Paragoniastreavariabilis Kishi, Nomura & Fukami, sp. nov. (Cnidaria, Anthozoa, Scleractinia), a new coral species previously considered as a variant of Paragoniastreadeformis, from Japan and northern Taiwan.

A new zooxanthellate scleractinian coral, Paragoniastreavariabilis Kishi, Nomura & Fukami, sp. nov. (Scleractinia, Merulinidae), is described from non-coral reef regions of Japan and northern Taiwan. This new species was previously recognized as a morphological variant of Paragoniastreadeformis (Veron, 1990) and can be morphologically distinguished from that species by lacking groove-and-tube structures on corallite wall joints, and by having larger calices, numerous septa, and up to three corallites in one valley. The new species also formed an independent clade from its congeners, P.australensis (Milne Edwards & Haime, 1857), P.deformis and P.russelli (Wells, 1954), in the molecular phylogeny based on the mitochondrial intergenic region and nuclear ribosomal internal transcribed spacers.

Genomic landscape of introgression from the ghost lineage in a gobiid fish uncovers the generality of forces shaping hybrid genomes.

Extinct lineages can leave legacies in the genomes of extant lineages through ancient introgressive hybridization. The patterns of genomic survival of these extinct lineages provide insight into the role of extinct lineages in current biodiversity. However, our understanding on the genomic landscape of introgression from extinct lineages remains limited due to challenges associated with locating the traces of unsampled 'ghost' extinct lineages without ancient genomes. Herein, we conducted population genomic analyses on the East China Sea (ECS) lineage of Chaenogobius annularis, which was suspected to have originated from ghost introgression, with the aim of elucidating its genomic origins and characterizing its landscape of introgression. By combining phylogeographic analysis and demographic modelling, we demonstrated that the ECS lineage originated from ancient hybridization with an extinct ghost lineage. Forward simulations based on the estimated demography indicated that the statistic γ of the HyDe analysis can be used to distinguish the differences in local introgression rates in our data. Consistent with introgression between extant organisms, we found reduced introgression from extinct lineage in regions with low recombination rates and with functional importance, thereby suggesting a role of linked selection that has eliminated the extinct lineage in shaping the hybrid genome. Moreover, we identified enrichment of repetitive elements in regions associated with ghost introgression, which was hitherto little known but was also observed in the re-analysis of published data on introgression between extant organisms. Overall, our findings underscore the unexpected similarities in the characteristics of introgression landscapes across different taxa, even in cases of ghost introgression.

Analysis of spatial niche structure in coexisting tidepool fishes: null models based on multi-scale experiments.

1. Fundamental and realized spatial niches were investigated through a combination of laboratory and mesocosm experiments, field observations and null model analysis in three intertidal gobiid species (Bathygobius fuscus, Chaenogobius annularis and C. gulosus). Null models based on the results of single-species experiments were used to assess interspecific spatial use and coexistence on two different scales: (i) microhabitats within a tidepool ('microhabitat' scale); and (ii) distribution among a set of tidepools ('habitat-wide' scale). 2. Patterns of microhabitat use varied from single to paired treatments, depending on paired species. Realized overlap of microhabitat use was smaller than would be expected from single-individual situations for intraspecific combinations, but not for interspecific ones. 3. Patterns of tidepool occupancy (a measure of spatial niche breadth) in the mesocosm were influenced by interspecific interactions. Two Chaenogobius species, but not B. fuscus, decreased tidepool occupancy in the hetero-specific treatments compared with the mono-specific ones. For all interspecific combinations, spatial overlap (habitat-wide scale) was significantly lower than the values expected from mono-specific situations. The results also indicated a possible trade-off between competitiveness and growth efficiency in these fishes. 4. Interspecific spatial overlap in the field was similar to that in the mesocosm experiment and the pattern of coexistence of gobiids can be explained by the results of our experiments. 5. This study demonstrates that niches of intertidal fishes may experience modifications under the influence of species interactions and that null models based on controlled experiments can greatly facilitate the deciphering of such changes in niche structure.