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1.
The potential for and constraints on the evolution of compensatory ability in Asclepias syriaca 总被引:2,自引:0,他引:2
To investigate the potential for and constraints on the evolution of compensatory ability, we performed a greenhouse experiment
using Asclepias syriaca in which foliar damage and soil nutrient concentration were manipulated. Under low nutrient conditions, significant genetic
variation was detected for allocation patterns and for compensatory ability. Furthermore, resource allocation to storage was
positively, genetically correlated both with compensatory ability and biomass when damaged, the last two being positively,
genetically correlated with each other. Thus, in the low nutrient environment, compensatory ability via resource allocation
to storage provided greater biomass when damaged. A negative genetic correlation between compensatory ability and plant biomass
when undamaged suggests that this mechanism entailed an allocation cost, which would constrain the evolution of greater compensatory
ability when nutrients are limited. Under high nutrient conditions, neither compensatory ability nor allocation patterns predicted
biomass when damaged, even though genetic variation in compensatory ability existed. Instead, plant biomass when undamaged
predicted biomass when damaged. The differences in outcomes between the two nutrient treatments highlight the importance of
considering the possible range of environmental conditions that a genotype may experience. Furthermore, traits that conferred
compensatory ability did not necessarily contribute to biomass when damaged, demonstrating that it is critical to examine
both compensatory ability and biomass when damaged to determine whether selection by herbivores can favor the evolution of
increased compensation.
Received: 2 April 1999 / Accepted: 21 September 1999 相似文献
2.
Kirk A. Stowe 《Evolution; international journal of organic evolution》1998,52(3):703-712
The evolutionary response of plant populations to selection for increased defense may be constrained by costs of defense. The purpose of this study was to investigate such constraints on the evolution of defense due to a cost of defense manifested as a trade-off between defense and tolerance. Variation in the response to artificial damage (tolerance) among lines of Brassica rapa that had been artificially selected for foliar glucosinolate content (defense) was examined. Leaf area was removed from replicates of three selection lines (high glucosinolates, control, and low glucosinolates) at three damage levels (0%, 20%, and 60% damage). An external cost of defense would result in a statistically significant selection line by damage treatment interaction, with those selected for high defense expressing less tolerance than those selected for low defense. Damage treatment had a significant overall effect on estimated total fitness, with fitness declining with increasing damage level. Further, selection line also had a significant overall effect on estimated total fitness, with low-defense selection lines having higher fitness compared to both control and high-defense selection lines. More importantly, a cost of defense in terms of tolerance was demonstrated by a significant selection line-by-damage treatment interaction. This interaction was in the direction to demonstrate a genetic trade-off between defense and tolerance, with low-defense selection lines decreasing estimated total fitness in response to damage less than both control and high-defense selection lines. Variation in tolerance among selection lines was due to the greater ability of low-defense lines to maintain fruit and seed production despite the presence of damage. In terms of tolerance, this cost of glucosinolate production in B. rapa could constrain the evolution of increased defense and, in so doing, maintain individuals within the population that are poorly defended yet tolerant. 相似文献
3.
Comparison of Triazine-Resistant and -Susceptible Biotypes of Senecio vulgaris and Their F(1) Hybrids 总被引:3,自引:3,他引:0 下载免费PDF全文
The relationship of triazine resistance to decreased plant productivity was investigated in Senecio vulgaris L. F1 reciprocal hybrids were developed from pure-breeding susceptible (S) and resistant (R) lines. The four biotypes (S, S × R, R, R × S) were compared in terms of atrazine response, electron transport, carbon fixation, and biomass production. Atrazine response, carbon fixation rate, and PSII and whole-chain electron transport rates of hybrids were nearly identical to those of their respective maternal parents. Significant differences occurred between the two susceptible (S, S × R) and two resistant (R, R × S) biotypes in atrazine response (I50), carbon fixation rate, and PSII and whole-chain electron transport rates; PSI rates were identical in all four biotypes. Coupled and uncoupled, whole-chain electron transport rates of thylakoids of the two susceptible biotypes were approximately 50% greater than those of the two resistant biotypes at photon flux densities greater than 215 micromoles per square meter per second. Carbon exchange rates of the two susceptible biotypes were 23% greater than those of the two resistant biotypes. Hybrid biotypes (S × R, R × S) were not identical to their maternal parents in biomass production. The S, S × R, and R × S plants all achieved greater biomass than R plants. These results suggest that while the resistance mutation influences thylakoid performance, reduced productivity of triazine-resistant plants cannot be ascribed solely to decreases in electron transport or carbon assimilation rates brought about by the altered binding protein. Since the F1 hybrids differed from their maternal parents only in nuclear genes, it appears that the detrimental effects of the triazine resistance mutation on plant growth may be attenuated by interactions of the plastid and nuclear genomes. 相似文献
4.
