Influence of different substrates on the evolution of morphology and life‐history traits of azooxanthellate solitary corals (Scleractinia: Flabellidae)

Sessile organisms are influenced considerably by their substrate conditions, and their adaptive strategies are key to understanding their morphologic evolution and traits of life history. The family Flabellidae (Cnidaria: Scleractinia) is composed of the representative azooxanthellate solitary corals that live on both soft and hard substrates using various adaptive strategies. We reconstructed the phylogenetic tree and ancestral character states of this family from the mitochondrial 16S and nuclear 28S ribosomal DNA sequences of ten flabellids aiming to infer the evolution of their adaptive strategies. The Javania lineage branched off first and adapted to hard substrates by using a tectura‐reinforced base. The extant free‐living flabellids, including Flabellum and Truncatoflabellum, invaded soft substrates and acquired the flabellate corallum morphology of their common ancestor, followed by a remarkable radiation with the exploitation of adaptive strategies, such as external soft tissue [e.g. Flabellum (Ulocyathus)], thecal edge spine, and transverse division (e.g. Placotrochus and Truncatoflabellum). Subsequently, the free‐living ancestors of two genera (Rhizotrochus and Monomyces) invaded hard substrates independently by exploiting distinct attachment apparatuses such as tube‐like and massive rootlets, respectively. In conclusion, flabellids developed various morphology and life‐history traits according to the differences in substrate conditions during the course of their evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 184–192.     

Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula

Sentoku, A. & Ezaki, Y. 2011: Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula. Lethaia, Vol. 45, pp. 62–70. Scleractinia display a variety of growth forms, whether zooxanthellate or azooxanthellate, as the consequence of the combined effects of both intrinsic and extrinsic factors. New modules arise in colonial corals through asexual reproduction, including budding and division. The azooxanthellate, branching dendrophylliid Dendrophyllia arbuscula van der Horst 1922 , is a good species to investigate intrinsic regularities in budding, because: (1) the lateral corallites always occur in the vicinity of four primary septa, excluding the two directive primary septa; (2) the two directive septa in lateral corallites tend to be oriented almost perpendicular to the growth orientation of parental corallites; (3) the lateral corallites grow more‐or‐less diagonally upwards; and (4) these regularities are retained from the axial to the derived lateral corallites during colony growth. Accordingly, a colony of apparently complex dendroid corals is formed according to certain universal rules that apply to successive generations of corallites. The presence of two opposite sectors in which budding do not occur seems to be common to other azooxanthellate scleractinian families. Regularities, other than the orientation of the directive septa, are also commonly found at least in other azooxanthellate dendrophylliid genera. These regularities suggest the presence of strict developmental constraints on the asexual reproduction of the Scleractinia, both extant and extinct. These regularities by azooxanthellate scleractinians, as one of the representative colonial metazoan groups, provide us with fundamental data with which we can understand how colonies are constructed. □Azooxanthellate coral, budding, colony, Dendrophyllia arbuscula, regularity.     

Mate desertion by male Great Reed Warblers Acrocephalus arundinaceus at the end of the breeding season

Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains.     

Regular mode of increase, and constrained but variable growth, in the Silurian rugose coral Stauria favosa

Stauria favosa exhibits a typical pattern of axial division (tripartite or quadripartite). The four protosepta first appear with a definite polarity in offset corallites, and metasepta are inserted serially, following Kunth's rule. There are no variations in essential modes of asexual reproduction. However, at the corallum periphery, up to four offset corallites appear to have been derived by discrete offsetting within the parent calices. Detailed observations of vertical morphological changes, however, indicate that this apparently unique mode of increase is derived from axial division at the sites of the four protosepta, as usual in this species. Just after the initiation of division, the contraction of polyps occurred in response to somewhat accidental, deteriorating habitat conditions. The combination of asexually divided corallites and rejuvenescence resulted in phaceloid daughter corallites, which subsequently underwent partial mortality at the corallum periphery. Stauria favosa always exhibits not only regular modes of asexual reproduction and septal insertion under the strict control of phylogenetic and developmental constraints, but also variable growth forms of corallites and coralla. This variability, though within limited options, is palaeoecologically significant for successfully coping with unpredictable habitats.     

