Phylogeny and oscillating expression of period and cryptochrome in short and long photoperiods suggest a conserved function in Nasonia vitripennis.

Photoperiodism, the ability to respond to seasonal varying day length with suitable life history changes, is a common trait in organisms that live in temperate regions. In most studied organisms, the circadian system appears to be the basis for photoperiodic time measurement. In insects this is still controversial: while some data indicate that the circadian system is causally involved in photoperiodism, others suggest that it may have a marginal or indirect role. Resonance experiments in the parasitic wasp Nasonia vitripennis have revealed a circadian component in photoperiodic time measurement compatible with a mechanism of internal coincidence where a two components oscillator system obtains information from dawn and dusk, respectively. The identity of this oscillator (or oscillators) is still unclear but possible candidates are the oscillating molecules of the auto-regulatory feedback loops in the heart of the circadian system. Here, we show for the first time the circadian oscillation of period and cryptochrome mRNAs in the heads of Nasonia females kept under short and long photoperiods. Period and cryptochrome mRNA levels display a synchronous oscillation in all conditions tested and persist, albeit with reduced amplitude, during the first day in constant light as well as constant darkness. More importantly, the signal for the period and cryptochrome oscillations is set by the light-on signal. These results, together with phylogenetic analyses, indicate that Nasonia's period and cryptochrome display characteristics of homologous genes in other hymenopteran species.

Circadian rhythms differ between sexes and closely related species of Nasonia wasps.

Activity rhythms in 24 h light-dark cycles, constant darkness, and constant light conditions were analyzed in four different Nasonia species for each sex separately. Besides similarities, clear differences are evident among and within Nasonia species as well as between sexes. In all species, activity in a light-dark cycle is concentrated in the photophase, typical for diurnal organisms. Contrary to most diurnal insect species so far studied, Nasonia follows Aschoff's rule by displaying long (>24 h) internal rhythms in constant darkness but short (<24 h) in constant light. In constant light, N. vitripennis males display robust circadian activity rhythms, whereas females are usually arrhythmic. In contrast to other Nasonia species, N. longicornis males display anticipatory activity, i.e. activity shortly before light-on in a light-dark cycle. As expected, N. oneida shows activity patterns similar to those of N. giraulti but with important differences in key circadian parameters. Differences in circadian activity patterns and parameters between species may reflect synchronization of specific life-history traits to environmental conditions. Scheduling mating or dispersion to a specific time of the day could be a strategy to avoid interspecific hybridization in Nasonia species that live in sympatry.

Morphology and behaviour: functional links in development and evolution.

Development and evolution of animal behaviour and morphology are frequently addressed independently, as reflected in the dichotomy of disciplines dedicated to their study distinguishing object of study (morphology versus behaviour) and perspective (ultimate versus proximate). Although traits are known to develop and evolve semi-independently, they are matched together in development and evolution to produce a unique functional phenotype. Here I highlight similarities shared by both traits, such as the decisive role played by the environment for their ontogeny. Considering the widespread developmental and functional entanglement between both traits, many cases of adaptive evolution are better understood when proximate and ultimate explanations are integrated. A field integrating these perspectives is evolutionary developmental biology (evo-devo), which studies the developmental basis of phenotypic diversity. Ultimate aspects in evo-devo studies--which have mostly focused on morphological traits--could become more apparent when behaviour, 'the integrator of form and function', is integrated into the same framework of analysis. Integrating a trait such as behaviour at a different level in the biological hierarchy will help to better understand not only how behavioural diversity is produced, but also how levels are connected to produce functional phenotypes and how these evolve. A possible framework to accommodate and compare form and function at different levels of the biological hierarchy is outlined. At the end, some methodological issues are discussed.

Circadian rhythms of adult emergence and activity but not eclosion in males of the parasitic wasp Nasonia vitripennis.

