Morphological differences among three species of newly settled pocilloporid coral recruits

 Investigation of the life history of corals is hampered by an inability to identify early recruits. In this study, the pattern of formation and morphology of the juvenile skeletons of three laboratory-reared pocilloporids, Seriatopora hystrix, Stylophora pistillata and Pocillopora damicornis, were compared to determine whether they could be reliably distinguished. The pattern of skeleton formation, including the origin and structure of the septa, columella and corallite wall was similar in all species. Following the completion of the primary corallite wall after 4–5 days, these species could be identified by differences in the diameter of the primary corallite. The mean diameter (±SE) of each species differed markedly: S. hystrix 400 ± 2.7 μm, range 325–450 μm; S. pistillata 505 ± 3.5 μm, range 400–550 μm; P. damicornis 697 ± 7.5 μm, range 492–885 μm. Values for the primary corallite diameter overlapped in only 3% of samples, demonstrating the potential utility of this feature as a tool for classifying recruits obtained from the field. Accepted: 4 January 2000     

Functional Diversification within a Predatory Species Flock

Ecological speciation is well-known from adaptive radiations in cichlid fishes inhabiting lentic ecosystems throughout the African rift valley and Central America. Here, we investigate the ecological and morphological diversification of a recently discovered lotic predatory Neotropical cichlid species flock in subtropical South America. We document morphological and functional diversification using geometric morphometrics, stable C and N isotopes, stomach contents and character evolution. This species flock displays species-specific diets and skull and pharyngeal jaw morphology. Moreover, this lineage appears to have independently evolved away from piscivory multiple times and derived forms are highly specialized morphologically and functionally relative to ancestral states. Ecological speciation played a fundamental role in this radiation and our data reveal novel conditions of ecological speciation including a species flock that evolved: 1) in a piscivorous lineage, 2) under lotic conditions and 3) with pronounced morphological novelties, including hypertrophied lips that appear to have evolved rapidly.     

Speciation below ground: Tempo and mode of diversification in a radiation of endogean ground beetles

Dispersal is a critical factor determining the spatial scale of speciation, which is constrained by the ecological characteristics and distribution of a species’ habitat and the intrinsic traits of species. Endogean taxa are strongly affected by the unique qualities of the below‐ground environment and its effect on dispersal, and contrasting reports indicate either high dispersal capabilities favoured by small body size and mediated by passive mechanisms, or low dispersal due to restricted movement and confinement inside the soil. We studied a species‐rich endogean ground beetle lineage, Typhlocharina, including three genera and more than 60 species, as a model for the evolutionary biology of dispersal and speciation in the deep soil . A time‐calibrated molecular phylogeny generated from >400 individuals was used to delimit candidate species, to study the accumulation of lineages through space and time by species–area–age relationships and to determine the geographical structure of the diversification using the relationship between phylogenetic and geographic distances across the phylogeny. Our results indicated a small spatial scale of speciation in Typhlocharina and low dispersal capacity combined with sporadic long distance, presumably passive dispersal events that fuelled the speciation process. Analysis of lineage growth within Typhlocharina revealed a richness plateau correlated with the range of distribution of lineages, suggesting a long‐term species richness equilibrium mediated by density dependence through limits of habitat availability. The interplay of area‐ and age‐dependent processes ruling the lineage diversification in Typhlocharina may serve as a general model for the evolution of high species diversity in endogean mesofauna.     

The Time to Most Recent Common Ancestor Does Not (Usually) Approximate the Date of Divergence

With the advent of more sophisticated models and increase in computational power, an ever-growing amount of information can be extracted from DNA sequence data. In particular, recent advances have allowed researchers to estimate the date of historical events for a group of interest including time to most recent common ancestor (TMRCA), dates of specific nodes in a phylogeny, and the date of divergence or speciation date. Here I use coalescent simulations and re-analyze an empirical dataset to illustrate the importance of taxon sampling, in particular, on correctly estimating such dates. I show that TMRCA of representatives of a single taxon is often not the same as divergence date due to issues such as incomplete lineage sorting. Of critical importance is when estimating divergence or speciation dates a representative from a different taxonomic lineage must be included in the analysis. Without considering these issues, studies may incorrectly estimate the times at which historical events occurred, which has profound impacts within both research and applied (e.g., those related to public health) settings.     

