The photoperceptive sites and the function of tissue light-piping in photomorphogenesis of etiolated oat seedlings*

Abstract. Responses to red light irradiation of discrete areas along the intact, etiolated oat seedling indicate that illumination of the region around the coleoptilar node results in maximal coleoptile growth stimulation and mesocotyl growth suppression. Quantitation of the fibre optic properties of these etiolated tissues shows that the amount of axially transmitted light is log linear as a function of distance for both the mesocotyl and coleoptile (plus primary leaf). Using the fibre optic properties of the tissues to predict the response of the etiolated seedling to defined illumination fields allows one to localize two sites of photoperception: although the mesocotyl response pattern can be explained by the action of a single site found near the top of the mesocotyl itself, the coleoptile response depends on irradiation of both the mesocotyl site and an additional site located just above the node. The very low- and the low-fluence responses of etiolated oats independently predict similar regions of the seedling as sites of photo-perception. The fibre optic properties of the seedling could allow the seedling to increase the effective light signal received by the photosensitive area significantly.     

Isolation and characterization of microsatellite markers in the Atlantic slipper shell Crepidula fornicata for use in paternity analysis

Crepidula fornicata is an ideal species in which to study the evolution and timing of sex change. In order to test current theory on the timing of sex change, male reproductive success must be quantified. Because C. fornicata is polygamous, this can only be achieved through the development of molecular markers and paternity analysis. Here, I report the development of five polymorphic microsatellite loci that are inherited in a Mendelian fashion. The levels of polymorphism and the inheritance patterns of these loci make them suitable for paternity analysis despite the presence of null alleles.     

Are predatory birds effective secondary seed dispersers?

We have studied the unusual phenomenon of secondary seed dispersal of Lycium intricatum seeds on a small oceanic Atlantic island (Alegranza, Canarian Archipelago) in which a small frugivorous lizard ( Gallotia atlantica ) and two different predatory birds participate, a shrike ( Lanius excubitor ) and a kestrel ( Falco tinnunculus ). Endemic lizards that are common prey of both bird species consume Lycium fruits. Lizard remains were significantly matched with the presence of Lycium fruits in the regurgitation pellets of the two predatory birds. Seeds were found in 7.3% of the lizard droppings, 31.0% of kestrel pellets and 55.7% of shrike regurgitations. The mean number of seeds per dropping or pellet was 4.8 ±4 in lizard, 20.2 ±34.5 in shrike and 6.7 ±8.1 in kestrel. The percentage of viable seeds showed significant differences among all four treatments, decreasing in the following direction: seeds collected directly from plants (98.0%), shrikes (88.0%), lizards (72.3%), and kestrels (31.7%). Seeds from Lycium fresh fruits and shrike pellets showed significantly higher germination rates than those from lizard droppings and kestrel pellets. While lizards and shrikes are effective seed dispersers, kestrel gut treatment decreases seed viability. Seed viability is always higher than seed germination in each of the four treatments. In this island environment, Lycium seeds are under an important random influence during the seed dispersal process. Secondary seed dispersal seems to acquire a relevant dimension in small and remote insular environments or isolated continental systems where interactions among the different elements involved are intense, all of them are abundant native residents, and they have been coexisting for a long time. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 345–352.     

Atmospheric water vapor as driver of litter decomposition in Mediterranean shrubland and grassland during rainless seasons

Litter production in many drought‐affected ecosystems coincides with the beginning of an extended season of no or limited rainfall. Because of lack of moisture litter decomposition during such periods has been largely ignored so far, despite potential importance for the overall decay process in such ecosystems. To determine drivers and extent of litter decay in rainless periods, a litterbag study was conducted in Mediterranean shrublands, dwarf shrublands and grasslands. Heterogeneous local and common straw litter was left to decompose in open and shaded patches of various field sites in two study regions. Fresh local litter lost 4–18% of its initial mass over about 4 months without rainfall, which amounted to 15–50% of total annual decomposition. Lab incubations and changes in chemical composition suggested that litter was degraded by microbial activity, enabled by absorption of water vapor from the atmosphere. High mean relative humidity of 85% was measured during 8–9 h of most nights, but the possibility of fog deposition or dew formation at the soil surface was excluded. Over 95% of the variation in mass loss and changes in litter nitrogen were explained by characteristics of water‐vapor uptake by litter. Photodegradation induced by the intense solar radiation was an additional mechanism of litter decomposition as indicated by lignin dynamics. Lignin loss from litter increased with exposure to ultraviolet radiation and with initial lignin concentration, together explaining 90%–97% of the variation in lignin mass change. Our results indicate that water vapor, solar radiation and litter quality controlled decomposition and changes in litter chemistry during rainless seasons. Many regions worldwide experience transient periods without rainfall, and more land area is expected to undergo reductions in rainfall as a consequence of climate change. Therefore, absorption of water vapor might play a role in decomposition and nutrient cycling in an increasing number of ecosystems.