The putative gymnosperm plant defensin polypeptide (SPI1) accumulates after seed germination,is not readily released,and the SPI1 levels are reduced in Pythium dimorphum-infected spruce roots

The putative plant defensin SPI1 cDNA from the conifer Norway spruce (Picea abies) is the only known plant defensin-like sequence from a gymnosperm. The predicted translational product SPI1 was not detected in the embryo or other parts of the seed by means of antibodies, but it accumulated in the root cortex after germination. In roots of seedlings infected with the root pathogenic oomycete Pythium dimorphum and the blue stain fungus Ceratocystis polonica, variable levels of SPI1 was detected during the first day as a response to the infection, however a significant increase was seen as an initial response to the root-rot fungus Heterobasidion annosum. After the first day of infection, the amount of SPI1 polypeptide was dramatically reduced in response to either of the pathogens, but not in response to the ectomycorrhizal fungus Laccaria bicolor. During the same time of infection, extensive damage to cortical root cells resulted from the infecting pathogens, but not from the mycorrhiza. These results indicate that pathogens may reduce the level of SPI1 by suppressing its expression, but may also reduce the SPI1 level by invading and disrupting the root cortical cells or by a combination of these mechanisms.     

Induction of plant responses by a sequestering insect: Relationship of glucosinolate concentration and myrosinase activity

Induction of plant allelochemicals is of particular ecological importance for interactions with herbivores that can make use of induced metabolites by incorporating them for their own defence. Induction patterns in white mustard, Sinapis alba, were investigated following herbivory of the turnip sawfly, Athalia rosae, which sequesters plant glucosinolates. Larvae of different age were allowed to feed for 24 h on young leaves of premature, non-flowering plants. Changes in primary and secondary metabolites were recorded in the damaged leaves (local) and in the adjacent leaves and stems (systemic) for several days. Organ- and time-specific patterns were evident. Local responses included increases in glucosinolate concentrations, soluble and insoluble myrosinase activity and glucose levels, while systemic responses in leaves were restricted to increases in myrosinase activities and glucose. All effects were strongest immediately after feeding and declined mostly within a day. Stems had overall lower constitutive levels of glucosinolates and myrosinase activities than leaves. Feeding by one large larva had a greater impact on the plant's physiology than feeding by three small ones, even though both treatments resulted in quantitatively similar leaf destruction. Local increase in glucosinolate concentration could be beneficial for larvae, while conspecifics feeding on induced adjacent leaves might be negatively affected due to higher myrosinase activity levels. The results are discussed in the context of the ‘optimal defence theory’ and the ‘lethal plant defence paradox’.     

El géneroJacquinia L. (Theophrastaceae) en Cuba

The term phyletic diversity is used here to denote the continued co-existence and evolution of separate major phyletic groups which have a similar mode of life (e.g. within the angiosperms). This work attempts to show that an understanding of the factors which determine the degree of phyletic diversity could contribute to understanding the nature and evolution of higher taxonomic categories, such as families. The opposite of phyletic diversity, phyletic uniformity (Fig. 1A—B), should result from unequal evolutionary rates of different groups and repeated adaptive radiations of the most successful groups; the following competition for essential, limiting resources should lead to the extinction of all less rapidly evolving, inferior groups. At least some plant families are shown to have specific adaptive specializations which give them competitive advantages for part of the environmental resources only. This ensures their co-existence and the maintainance of phyletic diversity. The nature of these family specializations is considered briefly. It is shown that physiological adaptations to particular conditions, symbioses which aid in obtaining nutrients and, especially, chemical defence mechanisms could be major components of these specializations and thereby the raison d'être of plant families.     

