A geometric morphometric appraisal of beak shape in Darwin's finches

Beak size and shape in Darwin's finches have traditionally been quantified using a few univariate measurements (length, depth, width). Here we show the improved inferential resolution of geometric morphometric methods, as applied to three hierarchical levels: (i) among seven species on Santa Cruz Island, (ii) among different sites on Santa Cruz for a single species (Geospiza fortis), and (iii) between large and small beak size morphs of G. fortis at one site (El Garrapatero). Our results support previous studies in finding an axis of shape variation (long/shallow/pointy vs. short/deep/blunt) that separates many of the species. We also detect additional differences among species in the relative sizes and positions of the upper and lower mandibles and in curvature of the mandibles. Small-scale, but potentially relevant, shape variation was also detected among G. fortis from different sites and between sympatric beak size morphs. These results suggest that adaptation to different resources might contribute to diversification on a single island.     

Inbreeding and interbreeding in Darwin's finches

Studies of inbreeding and interspecific hybridization are generally pursued separately with different metrics. There is a need to integrate them because they have the common goal of seeking an understanding of the genetic and ecological basis of fitness variation in populations. We use mean expected heterozygosity as an axis of variation on which to compare the fitness of inbreeding and hybridizing Darwin's finches (Geospiza scandens and G. fortis) relative to the fitness of matched outbred controls. We find that relative fitness of inbred finches is less than one in the 1991 cohorts of both species. Inbreeding depression is stronger in the species (G. scandens) with the lower genetically effective population size. Relative fitness of hybrids (backcrosses) in the same cohort of G. scandens is greater than one. Evidence of heterosis in G. fortis is mixed. Thus the two interbreeding species displayed somewhat different fitness patterns under the same set of environmental conditions. Hybridization may enhance fitness to different degrees by counteracting the effects of inbreeding depression, by other additive and nonadditive genetic effects, and by producing phenotypes well suited to exploit particular ecological conditions.     

Beak morphology and song features covary in a population of Darwin's finches (Geospiza fortis)

Animal mating signals evolve in part through indirect natural selection on anatomical traits that influence signal expression. In songbirds, for example, natural selection on beak form and function can influence the evolution of song features, because of the role of the beak in song production. In this study we characterize the relationship between beak morphology and song features within a bimodal population of Geospiza fortis on Santa Cruz Island, Galápagos. This is the only extant population of Darwin's finches that is known to possess a bimodal distribution in beak size. We test the hypothesis that birds with larger beaks are constrained to produce songs with lower frequencies and decreased vocal performance. We find that birds with longer, deeper, and wider beaks produce songs with significantly lower minimum frequencies, maximum frequencies and frequency bandwidths. Results from the analysis of the relationship between beak morphology and trill rate are mixed. Measures of beak morphology correlated positively with 'vocal deviation', a composite index of vocal performance. Overall these results support a resonance model of vocal tract function, and suggest that beak morphology, a primary target of ecological selection in Darwin's finches, affects the evolution of mating signals. We suggest that differences in song between the two modes of the distribution may influence mate recognition and perhaps facilitate assortative mating by beak size and population divergence.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 489–498.     

Phylogenetic relationships and morphological diversity in Darwin's finches and their relatives

Despite the importance of Darwin's finches to the development of evolutionary theory, the origin of the group has only recently been examined using a rigorous, phylogenetic methodology that includes many potential outgroups. Knowing the evolutionary relationships of Darwin's finches to other birds is important for understanding the context from which this adaptive radiation arose. Here we show that analysis of mitochondrial DNA sequence data from the cytochrome b gene confirm that Darwin's finches are monophyletic. In addition, many taxa previously proposed as the sister taxon to Darwin's finches can be excluded as their closest living relative. Darwin's finches are part of a well-supported monophyletic group of species, all of which build a domed nest. All but two of the non-Darwin's finches included in this clade occur on Caribbean islands and most are Caribbean endemics. These close relatives of Darwin's finches show a diversity of bill types and feeding behaviors similar to that observed among Darwin's finches themselves. Recent studies have shown that adaptive evolution in Darwin's finches occurred relatively quickly. Our data show that among the relatives of Darwin's finches, the evolution of bill diversity was also rapid and extensive.     

