Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method

Monnet, C., Klug, C., Goudemand, N., De Baets, K. & Bucher, H. 2011: Quantitative biochronology of Devonian ammonoids from Morocco and proposals for a refined unitary association method. Lethaia, Vol. 44, pp. 469–489. Based on a rich dataset, the biostratigraphy of the late Emsian and the Eifelian (Early–Middle Devonian) ammonoids from the Moroccan Tafilalt is re‐evaluated. We processed this dataset (comprising 53 species from 15 sections) with the unitary association method (UAM), by means of the UA‐graph freeware. This led to the construction of a sequence of 17 UAs (maximal sets of actually or virtually coexisting taxa), which are grouped into 10 laterally reproducible association zones. This biostratigraphical subdivision of this interval is in some parts finer than the classically used empirical stratigraphical scheme and than a previous graphic correlation analysis. It enabled us to measure regional ammonoid diversity of this interval in detail. The UAM is a powerful biochronological method, which benefits from complementary tools to analyse conflicting inter‐taxon stratigraphical relationships inherent to complex biostratigraphical datasets. In cases of under‐constrained superpositional relationships between the taxa, the UAM can yield results, which are not parsimonious in terms of reconstructed virtual coexistences. We suggest several additions to complement the algorithmic steps of the method. The most important is the exhaustive or heuristic reconstruction of possible solutions resolving the observed biostratigraphical contradictions (conflicting inter‐taxon superpositional relationships and cycles between maximal cliques) and the selection among the solutions of the most‐parsimonious one(s) in terms of reconstructed virtual coexistences. Multiple equivalent results may then be processed with standard consensus techniques. Finally, the robustness of the results can be tested by bootstrapping methods to provide confidence estimates on the ranges and associations of studied taxa. □Ammonites, Anti‐Atlas, biostratigraphy, correlation, zonation, diversity.     

A multivariate morphometric and meristic description of a population of freshwater-feeding river lampreys, Lampetra fluviatilis (L.), from Loch Lomond, Scotland

Adults of a freshwater-feeding population of Lampetra fluviatilis (L.) in Loch Lomond, Scotland, were trapped on their upstream (spawning) migration in the main inflow to the loch, the Endrick Water. These animals could be distinguished from the more typical anadromous upstream migrant L. fluviatilis , from the Endrick Water and the nearby catchment of the River Forth, principally by their smaller total length, greater disc, snout and eye size and much darker pigmentation. These, and other morphometric and meristic characteristics have been compared for populations of L. fluviatilis and Lampetra planeri (Bloch) from the Lomond and Forth catchments using univariate and multivariate statistics. The Endrick Water 'dwarf' L. fluviatilis was found to differ significantly from the other Lampetra studied, in a number of body proportions in addition to those traits mentioned above, and also in mean numbers of trunk myomeres and teeth. These differences are likely to be due to a combination of the effects of genetic isolation, and the short (freshwater) feeding phase of the 'dwarf' L. fluviatilis , which may, therefore, represent the intermediate stage between parasitic and non-parasitic forms in the L. fluviatilis/L. planeri species pair.     

ACTION OF KINETIN ON PHOTOSENSITIVE GERMINATION OF LETTUCE SEED AS COMPARED WITH THAT OF GIBBERELLIC ACID

1. Experiments with the seeds of Grand Rapids lettuce showedthat the germination induced by gibberellic acid or by red lightis strongly accelerated by kinetin, although the latter itselfcan promote the germination in the dark only slightly. The reversiblelight reactions of the phytochrome system interact with kinetintreatment just as effectively as with water-imbibed controls.The site of primary action of red light is not altered by kinetintreatment. Kinetin does not modify the water uptake of the seedsfor at least 8 hours. 2. Kinetin was found to inhibit the growth of the hypocotyland root of the seed, but to promote very markedly the expansionof the cotyledons. This effect was observed not only with cotyledonsin intact seeds but also with isolated cotyledons. The expansionof kinetin-treated cotyledons is further promoted by red light,but not by far-red, as is also the case with germination itself. 3. A number of purine derivatives which have been reported topromote germination also cause expansion of isolated cotyledons. 4. Gibberellic acid promotes both hypocotyl elongation and cotyledonexpansion in the dark, but this effect does not interact withthe phytochrome system. The site of action of gibberellic acidprobably lies in the axis. 5. It is concluded, therefore, that the site of kinetin actionis in the cotyledons, whose expansion helps to break the seed-coatwhen light or gibberellin has contributed the primary stimulus. ¹ Present address: Johnson Foundation for Medical Physics, Universityof Pennsylvania, Philadelphia, Pa. (Received January 16, 1963; )     

