Principal Dispersion Research Articles

People socialize ecological information about the environment but may forget their own experiences: a case study of local ecological knowledge about seed-dispersing animals

Local ecological knowledge (LEK) has been increasingly used in the search for efficient strategies to maintain biological diversity. However, considering the rapid environmental changes in ecosystems, such knowledge may have been lost between generations, affecting its potential application. In this study, we adopted the LEK of the potential dispersers of Caryocar coriaceum Wittm. (Caryocaraceae), an endangered plant species of socioeconomic and cultural importance from northeast Brazil, as a model. We evaluated whether there is intergenerational variation in the LEK about the abundance of Dasyprocta prymnolopha (the principal disperser of C. coriaceum) associated with the local practice of hunting. We collected LEK data from 39 hunter-gatherers aged 31 to 84 years, and camera traps were used during two annual C. coriaceum harvests to record its potential dispersers. Our results indicate that the LEK of the potential animal dispersers of C. coriaceum does not vary between generations; it is disseminated and shared between different generations. The strong interactions among people during the C. coriaceum harvest period facilitate the sharing of information about the potential dispersers of this species. Our results show that hunting D. prymnolopha does not depend on perceptions regarding the availability of this resource in the forest, which may be causing overexploitation. Therefore, local knowledge may need to be updated and connected to the recent and rapid environmental changes because people may believe that current environmental conditions are like those of the past. If this is the case, people may be less cooperative with conservation strategies because they are not aware of environmental changes, so measures to update knowledge about environmental conditions may be necessary to encourage effective participation in management and conservation plans.

Protist communities along freshwater–marine transition zones in Hudson Bay (Canada)

One of the most striking ecological divides on Earth is between marine and nearby freshwater environments, as relatively few taxa can move between the two. Microbial eukaryotes contribute to biogeochemical and energy cycling in both fresh and marine waters, with little species overlap between the two ecosystems. Arctic and sub-Arctic marine systems are relatively fresh compared to tropical and temperate systems, but details of microbial eukaryote communities along river-to-sea transitions are poorly known. To bridge this knowledge gap, we investigated three river-to-sea transitions (Nelson, Churchill, and Great Whale Rivers) in sub-Arctic Hudson Bay through 18S rRNA amplicon sequencing to identify microbial eukaryotes along the salinity and biogeochemical gradients. Salinity acted as the principal dispersal barrier preventing freshwater microorganisms from colonizing marine coastal waters, with microbial eukaryote communities of the three rivers clustering together. Just offshore, communities clustered by coastal regions associated with nutrient concentrations. Analysis of indicator species revealed that communities in the nitrate-depleted coastal water off the Churchill and Great Whale Rivers were dominated by heterotrophic taxa and small photosynthetic protists. In contrast, the Nelson offshore community was characterized by a high proportion of the diatom Rhizosolenia. A distinct community of heterotrophic protists was identified in the three estuarine transition zones, suggesting specialized estuarine communities. Such specialization was most marked in the Nelson River system that was sampled more intensely and showed estuarine circulation. The autochthonous community was composed of the bacterial grazers Katablepharis, Mataza, and Cryothecomonas, as well as brackish species of the diatoms Skeletonema and Thalassiosira. These findings suggest that flow regulation on the Nelson River that modifies estuarine circulation would affect estuarine community composition and distribution in the transition zone.

English

Yam is a promising income source for small producers in the Reconcavo Baiano region. However, few genetic studies have been conducted with this culture. In this sense, the aim of this study was to assess genetic variability among 89 genotypes of yam (Dioscorea rotundata Poir.) collected in four municipalities in Bahia State, Brazil. These were assessed based on eight quantitative descriptors. Data were subjected to descriptive statistics, Spearman's rank correlation, Singh criterion, cluster analysis, principal component analysis and dispersion graph. The tuber weight showed the highest coefficient of variation and correlated positively and significantly with width and length of tuber. The tuber length characteristics contributed most to the genetic divergence. The criterion pseudo-t2 divided 89 genotypes into seven groups, being that groups 4, 5 and 7 showed the highest averages for the production characteristics. The first three principal components explained 69.49% variation and dispersion graph showed partly concordant with UPGMA method. This study revealed the existence of genetic variability of yam, which may be explored in future genetic improvement programs. Key words: Dioscorea rotundata Poir., multivariate methods, plant genetic resources, plant breeding.

