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As a part of a comprehensive survey of macroparasites of commercially exploited fish species off the coast of Otago, New Zealand, the parasite fauna of the New Zealand sole Peltorhamphus novaezeelandiae Günther was recently studied. Steringotrema robertpoulini n. sp. is described from this host and compared with known species of Steringotrema Odhner, 1911. The new species is readily distinguished from all of its congeners, except for S. divergens (Rudolphi, 1809) Odhner, 1911, by having the follicular vitellarium divided in four zones rather than two, and can be differentiated from S. divergens mainly by the posterior extent of the intestinal caeca in the hindbody, as well as by host association and geographical distribution. DNA sequences of the 28S ribosomal gene were generated and phylogenetic analyses were undertaken using maximum likelihood and Bayesian inference to assess the phylogenetic position of the new species within the family Fellodistomidae Nicoll, 1909. Analyses included the available sequences for 14 species of the family distributed among eight genera, along with nine species of other members of the order Plagiorchiida La Rue, 1957 as outgroups. The resulting topology shows that the new species of Steringotrema is nested as the sister species of Steringophorus dorsolineatus (Reimer, 1985) Bray, 1995. However, low nodal support indicates that relationships among these species are not fully resolved and require further revision and denser taxon sampling for more detailed molecular work. More information is required to draw further conclusions about the taxonomic status of the genera Steringotrema and Steringophorus Odhner, 1905.

Most parasites from known host species are yet to be discovered and described, let alone those from host species not yet known to science. Here, we use tapeworms of elasmobranchs to identify factors influencing their discovery and explaining the time lag between the descriptions of elasmobranch hosts and their respective tapeworm parasites. The dataset included 918 tapeworm species from 290 elasmobranch species. Data were analysed using linear mixed-effects models. Our findings indicated that we are currently in the midst of the greatest rate of discovery for tapeworms exploiting elasmobranchs. We identified tapeworm size, year of discovery of the type host, host latitudinal range and type locality of the parasite influencing most on the probability of discovery of tapeworms from elasmobranchs and the average time lag between descriptions of elasmobranchs and their tapeworms. The time lag between descriptions is decreasing progressively, but, at current rates and number of taxonomic experts, it will take two centuries to clear the backlog of undescribed tapeworms from known elasmobranch species. Given that the number of new elasmobranch species described each year is on the rise, we need to re-assess funding strategies to save elasmobranchs (and, thus, their tapeworm parasites) before they go extinct.

Parasites are important components of natural systems, and among their various roles, parasites strongly influence the flow of energy between and within food webs. Over 1000 tapeworm species are known to parasitise elasmobranchs, although full life cycles are resolved for fewer than 10 of them. The lack in resolution stems from the inability to distinguish larval from adult stages using morphology alone. Molecular elucidation of trophic transmission pathways is the next step in understanding the role of hosts and parasites within food webs. We investigated the parasite assemblage of New Zealand’s rough skate, Zearaja nasuta. Skates and their prey items (obtained from the skates’ stomachs) were dissected for the recovery of adult and larval tapeworms, respectively. A fragment of the 28S rDNA region was amplified for worm specimens with the aim to confirm species identity of parasites within rough skates and to uncover trophic transmission pathways that exploit the predation links between rough skates and their prey. We identified seven species of tapeworms from four tapeworm orders. Four trophic transmission pathways were resolved between three prey items from skates stomachs and skates, and one pathway between larval tapeworm sequence from a New Zealand sole and skate, i.e. a genetic match was found between larval tapeworms in prey and adult worms in skates. We report the first case of an adult trypanorhynch parasitising rough skate. These findings contribute to our limited understanding of cestode life cycles as well as providing insights into the importance of predator-prey relationships for parasite transmission.

Metacestodes are often found in the body cavity of the common bully (Gobiomorphus cotidianusMcDowall), from freshwater habitats in Otago, New Zealand. Identification of metacestodes relies only on the number, size and shape of the rostellar hooks. To attempt species determination, we cultivated metacestodesin vitrofor up to 23 days, during which they matured to at least the male stage of development, although female organs were not discernable. Identified as members of the genusParadilepisHsü, 1935 (family Gryporhynchidae), these specimens are compared to previously described species, in particularP. minima(Goss, 1940), from Australia, the closest species, both geographically and morphologically. Although the size of scolex, suckers and proglottids differ significantly from those ofP. minima, we are cautious about interpreting ‘adults’ grownin vitro, because we are unsure whether the artificial conditions alter development. For this reason, and because of the lack of female organs, we refrain from erecting a new species, and refer to the specimens asParadilepiscf.minimauntil such time as the adults are found in the definitive host. With this proviso we present here a description of thein vitro-grown worms and the metacestodes as a preliminary study of this cestode. A molecular analysis of small subunit (SSU) rDNA sequences, shows the position ofP.cf. minimaand another gryporhynchid,Neogryporhynchus cheilancristrotus(Wedl, 1855), to be equivocal, but confirms their exclusion from the Dilepididae and Hymenolepididae. This is the first record of a gryporhynchid from New Zealand, and the first from the fish family Eleotridae.

