Recent non‐native invertebrate plant pest establishments in Great Britain: origins,pathways, and trends

1 An appraisal of non‐native invertebrate plant pest establishments in Great Britain, between 1970 and 2004, was carried out to improve our understanding of current invasion processes by non‐native plant pests, and to assist national strategies in managing the risks they pose. 2 A total of 164 establishments, comprising 50 natural colonists and 114 human‐assisted introductions, were recorded across 13 major taxonomic groups. 3 The mean rate of establishment was 22.1 species per 5‐year period: 19.1 and 3.0 species outside and inside protected cultivation, respectively. Despite the continuing rapid growth in international trade and a general perception that rates of pest invasions are accelerating, no significant temporal trends in the rate of establishments in Great Britain were detected, either for natural colonists or human‐assisted introductions, or for pests of plants grown indoors or outside. 4 The plant trade, particularly in ornamental plants, accounted for nearly 90% of human‐assisted introductions; apiculture, biological control, timber imports, transport stowaways and intentional releases each contributed less than 5%. Only eight (4.9%) of the establishments could be considered as having no direct potential economic impact because all other species have been recorded as feeding on cultivated plants. A greater proportion of establishments by both natural colonists and human‐assisted introductions occurred on non‐native, woody plants. 5 The present study confirms previous work in other European countries that highlight the predominant role of the ornamental plant trade in introducing new plant pests to the European continent, mainly from Asia and North America.     

Comparative morphology of the epidermis of seven species of polyclad flatworms (Platyhelminthes: Rhabditophora)

The ultrastructure of the epidermis of seven species of polyclad flatworms (Phaenocelis medvedica, Phaenocelis peleca, Pleioplana atomata, Boninia divae, Pericelis orbicularis, Enchiridium periommatum, and Cycloporus variegatus) representing six families is described. In all seven species, the epidermis consists of a single layer of columnar cells that rests on a bipartite basement membrane. Epithelial cell surfaces are covered by numerous microvilli and cilia. Cilia contain microtubules arranged in the 9 + 2 pattern, and from their basal bodies two striated rootlets arise, a rostrally directed one running parallel to the apical cell membrane, and a vertical one at a right angle to the first rootlet. Numerous epithelosomes and mitochondria occupy the apical parts of the cells. The basal part of the cells is highly folded, forming a cell web that connects to the basement membrane. The basement membrane consists of a thin basal lamina and a thick, multilayered reticular lamina. The number of layers in the reticular lamina varies among the different species and appears to be correlated with body size. Numerous canals containing either pigment granules or nervous processes perforate the basement membrane. We have identified four different types of glands: rhabdite glands, rhabdoid glands, mucoid glands containing vacuoles filled with flocculent material, and mucoid glands resembling thread cells of hagfish slime glands. The latter have been found only in P. orbicularis. Pigment cells were found in all species examined with the exception of C. variegatus, which takes its coloration from its ascidian prey. Our results further support the unique taxonomic status of Boniniidae.     

Predation potential of three flatworm species (Platyhelminthes: Turbellaria) on mosquitoes (Diptera: Culicidae)

We conducted a field survey for flatworms to select species as potential biological control agents against Aedes aegypti and Culex pipiens (Diptera, Culicidae) breeding in artificial containers. Laboratory experiments were performed to determine the daily predation rate, differential predation on each mosquito larval instar, selective predation on either A. aegypti or C. pipiens, and predator tolerance to water from artificial containers. Girardia anceps (Tricladida, Paludicola, Dugesiidae), Mesostoma ehrenbergii and Bothromesostoma cf. evelinae (Rhabdocoela, Typhloplanoida, Typhloplanidae) were found in temporary puddles and permanent pools. In the laboratory, they killed between 52% and 100% of immature mosquitoes coexisting in the same habitat. No preference of flatworms for mosquito preys was detected. Predation rate was related to predator size and instar of preys. Girardia anceps and B. evelinae survived after a dry period and when re-flooding occurred, they laid eggs. Tolerance to water from artificial containers was highest in G. anceps and this species could be a suitable predator to reduce mosquito populations from artificial containers using an inoculative approach.     

