Role of evolutionary and ecological factors in the reproductive success and the spatial genetic structure of the temperate gorgonian Paramuricea clavata

Dispersal and mating features strongly influence the evolutionary dynamics and the spatial genetic structure (SGS) of marine populations. For the first time in a marine invertebrate, we examined individual reproductive success, by conducting larval paternity assignments after a natural spawning event, combined with a small‐scale SGS analysis within a population of the gorgonian Paramuricea clavata. Thirty four percent of the larvae were sired by male colonies surrounding the brooding female colonies, revealing that the bulk of the mating was accomplished by males from outside the studied area. Male success increased with male height and decreased with increasing male to female distance. The parentage analyses, with a strong level of self‐recruitment (25%), unveiled the occurrence of a complex family structure at a small spatial scale, consistent with the limited larval dispersal of this species. However, no evidence of small scale SGS was revealed despite this family structure. Furthermore, temporal genetic structure was not observed, which appears to be related to the rather large effective population size. The low level of inbreeding found suggests a pattern of random mating in this species, which disagrees with expectations that limited larval dispersal should lead to biparental inbreeding. Surface brooding and investment in sexual reproduction in P. clavata contribute to multiple paternity (on average 6.4 fathers were assigned per brood), which enhance genetic diversity of the brood. Several factors may have contributed to the lack of biparental inbreeding in our study such as (i) the lack of sperm limitation at a small scale, (ii) multiple paternity, and (iii) the large effective population size. Thus, our results indicate that limited larval dispersal and complex family structure do not necessarily lead to biparental inbreeding and SGS. In the framework of conservation purposes, our results suggested that colony size, proximity among colonies and the population size should be taken into consideration for restoration projects.     

Genetic assignment of recruits reveals short‐ and long‐distance larval dispersal in Pocillopora damicornis on the Great Barrier Reef

Understanding connectivity of coral populations among and within reefs over ecologically significant timescales is essential for developing evidence‐based management strategies, including the design of marineprotected areas. Here, we present the first assessment of contemporary connectivity among populations of two Molecular Operational Taxonomic Units (MOTUs) of the brooding coral Pocillopora damicornis. We used individual‐based genetic assignment methods to identify the proportions of philopatric and migrant larval recruits, settling over 12 months at sites around Lizard Island (northern Great Barrier Reef [GBR]) and over 24 months at sites around the Palms Islands (central GBR). Overall, we found spatially and temporally variable rates of self‐recruitment and dispersal, demonstrating the importance of variation in local physical characteristics in driving dispersal processes. Recruitment patterns and inferred dispersal distances differed between the two P. damicornis MOTUs, with type α recruits exhibiting predominantly philopatric recruitment, while the majority of type β recruits were either migrants from identified putative source populations or assumed migrants based on genetic exclusion from all known populations. While P. damicornis invests much energy into brooding clonal larvae, we found that only 15% and 7% of type α and type β recruits, respectively, were clones of sampled adult colonies or other recruits, challenging the hypothesis that reproduction is predominantly asexual in this species on the GBR. We explain high rates of self‐recruitment and low rates of clonality in these MOTUs by suggesting that locally retained larvae originate predominantly from spawned gametes, while brooded larvae are mainly vagabonds.     

Geographical variation in reproductive biology is obscured by the species problem: a new record of brooding in Porites cylindrica,or misidentification?

Little is known about the reproductive biology of corals from the Philippines, despite this archipelago being at the center of coral reef biodiversity. Here, we report on the reproductive biology of a branching poritid species provisionally identified as Porites cf. cylindrica in the Bolinao‐Anda reef complex (BARC), northwestern Philippines. Histological examination and ex situ planulation observations reveal P.cf. cylindrica colonies to be gonochoric brooders that release actively swimming zooxanthellate larvae. Planulation appeared to occur throughout the year and there was significant lunar periodicity in planular release. The mean peak of release occurred from the 25th to 29th lunar day or just before the new moon, while peak in diel timing in planulation occurred during daytime between 08:00–11:00 h. Elsewhere in the Pacific, Porites cylindrica colonies are reported to broadcast spawn. If our species identification is correct, then this is the first report of brooding in P. cylindrica. Although there are no apparent morphological differences between the coral in this study and P. cylindrica reported from other sites, an alternative explanation for our findings is that our provisionally identified Porites cf. cylindrica is a different species. If so, our findings further highlight how difficulties with species identification in corals can influence our understanding of geographical variation in reproductive biology.     

