Bisexual population of the parthenogenetic tick Amblyomma rotundatum: bioecological data from the field and laboratory

The tick Amblyomma rotundatum parasitizes primarily cold-blooded animals and is widely distributed in the Neotropics. This tick is considered parthenogenetic, with rare reports of males in nature. In the present study, we identified for the first time a bisexual population of A. rotundatum which generates males and females in the same proportion, both in nature and in the laboratory. Ticks were collected specifically from reptiles ( Iguana iguana ) in Amazon biome, Maranhão state, Brazil. The ticks were identified as A. rotundatum using a combination of morphological and molecular characterization. Specimens of A. rotundatum collected in the field were kept in BOD incubators for laboratory observations of their biology. Infestations of larvae, nymphs, and adults from two consecutive generations were performed on toads ( Rhinella marina ) (~ 500 larvae/host, ~25 nymphs/host, 4 adults /host). In total, three R. marina hosts were used. Overall, 517 ticks were collected in the larval (n = 82), nymphal (n = 95), and adult [n = 340 (130 males and 210 females)]. The sex ratio of males/females in the field was of ~1 M/0.6F ( P > 0.05). A total of 25 engorged and semi-engorged nymphs were collected from wild iguanas in nature, of which seventeen successfully molted, resulting in 10 males and 7 females (ratio ~1 M/0.7F). The cycle in the laboratory was carried out in the presence of female and male. In the laboratory, toads were kept individually in glass aquarium in a room with controlled temperature (27º C) and humidity (~ 90% RH). The ticks were kept in desiccators, in an incubator at 27º C and ~90% RH. Toads were artificially infested with A. rotundatum and monitored for two consecutive generations. Approximately 27% of the engorged larvae molted to nymphs, and 61% of the nymphs molted to adults, with 23 males and 18 females (ratio 1 M/0.8F). The mean egg incubation period was 33.7 ± 1.5 days, and mean egg hatching percentage was 90.0% ± 7.0. The tick A. rotundatum exhibited males and females in similar proportions both in the field and in the laboratory. This indicates the existence of a bisexual population of this species in Amazon biome.