Evolutionary changes in craniomandibular shape in the great cats (Neofelis Griffith and Panthera Oken)

Evolutionary shape changes in skull and mandibular anatomy was analysed in 223 specimens of pantherine felids (Neofelis nebulosa, Panthera leo, Panthera onca, Panthera pardus, Panthera tigris, Panthera uncia) compared to a small‐felid outgroup, consisting of 86 specimens of nine different species, using digital surface morphometry on 25 (skull) and 17 (mandible) landmarks. Shape evolution in the pantherine species is complex and nonlinear, and involves both large‐scale and small‐scale shape changes. Shape changes frequently differ among the ingroup species, but the four large Panthera species (leo, onca, pardus, tigris) bear some resemblance to each other. The leopard and jaguar bear the closest resemblance to each other, and several shape changes are common to the lion and tiger, but have probably evolved convergently as a result of large size. The lion has undergone the largest and most numerous shape changes from a small‐felid outgroup. Certain shape changes in the skull and, in some respects, the mandible of the clouded leopard bear resemblance to those in the four large Panthera species. The snow leopard is often regarded as the most primitive of the extant Panthera, and skull and mandibular shape changes often diverge markedly from those observed in the other five ingroup taxa; its overall skull shape is rather similar to the small‐felid outgroup. This indicates that the shape changes in the clouded leopard are convergent with those of the four large Panthera species. Landmark integration showed no significant correlation with molecular phylogeny, chiefly owing to the snow leopard being placed among the four large Panthera species. A traditional phylogenetic topology with the snow leopard as the basal‐most species of Panthera yielded a weak but nonsignificant phylogenetic signal. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 766–778.     

Pollination efficiency and reproductive patterns in relation to local plant density,population size,and floral display in the rewarding Listera ovata (Orchidaceae)

Pollination efficiency and reproductive success vary strongly among populations of most animal‐pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above‐mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross‐ vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30–40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 713–721.     

Identifiability analysis and improvement of a tree water flow and storage model

A recently published tree water flow and storage model (RCGro) for simulating water transport dynamics in trees and related stem diameter variations was improved in order to better describe a data set gathered under mild drought stress conditions. Model improvements were carried out based on the results of a mathematical identifiability analysis. This analysis provided important information with respect to the balance between model complexity and data availability. Using the identifiability analysis results, we were able to (1) highlight weaknesses of the model; (2) obtain information on how the model could be reduced in some places, to improve its identifiability properties, and extended in others, to enhance model performance; (3) identify which measurements are necessary to optimally calibrate the model. The resulting improved model was less complex (contained less unidentifiable parameters), had better dynamic properties and was able to better describe the stress data set.     

Correlated evolution of fig size and color supports the dispersal syndromes hypothesis

The influence of seed dispersers on the evolution of fruit traits remains controversial, largely because most studies have failed to account for phylogeny and or have focused on conservative taxonomic levels. Under the hypothesis that fruit traits have evolved in response to different sets of selective pressures by disparate types of seed dispersers (the dispersal syndromes hypothesis), we test for two dispersal syndromes, defined as groups of fruit traits that appear together more often than expected by chance. (1) Bird syndrome fruits are brightly colored and small, because birds have acute color vision, and commonly swallow fruits whole. (2) Mammal syndrome fruits are dull-colored and larger on average than bird syndrome fruits, because mammals do not rely heavily on visual cues for finding fruits, and can eat fruits piecemeal. If, instead, phylogenetic inertia determines the co-occurrence of fruit size and color, we will observe that specific combinations of size and color evolved in a small number of ancestral species. We performed a comparative analysis of fruit traits for 64 species of Ficus (Moraceae), based on a phylogeny we constructed using nuclear ribosomal DNA. Using a concentrated changes test and assuming fruit color is an independent variable, we found that small-sized fruits evolve on branches with red and purple figs, as predicted by the dispersal syndromes hypothesis. When using diameter as the independent variable, results vary with the combination of algorithms used, which is discussed in detail. A likelihood ratio test confirms the pattern found with the concentrated changes test using color as the independent variable. These results support the dispersal syndromes hypothesis.     