Intraspecific variation in fruit size and shape in Corema album (Ericaceae) along a latitudinal gradient: from fruits to populations

Plant trait variation can be the result of environmental variability, developmental instability, and plasticity, although it can also arise from previous selective pressures on fruit traits themselves or directly on their variation. We aimed to quantify fruit size and shape variability at within‐plant, among‐plant, among‐population, and among‐year levels. For 2 years, we measured fruit size and shape along the geographical range of Corema album, aiming to determine whether (1) the population level among‐plant variation is lower than within‐plant and among‐population variation and (2) the ratio of within‐plant to among‐plant variation follows a latitudinal pattern. Levels of fruit variation were in accordance with the reported mean levels for reproductive organs. Most variance concentrated on within‐ and among‐individual levels for size, showing higher values for among‐individual variation in fruit shape. Although fruit size retained important variation among populations, this source of variance was negligible for fruit shape. This difference could arise from contrasting mechanical or developmental constraints. Despite the marked climatic differences along the latitudinal range of the species, latitude did not affect the ratio of within‐ to among‐plant variation. We show that an analysis of the often‐disregarded sources of intraspecific variation can produce unexpected results that deserve further investigation.     

中国东部亚热带青冈果实形态变异的研究

青冈为我国亚热带地我广泛分布,并具有较强耐寒和耐瘠薄能力的少数几个常绿树种之一,以果实长度,宽度和体积作为果实大小的指标,宽／长作为果实形状的指标,对采自东部亚热带的１０个青冈和群果实形态进行了比较分析,结果如下：（１）青冈果实的大小和形状在种群间,种群内均存在着显著差异,变异幅度最大的是果实的体积（种群间的变异幅度ＣＶ１为５７．１％,种群间平均单粒果实体积的最大差异为３．５倍）其次为宽度（２１．     

Morphometrics of the callitrichid forelimb: A case study in size and shape

Mosimann and colleagues formulated a technique that distinguishes between size and shape, based on the concept of geometric similarity and the distinction between log size-and-shape and log shape variables. We extend these formulations in an examination of the forelimb of three callitrichid species (adultSaguinus oedipus, Saguinus fuscicollis, andCallithrix jacchus). We employ principal components analysis to explore the relationship between variance explained by size-and-shape versus shape alone. Independence of shape vectors is examined via correlation analysis. Then we use log shape data to construct intersample (species means) and total sample (between all paris of individuals) matrices of average taxonomic distances. These distance matrices are subjected to cluster analysis and principal coordinate ordinations. Results of principal components analysis suggest that after isometric size is removed, there remains sufficient shape information to discriminate among the three taxa. Careful examination and quantification of the relationships between shape and size suggest that size information (e.g., geometric mean) is fundamental for understanding shape differences within and among callitrichid species; in other words, most aspects of forelimb shape are significantly correlated with size. Contrary to conventional wisdom, we also demonstrate that such correlations are not spurious. Ordinations and clustering of log shape distance matrices (based on means and individuals) support the notion that, despite differences in size, the two tamarins are more similar in shape than either is toC. jacchus (despite size similarity betweenS. fuscicollis andC. jacchus). Although shape variation in the forelimb of calliirichids may have a functional component, the phylogenetic signal remains strong and serves to group individuals accordingly.     