Experimental evidence that high levels of inbreeding depress sperm competitiveness

The effects of inbreeding on sperm quantity and quality are among the most dramatic examples of inbreeding depression. The extent to which inbreeding depression results in decreased fertilization success of a male’s sperm, however, remains largely unknown. This task is made more difficult by the fact that other factors, such as cryptic female choice, male sperm allocation and mating order, can also drive patterns of paternity. Here, we use artificial insemination to eliminate these extraneous sources of variation and to measure the effects of inbreeding on the competitiveness of a male’s sperm. We simultaneously inseminated female guppies (Poecilia reticulata) with equal amounts of sperm from an outbred (f = 0) male and either a highly (f = 0.59) or a moderately inbred (f = 0.25) male. Highly inbred males sired significantly fewer offspring than outbred males, but share of paternity did not differ between moderately inbred and outbred males. These findings therefore confirm that severe inbreeding can impair the competitiveness of sperm, but suggest that in the focal population inbreeding at order of a brother–sister mating does not reduce a male’s sperm competitiveness.     

How relatedness between mates influences reproductive success: An experimental analysis of self‐fertilization and biparental inbreeding in a marine bryozoan

Kin associations increase the potential for inbreeding. The potential for inbreeding does not, however, make inbreeding inevitable. Numerous factors influence whether inbreeding preference, avoidance, or tolerance evolves, and, in hermaphrodites where both self‐fertilization and biparental inbreeding are possible, it remains particularly difficult to predict how selection acts on the overall inbreeding strategy, and to distinguish the type of inbreeding when making inferences from genetic markers. Therefore, we undertook an empirical analysis on an understudied type of mating system (spermcast mating in the marine bryozoan, Bugula neritina) that provides numerous opportunities for inbreeding preference, avoidance, and tolerance. We created experimental crosses, containing three generations from two populations to estimate how parental reproductive success varies across parental relatedness, ranging from self, siblings, and nonsiblings from within the same population. We found that the production of viable selfed offspring was extremely rare (only one colony produced three selfed offspring) and biparental inbreeding more common. Paternity analysis using 16 microsatellite markers confirmed outcrossing. The production of juveniles was lower for sib mating compared with nonsib mating. We found little evidence for consistent inbreeding, in terms of nonrandom mating, in adult samples collected from three populations, using multiple population genetic inferences. Our results suggest several testable hypotheses that potentially explain the overall mating and dispersal strategy in this species, including early inbreeding depression, inbreeding avoidance through cryptic mate choice, and differential dispersal distances of sperm and larvae.     

Diel timing of planulation and larval settlement in the coral Isopora cuneata (Scleractinia: Acroporidae)

The prevailing environmental conditions when reproductive products are released in the water column can have a profound influence on the biology and ecology of marine organisms. In reef-building corals, brooding species that release azooxanthellate larvae are expected to release their larvae before sunrise, similar to species releasing zooxanthellate larvae as established in previous studies. This study investigated the diel timing of release of asymbiotic larvae by Isopora cuneata in northwestern Philippines during 2 years through ex situ observations on gravid colonies collected from the reef. Planulation mainly occurred after sunset until midnight, with grand mean hour of release at 19:35 h (95% confidence limit: 18:44–21:02 h) in April 2010 and 19:41 h (18:10–20:59 h) in March 2011. This pattern of release timing is distinct from what has been previously reported for brooding scleractinian coral species with zooxanthellate larvae (i.e., release close to sunrise). The release coincides with the low tidal stand, which may provide opportunity for the prompt settlement of newly released, buoyant larvae to shallow reef areas where adult colonies are generally distributed. The larvae were able to settle with 20 ± 25% success within a day of release, though a distinct settlement peak at 3 days post-release (70 ± 25%). This study provides new information on the early life strategies of the reef-building coral Isopora cuneata. The unique pattern of larval release time and the settlement behavior may influence the population dynamics and success of the species through space and time.     

