Multivariate variation in feral American mink (Mustela vison) from Southern Norway

Multiple group principal component analysis was used to investigate the morphological relationships between feral American mink from three areas of Southern Norway based on 15 skull dimensions. The first principal axis calculated from the variance-covariance matrix of log-transformed data is usually interpreted as a growth axis. In the present analysis, the scores of the first principal axis of males were found to be uncorrelated with estimated age for specimens younger than seven months old, and was interpreted as a growth-free size axis. However, the second component of males was found to reflect mainly growth in the postorbital area. The first component of females was thought to reflect a mixing of growth-out and growth-in size variation. One of the reasons for separating size and size-free variation in the present work was to test whether growth-dependent size influenced the assessment of geographic variation within each sex. The scores on the components reflecting size variation (growthout and growth-in) were, however, not found to deviate significantly between the areas. Discriminant analyses run on the component scores, both with size variation included and excluded, gave the same result. In mean, the mink from Western Norway deviated significantly from the mink from Trondelag and Eastern Norway, while the mink from the two latter areas did not deviate morphometrically. The deviation found was in shape rather than in size of both sexes.     

猕猴属种间颅骨差异的探讨

为了研究狒猴属的颅骨差异性,从面探讨种间在形态、功能和系统分化方面联系,测定了１１１个猕猴种类的７７个颅骨变量,用于主成分分析和判别分析。应用巢式分析方法,分析过程包括３个步骤。所有变量根据功能和部位的不同首先分为７个单位：下颌、下颌齿、上颌齿、上面颅、下面颅,、面颅后部和颅腔。第２步根据它们所揭示的相似性（具有相同的种间及种内差异性类型）合并为３个解剖区域：咀嚼器官（下颌、下颌齿、上颌齿）,面颅     

Size,shape, and sex‐dependent variation in force production by crayfish chelae

The ability to generate large closing forces is important for many animals. Several studies have demonstrated that bite or pinching force capacity is usually related to the linear dimensions of the closing apparatus. However, relatively few studies have applied geometric morphometrics to examine the effects of size‐independent shape on force production, particularly in studies of crustacean pinching force. In this study, we utilized traditional and geometric morphometric techniques to compare the pinching force of Procambarus clarkii crayfish to their chela morphology. We found that males possessed larger chelae and pinched harder than females, but that their chela shape and size were weak predictors of strength. Female pinching force was significantly affected by both chela size and shape, with shape variation along the short axis of the claw contributing most to pinching force. We discuss our results in the context of reliable signaling of strength by males and females, and the different selective forces acting on chela shape in the two sexes.     

Size, shape and structural versatility of the skull of the subterranean rodent Ctenomys (Rodentia, Caviomorpha): functional and morphological analysis

Morphological analysis of the skull of the subterranean rodent Ctenomys , a highly speciose genus which uses both claws and teeth when digging, shows that for a broad range of species size, scaling was associated with both variation and maintenance of shape. Our results show that the angle of incisor procumbency (AIP), a character largely viewed as an adaptation to digging with teeth, is highly variable. We found a non-significant relationship between AIP and basicranial axis (basioccipital + basisphenoid) length, a measure of overall skull size. Accordingly, both small and large Ctenomys species possess either high or low AIP. A significant relationship between AIP and diastema length, given the rostral allometry seen in Ctenomys , suggests that hypermorphosis to a certain extent influences AIP. However, the roots of the incisor are lateral to those of the cheek teeth and their position may thus shift freely. This observation supports the notion that skull structural design, and to a certain extent rostral allometry, underlies variation in AIP. On the other hand, the positive allometry of incisor width and thickness indicates that, in larger species, proportionately powerful incisors are able to resist greater bending forces. We found that the out-lever arm of the jaw adductor muscles scales with positive allometry against basicranial axis length. However, we found an isometric relationship between in- and out-lever arms. In this case, conservation of skull proportions, regardless of variation in size, is a feature possibly related to the maintenance of an effective tooth digging capability. Functional and ecological data are discussed when assessing the implications of size and shape variation in the skull of Ctenomys .  © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 78 , 85−96.     

