Disentangling the relative importance of climate,size and competition on tree growth in Iberian forests: implications for forest management under global change

Most large‐scale multispecies studies of tree growth have been conducted in tropical and cool temperate forests, whereas Mediterranean water‐limited ecosystems have received much less attention. This limits our understanding of how growth of coexisting tree species varies along environmental gradients in these forests, and the implications for species interactions and community assembly under current and future climatic conditions. Here, we quantify the absolute effect and relative importance of climate, tree size and competition as determinants of tree growth patterns in Iberian forests, and explore interspecific differences in the two components of competitive ability (competitive response and effect) along climatic and size gradients. Spatially explicit neighborhood models were developed to predict tree growth for the 15 most abundant Iberian tree species using permanent‐plot data from the Spanish Second and Third National Forest Inventory (IFN). Our neighborhood analyses showed a climatic and size effect on tree growth, but also revealed that competition from neighbors has a comparatively much larger impact on growth in Iberian forests. Moreover, the sensitivity to competition (i.e. competitive response) of target trees varied markedly along climatic gradients causing significant rank reversals in species performance, particularly under xeric conditions. We also found compelling evidence for strong species‐specific competitive effects in these forests. Altogether, these results constitute critical new information which not only furthers our understanding of important theoretical questions about the assembly of Mediterranean forests, but will also be of help in developing new guidelines for adapting forests in this climatic boundary to global change. If we consider the climatic gradients of this study as a surrogate for future climatic conditions, then we should expect absolute growth rates to decrease and sensitivity to competition to increase in most forests of the Iberian Peninsula (in all but the northern Atlantic forests), making these management considerations even more important in the future.     

Herbicide resistant rice (Oryza sativa L.): Global implications for weedy rice and weed management*

Rice cultivars resistant to broad‐spectrum herbicides have been developed and their commercial release is imminent, especially for imidazolinone and glufosinate resistant varieties in the USA and Latin America. Glyphosate‐resistant rice should follow within a few years. Rice growers throughout the world could benefit from the introduction of herbicide‐resistant rice cultivars that would allow in‐crop, selective control of weedy Oryza species. Other perceived benefits are the possibility to control ‘hard‐to‐kill’ weed species and weed populations that have already evolved resistance to herbicides currently used in rice production, especially those of the Echinochloa species complex. Weed management could also be improved by more efficient post‐emergence control. Introduction of herbicide resistant rice could also bring areas heavily infested with weedy rice that have been abandoned back to rice production, allow longer term crop rotations, reduce consumption of fossil fuels, promote the replacement of traditional chemicals by more environmentally benign products, and provide more rice grain without adding new land to production. There are also concerns, however, about the impact of releasing herbicide‐resistant rice on weed problems. Of most concern is the possibility of rapid transfer of the resistance trait to compatible weedy Oryza species. Development of such herbicide resistant weedy rice populations would substantially limit the chemical weed management options for farmers. Herbicide‐resistant rice volunteers also could become problematic, and added selection pressure to weed populations could aggravate already serious weed resistance problems. Because of the risk of weedy Oryza species becoming resistant to broad‐spectrum herbicides, mitigating measures to prevent gene flow, eventually attainable by both conventional breeding and molecular genetics, have been proposed. With commercialisation of the first herbicide resistant varieties planned for 2001, these mitigating measures will not be available for use with this first generation of herbicide resistant rice products. Release of herbicide resistant rice should depend on a thorough risk assessment especially in areas infested with con‐specific weedy rice or intercrossing weedy Oryza species. Regulators will have to balance risks and benefits based on local needs and conditions before allowing commercialisation of herbicide‐resistant rice varieties. If accepted, these varieties should be considered as components of integrated weed management, and a rational herbicide use and weedy rice control should be promoted to prevent losing this novel tool.     

