Larval settlement preference maximizes genetic mixing in an inbreeding population of a simultaneous hermaphrodite (Bugula stolonifera, Bryozoa)

Conspecific aggregations in terrestrial and aquatic organisms can have a significant effect on an individual's survival, growth and reproductive fitness, particularly if these aggregations are composed of closely related individuals. Such aggregations can form passively, as a consequence of dispersal, or actively, as a consequence of kin recognition. In this study, we investigated the genetic composition of individuals in conspecific aggregations in the simultaneous hermaphroditic marine bryozoan Bugula stolonifera. Conspecific larvae routinely metamorphose on adult colonies; the possibility that larvae select or avoid their maternal colony was investigated utilizing 10 newly developed polymorphic microsatellite loci. Adult colonies were collected from Eel Pond, Woods Hole, Massachusetts and inspected for the presence of attached individuals. Adult colonies and their attached individuals were genotyped and compared to assess genetic relatedness within and among these groups relative to the overall genetic variability of the sampling site. Overall, the population of B. stolonifera at this site was found to be outside Hardy-Weinberg equilibrium because of significant levels of inbreeding. No significant genetic differentiation, however, was found between any groups, documenting that a group containing an adult colony and its attached individuals had as much genetic variability as was found for the entire sampling site. Parentage-exclusion analyses showed that the vast majority of attached individuals (>93%) could not have derived from the colony on which they were attached. Kinship analyses showed that the majority of attached individuals (≈63%) shared less than a half-sibling relationship. These results suggest that a colony's nearest neighbours are not composed of siblings, and thus, larval settlement preference can maximize outcrossing in this inbreeding population.     

Genetic evidence for a family structure in stable social aggregations of the Australian lizard Egernia stokesii

In this study we used data from six unlinked microsatellite loci to examine stable aggregations of Egernia stokesii, from a population in the southern Flinders Ranges of South Australia. We show that these aggregations are comprised of breeding partners, their offspring from two or more cohorts, and related adults, providing the first genetic evidence of a family structure in any lizard species. Despite this high level of relatedness within aggregations, most breeding pairs were unrelated and partners were less closely related to each other than they were to other potential within-group partners. Where individuals dispersed, both sexes usually moved to social groups close to their natal group. Although both sexes showed natal philopatry, there was some evidence that females in groups were more related than males in groups. These data suggest that an active choice of unrelated partners and male-biased dispersal may be the mechanisms used by E. stokesii to avoid inbreeding within groups.     

Genetic structure of an Apis dorsata population: the significance of migration and colony aggregation

Eight microsatellite loci were used to investigate the genetic structure of the giant honeybee (Apis dorsata) population in northeast India. This species migrates seasonally between summer and winter nesting sites, and queens appear to return to their previously occupied site. Furthermore, there is a strong tendency for colonies of this species to aggregate at perennially utilized nesting sites that may be shared by more than 150 colonies. These behavioral features suggest that colonies within aggregations should be more related than random colonies, but that the long-distance migration could act to minimize genetic differentiation both between geographical areas and within aggregations. Our genetic study supports these conjectures arising from natural history. A. dorsata aggregations are comprised of colonies that share more alleles than expected by chance. Although queens heading neighboring colonies are not close relatives, fixation indices show significant genetic differentiation among aggregation sites. However, there appears to be sufficient gene flow among aggregations to prevent high degrees of relatedness developing between colonies within aggregations. The results also suggest that there is significant population structuring between geographical regions, although the level of structuring caused by aggregation exceeds the differentiation attributable to geographic region.     

The aggregating behaviour of <Emphasis Type="Italic">Argiope radon</Emphasis>, with special reference to web decorations

The existence of aggregations in taxa that are normally solitary poses questions regarding the costs and benefits of group living. Most orb-web spiders are solitary and are aggressive to conspecifics, but a few species aggregate in large numbers. These spiders benefit by enhancing the prey interception potential, but also suffer costs of increased predation and parasitism. In this study, we report on the natural history characteristics of the orb-web spider, Argiope radon, which not only lives in aggregations but also builds silk decorations. Our results show that A. radon aggregates facultatively and that the main benefit of aggregation that we could identify is enhanced mating potential. We also show that decorations built by A. radon are highly visible to both model prey and predator, and suggest that solitary individuals with longer and more frequent decorations may offset the foraging advantage of being in aggregations.     

Male reproductive competition in spawning aggregations of cod (Gadus morhua, L.)

