Introduction
Bats are the second most diverse group of mammals, with more than 1,500 species (Simmons and Cirranello Reference Simmons and Cirranello2026). They occur in almost all terrestrial ecosystems, with the greatest diversity occurring in tropical regions (Fenton and Ratcliffe Reference Fenton and Ratcliffe2010). Although bats exhibit a wide diversity of feeding habits (e.g., frugivorous, nectivorous, and sanguivorous), over two-thirds of bat species are insectivorous. Bats contribute to environmental stability by providing ecosystem services, such as pollination, seed dispersal, and insect pest control (Kunz et al. Reference Kunz, Braun, Bauer, Lobova and Fleming2011; Ramírez‐Fráncel et al. Reference Ramírez‐Fráncel, García‐Herrera, Losada‐Prado, Reinoso‐Flórez, Sánchez‐Hernández, Estrada‐Villegas, Lim and Guevara2022). However, little is known about the parasites harboured by bats.
Studies focusing on bat helminth communities remain limited compared with those focusing on other wild mammals, such as rodents (Lord et al. Reference Lord, Parker, Parker and Brooks2012). Bats represent an excellent model for parasitological studies due to their high population densities, broad geographical distribution, and dietary diversity (Morand et al. Reference Morand, Krasnov and Poulin2006). However, most research on bat helminths has been limited to reporting new host or locality records (Guzmán-Cornejo et al. Reference Guzmán-Cornejo, García-Prieto, Pérez-Ponce de León and Morales-Malacara2003; Martínez-Salazar et al. Reference Martínez-Salazar, Medina-Rodríguez, Rosas-Valdez, Del Real-Monroy and Falcón-Ordaz2020), describing new species (Tkach et al. Reference Tkach, Gasperetti, Fernandes, Carrión-Bonilla, Cook and Achatz2024), or compiling checklists (Jiménez et al. Reference Jiménez, Caspeta-Mandujano, Ramírez-Chávez, Ramírez-Díaz, Juárez-Urbina, Peralta-Rodríguez and Guerrero2017; Santos and Gibson Reference Santos and Gibson2015). In contrast, studies examining helminth community structure and the biotic and abiotic factors associated with the diversity of these endoparasites remain scarce (Salinas-Ramos et al. Reference Salinas-Ramos, Herrera, Hernández-Mena, Osorio-Sarabia and León-Règagnon2017).
The helminth fauna can be influenced directly or indirectly by host characteristics (Froy et al. Reference Froy, Sparks, Watt, Sinclair, Bach, Pilkington, Pemberton, McNeilly and Nussey2019; Wesołowska Reference Wesołowska2022), parasite traits (Parker et al. Reference Parker, Ball and Chubb2015), and seasonal variation (Brooks and Hoberg Reference Brooks and Hoberg2007). Factors such as host reproductive behaviour, parasite life cycle, and abiotic conditions (e.g., temperature and humidity) can affect the development and transmission of helminths (Salinas-Ramos et al. Reference Salinas-Ramos, Herrera, Hernández-Mena, Osorio-Sarabia and León-Règagnon2017). Several studies have emphasised the role of feeding habits in shaping helminth infections in bats, with insectivorous species harbouring particularly high helminth diversity (de Albuquerque et al. Reference de Albuquerque, Duarte, Silva, Lapera, Tebaldi and Lux-Hoppe2016; Milano Reference Milano2016).
Authors such as Lord et al. (Reference Lord, Parker, Parker and Brooks2012) have reported lower trematode abundance (e.g., Lecithodendrium linstowi and Prosthodendrium sp.) in males of pipistrelle bats Pipistrellus spp. compared with females in England. In contrast, Milano et al. (Reference Milano, González, Gomez-Muñoz and Colunga2020) found a higher prevalence in females and greater helminth abundance in males of Patagonian bonneted bats Eumops patagonicus from Argentina. Other host traits, such as age, have been evaluated less frequently. For example, a study by Guterres and Marques (Reference Guterres and Marques2020) found no significant differences in the abundance of helminths such as Urotrema scabridum and Tadaridanema delicatus between adults and juveniles of the Brazilian free-tailed bat Tadarida brasiliensis from Brazil.
Seasonal fluctuations in helminth infections in bats have also been documented. Nickel and Hansen (Reference Nickel and Hansen1967) reported higher abundance of helminth species (e.g., Plagiorchis vespertilionis) in bats (e.g., mouse-eared bats Myotis spp.) during autumn in the United States. In contrast, Lord et al. (Reference Lord, Parker, Parker and Brooks2012) observed that both the prevalence and abundance of helminths peaked at the beginning of summer in Pipistrellus spp. These studies show that the influence of biotic and abiotic factors can vary among localities and highlight the importance of ecological research for understanding the mechanisms underlying host-parasite interactions, particularly in the Neotropical region where such studies remain scarce.
In Mexico, the helminth fauna of many bat species remains largely undescribed, and few studies have examined the influence of biotic and abiotic factors on helminth infections (Clarke-Crespo et al. Reference Clarke-Crespo, Pérez-Ponce de León, Montiel-Ortega and Rubio-Godoy2017; Salinas-Ramos et al. Reference Salinas-Ramos, Herrera, Hernández-Mena, Osorio-Sarabia and León-Règagnon2017). Many bat species, including members of the family Molossidae, lack helminthological records and ecological assessments of their parasites. The broad-tailed bat Nyctinomops laticaudatus is one of the molossid species with the highest number of recorded helminths in Mexico, with 17 documented taxa (Moguel-Chin et al. Reference Moguel-Chin, Suárez-Galaz, Chan-Casanova, Concha-Guillermo, Tzec-Che, Torres, MacSwiney and Panti-May2025).
