Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish Saurichthys (Actinopterygii,Saurichthyidae)

Viviparity has evolved independently at least 12 times in ray‐finned fishes. However, the fossil record of actinopterygian viviparity is poor, with only two documented occurrences. Both of these are from the non‐teleost actinopterygian Saurichthys, and include S. curionii and S. macrocephalus from the Middle Triassic Meride Limestone (Monte San Giorgio, Switzerland). Here, we present new data on the reproductive biology of these species, giving unprecedented insights into their life‐history. Based on positional and preservational criteria, six specimens were identified as unambiguously gravid. Embryos were positioned dorsal to the gastrointestinal tract, parallel to the axial skeleton and to each other, in the posterior two‐thirds of the abdominal region. A minimum of 16 embryos are preserved in the most fecund females and, based on the largest preserved embryos and smallest preserved neonates, birth must have occurred at 7–12% of maternal fork length. Embryonic crania and teeth are relatively well‐ossified, however ossification of the parietal region is delayed. In the postcranium, the median scale rows and lepidotrichia are ossified, but not the lateral scale rows. Ossified squamation and gradual allometric growth suggests that neonates did not undergo metamorphosis and were relatively precocial. When considered in a phylogenetic context, neither live birth nor internal fertilization appears to represent the primitive state for saurichthyid fishes.     

Two new species of Saurichthys (Actinopterygii: Saurichthyidae) from the Middle Triassic of Monte San Giorgio,Switzerland, with implications for character evolution in the genus

Saurichthys, characterized by a long slender body and an elongated rostrum, is one of the most iconic genera of Late Paleozoic–Early Mesozoic fishes. The genus was particularly speciose in the Triassic, with a global distribution in both marine and freshwater habitats. Here, we describe two new species from the Middle Triassic Besano Formation of Monte San Giorgio, Switzerland, Saurichthys breviabdominalis sp. nov. and Saurichthys rieppeli sp. nov. S. breviabdominalis is characterized by a proportionately long operculum, short abdominal region and rib‐like mid‐lateral scales, whereas S. rieppeli is divergent from other Middle Triassic saurichthyids in the block‐like haemal arches, fringing fulcra on the pelvic and unpaired fins, and reduction of the squamation to a single row in the abdominal region. Phylogenetic analysis places S. rieppeli in a basal position relative to congeners from the Alpine Triassic, and supports previous hypotheses regarding the convergent evolution of reduced squamation within saurichthyids. S. breviabdominalis forms a monophyletic group with species from the same locality, suggesting divergence in sympatry. This finding has implications for our understanding of disparity and character evolution in saurichthyid fishes, as well as ecomorphological divergence and resource partitioning between closely related fishes in Triassic marine ecosystems. © 2015 The Linnean Society of London     

Evolution of opercle bone shape along a macrohabitat gradient: species identification using mtDNA and geometric morphometric analyses in neotropical sea catfishes (Ariidae)

Transitions between the marine and freshwater macrohabitat have occurred repeatedly in the evolution of teleost fishes. For example, ariid catfishes have moved from freshwater to marine environments, and vice versa. Opercles, a skeletal feature that has been shown to change during such transitions, were subjected to 2D geometric morphometric analyses in order to investigate evolutionary shape changes during habitat transition in ariid catfishes and to test the influence of habitat on shape changes. A mtDNA marker, which proved useful in previous studies, was used to verify species identities. It greatly improved the assignment of specimens to a species, which are difficult to assign by morphology alone. The application of a mtDNA marker confirmed the occurrence of Notarius biffi in Central America, South of El Salvador. Molecular identification together with principal component analysis (PCA) and further morphological inspection of neurocrania indicated the existence of a cryptic species within Bagre pinnimaculatus. Principal component (PC) scores of individual specimens clustered in morphospace by genus rather than by habitat. Strong phylogenetic structure was detected using a permutation test of PC scores of species means on a phylogenetic tree. Calculation of Pagel's λ suggested that opercle shape evolved according to a Brownian model of evolution. Yet canonical variate analysis (CVA) conducted on the habitat groups showed significant differences in opercle shapes among freshwater and marine species. Overall, opercle shape in tropical American Ariidae appears to be phylogenetically constrained. This verifies the application of opercle shape as a taxonomic tool for species identification in fossil ariid catfishes. At the same time, adaptation to freshwater habitats shows characteristic opercle shape trajectories in ariid catfishes, which might be used to detect habitat preferences in fossils.     