Effects of tree architecture on pollen dispersal and mating patterns in Abies pinsapo Boiss. (Pinaceae)

Plant architecture is crucial to pollination and mating in wind‐pollinated species. We investigated the effect of crown architecture on pollen dispersal, mating system and offspring quality, combining phenotypic and genotypic analyses in a low‐density population of the endangered species Abies pinsapo. A total of 598 embryos from three relative crown height levels (bottom, middle and top) in five mother plants were genotyped using eleven nuclear microsatellite markers (nSSRs). Paternity analysis and mating system models were used to infer mating and pollen dispersal parameters. In addition, seeds were weighed (N = 16 110) and germinated (N = 736), and seedling vigour was measured to assess inbreeding depression. Overall, A. pinsapo shows a fat‐tailed dispersal kernel, with an average pollen dispersal distance of 113–227 m, an immigration rate of 0.84–26.92%, and a number of effective pollen donors (N_ep) ranging between 3.5 and 11.9. We found an effect of tree height and relative crown height levels on mating parameters. A higher proportion of seeds with embryo (about 50%) and a higher rate of self‐fertilization (about 60%) were found at the bottom level in comparison with the top level. Seed weight and seedling vigour are positively related. Nevertheless, no differences were found in seed weight or in seedling‐related variables such as weight and length of aerial and subterranean parts among the different relative crown height levels, suggesting that seeds from the more strongly inbred bottom level are not affected by inbreeding depression. Our results point to vertical isotropy for outcross‐pollen and they suggest that self‐pollen may ensure fertilization when outcross‐pollen is not available in low‐density population.     

Limited pollen-mediated dispersal and partial self-incompatibility in the rare ironstone endemic <Emphasis Type="Italic">Tetratheca paynterae</Emphasis> subsp. <Emphasis Type="Italic">paynterae</Emphasis> increase the risks associated with habitat loss

Patterns of mating and dispersal are key factors affecting the dynamics, viability and evolution of plant populations. Changes in mating system parameters can provide evidence of anthropogenic impacts on populations of rare plants. Tetratheca paynterae subsp. paynterae is a critically endangered perennial shrub confined to a single ironstone range in Western Australia. Mining of the range removed 25% of plants in 2004 and further plants may be removed if the viability of the remaining populations is not compromised. To provide baseline genetic data for monitoring mining impacts, we characterised the mating system and pollen dispersal over two seasons in T. paynterae subsp. paynterae and compared mating system parameters with two other ironstone endemics, T. paynterae subsp. cremnobata and T. aphylla subsp. aphylla that were not impacted by mining. T. paynterae subsp. paynterae was the only taxon showing evidence of inbreeding (t _m = 0.89), although hand pollination revealed pre-zygotic self-incompatibility limits the production of seed from self-pollen. In a year of lower fruit set (2005), the estimate of correlated paternity increased from 20 to 35%. Direct estimates of realised pollen dispersal, made by paternity assignment in two small populations where all adult plants were genotyped, revealed a leptokurtic distribution with 30% of pollen dispersed less than 3 m and 90% less than 15 m. Restricted pollen dispersal maintains the strong genetic structuring of the adult populations in succeeding generations. As a consequence of preferential outcrossing, any reduction in effective population size, flowering plant density and/or the abundance and activity of pollinators may impact negatively on population viability through reduced seed set, increased inbreeding and increased correlated paternity.     

Extra‐pair mating in a socially monogamous and paternal mouth‐brooding cardinalfish

Many vertebrates form monogamous pairs to mate and care for their offspring. However, genetic tools have increasingly shown that offspring often arise from matings outside of the monogamous pair bond. Social monogamy is relatively common in coral reef fishes, but there have been few studies that have confirmed monogamy or extra‐pair reproduction, either for males or for females. Here, long‐term observations and genetic tools were applied to examine the parentage of embryos in a paternally mouth‐brooding cardinalfish, Sphaeramia nematoptera. Paternal care in fishes, such as mouth‐brooding, is thought to be associated with a high degree of confidence in paternity. Two years of observations confirmed that S. nematoptera form long‐term pair bonds within larger groups. However, genetic parentage revealed extra‐pair mating by both sexes. Of 105 broods analysed from 64 males, 30.1% were mothered by a female that was not the partner and 11.5% of broods included eggs from two females. Despite the high paternal investment associated with mouth‐brooding, 7.6% of broods were fertilized by two males. Extra‐pair matings appeared to be opportunistic encounters with individuals from outside the immediate group. We argue that while pair formation contributes to group cohesion, both males and females can maximize lifetime reproductive success by taking advantage of extra‐pair mating opportunities.     

