Developmental acclimation affects clinal variation in stress resistance traits in Drosophila buzzatii

Patterns of clinal genetic variation in Drosophila are often characterized after rearing at constant temperatures. However, clinal patterns might change after acclimation if populations differ in their plastic response to fluctuating environments. We studied longevity, starvation and heat knock‐down resistance after development at either constant or fluctuating temperatures in nine Drosophila buzzatii populations collected along an altitudinal gradient in Tenerife, Spain. Flies that developed at fluctuating temperatures had higher stress resistance despite experiencing a slightly lower average temperature than those at constant temperatures. Genetic variation along the gradient was found in both stress‐resistance traits. Because Q_ST values greatly exceeded F_ST values, genetic drift could not explain this diversification. In general, differences among populations were larger after rearing at fluctuating temperatures, especially in heat knock‐down, for which clinal patterns disappeared when flies were reared at constant temperatures. This result emphasizes the importance of determining whether populations originating from different environments differ in their plastic responses to stress.     

Clinal variation in developmental time and viability,and the response to thermal treatments in two species of Drosophila

The present study first addressed the question of whether developmental time (DT) and viability (VT) vary clinally along latitudinal and altitudinal gradients in Drosophila buzzatii, an autochthonous specialist and the generalist invasive Drosophila melanogaster. Coincident and positive altitudinal clines across species and, direct and inverse latitudinal clines were observed for DT in D. melanogaster and D. buzzatii, respectively. Opposing latitudinal and altitudinal clines were detected for VT only in D. melanogaster. The patterns observed along altitudinal gradients prompted us to investigate whether flies living at lowland and highland environments may respond differentially to thermal treatments consisting of regimes of constant and alternating temperatures. Flies reared at higher mean temperature developed faster than at lower mean temperature in both species. By contrast, the response in VT differed greatly between species. Highland D. melanogaster were more viable than lowland regardless the treatment, whereas, in D. buzzatii, highland flies were more viable than lowland in alternating thermal regimes and the reverse was true in treatments of constant temperature. The results obtained suggest that thermal amplitude may be an important factor that should be considered in investigations of thermal adaptation. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 233–245.     

Lowering sample size in comparative analyses can indicate a correlation where there is none: example from Rensch's rule in primates

The fact that characters may co-vary in organism groups because of shared ancestry and not always because of functional correlations was the initial rationale for developing phylogenetic comparative methods. Here we point out a case where similarity due to shared ancestry can produce an undesired effect when conducting an independent contrasts analysis. Under special circumstances, using a low sample size will produce results indicating an evolutionary correlation between characters where an analysis of the same pattern utilizing a larger sample size will show that this correlation does not exist. This is the opposite effect of increased sample size to that expected; normally an increased sample size increases the chance of finding a correlation. The situation where the problem occurs is when co-variation between the two continuous characters analysed is clumped in clades; e.g. when some phylogenetically conservative factors affect both characters simultaneously. In such a case, the correlation between the two characters becomes contingent on the number of clades sharing this conservative factor that are included in the analysis, in relation to the number of species contained within these clades. Removing species scattered evenly over the phylogeny will in this case remove the exact variation that diffuses the evolutionary correlation between the two characters - the variation contained within the clades sharing the conservative factor. We exemplify this problem by discussing a parallel in nature where the described problem may be of importance. This concerns the question of the presence or absence of Rensch's rule in primates.     

Perspective: female remating,operational sex ratio,and the arena of sexual selection in Drosophila species

Abstract.— As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila . Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well.     

Genetic variation for resistance and acclimation to high temperature stress in Drosophila buzzatii

Genetic variation for resistance to a high temperature stress under saturated humidity was examined within and among three Drosophila buzzatii populations from Australia. Further, the acclimation of this species to high temperatures was tested by prelreating flies for a shorter, sublethal, time period under conditions that lead to expression of heat shock proteins. Genetic variation for temperature resistance was present among lines for flies either pretreated to high temperature or not. Pro-treating increased survival, with the benefit significantly higher if pretreating was performed 24 h rather than 96 h before exposure to the potentially lethal stress. For (lies pretreated at both times, resistance to heat stress was even greater. The lack of a significant treatment by line interaction term suggested that all lines were similarly plastic for acclimation following previous exposure(s) to a high temperature. Significantly more males survived the heat stress than females, and, within each sex, larger flies were generally more heat resistant than smaller ones. Additionally, the lines from the population that naturally encounters the highest temperatures were generally more resistant to high temperature stress.     