Formation of a ZnO–C Composite with a Nanocrystalline Structure

The formation of a nanocrystalline composite of a ZnO–C system with simultaneous mechanical activation of a mixture of zinc oxide and graphite powders in a ball mill in an inert atmosphere is studied. It is shown that the presence of graphite reduces the efficiency of dispersing ZnO crystallites. The following principal dispersion mechanisms of graphite are determined: the fragmentation of particles due to the impact of grinding bodies and the exfoliation of flakes by submicron zinc oxide particles. It has been established that a composite system is formed as a result of the prolonged mechanical activation effect on the ZnO–graphite mixture, which is a nanocrystalline zinc oxide powder with uniformly distributed inclusions of micro- and nanocrystalline graphite, turbostratic carbon, exfoliated graphene structures, and amorphous carbon.

Образование композита ZnO-C с нанокристаллической структурой

AbstractThe formation of a nanocrystalline composite of a ZnO–C system with simultaneous mechanical activation of a mixture of zinc oxide and graphite powders in a ball mill in an inert atmosphere is studied. It is shown that the presence of graphite reduces the efficiency of dispersing ZnO crystallites. The following principal dispersion mechanisms of graphite are determined: the fragmentation of particles due to the impact of grinding bodies and the exfoliation of flakes by submicron zinc oxide particles. It has been established that a composite system is formed as a result of the prolonged mechanical activation effect on the ZnO–graphite mixture, which is a nanocrystalline zinc oxide powder with uniformly distributed inclusions of micro- and nanocrystalline graphite, turbostratic carbon, exfoliated graphene structures, and amorphous carbon.

A numerical analysis of the summertime Pearl River plume from 1999 to 2010: Dispersal patterns and intraseasonal variability

Abstract A three-dimensional unstructured-grid Finite Volume Community Ocean Model was applied to investigate the principal dispersal patterns and intraseasonal variability of the Pearl River plume in summer (June–August) during 1999–2010. The favorable forcing conditions and underlying dynamics for the formation of plume patterns were also explored. The model was validated against a suite of water level, salinity and temperature observations collected during the simulation periods. The simulated results agree well with the observed data, indicating that the model reasonably reproduces the main hydrodynamic processes occurring in the Pearl River estuary. Using Self-Organizing Maps, we extracted eight typical dispersal patterns of the Pearl River plume from the multiyear simulated daily surface salinity fields and estimated the occurrence frequency of each pattern. The eight plume patterns were further categorized into five types based on the morphologies and extension distances of each pattern, namely, west alongshore spreading, fettered spreading, offshore bulge spreading, bidirectional spreading and east offshore spreading; these five types account for 26.3%, 9.8%, 11.5%, 29.1% and 23.3% of the total occurrence frequency, respectively. The pattern that is characterized by bidirectional spreading with a strong eastward extension has the largest occurrence frequency among the eight patterns. Through an analysis of the best matching units derived from Self-Organizing Maps and the corresponding river discharge and wind conditions, we find that both wind and river discharge can significantly affect the Pearl River plume patterns. The plume orientation is mainly modulated by the wind, while the plume area and eastward extension distance are mainly affected by the river discharge. Generally, the favorable forcing conditions and underlying dynamics are different for each plume pattern, and various combinations of river discharge and wind can generate different dynamics to form different plume patterns. The climatological surface salinity field in summer shows a bidirectional structure with the plume extending westward attaching to the coast and eastward detaching from the coast. The areas and eastward extension distances of the Pearl River plume gradually decrease from June to August, affected by the intraseasonal changes in river discharge and wind. The statistical results of the daily plume patterns for June–August show that east offshore spreading, bidirectional spreading and west alongshore spreading are the primary types occurring in June, July and August, respectively. Furthermore, the occurrence frequencies of the west alongshore spreading and offshore bulge spreading increase, while the occurrence frequency of the east offshore spreading decreases from June to August.

