Genetic evidence for the cryptic species pair, <Emphasis Type="Italic">Lottia digitalis </Emphasis>and <Emphasis Type="Italic">Lottia austrodigitalis</Emphasis> and microhabitat partitioning in sympatry

It has been proposed that the common West Coast limpet, Lottia digitalis, is actually the northern counterpart of a cryptic species duo including, Lottia austrodigitalis. Allele frequency differences between southern and northern populations at two polymorphic enzyme loci provided the basis for this claim. Due to lack of further evidence, L. austrodigitalis is still largely unrecognized in the literature. Seven additional enzyme loci were examined from populations in proposed zones of allopatry and sympatry to determine the existence of L. austrodigitalis as a sibling species to L. digitalis. Significant allele frequency differences were found at five enzyme loci between populations in Laguna Beach, southern California, and Bodega Bay, northern California; strongly supporting the existence of separate species. Both species exhibit two microhabitat morphotypes, a gooseneck barnacle morph in the mid-intertidal zone and a rock morph in the high-intertidal zone. In sympatry, L. austrodigitalis was more abundant higher in the intertidal on rocks, whereas L. digitalis was more abundant lower in the intertidal on barnacles. This finding supports earlier claims of microhabitat partitioning in this sibling species pair. In addition to this finding, the transition zone between the species was found to have shifted substantially northward in only two decades, from Monterey Peninsula, CA to near Pigeon Point, CA, where L. digitalis previously dominated.     

Comparative analysis on the genetic population structures of the deep-sea whelks <Emphasis Type="Italic">Buccinum tsubai</Emphasis> and <Emphasis Type="Italic">Neptunea constricta</Emphasis> in the Sea of Japan

The population structures of Buccinum tsubai and Neptunea constricta were compared using partial sequences of the mitochondrial COI gene. B. tsubai included four genetically distinguishable subpopulations (Hokkaido, Yamagata-Toyama, Yamato Bank, and San’in), which is consistent with the results of our previous study using mitochondrial 16SrRNA sequences. The genetic structure of N. constricta was also clear, but the lineage sorting corresponding to the geographical distribution was not as clear as that of B. tsubai. The difference between the genetic structures of these two species might be due to a difference in either their dispersal abilities or the historic distribution patterns in the Sea of Japan. The fossil record and nested clade analyses support the latter alternative. The four subpopulations of B. tsubai are estimated to have diverged 0.42–1.46 million years ago, providing support for the existence of intermediate water of normal salinity and oxygen concentration capable of sustaining B. tsubai between the low-salinity surface water and anoxic deep water during the Pleistocene glacial periods. The genetic diversity of the Yamato Bank subpopulation of B. tsubai was lower than that of the other subpopulations, which is likely attributable to the small size of the Yamato Bank subpopulation.     

Molecular population structure of the kuruma shrimp <Emphasis Type="Italic">Penaeus</Emphasis><Emphasis Type="Italic"> japonicus</Emphasis> species complex in western Pacific

In a previous study on the kuruma shrimp Penaeus japonicus from the South China Sea, we detected high genetic divergence between two morphologically similar varieties (I and II) with distinct color banding patterns on the carapace, indicating the occurrence of cryptic species. In the present study, we clarify the geographical distribution of the two varieties in the western Pacific by investigating the genetic differentiation of the shrimp from ten localities. Two Mediterranean populations are also included for comparison. Based on the mitochondrial DNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises populations from Japan and China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam, Singapore and the Philippines), Australia and the Mediterranean. Population differentiation is evident in variety II, as supported by restriction profiles of two mitochondrial markers and analysis of two microsatellite loci. The Australian population is genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship. Variety I does not occur in these three localities, while a small proportion of variety II is found along the northern coast of the South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean, are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery management and aquaculture development programs of this important biological resource.     

