Inbreeding in a lek-mating ant species, Pogonomyrmex occidentalis

In this paper we have two goals. First, we examine the effects of sample size on the statistical power to detect a given amount of inbreeding in social insect populations. The statistical power to detect a given level of inbreeding is largely a function of the number of colonies sampled. We explore two sampling schemes, one in which a single individual per colony is sampled for different sample sizes and a second sampling scheme in which constant sampling effort is maintained (the product of the number of colonies and the number of workers per colony is constant). We find that adding additional workers to a sample from a colony makes it easier to detect inbreeding in samples from given number of colonies; however, adding more colonies rather than more workers per colony always gives greater power to detect inbreeding. Because even relatively large amounts of sib-mating generate relatively small inbreeding coefficients, detection of even substantial deviations from random mating will require very large samples. Second, we look at the amount of inbreeding in a large population of the western harvest ant, Pogonomyrmex occidentalis. We find deviations from Hardy-Weinberg equilibrium equivalent to approximately 27% sib-mating in our population ( f = 0.09). Review of past studies on the population structure of other Pogonomyrmex species suggests that inbreeding may be a regular feature of the mating system of these ants. Although P. occidentalisis a swarm-mating species, there are a number of features of its population biology which suggest that the effective population size may be small. These include topographical variation that potentially breaks the population into demes, variation in the reproductive output of colonies, and variation in the size of reproductives produced by colonies. Received: 6 May 1996 / Accepted after revision: 6 October 1996     

Coexistence of nine anemonefish species: differential host and habitat utilization, size and recruitment

The region of Madang, Papua New Guinea, has the highest reported species diversity of both anemonefishes (nine species) and their host anemones (ten species). To determine which factors may allow so many anemonefish species to coexist at this location, we studied their patterns of distribution, abundance, and recruitment. Population surveys at three replicate reef sites within four zones situated at varying distances from the mainland (nearshore, mid-lagoon, outer barrier, and offshore) indicated that each species of host anemone and anemonefish lived within a particular range of zones. Each species of anemonefish lived primarily with one species of host. Anemonefish species that lived with the same host species usually had different distribution patterns among zones (e.g., Amphiprion percula occupied Heteractis magnifica in nearshore zones, while A. perideraion occupied H. magnifica in offshore zones). Monitoring of natural populations showed that there were few changes (losses or recruitment) in the number or species of fishes associated with each individual anemone over periods ranging from 3 to 9 months. Recruitment was monitored on anemones with and without residents (resident fishes were removed) within each of three zones (nearshore, mid-lagoon, outer barrier). Significantly more anemonefishes recruited to anemones without resident fishes than to anemones with resident fishes. Each anemonefish species recruited to particular host species and zones. The distribution and abundance of the recruits of each fish species among zones were positively correlated with the distribution and abundance of resident fishes in the benthic habitat. This suggests that the spatial patterns of recruitment among zones strongly determined the distribution and abundance patterns of the benthic populations, and they were not the result of post-recruitment mortality or movement. Coexistence of the nine anemonefish species on the limited anemone resource was considered possible because of niche differentiation (i.e., differences in host and habitat utilization among zones), and the ability of two small species (i.e., Amphiprion sandaracinos and A. leucokranos) to cohabit individual anemones with other anemonefish species. Received: 29 July 1999 / Accepted: 1 September 2000     

High relatedness and inbreeding in two species of haplodiploid eusocial thrips (Insecta: Thysanoptera) revealed by microsatellite analysis

Relatedness and inbreeding coefficients were estimated for Oncothrips tepperi and O. habrus, two species of eusocial gall-forming thrips, using data from two microsatellite loci. Relatedness between sets of individuals (sexes and castes) for O. tepperi ranged from 0.5 to 0.85 and for O. habrus estimates were centered around 0.5. Multiple mating in O. habrus was implicated in lowering relatedness within a gall. We estimated the inbreeding coefficient to be 0.38 for both species, the highest estimates known for eusocial insects. Our findings imply that high relatedness and inbreeding are important for the evolution and form of social behavior in Australian gall-forming Thysanoptera. Received: 14 November 1997 / Accepted after revision: 14 March 1998     

Genetic study of the extent and consequences of sexual and asexual reproduction in the deep-sea epizoic anemones Amphianthus inornata and Kadosactis commensalis (Cnidaria: Anthozoa)

