Distribution and long-term temporal patterns of four invasive colonial ascidians in the Gulf of Maine

Invasive ascidians are a growing concern for ecologists and natural resource managers, yet few studies have documented their short- and long-term temporal patterns of abundance. This study focuses on the invasion of the Gulf of Maine by the colonial ascidians Botryllus schlosseri, Botrylloides violaceus, Diplosoma listerianum and Didemnum sp. A. We examined the time of arrival and potential vectors for these four invasive ascidians using survey data (collected from 1969 onwards) and literature documentation. We also compared the dominance and seasonal patterns of abundance of these species using data from two identical panel studies; one conducted from 1979 to 1980, the other from 2003 to 2005. Didemnum and Botrylloides were most likely first introduced into the Damariscotta River, Maine in the early 1970's through oyster aquaculture while Botryllus and Diplosoma were probably transported by commercial and recreational vessels. The overall abundance of colonial ascidians has increased since 1979 and 1980. Botryllus was the only invasive colonial ascidian present during the 1979 to 1980 study and accounted for an average of 6.16% cover on panels. From 2003 to 2005, the more recently arrived colonial ascidians Botrylloides and Didemnum accounted for 7.38% and 2.08% cover respectively, while Botryllus covered only 1.16%. Our results reveal a shift in seasonal abundance between 1979 to 1980 and 2003 to 2004. In 1979 and 1980, colonial ascidians had the highest percent cover in fall and winter while in 2003 and 2005 they had highest percent cover in summer and fall. Seasonal patterns of space occupation by colonial ascidians were correlated with seasonal changes in seawater temperature.     

Spatial and temporal effects of pre-seeding plates with invasive ascidians: Growth, recruitment and community composition

Many shallow water subtidal habitats in Massachusetts, USA have recently been invaded by five non-indigenous ascidian species: Ascidiella aspersa, Botrylloides violaceus, Didemnum sp., Diplosoma listerianum and Styela clava. This study examined the effects of seawater temperature, as a proxy for climate change, on B. violaceus and D. listerianum and the impact these ascidians have on native sessile fouling communities. Field experiments were conducted over a four month period at two locations (Lynn and Woods Hole, MA) to examine growth dynamics over regional thermal and geographic ranges. Invasive ascidians occupied as much as 80% of the primary substratum and accounted for the majority of species richness. B. violaceus and D. listerianum growth were similar at both study sites, but initial colony growth of D. listerianum was positively affected by temperature. B. violaceus and D. listerianum exhibited rapid two-week growth rates during the summer months with more rapid growth at the warmer Woods Hole site. Competition for space between B. violaceus and D. listerianum typically resulted in neutral borders between colonies. Overgrowth occurred if the colony of one species was disproportionably larger than the colony of the other species. Recruitment and growth of native species influenced the long-term composition of experimental communities more than the pre-seeding with B. violaceus or D. listerianum colonies. Elevated temperatures, however, increased initial growth of B. violaceus and D. listerianum and may have facilitated the species success to invade the communities during crucial periods of introduction. With projected global climate change, a rise in sea surface temperatures may exacerbate the cumulative impacts of invasions on benthic communities and facilitate the invasion of other non-native ascidian species.     

Recent population expansions of non-native ascidians in The Netherlands

Over the last 50 yrs seven non-native ascidians have settled in The Netherlands, concentrated in the two periods 1974-1977 and 1991-2004 (i.e., Styela clava, Aplidium glabrum, Diplosoma listerianum, Didemnum sp., Botrylloides violaceus, Molgula complanata and Perophora japonica). The year of the introduction of B. violaceus remains a matter of dispute because many of the Botrylloides specimens that are recorded in western Europe, have been identified as the closely resembling species B. leachi. Only Didemnum sp. has become a true invasive species and has become a threat to native ecosystems, especially in the province of Zeeland, by its ability to overgrow virtually all hard substrata present. This includes rocks, stones, sand, algae and almost all sessile marine animals. The sudden population expansion of the didemnid from 1996 onward, coincided with the cold winter of 1995-1996, which caused decreased population sizes of many marine animals. The resulting increase in the availability of suitable substrates for settlement and the strong decrease of grazing sea urchins, may have triggered the population expansion. Studying its population dynamics, the optimal growing temperature for Didemnum sp. appears to be 14-18 °C. Virtually all colonies die when the water temperature gets colder than 5 °C. Colonies growing on live marine animals seem to be more resistant to the cold, than those growing on rocks, stones and plants. Two potential predators of the didemnid have also been recorded in Dutch waters: the gastropods Trivia arctica and Lamellaria sp.     

