Ecological gradient of sexual selection: elevation and song elaboration in finches

Ecological gradients in natural and sexual selection often result in evolutionary diversification of morphological, life history, and behavioral traits. In particular, elevational changes in habitat structure and climate not only covary with intensity of sexual selection in many taxa, but may also influence evolution of mating signals. Here we examined variation in courtship song in relation to elevation of breeding across cardueline finches-a subfamily of birds that occupies the widest elevational range of extant birds and shows extensive variation in life histories and sexual selection along this range. We predicted that decrease in sexual selection intensity with elevation of breeding documented in this clade would result in a corresponding evolutionary reduction in elaboration of courtship songs. We controlled for the effects of phylogeny, morphology, and habitat structure to uncover a predicted elevational decline in courtship song elaboration; species breeding at lower elevations sang more elaborated and louder songs compared to their sister species breeding at higher elevations. In addition, lower elevation species had longer songs with more notes, whereas frequency components of song did not vary with elevation. We suggest that changes in sexual selection account for the observed patterns of song variation and discuss how elevational gradient in sexual selection may facilitate divergence in mating signals potentially reinforcing or promoting speciation.     

Morphological dispersion of introduced Hawaiian finches: evidence for competition and a Narcissus effect

Summary Morphological analyses were conducted on finch species introduced to Oahu, Hawaii. As many as 25 species of finches representing four families (Emberizidae, Fringillidae, Ploecidae, Estrildidae) have been introduced to Oahu. Of these, 15 species currently have established wild populations. When compared with pools of 25 and 23 species introduced to Oahu, the 15 surviving species are morphologically overdispersed. This result is consistent with the hypothesis that competition has influenced the outcome of these introductions. We also tested the hypothesis that surviving introduced finches in one habitat (sugarcane fields) were morphologically overdispersed. When the seven surviving finch species found in sugarcane were compared with the pools of 25 and 23 species, they too were morphologically overdispersed. However, when the seven sugarcane species were compared with a species pool consisting of only the surviving 15 species found across Oahu, they were not morphologically overdispersed. This result suggests that morphological analyses of community structure based only on comparisons of assemblages of surviving species may be biased by a Narcissus effect.     

三种养殖模式下日本鳗鲡养成品的形质差异

随机选取池塘专养(M1)、日本沼虾套养(M2)以及水库放养(M3)3种养殖模式下培育的肛长为(25.91±3.26) cm的日本鳗鲡作为研究材料,比较了不同养殖模式下日本鳗鲡的形质指标,并采用聚类分析、主成分分析和判别分析等方法研究了3种养殖模式日本鳗鲡养成品的差异.结果表明:在所涉21项生物学指标和23项形质评价指数中,M1与M2之间具显著差异的分别为15项和14项,M1与M3之间具显著差异的分别为19项和18项,M2与M3之间具显著差异的分别为11项和8项;M1-M2、M1-M3、M2-M3之间的欧氏距离依次为1.433、3.516和2.167,均具显著差异;经主成分分析,提取到的5个特征值均大于1的主成分,累计贡献率达82.1％,其中第1主成分和第2主成分依次为与体型相关的肥瘦因子和与摄食行为相关的运动因子,后3个主成分为与营养状况有关的消化吸收因子,仅通过第1主成分便可较清晰地将3种养殖模式试验对象分开;采用逐步判别法,以判别贡献率较大的体宽/肛长、体长/肛长、净体积系数、鳔体积系数和肝系数为自变量,所建Fisher分类函数方程组可清晰区分3种模式的养殖群体,其判别准确率和综合判别准确率均为100％.     

