The Mechanical Significance of Clasping Leaf Sheaths in Grasses: Evidence from Two Cultivars of Avena sativa

The elastic (Young's) modulus and flexural rigidity of internodeswith and without their clasping leaf sheaths were determinedfor culms from two cultivars (‘Astro’) and (‘Garry’)of Avena sativa L. Data indicate that early in the developmentof culms, leaf sheaths can have a higher elastic modulus thanthe internodes they envelope, and by virtue of their location,leaf sheaths contribute significantly to the flexural rigidity(hence, resistance to bending) of internodal segments. As culmsmature, the elastic modulus of leaf sheath and internodal tissuesreach parity. However, because of the acropetal pattern by whichnew internodes are produced by shoot apices, sheaths continueto provide mechanical support to distal internodes, particularlythe peduncle. Data for the two cultivars indicate that the elasticmodulus and flexural rigidity of culms can vary significantlywithin the species. Comparisons between the flexural rigidityof the two cultures and the resistance of stems to lodging indicatethat flexural rigidity is not significant to lodging. The engineeringprinciples relevant to the mechanical advantages conferred byclasping leaf sheaths are discussed within the context of grassshoot morphology. Biomechanics, leaf sheath, Avena, elastic modulus     

Phylogenetic analysis of the latitude‐niche breadth hypothesis in the butterfly subfamily Nymphalinae

1. One possible explanation for the latitudinal gradient in species richness often demonstrated is a related gradient in niche breadth, which may allow for denser species packing in the more stable environments at low latitudes. 2. The evidence for such a gradient is, however, ambiguous, and the results have varied as much as the methods. Several studies have considered the non‐independence of species, but few have performed explicit phylogenetic analyses. 3. In the present study, we tested for a correlation between diet breadth and latitude of distribution in Nymphalinae butterflies using generalised estimating equations (GEE) and accounting for phylogenetic independence. 4. Using a simple model with only latitude of distribution as a predictor variable revealed a significant positive relationship with diet breadth. Previous studies, however, have shown that diet breadth is also correlated with butterfly range size, and in turn, that range size may be correlated with latitude of distribution. Including geographical range size in the model also turned out to have a profound effect on the results – to the extent that the relationship between latitude of distribution and diet breadth was effectively reversed. 5. We conclude that, at least for this group of butterflies, there is no evidence for a positive correlation between latitude of species distribution and diet breadth when controlling for range size, and that the effect may actually even be reversed.     

Phylogeny and biogeography of Coenonympha butterflies (Nymphalidae: Satyrinae) – patterns of colonization in the Holarctic

Abstract We studied the historical biogeography of a group of butterflies in the Holarctic region belonging to the genus Coenonympha (Nymphalidae: Satyrinae: Coenonymphina), based on a phylogenetic hypothesis estimated from three genes. The genus is distributed mainly in the Palaearctic region, with two species extending into the Nearctic region. The tree is generally well supported and shows that Coenonympha is paraphyletic with respect to Lyela ( syn.n. ) and Triphysa ( syn.n. ), and we hence synonymize the latter two with Coenonympha. Within Coenonympha we identify three species groups, the tullia, glycerion and hero groups. The North American tullia exemplars are not sister to the Eurasian ones. A diva analysis indicates that the ancestor of the group was present in the Central Palaearctic or Central Palaeartic + Western Palaearctic or Central Palaearctic + Eastern Palaearctic. We conclude that the most likely origin of extant members of Coenonympha was in the Central Asian mountains. The tullia and hero groups started diverging in Europe following dispersal into the region. There have been two independent colonizations into Africa. The drying up of the Mediterranean during the Messinian period probably played an important role, allowing colonization into the Mediterranean islands and Africa.     

Diversification of Morpho butterflies (Lepidoptera,Nymphalidae): a re‐evaluation of morphological characters and new insight from DNA sequence data

This study compiles previously published morphological, colour and behavioural characters and includes new DNA sequence data for eight markers (one mitochondrial and seven nuclear) to re‐evaluate phylogenetic relationships and estimate times of divergence for Morpho butterflies using parsimony and Bayesian methods. We note an effect of missing data on phylogenetic inference and calculations of Partitioned Bremer Support. Morphology and DNA trees were moderately congruent, and the combined analyses of all data included elements of both sources. Both morphology and DNA support the monophyly of Morpho and the early separation of the sister pair M. marcus plus M. eugenia, but trees from different data sources are congruent mostly at derived nodes, and differ at several internal nodes. The analyses of combined data indicate that Morpho is composed of four clades each of which include one or more previously proposed subgenera. The subgenera Pessonia and Morpho were not monophyletic, and to address this issue we propose that Pessonia, syn.nov. be subsumed within Morpho. The ancestor of Morpho probably arose during the Oligocene, and most diversification seems to have occurred during the late Miocene. S‐DIVA analysis suggests eastern Andean region as the ancestral area for Morpho, and that the South American Atlantic Forest was colonized multiple times.     