BFO-FMD: bacterial foraging optimization for functional module detection in protein–protein interaction networks

Identifying functional modules in PPI networks contributes greatly to the understanding of cellular functions and mechanisms. Recently, the swarm intelligence-based approaches have become effective ways for detecting functional modules in PPI networks. This paper presents a new computational approach based on bacterial foraging optimization for functional module detection in PPI networks (called BFO-FMD). In BFO-FMD, each bacterium represents a candidate module partition encoded as a directed graph, which is first initialized by a random-walk behavior according to the topological and functional information between protein nodes. Then, BFO-FMD utilizes four principal biological mechanisms, chemotaxis, conjugation, reproduction, and elimination and dispersal to search for better protein module partitions. To verify the performance of BFO-FMD, we compared it with several other typical methods on three common yeast datasets. The experimental results demonstrate the excellent performances of BFO-FMD in terms of various evaluation metrics. BFO-FMD achieves outstanding Recall, F-measure, and PPV while performing very well in terms of other metrics. Thus, it can accurately predict protein modules and help biologists to find some novel biological insights.

Structure of a modulated narrow light beam in seawater: Monte Carlo simulation

Dispersion properties of photon density waves propagating in seawater from a unidirectional point source have been studied using the Monte Carlo technique. It is shown that the spatial distribution of irradiance of the photon density waves at high modulation frequencies is significantly different from that of the stationary light field. Principal dispersion effects predicted earlier in the approximation solutions of the nonstationary radiation transfer equation are confirmed. An increase in the wave decrement and a decrease in the transversal cross section of the initially narrow beam at the modulation frequency with the increase of the modulation frequency are demonstrated. Frequency dependencies of phase and group velocities of photon density waves are calculated. It is shown that seawater possesses anomalous dispersion in a wide frequency range with respect to these waves.

Recent Landscape Changes on a Small Mediterranean Island

The Mediterranean region is a major hotspot of biodiversity. However, over the last 50 to 100 years, this area has suffered dramatic changes in human pressure that has led to significant landscape changes resulting in a recovery of the vegetation cover to one of higher biomass. A multi-temporal vegetation analysis of Giannutri Island, based on inspection of a 50-year series of vegetation maps (1958–2008), shows an increase in high maquis and Juniperus-thickets positively correlated with a decrease in open and low maquis. The increase of high maquis and Juniperus-thickets shows two distinct types of strategies in their advancement: the first increases its coverage with new patches arising some distance away from one another, while Juniperus-thickets expand from the margins. These two behaviour types may be correlated to a different pressure from thrushes (Turdus spp.) their disperser found on the island. The few patches of Quercus ilex woodland have remained constant due to the absence in Giannutri of its principal disperser: the jay (Garrulus glandarius). Based on this it would be impossible to take into consideration the Potential Natural Vegetation (PNV) concept in addressing conservation activities on an island like Giannutri.

Frugivory and seed dispersal by birds in Cereus jamacaru DC. ssp. jamacaru (Cactaceae) in the Caatinga of Northeastern Brazil.

Studies of the dispersal modes of plants aid our understanding of the dynamics of resource and its availability for dispersal agents. The present work sought to characterize the fruiting patterns of the native Caatinga (dryland) cactus Cereus jamacaru, identify its principal dispersers, and evaluate the effects of seed passage through digestive tract of dispersers on its germination. Cereus jamacaru present an annual fruiting pattern and fruiting peaks occurred during June/2009 and February/2010. A total of 135 visits by nine species of resident Caatinga bird species were recorded. The most frequent visiting bird species were Paroaria dominicana and Euphonia chlorotica. Length of bird visits varied from 15 seconds to 4 minutes and seeds removed by birds travelled 10.6 ± 11.2 m until dispersers make the first landing perch, in some cases more than 40 meters away. Germination tests show birds had a high quantity of viable seeds of C. jamacaru in its feces. Seeds that passed through the digestive tract of birds showed a similar germinability of the seeds of the control group. However, the seeds dispersed by birds showed lowest mean germination time related to the control group seeds. This study highlights the potential role of birds as seed dispersers of C. jamacaru, swallowing the whole seeds and defecating intact seeds, accelerating the germination process and transporting seeds away from the mother plant.