Phylogeography of two species of <Emphasis Type="Italic">Lysidice</Emphasis> (Polychaeta,Eunicidae) associated to the seagrass <Emphasis Type="Italic">Posidonia oceanica</Emphasis> in the Mediterranean Sea

The aim of this work was to define the phylogeographic patterns of the two species of polychaete Eunicidae, Lysidice ninetta Audouin and Milne Edwards and Lysidice collaris Grube, both associated as sheath borers to the Mediterranean seagrass Posidonia oceanica, and with reference to their different origin and their actual geographic distribution. L. ninetta is distributed in the Atlantic and in the Mediterranean Sea while L. collaris is a tropical species, whose introduction into the Mediterranean Sea through the Suez Canal (lessepsian migrant) has been hypothesized in recent years. The two species have been often confused in the past, although they appear morphologically distinct. They share the same microhabitat (Posidonia sheaths) and they co-exist along a broad bathymetric range (1–30 m). Several populations for both taxa were sampled all along the coast of the Mediterranean basin. A variable no coding region of nuclear DNA (rDNA, ITS1) and a portion of a more conservative coding region of mitochondrial DNA (sub-unit one of citochrome oxidase, COI) were used as molecular markers. Both markers confirmed the separation between the two species. Low intraspecific polymorphism was present in L. collaris, together with absence of phylogeographic structure. In L. ninetta, instead, the presence of intraspecific cryptic lineages, sympatric in some sites, was recorded. Clustering of single populations in the two main clades was not always consistent between markers. The mitochondrial COI region showed more resolution at the given spatial scale. Our results suggest that Lysidice collaris could be recently introduced into the Mediterranean Sea from one or more separate events. On the other hand, for L. ninetta one could presume a re-colonization of the Mediterranean basin from the Atlantics, after the Messinian crisis (dry-out of the Mediterranean Sea, 5.5 my) with the subsequent separation of intraspecific lineages. The phylogeographic patterns of both Lysidice spp. are disjoined with respect to that of the host plant, P. oceanica. The obtained results suggest that environmental constraints and evolutionary history of these polychaetes and their host plant act in different ways to determine their actual genetic spatial structure.     

Evidence of a spawning area of <Emphasis Type="Italic">Anguilla</Emphasis><Emphasis Type="Italic">marmorata</Emphasis> in the western North Pacific

Leptocephali of the tropical eel Anguilla marmorata have been consistently collected in the same area of the North Equatorial Current (NEC) in the western North Pacific during three consecutive cruises in June and July of 1991 (N=28) and 1994 (N=20), and July and September of 1995 (N=27), indicating that this is a spawning area of this species. These leptocephali were collected from 130°E to 142°E and 12°N to 20°N, to the west of the Mariana Islands, in 20 tows in 1991, in 13 tows in 1994 and in 17 tows in 1995, indicating a widespread presence, but a relatively low abundance. Six of these specimens (16.3-36.0 mm total length) from the 1995 cruise, which were of the typical size range of these leptocephali, were genetically confirmed to be A. marmorata in a previous study. The consistent presence of recently spawned A. marmorata leptocephali (9-20 mm) in all 3 years, suggests that the western region of the NEC is the spawning area of the northern population of A. marmorata that was identified in a recent population genetics study. These leptocephali would thus be transported westward by the NEC and then transported north into the Kuroshio Current and toward Taiwan and Japan, or south toward the southern Philippines and into the Celebes Sea by the Mindanao Current. Available evidence indicates that A. marmorata may have potentially year-round spawning, and the presence of a spawning area of this species in the same region as that of Anguilla japonica suggests that the northern population of A. marmorata has evolved a spawning migration from East Asia, the Philippines and the Celebes Sea region to the NEC area, but differs from A. japonica by having some individuals that recruit to more southern areas.     

On the consortium of the tintinnid <Emphasis Type="Italic">Eutintinnus</Emphasis> and the diatom <Emphasis Type="Italic">Chaetoceros</Emphasis> in the Pacific Ocean

