Shape disparity of bovid (Mammalia,Artiodactyla) horn sheaths and horn cores allows discrimination by species in 3D geometric morphometric analyses

The bony cranial structures of even‐toed hoofed mammals are important for understanding ecology and behavior of ruminants. Horns, the cranial appendages of the family Bovidae, are covered in a layer of keratin that is often not preserved in the fossil record; however, this keratin sheath is intimately involved in the processes that influence horn shape evolution. To understand the relationship between these two components of horns, we quantified both core and sheath shape for four extant species using three‐dimensional geometric morphometric analyses in separate, core‐ and sheath‐specific morphospaces as well as a combined morphospace. We assessed correlations between the horn and sheath morphospaces using two‐block partial least squares regression, a Mantel test of pairwise distances between species, and Procrustes ANOVA. We measured disparity in the combined morphospace as Procrustes distances between mean shapes of cores and sheaths within and between species and as Procrustes variance. We also tested whether core and sheath shapes could be discriminated by taxon with a canonical variate analysis. Results show that horn core and sheath morphospaces are strongly correlated. The differences in shape between a species' core and sheath were statistically significant, but not as great as those between the cores and sheaths of different species when close relatives were not considered, and core and sheath Procrustes variances are not significantly different within species. Cores and sheath shapes were highly identifiable and were assigned to the correct clade 93% of the time in the canonical variate analysis. Based on these tests, horn cores are distinguishable in geometric morphometric analyses, extending the possibility of using geometric morphometrics to study the ecology and evolution of bovid horns to the fossil record.     

Geographic morphological variation in parapatric Western Palearctic tree frogs,Hyla arborea and Hyla savignyi: are related species similarly affected by climatic conditions?

Tree frogs Hyla arborea and Hyla savignyi are similar, closely‐related species distributed in Europe and the Middle East. We investigated geographic variation in body shape within and between these species, and tested its relationships to macroclimatic conditions. We used morphometric distances (based on size corrected external measurements) to construct phenetic trees (unweighted pair‐group method of arithmetical averages, Neighbour‐joining), and to test correlations between morphology, geography, and climate by the partial Mantel test. Regardless of their specific affiliation, the parapatric populations of both species from the eastern Mediterranean, where they occupy comparable habitats, are closer to each other in morphospace than to conspecific populations from distal regions. This local interspecific similarity is probably driven by the common response to environment, expressed here as macroclimatic conditions. In support, the geographically close but ecologically vicariant populations of both species from the Caucasus region differ quite substantially in body shape. We suggest that climate‐provoked phenotypic variation in closely‐related parapatric species should be taken into account as a potential complication to character displacement in morphology. Contrariwise, morphological diversification between related species or their populations could be enhanced by habitat shifts resulting in occupation of different environmental space. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 539–556.     

Lobule shape evolution in Radula (Jungermanniopsida): one rate fits all?

The quantification of lobule shape for Radula spp. shows that there is overlap in lobule shape space occupied by subgenera, such that lobule shape does not always reflect relationships. Morphological convergence caused by lineages repeatedly traversing shared regions of morphospace appears commonplace in Radula, and means that many pairs of relatively unrelated species have similar lobule shapes. When observed over time, as in comparisons between fossil and extant species, this may give the impression of stasis if fossil species resemble modern species by chance, independent of their relatedness. This poses a challenge to relating fossils of known age to extant lineages, particularly when fossils are sterile. Significant rate variation between lineages was identified by Adams' Q‐mode analysis, with the fastest subgenus evolving 23 times more quickly than the slowest. Species of subgenus Volutoradula and subgenus Metaradula are apparently over‐dispersed throughout lobule morphospace according to Sidlauskas' method; morphometric branch lengths and hypervolumes in other subgenera can be explained by a stochastic process. In contrast, Bayesian analysis of macroevolutionary mixtures (BAMM) identified a single evolutionary rate as having the highest posterior probability. Consideration of the three independent accessions into auriculate lobule morphospace by Cladoradula and Radula, wherein convergent lobule shapes result from convergent lobule ontogenies and are correlated with bipinnately branched shoot systems and robust primary stems, leads to an ontogenetic hypothesis driven by structural requirements for light interception, under which auriculate lobules are a spandrel. It is speculated that lobules themselves, however, may be a key innovation facilitating radiation into microsites devoid of or depauperate in fungal endophytes. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 222–242.     