Variation in foot size and shape in some British land snails and its functional significance

Live weight, and the length, breadth and surface area of the extended foot sole were measured in 24 species of British terrestrial snails. Allometric relationships between these variables are described, concentrating on the relationship between foot surface area and weight. Intraspecific foot area/weight relationships deviate from isometric expectation for several species; this may be attributed to density changes, foot-shape variation or the physical constraint imposed by shell aperture size.
The rate of increase of foot sole area with live weight among species is greater than expected under isometry, indicating that larger species partially compensate for the increase in foot loading (weight per unit foot area). The rate of whorl expansion of the shell is related to the deviations from the interspecific foot area/weight relationship, reinforcing the possibility that shell aperture area may limit foot size in some species. Foot ratio (foot length:foot width) is negatively related to live weight and foot loading.
The findings are discussed in relation to the known behaviour and microdistribution patterns of the species.     

Relationship between size and shape in the sexually dimorphic beetle Prosopocoilus inclinatus (Coleoptera: Lucanidae)

Male characters that are used for male−male combat are often developed and exaggerated, whereas female equivalent characters are vestigial or vanished. In order to assess whether the characters common to both sexes share the same phenotypic variability due to common genetic architecture, we compared males and females of the stag beetle Prosopocoilus inclinatus using recently developed geometric morphometric methods. Elliptic Fourier analysis was used to compare shape variation between male characters (including exaggerated mandibles) and developmentally homologous female characters. A significant positive correlation was found between the size or between the weight of different body parts in both sexes, but a conspicuous difference was detected in the frequency distribution of the weight of all the body parts. Elliptic Fourier analysis demonstrated that there was marked discontinuous variation in mandibles in males, whereas such a discontinuity was not clear in females. The shape of a character in males exhibited some similarity with that of other characters, but this was not found in females. In a character, growth trajectory of shape was significantly affected by both size and weight in males, whereas size and shape tended to vary independently in female characters. These results support the hypothesis that a large sexual dimorphism in variation in shape is due to alleles accumulating in tight linkage with a sex-determining gene.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 219–233     

Island area,body size and demographic history shape genomic diversity in Darwin's finches and related tanagers

Genomic diversity is the evolutionary foundation for adaptation to environmental change and thus is essential to consider in conservation planning. Island species are ideal for investigating the evolutionary drivers of genomic diversity, in part because of the potential for biological replicates. Here, we use genome data from 180 individuals spread among 27 island populations from 17 avian species to study the effects of island area, body size, demographic history and conservation status on contemporary genomic diversity. Our study expands earlier work on a small number of neutral loci to the entire genome and from a few species to many. We find significant positive correlation between island size and genomic diversity, a significant negative correlation between body size and genomic diversity, and that historical population declines significantly reduced contemporary genomic diversity. Our study shows that island size is the key factor in determining genomic diversity, indicating that habitat conservation is key to maintaining adaptive potential in the face of global environmental change. We found that threatened species generally had a significantly smaller values of Watterson's theta (θ_W = 4N_eμ) compared to nonthreatened species, suggesting that θ_W may be useful as a conservation indicator for at‐risk species. Overall, these findings (a) provide biological insights into how genomic diversity scales with ecological, morphological and demographic factors; and (b) illustrate how population genomic data can be leveraged to better inform conservation efforts.     

Body size and allometric variation in facial shape in children

Objectives

In group‐living primates, it has been reported that the alpha male exhibits high concentrations of cortisol and testosterone in the context of mating competition. We investigated how the presence of females affected salivary cortisol and testosterone levels in males from a small captive group of chimpanzees (Pan troglodytes). Specifically, we assessed whether the presence of females resulted in a rapid increase in salivary cortisol and testosterone levels in the alpha male.

Materials and methods

We compared the social behavior and salivary hormone concentrations of four males before and after the presentation of receptive females. Three times a day, we collected saliva samples, a useful matrix for investigating short‐term hormonal changes, and measured cortisol and testosterone concentration by liquid chromatography–tandem mass spectrometry (LC–MS/MS).