Brain evolution and development: adaptation,allometry and constraint

Phenotypic traits are products of two processes: evolution and development. But how do these processes combine to produce integrated phenotypes? Comparative studies identify consistent patterns of covariation, or allometries, between brain and body size, and between brain components, indicating the presence of significant constraints limiting independent evolution of separate parts. These constraints are poorly understood, but in principle could be either developmental or functional. The developmental constraints hypothesis suggests that individual components (brain and body size, or individual brain components) tend to evolve together because natural selection operates on relatively simple developmental mechanisms that affect the growth of all parts in a concerted manner. The functional constraints hypothesis suggests that correlated change reflects the action of selection on distributed functional systems connecting the different sub-components, predicting more complex patterns of mosaic change at the level of the functional systems and more complex genetic and developmental mechanisms. These hypotheses are not mutually exclusive but make different predictions. We review recent genetic and neurodevelopmental evidence, concluding that functional rather than developmental constraints are the main cause of the observed patterns.     

Morphological differentiation within the Daphnia longispina group

Although morphological evolution is assumed to be slow within Daphnia species complexes, discontinuities in morphological space can be detected. Here, morphological data derived from females of genetically-defined clones (cf. Gießler et al., 1999) are presented, in order to estimate the genetic component of phenotypic variance under standardised laboratory conditions. Animals originated from clonal assemblages of pre-alpine lakes and ponds, and a remote lake in western Germany, covering a wide range of morphotypes known from the traditional species D. cucullata, D. galeata, D. hyalina, D. rosea, and a variety of interspecific hybrids. Phenotypic analyses were based on quantitative and qualitative morphological characters of females in the first and fifth instars. Morphological divergence between clones was analysed using discriminant analysis or multidimensional scaling and the significance of the morphological groupings was estimated using neighbour-joining trees and bootstrapping. All analyses confirmed that (a) phenotypic similarities among taxa change with instar, (b) in contrast to low genetic divergence, pronounced morphological divergence exists between animals separated on the lake/pond level favouring speciation by the habitat shift hypothesis.     

Morphological integration of fluctuating asymmetry in the mouse mandible

Morphological integration of fluctuating asymmetry (FA) was assessed for nine mandibular characters in random-bred house mice to test the hypothesis that there should be a significant integration or concordance of FAs at the population level, but not at the individual level. FA estimates for each of the nine characters were made for each of 16 subpopulations (two replicates each for mice varying in sex and age) and their correlations indicated a moderate level of integration (index of integration = 0.42). A matrix permutation test of the differences of the correlations within two (‘incisor’ and ‘muscle’) developmentally different character groups versus correlations between groups was significant, indicating the presence of morphological integration. Kendall's coefficient of concordance also indicated a significant population asymmetry parameter for FAs within the two character groups. Correlations among individual FA estimates were generally lower than those calculated from subpopulations, the index of integration being 0.21. The matrix permutation test failed to show significant morphological integration among individual FAs, but Kendall's coefficient of concordance was significant, indicating the presence of an ‘individual asymmetry parameter’ among the nine characters. Principal components analysis and canonical correlation analysis confirmed the overall higher level of integration of FAs among the subpopulations and within the two character groupings.     

Evolution of bite force in Darwin's finches: a key role for head width

Studies of Darwin's finches of the Galapagos Islands have provided pivotal insights into the interplay of ecological variation, natural selection, and morphological evolution. Here we document, across nine Darwin's finch species, correlations between morphological variation and bite force capacity. We find that bite force correlates strongly with beak depth and width but only weakly or not at all with beak length, a result that is consistent with prior demonstrations of natural selection on finch beak morphology. We also find that bite force is predicted even more strongly by head width, which exceeds all beak dimensions in predictive strength. To explain this result we suggest that head width determines the maximum size, and thus maximum force generation capacity of finch jaw adductor muscles. We suggest that head width is functionally relevant and may be a previously unrecognized locus of natural selection in these birds, because of its close relationship to bite force capacity.     