Love the one you're with: proximity determines paternity success in the barnacle Tetraclita rubescens

A species' mating system sets limits on the strength of sexual selection. Sexual selection is widespread in dioecious species, but is less well documented in hermaphrodites, and may be less important. We used four highly polymorphic microsatellite markers to assign paternity to broods of the hermaphroditic eastern Pacific volcano barnacle Tetraclita rubescens. These data were used to describe the species' mating system and to examine factors affecting male reproductive success. Tetraclita can sire broods over distances of 11.2 cm, but proximity to the sperm recipient had a highly significant effect on the probability of siring success. There was no effect of body size or the mass of male reproductive tissues on siring success. Broods showed relatively low frequencies of multiple paternity; even at high densities, 75% of broods had only one father. High frequencies of single‐paternity broods imply either that this species does not compete via sperm displacement, or that sperm displacement is extremely effective, potentially explaining the lack of a positive relationship between male investment and paternity. In addition, there was low variance in siring success among individuals, suggesting a lack of strong sexual selection on male traits. Low variance among sires and the strong effect of proximity are probably driven by the unusual biology of a sessile copulating species.     

Population- and sociogenetic structure of the leaf-cutter ant <Emphasis Type="Italic">Atta colombica</Emphasis> (Formicidae,Myrmicinae)

Relatedness and genetic variability in colonies of social insects are strongly influenced by the number of queens present and the number of matings per queen, but also by the genetic variability in the population. Thus, multiple paternity will enhance within-colony genetic variability more strongly when the males a queen mates with are unrelated. To study the kin-structure within colonies of the leaf-cutter ant Atta colombica and the population structure of this species around Barro Colorado Island, Panama, we developed five polymorphic microsatellite loci with a range of three to 17 alleles in At. colombica, all of which cross-amplify in other higher attines as well. The average effective mating frequency calculated from four-locus microsatellite genotypes was 1.89 ± 0.12 (harmonic mean ± SE) and thus slightly lower than the average observed mating frequency of 2.50 ± 0.11 (arithmetic mean ± SE) over the 55 colonies studied, confirming former studies that utilized fewer loci. The discrepancy between observed mating frequency and effective mating frequency is most probably due to paternity skew within colonies. The study population proved to be genetically diverse and in Hardy-Weinberg equilibrium, suggesting random mating within the study area. No population substructure was observed, neither considering nuclear (global F _ST = 0.011 ± 0.003 SE) nor mitochondrial markers (mean Φ_ST = 0.008). Consequently, gene flow is obviously promoted by both sexes across the range investigated here. Thus, multiple mating and long-distance dispersal appear to be two interconnected behavioural mechanisms to create and maintain genetic diversity in At. colombica. The advantages of this system are partly offset by paternity skew and the non-zero relatedness among colony fathers found in the study population. Received 18 March 2008; revised 14 July 2008; accepted 18 July 2008.     

Influence of translocation strategy and mating system on the genetic structure of a newly established population of island ptarmigan

Island populations and populations established by reintroductions are prone to extinction, in part because they are vulnerable to deterministic and stochastic phenomena associated with geographic isolation and small population size. As population size declines, reduced genetic diversity can result in decreased fitness and reduced adaptive potential, which may hinder short- or long-term population viability. We used 32 microsatellite markers to investigate the conservation genetics of a newly established population of Evermann’s Rock Ptarmigan (Lagopus muta evermanni) at Agattu Island, in the western Aleutian Archipelago, Alaska. We found low genetic diversity (observed heterozygosity = 0.41, allelic richness = 2.2) and a small effective population size (N _e  = 28.6), but a relatively large N _e /N ratio = 0.55, which was attributed to multiple paternity in 80% of the broods and low reproductive skew among males (λ = 0.29). Moreover, successful breeding pairs were less related to each other than random male–female pairs. For conservation efforts based on reintroductions, a mating system with high rates of multiple paternity may facilitate retention of genetic diversity, thereby reducing the potential for inbreeding in small or isolated populations. Our results underscore the importance of quantifying genetic diversity and understanding the breeding behavior of translocated populations.     

