Another aspect of the role of parasites of shellfish which is of potential importance to public health is the possible role of parasites, protozoa, helminths and arthropods, as carriers of pathogenic bacteria, viruses and other microorganisms. This concept is not as far-fetched as it would appear. Recently Moewus has reported that a holotrichous hymenostome ciliate, later named Miamiensis avidus by Thompson and Moewus , a facultative parasite associated with skin tumors of seahorses, was experimentally found to be able to harbor polio viruses of the Mahoney strain.
Thus, a more thorough understanding of both the types of parasites found in commercially important and potentially important marine molluscs and their metabolic effects on hosts are of importance to medical and public health workers. These schistosome trematodes develop to the cercarial stage in various littoral gastropods that commonly share the same habitat as certain commercially important shellfish. For example, the bird schistosome Austrobilharxia variglandis is found along the Atlantic coast of the United States in Nassarius obsoletus which shares the same mud flats with the soft clam, M y a arenaria, and the quahaug clam, Mercenaria mercenaria.
Thus, individuals digging for clams in these areas may be subjected to cercarial attack resulting in dermatitis on exposed skin. These, like P. I n the case of P.
Cercariae escaping from parasitized snails encyst ectopically and develop into metacercariae. When these metacercariae are fed to certain birds, migration to the eyes occurs and mature trematodes can be recovered from under the nictitating membrane. Although Philophthalmus hegneri, P. Furthermore, another related freshwater species, P. Philophthalmus is an example of a marine trematode of potential public health importance. Since this area of parasitology, i.
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With the world looking increasingly more to the ocean for food substances, medical or public health marine parasitology will undoubtedly receive increased attention. By analyzing these associations, it is possible to seek and obtain answers to such questions as these. Are symbionts attracted to their hosts, and, if so, what are the attracting forces! What are the nutritional requirements of symbiotic protozoa, mesozoa, helminths, molluscs, annelids, arthropods and other categories of symbionts, and what are the sources of these requirements?
Do differences exist between aspects of the metabolism of ectophoretic and endoparasitic symbionts, and, if so, do these differences suggest mechanisms involved in the adaptation to endopara- 3. The number of questions that can be asked are numerous. Many already have been investigated and answers are available ; however, in comparison with what potentially can be done, we have barely begun.
I n the following chapter some of the information now available is reviewed. The phases I am proposing are: 1 the period of initial host-symbiont contact ; 2 the establishment of the symbiont on or within the host, and 3 the eventual escape of the symbiont or its progeny so as to effect other similar associations. AS outlined in Table I, each of these major phases can be subdivided into several factors, each of which can be subjected to experimental or observational analysis.
Accidental contact 1. Successful attachment 2. Developmental stimuli contributed by host 3. Contact influenced by chemotaxis 4. Contact influenced by other taxes 5. Selectivity by symbiont 6. Influence of nature of substrate 4. Pathological changes induced by symbiont C Escape of the symbiont 1. Active escape 2. Involuntary escape 3. Passive escape 4.
Two additional factors may well be involved when one considers ectosymbionts : 6 for example, for hydroids that become attached to the shells of marine molluscs, selectivity on the part of the settling larvae could also influence the contact; 7 furthermore, in those associations in which the symbiont has to be in continuous contact with a solid or semi-solid substrate while approaching the host, the chemical and physical nature of the substrate could be of importance. I n the case of commensals and phoronts, the availability of nutrients, although not directly of host origin, is also necessary.
The occurrence of developmental stimuli and control of maturation implies metabolic dependence, and hence occurs only during mutualism and parasitism. This is particularly true during parasitic relationships. For example, if a parasite is highly pathogenic and causes the death of the host within a relatively brief period, the relationship, and therefore the establishment, from the standpoint of the parasite, could hardly be considered a biologically successful one. Eventually either the symbiont or its germ cell-bearing progeny must successfully escape from the host to perpetuate a similar association with another or the same host.
