Flea community
We captured and sampled 2,254 small mammals belonging to the species Microtus arvalis (61.2%), Apodemus sylvaticus (23.1%), Mus spretus (13.5%), Crocidura russula (1.9%) and other species (0.3%). A total of 4,266 individual fleas were identified from 1,239 small mammal hosts (Table 1): Ctenophthalmus apertus apertus (n = 2), Ctenophthalmus apertus gilcolladoi (n = 1879; C. apertus hereafter), Ctenophthalmus baeticus baeticus (n = 11), Leptopsylla taschenbergi amitina (n = 460), Nosopsyllus fasciatus (n = 1903) and Rhadinopsylla beillardae (n = 8); in addition, 2 specimens were identified at genus level only (Ctenophthalmus sp.).
Table 1
Flea species infesting all small mammal captured.
Small mammal host species: | Microtus arvalis | Apodemus sylvaticus | Mus spretus | Crocidura russula | Microtus duodecimcostatus/ lusitanicus | Mustela nivalis |
n. collected fleas [n hosts 1/ n total hosts 2] | 3900 [1380/941] | 698 [522/238] | 87 [304/49] | 14 [42/6] | 14 [4/3] | 2 [2/2] |
n. identified fleas [n hosts3] | 3463 [872] | 691 [237] | 82 [45] | 14 [6] | 14 [3] | 2 [2] |
Flea species: n fleas [n host] | | | | | | |
CAA | 2 [1] | 0 | 0 | 0 | 0 | 0 |
CAG | 1731 [539] | 116 [75] | 13 [11] | 7[2] | 12 [2] | 0 |
CB | 11 [8] | 0 | 0 | 0 | 0 | 0 |
Csp | 2 [2] | 0 | 0 | 0 | 0 | 0 |
NF | 1681 [643] | 182 [116] | 29 [21] | 7 [5] | 2 [1] | 2 [2] |
LT | 34 [29] | 387 [140] | 39 [18] | 0 | 0 | 0 |
RB | 2 [2] | 5 [2] | 1 [1] | 0 | 0 | 0 |
1 Number of hosts infested |
2 Number of hosts brought alive to the lab and euthanized, infested or uninfested |
3 Number of hosts infested with all fleas identified |
Abbreviations: CAA, Ctenophthalmus apertus apertus; CAG, Ctenophthalmus apertus gilcolladoi; CB, Ctenophthalmus baeticus; Csp, other Ctenophthalmus sp.; NF, Nosopsyllus fasciatus; LT, Leptopsylla taschenbergi; RB, Rhadinopsylla beillardae |
Patterns of flea infestation differed between small mammal host species (Table 1 and Fig. 1). The most abundant flea species infesting common voles were N. fasciatus and C. apertus (98.5% of all fleas identified). By contrast, L. taschenbergi was the most abundant flea infesting mice (56% and 48% of all fleas for A. sylvaticus and M. spretus, respectively). Regarding shrews, we found that individuals were mainly infested by C. apertus and N. fasciatus. R. beillardae, C. a. apertus and C. baeticus were seldom found in M. arvalis. Overall, flea prevalence on small mammal hosts averaged 51.6% (CI = 49.5–53.7), and flea intensity averaged 3.66 fleas per infested host (CI = 3.41-4.00; range = 0–68).
Overall, two species dominated the small mammal flea community: N. fasciatus and C. apertus (NF = 44.6%; 0.84, CI = 0.77–0.93; CAG = 44.1%; 0.83, CI = 0.72–0.95, respectively), followed by L. taschenbergi (frequency = 10.8%; abundance = 0.2, CI = 0.16–0.25). Detailed information on abundance, prevalence and intensity of each flea species and host is provided in Table 2. Fleas were highly aggregated on their small mammal hosts (Table 2; D-Index values close to 1). Variance to mean ratios were also indicative of a marked parasite aggregation, with greater ratios for those fleas typically more abundant on a given host (C. apertus and N. fasciatus for M. arvalis; L. taschenbergi for A. sylvaticus and M. spretus).
Table 2
Flea abundance, prevalence and intensity on the four main small mammal hosts (Rodents and Insectivores).
