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11.
Robert K. VickeryJr. 《Evolutionary biology》2008,35(3):199-207
Mimulus verbenaceus has successfully invaded and/or competed for the very specialized habitats of desert seeps and springs characterized by scarce
or no pollinators (personal observation). It has done so by evolving an ingenious mechanism of reproductive assurance in which
the senescing epipetalous corolla bends down, abscisses and slides down its style dragging its anthers over the stigma lobes,
resulting in self-pollination. This dragging mechanism both depends on the plants ability to self-pollinate and presumably
promotes the evolution of self-pollination by providing an advantage—invasion of new habitats—to counter-balance the disadvantages
of selfing. M. verbenaceus has evolved a second means of reproductive assurance that depends on the nearness of the anthers to the stigma lobes. They
are close, even touching, in the red flowers, leading to much self-pollination and are well separated in the yellow flowers
leading to little self-pollination. This advantage of the red-flowered plants likely explains the relative abundance of the
red morph and the rarity of the yellow morph in nature as well as the greater seed set of the red-flowered morph than that
of the yellow-flowered morph. 相似文献
12.
Pollination biology of the saprophytic speciesPetrosavia sakuraii was investigated in Central Japan. The flower opens at any time of the day, and the anthers of outer stamens dehisce after
about one day and those of the inner stamens after two days. The stigmata on the semicarpous (nearly apocarpous) pistil, which
are already receptive when the flower opens, are situated in the center of the flower and move gradually outwards to touch
the anthers of outer stamens about five days after anthesis. The breeding experiments show that the stigmata are receptive
at least for five days, and many seeds are produced through autonomous self-pollination. That means the nearly apocarpous
pistil, which is in a primitive condition, is adapted to the autonomous self-pollination. The selfing rate including insect-mediated
self-pollination is very high, and this sexual-reproductive system seems favorable to the saprophytic plant which is probably
severely limited in its resources. However, cross-pollination also may be performed by the small bees of Lasioglossum and
some other insects, even though they do not so frequently visit the flowers and the out-crossing rate is low. 相似文献
13.
Felix Gugerli 《Oecologia》1998,114(1):60-66
Self-compatibility in high arctic and alpine areas is regarded as an adaptation to low pollinator abundance. However, high
genetic variability as a consequence of outcrossing is, with regard to population persistence, favorable in highly stochastic
environments such as tundra habitats. To evaluate these contradictory scenarios, I performed in situ pollination experiments
to examine the breeding system of the predominant outcrosser Saxifraga oppositifolia in ten populations at two different elevations in the Swiss Alps. Pollinator limitation was detected at both elevations,
but fruit set in naturally pollinated flowers was only slightly less at the higher elevation. Increased pollinator limitation
at high compared with low elevation thus could not be demonstrated in this experiment. Hand-crossings yielded equal mean proportion
seed set at both elevations, and so did hand-selfings. This constant pattern of the breeding system in S. oppositifolia indicates selective factors that lead to the maintenance of a high level of outcrossing even in high-elevation populations.
Based on sex allocation models, it was expected that a high ovule number should be selectively advantageous in a plant-pollinator
system where chance visitation or selfing play important roles. However, female reproductive offer in terms of ovule number
per flower did not change from low to high elevation. Since neither increased pollinator limitation nor increased seed set
in selfed flowers was found at high compared with low elevation, the prerequisites for testing the hypothesis were not given.
This study contradicts the hypothesis that inimical environmental factors in alpine or arctic habitats necessarily select
for increased selfing rates in a preferentially outcrossing species like S. oppositifolia.
Received: 28 April 1997 / Accepted: 20 October 1997 相似文献
14.
