Phenotypic plasticity or speciation? A case from a clonal marine organism

Integrating cryptic diversity into coral evolution, symbiosis and conservation

Understanding how diversity evolves and is maintained is critical to predicting the future trajectories of ecosystems under climate change; however, our understanding of these processes is limited in marine systems. Corals, which engineer reef ecosystems, are critically threatened by climate change, and global efforts are underway to conserve and restore populations as attempts to mitigate ocean warming continue. Recently, sequencing efforts have uncovered widespread undescribed coral diversity, including 'cryptic lineages'-genetically distinct but morphologically similar coral taxa. Such cryptic lineages have been identified in at least 24 coral genera spanning the anthozoan phylogeny and across ocean basins. These cryptic lineages co-occur in many reef systems, but their distributions often differ among habitats. Research suggests that cryptic lineages are ecologically specialized and several examples demonstrate differences in thermal tolerance, highlighting the critical implications of this diversity for predicting coral responses to future warming. Here, we draw attention to recent discoveries, discuss how cryptic diversity affects the study of coral adaptation and acclimation to future environments, explore how it shapes symbiotic partnerships, and highlight challenges and opportunities for conservation and restoration efforts.

Morphologic Differentiation of the Exotic Parasitoid Eupelmus pulchriceps (Hymenoptera: Eupelmidae) in the Galapagos Archipelago

The historical and geographical properties of the archipelagos allow a detailed study of species diversification, and phenotypic traits can indicate the extent of such processes. Eupelmus pulchriceps (Cameron, 1904) is an exotic species to the Galapagos archipelago, and generalist parasitoid that attacks a beetle species that consumes the seeds of the invasive shrub Leucaena leucocephala (Lam.) de Wit. Despite extensive sampling, the wasp is recorded only in Santa Cruz and San Cristobal islands of the Galapagos archipelago. Thus, using 112 female wasps, we compare body size, proportion, and allometric differentiations within and between the two islands. There were no body size differences between islands. A PerMANOVA indicates differences between the islands and a single differentiation between two localities of one island. Allometric differences between islands were not the same for all structures. These results are consistent with the greater distance between islands than between localities and suggest a differentiation process. The variables with allometric differentiation are associated with wings and ovipositor, possibly responding to different ecological pressures. It is interesting that this parasitoid, recently arrived at the archipelago, is already showing differentiation. Also, it is essential to monitor the behavior of these wasps in the archipelago, given their potential to access other species affecting the trophic interactions of the local biota.

SEA PENS (CNIDARIA: OCTOCORALLIA: PENNATULOIDEA) FROM THE MAR DEL PLATA SUBMARINE CANYON AND OUTSKIRTS

During this work, over 200 specimens of sea pens (Anthozoa: Octocorallia: Pennatuloidea), collected in the Mar del Plata submarine canyon and outskirts (38S, up to 3500 m depth) during 2012 and 2013 were analyzed. Of the total, about 160 were identified in seven species of Anthoptilum, Distichoptilum, Kophobelemnon, Pseudumbellula, Solumbellula and Umbellula. Three of those represent new records for the southwestern Atlantic Ocean off Argentina.

Morphometric responses of two zooxanthellate octocorals along a water quality gradient in the Cuban northwestern coast

Octocoral abundance is increasing on Caribbean reefs, and one of the possible causes is their vertical morphological plasticity that allows them to grow above the substrate to reduce the effect of processes that occur in it (e.g., scour by sediments) as well as adapt to environmental gradients. The aim of this study was to determine the morphometric response of two octocorals species (Eunicea flexuosa and Plexaura kükenthali) with different life strategies in a water quality gradient. The research was carried out between 2008 and 2016 on eight forereefs of northwest Cuba. Different morphometric indicators were measured in the colonies of both species found within a belt transect (100 x 2 m) randomly located at each site. The lowest means in height, diameter, number of terminal branches/colony, cover index, and least arborescent colonies of E. flexuosa were detected at the sites with the greatest anthropogenic pollution. The water quality gradient did not explain the variability of the five morphometric indicators of P. kükenthali. However, hydrodynamic stress was the factor that most negatively affected the morphometry of this species. The chronic effect of poor water quality over time resulted in more small sized colonies of E. flexuosa at the polluted site, probably due to higher mortality. The size distribution of P. kükenthali also showed the same trend but at the sites with greater hydrodynamic stress. These results show that the morphometric response of octocorals along a water quality gradient is species-specific. This study suggests that poor water quality decreases the size and thus availability of habitat provided by octocorals sensitive to that factor (e.g., E. flexuosa) while other tolerant species (e.g., P. kükenthali) could provide the habitat of several organisms in a scenario of increasing anthropogenic pollution.

Multiscale flow between the branches and polyps of gorgonians

Gorgonians, including sea fans, are soft corals well known for their elaborate branching structure and how they sway in the ocean. This branching structure can modify environmental flows to be beneficial for feeding in a particular range of velocities and, presumably, for a particular size of prey. As water moves through the elaborate branches, it is slowed, and recirculation zones can form downstream of the colony. At the smaller scale, individual polyps that emerge from the branches expand their tentacles, further slowing the flow. At the smallest scale, the tentacles are covered in tiny pinnules where exchange occurs. In this paper, we quantified the gap to diameter ratios for various gorgonians at the scale of the branches, the polyp tentacles and the pinnules. We then used computational fluid dynamics to determine the flow patterns at all three levels of branching. We quantified the leakiness between the branches, tentacles and pinnules over the biologically relevant range of Reynolds numbers and gap-to-diameter ratios, and found that the branches and tentacles can act as either leaky rakes or solid plates depending upon these dimensionless parameters. The pinnules, in contrast, mostly impede the flow. Using an agent-based modeling framework, we quantified plankton capture as a function of the gap-to-diameter ratio of the branches and the Reynolds number. We found that the capture rate depends critically on both morphology and Reynolds number. The results of the study have implications for how gorgonians modify ambient flows for efficient feeding and exchange.

A turn in species conservation for hairpin banksias: demonstration of oversplitting leads to better management of diversity

PREMISE

Understanding evolutionary history and classifying discrete units of organisms remain overwhelming tasks, and lags in this workload concomitantly impede an accurate documentation of biodiversity and conservation management. Rapid advances and improved accessibility of sensitive high-throughput sequencing tools are fortunately quickening the resolution of morphological complexes and   thereby improving the estimation of species diversity. The recently described and critically endangered Banksia vincentia is morphologically similar to the hairpin banksia complex (B. spinulosa s.l.), a group of eastern Australian flowering shrubs whose continuum of morphological diversity has been responsible for taxonomic controversy and possibly questionable conservation initiatives.

METHODS

To assist conservation while testing the current taxonomy of this group, we used high-throughput sequencing to infer a population-scale evolutionary scenario for a sample set that is comprehensive in its representation of morphological diversity and a 2500-km distribution.

RESULTS

Banksia spinulosa s.l. represents two clades, each with an internal genetic structure shaped through historical separation by biogeographic barriers. This structure conflicts with the existing taxonomy for the group. Corroboration between phylogeny and population statistics aligns with the hypothesis that B. collina, B. neoanglica, and B. vincentia should not be classified as species.