Influence of cadmium on the morphology and functionality of haemocytes in the compound ascidian Botryllus schlosseri

In order to get insights into the effects of cadmium (Cd) on cell morphology and functions, we exposed haemocytes of the colonial ascidian Botryllus schlosseri to sub-lethal concentrations of CdCl₂. Results indicate that Cd hampers haemocyte spreading and phagocytosis in a dose-dependent way, through the alteration of the actin cytoskeleton. In addition, the metal decreases the stability of the internal membranes, as revealed by the Neutral Red assay. The fraction of cells showing positivity for the lysosomal enzyme acid phosphatase is also reduced in the presence of Cd, whereas the number of cells responsive to the Annexin-V assay and showing chromatin condensation increases, suggesting a metal-dependent induction of apoptosis in exposed cells. As Cd is a known cause of oxidative stress, the decrease in the percentage of cells positive to the assay for superoxide anion, observed at low Cd concentrations, is indicative of the synthesis of metal-chelating molecules, such as metallothioneins, whereas, the increase at high Cd concentrations suggests a depletion of the cell reducing redox potential.     

Programmed cell death in vegetative development: apoptosis during the colonial life cycle of the ascidian Botryllus schlosseri

Programmed cell death (PCD) by apoptosis is a physiological mechanism by which cells are eliminated during embryonic and post-embryonic stages of animal life cycle. During asexual reproduction, the zooids of colonial ascidians originate from an assorted cell population instead of a single zygote, so that we assume that regulation of the equilibrium among proliferation, differentiation and cell death may follow different pathways in comparison to the embryonic development. Here we investigate the presence of apoptotic events throughout the blastogenetic life cycle of the colonial ascidian Botryllus schlosseri, by means of terminal deoxynucleotidyl transferase dUTP Nick End Labeling (TUNEL) coupled with histochemical and electron microscopy techniques. The occurrence of low levels of morphogenetic cell death suggests that, in contrast to what happens during sexual development (embryogenesis and metamorphosis), apoptosis does not play a pivotal role during asexual propagation in botryllid ascidian. Nevertheless, PCD emerges as a key force to regulate homeostasis in adult zooids and to shape and modulate the growth of the whole colony.     

Genomic Differences among Pathotypes of Bursaphelenchus xylophilus

Total genomic DNA from Bursaphelenchus xylophilus pathotypes MPSy-1 and VPSt-1 and from B. mucronatus was digested with restriction endonucleases. DNA fragments were electrophoretically separated, Southern blotted to nitrocellulose, and hybridized to genomic DNA from one of the isolates. The resulting hybridization patterns indicate genomic differences in repetitive DNA sequences among these populations. Greatest differences were seen between B. xylophilus and B. mucronatus, but genomic differences were also apparent between B. xylophilus pathotypes MPSy-1 and VPSt-1 and between a population from P. nigra in New Jersey and a population of a mucronate form from Abies balsamea in Quebec, Canada.     

Onychiurid species from Wanda Mountains in China,with descriptions of two new species (Collembola,Onychiuridae)

A checklist of onychiurid species from the Wanda Mountains in China is presented. Eighteen species belonging to twelve genera have been found, including two new species. Bionychiurus qinglongensissp. n. can be easily distinguished from other known species of the genus by the absence of pseudocelli on Th. I tergum and fewer number of vesicles in postantennal organ. Onychiurus heilongjiangensissp. n. is diagnosed by pseudocellar formulae as 32/133/33352 dorsally and 3/011/31120 ventrally, parapseudocellar formula as 0/000/111001+1^m, ratio of anal spine/unguis as 0.6, unguiculus without inner basal lamella, and male ventral organ absent.     

