Justin L. Tank

Developmental profiles in tick water balance with a focus on the new Rocky Mountain spotted fever vector, Rhipicephalus sanguineus

Abstract Recent reports indicate that the common brown dog tick, or kennel tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) is a competent vector of Rocky Mountain spotted fever in the U.S.A. This tick is of concern to public health because of its high frequency of contact, as it has a unique ability to thrive within human homes. To assess the moisture requirements necessary for survival, water balance characteristics were determined for each developmental stage, from egg to adult. This is the first time that water relations in ticks have been assessed throughout the complete lifecycle. Notably, R. sanguineus is differentially adapted for life in a dry environment, as characterized by a suppressed water loss rate distinctive for each stage that distinguishes it from other ticks. Analysis of its dehydration tolerance limit and percentage body water content provides no evidence to suggest that the various stages of this tick can function more effectively containing less water, indicating that this species is modified for water conservation, not desiccation hardiness. All stages, eggs excepted, absorb water vapour from the air and can drink free water to replenish water stores. Developmentally, a shift in water balance strategies occurs in the transition from the larva, where the emphasis is on water gain (water vapour absorption from drier air), to the adult, where the emphasis is on water retention (low water loss rate). These results on the xerophilic‐nature of R. sanguineus identify overhydration as the primary water stress, indicating that this tick is less dependent upon a moisture‐rich habitat for survival, which matches its preference for a dry environment. We suggest that the controlled, host‐confined conditions of homes and kennels have played a key role in promoting the ubiquitous distribution of R. sanguineus by creating isolated arid environments that enable this tick to establish within regions that are unfavourable for maintaining water balance.

High temperature effects on water loss and survival examining the hardiness of female adults of the spider beetles, Mezium affine and Gibbium aequinoctiale

Abstract A remarkable ability to tolerate temperatures as high as 52°C for Mezium affine Boieldieu and 56°C for Gibbium aequinoctiale Boieldieu (Coleoptera: Anobiidae) was discovered as part of a water balance study that was conducted to determine whether desiccation-resistance (xerophilic water balance classification) is linked to survival at high temperature. Characteristics of the heat shock response were an intermediate, reversible level of injury, appearing as though dead; greater recovery from heat shock by G. aequinoctiale (57%) than M. affine (30%) that supplemented higher temperature survival by G. aequinoctiale; and lack of protection generated by conditioning at sublethal temperature. Heatinduced mortality is attributed to an abrupt, accelerated water loss at 50°C for M. affine and 54°C for G. aequinoctiale, not to the species (M. affine) that loses water the slowest and has the lower activation energy, Ea as a measure of cuticular boundary effectiveness. These temperatures where water loss increases sharply are not critical transition temperatures because Arrhenius analysis causes them to be erased (uninterrupted Boltzmann function) and Ea fails to change when cuticular lipid from these beetles is removed. Our conclusion is that the temperature thresholds for survival and accelerated water loss closely match, and the key survival element in hot and dry environments contributing to wide distribution of G. aequinoctiale and M. affine derives from rising temperature prompting entry into quiescence and a resistance in cuticular lipid fluidity.

Moisture requirements for activity/survival of the gulf coast tick, Amblyomma maculatum Koch (Acari: Ixodidae), based on a water balance study of all life cycle stages

Abstract To provide information pertaining to features fundamental for survival, activity and spread of the Gulf Coast tick Amblyomma maculatum Koch (Acari: Ixodidae), vector of agents of human spotted fever rickettsiosis (boutonneuse fever) and canine hepatozoonosis, we determined water balance characteristics for each life stage, supplementing earlier work on adults, for a more comprehensive evaluation through the life cycle. The water balance profile of A. maculatum follows a consistent developmental pattern where the egg is the major water-conservation stage, the larva emphasizes water gain (water vapor absorption from drier air; low critical equilibrium activity, CEA), the adult emphasizes water retention (low net transpiration rate) and the nymph is transitional. A. maculatum in the various stages shares a similar dehydration tolerance limit, CEA, percentage body water content and inability to drink free water from droplets with other ticks. The low net transpiration rate of A. maculatum is the distinguishing feature, classifying A. maculatum as xerophilic compared to other tick species and their corresponding stages. Of importance, the low net transpiration rate of A. maculatum does not match the humid environment (predicting high net transpiration rate) where this tick is distributed, rather it reflects conditions of the microhabitat and slightly altered behaviors relevant to drying out that permit survival in the larger areas that they occupy. Thus, the view that net transpiration rate is an indicator of habitat preference in terms of moisture requirements needs to be modified. Ticks operate on a smaller scale (i.e., microhabitat), indicating a need for direct field observations.