Nyctinomops laticaudatus is a complex of species of free-tailed bat distributed from the United States to northern Argentina (Moras et al. Reference Moras, Tavares, De Almeida, Dos Santos Júnior and Gregorin2026). This bat species exhibits chocolate brown coloration on the dorsum and a lighter coloration on the ventral surface, with no sexual dimorphism. Nyctinomops laticaudatus may form resident colonies throughout the year in stable numbers, although its population dynamics are complex. Its colonies range from 150 to more than 1,000 individuals in roosts such as caves (Avila-Flores et al. Reference Avila-Flores, Flores-Martínez and Ortega2002; Ortega et al. Reference Ortega, Hernández-Chávez, Rizo-Aguilar and Guerrero2010). This bat species feeds on insects, including moths (Lepidoptera), beetles (Coleoptera), and leafhoppers (Homoptera), which it captures during flight at high altitudes (up to thousands of metres above ground level) (Avila-Flores et al. Reference Avila-Flores, Flores-Martínez and Ortega2002; Sparks and Valdez Reference Sparks and Valdez2003). Due to these characteristics, N. laticaudatus is an appropriate model for ecological and parasitological studies on helminths. Therefore, in this study, we explored the effects of selected host attributes (sex, age, and reproductive condition) and environmental variables (locality, rainfall, temperature, and humidity) on the helminth fauna of two populations of N. laticaudatus.
Materials and methods
Study site
This study was conducted in two caves located in the state of Yucatán, southeastern Mexico: one in the municipality of Calcehtok (20°33′02.5′′ N, 89°54′44.4′′ W) with a separation of 68 km from the other cave in the municipality of Homún (20°44′48.1′′ N, 89°17′48.9′′ W). Calcehtok has a warm subhumid climate with summer rains, an average annual temperature of 28 °C, and annual mean precipitation of 444 mm. The locality lies on a plain, although a nearby hill range reaches an elevation of up to 100 m above sea level. The region’s vegetation pattern is mainly tropical deciduous forest (SEFOET 2024a). Other bat species recorded in the cave are Pteronotus fulvus, Pteronotus mesoamericanus, Pteronotus psilotis, Mormoops megalophylla, Natalus mexicanus, Peropteryx macrotis, Desmodus rotundus, Artibeus jamaicensis, and Glosophaga mutica. Homún also has a warm subhumid climate with summer rains, an average annual temperature of 25.5°C, and a mean annual precipitation of 1,200 mm. The area is located on a plain and is covered by secondary vegetation of tropical deciduous forest. In addition, underground water deposits known locally as ‘cenotes’ are present (SEFOET 2024b). The bats Molossus nigricans, A. jamaicensis, and P. macrotis also inhabit this cave.
Collection and examination of bats
In each cave, individuals of N. laticaudatus were captured bimonthly from January 2024 to May 2025. Following a previously described methodology (Moguel-Chin et al. Reference Moguel-Chin, Suárez-Galaz, Chan-Casanova, Concha-Guillermo, Tzec-Che, Torres, MacSwiney and Panti-May2025), bats were captured using a mist net placed at the cave entrances and subsequently transported to a laboratory. The bats were captured under permits from the Ministry of Environment and Natural Resources of Mexico (SEMARNAT) (SPARN/DGVS/00788/24 and SBRA/DGVS/02452/25). In the laboratory, bats were euthanized using isoflurane (Leary et al. Reference Leary, Underwood, Anthony, Cartner, Grandin, Greenacre, Gwaltney-Brant, McCrackin, Meyer, Miller, Shearer, Turner and Yanong2020), after which the gastrointestinal tract of each bat was dissected and examined for helminths under a stereomicroscope. Details of the morphological identification of helminths and the parasite collections where they were deposited are provided in Moguel-Chin et al. (Reference Moguel-Chin, Suárez-Galaz, Chan-Casanova, Concha-Guillermo, Tzec-Che, Torres, MacSwiney and Panti-May2025).
Host and environmental data
For each bat, sex, age, and reproductive condition were recorded. Age was determined based on the degree of ossification of the phalangeal epiphyses. Males with scrotal testes and females that were pregnant, lactating, post-lactating, or had an open vagina were classified as reproductive (Anthony Reference Anthony and Kunz1988; Ortega and Arita Reference Ortega and Arita1999).
Inside each cave, temperature (°C) and relative humidity (%) were recorded daily from January 2024 to May 2025 using a data logger (UNI-T UT330B). In addition, a data logger and a digital rain gauge with a self-emptying rain collector (AcuRite 02446M) were installed to record the temperature and relative humidity and the rainfall (mm), respectively, in a household in the locality closest to each cave (8.1 and 3.8 km from Calcehtok and Homún, respectively). During periods when on-site data could not be obtained, information from nearby weather stations of the National Water Commission of Mexico (CONAGUA) was used.
Data analysis
Prevalence, mean intensity, and mean abundance of infection for each helminth taxon were estimated following Bush et al. (Reference Bush, Lafferty, Lotz and Shostak1997). Ninety-five percent confidence intervals for these parameters were calculated according to Rózsa et al. (Reference Rózsa, Reiczigel and Majoros2000). Species accumulation curves were generated to assess sampling adequacy using EstimateS version 9.1 (Colwell Reference Colwell2019).