Parmelina quercina (Parmeliaceae, Lecanorales) includes four phylogenetically supported morphospecies

Morphological and phylogenetic relationships of the worldwide Mediterranean lichen forming fungus, Parmelina quercina , have been studied. Specimens from western Europe, western North America and southern Australia were analysed using molecular data (nuITS rDNA, nuLSU rDNA and mtSSU rDNA) and selected morphological features (upper cortex maculae, scanning electron microscopy examination of the epicortex, ascospores and conidia shape and size, and amphithecial retrorse rhizines). The results conclusively reveal that: (1) there is not one single species but four separate species in the Mediterranean or sub Mediterranean areas of the world. Parmelina quercina and Parmelina carporrhizans (Euroasiatic species), Parmelina coleae sp. nov. (North America) and Parmelina elixia sp. nov. (Australia); (2) largely debated P. carporrhizans is not a synonym of P. quercina but supported as a valid species circumscribed to Macaronesic relict sites; (3) the geographical isolation of the Australian population is correlated with a large genetic distance; (4) morphological characters (ascospores and conidial variability and thallus epicortex) correlate with the phylogenetic hypothesis; (5) the new or revalidated species within Parmelina quercina are not cryptic species but morphologically recognizable taxa.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 455–467.     

The adaptive role of Phosphoglucomutase and other allozymes in a marine snail across the vertical rocky-shore gradient

Natural selection can play an important role in the maintenance of genetic polymorphisms, despite ongoing gene flow. In the present study, we use previously analysed allozymic loci and perform an F _ST outlier-based analysis to detect the signatures of divergent selection between sympatric ecotypes of the marine snail Littorina saxatilis at different localities. The results obtained show that different allozyme polymorphisms are affected (directly or indirectly) by selection at distinct geographical regions. The Phosmogluco mutase-2 locus was the best candidate for adaptation and further biochemical analyses were performed. The kinetic properties of the three more common genotypes of Pgm-2 were studied. The results obtained are concordant with two alternative hypotheses: (1) natural selection is acting directly on this locus or, more probably, (2) selection is affecting a genomic region tightly linked to the enzyme locus. In both cases, the known existence of a parallel and partially independent origin of these ecotypes would explain why different candidate loci were detected in different localities.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 225–233.     

Predictions of response to selection caused by angling in a wild population of Atlantic salmon (Salmo salar)

1. Recreational angling activities in wild populations of Atlantic salmon may induce a selection pressure towards a reduction in body size and length if the angling season coincides with the return of the largest sea age fish class. 2. Using estimates of heritability for growth traits and estimates of the selection pressure from angling operating on growth, we predicted the response to selection expected to occur in a wild population of Atlantic salmon. 3. The dataset used here comprised individuals from two consecutive generations (parents and offspring) from the River Bidasoa (NW Spain). Offspring were assigned to parents using six highly polymorphic microsatellite loci. Use of restricted maximum likelihood methodology and the animal model allowed us to estimate the heritability for body length and body weight as well as their genetic correlation. 4. Estimated heritabilities (0.32 ± 0.12 for length and 0.32 ± 0.11 for weight) and selection pressure caused by angling were used to obtain predictions of response to selection because of angling. Our results suggested a decline of 1.9 mm in body length and 103.3 g in body weight per generation because of angling pressure. 5. The results derived from this study suggest that the angling season should be annually delayed in order to avoid selective angling of the multi‐year class and further reductions in body weight and length.     

Activation of Tyrosinase Reduces the Cytotoxic Effects of the Superoxide Anion in B16 Mouse Melanoma Cells

Tyrosinase may protect against oxidative stress by using the superoxide anion (O^?₂) in the production of melanin. We have examined this by comparing its cytotoxic effects in B16/F10 and B16/F10-differential deficient (-DD) mouse melanoma cells that express high and low levels of tyrosinase activity respectively. Xanthine oxidase (XO) was used to generate O^?₂ and cytotoxicity assessed by measuring cell survival. XO increased O^?₂ concentrations and 3 h later dose related decreases in cell survival were seen. F10 cells were more resistant to these cytotoxic effects than the F10-DD cells. [Nle⁴,DPhe⁷]MSH increased tyrosinase activity and melanin content, reduced O^?₂ concentration and increased the resistance of F10 cells to the cytotoxic effects of O^?₂. No such effects were seen in F10-DD cells. The effect of [Nle⁴,DPhe⁷]MSH on the resistance of the F10 cells was time-dependent and noticeable when tyrosinase activity but not melanin was increased. This suggests that it was the activation of tyrosinase rather than the increase in the melanin that provided the protection against O^?₂. In support of this, inhibition of tyrosinase with phenylthiocarbamide reduced the increased resistance induced by [Nle⁴,DPhe⁷]MSH. Moreover, although melanin was capable of scavenging O^?₂ it had little effect at concentrations comparable to those in the activated F10 cells. XO also increased the melanin content of F10 but not F10-DD cells. We conclude that tyrosinase is able to utilise O^?₂ to produce melanin and this provides pigment cells with a unique anti-oxidant mechanism.     

