Macroevolution of perfume signalling in orchid bees

Theory predicts that both stabilising selection and diversifying selection jointly contribute to the evolution of sexual signalling traits by (1) maintaining the integrity of communication signals within species and (2) promoting the diversification of traits among lineages. However, for many important signalling traits, little is known about whether these dynamics translate into predictable macroevolutionary signatures. Here, we test for macroevolutionary patterns consistent with sexual signalling theory in the perfume signals of neotropical orchid bees, a group well studied for their chemical sexual communication. Our results revealed both high species‐specificity and elevated rates of evolution in perfume signals compared to nonsignalling traits. Perfume complexity was correlated with the number of congeners in a species’ range, suggesting that perfume evolution may be tied to the remarkably high number of orchid bee species coexisting together in some neotropical communities. Finally, sister‐pair comparisons were consistent with both rapid divergence at speciation and character displacement upon secondary contact. Together, our results provide new insight into the macroevolution of sexual signalling in insects.     

Effect of surface-screening parameter of the Yukawa potential model on vapour–liquid phase coexistence and critical-point properties of confined Yukawa fluid

We report the effect of surface-screening parameter of Yukawa potential model on vapour–liquid phase coexistence and critical-point properties of slit–pore-confined Yukawa fluid, using grand canonical transition-matrix Monte Carlo along with the histogram reweighting method. The effect of surface-screening parameter on the vapour–phase coexistence density is insignificant for the studied system. On the other hand, significant effect of surface-screening parameter is observed on liquid phase coexistence density. With increasing surface-screening parameter, liquid phase coexistence density decreases. Critical-point properties have shown monotonic decreasing trends with increase in surface-screening parameter. Moreover, the effect of change of surface-screening parameter is least on critical temperature changes as compared to critical density and critical pressure changes for the studied Yukawa system in this work.     

When and where plant‐soil feedback may promote plant coexistence: a meta‐analysis

Plant‐soil feedback (PSF) theory provides a powerful framework for understanding plant dynamics by integrating growth assays into predictions of whether soil communities stabilise plant–plant interactions. However, we lack a comprehensive view of the likelihood of feedback‐driven coexistence, partly because of a failure to analyse pairwise PSF, the metric directly linked to plant species coexistence. Here, we determine the relative importance of plant evolutionary history, traits, and environmental factors for coexistence through PSF using a meta‐analysis of 1038 pairwise PSF measures. Consistent with eco‐evolutionary predictions, feedback is more likely to mediate coexistence for pairs of plant species (1) associating with similar guilds of mycorrhizal fungi, (2) of increasing phylogenetic distance, and (3) interacting with native microbes. We also found evidence for a primary role of pathogens in feedback‐mediated coexistence. By combining results over several independent studies, our results confirm that PSF may play a key role in plant species coexistence, species invasion, and the phylogenetic diversification of plant communities.     

Evolution of resource specialisation in competitive metacommunities

Spatial environmental heterogeneity coupled with dispersal can promote ecological persistence of diverse metacommunities. Does this premise hold when metacommunities evolve? Using a two‐resource competition model, we studied the evolution of resource‐uptake specialisation as a function of resource type (substitutable to essential) and shape of the trade‐off between resource uptake affinities (generalist‐ to specialist‐favouring). In spatially homogeneous environments, evolutionarily stable coexistence of consumers is only possible for sufficiently substitutable resources and specialist‐favouring trade‐offs. Remarkably, these same conditions yield comparatively low diversity in heterogeneous environments, because they promote sympatric evolution of two opposite resource specialists that, together, monopolise the two resources everywhere. Consumer diversity is instead maximised for intermediate trade‐offs and clearly substitutable or clearly essential resources, where evolved metacommunities are characterised by contrasting selection regimes. Taken together, our results present new insights into resource‐competition‐mediated evolutionarily stable diversity in homogeneous and heterogeneous environments, which should be applicable to a wide range of systems.     

