Ballistic seed projection in two herbaceous species

Abstract

We found that the majority of ballistic seeds tested [N = 74 of 78 in Vicia sativa ssp. nigra (Fabaceae); N = 25 of 27 in Croton capitatus var. capitatus (Euphorbiaceae)] were projected at angles that would yield a greater distance than the average of seeds with the same initial speed projected at random angles. In addition, the median of fractional distance error (maximum distance - seed distance)/(maximum distance), of the seeds were 0.11 and 0.04 for V. sativa and C. capitatus, respectively. Seed projection distance was modeled by using initial projection angle, initial speed, and measured drag, along with other seed data. We improved upon previous such studies by using dual-angle high-speed stroboscopic photography to determine initial projection angle and speed. We also measured seed drag in a low-turbulence wind tunnel. Seed projection positions on the plant, which also affect seed projection distance, were found to be primarily from the top of the plant, with 98 of 137 and 407 of 407 fruits in the upper half of the plant for V. sativa and C. capitatus, respectively. Our findings are significant because they suggest that in addition to the ballistic projection mechanism itself, the species studied have additional adaptations that result in enhanced seed projection distance from the parent plant.

The seed dispersal catapult of Cardamine parviflora (Brassicaceae) is efficient but unreliable

“…Ballistic dispersal may be the sole mechanism, or in ballistic diplochores, serve as a precursor to secondary dispersal by other means ( Beattie and Lyons, 1975 ;Stamp and Lucas, 1983 ;Ohkawara and Higashi, 1994 ;Webb, 1998 ;Garrison et al, 2000 ;Vander Wall and Longland, 2004 ;Hayashi et al, 2009 ). Plants entirely reliant on ballistic dispersal have been termed distance maximizers because they typically exhibit more effective ballistic dispersal than do ballistic diplochores ( Stamp and Lucas, 1983 ).…”

“…Of the many potential mechanisms, including air and water fl ows and carriage by animals ( Willson and Traveset, 2000 ;Levin et al, 2003 ), ballistic dispersal is the most mechanically complex ( Howe and Smallwood, 1982 ;Stamp and Lucas, 1983 ;Witztum and Schulgasser, 1995 ;Garrison et al, 2000 ;Beaumont et al, 2009 ;Vogel, 2009 ), relying on mechanical energy stored in specialized fruit tissues to launch seeds ( Niklas, 1992 ;Witztum and Schulgasser, 1995 ;Hayashi et al, 2009 ). Ballistic dispersal may be the sole mechanism, or in ballistic diplochores, serve as a precursor to secondary dispersal by other means ( Beattie and Lyons, 1975 ;Stamp and Lucas, 1983 ;Ohkawara and Higashi, 1994 ;Webb, 1998 ;Garrison et al, 2000 ;Vander Wall and Longland, 2004 ;Hayashi et al, 2009 ).…”

Biology doesn't waste energy: that's really smart

“…Another example is the wide-spread mechanisms in plants which rely on the absorption of water vapour to power shape-change in a dead structure. Examples are the pine cone opening and closing 7 and the powering of dehiscence mechanisms for the distribution of seeds and pollen in a wide variety of plants [8][9][10][11] . In this instance the signal to disperse the seeds is a function of their dehydration (many seeds are dehydrated when mature to make them more resistant to environmental stress) and the presence of sufficient water to enable them to imbibe and start to develop.…”

The mechanics of explosive dispersal and self-burial in the seeds of the filaree, Erodium cicutarium (Geraniaceae)

“…Launch angle and height were not considered here, but in other seed-launching plants, such as V. sativa and C. capitatus, the height of flowers and a slight upward angle of launch appear to provide increases in range relative to random angles and locations low on the plant (Garrison et al, 2000). Fig.9A shows that awns that are too wet (red line, left side) do not store enough energy to launch, because any cracks in them will not propagate to completion.…”