From what is known about the severance of symbionts from hosts, various mechanisms could be involved to effect the escape. The conceptual factor analysis of the phases involved in symbiosis presented above serves as the guide line along which the following review is based. Accidental contact The first type of host-symbiont contact may be thought of as a casual and accidental one. There is no reason to believe that many epiphoretic organisms found clinging to the shells of marine molluscs had actively sought out and became attached to their hosts, nor is there experimental evidence to suggest that there is host-specificity in the choice of hosts by all epiphoronts.
Although Dales has chosen to interpret the association of the hydroid Clytia bakeri with certain molluscs on the surf-swept beaches of southern California as reported by Torrey to be beneficial for the survival of the hydroids, and probably correctly so, there is no reason to believe that C. The abundance of these molluscs, coupled with their availability when the planula larvae were settling, most probably accounts for their relationships with these more or less sedentary molluscs.
Because of the sedentary habits of these molluscs, the hydroids are prevented from being swept away with the tide. I n addition, Dales has suggested that the hydroids probably benefit from their position near the feeding currents of the clams. A list of some hydroids known to be symbiotic on marine molluscs is given in Table The thigmotrichous ciliates, often found in the mantle cavity or on the gills and palps of estuarine pelecypods, belong to the second group, while the ciliate Trichodina myicola, found in the alimentary canal of M y a arenaria, belongs to the first.
If the host, as in the case of many marine gastropods, is an active detritus feeder, various symbionts could be included in the food. Various protozoa and helminths, including cysts and eggs, could be introduced into the host in this manner. Although examples have not yet been found among marine molluscs, it is possible that cannibalistic molluscs could become parasitized while feeding on other molluscs that are parasitized. Cheng and Alicata have reported that the transfer of the third-stage larvae of Angiostrongylus cantonensis from one land snail, A c h t i n a fulica, to another can be effected by this method.
Contact inpuenced by chemotaxis In addition to the two methods of host-symbiont contact given above, many symbionts, ranging from ectocommensals to endoparasites, in varying degrees, seek and contact their hosts. It is primarily with such active symbionts that specific attraction to the host is suspected. Unfortunately, information pertaining to the chemotactic response of symbionts to marine molluscs is extremely sparse.
Although specially designed studies have been carried out to determine the attraction for symbionts, primarily commensal polychaetes, to nonmolluscan hosts Davenport, ; Davenport and Hickok, , the attraction of the sea anemone Stoichactis for the pomacentrid fish Amphiprion percula Davenport and Norris, , the attraction of the east coast pinnotherid crab, Dissodactylus mellitae, to its echinoid host, Mellita Johnson, , and the attraction between Anodonta implicata glochidia and the alewife, Pomolobus pseudoharengus Davenport and Warmuth, , parallel studies involving marine molluscan hosts are few see reviews by Davenport, , Among commensalistic relationships, Ross , who studied the relationship between the actinian anemone, Calliactis parasitica, and the hermit crab, Eupagurus bernhardus, with the latter within the shell of the whelk, Buccinum undatum, has demonstrated that Calliactis parasitica will readily settle on shells of living Buccinum undatum in the laboratory and will not desert these for shells occupied by crabs.
Also found on Dentaliurn sp. Howillustrations ; ever, evidence indicates the oppoMartin and site-that the nudibranch begins Brinckmann as a commensal inside the bell of life hist'ory Zanclea, and when this habitat is outgrown it attaches itself to its manubrium which it later devours with its tentacles North and South Large, few-tentacled, naked polyps.
Atlantic, Gonophores produced from hydroIndian Ocean rhizal net Ei 5w m 0 w w! Subsequently, Ross and Sutton , as the result of a series of tests designed to determine the frequency and speed of the clinging response of C. Furthermore, the anemone does respond to isolated strips of periostracum as to untreated shells.
In addition, C. An extension of this work by Davenport et al. Moreover, the threshold of nematocyst discharge changes markedly in accordance with the attachment behavior of the animal. The discharge threshold is lower in free animals than in animals already attached by their pedal disks to a shell. Thus it would appear that an anemone receives information from the contact of the pedal disk with the shell which in turn influences the discharge threshold. It has been suggested that chemoreceptors in the pedal disk may be responsible for initiating this reaction after responding to some organic material in the periostracum.
