776,487 research outputs found
Measuring, comparing and interpreting phenotypic selection on floral scent
Natural selection on floral scent composition is a key element of the hypothesis that pollinators and other floral visitors drive scent evolution. The measure of such selection is complicated by the high-dimensional nature of floral scent data and uncertainty about the cognitive processes involved in scent-mediated communication. We use dimension reduction through reduced-rank regression to jointly estimate a scent composite trait under selection and the strength of selection acting on this trait. To assess and compare variation in selection on scent across species, time and space, we reanalyse 22 datasets on six species from four previous studies. The results agreed qualitatively with previous analyses in terms of identifying populations and scent compounds subject to stronger selection but also allowed us to evaluate and compare the strength of selection on scent across studies. Doing so revealed that selection on floral scent was highly variable, and overall about as common and as strong as selection on other phenotypic traits involved in pollinator attraction or pollen transfer. These results are consistent with an important role of floral scent in pollinator attraction. Our approach should be useful for further studies of plant-animal communication and for studies of selection on other high-dimensional phenotypes. In particular, our approach will be useful for studies of pollinator-mediated selection on complex scent blends comprising many volatiles, and when no prior information on the physiological responses of pollinators to scent compounds is available
Evolvability and trait function predict phenotypic divergence of plant populations
Understanding the causes and limits of population divergence in phenotypic traits is a fundamental aim of evolutionary biology, with the potential to yield predictions of adaptation to environmental change. Reciprocal transplant experiments and the evaluation of optimality models suggest that local adaptation is common but not universal, and some studies suggest that trait divergence is highly constrained by genetic variances and covariances of complex phenotypes. We analyze a large database of population divergence in plants and evaluate whether evolutionary divergence scales positively with standing genetic variation within populations (evolvability), as expected if genetic constraints are evolutionarily important. We further evaluate differences in divergence and evolvability-divergence relationships between reproductive and vegetative traits and between selling, mixed-mating, and outcrossing species, as these factors are expected to influence both patterns of selection and evolutionary potentials. Evolutionary divergence scaled positively with evolvability. Furthermore, trait divergence was greater for vegetative traits than for floral (reproductive) traits, but largely independent of the mating system. Jointly, these factors explained similar to 40% of the variance in evolutionary divergence. The consistency of the evolvability-divergence relationships across diverse species suggests substantial predictability of trait divergence. The results are also consistent with genetic constraints playing a role in evolutionary divergence
The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey
We analysed the optical spectra of HII regions extracted from a sample of 350
galaxies of the CALIFA survey. We calculated total O/H abundances and, for the
first time, N/O ratios using the semi-empirical routine HII-CHI-mistry, which,
according to P\'erez-Montero (2014), is consistent with the direct method and
reduces the uncertainty in the O/H derivation using [NII] lines owing to the
dispersion in the O/H-N/O relation. Then we performed linear fittings to the
abundances as a function of the de-projected galactocentric distances. The
analysis of the radial distribution both for O/H and N/O in the non-interacting
galaxies reveals that both average slopes are negative, but a non-negligible
fraction of objects have a flat or even a positive gradient (at least 10\% for
O/H and 4\% for N/O). The slopes normalised to the effective radius appear to
have a slight dependence on the total stellar mass and the morphological type,
as late low-mass objects tend to have flatter slopes. No clear relation is
found, however, to explain the presence of inverted gradients in this sample,
and there is no dependence between the average slopes and the presence of a
bar. The relation between the resulting O/H and N/O linear fittings at the
effective radius is much tighter (correlation coefficient = 0.80) than
between O/H and N/O slopes ( = 0.39) or for O/H and N/O in the
