Aggregation and mating of thrips in flowers of Calystegia sepium

Abstract. 1. Aggregation and mating of Thrips major Uzel and Thrips fuscipennis Haliday (Thysanoptera: Thripidae) in the 1-day flowers of Calystegia sepium (L.) R.Br. are described.
2. The number of thrips per flower increased rapidly after flower-opening at dawn and decreased during the evening and following morning.
3. Males patrolled the corolla, attempting to copulate with any females that landed. Their movement was affected by the density of thrips on the corolla. Most females were among the stamens and style, apparently feeding on pollen.
4. These thrips were also abundant in flowers of Filipendula ulmaria (L.) Maxim. They fed on pollen, and grains adhered to them. They may be significant pollinators because of their high frequency of flights.
5. The aggregations appear to be a simple consequence of general flower-finding responses to colour and scent that are particularly elicited by flowers of C.sepium and F.ulmaria. The ecological significance of male aggregations is discussed.     

New fan worm genera and species (Polychaeta, Sabellidae, Fabriciinae) from the western Pacific, and cladistic relationships among genera

Five new species are described from among the genera Fabriciola Friedrich, 1939 (one species from Okinawa), Novafabricia Fitzhugh, 1990 (two species from Australia and Papua New Guinea, respectively), and two new monotypic genera, Brifacia gen. n. (Australia), and Pseudoaugeneriella gen. n. (Okinawa). All species are known only from the intertidal. Fabriciola rubra sp. n. is a member of the species complex with red peristomial and pygidial eyes, inferior thoracic flagellate setae, and abdominal pin-head setae. Novafabricia labrus sp. n., and N. exiguus sp. n., are distinguished from other species based on the distribution of inferior thoracic pseudospatulate setae. Brifacia metastellaris sp. n., resembles Fabricia stellaris (Müller, 1774) with regard to anterior peristomial ring collar construction and distribution of pseudospatulate setae, but differs in having abdominal uncini with relatively short manubria. Pseudoaugeneriella unirama sp. n., most closely resembles species of Augeneriella Banse, 1956 in general form, but has unbranched vascularized ventral filamentous appendages. Revised keys to fabriciin genera and selected species are provided. Cladistic relationships of these new genera and species to other Fabriciinae are examined and the status of some characters are reviewed. Whereas previous analyses have supported a monophyletic Augeneriella on the basis of branched, vascularized ventral filamentous appendages, present results show Augeneriella paraphyletic relative to Fabricia Blainville, 1828, Novafabricia, Fabricinuda Fitzhugh, 1990 Parafabricia Fitzhugh, 1992 and Brifacia. Similarly, some topologies show Novafabricia, which has only been defined by the presence of poorly developed dorsal lips, to be paraphyletic relative to Fabricia, Fabricinuda, Parafabricia, and Brifacia. The cladistic analyses do, however, support recognition of Brifacia and Pseudoaugeneriella. With the addition of Brifacia, the presence of unbranched, vascularized appendages is plesiomorphic for the Fabriciinae, which has not been previously hypothesized.     

Identification and characterization of QTL underlying whole-plant physiology in Arabidopsis thaliana: δ13C, stomatal conductance and transpiration efficiency

Water limitation is one of the most important factors limiting crop productivity world-wide and has likely been an important selective regime influencing the evolution of plant physiology. Understanding the genetic and physiological basis of drought adaptation is therefore important for improving crops as well as for understanding the evolution of wild species. Here, results are presented from quantitative trait loci (QTL) mapping of flowering time (a drought escape mechanism) and carbon stable isotope ratio (δ¹³C) (a drought-avoidance mechanism) in Arabidopsis thaliana. Whole-genome scans were performed using multiple-QTL models for both additive and epistatic QTL effects. We mapped five QTL affecting flowering time and five QTL affecting δ¹³C, but two genomic regions contained QTL with effects on both traits, suggesting a potential pleiotropic relationship. In addition, we observed QTL–QTL interaction for both traits. Two δ¹³C QTL were captured in near-isogenic lines to further characterize their physiological basis. These experiments revealed allelic effects on δ¹³C through the upstream trait of stomatal conductance with subsequent consequences for whole plant transpiration efficiency and water loss. Our findings document considerable natural genetic variation in whole-plant, drought resistance physiology of Arabidopsis and highlight the value of quantitative genetic approaches for exploring functional relationships regulating physiology.     

The spectral absorption and scattering properties of dissolved and particulate components in relation to the underwater light field of some tropical Australian fresh waters

SUMMARY. 1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.
2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).
3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow-brown humic pigments, both soluble and particulate, in the water.
4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.
5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic material.     

