Pollination failure in mediterranean Ruscus aculeatus L.

Abstract

The rcproductive biolog-of Ruscus aculeatuc L. was studied at a mediterranean sitc during 1996-1 999. Field obsenations showed that reproductive success was very low, because only 3"h of the marked flowers developed fruits in 1996 and none in 1997 and 1998. Several experiments w-ere performed to investigate the reasons for reproductive failure in this species.Pollen viabilitl-\\-as on average 85%. showing that reproductive failure is not dur to poor pollen quality. Two hand-pollination experiments showed that all flowers are potentially able to develop fruits throughout the flowering period, suggesting that no aberration occurs in sporogenesis, fertilization or post-zygote processes in R. aculeatus and that low reproductive success in the field occurs because of lack of pollination. This hipothesis xras tested b!looking for pollen on the sticgmatic surface of randomly sampled flowers, but without success. Moreover. the bodies of insects trapped in the proximity of the female plants \\'ere carefully checked for pollen but none Lvas found. The number of pollen grains produced per flower is lower than that reported for wind-pollinated species. Nevertheless, tve showed with empirical probes that the possibilih of wind pollination cannot be ruled out. The breeding system and reproductix-e characteristics of R. acu1eatu.r seem to match the traits of the sclerophyllous taxa remnants of the tropical Tertiary flora. hforeover, the climatic fluctuation of the Quaternary and the cstablishment of the mediterranean climate might have changed the conditions of a good pollination process. At present, the low sexual reproduction of R. aculeatus is due to the lack of pollen transport. Within a population of R. aculeatus. genetic variability is re\.ealed by seeds from the few developed fruits which have been shown to be viable. However, maintenance of the individual plants in the population relies on thc resprouting capaciv of the species in question 0 2000 Thr I,imr.in Siicim of-London

Low fruit set in the abundant dioecious tree Clusia hilariana (Clusiaceae) in a Brazilian restinga

“…Other comparable studies of fruit set in dioecious, abundant plants considered as low fruit set values ranging from 3% to 15% for natural pollination (Niesenbaum, 1992;Voigt et al, 2005), as compared to hand pollination treatments ranging from 40% to 80% i.e., hand pollination in these cases increased fruit set from 3 to 5 times, in the range of what we found for C. hilariana. The case of Ruscus aculeatus L. is the most extreme we found in the literature, where hand pollination increased fruit set by 20 times (Martı´nez-Palle´and Aronne, 2000).…”

“…Vegetative reproduction through underground organs does take place in C. hilariana (Scarano et al, 2004) and this is a common feature to many other restinga shrubs (Cirne and Scarano, 2001). Genetic studies are necessary to test this second hypothesis, but a similar hypothesis has been forwarded by Martı´nez-Palle´and Aronne (2000) in a study of the dioecious Ruscus aculeatus. However, if clonal reproduction dominates such that genetic variability of this nurse plant is low, this plant community may be even more fragile and of greater conservation concern than previously stated (Scarano, 2002).…”

Are differences in breeding mechanisms and fertility among populations contributing to rarity in Grevillea rhizomatosa (Proteaceae)?

“…Low fruit to flower ratios were detected in three fertile populations and experiments revealed that the cause of this was more likely to be ecological factors (resources for growth) and pollen quality than pollen quantity. Lowered fecundity in plants is often due to pollen limitation incurred by a shortage of pollinator visits (Copland and Whelan, 1989;Martínez-Palle and Aronne, 2000) although less often is an absolute failure in seed set caused by a total lack of pollinators (but see Lamont et al, 1993). Presumably absolute pollinator limitation is rare because it would quickly lead to local extinctions when populations cannot be maintained by asexual reproduction.…”

Biological Flora of the British Isles: Ruscus aculeatus

“…Despite the long flowering period, fruit development usually begins only in late April (Martínez‐Pallé & Aronne ), taking 6–8 months to mature, and so producing mature fruits usually by the end of October (Fuentes ; de Lillis & Fontanella ; Aronne & Wilcock ). Ripe fruits remain on the plant for long time, certainly through the winter (Herrera ) and often for 1–2 years (Martínez‐Pallé & Aronne ) so that plants tend to carry fruits all year round.…”