The Status Of Two New England “Endemic” Carices: Carex Elachycarpa And C. Josselynii (Cyperaceae)

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149729/1/tax00494.pd

The evolution of reproductive isolation in a simultaneous hermaphrodite, the freshwater snail Physa

<p>Abstract</p> <p>Background</p> <p>The cosmopolitan freshwater snail <it>Physa acuta </it>has recently found widespread use as a model organism for the study of mating systems and reproductive allocation. Mitochondrial DNA phylogenies suggest that <it>Physa carolinae</it>, recently described from the American southeast, is a sister species of <it>P. acuta</it>. The divergence of the <it>acuta/carolinae </it>ancestor from the more widespread <it>P. pomilia </it>appears to be somewhat older, and the split between a hypothetical <it>acuta/carolinae/pomilia </it>ancestor and <it>P. gyrina </it>appears older still.</p> <p>Results</p> <p>Here we report the results of no-choice mating experiments yielding no evidence of hybridization between <it>gyrina </it>and any of four other populations (<it>pomilia, carolinae</it>, Philadelphia <it>acuta</it>, or Charleston <it>acuta</it>), nor between <it>pomilia </it>and <it>carolinae</it>. Crosses between <it>pomilia </it>and both <it>acuta </it>populations yielded sterile F1 progeny with reduced viability, while crosses between <it>carolinae </it>and both <it>acuta </it>populations yielded sterile F1 hybrids of normal viability. A set of mate-choice tests also revealed significant sexual isolation between <it>gyrina </it>and all four of our other <it>Physa </it>populations, between <it>pomilia </it>and <it>carolinae</it>, and between <it>pomilia </it>and Charleston <it>acuta</it>, but not between <it>pomilia </it>and the <it>acuta </it>population from Philadelphia, nor between <it>carolinae </it>and either <it>acuta </it>population. These observations are consistent with the origin of hybrid sterility prior to hybrid inviability, and a hypothesis that speciation between <it>pomilia </it>and <it>acuta </it>may have been reinforced by selection for prezygotic reproductive isolation in sympatry.</p> <p>Conclusions</p> <p>We propose a two-factor model for the evolution of postzygotic reproductive incompatibility in this set of five <it>Physa </it>populations consistent with the Dobzhansky-Muller model of speciation, and a second two-factor model for the evolution of sexual incompatibility. Under these models, species trees may be said to correspond with gene trees in American populations of the freshwater snail, <it>Physa</it>.</p

Variations on a theme: diversification of cuticular hydrocarbons in a clade of cactophilic Drosophila

<p>Abstract</p> <p>Background</p> <p>We characterized variation and chemical composition of epicuticular hydrocarbons (CHCs) in the seven species of the <it>Drosophila buzzatii </it>cluster with gas chromatography/mass spectrometry. Despite the critical role of CHCs in providing resistance to desiccation and involvement in communication, such as courtship behavior, mating, and aggregation, few studies have investigated how CHC profiles evolve within and between species in a phylogenetic context. We analyzed quantitative differences in CHC profiles in populations of the <it>D. buzzatii </it>species cluster in order to assess the concordance of CHC differentiation with species divergence.</p> <p>Results</p> <p>Thirty-six CHC components were scored in single fly extracts with carbon chain lengths ranging from C₂₉to C₃₉, including methyl-branched alkanes, <it>n</it>-alkenes, and alkadienes. Multivariate analysis of variance revealed that CHC amounts were significantly different among all species and canonical discriminant function (CDF) analysis resolved all species into distinct, non-overlapping groups. Significant intraspecific variation was found in different populations of <it>D. serido </it>suggesting that this taxon is comprised of at least two species. We summarized CHC variation using CDF analysis and mapped the first five CHC canonical variates (CVs) onto an independently derived <it>period </it>(<it>per</it>) gene + chromosome inversion + mtDNA COI gene for each sex. We found that the COI sequences were not phylogenetically informative due to introgression between some species, so only <it>per </it>+ inversion data were used. Positive phylogenetic signal was observed mainly for CV1 when parsimony methods and the test for serial independence (TFSI) were used. These results changed when no outgroup species were included in the analysis and phylogenetic signal was then observed for female CV3 and/or CV4 and male CV4 and CV5. Finally, removal of divergent populations of <it>D. serido </it>significantly increased the amount of phylogenetic signal as up to four out of five CVs then displayed positive phylogenetic signal.</p> <p>Conclusions</p> <p>CHCs were conserved among species while quantitative differences in CHC profiles between populations and species were statistically significant. Most CHCs were species-, population-, and sex-specific. Mapping CHCs onto an independently derived phylogeny revealed that a significant portion of CHC variation was explained by species' systematic affinities indicating phylogenetic conservatism in the evolution of these hydrocarbon arrays, presumptive waterproofing compounds and courtship signals as in many other drosophilid species.</p

The present and future of QCD

This White Paper presents an overview of the current status and future perspective of QCD research, based on the community inputs and scientific conclusions from the 2022 Hot and Cold QCD Town Meeting. We present the progress made in the last decade toward a deep understanding of both the fundamental structure of the sub-atomic matter of nucleon and nucleus in cold QCD, and the hot QCD matter in heavy ion collisions. We identify key questions of QCD research and plausible paths to obtaining answers to those questions in the near future, hence defining priorities of our research over the coming decades

The present and future of QCD

This White Paper presents an overview of the current status and future perspective of QCD research, based on the community inputs and scientific conclusions from the 2022 Hot and Cold QCD Town Meeting. We present the progress made in the last decade toward a deep understanding of both the fundamental structure of the sub-atomic matter of nucleon and nucleus in cold QCD, and the hot QCD matter in heavy ion collisions. We identify key questions of QCD research and plausible paths to obtaining answers to those questions in the near future, hence defining priorities of our research over the coming decades

Rime length, stress, and association domains

Every regular Chinese syllable has a syllable tone (the tone we get when the syllable is read in isolation). In some Chinese languages, the tonal pattern of a multisyllabic expression is basically a concatenation of the syllable tones. In other Chinese languages, the tonal pattern of a multisyllabic expression is determined solely by the initial syllable. I call the former M -languages (represented by Mandarin) and the latter S -languages (represented by Shanghai). I argue that there is an additional difference in rime structures between the two language groups. In S-languages, all rimes are simple, i.e., there are no underlying diphthongs or codas. In M-languages, all regular rimes are heavy. I further argue that a syllable keeps its underlying tones only if it has stress. Independent metrical evidence tells us that heavy rimes may carry inherent stress. Thus, in M-languages, all regular syllables are stressed and retain their underlying tones (which may or may not undergo further changes). In contrast, in S-languages, regular rimes do not carry inherent stress; instead, only those syllables that are assigned stress by rule can keep their underlying tones and hence head a multisyllabic tonal domain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42998/1/10831_2005_Article_BF01440582.pd

The present and future of QCD

This White Paper presents an overview of the current status and future perspective of QCD research, based on the community inputs and scientific conclusions from the 2022 Hot and Cold QCD Town Meeting. We present the progress made in the last decade toward a deep understanding of both the fundamental structure of the sub-atomic matter of nucleon and nucleus in cold QCD, and the hot QCD matter in heavy ion collisions. We identify key questions of QCD research and plausible paths to obtaining answers to those questions in the near future, hence defining priorities of our research over the coming decades