A qualitative analysis of the form, function and interrelationships of fat body and associated tissues in adult ticks (Acari-Ixodoidea).

Abstract

AbstractTick peripheral and central fat body (FB) contains distinct acidophilic and basophilic cell types. Previous workers call them trophocytes and nephrocytes, respectively, but overlapping physiological functions make histological descriptors more serviceable. Acidophils in Argasidae and Ixodidae contain sudanophilic vacuoles with localized caps showing nonspecific esterase activity. They are implicated in trophic lipid storage but also contain carbohydrate and protein. FB acidophils are also implicated in purine metabolism and may serve the function of insect urate cells. Basophils may contain abundant carbohydrate and protein but little lipid. Pinocytosis of dyes and incorporation of presumptive hemoglobin derivatives implicates them in deposit excretion. Pinocytosis by hemocytes, pericardial cells, Malpighian tubules and basophils indicates a probable division of labor in uptake of various sized particles from tick hemolymph.Differentiation of central FB is coordinated with maturation of reproductive organs, usually in response to adult blood meals. There is a simultaneous development of central and peripheral FB only in ixodid females. Timing and extent of FB differentiation implicates these tissues in vitellogenic processes associated with the extensive fecundity and strict gonotrophic requirements of female ixodids. Absence of peripheral differentiation in male ixodids and most argasids appears related to persistence of gonotrophic rhythms. Ixodid peripheral FB autolysis may be related to connective tissue formation or reproductive development but should also release tick symbiotes or agents of disease. Resulting increases in circulating titer should significantly affect the vector capacity of ixodid ticks.