The morphology and distribution of the diatoms Chaetoceros tetrastichon and Ch. dadayi as epiphytes on the loricae of the tintinnids Eutintinnus apertus and E. pinguis investigated in the open waters of the Pacific Ocean. The Eutintinnus–Chaetoceros consortia was encountered in 38 of the 52 sampling stations from 34°N to 33°S, and together were among represented the most wide-spread species. The abundance was low with a maximum of 32 consortia l⁻¹ and E. apertus was often the most abundant species of the genus. The free-living Eutintinnus congeneric species showed a wider vertical distribution, whereas E. apertus–Chaetoceros tended to be near the surface. The success of E. apertus in consortium with Chaetoceros may be due to increase of the clearance rate and/or the lower susceptibility to predation. Chaetoceros modifies its morphology to adapt the epiphytic life, especially Ch. dadayi. The shorter curved setae may facilitate the transfer to the lorica of the daughter tintinnid after the cell division. The free-living Ch. tetrastichon and Ch. dadayi are very rare and Chaetoceros remained attached to empty loricae or encysted tintinnid cells. This suggests that the Eutintinnus–Chaetoceros consortium is obligate for the success of the diatom and renders the tintinnid more competitive versus congeneric species.     

Spatial distribution patterns of the gorgonians <Emphasis Type="Italic">Eunicella singularis</Emphasis>, <Emphasis Type="Italic">Paramuricea clavata</Emphasis>, and <Emphasis Type="Italic">Leptogorgia sarmentosa</Emphasis> (Cape of Creus,Northwestern Mediterranean Sea)

Most of the current knowledge on Mediterranean gorgonians is restricted to investigations of those populations found within shallow sublittoral waters, and only limited data are available for populations located below scuba depth. To overcome this lack of information, the occurrence and abundance of the gorgonians Eunicella singularis, Paramuricea clavata, and Leptogorgia sarmentosa were investigated in northwestern Mediterranean benthic communities over a wide geographical (60 km of coastline) and bathymetrical (0–70 m deep) extent using a remotely operated vehicle (ROV). The greatest occurrence and abundances of E. singularis and P. clavata were concentrated in areas that are directly exposed to strong near-bottom currents. E. singularis was the most common and abundant species and displayed great plasticity and amplitude in its environmental preferences. Conversely, P. clavata showed a very patchy distribution that was associated with vertical rocky walls. Only isolated colonies of L. sarmentosa were observed in the study area. Hot spots of abundance of E. singularis and P. clavata were identified below a depth of 40 m, which demonstrates the importance of studying the distribution of benthic species over a wide geographical and bathymetrical extent.     

Foraging responses in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae) to floral scents

Summary. For butterflies to be efficient foragers, they need to be able to recognize rewarding flowers. Flower signals such as colours and scents assist this recognition process. For plant species to attract and keep butterflies as pollinators, species-specific floral signals are crucial. The aim of this study is to investigate foraging responses to floral scents in three temperate butterfly species, Inachis io L. (Nymphalidae), Aglais urticae L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae), in behavioural choice bioassays. The butterflies were allowed to choose bet-ween flower models varying in scent and colour (mauve or green). Flowers or vegetative parts from the plants Centaurea scabiosa L. (Asteraceae), Cirsium arvense (L.) (Asteraceae), Knautia arvensis (L.) (Dipsacaceae), Buddleja davidii Franchet (Loganicaeae), Origanum vulgareL. (Lamiaceae), Achillea millefolium L. (Asteraceae), and Philadelphus coronarius L. (Hydrangiaceae) were used as scent sources. All visits to the models — those that included probing and those that did not — were counted, as was the duration of these behaviours. Both flower-naive and flower-experienced (conditioned to sugar-water rewards, the colour mauve, and specific floral scents) butterflies were tested for their preference for floral versus vegetative scents, and to floral scent versus colour. The butterflies were also tested for their ability to switch floral scent preferences in response to rewards. Flower-naive butterflies demonstrated a preference for the floral scent of the butterfly-favourable plants C. arvense and K. arvensis over the floral scent of the non-favourable plants Achillea millefolium (Asteraceae), and Philadelphus coronarius cv. (Hydrangiaceae). Most of the butterflies that were conditioned to floral scents of either C. arvense, K. arvensis, or B. davidii readily switched theirfloral scent preferences to the one most recently associated with reward, thus demonstrating that floral scent constancy is a result from learning. These findings suggest that these butterflies use floral scent as an important cue signal to initially identify and subsequently recognize and distinguish among rewarding plants. Received 2 September 2001; accepted 9 September 2002.     