Generalised linear models (GLMs) were used to evaluate associations of the independent variables sex (male or female), age (adult or juvenile), reproductive condition (reproductive or non-reproductive), and locality (Calcehtok or Homún) with the dependent variables prevalence and abundance. Moreover, generalised linear mixed models (GLMMs) were fitted to evaluate associations of temperature, humidity, and rainfall with the prevalence and abundance of helminth taxa. For the GLMMs, the capture date was used as a random intercept. For environmental variables, the mean values for the month of capture were used. Only environmental data collected outside the caves were considered, as measurements obtained inside the caves showed minimal variation in temperature (Calcehtok: 25.6–27 °C; Homún: 23.2–27 °C) and humidity (Calcehtok: 99–100%; Homún: 94–100%) (Supplementary Figures S1–S2). These analyses were performed only on helminth species with prevalences higher than 10% (Panti-May et al. Reference Panti-May, Palomo-Arjona, Gurubel-González, Barrientos-Medina, Digiani, Robles, Hernández-Betancourt and Machain-Williams2019). Additionally, species within the same genus (Vampirolepis and Urotrema) were analysed together. The statistical models (GLMs and GLMMs) for prevalence were fitted using binomial error distributions, whereas those for abundance were fitted using quasi-Poisson or Poisson error distributions. Univariate analyses were performed between the dependent variables and their predictors to quantify the strength of association and identify variables likely to be included in the multivariate GLMs and GLMMs (p < 0.15) (Thrusfield et al. Reference Thrusfield, Christley, Brown, Diggle, French, Howe, Kelly, O’Connor, Sargeant and Wood2018). Model selection was based on the Akaike information criterion (AIC) for models with binomial or Poisson distributions and the quasi-Akaike information criterion (QAIC) for models with quasi-Poisson distributions; the model with the lowest AIC or QAIC value was considered the best fit. Chi-squared tests were used to compare model deviances and confirm selection of the final model, and the variance inflation factor (VIF) was used to detect multicollinearity among variables included in the models. Subsequently, estimates, exp(B) values, 95% confidence intervals (CIs), and p values were calculated. For models that included host age, Firth’s penalised-likelihood logistic regression was performed as a sensitivity analysis to verify model stability given the strong class imbalance between age groups. For graphical representation of the relationship between environmental variables (e.g., rainfall) and helminth abundance, abundance values were log-transformed. All analyses were conducted in R version 4.3.0 (R Core Team 2021) using the packages ‘lme4’ (Bates et al. Reference Bates, Mächler, Bolker and Walker2015), ‘ggplot2’ (Wickham et al. Reference Wickham, Chang, Henry, Pedersen, Takahashi, Wilke, Woo, Yutani, Dunnington and van den Brand2025), ‘car’ (Fox and Weisberg Reference Fox and Weisberg2019), and ‘effects’ (Fox et al. Reference Fox, Weisberg, Price, Friendly, Hong, Andersen, Firth and Taylor2025).
Results
Helminth fauna of collected bats
A total of 366 bats were examined, including 197 males and 169 females. Of these bats, 346 were adults and 20 were juveniles; 167 were reproductive and 199 were non-reproductive; and 182 were captured in Calcehtok and 184 in Homún. In total, 17 helminth taxa were identified: the trematodes Brachylecithum rileyi, Euparadistomum sp., Limatulum nanum, Phaneropsolidae gen. sp., Ochoterenatrema sp., Urotrema minuta, and Urotrema sp.; the cestodes Vampirolepis cf. christensoni and V. cf. phyllostomi; the nematodes Aonchotheca pulchra, Anoplostrongylus allami, Physaloptera sp., Physocephalus sexalatus, Spirura mexicana, and Litomosoides sp.; and the acanthocephalans Mediorhynchus sp. and Oncicola sp. The nematode A. allami showed the highest prevalence and mean intensity of infection (Table 1).
Prevalence (P), mean intensity (MI), mean abundance (MA), 95% confidence intervals (CIs), and infection sites for helminths of N. laticaudatus (n = 366)
Table 1. Long description
The table contains five columns: Helminth species, P (percent), M I (C I), M A (C I), and Infection site.
Under Trematoda:
* Brachylecithum rileyi: P 27.9 (23.3–32.8); M I 6.5 (5.2–8.4); M A 1.8 (1.3–2.5); Site L, G.
* Euparadistomum sp.: P 1.1 (0.3–2.8); M I 1.5 (1–1.7); M A 0.01 (0.002–0.03); Site G.
* Limatulum nanum: P 19.1 (15.2–23.5); M I 1.6 (1.4–2); M A 0.3 (0.2–0.4); Site E, I.
* Phaneropsolidae gen. sp.: P 3.6 (1.9–6); M I 1 (1); M A 0.03 (0.01–0.05); Site E.
* Ochoterenatrema sp.: P 12.8 (9.6–16.7); M I 8.3 (5.7–14.8); M A 1.0 (0.6–2.1); Site I.
* Urotrema spp.: P 32.8 (28–37.9); M I 2.6 (2.2–3.2); M A 0.8 (0.6–1.1); Site I.
Under Cestoda:
* Vampirolepis spp.: P 44.3 (39.1–49.5); M I 2.5 (2.1–3.3); M A 1.1 (0.9–1.5); Site I.
Under Nematoda:
* Aonchotheca pulchra: P 49.7 (44.5–55); M I 2.7 (2.4–3.1); M A 1.3 (1.1–1.6); Site E.
* Anoplostrongylus allami: P 87.4 (83.6–90.6); M I 12.3 (11.2–13.9); M A 10.8 (9.6–12.2); Site I.
* Physaloptera sp.: P 2.7 (1.6–5.0); M I 2.7 (1.4–4.9); M A 0.07 (0.03–0.18); Site E.
* Physocephalus sexalatus: P 3.0 (1.6–5.3); M I 1.5 (1.1–1.9); M A 0.04 (0.02–0.07); Site E.
* Spirura mexicana: P 3.0 (1.6–5.3); M I 1.2 (1–1.8); M A 0.03 (0.01–0.07); Site E S.
* Litomosoides sp.: P 1.9 (0.8–3.9); M I 1 (1); M A 0.01 (0.005–0.03); Site T C, M.
Under Acanthocephala:
* Mediorhynchus sp.: P 0.3 (0–1.5); M I 1 (1); M A 0.002 (0–0.008); Site M.
* Oncicola sp.: P 0.3 (0–1.5); M I 1 (1); M A 0.002 (0–0.008); Site H.
