Notes on the Biology of Three Trematodes (Digenea: Cryptogonimidae)

Transcription

1 Proc. Helminthol. Soc. Wash. 47(1), 1980, p Notes on the Biology of Three Trematodes (Digenea: Cryptogonimidae) GEORGE J. GREERJ AND KENNETH C. CoRKUM2 Department of Zoology and Physiology, Louisiana State University, Baton Rouge, Louisiana ABSTRACT: We studied several aspects of the life histories of Caecincola latostoma Greer and Corkum, 1979, Cryptogonimus spinovum Greer and Corkum, 1979, and Tcxtrema hopkinsi Dronen, Underwood, and Sunderman, 1977 in south Louisiana. Under natural conditions C. latostoma and T. hopkinsi cercariae exhibit a bimodal, diurnal emergence. In the three species we noted an inverse relationship between the rates of metacercarial development and adult maturation and a strong correlation between the prevalence of each species in the molluscan host and its prevalence and intensity in the second intermediate and definitive hosts. In a previous report (Greer and Corkum, 1979) we described the life cycles of three cryptogonimid trematodes: Caecincola latostoma and Cryptogonimus spinovum, described in that study, and Textrema hopkinsi Dronen, Underwood, and Sunderman, The three species use the same hosts: Cincinnatia peracuta (Pilsbury and Walker) is the molluscan host; Micropterus salmoides (Lacepede), Elassoma zonatum (Jordan), and several species of Lepomis are the second intermediate hosts; and M. salmoides and M. punctulatus (Rafinesque) are the definitive hosts. In the present study we report patterns of cercarial emergence, metacercarial and adult development, and population densities in the vertebrate and invertebrate hosts of these three sympatric species. Materials and Methods Infected hosts were collected from False River, an oxbow lake in Pointe Coupee Parish, and from Beaver Pond Branch, a small stream in Livingston Parish, Louisiana. Micropterus salmoides, Lepomis machrochirus (Rafinesque), and L. megalotis (Rafinesque) were collected for experimental use from areas where infections are absent. Positive identification of cercariae was determined by rearing representatives to the metacercarial stage in previously uninfected sunfishes. To determine cercarial emergence patterns under natural conditions, four C. peracuta infected with C. latostoma and four with T. hopkinsi were isolated and maintained at Beaver Pond Branch in vials of filtered pond water which were partially submerged along the bank of the stream. During the experimental periods, water temperature in and around the vials varied not more than 1 C. On August 25 and 26, 1975, at 2-hour intervals for 48 hours, the contents of the vials were removed and preserved in 70% ethanol. Measured samples were aspirated through Whatman No. 1 filter paper on a Buchner funnel. Dried filter papers were sprayed with 1% ninhydrin and cercariae counted after color development. The entire body musculature of nine False River L, macrochirus, cm 1 Present address: University of California International Center for Medical Research, Institute for Medical Research, Kuala Lumpur, Malaysia. - To whom reprint request should be addressed.

2 48 PROCEEDINGS OF THE HELMINTHOLOGICAL SOCIETY r 30- <u 0 U V////SA 150-, C.latostoma 12 " _ I ' i ~^^^^^^^F^^^^^\^^^^^^^^^^^^ i I T~~-~~^^ i * i" ^^^^^^^^^ II TIME Figure 1. Cercarial emergence patterns for Caecincola latostoma and Textrema hopkinsi from naturally infected Cincinnatia peracuta. Eight snails, four infected with C. latostoma and four with T. hopkinsi, were maintained under natural conditions at Beaver Pond Branch, Livingston Parish, Louisiana. Samples were taken at 2-hour intervals over a 48-hour period from August 25 to 26, D represents day and represents night, as determined by the official sunrise and sunset. Temperatures are of habitat water. in length, was carefully dissected and examined for metacercarial infections and the results were quantified. Adult worm burdens were determined for 41 M. salmoides of kg collected from False River between April 7, 1975 and December 8, The intestinal tracts were cut into three equal lengths and examined for parasites. Results and Discussion Cercarial emergence (Fig. I) Cercariae of C. latostoma, C. spinovum, and T. hopkinsi are morphologically similar and exhibit no behavioral differences in the laboratory (Greer and Corkum, 1979). However, we observed slight differences in the emergence patterns of C. latostoma and T. hopkinsi cercariae under natural conditions. The similar diel rhythms of both species suggest a correlation between daylight and cercarial emergence, but light alone does not explain their bimodal patterns. Likewise, the timing of the peak emergence periods indicates that neither light intensity nor