<Emphasis Type="Italic">Semibalanus</Emphasis><Emphasis Type="Italic">balanoides</Emphasis> in winter and spring: larval concentration,settlement, and substrate occupancy

This study measured the progression from pelagic larvae to juvenile barnacles, and examined whether recruitment of barnacles, Semibalanus balanoides Linnaeus, at two intertidal sites in contrasting hydrodynamic regimes was determined by pre-settlement or post-settlement processes. The two sites were 1.5 km apart in the vicinity of Woods Hole, Mass., USA. Quantitative plankton samples were taken twice weekly from December 1997 to May 1998 at a nearby site as an estimate of nearshore larval abundance. The presence of S. balanoides nauplii was noted, and cyprids were enumerated and measured. Larval settlement at the two sites [Gansett Point, Buzzards Bay (GP) and Little Harbor, Vineyard Sound (LH)] was estimated from examination of replicate settlement plates exposed for 2 or 3 days throughout the settlement season, and from replicate plots on marked rock quadrats at each site. On both plates and rocks settled cyprids and metamorphs were enumerated. Space occupancy on unmanipulated rock quadrats by all stages from cyprids to adult barnacles was also examined. Settlement occurred from 2 January to 20 May, and major settlement peaks coincided with peaks in pelagic cyprid concentration at LH, but not at GP. Space occupied by juvenile barnacles was close to zero up until late February despite substantial settlement prior to that. At LH, juvenile barnacle cover was zero at the end of the observations; all settlement failed. Almost 100% of settled cyprids failed to metamorphose within 2 days from late January to late March. Then the proportion metamorphosing increased sharply coinciding with a sudden increase of 3°C in water temperature. Observed site differences in space occupancy by juvenile barnacles suggest that while cyprid supply is a necessary condition for barnacle settlement, other factors affecting metamorphosis of settled cyprids and early juvenile mortality determine recruitment.     

Spatiotemporal analysis of population genetic structure in <Emphasis Type="Italic">Geomonhystera disjuncta</Emphasis> (Nematoda,Monhysteridae) reveals high levels of molecular diversity

Species identification in the phylum Nematoda is complicated due to the paucity of easily obtainable diagnostic morphological features. Furthermore, the cosmopolitan distribution of several species despite low dispersal abilities makes cryptic diversity potentially substantial within this phylum. We conducted a population genetic survey in the marine nematode Geomonhystera disjuncta in Belgium and The Netherlands in two seasons. The mitochondrial cytochrome oxidase c subunit 1 (COI) gene was screened with the single-strand conformation polymorphism method in 759 individuals. The 43 haplotypes were grouped into five lineages, with low divergences within (<3%) and high divergences between lineages (>14%). Analysis of the nuclear ITS region yielded concordant tree topologies, indicating the presence of five cryptic taxa within G. disjuncta. Analysis of Molecular Variance (AMOVA) illustrated a significant structuring in all lineages and temporal fluctuations in haplotype frequencies within and between locations. Metapopulation dynamics and/or priority effects best explained this structuring. Finally, our data indicate that the COI gene may be useful for DNA barcoding purposes.     

Individual specialization in the hunting wasp <Emphasis Type="Italic">Trypoxylon</Emphasis> (<Emphasis Type="Italic">Trypargilum</Emphasis>) <Emphasis Type="Italic">albonigrum</Emphasis> (Hymenoptera,Crabronidae)

Individual-level variation in resource use occurs in a broad array of vertebrate and invertebrate taxa and may have important ecological and evolutionary implications. In this study, we measured the degree of individual-level variation in prey preference of the hunting wasp Trypoxylon albonigrum, which inhabits the Atlantic Forest in southeastern Brazil. This wasp captures several orb-weaving spider genera to provision nests. Individuals consistently specialized on a narrow subset of the prey taxa consumed by the population, indicating the existence of significant individual-level variation in prey preferences. The population niche was broader in the wet season in terms of both prey size and taxa. In the case of prey size, the population niche expansion was achieved via increased individual niche breadths, whereas in the case of prey taxa, individual niches remained relatively constrained, and the population niche expanded via increased interindividual variation. The observed pattern suggests the possibility of functional trade-offs associated with the taxon of the consumed prey. The nature of the trade-offs remains unknown, but they are likely related to learning in searching and/or handling prey. We hypothesize that by specializing on specific prey taxa, individuals increase foraging efficiency, reducing foraging time and ultimately increasing reproductive success.     

