21 research outputs found
Evolutionary processes involved in the diversification of chelonian and mammal polystomatid parasites (Platyhelminthes, Monogenea, Polystomatidae) revealed by palaeoecology of their hosts
No full textPolystomatid flatworms (Platyhelminthes) are monogenean parasites that infect exclusively aquatic or
semi-aquatic sarcopterygians such as the Australian lungfish, amphibians, freshwater turtles and the
African common hippopotamus. Previous studies on the phylogenetic relationships of these parasites,
excluding Oculotrema hippopotami infecting common hippos, showed a global coevolution between hosts
and their parasites at a macroevolutionary scale. These studies also demonstrated a strong correlation
between the diversification of early neobatrachian polystomes and Gondwana breakup in the Mesozoic
period. However the origin of chelonian polystomes is still in question as a switch from presumably primitive
aquatic amniotes to turtles at the time of their first appearance, or soon after during their radiation,
was assumed. In order to resolve this sticking point, we extended the phylogeny of polystomes with
broader parasite sampling, i.e. 55 polystome species including Nanopolystoma tinsleyi a polystome infecting
caecilians and O. hippopotami, and larger set of sequence data covering two nuclear and two mitochondrial
genes coding for the ribosomal RNA 18S and 28S, the Cytochrome c Oxidase I and the
ribosomal RNA 12S, respectively. The secondary structure of nuclear rRNAs genes (stems and loops)
was taken into account for sequence alignments and Bayesian analyses were performed based on the
appropriate models of evolution selected independently for the four designed partitions. Molecular calibrations
were also conducted for dating the main speciation events in the polystome tree. The phylogenetic
position of chelonian parasites that are phylogenetically closer to N. tinsleyi than all other
amphibian polystomes and molecular time estimates suggest that these parasites originated following
a switch from caecilians, at a geological period when primitive turtles may already have adapted to an
aquatic life style, i.e. at about 178 Million years ago, or a little later when the crown group of extant turtles
have already diversified, i.e. at about 152 Mya. Similarly, because O. hippopotami constitutes the sister
group of chelonian parasites, proposing that an African caecilian could be the ancestral host for this polystome
species seems at this stage the most likely hypothesis to explain its occurrence within the common
hippo. Regardless of the scenario that may be predicted to explain the origin of polystomes within aquatic
or semi-aquatic amniotes, their presence and evolution are indicative of early aquatic ecological habits
within ancestral lineage
Tracking platyhelminth parasite diversity from freshwater turtles in French Guiana: First report of Neopolystoma Price, 1939 (Monogenea: Polystomatidae) with the description of three new species
No full textPolystomatid flatworms in chelonians are divided into three genera, i.e. Polystomoides Ward, 1917,
Polystomoidella Price, 1939 and Neopolystoma Price, 1939, according to the number of haptoral hooks. Among the
about 55 polystome species that are known to date from the 327 modern living chelonians, only four species of
Polystomoides are currently recognised within the 45 South American freshwater turtles.National Research Foundation of South AfricaMinistère des Affaires Étrangères Françai
Hox genes from the Polystomatidae (Platyhelminthes, Monogenea).