Although the studies cited above strongly suggest chemotaxis of C. According to him, one can dredge up numerous Buccinum in the English Channel, but one almost never finds Calliactis parasitica on these. It is only on empty shells harboring hermit crabs that C. Since it is known that the hermit crab, Eupagurus bernhardus, does not aid the anemone in becoming attached Ross, , the question arises as to whether the reaction of the anemone to the periostracum of Buccinum undatum is a conditioned reflex that only appears after the molluscs vacate their shells.
This remains to be determined. Another study which demonstrates chemotaxic attraction of a symbiont to its molluscan host was carried out by Muriel A. Wikswo 4. I n brief, she has been able to demonstrate that the polynoid polychaete Arctonoe wittata is stimulated when exposed to sea water in which its host, the keyhole limpet, Diodora aspera, had been placed. Wikswo has also shown that the nature of the substrate does influence the attraction of Arctonoe vittata to Diodora aspera. If both organisms are placed in a glass-bottomed bowl the polychaete readily moves towards the host, but if placed in a sandy bottom bowl it does not.
Similarly, if the bottom of the bowl is lined with cheese cloth, Arctonoe vittata rarely moves towards its host. Wikswo has also demonstrated that Arctonoe vittata is repelled by dead Diodora aspera. This observation confirms the finding of Davenport and Hickok who have demonstrated that commensals, Arctonoe fragilis in their case, are repelled by water from an aquarium that contained injured starfish, Ewasterias, its natural host.
It would thus appear that the attractant can be either destroyed or masked by substances produced by dead or damaged hosts. This would undoubtedly be of advantage to symbionts in nature, since they would actively migrate from a dead or moribund host. Among parasites of molluscs, studies designed to determine the attraction or non-attraction of parasites are primarily limited to those concerned with the attraction of trematode miracidia to freshwater gastropod intermediate hosts. Since the results of such studies, which are still highly controversial, may contribute further insights into the nature of host-secreted attractants host factors , the available information is briefly reviewed herein.
The pitfalls and misinterpretations by those working with freshwater molluscs, as well as their concrete findings, can no doubt serve as guards against similar mistakes and act as profitable guides in future work with marine molluscan hosts. The subject at hand has been reviewed by Wright a. My review incorporates, but extends beyond, his.
I n brief, two schools of thought are in existence relative to the mechanisms involved in miracidiummollusc, primarily gastropod, contact. There are those who champion the concept that a host-elaborated attractant or stimulant exists, and there are those who believe that host contact is strictly a random process.
The response to K. These are among the first experimental demonstrations of the manner in which specificity may be determined by precise behavior of a parasite under host influence. The exact attraction-mechanism is unknown, but the work of Barlow on Fasciolopsis buski and of Tubangui and Pasco on Echinostoma ilocanum miracidia indicates that it is some fraction of the tissue juice of tho appropriate snail. Wesenberg-Lund was convinced by his field observations that the miracidia of a species of trematode demonstrate a pronounced preference for a distinot species of mollusc within a given locality.
Neuhaus , who observed the behavior of Fasciola hepatica miracidia, has suggested that these ciliated larvae are initially attracted by the ciliary currents maintained by the epithelia of Lymnaea spp. In an extension of his earlier observations, Neuhaus reported a definite chemotaxis between various species of Lymnaea and F. I n more recent years, several investigators have designed and carried out more elaborate experiments to prove or disprove the occurrence of attraction between trematode miracidia and molluscs. Kloetzel has carried out a series of carefully controlled experiments with Schistosoma mansoni miracidia and the snail Australorbis glabratus.
I n the initial experiment he placed a single snail in a dish containing a known number of miracidia. He made counts of the number of miracidia in the immediate vicinity of the snail and a t other points in the dish at known time intervals. Thus he was able to demonstrate that the number of miracidia around the snail was significantly higher than at a point diametrically opposed to it after 15 min.