Diet and predation by three leaf-associated stoneflies (Plecoptera) in an Arkansas mountain stream

SUMMARY. 1. Life cycles, food habits, mouthpart morphologies, prey preferences, and predator-prey size relationships were investigated for the three most common stoneflies in leaf packs in the Little Missouri River, Arkansas: Clioperla clio (Newman), Isoperla namata Prison, and Perlesta spp. Each species was univoltine and had a fast seasonal cycle, with extended egg or nymphal diapause, rapid nymphal growth and emergence in spring to early summer.
2. Foregut analysis showed predictable dietary shifts by C. clio and Perlesta spp., from detritus and diatoms in early instars to invertebrate prey in later instars. Isoperla namata fed facultatively on insects, detritus and diatoms, with no conspicuous ontogenetic shifts. The mouthparts of all three species strongly reflected their diet.
3. Electivity analysis indicated opportunistic feeding by the three species, with feeding rarely differing significantly from random.
4. Sizes of stonefly predators and their ingested prey were highly correlated ( P <0.01). However, rather than shifting toward larger prey sizes, growing predators expanded their size thresholds and continued to include numerous small prey items in their diet. Prey choice was governed most directly by prey availability, because stoneflies selected the most abundant groups, irrespective of size or taxon.
5. The likelihood of competition among the three stoneflies for prey was minimized by timing of their life cycles, differential food use and probably the temporary nature of leaf pack habitats.     

Factors affecting egg maturation in the bean weevil Callosobruchus maculatus

Abstract. This paper concerns the effects of mate and seed availability on the rate of egg maturation in the bean weevil Callosobruchus maculatus (F.). Egg maturation starts before emergence from the seed and, provided that both oviposition sites and mates are available, eggs are laid at a rate determined by the number of oviposition sites, and mature at a similar rate. If seeds or mates are absent then a small number of eggs are laid, but oocytes continue to mature until the oviduct-capacity is approached. The number of eggs that a female can store is dependent on her body weight and does not correlate with the number of ovarioles. If, after a period in which oocyte development has been halted, conditions for egg-laying become suitable, then egg maturation can be re-started, but only after the oviducts have been emptied of eggs. The rate of egg maturation is then similar to that for females of the same age which have been maturing eggs since emergence.     

Diapause, migration and pyrethroid-resistance dynamics in the cotton bollworm, HeIicoverpa armigera (Lepidoptera: Noctuidae)

Abstract.

• 1 A diapause induction and duration experiment was conducted in the laboratory on Indian Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) where 79% of individuals had extended pupal periods. At 22°C and 26°C respectively, 57% and 100% of the pupae had emerged 145 days after pupation.
• 2 A mathematical model was developed to investigate the interactions between diapause, migration and pyrethroid resistance frequency development in both eastern Australia and Andhra Pradesh, India.
• 3 The effect of diapause was different in the Australian and Indian cases, providing a mechanism to conserve resistance and susceptibility respectively.
• 4 For Australia, the model simulated discriminating dose data reasonably well and showed that resistance frequencies could rise prior to the pyrethroid window without invoking cross-resistance to non-pyrethroid insecticides applied to cotton.
• 5 The saw-toothed seasonal cycle of resistance development could be simulated in the Indian case without hypothesizing the existence of susceptible migrants.
• 6 The implications of‘refugia’populations for H.armigera insecticide resistance management programmes are discussed.

     

Ocean barriers and glaciation: evidence for explosive radiation of mitochondrial lineages in the Antarctic sea slug Doris kerguelenensis (Mollusca, Nudibranchia)

Strong currents and deep passages of water can be barriers for larval dispersal of continental marine animals, but potential effects on direct developers are under-investigated. We examined the genetic structure of Doris kerguelenensis , a directly developing sea slug that occurs across the Drake Passage, the body of water separating Antarctica from South America. We found deep mitochondrial divergences within populations on both sides of the Drake Passage, and South American animals formed multiple sister-group relationships with Antarctic animals. A generalised molecular clock suggested these trans-Drake pairs diverged during the Pliocene–Pleistocene, after the formation of the Drake Passage. Statistical parsimony methods recovered 29 separate haplotype networks (many sympatric) that likely correlate with allopatric events caused by repeated glacial cycles. Data from 16S were congruent but more conserved than COI, and the estimated ancestral 16S haplotype was widespread. The marked difference in the substitution rates between these two mitochondrial genes results in different estimates of connectivity. Demographic analyses on networks revealed some evidence for selection and expanding populations. Contrasting with the Northern Hemisphere, glaciation in Antarctica appears to have increased rather than reduced genetic diversity. This suggests orbitally forced range dynamics based on Northern Hemisphere phylogeography do not hold for Antarctica. The diverse lineages found in D. kerguelenensis point towards a recent, explosive radiation, likely reflecting multiple refuges during glaciation events, combined with limited subsequent dispersal. Whether recognised as cryptic species or not, genetic diversity in Antarctic marine invertebrates appears higher than expected from morphological analyses, and supports the Antarctic biodiversity pump phenomenon.     

