Water absorption through salivary gland type I acini in the blacklegged tick,Ixodes scapularis

Abstract

Tick salivary glands play critical roles in maintaining water balance for survival, as they eliminate excess water and ions during blood feeding on hosts. In the long duration of fasting in the off-host period, ticks secrete hygroscopic saliva into the mouth cavity to uptake atmospheric water vapor. Type I acini of tick salivary glands are speculated to be involved in secretion of hygroscopic saliva based on ultrastructure studies. However, we recently proposed that type I acini play a role in resorption of water/ions from the primary saliva produced by other salivary acini (i.e., types II and III) during the tick blood feeding phase. In this study, we tested the function of type I acini in unfed female Ixodes scapularis. The route of ingested water was tracked after forced feeding of water with fluorescent dye rhodamine123. We found that type-I acini of the salivary glands, but not type II and III, are responsible for water uptake. In addition, the ingestion of water through the midgut was also observed. Injection or feeding of ouabain, a Na/K-ATPase inhibitor, suppressed water absorption in type I acini. When I. scapularis was offered a droplet of water, ticks rarely imbibed water directly (5%), while some approached the water droplet to use the high humidity formed in the vicinity of the droplet (23%). We conclude that during both on- and off-host stages, type I acini in salivary glands of female Ixodes scapularis absorb water and ions.

Liquid water intake of the lone star tick, Amblyomma americanum: Implications for tick survival and management

“…However, these authors could not distinguish between water vapor and water drinking. In our previous study on I. scapularis 17 , we observed water in the type I acini of the salivary glands and the midgut after capillary feeding. However, water droplet drinking behavior was rare with only 5% (2/43) ticks ingesting water this way.…”

“…The water volume measured in droplet feeding using bacteria, as a quantifiable tracer, was lower than that with the capillary feeding and this is likely because of the underestimation of water volume due to digestion of bacteria in the midgut and some loss during bacterial recovery and culturing. These bacteria were recovered from the internal soft tissues and likely derived from the midgut and the salivary glands, as these are the sites for water absorption 17 .…”

“…1d,f). This suggests that the uptake of water occurs through both, the salivary glands and the midgut as proposed for I. scapularis 17 , whereas the uptake through the salivary glands is the primary mechanism in the voluntary feeding of the water droplet. exploitation of water drinking behavior for tick management.…”

Dissecting Flavivirus Biology in Salivary Gland Cultures from Fed and UnfedIxodes scapularis(Black-Legged Tick)

“…5A; see also Movie S1 and S5) throughout the SG. The tracheal ducts, involved in respiration, are not part of the SG apparatus but are often found intertwined with SGs (27,47). The GFP expression around these ducts was often noted in areas where acini were attached.…”

“…The type 1 acini are agranular and nonsecretory in nature; they are implicated in osmoregulation and ion uptake. The type 2 and 3 acini are granular and secretory in nature; they are involved in production and secretion of saliva (27)(28)(29). The type 2 acinus is composed of cell types a, b, and c, whereas the type 3 acinus has cell types d, e, and f (30,31).…”