Half a million species of herbivorous insects have been described. Most of them are diet specialists, using only a few plant species as hosts. Biologists suspect that their specificity is key to ...their diversity. But why do herbivorous insects tend to be diet specialists? In this review, we catalog a broad range of explanations. We review the evidence for each and suggest lines of research to obtain the evidence we lack. We then draw attention to a second major question, namely how changes in diet breadth affect the rest of a species' biology. In particular, we know little about how changes in diet breadth feed back on genetic architecture, the population genetic environment, and other aspects of a species' ecology. Knowing more about how generalists and specialists differ should go a long way toward sorting out potential explanations of specificity, and yield a deeper understanding of herbivorous insect diversity.
How can we best vary the application of pesticides and antibiotics to delay resistance evolution? Previous theoretical comparisons of deployment strategies have focused on qualitative resistance ...traits and have mostly assumed that resistance alleles are already present in a population. But many real resistance traits are quantitative, and the evolution of resistant genotypes in the field may depend on de novo mutation and recombination. Here, I use an individual‐based, forward‐time, quantitative‐genetic simulation model to investigate the evolution of quantitative resistance. I evaluate the performance of four application strategies for delaying resistance evolution, to wit, the (1) sequential, (2) mosaic, (3) periodic, and (4) combined strategies. I find that which strategy is best depends on initial efficacy. When at the onset, xenobiotics completely prevent reproduction in treated demes, a combined strategy is best. On the other hand, when populations are partially resistant, the combined strategy is inferior to mosaic and periodic strategies, especially when resistance alleles are antagonistically pleiotropic. Thus, the optimal application strategy for managing against the rise of quantitative resistance depends on pleiotropy and whether or not partial resistance is already present in a population. This result appears robust to variation in pest reproductive mode and migration rate, direct fitness costs for resistant phenotypes, and the extent of refugial habitats.
The Oscillation Hypothesis posits that plant-eating insect diversity is generated by cycles of diet breadth expansion and contraction. Although at any given time most plant-eating insect species are ...host specialists, host-use evolution and speciation tend to entail a phase of generalism. The main evidence for this comes from comparative phylogenetic studies, but with mixed support. Here, I review and add to this evidence. I show that some of the original work that inspired the Oscillation Hypothesis is flawed in a way that leads to spurious inferences about trends in the evolution of diet diversity. And I present a new analysis which fails to support its predictions about patterns of species diversity. On the other hand, some of the published work that claims to reject the Oscillation Hypothesis may actually provide some of the strongest support for it, and I present new analyses which support its prediction that host-use generalism facilitates host-use evolution. In summary, the Oscillation Hypothesis successfully predicts some phylogenetic patterns but not others. Generalism appears to facilitate host-use evolution, but it does not appear to be inevitably chased by host-use specialization and speciation.
The nearby extrasolar planet GJ 436b-which has been labelled as a 'hot Neptune'-reveals itself by the dimming of light as it crosses in front of and behind its parent star as seen from Earth. ...Respectively known as the primary transit and secondary eclipse, the former constrains the planet's radius and mass, and the latter constrains the planet's temperature and, with measurements at multiple wavelengths, its atmospheric composition. Previous work using transmission spectroscopy failed to detect the 1.4- m water vapour band, leaving the planet's atmospheric composition poorly constrained. Here we report the detection of planetary thermal emission from the dayside of GJ 436b at multiple infrared wavelengths during the secondary eclipse. The best-fit compositional models contain a high CO abundance and a substantial methane (CH4) deficiency relative to thermochemical equilibrium models for the predicted hydrogen-dominated atmosphere. Moreover, we report the presence of some H2O and traces of CO2. Because CH4 is expected to be the dominant carbon-bearing species, disequilibrium processes such as vertical mixing and polymerization of methane into substances such as ethylene may be required to explain the hot Neptune's small CH4-to-CO ratio, which is at least 105 times smaller than predicted.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
What causes host use specificity in herbivorous insects? Population genetic models predict specialization when habitat preference can evolve and there is antagonistic pleiotropy at a ...performance-affecting locus. But empirically for herbivorous insects, host use performance is governed by many genetic loci, and antagonistic pleiotropy seems to be rare. Here, we use individual-based quantitative genetic simulation models to investigate the role of pleiotropy in the evolution of sympatric host use specialization when performance and preference are quantitative traits. We look first at pleiotropies affecting only host use performance. We find that when the host environment changes slowly, the evolution of host use specialization requires levels of antagonistic pleiotropy much higher than what has been observed in nature. On the other hand, with rapid environmental change or pronounced asymmetries in productivity across host species, the evolution of host use specialization readily occurs without pleiotropy. When pleiotropies affect preference as well as performance, even with slow environmental change and host species of equal productivity, we observe fluctuations in host use breadth, with mean specificity increasing with the pervasiveness of antagonistic pleiotropy. Thus, our simulations show that pleiotropy is not necessary for specialization, although it can be sufficient, provided it is extensive or multifarious.