In the second series of experiments he removed the snail from the miracidia-containing dish after 15 min and, after washing it to remove adhering larvae, replaced it at the opposite side of the dish for an additional 15 min. This suggests that some substance was left behind at the initial site which continued to attract miracidia. Subsequently, Kloetzel has found that miracidia are even more strongly attracted to a snail squashed on filter paper than to a living snail and that their attraction to an empty shell is not significantly more than random.
It was found that in such a preparation the number of miracidia which aggregated around the snail is markedly reduced when compared with control snail and miracidia preparations to which no snail extract had been added. Comparable evidences were again reported by Kloetzel His studies certainly give strong support to the belief that some degree of chemical attraction exists between Austrabrbis glabratus and Schistosoma mansoni miracidia although the attraction appears to be effective only over short distances.
Diagram of Y-shaped chemotrometer for testing reactions of miracidia. Size in mm. I n chamber A is placed the attractant snails or other substances , in chamber B any substance, and in chamber C the miracidia. Redrawn after Kawashima et al. Another study of attraction between miracidia and molluscs, one which has been often overlooked by European and American workers, was contributed by Kawashima et al.
These Japanese investigators studied the attraction between the miracidia of one of the mammalian lung flukes, Paragonimus ohirai, and three species of snails of the genus Assiminea-A. These snails are found in brackish waters at the mouths of rivers but at different salinities.
By using a modified Y-tube choice apparatus Fig. Furthermore, the miracidia are also attracted to homogenates of Assiminea 4. Kawashima et al. It was also pointed out that the host-preference of the miracidia occurs without any relation to the suitability of the snails as hosts since it is known that A. I n fact, studies have shown that A.
On the other hand, A. It is thus apparent that some additional factor must be operative in nature to bring about the selection by the miracidia for A. I n a later paper Kawashima et al.
While studying the locomotive speed and survival of Paragonimus ohirai miracidia in various concentrations of NaCl, it was found that the lower the salt concentration is, the more active the miracidia become. These findings explain the preferred habitats of the snails, since A. These also serve to explain why A. Furthermore, they have demonstrated how the salinity tolerances of the parasite and the host can serve as natural mechanisms responsible for host specificity. Another study of mollusc-miracidium attraction was contributed by Etges and Decker These investigators employed a cast-iron maze consisting of a central cylindrical chamber 4 x 8 cm diam.
The inner surface of the maze was coated with inert waterproof lacquer to prevent contamination and to facilitate cleaning between trials. I n the first series of experiments, two specimens of Australorbis glabratus, the shells of which had been crushed, were placed in two of the terminal chambers, one in each. I n each of the other two terminal chambers was placed a sham snail modelled out of inert aquarium cement.
About Xchistosoma mansoni miracidia were placed in the central chamber in conditioned water after the crushed and sham snails had been permitted to stand in the terminal chambers for 1 h, during which time substances of crushed snail origin had entered the water. After the central chamber was covered, the entire apparatus was placed under a strong light source to prevent miracidia which had reached any of the terminal chambers from returning to the central chamber. This was carried out since it is known that certain schistosome miracidia are positively phototactic.
Etges and Decker were careful to state that with the sham snails in pIace, the amounts of light reflected into the central chamber through the four arms were essentially equal. Counts of the number of miracidia in each of the terminal chambers and adjoining arms during nine runs revealed that the number of miracidia in the terminal chambers and arms associated with crushed snails was significantly greater. Again, the live snails attracted significantly more miracidia.
I n addition to using A. Physopsis sp. The results revealed that the miracidia were distributed in all cases in favor of the sham snails.
Advances in Marine Biology, Volume 50
Rather than interpreting this to mean that repulsion occurred between Bulinus spp. Control experiments with four sham snails revealed no statistically significant difference in miracidial distribution. Thus, Etges and Decker have quite convincingly dernonstrated chemotactic attraction of miracidia to their normal host, although these workers expressed their uncertainty as to whether such a stimulus is operative under natural conditions.
