Pea Root Regeneration After Tip Excisions at Different Levels: Polarity of New Growth

The roots of light-grown pea seedlings (Pisum sativum L. cv.Alaska) were excised at 250, 500 or 1500 µm from the body/capjuncture. Tips were sampled for 7 d after excision to monitorthe polarity and structure of the regeneration response. Inroots excised at 250 µm a new single apex regeneratedwithout swelling or any sign of repair. The new root cap appearedidentical to the control. After the 500 µm excision tworesponses occurred. In 45% of the roots examined, a single newapex regenerated, in 55% two or three new apices regeneratedto form a dichotomized or trichotomized root in the same longitudinalaxis as the primary root. In roots excised at 1500 µm,one, two or three lateral roots formed adjacent to the xylemat right angles to the primary root axis. In most instancesthe new roots developed triarch xylem. The discussion concentrateson the relationship of the differentiation state of the vascularcylinder and the pericycle, at the excision site, to the regenerationresponse. Root regeneration, Pisum sativum, Pericycle, Root apex     

The Growth Forms of Developing Fern Gametophytes: a Theoretical Consideration of Form and Function Relationships

This paper examines the hypothesis that the primary physiologicalroles of the different structures of fern gametophytes haveacted as significant evolutionary constraints on the growthforms of these structures. Geometric models of absorptive andphotoreceptive structures were constructed to describe the spherical,tip-growing, and planar growth forms, which are actually orcould hypothetically be adopted by each gametophytic structure.The surface-to-volume ratios calculated for the different absorptivestructures suggest that the tip-growing form of the fern rhizoidprovides the most favorable geometric circumstance for waterand nutrient absorption; thus, the selection pressure to optimizeabsorptive processes has apparently influenced the growth formof the absorptive structure. In contrast, similar calculationsfor photoreceptive structures demonstrate that these forms havealmost identical surface-to-volume relationships; thus, thepresumptive need to increase photoreceptive efficiency has notacted as a selection pressure for a specific photoreceptiveform. This result is interpreted in terms of how different growthforms may offer specific advantages for accomplishing otheraspects of the photosynthetic process, e.g. phototropic growthand assimilate transport, which are unrelated to photoreceptionper se. Fern gametophyte, photoreception, absorption, optimal shape, spore, protonema, prothallus     

Oscillatory Transpiration in a Cotton Plant: I. EXPERIMENTAL CHARACTERIZATION

A resistance-capacitance model of oscillatory transpirationin a cotton plant under constant environmental conditions isdiscussed. Experimental results showed that a cotton plant exposedto a sudden and large evaporative demand went through a periodof self-adjustment indicating the presence of negative feedbackmechanisms. Phase relationships between flow in stem, leaf waterpotential, water uptake by roots, and leaf turgor were characterizedthrough the day. The water-based oscillatory processes are explainedthrough a proposed model based upon a hysteresis-controlledfunction and delayed coupling in the leaf component. The periodof oscillation was found to be about 30 min. Results also indicatedthat the lag between the transpiration and water uptake ratesduring oscillations was strongly influenced by the capacitanceof the leaf and that stem capacitance was negligible.     

Sensitivity Analyses of a Population Projection Model of Ring-Necked Pheasants

Abstract A large literature exists on population dynamics of ring-necked pheasant (Phasianus colchicus) in North America, but there has not been an attempt to formulate a matrix model nor a sensitivity analysis of the relationships between vital rates and population finite growth rate (Λ) that can be used to guide management. We summarized demographic data available from a 5-year field study in Iowa, USA, collected in Kossuth County (low composition of perennial habitat) and Palo Alto County (high composition of perennial habitat) into a 2-stage (young and adult) matrix projection model. We estimated Λ₁ (the dominant eigenvalue of the deterministic matrix), the stable age distribution (ω), relative reproductive value vector (n̈), other demographic parameters, and Λ_iid, a bootstrap estimate of growth that includes interannual variation in life history parameters. We analyzed the relative importance of vital rates on population growth rate using sensitivity and elasticity of both matrix elements and lower-level parameters such as winter survival and nest success. We first characterized general life history using averaged data from both areas and all years that yielded Λ₁ = 1.086, and a stable stage distribution of. Minimum success of the initial nesting attempt (H₁) that would maintain Λ ≥ 1 under average conditions was estimated to be 42%. Changes in Λ₁ were most sensitive to survival of chicks during brood rearing (S_B), followed in importance by survival during the subsequent winter (S_W), followed by H₁. We followed the general analyses with analyses that helped us to focus on the differences in the landscapes of northwest Iowa. Λ_iid was ≥1 in only 9% of simulations of data from Kossuth whereas estimated Λ_iid was ≥1 in 88% of simulations from Palo Alto. Our analyses of the relative importance and interactions between S_B, S_W, and total recruitment (M, including H₁ and renesting), if combined with data more specific to a local area, would guide management aimed at affecting multiple life history stages whose relative importance will vary across the landscape.     

Giving‐up densities and ideal pre‐emptive patch use in a predatory benthic stream fish

1. We used observational and experimental field studies together with an individual‐based simulation model to demonstrate that behaviours of mottled sculpin (Cottus bairdi) were broadly consistent with the expectations of Giving‐Up Density theory and an Ideal Pre‐emptive Distribution habitat selection model. 2. Specifically we found that: (i) adult mottled sculpin established territories within patches characterised by significantly higher prey densities and prey renewal rates than patches occupied by juveniles or randomly selected patches; (ii) patches abandoned by adult sculpin possessed significantly lower prey densities than newly occupied patches, although this was not true for juveniles; (iii) the observed giving‐up density (GUD) for adult sculpin (i.e. average prey density in patches recently abandoned) increased linearly with increasing fish size up to the average prey density measured in randomly selected patches (i.e. 350 prey items per 0.1 m²) and decreased with increasing sculpin density and (iv) juveniles rapidly shifted their distribution towards the highest quality patches following removal of competitively dominant adult sculpin. 3. These results provide the first evidence of the applicability of GUD theory to a stream‐dwelling organism, and they elucidate the underlying factors influencing juvenile and adult sculpin habitat selection and movement behaviours. Furthermore, optimal patch use, ideal pre‐emptive habitat selection and juvenile ‘floating’ provide behavioural mechanisms linking environmental heterogeneity in the stream benthos to density‐dependent regulation of mottled sculpin populations in this system.     

Tetranucleotide microsatellites for aquila and haliaeetus eagles

A unique community of four syntopic eagle species exists in north‐central Kazakhstan. Questions about behaviour and genetics in these four species would benefit from the development of microsatellite markers. We isolated eight polymorphic microsatellite repeats (AAAG)_n from the eastern imperial eagle (Aquila heliaca) genome using a hybridization enrichment technique. These loci revealed moderate diversity in a local population of eastern imperial eagles (observed heterozygosity 0.26–0.78), and were also polymorphic in steppe eagles (A. nipalensis) and white‐tailed sea eagles (Haliaeetus albicilla). These primers may be polymorphic in other species of Aquila and Haliaeetus eagles.     

Discussion of Work on Isospora Species1

Comments are made concerning the work reported at this Conference by Dr. Edith Box. The importance of stress on the animals used in experimental work is emphasized. Difficulties in identification of isosporan species in birds are mentioned.