A three‐dimensional geometric morphometric study of the development of sulcus versus shell outline in Permian neospiriferine brachiopods

The morphological variation of the sulcal development and shell outline in large Permian neospiriferine brachiopods including Fasciculatia Waterhouse, 2004 is investigated using geometric morphometrics. The sulcal tongues of spiriferide brachiopods can be, in a qualitative sense, categorized into three types according to the degree of their development: short sulcal tongue, long sulcal tongue and geniculated sulcal tongue. All three types have been noted within Fasciculatia striatoparadoxa, regardless of the nature of the substrate which they originally inhabited. To quantify its morphological variation both in sulcal development and shell outline, 51 brachiopod shells were scanned with a three‐dimensional (3‐D) surface imaging device, and their 3‐D models were reconstructed. Using two landmarks and 58 semilandmarks designated on the surface of the reconstructed 3‐D models, a landmark‐based morphometric analysis was performed. Our result demonstrates a significant intraspecific variation of sulcal development in F. striatoparadoxa and its relatives. Local environmental factors, especially the intensity of ambient water flow, are invoked as the most likely cause for this intraspecific variation. Additionally, this study also shows that there are considerable interspecific distinctions in shell outline among Fasciculatia species, independent of the high variation in the sulcal development. The strong stability of overall shell outline at species level implies a decoupled morphological development between sulcal tongue and whole shell outline. The 3‐D morphometric approach applied here demonstrates its great utility as a tool for quantifying and analysing the morphological variation of highly convex brachiopod shells.     

Developmental Dynamics and G-Matrices: Can Morphometric Spaces be Used to Model Phenotypic Evolution?

Modern morphometrics, especially geometric morphometrics, is a powerful tool for modeling the evolution and development of the phenotype. Complicated morphological transformations can be simulated by using standard evolutionary genetic equations for processes such as selection and drift in the same morphospaces that are used for empirical morphometric studies. Such applications appear to be consistent with the theory of quantitative evolution of the phenotype. Nevertheless, concerns exist whether simulations of phenotypic changes directly in morphospaces is realistic because trajectories traced in such spaces describe continuous gradations in the phenotype and because the gain and loss of structures is often impossible because morphospaces are necessarily constructed from variables shared in common by all the phenotypes being considered. Competing models of phenotypic change emphasize morphological discontinuity and novelty. Recently developed models of phenotypic evolution that introduce a “phenotypic landscape” between evolutionary genetic constructs like the adaptive landscape and morphospace may correct this shortcoming.     

The geographic structure of morphological variation in eight species of fiddler crabs (Ocypodidae: genus Uca) from the eastern United States and Mexico

Species with larger geographic distributions are more likely to encounter a greater variety of environmental conditions and barriers to gene flow than geographically‐restricted species. Thus, even closely‐related species with similar life‐history strategies might vary in degree and geographic structure of variation if they differ in geographic range size. In the present study, we investigated this using samples collected across the geographic ranges of eight species of fiddler crabs (Crustacea: Uca) from the Atlantic and Gulf coasts of North America. Morphological variation in the carapace was assessed using geometric morphometric analysis of 945 specimens. Although the eight Uca species exhibit different degrees of intraspecific variation, widespread species do not necessarily exhibit more intraspecific or geographic variation in carapace morphology. Instead, species with more intraspecific variation show stronger morphological divergence among populations. This morphological divergence is partly a result of allometric growth coupled with differences in maximum body size among populations. On average, 10% of total within‐species variation is attributable to allometry. Possible drivers of the remaining morphological differences among populations include gene flow mediated by ocean currents and plastic responses to various environmental stimuli, with isolation‐by‐distance playing a less important role. The results obtained indicate that morphological divergence among populations can occur over shorter distances than expected based on dispersal potential. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 248–270.     