Reproductive competition may lead to a large skew in reproductive success among individuals. Very few studies have analysed the paternity contribution of individual males in spawning aggregations of fish species with huge census population sizes. We quantified the variance in male reproductive success in spawning aggregations of cod under experimental conditions over an entire spawning season. Male reproductive success was estimated by microsatellite-based parentage analysis of offspring produced in six separate groups of spawning cod. In total, 1340 offspring and 102 spawnings distributed across a spawning season were analysed. Our results show that multiple males contributed sperm to most spawnings but that paternity frequencies were highly skewed among males, with larger males on average siring higher proportions of offspring. It was further indicated that male reproductive success was dependent on the magnitude of the size difference between a female and a male. We discuss our results in relation to the cod mating system. Finally, we suggest that the highly skewed distribution of paternity success observed in cod may be a factor contributing to the low effective population size/census population size ratios observed in many marine organisms.     

The adaptive significance of aggregation behaviour in the dogwhelk Nucella lapillus (L.)

Summary Three kinds of aggregation behaviour were observed in an exposed shore population of Nucella lapillus. Aggregations on the open rock surface during the summer protected dogwhelks from water movement, and were not found on shores where the topography conferred protection. Feeding occurred mainly within these aggregations, probably because individuals experienced less disturbance there than when isolated. Physical contact was important in holding animals together.Winter and pre-breeding aggregations were usually found in clefts or pools. All age groups formed winter aggregations, but those of immature dogwhelks were not as permanent as those of adults, and the latter merged with the prebreeding aggregations. Winter aggregations protected dogwhelks from dislodgment when their ability to regain a foothold was reduced by low temperatures, while pre-breeding aggregations brought the sexes together for fertilization, but the permanence of adult winter aggregations suggested that reproductive activity may have been occurring within them.     

Aggregation and mating success of Capnodis tenebrionis （Coleoptera： Buprestidae）

An understanding of the relative importance of extrinsic and intrinsic factors in determining the potential distribution and mating success of individuals is critical for the successful monitoring and management of pest species. Using a combination of field observations and a caged field experiment, we explored the roles of environmental and individual variation on the formation of mating aggregations and mating success in the buprestid beetle Capnodis tenebrionis （Linnaeus, 1767）, a pest species of stone fruit trees. Our field observations revealed that the formation of aggregations is influenced by a range of environmental factors including temperature, photoperiod, and population density. However, aggregations were not at random and were more likely to occur on the section of the plant with highest incidence of solar radiation and thus higher temperatures. Data from our experiment with caged beetles in the field further indicate that the reproductive behavior of this species varies with temperature. The probability of a successful mating occurring was also positively related to both male and female size. Females of C. tenebrionis mate several times over a 4-h period, but generally not with the same male. Information obtained from these studies is useful to define the most appropriate time for pest control, especially adopting strategies that interfere with reproduction.     

Stress tolerance and burrowing behaviour in the southern African millipede Alloporus uncinates

Laboratory experiments were carried out to assess the tolerance and behaviour of the southern African spirostreptid millipede Alloporus uncinates (Attems) to moisture and temperature stress. Rates of water loss in dry air were 0–026 mg H₂0 cm^-2 hour^-1 for females and 0021 for males and remained relatively constant with an increase in temperature from 20 to 30°C but at higher temperatures there was a rapid increase in water loss, especially for females. In dry laboratory conditions at 30°C all individuals died within 30 days, whilst at 20°C at least 90% of individuals survived this period. Aggregation appeared to have no significant effect on survivorship but small body size conferred a survivorship advantage. Females burrowed earlier and to a greater depth than males, and initial moisture content of soil had a significant effect on mean burrow depth. Alloporus uncinatus , like other spirostreptid millipedes, appears to have considerable tolerance to dry conditions but the wide geographic and habitat range of this species may mean that the intensity of selection for tolerance to moisture stress may vary.     

Population dynamics of a threatened giant millipede: implications for restoration

The population dynamics of threatened invertebrates have important implications for their conservation and restoration. The Seychelles giant millipede (SGM), Sechelleptus seychellarum, is a threatened and functionally important macro‐detritivore endemic to the Seychelles granitic islands. Here, we studied the population dynamics of the SGM from 1998 to 2009 on Cousine Island, Seychelles, to make practical restoration recommendations. Large fluctuations in millipede densities were found between 1998 and 2009. In 2002, 2003, 2005, and 2007 millipede densities were low, while densities were high in 1998 and 2009. Although the SGM is active all year round, millipede surface activity was positively correlated with rainfall, with millipede density high during the wet NW monsoon period (i.e., October to April) and low during the SE trade wind period (i.e., May to September). Female:male:juvenile ratios were ～3:1:1. The implications of these results for restoration are that translocations should preferably be done in years of high millipede densities and during the wet season. Furthermore, chemical control of the invasive ant Pheidole megacephala, which is currently being carried out on Cousine Island and in future could be conducted on other Seychelles islands, should preferably be done during the low rainfall months, as the SGM readily consumes the hydramethylnon‐based bait.     