They further maintained that both light and gravity are far more powerful influences in determining the orientation of Sch. Standard truncated pyramids used in miracidia chemotaxis studies. After Machnis, Davenport and Hickok have shown that the commensal polychaete Arctonoe fragilis is repelled from water which had contained injured starfish, its natural host. These seemingly opposing results indicate that the response of Arctonoe fragilis to injured host is different from that of Schistosoma mansoni miracidia, with the former showing definite repulsion.
MacInnis , using another set of procedures involving agar pyramids Fig. He constructed the experimental apparatus in the following manner. I n order to test the reactions of miracidia to various amino acids, short-chain fatty acids, sugars, and various salts Table ,two types of agar pyramids were used. I n the second type, referred to as " integral pyramids ", the agar pyramids incorporated an aqueous solution of the chemical to be tested. These were not subsequently soaked in river water.
After MacInnis, A known number of miracidia was added to each dish or bowl and a pyramid containing the test chemical, or a control pyramid, was placed in the center of the container. I n addition, Australorbis gbbratus tissues were also used in another series of observations. Uninterrupted observations were recorded for min during the experiments. Responses of Schistosoma rnansoni miracidia to test pyramids contact without return. A, Normal change of direction upon contact with an obstruction; B, increased random turning ;C, directed turn at a distance ;D, encircling at a distance ; E, " turnback; F, circus movements.
Schistosorna rnansoni rniracidia normally swim with a uniform speed in a straight line while rotating clockwise or counterclockwise along the longitudinal axis. If such a miracidium should encounter a surface, including the surface film, it changes its direction of movement so as to by-pass the obstruction and continues to swim normally Fig. MacInnis reported that if miracidia enter the vicinity mm of a snail or impregnated pyramid, they portray a variety of behavior patterns. These can be summarized as follows.
This, according to the definition of Fraenkel and Gunn , is known as " chemo-orthokinesis" i. This movement appears to be an exaggeration of the rotation of the miracidium along its longitudinal axis and subscribes to the definition of " chemo-klino-kinesis" of Fraenkel and Gunn i. According to MacInnis, this type of movement, which may commence at 7 mm or more from the pyramid, appears to aid in locating a gradient of diffusing chemicals, and thus the source.
I n these instances, if a miracidium is attracted by the pyramid it suddenly turns and swims toward test object Fig. This response can be considered as Fraenkel and Gunn's " chemo-tropo-taxis " in part i. MacInnis has reported, however, that the directional turn is often accompanied by increased speed chemo-ortho-kinesis and increased " wigwagging " chemo-klino-kinesis. The combination of these three behavior patterns had been reported by Campbell and Todd a who referred to the condition as " excitement ".
This behavior pattern can be considered as " chemo-klino-taxis " i.
MacInnis has suggested that this behavior might be explained as a reaction occurring at a boundary of the moving front of the diffusing chemical, or at one place in the gradient where the concentration of the chemical is at the threshold of intensity for a positive reaction. These execute a " turn, thus pointing themselves toward the source of the stimulus Fig.
This type of behavior is considered by Fraenkel and Gunn as " chemo-tropo-taxis ". This type of behavior appears to be identical with the " whirling dance " of Davenport et al.
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It has also been described by Campbell for the miracidium of Fascioloides magna, and according to Campbell was found by Hugghins for the miracidium of Hysteromorpha triloba, a strigeid trematode. Earlier, Fraenkel and Gunn had reported this behavior among 33 4. It appears to reflect the response of only one of a pair of bilateral receptors, causing a complete turning towards a favorable stimulus or away from an unfavorable one. I n addition to utilizing the behavior patterns described above, MacInnis also has recorded six types of behavior portrayed by miracidia upon contact with a test object containing a chemical stimulus.
The detailed descriptions of these can be consulted in his paper. Responses of Schistosoma mansoni miracidia t o test pyramids contact with return. A, One loop; B, several loops; C, dipping response; D, body parallel; E, body perpendicular ; F, beeline drive, attachment, and partial penetration. Utilizing these two series of behavior patterns and agar pyramids which contained various test chemicals, MacInnis has demonstrated that short-chain fatty acids, some amino acids, and a sialic acid Table are attractive to Schistosoma mansoni miracidia and also stimulate attachment to and penetration of the agar.