CONCLUSIONS

The pattern here supports how morphological diversity can be indicative of a locally expressed suite of traits rather than relationship. Oversplitting in the hairpin banksias is atypical since genomic analyses often reveal that species diversity is underestimated. However, we show that erring on overestimation can yield negative consequences, such as the disproportionate prioritization of a geographically anomalous population.

A turn in species conservation for hairpin banksias: demonstration of oversplitting leads to better management of diversity

PREMISE

Understanding evolutionary history and classifying discrete units of organisms remain overwhelming tasks, and lags in this workload concomitantly impede an accurate documentation of biodiversity and conservation management. Rapid advances and improved accessibility of sensitive high-throughput sequencing tools are fortunately quickening the resolution of morphological complexes and   thereby improving the estimation of species diversity. The recently described and critically endangered Banksia vincentia is morphologically similar to the hairpin banksia complex (B. spinulosa s.l.), a group of eastern Australian flowering shrubs whose continuum of morphological diversity has been responsible for taxonomic controversy and possibly questionable conservation initiatives.

METHODS

To assist conservation while testing the current taxonomy of this group, we used high-throughput sequencing to infer a population-scale evolutionary scenario for a sample set that is comprehensive in its representation of morphological diversity and a 2500-km distribution.

RESULTS

Banksia spinulosa s.l. represents two clades, each with an internal genetic structure shaped through historical separation by biogeographic barriers. This structure conflicts with the existing taxonomy for the group. Corroboration between phylogeny and population statistics aligns with the hypothesis that B. collina, B. neoanglica, and B. vincentia should not be classified as species.

CONCLUSIONS

The pattern here supports how morphological diversity can be indicative of a locally expressed suite of traits rather than relationship. Oversplitting in the hairpin banksias is atypical since genomic analyses often reveal that species diversity is underestimated. However, we show that erring on overestimation can yield negative consequences, such as the disproportionate prioritization of a geographically anomalous population.

Mesophotic Gorgonian Corals Evolved Multiple Times and Faster Than Deep and Shallow Lineages

Mesophotic Coral Ecosystems (MCEs) develop on a unique environment, where abrupt environmental changes take place. Using a time-calibrated molecular phylogeny (mtDNA: mtMutS), we examined the lineage membership of mesophotic gorgonian corals (Octocorallia: Cnidaria) in comparison to shallow and deep-sea lineages of the wider Caribbean-Gulf of Mexico and the Tropical Eastern Pacific. Our results show mesophotic gorgonians originating multiple times from old deep-sea octocoral lineages, whereas shallow-water species comprise younger lineages. The mesophotic gorgonian fauna in the studied areas is related to their zooxanthellate shallow-water counterparts in only two clades (Gorgoniidae and Plexauridae), where the bathymetrical gradient could serve as a driver of diversification. Interestingly, mesophotic clades have diversified faster than either shallow or deep clades. One of this groups with fast diversification is the family Ellisellidae, a major component of the mesophotic gorgonian coral assemblage worldwide.

Local Adaptation in Marine Foundation Species at Microgeographic Scales

AbstractNearshore foundation species in coastal and estuarine systems (e.g., salt marsh grasses, mangroves, seagrasses, corals) drive the ecological functions of ecosystems and entire biomes by creating physical structure that alters local abiotic conditions and influences species interactions and composition. The resilience of foundation species and the ecosystem functions they provide depends on their phenotypic and genetic responses to spatial and temporal shifts in environmental conditions. In this review, we explore what is known about the causes and consequences of adaptive genetic differentiation in marine foundation species over spatial scales shorter than dispersal capabilities (i.e., microgeographic scales). We describe the strength of coupling field and laboratory experiments with population genetic techniques to illuminate patterns of local adaptation, and we illustrate this approach by using several foundation species. Among the major themes that emerge from our review include (1) adaptive differentiation of marine foundation species repeatedly evolves along vertical (i.e., elevation or depth) gradients, and (2) mating system and phenology may facilitate this differentiation. Microgeographic adaptation is an understudied mechanism potentially underpinning the resilience of many sessile marine species, and this evolutionary mechanism likely has particularly important consequences for the ecosystem functions provided by foundation species.

Phylogenomics of Porites from the Arabian Peninsula

The advent of high throughput sequencing technologies provides an opportunity to resolve phylogenetic relationships among closely related species. By incorporating hundreds to thousands of unlinked loci and single nucleotide polymorphisms (SNPs), phylogenomic analyses have a far greater potential to resolve species boundaries than approaches that rely on only a few markers. Scleractinian taxa have proved challenging to identify using traditional morphological approaches and many groups lack an adequate set of molecular markers to investigate their phylogenies. Here, we examine the potential of Restriction-site Associated DNA sequencing (RADseq) to investigate phylogenetic relationships and species limits within the scleractinian coral genus Porites. A total of 126 colonies were collected from 16 localities in the seas surrounding the Arabian Peninsula and ascribed to 12 nominal and two unknown species based on their morphology. Reference mapping was used to retrieve and compare nearly complete mitochondrial genomes, ribosomal DNA, and histone loci. De novo assembly and reference mapping to the P. lobata coral transcriptome were compared and used to obtain thousands of genome-wide loci and SNPs. A suite of species discovery methods (phylogenetic, ordination, and clustering analyses) and species delimitation approaches (coalescent-based, species tree, and Bayesian Factor delimitation) suggested the presence of eight molecular lineages, one of which included six morphospecies. Our phylogenomic approach provided a fully supported phylogeny of Porites from the Arabian Peninsula, suggesting the power of RADseq data to solve the species delineation problem in this speciose coral genus.

Speciation across the Tree of Life

Much of what we know about speciation comes from detailed studies of well-known model systems. Although there have been several important syntheses on speciation, few (if any) have explicitly compared speciation among major groups across the Tree of Life. Here, we synthesize and compare what is known about key aspects of speciation across taxa, including bacteria, protists, fungi, plants, and major animal groups. We focus on three main questions. Is allopatric speciation predominant across groups? How common is ecological divergence of sister species (a requirement for ecological speciation), and on what niche axes do species diverge in each group? What are the reproductive isolating barriers in each group? Our review suggests the following patterns. (i) Based on our survey and projected species numbers, the most frequent speciation process across the Tree of Life may be co-speciation between endosymbiotic bacteria and their insect hosts. (ii) Allopatric speciation appears to be present in all major groups, and may be the most common mode in both animals and plants, based on non-overlapping ranges of sister species. (iii) Full sympatry of sister species is also widespread, and may be more common in fungi than allopatry. (iv) Full sympatry of sister species is more common in some marine animals than in terrestrial and freshwater ones. (v) Ecological divergence of sister species is widespread in all groups, including ~70% of surveyed species pairs of plants and insects. (vi) Major axes of ecological divergence involve species interactions (e.g. host-switching) and habitat divergence. (vii) Prezygotic isolation appears to be generally more widespread and important than postzygotic isolation. (viii) Rates of diversification (and presumably speciation) are strikingly different across groups, with the fastest rates in plants, and successively slower rates in animals, fungi, and protists, with the slowest rates in prokaryotes. Overall, our study represents an initial step towards understanding general patterns in speciation across all organisms.

