Foregut morphology and ontogeny of the spider crab Maja brachydactyla (Brachyura,Majoidea, Majidae)

We describe the morphology of the foregut of the spider crab Maja brachydactyla Balss, 1922, from first larval stage to adult, with detailed stage‐specific documentation using light and scanning electron microscopy. A total of 40 ossicles have been identified in the foregut of adults of M. brachydactyla using Alizarin‐Red staining. The morphological pattern of the ossicles and gastric mill is very similar to other Majoidea species with only a few variations. The foregut of the zoeae stages appeared as a small and simple cavity, with a cardio‐pyloric valve that separates the stomach into cardiac and pyloric regions. The pyloric filter is present from the first zoea, in contrast to the brachyuran species which have an extended larval development. Calcified structures have been identified in the cardio‐pyloric valve and pyloric region of the zoeal stages. The most significant changes in foregut morphology take place after the metamorphosis from ZII to megalopa, including the occurrence of the gastric mill. In the megalopa stage, the foregut ossicles are recognizable by their organization and general morphology, but are different from the adult phase in shape and number. Moreover, the gastric teeth show important differences: the cusps of the lateral teeth are sharp (no molariform); the dorsal tooth have a small, dentate cusp (not a well‐developed quadrangular cusp); and the accessory teeth are composed of one sharp peak (instead of four sharp peaks). The gastric mill ontogeny from megalopa to adult reveals intermediate morphologies during the earlier juvenile stages. The relationship between gastric mill structures with food preferences and their contribution to the brachyuran phylogeny are briefly discussed. J. Morphol. 276:1109–1122, 2015. © 2015 Wiley Periodicals, Inc.     

Karyotype Rearrangements in a Wine Yeast Strain by rad52-Dependent and rad52-Independent Mechanisms

Yeast strains isolated from the wild may undergo karyotype changes during vegetative growth, a characteristic that compromises their utility in genetic improvement projects for industrial purposes. Karyotype instability is a dominant trait, segregating among meiotic derivatives as if it depended upon only a few genetic elements. We show that disrupting the RAD52 gene in a hypervariable strain partially stabilizes its karyotype. Specifically, RAD52 disruption eliminated recombination at telomeric and subtelomeric sequences, had no influence on ribosomal DNA rearrangement rates, and reduced to 30% the rate of changes in chromosomal size. Thus, there are at least three mechanisms related to karyotype instability in wild yeast strains, two of them not requiring RAD52-mediated homologous recombination. When utilized for a standard sparkling-wine second fermentation, Δrad52 strains retained the enological properties of the parental strain, specifically its vigorous fermentation capability. These data increase our understanding of the mechanisms of karyotype instability in yeast strains isolated from the wild and illustrate the feasibility and limitations of genetic remediation to increase the suitability of natural strains for industrial processes.