William F. Font

Excess positive associations in communities of intestinal helminths of bats : a refined null hypothesis and a test of the facilitation hypothesis

The null hypothesis that the number of positive pairwise covariances should equal the number of negative pairwise covariances in samples from communities of randomly associated helminth species was reevaluated. The proportion of positive covariances in a sample from a community of independent species depends upon the proportion of rare species (prevalence less than 10%), the proportion of common species (prevalence greater than 90%), and the size of the sample of hosts. If rare species dominate, then there will be an excess of negative associations; if common species dominate there will be an excess of positive associations. Many helminth communities have more rare than common species, therefore samples from communities that show an equal number of positive and negative covariances have a greater number of positive associations than is expected for randomly associated species. Increased sample size will reduce the sampling bias, but at least 100 hosts are necessary and often 500-7,500 hosts are required. The excess of positive covariances between helminth species in 10 populations of bats disappeared after restricting the analyses to hosts in which both members of a species pair were present. This result suggests that excess positive associations between helminth species in bats are due to joint presences and absences in hosts rather than to interspecific facilitation. Interspecific facilitation would be supported by observed positive correlations between the intensities of individuals of the species pairs.

Recruitment-driven, spatially discontinuous communities: a null model for transferred patterns in target communities of intestinal helminths.

Populations and therefore communities of intestinal helminths of vertebrates are fueled by recruitment of new individuals from outside the host. The source of new individuals is often an intermediate host that harbors several infective propagules of 1 or more species. Hence these source communities are transmitted in packets of infective propagules to target communities in definitive hosts. Packets not only provide recruits to target communities, but, because a packet of propagules possesses its own structure, it may also transmit structure to the target community. We use this system to examine the contribution that structure in the source pool of propagules makes to the structure of recruitment-driven target populations and communities. By treating the dynamics of such target populations and communities as immigration-death processes, we conclude: (1) Unlike a birth-driven population a recruitment-driven target population will grow to an asymptotic limit even in the absence of density-dependent processes or reaching carrying capacity; (2) the frequency distribution of the number of recruits entering target populations will determine the frequency distribution of adults in target populations; (3) interspecific associations among species in the source community will be transmitted to target communities, but the magnitude of the transmitted associations will depend upon the relative survival rates of the species; and (4) for associations of equal magnitude in a source community, the magnitude of a transferred negative association will be less than the magnitude of a positive association in a target community. Two examples of source communities in salt marsh crabs reveal that source infracommunities exist with the hypothesized structure. Further, the source helminth communities display a greater number of positive than negative interspecific associations. The inequity in transfer and the existence of a greater proportion of positive associations in source communities may explain the widespread occurrence of excess positive associations that has been noted in recruitment-driven communities.

THE GUEST PLAYING HOST: COLONIZATION OF THE INTRODUCED MEDITERRANEAN GECKO, HEMIDACTYLUS TURCICUS, BY HELMINTH PARASITES IN SOUTHEASTERN LOUISIANA

Parasite surveys of exotic hosts offer the opportunity to examine parasite colonization on different scales (i.e., host individual, host population, host species, and new geographic locality). Ten helminths (Macracanthorhynchus ingens, Mesocestoides lineatus, Oochoristica javaensis, Haematoloechus varioplexus, Mesocoelium monas, Telorchis corti, Cosmocercoides variabilis, Oswaldocruzia leidyi, Skrjabinoptera sp., and a larval acuariid nematode) were recovered from the exotic Mediterranean gecko Hemidactylus turcicus, in southeastern Louisiana. Only 1 exotic parasite, O. javaensis, colonized a new geographic locality, but 7 local helminths colonized a new host species. Helminth communities of H. turcicus were similar in structure to what has been hypothesized or observed for lizards. Thus, communities were composed of generalists and were depauperate (i.e., colonization of individual geckos or host populations was rare for most of the helminths); however, there was significant variation in community structure among local habitats. Although the geckos behavioral and physiological attributes predict colonization by monoxenous helminths, only 2, C. variabilis and O. leidyi, were recovered. Eight heteroxenous helminths, 2 of which (the acuariid and O. javaensis) were the most widely distributed and abundant, were the better colonizers. The geckos generalist diet may have exposed it to a diverse parasite fauna and thus been important in determining the helminths that could colonize.