Host species [n] 1 | Flea species | Flea abundance Mean (CI) | Flea prevalence % Mean (CI) | Flea intensity Mean (CI) | Fleas intensity range | Variance / Mean ratio | Discrepancy index2 Mean (CI) |
M. arvalis [1380] | CAG | 1.25 (1.09–1.46) | 39.1 (36.5–41.7) | 3.21 (2.85–3.71) | 1–18 | 9.8 | 0.81* (0.79–0.83) |
NF | 1.22 (1.12–1.36) | 46.6 (43.9–49.3) | 2.61 (2.42–2.85) | 1–30 | 4.19 | 0.73* (0.71–0.75) |
LT | 0.02 (0.02–0.04) | 2.1 (1.4-3.0) | 1.17 (1.03–1.52) | 1–4 | 1.45 | 0.98* (0.97–0.99) |
A. sylvaticus [522] | CAG | 0.22 (0.17–0.28) | 14.4 (11.5–17.7) | 1.55 (1.33–1.88) | 1–7 | 2.2 | 0.90 (0.87–0.92) |
NF | 0.35 (0.29–0.43) | 22.2 (18.7–26.0) | 1.57 (1.41–1.82) | 1–7 | 1.97 | 0.84 (0.81–0.87) |
LT | 0.74 (0.60–0.93) | 26.8 (23.1–30.8) | 2.76 (2.36–3.39) | 1–23 | 5.21 | 0.85 (0.82–0.87) |
M. spretus [304] | CAG | 0.04 (0.02–0.08) | 3.6 (1.8–6.4) | 1.18 (1.00-1.55) | 1–3 | 1.42 | 0.97 (0.95–0.98) |
NF | 0.1 (0.06–0.16) | 6.9 (4.3–10.4) | 1.38 (1.10–1.95) | 1–5 | 1.88 | 0.94 (0.92–0.97) |
LT | 0.13 (0.07–0.22) | 5.9 (3.5–9.2) | 2.17 (1.56–3.16) | 1–7 | 3.24 | 0.96 (0.94–0.97) |
C. russula [42] | CAG | 0.17 (0.00-0.57) | 4.8 (0.6–16.2) | 3.5 (2.00-3.50) | 2–5 | 4.07 | 0.94 (0.86–0.95) |
NF | 0.17 (0.05–0.41) | 11.9 (4.0-25.6) | 1.4 (1.00-1.80) | 1–3 | 1.73 | 0.89 (0.79–0.95) |
LT | 0 | 0 | 0 | - | - | - |
1 Number of host life-trapped and euthanized: infested and uninfested |
2 95% confidence interval bootstrap with 1000 replications |
* Sample too big for bootstrap confidence limits with 1000 replications. The percentile method was used instead. |
Abbreviations: CAG, Ctenophthalmus apertus gilcolladoi; NF, Nosopsyllus fasciatus; LT, Leptopsylla taschenbergi; CI, 95% confidence interval (Clopper-Pearson). |
Flea abundance variation according to season and host sex
We focused our analyses on flea abundance data, which is the most informative and recommended parameter in parasite community studies [40]. More details about prevalence and intensity in the supplementary material (see Additional file 1).
Flea abundances were highest in M. arvalis and A. sylvaticus (2.83, CI = 2.57–3.12; and 1.34, CI = 1.14–1.59, respectively), and noticeably lower in M. spretus and C. russula (0.29, CI = 0.21–0.40; and 0.33, CI = 0.12–0.75, respectively). M. arvalis harboured the highest number of fleas per host [range 1–68], followed by A. sylvaticus [1–29], while M. spretus and C. russula had fewer fleas per host ([1–5] and [1–7], respectively). For further analyses of infestation patterns, we focused on the main flea species (C. apertus, N. fasciatus and L. taschenbergi) and the most frequently captured small mammal hosts (M. arvalis, A. sylvaticus and M. spretus).
Variation in C. apertus abundance on M. arvalis was significantly explained by month (Χ2 = 33.74, df = 2, p < 0.001), but not by host sex. Post-hoc tests (Tukey) indicated that C. apertus was less abundant on voles in July (0.87 ± 1.87, n = 981) than March (3.48 ± 8.29, n = 164), and intermediate in November (1.31 ± 2.40, n = 235). In A. sylvaticus, C. apertus abundance did not differ between months, but differed between sexes (Χ2 = 9.43, df = 1, p = 0.002), being greater for male (0.28 ± 0.82, n = 329) than female hosts (0.12 ± 0.38, n = 193). In M. spretus, neither month nor sex explained C. apertus abundance variation.
Regarding N. fasciatus abundance, we found a significant sex ⋅ month interaction in M. arvalis (Χ2 = 8.57, df = 2, p = 0.014): N. fasciatus was more abundant on male than on female voles during March (1.80 ± 4.13, n = 82 and 1.02 ± 3.71, n = 82, respectively), but not during other months (July = 1.31 ± 2.07, n = 465 and 1.31 ± 1.94, n = 516; November: 0.72 ± 1.44, n = 118 and 0.68 ± 1.48, n = 117, respectively). In A. sylvaticus, N. fasciatus abundance did not differ between sexes, but differed between months (Χ2 = 18.14, df = 2, p < 0.001), with greater abundances during July (0.52 ± 0.91, n = 212) than March (0.35 ± 0.94, n = 114) or November (0.16 ± 0.61, n = 196). A similar pattern was found for M. spretus, although the effect of month was only marginally significant (Χ2 = 8.08, df = 1, p = 0.098); there was also a tendency for N. fasciatus to be more abundant on males than females (Χ2 = 5.47, df = 2, p = 0.065; males = 0.12 ± 0.49, n = 201 and females = 0.05 ± 0.26, n = 103).
Regarding L. taschenbergi, we found that this flea was more abundant on males than females in M. arvalis (Χ2 = 4.50, df = 1, p = 0.034; males = 0.04 ± 0.24, n = 665 and females = 0.01 ± 0.12), n = 715). In both murid species, we found a significant effect of both sex (A. sylvaticus = Χ2 = 7.45, df = 2, p < 0.001; M. spretus = Χ2 = 9.01, df = 2, p = 0.011) and month (A. sylvaticus = Χ2 = 84.21, df = 1, p < 0.001; M. spretus = Χ2 = 4.797, df = 1, p = 0.029). L. taschenbergi was more abundant on males than on females in both A. sylvaticus (males = 0.89 ± 2.12, n = 329 and females = 0.48 ± 1.63, n = 193) and M. spretus (males = 0.18 ± 0.78, n = 201 and females = 0.03 ± 0.17, n = 103). This flea was also more abundant during July than other months.