Among the amino acids tested, the dibasic forms showed little or no attracting ability. It was also demonstrated that the solvent action of distilled water, ethyl ether, acetone, and ethyl alcohol can remove attracting substances from Australorbis glabratus. Furthermore, subsequent addition of butyric A. Although there is some indication that amino acids and amino sugars are present in snail mucus Wright, b , these substances have not been shown conclusively to be present.
Relative to short-chain fatty acids, there is no evidence at this time that they occur in snail mucus although they may be end-products of snail metabolism von Brand et al. If butyric acid is as commonly found as an end-product of molluscan metabolism as suggested by von Brand et al. Similarly, glutamic acid, which is a commonly occurring amino acid, could not again be expected to serve as a selective guide. On the other side of the fence, there are evidences suggesting that symbiont selection of hosts, specifically miracidia-mollusc contact, is strictly a random phenomenon without the occurrence of attracting factors.
Similarly, Griffiths and LaRue believed that miracidia-mollusc contact is primarily a random phenomenon. LaRue, however, has indicated that, although under laboratory conditions trial and error appears to be much more important than chemotactic response in bringing miracidium and snail together, in nature the possibility of the 4.
Abdel-Malek , who specifically looked for attraction, reported that Schistosoma mansoni miracidia will attack any object including empty snail shells and particles of fine gravel. Similarly, Stirewalt working with Schistosoma mansoni and Australorbis glabratus, Chu and Cutress working with the marine avian schistosome believed to be Azcstrobilharzia variglundis and the marine snail Littorina pintado, and Najim working with the freshwater avian schistosome, Bigantobilharxia huronensis, and its molluscan host, Physa gyrina, have all reported the lack of any apparent attraction.
It should be mentioned that, except in the instance of Abdel-Malek, the other earlier reports were incidental observations not subjected to critical analyses. More recently, Sudds has examined for the presence or absence of chemotaxis between four different species of schistosome miracidia Trichobilharzia elvae, T. It is my opinion that attraction of symbiont to host should be considered a distinct operation from successful establishment of symbiont in or on its host, although there are suggestionsthat host-symbiont contact may influence morphogenetic changes.
For example, Campbell and Todd b have reported the in vitro metamorphosis of Fascioloides magna miracidium into a sporocyst after a short contact with snail tissue. I n eleven other incompatible host-parasite combinations, the miraoidia were observed making brief attempts to penetrate.
Of the seven normal host-parasite combinations, all demonstrated either type 3 or type 4 behavior patterns. On the other hand, 17 of the 19 combinations yielded results supporting the view that contact with snail hosts occurs by chance, and that, once contact is made, the miracidia are stimulated to attempt penetration. The reasons for this doubt are discussed below. They further stated that:. I n critically analyzing the data by Chernin and Dunavan, I failed t o see how their experiments in any manner either support or deny the existence of a chemotactic factor.
Their experiments were designed t o determine whether a t a constant water level, regardless of volume, the capacity of miracidia to infect snails was influenced. They found that there is no significant difference in the different volumes used. They also studied the preference of miracidia for different depths and distances in reaching hosts. They found that miracidia do not demonstrate a preference for any specific depth when placed in 20 cm of water and that some miracidia traverse a t least 86 cm horizontally or 33 cm downwards to reach molluscan hosts.
Their other experiments demonstrated that miracidia do not follow a linear course and travel a t a velocity of 2. Their studies on miracidial taxes disclosed that negative geotaxis has a stronger influence on their 4. For example, Cort to illustrate his point that Schistosoma haematobiurn lacks host specificity and indirectly denying the existence of specific hostelaborated chemotactic agents, stated that in Egypt X. More recent studies have shown that the two Egyptian snails are synonyms for Bulinus truncatus. Furthermore, the investigations of McCullough and Le Roux have suggested that the schistosomes utilizing Bulinus Physopsis spp.