Species composition, host association and niche differentiation in fleas of small mammals in the Ilmen-Volkhov lowland

Species composition, abundance, annual cycles, and host association of fleas parasitizing small mammals were investigated. The problem of niche differentiation in these insects is considered on the base of the comparative analysis of their annual cycles. The annual cycles of the fleas are revealed to be similar in the case of few number of flea species in parasite community. Thus, two species parasitizing Sorex araneus (Doratopsylla dasycnema and Palaeopsylla soricis), as well as three species associated with Apodemus uralensis (Megabothris turbidus, Ctenophthalmus agyrtes, and Ct. uncinatus) have equal phenology of parasitizing. The fleas community of Clethrionomys glareolus is characterized by a large species number and high diversity of the annual cycles. The differentiation by the seasons of parasitizing is observed most clearly in the dominant flea species, namely Amalaraeus penicilliger, Ct. uncinatus, and Peromyscopsylla bidentata. The periods of imaginal life are overlapped significanly in these species, but they are differed by the season of dominance. Ct. uncinatus predominates in spring and summer, while P. bidentata predominates in autumn, and A. penicilliger predominates in winter and early spring. It may be noted also, that niche partitioning was not observed in the fleas having wide range of hosts. The imaginal life of such fleas usually does not go beyond the warm season.     

Methane Production and Methanogenic Archaea in the Digestive Tracts of Millipedes (Diplopoda)

Methane production by intestinal methanogenic Archaea and their community structure were compared among phylogenetic lineages of millipedes. Tropical and temperate millipedes of 35 species and 17 families were investigated. Species that emitted methane were mostly in the juliform orders Julida, Spirobolida, and Spirostreptida. The irregular phylogenetic distribution of methane production correlated with the presence of the methanogen-specific mcrA gene. The study brings the first detailed survey of methanogens’ diversity in the digestive tract of millipedes. Sequences related to Methanosarcinales, Methanobacteriales, Methanomicrobiales and some unclassified Archaea were detected using molecular profiling (DGGE). The differences in substrate preferences of the main lineages of methanogenic Archaea found in different millipede orders indicate that the composition of methanogen communities may reflect the differences in available substrates for methanogenesis or the presence of symbiotic protozoa in the digestive tract. We conclude that differences in methane production in the millipede gut reflect differences in the activity and proliferation of intestinal methanogens rather than an absolute inability of some millipede taxa to host methanogens. This inference was supported by the general presence of methanogenic activity in millipede faecal pellets and the presence of the 16S rRNA gene of methanogens in all tested taxa in the two main groups of millipedes, the Helminthophora and the Pentazonia.     

Distribution of millipedes (Myriapoda,Diplopoda) along a forest interior – forest edge – grassland habitat complex

We studied the distribution of millipedes in a forest interior-forest edge-grassland habitat complex in the Hajdúság Landscape Protection Area (NE Hungary). The habitat types were as follows: (1) lowland oak forest, (2) forest edge with increased ground vegetation and shrub cover, and (3) mesophilous grassland. We collected millipedes by litter and soil sifting. There were overall 30 sifted litter and soil samples: 3 habitat types × 2 replicates × 5 soil and litter samples per habitats. We collected 9 millipede species; the most abundant species was Glomeris tetrasticha, which was the most abundant species in the forest edge as well. The most abundant species in the forest interior was Kryphioiulus occultus, while the most abundant species in the grassland was Megaphyllum unilineatum. Our result showed that the number of millipede species was significantly lower in the grassland than in the forest or in the edge, however there were no significant difference in the number of species between the forest interior and the forest edge. We found significantly the highest number of millipede individuals in the forest edge. There were differences in the composition of the millipede assemblages of the three habitats. The results of the DCCA showed that forest edge and forest interior habitats were clearly separated from the grassland habitats. The forest edge habitat was characterized by high air temperature, high soil moisture, high soil pH, high soil enzyme activity, high shrub cover and low canopy cover. The IndVal and the DCCA methods revealed the following character species of the forest edge habitats: Glomeris tetrasticha and Leptoiulus cibdellus. Changes in millipede abundance and composition were highly correlated with the vegetation structure.     