Fungal pathogen-induced changes in the antioxidant systems of leaf peroxisomes from infected tomato plants

Peroxisomes, being one of the main organelles where reactive oxygen species (ROS) are both generated and detoxified, have been suggested to be instrumental in redox-mediated plant cell defence against oxidative stress. We studied the involvement of tomato (Lycopersicon esculentum Mill.) leaf peroxisomes in defence response to oxidative stress generated upon Botrytis cinerea Pers. infection. The peroxisomal antioxidant potential expressed as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and glutathione peroxidase (GSH-Px, EC 1.11.1.19) as well as the ascorbate-glutathione (AA-GSH) cycle activities was monitored. The initial infection-induced increase in SOD, CAT and GSH-Px indicating antioxidant defence activation was followed by a progressive inhibition concomitant with disease symptom development. Likewise, the activities of AA-GSH cycle enzymes: ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) as well as ascorbate and glutathione concentrations and redox ratios were significantly decreased. However, the rate and timing of these events differed. Our results indicate that B. cinerea triggers significant changes in the peroxisomal antioxidant system leading to a collapse of the protective mechanism at advanced stage of infection. These changes appear to be partly the effect of pathogen-promoted leaf senescence.     

Patterns of <Emphasis Type="Italic">Azteca</Emphasis> ants’ defence of <Emphasis Type="Italic">Cecropia</Emphasis> trees in a tropical rainforest: support for optimal defence theory

Optimal defence theory (ODT) predicts that, whereas high risk of herbivory should select for high constitutive levels of defence, induced defences should be more advantageous in environments with a low probability of herbivory. In the present field study, conducted on the Azteca–Cecropia ant–plant system in a Neotropical rainforest, we evaluated whether the constitutive and induced ant defence of leaves are directly and inversely related to an estimate of herbivory risk, respectively. To assess the constitutive level of Azteca defence in Cecropia obtusifolia trees, we recorded the number of ants patrolling undamaged leaves. To evaluate the induced level of Azteca defence, the same leaves were subjected to simulated herbivory by punching circular holes in them. We recorded the maximum number of ants patrolling the damaged leaves from 2 to 15 min after damage. Past herbivory (% defoliation of old leaves) was assumed to indicate a risk of herbivory. Regression analyses showed that, whereas the constitutive level of ant patrolling was positively associated with the magnitude of herbivory on old leaves, there was a negative association between the magnitude of induced ant defence and past herbivory. These preliminary results lend support to ODT.     

Primary structure and expression of mRNAs encoding basic chitinase and 1,3-β-glucanase in potato

Infection of potato leaves (Solanum tuberosum L. cv. Datura) by the late blight fungus Phytophthora infestans, or treatment with fungal elicitor leads to a strong increase in chitinase and 1,3--glucanase activities. Both enzymes have been implicated in the plant's defence against potential pathogens. In an effort to characterize the corresponding genes, we isolated complementary DNAs encoding the basic forms (class I) of both chitinase and 1,3--glucanase, which are the most abundant isoforms in infected leaves. Sequence analysis revealed that at least four genes each are expressed in elicitor-treated leaves. The structural features of the potato chitinases include a hydrophobic signal peptide at the N-terminus, a hevein domain which is characteristic of class I chitinases, a proline- and glycine-rich linker region which varies among all potato chitinases, a catalytic domain, and a C-terminal extension. The potato 1,3--glucanases also contain a N-terminal hydrophobic signal peptide and a C-terminal extension, the latter comprising a potential glycosylation site. RNA blot hybridization experiments showed that basic chitinase and 1,3--glucanase are strongly and coordinately induced in leaves in response to infection, elicitor treatment, ethylene treatment, or wounding. In addition to their activation by stress, both types of genes are regulated by endogenous factors in a developmental and organ-specific manner. Appreciable amounts of chitinase and 1,3--glucanase mRNAs were found in old leaves, stems, and roots, as well as in sepals of healthy, untreated plants, whereas tubers, root tips, and all other flower organs (petals, stamen, carpels) contained very low levels of both mRNAs. In young leaves and stems, chitinase and 1,3--glucanase were differentially expressed. While chitinase mRNA was abundant in these parts of the plant, 1,3--glucanase mRNA was absent. DNA blot analysis indicated that in potato, chitinase and 1,3--glucanase are encoded by gene families of considerable complexity.     