Selection on floral traits through male fertility in a natural plant population

Most studies on selection in plants estimate female fitness components and neglect male mating success, although the latter might also be fundamental to understand adaptive evolution. Information from molecular genetic markers can be used to assess determinants of male mating success through parentage analyses. We estimated paternal selection gradients on floral traits in a large natural population of the herb Mimulus guttatus using a paternity probability model and maximum likelihood methods. This analysis revealed more significant selection gradients than a previous analysis based on regression of estimated male fertilities on floral traits. There were differences between results of univariate and multivariate analyses most likely due to the underlying covariance structure of the traits. Multivariate analysis, which corrects for the covariance structure of the traits, indicated that male mating success declined with distance from and depended on the direction to the mother plants. Moreover, there was directional selection for plants with fewer open flowers which have smaller corollas, a smaller anther–stigma separation, more red dots on the corolla and a larger fluctuating asymmetry therein. For most of these traits, however, there was also stabilizing selection indicating that there are intermediate optima for these traits. The large number of significant selection gradients in this study shows that even in relatively large natural populations where not all males can be sampled, it is possible to detect significant paternal selection gradients, and that such studies can give us valuable information required to better understand adaptive plant evolution. Second affiliation for Mark Van Kleunen is temporary until February 2007.     

不同扰动生境中动物对酸苔菜种子的捕食和散布

有效的种子散布是木本植物形成入侵种需要经历的过程之一,但在预测入侵种时却常常被忽略.紫金牛科东方紫金牛(Ardisia elliptica)原产热带亚洲而在北美成为入侵植物,分布在云南南部的其同属种酸苔菜(A.solariacea)与之具有相似的生物学特征.本文以酸苔菜为研究对象,于2004年12月至次年2月分别在人为干扰轻的野象谷和人为干扰重的植物园进行酸苔菜的种子散布及捕食研究,试图了解生境变化对其种子散布和种子捕食的影响.结果表明,酸苔菜在两地的种子散布者均为白喉冠鹎(Alophoixus pallidus)、黑冠黄鹎(Pycnonotus melanicterus)和灰眼短脚鹎(Iole propinqua),但3种食果实鸟类的组成比例、拜访行为、频率及种子捕食者的影响在两地均不相同.人为干扰轻的野象谷生境中白喉冠鹎、黑冠黄鹎与灰眼短脚鹎的拜访频率分别为25%、32%和26%.取食后的第一次停栖地点有4%在10 m以外;人为干扰重的植物园生境中3种鸟的拜访频率分别为67%、8%、5%,取食后的第一次停栖地点有26%在10 m以外.人工摆放种子试验表明,地面上种子捕食者主要是啮齿类;在两生境中种子捕食率均较低(2-6%),但野象谷生境中种子捕食率仍显著高于植物园生境.野象谷生境中种子还受到象鼻虫幼虫的危害,危害率为17.9±3.5%(n=512);而植物园生境中未发现种子被象鼻虫危害(n=489).干扰对生境中的动物组成及行为造成了明显影响,并可能通过种子散布与捕食的改变而间接影响与其有密切关系植物的种群动态.     

Migration load in plants: role of pollen and seed dispersal in heterogeneous landscapes

Evolution of local adaptation depends critically on the level of gene flow, which, in plants, can be due to either pollen or seed dispersal. Using analytical predictions and individual-centred simulations, we investigate the specific influence of seed and pollen dispersal on local adaptation in plant populations growing in patchy heterogeneous landscapes. We study the evolution of a polygenic trait subject to stabilizing selection within populations, but divergent selection between populations. Deviations from linkage equilibrium and Hardy-Weinberg equilibrium make different contributions to genotypic variance depending on the dispersal mode. Local genotypic variance, differentiation between populations and genetic load vary with the rate of gene flow but are similar for seed and pollen dispersal, unless the landscape is very heterogeneous. In this case, genetic load is higher in the case of pollen dispersal, which appears to be due to differences in the distribution of genotypic values before selection.     