Molecular characterization of the zoanthid genus <Emphasis Type="Italic">Isaurus</Emphasis> (Anthozoa: Hexacorallia) and associated zooxanthellae (<Emphasis Type="Italic">Symbiodinium</Emphasis> spp.) from Japan

The zoanthid genus Isaurus (Anthozoa: Hexacorallia) is known from both the Indo-Pacific and Atlantic Oceans, but phylogenetic studies examining Isaurus using molecular markers have not yet been conducted. Here, two genes of markers [mitochondrial cytochrome oxidase subunit I (COI) and mitochondrial 16S ribosomal DNA (mt 16S rDNA)] from Isaurus specimens collected from southern Japan (n = 19) and western Australia (n = 3) were sequenced in order to investigate the molecular phylogenetic position of Isaurus within the order Zoantharia and the family Zoanthidae. Additionally, obtained sequences and morphological data (polyp size, mesentery numbers, mesogleal thickness) were utilized to examine Isaurus species diversity and morphological variation. By comparing our obtained sequences with the few previously acquired sequences of genera Isaurus as well as with Zoanthus, Acrozoanthus (both family Zoanthidae), and Palythoa spp. (family Spenophidae) sequences, the phylogenetic position of Isaurus as sister to Zoanthus within the Family Zoanthidae was suggested. Based on genetic data, Isaurus is most closely related to the genus Zoanthus. Despite considerable morphological variation (in particular, polyp length, mesentery numbers, external coloration) between collected Isaurus specimens, all specimens examined are apparently conspecific or very closely related based on molecular data and observed morphological variation within colonies. Additionally, obtained internal transcribed spacer of ribosomal DNA (ITS-rDNA) sequences from symbiotic zooxanthellae (Symbiodinium spp.) from all Isaurus specimens were shown to be subclade C1-related Symbiodinium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Flexible habitat selection and interactive habitat segregation in the marine congeners <Emphasis Type="Italic">Idotea baltica</Emphasis> and <Emphasis Type="Italic">Idotea emarginata</Emphasis> (Crustacea,Isopoda)

Habitat segregation among competing species is widespread yet very little is know how this is achieved in practice. In a case study, we examined short-term effects of conspecific and congeneric density on habitat selection in two competing marine isopod species, Idotea emarginata and Idotea baltica. Under semi-natural conditions in large outdoor cylindrical tanks (4 m high; volume 5.5 m³), animal groups of different size and composition had the choice between a set of relevant habitat samples (surface-floating seaweed, the water column, seaweed on the bottom). Habitat selection in both I. baltica and I. emarginata proved to be largely independent of conspecific density (level of intraspecific competition). In single-species treatments, both species showed a similar and stable pattern of distribution, with a clear preference for seaweed on the bottom. In mixed-species treatments (MST), however, the species were largely separated by habitat. While the distribution of I. emarginata was completely unaffected by the mere presence of interspecific competitors, habitat selection of I. baltica changed notably when I. emarginata was present. The habitat use patterns observed in MST conformed to those realized in geographical areas where the two species overlap in distribution: I. emarginata is dominant among decaying seaweed on the sea floor, and I. baltica is the dominant species among surface-floating seaweed. Our findings suggest that habitat segregation between the two species is essentially interactive, resulting from rapid decision-making of I. baltica with respect to habitat selection. The underlying mechanism is discussed. I. emarginata is highly superior to I. baltica in interference competition and rapidly eliminates the latter from one-habitat systems which do not allow I. baltica to escape from this interaction. In more natural, heterogeneous environments, however, I. baltica seems to be able to coexist with the superior competitor due to its broader habitat niche, flexibility in habitat selection, and a behavioural disposition to avoid normally preferred habitats when these are occupied by I. emarginata.     