The Biology and Evolution of Calcite and Aragonite Mineralization in Octocorallia

Octocorallia (class Anthozoa, phylum Cnidaria) is a group of calcifying corals displaying a wide diversity of mineral skeletons. This includes skeletal structures composed of different calcium carbonate polymorphs (aragonite and calcite). This represents a unique feature among anthozoans, as scleractinian corals (subclass Hexacorallia), main reef builders and focus of biomineralization research, are all characterized by an aragonite exoskeleton. From an evolutionary perspective, the presence of aragonitic skeletons in Octocorallia is puzzling as it is observed in very few species and has apparently originated during a Calcite sea (i.e., time interval characterized by calcite-inducing seawater conditions). Despite this, octocorals have been systematically overlooked in biomineralization studies. Here we review what is known about octocoral biomineralization, focusing on the evolutionary and biological processes that underlie calcite and aragonite formation. Although differences in research focus between octocorals and scleractinians are often mentioned, we highlight how strong variability also exists between different octocoral groups. Different main aspects of octocoral biomineralization have been in fact studied in a small set of species, including the (calcitic) gorgonian Leptogorgia virgulata and/or the precious coral Corallium rubrum. These include descriptions of calcifying cells (scleroblasts), calcium transport and chemistry of the calcification fluids. With the exception of few histological observations, no information on these features is available for aragonitic octocorals. Availability of sequencing data is also heterogeneous between groups, with no transcriptome or genome available, for instance, for the clade Calcaxonia. Although calcite represents by far the most common polymorph deposited by octocorals, we argue that studying aragonite-forming could provide insight on octocoral, and more generally anthozoan, biomineralization. First and foremost it would allow to compare calcification processes between octocoral groups, highlighting homologies and differences. Secondly, similarities (exoskeleton) between Heliopora and scleractinian skeletons, would provide further insight on which biomineralization features are driven by skeleton characteristics (shared by scleractinians and aragonitic octocorals) and those driven by taxonomy (shared by octocorals regardless of skeleton polymorph). Including the diversity of anthozoan mineralization strategies into biomineralization studies remains thus essential to comprehensively study how skeletons form and evolved within this ecologically important group of marine animals.

Extended phenotypes on coral reefs: cryptic phenotypes modulate coral-vermetid interactions

Phenotypic variation can lead to variation in the strength and outcome of species interactions. Variation in phenotypic traits can arise due to plastic responses to environmental stimuli, underlying genetic variation, or both, and may reflect differences in the focal organism or aspects of the extended phenotype (e.g., associated microbes). We used a reciprocal transplant experiment of Porites corals to evaluate the role of plasticity vs. heritable diversity on phenotypic traits and performance of corals that varied in their prior exposure to vermetid gastropods, an organism known to reduce coral growth and survival. We measured a suite of phenotypic traits associated with coral performance, many of which showed a plastic response to vermetid exposure. Vermetids decreased calcification of corals, increased microbial diversity, and shifted microbial composition. Most traits also showed a signature of previous exposure environment that persisted even when exposure was reversed: i.e., under the same conditions, corals naïve to vermetids had slower calcification rates, thicker tissues, higher Symbiodiniaceae densities, and different microbiomes than corals previously exposed to vermetids. We suggest the phenotypic differences are heritable, as reefs with and without vermetids were comprised of two different mitotypes, that revealed high, consistent genetic variation. Vermetids were only found on the fast-growing coral mitotype that was characterized by thin tissue, and that likely had a history of disturbance. As extended phenotypes can have community impacts, we suggest vermetid, in addition to microbes, are part of the extended community phenotype of these corals. Coral genotypes can establish different reef trajectories, with thin-tissue types more prone to disturbance and subsequent colonization by other species, like vermetids, which can further facilitate the degradation of coral reefs. The effects of the extended phenotype of species likely influence heterogeneity across landscapes as well as temporal differences in community composition.

Revision of the genus Plexaurella Kölliker, 1865 (Anthozoa: Octocorallia) and resurrection of Plexaurellidae Verrill, 1912 new rank

The current knowledge on the diversity of the genus Plexaurella is based on a series of dated revisions, often with no examination of types. Although being common octocorals in western Atlantic reefs, there is no consensus on an exact number of valid species. Furthermore, phylogenetic reconstructions do not support the current classification of Plexaurella within the family Plexauridae. Thus, this study reviews the genus based on examination of available types and assesses monophyly using mitochondrial (COI+igr, mtMutS) and nuclear (28S) markers, mostly from available molecular data. Until now, up to six species were considered valid. Our results show that the group is composed of at least seven previously described species: P. dichotoma, P. nutans, P. grisea, P. teres, P. grandiflora, P. regia and P. obesa; and one new species: Plexaurella rastrera sp. nov. An illustrated key to the valid species and a list of all available names are provided and the current classification of the genus is discussed. Based on congruent phylogenetic reconstructions and genetic distances, we propose the elevation of the former plexaurid subfamily Plexaurellinae to family level. Finally, based on examination of types, we propose the synonymy between Pseudoplexaura crucis and Plexaurella tenuis under Pseudoplexaura tenuis new comb.

Molecular systematics of Thouarella (Octocorallia:Primnoidae) with the description of three new species from the Southern Ocean based on combined molecular and morphological evidence

Thouarella Gray, 1870, is one of the most speciose genera among gorgonians of the family Primnoidae (Cnidaria:Octocorallia:Anthozoa), being remarkably diverse in the Antarctic and sub-Antarctic seafloor. However, their diversity in the Southern Ocean is likely underestimated. Phylogenetic analyses of mitochondrial and nuclear DNA markers were integrated with species delimitation approaches as well as morphological colonial and polyps features and skeletal SEM examinations to describe and illustrate three new species within Thouarella, from the Weddell Sea, Southern Ocean: T. amundseni sp. nov., T. dolichoespinosa sp. nov. and T. pseudoislai sp. nov. Our species delimitation results suggest, for the first time, the potential presence of Antarctic and sub-Antarctic cryptic species of primnoids, based on the likely presence of sibling species within T. undulata and T. crenelata. With the three new species here described, the global diversity of Thouarella has increased to 41 species, 15 of which are endemic to the Antarctic and sub-Antarctic waters. Consequently, our results provide new steps for uncovering the shelf benthonic macrofauna’s hidden diversity in the Southern Ocean. Finally, we recommend using an integrative taxonomic framework in this group of organisms and species delimitation approaches because the distinctions between some Thouarella species based only on a superficial examination of their macro- and micromorphological features is, in many cases, limited.

Speciation-by-depth on coral reefs: Sympatric divergence with gene flow or cryptic transient isolation?

