and Bursey2012), Tropidurus hispidus (Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014; Galdino et al., Reference Galdino, Ávila, Bezerra, Passos, Melo and Zanchi-Silva2014) and Tropidurus semitaeniatus (Bezerra et al., Reference Bezerra, Ávila, Passos, Zanchi-Silva and Galdino2015). The nematode S. oscari, is considered to be a host generalist (i.e. parasitizing many host species), with a heteroxenic life cycle with arthropods as intermediate hosts (Barreto-Lima & Anjos, Reference Barreto-Lima and Anjos2014), and is a common parasite of lizards of the genus Tropidurus (Ávila & Silva, Reference Ávila and Silva2010), having been found in T. guarani, T. spinulosus, T. torquatus, T. melanopleurus and T. hispidus (Bursey & Goldberg, Reference Bursey and Goldberg2004; Ávila & Silva, Reference Ávila and Silva2010; Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014). Moreover, S. oscari is known to infect lizards of other taxa, such as Ameiva ameiva, Anolis fuscoauratus, A. punctatus, A. transversalis, Enyalius bilineatus, Eurolophosaurus nanuzae, Brasiliscincus agilis, Plica plica and P. umbra (Fontes et al., Reference Fontes, Vicente, Kiefer and Van Sluys2003; Ávila & Silva, Reference Ávila and Silva2010; Barreto-Lima & Anjos, Reference Barreto-Lima and Anjos2014). The third parasite species found, Physaloptera sp., is known to parasitize A. ameiva, Glaucomastix littoralis, Ameivula ocellifera, H. mabouia, B. agilis, Psychosaura macrorhyncha, Polychrus acutirostris, Tropidurus etheridgei, T. torquatus, T. hispidus, Salvator meriane and Tupinambis teguixin (Ávila & Silva, Reference Ávila and Silva2010; Ávila et al., Reference Ávila, Anjos, Ribeiro, Morais, Silva and Almeida2012; Pereira et al., Reference Pereira, Sousa and Lima2012). Therefore, the component community of helminths parasitizing the lizard T. montanus can be considered to be comprised of host generalist parasites, and our record extends hosts species for P. alvarengai and S. oscari.
The component community of parasites of T. montanus is species poor when compared to those found for other species of the genus (e.g. T. torquatus (Pereira et al., Reference Pereira, Sousa and Lima2012), T. hispidus (Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014; Galdino et al., Reference Galdino, Ávila, Bezerra, Passos, Melo and Zanchi-Silva2014) and T. semitaeniatus (Brito et al., Reference Brito, Ferreira, Ribeiro, Anjos, Almeida, Mesquita and Vasconcellos2014, Bezerra et al., Reference Bezerra, Ávila, Passos, Zanchi-Silva and Galdino2015)). The high-elevation formations of the mountains from eastern Brazil, such as the rocky outcrops from the highlands of the Espinhaço Range, are considered to be an archipelago of isolated insular mountaintop habitats (e.g. Chaves et al., Reference Chaves, Freitas, Vasconcelos and Santos2015). Therefore, the insularity of the mountaintop rocky outcrops of the Serra da Piedade is remarkable as this mountain is apart from the main Espinhaço Mountain Range where T. montanus is distributed. The helminth fauna of hosts inhabiting insular environments can be expected to be poorer than those parasitizing hosts on the mainland (e.g. Dobson et al., Reference Dobson, Pacala, Roughgarden, Carper and Harris1992). For example, the pattern of helminths infecting rodent species differed between insular and continental populations, with insular populations having lower helminth richness (Kuhnen et al., Reference Kuhnen, Graipel and Pinto2012). The same pattern seems to hold true for lizards, with species-poor helminth infracommunities being found on hosts from insular environments (Dobson et al., Reference Dobson, Pacala, Roughgarden, Carper and Harris1992; Martin & Roca, Reference Martin and Roca2005). Therefore, the insular nature of the sampled area might constrain the available pool of helminth species that can infect individuals of T. montanus.