Results

The frequency of inter‐male aggression increased in the presence of females, indicating intense competition among males. Salivary cortisol levels increased in all males in the presence of females; however, the increase was significantly more pronounced in the alpha male. We found a complex three‐way interaction among the presence of females, sampling timings, and male dominance rank in the analysis of salivary testosterone. Contrary to our prediction, a post hoc analysis revealed that salivary testosterone levels decreased after female introduction and that the alpha male did not show a higher level of salivary testosterone.

Conclusions

Our study provides experimental evidence suggesting that the presence of females plays a significant role in the rank‐related variation in the cortisol levels in male chimpanzees. Furthermore, our findings demonstrate the usefulness of salivary hormones for detecting short‐term physiological changes in studies of socioendocrinology.

     

Differential sexual dimorphism: size and shape in the cranium and pelvis of grey foxes (Urocyon)

Patterns of sexual size dimorphism (SSD) and cranial dimorphism are well documented. However, limited examinations exist of the contrasts in the patterns and nature of dimorphism across body regions (e.g. cranium, pelvis), particularly when these regions have different sex-specific functions (e.g. display in mating, locomotion, and reproduction). Using landmark-based morphometric techniques, we investigated size and shape dimorphism variation in the crania and pelves of two closely-related fox species within the genus Urocyon . Although we found no significant size and shape dimorphism in the crania of either species, we did find significant dimorphism in the pelvis: its size was dimorphic in Urocyon littoralis (but not in Urocyon cinereoargenteus ) and its shape was dimorphic in both species (though more pronounced in U. littoralis ). The observation of greater dimorphism in the pelvis than in the cranium suggests that factors such as offspring size and locomotor mode play a greater role in sexual dimorphism than simple 'whole body' allometric affects associated with dimorphism in body size.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 339–353.     

北京地区植被景观中斑块形状的指数分析

选取４个斑块形状指数（斑块的击长面积比ＳＩ１、斑块周长与等面积的圆周长之比ＳＩ２和身份个斑块分维ＳＩ３和ＳＩ４）并借助ＧＩＳ软件ＡＲＣ／ＩＮＦＯ对北京地区植被景观中的斑块形状进行分析,又地这四个形状指数进行 ｅａｒｓｏｎ相关分析和Ｓｐｅａｒｍａｎ秋相关分析,结果表明,ＳＩ１与ＳＩ４,ＳＩ２与ＳＩ３两两之间均呈显著的正的秩相关,ＳＩ１与ＳＩ２,ＳＩ２与ＳＩ４,ＳＩ３与ＳＩ４两两之间于垢负和秩相关。因     

Darwin's finches and their diet niches: the sympatric coexistence of imperfect generalists

Adaptive radiation can be strongly influenced by interspecific competition for resources, which can lead to diverse outcomes ranging from competitive exclusion to character displacement. In each case, sympatric species are expected to evolve into distinct ecological niches, such as different food types, yet this expectation is not always met when such species are examined in nature. The most common hypotheses to account for the coexistence of species with substantial diet overlap rest on temporal variation in niches (often diets). Yet spatial variation in niche overlap might also be important, pointing to the need for spatiotemporal analyses of diet and diet overlap between closely related species persisting in sympatry. We here perform such an analysis by characterizing the diets of, and diet overlap among, four sympatric Darwin's ground finch species at three sites and over 5 years on a single Galápagos island (Santa Cruz). We find that the different species have broadly similar and overlapping diets – they are to some extent generalists and opportunists – yet we also find that each species retains some ‘private’ resources for which their morphologies are best suited. Importantly, use of these private resources increased considerably, and diet overlap decreased accordingly, when the availability of preferred shared foods, such as arthropods, was reduced during drought conditions. Spatial variation in food resources was also important. These results together suggest that the ground finches are ‘imperfect generalists’ that use overlapping resources under benign conditions (in space or time), but then retreat to resources for which they are best adapted during periods of food limitation. These conditions likely promote local and regional coexistence.     