Function of the Urnulae in Protecting the Red Velvet Mite, Balaustium Sp., Against Water Loss and in Enhancing its Activity at High Temperatures

Abstract Features of Balaustium sp. include resistance to intense heat and desiccation, affinity for hot surfaces in bright light, abundance in semi-arid/arid biotopes, and a large pair of secretory glands called umulae with no known function (defense secretion excepted). Here we show that the urnulae secrete a waterproofing barrier that reduces the mites cuticular permeability to water. Exposure to white light was used to stimulate release of the secretion; the urnulae protruded and exuded streams of red fluid at the tip of this structure that covered the entire body. Results showed that mites coated with urnulae secretion lost water at approximately half the rate of mites that did not secrete. Similarly, urnulae secretion coated mites demonstrated an increase in water-tightness of the cuticle reflected by a 9°C elevation in temperature threshold for water loss on an evaporation curve, increasing their optimal temperature tolerance for survival (lethal permeability temperature, LPT). Results also show a 10 kJ/mol drop in activation energy (E a) for water loss, representative of a substantial cuticular modification, and a decrease in Arrhenius frequency steric factor A, indicating an overall decrease in body water losses. The absence of a critical transition temperature (CTT), however, reveals that urnulae secretion coating functions to resist a phase change as the temperature rises, permitting the mites to cope with high temperature without succumbing to water and heat stress, by inhibiting cuticular breakdown.

DIFFERENCES IN BODY SIZE AND WATER BALANCE STRATEGIES BETWEEN NORTH CAROLINA AND FLORIDA POPULATIONS OF THE SAND FIDDLER CRAB, UCA PUGILATOR

Abstract Sand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower body water content, however, overlaps with features of arthropods that thrive at low temperature, suggesting that U. pugilator-NC may be more cold tolerant.

Water exchange pertaining to host attachment sites and stream preference in crayfish-associated branchiobdellids, Cambarincola fallax and Cambarincola ingens (Annelida: Clitellata)

Water balance profiles were constructed for adults of two branchiobdellid species (Cambarincola fallax and Cambarincola ingens) to examine how they are differentially adapted for a freshwater habitat on different crayfish hosts. Both exhibited a high (75%) body water content and high net transpiration rate, reflecting that they are hyperosmotic to freshwater and display a consistent strategy that emphasizes water loss. In contrast to C. ingens, C. fallax was 6× smaller in body size, lost water 2× faster, and had heightened activation energy (Ea) for water permeability. Thus, C. fallax relies on high net transpiration rate with a focus on elimination, whereas the larger C. ingens are modified for water retention and rely on their low activation energy to suppress the amount of water that enters the body. Neither species showed evidence of a critical transition temperature (CTT), as indicated by an uninterrupted Boltzmann temperature function of passive water loss rates. No influence on favoring water balance was apparent in relation to the crayfish host with regard to preferred attachment sites (subrostral or branchial chamber) or preference for occupying different regions (pool vs. riffle) of the stream. Thus, water balance strategies between the two species are complementary, reflecting trade-offs that adjust for body size to promote survival in similar freshwater habitats. The ability of C. ingens and C. fallax to survive with a low water content, down to nearly 1/2 their body mass, however, enables them to cope with the excess water by permitting a high rate of water loss.

Demonstration of an enhanced ability to tolerate high temperature in unfed larvae of the Brown dog (Kennel) tick, Rhipicephalus sanguineus (Acari: Ixodidae)