Multi‐year stigmatic pollen‐load sampling reveals temporal stability in interspecific pollination of flowers in a subalpine meadow

Co‐flowering plants may commonly experience interspecific pollination. It remains unknown, however, whether interspecific pollination is a largely stochastic process or consistent enough over years to exert selection for traits that can reduce interspecific pollination or ameliorate its deleterious effects on reproduction. To assess the likelihood of this precondition being met, stigmatic pollen loads on 17–34 insect‐pollinated plant species over three consecutive years were scored in a subalpine meadow in southwestern China. Plant species varied significantly in the amount and proportion of heterospecific pollen (HP) on stigmas. Both the number of HP species and the proportion of the pollen load that was HP for each recipient species correlated positively between years (reflected in pairwise correlations for all year‐by‐year combinations). Although inter‐annual variation was smaller for conspecific pollen (CP) than for HP loads, species tended to experience either consistently high or consistently low HP proportions across years. We found that species with higher stigmatic HP proportions generally experienced lower proportional variation in stigmatic HP, an unexpected result if high HP loads are the result of rare stochastic events. The novel finding of between‐year consistency in stigmatic loads of heterospecific pollen suggests that adaption to stigmatic loads of HP is possible, and two divergent strategies may have evolved: HP avoidance and HP tolerance. The observation of temporally consistent differences among species in levels of HP supports the idea that natural selection may be operating either to increase tolerance or to minimize arrival of heterospecific pollen on stigmas in co‐flowering plants. Such adaptations may be important for the maintenance of high levels of local plant diversity in biodiversity hotspots such as our study area.     

Fire‐sensitive species dominate seed rain after fire suppression: Implications for plant community diversity and woody encroachment in the Cerrado

Woody encroachment is becoming common in tropical savannas. We studied natural seed rain and performed seed addition experiments in a Brazilian savanna that had not been burned for several decades. We found greater abundance of fire‐sensitive species in the seed rain, likely contributing to woody encroachment. Flexible fire management policies that allow for natural and prescribed fires may be required to maintain savanna diversity.     

贮食动物的盗食与反盗食行为策略

食物贮藏是许多动物应对食物短缺、保障其生存和繁衍的一种适应性行为。保护好贮藏食物以供食物短缺期利用,是食物贮藏成功的标志和进化动力。同种或异种动物盗食是贮藏食物损失的重要原因。嗅觉、视觉与空间记忆、随机搜寻等是动物搜寻和盗取食物的重要手段;避免盗食、阻止盗食和容忍盗食是动物反盗食的重要策略。动物通常采用多种行为策略进行盗食和反盗食,分配食物资源,形成相对稳定的种内、种间关系。盗食与反盗食互作及其对贮食行为进化的意义已成为行为生态学的研究热点和前沿之一,针对鸟类和哺乳类动物的研究尤为丰富。本文总结了贮食动物常见的盗食和反盗食行为策略及其相互作用的研究进展,主要内容涉及贮食动物利用嗅觉、视觉与空间记忆、随机搜寻等盗取其他个体食物的盗食策略,以及通过隐藏、转移、保卫、容忍等方式减少被盗食,保护贮藏食物的行为策略。针对现有研究状况,从种间盗食与反盗食及其与物种共存的关系,种间非对称盗食关系及其适应意义,盗食与反盗食最适行为策略及其与贮食动物适合度的关系等方面对今后研究提出了建议。     

Interspecific competition in Drosophila II. Competitive outcome in some 2–resource environments

Populations of Drosophila metanogaster and D. simulans were made to compete in a number of 2– resource environments. The resources used were all based on a standard Drosophila medium and differed from each other only in their concentrations of ethanol. Each experiment comprised three cages started at a species–frequency of 0.8 D. melanogaster and three at 0.2 D. melanogaster. This enabled screening for a wide range of equilibria.
Reversal of competitive superiority was achieved (unintentionally) by raising the alcohol level of one of the resources. Thus while D. simulans won in an environment with media containing 0 and 896 ethanol, D. melanogaster won if the ethanol concentrations were 0 and 10%, or 0 and 12%. This parallels the reversal of dominance reported earlier for single–resource systems. However, in none of the 2–resource systems studied was there a stable equilibrium in species–frequency–in fact there was no significant frequency–dependence at all.
An artificial selection experiment produced a stock of D. melanogaster ovipositing a higher proportion of eggs on the alcoholic resource. Thus, this stock was more divergent from D. simulans , in at least one aspect of resource use, than was the original stock of D. melanogaster. However, competition between stock D. simulans and selected D. melanogaster showed no frequency–dependence. Again, reversal of competitive dominance was unintentionally achieved.
The implications of these results are discussed, and the need for a comprehensive study of resource–utilization in a pair of competing species is stressed.