Hyperparasitism is displayed by argasid (Argasidae) and less frequently ixodid (Ixodidae) ticks and occurs when engorged ticks are parasitized by conspecifics in order to obtain a bloodmeal (Moorhouse & Heath 1975; Ntiamoa-Baidu 1986; Labruna et al. 2007). This behaviour has been described in eight species of Ornithodoros ticks namely Ornithodoros erraticus (Helmy et al. 1983), Ornithodoros hermsi (Williamson & Schwan 2018), Ornithodoros verrucosus (Skrynnik 1939), Ornithodoros parkeri (Davis 1941), Ornithodoros puertoricensis (Endris et al. 1991), Ornithodoros tartakovskyi (Londoño 1976), Ornithodoros tholozani (Bhat 1969), and Ornithodoros turicata (Beck et al. 1986).

The tick Ornithodoros amblus inhabits Pacific Ocean shores of Peru and northern Chile, and sustains its life cycle parasitizing seabird, such as Larus sp., Pelecanus thagus, Phalacrocorax bougainvilliorum, Phalacrocorax gaimardi, Spheniscus humboldti, Sula neuboxi, and Sula variegata (Clifford et al. 1980). While feeding behaviour of this tick has never been observed in situ, laboratory results point that adults engorge in 20–145 min on avian hosts (Khalil & Hoogstraal 1981). As hyperparasitism events have never been documented in O. amblus, the objective of this study was to report a related case for this species.

During January and February of 2005, 472 adult ticks were collected in the Pan de Azúcar National Park, Chile (26° 9′27.17″S, 70°41′7.63″W). All ticks were taken from the soil underneath rocks near S. humboldti nests. In the laboratory, 265 females and 207 males were identified as O. amblus following Clifford et al. (1980). In order to perform observations on developmental traits (results not described in the current study), females were allowed to feed in Gallus gallus for obtaining subsequent ovipositions. To ensure fertilization, 36 couples composed by laboratory-engorged females and males with different engorgement degrees were placed in plastic vials inside a dark incubator at 24°C and 75% of relative humidity. Daily checks after the disposition of couples inside the incubator were performed to determine the day of oviposition. Twenty-two days after, a male was observed attached on the anterior dorsal idiosoma of a fully engorged female (Figure 1A). The removing of the male with tweezers resulted into a bleeding wound that clotted seconds after, leaving a dark scar on the dorsum of the female (Figure 1B). The male was placed with the female again. Minutes later, another event of hyperparasitism was observed, but this time the male attached itself to the posterior region of the idiosoma (Figure 1C). The parasitized female and the male were then prepared for scanning electron microscopy. Micrographs showed that the cuticle of the female regenerated after the first event of hyperparasitism without a mammillated pattern, resulting into a marked scar (Figure 1D). Engorged male (Figure 1E) and female examined in the current study were deposited in the tick collection “Colección del Departamento de Ciencia Animal (CDCA)” of the Facultad de Ciencias Veterinarias, Universidad de Concepción, Chile, under the following accession number Or.am.CDCA-54.3 and Or.am.CDCA-54.4.

This is the first case of hyperparasitism reported for O. amblus and the ninth event of this nature documented in ticks of the Ornithodoros genus. Moorhouse (1966) and Ntiamoa-Baidu (1986) suggested that hyperparasitism in ticks may play a significant role in their life cycle as an alternative feeding strategy. However, it is also possible that this behaviour rose in some ticks as a consequence of enduring long periods of starvation rather than a specific adaptation to increase survivability (Gray et al. 2013). For example, in O. erraticus this hypothesis seems to be supported by the fact that part of unfed ticks maintained under laboratory conditions parasitize on well-engorged ticks (Helmy et al. 1983). Particularly, it is possible that hyperparasitism in O. amblus could represent an opportunistic strategy to maximize it life span during starving periods when seabirds are away from their colonies.

FIGURE 1.

Events of hyperparastism observed under light microscopy and scanning electron micrographs of the parasitized female. A. Ornithodoros amblus male attached to the anterior dorsal idiosoma of a conspecific engorged female. B. View of the dark-colored scar on the female's dorsum (arrowed) after manually detaching the male. C. Second event of hyperparastism on the same female tick. D. Scanning electron micrograph of the scar on female's dorsum after the first episode of hyperparasitism. E. Scanning electron micrograph showing the engorged male of O. amblus observed in this study. Dark bar = 1 mm, white bar = 1 mm.

On the other hand, hyperparasitism has been suggested as an alternative mechanism for transmission of microorganisms between ticks (Labruna et al. 2007). In the case of Ornithodoros spp., laboratory tick-to-tick transmission has been observed even while ticks are on the host (i.e., O. erraticus, Helmy et al. 1983), which could increase pathogen dissemination between conspecific ticks. This fact was further supported by Williamson and Schwan (2018), who demonstrated that events of hyperparasitism in O. hermsi resulted in the transmission of Borrelia hermsi between adult and nymphal stages. Noteworthy, some populations of O. amblus have been described to harbor Orbivirus, Nairovirus, and Coxiella-like endosymbionts (Clifford et al. 1980, Hoogstraal 1985, Duron et al. 2015). Whether it is reasonable to suggest that hyperparasitism would represent a transmission route for these agents in O. amblus, this hypothesis still remains unsolved for this tick species and requires further assessment.

We deeply thank Dr. Lucila Moreno from Universidad de Concepción for her comments on early versions of this manuscript. This reseach was funded by FONDECYT Project 1170972.