Aponomma Hydrosauri Research Articles

Interspecific differences in microhabitat choice by two species of Australian reptile tick

The microhabitat choice of all life cycle stages, both unfed and engorged, of two Australian ixodid ticks, Amblyomma limbatum and Aponomma hydrosauri, were compared in the laboratory. When offered a choice between bare soil (or sand) and soil covered with litter, most ticks moved into the litter, except unfed larvae which often took refuge within crevices on the surface of exposed sand. The two species differed in the position they adopted within the litter. Ap. hydrosauri were predominately found at the interface between the soil and litter. Amb. limbatum were more often found higher up in the litter. There were also interspecific differences in the body orientation of ticks within the litter. All life cycle stages of Ap. hydrosauri adopted a position with their dorsal surface facing upwards, whereas unfed stages of Amb. limbatum were more frequently found with their ventral surface facing upwards. The behaviour of each species probably represents a different compromise between two factors, maximizing host detection, and minimizing their exposure to desiccation or predation.

The impact of tick load on the fitness of their lizard hosts.

A survey was conducted of natural populations of the sleepy lizard Tiliqua rugosa in South Australia to determine whether infestation by ectoparasitic ticks reduced their fitness. Between 1982 and 1990, 2183 captures of 824 individual lizards were made in an area where they were infested by the tick Aponomma hydrosauri, and 3668 captures of 586 individual lizards were made in an area where they were infested with the tick Amblyomma limbatum. Lizards with high tick loads in one year tended to have high loads the next year. Longevity of lizards in the study was either not correlated with tick load, or positively correlated. Size achieved was greater amongst lizards with greatest tick load, and lizards in mating pairs had higher tick loads than those never found in pairs. The data do not support the hypothesis that tick load diminishes host fitness.

A comparison of the off-host survival times of larvae and nymphs of two species of reptile ticks

Chilton N. B. and Bull C. M. 1993. A comparison of the off-host survival times of larvae and nymphs of two species of reptile ticks. International Journal for Parasitology 23: 693–696. A comparison was made of the survival times of unfed larvae and unfed nymphs of two Australian species of ixodid tick. Under desiccating conditions of high temperature and low humidity, Aponomma hydrosauri nymphs had significantly shorter survival times than Amblyomma limbatum nymphs. The survival times of unfed larvae of both species declined as temperature increased and as relative humidity decreased. Ap. hydrosauri larvae had equivalent or longer survival times than Amb. limbatum larvae in most conditions. These results are discussed in relation to the geographical ranges of the two species.

Delayed mating and the reproductive fitness of aponomma hydrosauri (Acari: Ixodidae)

Chilton N. B., Andrews R. H. and Bull C. M. 1992. Delayed mating and the reproductive fitness of Aponomma hydrosauri (Acari: Ixodidae). International Journal for Parasitology 22: 1197–1200. This study examines whether delayed mating influences the reproductive fitness of female reptile ticks, Aponomma hydrosauri. Delayed mating was induced by the prevention of male attachment to hosts for 20 or 40 days after females had been attached. The results showed that delayed mating had no significant influence on the number of viable progeny produced by female ticks. This may represent an important advantage for colonizing Ap. hydrosauri females in marginal population areas, particularly at parapatric boundaries.

Niche segregation in reptile ticks: attachment sites and reproductive success of females.

This study examined whether the mating or feeding success of females of two tick species, Amblyomma limbatum and Aponomma hydrosauri, is influenced by their site of attachment on a host. Marked interspecific differences were detected in the preferred sites of attachment of females to their common host, the sleepy lizard Tiliqua rugosa, with Amb. limbatum found predominantly in the ears and on the lower back, while Ap. hydrosauri preferred to attach under the forelimbs and on the midback. Data from field surveys suggested that higher proportions of females were mated in the preferred sites for Ap. hydrosauri, and in one of the preferred sites for Amb. limbatum. However, laboratory and field experiments showed that for both species, the mean time before females were mated, mean engorgement time and mean feeding rate were independent of where they were attached to a host. Four hypotheses were considered as explanations of the observed niche segregation; intespecific competition, avoidance of pheromone jamming or adaptations, to maximize mating and feeding, and minimize physical disturbance. These could not totally explain the observed site specificity in either tick species. Site specificity may represent adaptations by each species to other host species encountered within their distributional range.