Habitat-induced morphological variation influences photosynthesis and drag on the marine macroalga <Emphasis Type="Italic">Pachydictyon coriaceum</Emphasis>

Photosynthesis, growth, distribution, and persistence of macroalgae are determined in part by the physical environment in which they live. Therefore, discerning how macroalgae interact with their physical environment is necessary to better understand their physiological performance. The purpose of this study was to examine what photosynthetic and hydrodynamic costs and benefits the morphology of Pachydictyon coriaceum (Phaeophyta) confers on the thallus in a given environment. Principal components analysis of morphometric measurements of Pachydictyon coriaceum from different flow habitats and depths separated thalli into three distinct morphs: shallow wave-exposed, shallow wave-protected, and deep. To test the hypothesis that thallus morphology affects net photosynthesis (NP), thalli of three morphotypes of P. coriaceum were incubated in an enclosed recirculating flume under three simulated light/water flow environments representing conditions from which the three morphotypes were collected. The wave-protected and deep morphs had significantly higher rates of photosynthesis than the wave-exposed morph for all three simulated environments. The dense, compact shape of the wave-exposed morph readily streamlines with flow and in doing so, potentially shades many of its internal blades likely accounting for its lower biomass-specific NP. Drag coefficients (C _d) were estimated for the three morphotypes over a range of flow velocities between 0.08 and 0.47 m s⁻¹. At lower water flow velocities (0.08–0.21 m s⁻¹), wave-exposed morphs had the lowest C _d among the three morphotypes. But drag coefficients of the three morphotypes converged with increasing flow velocities, and at velocities >0.31 m s⁻¹ there were no differences in C _d among the three morphotypes. The results of this study indicate that the environmentally-shaped morphs influence photosynthesis and, to a lesser degree, hydrodynamic forces acting on P. coriaceum.     

Lack of sequestration of host plant glucosinolates in <Emphasis Type="Italic">Pieris rapae</Emphasis> and <Emphasis Type="Italic">P. grarricae</Emphasis>

Summary. Sequestration of plant toxins in herbivores is often correlated with aposematic coloration and gregarious behaviour. Larvae of Pieris brassicae show these conspicuous morphological and behavioural characteristics and were thus suggested to sequester glucosinolates that are characteristic secondary metabolites of their host plants. P. rapaeare camouflaged and solitary, and are thus not expected to sequester. To test this hypothesis and to check the repeatabi-lity of a study that did report the presence of the glucosinolate sinigrin in P. brassicae, larvae were reared on three species of Brassicaceae (Sinapis alba, Brassica nigra and Barbarea stricta), and different leaf and insect samples were taken for glucosinolate analysis. The major host plant glucosinolates could only be found in traces or not at all in larval haemolymph, bled or starved larvae, faeces or pupae of both species or P. brassicae regurgitant. Haemolymph of both Pieris spp. was not rejected by the ant Myrmica rubra in dual-choice assays; the regurgitant of P. brassicae was rejected. This suggests the presence of compounds other than glucosinolates that might be sequestered in or produced by P. brassicae only. In faeces of both Pieris spp. a compound which yielded 4-hydroxybenzylcyanide (HBC) upon incubation with sulfatase was detected in high concentrations when larvae had been reared on S. alba. This compound may be derived from hydrolysis of sinalbin, the main glucosinolate of that plant. The unidentified HBC progenitor was apparently not sequestered in the two Pieris spp., and was not detected in faeces of larvae reared on B. nigra or B. stricta. Received 18 July 2002; accepted 11 September 2002.     