In view of the work of Newton , , on Australorbis glabratus infected with Schistosoma mansoni, it is apparent that successful establishment of the parasite, which must in most cases be considered distinct from the initial host-parasite contact, is dependent upon the genetic strain of the host, and perhaps also of the parasite, beside other factors. Another example of confusion resulting from misidentification of molluscan hosts has been cited by Wright who pointed out that Stunkard in presenting evidence to indicate that a high degree of host-specificity need not exist in trematode-mollusc relationships, stated that the intermediate hosts of S.
However, Wright has pointed out that Isadora is a synonym for Bulinus and Physopsis is a subgenus of Bulinus. He indicated that the Planorbis referred to by Stunkard is the African genus Biomphalaria since Planorbis does not occur in the Ethiopian region. Thus it would appear that the confirmed natural intermediate hosts of Schistosoma mansoni all belong to one genus.
The type of confusion which exists relative to schistosomes and their molluscan hosts has not yet plagued studies on marine parasites and their molluscan hosts. This does not mean that such problems will not arise, especially since the taxonomy of marine molluscs shows indications of becoming just as complex, but the lack of such confusion merely reflects the less intensive nature of research in marine parasitology. Another factor which evidently has an important influence on miracidium-mollusc contact but which, in my opinion, has not received sufficient attention by those interested in the presence or absence of chemotactic response has to do with the age of the miracidium.
Differences in the ability of miracidia to make contact with their hosts as a function of age was discovered by Campbell and Todd a. These investigators studied contact between Fascioloides magna miracidia and Xtagnicola refZexa. They divided their miracidia into three age groups. A total of miracidia and forty-eight small snails of approximately the same size were used. Each snail was exposed to a known number of miracidia of a specific group. The snail was examined at time intervals and the number of miracidia not attached to the snail was recorded.
I n some instances a miracidium became detached from the snail, hence the number of detached miracidia at any time may have been slightly more than at the previous count. It was also noted that in each series of exposures more miracidia became attached to snails during the first 15 min than during the succeeding 55 min. It is of importance to note that Campbell and Todd have stated that : The effect of age on the attacking power of miracidia may help to explain inconsistencies found among previous reports on the behavior of miracidia in the presence of a snail.
The age of the miracidia at the time of hatching perhaps controls their ability to respond to the presence of a snail. It is possible that miracidia which hatch as soon as their development permits, have not yet acquired a sensitivity to whatever stimulus chemical or otherwise the snail may provide. Since miracidia have been observed to exhibit excitement [italics added] in the presence of a snail, it is felt that under certain conditions, not yet understood, a marked attraction on the part of a snail for a miracidium may exist. Since the age of the parasite does influence the efficiency of contact with its host, it appears feasible that other factors, such as the age of the host, may also be influential but this has not yet been tested.
After Campbell and Todd, a. The parasites used were between 41 and 56 min old. The significance of this last study, in my opinion, rests with the fact that the miracidia did become attached to two species of molluscs. A large part of this controversy pertaining t o the existence or nonexistence of an attractant of host origin, as I interpret it, is based on several fallacies. If it exists, as these data suggest, it is a very subtle process which is operative only within short ranges and can be only fully appreciated upon analysis of quantitative data. Various studies of this nature in related areas have convincingly shown that chemotaxis does occur.
For example, host-localization among parasitic insects as reported by Salt and Laing ,host attraction of the annelid Acholoe as reviewed by Davenport , , chemoreception and responses to chemical stimuli in free-living flatworms as reported by Pearl , Koehler , Hyman , and Fraenkel and Gunn are all now widely accepted discoveries.
These and other authors have suggested that even prior to the operation of chemotaxis the symbiont is initially attracted to a certain type of environment and, if such an environment coincides with the natural habitat of the host, the first stage of host-symbiont contact is accomplished. This is what Wright a, has also proposed. Although the observations of Faust and Meleney ,Barlow ,Neuhaus , and the data of Etges and Decker suggest specific attraction of S. As molluscan blood does not clot, this fluid is technically not serum, but because of common usage these three terms are used interchangeably in this review.
