Corticosterone promotes scramble competition over sibling negotiation in Barn Owl nestlings (Tyto alba)

In species with parental care, siblings compete for access to food resources. Typically, they vocally signal their level of need to each other and to parents, and jostle for the position in the nest where parents deliver food. Although food shortage and social interactions are stressful, little is known about the effect of stress on the way siblings resolve the conflict over how food is shared among them. Because glucocorticoid hormones mediate physiological and behavioral responses to stressors, we tested whether corticosterone, the main glucocorticoid in birds, modulates physical and vocal signaling used by barn owl siblings (Tyto alba) to compete for food. Although corticosterone-implanted (cort-) nestlings and placebo-nestlings were similarly successful to monopolize food, they employed different behavioral strategies. Compared to placebo-nestlings, cort-individuals reduced the rate of vocally communicating with their siblings (but not with their parents) but were positioned closer to the nest-box entrance where parents predictably deliver food. Therefore, corticosterone induced nestlings to increase their effort in physical competition for the best nest position at the expense of investment in sib-sib communication without modifying vocal begging signals directed to parents. This suggests that in the barn owl stress alters nestlings' behavior and corticosterone could mediate the trade-off between scramble competition and vocal sib-sib communication. We conclude that stressful environments may prevent the evolution of sib-sib communication as a way to resolve family conflicts peacefully.

Wave competition in excitable modulated media.

The propagation of an initially planar front is studied within the framework of the photosensitive Belousov-Zhabotinsky reaction modulated by a smooth spatial variation of the local front velocity in the direction perpendicular to front propagation. Under this modulation, the wave front develops several fingers corresponding to the local maxima of the modulation function. After a transient, the wave front achieves a stationary shape that does not necessarily coincide with the one externally imposed by the modulation. Theoretical predictions for the selection criteria of fingers and steady-state velocity are experimentally validated.

Experimental evidence that intra-specific competition in seagrass meadows reduces reproductive potential in the sea urchin Paracentrotus lividus (Lamarck)

To better understand the biological controls that regulate sea urchin dynamics, we studied the effects of potential inter- and intra-specific competition for food on several biological variables of the main sea urchin in the Mediterranean (Paracentrotus lividus). We carried out a caging experiment in which we manipulated sea urchin density (natural vs. high density) and herbivorous fish (Sarpa salpa) accessibility (free access vs. exclusion) in a Posidonia oceanica meadow. No evidence of competition between fish and urchins was detected. Neither density-dependent mortality nor changes in the somatic variables were found; however, we detected that intra-specific competition affected the reproductive potential of P. lividus. The gonad index of urchins at high population densities was ca. 30% lower than that of urchins at natural densities. As a spawning event had just occurred when urchins were collected, these differences probably reflect differences in reserve content, which may compromise the following reproductive period and decrease survival in the long term, as the gonads are also used as storage organs. For the time period studied, mortality rates appeared to be independent of local densities. The results indicate that a long-term negative feedback mechanism appears to take place in P. lividus in response to increased population density.

Do we fear tax competition among new and old European countries ?

The purpose of this paper is to study both theoretically and empirically tax competition in the enlarged EU and to provide some insights on ongoing reforms concerning business taxation. We support the idea that even if one can observe cuts in "new" members statutory business tax rates, this should not result in fiercer tax competition between the "core" and "the "periphery" since infrastructure endowments and the existence of agglomeration rents in the core of the EU may prevent (at least partially) activities to relocate to the "new" members.

Catch-up growth strategies differ between body structures: interactions between age and structure-specific growth in wild nestling Alpine swifts

1. Little is known on the occurrence and magnitude of faster than normal (catch-up) growth in response to periods of undernutrition in the wild, and the extent to which different body structures compensate and over what timescales is poorly understood. 2. We investigated catch-up growth in nestling Alpine Swifts, Apus melba, by comparing nestling growth trajectories in response to a naturally occurring 1-week period of inclement weather and undernutrition with growth of nestlings reared in a good year. 3. In response to undernutrition, nestlings exhibited a hierarchy of tissues preservation and compensation, with body mass being restored quickly after the end of the period of undernutrition, acceleration of skeletal growth occurring later in development, and compensation in wing length occurring mostly due to a prolongation of growth and delayed fledging. 4. The effect of undernutrition and subsequent catch-up growth was age-dependent, with older nestlings being more resilient to undernutrition, and in turn having less need to compensate later in the development. 5. This shows that young in a free-living bird population can compensate in body mass and body size for a naturally occurring period of undernutrition, and that the timing and extent of compensation varies with age and between body structures.