Multiple paternity is a shared reproductive strategy in the live‐bearing surfperches (Embiotocidae) that may be associated with female fitness

According to Bateman's principle, female fecundity is limited relative to males, setting the expectation that males should be promiscuous, while females should be choosy and select fewer mates. However, several surfperches (Embiotocidae) exhibit multiple paternity within broods indicating that females mate with multiple males throughout the mating season. Previous studies found no correlation between mating success and reproductive success (i.e., a Bateman gradient). However, by including samples from a broader range of reproductive size classes, we found evidence of a Bateman gradient in two surfperch species from distinct embiotocid clades. Using microsatellite analyses, we found that 100% of the spotfin surfperch families sampled exhibit multiple paternity (Hyperprosopon anale, the basal taxon from the only clade that has not previously been investigated) indicating that this tactic is a shared reproductive strategy among surfperches. Further, we detected evidence for a Bateman gradient in H. anale; however, this result was not significant after correction for biases. Similarly, we found evidence for multiple paternity in 83% of the shiner surfperch families (Cymatogaster aggregata) sampled. When we combine these data with a previous study on the same species, representing a larger range of reproductive size classes and associated brood sizes, we detect a Bateman gradient in shiner surfperch for the first time that remains significant after several conservative tests for bias correction. These results indicate that sexual selection is likely complex in this system, with the potential for conflicting optima between sexes, and imply a positive shift in fertility (i.e., increasing number) and reproductive tactic with respect to the mating system and number of sires throughout the reproductive life history of females. We argue that the complex reproductive natural history of surfperches is characterized by several traits that may be associated with cryptic female choice, including protracted oogenesis, uterine sac complexity, and sperm storage.     

An integrative mating system assessment of a nonmodel,economically important Pacific rockfish (Sebastes melanops) reveals nonterritorial polygamy and conservation implications for a large species flock

Characterizing the mating systems of long‐lived, economically important Pacific rockfishes comprising the viviparous Sebastes species flock is crucial for their conservation. However, direct assignment of mating success to sires is precluded by open, offshore populations and high female fecundity. We addressed this challenge by integrating paternity‐assigned mating success of females with the adult sex ratio (ASR) of the population, male evolutionary responses to receptive females, and reproductive life history traits—in the framework of sexual selection theory—to assess the mating system of Sebastes melanops. Microsatellite parentage analysis of 17 pregnant females, 1,256 of their progeny, and 106 adults from the population yielded one to four sires per brood, a mean of two sires, and a female mate frequency distribution with a truncated normal (random) pattern. The 11 multiple paternity broods all contained higher median allele richness than the six single paternity broods (Wilcoxon test: W = 0, p < .001), despite similar levels of average heterozygosity. By sampling sperm and alleles from different males, polyandrous females gain opportunities to enhance their sperm supply and to lower the cost of mating with genetically incompatible males through reproductive compensation. A mean of two mates per mated female with a variance of one, an ASR = 1.2 females per male, and the expected population mean of 2.4 mates for mated males (and the estimated 35 unavailable sires), fits polygamous male mate frequency distributions that distinguish polygynandry and polyandrogyny mating systems, that is, variations of polygamy, but not polyandry. Inference for polygamy is consistent with weak premating sexual selection on males, expected in mid‐water, schooling S. melanops, owing to polyandrous mating, moderately aggregated receptive females, an even ASR, and no territories and nests used for reproduction. Each of these characteristics facilitates more mating males and erodes conspicuous sexual dimorphism. Evaluation of male evolutionary responses of demersal congeners that express reproductively territorial behavior revealed they have more potential mechanisms for producing premating sexual selection, greater variation in reproductive success, and a reduced breeding effective population size of adults and annual effective size of a cohort, compared to S. melanops modeled with two mates per adult. Such divergence in behavior and mating system by territorial species may differentially lower their per capita birth rates, subsequent population growth, and slow their recovery from exploitation.     