Immunocytochemical localization of histamine in flatworms

Summary Specific antibodies against histamine were used to demonstrate the occurrence and cellular distribution of histamine-like immunoreactivity in three species of flatworms (phylum Platyhelminthes). In the parasitic cestode Diphyllobothrium dendriticum, histamine-reactivity was found in neurons of the main nerve cords, and in cells lining the central and peripheral excretory ducts. In the free-living microturbellarian Microstomum lineare and in the planarian Polycelis nigra, histamine-immuno-reactivity was restricted to cells and fibres of the nervous system. The occurrence of histamine or a related substance in the nervous system of flatworms, which represent primary bilateria, indicates the importance of this neuroactive substance in the animal kingdom.     

Microturbellarian species richness and community similarity among temporary pools:relationships with habitat properties

Temporary water bodies exhibit a high level of biodiversity,much of which is unique tothese habitats.Studies of microturbellarian community ecology in temporary pools are scarce,eventhough turbellarians are potentially important in organizing community structure.Moreover,therehas been virtually no documentation of microturbellarians from Israel.We examined the re-lationships between several pool properties (surface area,water depth,permanence and sedimentdepth)and microturbellarian species richness among 52 temporary pools at a single site.A total of17 taxa of microturbellarians were identi ed,of which 14 were determined to genus or species level.Richness was positively related with surface area and with maximal sediment depth,togetherexplaining 54%of the variance.In more intensive sampling of a subset of 18 pools,surface areawas the only signi cant predictor,explaining 76%of the variance.Community dissimilarity waspositively related with di erences in both surface area and permanence.We identi ed three cate-gories of pool size,each characterized by di erent turbellarian species:large pools were dominatedbyCastrada viridis andGieysztoria cuspidata ,intermediate pools byDochmiotrema limicola ,and many of the small pools byGieysztoria ornata andOlisthanella obtusa .Large pools contributed themost to regional diversity,with 11 of the 17 observed taxa.However,some species were unique tosmall pools.Thus,in order to maintain maximal regional diversity of temporary water turbellar-ians,it is important to conserve habitats containing pools of various sizes.     

Phenotypically flexible sex allocation in a simultaneous hermaphrodite

Previous studies on sex allocation in simultaneous hermaphrodites have typically focused either on evolutionary or one-time, ontogenetic optimization of sex allocation, ignoring variation within an individual's lifetime. Here, we study whether hermaphrodites also possess facultative sex allocation, that is, a phenotypic flexibility, allowing them to distribute resources to either sex in an opportunistic way during their adult lifetime. We used the simultaneously hermaphroditic free-living flatworm Macrostomum lignano and raised individuals in pairs and groups of eight worms (further called octets) until sexual maturity was reached and sex allocation for the current conditions was expected to be set. Treatment groups were subsequently transferred to the alternative group size, that is, from pairs to octets or from octets to pairs, and compared to two control groups, which were transferred without changing group size. The results show that worms in treatment groups responded as expected by the local mate competition theory for simultaneous hermaphrodites: increasing group size resulted in a shift toward a more male-biased sex allocation and vice versa. These findings reveal that sex allocation in these animals is not fixed during ontogeny, but remains flexible after maturation. We argue that phenotypically flexible sex allocation in hermaphroditic animals may help us to understand the evolution and ecology of hermaphroditism.     

Boule-like genes regulate male and female gametogenesis in the flatworm Macrostomum lignano

Members of the DAZ (Deleted in AZoospermia) gene family are important players in the process of gametogenesis and their dysregulation accounts for 10% of human male infertility. Boule, the ancestor of the family, is mainly involved in male meiosis in most organisms. With the exception of Drosophila and C. elegans, nothing is known on the function of boule in non-vertebrate animals. In the present study, we report on three boule orthologues in the flatworm Macrostomum lignano. We demonstrate that macbol1 and macbol2 are expressed in testes whilst macbol3 is expressed in ovaries and developing eggs. Macbol1 RNAi blocked spermatocyte differentiation whereas macbol2 showed no effect upon RNAi treatment. Macbol3 RNAi resulted in aberrant egg maturation and led to female sterility. We further demonstrated the evolutionary functional conservation of macbol1 by introducing this gene into Drosophila bol¹ mutants. Macbol1 was able to rescue the progression of fly meiotic divisions. In summary, our findings provide evidence for an involvement of boule genes in male and female gamete development in one organism. Furthermore, boule gene function is shown here for the first time in a lophotrochozoan. Our results point to a more diverse functional assignment of boule genes. Therefore, a better understanding of boule function in flatworms can help to elucidate the molecular mechanisms of and concomitant infertility in higher organisms including humans.     