A geometric morphometric approach to the study of ecogeographical and clinal variation in vervet monkeys

Aim To examine and visualize clines in size and shape of Cercopithecus aethiops Linneus, 1758 (Primate, Cercopithecidae) skulls, and to investigate environmental factors which might best explain the observed variation. Location Sub‐Saharan Africa. Methods Eighty‐six three‐dimensional anatomical landmarks were used to describe 306 skulls of adult C. aethiops sampled over its entire distribution. Geometric morphometric methods for the quantitative analysis of form variation were applied. Size and shape variables were computed and regressed onto geographical coordinates and environmental variables (elevation, temperature, rainfall, moisture and Shannon rainfall diversity index) using both linear and curvilinear models. Components (geographical, environmental, spatially structured environmental and residual) of ecogeographical variation in skull form were partitioned using partial regression. A novel approach for summarizing and visualizing nonlinear patterns of clinal variation using surface rendering of three‐dimensional shapes is presented. Results Clinal variation in size and shape was highly significant, and was best described by curvilinear models. There were strong similarities between females and males. The cline in size was especially pronounced, explaining up to about 40% of observed variation, and was mainly longitudinal rather than latitudinal. A major trend of clinal shape variation also occurred from west to east, and corresponded to an expansion of the face relative to the neurocranium in the west. In the east, skulls also tended to be deeper and with narrower zygomatic arches. Geography and the spatially structured environmental component were the major contributors to the explained variance in size in both sexes, but the proportion of variance explained by the latter was smaller in females. In contrast, geography and environment explained similar amounts of variation in shape and their contribution was about twice that of the spatially structured environmental component. About 60–80% of variation in skull form was not explained by any variable in the analysis. The main factors influencing skull size differed in females and males, with rainfall being very influential in males. Both female and male skull shapes were strongly affected by average annual rainfall. Main conclusions A strong spatial and environmental basis to variations in African vervet monkey skull form was evident. However, the observed pattern did not conform to predictions based on Bergmann's rule. Rainfall consistently emerged as an important predictor, which may contribute to intraspecific variation in the size and shape of vervet monkey skulls through its effect on habitat productivity.     

Variation in guenon skulls (II): sexual dimorphism

Patterns of size and shape sexual dimorphism in adult guenons were examined using a large sample of skulls from almost all living species. Within species, sexual dimorphism in skull shape follows the direction of size-related shape variation of adults, is proportional to differences in size, and tends to be larger in large-bodied species. Interspecific divergence among shape trajectories, which explain within species sex differences, are small (i.e., trajectories of most species are nearly parallel). Thus, changes in relative proportions of skull regions that account for the distinctive shape of females and males are relatively conserved across species, and their magnitude largely depends on differences in size between sexes. A conservative pattern of size-related sexual dimorphism and a model of interspecific divergence in shape which strongly reflects size differences suggest a major role of size and size-related shape variation in the guenon radiation. It is possible that in the guenons, as in the neotropical primates (with whom they have obvious parallels), size has helped to determine morphological change along lines of least evolutionary resistance, influencing sexual dimorphism. In Miopithecus and Erythrocebus, the smallest and largest guenon genera, it is likely that the interaction of ecology and size contributes significantly to patterns of sexual dimorphism. The results of this study thus emphasise the need to consider allometry and size alongside ecology and behaviour when examining primate sexual dimorphism.     

Cranial capacity/cranial base relationships and prediction of vault form: A canonical correlation analysis

Canonical correlation analysis was used to test an hypothesized morphological relationship between vault form and cranial capacity relative to length of the chondrocranium. Ninety-five adult male Czech skulls were measured for vault form expressed as length, width and height of the brain case; the chondrocranium was represented by nasion-basion and basion-opisthion lengths. In terms of explained variation, the first and most important dimension of covariation between vault and chondrocranial variables was size. The second most significant dimension of covariation expressed the hypothesized shape relationships—i.e., overall size being equal, the shorter the chondrocranial base relative to cranial capacity, the shorter and wider the vault. Furthermore, the competing hypothesis that vault form is determined by facial length proved untenable since facial length was predictive of vault shape only when measured as prosthion-basion, a measure that incorporates basal length. When corrected for basal length, facial length is unrelated to vault form. The results are consistent with the assumption that phylogenetic and microevolutionary trends toward brachycephaly in man stem from changes in the relationship between two components of skull growth, the chondrocranial base and the brain.     

