8. Eichorn, C; Hrabar, M; Van Ryn, EC; Brodie, BS; Blake, AJ; Gries, G. (2017) How flies are flirting on the fly.BMC Biology 15 How flies are flirting on the fly
Lucilia sericata; Mate location; Visual mate signals; Wing flashes; Flicker fusion frequency
Background: Flies have some of the most elaborate visual systems in the Insecta, often featuring large, sexually dimorphic eyes with specialized "bright zones" that may have a functional role during mate-seeking behavior. The fast visual system of flies is considered to be an adaptation in support of their advanced flight abilities. Here, we show that the immense processing speed of the flies' photoreceptors plays a crucial role in mate recognition. Results: Video-recording wing movements of abdomen-mounted common green bottle flies, Lucilia sericata, under direct light at 15,000 frames per second revealed that wing movements produce a single, reflected light flash per wing beat. Such light flashes were not evident when we video-recorded wing movements under diffuse light. Males of L. sericata are strongly attracted to wing flash frequencies of 178 Hz, which are characteristic of free-flying young females (prospective mates), significantly more than to 212, 235, or 266 Hz, characteristic of young males, old females, and old males, respectively. In the absence of phenotypic traits of female flies, and when given a choice between light emitting diodes that emitted either constant light or light pulsed at a frequency of 110, 178, 250, or 290 Hz, males show a strong preference for the 178-Hz pulsed light, which most closely approximates the wing beat frequency of prospective mates. Conclusions: We describe a previously unrecognized visual mate recognition system in L. sericata. The system depends upon the sex- and age-specific frequencies of light flashes reflecting off moving wings, and the ability of male flies to distinguish between the frequency of light flashes produced by rival males and prospective mates. Our findings imply that insect photoreceptors with fast processing speed may not only support agile flight with advanced maneuverability but may also play a supreme role in mate recognition. The low mating propensity of L. sericata males on cloudy days, when light flashes from the wings of flying females are absent, seems to indicate that these flies synchronize sexual communication with environmental conditions that optimize the conspicuousness of their communication signals, as predicted by sensory drive theory. DOI
7. Lambinet, V; Hayden, ME; Reigl, K; Gomis, S; Gries, G. (2017) Linking magnetite in the abdomen of honey bees to a magnetoreceptive function.Proceedings of the Royal Society B-Biological Sciences 284 Linking magnetite in the abdomen of honey bees to a magnetoreceptive function
honey bees; magnetoreception; magnetic sense; magnetite; hysteresis loop; magnetic remanence
Previous studies of magnetoreception in honey bees, Apis mellifera, focused on the identification of magnetic material, its formation, the location of the receptor and potential underlying sensory mechanisms, but never directly linked magnetic material to a magnetoreceptive function. In our study, we demonstrate that ferromagnetic material consistent with magnetite plays an integral role in the bees' magnetoreceptor. Subjecting lyophilized and pelletized bee tagmata to analyses by a superconducting quantum interference device generated a distinct hysteresis loop for the abdomen but not for the thorax or the head of bees, indicating the presence of ferromagnetic material in the bee abdomen. Magnetic remanence of abdomen pellets produced from bees that were, or were not, exposed to the 2.2-kOe field of a magnet while alive differed, indicating that magnet exposure altered the magnetization of this magnetite in live bees. In behavioural two-choice field experiments, bees briefly exposed to the same magnet, but not sham-treated control bees, failed to sense a custom-generated magnetic anomaly, indicating that magnet exposure had rendered the bees' magnetoreceptor dysfunctional. Our data support the conclusion that honey bees possess a magnetite-based magnetoreceptor located in the abdomen. DOI