Geographic isolation trumps coevolution as a driver of yucca and yucca moth diversification

Coevolution is thought to be especially important in diversification of obligate mutualistic interactions such as the one between yuccas and pollinating yucca moths. We took a three-step approach to examine if plant and pollinator speciation events were likely driven by coevolution. First, we tested whether there has been co-speciation between yuccas and pollinator yucca moths in the genus Tegeticula (Prodoxidae). Second, we tested whether co-speciation also occurred between yuccas and commensalistic yucca moths in the genus Prodoxus (Prodoxidae) in which reciprocal evolutionary change is unlikely. Finally, we examined the current range distributions of yuccas in relationship to pollinator speciation events to determine if plant and moth speciation events likely occurred in sympatry or allopatry. Co-speciation analyses of yuccas with their coexisting Tegeticula pollinator and commensalistic Prodoxus lineages demonstrated phylogenetic congruence between both groups of moths and yuccas, even though moth lineages differ in the type of interaction with yuccas. Furthermore, Yucca species within a lineage occur primarily in allopatry rather than sympatry. We conclude that biogeographic factors are the overriding force in plant and pollinator moth speciation and significant phylogenetic congruence between the moth and plant lineages is likely due to shared biogeography rather than coevolution.     

Evolution of the tribe Tropheini from Lake Tanganyika: synchronized explosive speciation producing multiple evolutionary parallelism

One of the most surprising outcomes of recent molecular studies on cichlid fishes of the three Great East African Lakes Victoria, Malawi and Tanganyika, was the stunning rapidity of speciation and cladogenesis at early stages of adaptive radiation. Despite their rapid pace, speciation events were so far intuitively assumed to proceed in a bifurcating and tree-like fashion, even if they could not be resolved by gene phylogenies due to a lack of resolution. On the basis of phylogenetic analyses of the Tropheini, a lineage of endemic rock-dwelling cichlid fishes from Lake Tanganyika, we suggest a pathway of explosive speciation that accounts for a non-bifurcating manner of cladogenesis. This pattern is likely to be the result of the contemporaneous origin of a multitude of founder populations in geographically isolated rock habitats among which gene flow was interrupted simultaneously by a major change of the lake habitat in the form of a rapid rise of the lake level. As a consequence, all new species arising from that vicariance event must exhibit almost equal genetic distances to each other, within the scope of genetic diversity of the founder population(s), even if the actual processes of subsequent speciation and eco-morphological diversification followed independent routes. Our phylogeny also suggests a high frequency of parallel evolution of equivalent trophic specialization in the Tropheini. This phenomenon seems to be an inherent feature of this pathway of speciation, due to the action of similar selective forces on the same set of species colonizing isolated habitats of the same type. Explosive speciation via synchronization of genetic divergence triggered by rapid environmental changes seems to be particularly likely to occur at advanced stages of adaptive radiation, when species are already adapted to particular habitats and have a reduced ability for dispersal.     