The distributions of many sister species in the sea overlap geographically but are partitioned along depth gradients. The genetic changes leading to depth segregation may evolve in geographic isolation as a prerequisite to coexistence or may emerge during primary divergence leading to new species. These alternatives can now be distinguished via the power endowed by the thousands of scorable loci provided by second-generation sequence data. Here, we revisit the case of two depth-segregated, genetically isolated ecotypes of the nominal Caribbean candelabrum coral Eunicea flexuosa. Previous analyses based on a handful of markers could not distinguish between models of genetic exchange after a period of isolation (consistent with secondary contact) and divergence with gene flow (consistent with primary divergence). Analyses of the history of isolation, genetic exchange and population size based on 15,640 new SNP markers derived from RNAseq data best support models where divergence began 800K BP and include epochs of divergence with gene flow, but with an intermediate period of transient isolation. Results also supported the previous conclusion that recent exchange between the ecotypes occurs asymmetrically from the Shallow lineage to the Deep. Parallel analyses of data from two other corals with depth-segregated populations (Agaricia fragilis and Pocillopora damicornis) suggest divergence leading to depth-segregated populations may begin with a period of symmetric exchange, but that an epoch of population isolation precedes more complete isolation marked by asymmetric introgression. Thus, while divergence-with-gene flow may account for much of the differentiation that separates closely related, depth-segregated species, it remains to be seen whether any critical steps in the speciation process only occur when populations are isolated.

Host-symbiont coevolution, cryptic structure, and bleaching susceptibility, in a coral species complex (Scleractinia; Poritidae)

The 'species' is a key concept for conservation and evolutionary biology, yet the lines between population and species-level variation are often blurred, especially for corals. The 'Porites lobata species complex' consists of branching and mounding corals that form reefs across the Pacific. We used reduced representation meta-genomic sequencing to examine genetic relationships within this species complex and to identify candidate loci associated with colony morphology, cryptic genetic structure, and apparent bleaching susceptibility. We compared existing Porites data with bleached and unbleached colonies of the branching coral P. compressa collected in Kāne'ohe Bay Hawai'i during the 2015 coral bleaching event. Loci that mapped to coral, symbiont, and microbial references revealed genetic structure consistent with recent host-symbiont co-evolution. Cryptic genetic clades were resolved that previous work has associated with distance from shore, but no genetic structure was associated with bleaching. We identified many candidate loci associated with morphospecies, including candidate host and symbiont loci with fixed differences between branching and mounding corals. We also found many loci associated with cryptic genetic structure, yet relatively few loci associated with bleaching. Recent host-symbiont co-evolution and rapid diversification suggests that variation and therefore the capacity of these corals to adapt may be underappreciated.

When morphometry meets taxonomy: morphological variation and species boundaries in Proboscoida (Cnidaria: Hydrozoa)

Species delimitation in marine taxa is often problematic given large intraspecific variation. Based on extensive, recently published genetic sampling from specimens of the hydrozoan families Campanulariidae, Clytiidae and Obeliidae, we evaluate morphological variation in this group, correlating morphometric and phylogenetic patterns for species delimitation. Several species of Campanulariidae are confidently delimited based on differences in size (e.g. Bonneviella species, Tulpa tulipifera and Rhizocaulus verticillatus), while others are re-identified and corroborated based on differences in perisarc thickness (e.g. Silicularia rosea, Orthopyxis and Campanularia species). In Clytiidae, the length and diameter of hydrothecae, height of hydrothecal cusps and perisarc thickness delimit the species Clytia linearis, C. elsaeoswaldae and C. noliformis from others. However, few characters reliably differentiate the clades associated with the nominal species C. gracilis and C. hemisphaerica. In Obeliidae, Obelia geniculata is distinctive in its higher perisarc thickness, and corroborated as a widely distributed species. Obelia longissima and clades refered to O. dichotoma are subtly distinguished, showing a few differences in size and branching of colonies. The taxonomic implications of these results are discussed. With a few exceptions, species can be delimited based on morphometric patterns, once morphological variation is compared.

Ocean warming is the key filter for successful colonization of the migrant octocoral Melithaea erythraea (Ehrenberg, 1834) in the Eastern Mediterranean Sea

Climate, which sets broad limits for migrating species, is considered a key filter to species migration between contrasting marine environments. The Southeast Mediterranean Sea (SEMS) is one of the regions where ocean temperatures are rising the fastest under recent climate change. Also, it is the most vulnerable marine region to species introductions. Here, we explore the factors which enabled the colonization of the endemic Red Sea octocoral Melithaea erythraea (Ehrenberg, 1834) along the SEMS coast, using sclerite oxygen and carbon stable isotope composition (δ ¹⁸O_SC and δ ¹³C_SC), morphology, and crystallography. The unique conditions presented by the SEMS include a greater temperature range (∼15 °C) and ultra-oligotrophy, and these are reflected by the lower δ ¹³C_SCvalues. This is indicative of a larger metabolic carbon intake during calcification, as well as an increase in crystal size, a decrease of octocoral wart density and thickness of the migrating octocoral sclerites compared to the Red Sea samples. This suggests increased stress conditions, affecting sclerite deposition of the SEMS migrating octocoral. The δ ¹⁸Osc range of the migrating M. erythraea indicates a preference for warm water sclerite deposition, similar to the native depositional temperature range of 21-28 °C. These findings are associated with the observed increase of minimum temperatures in winter for this region, at a rate of 0.35 ± 0.27 °C decade^-1 over the last 30 years, and thus the region is becoming more hospitable to the Indo-Pacific M. erythraea. This study shows a clear case study of "tropicalization" of the Mediterranean Sea due to recent warming.

Genomic signatures of sympatric speciation with historical and contemporary gene flow in a tropical anthozoan (Hexacorallia: Actiniaria)

Sympatric diversification is recognized to have played an important role in the evolution of biodiversity. However, an in situ sympatric origin for codistributed taxa is difficult to demonstrate because different evolutionary processes can lead to similar biogeographic outcomes, especially in ecosystems that can readily facilitate secondary contact due to a lack of hard barriers to dispersal. Here we use a genomic (ddRADseq), model-based approach to delimit a species complex of tropical sea anemones that are codistributed on coral reefs throughout the Tropical Western Atlantic. We use coalescent simulations in fastsimcoal2 and ordinary differential equations in Moments to test competing diversification scenarios that span the allopatric-sympatric continuum. Our results suggest that the corkscrew sea anemone Bartholomea annulata is a cryptic species complex whose members are codistributed throughout their range. Simulation and model selection analyses from both approaches suggest these lineages experienced historical and contemporary gene flow, supporting a sympatric origin, but an alternative secondary contact model receives appreciable model support in fastsimcoal2. Leveraging the genome of the closely related Exaiptasia diaphana, we identify five loci under divergent selection between cryptic B. annulata lineages that fall within mRNA transcripts or CDS regions. Our study provides a rare empirical, genomic example of sympatric speciation in a tropical anthozoan and the first range-wide molecular study of a tropical sea anemone, underscoring that anemone diversity is under-described in the tropics, and highlighting the need for additional systematic studies into these ecologically and economically important species.