No full textInternational audienceHox genes form a multigenic family that play a fundamental role during the early stages of development. They are organised in a single cluster and share a 60 amino acid conserved sequence that corresponds to the DNA binding domain, i.e. the homeodomain. Sequence conservation in this region has allowed investigators to explore Hox diversity in the metazoan lineages. Within parasitic flatworms only homeobox sequences of parasite species from the Cestoda and Digenea have been reported. In the present study we surveyed species of the Polyopisthocotylea (Monogenea) in order to clarify Hox identification and diversification processes in the neodermatan lineage. From cloning of degenerative PCR products of the central region of the homeobox, we report one ParaHox and 25 new Hox sequences from 10 species of the Polystomatidae and one species of the Diclidophoridae, which extend Hox gene diversity from 46 to 72 within Neodermata. Hox sequences from the Polyopisthocotylea were annotated and classified from sequence alignments and Bayesian inferences of 178 Hox, ParaHox and related gene families recovered from all available parasitic platyhelminths and other bilaterian taxa. Our results are discussed in the light of the recent Hox evolutionary schemes. They may provide new perspectives to study the transition from turbellarians to parasitic flatworms with complex life-cycles and outline the first steps for evolutionary developmental biological approaches within platyhelminth parasites
Phoretic interaction between the kangaroo leech Marsupiobdella africana (Hirudinea: Glossiphoniidae) and the cape river crab Potamonautes perlatus (Decapoda: Potamonautidae)
No full textAbstractThe South African leech Marsupiobdella africana is a temporary ectoparasite of the amphibian Xenopus laevis, has a phoretic association with a freshwater crab Potamonautes perlatus, and exhibits advanced parental care by incubating its offspring in a brood pouch. Because phoretic associations are usually regarded to favor the phoront’s dispersion, its occurrence within the biology of a parasitic species reflects an intimate context of interactions. In addition to phoresy, attachment to the crab may confer other advantages pertaining to offspring development and predator avoidance, dispersion and the parasitic life cycle. Two ponds where amphibian and crab hosts co-occur were sampled twice a month for a period of 1year. The population dynamics of the leeches and their use of specific microhabitats as attachment sites on the crabs were also investigated. Results indicate a direct relationship between intra-specific variation in the sex ratio among captured crab hosts and the number of leeches recruited over time. The attachments to specific microhabitats on the hard surfaces of the host suggest a proximal proximate anti-predatory strategy. Finally, the importance of oxygen accessibility for the offspring development has been investigated experimentally. Results revealed a remarkable network of interactions linking all partners of this system raising the question as to whether the crabs merely act as a vehicle or play a role within the parasitic life cycle
Origin and evolution of alternative developmental strategies in amphibious sarcopterygian parasites (Platyhelminthes, Monogenea, Polystomatidae)
No full textAbstractMost integrative studies involving phylogenetic, developmental and ecological trends showed that the diversity of developmental modifications among the Platyhelminthes was linked to transmission opportunity pressures. For parasitic flatworms with complex life cycles it was suggested that the evolutionary forces that constrained or enhanced developmental strategies implied heterochronic patterns. Similar patterns were also reported from the Monogenea with direct life cycles, especially for Polystomatidae, which infest amphibious Sarcopterygians. Polystoma, whose members are recovered almost exclusively from anuran hosts of the Neobatrachia, is capable of following two alternative developmental strategies depending on the physiological stage of its host. Processes by which parasites reach maturity are strikingly different, and lead to discrete adult phenotypes within the same parasite species. In the present study, we investigate the origin and evolution of developmental patterns of polystomatids in a phylogenetic framework, using an integrative approach of heterochrony and evolutionary ecology. The results suggest that both phenotypes have coexisted during the early stages of polystome evolution, and that neither of them can be considered as the ancestral one. The two developmental pathways, each associated with one life cycle, may have arisen independently prior to polystome diversification, when strictly aquatic sarcopterygians attempted colonization of temporary freshwater environments. The occurrence of these two patterns within species of the genus Polystoma is suggested to reflect the ancestral condition, and to have allowed both developmental strategies to be successful depending on shifts in transmission opportunities. Thus, host evolutionary ecology may be the main factor in shaping developmental strategies within polystomatids
Assessment of platyhelminth diversity within amphibians of French Guiana revealed a new species of Nanopolystoma (Monogenea: Polystomatidae) in the caecilian Typhlonectes compressicauda
