Riverside wren pairs jointly defend their territories against simulated intruders

Duets are a jointly produced signal where two or more individuals coordinate their vocalizations by overlapping or alternating their songs. Duets are used in a wide array of contexts within partnerships, ranging from territory defence to pair bond maintenance. It has been proposed that pairs that coordinate their songs might also better coordinate other activities, including nest building, parental care and defending shared resources. Here, we tested in the riverside wren (Cantorchilus semibadius), a neotropical duetting species that produces highly coordinated duet songs, whether males and females show similar responses to playback. During territorial disputes in songbird species, individuals tend to direct their attention towards same‐sex territorial intruders, but this bias might be less pronounced in duetting species. We performed a dual‐speaker playback experiment to examine how mated individuals respond to speakers broadcasting female‐versus‐male duet contributions. We found that riverside wrens have high levels of converging behaviour by duetting and remaining in close proximity to one another when responding to simulated paired intruders. Males and females spent more than 80% of their time less than 1 m apart while defending their territory. Both individuals in a pair aggressively engaged with both male and female simulated trespassers by approaching equally close and spending equal time near the two speakers. These results suggest that both sexes perceive a paired territorial intrusion as a similar threat and that both partners are highly invested in defending the shared resources. This study is one of the few to demonstrate equal attention and aggression from mated pairs towards simulated same‐sex and opposite‐sex intruders. We suggest that pairs responding together, in close proximity to one another, might be favourable in duetting species when defending the territory because maintaining a close distance between partners facilitates the extreme coordination of their joint territorial signals.     

Rival imprinting: interspecifically cross-fostered tits defend their territories against heterospecific intruders

Failure to recognize conspecifics in social interactions such as mate choice and aggressive encounters will often result in reduced fitness. Studies on mate choice show that the ability to recognize conspecifics as mates is not universally present at birth, but often needs to be learned. In contrast, little is known about the ontogeny of intrasexual species recognition. To test whether learning influences the recognition of sexual rivals, we compared the aggressive response towards intruders of interspecifically cross-fostered individuals and controls reared by conspecific parents. We simulated territorial intrusion by presenting either a caged individual or playback song near the nest of breeding pairs of great tits, Parus major, and blue tits, P. caeruleus. Great tits reared by blue tit parents responded much more to blue tit stimuli than did great tit controls, and furthermore showed stronger responses to blue tit stimuli than to those of their own species. Blue tits reared by great tits responded much more to great tit stimuli than did blue tit controls. In contrast, blue tits cross-fostered to coal tits, P. ater, did not respond more to coal tits than did blue tit controls. There was a species difference in the response to conspecifics: blue tits cross-fostered to great tits responded more to conspecifics than did cross-fostered great tits. The results were similar for males and females. We conclude that learning influences intrasexual species recognition in these tits. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Plasmodesmata: the battleground against intruders

Plasmodesmata are intercellular channels that establish a symplastic communication pathway between neighboring cells in plants. Owing to this role, opportunistic microbial pathogens have evolved to exploit plasmodesmata as gateways to spread infection from cell to cell within the plant. However, although these pathogens have acquired the capacity to breach the plasmodesmal trafficking pathway, plants are unlikely to relinquish control over a structure essential for their survival so easily. In this review, we examine evidence that suggests plasmodesmata play an active role in plant immunity against viral, fungal and bacterial pathogens. We discuss how these pathogens differ in their lifestyles and infection modes, and present the defense strategies that plants have adopted to prevent the intercellular spread of an infection.     

Caretaker tumour suppressor genes that defend genome integrity

Cancers arise as a result of genetic changes that impact upon cell proliferation through promoting cell division and/or inhibiting cell death. Tumour suppressor (TS) genes are the targets for many of these genetic changes. In general, both alleles of TS genes must be disrupted to observe a phenotypic effect. Broadly speaking, there are two types of TS gene: 'gatekeepers' and 'caretakers'. In contrast to gatekeepers, caretaker genes do not directly regulate proliferation, but act to prevent genomic instability. Thus, mutation of caretaker genes leads to accelerated conversion of a normal cell to a neoplastic cell. Many caretaker genes are required for the maintenance of genome integrity. This review focuses on those caretaker genes that play a role, directly or indirectly, in the repair of DNA strand breaks by the homologous recombination pathway, and that are associated with cancer-prone clinical syndromes, in particular ataxia telangiectasia, hereditary breast cancer, Bloom's syndrome and Werner's syndrome.     