内蒙古中东部草原不同生境克氏针茅（Stipa krylovii Roshev.）种群的形态差异分析

对内蒙古中东部草原分布的克氏针茅进行了种群内和种群间的形态差异分析。结果表明：（1）种群内不同的形态性状存在不同程度的差异;（2）种群间生殖枝中的一部分形态性状以及营养枝高度和营养枝干重均存在较大差异;（3）每穗小花数、每穗籽粒数、每穗小穗数、生殖枝高、穗干重、生殖枝干重、每穗种子重、种子重/生殖枝重比等性状的变化趋势相同,均表现为随生境条件变差而增加,即在生殖上投入增加以增大适合度;（4）主成分分析表明穗长、种子重/生殖枝重比、每穗小花数、每穗籽粒数、生殖枝高、基盘长、第二芒柱长、营养枝高、千粒重、芒针长是不同种群差异的主要指标。这些形态性状的差异可以看作克氏针茅对不同生境的适应性表现。     

濒危植物夏蜡梅花的形态变异

研究了不同地理位置的3个夏蜡梅自然种群间以及种群内花部形态变异,并对3个种群进行聚类分析。结果表明：夏蜡梅花部表型性状在种群间和种群内都存在一定程度的变异;各性状总的平均变异系数在6.293（内瓣长）~46.90（花柄长）之间,种群间总的平均变异系数在13.430（DMS）~15.720 8（DLS）,因此认为夏蜡梅花的表型性状无论是在物种水平还是在种群水平都具有较丰富的表型多样性,其中又以大雷山种群最高;单因素方差分析显示：部分指标分化显著或极显著,13个指标在种群内的变异占了总变异的82.9%,这说明夏蜡梅种群内变异是表型变异的主要来源,由此可以推测遗传上的多样性是形成夏蜡梅花部形态变异的主导因素;种群间平均变异组分占了17.1%,表明花部形态在种群间存在一定程度的表型分化;聚类分析显示距离较近的大明山种群和龙须山种群先聚在一起,表型差异与地理距离之间存在显著正相关,经分析认为微生境的异质性和种群隔离以及遗传漂变均可能导致夏蜡梅种群间的表型分化;相关性分析显示部分性状之间存在显著的相关性。     

Walk the line: 600000 years of molar evolution constrained by allometry in the fossil rodent Mimomys savini

The allometric-constraint hypothesis states that evolutionary divergence of morphological traits is restricted by integrated growth regulation. In this study, we test this hypothesis on a time-calibrated and well-documented palaeontological sequence of dental measurements on the Pleistocene arvicoline rodent species Mimomys savini from the Iberian Peninsula. Based on 507 specimens representing nine populations regularly spaced over 600 000 years, we compare static (within-population) and evolutionary (among-population) allometric slopes between the width and the length of the first lower molar. We find that the static allometric slope remains evolutionary stable and predicts the evolutionary allometry quite well. These results support the hypothesis that the macroevolutionary divergence of molar traits is constrained by static allometric relationships.     

Electrophoretic differentiation in isolated populations of Lolium rigidum Gaud.

Sixteen wild populations of Lolium rigidum Gaud. were collected from island and mainland locations in Mediterranean Europe and western Asia. Five loci, controlling isozymes at four enzyme systems, were assayed on 60 plants per population using starch gel electrophoresis. Gene diversity measures and Nei’s genetic distance were calculated, and the relationships between the populations were analysed using principal component (PCA) and cluster analyses. All populations were found to show a gene diversity index that is consistent with that expected in a cross-fertilising species. The highest gene diversity measures were recorded in some of the island populations. Both PCA and cluster analysis grouped the Balearic Island populations together and separated the Spanish and Sardinian populations from any of the others. The results are discussed with respect to a number of theories of migration between populations, and in relation to the colonization history of each island. It is suggested that the preservation of these island populations in gene banks is important as part of a core collection of the species.     

