The Compatibility and Incompatibility Concept as Related to Trematodes and Molluscs! THOMAS C. CJ-IENG2 IN THIS PAPERI propose to bring together dur ing the evolutionary adaptation to para­ significant facts already known to have some sitism of the progenitors of modern day di­ bearing on the mechanisms which govern or genetic trematodes, one might expect to find influence host compatibility or incompatibility the occurrence of certain adaptive mechanisms during parasitism, to add information based on more firmly entrenched in them than in verte­ my own recent research, and to present some brate definitive hosts. Furthermore, it is easier speculations. to simulate experimentally the natural environ­ From the broad viewpoint, host compatibility mental conditions of molluscs than those of may be defined as the expression of the physical vertebrates in captivity, and, with relative ease, and physiological (including chemical) states one can test basic prem ises on a numb er of of the host and parasite which enable the para­ species from a variety of habitats, ranging from site to invade and carry out its life processes, marine to fresh water, and from various atti­ includ ing perpetuation of the species. Incom­ tudes. patibi lity refers to those factors which com­ It has long been known that compat ibility pletely or part ially prevent the establishment and incompatibility need not be "all or none" and normal development of the parasite. Both phenomena, since both interspecific and intra­ of these are highl y complex phenomena influ­ specific (o r strain) differences do occur, as is enced to one degree or another by a series of indicated by the rate of parasite developm ent, separate but commonly interrelated factors. infectivity of the cercariae or metacercariae, the As working models from which we can seek number of progeny produced by delayed poly­ evidence to support or reject various working embryony, etc. In fact, an understandin g of the hypotheses, we have chosen to examine the re­ factors governing compatibility and incompati­ lationship between molluscs and digenetic trem­ bility in turn most probably will provide an­ atodes, since this category of association, unlike swers for why these manifestations occur. a num ber of others, is an example of parasitism Since the initial host-parasite contact, the whether the definition of "parasitism" is invasion process, the establishment of the para­ couched in nutritional, pathological, ecological, site within the host, and the escape process are or immunological terms. Molluscs, except in a distinct aspects of a successful parasitic relation­ very few unusual instances, serve as interm edi­ ship (see the review by Cheng, 1967) , one ate hosts for the Digenea, but this fact does would expect factors correlated with all of these not render them less appropriate as experimental phases to contribute to some degree in regu ­ tools. In fact, inasmuch as it is generally ac­ lating compatibility and/ or incompatibility, and, cepted that molluscs were the original hosts indeed , available evidence indicates that this is so. In the following paragraphs are briefly re­ 1 Th e research reported in this pap er was supp orted viewed those facts which support this concept. by grants from the American Cancer Society and the Space does not permit the citation of all the Office of Research Administration, Un iversity of relevant literature; therefore, only selected Hawaii. Th is paper was originally presented at a symposi um sponsored by the Di vision of Invertebrate studies are cited as examples. Zoology, American Society of Zoologists, entitled "The Parasites of Invertebrates," held on December 30, 1966 in W ashington, D .C. Manuscript received INITIAL HOST-PARASITECONTACT December 13, 1966. 2 Dep artment of Zoology, University of H awaii, Recently, Timon-David (1965) has again H onolulu, Hawaii 96822 . raised the question of the importance of host- 141 142 PACIFIC SCIENCE, Vol. XXII, April 1968 attraction in governing host-specificity In speed of a single miracidium was timed, re­ mollusc-trematode relationships. This topic, corded as seconds/2.54 mm, and later expressed which has been critically reviewed by myself as mru/s ec (Tables 1 and 2) . As controls, the (Cheng, 1967), among others, is still a con­ swimming velocities of miracidia of similar age troversial one. The controversy is not whether placed in distilled water were determined. host-attraction does occur since, in my opinion, The six test media consisted of 1:10, 1:50, the studies of Faust and Meleney (1924), Faust and 1: 100 dilutions of molluscan plasma and (1934), Faust and Hoffman (1934), Barlow similar dilutions of tissue extracts. Blood was (1925), Tubangui and Pasco (1933), Mathias collected from the molluscs' body sinuses by (1925), Kloetzel (1958, 1960), Kawashima gently cracking the shell of each snail, without et al. (1961a), Campbell (1961), Davenport