Diapause hormone in the Helicoverpa/Heliothis complex: A review of gene expression, peptide structure and activity, analog and antagonist development, and the receptor
This review summarizes recent studies focusing on diapause hormone (DH) in the Helicoverpa/Heliothis complex of agricultural pests. Moths in this complex overwinter in pupal diapause, a form of developmental arrest used to circumvent unfavorable seasons. DH was originally reported in the silkmoth Bombyx mori, a species that relies on DH to induce an embryonic diapause. But, in the case of Helicoverpa/Heliothis, levels of dh transcripts and DH peptides are more abundant in nondiapausing pupae than in diapausing individuals, and DH effectively terminates diapause within a specific temperature range. A structure activity relationship study indicated that the active core of DH is the C-terminal hepta-peptide, LWFGPRLa. We designed and synthesized a first generation of DH agonists and identified two agonists (PK-2Abf and PK-Etz) that were nearly 50- and 13-fold more potent than the native hormone. These studies revealed two structural characteristics of DH and its agonists that are essential for interaction with the receptor: a trans-Pro configuration to form a type I β-turn and a hydrophobic moiety involved in ligand binding. Modification of DH at the active core yielded a potent DH antagonist (DH-Jo, acetyl-GLWA[Jo]RLa) as well as an agonist (DH-2Abf-K). Three compounds (Decyl-1963, Dodecyl-1967, Heptyl-1965) were identified as agents capable of penetrating the cuticle of young pupae and thereby preventing the entry into diapause. DH receptor cDNA was cloned and an effective in vitro high throughput screen system was established for future use. This work sets the stage for further development of DH analogs and antagonists that have the potential to disrupt insect diapause as a tool for pest management.
Posterior predictive checks of coalescent models: P2C2M, an R package
Gruenstaeudl, M., Reid, N. M., Wheeler, G. L. and Carstens, B. C. 2015. Molecular Ecology Resources. doi: 10.1111/1755-0998.12435
Bayesian inference operates under the assumption that the empirical data are a good statistical fit to the analytical model, but this assumption can be challenging to evaluate. Here, we introduce a novel r package that utilizes posterior predictive simulation to evaluate the fit of the multispecies coalescent model used to estimate species trees. We conduct a simulation study to evaluate the consistency of different summary statistics in comparing posterior and posterior predictive distributions, the use of simulation replication in reducing error rates and the utility of parallel process invocation towards improving computation times. We also test P2C2M on two empirical data sets in which hybridization and gene flow are suspected of contributing to shared polymorphism, which is in violation with the coalescent model: Tamias chipmunks and Myotis bats. Our results indicate that (i) probability-based summary statistics display the lowest error rates, (ii) the implementation of simulation replication decreases the rate of type II errors, and (iii) our r package displays improved statistical power compared to previous implementations of this approach. When probabilistic summary statistics are used, P2C2M corroborates the assumption that genealogies collected from Tamias and Myotis are not a good fit to the multispecies coalescent model. Taken as a whole, our findings argue that an assessment of the fit of the multispecies coalescent model should accompany any phylogenetic analysis that estimates a species tree.
Inside or out? Possible genomic consequences of extracellular transmission of crypt-dwelling stinkbug mutualists
Alejandro Otero-Bravo and Zakee L. Sabree. 2015. Frontiers in Ecology and Evolution. doi: 10.3389/fevo.2015.00064
Genome reduction has been widely studied in obligate intracellular bacterial mutualists of insects because they have, in comparison to closely-related, nonhost-associated bacteria, extremely small genomes. Pentatomid stinkbugs also maintain bacterial symbionts, yet they are extracellular, residing within host-derived crypts, and are transmitted to offspring outside of the host’s tissues, which exposes them to the external environment. In this review, we explore how the multiphasic lifestyle of stinkbug symbionts (e.g., on the surfaces of eggs in various matrices during transmission and inside host-derived tissues during much of the host’s life), in contrast with the solely intracellular lifestyle of many insect endosymbionts, may impact their genome’s architecture, size and content. Furthermore, we demonstrate how additional stinkbug symbiont genomes are needed to more fully explore the sequestions and the potential value of the stinkbug-symbiont system in understanding genome evolution and reduction in the absence of intracellularity.
The role of social experience in eavesdropping by male wolf spiders (Lycosidae)
Animal Behaviour 106: 89–97. doi:10.1016/j.anbehav.2015.05.001, , , , , . 2015.
When reproductive success is limited by mate search costs, males can reduce costs by eavesdropping and initiating displays if conspecific courtship is detected. Here, we examine eavesdropping by male Schizocosa ocreata wolf spiders, with field studies, laboratory studies using video playback and live exposure studies. In field enclosure experiments, introduced males responded with increased courtship signalling behaviour in the presence of a courting male. In the laboratory, field-collected males spent more time engaged in interaction behaviours and performed more bouts of courtship activity in response to a courting video male stimulus than did laboratory-reared males, suggesting that eavesdropping might arise as a consequence of field experience. To explore this further, we conducted associative learning studies on naïve, laboratory-reared males, pairing video playback of male courtship with sensory cues indicating female presence. Results showed that males with no prior exposure learned to associate courtship of other males with cues indicating the presence of females. In subsequent video playback experiments, field-collected males recognized differences in male behaviour, responding with courtship more often and for longer periods to video stimuli of courting male spiders than to walking males or an empty leaf litter background (no spider). Additional studies showed that males spent significantly more time in courtship displays when presented with two to three live or video male stimuli simultaneously. Together, these findings confirm that male wolf spiders meet assumptions of eavesdropping behaviour, and suggest that social experience arising from exposure to courtship interactions of conspecifics may impact male eavesdropping and subsequent courtship behaviour.
Changes in Performance of Shared and Unshared Songs Within and Between Years in the White-crowned Sparrow
Angelika Poesel and Douglas A. Nelson. 2015. Ethology. DOI: 10.1111/eth.12399
Song of passerine birds is one of the few animal signals that is learned and that improves with practice. Vocal practice is crucial early in life to perfect a song imitation, but it also occurs throughout life and may continue to improve aspects of song performance. Differences in song performance among males that share song types, that is sing structurally similar songs may be particularly salient to receivers. We here test the hypothesis that aspects of song performance improve in a songbird species that deletes song types from its repertoire early in the first breeding season to share their final single song type with territorial neighbours. Over 3 yrs, we recorded songs in a population of Puget Sound white-crowned sparrows Zonotrichia leucophrys pugetensis and measured percentage peak performance and consistency thereof in all of the song types in each male's repertoire. We found that within the first year on territory, percentage peak performance was higher in shared than unshared songs but did not change from first to second recording. Contrary to the hypothesis that song performance improves with age, song performance declined from the first to the second year. Our results support the hypothesis that high-performance singers share songs. We did not find support for song performance improving within or between years, like it does in some other songbird species.