Dynamics of pigment degradation by the copepodite stage of <Emphasis Type="Italic">Pseudodiaptomus</Emphasis><Emphasis Type="Italic">euryhalinus</Emphasis> feeding on <Emphasis Type="Italic">Tetraselmis</Emphasis><Emphasis Type="Italic">suecica</Emphasis>

Short-term (3 h) changes in concentration of chlorophylls and their derivatives in stage V Pseudodiaptomus euryhalinus and their fecal material were followed by HPLC during a 24 h experiment. Copepodites were fed with the prasinophyte Tetraselmis suecica. Intact chlorophyll a and b were found in animals and fecal material and had similar dynamics of accumulation over time. The extent of transformation of chlorophyll a and b to colorless compounds was different with chlorophyll a being more extensively degraded. Additionally, several chlorophyll derivatives (pheophytin and pyropheophytin-like pigments) were found. Pyropheophytin a was the most abundant followed by pheophytin b, pheophytin a, and pheophorbide a. Relative amounts of pheopigments were different in copepodites and fecal material, and pheophytin a, pheophorbide a, and pheophytin b concentrations were low and variable. The amount of ingested chlorophyll recovered as chlorophyll a and its derivatives in fecal and copepodite pools was generally low (<5%), with one exception occurring after 9 h, when it accounted for >70%. These data suggest individual pheopigments are produced at different rates and that chemical or enzymatic mechanisms in the gut of copepodites act on the two chlorophylls in different ways.     

Seasonal variations in the growth rates of euphausiids (<Emphasis Type="Italic">Thysanoessa inermis</Emphasis>, <Emphasis Type="Italic">T. spinifera</Emphasis>, and <Emphasis Type="Italic">Euphausia pacifica</Emphasis>) from the northern Gulf of Alaska

The euphausiids Thysanoessa inermis (Kroyer 1846), Thysanoessa spinifera (Holmes 1900), and Euphausia pacifica (Hansen 1911) are key pelagic grazers and also important prey for many commercial fish species in the Gulf of Alaska (GOA). To understand the role of the euphausiids in material flows in this ecosystem their growth rates were examined using the instantaneous growth rate (IGR) technique on the northern GOA shelf from March through October in 2001–2004. The highest mean molting increments (over 5% of uropod length increase per molt) were observed during the phytoplankton bloom on the inner shelf in late spring for coastal T. inermis, and on the outer shelf in summer for T. spinifera and more oceanic E. pacifica, suggesting tight coupling with food availability. The molting rates were higher in summer and lower in spring, for all species and were strongly influenced by temperature. Mean inter-molt periods calculated from the molting rates, ranged from 11 days at 5°C to 6 days at 8°C, and were in agreement with those measured directly during long-term laboratory incubations. Growth rate estimates depended on euphausiid size, and were close to 0 in early spring, reaching maximum values in May (0.123 mm day⁻¹ or 0.023 day⁻¹ for T. inermis) and July (0.091 mm day⁻¹ or 0.031 day⁻¹ for T. spinifera). The growth rates for E. pacifica remained below 0.07 mm day⁻¹ (0.016 day⁻¹) throughout the season. The relationship between T. inermis weight specific growth rate (adjusted to 5°C) and ambient chlorophyll-a concentration fit a Michaelis–Menten curve (r ² = 0.48) with food saturated growth rate of 0.032 day⁻¹ with half saturation occurring at 1.65 mg chl-a m⁻³, but such relationships were not significant for T. spinifera or E. pacifica.     

Antennal responses to floral scents in the butterflies <Emphasis Type="Italic">Inachis io</Emphasis>, <Emphasis Type="Italic">Aglais urticae</Emphasis> (Nymphalidae), and <Emphasis Type="Italic">Gonepteryx rhamni</Emphasis> (Pieridae)