The anemone Amphianthus inornata is found at bathyal depths living on colonies of the gorgonian Acanella arbuscula. Previous studies of the morphology and reproductive stage of this anemone, during different times of the year, have indicated that it reproduces sexually on a seasonal basis. A small proportion of the study population were also reported to be undergoing asexual reproduction by fission. The anemone Kadosactis commensalis is also bathyal, but lives mainly on the holothurian Paroriza prouhoi. Previous morphological studies have indicated that K. commensalis is a protandrous hermaphrodite that exhibits non-seasonal sexual reproduction only. In the present study, allozyme electrophoresis was used to examine the prevalence and genetic consequences of asexual reproduction in a population of Amphianthus inornata from 2 200 m in the Rockall Trough, North Atlantic Ocean. Genetic evidence, from five randomly selected polymorphic enzyme loci, for asexual reproduction in this species was weak. Exact tests indicated that genotype frequencies did not differ significantly from those expected under Hardy–Weinberg equilibrium. F _IS (correlation of homologous alleles with reference to local population, assuming random mating) values also did not differ significantly from zero, and observed heterozygosity (H _o =0.446) and genotypic diversity (G _o =17.0387) were very similar to Hardy–Weinberg expected frequencies (H _e =0.446; G ^* _e =17.0010). Evidence suggests that the contribution of asexual reproduction to recruitment in the study population of A. inornata is low. For a single population of K. commensalis from 4 850 m on the Porcupine Abyssal Plain, North Atlantic Ocean, the hypothesis that inbreeding due to reduced occurrence of outcrossing between anemones on a single holothurian host was examined by electrophoresis of ten randomly selected enzyme loci. Single-locus genotypic frequencies were significantly different from expected frequencies for one locus P≤ 0.05, hexokinase-1 (Hex-1)]. F _IS values were significantly different from zero for two enzyme loci (Hex-1 and Hex-2, P≤ 0.01 and P≤ 0.05, respectively), and the overall observed heterozygosity was lower than the expected heterozygosity (H _o =0.125, H _e =0.140). The hypothesis of inbreeding could not be rejected by the present study, although sample size was small (N=55), leading to possible bias in tests of significance. Genetic variation in A. inornata was higher than that recorded for most eukaryotes, although interlocus sampling error for only five loci is high. High genetic variability has been found in other sea anemones, and has been related to high longevity and mixed reproductive modes. Genetic variation in K. commensalis was in the higher range of that found in other eukaryotes, and is not unusual for anemones. Received: 5 August 1996 / Accepted: 11 December 1996     

Polyandry and enhanced reproductive success in the harlequin-beetle-riding pseudoscorpion

The growing molecular evidence that females of many species mate with several males calls for a critical reassessment of the selective forces which act to shape female mating tactics. In natural populations of the harlequin-beetle-riding pseudoscorpion, Cordylochernes scorpioides, females are polyandrous and typically produce mixed-paternity broods. Laboratory behavioral analyses and breeding experiments indicate that polyandry in this pseudoscorpion is an active strategy which increases female reproductive success. Females restricted to mating with a single male experienced a higher rate of embryo failure and produced significantly fewer offspring than either females mated to more than one male in the laboratory or females naturally inseminated in the field. Forced copulation, insufficient sperm from a single mating, male nutrient donations and variation in inherent male genetic quality cannot explain the greater number of nymphs hatched by polyandrous females in this study. Evidence suggests that, by mating with several males, C. scorpioides females may exploit postcopulatory mechanisms for reducing the risk and/or cost of embryo failure resulting from fertilization by genetically incompatible sperm. Received: 5 May 1996 / Accepted after revision: 16 October 1996     

Reproductive patterns of scleractinian corals in the northern Red Sea

The majority of published accounts on scleractinian coral reproduction are from the tropical Pacific and Caribbean, with very little information known about Red Sea species. This report examines variation in reproductive mode in 24 species of hermatypic corals (belonging to seven families) in the Gulf of Eilat, Red Sea. Eighteen species are hermaphroditic broadcasters, two are hermaphroditic brooders and three are gonochoric broadcasters. In the Pocilloporidae, the gonads project into the body cavity, while in the other six families the gonads reside inside the mesenteries. The number of gonads per polyp in broadcasting species follows family or genus lines. Fecundity (eggs per polyp) increases with polyp size. Brooding species usually exhibit one or two gonads per polyp and each gonad contains only one to three oocytes. Oocyte size varies widely and does not relate to mode of reproduction. The largest oocytes (diameter = 450 μm) occur in the brooding coral Alveopora daedalea and in broadcasting species of the genus Acropora (diameter = 420 μm). Gonad morphology and gonochorism versus hermaphroditism appear to be constrained phylogenetically at the family or genus level. Lastly, this report compares the data presented for Red Sea scleractinian species with the data available on scleractinian corals from other geographical regions. Received: 2 February 1993 / Accepted: 9 March 1998     