Over-expression of a scopoletin glucosyltransferase in Nicotiana tabacum leads to precocious lesion formation during the hypersensitive response to tobacco mosaic virus but does not affect virus resistance

Nicotiana tabacum Togt encodes a scopoletin glucosyltransferase (UDPglucose:scopoletin O -beta-D-glucosyltrans- ferase, EC 2.4.1.128) known to act in vitro on many different substrates including the 6-methoxy-7-hydroxy- coumarin scopoletin. This phenolic compound accumulates in vast amounts, essentially in its glucosylated form scopolin, in tobacco during the hypersensitive response (HR) to tobacco mosaic virus (TMV). To identify the physiological role of this pathogen-inducible UDP-Glc glucosyltransferase (UGT), we generated TOGT over-expressing transgenic plants. Although no endogenous scopoletin or scopolin could be detected before infection, the accumulation of both the aglycone and the glucoside was found to be 2-fold higher in transgenic plants after inoculation with TMV than in wild-type plants. Scopoletin UGT activity in plants over-expressing Togt was significantly higher during the HR than in control plants. This up-regulated activity was associated with a strong increase of the bright blue fluorescence surrounding the HR-necrotic lesions under UV light, which is known to correlate with scopoletin and scopolin abundance. Necrosis appeared sooner in transgenic plants and lesions developed faster, suggesting an accelerated HR. Unexpectedly, the viral content in each lesion was not significantly different in transgenic and in wild-type plants. These results are discussed in relation to the role of TOGT as the major UDP-Glc: scopoletin glucosyltransferase and to the importance of scopoletin accumulation during the HR.     

Specific patterns of changes in wheat gene expression after treatment with three antifungal compounds

The two fungicides azoxystrobin and fenpropimorph are used against powdery mildew and rust diseases in wheat (Triticum aestivumL). Azoxystrobin, a strobilurin, inhibits fungal mitochondrial respiration and fenpropimorph, a morpholin, represses biosynthesis of ergosterol, the major sterol of fungal membranes. Although the fungitoxic activity of these compounds is well understood, their effects on plant metabolism remain unclear. In contrast to the fungicides which directly affect pathogen metabolism, benzo(1,2,3) thiadiazole-7-carbothioic acid S-methylester (BTH) induces resistance against wheat pathogens by the activation of systemic acquired resistance in the host plant. In this study, we monitored gene expression in spring wheat after treatment with each of these agrochemicals in a greenhouse trial using a microarray containing 600 barley cDNA clones. Defence-related genes were strongly induced after treatment with BTH, confirming the activation of a similar set of genes as in dicot plants following salicylic acid treatment. A similar gene expression pattern was observed after treatment with fenpropimorph and some defence-related genes were induced by azoxystrobin, demonstrating that these fungicides also activate a defence reaction. However, less intense responses were triggered than with BTH. The same experiments performed under field conditions gave dramatically different results. No gene showed differential expression after treatment and defence genes were already expressed at a high level before application of the agrochemicals. These differences in the expression patterns between the two environments demonstrate the importance of plant growth conditions for testing the impact of agrochemicals on plant metabolism.     

The effects of feeding damage in ragweed Ambrosia artemisiifolia (Asteraceae) on populations of Zygogramma suturalis (Coleoptera,Chrysomelidae)

Summary Field sampling indicated that the number of eggs laid by a Zygogramma suturalis female within a sampling plot correlated inversely with the mean degree of ragweed damage. Feeding on extensively damaged ragweed in the laboratory caused a drop in oviposition intensity, and a considerable proportion of females completely stopped oviposition. Feeding on slightly damaged ragweed had no significant effect on oviposition intensity. Ovipositing females preferred to feed on the intact ragweed and lay their eggs close to it. The locomotory activity of ovipositing females was significantly higher on highly damaged ragweed whereas non-ovipositing (diapausing) females and males were behaviourally indifferent to the extent of ragweed damage. Under natural conditions, ovipositing females more frequently left damaged host plants for less damaged one. If the degree of ragweed damage is high over a large area, the insects that were unable to find undamaged plants for several days oviposited less and some females entered diapause. The adaptive effect of these reactions is a decrease of population density in advance, before it might drop as a result of starvation. These results are in agreement with the second model of insect reaction to the damage-induced changes in a host plant (Edwards and Wratten 1987).     