New species of Rhabdochona Railliet, 1916 (Nemata: Rhabdochonidae) from Rainbow Trout in California Streams

Three new species of Rhabdochona Railliet, 1916 are described and illustrated from Salmo gairdneri Richardson (rainbow trout) in freshwater streams in California: Rhabdochona californiemis n. sp., R. paxmani n. sp., and R. satmonis n. sp. Rhabdochona californiensis n. sp. is characterized by 14 anteriorly directed teeth in the prostome, egg devoid of filaments or floats, male and female tail terminus with a single mucro, left (long) spicule slender with a moderate distended podoid terminal end, spicular ratio 1:3.8. Rhabdochona paxmani n. sp. is characterized by 10 teeth in the prostome, eggs with polar floats, left (long) spicule slender with podoid terminus distended and having a minute subterminal spine; right spicule with prominent gorgeret (barb), spicular ratio 1:4.3, male and female tail terminus with a cuticular conical rounded short projection. Rhabdochona salmoni, n. sp. is characterized by 10 teeth anteriorly directed in the prostome, eggs with polar floats, left spicule slender with a distended podoid terminus; right spicule with a sharply indented gorgeret, spicular ratio 1:4.3, male and female tail terminus with a conical or rounded tip.     

The colonial ascidian Didemnum sp. A: Current distribution, basic biology and potential threat to marine communities of the northeast and west coasts of North America

Didemnum sp. A is a colonial ascidian with rapidly expanding populations on the east and west coasts of North America. The origin of Didemum sp. A is unknown. Populations were first observed on the northeast coast of the U.S. in the late 1980s and on the west coast during the 1990s. It is currently undergoing a massive population explosion and is now a dominant member of many subtidal communities on both coasts. To determine Didemnum sp. A's current distribution, we conducted surveys from Maine to Virginia on the east coast and from British Columbia to southern California on the west coast of the U.S. between 1998 and 2005. In nearshore locations Didemnum sp. A currently ranges from Eastport, Maine to Shinnecock Bay, New York on the east coast. On the west coast it has been recorded from Humboldt Bay to Port San Luis in California, several sites in Puget Sound, Washington, including a heavily fouled mussel culture facility, and several sites in southwestern British Columbia on and adjacent to oyster and mussel farms. The species also occurs at deeper subtidal sites (up to 81 m) off New England, including Georges, Stellwagen and Tillies Banks. On Georges Bank numerous sites within a 230 km² area are 50-90% covered by Didemnum sp. A; large colonies cement the pebble gravel into nearly solid mats that may smother infaunal organisms. These observations suggest that Didemnum sp. A has the potential to alter marine communities and affect economically important activities such as fishing and aquaculture.     

Ecological observations on the colonial ascidian Didemnum sp. in a New England tide pool habitat

The colonial ascidian Didemnum sp. has colonized northwestern Atlantic coastal habitats from southern Long Island, New York, to Eastport, Maine. It is also present in offshore habitats of the Georges Bank fishing grounds. It threatens to alter fisheries habitats and shellfish aquacultures.Observations in a tide pool at Sandwich, MA from December 2003 to February 2006 show that Didemnum sp. tolerates water temperatures ranging from ≤ 1 to > 24 °C, with daily changes of up to 11 °C. It attaches to pebbles, cobbles, and boulders, and it overgrows other tunicates, seaweeds, sponges, and bivalves. From May to mid July, colonies appear as small patches on the bottoms of rocks. Colonies grow rapidly from July to September, with some growth into December, and they range in color from pink to pale yellow to pale orange. Colony health declines from October through April, presumably in response to changes in water temperatures, and this degenerative process is manifested by color changes, by the appearance of small dark brown spots that represent clumps of fecal pellets in the colony, by scavenging by periwinkles, and by a peeling-away of colonies from the sides of cobbles and boulders. At Sandwich, colonies died that were exposed to air at low tide. The species does not exhibit this seasonal cycle of growth and decline in subtidal habitats (40-65 m) on the Georges Bank fishing grounds where the daily climate is relatively stable and annual water temperatures range from 4 to 15 °C. Experiments in the tide pool with small colony fragments (5 to 9 cm²) show they re-attach and grow rapidly by asexual budding, increasing in size 6- to 11-fold in the first 15 days. Didemnum sp. at Sandwich has no known predators except for common periwinkles (Littorina littorea) that graze on degenerating colonies in the October to April time period and whenever colonies are stressed by desiccation.The tendencies of the ascidian (1) to attach to firm substrates, (2) to rapidly overgrow other species, (3) to tolerate a wide temperature range, (4) to be free from predation, and (5) to spread by colony fragmentation combine to make it a potential threat to benthic marine habitats and aquacultures. Didemnum sp. is known to overgrow mussels, oysters, and sea scallops, and it likely envelops other bivalves too.     