Reproductive biology of a deep-sea brittle star Amphiura carchara (Echinodermata: Ophiuroidea)

 New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples indicated that there are seasonal trends in reproduction. Received: 14 February 2000 / Accepted: 3 July 2000     

Genetic structure of populations of two species of Chthamalus (Crustacea: Cirripedia) in the north-east Atlantic and Mediterranean

Protein electrophoresis on starch gels was used to investigate population genetic structure of the barnacles Chthamalus montagui Southward and C. stellatus (Poli) over their north-east Atlantic and Mediterranean ranges. In each species, a single locus exhibited marked differentiation of allele frequencies between Atlantic and Mediterranean localities; in C. stellatus, genetic differentiation between the two basins had not previously been noted. In both species, mean heterozygosity per locus appeared higher in the Mediterranean samples than in the Atlantic, and Mediterranean populations had more alleles at the loci studied. Possible explanations for the differentiation between the Atlantic and the Mediterranean populations are discussed. Received: 30 May 1996 / Accepted: 17 September 1996     

Feeding and predator-avoidance by the rose anemone Urticina piscivora

We investigated the influence of feeding rate on the behavior of the rose anemone Urticina piscivora. We predicted that anemones would travel less and be less willing to detach from the substrate in response to contact with a predator (Dermasterias imbricata) as feeding rate was experimentally increased. As predicted, anemones receiving 0 mussels (Mytilustrossulus) daily moved significantly more than those receiving either 1 or 2 mussels daily. Anemones receiving 0 mussels daily also detached significantly quicker in response to predator contact compared to the 1 mussel per day group, which in turn detached significantly quicker than did the 2 mussels per day group. A field test of the same prediction gave mixed results. We also examined whether anemones could detect feeding rates of neighbors. Movement rates of anemones receiving 1 mussel daily when neighbors received 0 mussels daily were compared with those when neighbors received 2 mussels daily. We predicted that if the subjects could detect feeding rates of neighbors, they should move less when neighbors received less food than themselves (since their position is relatively good) than when neighbors received more food. The results support this interpretation. Received: 21 August 1996 / Accepted: 22 October 1996     

Molecular phylogeny of vestimentiferans collected around Japan, revealed by the nucleotide sequences of mitochondrial DNA

The phylogenetic relationships among local populations of undescribed vestimentiferan species that belong to the genera Lamellibrachia and Escarpia and had been collected at six sites around Japan were analyzed on the basis of the partial (1023 bp) nucleotide sequences of the mitochondrial gene for cytochrome oxidase I (COI), using a pogonophoran and a polychaete as outgroups. The identical amino acid sequence was deduced from the nucleotide sequence obtained from each of the vestimentiferans analyzed. The strong similarity among deduced amino acid sequences of COI suggested a close relationship between vestimentiferans and pogonophorans. On the basis of the phylogenetic relationships, the analyzed vestimentiferan populations were classified tentatively as five species. The genetic differentiation of vestimentiferans was suggested to occur bathymetrically as well as being a consequence of horizontal segregation. Two of these tentatively identified species inhabit both a hydrothermal area and a cold seep area, as is the case for some species of bivalves that belong to the genera Bathymodiolus and Calyptogena. Received: 28 August 1996 / Accepted: 2 October 1996     

Variation among populations of the sailfin molly in the rate of concurrent multiple paternity and its implications for mating-system evolution

We examined patterns of concurrent multiple mating in a live-bearing poeciliid fish, the sailfin molly (Poecilia latipinna). We tested whether the probability of multiple paternity was related to female body size or fertility and whether the rate of multiple paternity varied among four populations that differed in their distributions of female body size and fertility. We analyzed data on mother and offspring genotypes for three polymorphic allozymes by three techniques, including a maximum-likelihood estimator that accounts for sampling error in both parental and offspring allele frequencies. The estimated rate of multiple paternity varied between 0.09 and 0.85, and the rate in one population varied seasonally between 0.33 (spring) and 0.85 (autumn). The variation in these rates was not associated with variation in body-size distributions among populations but was closely associated with variation in size-specific fertility: populations with greater variation in female fertility had higher multiple-paternity rates. Within two populations, logistic regression revealed that individual females of larger body size and greater size-specific fertility were more likely to carry multiply sired broods. This result is consistent with observations made in one of the populations 5 years earlier. In general, the results strongly suggest that the mating system varies markedly among conspecific populations of sailfin mollies and that larger, more fertile females are the objects of intermale competition. Received: 6 May 1996 / Accepted in revised form: 5 December 1996     