Evolutionary diversification of opercle shape in Cook Inlet threespine stickleback

We investigated the evolution of a large facial bone, the opercle (OP), in lake populations of the threespine stickleback that were founded by anadromous ancestors, in Cook Inlet, Alaska. Recent studies characterized OP variation among marine and lake populations and mapped a quantitative trait locus with a large influence on OP shape. Using populations from diverse environments and independent evolutionary histories, we examined divergence of OP shape from that of the anadromous ancestor. We report preliminary evidence for divergence between benthic and generalist lake ecotypes, necessitating further investigation. Furthermore, rapid divergence of OP shape has occurred in a lake population that was founded by anadromous stickleback in the 1980s, which is consistent with divergence of other phenotypic traits and with OP diversification in other lake populations. By contrast, there has been limited evolution of OP shape in a second lake population that may have experienced a genetic bottleneck early in its history and lacks genetic variation for OP divergence. Taken together, the results obtained from these two populations are consistent with studies of other stickleback phenotypic traits that implicate ancestral variation in postglacial adaptive radiation of threespine stickleback in fresh water.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 832–844.     

Supporting the existence of two isolated evolutionary lineages of Gerres (Perciformes: Gerreidae) in America

For many years in America, many authors have considered that the Gerres genus contained a single species, the yellowfin mojarra Gerres cinereus (Walbaum, 1792); however, others have recognized two species in this genus in the Neotropics. In this study, specimens of G. cinereus (sensu lato) caught throughout its geographic range on both coasts of America were compared for the first time to analyse divergence among the sampled populations. A genetic analysis based on DNA sequences from three mitochondrial genes and one nuclear gene revealed a clear separation of two clades, one in the Pacific and one in the Atlantic. Geometric morphometric differences, based on body shape, sagittae otoliths and urohyal bone features, were significant between the two groups, including separation by an accurate classification a posteriori by a canonical variate analysis (CVA) > 82% in all data sets (overall mean >91%). Integration of the results of these approaches indicates that there is sufficient evidence to support species status for Gerres simillimus Regan, 1907, and it should be considered a valid species in the neotropical Pacific.     

Spatial patterns of variation in color and spine shape in the sea urchin Heliocidaris erythrogramma

Abstract. Here we report on the first quantitative survey of morphological variation in the sea urchin Heliocidaris erythrogramma within Western Australia and distinguish between two subspecies found to co‐occur in this region. We surveyed urchins at multiple spatial scales along the Western Australian coastline to assess variation in dermis and spine color and, using landmark‐based geometric morphometrics, spine morphology. Both color and morphology proved to be useful for separating subspecies within Western Australia. There were four major color morphs: red dermis/violet spines (56%), red/violet‐green (23%), red/green (7%), and white/green (10%). Members of the first two color morphs had bulbous spines with wide, flattened tips, a morphology that is unique to Western Australia and characteristic of H. e. armigera, and members of the latter two consistently exhibited the narrow, pointed spines typical of specimens of H. e. erythrogramma, which has a broader distribution. In Western Australia, H. e. armigera was relatively abundant both within and among sites, but H. e. erythrogramma was found only in a few localized patches. Shifts in the relative abundance of these two subspecies occurred at fine spatial scales (<5 km), although environmental correlates of these transitions were unclear. Contrary to expectations, neither dermis color nor spine morphology varied with relative wave exposure: individuals with a red dermis or thickened spine morphology occurred at most sites regardless of exposure, and while white dermis and thinner spines only occurred at high‐exposure sites, these features were not common across the majority of exposed sites. Both color morph frequencies and spine morphology remained stable within sites over the 3‐year duration of this study. While the ecological significance of this morphological variation remains unclear, the consistency of the association between color and spine morphology, occurring across fine spatial scales, suggests that strong environmental or genetic factors are involved in maintaining morphological differentiation between these two subspecies.     

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.     

Morphological convergence of shell shape in distantly related scallop species (Mollusca: Pectinidae)

Morphological convergence is a central concept in evolutionary biology, but convergent patterns remain under‐studied in nonvertebrate organisms. Some scallop species exhibit long‐distance swimming, a behaviour whose biomechanical requirements probably generate similar selective regimes. We tested the hypothesis that shell shape similarity in long‐distance swimming species is a result of convergent evolution. Using landmark‐based geometric morphometrics, we quantified shell shape in seven species representing major behavioural habits. All species displayed distinct shell shapes, with the exception of the two long‐distance swimmers, whose shells were indistinguishable. These species also displayed reduced morphological variance relative to other taxa. Finally, a phylogenetic simulation revealed that these species were more similar in their shell shape than was expected under Brownian motion, the model of character evolution that best described changes in shell shape. Together, these findings reveal that convergent evolution of shell shape occurs in scallops, and suggest that selection for shell shape and behaviour may be important in the diversification of the group. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 571–584.     