Piwis and piwi-interacting RNAs in the epigenetics of cancer

An increasing body of evidence suggests that cancer cells acquire "stem-like" epigenetic and signaling characteristics during the tumorigenic process, including global DNA hypo-methylation, gene-specific DNA hyper-methylation, and small RNA deregulation. RNAs have been known to be epigenetic regulators, both in stem cells and in differentiated cells. A novel class of small RNAs, called piwi-interacting RNAs (piRNAs), maintains genome integrity by epigenetically silencing transposons via DNA methylation, especially in germline stem cells. piRNAs interact exclusively with the Piwi family of proteins. The human Piwi ortholog, Hiwi, has been found to be aberrantly expressed in a variety of human cancers and in some, its expression correlates with poor clinical prognosis. However, there has been little investigation into the potential role that Piwi and piRNAs might play in contributing to the "stem-like" epigenetic state of a cancer. This review will highlight the current evidence supporting the importance of Piwi and piRNAs in the epigenetics of cancer and provide a potential model for the role of Piwi and piRNAs in tumorigenesis.     

piRNAs, transposon silencing, and germline genome integrity

Integrity of the germline genome is essential for the production of viable gametes and successful reproduction. In mammals, the generation of gametes involves extensive epigenetic changes (DNA methylation and histone modification) in conjunction with changes in chromosome structure to ensure flawless progression through meiotic recombination and packaging of the genome into mature gametes. Although epigenetic reprogramming is essential for mammalian reproduction, reprogramming also provides a permissive window for exploitation by transposable elements (TEs), autonomously replicating endogenous elements. Expression and propagation of TEs during the reprogramming period can result in insertional mutagenesis that compromises genome integrity leading to reproductive problems and sporadic inherited diseases in offspring. Recent work has identified the germ cell associated PIWI Interacting RNA (piRNA) pathway in conjunction with the DNA methylation and histone modification machinery in silencing TEs. In this review we will highlight these recent advances in piRNA mediated regulation of TEs in the mouse germline, as well as mention the repercussions of failure to properly regulate TEs.     

Partners coordinate territorial defense against simulated intruders in a duetting ovenbird

Duets in breeding pairs may reflect a situation of conflict, whereby an individual answers its partner's song as a form of unilateral acoustic mate guarding or, alternatively, it may reflect cooperation, when individuals share in territory defense or safeguard the partnership. The degree of coordination between the sexes when responding to solo versus paired intruders may elucidate the function of songs in duets. We examined this issue in a study with rufous horneros (Furnarius rufus), a duetting, socially monogamous Neotropical species with low levels of extrapair paternity. We exposed social pairs during the nonbreeding season to playbacks of duets, male solos, female solos, and control heterospecific songs. Partners approached all conspecific stimuli together and responded by singing quickly, at higher rates and by coordinating ~80% of their songs into duets. For both sexes, most response variables (seven of nine) did not vary across conspecific treatments. These results suggest that partners duet and coordinate behaviors to cooperatively defend common territories. However, females spent more time in territorial vigilance, and partners were highly coordinated (correlated responses) in response to duets and female solos in comparison with male solos. This indicates that female intrusions (paired or solo) might be more threatening than male intrusions in the nonbreeding season, especially for territorial females, and that females are less cooperative with their partners in territory defense against male intruders.     

Sword in the woods: How plant hosts defend against vascular pathogens

This Commentary discusses two recent papers exploring how plants combat infection by vascular pathogens via modulating lignin production and via MAP kinase signaling cascades.     