No full textInternational audienceScientists attending the First World Congress of Her-petology in 1989 first became concerned about a widespread decline in amphibian population numbers (Stuart et al. 2004). Since then, the number of studies and publications on amphibians increased considerably and the number of species known nearly doubled to the current figure of 7 044 (Frost 2013). In their comprehensive study to identify biodiversity hotspots for conservation priorities , Meyers et al. (2000) reported on the unique biodiversity of the Neotropical realm and the high levels of endemism. This biogeographical area hosts indeed the highest amphibian diversity in the world with 49% of all known amphibian species (Stuart et al. 2004, Vredenburg and Wake 2007). Amphibians serve as hosts to a variety of parasites. For example, the African clawed frog, Xenopus laevis (Dau-din), may be infected by no less than 25 different parasite genera from seven higher taxa (Tinsley 1996). Polysto-matid flatworms of the class Monogenea Carus, 1863, which comprises 24 genera, are known from a large range of hosts including the Australian lungfish (one genus), amphibians (19 genera), freshwater turtles (three genera) and the hippopotamus (one genus). The vast majority of polystomatids reported are parasite of amphibians, among which 16 genera are from anurans, two from urodelids and one from caecilians
Expression patterns of Abd-A/Lox4 in a monogenean parasite with alternative developmental paths
No full textInternational audienceA key issue in Evolutionary Developmental Biology is to assess the roles of homeotic genes in order to uncover the origins of animal diversity. Within parasitic platyhelminths which show a large diversity of developmental strategies, only one study related to the expression of Hox genes has so far been conducted involving a digenean species with a complex life cycle. In the present study, we considered the expression levels of the Pg-Lox4 gene within Polystoma gallieni of the Monogenea which displays alternative phenotypes throughout its direct life cycle, depending on the physiological stage of its amphibian host Hyla meridionalis upon which free swimming larvae attach. Dissimilar expression patterns were found along the two morphogenetic routes revealing a putative role of Pg-Lox4 in the process of developmental plasticity. Pg-Lox4 was also shown to be upregulated in both reproducing parasite phenotypes indicating its apparent involvement in tissue differentiation of the reproductive organs
Alternative development in polystoma gallieni (platyhelminthes, monogenea) and life cycle evolution
No full textConsidering the addition of intermediate transmission steps during life cycle evolution, developmental
plasticity, canalization forces and inherited parental effect must be invoked to explain new host colonization.
Unfortunately, there is a lack of experimental procedures and relevant models to explore the
adaptive value of alternative developmental phenotypes during life cycle evolution. However, within
the monogeneans that are characterized by a direct life cycle, an extension of the transmission strategy
of amphibian parasites has been reported within species of Polystoma and Metapolystoma (Polyopisthocotylea;
Polystomatidae). In this study, we tested whether the infection success of Polystoma gallieni
within tadpoles of its specific host, the Stripeless Tree Frog Hyla meridionalis, differs depending on the
parental origin of the oncomiracidium. An increase in the infection success of the parasitic larvae when
exposed to the same experimental conditions as their parents was expected as an adaptive pattern of
non-genetic inherited information. Twice as many parasites were actually recorded from tadpoles
infected with oncomiracidia hatching from eggs of the bladder parental phenotype (1.63 ± 0.82 parasites
per host) than from tadpoles infected with oncomiracidia hatching from eggs of the branchial parental
phenotype (0.83 ± 0.64 parasites per host). Because in natural environments the alternation of the two
phenotypes is likely to occur due to the ecology of its host, the differential infection success within young
tadpoles could have an adaptive value that favors the parasite transmission over time.http://www.journals.elsevier.com/experimental-parasitology
Lessons from parasitic flatworms about evolution and historical biogeography of their vertebrate hosts
No full texthttp://dx.doi.org/10.1016/j.crvi.2008.08.01
Actions speak louder than words: comparing automatic imitation and verbal command
No full textAutomatic imitation – copying observed actions without intention – is known to occur, not only in neurological patients and those with developmental disorders, but also in healthy, typically-developing adults and children. Previous research has shown that a variety of actions are automatically imitated, and that automatic imitation promotes social affiliation and rapport. We assessed the power of automatic imitation by comparing it with the strength of the tendency to obey verbal commands. In a Stroop interference paradigm, the stimuli were compatible, incompatible and neutral compounds of hand postures and verbal commands. When imitative responses were required, the impact of irrelevant action images on responding to words was greater than the effect of irrelevant words on responding to actions. Control group performance showed that this asymmetry was not due to modality effects or differential salience of action and word stimuli. These results indicate that automatic imitation was more powerful than verbal command
