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71.
72.
Yurena Yanes Micha? Kowalewski Carolina Castillo Julio de la Nuez 《Palaeogeography, Palaeoclimatology, Palaeoecology》2007,251(2):283-299
Quantitative estimates of time-averaging (age mixing) in gastropod shell accumulations from Quaternary (the late Pleistocene and Holocene) eolian deposits of Canary Islands were obtained by direct dating of individual gastropods obtained from exceptionally well-preserved dune and paleosol shell assemblages. A total of 203 shells of the gastropods Theba geminata and T. arinagae, representing 44 samples (= stratigraphic horizons) from 14 sections, were dated using amino acid (isoleucine) epimerization ratios calibrated with 12 radiocarbon dates. Most samples reveal a substantial variation in shell age that exceeds the error that could be generated by dating imprecision, with the mean within-sample shell age range of 6670 years and the mean standard deviation of 2920 years. Even the most conservative approach (Monte Carlo simulations with a non-sequential Bonferroni correction) indicates that at least 25% of samples must have undergone substantial time-averaging (e.g., age variations within those samples cannot be explained by dating imprecision alone). Samples vary in shell age structure, including both left-skewed (17 out of 44) and right-skewed distributions (26 out of 44) as well as age distributions with a highly variable kurtosis. Dispersion and shape of age distributions of samples do not show any notable correlation with the stratigraphic age of samples, suggesting that the structure and scale of temporal mixing is time invariant. The statistically significant multi-millennial time-averaging observed here is consistent with previous studies of shell accumulations from various depositional settings and reinforces the importance of dating numerous specimens per horizon in geochronological studies. Unlike in the case of marine samples, typified by right-skewed age distributions (attributed to an exponential-like shell loss from older age classes), many of the samples analyzed here displayed left-skewed distributions, suggestive of different dynamics of age mixing in marine versus terrestrial shell accumulations. 相似文献
73.
Sheila K. Schueller 《Evolutionary ecology》2007,21(1):81-98
A match between floral and pollinator traits, such as that between unique island plants and pollinators, is often thought
to be the product of pollinator-mediated selection. I examined whether the floral morphology of an introduced hummingbird-pollinated
plant, Nicotiana glauca (tree tobacco, Solanaceae), is under selection by pollinators on the California Channel Islands where it is a recent colonist.
I first determined differences in floral morphology and pollinator composition between island and mainland populations of
N. glauca. I found that island plants have detectably longer corollas (on average 1 mm) and are visited by hummingbird species with
on average 1–2 mm longer bills than common mainland visitors. Corolla length differences were not found to be associated with
site abiotic differences. Flower size does not vary consistently with season and corolla width is very consistent across sites.
I tested whether island–mainland corolla length differences are the product of pollinator-mediated selection by measuring
phenotypic selection and per visit effectiveness. Contrary to expectations, a longer corolla was not consistently associated
with higher pollen transfer or seed count on the islands. Per visit effectiveness of longer and shorter-billed hummingbirds
did differ; however, effectiveness did not depend on corolla length. Although I failed to detect expected patterns of selection
for longer corollas on islands, I cannot rule out weak or past pollinator-mediated selection. It is also possible that despite
the apparent match between pollinator and floral traits, island–mainland differences in corolla length are instead due to
other environmental effects, selection unrelated to pollinators, or stochastic processes such as drift. 相似文献
74.
A previous study showed that some individuals of the tetraploid Galápagos endemic Scalesia affinis were able to produce offspring after selfing. The present study compares the fitness of self-pollinated offspring with the
fitness of cross-pollinated offspring. Germination success, seedling survival, and four different growth parameters was measured.
In most of the studied characters selfed offspring were significantly inferior to outcrossed progeny. The effect was very
clear in germination and survival. Outcrossed embryos were 3.4 times more likely to germinate than those that were selfed-fertilized,
and the mortality was 84% higher among selfed individuals. Also, there was no genetic variation in inbreeding depression.
The present study is based on material from a large population on Isabela Island, Galápagos. At other localities in the archipelago,
populations have been through recent dramatic bottlenecks due to the grazing of introduced mammals. Considering the significant
inbreeding depression found in the large population and the presence of a partial self-incompatibility system, these small
populations are likely to be highly vulnerable and their future survival critically threatened. 相似文献
75.