Occurrence and assemblage composition of millipedes (Myriapoda, Diplopoda) and terrestrial isopods (Crustacea, Isopoda, Oniscidea) in urban areas of Switzerland

Terrestrial isopods and millipedes, members of the invertebrate macro-decomposer guild, were collected through pitfall traps in three Swiss cities (Zurich, Lucerne, Lugano). A total of 7,198 individuals of 17 isopod species (7093 ind.), and 10 millipede species (105 ind.) were captured. Besides the Alpine endemic isopod (Trichoniscus alemannicus) and millipede (Cylindroiulus verhoeffi), urban assemblages were mainly composed of widespread, native European and even cosmopolitan species, which are frequent in anthropogenic areas. Overall species richness (isopods and millipedes combined) was similar in Zurich (17 species) and Lucerne (16), while only 13 species were sampled in Lugano. According to the Sørensen index of similarity, species composition of Zurich and Lucerne were more alike, while the one of Lugano was more distinct from the other two cities. This result can be explained by the spatial proximity of Zurich and Lucerne in the north of the Alps compared to Lugano, which is located more distantly and in the south of the Alps. Dominant isopods and millipedes in Zurich and Lucerne were found to be widespread synanthropic species in temperate Europe(Porcellio scaber, Trachelipus rathkii and Ophyiulus pilosus) while the dominant isopod in Lugano (Trachelipus razzautii) is a species with a north-eastern Mediterranean distribution. Our study reveals that the urban millipede and isopod fauna in Swiss cities mainly consists of widespread species, but species of narrower distribution (e.g. Trichoniscus alemannicus, Cylindroiulus verhoeffi) may also find suitable habitats in cities. Despite some signs of biotic homogenization, our study also found compositional differences of millipede and isopod assemblages between northern and southern cities that suggest geographical effects of the regional species pool.     

The water and temperature relationships of Ommatoiulus moreletii (Diplopoda: Iulidae)

During summer, Ommatoiulus moreletii aggregates in cool, moist sites. O. moreletii prefers high relative humidities and temperatures of 20 to 25°C throughout the year. These preferences explain the summer aggregations.
O. moreletii develops a strong ability to survive exposure to low humidity and high temperature during summer. This may explain why summer mortality of the millipede has only been demonstrated during an extremely hot and dry summer. The percentage water contents of O. moreletii are higher during spring and summer than during autumn and winter. They are also higher in small animals than in large. The ecological and physiological significances of these facts are discussed.     

Millipede (Diplopoda) communities in an arboretum: Influence of tree species and soil properties

The paper deals with the influence of tree species on millipede communities (Diplopoda). The research was carried out in nine sites in the Borová hora arboretum (Zvolen town, Central Slovakia). Each studied site represents a monoculture of one of nine tree species: Betula pubescens Ehrh., Pinus sylvestris L., Larix decidua Mill., Carpinus betulus L., Abies alba Mill., Picea abies (L.) Karst., Alnus incana (L.) Moench, Populus nigra L., Ulmus laevis Pall. Millipedes were collected by pitfall trapping during vegetation periods in 2008-2011. In total, 1064 individuals of 17 species and 7 families were obtained. The results of research confirmed (i) an influence of tree species on the composition of millipede communities, (ii) a significant influence of soil nitrogen on the species richness and biodiversity, and (iii) an impact of soil pH on the species composition of these terrestrial invertebrate communities. In terms of total dynamic activity and species richness of millipedes, the most favourable conditions were revealed in the forest stands of Alnus incana, Populus nigra, Ulmus laevis and Carpinus betulus. On the contrary, the least favourable biotopes were (from both points of view) the forest stands of Betula pubescens and Larix decidua.     

High warning colour polymorphism in Heliconius hybrid zone roosts

1. Communal roosting behaviour has been documented among a wide range of taxa, particularly among groups of butterflies that display warning colourations. These aggregations of conspecifics and/or other species that share mimetic warning colour patterns can have a large impact on predator learning, and thus the survival of an aposematic form. Yet there has been limited investigation of communal roosting within areas where new and diverse warning colour forms are generated, such as hybrid zones. 2. Here, roosting behaviour was examined in a Heliconius erato hybrid zone in French Guiana between races with divergent warning colourations on their wings. In this hybrid zone, native individuals with nine distinct warning colourations, as well as individuals with altered forms that are not native in the French Guiana population, were marked and observed to determine if divergently coloured individuals participated in communal roosting, and if the proportions of colour pattern forms at roosts differed from the proportions that are found in the population. 3. The results demonstrated that divergently coloured individuals of the same species, including altered, non‐native forms, will readily and repeatedly participate in nocturnal communal roosting, often with extreme fidelity to specific perch locations. 4. These findings suggest that roosts composed of polymorphic warning patterns may be common in phenotypic transition zones, which could have major implications on predator training and selection dynamics in hybrid zones.     