Infection site key: I is intestine; E is stomach; L is liver; G is gallbladder; E S is oesophagus; T C is thoracic cavity; M is mesentery.
I: intestine; E: stomach; L: liver; G: gallbladder; ES: oesophagus; TC: thoracic cavity; M: mesentery.
In total, 345 bats were infected with helminths. Among these, 291 (79.5%) exhibited coinfections with two to eight helminth taxa, although most individuals were infected with two or three taxa (n = 80 for each category). The parasite species accumulation curve for N. laticaudatus increased sharply at first and reached a plateau after approximately 100 and 120 bats were examined in Calcehtok and Homún, respectively, indicating a sufficient sample size for the observed helminth (Figure 1).
Species accumulation curve of helminths of Nyctinomops laticaudatus from Calcehtok (Ca) and Homún (Ho) from January 2024 to May 2025.
Figure 1. Long description
The x-axis is labeled Number of bats examined, ranging from 0 to approximately 180. The y-axis is labeled Number of helminths species, ranging from 0 to 16. Two curves represent the data:
* The upper curve, labeled C a, is blue. It shows a steep initial increase in species count, reaching an asymptote of 16 species after approximately 100 bats are examined.
* The lower curve, labeled H o, is green. It follows a similar trajectory but remains below the C a curve, reaching an asymptote of 15 species at the end of the x-axis.
Both curves include vertical gray error bars representing confidence intervals. These bars are widest at the beginning of the sampling (left side) and narrow significantly as the curves flatten out toward the right, indicating increased statistical certainty as more bats are examined.
Helminth infection with respect to host and environmental factors
GLMs and GLMMs were performed for B. rileyi, L. nanum, Ochoterenatrema sp., Urotrema spp., Vampirolepis spp., A. pulchra, and A. allami. All the most parsimonious models are summarised in Table 2. According to the best GLMs, the prevalence of B. rileyi was associated with sex and locality. Females (exp(B) = 1.499, 95% CI = 1.180–1.913, p < 0.001) and bats from Calcehtok had a higher chance of being infected (exp(B) = 1.769, 95% CI = 1.387–2.278, p < 0.001) with B. rileyi (Figure 2A–B). For L. nanum, individuals from Calcehtok had a higher chance of infection (exp(B) = 1.413, 95% CI = 1.007–1.983, p = 0.045); furthermore, for each 1 mm of rainfall, the probability of infection decreased by 1.1% (exp(B) = 0.989, 95% CI = 0.981–0.997, p = 0.006) (Figure 2C–D).
Best generalised linear models (GLMs) and generalised linear mixed models (GLMMs) for helminth prevalence (binomial distribution) and abundance (Poisson and quasi-Poisson distributions)
Table 2. Long description
The table is divided into two main sections.
Section 1: Models for prevalence.
* Brachylecithum rileyi: Sex plus Locality, G L M, 405.2.
* Limatulum nanum: Locality plus Rainfall, G L M M, 345.9.
* Ochoterenatrema species: Rainfall or Sex plus Locality, G L M M, 242.8.
* Urotrema species: Locality plus Age, G L M, 461.2.
* Vampirolepis species: Locality plus Reproductive condition, G L M, 482.3.
* Aonchotheca pulchra: Rainfall or Sex plus Locality, G L M M, 469.
Section 2: Models for abundance.
* Brachylecithum rileyi: Sex plus Reproductive condition, G L M, 165.
* Limatulum nanum: Locality plus Rainfall, G L M M, 490.9.
* Ochoterenatrema species: Locality plus Rainfall, G L M M, 472.8.
* Urotrema species: Rainfall or Sex plus Locality, G L M M, 857.3.
* Vampirolepis species: Locality plus Rainfall plus Temperature, G L M M, 994.3.
* Aonchotheca pulchra: Locality plus Rainfall, G L M M, 1104.
Footnote: A I C stands for Akaike information criterion and Q A I C stands for quasi-Akaike information criterion.
AIC: Akaike information criterion; QAIC: quasi-Akaike information criterion.
Associations of helminth prevalence in Nyctinomops laticaudatus with host characteristics and environmental variables modelled using GLMs or GLMMs with binomial distributions. A–B. Association of Brachylecithum rileyi prevalence with sex and locality; C–D. Association of Limatulum nanum prevalence with locality and rainfall; E–F. Association of Ochoterenatrema sp. prevalence with sex, locality, and rainfall; G–H. Association of Urotrema spp. prevalence with age and locality; I–J. Association of Vampirolepis spp. prevalence with reproductive condition and locality; K–L. Association of Aonchotheca pulchra prevalence with sex, locality, and rainfall.
Figure 2. Long description
A multi-panel figure containing 12 graphs labeled A through L.
Panel A. Line graph of Brachylecithum rileyi prevalence on the Y axis against Sex on the X axis. Prevalence decreases from approximately 0.35 in females to 0.20 in males.
Panel B. Line graph of B. rileyi prevalence against Locality. Prevalence decreases from 0.38 in Calcehtok to 0.17 in Homún.
Panel C. Line graph of Limatulum nanum prevalence against Locality. Prevalence decreases from 0.23 in Calcehtok to 0.14 in Homún.
Panel D. Scatter plot with a regression line showing L. nanum prevalence against Rainfall in millimeters. The curve shows a slight non-linear decrease from 0.20 to near 0.05 as rainfall increases to 150 millimeters.
Panel E. Line graph of Ochoterenatrema sp. prevalence against Locality. Prevalence drops sharply from 0.22 in Calcehtok to 0.03 in Homún.
Panel F. Scatter plot with two regression lines for Ochoterenatrema sp. prevalence against Rainfall. The solid line for females shows a steep increase from 0.15 to 0.60. The dashed line for males shows a shallower increase from 0.15 to 0.25.
Panel G. Line graph of Urotrema spp. prevalence against Age. Prevalence decreases from 0.34 in adults to 0.14 in juveniles.