Extensive seed and pollen dispersal and assortative mating in the rain forest tree Entandrophragma cylindricum (Meliaceae) inferred from indirect and direct analyses

Pollen and seed dispersal are key processes affecting the demographic and evolutionary dynamics of plant species and are also important considerations for the sustainable management of timber trees. Through direct and indirect genetic analyses, we studied the mating system and the extent of pollen and seed dispersal in an economically important timber species, Entandrophragma cylindricum (Meliaceae). We genotyped adult trees, seeds and saplings from a 400‐ha study plot in a natural forest from East Cameroon using eight nuclear microsatellite markers. The species is mainly outcrossed (t = 0.92), but seeds from the same fruit are often pollinated by the same father (correlated paternity, r_p = 0.77). An average of 4.76 effective pollen donors (N_ep) per seed tree contributes to the pollination. Seed dispersal was as extensive as pollen dispersal, with a mean dispersal distance in the study plot approaching 600 m, and immigration rates from outside the plot to the central part of the plot reaching 40% for both pollen and seeds. Extensive pollen‐ and seed‐mediated gene flow is further supported by the weak, fine‐scale spatial genetic structure (Sp statistic = 0.0058), corresponding to historical gene dispersal distances (σ_g) reaching approximately 1,500 m. Using an original approach, we showed that the relatedness between mating individuals (F_ij = 0.06) was higher than expected by chance, given the extent of pollen dispersal distances (expected F_ij = 0.02 according to simulations). This remarkable pattern of assortative mating could be a phenomenon of potentially consequential evolutionary and management significance that deserves to be studied in other plant populations.     

Seed and pollen dispersal distances in two African legume timber trees and their reproductive potential under selective logging

The natural regeneration of tree species depends on seed and pollen dispersal. To assess whether limited dispersal could be critical for the sustainability of selective logging practices, we performed parentage analyses in two Central African legume canopy species displaying contrasted floral and fruit traits: Distemonanthus benthamianus and Erythrophleum suaveolens. We also developed new tools linking forward dispersal kernels with backward migration rates to better characterize long‐distance dispersal. Much longer pollen dispersal in D. benthamianus (mean distance d_p = 700 m, m_p = 52% immigration rate in 6 km² plot, s = 7% selfing rate) than in E. suaveolens (d_p = 294 m, m_p = 22% in 2 km² plot, s = 20%) might reflect different insect pollinators. At a local scale, secondary seed dispersal by vertebrates led to larger seed dispersal distances in the barochorous E. suaveolens (d_s = 175 m) than in the wind‐dispersed D. benthamianus (d_s = 71 m). Yet, seed dispersal appeared much more fat‐tailed in the latter species (15%–25% seeds dispersing >500 m), putatively due to storm winds (papery pods). The reproductive success was correlated to trunk diameter in E. suaveolens and crown dominance in D. benthamianus. Contrary to D. benthamianus, E. suaveolens underwent significant assortative mating, increasing further the already high inbreeding of its juveniles due to selfing, which seems offset by strong inbreeding depression. To achieve sustainable exploitation, seed and pollen dispersal distances did not appear limiting, but the natural regeneration of E. suaveolens might become insufficient if all trees above the minimum legal cutting diameter were exploited. This highlights the importance of assessing the diameter structure of reproductive trees for logged species.     

Pollination by sexual deception promotes outcrossing and mate diversity in self‐compatible clonal orchids

The majority of flowering plants rely on animals as pollen vectors. Thus, plant mating systems and pollen dispersal are strongly influenced by pollinator behaviour. In Australian sexually deceptive orchids pollinated by male thynnine wasps, outcrossing and extensive pollen flow is predicted due to floral deception, which minimizes multiple flower visitations within patches, and the movement of pollinators under mate‐search rather than foraging behaviours. This hypothesis was tested using microsatellite markers to reconstruct and infer paternity in two clonal, self‐compatible orchids. Offspring from naturally pollinated Chiloglottis valida and C. aff. jeanesii were acquired through symbiotic culture of seeds collected over three seasons. In both species, outcrossing was extensive (t_m = 0.924–1.00) despite clone sizes up to 11 m wide. The median pollen flow distance based on paternity for both taxa combined was 14.5 m (n = 18, range 0–69 m), being larger than typically found by paternity analyses in other herbaceous plants. Unexpectedly for orchids, some capsules were sired by more than one father, with an average of 1.35 pollen donors per fruit. This is the first genetic confirmation of polyandry in orchid capsules. Further, we report a possible link between multiple paternity and increased seed fitness. Together, these results demonstrate that deceptive pollination by mate‐searching wasps enhances offspring fitness by promoting both outcrossing and within‐fruit paternal diversity.     