Divergence and hybridization in the desert plant Reaumuria soongarica

Speciation is widely accepted to be a complex and continuous process. Due to complicated evolutionary histories, desert plants are ideal model systems to understand the process of speciation along a continuum. Here, we elucidate the evolutionary history of Reaumuria soongarica (Pall.) Maxim., a typical desert plant that is wildly distributed across arid central Asia. Based on variation patterns present at nine nuclear loci in 325 individuals (representing 41 populations), we examined the demographic history, patterns of gene flow, and degree of ecological differentiation among wild R. soongarica. Our findings indicate that genetic divergence between the ancient western and eastern lineages of R. soongarica occurred approximately 0.714 Mya, probably due to the Kunlun–Yellow River tectonic movement and the Naynayxungla glaciation. Later, multiple hybridization events between the western and eastern lineages that took place between 0.287 and 0.543 Mya, and which might have been triggered by the asynchronous historical expansion of the western and eastern deserts, contributed to the formation of a hybrid northern lineage. Moreover, despite continuing gene flow into this population from its progenitors, the northern lineage maintained its genetic boundary by ecological differentiation. The northern lineage could be an incipient species, and provides an opportunity to study the continuous process of speciation. This study suggests that two opposite evolutionary forces, divergence and hybridization, coexisting in the continuous speciation of the desert plant R. soongarica in a short time. Moreover, we provide evidence that this continuous speciation process is affected by geological events, climatic change, and ecological differentiation.     

Sympatric Speciation in the Post “Modern Synthesis” Era of Evolutionary Biology

Sympatric speciation is among the most controversial and challenging concepts in evolution. There are a multitude of definitions of speciation alone, and when combined with the biogeographic concept of sympatric range overlap, consensus on what sympatric speciation is, whether it happens, and its importance, is even more difficult to achieve. Providing the basis upon which to define and judge sympatric speciation, the Modern Evolutionary Synthesis (Huxley in Evolution: the modern synthesis. MIT Press, Cambridge, 1942) led to the conclusion that sympatric speciation is an inconsequential process in the generation of species diversity. In the post Modern Synthesis era of evolutionary biology, the PCR revolution and associated accumulation of DNA sequence data from natural populations has led to a resurgence of interest in sympatric speciation, and more importantly, the role of natural selection in lineage diversification. Much effort is currently being devoted to elucidating the processes by which the constituents of an initially panmictic population can become reproductively isolated and evolve some level of reproductive incompatibility without the complete cessation of gene flow due to geographic barriers. The evolution of reproductive isolation solely due to natural selection is perhaps the most controversial manner by which sympatric speciation occurs, and it is that which we focus upon in this review. Mathematical model simulations indicate that even strict definitions of sympatric speciation are possible to satisfy, empirical data consistent with sympatric divergence are accumulating, but irrefutable evidence of sympatric speciation in natural populations remains elusive. Genomic investigations are advancing our ability to identify genetic patterns caused by natural selection, thereby advancing our understanding of the power of natural selection relative to gene flow. Overall, sympatric lineage divergence, especially at the sub-species level, may have led to a substantial portion of biodiversity.     

Examining the Role of Effective Population Size on Mitochondrial and Multilocus Divergence Time Discordance in a Songbird

Estimates of speciation times are subject to a number of potential errors. One source of bias is that effective population size (N_e) has been shown to influence substitution rates. This issue is of particular interest for phylogeographic studies because population sizes can vary dramatically among genetically structured populations across species’ ranges. In this study, we used multilocus data to examine temporal phylogeographic patterns in a widespread North American songbird, the Northern Cardinal (Cardinalis cardinalis). Species tree estimation indicated that the phylogeographic structure of C. cardinalis was comprised of four well-supported mainland lineages with large population sizes (large N_e) and two island lineages comprised of much smaller populations (small N_e). We inferred speciation times from mtDNA and multilocus data and found there was discordance between events that represented island-mainland divergences, whereas both estimates were similar for divergences among mainland lineages. We performed coalescent simulations and found that the difference in speciation times could be attributed to stochasticity for a recently diverged island lineage. However, the magnitude of the change between speciation times estimated from mtDNA and multilocus data of an older island lineage was substantially greater than predicted by coalescent simulations. For this divergence, we found the discordance in time estimates was due to a substantial increase in the mtDNA substitution rate in the small island population. These findings indicate that in phylogeographic studies the relative tempo of evolution between mtDNA and nuclear DNA can become highly discordant in small populations.     