Biomechanical and Morphometric Differences in Triticum aestivum Seedlings Differing in Rht Gene-Dosage

Biomechanical and morphometric comparisons among coleoptilesfrom wheat seedlings differing in Rht gene-dosage (Rht = 0,2, 4 doses) are presented in an effort to evaluate the influenceof Rht on the mechanics of soil penetration by this organ. Rhtis known to reduce seedling establishment compared to the wildtype. Data from 3–7-day-old seedlings indicate that Rhtreduces tissue elastic modulus E, increases the second momentof area I, and decreases the slenderness ratio (l/r) of coleoptiles.Rht-relatedchanges in E and I are such that the flexural stiffness of coleoptilesfrom Rht plants does not differ significantly from the wildtype-hence the growing coleoptiles of all three genotypes haveequivalent biomechanical capacity to penetrate the soil. Rhtreduction of coleoptile slenderness ratios confers a capacityto safely sustain higher axial compressive loads compared tocoleoptiles with equivalent flexural stiffness but higher ratios.However, wild type seedlings produce longer coleoptiles andlonger subcrown internodes than Rht seedlings. Longer coleoptilesdeliver the crown node closer to the top of the soil beforethe crown node extends beyond the lateral confinement of thecoleoptile. This reduces the potential for buckling of the subcrowninternode and leaves due to the compressive loading of soil.Rht affects a variety of mechanical features whose influenceis dependent upon the stage of seedling growth and the degreeof soil compaction. However, at equivalent depths of burialwhich exceed the maximum length of coleoptiles and moderatesoil compaction, Rht is biomechanically disadvantageous to seedlingestablishment. Wheat, germination, biomechanics, Rht-gene     

Seasonal changes in morphometric and biochemical endpoints in northern pike (Esox lucius), burbot (Lota lota) and slimy sculpin (Cottus cognatus)

1. Morphometric and biochemical endpoints were used to assess growth and energetics in young‐of‐the‐year (YOY) northern pike (Esox lucius), YOY burbot (Lota lota) and slimy sculpin (Cottus cognatus) collected upstream and downstream of a uranium mining operation in northern Saskatchewan, Canada. 2. Water sampled at sites downstream of uranium mining and milling effluent discharge was higher in certain trace metals (arsenic, molybdenum), ions (conductivity, hardness, ammonia and sulphate) and total dissolved solids compared with ecologically similar reference sites. 3. Overwinter survival potential was estimated by determining total body lipids and total body triglycerides in fishes collected in late autumn and early spring. Two‐factor anova indicated no site or season differences in total body lipids or triglycerides in YOY northern pike. In spring, burbot collected from the exposure site were higher in total body lipids and triglycerides compared with the previous autumn and compared with fish collected from the reference site. Slimy sculpin from both exposure and reference sites had lower total body lipid and triglyceride content in spring compared with the previous autumn. In addition, sculpin from the exposure site had lower total body lipids and triglycerides in spring compared with fish collected from the reference site. 4. Biochemical estimates of fish growth (muscle RNA/DNA ratio and muscle protein concentration) exhibited clear seasonal differences, with consistent decreases in this endpoint for all fish species in spring relative to the previous autumn at both exposure and reference sites. 5. Results for total body lipids and triglycerides were inconclusive and inconsistent between species and exposure scenarios. However, all species exhibited a similar seasonal decrease in muscle protein and to a lesser extent, muscle RNA/DNA ratio.     

Voigt and Reuss Models for Predicting Changes in Young's Modulus of Dehydrating Plant Organs

A general modelling approach was used to predict the changesresulting from dehydration in the Young's modulus (E) of a tereteorgan with a simple anatomy (e.g. hypodermis of thick-walledtissue surrounding a parenchymatous core of ground tissue).Two general anatomical models were investigated: (1) an ‘apoplastmodel’ in which each cross section through the organ wasconsidered as a composite elastic material consisting of a solid(cell wall) and liquid (protoplasm) phase; and (2) a ‘core-rindmodel’ in which the organ consisted of a thick-walledand a thin-walled tissue. For each of these two anatomical models,two composite material models were considered, i.e. a Voigtor Reuss equation was used to predict the changes in E attendingdehydration. The predictions from the variants of the generalmodel were evaluated on the basis of observed changes in E ascylindrical segments of the pseudopetioles of Spathiphyllumwere allowed to desiccate at room temperature. Statistical comparisonsbetween predicted and observed values of E revealed that oneof the simple variants of the model, the ‘Voigt apoplastmodel’, was the most successful in predicting the observedtrend seen in the changes in E. However, when the Voigt andReuss apoplast models were combined, the ‘hybrid’model provided estimates of changes in E that were statisticallyindistinguishable from those observed. Based on the hybrid model,it was estimated that roughly 76.7% of the tissues with a representativeSpathiphyllum pscudopetiole operated according to a Voigt apoplastmodel. Young's modulus, dehydration, plant tissues     

Simulations of Apical Developmental Sequences in Bryophytes

The developmental sequences of the apex of bryophyte gametophytesare simulated by means of a reiterative algorithm. The productionof apical cell derivatives by this model is based upon a fewrelatively simple assumptions: (1) each cycle of derivativesoccupies a finite space determined by their fixed surface area,(2) the next cycle displaces the previous set of derivativesby a distance comparable to their length, (3) the time necessaryto achieve each successive cycle is constant, (4) as the ‘apex’grows, each cycle must either increase in surface area or produceadditional (intercalary) derivatives, and (5) the event of eachderivative's formation may be expressed by a function comparableto that of phyllotaxy, e.g. in triradial symmetries analogousto leafy liverworts this function is a phyllotaxy. Simulationshaving a priori constraints on surface area, rate of surfacerecurvature, and rate of cycle production may be used to determinedifferential rates of cell division, elongation and surfacearea change. Computer program length and running times are usedto determine the relative degree of complexity among radialand dorsiventral forms. Based upon these criteria, the dorsiventralsymmetry is considered derived rather than archaic. Simulationsare used to propose the most probable symmetry of early landplants. bryophytes, apical development, computer analysis