Plasticity in Three-Dimensional Geometry of Branching Corals Along a Cross-Shelf Gradient

Scleractinian corals often exhibit high levels of morphological plasticity, which is potentially important in enabling individual species to occupy benthic spaces across a wide range of environmental gradients. This study tested for differences in the three-dimensional (3D) geometry of three branching corals, Acropora nasuta, Pocillopora spp. and Stylophora pistillata among inner-, mid- and outer-shelf reefs in the central Great Barrier Reef, Australia. Important attributes of coral morphology (e.g., surface area to volume ratio) were expected to vary linearly across the shelf in accordance with marked gradients in environmental conditions, but instead, we detected non-linear trends in the colony structure of A. nasuta and Pocillopora spp. The surface area to volume ratio of both A. nasuta and Pocillopora spp. was highest at mid-shelf locations, (reflecting higher colony complexity) and was significantly lower at both inner-shelf and outer-shelf reefs. The branching structure of these corals was also far more tightly packed at inner-shelf and outer-shelf reefs, compared to mid-shelf reefs. Apparent declines in complexity and inter-branch spacing at inner and outer-shelf reefs (compared to conspecifics from mid-shelf reefs) may reflect changes driven by gradients of sedimentation and hydrodynamics. The generality and explanations of observed patterns warrant further investigation, which is very feasible using the 3D-photogrammetry techniques used in this study.

Molecular assessment of Pocillopora verrucosa (Scleractinia; Pocilloporidae) distribution along a depth gradient in Ludao, Taiwan

It can be challenging to identify scleractinian corals from the genus Pocillopora Lamarck 1816 in the field because of their large range of inter- and intra-specific morphological variation that co-occur with changes in the physical environment. This task is made more arduous in the context of a depth gradient, where light and water current could greatly affect the morphology of the corallum. Pocillopora verrucosa (Ellis & Solander 1786) in Taiwan was previously reported exclusively from shallow waters (<10 m in depth), but a recent observation of this species in the mesophotic zone (>40 m in depth) questions this bathymetric distribution. We used the mitochondrial open reading frame and the histone 3 molecular markers to investigate the vertical and horizontal spatial distribution of P. verrucosa around Ludao (Green Island), Taiwan. We genotyped 101 P. verrucosa-like colonies collected from four depth zones, ranging from 7 to 45 m, at three sites around the island. Of the 101 colonies sampled, 85 were genotyped as P. verrucosa, 15 as P. meandrina, and one specimen as an undescribed Pocillopora species. P. verrucosa was found at all depths, while P. meandrina and the undescribed Pocillopora specimen were limited to 15 m depth. P. verrucosa has a large bathymetric distribution around Ludao and could benefit from the refuge that the mesophotic zone offers. This study illustrates the difficulty of identifying Pocillopora corals in the field and emphasizes the relevance of molecular taxonomy as an important and complementary tool to traditional taxonomy for clarifying vertical and horizontal species distribution. Our results also illustrate the need in conservation biology to target species genetic diversity rather than just species diversity.

Spatial variation in the morphological traits of Pocillopora verrucosa along a depth gradient in Taiwan

Pocillopora verrucosa is a widely distributed depth-generalist coral that presents plasticity in its skeletal macro- and microstructure in response to environmental gradients. Light and water movement, which covary with depth, are the main environmental drivers of morphological plasticity in this genus; however, assessing environmentally-induced plasticity may be confounded by the extent of interspecific variation in Pocillopora. We examine the morphology of 8 typed P. verrucosa specimens collected along a depth gradient ranging from 7 to 45 meters and comprising 3 sites throughout Ludao, Taiwan. We measured 36 morphological characters, 14 which are novel, in 3 regions on the corallum-the apex, branch and base-in order to quantify their relationship to site and depth. We found significant correlation between depth and 19 morphological characters, notably branch verruca area, branch verruca height, base verruca spacing, base spinule length, and branch corallite area. 60% of microstructural characters and 25% of macrostructural characters showed a correlative relation to depth, suggesting that depth acclimatization is manifested primarily at the microstructural level. Canonical discriminant analysis of all morphometric characters by depth supports clustering into 3 groups: an overlapping 7m and 15m group, a 23-30m group, and a 38-45m group. Canonical discriminant analysis by site supports clustering into low- and high-current sites, differentiated primarily by branch septa width, base septa width, pre-terminal branch width, terminal branch maximum length, and terminal branch minimum length. We conclude that distinctive patterns of morphological variation in mesophotic specimens of P. verrucosa could reflect the effects of abiotic parameters such as light and water flow. Elucidating the mechanisms behind the morphological changes that occur in response to environmental gradients can help clarify the role that physiological plasticity plays in the acclimatization of corals to the unique environmental settings of mesophotic coral ecosystems.

A case of modular phenotypic plasticity in the depth gradient for the gorgonian coral Antillogorgia bipinnata (Cnidaria: Octocorallia)

BACKGROUND

Phenotypic plasticity, as a phenotypic response induced by the environment, has been proposed as a key factor in the evolutionary history of corals. A significant number of octocoral species show high phenotypic variation, exhibiting a strong overlap in intra- and inter-specific morphologic variation. This is the case of the gorgonian octocoral Antillogorgia bipinnata (Verrill 1864), which shows three polyphyletic morphotypes along a bathymetric gradient. This research tested the phenotypic plasticity of modular traits in A. bipinnata with a reciprocal transplant experiment involving 256 explants from two morphotypes in two locations and at two depths. Vertical and horizontal length and number of new branches were compared 13 weeks following transplant. The data were analysed with a linear mixed-effects model and a graphic approach by reaction norms.

RESULTS

At the end of the experiment, 91.8% of explants survived. Lower vertical and horizontal growth rates and lower branch promotion were found for deep environments compared to shallow environments. The overall variation behaved similarly to the performance of native transplants. In particular, promotion of new branches showed variance mainly due to a phenotypic plastic effect.

CONCLUSIONS

Globally, environmental and genotypic effects explain the variation of the assessed traits. Survival rates besides plastic responses suggest an intermediate scenario between adaptive plasticity and local adaptation that may drive a potential process of adaptive divergence along depth cline in A. bipinnata.

Evolutionary Developmental Biology (Evo-Devo) Research in Latin America

Famous for its blind cavefish and Darwin's finches, Latin America is home to some of the richest biodiversity hotspots of our planet. The Latin American fauna and flora inspired and captivated naturalists from the nineteenth and twentieth centuries, including such notable pioneers such as Fritz Müller, Florentino Ameghino, and Léon Croizat who made a significant contribution to the study of embryology and evolutionary thinking. But, what are the historical and present contributions of the Latin American scientific community to Evo-Devo? Here, we provide the first comprehensive overview of the Evo-Devo laboratories based in Latin America and describe current lines of research based on endemic species, focusing on body plans and patterning, systematics, physiology, computational modeling approaches, ecology, and domestication. Literature searches reveal that Evo-Devo in Latin America is still in its early days; while showing encouraging indicators of productivity, it has not stabilized yet, because it relies on few and sparsely distributed laboratories. Coping with the rapid changes in national scientific policies and contributing to solve social and health issues specific to each region are among the main challenges faced by Latin American researchers. The 2015 inaugural meeting of the Pan-American Society for Evolutionary Developmental Biology played a pivotal role in bringing together Latin American researchers eager to initiate and consolidate regional and worldwide collaborative networks. Such networks will undoubtedly advance research on the extremely high genetic and phenotypic biodiversity of Latin America, bound to be an almost infinite source of amazement and fascinating findings for the Evo-Devo community.