An endogenous circadian system is responsible for the rhythms observed in many physiological and behavioural traits in most organisms. In insects, the circadian system controls the periodicity of eclosion, egg-laying, locomotor and mating activity. The parasitoid wasp Nasonia vitripennis has been extensively used to study the role of the circadian system in photoperiodism. In this study, behavioural activities expected to be under the control of the endogenous circadian system were characterized in Nasonia. Male emergence from the host puparium is rhythmic under light-darkness conditions while eclosion from the own pupal integument is not rhythmic but continuous. Following entrainment in light-dark conditions, males show robust free-running circadian activity rhythms with a period (tau, tau) of approximately 25.6h in constant darkness. While the endogenous circadian system is enough to trigger male emergence in Nasonia, light seems to have a modulatory effect: when present it induces more males to emerge. Our results add to the understanding of chronobiological phenotypes in insects and provide a basis towards the molecular characterization of the endogenous circadian system in Nasonia.

Functional and evolutionary insights from the genomes of three parasitoid Nasonia species.

We report here genome sequences and comparative analyses of three closely related parasitoid wasps: Nasonia vitripennis, N. giraulti, and N. longicornis. Parasitoids are important regulators of arthropod populations, including major agricultural pests and disease vectors, and Nasonia is an emerging genetic model, particularly for evolutionary and developmental genetics. Key findings include the identification of a functional DNA methylation tool kit; hymenopteran-specific genes including diverse venoms; lateral gene transfers among Pox viruses, Wolbachia, and Nasonia; and the rapid evolution of genes involved in nuclear-mitochondrial interactions that are implicated in speciation. Newly developed genome resources advance Nasonia for genetic research, accelerate mapping and cloning of quantitative trait loci, and will ultimately provide tools and knowledge for further increasing the utility of parasitoids as pest insect-control agents.

The Fruitless gene in Nasonia displays complex sex-specific splicing and contains new zinc finger domains.

The transcription factor Fruitless exerts a broad range of functions during Drosophila development, the most apparent of which is the determination of sexual behavior in males. Although fruitless sequences are found in other insect orders, little is known about fruitless structure and function outside Diptera. We have performed a thorough analysis of fruitless transcripts in the haplo-diploid wasp Nasonia vitripennis and found both sex-specific and non-sex-specific transcripts similar to those found in Drosophila. In Nasonia, however, a novel, large fruitless transcript is present in females only. Putative binding sites for sex-specific splicing factors found in Nasonia fruitless and doublesex as well as Apis mellifera doublesex transcripts were sufficient to identify a corresponding female-specific fruitless exon in A. mellifera, suggesting that similar factors in both hymenopteran species could be responsible for sex-specific splicing of both genes. Furthermore, new C(2)H(2) zinc finger domains found in Nasonia fruitless transcripts were also identified in the fruitless locus of major holometabolous insect species but not in drosophilids. Conservation of important domains and sex-specific splicing in Diptera and Hymenoptera support the hypothesis that fruitless is an ancient gene and has conserved functions in insects. Considerable divergences in other parts of the gene are expected to underlie species-specific differences and may help to explain diversity observed in insect sexual behaviors.

Promoter analysis of cgl2, a galectin encoding gene transcribed during fruiting body formation in Coprinopsis cinerea (Coprinus cinereus).

In the homobasidiomycete Coprinopsis cinerea, expression of the two fruiting body-specific galectins, CGL1 and CGL2, is controlled by nutrients, light and darkness and the A mating type genes. In this study, we analyzed the promoter of the cgl2 gene by measuring transcript levels by quantitative real-time PCR and show that regulation of CGL2 expression occurs at the transcriptional level. A minimal promoter sufficient to confer regulated expression of a heterologous reporter gene and comprising 627 base pairs from the start codon was defined. On the minimal promoter we identified a 120 bp sequence mediating induction of the cgl2 gene in constant darkness. Along with direct repeats (TGGAAG/TGGAAG/GGAA), the sequence contains a CRE consensus site (cAMP-responsive element, TGCGTCA) suggesting the involvement of cAMP signaling in cgl2 activation. No specific elements responsible for light repression and mating type regulation were found in the promoter.