Differences in penetration routes and establishment rates of four entomopathogenic nematode species into four white grub species

We compared the penetration of the entomopathogenic nematodes Steinernema scarabaei (AMK001 strain), S. glaseri (NC1 strain), Heterorhabditis zealandica (X1 strain), and H. bacteriophora (GPS11 strain) into third-instars of the scarabs Popillia japonica, Anomala orientalis, Cyclocephala borealis, and Rhizotrogus majalis. When larvae were exposed to nematodes for 6-72 h larval mortality and nematode establishment rate and occasionally speed of kill often showed the same pattern within nematode-white grub combinations. But no two nematodes or white grub species had the same pattern for these observations for all white grub or nematode species, respectively. Mortality, establishment, and speed of kill followed a similar pattern for H. zealandica, S. glaseri, and S. scarabaei, but there was no clear relationship for H. bacteriophora. Significant nematode establishment was only observed after at least 48 h exposure in most nematode-white grub combinations. Faster establishment was observed only for H. zealandica in A. orientalis and R. majalis (after 24 h) and for S. scarabaei in P. japonica and R. majalis (after 12 h). Nematode establishment after 72 h in the different scarab species was generally low for S. glaseri (<1.5%) and H. bacteriophora (<3%), higher for H. zealandica (2-5%), and the highest for S. scarabaei (1-14%). However, in another experiment establishment was generally higher after 96h exposure. Nematode penetration sites were determined by comparing nematode establishment in larvae with mouth, anus, mouth+anus, or none sealed with glue. The trends for each nematode species were very similar in the different white grub species. H. zealandica and H. bacteriophora showed excellent cuticular penetration ability but may also penetrate through mouth and/or anus. S. glaseri also penetrated through the cuticle but lower establishment in larvae with mouth or mouth+anus sealed suggested that the mouth is an important penetration site. S. scarabaei showed a preference for the mouth as a penetration site, but it showed some cuticular penetration ability and may also use the anus as a penetration site. The methodology used cannot exclude that cuticular penetration also included penetration through the spiracles. To fully understand the effect of nematode and white grub species on nematode virulence, future studies will have to compare host immune response to the penetrating IJs and the role of the symbiotic bacteria in these interactions.     

Sterols and related metabolites from five species of sponges

Free sterol fractions were isolated from the marine sponges Phyllospongia madagascarensis, Scalarispongia sp., Oceanapia sp., Monanchora clathrata and studied by GLC, GLC–MS, and spectroscopy NMR. P. madagascarensis and Scalarispongia sp. contained common Δ⁵-sterols; cholesterol was shown to be a main sterol of both the sponges. Oceanapia sp. contained stanols and minor Δ⁵-sterols with 24R-24,25-methylene-5α-cholestan-3β-ol as a main constituent. Many free sterols from M. clathrata were Δ⁷-series compounds, and latosterol was a main sterol. Δ⁴-3-Ketosteroids and Δ⁵-sterol esters were found in the Antarctic sponge Haliclona sp., but free sterols were practically absent except for trace amount of cholesterol. A chemotaxonomic application of sterols in relation to the genera Phyllospongia, Oceanapia and the family Crambeidae is provided. The known cases of the absence of sterols in sponges and probable reasons of the phenomenon are discussed.     

Variations in lipophilic and vacuolar flavonoids among European Pulicaria species

Four European Pulicaria species, P. odora, P. paludosa, P. sicula and P. vulgare, were analysed for their surface and vacuolar constituents for comparison with previous data obtained for P. dysenterica. Each species had a distinct flavonoid pattern with notable differences between leaf and inflorescence. 6-Hydroxyflavonols were the major lipophilic components in all of the species and tissues except in the leaves of P. paludosa and P. vulgare, where scutellarein 6-methyl ether was the main constituent. In the leaves of P. sicula a more unusual flavone, 6-hydroxyluteolin 5,6,7,3',4'-pentamethyl ether, was a major component. Pulicaria odora was distinguished by the presence of a series of methylated 6-hydroxykaempferol derivatives including a 3,5,6,7,4'-pentamethyl ether. Quercetagetin hexamethyl ether occurred in both tissues of P. sicula together with the 3,7,3,4'-tetra methyl ether and other quercetagetin derivatives, which were 5-methylated. Quercetagetin 3,7,3'-methyl ether was present in all species except P. odora. Flavonol glucuronides were characteristic vacuolar constituents of all the taxa studied. Two rare glycosides, patuletin and 6-hydroxykaempferol 6-methyl ether 7-glucuronides were identified in the inflorescence of P. odora. Pulicaria vulgaris, a rare plant of southern England, had the vacuolar flavonoid profile most similar to the other more abundant British plant, P. dysenterica.     