Patterns of mistletoe infection in four Acacia species in a semi-arid southern African savanna

In a range of systems, studies on mistletoe distribution on the host plant have documented a number of factors that affect their occurrence and spread (Aukema & Martinez del Rio 2002a, Bowie & Ward 2004, Overton 1996, Reid et al. 1995). These patterns can be determined by host specificity, environmental conditions, host plant characteristics (Martinez del Rio et al. 1995) and the movement patterns of dispersal agents (Aukema & Martinez del Rio 2002a, 2002b). In mistletoe plants, host choice can be considerably influenced by the advantages of interacting with relatively abundant hosts (Norton & Carpenter 1998, Norton & De Lange 1999). Besides the relative abundance of host species, characteristics such as branch size, age and height can have a strong effect on mistletoe attachment resulting in size-related mistletoe infection patterns (Overton 1994). Generally positive relationships between mistletoe infection and host size have been demonstrated worldwide (Donohue 1995, Martinez del Rio et al. 1996, Norton et al. 1997, Reid & Stafford Smith 2000) and they have been interpreted in terms of the preferences by dispersing birds to perch and feed in taller trees (Aukema & Martinez del Rio 2002a) and trees accumulating infections as they age (Overton 1994). Aukema & Martinez del Rio (2002a) reported more frequent perching in taller-than-average trees by the phainopepla (Phainopepla nitens), which is the principal disperser of the desert mistletoe Phoradendron californicum. Thus, visits by mistletoe-seed-dispersing birds, and therefore mistletoe seeds received, tend to increase with tree height (Aukema & Martinez del Rio 2002a). Using a simple metapopulation model, Overton (1994) predicted the frequency of parasitized trees to increase with host age. Therefore, assuming that size is a good proxy for age, large trees are likely to be more infected than smaller trees. Reid & Stafford Smith (2000), using experimentally disinfected trees, found that larger trees were disproportionately re-infected with mistletoes. This size–intensity relationship may be used to describe mistletoe infection patterns. However, several previous studies have shown size–intensity relationships to be weak (Aukema & Martinez del Rio 2002a, Donohue 1995, Overton 1994, Reid & Stafford Smith 2000). This indicates that other factors may be important in determining mistletoe infection intensity, including that already parasitized hosts of a specific height are more likely to receive seeds than non-parasitized hosts of the same height or dispersers are likely to be attracted to trees for reasons other than size (Aukema & Martinez del Rio 2002a).

Dielectric relaxation study of hexamethylphosphoramide–1,4-dioxane mixtures using time domain reflectometry (TDR) technique

Dielectric relaxation study on hexamethylphosphoramide–1,4-dioxane binary mixtures has been carried out at 16 concentrations over the frequency range of 10 MHz to 30 GHz at different temperatures using time domain reflectometry technique. The mixtures exhibit a principal dispersion of the Debye relaxation type at microwave frequencies. The concentration-dependent static dielectric constant, excess dielectric properties and thermodynamic parameters have been determined. The hydrogen-bonded theory is applied to compute the Kirkwood correlation factors for the mixture. The average numbers of the hydrogen bonds between hexamethylphosphoramide–hexamethylphosphoramide and hexamethylphosphoramide–1,4-dioxane pairs are estimated from the dielectric constant.

Influence of Secondary Currents on Solute Dispersion in Curved Open Channels

The dispersion coefficient tensor including off‐diagonal components was introduced in the flow with secondary currents, which is called skewed shear flow dispersion (SSFD) coefficient tensor, in this paper. To observe the detailed effect of cross‐dispersion terms in SSFD model on solute dispersion, mathematical analysis of eigenvalue problem with respect to the equation with SSFD coefficient tensor was performed. The analysis results show the several differences of SSFD model compared to CSFD (conventional shear flow dispersion) model: the oblique direction of principal dispersion with respect to the streamline, the increase of peak concentration, and the change in the eccentricity of elliptical tracer cloud. SSFD coefficient tensor in a streamwise curvilinear coordinate system of curved channel was transformed to those components of fixed Cartesian coordinate system, and 2D numerical model with finite element method was established in the Eulerian‐Cartesian coordinate. Through this process, the transformation equation using the depth‐averaged velocity field was derived. Several numerical tests were performed to assure the results obtained in the mathematical analysis and to show the applicability of the derived transformation equation on the flow with continuously changing flow direction.