Cranial shape and correlated characters in crocodilian evolution

Crocodilians show a high degree of cranial variation and convergence throughout their 80 million-year fossil record that complicates their phylogenetic reconstruction. Conflicting phylogenetic results from different data partitions and character homoplasies typify crocodilian phylogeny, and differences between molecular and morphological phylogenetic hypotheses are believed to be associated with the slender-snout skull shape of Gavialis gangeticus and Tomistoma schlegelii. Slender-snout skulls are one of five identified eusuchian cranial ecomorph shape categories (ESCs) thought to reflect functional or ecological specialization. This paper tested the effect of transitions among general, blunt and slender ESCs on cranial character-state distributions in phylogeny using the concentrated changes test. In addition, 'tree-free' character compatibility analysis of character independence was conducted on the morphological character matrix to determine if character correlations are observed independent of specific tree topologies. Results suggest cranial ESCs do affect cranial character-state gains in phylogeny. Concentrated changes identify a broad suite of character-state changes that significantly correlate with transitions to slender, general and blunt ESCs on morphological, molecular and combined-data tree topologies, but numbers of correlated characters for each category differ according to topology. Character compatibility analysis results do not mirror the concentrated changes test results and reflect hierarchically distributed support throughout the data. As cranial ESCs affect character-state transitions, it is possible that nonphylogenetic variables could affect inferences of crocodilian phylogeny by affecting cranial morphology.     

Establishing a perimeter position: speciation around the Indian Ocean Basin

Historical biological interactions among peripheral landmasses on the periphery of the Indian Ocean Basin (IOB) are generally poorly understood. While interactions based on early Gondwanan vicariance have been used to explain present day lineage distributions, several recent studies have instead inferred dispersal across the IOB. This inference is often advanced because lineages under study have species inhabiting IOB islands. Here we examine the roles of continental vicariance vs. trans-IOB dispersal in the distribution of an avian genus found around the perimeter of the IOB. A molecular phylogeny does reveal evidence of a relationship that would require the inference of trans-IOB dispersal between eastern Africa and Sri Lanka. However, molecular clock data, ancestral area analyses and paleoclimatic reconstructions suggest that vicariance related to tropical forest expansion and retraction is more likely to have facilitated African-Asian interchange, with an initial colonization of Africa from Asia quickly followed by a recolonization of Asia. Subsequent dispersal from Asia to Sri Lanka and islands east of the Sunda Shelf are inferred; these latter islands were colonized in a stepping-stone fashion that culminated in colonization of the Sunda Shelf, and a recolonization of mainland Asia. We propose that circum-IOB distributions, which post-date early Gondwanan breakup, are most likely the result of continent-based vicariant events, particularly those events related to large-scale habitat alterations, and not trans-IOB dispersals.     

Composition and dispersal of riverine and lake phytoplankton communities in connected systems with different water retention times

1. Lake phytoplankton community structure may be influenced by both internal factors (predation, competition, resource constraints) and external ones, such as dispersal of materials and cells between connected habitats. However, little is known about the importance of cell dispersal for phytoplankton community structure in lakes. 2. We investigated the abundance and dispersal of phytoplankton cells between connected rivers and lakes, and analysed whether similarities in phytoplankton community composition between rivers and lakes were primarily related to cell import rates or to characteristics of the local habitat. We focused on lakes along a gradient of theoretical water retention times (TWRT). Two data sets from Swedish lakes were used; a seasonal study of two connected boreal forest lakes, differing in TWRT, and a multi‐lake study of 13 lakes with a continuous range of TWRTs. 3. Phytoplankton cells were transported and dispersed in all investigated rivers. In the seasonal study, cell import rates and similarities in phytoplankton community composition between the lake and its inlet(s) were much higher in the lake with a shorter TWRT. Phytoplankton community structure in different habitats was associated with total organic carbon (TOC). This indicates that local habitat characteristics may be important in determining lake phytoplankton community composition, even in the presence of substantial cell import. 4. The multi‐lake study also showed a negative relationship between TWRT and similarities in phytoplankton community composition between inlets and lakes. Moreover, similarity in community structure was related to both cell import rates from inlet to lake and differences in habitat characteristics between inlet and lake. However, the variable most strongly correlated with community structure was TOC, indicating that species sorting rather than a mass effect was the most important mechanism underlying the correlation between community structure and retention time. 5. Overall, our data suggest that local habitat characteristics may play a key role in determining community similarity in this set of lakes covering a large range of habitat connectedness. Due to the strong co‐variations between cell dispersal and TOC, it was hard to unequivocally disentangle the different mechanisms; hence, there is a need for further studies of the role of dispersal for phytoplankton community structures.