12165 research outputs found
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A novel indirect defence in Brassicaceae: Structure and function of extrafloral nectaries in Brassica juncea
No full textWhile nectaries are commonly found in flowers, some
plants also form extrafloral nectaries on stems or leaves. For
the first time in the family Brassicaceae, here we report
extrafloral nectaries in Brassica juncea. The extrafloral
nectar (EFN) was secreted from previously amorphic sites
on stems, flowering stalks and leaf axils from the onset of
flowering until silique formation. Transverse sections at the
point of nectar secretion revealed a pocket-like structure
whose opening was surrounded by modified stomatal guard
cells. The EFN droplets were viscous and up to 50% of the
total weight was sugars, 97% of which was sucrose in the
five varieties of B. juncea examined. Threonine, glutamine,
arginine and glutamate were the most abundant amino
acids. EFN droplets also contained glucosinolates, mainly
gluconapin and sinigrin. Nectar secretion was increased
when the plants were damaged by chewing above- and
belowground herbivores and sap-sucking aphids. Parasitoids
of each herbivore species were tested for their preference,
of which three parasitoids preferred EFN and sucrose
solutions over water. Moreover, the survival and fecundity
of parasitoids were positively affected by feeding on EFN.
We conclude that EFN production in B. juncea may
contribute to the indirect defence of this plant species.
A thready affair: linking fungal diversity and community dynamics to terrestrial decomposition processes
No full textFilamentous fungi are critical to the decomposition of terrestrial organic matter and, consequently, in the global carbon cycle. In particular, their contribution to degradation of recalcitrant lignocellulose complexes has been widely studied. In this review, we focus on the functioning of terrestrial fungal decomposers and examine the factors that affect their activities and community dynamics. In relation to this, impacts of global warming and increased N deposition are discussed. We also address the contribution of fungal decomposer studies to the development of general community ecological concepts such as diversity–functioning relationships, succession, priority effects and home–field advantage. Finally, we indicate several research directions that will lead to a more complete understanding of the ecological roles of terrestrial decomposer fungi such as their importance in turnover of rhizodeposits, the consequences of interactions with other organisms and niche differentiation.
The fate of cyanobacterial detritus in the food web of Lake Taihu: a mesocosm study using 13C and 15N labeling
No full textThe ecosystem of the highly eutrophic
Lake Taihu (China) is seriously affected by recurrent
cyanobacterial blooms, but little is known about the
contribution made by cyanobacteria to the food web.
In this study, we investigated the fate of detritus of the
cyanobacterium Microcystis in the food web of Lake
Taihu through a 19-day mesocosm experiment using
stable-isotopic tracers of carbon (13C) and nitrogen
(15N). 13C- and 15N-labeled Microcystis detritus was
added to the mesocosm tanks and tracked through
different elements of the food web. We found clear
enrichment with both 13C and 15N in some zooplankton
species, including Daphnia, Diaphanosoma, and
Sinocalanus, which suggests that these zooplankters
can utilize cyanobacterial detritus as a food source.
Benthic animals, chironomid larvae and Limnodrilus,
also showed pronounced increases in 13C and 15N, but
the isotope increase was relatively smaller in the
gastropods, Radix sp. and Bellamya sp., implying that
they either exploited this food source differently or
responded slower than the zooplankton, which apparently
grew faster than the snails. Our study suggests
that cyanobacterial detritus, originating almost wholly
from the bloom-forming Microcystis, is an important
food source for both planktonic and benthic food webs
in eutrophic lakes such as Lake Taihu.
Intraspecific variation in plant size, secondary plant compounds, herbivory and parasitoid assemblages during secondary succession
No full textDuring secondary succession on abandoned agricultural fields the diversity and abundance of insect communities often increases, whereas the performance and nutritional quality of early successional plants often declines. As the diversity and abundance of insects on a single plant are determined by characteristics of the environment as well as of the host plant, it is difficult to predict how insects associated with a single plant species will change during succession. We examined how plant characteristics of the early successional plant species ragwort (Jacobaea vulgaris), and the herbivores and parasitoids associated with these plants change during secondary succession. In ten grasslands that differed in time since abandonment (3–26 years), we measured the size and primary and secondary chemistry of individual ragwort plants. For each plant we also recorded the presence of herbivores in flowers, leaves and stems, and reared parasitoids from these plant parts. Ragwort plants were significantly larger but had lower nitrogen concentrations in recently abandoned sites than in older sites. Pyrrolizidine alkaloid (PA) composition varied among plants within sites but also differed significantly among sites. However, there was no relationship between the age of a site and PA composition. Even though plant size decreased with time since abandonment, the abundance of stem-boring insects and parasitoids emerging from stems significantly increased with site age. The proportion of plants with flower and leaf herbivory and the number of parasitoids emerging from flowers and leaves was not related to site age. Parasitoid diversity significantly increased with site age. The results of our study show that ragwort and insect characteristics both change during secondary succession, but that insect herbivore and parasitoid abundances are not directly related to plant size or nutritional quality.
Is microevolution the only emergency exit in a warming world? Temperature influences egg laying but not its underlying mechanisms in great tits
No full textMany bird species have advanced their seasonal timing in response to global warming, but we still know little about the causal effect of temperature. We carried out experiments in climate-controlled aviaries to investigate how temperature affects luteinizing hormone, prolactin, gonadal development, timing of egg laying and onset of moult in male and female great tits. We used both natural and artificial temperature patterns to identify the temperature characteristics that matter for birds. Our results show that temperature has a direct, causal effect on onset of egg-laying, and in particular, that it is the pattern of increase rather than the absolute temperature that birds use. Surprisingly, the pre-breeding increases in plasma LH, prolactin and in gonadal size are not affected by increasing temperature, nor do they correlate with the onset of laying. This suggests that the decision to start breeding and its regulatory mechanisms are fine-tuned by different factors. We also found similarities between siblings in the timing of both the onset of reproduction and associated changes in plasma LH, prolactin and gonadal development. In conclusion, while temperature affects the timing of egg laying, the neuroendocrine system does not seem to be regulated by moderate temperature changes. This lack of responsiveness may restrain the advance in the timing of breeding in response to climate change. But as there is heritable genetic variation on which natural selection can act, microevolution can take place, and may represent the only way to adapt to a warming world.