Genetic Markers for the Identification of Three Australian Tick Species at Various Stages in Their Life Cycles

An allozyme electrophoretic study was conducted on different life cycle stages of 3 Australian tick species, Amblyomma limbatum Neumann, 1899, Aponomma hydrosauri (Denny, 1843), and Ixodes holocyclus Neumann, 1899. Sixteen enzymes encoding a presumptive 19 loci were of sufficient staining intensity and resolution to identify accurately the 3 species at either the larval, nymphal, or adult stage of the life cycle. For each species, the larvae, nymphs, and adults all had alleles in common at all 19 loci. However, fixed genetic differences were detected among the 3 species at 15 or 16 of the 19 enzyme loci examined. The large number of genetic markers that have been established from a limited sample volume (e.g., individual unfed larvae) allows accurate identification of the species at each life cycle stage. Data presented show that the technique of allozyme electrophoresis can provide genetic evidence for the identification of species at any life cycle stage even where life cycle stages are morphologically quite different. A major problem facing researchers in parasitology and indeed pest control management is the inability to identify confidently, by morphological characters, life cycle stages of many parasite taxa. Different parasites often have evolved along lines that culminate in remarkable morphological similarity between disparate species. Inability to detect and use morphological characters to assign individuals to a species with confidence is compounded when within a species there are marked differences in the structure at various stages in the life cycle and where morphological changes occur during feeding on the host. Electrophoretic studies have revealed the existence of morphologically similar but genetically distinct (i.e., cryptic) parasite species (e.g., Bull et al., 1984; Baverstock et al., 1985; Andrews et al., 1989), demonstrating that conventional morphological classifications are not always adequate for species recognition. It is surprising that few investigators have applied the technique to assist in the identification of species at different life cycle stages. Insufficient numbers of enzyme loci have been established for species identification due to the small volume of sample available for electrophoresis. Species of ticks often are diagnosed on the basis of slight morphological differences, host specificity, and/or the geographical locality from which they were collected. However, morphological characters sometimes are insufficient to identify unequivocally the species to which specimens belong. For example, the tick known to transmit Lyme disease in America, Ixodes dammini Spielman, Clifford, Piesman, and Corwin, 1979, is difficult to distinguish morphologically from the closely related species Ixodes scapularis Say, 1821, in areas where they coexist (Oliver, 1988). Similarly, Ixodes holocyclus Neumann, 1899, has been implicated as the vector of Lyme disease in Australia (Munro and Dickeson, 1989), and yet morphological characters are insufficient to distinguish it from other closely related ixodid species (Arundel and Sutherland, 1988). Furthermore, ticks feeding on hosts undergo structural changes and are particularly difficult to identify using morphological characters. Moreover, the identification of larvae and nymphs of many species requires laboratory culture until they engorge to repletion and molt to the adult stage. In view of the significant morphological changes between different life cycle stages, the accurate identification of larvae, nymphs, and adults to a given species by the use of diagnostic genetic markers would be of taxonomic and systematic value. Allozyme electrophoresis has been used to distinguish several tick species worldwide (Bull et al., 1984; Hunt and Hilburn, 1985; Hilburn et al., 1989), but no comprehensive genetic study has been conducted to identify and characterize larvae and nymphs of any of these species. For the present study we selected 3 morphologically distinct species, 2 reptile ticks, Amblyomma limbatum Neumann, 1899, and Aponomma hydrosauri (Denny, 1843), and 1 mammal tick, I. holo-

Interspecific differences in the movements of female ticks on reptiles

Movements of females of two reptile ticks, Amblyomma limbatum and Aponomma hydrosauri were studied to determine whether the behaviour of the species on hosts was similar or different. Experiments were conducted to determine if the movement of females on hosts prior to mating was influenced by the delayed attachment of conspecific males. A field experiment was also undertaken to determine whether data obtained during laboratory experiments reflected the behaviour of females on hosts in the field. Both in laboratory and field experiments, a significantly greater proportion of Ap. hydrosauri females changed their site of attachment prior to mating. Individual Ap. hydrosauri females made significantly more positional changes than Amb. limbatum females. These interspecific differences occurred irrespective of the absence of conspecific males or presence of non-conspecific adults on hosts. These data may have important ecological implications in relation to the success of colonizing females at their parapatric boundary.