Panel H. Line graph of Urotrema spp. prevalence against Locality. Prevalence decreases from 0.38 in Calcehtok to 0.27 in Homún.
Panel I. Line graph of Vampirolepis spp. prevalence against Reproductive condition. Prevalence increases from 0.35 in reproductive bats to 0.52 in non-reproductive bats.
Panel J. Line graph of Vampirolepis spp. prevalence against Locality. Prevalence decreases from 0.54 in Calcehtok to 0.34 in Homún.
Panel K. Line graph of Aonchotheca pulchra prevalence against Locality. Prevalence decreases from 0.62 in Calcehtok to 0.37 in Homún.
Panel L. Scatter plot with two regression lines for A. pulchra prevalence against Rainfall. Both the solid female line and dashed male line show a downward trend as rainfall increases, with females maintaining higher prevalence overall.
For Ochoterenatrema sp., a higher chance of infection was found in bats from Calcehtok (exp(B) = 2.719, 95% CI = 1.769–4.181, p < 0.001). Infection with this trematode was positively associated with rainfall; for each additional 1 mm of rainfall, the probability of infection increased by 0.8% (exp(B) = 1.008, 95% CI = 1.003–1.01, p = 0.002), particularly in females (exp(B) = 1.004, 95% CI = 1.001–1.009, p = 0.020) (Figure 2E–F).
The analysis of Urotrema spp. infection showed that the probability of infection was associated with age and locality. Age showed a marginal tendency towards a higher probability of infection in adults (exp(B) = 1.816, 95% CI = 1.034–3.800, p = 0.062). Firth’s penalized regression yielded consistent results (OR = 1.71, 95% CI = 0.95–3.08, p = 0.050), reinforcing the observed trend. Furthermore, bats from Calcehtok had a higher chance of infection (exp(B) = 1.265, 95% CI = 1.014–1.582, p = 0.037) (Figure 2G–H).
The best model for Vampirolepis infection included reproductive condition and locality as predictors of prevalence. Reproductive bats had a lower probability of infection with these cestodes (exp(B) = 0.714, 95% CI = 0.574–0.887, p = 0.002), whereas bats from Calcehtok had a higher chance of infection (exp(B) = 1.487, 95% CI = 1.201–1.847, p < 0.001) (Figure 2I–J).
Finally, for A. pulchra, a higher chance of infection was found in bats from Calcehtok (exp(B) = 1.740, 95% CI = 1.256–2.410, p < 0.001); furthermore, each 1 mm of rainfall reduced the probability of infection by 0.8% (exp(B) = 0.991, 95% CI = 0.985–0.998, p = 0.010), with a marginally significant interaction between rainfall and host sex (exp(B) = 1.003, 95% CI = 0.999–1.006, p = 0.068) (Figure 2K–L). For A. allami, no variables were associated with the probability of infection.
The best model for the abundance of B. rileyi infection included sex and reproductive condition. Host sex showed a marginal effect, with females exhibiting higher abundance (exp(B) = 1.401, 95% CI = 1.007–2.001, p = 0.053), whereas reproductive bats showed a marginal tendency toward lower abundance (exp(B) = 0.721, 95% CI = 0.490–1.033, p = 0.085) (Figure 3A–B). For L. nanum, infection was associated with locality and rainfall. Higher abundance was observed in bats from Calcehtok (exp(B) = 1.442, 95% CI = 1.067–1.950, p = 0.017); additionally, for each 1 mm of rainfall, parasite abundance decreased by 0.008 (95% CI = −0.015 to −0.001, p = 0.013) (Figure 3C–D).
Relationships of helminth abundance in Nyctinomops laticaudatus with host characteristics and environmental variables modelled using GLMs with quasi-Poisson distributions or GLMMs with Poisson distributions. A–B. Association of Brachylecithum rileyi abundance with sex and reproductive condition; C–D. Association of Limatulum nanum abundance with locality and rainfall; E–F. Association of Ochoterenatrema sp. abundance with locality and rainfall; G–H. Association of Urotrema spp. abundance with sex, locality, and rainfall; I–K. Association of Vampirolepis spp. abundance with locality, rainfall, and temperature; L–M. Association of Aonchotheca pulchra abundance with locality and rainfall.
Figure 3. Long description
A multi-panel figure containing 13 graphs labeled A through M.
Panel A. Line graph of Brachylecithum rileyi abundance on the y axis against sex on the x axis. Abundance decreases from female to male.
Panel B. Line graph of B. rileyi abundance against reproductive condition. Abundance increases from reproductive to non-reproductive individuals.
Panel C. Line graph of Limatulum nanum abundance against locality. Abundance is higher in Calcehtok than in Homún.
Panel D. Scatter plot with a regression line showing a slight linear decrease in the log of L. nanum abundance as rainfall in millimeters increases from 0 to 150.
Panel E. Line graph of Ochoterenatrema sp. abundance against locality. Abundance is higher in Calcehtok than in Homún.
Panel F. Scatter plot showing a slight linear increase in the log of Ochoterenatrema sp. abundance as rainfall increases.
Panel G. Line graph of Urotrema spp. abundance against locality. Abundance is higher in Calcehtok than in Homún.
Panel H. Scatter plot of the log of Urotrema spp. abundance against rainfall. A solid line for females shows an exponential increase, while a dashed line for males remains nearly flat.
Panel I. Line graph of Vampirolepis spp. abundance against locality. Abundance is higher in Calcehtok than in Homún.
Panel J. Scatter plot showing a gradual linear decrease in the log of Vampirolepis spp. abundance as rainfall increases.
Panel K. Scatter plot showing a gradual linear decrease in the log of Vampirolepis spp. abundance as temperature in degrees Celsius increases from 25 to 35.