injuring the soft tissues, and permitting the et al. (1962) , Etges and Decker (1963), and blood to drain to the lower edge of an inclined MacInnis (1965) have demonstrated rather Stender dish from whence it was rapidly col­ conclusively that attraction between miracidia lected with a hypodermic needle and syringe. and molluscs does occur. This is a subtle phe­ The cellular components of whole-blood samples nomenon, however, which is operative only were removed by centrifugation. The tissue ex­ within very restricted distances and can be ob­ tracts were prepared by homogenizing the soft served only with the application of quantitative tissues of each snail in 1 cc of distilled water techniques. The controversy is over the question after the tissues had been completely desan­ whether chemotaxis is in any way related to guinated and perfused with running distilled host-specificity and hence influences compatibil­ water for 15 minutes. After homogeniz ation in ity. Although the studies of Faust and Meleney an ice bath, the homogenates were centrifuged (1924) , Barlow (1 925), Neuhaus (1953) , and and the aqueous extracts collected were con­ Etges and Decker (1963) suggest that rniracid­ sidered the "concentrated" extracts. ial attraction is host-specific, the results of Sudds All snails used were laboratory-raised and ( 1960) , Kawashima et al. (1 961a) , and Bar­ known to be parasite-free. The concentrated bosa (1965) suggest that attraction of miracidia plasma and tissue extracts of each species were to a specific mollusc need not be correlated with pooled and the desired diluti ons were made subsequent compatibility. from the pooled samples. All observations were Experiments carried out in our laboratory made at 22 -+ 10 C. have revealed that the miracidia of Fasciola From the data presented in Tables 1 and 2, gigantica are stimulated by the plasma and tissue it is evident that all three dilutions of the extracts of laboratory-raised Galba ollula, the plasma and tissue extracts of G. ollnla (the natural host in Hawaii. These reactions, how­ natural host), H. dltryi normale, and T . grani­ ever, are not specifically elicited by G. ollula, [er« stimulated F. gigantica miracidia to increase since similar reactions were observed when their swimming velocities. In addition, the mira­ miracidia were exposed to the plasma and tissue cidial swimming pattern was conspicuously extracts of two other species of freshwater altered. Miracidia in distilled water usually gastropods, T arebia granifera mauiensis and swam linearly, rotating along their longitudinal H elisoma dllryi uormale. axes. Divergences from such a course were grad­ In the first series of experiments, F. gigantica ual rather than abrupt. When placed in plasma miracidia, between 15 and 25 minutes post­ or extracts, their swimming behavior became hatching, were placed in shallow Petri dishes erratic. They turned abruptly and frequently. (50 mm in diameter, 15 mm high) in which In the second series of experiments, 10 mira­ had been placed specific dilutions of the plasma cidia, 10-15 minutes post-hatching, were placed or tissue extracts of H. dllryi normale, T. grani­ in small Petri dishes (6 0 mm in diameter, 13 fera manlensis, or G. ollula. Each dish was mm high ) which contained 10 cc of distilled placed over a grid marked off in 2.54-mm water. In the center of each dish was placed an squares. Using a 1'lo-second-interval stop-watch agar block of three mm" which had been pre­ and observing under a dissection microscope soaked in concentrated plasma or tissue extracts illuminated by indirect lighting, the swimming of G. olinl«, H . dNryi normale, or T . granifera () ~ I"..... TABLE 1 [ COMPARISO NS OF THE SWIMMING V ELOCITIES OF Fasciola gigantica MIRACIDIA IN DISTILLED WATER (CONTROLS) AND IN THREE DILUTION S OF q' M OLL USCAN P LASMA (THE STUDENT t T EST WAS EMPLOYED TO D ETERMIN E SIGNIFICAN CES) S' DISTILLED W ATER ~ ( CON TROLS) 1 :10 P LASMA 1 :50 PL ASMA 1:100 PL ASMA I"3 S- M OLLUSCAN NO . OF VELOCITY N O. OF VELOCITY SIG· N O. OF VELOCITY SIG- N O. OFVELOC ITY SIG· c, SPECIES TRIALS ( MM /SEC) TRIALS ( M M/ SEC) P N IF . TRIALS (MM/SEC) P N IF. TRIALS (MM/SEC) PN IF. Dl I" G. ollula! 40 0.79 25 1.65 > 0.001 30 1.88 0.01 20 1.91 0.01 ;:l + + + 0.. H. duryi normals- 101 1.96 81 2.70 > 0.001 + 81 2.80 > 0.001 + 118 2.85 > 0.001 + T . g1'anijera3 60 2.30 60 3.5 < om 60 3.5 < om 60 3.5 < 0.01 ~ + + + 2­ I Th e miracidia used were 25 minutes post-hatching , C 2 Th e miracidia used were 18-20 minutes post-hatching. en 3 The miracidia used were 15 minutes post-hatching. Cl I () :r: t11 oZ TABLE 2 COMPARISONS OF THE SW IM MING V ELOCITI ESOF Fasciola gigantica MIRACIDIA IN DISTILLED WATER (CON TROL S) AN D IN THREE DILUTIONS OF M OLL USCAN A QUEOUS T ISSU E E XTRA CTS (TH E STUD ENT t T ESTW AS U SED TO D ETERMI N E SIGNI FICANCES) DISTILL ED WATER (CON TROLS) 1:10 EXT RACT 1 : 50 EXTRACT 1:100 EXTRACT MOL LUSCAN NO .