DNA double-strand break repair functions defend against parvovirus infection.

We measured parvovirus replication and sensitivity to X-ray damage in nine CHO cell lines representing a variety of DNA repair deficiencies. We found that parvovirus replication efficiency increases with radiosensitivity. Parvovirus replication is disrupted at an early stage of infection in DNA repair-proficient cells, before conversion of the single-stranded viral DNA genome into the double-stranded replicative form. Thus, status of the DNA repair machinery inversely correlates with parvovirus replication and is proportional to the host's ability to repair X-ray-induced damage.     

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of “pathogen-proof” plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.     

A graph-based approach to defend agro-ecological systems against water vole outbreaks

The cyclic spread of montane water vole populations in the grasslands of the Jura plateaus causes severe economic, ecological, and public-health problems. Since this phenomenon cannot be managed by massive use of the anticoagulant rodenticide bromadiolone, the challenge is to limit it by reducing regional-level connectivity through landscaping and agro-environmental interventions such as planting hedgerows, ploughing, and cultivating cereals. We used landscape graphs – a spatial modelling approach based on graph theory – to represent the grassland network and identify key areas for intervention. Several strategies were compared in terms of their capacity to fulfil operational requirements by interchanging patches and meta-patches as nodes of the graph, and least-cost distances and resistance distances to weight links. The combination of meta-patches and resistance distances provides a relevant basis on which to design concrete action to decrease regional-level connectivity of grasslands. The results also indicate that the usual removal method applied to the links of the graph would benefit from data on the statistical distribution of cost values along the shortest paths. More broadly, this suggests the modelling approach should be better matched the actual field interventions if the connectivity analysis is to be operational.     

Multiple indole glucosinolates and myrosinases defend Arabidopsis against Tetranychus urticae herbivory

Arabidopsis (Arabidopsis thaliana) defenses against herbivores are regulated by the jasmonate (JA) hormonal signaling pathway, which leads to the production of a plethora of defense compounds. Arabidopsis defense compounds include tryptophan-derived metabolites, which limit Arabidopsis infestation by the generalist herbivore two-spotted spider mite, Tetranychus urticae. However, the phytochemicals responsible for Arabidopsis protection against T. urticae are unknown. Here, we used Arabidopsis mutants disrupted in the synthesis of tryptophan-derived secondary metabolites to identify phytochemicals involved in the defense against T. urticae. We show that of the three tryptophan-dependent pathways found in Arabidopsis, the indole glucosinolate (IG) pathway is necessary and sufficient to assure tryptophan-mediated defense against T. urticae. We demonstrate that all three IGs can limit T. urticae herbivory, but that they must be processed by myrosinases to hinder T. urticae oviposition. Putative IG breakdown products were detected in mite-infested leaves, suggesting in planta processing by myrosinases. Finally, we demonstrate that besides IGs, there are additional JA-regulated defenses that control T. urticae herbivory. Together, our results reveal the complexity of Arabidopsis defenses against T. urticae that rely on multiple IGs, specific myrosinases, and additional JA-dependent defenses.

Three IGs and specific myrosinases help protect Arabidopsis thaliana against herbivory by the two-spotted spider mite T. urticae.     

The rules of engagement: how to defend against combinations of predators

Studies of inducible defenses have traditionally examined prey responses to one predator at a time. However, prey in nature encounter combinations of predators that should force them to produce phenotypic compromises. We examined how snails (Helisoma trivolvis) alter their phenotype in the presence of three different predator species that were presented alone and in pairwise combinations. When snails were exposed to each predator alone, they formed predator-specific defenses that reflected the differences in each predator’s foraging mode. When snails were exposed to pairwise combinations of predators, their phenotype was dependent on their ability to detect each predator, the risk posed by each predator, and the effectiveness of a given defense against each predator. Consequently, responses to combined predators were typically biased towards one of the predators in the pair. This suggests that prey facing combined predators do not form simple intermediate defenses and, as a result, may experience enhanced mortality risk when they encounter natural predator regimes.