BackgroundPlants have inducible defenses to combat attacking organisms. Hence, some herbivores have adapted to suppress these defenses. Suppression of plant defenses has been shown to benefit herbivores by boosting their growth and reproductive performance.ResultsWe observed in field-grown tomatoes that spider mites (Tetranychus urticae) establish larger colonies on plants already infested with the tomato russet mite (Aculops lycopersici). Using laboratory assays, we observed that spider mites have a much higher reproductive performance on russet mite-infested plants, similar to their performance on the jasmonic acid (JA)-biosynthesis mutant def-1. Hence, we tested if russet mites suppress JA-responses thereby facilitating spider mites. We found that russet mites manipulate defenses: they induce those mediated by salicylic acid (SA) but suppress those mediated by JA which would otherwise hinder growth. This suppression of JA-defenses occurs downstream of JA-accumulation and is independent from its natural antagonist SA. In contrast, spider mites induced both JA- and SA-responses while plants infested with the two mite species together display strongly reduced JA-responses, yet a doubled SA-response. The spider mite-induced JA-response in the presence of russet mites was restored on transgenic tomatoes unable to accumulate SA (nahG), but russet mites alone still did not induce JA-responses on nahG plants. Thus, indirect facilitation of spider mites by russet mites depends on the antagonistic action of SA on JA while suppression of JA-defenses by russet mites does not. Furthermore, russet mite-induced SA-responses inhibited secondary infection by Pseudomonas syringae (Pst) while not affecting the mite itself. Finally, while facilitating spider mites, russet mites experience reduced population growth.ConclusionsOur results show that the benefits of suppressing plant defenses may diminish within communities with natural competitors. We show that suppression of defenses via the JA-SA antagonism can be a consequence, rather than the cause, of a primary suppression event and that its overall effect is determined by the presence of competing herbivores and the distinct palette of defenses these induce. Thus, whether or not host-defense manipulation improves an herbivore’s fitness depends on interactions with other herbivores via induced-host defenses, implicating bidirectional causation of community structure of herbivores sharing a plant.Electronic supplementary materialThe online version of this article (doi:10.1186/s12915-014-0098-9) contains supplementary material, which is available to authorized users.

ABSTRACT. Vertebrate remains are reported from the Emsian±Eifelian Floresta Formation and the Late Devonian (?Frasnian) Cuche Formation of north-eastern Colombia. The material from the Floresta Formation is associated with a marine invertebrate fauna and includes an arthrodire and probably a rhenanid. Several vertebrate-bearing localities are recorded from the Cuche Formation; vertebrates occur with plant remains and lingulid fragments. They include an acanthodian (Cheiracanthoides? sp.), a chondrichthyan (Antarctilamna? sp.), placoderms (Bothriolepis sp., Asterolepis? sp. and an undetermined groenlandaspidid or primitive brachythoracid arthrodire), a stegotrachelid actinopterygian, and three sarcopterygians (a cosmine-covered form tentatively referred to an osteolepidid, the porolepiform Holoptychius sp., and the rhizodontid Strepsodus? sp.). This assemblage suggests a Late Frasnian age and is surprisingly similar to Late Devonian vertebrate assemblages found in similar facies of Europe and North America, notwithstanding the presence of the Gondwanan chondrichthyan Antarctilamna?.

-Plant fossils are described from the Cuche Formation, Eastern Cordillera, Colombia in the area of Floresta. Those identified as Colpodexylon cf. deatsii Banks and cf. Archaeopteris sp. suggest an earliest Late Devonian (Frasnian) age for the formation. These or similar taxa are also found in

International audienceThe study of Devonian Colombian trilobites and inarticulate brachiopods allows to recognize two biostratigraphic levelswithin the Floresta Formation. The first level, in the lower part of the formation, is late Emsian in age, and yields 14 distincttrilobite taxa, including Colombianaspis carvalhoae gen. et sp. nov. The second one, in the upper part of the formation,is assigned to the Givetian based on the co-occurrence of the genera Dipleura and Greenops; this is the first recordof a Givetian age for the upper part of the Floresta Formation. The inarticulate brachiopods collected from the uppermostpart of the formation suggest a Givetian age. Inarticulate brachiopods as well as the trilobites show close affinities withthe North Eastern Americas Realm, but they also suggest European affinities. The late Emsian occurrence of calmoniidsfrom Colombia is indicative of restricted faunal exchanges with the Malvinokaffric Realm