Inbreeding level does not induce female discrimination between sibs and unrelated males in guppies

Significant empirical evidence has demonstrated the importance of discriminative mate choice as a mechanism to avoid inbreeding. Incestuous mating can be avoided by recognition of kin. The guppy, Poecilia reticulata, is a livebearer with a polygamous mating system and active female choice. Despite potential inbreeding costs in the guppy, Viken et al. (Ethology 112:716–723, 2006) and Pitcher et al. (Genetica 134:137–146, 2008) have found that females do not discriminate between sibs and unrelated males. However, populations experiencing different inbreeding histories can have different levels of inbreeding avoidance, and it is possible that the lack of inbreeding avoidance observed in guppies is a consequence of using outbred fish only. Here we tested the preference of female guppies with different inbreeding coefficients, for olfactory cues of males that were either unrelated but had the same inbreeding coefficient, or were related (i.e. brother) with the same inbreeding coefficient. We found no evidence that female guppies preferred unrelated males with the same inbreeding coefficient. Moreover, inbreeding level did not influence female preference for unrelated males, suggesting that inbreeding history in a population has no influence on female discrimination of unrelated males in guppies.     

Genetic evidence of the presence of two species of Crassostrea (Bivalvia: Ostreidae) on the coast of Brazil

 Although oysters are commercially very important in Brazil, there is still much dispute about the number of Crassostrea species occurring on the Brazilian coast. The dispute is centered around C. brasiliana, considered by some authors to be a junior synonym of C. rhizophorae. In this paper we compared, by allozyme electrophoresis, sympatric and allopatric populations of the two putative species. Of the 17 loci analysed, five were diagnostic for the two species in sympatry (gene identity = 0.46 to 0.47), clearly demonstrating that they are distinct biological species. Heterozygosity (h) levels were high for both species (h = 0.24 to 0.28), and no heterozygote deficiencies were observed in any population (local inbreeding, F _IS  = 0.141; P > 0.70). Levels of population structure in C. rhizophorae along 1300 km of coast were very low (population inbreeding, F _ST  = 0.026; P > 0.15), indicating that the planktonic, planktotrophic larvae of these species are capable of long-range dispersal. Received: 14 January 1999 / Accepted: 8 December 1999     

Mating systems in the sea anemone genus Epiactis

Four morphologically similar species in the sea anemone genus Epiactis exhibit overlapping distributions on the Pacific coast of North America; E. prolifera, E. lisbethae, E. ritteri and E. fernaldi. All brood their offspring up to the juvenile stage, but each has a different combination of internal versus external brooding and hermaphroditism versus gonochory (separate sexes). Specimens were collected from sites ranging from British Columbia to southern California between December 1988 and July 1992. Mating systems were inferred from genetic comparisons of mothers and offspring histological analyses of sex expression and observations on brooding and spawning behavior. Allozyme and multilocus DNA fingerprint analyses of the gynodioecious hermaphrodite E. prolifera showed that offspring were all identical to their mothers, a result consistent with either asexual reproduction, self-fertilization or extreme biparental inbreeding. In the gonochore E. lisbethae, mothers and offspring were also electrophoretically identical, but variation in DNA fingerprints indicated cross-fertilization. Similar DNA fingerprint differences between mother and offspring in the gonochore E. ritteri implied that cross-fertilization also occurs in this species. No mother-offspring comparisons were performed on E. fernaldi, as this species was not observed brooding offspring during this study. Although incomplete, the results of this study increase our knowledge of the very unusual combination of reproductive modes in the genus Epiactis, and argue for further investigations of the evolution and genetic consequences of mating systems in these species.     