Peroxisome proliferator-activated receptor mediates cross-talk with thyroid hormone receptor by competition for retinoid X receptor. Possible role of a leucine zipper-like heptad repeat.

The peroxisome proliferator-activated receptors (PPAR) and thyroid hormone receptors (TR) are members of the nuclear receptor superfamily, which regulate lipid metabolism and tissue differentiation. In order to bind to DNA and activate transcription, PPAR requires the formation of heterodimers with the retinoid X receptor (RXR). In addition to activating transcription through its own response elements, PPAR is able to selectively down-regulate the transcriptional activity of TR, but not vitamin D receptor. The molecular basis of this functional interaction has not been fully elucidated. By means of site-directed mutagenesis of hPPAR alpha we mapped its inhibitory action on TR to a leucine zipper-like motif in the ligand binding domain of PPAR, which is highly conserved among all subtypes of this receptor and mediates heterodimerization with RXR. Replacement of a single leucine by arginine at position 433 of hPPAR alpha (L433R) abolished heterodimerization of PPAR with RXR and consequently its trans-activating capacity. However, a similar mutation of a leucine residue to arginine at position 422 showed no alteration of heterodimerization, DNA binding, or transcriptional activation. The dimerization deficient mutant L433R was no longer able to inhibit TR action, demonstrating that the selective inhibitory effect of PPAR results from the competition for RXR as well as possibly for other TR-auxiliary proteins. In contrast, abolition of DNA binding by a mutation in the P-box of PPAR (C122S) did not eliminate the inhibition of TR trans-activation, indicating that competition for DNA binding is not involved. Additionally, no evidence for the formation of PPAR:TR heterodimers was found in co-immunoprecipitation experiments. In summary, we have demonstrated that PPAR selectively inhibits the transcriptional activity of TRs by competition for RXR and possibly non-RXR TR-auxiliary proteins. In contrast, this functional interaction is independent of the formation of PPAR:TR heterodimers or competition for DNA binding.

Stability of soybean yield through different sowing periods

Soybean yield is highly affected by sowing period and there are significant productivity losses when sowings are done outward a relatively restricted period in many regions of Brazil. Breeding cultivars less sensitive to photoperiod and to temperature variations is desirable for adaptation to wider sowing period and wider latitude range and also make irrigated soybean cultivation possible during the fall-winter seasons in frost free regions. The possibility of selecting high yielding and stable lines for yield during various sowing periods was studied by analyzing the behavior of 100 non-selected advanced lines (F9 and F10), from each one of all possible biparental crosses involving the genotypes BR85-29009, OCEPAR 8, FT-2, and BR-13. Experiments were set up in a completely randomized design with single-plant hill plots and received supplementary irrigation. Sowing was on Sept 27, Oct 20, Nov 17, and Dec 17 in 1993/94 and Sept 20, Oct 20, Nov 17, and Dec 14 in 1994/95 at Londrina, PR, Brazil. Procedures of regression analysis and minimum variance among planting date means were efficient for selecting stable lines during the four sowing seasons. It was possible to select stable and high yielding genotypes through the four sowing periods in all the crosses. No specific cross was clearly better to produce a greater number of stable genotypes.

