Maximal ecological diversity exceeds evolutionary diversity in model ecosystems

Understanding community saturation is fundamental to ecological theory. While investigations of the diversity of evolutionary stable states (ESSs) are widespread, the diversity of communities that have yet to reach an evolutionary endpoint is poorly understood. We use Lotka–Volterra dynamics and trait-based competition to compare the diversity of randomly assembled communities to the diversity of the ESS. We show that, with a large enough founding diversity (whether assembled at once or through sequential invasions), the number of long-time surviving species exceeds that of the ESS. However, the excessive founding diversity required to assemble a saturated community increases rapidly with the dimension of phenotype space. Additionally, traits present in communities resulting from random assembly are more clustered in phenotype space compared to random, although still markedly less ordered than the ESS. By combining theories of random assembly and ESSs we bring a new viewpoint to both the saturation and random assembly literature.     

春小麦不同发育阶段抗氧化系统对田间缓慢干旱的响应

研究了两种抗旱性不同的春小麦(Triticum aestivum L.)品种定西24(抗旱性较强)和品种8139(抗旱性较弱)不同发育阶段体内抗氧化系统对田间缓慢干旱的响应情况。结果表明,在田间自然干旱条件下,随着土壤水分含量的逐渐降低,两品种小麦叶片水势和含水量均缓慢降低,叶片色素及可溶性蛋白含量也于幼苗期显著降低,植株生长受抑。叶片抗氧化酶系统如SOD、：POD、CAT以及GSH—ASC循环中的两种关键酶APX和GR活性,均在小麦发育前期如幼苗期和拔节期显著升高而于后期下降。主要抗氧化物质ASC含量也表现出相似的变化趋势。虽然抗氧化系统在两春小麦品种不同发育阶段对田间干旱的响应行为大体相同,而且干旱较敏感品种8139各物质对干旱的响应强于干旱较耐受品种定西24,但后者减轻干旱导致的氧化损伤的效率高于前者。试验还表明,在作物的不同发育阶段,抗氧化系统对田间缓慢干旱响应的策略不同,前期如幼苗期和拔节期主要表现为积极应对,后期如抽穗期和灌浆期主要表现为被动忍耐。     

Along the speciation continuum in sticklebacks

Speciation can be viewed as a continuum, potentially divisible into several states: (1) continuous variation within panmictic populations, (2) partially discontinuous variation with minor reproductive isolation, (3) strongly discontinuous variation with strong but reversible reproductive isolation and (4) complete and irreversible reproductive isolation. Research on sticklebacks (Gasterosteidae) reveals factors that influence progress back and forth along this continuum, as well as transitions between the states. Most populations exist in state 1, even though some of these show evidence of disruptive selection and positive assortative mating. Transitions to state 2 seem to usually involve strong divergent selection coupled with at least a bit of geographic separation, such as parapatry (e.g. lake and stream pairs and mud and lava pairs) or allopatry (e.g. different lakes). Transitions to state 3 can occur when allopatric or parapatric populations that evolved under strong divergent selection come into secondary contact (most obviously the sympatric benthic and limnetic pairs), but might also occur between populations that remained in parapatry or allopatry. Transitions to state 4 might be decoupled from these selective processes, because the known situations of complete, or nearly complete, reproductive isolation (Japan Sea and Pacific Ocean pair and the recognized gasterosteid species) are always associated with chromosomal rearrangements and environment‐independent genetic incompatibilities. Research on sticklebacks has thus revealed complex and shifting interactions between selection, adaptation, mutation and geography during the course of speciation.     

Is MHC diversity a better marker for conservation than neutral genetic diversity? A case study of two contrasting dolphin populations

Genetic diversity is essential for populations to adapt to changing environments. Measures of genetic diversity are often based on selectively neutral markers, such as microsatellites. Genetic diversity to guide conservation management, however, is better reflected by adaptive markers, including genes of the major histocompatibility complex (MHC). Our aim was to assess MHC and neutral genetic diversity in two contrasting bottlenose dolphin (Tursiops aduncus) populations in Western Australia—one apparently viable population with high reproductive output (Shark Bay) and one with lower reproductive output that was forecast to decline (Bunbury). We assessed genetic variation in the two populations by sequencing the MHC class II DQB, which encompasses the functionally important peptide binding regions (PBR). Neutral genetic diversity was assessed by genotyping twenty‐three microsatellite loci. We confirmed that MHC is an adaptive marker in both populations. Overall, the Shark Bay population exhibited greater MHC diversity than the Bunbury population—for example, it displayed greater MHC nucleotide diversity. In contrast, the difference in microsatellite diversity between the two populations was comparatively low. Our findings are consistent with the hypothesis that viable populations typically display greater genetic diversity than less viable populations. The results also suggest that MHC variation is more closely associated with population viability than neutral genetic variation. Although the inferences from our findings are limited, because we only compared two populations, our results add to a growing number of studies that highlight the usefulness of MHC as a potentially suitable genetic marker for animal conservation. The Shark Bay population, which carries greater adaptive genetic diversity than the Bunbury population, is thus likely more robust to natural or human‐induced changes to the coastal ecosystem it inhabits.     