Effectiveness of modern leaf analysis tools for the morpho‐ecological study of plants: the case of Primula albenensis

Scientific and technological progress has led to the creation of analysis tools that have revolutionized traditional studies in morphology and plant ecology. Recently developed methods and tools which, on the basis of leaf samples, allow for geometric morphometric analyses and the evaluation of functional strategies are good examples. These methods, still little used, have never been applied on leaf samples to simultaneously obtain information on their morphometry and the ecology of the plants. This article discusses the effectiveness of modern leaf analysis tools for geometric morphometrics (outline analysis) and studies of functional strategies based on the competitor‐stress tolerator‐ruderal (CSR) scheme, using a study of a steno‐endemic plant of the Alps, Primula albenensis Banfi et Ferl. as an example. These aspects were analyzed using leaf samples collected in the only two areas where this species grows. CSR analyses revealed that P. albenensis is not a stress‐tolerant species (C:S:R = 37:1:62), as previously thought. Moreover, no significant intraspecific differences in functional strategy were revealed. Instead, outline analysis highlighted a significant difference (p < 0.001) between leaves collected from the two sampling areas. The results of this study and others reported in the literature therefore suggest that these modern methods of leaf analysis are cheap, effective and relatively simple to perform. Furthermore, researchers are able to carry out geometric morphometric and CSR analysis using the same samples of leaves in order to maximize the information content provided by the analysis of a plant material which may not be easily available.     

A morphometric and genetic framework for the genus Gazella de Blainville, 1816 (Ruminantia: Bovidae) with special focus on Arabian and Levantine mountain gazelles

Gazella is one of the most species‐rich genera within horned ruminants. Despite overall similarity in body size and morphology, gazelles show variability in coloration and horn morphology. Unfortunately, however, species differentiation based on these characters, or on discrete skull characters, is very difficult due to high intraspecific variability. Furthermore, most species have fragmented and allopatric distributions, so that species boundaries were hard to define in the past. Mitochondrial DNA sequences have proven useful for investigating gazelle taxonomy in recent years, but especially for old museum material, i.e. type specimens, destructive sampling is often impossible. We provide a comprehensive morphometric framework for the genus Gazella based on linear skull measurements reconciled with results from molecular phylogenetic analysis based on the largest dataset available so far. In particular for males, the skull morphology shows interspecific differences concurrent with DNA data and provides a reliable tool for species identification. Based on morphometric data we synonymize G. karamii with G. marica, and confirm the identification of the G. arabica and G. a. rueppelli type skulls from analyses of mitochondrial DNA sequences. © 2013 The Linnean Society of London     

Primary feather lengths may not be important for inferring the flight styles of Mesozoic birds

Chan, N.R., Dyke, G.J. & Benton, M.J. 2013: Primary feather lengths may not be important for inferring the flight styles of Mesozoic birds. Lethaia, Vol. 46, pp. 146–152. Although many Mesozoic fossil birds have been found with primary feathers preserved, these structures have rarely been included in morphometric analyses. This is surprising because the flight feathers of modern birds can contribute approximately 50% of the total wing length, and so it would be assumed that their inclusion or exclusion would modify functional interpretations. Here we show, contrary to earlier work, that this may not be the case. Using forelimb measurements and primary feather lengths from Mesozoic birds, we constructed morphospaces for different clades, which we then compared with morphospaces constructed for extant taxa classified according to flight mode. Consistent with older work, our results indicate that among extant birds some functional flight groups can be distinguished on the basis of their body sizes and that variation in the relative proportions of the wing elements is conservative. Mesozoic birds, on the other hand, show variable proportions of wing bones, with primary feather length contribution to the wing reduced in the earlier diverging groups. We show that the diverse Mesozoic avian clade Enantiornithes overlaps substantially with extant taxa in both size and limb element proportions, confirming previous morphometric results based on skeletal elements alone. However, these measurements cannot be used to distinguish flight modes in extant birds, and so cannot be used to infer flight mode in fossil forms. Our analyses suggest that more data from fossil birds, combined with accurate functional determination of the flight styles of living forms is required if we are to be able to predict the flight modes of extinct birds. □Birds, flight, morphospace, Mesozoic, wing.     