The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated ...interior, as opposed to the silicate-dominated composition found on Earth; the atmosphere can also differ from those in the Solar System. The solar C/O is 0.54 (ref. 3). Here we report an analysis of dayside multi-wavelength photometry of the transiting hot-Jupiter WASP-12b (ref. 6) that reveals C/O ≥ 1 in its atmosphere. The atmosphere is abundant in CO. It is depleted in water vapour and enhanced in methane, each by more than two orders of magnitude compared to a solar-abundance chemical-equilibrium model at the expected temperatures. We also find that the extremely irradiated atmosphere (T > 2,500 K) of WASP-12b lacks a prominent thermal inversion (or stratosphere) and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Phylogenomics and the evolution of hemipteroid insects Johnson, Kevin P.; Dietrich, Christopher H.; Friedrich, Frank ...
Proceedings of the National Academy of Sciences,
12/2018, Letnik:
115, Številka:
50
Journal Article
Recenzirano
Odprti dostop
Hemipteroid insects (Paraneoptera), with over 10% of all known insect diversity, are a major component of terrestrial and aquatic ecosystems. Previous phylogenetic analyses have not consistently ...resolved the relationships among major hemipteroid lineages. We provide maximum likelihood-based phylogenomic analyses of a taxonomically comprehensive dataset comprising sequences of 2,395 single-copy, protein-coding genes for 193 samples of hemipteroid insects and outgroups. These analyses yield a well-supported phylogeny for hemipteroid insects. Monophyly of each of the three hemipteroid orders (Psocodea, Thysanoptera, and Hemiptera) is strongly supported, as are most relationships among suborders and families. Thysanoptera (thrips) is strongly supported as sister to Hemiptera. However, as in a recent large-scale analysis sampling all insect orders, trees from our data matrices support Psocodea (bark lice and parasitic lice) as the sister group to the holometabolous insects (those with complete metamorphosis). In contrast, four-cluster likelihood mapping of these data does not support this result. A molecular dating analysis using 23 fossil calibration points suggests hemipteroid insects began diversifying before the Carboniferous, over 365 million years ago. We also explore implications for understanding the timing of diversification, the evolution of morphological traits, and the evolution of mitochondrial genome organization. These results provide a phylogenetic framework for future studies of the group.
Scale insects (Hemiptera: Coccoidea) are small herbivorous insects found on all continents except Antarctica. They are extremely invasive, and many species are serious agricultural pests. They are ...also emerging models for studies of the evolution of genetic systems, endosymbiosis and plant-insect interactions. ScaleNet was launched in 1995 to provide insect identifiers, pest managers, insect systematists, evolutionary biologists and ecologists efficient access to information about scale insect biological diversity. It provides comprehensive information on scale insects taken directly from the primary literature. Currently, it draws from 23,477 articles and describes the systematics and biology of 8194 valid species. For 20 years, ScaleNet ran on the same software platform. That platform is no longer viable. Here, we present a new, open-source implementation of ScaleNet. We have normalized the data model, begun the process of correcting invalid data, upgraded the user interface, and added online administrative tools. These improvements make ScaleNet easier to use and maintain and make the ScaleNet data more accurate and extendable. Database URL: http://scalenet.info.
To understand the generation and maintenance of biodiversity hotspots, we tested three major hypotheses: rates of diversification, ecological limits to diversity, and time for species accumulation.
...Using dated molecular phylogenies, measures of species' range size and geographical clade overlap, niche modelling, and lineages-through-time plots of Australian Fabaceae, we compared the southwest Australia Floristic Region (SWAFR; a global biodiversity hotspot) with a latitudinally equivalent non-hotspot, southeast Australia (SEA).
Ranges of species (real and simulated) were smaller in the SWAFR than in SEA. Geographical overlap of clades was significantly greater for Daviesia in the SWAFR than in SEA, but the inverse for Bossiaea. Lineage diversification rates over the past 10 Myr did not differ between the SWAFR and SEA in either genus.
Interaction of multiple factors probably explains the differences in measured diversity between the two regions. Steeper climatic gradients in the SWAFR probably explain the smaller geographical ranges of both genera there. Greater geographical overlap of clades in the SWAFR, combined with a longer time in the region, can explain why Daviesia is far more species-rich there than in SEA. Our results indicate that the time for speciation and ecological limits hypotheses, in concert, can explain the differences in biodiversity.
Polymorphic phenotypes have long been used to examine the maintenance of genetic variation within and between species. Most studies have focused on persistent polymorphisms, which are retained across ...species boundaries, and their positive effects on speciation rates. Far less is known about the macroevolutionary impacts of more transient polymorphisms, which are also common. Here we investigated male wing polymorphisms in aphids. We estimated the phylogenetic history of wing states across species, along with several other traits that could affect wing evolution. We found that male wing polymorphisms are transient: they are found in only ~4% of extant species, but have likely evolved repeatedly across the phylogeny. We reason that the repeated evolution of transient polymorphisms might be facilitated by the existence of the asexual female wing plasticity, which is common across aphids, and would maintain the wing development program even in species with wingless males. We also discovered that male wingedness correlates positively with host plant alternation and host plant breadth, and that winged morphs and wing polymorphisms may be associated with higher speciation rates. Our results provide new evolutionary insights into this well-studied group and suggest that even transient polymorphisms may impact species diversification rates.
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