Morphological variation among Betula nana (diploid), B. pubescens (tetraploid) and their triploid hybrids in Iceland

BACKGROUND AND AIMS: Introgressive hybridization between two co-existing Betula species in Iceland, diploid dwarf birch B. nana and tetraploid downy birch B. pubescens, has been well documented. The two species are highly variable morphologically, making taxonomic delineation difficult despite stable ploidy levels. Here an analysis is made of morphological variation within each ploidy group with an aim to establishing a reliable means to distinguish the species. METHODS: Plant materials were collected from 14 woodlands in Iceland. The plants were identified based on 2n chromosome numbers. Morphological variation in species-specific characters within each ploidy group was analysed qualitatively and quantitatively. The morphological index was based on eight discrete characters, whereas the multivariate analysis was based on nine leaf variables. KEY RESULTS: Of the 461 plants examined, 9.5 % were found to be triploid hybrids. The three ploidy groups were morphologically distinguishable but their variation overlapped. The diploid, triploid and tetraploid groups had average scores of 1.3, 4.1 and 8.3, respectively, in the morphology index scale from 0 (B. nana) to 13 (B. pubescens). A linear discriminant analysis also revealed significant separation among the three ploidy groups and the model assigned 96 % and 97 % of the B. nana and B. pubescens individuals correctly. The triploid hybrids were difficult to predict since only half of them could be assigned correctly. Leaf length was the most useful variable identifying triploid hybrids. Geographical patterns within the ploidy groups could partly be explained by differences in mean July temperature. CONCLUSIONS: Hybridization between B. nana and B. pubescens is widespread in Iceland. The species can be distinguished from each other morphologically, and from the triploid hybrids. The overlapping morphological variation indicates bidirectional introgression between the two species via triploid hybrids. Iceland could be considered a birch hybrid zone, harbouring genetic variation which may be advantageous in subarctic regions.     

Degrees of freedom in interspecific allometry: An adjustment for the effects of phylogenetic constraint

The data used in studies of bivariate interspecific allometry usually violate the assumption of statistical independence. Although the traits of each species are commonly treated as independent, the expression of a trait among species within a genus may covary because of shared common ancestry. The same effect exists for genera within a family and so on up the phylogenetic hierarchy. Determining sample size by counting data points overestimates the effective sample size, which then leads to overestimating the degrees of freedom that should be used in calculating probabilities and confidence intervals. This results in an inflated Type 1 error rate. Although some workers (e.g., Felsenstein [1985] Am. Nat. 125:1–15) have suggested that this issue may invalidate interspecific allometry as a comparative method, a correction for the problem can be approximated with variance components from a nested analysis of variance. Variance components partition the total variation in the data set among the levels of the nested hierarchy. If the variance component for each nested level is weighted by the number of groups at that level, the sum of these values is an estimate of an effective sample size for the data set which reflects the effects of phylogenetic constraint. Analysis of two data sets, using taxonomy to define levels of the nested hierarchy, suggests that it has been common for published studies of interspecific allometry to severely overestimate the number of degrees of freedom. Interspecific allometry remains an important comparative method for evaluating questions concerning individual species that are not similarly addressed by the format of most of the newer comparative methods. With the correction proposed here for estimating degrees of freedom, the major statistical weakness of the procedure is substantially reduced. © 1994 Wiley-Liss, Inc.     

Morphological and pollen differentiation in Solanum cardiophyllum ssp. cardiophyllum and S. cardiophyllum ssp. ehrenbergii

A multivariate analysis to differentiate morphologically the populations of wild potatoes Solanum cardiophyllum ssp. cardiophyllum and S. cardiophyllum ssp. ehrenbergii was carried out. An analysis of the morphology and the viability of pollen of these potato populations was also made. The results of the morphometric analysis indicate that both subspecies are phenetically different. The pollen grain shape and size in ssp. cardiophyllum are different in northern and southern populations. Pollen diameter is significantly different between subspecies. Based on these results we propose that these taxa should be considered as two separate species.  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 415–426.     