Surface facial modelling and allometry in relation to sexual dimorphism

Sexual dimorphism is responsible for a substantial part of human facial variability, the study of which is essential for many scientific fields ranging from evolution to special biomedical topics. Our aim was to analyse the relationship between size variability and shape facial variability of sexual traits in the young adult Central European population and to construct average surface models of adult males and females. The method of geometric morphometrics allowed not only the identification of dimorphic traits, but also the evaluation of static allometry and the visualisation of sexual facial differences.Facial variability in the studied sample was characterised by a strong relationship between facial size and shape of sexual dimorphic traits. Large size of face was associated with facial elongation and vice versa. Regarding shape sexual dimorphic traits, a wide, vaulted and high forehead in combination with a narrow and gracile lower face were typical for females. Variability in shape dimorphic traits was smaller in females compared to males. For female classification, shape sexual dimorphic traits are more important, while for males the stronger association is with face size.Males generally had a closer inter-orbital distance and a deeper position of the eyes in relation to the facial plane, a larger and wider straight nose and nostrils, and more massive lower face. Using pseudo-colour maps to provide a detailed schematic representation of the geometrical differences between the sexes, we attempted to clarify the reasons underlying the development of such differences.     

Basicranial axis length v. skull length in analysis of carnivore skull shape

Skull length is the measurement most commonly used as a standard against which other aspects of cranial morphology are compared to derive an index of relative size or proportions. However, skull length is composed of two different functional components, facial skull and cerebral skull, which vary independently and have different scaling relationships with body size. An analysis of carnivore skull shape with measurements standardized against basicranium length produced very different results than an analysis using skull length as the standard. For example, expressions of relative size of cranial measurements were reduced by 13% in mustelids and increased by 20% in canids, reflecting removal of jaw length (short in mustelids and long in canids) from the comparative standard (basicranial axis length). Cranial measurements scale with higher allometric exponents against basicranial axis length than against skull length.     

Size,shape and sex differences in three subspecies of Black-tailed Godwits Limosa limosa

ABSTRACT

Capsule: Black-tailed Godwits Limosa limosa show sexual size dimorphism and size differences between the subspecies. The shape varies slightly between the subspecies, but not between the sexes.

Aims: To investigate whether and how the three subspecies of Black-tailed Godwits, and the sexes of these subspecies, differ in size and shape.

Methods: We collected body dimensions (lengths of the bill, total head, tarsus, tarsus-toe and wing) of adult Black-tailed Godwits from three locations (Iceland, the Netherlands and northwest Australia) corresponding to the breeding or wintering grounds of three known subspecies (islandica, limosa and melanuroides, respectively). Determining sex by molecular assays, we computed degrees of sexual size dimorphism. Using principal component analysis (PCA), we compared differences in size and shape among the different subspecies.

Results: The limosa subspecies was the largest and also showed the most significant sexual size dimorphism. Sexual size dimorphism was smallest for wing length and largest for bill length. The first two axes of the PCA that included all subspecies of both sexes explained 94% of the total variation. Most body dimensions were highly correlated with each other, but wing length varied independently of the other dimensions. Males and females differed only in size (the first axis). However, one of the two small subspecies, islandica, also differed in shape (the second axis) from limosa and melanuroides.

Conclusions: In all three subspecies of Black-tailed Godwits, females are larger than males. The fact that subspecies differed in the degree of size dimorphism and slightly in shape hints at sex-related differences in the ecological selection pressures between the different flyways.     