The endogenous neuropeptide, neurotensin (NT) alters the firing frequencies of certain neurons in the central nervous system (CNS). This is one of the findings that support the hypothesis that NT is a neurotransmitter substance. The direct application of NT on CNS neurons causes predominantly excitatory effects. These effects occur in a dose-related fashion via a calcium-dependent postsynaptic mechanism. The C-terminal hexapeptide fragment, NT 8-13 exerts similar electrophysiological effects to NT, while the N-terminal octapeptide fragment, NT 1-8 is devoid of such activity. NT produces a significant increase in the firing rates of individual neurons in the substantia nigra (SN), ventral tegmental area (VTA), medial prefrontal cortex (MPF), hypothalamus, and periaqueductal grey (PAG). This excitation occurs with a rapid onset and is readily reversible after cessation of NT application. In contrast, NT has no effect or weak inhibitory effects on the firing rates of neurons in the locus coeruleus (LC) and cerebellum. These electrophysiological actions of NT appear to be unique and not shared by other neurotransmitter and neuropeptide receptor antagonists and agonists that have been studied via direct co-application. NT attenuates dopamine (DA)-induced inhibition associated with direct application onto neurons in the SN and VTA both in vivo and in vitro. Intracellular recordings suggest that direct application of higher concentrations of NT appears to produce 'depolarization block' on individual neurons in the SN, VTA, MPF, and hypothalamus. The electrophysiological consequences of NT application not only show similarities to clinically efficacious antipsychotic medications, but also demonstrate the ability of NT to modulate the activity of dopamine (DA) neurons at the cellular level via specific NT binding sites. These findings further underscore the possibility that NT may play a pre-eminent role in the pathogenesis of, and psychopharmacological management of neurological and psychiatric disorders purportedly related to perturbation of CNS DA systems including schizophrenia. 相似文献
5.
Summary Crab photoreceptors were examined after treatment by the osmium-DMSO-osmium method for high-resolution scanning electron microscopy. This technique of specimen preparation was also adapted for transmission electron microscopy, enabling sections up to 1 urn thick to be viewed in a conventional microscope at 75 kV. With appropriate pretreatment, some cytoskeletal elements can be visualised by both techniques. The methods were then used to investigate some of the daily changes known to occur in photoreceptor cell structure. Striking differences were found in the structure of Golgi bodies present in retinula cells during the synthesis and breakdown phases of the daily cycle of photoreceptor membrane turnover. Cyclic changes were also noticed in the mitochondria of retinula cells, and additional evidence was found for a previously proposed model of rhabdomeral microvillus formation. 相似文献
6.
Hardies SC; Martin SL; Voliva CF; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1986,3(2):109-125
7.
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9.
A major difference between the divergence patterns within the lines-1 families in mice and voles 总被引:3,自引:0,他引:3
Vanlerberghe F; Bonhomme F; Hutchison CA d; Edgell MH 《Molecular biology and evolution》1993,10(4):719-731
L1 retroposons are represented in mice by subfamilies of interspersed
sequences of varied abundance. Previous analyses have indicated that
subfamilies are generated by duplicative transposition of a small number of
members of the L1 family, the progeny of which then become a major
component of the murine L1 population, and are not due to any active
processes generating homology within preexisting groups of elements in a
particular species. In mice, more than a third of the L1 elements belong to
a clade that became active approximately 5 Mya and whose elements are >
or = 95% identical. We have collected sequence information from 13 L1
elements isolated from two species of voles (Rodentia: Microtinae: Microtus
and Arvicola) and have found that divergence within the vole L1 population
is quite different from that in mice, in that there is no abundant
subfamily of homologous elements. Individual L1 elements from voles are
very divergent from one another and belong to a clade that began a period
of elevated duplicative transposition approximately 13 Mya. Sequence
analyses of portions of these divergent L1 elements (approximately 250 bp
each) gave no evidence for concerted evolution having acted on the vole L1
elements since the split of the two vole lineages approximately 3.5 Mya;
that is, the observed interspecific divergence (6.7%-24.7%) is not larger
than the intraspecific divergence (7.9%-27.2%), and phylogenetic analyses
showed no clustering into Arvicola and Microtus clades.
相似文献
10.
Rapid synthesis of photoreceptor membrane and assembly of new microvilli in a crab at dusk 总被引:4,自引:0,他引:4
Dr. Sally Stowe 《Cell and tissue research》1980,211(3):419-440
Summary Large areas of photoreceptor membrane are synthesized in the retinula cells of the crab Leptograpsus variegatus at dusk. Initially, new membrane differentiates from rough endoplasmic reticulum (ER) as large tubules of smooth ER. These tubules transform to concentric ellipsoids of closely apposed pairs of membranes (doublet ER), sometimes passing through an intervening crenate form. The new membrane is transported through bridges of cytoplasm that cross the palisade to the rhabdom region, from which the remains of the rhabdomeres that were built during the previous dusk have been dissolved. The degradation of the old microvilli of one rhabdomere is accomplished without affecting neighbouring rhabdomeres of other cells. New microvilli are assembled in situ from sheets of doublet ER, which are converted to tubules oriented in the same direction as the future microvilli. The cytoplasmic face of the ER remains the cytoplasmic face of the tubules, which become progressively narrower, partly by further longitudinal division, until the final diameter of the microvillus is reached. A central core is often seen in transverse sections of mature microvilli. It may be involved in the final consolidation, but rhabdomeric microvilli are not formed in the same manner as those of intestinal brush border cells. There is no evidence that new membrane passes through the Golgi compartment before incorporation into the rhabdom, as is the case for rod outer segment membrane in vertebrate photoreceptors. 相似文献