Clinal variation and laboratory adaptation in the rainforest species Drosophila birchii for stress resistance, wing size, wing shape and development time

Clinal variation has been described in many invertebrates including drosophilids but usually over broad geographical gradients. Here we describe clinal variation in the rainforest species Drosophila birchii from Queensland, Australia, and potential confounding effects of laboratory adaptation. Clinal variation was detected for starvation and development time, but not for size or resistance to temperature extremes. Starvation resistance was higher at southern locations. Wing shape components were not associated with latitude although they did differ among populations. Time in laboratory culture did not influence wing size or heat knockdown resistance, but increased starvation resistance and decreased recovery time following a cold shock. Laboratory culture also increased development time and altered wing shape. The results indicate that clinal patterns can be detected in Drosophila over a relatively narrow geographical area. Laboratory adaptation is unlikely to have confounded the detection of geographical patterns.     

Abundance, distribution and life histories of grassland plants: a comparative study of 81 species

1 This study examines the abundance and distribution of grassland plant species in particular relation to features affecting colonization. Seed production (inversely related to seed size) and recruitment success (positively related) affect colonization ability, suggesting that seed size can be used as a key trait.
2 Data on seed size, dispersal mode, life form, geographical range size and abundance were gathered for 81 grassland plant species in a field study area in Sweden. Seed production and plant size were estimated for 69 of these species. Analyses were performed both across species, with species treated as independent data points, and for 43 'phylogenetically independent contrasts'.
3 The cross-species analyses suggested that local abundance was related to life forms but not dispersal or plant size. Perennials were generally most abundant, as were clonal species. If abundance reflects colonization we predicted that species with intermediately sized seeds (or intermediate seed production) would be most abundant, and this was supported by the phylogenetic contrast but not by cross-species analyses. In the former analysis, a high abundance of species was significantly associated with a small seed size deviation (and seed number deviation) from the median values of these traits in the community.
4 Local abundance, seed production and seed size deviation from the community median value were positively related to geographical range size in the cross-species analysis, but no relationships were seen in the phylogenetic contrast analysis.
5 We conclude that colonization processes do have a significant influence on abundance patterns in grasslands. Seed size is a key trait for colonizing ability, and the effects of the trade-off of seed size vs. seed number must be considered. No single mechanism can be identified that influences both abundance and geographical distribution range.     

A taxonomic study of Whitehead's torrent frog,Meristogenys whiteheadi,with descriptions of two new species (Amphibia: Ranidae)

The genus Meristogenys (Anura: Ranidae), endemic to Borneo, presents serious taxonomic problems despite being one of the commonest frogs in the mountainous regions of this island. We investigated molecular and morphological variations in Meristogenys whiteheadi (Boulenger, 1887) using larval and adult specimens from Sabah and Sarawak (Malaysia). We found three allopatric lineages in this species. We regard each of these as a distinct species because they are separated by a large genetic distance, and do not form any monophyletic group. Their morphological characters indicate that the distributional range of M. whiteheadi s.s. is divided into two disjunct areas: Mt Kinabalu (northern Sabah) and northern Sarawak. The two other lineages occupy ranges between those of M. whiteheadi, and represent undescribed cryptic species. One of these, Meristogenys stigmachilus sp. nov. , collected from the northern part of the Crocker Range, is distinguished from M. whiteheadi by black spots on the upper lip and dark dots scattered on the back. A second undescribed species, Meristogenys stenocephalus sp. nov. , was collected mainly from the southern part of the Crocker Range, and is characterized by the large body size of males and a relatively narrow head. Meristogenys stenocephalus sp. nov. also differs from M. stigmachilus sp. nov. and M. whiteheadi in larval morphology, but larvae of the latter two cannot be differentiated morphologically. We discuss relative tibia length, a diagnostic specific characteristic in the genus Meristogenys, and the relationships between body size and sexual size dimorphism in this genus. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 157–183.     