The on-Host Temperature Environment for 2 Australian Reptile Ticks

The temperatures experienced by the ixodid ticks Amblyomma limbatum and Aponomma hydrosauri whilst attached to sleepy lizards, Tiliqua rugosa, were examined to determine whether differences in the body temperature of the host could explain (1) interspecific differences in the feeding and mating sites of ticks on hosts, and/or (2) the position of the tick parapatric boundary near the transition from mallee to non-mallee vegetation. Attached ticks were exposed to temperatures that were related to, but often higher than, ambient temperatures. Ground surface temperature was a better predictor of lizard body temperature than was air temperature. Mean body temperatures of lizards during winter were lower than those in spring, due to lower ambient temperatures, and were consistently below the threshold temperature required to induce mating in both tick species. Low temperature can also explain the cessation of feeding by larval and nymphal ticks on hosts during winter. The selection of feeding and mating sites by ticks could not be attributed to specific temperature requirements because no attachment site was consistently warmer than another. Furthermore, no change in body temperature of the lizards was detected across the tick parapatric boundary.

A comparison of the reproductive parameters of females of two reptile tick species

In comparisons of females of two reptile tick species Aponomma hydrosauri and Amblyomma limbatum, Ap. hydrosauri was initially larger, and after mating on the host engorged faster and remained attached for a shorter time before completing engorgement and detaching. Amb. limbatum had a longer period of engorgement, and achieved a greater engorged weight. Engorged Amb. limbatum females laid significantly more eggs than equivalent sized Ap. hydrosauri. Although the two species are ecologically similar and were collected from the same site for this study, their reproductive differences probably reflect adaptations to different conditions in their largely allopatric ranges.

No competition for resources between two tick species at their parapatric boundary.

Aponomma hydrosauri and Amblyomma limbatum are tick species with the same major host species, the sleepy lizard Trachydosaurus rugosus, but parapatric distributions in South Australia. Near Mt. Mary one species is abruptly replaced by the other over one kilometre. There is substantial overlap in feeding sites on the hosts. This suggested that interspecific competition, during feeding, may be an important mechanism preventing further overlap of the distributions of the two species. However, in the overlap region there was no resource shortage, and each species infested hosts independently of the other species. Also in laboratory experiments at the highest densities encountered in the field, larvae and nymphs of each species attached and engorged equally well whether alone or mixed with the other species. These data refuted the, hypothesis of interspecific competition between the two species while feeding.

Mating behaviour and parapatry in two species of Australian reptile tick.

Few quantitative studies have examined the ecological consequences of similarities and/or differences in mating behaviour of parapatric species. Reproductive interference occurs between several parapatric species of Australian reptile tick, due to similarities in their mating behaviour (Andrews et al. 1982a). Attempts to determine whether reproductive interference serves to maintain parapatry between Amblyomma limbatum and Aponomma hydrosauri have been hindered because of difficulties in providing conditions conducive to conspecific mating in Amb. limbatum. The present study examined whether off-host and/or onhost temperature influenced the subsequent mating behaviour (i.e. the proportion of females that mate and the time when mating occurs) of these two species. Irrespective of the temperature experienced by ticks prior to host attachment, specific on-host temperatures were needed to induce mating in Amb. limbatum (i.e. host cloacal temperatures >32° C prior to the time of peak mating activity). Significantly more Amb. limbatum females were mated and the time taken by females to mate decreased with increasing on-host temperatures. mating in Ap. hydrosauri occurred over a wider range of on-host temperatures and the time when mating occurred did not alter at different on-host temperatures. In addition, significantly more Ap. hydrosauri males moved and each male made more moves on hosts than did Amb. limbatum males. It is suggested that Ap. hydrosauri may in consequence have a competitive mating advantage over Amb. limbatum at a boundary. Similarities in mating behaviour, on the other hand, increase the probability of reproductive interference, hence reduce the reproductive fitness of colonizing females of both species. We propose that similarities and differences in mating behaviour could play a critical role in the maintenance of parapatric boundaries.