PHYLOGENETIC ANALYSIS OF ALLOGLOSSIDIUM (DIGENEA: MACRODEROIDIDAE) AND RELATED GENERA: LIFE-CYCLE EVOLUTION AND TAXONOMIC REVISION

A phylogenetic analysis was performed on 13 species of digenetic trematodes in the Macroderoididae, including 10 species of Alloglossidium, 2 species of Alloglossoides, and Hirudicolotrema richardsoni. The evolution of the unusual life-cycle patterns in the group was assessed in light of the proposed phylogeny. The results support previous hypotheses that taxa with a 3-host life cycle involving catfish as definitive hosts are basal to taxa with a 2-host life cycle involving invertebrates such as crustaceans and leeches as definitive hosts. Our results also strongly suggest that species maturing in leeches evolved from an ancestor that matured in crustaceans. Our phylogeny places Alloglossoides and Hirudicolotrema within Alloglossidium, showing Alloglossidium to be paraphyletic. To achieve a natural classification, Alloglossoides and Hirudicolotrema are synonymized with Alloglossidium, and a revised generic diagnosis for Alloglossidium is given.

Seasonal and yearly population dynamics of two exotic helminths, Camallanus Cotti (Nematoda) and Bothriocephalus acheilognathi (Cestoda), parasitizing exotic fishes in Waianu stream, O'Ahu, Hawaii

Exotic poeciliid fishes introduced into Hawaiian freshwaters are responsible for the introduction of several exotic parasites, of which the most important are Camallanus cotti and Bothriocephalus acheilognathi in terms of potential disease threat to native stream fishes. This roundworm and tapeworm are the most prevalent and abundant freshwater fish helminths in Hawaiian streams. This study examined the seasonal and yearly population structure of C. cotti and B. acheilognathi to determine if the tropical Hawaiian environment characterized by low climatic variability permits continuous opportunities for parasite transmission regardless of time of year. Camallanus cotti displayed seasonal differences in prevalence and mean abundance, whereas B. acheilognathi did not. Camallanus cotti prevalence and mean abundance were higher in the Hawaiian summer (47.7%, 0.79) than in winter (25.8%, 0.36). A seasonal relationship of C. cotti levels is likely explained by extensive rains associated with the Hawaiian winter season, which may act to decrease parasite transmission by flushing infected poeciliid hosts, intermediate copepod hosts, and possibly free-living infective worm stages downstream. Bothriocephalus acheilognathi displayed low prevalence and mean abundance in both summer (4.0%, 0.06) and winter (6.5%, 0.07), and it may be difficult to detect seasonal changes due to these low levels. Camallanus cotti prevalence and mean abundance remained relatively constant from the summer of 1995 to the summer of 1999, indicating that levels of this roundworm are stable in Waianu Stream. Whereas B. acheilognathi prevalence and mean abundance were low during the summer of 1995 and the summer of 1997, a dramatic peak in prevalence and mean abundance was observed in the summer of 1998 (41.2%, 1.06), with levels decreasing sharply in the summer of 1999 (4.4%, 0.07). It appears that B. acheilognathi also is present in stable populations at low levels, even though levels rose sharply during a single year.

SEASONAL DYNAMICS OF THE HELMINTHS OF BLUEGILL (LEPOMIS MACROCHIRUS) IN A SUBTROPICAL REGION

Seasonal prevalence and abundance of the helminths of bluegill sunfish in a Louisiana oligohaline bayou were measured by a survey and a field “live-box” experiment. The survey took place from the spring of 1997 to the summer of 1998 and examined fish that were <7 cm. Three trematode species, Phagicola nana (Heterophyidae), Ascocotyle tenuicollis (Heterophyidae), and Posthodiplostomum minimum (Diplostomatidae), and 2 nematode species, Camallanus oxycephalus (Camallanidae) and Spinitectus carolini (Cystidicolidae), were examined. Camallanus oxycephalus was the only helminth that showed a distinct seasonal pattern. Abundance and prevalence peaked in summer, which was likely driven by concerted reproductive cycles of females. The survey data indicated that the other helminths fluctuated over time but did not seem to follow a distinct seasonal pattern. The fluctuations could be attributed to the variable nature of the habitat or to the stochastic events that influence transmission dynamics, particularly isolated events such as tropical storms, which cause dramatic changes in salinity. The live-box experiment successfully measured recruitment of A. tenuicollis and suggested a seasonal component of the distribution of this species, which was possibly caused by temperature-dependent emergence of cercariae from the snail intermediate host.