Adaptive speciation when assortative mating is based on female preference for male marker traits

Adaptive speciation occurs when frequency-dependent ecological interactions generate conditions of disruptive selection to which lineage splitting is an adaptive response. Under such selective conditions, evolution of assortative mating mechanisms enables the break-up of the ancestral lineage into diverging and reproductively isolated descendent species. Extending previous studies, I investigate models of adaptive speciation due to the evolution of indirect assortative mating that is based on three different mating traits: the degree of assortativity, a female preference trait and a male marker trait. For speciation to occur, linkage disequilibria between different mating traits, e.g. between female preference and male marker traits, as well as between mating traits and the ecological trait, must evolve. This can lead to novel speciation scenarios, e.g. when reproductive isolation is generated by a splitting in the degree of assortativeness, with one of the emerging lineages mating assortatively, and the other one disassortatively. I investigate the effects of variation in various model parameters on the likelihood of speciation, as well as robustness of speciation to introducing costs of assortative mating. Even though in the models presented speciation requires the genetic potential for strong assortment as well as rather restrictive ecological conditions, the results show that adaptive speciation due to the evolution of assortative mating when mate choice is based on separate female preference and male marker traits is a theoretically plausible evolutionary scenario.     

The ecological dynamics of clade diversification and community assembly

Clades diversify in an ecological context, but most macroevolutionary models do not directly encapsulate ecological mechanisms that influence speciation and extinction. A data set of 245 chordate, arthropod, mollusk, and magnoliophyte phylogenies had a majority of clades that showed rapid lineage accumulation early with a slowing more recently, whereas a small but significant minority showed accelerated lineage accumulation in their recent histories. Previous analyses have demonstrated that macroevolutionary birth-death models can replicate the pattern of slowing lineage accumulation only by a strong decrease in speciation rate with increasing species richness and extinction rate held extremely low or absent. In contrast, the metacommunity model presented here could generate the full range of patterns seen in the real phylogenies by simply manipulating the degree of ecological differentiation of new species at the time of speciation. Specifically, the metacommunity model predicts that clades showing decelerating lineage accumulation rates are those that have diversified by ecological modes of speciation, whereas clades showing accelerating lineage accumulation rates are those that have diversified primarily by modes of speciation that generate little or no ecological diversification. A number of testable predictions that integrate data from molecular systematics, community ecology, and biogeography are also discussed.     

Lineage divergence and speciation in the Web‐toed Salamanders (Plethodontidae: Hydromantes) of the Sierra Nevada,California

Peripatric speciation and the importance of founder effects have long been controversial, and multilocus sequence data and coalescent methods now allow hypotheses of peripatric speciation to be tested in a rigorous manner. Using a multilocus phylogeographical data set for two species of salamanders (genus Hydromantes) from the Sierra Nevada of California, hypotheses of recent divergence by peripatric speciation and older, allopatric divergence were tested. Phylogeographical analysis revealed two divergent lineages within Hydromantes platycephalus, which were estimated to have diverged in the Pliocene. By contrast, a low‐elevation species, Hydromantes brunus, diverged from within the northern lineage of H. platycephalus much more recently (mid‐Pleistocene), during a time of major climatic change in the Sierra Nevada. Multilocus species tree estimation and coalescent estimates of divergence time, migration rate, and growth rate reject a scenario of ancient speciation of H. brunus with subsequent gene flow and introgression from H. platycephalus, instead supporting a more recent divergence with population expansion. Although the small, peripheral distribution of H. brunus suggests the possibility of peripatric speciation, the estimated founding population size of the species was too large to have allowed founder effects to be important in its divergence. These results provide evidence for both recent speciation, most likely tied to the climatic changes of the Pleistocene, and older lineage divergence, possibly due to geological events, and add to evidence that Pleistocene glacial cycles were an important driver of diversification in the Sierra Nevada.     

