Morphomechanical Innovation Drives Explosive Seed Dispersal

How mechanical and biological processes are coordinated across cells, tissues, and organs to produce complex traits is a key question in biology. Cardamine hirsuta, a relative of Arabidopsis thaliana, uses an explosive mechanism to disperse its seeds. We show that this trait evolved through morphomechanical innovations at different spatial scales. At the organ scale, tension within the fruit wall generates the elastic energy required for explosion. This tension is produced by differential contraction of fruit wall tissues through an active mechanism involving turgor pressure, cell geometry, and wall properties of the epidermis. Explosive release of this tension is controlled at the cellular scale by asymmetric lignin deposition within endocarp b cells-a striking pattern that is strictly associated with explosive pod shatter across the Brassicaceae plant family. By bridging these different scales, we present an integrated mechanism for explosive seed dispersal that links evolutionary novelty with complex trait innovation.

(Table 1) Age determination of sediment core SO147_106KL

Here we present a high-resolution marine sediment record from the El Niño region off the coast of Peru spanning the last 20,000 years. Sea surface temperature, photosynthetic pigments, and a lithic proxy for El Niño flood events on the continent are used as paleo-El Niño-Southern Oscillation proxy data. The onset of stronger El Niño activity in Peru started around 17,000 calibrated years before the present, which is later than modeling experiments show but contemporaneous with the Heinrich event 1. Maximum El Niño activity occurred during the early and late Holocene, especially during the second and third millennium B.P. The recurrence period of very strong El Niño events is 60-80 years. El Niño events were weak before and during the beginning of the Younger Dryas, during the middle of the Holocene, and during medieval times. The strength of El Niño flood events during the last millennium has positive and negative relationships to global and Northern Hemisphere temperature reconstructions.

(Table 1) Sea surface temperature reconstruction for eastern equatorial Pacific surface sediment samples

Significant uncertainties persist in the reconstruction of past sea surface temperatures in the eastern equatorial Pacific, especially regarding the amplitude of the glacial cooling and the details of the post-glacial warming. Here we present the first regional calibration of alkenone unsaturation in surface sediments versus mean annual sea surface temperatures (maSST). Based on 81 new and 48 previously published data points, it is shown that open ocean samples conform to established global regressions of Uk'37 versus maSST and that there is no systematic bias from seasonality in the production or export of alkenones, or from surface ocean nutrient concentrations or salinity. The flattening of the regression at the highest maSSTs is found to be statistically insignificant. For the near-coastal Peru upwelling zone between 11-15°S and 76-79°W, however, we corroborate earlier observations that Uk'37 SST estimates significantly over-estimate maSSTs at many sites. We posit that this is caused either by uncertainties in the determination of maSSTs in this highly dynamic environment, or by biasing of the alkenone paleothermometer toward El Niño events as postulated by Rein et al. (2005).

(Table 1) Age determination of sediment core SO139-74KL

A multiproxy record has been acquired from a piston core (SO139-74KL) taken offshore southern Sumatra, an area which is situated in the southwestern sector of the tropical Indo-Pacific Warm Pool. The high-resolution data sets (X-ray fluorescence, total organic carbon, and C37 alkenones) were used to track changes in paleoproductivity, freshwater budget, and sea surface temperature (SST) of the tropical climate system at orbital time scales over the past 300 ka. Our paleoclimatic data show that enhanced marine paleoproductivity was directly related to strengthening of coastal upwelling during periods of increased boreal summer insolation and associated SE monsoon strength with a precessional cyclicity. Changes in freshwater supply were primarily forced by precession-controlled changes in boreal NW winter monsoon rainfall enclosing an additional sea level component. SST variations of 2°-5°C occurred at eccentricity and precessional cyclicity. We suggest that the sea surface temperature variability off southern Sumatra is predominantly related to three major causes: (1) variations in upwelling intensity; (2) an elevated freshwater input into the southern Makassar Strait leading to reduced supply of warmer surface waters from the western Pacific and increased subsurface water transport via the Indonesian Throughflow into the Indian Ocean; and (3) long-term changes in the intensity or frequency of low-latitude climate phenomena, such as El Niño-Southern Oscillation.

Principles and methods of sociology,

Bibliography at end of each chapter.

A midsummer night's dream.

Mode of access: Internet.

Problems in credits and collections /

Originally published: Advanced credit problems.

Photovoltaics information user study /

"October 1980."

Solar thermal electric power information user study /

This report describes the results of a series of telephone interviews with groups of users of information on solar thermal electric power. These results, part of a larger study on many different solar technologies, identify types of information each group needed and the best ways to get information to each group. The report is one of ten discussing study results. Results from five solar thermal electric power groups of respondents are analyzed in this report: DOE-funded researchers, non-DOE-funded researchers, representatives of utilities, electric power engineers, and educators.

Development of a motor vehicle materials historical high-volume industrial processing rates cost data bank (3500-4000 pound) full size car. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Analyses of selected automotive parts and assemblies for cost and material impacts. Final report.

National Highway Traffic Safety Administration, Office of Research and Development, Washington, D.C.

Entwicklungsgeschichte des Erbsündendogmas; seit der Reformation /

Bibliography: p. 353-356.

Geschichte des Erbsündendogmas; ein Beitrag zur Geschichte des Problems vom Ursprung des Übels.

Bibliography: v.l, p. 377-384; v.2, p. 574-580.

Practical guides to uranium ores on the Colorado Plateau /

"September 30, 1952."

Harms' Lehrbuch der tierärtzlichen Geburtshilfe.

1. Geschlechtsleben der Haussäugetiere / R. Schmaltz -- 2. Teil. Tierärztliche Geburtshilfe, Pathologie und Therapie / von J. Richter, J. Schmidt, R. Reinhardt.