Limited Genetic Connectivity between Gorgonian Morphotypes along a Depth Gradient

Gorgonian species show a high morphological variability in relation to the environment in which they live. In coastal areas, parameters such as temperature, light, currents, and food availability vary significantly with depth, potentially affecting morphology of the colonies and the structure of the populations, as well as their connectivity patterns. In tropical seas, the existence of connectivity between shallow and deep populations supported the hypothesis that the deep coral reefs could potentially act as (reproductive) refugia fostering re-colonization of shallow areas after mortality events. Moreover, this hypothesis is not so clear accepted in temperate seas. Eunicella singularis is one of the most common gorgonian species in Northwestern Mediterranean Sea, playing an important role as ecosystem engineer by providing biomass and complexity to the coralligenous habitats. It has a wide bathymetric distribution ranging from about 10 m to 100 m. Two depth-related morphotypes have been identified, differing in colony morphology, sclerite size and shape, and occurrence of symbiotic algae, but not in mitochondrial DNA haplotypes. In the present study the genetic structure of E. singularis populations along a horizontal and bathymetric gradient was assessed using microsatellites and ITS1 sequences. Restricted gene flow was found at 30-40 m depth between the two Eunicella morphotypes. Conversely, no genetic structuring has been found among shallow water populations within a spatial scale of ten kilometers. The break in gene flow between shallow and deep populations contributes to explain the morphological variability observed at different depths. Moreover, the limited vertical connectivity hinted that the refugia hypothesis does not apply to E. singularis. Re-colonization of shallow water populations, occasionally affected by mass mortality events, should then be mainly fueled by larvae from other shallow water populations.

Home Bodies and Wanderers: Sympatric Lineages of the Deep-Sea Black Coral Leiopathes glaberrima

Colonial corals occur in a wide range of marine benthic habitats from the shallows to the deep ocean, often defining the structure of their local community. The black coral Leiopathes glaberrima is a long-lived foundation species occurring on carbonate outcrops in the Northern Gulf of Mexico (GoM). Multiple color morphs of L. glaberrima grow sympatrically in the region. Morphological, mitochondrial and nuclear ribosomal markers supported the hypothesis that color morphs constituted a single biological species and that colonies, regardless of color, were somewhat genetically differentiated east and west of the Mississippi Canyon. Ten microsatellite loci were used to determine finer-scale population genetic structure and reproductive characteristics. Gene flow was disrupted between and within two nearby (distance = 36.4 km) hardground sites and two sympatric microsatellite lineages, which might constitute cryptic species, were recovered. Lineage one was outbred and found in all sampled locations (N = 5) across 765.6 km in the Northern Gulf of Mexico. Lineage two was inbred, reproducing predominantly by fragmentation, and restricted to sites around Viosca Knoll. In these sites the lineages and the color phenotypes occurred in different microhabitats, and models of maximum entropy suggested that depth and slope influence the distribution of the color phenotypes within the Vioska Knolls. We conclude that L. glaberrima is phenotypically plastic with a mixed reproductive strategy in the Northern GoM. Such strategy might enable this long-lived species to balance local recruitment with occasional long-distance dispersal to colonize new sites in an environment where habitat is limited.

Environmental influences on the Indo-Pacific octocoral Isis hippuris Linnaeus 1758 (Alcyonacea: Isididae): genetic fixation or phenotypic plasticity?

As conspicuous modular components of benthic marine habitats, gorgonian (sea fan) octocorals have perplexed taxonomists for centuries through their shear diversity, particularly throughout the Indo–Pacific. Phenotypic incongruence within and between seemingly unitary lineages across contrasting environments can provide the raw material to investigate processes of disruptive selection. Two distinct phenotypes of the Isidid Isis hippurisLinnaeus, 1758 partition between differing reef environments: long-branched bushy colonies on degraded reefs, and short-branched multi/planar colonies on healthy reefs within the Wakatobi Marine National Park (WMNP), Indonesia. Multivariate analyses reveal phenotypic traits between morphotypes were likely integrated primarily at the colony level with increased polyp density and consistently smaller sclerite dimensions at the degraded site. Sediment load and turbidity, hence light availability, primarily influenced phenotypic differences between the two sites. This distinct morphological dissimilarity between the two sites is a reliable indicator of reef health; selection primarily acting on colony morphology, porosity through branching structure, as well as sclerite diversity and size. ITS2 sequence and predicted RNA secondary structure further revealed intraspecific variation between I. hippuris morphotypes relative to such environments (Φ_ST = 0.7683, P < 0.001). This evidence suggests—but does not confirm—that I. hippuris morphotypes within the WMNP are two separate species; however, to what extent and taxonomic assignment requires further investigation across its full geographic distribution. Incongruence between colonies present in the WMNP with tenuously described Isis alternatives (Isis reticulataNutting, 1910, Isis minorbrachyblastaZou, Huang & Wang, 1991), questions the validity of such assignments. Furthermore, phylogenetic analyses confirm early taxonomic suggestion that the characteristic jointed axis of the Isididae is in fact a convergent trait. Thus the polyphyletic nature of the Isididae lies in its type species I. hippuris, being unrelated to the rest of its family members.

Genetic diversity, paraphyly and incomplete lineage sorting of mtDNA, ITS2 and microsatellite flanking region in closely related Heliopora species (Octocorallia)

Examining genetic diversity and lineage sorting of different genes in closely related species provide useful information for phylogenetic analyses and ultimately for understanding the origins of biodiversity. In this study, we examined inter- and intraspecific genetic variation in internal transcribed spacer 2 (ITS2), partial mitochondrial gene (mtMutS), and nuclear microsatellite flanking region in two closely related octocoral species (Heliopora coerulea, HC-A and HC-B). These species were recently identified in a population genetic study using microsatellite markers. The two species have different reproductive timing, which ecologically promotes lineage sorting. In this study, we examined whether species boundaries could be detected by the commonly used nuclear ITS2 and mtMutS, as well as by possibly neutral microsatellite flanking sequences. Haplotype network analysis of microsatellite flanking region revealed that a possible ancestral haplotype was still shared between the two species, indicating on-going lineage sorting. Haplotype network analysis of ITS2 and microsatellite flanking region revealed shared haplotypes between the two lineages. The two species shared fewer ITS2 sequences than microsatellite flanking region sequences. The almost fixed point mutation at the tip of helix 3 of ITS2 was not associated with the secondary structure or compensatory base changes (CBCs). The phylogenetic tree of ITS2 showed paraphyly and that of the microsatellite flanking region indicated that lineage sorting for the two species may be incomplete. Much higher intra- and inter-individual variation of ITS2 was observed in HC-B than that in HC-A, highlighting the importance of examining ITS2 from multiple individuals to estimate genetic diversity. The mitochondrial mtMutS gene sequences from 39 individuals, including both species collected from Japan and Taiwan, showed no variation because of slow rates of mitochondrial nucleotide substitution. This study suggests caution is warranted when reciprocal monophyly in a phylogenetic tree is used as the criterion for delimiting closely related octocoral species based on ITS2 or mtMtuS sequences. Detection of boundaries between closely related species requires multi-locus analysis, such as genetic admixture analysis using multiple individuals.