Variation in adult life history and stress resistance across five species of<Emphasis Type="Italic">Drosophila</Emphasis>

Dry weight at eclosion, adult lifespan, lifetime fecundity, lipid and carbohydrate content at eclosion, and starvation and desiccation resistance at eclosion were assayed on a long-term laboratory population ofDrosophila melanogaster, and one recently wild-caught population each of four other species ofDrosophila, two from themelanogaster and two from theimmigrans species group. The relationships among trait means across the five species did not conform to expectations based on correlations among these traits inferred from selection studies onD. melanogaster. In particular, the expected positive relationships between fecundity and size/lipid content, lipid content and starvation resistance, carbohydrate (glycogen) content and desiccation resistance, and the expected negative relationship between lifespan and fecundity were not observed. Most traits were strongly positively correlated between sexes across species, except for fractional lipid content and starvation resistance per microgram lipid. For most traits, there was evidence for significant sexual dimorphism but the degree of dimorphism did not vary across species except in the case of adult lifespan, starvation resistance per microgram lipid, and desiccation resistance per microgram carbohydrate. Overall,D. nasuta nasuta andD. sulfurigaster neonasuta (immigrans group) were heavier at eclosion than themelanogaster group species, and tended to have somewhat higher absolute lipid content and starvation resistance. Yet, these twoimmigrans group species were shorter-lived and had lower average daily fecundity than themelanogaster group species. The smallest species,D. malerkotliana (melanogaster group), had relatively high daily fecundity, intermediate lifespan and high fractional lipid content, especially in females.D. ananassae (melanogaster group) had the highest absolute and fractional carbohydrate content, but its desiccation resistance per microgram carbohydrate was the lowest among the five species. In terms of overall performance, the laboratory population ofD. melanogaster was clearly superior, under laboratory conditions, to the other four species if adult lifespan, lifetime fecundity, average daily fecundity, and absolute starvation and desiccation resistance are considered. This finding is contrary to several recent reports of substantially higher adult lifespan and stress resistance in recently wild-caught flies, relative to flies maintained for a long time in discretegeneration laboratory cultures. Possible explanations for these apparent anomalies are discussed in the context of the differing selection pressures likely to be experienced byDrosophila populations in laboratory versus wild environments. This paper is dedicated to the memory of our friend and former colleague Dr Hans Raj Negi, who tragically passed away at a very young age in a road accident in November 2003.     

Laboratory maintenance does not alter ecological and physiological patterns among species: a Drosophila case study

Large comparative studies in animal ecology, physiology and evolution often use animals reared in the laboratory for many generations; however, the relevance of these studies hinges on the assumption that laboratory populations are still representative for their wild living conspecifics. In this study, we investigate whether laboratory‐maintained and freshly collected animal populations are fundamentally different and whether data from laboratory‐maintained animals are valid to use in large comparative investigations of ecological and physiological patterns. Here, we obtained nine species of Drosophila with paired populations of laboratory‐maintained and freshly collected flies. These species, representing a range of ecotypes, were assayed for four stress‐tolerance, two body‐size traits and six life‐history traits. For all of these traits, we observed small differences in species‐specific comparisons between field and laboratory populations; however, these differences were unsystematic and laboratory maintenance did not eclipse fundamental species characteristics. To investigate whether laboratory maintenance influence the general patterns in comparative studies, we correlated stress tolerance and life‐history traits with environmental traits for the laboratory‐maintained and freshly collected populations. Based on this analysis, we found that the comparative physiological and ecological trait correlations are similar irrespective of provenience. This finding is important for comparative biology in general because it validates comparative meta‐analyses based on laboratory‐maintained populations.     