Tri-trophic consequences of UV-B exposure: plants,herbivores and parasitoids

In this paper we demonstrate a UV-B-mediated link between host plants, herbivores and their parasitoids, using a model system consisting of a host plant Brassica oleracea, a herbivore Plutella xylostella and its parasitoid Cotesia plutellae. Ultraviolet-B radiation (UV-B) is a potent elicitor of a variety of changes in the chemistry, morphology and physiology of plants and animals. Recent studies have demonstrated that common signals, such as jasmonic acid (JA), play important roles in the mechanisms by which plants respond to UV-B and to damage by herbivores. Plant responses elicited by UV-B radiation can affect the choices of ovipositing female insects and the fitness of their offspring. This leads to the prediction that, in plants, the changes induced as a consequence of UV damage will be similar to those elicited in response to insect damage, including knock-on effects upon the next trophic level, predators. In our trials female P. xylostella oviposited preferentially on host plants grown in depleted UV-B conditions, while their larvae preferred to feed on tissues from UV-depleted regimes over those from UV-supplemented ones. Larval feeding patterns on UV-supplemented tissues met the predictions of models which propose that induced defences in plants should disperse herbivory; feeding scars were significantly smaller and more numerous – though not significantly so – than those on host plant leaves grown in UV-depleted conditions. Most importantly, female parasitoids also showed a clear pattern of preference when given the choice between host plants and attendant larvae from the different UV regimes; however, in the case of the female parasitoids, the choice was in favour of potential hosts foraging on UV-supplemented tissues. This study demonstrates the potential for UV-B to elicit a variety of interactions between trophic levels, most likely mediated through effects upon host plant chemistry.     

Release of highly elicitor-active glucans by germinating zoospores of Phytophthora megasperma f. sp. glycinea

An in-vitro culture system allowing the simultaneous germination of cysts was used to study the early host-independent release of phytoalexin elicitors by Phytophthora megasperma f. sp. glycinea, a soybean pathogen. Significant elicitor activity could be detected in the culture medium as early as 2 h after germination of P.m. f. sp. glycinea, race 1, cysts. The phytoalexin elicitor was heat-stable and heterogeneous in size. The apparent molecular mass ranged from 3 to 80 kDa. Anion exchange and lectin-affinity chromatography followed by sugar analysis confirmed that the elicitor activity resided primarily in glucans. The time course of elicitor release could then be accurately monitored by means of a competitive radioligand-displacement assay using the -glucan elicitor-binding sites of soybean (Glycine max (L.) Merr.) membranes. Linkage-composition analysis of the glucan elicitors showed that they were primarily (1 3)-linked with (1 6)--branches, a composition similar to that of glucans obtained by heat release from mature mycelium but different from that of elicitors obtained by acid hydrolysis or from spontaneous autohydrolytic release by senescent cultures. The naturally released elicitors displayed a biological activity in soybean cotyledon bioassays higher than purified acid-hydrolysed glucan elicitor or than the hepta-(1 3, 1 6)--glucoside, the smallest known carbohydrate elicitor for soybean. The present results demonstrate that elicitor release from the pathogen and perception by the potential host can take place in this system as early as during germ-tube formation and independent of the presence of host-produced endoglucanases.Abbreviations EC₅₀ effector concentration necessary for halfmaximal response - GC-MS gas chromatography-mass spectrometry - HG-APEA 1-[2-(4-aminophenyl)ethyl]amino-1-[hexagluco-syl]-deoxyglucitol - IC₅₀ inhibitor concentration necessary for half-maximal inhibition - P.m. f. sp. glycinea Phytophthora megasperma f. sp. glycinea - V₀ void volume Deceased on March 19, 1990This work was supported by the Deutsche Forschungsgemeinschaft (SFB 206). We thank Dr. H. Mayer, C. Warth and D. Borowiak (Max-Planck-Institut für Immunbiologie, Freiburg) for helpful discussions and experienced technical assistance (glucosyl-linkage analysis).     