Genomic signatures of geographic isolation and natural selection in coral reef fishes

The drivers of speciation remain among the most controversial topics in evolutionary biology. Initially, Darwin emphasized natural selection as a primary mechanism of speciation, but the architects of the modern synthesis largely abandoned that view in favour of divergence by geographic isolation. The balance between selection and isolation is still at the forefront of the evolutionary debate, especially for the world's tropical oceans where biodiversity is high, but isolating barriers are few. Here, we identify the drivers of speciation in Pacific reef fishes of the genus Acanthurus by comparative genome scans of two peripheral populations that split from a large Central‐West Pacific lineage at roughly the same time. Mitochondrial sequences indicate that populations in the Hawaiian Archipelago and the Marquesas Islands became isolated approximately 0.5 Ma. The Hawaiian lineage is morphologically indistinguishable from the widespread Pacific form, but the Marquesan form is recognized as a distinct species that occupies an unusual tropical ecosystem characterized by upwelling, turbidity, temperature fluctuations, algal blooms and little coral cover. An analysis of 3737 SNPs reveals a strong signal of selection at the Marquesas, with 59 loci under disruptive selection including an opsin Rh2 locus. While both the Hawaiian and Marquesan populations indicate signals of drift, the former shows a weak signal of selection that is comparable with populations in the Central‐West Pacific. This contrast between closely related lineages reveals one population diverging due primarily to geographic isolation and genetic drift, and the other achieving taxonomic species status under the influence of selection.     

Towards a phylogenetic classification of reef corals: the Indo‐Pacific genera Merulina,Goniastrea and Scapophyllia (Scleractinia,Merulinidae)

Recent advances in scleractinian systematics and taxonomy have been achieved through the integration of molecular and morphological data, as well as rigorous analysis using phylogenetic methods. In this study, we continue in our pursuit of a phylogenetic classification by examining the evolutionary relationships between the closely related reef coral genera Merulina, Goniastrea, Paraclavarina and Scapophyllia (Merulinidae). In particular, we address the extreme polyphyly of Favites and Goniastrea that was discovered a decade ago. We sampled 145 specimens belonging to 16 species from a wide geographic range in the Indo‐Pacific, focusing especially on type localities, including the Red Sea, western Indian Ocean and central Pacific. Tree reconstructions based on both nuclear and mitochondrial markers reveal a novel lineage composed of three species previously placed in Favites and Goniastrea. Morphological analyses indicate that this clade, Paragoniastrea Huang, Benzoni & Budd, gen. n., has a unique combination of corallite and subcorallite features observable with scanning electron microscopy and thin sections. Molecular and morphological evidence furthermore indicates that the monotypic genus Paraclavarina is nested within Merulina, and the former is therefore synonymised.     

Repeated vicariance of Eurasian songbird lineages since the Late Miocene

Aim The evolution of avian speciation patterns across much of Eurasia is under‐explored. Excepting phylogeographic patterns of single species, or speciation involving the Himalayas, there has been no attempt to understand the evolution of avian distributional patterns across the rest of the continent. Within many genera there is a pattern of (presumed) sister species occurring in adjacent areas (western, eastern or southern Eurasia), yet this pattern cannot be explained by existing biogeographic barriers. My aim was to examine the possible role of climate‐driven vicariance events in generating avian distributions. Location Eurasia. Methods I constructed a molecular phylogeny of Phoenicurus redstarts, and assembled phylogenetic data from published studies of seven other Eurasian bird genera. On each phylogeny, I assessed the distributional patterns of species and clades relative to refugial areas in western, eastern and southern Eurasia. I also estimated the timing of lineage divergences via a molecular clock, to determine whether distributional patterns can be explained by well‐defined periods of climate change in Eurasia that are recorded from dated sediments in the Chinese Loess Plateau. Results Species relationships in a well‐supported phylogeny of Phoenicurus show a pattern of distributions consistent with repeated speciation in major refugial areas, where one lineage is isolated in a single area of Eurasia relative to its sister lineage. This same pattern is evident in Eurasian Turdus thrushes, and six additional avian genera distributed across Eurasia. Molecular clock dating indicates that divergences within each genus are the result of multiple rounds of speciation in refugia through time, during major climate‐driven episodes of vicariance. Main conclusions Analyses revealed substantial evidence supporting a repeated, non‐random pattern of speciation within and across eight songbird lineages since the Late Miocene. The pattern of speciation supports a model of isolation in refugia during major episodes of vicariance, specifically periods of either intensified desertification of Central Asia or Eurasian glacial cycles. The densely sampled clades used here preclude inter‐continental dispersal as an alternative explanation for distributions. The signature of climate‐driven vicariance across epochs is, given the absence of extant biogeographic barriers, a suitable hypothesis to explain major lineage divergences in widely distributed Eurasian songbird lineages.     