Studying resource specialization at the individual level can identify factors constraining the evolution of generalism. We quantified genotypic and phenotypic variability among infective stages of 20 clones of the parasitic trematode Maritrema novaezealandensis and measured their infection success and post-infection fitness (growth, egg output) in several crabs and amphipods. First, different clones varied in their infection success of different crustaceans. Second, neither genetic nor phenotypic traits had consistent effects on infection success across all host species. Although the results suggest a relationship between infection success and phenotypic variability, phenotypically variable clones were not better at infecting more host species than less variable ones. Third, genetic and phenotypic traits also showed no consistent correlations with post-infection fitness measures. Overall, we found no consistent clone-level specialization, with some clones acting as specialists and others, generalists. The trematode population therefore maintains an overall generalist strategy by comprising a mixture of clone-level specialists and generalists.

The lack of information on marine tapeworm life cycles can be addressed with knowl- edge derived from trophic interactions in marine environments. These trophically transmitted para- sites exploit transmission routes involving predator-prey interactions. Porbeagle sharks Lamna nasus are apex predators feeding on a wide range of organisms, including teleosts and cephalopods. Although the biology of this shark species is relatively well studied, there is a surprising lack of infor- mation about the trophic interactions involving this species that lead to the acquisition of tapeworms. Recently, the use of molecular tools, combined with phylogenetics, has proven useful in identifying trophic links involved in the transmission of marine tapeworms. In the present study, we used sequence data from the D2 domain of the large subunit ribosomal DNA to link adult tapeworms of the species Clistobothrium cf. montaukensis and Dinobothrium sp. parasitising porbeagle sharks to lar- vae recovered from the squid Doryteuthis gahi. To the best of our knowledge, it is the first to provide empirical evidence for a trophic link between porbeagle sharks and D. gahi as a definitive route for the successful transmission of these tapeworms. Furthermore, our data suggest an ontogenetic shift in diet away from squid. Parasite abundance data in D. gahi indicate that the abundance of porbea- gle sharks can be significant in some years.

The great white shark Carcharodon carcharias Linnaeus, 1758 is a versatile and fierce predator (and responsible for many shark attacks on humans). This apex predator feeds on a wide range of organisms including teleosts, other elasmobranchs, cephalopods, pinnipeds, and cetaceans. Although much is known about its diet, no trophic links have been empirically identified as being involved in the transmission of its tapeworm parasites. Recently, the use of molecular tools combined with phylogenetics has proven useful to identify larval and immature stages of marine tapeworms; utilization of the technique has been increasing rapidly. However, the usefulness of this approach remains limited by the availability of molecular data. Here, I employed gene sequence data from the D2 region of the large subunit of ribosomal DNA to link adults of the tapeworm Clistobothrium carcharodoni Dailey and Vogelbein, 1990 (Cestoda: Tetraphyllidea) to larvae for which sequence data for this gene are available. The sequences from the adult tapeworms were genetically identical (0% sequence divergence) to those available on GenBank for "SP" 'small' Scolex pleuronectis recovered from the striped dolphin (Stenella coeruleoalba) and Risso's dolphin (Grampus griseus). This study is the first to provide empirical evidence linking the trophic interaction between great white sharks and cetaceans as a definitive route for the successful transmission of a tetraphyllidean tapeworm. Using the intensity of infection data from this shark and from cetaceans as proxies for the extent of predation, I estimate that this individual shark would have consumed between 9 to 83 G. griseus , fresh, dead, or both, in its lifetime.