Effects of contrasting modes of larval development on the genetic structures of populations of three species of prosobranch gastropods

 In south-eastern Australia, the prosobranch gastropods Morula marginalba (Blainville), Cominella lineolata (Lamarck) and Bedeva hanleyi (Angas) have similar fine-scale distributions, but appear to possess very different dispersal capabilities due to contrasting modes of larval development. M.marginalba produce planktonic larvae, whereas C. lineolata and B. hanleyi undergo direct development in benthic egg capsules and emerge as crawling juveniles. To test for possible effects of contrasting life histories on levels of genetic variation within and among populations, a survey was conducted of allozyme variation at six polymorphic loci in 8 to 9 local populations of each species. Collections of snails were made between June 1992 and November 1993. Sampling ranges spanned between 162 and 180 km of coast. Regardless of larval type, proportions of single-locus genotypes in each collection were consistent with the recruitment of offspring which had been generated through random mating. However, genotypic diversity was lower in those species that undergo direct development. Loci surveyed in C. lineolata and B. hanleyi were polymorphic (i.e. frequency of most common allele <95%) in fewer populations than those examined for M.␣marginalba (P <0.001) and, where polymorphisms occurred, also possessed significantly fewer alleles (P <0.001). Consequently, average levels of expected heterozygosity were greater in populations of M. marginalba than in those of either of the other species (P <0.001). Genetic variation among populations, expressed as the standardised variance in allele frequencies (F _ST ), was inversely related to expected larval dispersal capability. The nine collections of M. marginalba showed little overall differentiation (F _ST  = 0.017; P <0.001), reflecting the ability of planktonic larvae to interconnect local populations, and so limit divergence due to drift and natural selection. In contrast, there were high levels of allelic heterogeneity among the nine collections of C. lineolata (F _ST  = 0.523; P <0.001) and eight collections of B. hanleyi (F _ST  = 0.140; P <0.001). These data imply that for species which undergo direct development, local populations are effectively closed and evolve largely independent of one another. Received: 3 May 1996 / Accepted: 12 July 1996     

Low genetic differentiation between isolated populations of the colonial ascidian Symplegma rubra Monniot, C. 1972

Pelagic larvae are highly important for maintaining the gene flow among populations of sessile marine invertebrates. Colonial ascidians consist, exclusively, of brooding species, with lecithotrophic larvae that have a limited dispersal. As a result, there is a marked differentiation among populations. In this work, we used allozyme electrophoresis to access the genetic variation in four populations of Symplegma rubra, a colonial ascidian frequently found in the intertidal zone of Southeastern Brazilian coast. High variability was found at three of the four sites sampled, the exception being Praia Grande in the State of Rio de Janeiro. At this site, there was a great preponderance of clones, which possibly reflected the enclosed nature of the location and its low water circulation that reduce the dispersal capabilities of these animals. S. rubra did not conform to expectations for random mating (Hardy–Weinberg equilibrium): there was a deficit of heterozygotes that was more related to the small population size than to inbreeding processes, since F _is analysis per locus revealed a deficiency of heterozygotes at only one locus—MDH*. The greatest variation in allele frequency was found for GPI-2*. Analyses of genetic variability revealed moderate differentiation among the populations (F _ST=0.051), which was unexpected for a species with a low dispersal capability. Rafting, a frequently underestimated means of dispersal, may be the main mode of gene flow in this species over large areas, since colonies of S. rubra are frequently seen growing on drift material and there is no evidence that the larva survive for a long time in the plankton.     

Genetic structure and allozyme variation of sea bass (Dicentrarchus labrax and D. punctatus) in the Mediterranean Sea

This paper reports data on 28 allozyme loci in wild and artificially reared sea bass (Dicentrarchus labrax) samples, originating from either coastal lagoon or marine sites in the Mediterranean Sea. F _ST analysis (θ estimator) indicated strong genetic structuring among populations; around 34% of the overall genetic variation is due to interpopulation variation. Pairwise θ estimates showed that, on average, the degree of genetic structuring was much higher between marine populations than between samples from lagoons. Six polymorphic loci showed differences in allele frequencies between marine and lagoon samples. Multivariate analyses of individual allozymic profiles and of allele frequencies suggested that different arrays of genotypes prevail in lagoons compared to marine samples, particularly at those loci that, on the basis of previous acclimation experiments, had been implicated in adaptation to freshwater. On the other hand, variation at “neutral” allozyme loci reflects to a greater extent the geographic location of populations. Allozyme differentiation was also studied in a D. labrax population from the Portuguese coast. Average genetic distance between this population and the Mediterranean populations was quite high (Nei's D = 0.236) and calls into question the taxonomic status of the Portuguese population. Finally, genetic relationships between D. labrax and D. punctatus were evaluated. Average Nei's D was 0.648, revealing high genetic differentiation between the two species, even for two sympatric populations of these species in Egypt; thus gene flow was not indicated between species. Received: 24 October 1996 / Accepted: 27 November 1996     