A Host-specific, Nitrogen Fixation Mutant of Bradyrhizobium: Physiology on Three Host Plants

NC92 #284 is a transposon mutant of Bradyrhizobium sp. (Arachis)strain NC92 and has a host-specific fixation phenotype. It appearsto be ineffective on the host pigeonpea (90% reduction in shootN compared to that of the wild type), but partially effectiveon two other host plants, groundnut and siratro (50% and 20%reduction in shoot N compared to the wild type, respectively).To understand this phenomenon of host-specific fixation, thephysiological basis of the phenotypes was investigated. Host-dependentdifferences in symbiotic effectiveness were largely explainedby the degree to which nitrogenase activity was impaired inthe various #284 symbioses. Nodulation and the onset of nitrogenfixation were found to be delayed on all three hosts, but tothe greatest degree on pigeonpea. The specific activity of nitrogenaseper gram nodule was also reduced on all three hosts, again tothe greatest extent on pigeonpea. By contrast, the carbon costsand relative efficiencies of each symbiosis were similar tothe wild type. The results indicate that the host-specific fixationphenotype of #284 is reflected in a quantitative reduction inthe amount of N₂ fixed. Thus the phenotypes reflect the differentability of the three host plants to tolerate or support the#284 mutation, rather than a defect in a specific interactionbetween #284 and a particular host plant. Key words: Bradyrhizobium, nodules, nitrogenase activity, relative efficiency, Arachis hypogaea, Cajanus cajan, Macroptilium atropurpureum     

不同耕作方式对内蒙古旱作农田土壤侵蚀的影响

研究黄河流域内蒙古黄土高原丘陵区农田土壤侵蚀状况,对本区域生态农业建设具有重要的意义。试验于2006年在内蒙古呼和浩特市清水河县进行,设免耕(NT)、免耕覆盖(NS)和传统耕作(CT)3种耕作处理方式,种植作物为胡麻和燕麦,观测了全年降雨量和地表水径流量及土壤流失量。结果表明:免耕覆盖及免耕能显著减少降雨对土壤的侵蚀,与传统耕作相比,免耕覆盖处理的燕麦地地表水径流量和土壤的流失量分别减少21.9%和88.3%;3种耕作方式的土壤侵蚀量均受到坡度的影响,并随着坡度的增大而增大,相同环境条件下,不同作物存在一定差异;通过对3种耕作方式下,胡麻和燕麦田土壤侵蚀量与降雨量的关系符合幂函数,且拟合优度良好,均>0.9。     

Relationship of macrophyte-mediated changes in the water column to periphyton composition and abundance

SUMMARY. 1. Dense growths of Myriophyllum heterophyllum influenced temperature, dissolved oxygen, pH and light levels in the littoral waters of Lake Winnipesaukee, a soft-water. New England lake. Periphyton species composition and abundance (algal units cm' stem) were related to the macrophyte-mediated changes in the physicochemical environment.
2. Duringearlysummer, M. heterophyllum occupied onlythe lower part of the water column. Limnetic and littoral waters exchanged readily and were chemically similar. Early summer periphyton species composition was dominated by diatoms from the phytoplankton, entangled in the finely dissected leaves of M. heterophyllum.
3. By mid-summer, M. heterophyllum occupied the entire watercolumn of the littoral zone. The metabolic and photosynthetic activity and dense foliage of M. heterophyllum created marked vertical gradients in physicochemical conditions. Mid-day temperature, dissolved oxygen, pH and light levels were maximal in the surface waters of the M. heterophyllum mat during the summer. Concurrently, periphyton species composition shifted to blue-green and then to a filamentous green alga on the apex and mid-stem. On the lower stem, diatoms consistently dominated the periphyton.
4. Periphyton abundance on the apex was inversely related to apical elongation. Temporal fluctuations of periphyton abundance on the lower and mid-stem were small throughout the study. Periphyton abundance was lowest on the lower stem, where the deteriorating leaves provided less surface area for colonization.