Responses to Environmental Cues by Unfed Larvae of the Australian Reptile Ticks Aponomma hydrosauri and Amblyomma limbatum

The behaviour of the unfed larvae of 2 Australian reptile ticks, Aponomma hydrosauri (Denny) and Amblyomma limbatum Neumann, was compared in the laboratory. When offered choices, Ap. hydrosauri larvae preferred cool temperatures, dark areas, and high humidities more than Amb. limbatum. Aponomma hydrosauri climbed less often to the tops of vials and climbed down through artificial litter layers more than did Amb. limbatum. Aponomma hydrosauri exposed itself less to environmental risk, presumbly at the cost of less efficient host finding. The interspecific differences are discussed in relation to the allopatric distributions of the 2 species.

The Mode of Transmission of the Excitant Sex Pheromone in Two Australian Reptile Ticks

Females of the Australian reptile ticks Aponomma hydrosauri (Denny) and Amblyomma albolim- batum Neumann feed on their host and then produce an excitant signal which induces males on the same host to detach and search about the host surface for mates. To determine whether the excitant signal is transmitted through the host circulation or in the air, male ticks were attached to hosts that were next to hosts infested with females. The female ticks moved as much as males attached to hosts also infested with females, and significantly more than males on hosts kept apart from hosts infested with females. Male activity could be increased or decreased by moving their host near to or away from hosts infested with females. This suggests that the excitant signal was transmitted through the air rather than through the host circulation.

GEOGRAPHICAL VARIATION IN THE MORPHOLOGY OF APONOMMA HYDROSAURI (DENNY) (ACARI: IXODIDAE)

AbstractMeasurements were made of 15 morphological parameters from 349 male Aponomma hydrosauri collected from 10 geographical regions throughout the distribution of this reptile tick species. A discriminant function analysis performed on the data, showed 3 groupings. Ticks from the geographically isolated populations in Western Australia were separated from the rest by a function with major contributions from measurements of body length. This supported previous studies which had indicated genetical divergence of the Western Australian populations. South eastern and south central regions were separated by a function with major contributions from measurements of body width. This may result from changes in the major host species or from climatic changes.

Microhabitat selection by two reptile ticks at their parapatric boundary

AbstractThe parapatric boundary between the reptile ticks. Aponomma hydrosauri and Amblyomma limbatum, near Mt Mary, South Australia, coincides with a vegetational ecotone. Samples of litter from each side of the tick boundary showed considerable heterogeneity, but there were consistent differences in the composition and quantity of litter. North of the boundary, where Amb. limbatum is found, there is less litter and an absence of Eucalyptus leaves in the litter. Since the litter retards evaporative water loss, and Ap. hydrosauri is less tolerant of dehydration, reduced litter quantity may reduce the fitness of colonizing Ap. hydrosauri. In laboratory and field trials, larvae and nymphs of both tick species chose litter microhabitats in preference to bare soil, with the exception of fed Ap. hydrosauri larvae which, in trials with litter from north of the boundary, rarely moved from the bare soil. This behaviour may also reduce the fitness of colonizing Ap. hydrosauri.The two species adopted different positions in the litter. Ap. hydrosauri were predominantly found on the surface, at the interface between soil and litter as fed larvae, and on or under the surface as nymphs. Amb. limbatum larvae were more often buried under the surface, while nymphs were found mostly in the litter above the soil surface. Hypotheses to explain the maintenance of the parapatric boundary are discussed in the light of these results.

Host-Location by the Reptile Tick Aponomma hydrosauri: The Roles of Physical Disturbance and Odor

whereas gametocytes predominated in the P. floridense infections. Finally, one of the 20 A. distichus from a golf course in La Romana, Dominican Republic showed P. azurophilum. The Schellackia-like parasite was found in leukocytes only in 15 lizards (Table I). It is elongate and pale, except for a red, bandlike nucleus. Possibly it is the same parasite reported as an undescribed Schellackia by Telford (1975, op. cit.) from Haiti, as a Schellackia-like parasite on Martinique (Ayala and Hertz, 1981, op. cit.), and as Schellackia golvani on Guadeloupe by Rogier and Landau (1975, Bull. Museum Natl. Hist. Nat. (Paris) 194: 91-97). Figure 1 shows the currently known distribution of malarial infections in anoline lizards on Puerto Rico. Ours was only a partial survey and much remains to be done to complete the picture, but all infections to date have been found only in Subtropical moist or wet forest habitats. Samples from the more arid regions of the island and from similar Culebra Island have yielded no plasmodia at all. We are grateful for the assistance of A. Gaa, T. Hazen, R. Thomas and J. Torres on Puerto Rico, for the help of K. Kliegel to examine the blood smears, and for extensive criticism of an earlier draft by S. Ayala. The University of Puerto Rico Biology Department at Rio Piedras and the El Verde Field Station provided facilities. Support came from a UCLA Academic Faculty Grant to G. Gorman (S. G.) and a Miller Institute postdoctoral fellowship (J. P.) at the University of California, Berkeley. e o e to co plete the picture,