Dominance of Vibrio fischeri in secreted mucus outside the light organ of Euprymna scolopes: the first site of symbiont specificity

Previous studies of the Euprymna scolopes-Vibrio fischeri symbiosis have demonstrated that, during colonization, the hatchling host secretes mucus in which gram-negative environmental bacteria amass in dense aggregations outside the sites of infection. In this study, experiments with green fluorescent protein-labeled symbiotic and nonsymbiotic species of gram-negative bacteria were used to characterize the behavior of cells in the aggregates. When hatchling animals were exposed to 10(3) to 10(6) V. fischeri cells/ml added to natural seawater, which contains a mix of approximately 10(6) nonspecific bacterial cells/ml, V. fischeri cells were the principal bacterial cells present in the aggregations. Furthermore, when animals were exposed to equal cell numbers of V. fischeri (either a motile or a nonmotile strain) and either Vibrio parahaemolyticus or Photobacterium leiognathi, phylogenetically related gram-negative bacteria that also occur in the host's habitat, the symbiont cells were dominant in the aggregations. The presence of V. fischeri did not compromise the viability of these other species in the aggregations, and no significant growth of V. fischeri cells was detected. These findings suggested that dominance results from the ability of V. fischeri either to accumulate or to be retained more effectively within the mucus. Viability of the V. fischeri cells was required for both the formation of tight aggregates and their dominance in the mucus. Neither of the V. fischeri quorum-sensing compounds accumulated in the aggregations, which suggested that the effects of these small signal molecules are not critical to V. fischeri dominance. Taken together, these data provide evidence that the specificity of the squid-vibrio symbiosis begins early in the interaction, in the mucus where the symbionts aggregate outside of the light organ.     

Distribution of euphausiids in the Kuroshio front and warm water tongue with special reference to the surface aggregation of Euphausia pacifica

The distribution of euphausiids and other macrozooplankton wasinvestigated in and around the Kuroshio front formed in theKa.shima-nada Sea. Japan. during the summer of 1993. Zooplanktonwere dominated by copepods, chaetognaths and euphausiids. andtheir biomass was significantly higher at the frontal stations.Eighteen species belonging to six genera of euphausiids werecollected. The species composition and community structure ofeuphausiids changed drastically with the ‘areas’corresponding to the hydrological conditions. In the area underthe influence of the Kuroshio. most euphausiids were warm-waterspecies. In contrast. euphausiids found in the frontal areawere those usually predominating in subarctic or cold Oyashiowaters. In the area of the warm water tongue. where warm Kuroshiowater lay above cold Oyashio water, the species compositionof euphausiids represented a mixture of both warm- and cold-waterspecies. Surface aggregations of Euphausia pacifica were observedin the frontal area during the night. The biomass and densityof the aggregations ranged between 90 and 136 mg C m^–3and 164 and 238 md. m^–3 respectively. These aggregationswere mostly made up of immature individuals of < 12 mm. Passivetransportation by convergent flow at the front seems to explainthe observed surface aggregations of E.pacifica.     

Environmental cues or conspecific attraction as causes for egg mass aggregation in hydrobiosid caddisflies

The distribution of egg masses throughout the environment can strongly influence the population dynamics of aquatic insects. Many species lay eggs in aggregations and most eggs will subsequently hatch from only a few locations—knowing how and why these aggregations arise is therefore needed to understand the population dynamics of these species. The hydrobiosid caddisfly Ulmerochorema rubiconum lays eggs in large aggregations on the undersides of emergent rocks in streams. Our aim was to test whether females oviposit in response to conspecific egg masses or the environmental characteristics of rocks by manipulating the number and age of egg masses initially present on rocks and monitoring the accumulation of new masses. Our first experiment used rocks that had recently been used for oviposition and initial egg masses encompassed a range of ages; our second used rocks with no history of oviposition and initial masses of uniform age. Females did not respond to conspecific eggs of any age, as removing initial egg masses had no impact on the number of new masses laid in either experiment. There was a strong positive relationship between the number of initial and new masses, regardless of whether initial egg masses were removed, at the scale of whole rocks and for rock microhabitats. The results suggest that females select oviposition sites based primarily on physical characteristics of emergent rocks. We demonstrate for the first time that the spatial arrangement of egg masses may be consistent and predictable through time, with females showing a high degree of fidelity for particular rocks and microhabitats.