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Tracking fungal community responses to maize plants by DNA- and RNA-based pyrosequencing
No full textWe assessed soil fungal diversity and community structure at two sampling times (t1 = 47 days and t2 = 104 days of plant age) in pots associated with four maize cultivars, including two genetically modified (GM) cultivars by high-throughput pyrosequencing of the 18S rRNA gene using DNA and RNA templates. We detected no significant differences in soil fungal diversity and community structure associated with different plant cultivars. However, DNA-based analyses yielded lower fungal OTU richness as compared to RNA-based analyses. Clear differences in fungal community structure were also observed in relation to sampling time and the nucleic acid pool targeted (DNA versus RNA). The most abundant soil fungi, as recovered by DNA-based methods, did not necessary represent the most “active” fungi (as recovered via RNA). Interestingly, RNA-derived community compositions at t1 were highly similar to DNA-derived communities at t2, based on presence/absence measures of OTUs. We recovered large proportions of fungal sequences belonging to arbuscular mycorrhizal fungi and Basidiomycota, especially at the RNA level, suggesting that these important and potentially beneficial fungi are not affected by the plant cultivars nor by GM traits (Bt toxin production). Our results suggest that even though DNA- and RNA-derived soil fungal communities can be very different at a given time, RNA composition may have a predictive power of fungal community development through time.
The predictive value of trill performance in a large repertoire songbird, the nightingale (Luscinia megarhynchos)
No full textIn animal communication, elaborate signals have been shown to be under sexual selection and often to reliably indicate a
signaler ’ s quality, condition, or motivation. For instance, the performance of physically challenging signals such as trills
– i.e. rapidly repeated elements of broad frequency bandwidth – is considered to refl ect signaler quality. Nightingales
Luscinia megarhynchos are renowned for their outstanding song repertoire sizes, and most songs include a variety of
complex trills. In the present study, we examined whether performance of trills can reliably refl ect male quality. We show
that vocal performance of trills predicts the age of a male. Older males sang trills that were closer to the performance
limit than did younger males. Moreover, males with narrower beaks sang more consistent trills than did males with
wider beaks. Vocal performance of trills, however, did not signifi cantly predict other measures of biometric quality such
as body size or body condition of the males. Th e fi ndings suggest that receivers could benefi t from the predictive value
of physically demanding song traits in assessing age as an important quality component of potential mates or rivals.
Particularly in species with high singing versatility, signaler assessment based on readily assessable structures may be
adaptive, as this will allow receivers to quickly gather relevant information about the singer without attending to the
full song repertoire.
An ecogenomic analysis of herbivore-induced plant volatiles in Brassica juncea
No full text[KEYWORDS: gene expression green leaf volatiles mustard parasitoids Spodoptera sulphides]
Upon herbivore feeding, plants emit complex bouquets of induced volatiles that may repel insect herbivores as well as attract parasitoids or predators. Due to differences in the temporal dynamics of individual components, the composition of the herbivore-induced plant volatile (HIPV) blend changes with time. Consequently, the response of insects associated with plants is not constant either. Using Brassica juncea as the model plant and generalist Spodoptera spp. larvae as the inducing herbivore, we investigated herbivore and parasitoid preference as well as the molecular mechanisms behind the temporal dynamics in HIPV emissions at 24, 48 and 72 h after damage. In choice tests, Spodoptera litura moth preferred undamaged plants, whereas its parasitoid Cotesia marginiventris favoured plants induced for 48 h. In contrast, the specialist Plutella xylostella and its parasitoid C. vestalis preferred plants induced for 72 h. These preferences matched the dynamic changes in HIPV blends over time. Gene expression analysis suggested that the induced response after Spodoptera feeding is mainly controlled by the jasmonic acid pathway in both damaged and systemic leaves. Several genes involved in sulphide and green leaf volatile synthesis were clearly up-regulated. This study thus shows that HIPV blends vary considerably over a short period of time, and these changes are actively regulated at the gene expression level. Moreover, temporal changes in HIPVs elicit differential preferences of herbivores and their natural enemies. We argue that the temporal dynamics of HIPVs may play a key role in shaping the response of insects associated with plants.