Environmental correlates of the intrinsic rate of natural increase in primates

Morphological and life history traits of two clones of the cladoceran Daphnia pulex were measured in the presence and absence of size-selective insect predators, the midge larva Chaoborus flavicans, which preys on small Daphnia, and the water bug Notonecta glauca, which preys on large Daphnia. The aim was to detect predator-induced phenotypic changes, particularly the effect of simultaneous exposure to both types of predators. Other work has shown that in the presence of Chaoborus americanus, Daphnia pulex produce a socalled neck spine which may carry several teeth. The morphological modifications are supposed to serve as an anti-predator device. Furthermore, females exposed to Chaoborus often delay their maturation; this has been interpreted as a cost that balances the benefits of the neck teeth. In this investigation, females of both clones produced fewer but larger offspring than control animals when reared in the presence of Chaoborus flavicans. The offspring showed the typical neck spine and delayed first reproduction. In the presence of Notonecta glauca, one of the clones produced more and smaller offspring, and maturation occurred at earlier instars. The other clone also produced more offspring than the control but there was no size difference. When both predators were present, in most cases the reactions of the daphnids were similar to those in the Notonecta experiment. The response to Chaoborus appeared to be suppressed. The observed modifications are interpreted as evolved strategies that reduce the impact of size-selective predation. They are consistent with predictions of life-history theory.     

The jasmonic acid-amino acid conjugates JA-Val and JA-Leu are involved in rice resistance to herbivores

The phytohormone jasmonic acid (JA) plays a core role in plant defence against herbivores. When attacked by herbivores, JA and its bioactive derivatives are accumulated at the damage site, and subsequently perceived by the jasmonate co-receptors COI1 and JAZ proteins. The (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile) is known to be the main active JA derivative controlling vascular plant responses to herbivores as well as other JA-regulated processes. However, whether other endogenous JA-amino acid conjugates (JA-AAs) are involved in herbivore-induced defence responses remain unknown. Here, we investigated the role of herbivore-elicited JA-AAs in the crop plant rice. The levels of five JA-AAs were significantly increased under the armyworm, leaf folder and brown planthopper attack. Of the elicited JA derivatives, JA-Ile, JA-Val and JA-Leu could serve as ligands to promote the interaction between rice COI1 and JAZs, inducing OsJAZ4 degradation in vivo. JA-Val or JA-Leu treatment increased the expression of JA- and defence-related pathway genes but not JA-Ile levels, suggesting that these JA-AAs may directly function in JA signalling. Furthermore, the application of JA-Val or JA-Leu resulted in JA-mediated plant growth inhibition, while enhancing plant resistance to herbivore attack. This study uncovers that JA-Val and JA-Leu also play a role in rice defence against herbivores.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

The fitness consequences of bearing domatia and having the right ant partner: experiments with protective and non-protective ants in a semi-myrmecophyte