3 OF WASHINGTON, VOLUME 47, NUMBER 1, JANUARY Parasite Minimum Development Period Minimum Period Before Egg for Metacercariae (Days) Production by Adults(Days) C. latostoma C.spinovum T.hopkinsi Figure 2. Comparisons of C. latostoma, C. spinovum, and T. hopkinsi metacercarial and adult development in L. macrochirus and M. salmoides, respectively, under laboratory conditions. temperature is solely responsible for eliciting emergence of C. latostoma. These factors may be of importance for T. hopkinsi where both peaks occur during periods of the day (morning and evening) when temperatures are nearly equivalent and light intensities are approximately at the same level. Two potential sources of stimuli may be eliciting cercarial emergence: changes in the external environment and physiological changes in the host. Neither light nor temperature directly elicits emergence of C. latostoma and T. hopkinsi, but these physical factors, in conjunction with snail-mediated stimuli, may account for the emergence patterns we observed. Lundahl (1941) reported two periods of emergence for C. parvulus cercariae in the laboratory: between 4 and 7 P.M. and between midnight and dawn. Though some of the disparities between C. parvulus and C. latostoma may be due to different experimental designs, the patterns probably reflect a fundamental difference between these congeners. Cable (1972) cited several examples of distinct emergence patterns among closely related trematode genera. The differences undoubtedly have evolved as a result of selection that favors cercarial transmission to the next host. Centrarchid and cyprinid fishes are the second intermediate hosts for C. parvulus (Lundahl, 1941), whereas M. salmoides, E. zonatum, and several species of Lepomis are such hosts for C. latostoma. Differences in cercarial emergence of these congeners may have evolved as a result of selective pressures derived from differences in the behavior of the fish hosts. Metacercarial and adult development (Fig. 2) Feeding experiments showed different rates of development for metacercariae and adults of C. latostoma, C. spinovum, and T. hopkinsi. Uninfected sunfishes, L. macrochirus and L. megalotis, were individually exposed for 1 day to cercariae of one of the three species. At intervals thereafter the sunfishes were fed to M. salmoides, which were subsequently killed and examined. The minimum time for cercariae to develop to infective metacercariae was 14 days for C. latostoma, 16 days for C. spinovum, and 18 days for T. hopkinsi. In repeated experiments we found the egg production begins by the 8th day after ingestion of C. latostoma metacercariae, by the 5th day in C. spinovum, and as early as

4 50. PROCEEDINGS OF THE HELMINTHOLOGICAL SOCIETY 80 T, 60 o «O H- o.5 40 O E T.h. PARASITE Figure 3. Comparison of C. latostoma (C.I.), C. spinovum (C.s.), and T. hopkinsi (T.h.) infection levels in the snail (C. peracuta), second intermediate (L. macrochirus), and definitive (M. salmoides) hosts from False River, Pointe Coupee Parish, Louisiana. Results are based on examination of 6,204 C. peracuta, nine L. macrochirus, and 41 M. salmoides. the 3rd day in T. hopkinsi. These data imply an inverse relationship between the developmental periods for the metacercariae and adults of these species. Parasite populations at False River (Fig. 3) Of various snails examined in quantities, only C. peracuta shed the cryptogonimid cercariae under study. About 1.5% of 6,204 snails screened were infected: 83 with C. latostoma, seven with C. spinovum, six with T. hopkinsi, and one with both C. latostoma and C. spinovum. We recovered metacercariae of C. latostoma, C. spinovum, and T. hopkinsi from the body musculature of L. machrochirus, L. megalotis, L. gulosus, (Cuvier) and E. zonatum, but not from other centrarchid or cyprinid fishes. Numbers of metacercariae of each cryptogonimid species were recovered from L. macrochirus in roughly the same relative proportions as were parthenitae from the snail host and adults from the definitive hosts. Caecincola latostoma was found in the pyloric ceca and anterior intestine of 39 of 41 M. salmoides. The worms usually extended into the middle, and occasionally to the posterior third, of the intestine. The large numbers of worms found in M. salmoides made exact determination of worm burdens impracticable. However, based on counts made from pyloric ceca from several fish we projected an average infection of several thousand worms. Cryptogonimus spinovum occupied the pyloric ceca and occasionally the anterior intestine of 21 of 41 bass. The most heavily infected fish harbored 101 worms. Adults of T. hopkinsi were present in 14 bass and were restricted to the middle third of the intestine. The heaviest infection encountered was 43 worms. Of the 39 largemouth ba.ss harboring at least one cryptogonimid species, 23%

5 OF WASHINGTON, VOLUME 47, NUMBER 1, JANUARY were infected with all three; 13% with both C. latostoma and T. hopkinsi; 31% with C. latostoma and C. spinovum; and 33%, mostly smaller fish, with only C. latostoma. Experimental infections indicated that location of these parasites in the host was not affected by the number of species present. Conclusions Similarities in the life histories and microhabitats of C. latostoma, C. spinovum, and T. hopkinsi from False River raise questions about the possible effects of interspecific competition on these populations. Pianka (1973) considered the three main resources apportioned among competitors to be space, food, and time. An obvious, but not absolute, apportioning of the microhabitat exists between adults of T. hopkinsi and the other two species. However, no spatial segregation was evident between C. latostoma and C. spinovum. Although an unequivocal determination of competition was not demonstrated, the greater abundance and broader niche of C. latostoma would indicate that this species represents a superior competitor (Ayala, 1972) or an ecological dominant (McNaughton and Wolf, 1970). Literature Cited Ayala, F. J Competition between species. Am. Sci. 60: Cable, R. M Behaviour of digenetic trematodes. Pages 1-18 in E. U. Canning and C. A. Wright, eds. Behavioural aspects of parasite transmission. Academic Press, New York. Greer, G. J., and K. C. Corkum Life cycle studies of three digenetic trematodes, including descriptions of two new species (Digenea: Cryptogonimidae). Proc. Helminthol. Soc. Wash. 46: Lundahl, W. S Life history of Caecincola parvulus Marshall and Gilbert (Cryptogonimidae, Trematoda) and the development of the excretory system. Trans. Am. Microsc. Soc. 60: McNaughton, S. J., and L. L. Wolf Dominance and the niche in ecological systems. Science 167: Pianka, E. R The structure of lizard communities. Ann. Rev. Ecol. Syst. 4:54-74.