Panel L. Line graph of Aonchotheca pulchra abundance against locality. Abundance is significantly higher in Calcehtok than in Homún.
Panel M. Scatter plot showing a linear decrease in the log of A. pulchra abundance as rainfall increases.
For Ochoterenatrema sp., higher abundance was observed in individuals from Calcehtok (exp(B) = 3.329, 95% CI = 1.376–8.053, p = 0.007). Furthermore, the relationship with rainfall showed a marginal effect: for each 1 mm of rainfall, the abundance increased by 0.011 (95% CI = −0.001 to 0.024, p = 0.063) (Figure 3E–F). In the case of Urotrema, bats from Calcehtok also exhibited higher infection abundance (exp(B) = 1.334, 95% CI = 1.058–1.683, p = 0.014). Moreover, abundance was positively associated with rainfall, increasing by 0.004 for each additional mm of precipitation (95% CI = 0.001–0.008, p = 0.027), particularly in females (exp(B) = 1.005, 95% CI = 1.002–1.008, p < 0.001) (Figure 3G–H).
For Vampirolepis, the most parsimonious model included locality, rainfall, and temperature. Higher infection values were recorded in bats from Calcehtok (exp(B) = 1.523, 95% CI = 1.240–1.871, p < 0.001), whereas for each 1 mm of rainfall the infection abundance decreased by 0.005 (95% CI = −0.009 to −0.001, p = 0.005) and for each 1 °C increase in temperature, the abundance decreased by 0.089 (95% CI = −0.151 to −0.027, p = 0.004) (Figure 3I–K). In the case of A. pulchra, higher infection abundance was observed in bats from Calcehtok (exp(B) = 1.736, 95% CI = 1.381–2.183, p < 0.001), additionally, rainfall exhibited a negative association with the abundance, with abundance decreasing by 0.005 per mm of rainfall (95% CI = −0.010 to −0.001, p = 0.012) (Figure 3L–M). For A. allami, no variables were associated with the abundance of the nematode.
Discussion
Nyctinomops laticaudatus exhibited a high diversity of helminth species, with trematodes representing the richest group. This may be explained by the insectivorous diet of N. laticaudatus (Avila-Flores et al. Reference Avila-Flores, Flores-Martínez and Ortega2002), which exposes it to potential intermediate hosts of helminths. The available information suggests that arthropods from different orders may harbour the infective stage for the helminth species identified in N. laticaudatus. For example, lecithodendriid trematodes such as Urotrema spp. and Ochoterenatrema sp. use insects from the orders Hemiptera and Diptera as second intermediate hosts (Lotz Reference Lotz, Gardner and Gardner2024), whereas hymenolepidid cestodes such as Vampirolepis spp. have coleopterans as intermediate hosts (Shostak Reference Shostak2014). In contrast, the life cycle of some species, such as A. pulchra, remains unclear. Nematodes of the genus Aonchotheca generally exhibit indirect life cycles, with oligochaetes serving as the typical intermediate hosts; however, for species such as A. putorii, transmission has been suggested to occur through both direct and indirect routes (Debenedetti et al. Reference Debenedetti, Sáez-Durán, Sainz-Elipe, Galán-Puchades and Fuentes2014; Moravec et al. Reference Moravec, Prokopic and Shlikas1987). Furthermore, Krasnov et al. (Reference Krasnov, Junker, Wood, Ueckermann, Venter, van der Mescht, Heyne and Jacobs2020) proposed that Aonchotheca species infecting some insectivorous bats (Miniopterus natalensis) most likely have a direct life cycle. Consequently, in the present study, a direct life cycle was assumed for A. pulchra.
This extensive study provides insight into the diversity of helminths that coexist in N. laticaudatus. The high coinfection rate observed in N. laticaudatus reflects a common pattern in wildlife, where the hosts typically harbour multiple parasite species (Bordes and Morand Reference Bordes and Morand2011). However, the fact that most species found exhibit low mean intensities (1–8.3) may also indicate that N. laticaudatus hosts can limit helminth infection, thereby preventing them from reaching higher intensity levels (Beldomenico et al. Reference Beldomenico, Telfer, Gebert, Lukomski, Bennett and Begon2009). Furthermore, these low values may indicate mutual regulation among helminths, given that during coinfections the populations of some species can be limited by those of other species because of factors such as competition for resources in their hosts (Poulin Reference Poulin2001).
Intrinsic (e.g., diet) and extrinsic factors (e.g., regional climate) are associated with host susceptibility to infection by helminths (Behnke Reference Behnke2008). Our results show that some intrinsic factors, such as sex, were associated with helminth prevalence and abundance in N. laticaudatus. Males were less frequently infected and showed a marginal trend toward lower B. rileyi abundance, whereas the effect of rainfall on the chance of infection by Ochoterenatrema sp., Urotrema spp., and A. pulchra differed between sexes. Lower prevalence and abundance of helminths in male bats have been previously reported (Lord et al. Reference Lord, Parker, Parker and Brooks2012; Milano et al. Reference Milano, González, Gomez-Muñoz and Colunga2020). In molossids, sex-based segregation of foraging areas may influence the consumption of certain prey types that serve as potential intermediate hosts (Bowles et al. Reference Bowles, Heideman and Erickson1990), which in turn could lead to differences in prevalence and abundance between sexes for B. rileyi, Ochoterenatrema sp., and Urotrema spp. Additionally, physiological and behavioural sex differences (e.g., hormonal variations) may promote differences in infection patterns between males and females (Szentiványi et al. Reference Szentiványi, Vincze and Estók2017; Wesołowska Reference Wesołowska2022), particularly under changes in rainfall, as found for A. pulchra.