Divergent abdominal bristle patterns in two distantly related drosophilids: antero-posterior variations and sexual dimorphism in a modular trait

The number of neurosensory bristles on abdominal sternites of Drosophila is a most investigated trait for quantitative genetic studies. However, the developmental pattern expressed on successive segments in both sexes has remained so far a neglected field. We explored three aspects of this general problem with an isofemale line design: comparing two distantly related species, Drosophila melanogaster and Zaprionus indianus, investigating bristle number variation along the antero-posterior axis, and analysing the sexual dimorphism. Antero-posterior variations could be analysed from segment A2 to A7 in females, and A2-A5 in males. In D. melanogaster, males and females showed parallel changes with a consistently lower number in males. In Z. indianus females the number was quite stable along the abdomen, while in males an important antero-posterior increase was found. The sexual dimorphism was further analysed by considering the female-male correlation and the female/male ratio. The results suggest that sternite bristle number is determined by several developmental genetic systems. One is acting along the antero-posterior axis and may be associated to a gradient, since the genetic correlation decreases when more distant segments are compared. Another is acting in the same way on most segments of both sexes, since the female-male genetic correlation is similar between homologous and non-homologous segments. Finally, genes with specific sex effects are acting on A7 in females of both species, and on A5 in Z. indianus males. The overall architecture of female and male abdomen seems to be constrained by the development of reproductive organs. A large difference between species suggests, however, that the sexual dimorphism of abdominal bristle number is not evolutionarily constrained.     

SEXUAL DIMORPHISM IN BOTTLENOSE DOLPHINS FROM THE EAST COAST OF FLORIDA

Skulls of 69 bottlenose dolphins (genus Tursiops ) from the Indian/Banana River on the east coast of Florida were examined for evidence of sexual dimorphism. The only sexual dimorphism shown by t -tests on 28 morphological and four meristic skull characters was that males have, on average, more teeth than females in all four arcades. Results of covariance analysis, employed to account for variation in size, indicate minor dimorphism in parietal width of the skull. Twenty body measurements of 29 Tursiops originating in the same area were also analysed for differences between males and females. Statistical results indicate the possibility of sexual dimorphism in the length from the snout to the umbilicus and in flipper width. No evidence was found for differences in overall skull or body length between the sexes.     

Patterns of sexual dimorphism in the Persian Leopard (Panthera pardus saxicolor) and implications for sex differentiation

Extant felids show a high degree of inter-sexual dimorphism, meaning significant size differences between males and females. Such a differentiation may have various ecological, behavioural and evolutionary implications, at both species and subspecies levels. We have investigated the sexual size differences in one of the most dimorphic felids, i.e. the Leopard (Panthera pardus), based on 63 craniometric and 55 morphometric samples from Iran which belong to the subspecies Persian Leopard (P. p. saxicolor). In order to explore patterns of sexual dimorphism, multivariate statistical analysis on 24 skull variables as well as univariate approaches for two body measurements were applied. We found significant inter-sexual differences in skull size whereas it was not meaningful after removing the effect of size to address skull shape. Moreover, inter-sexual differentiation was also remarkable when comparing morphometric body measurements in adults, showing that the males possess a larger head mass and longer body, but sub-adults did not show any remarkable differentiation between sexes. A combination of craniometric and morphological features is proposed for sex differentiation in Leopards.     

From Desert to Rainforest: Phenotypic Variation in Functionally Important Traits of Bushy-Tailed Woodrats (Neotoma cinerea) Across Two Climatic Extremes

Changes in body size inversely related to ambient temperatures have been described in woodrats (Neotoma) over time scales ranging from decades to millennia. However, climate-mediated variation in other traits has not been evaluated, and the effects of precipitation have been overlooked. We assessed variation in skull morphology among bushy-tailed woodrats (Neotoma cinerea) over two sampling transects spanning coastal rainforest and interior desert environments to determine whether skull morphology varied with climate. We also tested whether previously described size-temperature relationships could be generalized to our study populations. In both transects, linear measurements of functionally significant traits differed between coastal and interior populations. Geometric morphometric analyses of shape confirmed some of those differences and revealed additional patterns of skull variation. Variation in some linear measurements, including body size, was predicted by climate. However, body and skull size, as well as measurements of skull components, displayed varying responses. Although longitudinal patterns of body size variation supported Bergmann’s rule, skull size variation was only weakly associated with climate. The strongest phenotypic responses to climate were those of auditory, dental, and palatal skull traits. Altogether, our findings suggest that geographic variation in temperature and precipitation mediated selective heterogeneity and plasticity in skull traits associated with food processing and sensory organs in N. cinerea. This was consistent with our expectation of resource-dependent phenotypic variation among populations in environments with highly contrasting climatic regimes.     