BACKGROUND AND AIMS: Invasion by alien plants may be partially related to disturbance-related increases in nutrient availability and decreases of competition with native species, and to superior competitive ability of the invader. Oxalis pes-caprae is an invasive winter geophyte in the Mediterranean Islands that reproduces vegetatively via bulbs. An investigation was made into the relative responses of O. pes-caprae and the native annual grass Lolium rigidum to nutrient availability and to competition with each other in order to understand patterns of invasion in the field. Because Oxalis accumulates oxalic acid in its leaves, which could ameliorate soil phosphorous availability, field observations were made to determine whether the presence of Oxalis alters soil P availability. METHODS: A full-factorial glasshouse experiment was conducted with nutrient availability (high and low) and competition (Lolium alone, Oxalis alone, and Lolium and Oxalis together). Plant performance was assessed by determining (1) above- and below-ground biomass at the time of Oxalis maximum biomass and (2) reproductive output of Oxalis and Lolium at the end of their respective growth cycles. Measurements were also taken for leaf N and P content. Soil samples were taken in the field from paired Oxalis-invaded and non-invaded plots located in Menorca (Balearic Islands) and available P was determined. KEY RESULTS: High nutrient availability increased Oxalis and Lolium vegetative biomass and reproductive output to a similar degree. Competition with Lolium had a much stronger negative effect on Oxalis bulb production than reduced nutrients. Lolium was a superior competitor than Oxalis; the latter did not affect Lolium maximum biomass and spike production. Significantly greater soil-P availability in Oxalis-invaded field soils relative to paired non-invaded soils suggest that Oxalis influences soil P cycling. CONCLUSIONS: Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites. The results also suggest that certain disturbances (e.g. autumn ploughing) may greatly enhance Oxalis invasion. 相似文献
76.
Kubodera T Koyama Y Mori K 《Proceedings. Biological sciences / The Royal Society》2007,274(1613):1029-1034
Our newly developed underwater high definition video camera system took the first live images of adults of the mesopelagic large squid, Taningia danae, between 240 and 940 m deep off Ogasawara Islands, western North Pacific. The resulting footage includes attacking and bioluminescence behaviours, and reveals that T. danae is far from the sluggish neutrally buoyant deep-sea squid previously suspected. It can actively swim both forward and backward freely by flapping its large muscular triangular fins and changes direction quickly through bending its flexible body. It can attain speeds of 2-2.5 ms(-1) (7.2-9 km h(-1)) when attacking bait rigs. They emitted short bright light flashes from their large arm-tip photophores before final assault, which might act as a blinding flash for prey as well as a means of measuring target distance in a dark deep-sea environment. They also emitted long and short glows separated by intervals while wandering around the double torch lights attached to the bait rig, suggestive of potential courtship behaviours during mating. 相似文献
77.
S. D. Grebel’nyi 《Russian Journal of Marine Biology》2007,33(1):54-57
Twenty-two samples of a rare sea anemone Ptychodactis patula having an unusual structure were found in the collection of the Zoological Institute (Russian Academy of Sciences, St. Petersburg). This species was previously referred to the small order Ptychodactiaria, which included only three species. P. apatula was known only from the coasts of Norway (the type locality), Iceland, and the Bering Strait. Our samples greatly exceed the materials thus far published, both in the number of specimens and their places of discovery. 相似文献
78.
A new species of Neopetitia San Martín, 2003 is described from intertidal and shallow subtidal soft-bottom stations on the eastern and western coast of Tenerife, Canary
Islands. The new species is characterized by the presence in males of a modified acicular chaeta in chaetiger 11. A discussion
of known species of the genus is presented. 相似文献
79.
80.
Analysis of Pathogenic Diversity of the Rice Bacterial Blight Pathogen (Xanthomonas oryzae pv. oryzae) in the Andaman Islands and Identification of Effective Resistance Genes
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Raj K. Gautam Pankaj K. Singh Krishnan Sakthivel Muthulingam Srikumar Naresh Kumar Krishna Kumar Awnindra K. Singh Sibnarayan Dam Roy 《Journal of Phytopathology》2015,163(6):423-432
Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major disease of rice in the tropics for which genetic resistance in the host plants is the only effective solution. This study aimed at identification of resistance gene combinations effective against Xoo isolates and fingerprinting of the Xoo isolates of Andaman Islands (India). Here, we report the reaction of 21 rice BB differentials possessing Xa1 to Xa21 genes individually and in different combinations to various isolates of pathogen collected from Andaman Islands. Pathological screening results of 14 isolates revealed that among individual genes tested across 2 years, Xa4, Xa7 and Xa21 conferred resistance reaction across all isolates, whereas among combinations, IRBB 50 (Xa4 + xa5), IRBB 52 (Xa4 + Xa21) and IRBB 60 (Xa4 + xa5 + xa13 + Xa21) conveyed effective resistance against tested isolates. The nature of genetic diversity among four isolates selected on the basis of geographical isolation in the islands was studied through DNA finger printing. The RAPD primers S111, S119, S1117, S1109, S1103, S109 and S105 were found to be better indicators of molecular diversity among isolates than JEL primers. The diversity analysis grouped 14 isolates into three major clusters based on disease reaction wherein isolate no. 8 was found the most divergent as well as highly virulent. The remaining isolates were classified into two distinct groups. The importance of the study in the context of transfer of resistance gene(s) in the local cultivars specifically for tropical island conditions is presented and discussed. 相似文献