Bat age had a marginal effect on infection of Urotrema spp. This statistical trend should be interpreted with caution due to the severe class imbalance between age groups in our sample, which resulted in wide confidence intervals and reduced statistical power. Nonetheless, from an ecological perspective, this potential variation could be consistent with differences in feeding ecology. In molossid bats, adults have greater foraging success, cover larger areas, and spend more time foraging due to their superior flight capabilities; consequently, adults may consume a greater volume of certain groups of insects than juveniles (Hernández Reference Hernández2018; Lee Reference Lee1999), which may act as intermediate hosts of Urotrema spp., such as Hemiptera (Lotz Reference Lotz, Gardner and Gardner2024). These differences in foraging ecology could potentially contribute to the observed tendency towards a higher probability of infection in adult bats.
Reproductive condition was associated with the prevalence of Vampirolepis spp. and the abundance of B. rileyi. The higher prevalence of Vampirolepis spp. and the marginally higher abundance of B. rileyi in non-reproductive bats may be related to dietary differences. Insectivorous bats can exhibit changes in prey consumption according to reproductive stage, with different insect groups consumed by reproductive and non-reproductive individuals depending on energetic demands (Arango-Diago et al. Reference Arango-Diago, Castillo-Figueroa, Albarracín-Caro and Pérez-Torres2020; Kunz et al. Reference Kunz, Whitaker and Wadanoli1995). Non-reproductive molossid bats may consume a wider variety of insects such as Coleoptera (Hernández Reference Hernández2018), which can act as intermediate hosts of parasites such as Vampirolepis spp. Such variation in the consumption of potential intermediate hosts may explain the differences observed between reproductive and non-reproductive bats.
In this study, the prevalence and abundance of B. rileyi, L. nanum, Ochoterenatrema sp., Urotrema spp., Vampirolepis spp., and A. pulchra were higher in Calcehtok than in Homún. Because only two localities were sampled, these differences cannot be attributed to any single factor, given the absence of spatial replicates of the conditions and environment surrounding roost sites. In this regard, differences between sample sites could be due to local or peculiar characteristics that may include levels of vegetation or habitat disturbances, proximity to or availability of water sources for the studied colonies inside the caves, among other factors that may affect the local interaction between helminths and their hosts (Ramasindrazana et al. Reference Ramasindrazana, Dellagi, Lagadec, Randrianarivelojosia, Goodman and Tortosa2016; Warburton et al. Reference Warburton, Kohler and Vonhof2016). Consequently, a reasonable explanation for the observed differences between sampled sites could be due to the following. The abundance and diversity of insects are often related to plant species richness and forest composition, while habitat disturbance can affect prey availability and, consequently, bat foraging behaviour (Dodd et al. Reference Dodd, Lacki, Britzke, Buehler, Keyser, Larkin, Rodewald, Wigley, Wood and Rieske2012). The vegetation of Homún and nearby localities has different degrees of deforestation due to economic activities, such as agriculture and tourism (Ellis et al. Reference Ellis, Hernández-Gómez, Chacón-Castillo and Vázquez-Luna2024). This perturbation may reduce the abundance and diversity of insect communities in the region (Martín-Park et al. Reference Martín-Park, Delfín‑González, Sosenski, Reyes-Novelo, Meléndez‑Ramírez, Navarrete‑Carballo, Ibáñez‑Bernal, Dzul‑Manzanilla, González‑Moreno and Manrique‑Saide2018) (i.e., prey availability for N. laticaudatus). It is plausible that the better-preserved low deciduous forest in Calcehtok may promote a higher abundance of insects, potentially contributing to the higher prevalence and abundance of trematodes (B. rileyi, L. nanum, Ochoterenatrema sp., and Urotrema spp.) and cestodes (Vampirolepis spp.) in Calcehtok. However, entomological surveys are needed to provide evidence supporting this possible mechanism associated with infection in bats.
The microenvironmental characteristics of Calcehtok, the lower surrounding vegetation disturbance and higher foraging habitat availability, appear more favourable for bat communities, as reflected by a higher species richness (nine co-occurring species) compared with Homún (three species). Although colony size was not quantitatively assessed, field observations suggest a major bat aggregation at Calcehtok. Host density and aggregation are important ecological factors influencing parasite transmission (Webber and Willis Reference Webber, Willis and Ortega2016). Cave-dwelling bats may exhibit higher infection rates due to high levels of aggregation and large population sizes, which provide more potential hosts and facilitate parasite transmission (Duco et al. Reference Duco, Villancio, Paller and Alviola2024). These mechanisms are expected to be particularly important for helminths with direct life cycles (Anderson Reference Anderson2000). Thus, the apparently larger colony in Calcehtok may explain the higher prevalence and abundance observed in A. pulchra and potentially for other helminths (e.g., L. nanum).
Environmental variables were also associated with prevalence and abundance of some species analysed. Humidity and temperature can influence the survival and development of free-living stages of helminths; therefore, seasonal fluctuations in environmental conditions can affect prevalence, abundance, and the structure of helminth communities (Coggins Reference Coggins1984; Vanalli et al. Reference Vanalli, Mari, Casagrandi, Gatto and Cattadori2024).
Bats may also exhibit seasonal variation in prey consumption. In tropical regions such as Yucatán, the abundance of different insect groups (Coleoptera and Diptera) changes between seasons, with more insects available in rainy months (Martín-Park et al. Reference Martín-Park, Delfín‑González, Sosenski, Reyes-Novelo, Meléndez‑Ramírez, Navarrete‑Carballo, Ibáñez‑Bernal, Dzul‑Manzanilla, González‑Moreno and Manrique‑Saide2018; Reyes-Novelo and Morón Reference Reyes-Novelo and Morón2005). These changes in the consumption of insect groups are likely driven by differences in their energy content and availability, resulting in seasonal shifts in the diet of molossid bats (Arango-Diago et al. Reference Arango-Diago, Castillo-Figueroa, Albarracín-Caro and Pérez-Torres2020; McWilliams Reference McWilliams2005). Furthermore, these changes in the insect populations and dietary shifts in bats may help explain the contrasting associations observed between rainfall and parasite infection, including lower prevalence and abundance for L. nanum and Vampirolepis spp., respectively, and higher prevalence and abundance for Ochoterenatrema sp. and Urotrema spp. during months with increased rainfall.