Correlates of timing of spring migration in birds: a comparative study of trans-Saharan migrants

The evolution of migratory strategies in birds is likely to have been influenced by ecological as well as socio-sexual factors in both wintering and breeding areas. In this comparative study, we analysed timing of spring passage of 38 long-distance migratory bird species that winter south of the Sahara desert and breed in Europe, in relation to wintering and breeding latitudes, moult strategy, nesting site (open vs. cavity), and sexual dimorphism in size and coloration, which may reflect intensity of sexual selection. We employed a large data set consisting of more than 190 000 individuals ringed during spring migration in the Mediterranean Sea. We found that the species that migrated earlier were those wintering farther north, nesting in cavities and showing the largest degree of sexual size dimorphism (SSD). However, sexual dichromatism was not related to migration date. Among passerine species, moulting wing-feathers in Africa delayed migration. We found no support for the energetic constraint hypothesis, which proposes that early arrival selects for large male size, since early arriving species were not larger than late arriving ones. Thus, the observed associations suggest that variation in migration schedules at the interspecific level may have evolved in relation to ecological factors and SSD, possibly reflecting the intensity of mating competition.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 199–210.     

Seed viability in Bursera: The relative contribution of environmental variation and phylogenetic relatedness

Seed viability is a crucial factor affecting the regeneration potential of seeds, but there is little information on how this trait varies across habitats, populations, species, and higher taxonomic units, as well as on the relative contributions of evolutionary history and environmental factors to this trait. Here we evaluate the relative contributions of climatic variability and phylogenetic history to seed viability in a group of species of Bursera that belong to two distinct lineages (sections Bursera and Bullockia). We analyzed 39 seed lots from 11 species, comprising several populations and 2 years, and estimated embryo presence and viability in each lot. We examined spatial and temporal variation in viability and analyzed the relationship between this trait and water availability using regression models; the amount of phylogenetic signal in seed viability was also estimated. Mean seed viability was consistently low in species of section Bursera (mean 29.7%) and substantially higher in species of section Bullockia (mean 79.6%). A high proportion of unviable seeds were embryoless. Spatial and temporal variation in seed viability was significant but usually low among populations and species. The relationship between water availability and seed viability was not significant, but the amount of phylogenetic signal in seed viability was high and significant (λ = 0.74). There is a clear difference in seed viability among the two sections of Bursera. During the split of the two sections in the middle Eocene, the reorganization of the genome may have involved changes in fruit morphology associated with differences in parthenocarpy among them.     

物种多度和径级尺度对于评价群落系统发育结构的影响: 以尖峰岭热带山地雨林为例

研究不同径级尺度群落系统发育多样性有助于了解不同年龄模式下物种的亲缘关系及其群落系统发育结构; 但是关于物种多度对群落系统发育结构影响的研究较少。以海南尖峰岭热带山地雨林群落为例, 首先在不同径级尺度比较物种多度加权与否分别对4个广泛采用的系统发育指数的影响, 继而利用其中2个经过标准化处理的系统发育多样性指数: 净种间亲缘关系指数(net relatedness index, NRI)和净最近种间亲缘关系指数(nearest taxon index, NTI), 结合群落的生境类型来量度不同局域生境条件下不同径级尺度木本植物系统发育关系。结果发现: (1)未考虑物种多度加权的系统发育平均成对距离(mean pairwise distance, MPD)指数比考虑物种多度加权的MPD指数显著地高估了群落整体系统发育多样性, 且这种现象在小径级尺度(1 cm≤DBH<5 cm)最为明显。因此, 在森林监测样地中对于中、小径级群落系统发育结构研究中建议考虑物种多度信息。(2) 从群落组成整体系统发育结构来看, 尖峰岭热带山地雨林在几乎所有径级尺度和生境下均倾向于系统发育发散, 且随着径级的递增发散程度趋于明显(NRI<0)。(3)从群落组成局部系统发育结构来看, 尖峰岭热带山地雨林在中、小径级倾向于系统发育聚集(NTI>0), 而在大径级(DBH≥15 cm)则倾向于系统发育发散(NTI<0)。总之, 研究群落系统发育结构时应考虑物种多度的影响以及径级尺度效应。     