Effectiveness of Dispersal of an Ornithocorous Cactus Myrtillocactus geometrizans (Cactaceae) in a Patchy Environment

Effectiveness of seed dispersal by different species that feed on the fruits of Myrtillocactus geometrizans was evaluated, considering both quantity and quality of dispersal, in a patch of tropical deciduous forest in Zapotitlán de las Salinas. Effectiveness was estimated to be strongly influenced by the post-foraging movements of the frugivores, leading us to suggest that the quality component of seed dispersal occupies a central role in the assessment of disperser effectiveness and to expect that dispersers that stay in the tropical deciduous forest patch after foraging would have highest effectiveness. Birds were the principal dispersers of M. geometrizans. This was particularly true of Phainopepla nitens, since this species showed a high fidelity within the tropical deciduous forest. These observations emphasize that it is important to determine the post-foraging habits of seed dispersers that may move across vegetation patches over the landscape in order to obtain a complete assessment of their role in Neotropical environments.

Seed dispersal phenology and dispersal syndromes in a subtropical broad-leaved forest of China

This study describes the dispersal phenology and syndromes in Gutianshan 24 ha plot in a subtropical broad-leaved forest of China. The 130 0.5 m 2 seed traps collected 69,115 mature seeds, representing 27 species (belonging to 24 genera, and 15 families) in 12 months. One marked peak in the number of seeds and species during the year was found in dry season (November). Zoochory was the most common dispersal syndrome (70.4%), followed by anemochory (18.5%), ballistic dispersal (11.1%). Among fruit types, berry (33%), capsule (22%), nut (18%), and drupe (11%) were common in the subtropical evergreen forest. In fruit color, brown was the commonest (40%), followed by dark brown (30%), black (15%), red (11%), and yellow (4%). Overall, the community level seed rain study revealed that one marked peak in seed number occurred in the middle of dry season; zoochory was the principal dispersal mode of woody plants in subtropical forest, and dry seasons favor seed dispersal by animal and wind.

Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust

Two geochemical proxies are particularly important for the identification and classification of oceanic basalts: the Th–Nb proxy for crustal input and hence for demonstrating an oceanic, non-subduction setting; and the Ti–Yb proxy for melting depth and hence for indicating mantle temperature and thickness of the conductive lithosphere. For the Th–Nb proxy, a Th/Yb–Nb/Yb projection demonstrates that almost all oceanic basalts lie within a diagonal MORB–OIB array with a principal axis of dispersion along the array. However, basalts erupted at continental margins and in subduction zones are commonly displaced above the MORB–OIB array and/or belong to suites with principal dispersion axes which are oblique to the array. Modelling of magma–crust interaction quantifies the sensitivity of the Th–Nb proxy to process and to magma and crustal compositions. For the Ti–Yb proxy, the equivalent Ti/Yb–Nb/Yb projection features a discriminant boundary between low Ti/Yb MORB and high Ti/Yb OIB that runs almost parallel to the Nb/Yb axis, reflecting the fact that OIB originate by melting beneath thicker lithosphere and hence by less melting and with residual garnet. In the case of volcanic-rifted margins and oceanic plume–ridge interactions (PRI), where hot mantle flows toward progressively thinner lithosphere (often becoming more depleted in the process), basalts follow diagonal trends from the OIB to the MORB field. Modelling of mantle melting quantifies the sensitivity of the Ti–Nb proxy to mantle potential temperature and lithospheric thickness and hence defines the petrogenetic basis by which magmas plot in the OIB or MORB fields. Oceanic plateau basalts lie mostly in the centre of the MORB part of that field, reflecting a high degree of melting of fertile mantle. Application of the proxies to some examples of MORB ophiolites helps them to be further classified as C (contaminated)-MORB, N (normal)-MORB, E (enriched)-MORB and P (plume)-MORB ophiolites, which may add a useful dimension to ophiolite classification. In the Archean, the hotter magmas, higher crustal geotherms and higher Th contents of contaminants all result in widespread crustal input that is easy to detect geochemically with the Th–Nb proxy. Application of this proxy to Archean greenstones demonstrates that almost all exhibit a crustal component even when reputedly oceanic. This indicates, either that some interpretations need to be re-examined or that intra-oceanic crustal input is important in the Archean making the proxy less effective in distinguishing oceanic from continental settings. The Ti–Yb proxy is not effective for fingerprinting Archean settings because higher mantle potential temperatures mean that lithospheric thickness is no longer the critical variable in determining the presence or absence of residual garnet.