Only additional studies of this nature will reveal whether specific and general attractions both occur in nature. Direct evidences which indicate that molluscs do secrete substances to the exterior where they can influence symbionts in the immediate proximity is still in need of confirmation. Suggestive evidences, however, are available.
Wright b ,for example, has demonstrated by paper chromatography that there are what he considers species-specific substances in the body-surface mucus of a number of species of snails. Advances in marine biology Abbreviation. Abbreviation: Abbreviation Current protocols in microbiology Abbreviation. Next Journal: Advances in tracer methodology Abbreviation. Similar Journals. Journal of marine biotechnology; Molecular marine biology and biotechnology; Marine genomics; Marine biology; Marine pollution bulletin; Marine drugs.
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Biotechnology News Brasil: eBooks. Volume 50, Annual Review of Biochemistry. Advances in Marine Biology has been providing in-depth and up-to-date reviews on all aspects of marine biology since -- over 40 years of outstanding coverage! The series is well known for both its excellence of reviews and editing. Continuing demand for the book has therefore led to this fourth, completely revised and updated edition.
Developments in technology. Advances in Virol Download with Google Download with Facebook or download with email. Advances in Marine Biology - scimagojr. Get this from a library! Karlson, P. Lim, L. Mackenzie, M. Montresor, V. Trainer, G. Usup, and K. Oceanography, Vol. Brown and Hideshige Takada in August The special issue exemplifies how a variety of indicators can provide insight into the identification of legacy and emerging contaminants, the ranking of priority pollutants from various sources, and the impacts of contaminants on ecosystem health in the North Pacific. This issue provides the first compilation of research on marine pollution indicators in the North Pacific Ocean and provides guidance to inform mitigation and monitoring of contaminants in the region.
These indicators may facilitate the tracking of environmental response to regulations and source control. The goal of this issue is to provide an introduction to the important ways that oil spills may harm the biota, habitats and ecosystems using invited and targeted reviews complemented by original research articles. Included are thoughts on the challenges posed by oil spills and to response authorities. Yebra, T. Kobari, A. Sastri, F. In this review, we summarize the advances in biochemical methods made in recent years. Our approach explores the rationale behind each method, the design of calibration experiments, the advantages and limitations of each method and their suitability as proxies for in situ rates of zooplankton community growth and production.
We also provide detailed protocols for the existing methods and information relevant to scientists wanting to apply, calibrate or develop these biochemical indices for zooplankton production. Smith Annual Review of Marine Science. The papers provide a substantial update of the knowledge about this highly productive and important transitional region in the North Pacific. Year: Harmful Algae Review paper, Harmful algal blooms and climate change: Learning from the past and present to forecast the future based on PICES and other organization sponsored workshop.
Authors: M. Wells, V. Trainer, T. Smayda, B. Karlson, C. Trick, R. Kudela, A. Ishikawa, S. Bernard, A. Wulff, D. Anderson and W. Cochlan Harmful Algae , Vol. In January this article was the most frequently downloaded article in Harmful Algae in the last 90 days. Bern achieved many scientific accomplishments during his career in fisheries and oceanography and served PICES in many different roles, sometimes simultaneously. Curchitser, K. Rose, S. Ito, M. Peck and M. Kishi display some of the breadth of models in use for understanding the mechanisms linking environmental forcing to biological responses in ocean systems—it is a collection that Bern would be proud of.
Authors: S. Kim, A. Hollowed, M. Barange, and B. MacKenzie Oceanography, Vol. Hazen, R. Suryan, S. Bograd, Y. Watanuki and R. Wilson Mar. Drinkwater, G. Hunt, Jr. Johnson, and David L. Year: Fisheries Research Special Issue on Ecosystem-based approaches for the assessment of fisheries under data-limited situations Guest Editors: Dr. Patricia Livingston, Dr. Gordon Kruse and Dr. Laura Richards Fish.