individual \hii\ regions ( = 0.37). These O/H and N/O values at the
effective radius also correlate very tightly (less than 0.03 dex of dispersion)
with total luminosity and stellar mass. The relation with other integrated
properties, such as star formation rate, colour, or morphology, can be
understood only in light of the found relation with mass.Comment: Accepted for publication in A&A. 20 pages, 19 figure
The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra
We have derived the oxygen abundance for a sample of nearby galaxies in the
Data Release 5 of the Sloan Digital Sky Survey (SDSS) which possess at least
two independent spectra of one or several HII regions with a detected
[OIII]4363 auroral line. Since, for nearby galaxies, the [OII]3727 nebular line
is out of the observed wavelength range, we propose a method to derive (O/H)_ff
abundances using the classic Te method coupled with the ff relation. (O/H)_7325
abundances have also been determined, based on the [OII]7320,7330 line
intensities, and using a small modification of the standard Te method. The
(O/H)_ff and (O/H)_7325 abundances have been derived with both the one- and
two-dimensional t_2 - t_3 relations. It was found that the (O/H)_ff abundances
derived with the parametric two-dimensional t_2 - t_3 relation are most
reliable. Oxygen abundances have been determined in 29 nearby galaxies, based
on 84 individual abundance determinations in HII regions. Because of our
selection methods, the metallicity of our galaxies lies in the narrow range 8.2
< 12 + log (O/H) < 8.4. The radial distribution of oxygen abundances in the
disk of the spiral galaxy NGC 4490 is determined for the first time.Comment: 39 pages, 10 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Coevolution of metallicity and star formation in galaxies to z=3.7: I. A fundamental plane
With the aim of understanding the coevolution of star formation rate (SFR),
stellar mass (M*), and oxygen abundance (O/H) in galaxies up to redshift z=3.7,
we have compiled the largest available dataset for studying Metallicity
Evolution and Galaxy Assembly (MEGA); it comprises roughly 1000 galaxies with a
common O/H calibration and spans almost two orders of magnitude in metallicity,
a factor of 10^6 in SFR, and a factor of 10^5 in stellar mass. From a Principal
Component Analysis, we find that the 3-dimensional parameter space reduces to a
Fundamental Plane of Metallicity (FPZ) given by 12+log(O/H) = -0.14 log (SFR) +
0.37 log (M*) + 4.82. The mean O/H FPZ residuals are small (0.16 dex) and
consistent with trends found in smaller galaxy samples with more limited ranges
in M*, SFR, and O/H. Importantly, the FPZ is found to be redshift-invariant
within the uncertainties. In a companion paper, these results are interpreted
with an updated version of the model presented by Dayal et al. (2013).Comment: 19 pages, 10 figures, 4 tables, accepted for publication in MNRA
The direct oxygen abundances of metal-rich galaxies derived from electron temperature
We aim to derive the electron temperature Te in the gas of metal-rich
star-forming galaxies, which can be obtained from their ratios of auroral lines
[O II]7320,7330 to nebular lines [O II]3727, in order to establish a more
robust mass-metallicity relationship, and compare the Te-based (O/H) abundances
with those from empirical strong-line calibrations, such as R23. We obtained 27
spectra by stacking the spectra of several hundred (even several thousand)
star-forming galaxies selected from the SDSS-DR4 in each of the 27 stellar mass
bins from log(M*) ~8.0 to 10.6 (logMsun). This "stack" method sufficiently
improves the signal-to-noise ratio of the auroral lines [O II]7320,7330, which
allow us to reliably obtain the electron temperature t2 in the low ionization
region from the ratio of [O II]7320,7330 to [O II]3727, then t3 in the high
ionization region from t2 by using a relation, and then the direct (O/H)
abundances from Te. The results show that the empirical R23 method will
overestimate the log(O/H) by 0.2 to 0.6 dex for these moderate metal-rich
galaxies. The new metal-mass relationship of the galaxies with moderate
metallicities is fitted by a linear fit (12+log(O/H) =6.223+0.231*logM*)
confirming that empirical methods significantly overestimate (O/H). We also
derived their (N/O) abundance ratios on the basis of the Te method, which are
consistent with the combination of the primary and secondary components of
nitrogen. For actual use, we re-derive the relations of 12+log(O/H)(Bay) vs.
logM* and 12+log(O/H)(Bay) vs. logR23 from the SDSS-DR4 data, which are a bit
different from those derived from DR2.Comment: 13 pages, 12 figures, 2 tables, accepted by A&
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