Vegetation structure,species life span,and exotic status elucidate plant succession in a limestone quarry reclamation

An understanding of the processes involved in plant succession is pivotal in achieving an effective site restoration. In a former limestone quarry (northeastern Italy), we explored the effects of a technical reclamation on the plant community using changes in cover of vegetation layers and two sensitive plant traits (i.e. exotic status and life span), with a chronosequence approach. Four reclaimed areas of different ages (from 8 to 35 years old) and natural vegetation in the surroundings were investigated with seven permanent plots each, for a total of 35. Changes in vegetation layers and species richness of both exotic status and life span were analyzed by generalized linear (mixed) models. Relations with plant community assembly were also considered, using a multivariate approach. Both vegetation layers and plant traits were affected by the age of reclaimed areas, evidencing the main changes in plant succession. Annual and exotic species decreased toward the mature stages of reclamation and target vegetation, whereas overall plant diversity (species richness) was stable. Our findings show that both vegetation layer changes and plant traits can be used to assess the degree to which reclamation efforts produce results that approach the restoration of a natural vegetation reference. Implementation of management practices aimed at favoring native perennial species (e.g. appropriate seed mixtures, mowing, tree, and shrub planting) could limit weed‐control efforts, representing a reasonable trade‐off between biodiversity promotion and invasive plant control.     

Expression of sexual ornaments in a polymorphic species: phenotypic variation in response to environmental risk

Secondary sexual traits may evolve under the antagonistic context of sexual and natural selection. In some polymorphic species, these traits are only expressed during the breeding period and are differently expressed in alternative phenotypes. However, it is unknown whether such phenotypes exhibit phenotypic plasticity of seasonal ornamentations in response to environmental pressures such as in the presence of fish (predation risk). This is an important question to understand the evolution of polyphenisms. We used facultative paedomorphosis in newts as a model system because it involves the coexistence of paedomorphs that retain gills in the adult stage with metamorphs that have undergone metamorphosis, but also because newts exhibit seasonal sexual traits. Our aim was therefore to determine the influence of fish on the development of seasonal ornamentation in the two phenotypes of the palmate newt (Lissotriton helveticus). During the entire newt breeding period, we assessed the importance of phenotype and fish presence with an information‐theoretic approach. Our results showed that paedomorphs presented much less developed ornamentation than metamorphs and those ornamentations varied over time. Fish inhibited the development of sexual traits but differently between phenotypes: in contrast to metamorphs, paedomorphs lack the phenotypic plasticity of sexual traits to environmental risk. This study points out that internal and external parameters act in complex ways in the expression of seasonal sexual ornamentations and that similar environmental pressure can induce a contrasted evolution in alternative phenotypes.     

Altitudinal variation in sexual dimorphism: a new pattern and alternative hypotheses

The colder climate and disjunct distribution of nesting andforaging habitats at high elevations increases the necessityof biparental care for successful breeding in birds. If differencesin parental investment between the sexes correlate with intensityof sexual selection, the intensity of sexual selection shouldcovary with ecological factors associated with elevation. Iused sexual dimorphism as an indirect measure of intensity ofsexual selection and examined variation in sexual dimorphismin 126 extant species of cardueline finches. I controlled forphylogeny and potential confounding factors and tested the predictionthat the extent of sexual dimorphism negatively covaries withelevation of breeding. As predicted, interspecific variationin sexual dimorphism was more strongly associated with changesin elevation than with habitat, nest dispersion and placement,and migratory status. Species occupying lower elevations weremore sexually dimorphic in plumage than species at higher elevations.This variation was largely due to increased brightness of maleplumage at lower elevations. I address possible explanationsof this trend, which may include increased opportunities forextrapair fertilizations at lower elevations, an increase inthe cost of secondary sexual trait production (i.e., molt) andmaintenance at high elevations, and elevational variation inpredation pressure