6. Riesch, R; Muschick, M; Lindtke, D; Villoutreix, R; Comeault, AA; Farkas, TE; Lucek, K; Hellen, E; Soria-Carrasco, V; Dennis, SR; de Carvalho, CF; Safran, RJ; Sandoval, CP; Feder, J; Gries, R; Crespi, BJ; Gries, G; Gompert, Z; Nosil, P. (2017) Transitions between phases of genomic differentiation during stick-insect speciation.Nature Ecology & Evolution 1 Transitions between phases of genomic differentiation during stick-insect speciation
Speciation can involve a transition from a few genetic loci that are resistant to gene flow to genome-wide differentiation. However, only limited data exist concerning this transition and the factors promoting it. Here, we study phases of speciation using data from >100 populations of 11 species of Timema stick insects. Consistent with early phases of genie speciation, adaptive colour-pattern loci reside in localized genetic regions of accentuated differentiation between populations experiencing gene flow. Transitions to genome-wide differentiation are also observed with gene flow, in association with differentiation in polygenic chemical traits affecting mate choice. Thus, intermediate phases of speciation are associated with genome-wide differentiation and mate choice, but not growth of a few genomic islands. We also find a gap in genomic differentiation between sympatric taxa that still exchange genes and those that do not, highlighting the association between differentiation and complete reproductive isolation. Our results suggest that substantial progress towards speciation may involve the alignment of multi-faceted aspects of differentiation. DOI
5. Brodie, BS; Smith, MA; Lawrence, J; Gries, G. (2015) Effects of Floral Scent, Color and Pollen on Foraging Decisions and Oocyte Development of Common Green Bottle Flies.PLoS One 10 Effects of Floral Scent, Color and Pollen on Foraging Decisions and Oocyte Development of Common Green Bottle Flies
The common green bottle fly Lucilia sericata (Meigen) and other filth flies frequently visit pollen-rich composite flowers such as the Oxeye daisy, Leucanthemum vulgare Lam. In laboratory experiments with L. sericata, we investigated the effect of generic floral scent and color cues, and of Oxeye daisy-specific cues, on foraging decisions by recently eclosed flies. We also tested the effect of a floral pollen diet with 0-35% moisture content on the ability of females to mature their oocytes. Our data indicate that (1) young flies in the presence of generic floral scent respond more strongly to a uniformly yellow cue than to any other uniform color cue (green, white, black, blue, red) except for ultraviolet (UV); (2) the floral scent of Oxeye daisies enhances the attractiveness of a yellow cue; and (3) moisture-rich pollen provides nutrients that facilitate ovary maturation of flies. With evidence that L. sericata exploits floral cues during foraging, and that pollen can be an alternate protein source to animal feces and carrion, Pollen apparently plays a major role in the foraging ecology of L. sericata and possibly other filth flies. These flies, in turn, may play a significant role as pollinators, as supported by a recently published study. DOI
4. Foster, AJ; Hall, DE; Mortimer, L; Abercromby, S; Gries, R; Gries, G; Bohlmann, J; Russell, J; Mattsson, J. (2013) Identification of Genes in Thuja plicata Foliar Terpenoid Defenses.Plant Physiology 161: 1993-2004 Identification of Genes in Thuja plicata Foliar Terpenoid Defenses
WHITE-PINE WEEVIL; HIGH-QUALITY RNA; CONIFER DEFENSE; SITKA SPRUCE; WESTERN REDCEDAR; FUNCTIONAL-CHARACTERIZATION; CHAMAECYPARIS-NOOTKATENSIS; BIOSYNTHESIS; METABOLISM; DEER cedar
Thuja plicata (western redcedar) is a long-lived conifer species whose foliage is rarely affected by disease or insect pests, but can be severely damaged by ungulate browsing. Deterrence to browsing correlates with high foliar levels of terpenoids, in particular the monoterpenoid a-thujone. Here, we set out to identify genes whose products may be involved in the production of a-thujone and other terpenoids in this species. First, we generated a foliar transcriptome database from which to draw candidate genes. Second, we mapped the storage of thujones and other terpenoids to foliar glands. Third, we used global expression profiling to identify more than 600 genes that are expressed at high levels in foliage with glands, but can either not be detected or are expressed at low levels in a natural variant lacking foliar glands. Fourth, we used in situ RNA hybridization to map the expression of a putative monoterpene synthase to the epithelium of glands and used enzyme assays with recombinant protein of the same gene to show that it produces sabinene, the monoterpene precursor of a-thujone. Finally, we identified candidate genes with predicted enzymatic functions for the conversion of sabinene to a-thujone. Taken together, this approach generated both general resources and detailed functional characterization in the identification of genes of foliar terpenoid biosynthesis in T. plicata.Website DOI