Predispersal predation by rodents to beechnuts (Fagus crenata Blume)

The rodents predation intensity and discrimination ability toward the predispersal beechnuts (Fagus crenata) were investigated using a tree tower in a beech forest, central Japan in 1999 and 2000. In this stand, using seed traps, the densities of fallen viable nuts were 35.1m^–2 in 1999 and 8.4m^–2 in 2000. The vertebrate-damaged nuts had fallen 5.6 and 2.2m^–2 in 1999 and 2000, respectively. Yet, the crop of viable nuts in 1999 was not so rich as that in a mast year. In 1999, predispersal predation by rodents was recognized at 16–19m above ground through the bagging experiment. In 2000, there were no predispersal predation and yet we captured Apodemus argenteus three times and Glirulus japonicus frequently on the tree. Judging from the facts of their feeding behaviors and the tooth scars left on the cupules and nuts, Apodemus argenteus might have been more responsible for predation to the predispersal beechnuts rather than Glirulus japonicus. Apodemus argenteus population seemed to be abundant on the ground in both years. If the main agent of predispersal predator were Apodemus argenteus, their number shifted to the canopy would be much larger in 1999 than in 2000 according as the crop of viable nuts. In an additional experiment, rodents preferred intact cupules to insect-damaged cupules on the tree, suggesting that they discriminated the quality of the predispersal nuts, even in the cupule stage, through olfactory and/or visual senses. Thus, predispersal nut predation by rodents was prevalent during the limited period in autumn.     

Mate desertion by male Great Reed Warblers Acrocephalus arundinaceus at the end of the breeding season

Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains. Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains. Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains. Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains. Male Great Reed Warblers usually take part in the care of offspring as nest defenders and by feeding young, but at the end of the breeding season they desert their mates with eggs or nestlings. Deserted females continue offspring care. Desertion does not depend on the male's mated status (polygynous or monogamous) nor on his past breeding success. Deserted females compensate for the loss of their partners by increasing the frequency of food-bringing, resulting in a reduction in the amount of time the nestlings are brooded. Although desertion may lead to increased rates of offspring mortality through predation, breeding success of deserted females was high, especially if the male assisted during the early stages. Deserters pay costs by giving up the chance of additional matings and by lowering the reproductive success of existing mates. Male warblers reduce the former cost by choosing the season of desertion and the latter is lowered by the female's high parental ability. A deserter was found to start moulting while his mate was still feeding his nestlings, and an earlier start to the moult may be the primary benefit that he gains.     

Regularity and polarity in budding of the colonial scleractinian Dendrophyllia ehrenbergiana: consequences of radio‐bilateral symmetry of the scleractinian body plan

Sentoku, A. & Ezaki, Y. 2012: Regularity and polarity in budding of the colonial scleractinian Dendrophyllia ehrenbergiana: consequences of radio‐bilateral symmetry of the scleractinian body plan. Lethaia, Vol. 45, pp. 586–593. Regularities and polarity in budding of the azooxanthellate scleractinian Dendrophyllia ehrenbergiana were examined with the aim of understanding the developmental constraints on the formation of colonies. Its mode of budding, in light of the orientations of directive septa of offsets and the inclination angle of budding, is consistent with that of other dendrophyllids; however, the offsets of D. ehrenbergiana only occur near the two primary septa on the convex side of individual corallites, showing a plane of bilateral symmetry with a distinct polarity. These regularities and polarity are seen in the axial and its derived corallites throughout growth. Of note, the polarity at individual corallites is clearly reflected in subsequent colony growth by the branching pattern and corallite number. These characteristics imply the presence of radio‐bilateral symmetrical constraints on the asexual reproduction of the Scleractinia and give us invaluable clues to the understanding of shape‐making mechanisms of marine modular organisms. □Asexual reproduction, azooxanthellate coral, budding, colony, Dendrophyllia ehrenbergiana, polarity.     

The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three‐dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal‐dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal‐dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.