Expression of a neuropeptide similar to allatotropin in free living turbellaria (platyhelminthes)

Mechanisms coordinating cell–cell interaction have appeared early in evolution. Allatotropin (AT), a neuropeptide isolated based on its ability to stimulate the synthesis of juvenile hormones (JHs) in insects has also been found in other invertebrate phyla. Despite this function, AT has proved to be myotropic. In the present study we analyze its expression in two groups of Turbellaria (Catenulida, Macrostomida), and its probable relationship with muscle tissue. The results show the presence of an AT-like peptide in the free living turbellaria analyzed. The analysis of the expression of the peptide together with phalloidin, suggests a functional relationship between the peptide and muscle tissue, showing that it could be acting as a myoregulator. The finding of immunoreactive fibers associated with sensory organs like ciliated pits in Catenulida and eyes in Macrostomida makes probable that AT could play a role in the physiological mechanisms controlling circadian activities. Furthermore, the existence of AT in several phyla of Protostomata suggests that this peptide could be a synapomorphic feature of this group. Indeed, the presence in organisms that do not undergo metamorphosis, could be signaling that it was first involved in myotropic activities, being the stimulation of the synthesis of JHs a secondary function acquired by the phylum Arthropoda.     

New records for two mosquito predators [Turbellaria: Mesostoma] in the northeastern United States

The accumulated data indicate that mesostomid flatworms are efficient predators of mosquito larvae. This paper presents the 1st published records for 3Mesostoma Ehrenberg, including 2 predators of mosquitoes.Mesostoma californicum Hyman,Mesostoma vernale Hyman, andMesostoma sp. cf.lingua Abildgaard were discovered in a temporary pool in Massachusetts.M. californicum andM. sp. cf.lingua were found to be efficient predators on mosquitoe larvae.

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Résumé Les observations accumulées indiquent que les larves des Plathelminthes mesostomides sont des prédateurs efficaces des larves de moustiques. Cette note présente les premières mentions de 3Mesostoma Ehrenberg incluant 2 prédateurs de moustiques.Mesostoma californicum Hyman,Mesostoma vernale Hyman, etMesostoma sp. cf.lingua Abildgaard furent découverts dans une mare temporaire du Massachusetts.M. californicum etM. sp. cf.lingua ont été reconnus comme des prédateurs efficaces des larves de moustiques.

     

Predator-prey interactions in a benthic stream community: a field test of flow-mediated refuges

Ecological theory suggests that the impact of predation can be strongly modified by the existence of regions of the environment in which prey are less accessible to predators, which underscores the need for empirical studies examining the factors influencing the availability and importance of such prey refuges. Our study tested whether benthic microhabitats with high flows provide suspension-feeding larval black flies (Simulium␣vittatum) with a spatial refuge in which the negative impact of predatory flatworms (Dugesia dorotocephala) is reduced. We conducted a short-term field experiment in Chester Creek (southeastern Pennsylvania, United States) to examine how the number of black fly larvae inhabiting tile substrates responded to manipulated variations in flatworm abundance and current speed. The abundance of flatworms declined with increasing current speed, thereby creating the potential for sites with high flows to provide larvae with a refuge from these predators. Multiple regression analysis revealed that the final abundance of larvae exhibited a significant negative relationship to flatworm abundance and a significant positive relationship to current speed. After adjusting for variations in elapsed time and initial larval abundance, flow and predators explained 38% of the variation in the rate of change in larval abundance. The positive correlation between larval abundance and flow had two components: a positive, direct effect of flow on larvae, which arises because these food-limited consumers prefer to reside within sites with faster flows where they can feed at higher rates; and a negative effect of flow on predators, and of predators on larvae, which combine to yield a positive indirect effect of flow on larvae. This indirect effect demonstrates the existence of flow-mediated refuges (i.e., microhabitats in which the impact of predation is reduced due to high flows), although the effect accounts for a small proportion of total variation in larval abundance. A consideration of biomechanical relationships suggests that microhabitats with high flows are likely to create prey refuges in a wide range of freshwater and marine benthic environments. In particular, predators will often experience greater dislodgement forces than prey because of their larger size and because they project farther above the bed where current speeds are faster. Moreover, the ability to resist a given dislodgement force may be greater for many prey, especially those that are sessile or semi- sessile. Received: 31 March 1997 / Accepted: 25 October 1997