Genetic consequences of specialization: yucca moth behavior and self-pollination in yuccas 总被引:2,自引:0,他引:2
Reciprocal specialization in interspecific interactions, such as plant-pollinator mutualisms, increases the probability that
either party can have detrimental effects on the other without the interaction being dissolved. This should be particularly
apparent in obligate mutualisms, such as those that exist between yucca and yucca moths. Female moths collect pollen from
yucca flowers, oviposit into floral ovaries, and then pollinate those flowers. Yucca moths, which are the sole pollinators
of yuccas, impose a cost in the form of seed consumption by the moth larvae. Here we ask whether there also is a genetic cost
through selfish moth behavior that may lead to high levels of self fertilization in the yuccas. Historically, it has been
assumed that females leave a plant immediately after collecting pollen, but few data are available. Observations of a member
of the Tegeticula yuccasella complex on Yucca filamentosa revealed that females remained on the plant and oviposited in 66% of all instances after observed pollen collections, and
51% of all moths were observed to pollinate the same plant as well. Manual cross and self pollinations showed equal development
and retention of fruits. Subsequent trials to assess inbreeding depression by measuring seed weight, germination date, growth
rate, and plant mass at 5 months revealed significant negative effects on seed weight and germination frequency in selfed
progeny arrays. Cumulative inbreeding depression was 0.475, i.e., fitness of selfed seeds was expected to be less than half
that of outcrossed seeds. Single and multilocus estimates of outcrossing rates based on allozyme analyses of open-pollinated
progeny arrays did not differ from 1.0. The discrepancy between high levels of behavioral self-pollination by the moths and
nearly complete outcrossing in mature seeds can be explained through selective foreign pollen use by the females, or, more
likely, pollen competition or selective abortion of self-pollinated flowers during early stages of fruit development. Thus,
whenever the proportion of pollinated flowers exceeds the proportion that can be matured to ripe fruit based on resource availability,
the potential detrimental genetic effects imposed through geitonogamous pollinations can be avoided in the plants. Because
self-pollinated flowers have a lower probability of retention, selection should act on female moths to move among plants whenever
moth density is high enough to trigger abortion.
Received: 18 March 1996 \Accepted: 30 July 1996 相似文献
15.
Understanding reproductive systems of rare plants is critical for conservation efforts. Lakela's Mint, Dicerandra immaculata Lakela var. immaculata, is an endangered plant endemic to an approximately 4.8-km long area in Florida, USA. We used an experimental garden and three populations of Lakela's Mint to determine: (1) what is the breeding system (autonomous, asexual, self-fertile, cross-fertile) and are insects necessary for reproduction; (2) which native and nonnative insect species visit flowers and is the frequency of visits to a plant influenced by its height; (3) does the number of flowers visited within a plant by individual insects differ among native and nonnative insect species and due to plant height; and (4) is seed output influenced by plant height? Our results indicate that the breeding system of Lakela's Mint was facultative outcrossing. Insect-pollinated flowers produced more seeds than flowers that reproduced autonomously or asexually. The honey bee Apis mellifera L., a nonnative species, was the most frequent visitor to plants and visited more flowers within plants than native pollinators, but its behavior was not influenced by plant height. Native pollinators such as Bombus impatiens Cresson were attracted more frequently to shorter plants, but visited fewer flowers than on taller plants. Despite having fewer total and pollinated flowers, shorter plants had a higher output of intact seeds than taller plants, which could be due to differences in efficiency between native and nonnative pollinators or other factors. Our results add insight into factors influencing seed output and interactions between pollinators and rare plants. 相似文献
16.
Most crops grown in Europe, including sunflower (Helianthus annulus L.), benefit from insect pollination. However, valuing this benefit is not straightforward since estimates of the increase in sunflower yield vary from 18% to 100%. Most estimates have, moreover, been performed at plant scale, a scale that is not relevant for farmers who calculate at the field scale. In this four-year study, we quantified the contribution of insect pollination to sunflower yield at field and plant scales in working farm fields distributed along a gradient of pollinator diversity and abundance. Pollinators were found to increase field yield up to 40% (i.e. 0.7 t/ha) and by 31.3% at plant scale; the magnitude of effect on yield being therefore similar at both scales. The pollinators increased the yield by increasing the number of fertilized seeds per plant with no significant effect on the unit mass of the seeds although there was a trade-off between number of seeds and unit mass. Among pollinators, honeybees were the main taxon impacting sunflower yield. Sunflower plant density was a strong determinant of yield, with higher numbers attracting increased numbers of honeybees. Using pollinator and wind exclusion, we finally quantified the relative contributions of self-pollination (∼40%), insect pollination (∼35%) and wind pollination (∼20%). Our results show, to the best of our knowledge, the first evidence of the key role of pollinators in sunflower production at field scale in real farming conditions, and underscore the need to maintain suitable conditions for pollinators in agricultural landscapes. 相似文献
17.
C. Montaner E. Floris J. M. Alvarez 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,101(1-2):185-189
The polygenic postzygotic self-incompatible system reported in borage (Borago officinalis L.) is refuted. The behaviour of pollen tubes after self- and cross-pollination, analysis of the crossability coefficient,
seed set after continuous generations of self-pollination and the effects of inbreeding depression in borage were studied.
Evidence of self-compatibility was established. The influence of protandry in a self-compatible system is also discussed.
Received: 15 July 1999 / Accepted: 3 November 1999 相似文献