Populations composed entirely of hybrid colonies: bidirectional hybridization and polyandry in harvester ants

In eusocial Hymenoptera, haplodiploid life cycles, obligate sterile castes, and polyandry may facilitate selection for hybridization. We analyzed a broad hybrid zone between the ecologically distinct seed‐harvester ants Pogonomyrmex occidentalis (Cresson) and Pogonomyrmex maricopa (Wheeler) using mitochondrial (mt)DNA sequence data, eight morphological markers, and 14 random amplified polymorphic DNA (RAPD) markers. Average mtDNA sequence divergence among parental species was 11.34%, indicating secondary contact. RAPD markers were significantly correlated with morphological variation, confirming the interspecific hybrid origin of all morphologically putative hybrid colonies. A morphological hybrid index indicates an abundance of both F₁ hybrids and parental morphotypes within colonies. Individual character frequencies plotted against distance show coincident and concordant clines, suggesting little to no introgression. The structure of the hybrid zone is two‐fold. Within the western region, stark reversals in character frequencies coincide with overt soil differences, indicating a mosaic hybrid zone structure. The eastern region is a riparian habitat where four adjacent populations were composed entirely of hybrid colonies. These habitat associations suggest that hybrid worker genomes permit dispersal into intermediate environments that select against one or both parental species. The present study suggests that, in addition to retaining reproductive compatibility, ecologically distinct species of ants may generate hybrid colonies maintained by environmental selection. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 320–336.     

Regulation of photosynthetic carbon metabolism in synchronously growing Chlorella pyrenoidosa

The physical properties and photosynthetic metabolism of synchronizedcells of Chlorella pyrenoidosa are described. Cells, synchronizedby successive periods of light and dark, photosynthesized understeady-state conditions for 30 min with ¹⁴CO₂. Pool sizes ofmetabolic intermediate compounds, and rates of flow of carbonthrough these pools, were determined. Cell properties and metabolismwere studied for cells just divided, at three periods duringthe growing stage, at the time of maximum DNA synthesis, justprior to division (after continuous light, and after 5 hr darkness),and following division after continuous light for 37 hr. Changes in pool sizes and flow rates are correlated with relativeshifts between amino acid and protein synthesis, which is greatestduring the growing period and DNA-synthesizing stage, and sucrosesynthesis, which is greatest in the divided cells (after darkness)and pre-division cells (after darkness). The effects of thestage of cell growth and of a prior period of darkness can beseparated to some extent by these studies, and in some respectsare additive. Specific sites of metabolic regulation discerned in these experimentsinclude the following: 1) Ribulose diphosphate carboxylase,2) fructose diphosphatase and sedoheptulose diphosphatase, 3)the synthesis of sucrose, probably at the reaction between fructose-6-phosphateand uridine diphosphoglucose to give sucrose phosphate and uridinediphosphate, 4) amino acid synthesis, at the level of nitratereduction, and 5) amino acid synthesis, at the level of carbonflow from the photosynthetic carbon reduction cycle to aminoacid carbon skeletons. (Received October 31, 1969; )     

The statistical detection of threshold signals in the retina

1. Photographic records of impulses from single ganglion cells in the cat's retina were made while the retina was stimulated by flashes occurring once a second. Ten flashes at each of several intensities near threshold were used. 2. For the purpose of statistical analysis, the number of impulses (x) falling within a critical period following each flash was used as an index of the response. Histograms of x were plotted and used to calculate rates of transfer of information by the ganglion cell for the case of an ideal experiment, the yes-no choice, in which flashes of intensity I and blanks are to be distinguished. 3. The information rate increased (a) with increasing stimulus intensity and (b) with the number of identical flashes or blanks presented successively in a block. The intensity chosen as threshold by the experimenter, who observed the impulses visually and aurally, corresponded to an average information rate for single flashes of 0.7 bit/flash, compared to the maximum possible rate of 1 bit/flash. A threshold intensity giving 0.4 or more bit/flash, if presented in blocks of six identical flashes, corresponded to 0.95 or more bit/block, or near certainty. Thus the calculation of information rates using the index x provides an estimate of threshold at least as sensitive as those obtained during an experiment, which were made only after observing the responses to five to ten flashes of the same intensity. 4. The index x has statistical properties similar to those of the "index of neural activity" used by Tanner and Swets (1954) in their statistical model of human vision, and represents a possible physical interpretation of their index. However, x gave values (0.5 to 1.5) of the parameter called the slope which were consistently smaller than their values (2.1 to 3.1).     

Maintained activity in the cat''s retina in light and darkness

Nervous activity has been recorded from the unopened eye of decerebrate cats. Recordings were made with metal electrodes or with small micropipettes from ganglion cells or nerve fibers. Continuous maintained discharges were seen in all ganglion cells during steady illumination of their receptive fields, as well as in complete darkness. Possible artefacts, such as electrode pressure, abnormal circulation, anesthetic, and several other factors have been excluded as the source of the maintained discharge. Visual stimuli are therefore transmitted by modulating the ever present background activity. Discharge frequencies were measured following changes of retinal illumination. No consistent patterns of frequency change were found. The maintained discharge frequency may be permanently increased or decreased, or may remain practically unchanged by altering the steady level of illumination. In addition, there were often transient frequency changes during the first 5 to 10 minutes after changing illumination, before a final steady rate was established. A statistical analysis of the impulse intervals of the maintained discharge showed: (a) the intervals were distributed according to the gamma distribution (Pearson's type III), (b) the first serial correlation coefficient of the intervals was between –0.10 and –0.24, with a mean value of –0.17, which is significantly different from zero, (c) the higher order serial correlation coefficients were not significantly different from zero. Thus the firing probability at any time depends on the times of occurrence of the two preceding impulses only, and in such a way as to indicate that each impulse is followed by a transient depression of excitability that outlasts the following impulse. The possible sites at which spontaneous or maintained activity may originate in the retina are discussed.