Parasite species richness is a fundamental characteristic of host species and varies substantially among host communities. Hypotheses aiming to explain observed patterns of richness are numerous, and none is universal. In this study, we use tapeworm parasites of elasmobranch fishes to examine the phylogenetic and environmental influences on the variation in species richness for this specific system. Tapeworms are the most diverse group of helminths to infect elasmobranchs. Elasmobranchs are cosmopolitan in distribution and their tapeworm parasites are remarkably host specific; therefore, making this an ideal system in which to examine global patterns in species diversity. Here, we 1) quantify the tapeworm richness in elasmobranch fishes, 2) identify the host features correlated with tapeworm richness, and 3) determine whether tapeworm richness follows a latitudinal gradient. The individual and combined effects of host size, factors associated with water temperatures (influenced by latitude and depth), host habitat, and type of elasmobranch (shark or batoid) on measures of species diversity were assessed using general linear models. These analyses included tapeworm host records for 317 different elasmobranch species (124 species were included in our analyses) and were conducted with and without taking into account phylogenetic relationships between host species. Since sharks and batoids differ substantially in body form, analyses were repeated for each host subset. On average, batoids harboured significantly more tapeworm species than shark hosts. Tapeworm richness in sharks was influenced by median depth, whereas no predictor variable included in our models could adequately account for interspecific variation in tapeworm richness in batoid hosts. The taxonomic diversity of tapeworm assemblages of sharks and batoids was influenced by median depth and median latitude, respectively. When the influence of host phylogeny is accounted for, larger hosts harbour a greater tapeworm richness, whereas hosts exploiting wider latitudinal ranges harbour more taxonomically distinct tapeworm assemblages. Species richness and taxonomic diversity of tapeworm assemblages in elasmobranch fishes are influenced by different evolutionary pressures, including host phylogenetic relationships, space constraints and geographical area. Our results suggest that ca 3600 tapeworm species have yet to be described from elasmobranch fishes.

The objectives of this study were to (1) describe the host range for 6 tetraphyllidean species and quantify their host specificity using 5 specificity indices; (2) determine the role of morphological determinants in the host specificity of tetraphyllideans by comparing villar and bothridial measurements of species examined herein; and (3) determine the role of a physiological component in the host specificity of tetraphyllideans by exposing tetraphyllideans to blood sera from different fish species and other solutions. Our results indicate that Echeneibothrium dubium abyssorum (ex Amblyraja radiata), Echeneibothrium canadensis (ex A. radiata), and Zyxibothrium kamienae (ex Malacoraja senta) exhibit the highest degree of specificity, followed by Echeneibothrium vernetae (ex Leucoraja erinacea and Leucoraja ocellata), Pseudanthobothrium hanseni (ex A. radiata and M. senta), and Pseudanthobothrium purtoni (ex Leucoraja erinacea and L. ocellata). However, these results vary based on the specificity index used. Compatible bothridial and villar measurements indicate that there is no morphological determinant of host specificity but that there is a morphological determinant to attachment site specificity. Our data indicate that attachment site specificity may also be phylogenetically determined. Additionally, the exposure of parasites to blood sera from various hosts confirms that host specificity in this system has a physiological determinant. Therefore, host specificity in this system is determined, at least in part, by physiological factors, whereas attachment site specificity is an extension of host specificity and is phylogenetically determined.

SUMMARYThe range of hosts used by a parasite is influenced by macro-evolutionary processes (host switching, host–parasite co-evolution), as well as ‘encounter filters’ and ‘compatibility filters’ at the micro-evolutionary level driven by host/parasite ecology and physiology. Host specialization is hypothesized to result in trade-offs with aspects of parasite life history (e.g. reproductive output), but these have not been well studied. We used previously published data to create models examining general relationships among host specificity and important aspects of life history and reproduction for nematodes parasitizing animals. Our results indicate no general trade-off between host specificity and the average pre-patent period (time to first reproduction), female size, egg size, or fecundity of these nematodes. However, female size was positively related to egg size, fecundity, and pre-patent period. Host compatibility may thus not be the primary determinant of specificity in these parasitic nematodes if there are few apparent trade-offs with reproduction, but rather, the encounter opportunities for new host species at the micro-evolutionary level, and other processes at the macro-evolutionary level (i.e. phylogeny). Because host specificity is recognized as a key factor determining the spread of parasitic diseases understanding factors limiting host use are essential to predict future changes in parasite range and occurrence.