Functional basis for sexual differences in bite force in the lizard Anolis carolinensis

In many species of lizards, males attain greater body size and have larger heads than female lizards of the same size. Often, the dimorphism in head size is paralleled by a dimorphism in bite force. However, the underlying functional morphological basis for the dimorphism in bite force remains unclear. Here, we test whether males are larger, and have larger heads and bite forces than females for a given body size in a large sample of Anolis carolinensis . Next, we test if overall head shape differs between the sexes, or if instead specific aspects of skull shape can explain differences in bite force. Our results show that A. carolinensis is indeed dimorphic in body and head size and that males bite harder than females. Geometric morphometric analyses show distinct differences in skull shape between males and females, principally reflecting an enlargement of the jaw adductor muscle chamber. Jaw adductor muscle mass data confirm this result and show that males have larger jaw adductors (but not jaw openers) for a given body and head size. Thus, the observed dimorphism in bite force in A. carolinensis is not merely the result of an increase in head size, but involves distinct morphological changes in skull structure and the associated jaw adductor musculature.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 111–119.     

A Test of Rensch’s Rule in Greater Horseshoe Bat (Rhinolophus ferrumequinum) with Female-Biased Sexual Size Dimorphism

Sexual size dimorphism (SSD) is widespread within the animal kingdom. Rensch’s rule describes a relationship between SSD and body size: SSD increases with body size when males are the larger sex, and decreases with body size when females are the larger sex. Rensch’s rule is well supported for taxa that exhibit male-biased SSD but patterns of allometry among taxa with female-biased size dimorphism are mixed, there is evidence both for and against the rule. Furthermore, most studies have investigated Rensch’s rule across a variety of taxa; but among-population studies supporting Rensch’s rule are lacking, especially in taxa that display only slight SSD. Here, we tested whether patterns of intraspecific variation in SSD in greater horseshoe bats conform to Rensch’s rule, and evaluated the contribution of latitude to Rensch’s rule. Our results showed SSD was consistently female-biased in greater horseshoe bats, although female body size was only slightly larger than male body size. The slope of major axis regression of log₁₀ (male) on log₁₀ (female) was significantly different from 1. Forearm length for both sexes of greater horseshoe bats was significantly negatively correlated with latitude, and males displayed a slightly but nonsignificant steeper latitudinal cline in body size than females. We suggest that variation in patterns of SSD among greater horseshoe bat populations is consistent with Rensch’s rule indicating that males were the more variable sex. Males did not have a steeper body size–latitude relationship than females suggesting that sex-specific latitudinal variation in body size may not be an important contributing factor to Rensch’s rule. Future research on greater horseshoe bats might best focus on more comprehensive mechanisms driving the pattern of female-biased SSD variation.     

浙江丽水虎纹蛙形态特征的两性异形和食性

用数显游标卡尺测量了407只2001—2003年9月下旬至10月上旬浙江丽水罚没的死亡虎纹蛙的体长等10个形态指标,结果表明:雌性成体体长(SUL)大于雄性成体,幼体形态无显著两性差异;ANCOVA去除SUL差异的影响后,雌性成体的头长和后肢长大于雄性成体,前肢长、眼径和耳径则小于雄性成体。前肢两侧对称性的偏移度成体大于幼体,雌性大于雄性;后肢两侧对称性成幼体和两性无显著差异。10个形态指标主成分分析的前三个主成分共解释64·6%的变异:第一主成分中头宽、眼径和耳径,第二主成分中后肢长,第三主成分中眼间距和鼻间距分别有较高的正负载系数。用NikonSMZ-1000解剖镜鉴别277只个体胃内容物中的食物种类,发现其秋季食物以节肢动物为主;成幼体和两性食物生态位宽度为3·42~5·25,食物生态位重叠度较高为0·93~0·98。分析表明,虎纹蛙局部形态特征的两性差异微弱,而体长两性异形差异显著;雌体具有较大的体形与食性无关,而可能与生育力选择的作用有关。     