Morphological and genetic differentiation in anadromous smelt Osmerus mordax (Mitchill): disentangling the effects of geography and morphology on gene flow

Morphological analyses were combined with genetic analyses at nine microsatellite loci to examine the determinants of gene flow at 21 spawning locations of rainbow smelt Osmerus mordax along the east coast of Canada. Associations between morphology, geography and gene flow were examined using a computational geometric approach and partial Mantel tests. Significant barriers to gene flow and discontinuities in morphology were observed between Newfoundland and mainland Canada, as well as within Newfoundland samples. On regional scales, contrasting patterns were present with restricted gene flow between Newfoundland populations ( F _ST= c . 0·11) and high gene flow between mainland populations ( F _ST= c . 0·017). Within Newfoundland populations, geographic distance was significantly associated with gene flow ( r = 0·85, P < 0·001) contrasting mainland samples where gene flow was most associated with phenotypic divergence ( r = 0·33, P < 0·001). At large spatial scales, weak ( r = 0·19, P = 0·02) associations between gene flow and geographic distance were observed, and moderate associations were also observed between gene flow and morphology ( r = 0·28, P < 0·001). The presence of significant genetic isolation by distance in Newfoundland samples and the clear discontinuity associated with the Cabot Strait suggest geography may be the primary determinant of gene flow. Interestingly, the association between genetic and morphological divergence within mainland samples and overall, supports the hypothesis that gene flow may be moderated by morphological divergence at larger spatial scales even in high gene flow environments.     

Morphological variability among seven populations of brown trout, Salmo trutta L., in Greece

Morphological variation in five meristic and 21 morphometric characters was examined in the brown trout, Salmo trutta L., from seven distinct streams and rivers from N and NW Greece. Variation within each sample, estimated as the multivariate generalization of the coefficient of variation, did not vary substantially among the populations. The phenetic relationships of these populations were examined using the stepwise discriminant analysis. The taxonomic implications of these results are discussed.     

Geography of morphological differentiation in Asellus aquaticus (Crustacea: Isopoda: Asellidae)

We implemented a detailed morphometry and multivariate statistics to establish a general, large-scale racial differentiation in Asellus aquaticus (L.) sensu Racovitza. We ascertained that in surface populations a set of 11 morphometric characters might equivalently be represented by the pleopod respiratory area size alone. The analyses resulted in a distinct distribution pattern, with the large respiratory area populations disposed mainly along the Dinaric karst between southern Slovenia and western Macedonia and surrounded by the medium respiratory area morph, spatially irregularly substituted by the small area morph. This pattern is in contradiction with the distribution pattern of molecularly defined clades (as shown by Verovnik et al. 2005 ). We could find no ecological, hydrographical or paleogeographical explanations for such distribution pattern either. The only hypothetical explanation would be a preservation of the large respiratory area as a plesiomorphic character in the comparatively sheltered karst habitats, while throughout the easier accessible parts of the species range it was replaced by the 'modern' smaller area size. While a diminution of the respiratory area functionally means an increased sclerotization – hardening of pleopod IV–V exopodites, endopodites of pleopods III–V remain less sclerotized, probably respiratory and osmoregulatory functional.     

Altitudinal variation in behavioural thermoregulation: local adaptation vs. plasticity in California grasshoppers

We investigated the adaptive significance of behavioural thermoregulation in univoltine populations of the grasshopper Melanoplus sanguinipes along an altitudinal gradient in California using laboratory tests of animals raised under different temperatures. Trials consisted of continuous body temperature measurements with semi-implanted microprobes in a test arena, and observation and simultaneous recording of behavioural responses. These responses included mobility, basking and orientation of the body axes (aspect angle) towards a radiation source. Mobility and basking are determined by the altitudinal origin of the parental generation and not by the temperature treatments. With increasing altitude, individuals tend increasingly to raise body temperatures via mobility and increased basking. In contrast, body orientation towards the radiation source is influenced by the temperature treatments but not by the altitude of origin. Individuals experiencing higher temperatures during rearing show a lower tendency to lateral flanking. We conclude that body orientation responses are not adapted locally. In contrast other components of the behavioural syndrome that increase body temperature, such as mobility and basking, are adaptive in response to local selection pressure. The thermoregulatory syndrome of these grasshoppers is an important contribution to life-history adaptations that appropriately match season lengths.