Habitat selection in zones of parapatric contact between the common shrew Sorex araneaus and Millet's shrew S. coronatus

(1) The common shrew Sorex araneus and Millet's shrew S. coronatusare sibling species.They are morphologically and genetically very similar but do not hybridize.Their parapatric distribution throughout south-western Europe, with a few narrow zones of distributional overlap, suggests that they are in competitive parapatry. (2) Two of these contact zones were studied; there was evidence of coexistence over periods of 2 years as well as habitat segregation. In both zones, the species segregated on litter thickness and humidity variables. (3) A simple analysis of spatial distribution showed that habitats visible in the field corresponded to the habitats selected by the species. Habitat selection was found throughout the annual life-cycle of the shrews. (4) In one contact zone, a removal experiment was performed to test whether habitat segregation is induced by interspecific interactions. The experiment showed that the species select habitats differentially when both are present and abandon habitat selection when their competitor removed. (5)These results confirm the role of resource partitioning in promoting narrow ranges of distributional overlap between such parapatric species and qualitatively support the prediction of habitat selection theory that, in a two-species system, coexistence may be achieved by differential habitat selection to avoid competition. The results also support the view that the common shrew and Millet's shrew are in competitive parapatry.

Space Competition and Time Delays in Human Range Expansions. Application to the Neolithic Transition

Space competition effects are well-known in many microbiological and ecological systems. Here we analyze such an effectin human populations. The Neolithic transition (change from foraging to farming) was mainly the outcome of a demographic process that spread gradually throughout Europe from the Near East. In Northern Europe, archaeological data show a slowdown on the Neolithic rate of spread that can be related to a high indigenous (Mesolithic) population density hindering the advance as a result of the space competition between the two populations. We measure this slowdown from a database of 902 Early Neolithic sites and develop a time-delayed reaction-diffusion model with space competition between Neolithic and Mesolithic populations, to predict the observed speeds. The comparison of the predicted speed with the observations and with a previous non-delayed model show that both effects, the time delay effect due to the generation lag and the space competition between populations, are crucial in order to understand the observations

Changing patterns of cancer incidence in the early- and late-HAART periods: the Swiss HIV Cohort Study.

BACKGROUND: The advent of highly active antiretroviral therapy (HAART) in 1996 led to a decrease in the incidence of Kaposi's sarcoma (KS) and non-Hodgkin's lymphoma (NHL), but not of other cancers, among people with HIV or AIDS (PWHA). It also led to marked increases in their life expectancy. METHODS: We conducted a record-linkage study between the Swiss HIV Cohort Study and nine Swiss cantonal cancer registries. In total, 9429 PWHA provided 20,615, 17,690, and 15,410 person-years in the pre-, early-, and late-HAART periods, respectively. Standardised incidence ratios in PWHA vs the general population, as well as age-standardised, and age-specific incidence rates were computed for different periods. RESULTS: Incidence of KS and NHL decreased by several fold between the pre- and early-HAART periods, and additionally declined from the early- to the late-HAART period. Incidence of cancers of the anus, liver, non-melanomatous skin, and Hodgkin's lymphoma increased in the early- compared with the pre-HAART period, but not during the late-HAART period. The incidence of all non-AIDS-defining cancers (NADCs) combined was similar in all periods, and approximately double that in the general population. CONCLUSIONS: Increases in the incidence of selected NADCs after the introduction of HAART were largely accounted for by the ageing of PWHA.

Ecological niche overlap in sister species: how do oil-collecting bees Macropis europaea and M. fulvipes (Hymenoptera: Melittidae) avoid competition and hybridization?

Oil-collecting bees are found worldwide and always in association with particular oil-producing flowers. In the Western Palearctic, three oil-collecting bee species within the genus Macropis (Hymenoptera, Melittidae) interact in a tight pollination mutualism with species of the only European oil-producing plant genus Lysimachia L. (Myrsinaceae). Two of these oil-collecting bees (Macropis europaea and Macropis fulvipes) show overlapping geographic distributions, comparable morphologies, and similar ecological characteristics (e.g., habitat type, floral preferences). In view of these similarities, we presume that hybridization should occur between the two species unless potential variation among the species' ecological niches prevents it, simultaneously decreasing competition for resources. Using modern genetic analyses and ecological niche modeling on a large bee sampling throughout Europe, we discuss new perspectives on the ecology and evolutionary history of this mutualism.

Allocation of above-ground growth in Pinus sylvestris - impacts of tree size and competition

Abstract

Height distributions of Scots pine sapling stands affected by retained tree and edge stand competition

Abstract