Morphology of Normal and Theileria parva-Infected Salivary Glands of Rhipicephalus appendiculatus (Acari: Ixodoidea)

whether they actually mate in nature without first feeding. Another Aponomma species, A. concolor, which was examined for its ability to produce elongated spermatids without an adult blood meal, yielded similar results to those obtained from A. hydrosauri. Twoand 3-day-old, unfed males contained testes one-third to one-fourth full of rounded and elongating spermatids, whereas testes of 5to 6-day-old males were full of elongated spermatids. Although the critical experiment has not been conducted to demonstrate whether unfed, male A. hydrosauri and A. concolor will transfer spermatids to females, it is clear that fully mature spermatids are present. Interestingly, recent, unpublished information indicates that another Australian Metastriata tick, Amblyomma triguttatum, shows maturation similar to Aponomma hydrosauri and Aponomma concolor. Unfed male Amblyomma triguttatum can copulate and transfer spermatophores filled with elongated spermatids to females (Guglielmone and Moorhouse, pers. comm.). Species of Aponomma are often considered to be primitive (or specialized) Amblyomma, thus, phylogenetically A. triguttatum is rather closely related to the two Aponomma species. Obviously it is not as closely related to these two as it is to other congeneric species that require feeding before they produce spermatids. These three species with autogenous spermatid maturation also share another similarlity, viz., all have hether they actually mate in nature without irst feeding. nother Apon mma species, A. concolor, hich was examined for its ability to produce longated spermatids without an adult blood eal, yielde similar results to hose obtained rom A. hydrosauri. Twoand 3-day-old, unfed lower chromosome numbers than most of their congeneric relatives (Oliver, 1977, Ann. Rev. Ent mol. 22: 407-429). Aponomma hydrosauri infests a number of large reptile hosts, including skinks (Tiliqua and Trachydosaurus species), dragons (Amphibolurus) and goannas (Varanus species), and the echidna (Tachyglossus species). However, the most commonly recorded host is the sleepy lizard, Trachydosaurus rugosus (Smyth, 1973, Aust. J. Zool. 21: 91-101). Aponomma concolor appears confined to the echidna, Tachyglossus aculeatus and T. setosus. Amblyomma triguttatum feeds on a wider host range of species including marsupials, livestock and other domesticated animals (Roberts, 1970. Australian ticks. CSIRO, Australia, Melbourne, 267 p.). The discovery of species of Metastriata that are able to produce elongated spermatids without a blood meal represents the first exception in this taxon to the general rule of a need for adult feeding before spermatid production and mating occurs. This finding has important implications to studies dealing with reproduction, nutrition, hormones, phylogenetics, population density and vector-pathogen relationships of ticks. This work was supported in part by Grant 09556 from the National Institute of Allergy and Infectious Diseases (NIH), U.S.A., and the CSIRO Long Pocket Laboratories, Indooroopilly, Queensland, Australia.

