Rapid floral senescence following male function and breeding systems of some tropical orchids.

No comparative study of floral senescence following male function among a range of tropical orchid genera has previously been undertaken. The timing and pattern of floral senescence and occurrence of fruit formation were studied following self-, geitonogamous and cross-pollination in 14 epiphytic and two terrestrial orchid species to determine their breeding system and assess the occurrence of floral abscission following pollinaria removal. Both pollination and pollinaria removal caused rapid floral senescence, and the pattern and timing of the floral changes were the same in all treatments. Six Dendrobium species and Pelatantheria insectifera were self-incompatible (SI) and eight other species, including one terrestrial species, were self-compatible (SC). Capsules produced from outcrossing in four SC species, Phalaenopsis cornu-cervi, Eria pubescens, Cleisostoma appendiculatum and Arundina graminifolia, were larger and heavier than those produced after selfing. Reductions in flower life span following pollinaria removal were positively correlated with flower size and longevity of unpollinated flowers but not with position in the inflorescence or nature of the breeding system. Rapid flower senescence following pollinaria removal reported here suggests that it may be widespread in tropical species. The significant association of the response with size of flowers and inflorescences among the species studied suggests that the cost of flower maintenance outweighs the benefit of remaining open for female function after pollinaria have been removed. Both SC and SI species were found among tropical orchids, but variation in capsule size following self- and cross-pollination indicates that there may be a reduction in seed production following selfing, even in SC species, and that fruit formation alone should not be taken as reliable evidence of full self-compatibility.

Limited mate availability decreases reproductive success of fragmented populations of Linnaea borealis, a rare, clonal self-incompatible plant.

BACKGROUND AND AIMS: Small populations of rare plant species are increasingly reported to have high levels of reproductive failure. The objective of this study was to understand the principal constraints on sexual reproduction in small fragmented populations of a rare clonal self-incompatible plant. METHODS: The pollinator spectrum, diversity of flower colour, natural pollination and fruit-set levels of L. borealis were examined in Scotland. Artificially crossed seed production was compared within and between different flower colour types and patches. KEY RESULTS: Linnaea borealis was pollinated by a diverse spectrum of insect species and the principal pollinators were muscid, syrphid and empid flies which mostly moved only small distances (<0.25 m) between flowers when foraging. Natural pollination levels were high, indicating high pollinator effectiveness, but fruit set was very low in most patches. Flower colour diversity was low in most patches and only those with a diversity of flower colour types had high fruiting success. Pollination experiments showed L. borealis to be highly self-incompatible and artificial crosses within and between patches and flower colour types confirmed that low fruit success was the result of a lack of compatible mates and limited pollen movement between them. Evidence of isolation from pollen exchange was apparent at as little as 6 m and severe at 30 m and beyond. CONCLUSIONS: Limited mate availability and isolation from pollen exchange compromise the reproductive success of fragmented populations of L. borealis in Scotland. A diversity of compatible mates situated within close proximity (<6 m) is the key requirement to ensure high natural fruiting success. This study emphasizes that an understanding of the breeding system, pollinator spectrum and potential for interconnectivity via pollinator movement are fundamental to identify isolation distances and to establish when conservation intervention is necessary for rare species.

Biological activity of Euonymus europaeus.

The n-hexane, dichloromethane and methanol extracts of the seeds of Euonymus europaeus have been screened for antibacterial and free radical scavenging activity. General toxicity (brine shrimp lethality assay) of these extracts has also been assessed.

Fruit set, nectar reward, and rarity in the Orchidaceae.

A review of comparative levels of reproductive success among nectariferous and nectarless orchids worldwide was compiled from a comprehensive survey of fruit set from 117 orchid species in the literature and from our own field studies. It confirms the hypothesis that nectariferous orchids are more successful in setting fruit than are nectarless species. Overall fruit set figures for nectarless and nectariferous orchids were 19.5 and 49.3% for North America, 27.7 and 63.1% for Europe, 41.4 and 74.4% for the temperate southern hemisphere, and 11.5 and 24.9% for the tropics, demonstrating that the dichotomy is consistent across all geographical areas. On average, the provision of nectar doubles the probability of fruit set in both temperate and tropical areas, but tropical orchids are remarkable in that all (whether nectarless or nectariferous, or terrestrial or epiphytic) display low fruit productivity (<50%). Fruiting failure in the tropics may be balanced by higher productivity per capsule, since tropical orchid fruits contain on average 150 times more seeds than temperate ones. Hybridization occurs more frequently among nectarless orchids in Britain and Europe than among nectariferous ones, and there is a significant positive association between orchid rarity and lack of nectar reward in the British Isles. Sexual reproduction in the Orchidaceae is predominantly pollinator dependent, but this can sometimes be successfully circumvented by asexual seed production (agamospermy) or, more frequently, by automatic self-pollination (autogamy). The proportion of highly successful nectarless orchids from all geographic areas is very low and comparable with that of orchids offering rewards other than nectar (∼14% of species in each case) emphasizing that high reproductive success is only associated with nectar reward (53% of species). It is suggested that the evolution of nectar production within the family has been the most frequent means of escaping the reproductive limitations of low pollinator visitation frequencies.

First evidence of myrmecochory in fleshy-fruited shrubs of the Mediterranean region.

In the mediterranean ecosystems of South Africa and Australia, the role of ants in the dispersal of seeds is well known and antagonistic interactions as well as myrmecochory occur. The high prevalence of seed dispersal by ants, relative so that by vertebrates, is viewed as evidence of adaptation to the nutrient poor soils typical of these environments. Ant dispersal has been considered unimportant in the Mediterranean region and, until now, no systematic study of ant-seed interaction has been undertaken. In the Mediterranean shrubland of Southern Italy the seed content of functioning nests of the ant Messor minor (André) has been quantitatively analyzed. The existence in the nest of seeds from shrub species, as well as those of the Fabaceae and Poaceae, suggest that ant dispersal may be much more widespread in the Mediterranean environments than has been realized. A large proportion of the seeds came from fleshy-fruited shrub species previously reported to be bird dispersed, e.g. Rhamnus alaternus L., Myrtus communis L., Smilax aspera L., Pistacia lentiscus L. and Phillyrea latifolia L. Analysis of nest mounds showed that, although many seeds bad been partially predated by the ants, a very large number had been collected, transported to the nest and subsequently removed to the mound without damage. Examination of the structure of the fruits and seeds of R. alaternus and M. communis, and summer fruiting phenology of R. alaternus, provided further evidence of specific adaptation to ant dispersal. The presence of an elaiosome on the seed is reported for the first time in both specific. Feeding trials showed that ants selectively remove specific diaspores, preferentially collecting the seeds with the elaiosome.