Dinosaur egg‐laying and nesting: The case of an Upper Maastrichtian site at Rennes‐le‐Chateau (Aude,France)

Variation in longevity of taxa in the fossil record has been recognized, but few studies have tested for correlation between position in morphospace and differential survivorship. A sample of 322 Triassic ammonoid species, each one representing a genus, was studied to test whether longer-lived genera were significantly further from the centre of morphospace than shorter-lived genera. Two empirical morphospaces were constructed from morphological data, and the deviation of each genus from the “average form” (centroid) was calculated. Spearman Rank Correlation and Kruskal-Wallis tests were used to test for any significant relationships between distance from the centre of morphospace and longevity. Some longer-lived taxa tended to plot further from the centre of morphospace, but the amounts of variance in longevity accounted for were small and largely statistically non-significant. Ammonoid clade-level morphological stasis appears to be the product of repeated reoccupation of the centre of morphospaces after taxonomic turnover events.     

Ontogenic tracks and evolutionary vestiges in morphospace

Strombid shells were used to exemplify how to construct ontogenic tracks and evolutionary vestiges in morphological space (morphospace). Parameters in a mathematical model of shell form were used to construct morphospaces. Ontogenic information was mapped into these morphospaces to form 'tracks' Ontogenic tracks showed that the predominant trend of morphological evolution of strombid species consisted of an increase of vertical dimensions of whorls (apertures). Integrating information extracted from cladograms with ontogenic tracks in morphospace, 'evolutionary vestiges' were determined and used to infer and reconstruct ancestral shell forms.     

Macroevolutionary patterns in Rhynchocephalia: is the tuatara (Sphenodon punctatus) a living fossil?

The tuatara, Sphenodon punctatus, known from 32 small islands around New Zealand, has often been noted as a classic ‘living fossil’ because of its apparently close resemblance to its Mesozoic forebears and because of a long, low‐diversity history. This designation has been disputed because of the wide diversity of Mesozoic forms and because of derived adaptations in living Sphenodon. We provide a testable definition for ‘living fossils’ based on a slow rate of lineage evolution and a morphology close to the centroid of clade morphospace. We show that through their history since the Triassic, rhynchocephalians had heterogeneous rates of morphological evolution and occupied wide morphospaces during the Triassic and Jurassic, and these then declined in the Cretaceous. In particular, we demonstrate that the extant tuatara underwent unusually slow lineage evolution, and is morphologically conservative, being located near the centre of the morphospace for all Rhynchocephalia.     

Elliptic Fourier analysis of leaf shape in southern African Strychnos section Densiflorae (Loganiaceae)

Leaves can be a useful source of taxonomic information in plants particularly when flowers and fruits are absent during certain periods of the year. In this study, we applied an elliptic Fourier analysis (EFA)‐based morphometric technique to assess leaf morphological divergence among four species of southern African Strychnos section Densiflorae. Using leaf specimen images from field and herbarium collections, we extracted six shape variables [i.e. principal components (PCs)] from the Fourier coefficients and used these variables to describe leaf outline among the species. Our results indicate that the symmetric component of a leaf is the main source of shape differences accounting for 90.25% of total leaf shape variation and captures the more obvious range of observed shapes. PC1 of the symmetric variables describes a wide range of visually observable leaf shape among the species. MANOVA revealed significant interspecific differences except between S. innocua and S. madagascariensis, which could not be separated by outline analysis. A cross‐validated group classification suggests that S. gerrardii, with a classification rate of 88.4%, is distinct from S. madagascariensis, contrary to some taxonomic treatments. We discuss the value of geometric morphometrics at detecting subtle morphological variations and the evolutionary implications of such variations, which may be undetectable to the human eye. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170 , 542–553.