Taxonomic status of southern South American Conepatus (Carnivora: Mephitidae)

Despite recent taxonomic evaluations of Mephitidae and North American hog‐nosed skunks, southern South American species of Conepatus have not been thoroughly examined in a systematic context. Conepatus chinga and Conepatus humboldtii were described more than 150 years ago, based on external characters such as hair coloration and size. Although historically recognized as valid species, to date no detailed systematic analysis has been performed for either of these taxa. Herein, we evaluated the taxonomic status of C. chinga and C. humboldtii within the southern part of South America using geometric morphometrics of the skull and mandible, mitochondrial DNA analysis using the cytochrome b and cytochrome oxidase c subunit I genes, and also control region and pelage pattern variation. We failed to find morphological (skull shape and pelage coloration patterns) or molecular differences between these two species; thus, we considered that the specimens assigned to C. chinga and C. humboldtii belong to the same species. Our results indicate that environmental variation seems to be responsible for shape and size variation in Conepatus skulls from southern South America. © 2013 The Linnean Society of London     

Trends in the sand: Directional evolution in the shell shape of recessing scallops (Bivalvia: Pectinidae)

Directional evolution is one of the most compelling evolutionary patterns observed in macroevolution. Yet, despite its importance, detecting such trends in multivariate data remains a challenge. In this study, we evaluate multivariate evolution of shell shape in 93 bivalved scallop species, combining geometric morphometrics and phylogenetic comparative methods. Phylomorphospace visualization described the history of morphological diversification in the group; revealing that taxa with a recessing life habit were the most distinctive in shell shape, and appeared to display a directional trend. To evaluate this hypothesis empirically, we extended existing methods by characterizing the mean directional evolution in phylomorphospace for recessing scallops. We then compared this pattern to what was expected under several alternative evolutionary scenarios using phylogenetic simulations. The observed pattern did not fall within the distribution obtained under multivariate Brownian motion, enabling us to reject this evolutionary scenario. By contrast, the observed pattern was more similar to, and fell within, the distribution obtained from simulations using Brownian motion combined with a directional trend. Thus, the observed data are consistent with a pattern of directional evolution for this lineage of recessing scallops. We discuss this putative directional evolutionary trend in terms of its potential adaptive role in exploiting novel habitats.     

Independent axes of genetic variation and parallel evolutionary divergence of opercle bone shape in threespine stickleback

Evolution of similar phenotypes in independent populations is often taken as evidence of adaptation to the same fitness optimum. However, the genetic architecture of traits might cause evolution to proceed more often toward particular phenotypes, and less often toward others, independently of the adaptive value of the traits. Freshwater populations of Alaskan threespine stickleback have repeatedly evolved the same distinctive opercle shape after divergence from an oceanic ancestor. Here we demonstrate that this pattern of parallel evolution is widespread, distinguishing oceanic and freshwater populations across the Pacific Coast of North America and Iceland. We test whether this parallel evolution reflects genetic bias by estimating the additive genetic variance-covariance matrix (G) of opercle shape in an Alaskan oceanic (putative ancestral) population. We find significant additive genetic variance for opercle shape and that G has the potential to be biasing, because of the existence of regions of phenotypic space with low additive genetic variation. However, evolution did not occur along major eigenvectors of G, rather it occurred repeatedly in the same directions of high evolvability. We conclude that the parallel opercle evolution is most likely due to selection during adaptation to freshwater habitats, rather than due to biasing effects of opercle genetic architecture.     

Protocol for quantitative shape analysis of deformities in early larval European seabass Dicentrarchus labrax

This study established an optimized protocol for quantifying the shape variation of newly hatched larvae of European seabass Dicentrarchus labrax, focusing on the effect of fixatives and mounting on body shape from hatching until 14 days post hatching, while also minimizing the error introduced by handling. This assessment was performed based on both biometric and geometric shape data, with the latter relying on outline based elliptic Fourier analysis. The fixation and mounting effect on the total length and shape of newly hatched larvae of D. labrax was tested for four fixation treatments: (1) 8% formalin, (2) 70% ethanol, (3) 8% formalin for 48 h and then to 70% ethanol and (4) 3% phosphate‐buffered glutaraldehyde. The analyses showed that no significant size and shape effect was observed on anaesthetized specimens 5 months post‐fixation in glutaraldehyde, and that the glycerol mounting process of specimens fixed in glutaraldehyde provided the best results for further ontogenetic qualitative and quantitative analysis. The protocol proved to be sufficiently sensitive to even quantify and visualize subtle pre‐fixation shape differences originating from a different egg batch.     