Nutrient cycling in early coral life stages: Pocillopora damicornis larvae provide their algal symbiont (Symbiodinium) with nitrogen acquired from bacterial associates

The waters surrounding coral reef ecosystems are generally poor in nutrients, yet their levels of primary production are comparable with those reported from tropical rain forests. One explanation of this paradox is the efficient cycling of nutrients between the coral host, its endosymbiotic alga Symbiodinium and a wide array of microorganisms. Despite their importance for the animals' fitness, the cycling of nutrients in early coral life stages and the initial establishment of partnerships with the microbes involved in these processes has received little scrutiny to date. Nitrogen is an essential but limited nutrient in coral reef ecosystems. In order to assess the early nutrient exchange between bacteria and corals, coral larvae of the species Pocillopora damicornis were incubated with two coral‐associated bacteria (Alteromonas sp., or Vibrio alginolyticus), prelabeled with the stable nitrogen isotope ¹⁵N. The incorporation and translocation of nitrogen from Vibrio‐ and Alteromonas bacteria into P. damicornis coral larvae and specifically into the coral‐symbiotic Symbiodinium were detected by nanoscale secondary ion mass spectrometry (NanoSIMS). A significant increase in the amount of enriched ¹⁵N (two to threefold compared to natural abundance) was observed in P. damicornis larvae within 8 h of incubation for both bacterial treatments (one‐way ANOVA, F_5,53 = 18.03, P = 0.004 for Alteromonas sp. and F_5,53 = 18.03, P = 0.0001 for V. alginolyticus). These findings reveal that coral larvae acquire nutrients previously taken up from the environment by bacteria. The additional nitrogen may increase the survival rate and fitness of the developing coral and therefore contribute to the successful maintenance of coral reefs.     

Fine-scale analysis of genetic structure in the brooding coral Seriatopora hystrix from the Red Sea

The dispersal of gametes and larvae plays a key role in the population dynamics of sessile marine invertebrates. Species with internal fertilisation are often associated with very localised larval dispersal, which may cause small-scale patterns of neutral genetic variation. This study on the brooding coral Seriatopora hystrix from the Red Sea focused on the smallest possible scale: Two S. hystrix stands (~100 colonies each) near Dahab were completely sampled, mapped and analysed at five microsatellite markers. The sexual mode of reproduction, the likely occurrence of selfing and the level of immigration were in agreement with previous studies on this species. Contrary to previous findings, both stands were in Hardy–Weinberg proportions. Also, no evidence for spatially restricted larval dispersal within the sampled areas was found. Differences between this and previous studies on S. hystrix could reflect variation in life history or varying environmental conditions, which opens intriguing questions for future research.     

Caribbean massive corals not recovering from repeated thermal stress events during 2005–2013

Massive coral bleaching events associated with high sea surface temperatures are forecast to become more frequent and severe in the future due to climate change. Monitoring colony recovery from bleaching disturbances over multiyear time frames is important for improving predictions of future coral community changes. However, there are currently few multiyear studies describing long‐term outcomes for coral colonies following acute bleaching events. We recorded colony pigmentation and size for bleached and unbleached groups of co‐located conspecifics of three major reef‐building scleractinian corals (Orbicella franksi, Siderastrea siderea, and Stephanocoenia michelini; n = 198 total) in Bocas del Toro, Panama, during the major 2005 bleaching event and then monitored pigmentation status and changes live tissue colony size for 8 years (2005–2013). Corals that were bleached in 2005 demonstrated markedly different response trajectories compared to unbleached colony groups, with extensive live tissue loss for bleached corals of all species following bleaching, with mean live tissue losses per colony 9 months postbleaching of 26.2% (±5.4 SE) for O. franksi, 35.7% (±4.7 SE) for S. michelini, and 11.2% (±3.9 SE) for S. siderea. Two species, O. franksi and S. michelini, later recovered to net positive growth, which continued until a second thermal stress event in 2010. Following this event, all species again lost tissue, with previously unbleached colony species groups experiencing greater declines than conspecific sample groups, which were previously bleached, indicating a possible positive acclimative response. However, despite this beneficial effect for previously bleached corals, all groups experienced substantial net tissue loss between 2005 and 2013, indicating that many important Caribbean reef‐building corals will likely suffer continued tissue loss and may be unable to maintain current benthic coverage when faced with future thermal stress forecast for the region, even with potential benefits from bleaching‐related acclimation.