We found no intersexual difference in overall parasite prevalence. Intersexual differences in parasite prevalence are generally related to distinct social roles of male and female lizards, which in turn are associated with unequal blood hormone levels (Fuxjager et al., Reference Fuxjager, Foufopoulos, Diaz-Uriarte and Marler2011; see also Anjos et al., Reference Anjos, Ávila, Ribeiro, Almeida and Silva2012). Males of T. montanus use larger home ranges than females (Galdino et al., in prep.), which is a proxy for different social roles between the sexes. Thus, one might expect that the use of larger areas by males might expose them to greater chances of infection, at least by P. alvarengai, a monoxenous parasite species. Therefore, our results cannot be explained by the different social role and/or space use of males and females of T. montanus. Concerning heteroxenous parasites, we regarded the similarities in prevalence between the sexes as being due to a broad diet overlap between males and females, as shown by Kiefer (Reference Kiefer1998). Therefore, the similarity in overall prevalence of S. oscari between the sexes might be related to males and females having the same dietary patterns.
We did not find any relationship between T. montanus body size and intensity of infection of either P. alvarengai or S. oscari. It is argued that hosts with a larger body size would provide more space for helminths to colonize, thereby leading to a positive relationship between the two variables (Poulin, Reference Poulin1997; Ribas et al., Reference Ribas, Rocha, Teixeira-Filho and Vicente1998). It is also suggested that changes in infection intensity with size will be related to ontogenetic changes in diet (Fontes et al., Reference Fontes, Vicente, Kiefer and Van Sluys2003). In the case of T. montanus, young and adult lizards have similar diets, and so the non-relationship between intensity of infection and lizard body size might be associated with ontogenetic conservatism in diet, which in turn might expose both young and adults to the same chances of infection. A relationship between lizard body size and intensity of infection was not found for other species of lizards (e.g. T. torquatus and Brasiliscincus (former Mabuya) agilis (Van Sluys et al., Reference Van Sluys, Rocha, Bergallo, Vrcibradic and Ribas1997), T. hispidus (Galdino et al., Reference Galdino, Ávila, Bezerra, Passos, Melo and Zanchi-Silva2014) and T. semitaeniatus (Bezerra et al., Reference Bezerra, Ávila, Passos, Zanchi-Silva and Galdino2015)), suggesting that, in general, there is no trend between body size and intensity of infection for lizards.
Our results indicated that some patterns of helminth infection in lizards may vary seasonally. We found that the proportion of infected hosts was higher during the dry period than during the rainy period. Seasonal variation in helminth infection patterns has also been found for the Neotropical T. torquatus, with larger overall intensity of infection during the dry period (Pereira et al., Reference Pereira, Sousa and Lima2012). In the case of T. torquatus, Pereira et al. (Reference Pereira, Sousa and Lima2012) suggested that interseasonal differences in overall intensity of infection might be related to the consumption of a plant species with anthelmintic compounds. Although T. montanus increases its consumption of plant material during the dry period (Kiefer, Reference Kiefer1998), we are not able to relate the observed seasonal variation in overall helminth intensity directly to plant ingestion. Alternatively, as the diet composition of T. montanus varies seasonally (Kiefer, Reference Kiefer1998), the observed change in overall prevalence in our study might be related to seasonal changes in the types of ingested food items.
Acknowledgements
We are grateful to the administrative staff of Santuário Estadual Nossa Senhora da Piedade for the permit to work in the area. We thank M.J. Goulart, C.M. de Oliveira, L.K. Pereira, L.H.A. Glauss and C.C. Lisboa for their kind help during the fieldwork. We thank E. Wild for the English language review. C.A.B.G. and L.B.N. thank Instituto Chico Mendes (ICMBio) for the permit to collect the animals.
Financial support
A.B.H.P.V. thanks the Programa de Educação Tutorial/Ministério da Educação/Secretaria de Ensino Superior for grant funding. L.A.A. is thankful to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, process no. 2012/20978-2) for grant funding. L.B.N. thanks Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG, processes CRA APQ-00683-12 and CRA APQ-02067-14); Fundo de Incentivo à Pesquisa (FIP/PUC Minas) and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, process 479457/2012-3) for financial support.
Conflict of interest
None.
Ethical standards
We followed the Guidelines for the Euthanasia of Animals (2013) of the American Veterinary Medical Association for euthanizing the lizards. The Instituto Chico Mendes de Conservação da Biodiversidade issued the permits (SisBio 35541 and 37266-3) to collect the animals.