Summary. To better understand the biological role of floral scents for butterflies, electrophysiological responses to floral scents were investigated using combined gas chromatography and electroantennographic detection (GC-EAD). The antennal responses of three butterfly species, Aglais urticae L. (Nymphalidae), Inachis io L. (Nymphalidae), and Gonepteryx rhamni L. (Pieridae) to floral scent compounds from both natural and synthetic mixtures were examined. Floral scents were collected from the butterfly nectar plants Cirsium arvense (L.) (Asteraceae), and Buddleja davidii Franchet cv. (Loganicaeae) with dynamic head-space methods on Tenax-GR and eluted with pentane. These eluates, composed of natural floral scent blends, represent an array of compounds in their natural state. In the GC-EAD analyses eleven compounds were identified from C. arvense with the benzenoid compound phenylacetaldehyde in highest abundance. Seventeen compounds were identified from B. davidii with the irregular terpene oxoisophorone in highest abundance. Thirty-nine synthetic floral scent compounds were mixed in pentane, in equal amounts; about 35 ng were allowed to reach the antennae. The butterflies showed antennal responses to most of the floral scent compounds from both natural and synthetic blends except to the highly volatile monoterpene alkenes. Certain benzenoid compounds such as phenylacetaldehyde, monoterpenes such as linalool, and irregular terpenes such as oxoisophorone, were emitted in relatively large amounts from C. arvense and B. davidii, and elicited the strongest antennal responses. These compounds also elicited strong antennal responses when present in the synthetic scent blends. Thus, the butterflies seem to have many and /or sensitive antennal receptors for these compounds, which points to their biological importance. Moreover, these compounds are exclusively of floral scent origin. For B. davidii, which depends highly on butterflies for pollination, the exclusive floral scent compounds emitted in high abundance could be the result of an adaptive pressure to attract butterflies. Received 2 Septemter 2001; accepted 9 September 2002.     

Interactions between an invasive and a native bryozoan (<Emphasis Type="Italic">Membranipora membranacea</Emphasis> and <Emphasis Type="Italic">Electra pilosa</Emphasis>) species on kelp and <Emphasis Type="Italic">Fucus</Emphasis> substrates in Nova Scotia,Canada

Most research on biological invasions to date has focused on the population dynamics of very successful and disruptive introduced species; however, additional knowledge of the biology of the native species is essential for understanding interactions between the two and may reveal factors that limit invasion success. The invasive bryozoan Membranipora membranacea interacts with native Electra pilosa on two substrates in northwest Atlantic subtidal habitats: highly dynamic and fast-growing kelps; and smaller, more stable, and slow-growing fucoid algae. We quantified the relative abundance and evaluated encounter outcomes in different seasons of these two bryozoans on kelp and Fucus at four sites in Nova Scotia. We also examined the effects of substrate (kelp, Fucus), temperature (7, 10, 13°C), and food (limited, unlimited) on growth rates of E. pilosa in laboratory experiments and using field manipulations. We compared our findings on factors affecting the growth of E. pilosa to those on M. membranacea obtained in similar and thus directly comparable experiments from a previous study. The proportional abundance of M. membranacea was greater than that of E. pilosa on kelps, but the opposite was observed on Fucus. Competitive standoffs between the two bryozoans were more frequent than expected, with no differences recorded between substrates; most encounters were won by M. membranacea. Growth of E. pilosa was faster on Fucus than kelp, decreased with increasing temperature only on Fucus, and was not affected by food. Growth rate of E. pilosa in all treatments was slower than that previously measured for M. membranacea. Faster growth and strong overgrowth abilities likely interact on kelps to ensure success of the invasive bryozoan. Success can be limited by low space availability, which in turn restricts growth rate, and consequently, colony size, such as on fucoid substrates. The incorporation of alternative contexts into invasion research can reveal factors involved in the resilience of native communities.     

The effect of salinity on survival,bioenergetics and predation risk in the mud crabs <Emphasis Type="Italic">Panopeus simpsoni</Emphasis> and <Emphasis Type="Italic">Eurypanopeus depressus</Emphasis>

The effect of salinity on survival, bioenergetics and predation risk was studied in two common mud crabs in the Gulf of Mexico, Eurypanopeus depressus and Panopeus simpsoni. Eurypanopeus survived better at low salinities (the 28-day LC₅₀ of E. depressus was 0.19 PSU compared with 6.97 PSU for P. simpsoni). While low salinity increased energy expenditure and reduced food consumption and absorption, resulting in lower scope for growth, identical responses to salinity occurred in both species. Both species also had similar salinity-dependent patterns of hyper-osmoregulation. Because these physiological mechanisms could not explain differences between the two species in salinity tolerance, we explored the effect of salinity on competition for refugia. Eurypanopeus had higher resource holding potential for refugia, especially at low salinity. As a consequence it had lower predation risk to blue crabs in laboratory experiments. The higher tolerance by E. depressus for low salinities, and greater resource holding potential for refugia may explain why it has a more euryhaline distribution than P. simpsoni.