Abstract Reported are the results of a five-species comparison of heat tolerance in unfed tick larvae. Resistance to heat stress was quantified by scoring the behavioral tasks completed by larvae following 1 hour of exposure at 20°C, 30°C, 40°C, 50°C, or 60°C. Notably, all larvae were similar in age, reared under standardized thermal, photoperiod and relative humidity conditions, and had not yet fed, which minimized interference from potential acclimatization factors. Heat injury was signified by curling the front pair of legs (legs I) into a box-like shape, but none of these larvae survived. This ‘all or nothing’ (alive or dead) response in tick larvae differs from most insects, which typically undergo reversible, intermediate levels of injury. The most heat tolerant species was Rhipicephalus sanguineus (Latreille). Specifically, over 90% of the larvae resisted injury at 40°C, and about 1/3 were capable of surviving treatment at 50°C, a temperature where most other species were killed. Ixodes scapularis Say represented the opposite extreme, displaying significant injury and mortality at 30°C and increased mortality at higher temperatures. Between these two extremes were the responses by Amblyomma americanum (L.), Amblyomma maculatum Koch and Dermacentor variabilis (Say), all of which overlapped with each other. We concluded that enhanced heat tolerance contributes to the ability of R. sanguineus to function in a dry environment, but this capacity is less important for ticks that are differentially adapted for a moisture-rich environment. There was no evidence in any of these larvae that protection against high temperature could be generated by a brief exposure to a sublethal temperature similar to the rapid hardening response observed in certain insects.

Dehydration tolerance of the Rocky Mountain wood tick, Dermacentor andersoni stiles (Acari: Ixodidae), matches preference for a dry environment

Abstract Peak activity of the medically significant Rocky Mountain wood tick, Dermacentor andersoni Stiles (Acari: Ixodidae), during hot summer months in the Rocky Mountains and southwestern Canada was evaluated by determining water balance characteristics for each of its developmental stages. This tick is dry-adapted and has a water balance classification as xerophilic based upon interspecific comparison with other ticks and a low net transpiration (water loss) rate as the distinguishing feature. All stages (eggs excepted) rely on water vapor as the primary source of water, as evidenced by critical equilibrium humidity assessments and an inability to drink free water from droplets. A relatively low dehydration tolerance limit and high net transpiration rate is reported for the larva, indicating that it is the most sensitive stage to water stress in the lifecycle. The xerophilic nature of D. andersoni makes it less dependent upon a moisture-rich environment and identifies overhydration, although unstudied, as the primary factor limiting its distribution to the Rocky Mountain area.

High temperature resistance of the terrestrial red mite (Balaustium sp.) as a product of suppressed heat induced water permeability

Abstract An impressive capacity to thrive at temperatures as high as 50°C is reported for adults of the velvet mite, Balaustium sp. near putmani (Acari: Erythraeidae) from Ohio, USA. This mite also has the ability to recover from injury due to heat shock, demonstrating a 2/3 survival rate after treatment at 52°C. Exposure to 54°C was lethal and could not be protected against by conditioning at a sublethal temperature. These mites exhibit a 50-52°C threshold where evaporative water loss rate accelerates sharply, an inflection point that we have designated as the lethal permeability temperature (LPT); mortality is attributed to rapid water loss at temperatures above LPT. When data are plotted on an Arrhenius plot as in the case of critical transition temperature (CTT) however, this inflection point (LPT) disappears, thus implying that this mite resists an increase in cuticular lipid fluidity as the temperature rises.

Inability of the lone star tick, Amblyomma Americanum (L.), to resist desiccation and maintain water balance following application of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae (Deuteromycota)

Abstract We report that female lone star ticks (Amblyomma americanum) experience a rapid change in water permeability when treated with the entomopathogenic fungus Metarhizium anisopliae. The amount of water loss is nearly double the rate of control ticks not exposed to this fungus. As a result, ticks are prevented from stabilizing body water levels (water gain ≠ water loss) at hydrating atmospheres greater than the critical equilibrium activity (CEA) of 0.85a v-0.93av (a v = % RH/100) and reach their dehydration tolerance limit in less time. Thus, disruption of water balance is a pathogenic consequence of fungus infection. This served as a benchmark for evaluating effects on ticks of frequently encountered soil molds in nature (wild tick isolates), Aspergillus niger, Cladosporium cladosporioides, Penicillium glabrum and Scopulariopsis brevicaulis. In contrast to M. anisopliae treatment, no effect on tick water balance was noted with topical application of C. cladosporioides, but water loss rates of ticks following treatment with S. brevicaulis fell between both extremes. Water loss rates imply that P. glabrum may be a tick pathogen, whereas A. niger is apparently not able to use ticks as a substrate. Enhanced desiccation arising from these common molds shows the importance of local mycoflora as natural regulators of tick populations. Water loss rates also provide a tool to assess the pathogenicity of different fungal strains targeted for application in the biological control of ticks.