Molecular and Morphological Species Boundaries in the Gorgonian Octocoral Genus Pterogorgia (Octocorallia: Gorgoniidae)

Most gorgonian octocoral species are described using diagnostic characteristics of their sclerites (microscopic skeletal components). Species in the genus Pterogorgia, however, are separated primarily by differences in their calyx and branch morphology. Specimens of a morphologically unusual Pterogorgia collected from Saba Bank in the NE Caribbean Sea were found with calyx morphology similar to P. citrina and branch morphology similar to P. guadalupensis. In order to test morphological species boundaries, and the validity of calyx and branch morphology as systematic characters, a phylogenetic analysis was undertaken utilizing partial gene fragments of three mitochondrial (mtMutS, cytochrome b, and igr4; 726bp total) and two nuclear (ITS2, 166bp; and SRP54 intron, 143bp) loci. The datasets for nuclear and mitochondrial loci contained few phylogenetically informative sites, and tree topologies did not resolve any of the morphological species as monophyletic groups. Instead, the mitochondrial loci and SRP54 each recovered two clades but were slightly incongruent, with a few individuals of P. guadalupensis represented in both clades with SRP54. A concatenated dataset of these loci grouped all P. anceps and P. guadalupensis in a clade, and P. citrina and the Pterogorgia sp. from Saba Bank in a sister clade, but with minimal variation/resolution within each clade. However, in common with other octocoral taxa, the limited genetic variation may not have been able to resolve whether branch variation represents intraspecific variation or separate species. Therefore, these results suggest that there are at least two phylogenetic lineages of Pterogorgia at the species level, and the atypical Pterogorgia sp. may represent an unusual morphotype of P. citrina, possibly endemic to Saba Bank. Branch morphology does not appear to be a reliable morphological character to differentiate Pterogorgia species (e.g., branches "flat" or "3-4 edges" in P. guadalupensis and P. anceps, respectively), and a re-evaluation of species-level characters (e.g., sclerites) is needed.

Octocoral Species Assembly and Coexistence in Caribbean Coral Reefs

BACKGROUND

What are the determinant factors of community assemblies in the most diverse ecosystem in the ocean? Coral reefs can be divided in continental (i.e., reefs that develop on the continental shelf, including siliciclastic reefs) and oceanic (i.e., far off the continental shelf, usually on volcanic substratum); whether or not these habitat differences impose community-wide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown.

METHODS

Studying Caribbean octocorals as model system, we determined the phylogenetic community structure in a coral reef community, making emphasis on species coexistence evidenced on trait evolution and environmental feedbacks. Forty-nine species represented in five families constituted the species pool from which a phylogenetic tree was reconstructed using mtDNA. We included data from 11 localities in the Western Caribbean (Colombia) including most reef types. To test diversity-environment and phenotype-environment relationships, phylogenetic community structure and trait evolution we carried out comparative analyses implementing ecological and evolutionary approaches.

RESULTS

Phylogenetic inferences suggest clustering of oceanic reefs (e.g., atolls) contrasting with phylogenetic overdispersion of continental reefs (e.g., reefs banks). Additionally, atolls and barrier reefs had the highest species diversity (Shannon index) whereas phylogenetic diversity was higher in reef banks. The discriminant component analysis supported this differentiation between oceanic and continental reefs, where continental octocoral species tend to have greater calyx apertures, thicker branches, prominent calyces and azooxanthellate species. This analysis also indicated a clear separation between the slope and the remaining habitats, caused by the presence or absence of Symbiodinium. K statistic analysis showed that this trait is conserved as well as the branch shape.

DISCUSSION

There was strong octocoral community structure with opposite diversity and composition patterns between oceanic and continental reefs. Even habitats with similar depths and overall environmental conditions did not share similar communities between oceanic and continental reefs. This indicates a strong regional influence over the local communities, probably due to water transparency differences between major reef types, i.e., oceanic vs. continental shelf-neritic. This was supported by contrasting patterns found in morphology, composition and evolutionary history of the species between atolls and reef banks.

Morphological and genetic diversity of Briareum (Anthozoa: Octocorallia) from the Ryukyu Archipelago, Japan

The primary problem hindering the study of octocorals is the disordered situation regarding their taxonomy, chiefly caused by insufficient knowledge of valid morphological taxonomic characters. Briareum is an octocoral genus found in the Atlantic and Pacific in shallow tropical and subtropical waters, and occurs in both encrusting and branching colony forms. Their simple morphology and morphological plasticity have hindered taxonomic understanding of this genus. In this study three morphologically distinct types (= type-1, -2, and -3) of Briareum from the Ryukyu Archipelago and their genetic diversity were examined. Colony, anthostele morphology, and sclerite length were examined for each type. Four molecular markers (mitochondrial cytochrome c oxidase subunit 1, mitochondrial mismatch repair gene, nuclear 18S ribosomal DNA, internal transcribed spacer 2 (ITS2)) were used to evaluate molecular phylogenetic status of these variations. Although one morphological type ("deep" small colonies, = type-3) showed small differences in nuclear ITS2 sequences compared to the other two types, the remaining types had identical sequences for all molecular markers examined. The results suggest extremely low genetic diversity despite highly variable morphology of Briareum species in Okinawa. Nevertheless, considering the distribution patterns and discontinuous morphology of type-3 compared to the other two morphotypes, genetic isolation of type-3 is plausible. In Briareum, small variances in nuclear ITS2 sequences of type-3 may have much more importance than in molecular phylogenies of other octocorals. Further phylogenetic investigations and comparison with Briareum specimens from other regions are necessary to conclusively taxonomically identify the three types.

Potential for adaptive evolution at species range margins: contrasting interactions between red coral populations and their environment in a changing ocean

Studying population-by-environment interactions (PEIs) at species range margins offers the opportunity to characterize the responses of populations facing an extreme regime of selection, as expected due to global change. Nevertheless, the importance of these marginal populations as putative reservoirs of adaptive genetic variation has scarcely been considered in conservation biology. This is particularly true in marine ecosystems for which the deep refugia hypothesis proposes that disturbed shallow and marginal populations of a given species can be replenished by mesophotic ones. This hypothesis therefore assumes that identical PEIs exist between populations, neglecting the potential for adaptation at species range margins. Here, we combine reciprocal transplant and common garden experiments with population genetics analyses to decipher the PEIs in the red coral, Corallium rubrum. Our analyses reveal partially contrasting PEIs between shallow and mesophotic populations separated by approximately one hundred meters, suggesting that red coral populations may potentially be locally adapted to their environment. Based on the effective population size and connectivity analyses, we posit that genetic drift may be more important than gene flow in the adaptation of the red coral. We further investigate how adaptive divergence could impact population viability in the context of warming and demonstrate differential phenotypic buffering capacities against thermal stress. Our study questions the relevance of the deep refugia hypothesis and highlights the conservation value of marginal populations as a putative reservoir of adaptive genetic polymorphism.