Geographic variation in size and sexual dimorphism of North American weasels

Geographic variation in size (skull length) and sexual dimorphism in Mustela erminea, Mustela frenata and Mustela nivalis in North America is described and analysed in relation to latitude, longitude, climatic variables, and sympatry or allopatry of these species. Only erminea increases in size with latitude; it does so regardless of the presence or absence of frenata or nivalis. Latitude is a better predictor of size in erminea than available measures of climate, seasonality or prey size. There is no evidence for character displacement between any pair of species. The sexes covary in size in frenata and erminea , and probably in nivalis , although geographic variation in sexual dimorphism occurs in frenata and erminea. The principal cause of sexual dimorphism appears to be sexual selection for large size in males rather than the high energetic requirements resulting from an elongate body shape. However, prey size may constrain female size (and possibly also male size). Regional differences in the abundance of prey during the growth of young weasels may affect adult size much more in males than in females and contribute to geographic variation in sexual dimorphism.     

What Makes Vocalisation Frequency an Unreliable Signal of Body Size in Birds? A Study on Black Swans

In many animal species, the frequency (pitch) of vocalisations correlates negatively with body size and may thus signal competitive ability. However, this relationship is absent in other species. Understanding why this difference exists across species may help to explain some of the diversity of vocal communication systems. We assessed whether vocalisation frequency signals body size in black swans (Cygnus atratus), and how this is affected by (i) variation in frequency within individuals and (ii) size variation across individuals. Frequency was correlated with body size and mass, with slopes close to the allometry expected if the birds were maximising sound radiation, but the explained variation in frequency was low. Within‐individual variation in vocalisation frequency was greater in male than female swans, and the reliability of frequency as a signal of size in males was correspondingly lower. A review of the literature on the relationship between the frequency of avian vocalisations and body size also showed smaller effect sizes for more variable vocalisations (birdsongs), than for simpler vocalisations. Vocalisation frequency was more reliably correlated with body size when the sexes were pooled (creating a larger range of variation in size) than when the relationship was examined for either sex separately, although male and female data followed the same allometric line. These results show that variation in frequency within individuals and low variation in size across individuals reduce the reliability of vocalisation frequency as a signal of body size, which helps to understand differences among species in the signal value of vocalisation frequency.     

Morphological differences between an artificial lentic and adjacent lotic environments in a characid species

Dam constructions cause fundamental changes in the natural landscape, creating new ecological and evolutionary challenges for aquatic organisms. In some cases, such water impoundments have been related with morphological changes in organisms. Understanding how populations respond to rapid environmental changes imposed by dams is the first step to elucidate the consequences that disturbed habitats may have on species evolution. In this work, we analyzed shape and size variation in Bryconamericus iheringii Boulenger 1887 from the Chasqueiro stream basin, south of Brazil, which was recently dammed. We used linear measurements and geometric morphometrics to identify morphological differences among specimens from the reservoir (lentic habitat) compared to the habitat upstream and downstream of the dam (lotic habitats). We also tested for size- and shape-related sexual dimorphism to determine whether variations observed were the same for both sexes. We found that B. iheringii from the artificial reservoir were distinct in shape and size to those from their natural habitat in the stream. The size variation between environments was the same for both sexes, but the shape variation differed between males and females. Regarding the linear measurements, lotic populations were larger (greater body length, width, pectoral fin base length and caudal peduncle length), probably in response to increased swimming activity. Regarding body shape, we found that both sexes have a more fusiform body in lotic habitats than in the reservoir. In addition, females showed an altered mouth position that was distinct between these environments. This work indicates that the water reservoir seems to be an important factor influencing morphological variation in B. iheringii, a species with sexual shape dimorphism.