植物物种形成的模式与机制

物种形成是指由已有的物种通过各种进化机制进化出新物种的过程。持续不断的物种形成产生了地球上灿烂的生物物种多样性。然而,研究人员对物种形成的模式与机制的了解却非常有限。一直以来,谱系分裂被认为是最重要的物种形成模式,但在植物中,谱系融合,即通过杂交形成新物种的过程,也是一个非常重要的物种形成模式。经过几十年的研究才逐渐认识到,生殖隔离是差异适应和遗传漂变的副产品,而不是物种形成的前提。相比合子形成后隔离,合子形成前的隔离在物种形成过程中更早地发挥作用。合子形成前的隔离,尤其是生态地理的隔离是植物中最重要的隔离机制。一些基于QTLs分析的研究发现,基因组中的少数主效位点在物种形成中起了关键作用,并且这些位点往往受到自然选择的作用。适应性辐射往往发生在隆起的山脉和新形成的岛屿上,很可能与这些地方能够提供很多可利用的生态位有关。最新的物种形成理论认为,基因是物种形成的基本单位,不同的物种可以在非控制物种差异适应性状的位点上存在基因流。这一观点为植物物种形成的研究提供了新的思路。随着植物物种形成研究的深入,越来越多植物物种形成基因被分离,包括花色素苷合成通路和S-基因座上的一些关键基因,揭示了植物物种形成的分子机制。前期的研究主要集中在模式植物和农作物上,许多生态上非常有趣的非模式植物还未得到广泛的研究。在未来的研究中,还需要更多来自非模式植物的例子以全面理解植物物种形成的多样化机制。     

Robustness of the approximate likelihood of the protracted speciation model

The protracted speciation model presents a realistic and parsimonious explanation for the observed slowdown in lineage accumulation through time, by accounting for the fact that speciation takes time. A method to compute the likelihood for this model given a phylogeny is available and allows estimation of its parameters (rate of initiation of speciation, rate of completion of speciation and extinction rate) and statistical comparison of this model to other proposed models of diversification. However, this likelihood computation method makes an approximation of the protracted speciation model to be mathematically tractable: it sometimes counts fewer species than one would do from a biological perspective. This approximation may have large consequences for likelihood‐based inferences: it may render any conclusions based on this method completely irrelevant. Here, we study to what extent this approximation affects parameter estimations. We simulated phylogenies from which we reconstructed the tree of extant species according to the original, biologically meaningful protracted speciation model and according to the approximation. We then compared the resulting parameter estimates. We found that the differences were larger for high values of extinction rates and small values of speciation‐completion rates. Indeed, a long speciation‐completion time and a high extinction rate promote the appearance of cases to which the approximation applies. However, surprisingly, the deviation introduced is largely negligible over the parameter space explored, suggesting that this approximate likelihood can be applied reliably in practice to estimate biologically relevant parameters under the original protracted speciation model.     