How to tweak a beak: molecular techniques for studying the evolution of size and shape in Darwin's finches and other birds

A flurry of technological advances in molecular, cellular and developmental biology during the past decade has provided a clearer understanding of mechanisms underlying phenotypic diversification. Building upon such momentum, a recent paper tackles one of the foremost topics in evolution, that is the origin of species-specific beak morphology in Darwin's finches.1 Previous work involving both domesticated and wild birds implicated a well-known signaling pathway (i.e. bone morphogenetic proteins) and one population of progenitor cells in particular (i.e. cranial neural crest), as primary factors for establishing beak size and shape. But these results were limited in their ability to explain fully the morphogenetic bases of patterned outgrowth. So in a quest to identify novel genes whose expression correlated with differences in beak anatomy among Darwin's finches, a DNA microarray approach was undertaken using tissues harvested from the Galápagos Islands. The results are striking and point to a protein called calmodulin, which is a mediator of cellular calcium signaling, as a key determinant of beak length.     

Associations with habitat versus geographic cohesiveness: size and shape of Bembicium vittatum Philippi (Gastropoda: Littorinidae) in the Houtman Abrolhos Islands

In the Houtman Abrolhos Islands, Western Australia, the direct-developing littorine snail Bembicium vittatum occupies a wide range of habitats, which are replicated across the three major groups of islands. Earlier studies showed that allozyme similarities followed patterns related to gene flow, independent of habitat, providing an excellent opportunity to test for associations with habitat for traits more likely to be adaptively important. As the first test for adaptive divergence, we examined variation in size and shape of shells among 131 populations in the Abrolhos Islands. Two-fold variations were found in width of adults, the allometric coefficient of height with width, and shell height scaled to a standard width. Quantification of habitat characteristics was summarized by principal components analysis. In contrast with the patterns of divergence for allozymes, shell height, adjusted for width, was strongly associated with habitat: flatter shells are found on exposed, vertical shores, while domed, more globose shells predominate in sheltered sites. This association was stronger for shape of adult-sized snails than for height scaled to an arbitrary size, highlighting the importance of using biologically relevant measures. Even highly isolated and allozymically less variable populations in tidal ponds conformed to this association. Because differences in shape are highly heritable in B. vittatum , this association of shape with habitat, independent of patterns of gene flow, indicates local adaptation. Shell size also varied with habitat, but because growth rate is highly plastic, variation in size cannot be interpreted simply in terms of adaptation. Nevertheless, the pattern of variation indicates that, within realized limits, larger size is generally favourable, but may be constrained by local conditions. Thus, variation in size signals the potential for adaptive divergence of life histories among the many, isolated populations of this species.     

Variation of distal genitalia in the simultaneously hermaphroditic land snail Arianta arbustorum (Pulmonata,Stylommatophora) caused by sexual selection?

The most likely explanation for genitalic extravagance may be sexual selection acting either before, during, or after copulation. In promiscuous species, the intensity of postulating sexual selection may be a function of population density. In this study we examined the variability of the distal genitalia involved in spcrmatophore production, reception and manipulation of 113 adult individuals of the simultaneously hermaphroditic land snail Arianta arbustorum (L.) from six natural populations in the Eastern Alps (Gesause, Austria). We investigated the hypothesis that these genitalia increase in relation to shell size with increasing population density (range: 0.9 to 39.8 individuals/m²) and expected a higher variance of the genitalia compared to shell dimensions due to sexual selection. Genitalic size was unexpectedly inversely related to population density, probably due to increased inhibitor)^- effects of snail mucus. Patterns of variation of female and male characters did not differ. Coefficients of variation of the genitalia were significantly higher than those of the shell dimensions as predicted. This was due to a higher dispersion around the regression lines rather than higher allometric values. However, the influence of sexual selection on genitalic size and variance cannot be unambiguously determined. We discuss different scenarios emphasizing the importance of sexual selection to differing degrees and conclude that sexual selection has probably played only a minor role.