Projection-Pursuit Based Principal Component Analysis: a Large Sample Theory

The principal component analysis (PCA) is one of the most celebrated methods in analysing multivariate data. An effort of extending PCA is projection pursuit (PP), a more general class of dimension-reduction techniques. However, the application of this extended procedure is often hampered by its complexity in computation and by lack of some appropriate theory. In this paper, by use of the empirical processes we established a large sample theory for the robust PP estimators of the principal components and dispersion matrix.

Dielectric relaxation study of pyridine-alcohol mixtures using time domain reflectometry

Time domain reflectometry is applied to dielectric relaxation measurements on pyridine-alcohol (methanol, ethanol, propan- 1-o1 and butan-1 -o1) mixtures over the entire concentration range and over the frequency range 10MHz-10GHz at 5, 15, 25 and 35°C. From the data, static permittivity and the dielectric relaxation time are extracted using a bilinear calibration method and a nonlinear least-squares fit method. These mixtures exhibit a principal dispersion of the Debye type at microwave frequencies. The Kirkwood correlation factor, which contains information regarding solute-solvent interaction and corresponding structural information, was obtained for these systems, and the excess inverse relaxation time and molar energy of activation for all these systems were determined. The values of the static permittivity, the relaxation time and the Kirkwood correlation factor decrease with increased pyridine concentration in alcohol. The static permittivity of the mixtures fits the modified Brugemann model well.

NUTRITIONAL INTERACTIONS AND FRUIT REMOVAL: CEDAR WAXWING CONSUMPTION OFVIBURNUM OPULUSFRUITS IN SPRING

Fruits of Viburnum opulus (highbush cranberry, guelder rose) ripen in the fall and remain uneaten throughout the winter months. To investigate the fruiting strategy of this plant, I described the natural history of fruit removal from V. opulus shrubs in central New York and investigated nutritional mechanisms for the phenology of fruit re- moval by its principal disperser. Viburnum opulus fruit crops were often completely con- sumed in April and May, almost exclusively by Cedar Waxwings (Bombycilla cedrorum). Sugar solute concentration of V. opulus fruit pulp increased over the winter season through dehydration. When wild Cedar Waxwings were presented with early-season (removed and frozen in December) and remnant late-season (April) fruits, they strongly preferred early- season fruits. This result demonstrated that springtime consumption of V. opuius fruits by Cedar Waxwings is not caused by chemical changes in the fruit pulp during the winter months that enhance fruit palatability. Cedar Waxwings often fed intermittently on the male catkins of eastern cottonwoods (Populus deltoides) when eating V. opulus fruits. Feeding experiments with captive wax- wings showed that birds lost body mass on either V. opulus fruits or P. deltoides catkins alone, but maintained or gained body mass when offered both foods simultaneously. The combined diet provided Cedar Waxwings with nutritionally sufficient amounts of energy from fruit sugars and protein from pollen. Two chemical characteristics of V. opulus fruits were implicated in creating a short-term demand for supplemental protein: an especially low nitrogen/carbohydrate ratio and secondary compounds. The pulp of V. opulus fruits contains secondary compounds that make this fruit very acidic, presenting consumers with the challenge of maintaining acid/base homeostasis. Elevated nitrogen losses by waxwings eating only V. opulus fruits were consistent with the hypothesis that birds catabolized protein to produce bicarbonate as an acid buffer. Secondary compounds may play a central role in the evolution of plant fruiting syndromes because of their dual effects on microbes, me- diating persistence of fruits in the environment, and palatability of fruits to seed dispersers, presumably because they exact a protein cost from consumers. These results showed that nutritional interactions of seasonally ephemeral food items can determine temporal patterns of fruit consumption. The well-defended fruits of V. opulus are eaten when more palatable fruits no longer remain and when a complementary protein source becomes available. This fruiting strategy can result in wholesale seed dispersal. The restricted nature of the mutualism between waxwings and V. opulus appears to be a result of the extraordinary persistence of these fruits and the unique dietary habits of waxwings. Viburnum opulus fruits remain uneaten until the spring months, when waxwings are scav- enging remnant crops of sugary fruits and most other avian frugivores have switched to animal foods.