Scanning electron microscopy of Leucochloridiomorpha constantiae during development from metacercaria to adult

Scanning electron microscopy revealed that the tegument of Leucochloridiomorpha constantiae metacercariae was marked with interconnected longitudinal and transverse ridges. Alteration of the ridges began within 1 hr after implantation into the chick coelom. Ridges were completely lost by the 4th hr, leaving a smooth tegument. Body shape altered from that of a tapered metacercaria to a plump, rounded adult within 3 days, and was accompanied by doubling of the acetabular diameter. Papillae, present in both the metacercaria and adult, were located on the suckers, genital orifice, and body surface. The microtopography of the tegument consisted of knoblike protuberances that gave the surface a cobblestonelike appearance. Tegumental knobs in te vicinity of the genital pore contained minute, rounded inclusions.

Alloglossidium floridense n. sp. (Digenea: Macroderoididae) from a Spring Run in North Central Florida

Abstract:  A new species of Alloglossidium is described from the intestines of 2 madtom species (Noturus leptacanthus and Noturus gyrinus) that were collected from the run of a small, unnamed spring system that drains into the Santa Fe River, Florida. Alloglossidium floridense n. sp. is morphologically very similar to other nonprecocious Alloglossidium spp. that use ictalurids as definitive hosts, but can be distinguished by a combination of its smaller overall size (length and width), large eggs in relation to its small body size, position of the vitellaria, ovary shape, and position of the ovary in relation to the cirrus sac. A comparison of nuclear rDNA sequences (spanning partial 18s, complete ITS1, 5.8s, ITS2, and partial 28s regions) showed that A. floridense n. sp. diverged by 0.70–3.17% from the other 4, nonprecocious species that infect ictalurids (Alloglossidium corti, Alloglossidium fonti, Alloglossidium geminum, and Alloglossidium kenti). The new species of Alloglossidium, described herein, is the first of the genus to be reported from Florida and the first to be recorded from N. leptacanthus. In light of the subtle morphological differences among the nonprecocious species that infect ictalurids, we discuss how previous descriptions of species traits that are not supported with genetic data are difficult to interpret because of the possible past nonrecognition of distinct species.

Interaction of two myxozoan parasites from naked goby Gobiosoma bosc, in Lake Pontchartrain, Louisiana.

Abstract: During a parasitological survey of naked gobies (Gobiosoma bosc) in Lake Pontchartrain, Louisiana, U.S.A., 2 myxozoan parasites were found infecting the gall bladders of 84 of 90 fish. Parasite plasmodia of each were morphologically distinct; plasmodia bearing Ellipsomyxa-like spores were elongate and fusiform (1,126 by 403 μm), and those bearing Sphaeromyxa-like spores were large and discoid (1,400 μm diameter). Neither parasite conformed to any described species of myxozoan, and both are described here. Sphaeromyxa kenti n. sp. bears boomerang-shaped spores ranging 17.5–19.8 μm long by 3.8–5.2 μm wide. Two unequal sized polar capsules contain ribbon-like polar filaments characteristic of this genus. Ellipsomyxa adlardi n. sp. bears ovoid spores 11.3–14.4 by 7.1–8.8 μm, with 2 rounded polar capsules oriented in opposite directions relative to the longitudinal plane of the spore. Phylogenetically both species cluster with sequenced members of their respective genera. Plasmodia of E. adlardi n. sp. were encountered in 72.2% of gobies examined, and S. kenti n. sp. in 25.6%. Overall, 6.7% of animals were uninfected, and only 4.4% of the 90 fish examined were infected with both species. The observed co-occurrence was lower than expected by chance, strongly suggestive of an interaction between these species.

Trematode Parasites (Digenea) of the Slender Madtom Noturus exilis and Black River Madtom Noturus maydeni (Siluriformes: Ictaluridae) from Arkansas, U.S.A

ABSTRACT: Between June 2012 and July 2013, 43 slender madtoms (Noturus exilis) and 21 Black River madtoms (Noturus maydeni) were collected from 4 counties of northern Arkansas and examined for helminths. Eleven (26%) slender madtoms were infected with digenean trematodes, including 3 (7%) with metacercaria of Posthodiplostomum minimum, 3 (7%) with Alloglossidium sp., and 7 (16%) with Plagioporus sp.; a single (5%) Black River madtom was infected with Caecincola sp. We document new host records for each of these 4 helminths. Notable among these new host records are new distributional records for Caecincola sp. To our knowledge this represents the first report of any helminth from N. exilis and N. maydeni.