Vectored dispersal of Symbiodinium by larvae of a Caribbean gorgonian octocoral

The ability of coral reefs to recover from natural and anthropogenic disturbance is difficult to predict, in part due to uncertainty regarding the dispersal capabilities and connectivity of their reef inhabitants. We developed microsatellite markers for the broadcast spawning gorgonian octocoral Eunicea (Plexaura) flexuosa (four markers) and its dinoflagellate symbiont, Symbiodinium B1 (five markers), and used them to assess genetic connectivity, specificity and directionality of gene flow among sites in Florida, Panama, Saba and the Dominican Republic. Bayesian analyses found that most E. flexuosa from the Florida reef tract, Saba and the Dominican Republic were strongly differentiated from many E. flexuosa in Panama, with the exception of five colonies from Key West that clustered with colonies from Panama. In contrast, Symbiodinium B1 was more highly structured. At least seven populations were detected that showed patterns of isolation by distance. The symbionts in the five unusual Key West colonies also clustered with symbionts from Panama, suggesting these colonies are the result of long-distance dispersal. Migration rate tests indicated a weak signal of northward immigration from the Panama population into the lower Florida Keys. As E. flexuosa clonemates only rarely associated with the same Symbiodinium B1 genotype (and vice versa), these data suggest a dynamic host-symbiont relationship in which E. flexuosa is relatively well dispersed but likely acquires Symbiodinium B1 from highly structured natal areas prior to dispersal. Once vectored by host larvae, these symbionts may then spread through the local population, and/or host colonies may acquire different local symbiont genotypes over time.

Long prereproductive selection and divergence by depth in a Caribbean candelabrum coral

Long-lived corals, the foundation of modern reefs, often follow ecological gradients, so that populations or sister species segregate by habitat. Adaptive divergence maintains sympatric congeners after secondary contact or may even generate species by natural selection in the face of gene flow. Such ecological divergence, initially between alternative phenotypes within populations, may be aided by immigrant inviability, especially when a long period separates larval dispersal and the onset of reproduction, during which selection can sort lineages to match different habitats. Here, we evaluate the strength of one ecological factor (depth) to isolate populations by comparing the genes and morphologies of pairs of depth-segregated populations of the candelabrum coral Eunicea flexuosa across the Caribbean. Eunicea is endemic to the Caribbean and all sister species co-occur. Eunicea flexuosa is widespread both geographically and across reef habitats. Our genetic analysis revealed two depth-segregated lineages. Field survivorship data, combined with estimates of selection coefficients based on transplant experiments, suggest that selection is strong enough to segregate these two lineages. Genetic exchange between the Shallow and Deep lineages occurred either immediately after divergence or the two have diverged with gene flow. Migration occurs asymmetrically from the Shallow to Deep lineage. Limited recruitment to reproductive age, even under weak annual selection advantage, is sufficient to generate habitat segregation because of the cumulative prolonged prereproductive selection. Ecological factors associated with depth can act as filters generating strong barriers to gene flow, altering morphologies, and contributing to the potential for speciation in the sea.

DNA variation in the phenotypically-diverse brown alga Saccharina japonica

BACKGROUND

Saccharina japonica (Areschoug) Lane, Mayes, Druehl et Saunders is an economically important and highly morphologically variable brown alga inhabiting the northwest Pacific marine waters. On the basis of nuclear (ITS), plastid (rbcLS) and mitochondrial (COI) DNA sequence data, we have analyzed the genetic composition of typical Saccharina japonica (TYP) and its two common morphological varieties, known as the "longipes" (LON) and "shallow-water" (SHA) forms seeking to clarify their taxonomical status and to evaluate the possibility of cryptic species within S. japonica.

RESULTS

The data show that the TYP and LON forms are very similar genetically in spite of drastic differences in morphology, life history traits, and ecological preferences. Both, however, are genetically quite different from the SHA form. The two Saccharina lineages are distinguished by 109 fixed single nucleotide differences as well as by seven fixed length polymorphisms (based on a 4,286 bp concatenated dataset that includes three gene regions). The GenBank database reveals a close affinity of the TYP and LON forms to S. japonica and the SHA form to S. cichorioides. The three gene markers used in the present work have different sensitivity for the algal species identification. COI gene was the most discriminant gene marker. However, we have detected instances of interspecific COI recombination reflecting putative historical hybridization events between distantly related algal lineages. The recombinant sequences show highly contrasted level of divergence in the 5'- and 3'- regions of the gene, leading to significantly different tree topologies depending on the gene segment (5'- or 3'-) used for tree reconstruction. Consequently, the 5'-COI "barcoding" region (~ 650 bp) can be misleading for identification purposes, at least in the case of algal species that might have experienced historical hybridization events.

CONCLUSION

Taking into account the potential roles of phenotypic plasticity in evolution, we conclude that the TYP and LON forms represent examples of algae phenotypic diversification that enables successful adaptation to contrasting shallow- and deep-water marine environments, while the SHA form is very similar to S. cichorioides and should be considered a different species. Practical applications for algal management and conservation are briefly considered.

Deep-sea origin and in-situ diversification of chrysogorgiid octocorals

The diversity, ubiquity and prevalence in deep waters of the octocoral family Chrysogorgiidae Verrill, 1883 make it noteworthy as a model system to study radiation and diversification in the deep sea. Here we provide the first comprehensive phylogenetic analysis of the Chrysogorgiidae, and compare phylogeny and depth distribution. Phylogenetic relationships among 10 of 14 currently-described Chrysogorgiidae genera were inferred based on mitochondrial (mtMutS, cox1) and nuclear (18S) markers. Bathymetric distribution was estimated from multiple sources, including museum records, a literature review, and our own sampling records (985 stations, 2345 specimens). Genetic analyses suggest that the Chrysogorgiidae as currently described is a polyphyletic family. Shallow-water genera, and two of eight deep-water genera, appear more closely related to other octocoral families than to the remainder of the monophyletic, deep-water chrysogorgiid genera. Monophyletic chrysogorgiids are composed of strictly (Iridogorgia Verrill, 1883, Metallogorgia Versluys, 1902, Radicipes Stearns, 1883, Pseudochrysogorgia Pante & France, 2010) and predominantly (Chrysogorgia Duchassaing & Michelotti, 1864) deep-sea genera that diversified in situ. This group is sister to gold corals (Primnoidae Milne Edwards, 1857) and deep-sea bamboo corals (Keratoisidinae Gray, 1870), whose diversity also peaks in the deep sea. Nine species of Chrysogorgia that were described from depths shallower than 200 m, and mtMutS haplotypes sequenced from specimens sampled as shallow as 101 m, suggest a shallow-water emergence of some Chrysogorgia species.