Search

Sympatric speciation has been demonstrated in few empirical case studies, despite intense searches, because of difficulties in testing the criteria for this mode of speciation. Here, we report a possible case of sympatric speciation in ricefishes of the genus Oryzias on Sulawesi, an island of Wallacea. Three species of Oryzias are known to be endemic to Lake Poso, an ancient tectonic lake in central Sulawesi. Phylogenetic analyses using RAD-seq-derived single nucleotide polymorphisms (SNPs) revealed that these species are monophyletic. We also found that the three species are morphologically distinguishable and clearly separated by population-structure analyses based on the SNPs, suggesting that they are reproductively isolated from each other. A mitochondrial DNA chronogram suggested that their speciation events occurred after formation of the tectonic lake, and existence of a historical allopatric phase was not supported by coalescent-based demographic inference. Demographic inference also suggested introgressive hybridization from an outgroup population. However, differential admixture among the sympatric species was not supported by any statistical tests. These results all concur with criteria necessary to demonstrate sympatric speciation. Ricefishes in this Wallacean lake provide a promising new model system for the study of sympatric speciation., (© 2019 The Author(s). Evolution © 2019 The Society for the Study of Evolution.)

(25S)-3-Oxocholesta-1,4-dien-26-oic acid (1) and a new (25S)-18-acetoxy-3-oxocholesta-1,4-dien-26-oic acid (2) were isolated from a soft coral Minabea sp. (cf. aldersladei) collected in North Sulawesi, Indonesia, together with two known cholic-acid-type compounds, 3-oxochol-1,4-dien-24-oic acid (3) and 3-oxochol-4-en-24-oic acid (4). The structures of these compounds were determined on the basis of their spectroscopic data. The absolute stereochemistry at C-25 of 2 was determined by comparative (1)H NMR study using chiral anisotropic reagents [(S)- and (R)-phenylglycine methyl esters]. This is the first to report compound 1 as a natural product.

Two new hexahydroanthrones, tetrahydrobostrycin (1) and 1-deoxytetrahydrobostrycin (2), were isolated from a marine-derived fungus Aspergillus sp. strain 05F16 collected at the coral reef of Manado, Indonesia, together with bostrycin and abscisic acid. The structures of new compounds were determined on the basis of their spectral data. Compound 1 showed weak antibacterial activity against Staphylococcus aureus and Escherichia coli and 2 against S. aureus.

Two new imidazole alkaloids, naamidines H ( 1) and I ( 2), were isolated from the marine sponge Leucetta chagosensis, collected in North Sulawesi, Indonesia. The compounds ( 1 and 2) showed cytotoxicity against HeLa cells with IC50 values of 5.6 and 15 microg/mL, respectively.

Four new polysulfur aromatic alkaloids, lissoclibadins 4 (1), 5 (2), 6 (3), and 7 (4), were isolated from the ascidian Lissoclinum cf. badium collected in Indonesia, together with seven known alkaloids, lissoclibadins 1 (5), 2 (6), and 3 (7), lissoclinotoxins E (8) and F (9), 3,4-dimethoxy-6-(2'-N,N-dimethylaminoethyl)-5-(methylthio)benzotrithiane (10), and N,N-dimethyl-5-(methylthio)varacin (11). Compounds 1-11 were isolated from the ascidian collected in March (wet season), while 5-11 have been obtained previously from the organism collected in September (dry season) at the same site. The structures of the new compounds were assigned on the basis of their spectroscopic data. Lissoclibadins 4-7 (1-4) inhibited the colony formation of Chinese hamster V79 cells with EC50 values of 0.71, 0.06, 0.06, and 0.17 microM, respectively. Compounds 1-4 showed also weak antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Saccharomyces cerevisiae.

In interspecific hybridization between Oryzias latipes and O. javanicus, all hybrid embryos failed to develop and died before hatching. Cytological examination of fertilization and early development was performed to discover the cause of lethal development. When O. latipes eggs were inseminated by sperm of O. javanicus, the cortical reaction was induced normally. Chromosomal material in the fertilized eggs was visualized using the DNA-specific fluorochrome Hoechst. The spermatozoon was capable of penetrating into the egg cytoplasm through the micropyle, and the sperm nucleus transformed to the male pronucleus. The female pronucleus that formed after extrusion of the second polar body migrated towards the male pronucleus. The female and the male pronuclei underwent DNA synthesis and encountered each other in the center of the blastodisc, fused with one another and formed a zygote nucleus before breakdown of the nuclear envelope. Metaphase chromosomes with electron dense chromatin regions were abnormally divided into each blastomere in cleavage. The abnormally separating chromatin masses were also labeled by BrdU. The abnormal separation resulting in partial loss of fragmented chromatin might be a cause of abortive development in the interspecific hybrids between O. latipes and O. javanicus.