The fitness advantage provided by caulinary domatia to myrmecophytes has never been directly demonstrated because most myrmecophytic species do not present any individual variation in the presence of domatia and the removal of domatia from entire plants is a destructive process. The semi-myrmecophytic tree, Humboldtia brunonis (Fabaceae: Caesalpinioideae), is an ideal species to investigate the selective advantage conferred by domatia because within the same population, some plants are devoid of domatia while others bear them. Several ant species patrol the plant for extra-floral nectar. Fruit production was found to be enhanced in domatia-bearing trees compared to trees devoid of domatia independent of the ant associate. However, this domatium effect was most conspicuous for trees associated with the populous and nomadic ant, Technomyrmex albipes. This species is a frequent associate of H. brunonis, inhabiting its domatia or building carton nests on it. Ant exclusion experiments revealed that T. albipes was the only ant to provide efficient anti-herbivore protection to the leaves of its host tree. Measures of ant activity as well as experiments using caterpillars revealed that the higher efficiency of T. albipes was due to its greater patrolling density and consequent shorter lag time in attacking the larvae. T. albipes also provided efficient anti-herbivore protection to flowers since fruit initiation was greater on ant-patrolled inflorescences than on those from which ants were excluded. We therefore demonstrated that caulinary domatia provide a selective advantage to their host-plant and that biotic defence is potentially the main fitness benefit mediated by domatia. However, it is not the sole advantage. The general positive effect of domatia on fruit set in this ant–plant could reflect other benefits conferred by domatia-inhabitants, which are not restricted to ants in this myrmecophyte, but comprise a large diversity of other invertebrates. Our results indicate that mutualisms enhance the evolution of myrmecophytism.     

Specificity of predator-induced neck spine and alteration in life history traits in Daphnia pulex

It has been proposed that the predator-induced defensive neck spine in Daphnia pulex has a demographic cost. Our results show that this cost is not merely an allocation cost related to the formation and maintenance of the neck spine. In a life table experiment, we tested whether spine induction and life history traits in D. pulex are affected by different invertebrate predators: first and third instar Chaoborus, fourth instar Mochlonyx and two size classes of Notonecta and Dytiscus larvae. D. pulex showed sensitivity to the different predators. Predator-exposure affected one or more of the following life history traits of D. pulex: the timing of first reproduction, clutch size, and growth. In some cases, exposure to predators altered life history traits when neck spine induction did not occur. These shifts in life history traits occurring in the absence of spine induction may be caused by behavioral or physiological changes triggered by the predators.     

Evolution of caprine and ovine β-defensin genes

Defensins comprise an important family of anti-microbial peptides. Among vertebrates, numerous defensin genes have been detected, but their evolutionary background is still discussed. We investigated the molecular evolution and variability of β-defensins of Caprini via sequence analyses of defensin introns. Screening of several domestic and wild species of Caprini revealed a total of 13 discrete β-defensin coding sequences, with three of them described before this study. Phylogenetic analyses revealed that the array of newly described defensin genes is of monophyletic origin and has arisen in numerous independent duplication events after separation of the ancestral defensins. As a result of that scenario, recent defensin genes are distributed in a species-specific manner. Values of synonymous and non-synonymous substitutions demonstrated that both modes of evolutionary pressure, positive as well as negative selection, have acted. In addition, conservation of some β-defensin exons is demonstrated. Discrimination of certain β-defensin genes was possible only due to intron-specific differences. Therefore, sequence analyses restricted to the exons would result in underestimation of the number of β-defensin genes. Our study shows that for reconstruction of the phylogenetic history data of defensin introns are more appropriated. Comparisons among the amino acid sequences show moderate substitutions without changing the net charge of the mature peptides. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Winter territoriality and fruit defence by the fieldfare ( Turdus pilaris )

During the winter seasons of 2000/2001 and 2003/2004, 27 territorial fieldfares Turdus pilaris were observed in two study areas in southern Poland. Of these, 22 were in gardens or orchards with apple trees. Only 0.5% of all fieldfares noted during field surveys were territorial, and only 1.7% of the checked gardens and orchards were inhabited by that species. Fieldfares defended fruit against several species, including conspecifics. The probability of the presence of territorial fieldfares within a habitat patch was higher in patches with a higher density of apples, but was not related to the size or degree of isolation of the patch. The duration of holding territory was positively correlated with apple density and negatively correlated with the presence of intruders (mainly flocks of non-territorial fieldfares). The results suggest that food density and the presence of intruders are key factors affecting the presence of territorial thrushes during winter.