Spermatid Production in Unfed, Metastriata Ticks

Argasid ticks (Argas, Antricola, Ornithodoros, Otobius) undergo spermatogenesis and spermiogenesis prior to feeding as adults. A blood meal accelerates their germinal development (Balashov, 1972, Misc. Publ., Entomol. Soc. Amer. 8: 161-376; Oliver, 1974, J. Med. Entomol. 11: 26-34; Oliver and Osbum, 1977, J. Parasitol. 63: 176-178). Timing of meiosis and elongation of spermatids in Prostriata ticks (Ixodes) occur at similar developmental periods (late nymphal and teneral adult stages), and males of many Ixodes species do not feed as adults (Balashov, 1972, op. cit.; Oliver, 1974, op. cit.). It is common knowledge, however, that Metastriata ticks (Amblyomma, Aponomma, Boophilus, Dermacentor, Haemaphysalis, Hyalomma, Rhipicephalus, etc.) require a blood meal as adults for spermatogenesis and spermatid elongation to be completed (Balashov, 1972, op. cit.; Oliver, 1974, op. cit.). A slight modification of this generality is noted in one-host ticks whose life cycles and reproductive periods are significantly shortened. When these males are forcibly removed from the host during ecdysis from the nymphal to adult stage, some will continue the momentum of spermatogenesis and produce a few elongated spermatids (Osburn et al., 1980, Ann. Entomol. Soc. Am. 73: 613-616; Osburn, 1981, Ann. Entomol. Soc. Am. 74: 177-179; Oliver and Stone, unpubl.). In three-host, unfed, metastriate males, spermatogenesis in the primary spermatocyte does not progress beyond mid-prophase. However, upon feeding, spermatocytes begin to enlarge greatly, diplotene bivalents appear and meiosis and spermatid development are completed. We now report some exceptions among species of Australian Metastriata that are able to produce elongated spermatids without feeding as adults. Initial observations were made on unfed Aponomma hydrosauri males in which spermatids were seen during preparation of reproductive tracts for chromosome studies. Occasionally unfed males were also seen coupling females. Subsequent experiments were designed to (1) verify these intial observations of exceptional variation in maturation of a Metastriata species and (2) to gather more carefully controlled and detailed data on timing a d extent of male maturation. Reproductive tracts of unfed, male A. hydrosauri were separated into several parts, placed on microscope slides and stained with 2% lacto-aceto-orcein. Unfed males were dissected at 1, 5, 7, 8, 11, and 18 days postecdysis. Results indicated that 1-day-old males possessed rounded spermatids, and meiotically dividing primary and secondary spermatocytes. Elongated spermatids were abundant in 5-day-old and older males. Several fed nymphs were also examined and yielded meiotically dividing cells, but no spermatids. These results indicate that unfed males produced elongated spermatids at some time between days 1 and 5 postecdysis and might be expected to mate at that time. Lack of specimens precluded conducting the appropriate mating trials, but Andrews and Bull (1981, Animal Behavior 29: 518-522) provided useful data on this subject. They showed that approximately one-third of the unfed, male A. hydrosauri that were placed with recently-fed females off the host went through all six phases of courtship, but no spermatophores were observed. These performances compare favorably with similar trials using fed males. On the other hand, when males were attached to hosts with females that had been attached for 10 days (and presumably would have been sexually attractive), there was no mating activity until 6 days after male attachment. Thus, even though unfed, male A. hydrosauri produce mature spermatids and would appear capabl of mating, it is still problematical

Movement and Host Finding by Unfed Nymphs of Two Australian Reptile Ticks.

Unfed nymphs ofthe Australian reptile tick species Aponomma hydrosauri and Amblyomma limbatum stayed in aggregated groups in one spot, despite the presence of host lizards as close as 50 cm. The two tick species apparently wait for hosts to come by, in contrast to other species which actively respond to nearby hosts. It may be that, because the bodies ofthe reptile hosts are so close to the ground, the ticks do not have to give up the benefits of remaining in sheltered microhabitats for efficient host finding.

The influence of similar aggregation pheromones on the microhabitat choice of two parapatric species of reptile tick (Acari: Ixodidae).

Non-specificity of part of the sex pheromone system of three species of reptile tick has previously been suggested to result in reproductive interference between the species when they attach to the same host (Andrews et al. 1982). Two of the species, Aponomma hydrosauri and Amblyomma limbatum, have common aggregation pheromones which act when the ticks are detached from their hosts. As each species tends to occupy spatially separated microhabitats, the similarity of the aggregation pheromone could lead to interference between species when off their hosts by inducing one species to move away from its preferred microhabitat into that occupied by the other species. This study demonstrates that coaggregations of both species do occur, but that neither species shows a statistically significant shift in microhabitat preference attributable to interactions between species. We suggest that the behaviours leading to microhabitat choice in each species override the influence of the common aggregation pheromone.