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Homeosis is sometimes defined as the replacement of one member of a meristic series by another member normally formed in a different position. The pistillata floral mutant of Arabidopsis thaliana (Brassicaceae) has petals replaced by sepal-like organs ("petals"), is male sterile, and has abnormal gynoecial development. We compared the ontogeny of wild type and pistillata flowers to determine the developmental basis for their divergent final forms. Normal sepal development in wild type pistillata flowers is indistinguishable in terms of initiation events, anatomical and morphological development, and allometric growth. Wild type petals and pistillata "petals" are initially ontogenetically similar in these same respects. The first observable difference between the two floral forms is abnormal patterns of cell division in pistillata at stamen inception. Tissues in the normal position of the androecium appear congenitally fused to the gynoecium to various extents and differentiate gynoecial cell fates. Form divergence between wild type petals and pistillata "petals" becomes evident when these organs reach 90 μm in length, after androecial developmental divergence has occurred. Pistillata does not have petals replaced by sepals; pistillata "petals" are intermediate in form between wild type sepals and petals because of the developmental switching of petal primordia into the ontogenetic pattern characteristic of wild type sepals after petal primordia are initiated.

A nanoscale thermal anemometry probe (NSTAP) has been developed to measure velocity fluctuations at ultra-small scales. The sensing element is a free-standing platinum nanoscale wire, 100 nm × 2 μm × 60 μm, suspended between two current-carrying contacts and the sensor is an order of magnitude smaller than presently available commercial hot wires. The probe is constructed using standard semiconductor and MEMS manufacturing methods, which enables many probes to be manufactured simultaneously. Measurements were performed in grid-generated turbulence and compared to conventional hot-wire probes with a range of sensor lengths. The results demonstrate that the NSTAP behaves similarly to conventional hot-wire probes but with better spatial resolution and faster temporal response. The results are used to investigate spatial filtering effects, including the impact of spatial filtering on the probability density of velocity and velocity increment statistics.

SummaryQuantitative trait locus (QTL) mapping is a first step toward understanding the genetic basis of adaptive evolution and may also reveal reproductive incompatibilities unique to hybrids. In plants, the shift from outcrossing to self-pollination is common, providing the opportunity for comparisons of QTL architecture among parallel evolutionary transitions.We used QTL mapping in hybrids between the bee-pollinated monkeyflower Mimulus lewisii and the closely related selfer Mimulus parishii to determine the genetic basis of divergence in floral traits and flowering time associated with mating-system evolution, and to characterize hybrid anther sterility.We found a moderately polygenic and highly directional basis for floral size evolution, suggesting adaptation from standing variation or in pursuit of a moving optimum, whereas only a few major loci accounted for substantial flowering-time divergence. Cytonuclear incompatibilities caused hybrid anther sterility, confounding estimation of reproductive organ QTLs.The genetic architecture of floral traits associated with selfing in M. parishii was primarily polygenic, as in other QTL studies of this transition, but in contrast to the previously characterized oligogenic basis of a pollinator shift in close relatives. Hybrid anther sterility appeared parallel at the molecular level to previously characterized incompatibilities, but also raised new questions about cytonuclear co-evolution in plants.

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