A developing paradigm for the development of bird beaks

Some adaptive radiations are notable for extreme interspecific diversification in one or a few adult traits. How and why have trait differences evolved? Natural and sexual selection often provide answers to the question of why. An answer to the question of how is to be found in the genetic control of the phenotypic traits, especially in the early stages of development, when interspecific differences first become expressed. Recent studies of the molecular genetic control of beak development in Darwin's finches have shown that a signalling molecule (BMP4) plays a key role in the development of large and deep beaks. Expression of this molecule occurs earlier (heterochrony) and at higher levels in species with deep beaks compared with species with more pointed beaks. The implication of this finding is that variation in the regulation of one or a few genes that are expressed early could be the source of evolutionarily significant variation that is subject to natural selection in speciation and adaptive radiation. This view is reinforced by parallel findings with the same signalling molecule in the development of jaw morphology in cichlid fish of the Great Lakes of Africa. Further research into regulatory mechanisms is to be expected, as well as extension to other examples of radiation such as honeycreepers in Hawaii and Anolis lizards in the Caribbean. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88 , 17–22.     

Induction of Reactive Oxygen Species and Phytoalexins in Onion (Allium cepa) Cell Culture by Biotic Elicitors Derived from the Fungus Botrytis cinerea

Metabolites of a phytopathogenic fungus Botrytis cinerea Pers. were analyzed for the presence of biotic elicitors. Three groups of elicitors competent in inducing defense responses inAllium cepa cells were identified and partly purified. The recognition of the elicitor signal in onion cells was shown to elevate the concentration of reactive oxygen species (ROS), namely, superoxide anion-radical (O₂^{\overset{-}.}) and hydrogen peroxide (₂₂). The intensity of ROS release depended on chemical identity of elicitor and its concentration. The most active ROS production in onion cells was induced by a protein fraction isolated from the medium for fungus culturing. The carbohydrate elicitors extracted from the fungus cytoplasm and cell walls of mycelia were much less effective. The dynamics of ROS generation comprised two stages. The first stage represented fast and low-amplitude changes that peaked in 15 min after the elicitor treatment. The second stage was more durable and extensive; it occurred in 1.5–6 h after the treatment.     

西花蓟马诱导的番茄植株防御反应对B型烟粉虱行为的影响

【目的】明确外来入侵害虫西花蓟马Frankliniella occidentalis (Pergande)取食诱导的番茄植株防御反应对B型烟粉虱Bemisia tabaci (Gennadius) B-biotype行为的影响, 探讨西花蓟马与B型烟粉虱的种间竞争机制。【方法】利用“Y”型嗅觉仪行为分析法、 选择性试验法, 研究了不同处理组合（健康植株CK vs烟粉虱为害植株B、 健康植株CK vs西花蓟马为害植株F、 烟粉虱为害植株B vs烟粉虱和西花蓟马共同为害植株B+F）下, 烟粉虱对不同处理植株的取食行为反应及寄主偏好的差异性, 并利用GC-MS分析了不同处理植株挥发性物质的差异性。【结果】“Y”型嗅觉仪行为分析结果表明, 在CK vs B和CK vs F两个组合中, 烟粉虱雌成虫对健康植株和昆虫为害植株的偏好性差异不显著; 而在B vs B+F组合中, 烟粉虱为害株对烟粉虱雌成虫具有极显著的引诱作用（P<0.01）。选择性试验结果表明, 在CK vs B和CK vs F这两个组合中, 烟粉虱成虫均偏好健康株并喜好在其上产卵（P<0.01）, 在B vs B+F组合中, 烟粉虱成虫偏好烟粉虱单独为害株并喜好在其上产卵（P<0.01）。GC-MS分析结果显示, 本实验收集到9种挥发性物质, 其中有5种烯萜类物质, 其相对含量高达90%以上。与烟粉虱单独为害株相比, 烟粉虱和西花蓟马共同为害株所释放的挥发性物质中, 对烟粉虱具有排斥作用的β-水芹烯显著升高, 而对其具有吸引作用的β-月桂烯却显著减少。【结论】综合分析认为, 西花蓟马诱导的番茄植株防御反应可以显著影响B型烟粉虱的寄主选择行为及产卵选择性。     

The more food webs change,the more they stay the same

Here, we synthesize a number of recent empirical and theoretical papers to argue that food-web dynamics are characterized by high amounts of spatial and temporal variability and that organisms respond predictably, via behaviour, to these changing conditions. Such behavioural responses on the landscape drive a highly adaptive food-web structure in space and time. Empirical evidence suggests that underlying attributes of food webs are potentially scale-invariant such that food webs are characterized by hump-shaped trophic structures with fast and slow pathways that repeat at different resolutions within the food web. We place these empirical patterns within the context of recent food-web theory to show that adaptable food-web structure confers stability to an assemblage of interacting organisms in a variable world. Finally, we show that recent food-web analyses agree with two of the major predictions of this theory. We argue that the next major frontier in food-web theory and applied food-web ecology must consider the influence of variability on food-web structure.