Molecular Evidence for Cryptic Species ofAurelia aurita(Cnidaria, Scyphozoa)

Morphological taxonomy suggests that marine faunas are species poor compared to terrestrial and freshwater faunas (1). This dichotomy has been attributed to the unique potential of marine plankters for distant dispersal across homogenous oceans with few barriers to gene flow (2). The relative scarcity of opportunities for allopatric divergence has resulted in depauperate marine faunas characterized by a high proportion of widespread or cosmopolitan species. Aurelia aurita (Linnaeus) has been considered a good example of such a cosmopolite (3, 4, 5, 6). However, recent molecular studies have revealed cryptic species in many marine taxa (7), suggesting that marine biodiversity is higher and opportunities for speciation have been more frequent than generally recognized. Here, we present nuclear and mitochondrial DNA sequence evidence of seven sibling species of Aurelia aurita and two additional species, A. limbata Brandt and A. labiata Chamisso & Eysenhardt. These sequence data indicate speciation events as early as the late Cretaceous or early Tertiary, consistent with the formation of well-recognized biogeographic barriers to gene flow in the seas. Traditionally, the genus Aurelia comprises two species: A. limbata, a polar species, and A. aurita, a common inhabitant of nearshore waters circumglobally between about 50 °N and 55 °S (3, 4, 5; Fig. 1). Perhaps due to its ubiquity, A. aurita has become a popular research organism for studies as diverse as protein chemistry, development, ecology, ethology, and hydrodynamics (6). A. aurita also is economically important because worldwide it preys on or competes with larvae of commercial fisheries and because swarms of medusae may impede trawling or block power-plant intakes (8). Furthermore, this “pest” has been introduced at least into San Francisco Bay (9) and possibly many other places (10). A. aurita is also familiar to nonspecialists because it is the most commonly displayed medusa in public aquaria. The systematics of A. aurita therefore is of considerable scientific, economic, and general interest. Aurelia has a typical bipartite scyphozoan life history in which benthic scyphopolyps asexually strobilate ephyrae that grow into sexual medusae, the females of which brood larvae that settle into the shallow coastal benthos within a few days of being released. Of these life stages, the medusa probably is the principal dispersal phase because only the medusa is both long-lived (several months to more than one year; 11) and planktonic (6). The potential of medusae for distant dispersal is consistent with the current classification of A. aurita as a circumglobal, almost cosmopolitan, species (4, 5). However, A. aurita medusae in Saanich Inlet, British Columbia, and perhaps elsewhere, migrate directionally (12), maintaining breeding aggregations within isolated inlets and probably limiting gene flow among populations. Consistent with limited gene flow, allozyme differences have been found between populations of A. aurita in the eastern and western Atlantic Ocean, the Gulf of Mexico, and the eastern and western Pacific Ocean (9, 13). In addition, one species, A. labiata, was recently recognized as native to Pacific North America and distinct from A. aurita (10). Novel DNA sequence data from nuclear internal transcribed spacer one (ITS-1) and mitochondrial cytochrome oxidase c subunit I (COI) reveal highly structured gene genealogies and at least nine distinct clades of Aurelia (Figs. 1, 2). Several lines of argument suggest that these clades warrant recognition as distinct species. First, the length of ITS-1 varies from 240 nucleotides (Charlestown, RI) to 360 nucleotides (Cananeia, Brazil). Such length variation is comparable to that found among congeneric species of Received 7 August 2000; accepted 19 October 2000. * To whom correspondence should be addressed at Coral Reef Research Foundation, Box 1765, Koror, PW 96940, Palau. Reference: Biol. Bull. 200: 92–96. (February 2001)