Population genetics of the Antarctic heteronemertean Parbolasia corrugatus from the South Orkney Islands

An allozyme survey, using starch-gel electrophoresis, was carried out on eight populations of the Antarctic nemertean worm Parborlasia corrugatus (McIntosh, 1876) collected from locations around the South Orkney Islands, Antarctica. These populations were separated by distances in the order of tens of kilometres. Genetic variation was estimated over 22 enzyme loci for all populations examined, giving an observed heterozygosity of 0.142. This was much lower than the expected heterozygosity (H _e  = 0.201), and it was found that there was a significant deficiency of het‐erozygotes across four enzyme loci ( p ≤ 0.01). A more detailed examination of this deficiency of heterozygotes was undertaken for the six populations and six variable enzyme loci for which the most complete data sets existed. A significant deficiency of heterozygotes was found at the enzyme locus Odh-1 for four of the six populations examined ( p ≤ 0.01). Mean F _is (0.240) indicated a significant ( p ≤ 0.01) within-population component of the heterozygote deficiency estimated for the six populations sampled, and this was mainly due to the␣Ap-1, Odh-1 and Pgm-1 loci. The mean F _st value (0.036) was also significant ( p ≤ 0.01), indicating a degree of genetic differentiation between populations. The observed levels of genetic differentiation between populations of P. corrugatus and the significant heterozygote deficiencies were unexpected, because this species has been reported to have a long-lived planktotrophic larva. It is hypothesised that recruitment of P. corrugatus in the South Orkney Islands originates from genetically distinct populations located in the Weddell Sea and to the west of the Antarctic Peninsula. Shifts in the relative position of the Weddell Sea Front, Weddell–Scotia Confluence and Scotia Front, relative to the South Orkney Islands, provide a mechanism for variation in the origin of recruits over time. Received: 24 July 1997 / Accepted: 31 October 1997     

Carbon and nitrogen exchange between sandy beach clams (Donax serra) and kelp beds in the Benguela coastal upwelling region

Carbon consumption and nitrogen requirements were estimated for populations of the sandy beach bivalve Donax serra on nine beaches of the west coast of South Africa. Subtidal populations composed mainly of adult clams were responsible for the bulk of standing stock (3538 g C m⁻¹), annual carbon consumption (13 444 g C m⁻¹ yr⁻¹), faeces production (6478 g C m⁻¹ yr⁻¹ ) and nitrogen regeneration (2525 g N m⁻¹ yr⁻¹). Kelp detritus, bacteria and kelp consumers' faeces available in the water column surpass several times the carbon and nitrogen requirements of intertidal and subtidal clam populations. Individual Donax serra pop ulations, in turn, may regenerate up to 3.2% of the total nitrogen requirements of all primary producers from kelp beds and 14% of the requirements of phytoplankton. These high standing stocks of clams are presumably supported mainly by organic matter originating from kelp which, in contrast to phytoplankton, is in constant supply and comprises the largest proportion of the annual production of particulate organic matter on this coast. Wide and shallow continental shelves with gentle slopes probably limit the penetration of upwelled waters to the nearshore waters, decreasing the influence of external inputs and increasing the importance of internal flows of nutrients and carbon within the nearshore zone. In this context, sandy beaches, rocky shores and kelp beds may be more closely interlinked compartments of a larger ecosystem encompassing the whole nearshore than traditionally thought. Received: 28 August 1996 / Accepted: 7 October 1996     

Low paternity in the hornet Vespa crabro indicates that multiple mating by queens is derived in vespine wasps

Queen mating frequency was studied in the European hornet, Vespa crabro, by analyzing four DNA microsatellite loci in 20 workers from each of 14 nests. Queens were found to be predominantly singly mated (9/14), although double (4/14) and triple mating (1/14) also occurred. For most multiply mated queens, paternity was significantly biased with the majority male fathering on average 80% of the female offspring. The population-wide effective mating frequency was therefore low (1.11), and sister-sister relatedness high (0.701 ± 0.023 SE). Low effective mating frequency in Vespa, in combination with data from other vespines, suggests that high paternity frequency is derived in the group. Some problems with the non-detection of fathers, where the queen was not sampled or shared alleles with males, are analyzed. Received: 16 November 1998 / Received in revised form: 29 March 1999 / Accepted: 12 April 1999