Effect of Amphotericin B on Dopachrome Tautomerase Activity and Other Melanogenic Parameters in Cultured B16/F10 Melanoma Cells

The antifungal reagent Fungizone (amphotericin B and deoxycholate) caused an activation in dopachrome tautomerase and dopa oxidase activities of B16/F10 melanoma cells at the routine concentration (2.5 μg/ml) used for preventing molds and yeast growth in cultures of animal cells. However, higher amphotericin B concentrations caused a significant cell death and the inhibition of enzymatic activities. At the optimal concentration of Fungizone, the enzymatic activities and melanin content were augmented as incubation time increased. The detergent sodium deoxycholate alone exerted no effect on these melanogenic parameters, eliminating the possibility that this detergent was partially responsible for melanogenic modifications produced by Fungizone. After withdrawal of Fungizone from the reaction medium, the recovery of melanogenic parameters to normal values was slower for DCT than for tyrosinase. The behavior of dopa oxidase was very similar to that reported by Johnson and Bagnara (Pigment Cell Res. 3, 173–175) for tyrosine hydroxylase.     

Is parental care behavior in Belostoma species an evolutionary cause for their common sexual size dimorphism pattern?

Current evidence suggests that sexual size dimorphism (SSD) reflects the male and female adaptation to their different reproductive roles. Belostoma and Lethocerus species, included in Belostomatidae, present different kinds of paternal care. Females of Belostoma Latreille species lay their eggs on the back of males. Males carry, aerate and protect the clutch until hatching, which is critical for offspring survival. Males of Lethocerus Mayr species exhibit some parental care behavior but do not carry the eggs. The genera are nearly related. We studied and compared the SSD patterns of B. oxyurum (Dufour), B. micantulum (Stål), B. elegans (Mayr), B. bifoveolatum Spinola, B. gestroi Montandon and Lethocerus annulipes (Herrich‐Schäffer) by means of a multivariate approach to distinguish selection targets in different components of size. Morphometric analysis revealed that SSD patterns vary among traits and that the arrangements are similar in Belostoma species, showing a common trend under resembling selective mechanisms. The widespread SSD trend in insects is that all components of body size are biased towards females, generally related to a fecundity advantage, a pattern now also detected in L. annulipes. We found in Belostoma species that the male has relatively longer middle and hind legs. We propose that SSD in hind legs biased towards males is a selective response for paternal care; they denote a brood‐adapted morphology. The middle leg enlargement may be an associated response to maintain effective locomotion.     

Time course of nodule development in the Discaria trinervis (Rhamnaceae) –Frankia symbiosis

The time course of initiation and development of root nodules was investigated in the South American actinorhizal shrub Discaria trinervis (Rhamnaceae). A local strain of Frankia (BCU110501) which was isolated from D. trinervis nodules, was used as inoculum. Inoculated seedlings were periodically studied under the light microscope after clearing with aqueous NaClO. In parallel, semithin and ultrathin sections were analysed by light and electron microscopy. Infection by Frankia BCU110501 involved intercellular penetration among epidermal and cortical root cells. Nodule primordia were detected from 6 d after inoculation, while bacteria were progressing through intercellular spaces of the outer layers of cortical cells. Invasion of host cells by the symbiont occurred 7–9 d after inoculation, and hypertrophy of the primordium cells was associated with Frankia penetration. Root hairs were not deformed during the early events of nodule formation. From 13 to 16 d after inoculation, the proximal cellular zone of the primordia behaved differently from the other tissues after NaClO treatment and remained darkly pigmented. At the same time, differentiation of Frankia vesicles started to occur inside already infected cells. By 16 d after inoculation, spherical vesicles of BCU110501 were homogeneously distributed in the host cells. These vesicles were septate and surrounded by void space. Frankia spores or sporangia were not observed in the nodule tissue. This study has clarified the mode of Frankia penetration in D. trinervis , one of the Rhamnaceae which also includes Ceanothus . The events involved in infection, nodule induction, host-cell infection and vesicle differentiation have been characterized and identified as time-segregated developmental processes in the ontogeny of D. trinervis root nodules.