3. Schwander, T; Arbuthnott, D; Gries, R; Gries, G; Nosil, P; Crespi, BJ. (2013) Hydrocarbon divergence and reproductive isolation in Timema stick insects.BMC Evolutionary Biology 13 Hydrocarbon divergence and reproductive isolation in Timema stick insects
HOST-PLANT ADAPTATION; CRISTINAE WALKING-STICKS; MALE MATE CHOICE; CUTICULAR HYDROCARBONS; SEXUAL SELECTION; DROSOPHILA-MOJAVENSIS; MORPHOLOGICAL EVOLUTION; CACTOPHILIC DROSOPHILA; INCIPIENT SPECIATION; MATING PREFERENCES
Background: Individuals commonly prefer certain trait values over others when choosing their mates. If such preferences diverge between populations, they can generate behavioral reproductive isolation and thereby contribute to speciation. Reproductive isolation in insects often involves chemical communication, and cuticular hydrocarbons, in particular, serve as mate recognition signals in many species. We combined data on female cuticular hydrocarbons, interspecific mating propensity, and phylogenetics to evaluate the role of cuticular hydrocarbons in diversification of Timema walking-sticks. Results: Hydrocarbon profiles differed substantially among the nine analyzed species, as well as between partially reproductively-isolated T. cristinae populations adapted to different host plants. In no-choice trials, mating was more likely between species with similar than divergent hydrocarbon profiles, even after correcting for genetic divergences. The macroevolution of hydrocarbon profiles, along a Timema species phylogeny, fits best with a punctuated model of phenotypic change concentrated around speciation events, consistent with change driven by selection during the evolution of reproductive isolation. Conclusion: Altogether, our data indicate that cuticular hydrocarbon profiles vary among Timema species and populations, and that most evolutionary change in hydrocarbon profiles occurs in association with speciation events. Similarities in hydrocarbon profiles between species are correlated with interspecific mating propensities, suggesting a role for cuticular hydrocarbon profiles in mate choice and speciation in the genus Timema. DOI
2. Schwander, T; Crespi, BJ; Gries, R; Gries, G. (2013) Neutral and selection-driven decay of sexual traits in asexual stick insects.Proceedings of the Royal Society B-Biological Sciences 280 Neutral and selection-driven decay of sexual traits in asexual stick insects
TIMEMA WALKING-STICKS; WOLBACHIA-INDUCED PARTHENOGENESIS; LEPTOPILINA-CLAVIPES HYMENOPTERA; EVOLUTION; REPRODUCTION; ANCIENT; VESTIGIALIZATION; PHYLOGENETICS; PARASITOIDS; APHELINIDAE
Environmental shifts and lifestyle changes may result in formerly adaptive traits becoming non-functional or maladaptive. The subsequent decay of such traits highlights the importance of natural selection for adaptations, yet its causes have rarely been investigated. To study the fate of formerly adaptive traits after lifestyle changes, we evaluated sexual traits in five independently derived asexual lineages, including traits that are specific to males and therefore not exposed to selection. At least four of the asexual lineages retained the capacity to produce males that display normal courtship behaviours and are able to fertilize eggs of females from related sexual species. The maintenance of male traits may stem from pleiotropy, or from these traits only regressing via drift, which may require millions of years to generate phenotypic effects. By contrast, we found parallel decay of sexual traits in females. Asexual females produced altered airborne and contact signals, had modified sperm storage organs, and lost the ability to fertilize their eggs, impeding reversals to sexual reproduction. Female sexual traits were decayed even in recently derived asexuals, suggesting that trait changes following the evolution of asexuality, when they occur, proceed rapidly and are driven by selective processes rather than drift. DOI