SUMMARYParasites have evolved a myriad of attachment structures closely adapted to their hosts and sites of attachment. Here, using members of the genusAcanthobothriumvan Beneden, 1850 (Cestoda: Tetraphyllidea: Onchobothriidae), we (i) examined the influence of host body size and phylogeny, in addition to morphological features of these tapeworms, on the size of 3 structures used in attachment (bothridia, accessory suckers and hooks) by means of general linear models and phylogenetic-independent contrasts methods, and (ii) quantified the scaling exponents of relationships between size of attachment structures and tapeworm body size. Our results indicate that there exists a positive relationship, albeit not directly proportional, between size of attachment structures andAcanthobothriumspp. body size, and hook size and size of bothridia and accessory suckers. These results suggest that the resource investment in whole-body growth is greater than that in attachment structures, and that a greater investment in development of bothridia and accessory suckers is required to maintain an equivalent functional efficacy to hooks. In addition, host body size also influences, though less markedly, the size of attachment structures inAcanthobothriumspp. independently of parasite size itself.Acanthobothriumspecies have evolved a generalized mode of attachment that is successful in maintaining their position on various intestinal mucosal topographies across a variety of hosts exploiting different food resources.

Tetraphyllidean cestodes are cosmopolitan, remarkably host specific, and form the most speciose and diverse group of helminths infecting elasmobranchs (sharks, skates and rays). They show substantial interspecific variation in a variety of morphological traits, including body size. Tetraphyllideans represent therefore, an ideal group in which to examine the relationship between parasite body size and abundance. The individual and combined effects of host size, environmental temperature, host habitat, host environment, host physiology, and host type (all likely correlates of parasite body size) on parasite length were assessed using general linear model analyses using data from 515 tetraphyllidean cestode species (182 species were included in analyses). The relationships between tetraphyllidean cestode length and intensity and abundance of infection were assessed using simple linear regression analyses. Due to the contrasting morphologies between shark and batoid hosts, and contrasting physiologies between sharks of the Lamnidae family and other sharks, analyses were repeated in different subsets based on host morphology and physiologies (“sharks” vs. batoids) to determine the influence of these variables on adult tetraphyllidean tapeworm body size. Results presented herein indicate that host body size, environmental temperature and host habitat are relatively important variables in models explaining interspecific variations in tetraphyllidean tapeworm length. In addition, a negative relationship between tetraphyllidean body size and intensity of infection was apparent. These results suggest that space constraints and ambient temperature, via their effects on metabolism and growth, determine adult tetraphyllidean cestode size. Consequently, a trade-off between size and numbers is possibly imposed by external forces influencing host size, hence limiting physical space or other resources available to the parasites.

SUMMARYA parasitological survey in the Bay of Fundy, Canada, resulted in the recovery of mature specimens from 5 species of phyllobothriid tapeworms (Cestoda: Tetraphyllidea) from 4 rajid skates: Echeneibothrium canadensis and E. dubium abyssorum specimens from Amblyraja radiata; E. vernetae and Pseudanthobothrium n.sp. from Leucoraja erinacea and L. ocellata; and P. hanseni from A. radiata and Malacoraja senta. Partial sequence data of a variable region (D2) from the large subunit ribosomal DNA (LSU) were used here to determine the host distribution of immature specimens for 4 of these 5 species (E. d. abyssorum was not included in the analyses). Immature specimens from both Pseudanthobothrium spp. were identified in the same hosts as recorded previously for mature specimens, thus suggesting that there are mechanisms that prevent the attachment of the parasite in an ‘unsuitable’ host species. Immature E. canadensis specimens were recovered exclusively from A. radiata, whereas immature E. vernetae specimens were recovered from L. erinacea and A. radiata, despite the latter host species not harbouring mature E. vernetae specimens. Their presence in the latter host species may be explained by host restriction or resistance, which allows the attachment of the parasites in the ‘wrong’ host species, but not establishment or development.

During a parasitological survey of Leucoraja erinacea, L. ocellata, Malacoraja senta and Amblyraja radiata from Passamaquoddy Bay and waters surrounding the West Isles of the Bay of Fundy, NB, Canada, seven species of cestodes were recovered. Examination of these skates revealed the presence of two distinct species of Pseudanthobothrium Baer, 1956: one was retrieved from M. senta and A. radiata, identified as P. hanseni Baer, 1956 and redescribed herein; the other was retrieved from L. erinacea and L. ocellata and differs from previously described species. The new species is described herein as P. purtoni n. sp. on the basis of the degree of apolysis, the maximum width of the strobila, the length of the cirrus-sac and the number of testes. Additionally, the distinctiveness of both species of Pseudanthobothrium is supported by the characterisation of a 643 base-pair nuclear marker, which includes most of the D2 variable region of the large subunit ribosomal DNA (LSU). The recovery of two different tetraphyllidean species, each from two different host species, challenges the oioxeny (strict host-specificity) of echeneibothriine cestodes and can be explained, at least in part, by the similarities in diet and substrate preference within each host pair.