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It is well known that animals can exert strong selective pressures on plant traits. However, studies on the evolutionary consequences of plant-animal interactions have mainly focused on understanding how these interactions shape trait means, while overlooking its potential direct effect on the variability among structures within a plant (e.g. flowers and fruits). The degree of within-plant variability can have strong fitness effects but few studies have evaluated its role as a potential target of selection. Here we reanalyzed data on Ipomoea wolcottiana stigma-anther distance to test alternate mechanisms driving selection on the mean as well as on intra-individual variance in two years. We found strong negative selection acting on intra-individual variation but not on mean stigma-anther distance suggesting independent direct selection on the latter. Our result suggests that intra-individual variance has the potential to be an important target of selection in nature and that ignoring it could lead to the wrong characterization of the selection regime. We highlight the need for future studies to consider patterns of selection on the mean as well as on intra-individual variance if we want to understand the full extent of plant-animal interactions as an evolutionary force in nature. This article is protected by copyright. All rights reserved.

Administration of sodium salicylate (SS) to cows in early lactation has a positive effect on whole-lactation milk production but a negative effect on metabolism in some cases. The objective of this trial was to determine whether SS directly affects rumen fermentation. Experiment 1 was designed to investigate the effects of direct inclusion of SS in a 24-h batch culture, and experiment 2 was designed to test the fermentative ability of rumen fluid from heifers who had received SS. In experiment 1, we combined strained and pooled rumen fluid from 3 heifers in a 2:1 ratio with McDougall's buffer, and added 150 mL of the inoculum to each flask (n = 5/treatment) with 2.5 g of fermentation substrate similar to a lactating cow ration, ground to 1 mm. We then added premixed treatments (1-mL volume) to achieve the desired final amount of SS (CON1 = 0 mg, LOW = 125 mg, MED = 250 mg, HI = 375 mg). In experiment 2, 6 heifers (n = 3/treatment) were drenched daily for 3 d, either with 62.5 g of SS dissolved in water (SAL) or an equal volume of water (CON2). Rumen fluid was collected from each heifer and was not pooled. After the fluid was mixed 2:1 with McDougall's buffer, 150 mL of inoculum was added to the fermentation flasks (n = 4/heifer) with 2.5 g of fermentation substrate. This experiment was performed the day before SS treatment began and repeated 1, 13, and 35 d after the end of the treatment period. We also performed an in situ experiment at each of these time points. In the first experiment, inclusion of SS resulted in a decrease in dry matter disappearance (DMD) over 24 h, as well as an increase in final pH. We detected no difference between treatments for gas production asymptotic volume, rate, or lag. In the second experiment, we detected a significant treatment × day interaction for DMD: we observed no difference between groups during a 24-h batch culture on the day following treatment, but SAL resulted in lower DMD on d 13 and d 35. We detected no treatment effect on the final pH of the batch culture or on any gas-production parameters. We observed a tendency for SAL to decrease the DMD rate in situ on the day after treatment. These results indicate that SS administration has a negative effect on rumen microorganisms.

The endemic Mexican cactus, Mammillaria pectinifera, shows low dispersal capabilities and isolated populations within the highly dissected landscape of Tehuacán Valley. These characteristics can restrict gene flow and act upon the genetic divergence and speciation in arid plants. We conducted a phylogeographic study to determine if the origin, current distribution, and genetic structure of M. pectinifera were driven by Quaternary geomorphic processes. Sequences of the plastids psbA-trnH and trnT-trnL obtained from 66 individuals from seven populations were used to estimate genetic diversity. Population differentiation was assessed by an analysis of molecular variance. We applied a stepwise phylogenetic calibration test to determine whether species origin and genetic divergence among haplotypes were temporally concordant with recognizable episodes of geomorphic evolution. The combination of plastid markers yielded six haplotypes, with high levels of haplotype diversity (h = 0.622) and low nucleotide diversity (π = 0.00085). The populations were found to be genetically structured (F(ST) = 0.682; P0.00001), indicating that geographic isolation and limited dispersal were the primary causes of genetic population differentiation. The estimated origin and divergence time among haplotypes were 0.017-2.39 and 0.019-1.237 mya, respectively, which correlates with Pleistocene tectonics and erosion events, supporting a hypothesis of geomorphically-driven geographical isolation. Based on a Bayesian skyline plot, these populations showed long term demographic stability, indicating that persistence in confined habitats has been the main response of this species to landscape changes. We conclude that the origin and haplotype divergence of M. pectinifera were a response to local Quaternary geomorphic evolution.