Addition to the study of the genus Dusona (Hymenoptera,Ichneumonidae, Campopleginae) in Korea with description of a new species and key to the Korean species

Korean species of the genus Dusona Cameron (Hymenoptera: Ichneumonidae: Campopleginae) are reviewed. Twenty seven species of Dusona are reported from South Korea, including 12 previously unrecorded species, D. bellipes (Holmgren, 1872), D. bicoloripes (Ashmead, 1906), D. chabarowski Hinz & Horstmann, 2004, D. cultrator (Gravenhorst, 1829), D. japonica (Cameron, 1906), D. mactatoides Hinz, 1994, D. scalprata Horstmann, 2004, D. sasayamae Hinz & Horstmann, 2004, D. oblitera (Holmgren, 1872), D. obtutor Hinz, 1994, D. auriculator Aubert, 1964, D. longicauda (Uchida, 1928), and a new species, D. koreana sp. n. An illustrated key to Korean species of Dusona provided.     

Variation in the ability of Didemnum sp. to invade established communities

Over the past 30 years southern New England, USA has been invaded by several species of ascidians, including Botrylloides violaceus, Diplosoma listerianum, Styela clava, and Ascidiella aspersa. These species have become dominate in coastal embayments and marinas but are usually absent from more open water coastal areas. A colonial ascidian, Didemnum sp. has invaded southern New England during the past 10 years and we first observed this species in eastern Long Island Sound in 2000. It has become the dominant at several field sites while remaining in low abundance at others. We conducted an experiment at two places, a protected marina and an open coast site, to examine its ability to compete with the established fouling community. Small colonies of Didemnum were transplanted onto panels with communities that varied in age from one to four weeks old and these treatments along with controls with only Didemnum were exposed at both sites. In most treatments Didemnum became a dominant species in the communities at both sites but it reached higher abundances at the open coast site. Potential causes of the observed differences are predation on other species of ascidians at the open coast site reducing recruitment of these species and competition, lower tolerance for elevated temperatures at the marina site, or other environmental parameters that might affect growth rates.     

Suppression of programmed cell death regulates the cyclical degeneration of organs in a colonial urochordate

The survival of animal tissues and organs is controlled through both activation and suppression of programmed cell death. In the colonial urochordate Botryllus schlosseri, the entire parental generation of zooids in a colony synchronously dies every week as the asexually derived generation of buds reaches functional maturity. This process, called takeover, involves massive programmed cell death (PCD) of zooid organs via apoptosis followed by programmed removal of cell corpses by blood phagocytes within approximately 1 day. We have previously reported that developing buds in conjunction with circulating phagocytes are key effectors of zooid resorption and macromolecular recycling during takeover, and as such engineer the reconstitution of a functional asexual generation every week [Lauzon, R.J., Ishizuka, K.J., Weissman, I.L., 2002. Cyclical generation and degeneration of organs in a colonial urochordate involves crosstalk between old and new: a model for development and regeneration. Dev. Biol. 249, 333-348]. Here, we demonstrate that zooid lifespan during cyclic blastogenesis is regulated by two independent signals: a bud-independent signal that activates zooid PCD and a bud-dependent, survival signal that acts in short-range fashion via the colonial vasculature. As zooids represent a transient, mass-produced commodity during Botryllus asexual development, PCD regulation in this animal via both activation and suppression enables it to remove and recycle its constituent zooids earlier when intra-colony resources are low, while maintaining the functional filter-feeding state when resources are adequate. We propose that this crosstalk mechanism between bud and parent optimizes survival of a B. schlosseri colony with each round of cyclic blastogenesis.