Life‐history strategies of Manipora amicarum Sinclair, 1955 (Tabulata; Upper Ordovician; southern Manitoba,Canada)

Based on detailed study of transverse serial sections, we recognize various modes of corallite increase in a multichain cateniform coral, Manipora amicarum from the Selkirk Member, Red River Formation, in Manitoba. One type of axial increase and four types of lateral increase involve normal, undamaged corallites, and one type of axial increase and one type of lateral increase occur during recovery processes of corallites damaged by sediment or bioclast influx. All but one of these types of increase are comparable to those in a single‐chain coral, Catenipora foerstei, which we previously documented from the same stratigraphic unit and locality. In M. amicarum, the formation of double ranks and agglutinated patches of corallites by normal corallites, and by recovery processes following corallite damage, is common and presumably genetically controlled. Agglutinated patches originate differently in C. foerstei, occurring sporadically or temporarily in only some coralla. Average annual vertical corallum growth in M. amicarum, as indicated by cyclic fluctuations of tabularial area, is higher than in C. foerstei, which has comparatively smaller corallites. In general, annual growth in M. amicarum is positively correlated with average tabularial area, negatively correlated with frequency of damaged corallites, and is not related to the frequency of corallite increase. In C. foerstei, however, there is a positive association between annual growth rate and the frequency of increase by damaged corallites, related to episodes of sediment or bioclast influx probably generated by storms. In comparison with C. foerstei, M. amicarum has a low frequency of corallite termination and extensive partial mortality is rare. It seems that the relatively rapid overall vertical corallum growth in M. amicarum was effective for protecting the coral from unfavourable situations, possibly by maintaining the growth surface higher above the substrate than in C. foerstei. Although these two species show many similarities in the types of corallite increase, their reactions and strategies in relation to physical disturbance were quite different.     

Corallite size and spacing as an aspect of niche-partitioning in tabulate corals of Silurian reefs, Racine Formation, North America

Tabulate corals are common in reefs of the Silurian (Wenlockian) Racine Formation in Wisconsin and Illinois, North America. Variation in size and spacing of corallites in this fauna represents an aspect of niche-partitioning that is probably related to feeding. Corallite morphospace, represented by a plot of corallite diameter versus number of corallites per square cm, is characteristically partitioned among favositines, alveolitines, halysitines, syringoporids, and heliolitines, usually with minimal overlap between these major taxonomic groups. Within all groups except alveolitines, morphospace occupied by each major taxon is partitioned further between forms with small corallites and forms with larger corallites. This is probably related to differences in feeding, with ­larger corallite forms specializing in tentacular capture of larger prey, and smaller ­corallite forms specializing in smaller prey involving capture by cilia-directed sheets of mucus as well as by tentacles. Feeding-based differences among tabulates augmented niche-partitioning effected by colony form and relation to substrate. Cerioid, cateniform, coenenchymal, and fasciculate colony types in the Racine fauna were primarily adapted to a soft substrate. Ragged edges of colonies indicate growth during episodic sedimentation, and colonies were partially buried during life. Most tabulates are ­scattered through wackestone and packstone and were not major contributors to reef growth.     

Microstructural characteristics of the stony coral genus Acropora useful to coral reef paleoecology and modern conservation

Identification of fossil corals is often limited due to poor preservation of external skeleton morphology, especially in the genus Acropora which is widespread across the Indo‐Pacific. Based on skeleton characteristics from thin section, we here develop a link between the internal skeleton structure and external morphology. Ten characteristics were summarized to distinguish Acropora and five related genera, including the type and differentiation of corallites, the skeleton nature of corallites (septa, columellae, dissepiments, wall), and calcification centers within septa. Acropora is distinctive for its dimorphic corallites: axial and radial. Isopora is similar to Acropora but possess more than a single axial corallites. Montipora and Astreopora (family Acroporidae) have monomorphic corallites and a synapticular ring wall, with clustered calcification center in the former and medial lines in the latter. Pocillopora and Porties are classified by distinctive dissepiments, columellae and septa. These microstructural skeleton characteristics were effective in the genus identification of fossil corals from drilled cores in the South China Sea. Eighteen detailed characteristics (ten of axial corallites, four of radial corallites, and four of coenosteum) were used in the Acropora species classification. The axial corallites size and structure (including corallite diameter, synapticular rings, and septa), the septa of radial corallites, and the arrangement of coenosteum were critical indicators for species identification. This identification guide can help paleoenvironmental and paleoecological analyses and modern coral reef conservation and restoration.