Molossid bats (e.g., Molossus sinaloae and T. brasiliensis) increase their consumption of Coleoptera during the dry seasons (Hernández Reference Hernández2018). The increase in consumption of coleopterans during months with lower rainfall may facilitate helminth infection in bats and support their development, which could explain the observed pattern for Vampirolepis spp., whose life cycle may involve coleopterans as intermediate hosts (Shostak Reference Shostak2014). Similarly, the pattern observed for L. nanum suggests increased consumption of the intermediate host of this trematode during the dry months, potentially Odonata insects, which are intermediate hosts of trematodes of the same family of Limatulum (El-Zeiny et al. Reference El-Zeiny, Ghoneim, Abu Samak and Khidr2025). This is consistent with the finding of Salinas-Ramos et al. (Reference Salinas-Ramos, Herrera, Hernández-Mena, Osorio-Sarabia and León-Règagnon2017), who reported a higher prevalence of Limatulum gastroides during the dry season in the Dobson’s lesser mustached bat, Pteronotus psilotis, supporting a seasonal transmission. In contrast, molossid bats (e.g., T. brasiliensis) may increase the consumption of other groups of insects in rainy seasons, such as Hemiptera and Diptera (Hernández Reference Hernández2018), that may be intermediate hosts of Urotrema spp. and Ochoterenatrema sp. (Lotz Reference Lotz, Gardner and Gardner2024), which could explain the observed pattern for these trematodes.
Temperature was associated with infection by Vampirolepis spp. As with other helminths with indirect life cycles (e.g., L. nanum), transmission of this cestode may be influenced by external environmental conditions through their effects on arthropod intermediate hosts, as explained above. Higher temperatures may also increase insect mortality and affect the abundance and availability of intermediate hosts of Vampirolepis spp., thereby affecting transmission opportunities and potentially explaining the pattern observed for these cestodes (Harvey Reference Harvey2020; Rodríguez-San Pedro et al. Reference Rodríguez-San Pedro, Allendes, Bruna and Grez2024). Additionally, bat behaviour is sensitive to climatic variation. Increases in temperature and decreases in relative humidity may affect bat health, potentially increasing susceptibility to helminth infection (Salinas-Ramos et al. Reference Salinas-Ramos, Tomassini, Ferrari, Boga and Russo2023; Voigt and Kingston Reference Voigt and Kingston2016).
In contrast, A. pulchra has a direct life cycle, making its transmission dependent on the cave conditions. Therefore, the warm temperatures and high-moisture conditions in the caves (Supplementary Figures S1–S2) may promote the activity and survival of the larvae of these nematodes (Anderson Reference Anderson2000). However, external rainfall is unlikely to directly influence larval survival within the roost. Instead, the negative association between rainfall and A. pulchra abundance may reflect indirect effects of environmental conditions on bats. Low rainfall periods may reduce the flight energy cost and echolocation interference caused by rainfall, potentially increasing the foraging activity (Appel et al. Reference Appel, López-Baucells, Magnusson and Bobrowiec2019). This higher activity of bats may alter social interactions and increase contact among individuals (e.g., clustering or grooming), thereby promoting the transmission of parasites (Webber and Willis Reference Webber, Willis and Ortega2016). Therefore, the higher prevalence and abundance of A. pulchra during months with lower precipitation may reflect indirect effects of environmental conditions mediated through host behaviour and roost dynamics. Overall, external weather conditions may influence helminth transmission through indirect host activity and intermediate host availability, whereas directly transmitted parasites may be regulated by the stable microclimatic conditions of caves.
This study was limited by the inability to evaluate important factors such as bat feeding behaviour, parasite life cycles, and parasite life history, which may be associated with the infection patterns observed and need further evaluation in future studies. Additionally, further studies should incorporate a larger number of sampling localities with distinct environmental characteristics (e.g., vegetation) to determine which factors may influence helminth community composition, as has been documented in other bat species (Warburton et al. Reference Warburton, Kohler and Vonhof2016).
The observed effect of biotic and abiotic variables on helminths associated with N. laticaudatus in this study is consistent with patterns reported for other parasites of Neotropical bats. Investigating the interactions between bats, their helminth communities, and environmental factors can provide valuable insights into host-parasite ecology. The present study provides new information on the helminth fauna of N. laticaudatus and highlights the importance of conducting ecological surveys across different seasons to detect both common and rare helminth species in bats.
Supplementary material
The supplementary material for this article can be found at http://doi.org/10.1017/S0022149X2610217X.
Acknowledgements
The authors would like to thank Celia Selem Salas, Iván Rodríguez Vivas, and David Hernández Mena for the recommendations provided during the development of the study. We also thank Eliana Mendez Pino, Andrea España Medina, Andrea Yam Lozada, Melissa Suárez Galaz, Claudia Carrillo Chan, and Leticia Ruiz Hernández for their support in bat collection and examination of bat tissues. We thank the families of Calcehtok (Rubén Tzec) and Homún (Luis Acosta) for allowing us to place the equipment in their homes.
Financial support
The Mexican Secretariat of Science, Humanities, Technology, and Innovation (SECIHTI) awarded WIMC with a doctoral scholarship (No. 001399). The Centro de Investigaciones Tropicales-Universidad Veracruzana provided funds for travel expenses for MCMG and some lab materials.
Competing interests
The authors declare that they have no competing interests.
Ethical standards
The bioethics committee for the use of animals in research from the Campus de Ciencias Biológicas y Agropecuarias, Universidad Autónoma de Yucatán approved the protocols used in this study (protocol number CB-CCBA-D-2023-003).