Evolution of cranial shape in a continental‐scale evolutionary radiation of Australian lizards

A defining character of adaptive radiations is the evolution of a diversity of morphological forms that are associated with the use of different habitats, following the invasion of vacant niches. Island adaptive radiations have been thoroughly investigated but continental scale radiations are more poorly understood. Here, we use 52 species of Australian agamid lizards and their Asian relatives as a model group, and employ three‐dimensional geometric morphometrics to characterize cranial morphology and investigate whether variation in cranial shape reflects patterns expected from the ecological process of adaptive radiation. Phylogenetic affinity, evolutionary allometry, and ecological life habit all play major roles in the evolution of cranial shape in the sampled lizards. We find a significant association between cranial shapes and life habit. Our results are in line with the expectations of an adaptive radiation, and this is the first time detailed geometric morphometric analyses have been used to understand the selective forces that drove an adaptive radiation at a continental scale.     

Allometry in Anisian (Middle Triassic) segminiplanate conodonts and its implications for conodont taxonomy

Conodonts are a clade of chordates and are valuable indicator fossils for biostratigraphy. The segminiplanate (neogondolelliform) conodonts represent a major morphological group ranging from upper Carboniferous to Upper Triassic marine sediments. However, the morphological similarity of segminiplanate P₁ elements generates problems for taxonomy, especially in the Permian and Triassic clades. This paper represents the first study of morphological variation in Triassic segminiplanate conodonts using a geometric morphometric approach. The laminar microstructures observed in conodont cross‐sections indicate that, within our analysed specimens, smaller conodonts with fewer laminae are generally from an earlier ontogenetic stage while larger conodonts with more laminae are from a later stage of ontogeny. Using linear regressions between relative warp scores from both upper and lateral views and conodont length, we demonstrate strongly allometric growth patterns for the species Paragondolella bifurcata Budurov & Stefanov. Our results indicate that the species‐group taxon Pg. praeszaboi bystrickyi (Kovacs et al.) is an early growth stage of Pg. bifurcata and thus synonymous. We suggest that the allometry of conodonts should be considered seriously, especially when there are numerous transitional morphologies between large‐ and small‐sized conodonts. Reconstructing the ontogenetic series and using larger‐sized conodonts within the numerous transitional morphologies in the population of a rock sample for the definition of new species are suggested for future studies.     

Cranial shape variation and molecular phylogenetic structure of crested newts (Triturus cristatus superspecies: Caudata,Salamandridae) in the Balkans

In the present study, we investigated the degree of congruence between phylogeny, as inferred from mitochondrial (mt)DNA sequences, and cranium shape variation of crested newts (Triturus cristatus superspecies) in the Balkans. These newts belong to four phylogenetic clades defined by mtDNA analysis, and significantly differed in cranial shape. Allometry explained a high percentage of shape variation in crested newts. The clade‐specific allometric slopes significantly diverged for both the ventral cranium and dorsal cranium, indicating that differences in shape between clades could not be a simple consequence of their difference in size. The analysis of hierarchical and spatial variation showed similarity in the patterns of global and spatially localized hierarchical variation of cranial shape. We also found significant congruence between the pattern of cranial shape variation and molecular phylogeny. The differences in morphology of Triturus dobrogicus in comparison to other crested newt clades, including marked differences in cranium shape, is discussed in the context of the evolution and ecology of crested newts. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 348–360.     

Clinal variation in carapace shape in the South American freshwater crab,Aegla uruguayana (Anomura: Aeglidae)

South America has been influenced by different geoclimatic events ever since its separation from Africa. The inland water fauna has evolved in response to the changing landscape. Currently, there are indications of variations in populations, occurring to different degrees that would indicate a clinal pattern in morphology. Among South America's fauna, the freshwater anomuran, Aegla, is an enigmatic group as a result of its endemicity and is composed of only one genus. Of all the species in this family, Aegla uruguayana has the broadest distribution. Its native habitats have been influenced by several marine transgressions during the Miocene–Quaternary Periods; thus, it is likely that their current distribution has been more recent. Its habitat spreads across a number of isolated basins and sub‐basins that display distinct degrees of isolation/connection, making clinal variation patterns in the morphology of this species possible. The present study aimed to evaluate the pattern of carapace shape variation in A. uruguayana and how it relates to the isolation and/or connection of populations from different basins and sub‐basins, allowing the determination of any extant clinal patterns. The specimens studied belong to 25 separate populations, representing all areas in which the species currently exists. A total of 523 crabs were analyzed. We identified 13 landmarks and four semi‐landmarks in the carapace. The aeglids were divided into seven size intervals to avoid an allometry effect. In each size category, shape relationships analyzed by principal component analysis suggest a geographical pattern corresponding to the distribution of the populations studied. An evaluation of covariation between body shape and geographical coordinates reveals a strong pattern and shows that population distribution had a significant effect on species morphology. Additionally, according to covariance analysis, the variation in shape was not associated with the environmental variables studied. We observed a clinal pattern throughout the species distribution, which could be attributed to genetic drift. It is possible that this process is being amplified by the geographical isolation of the basins, differences in environmental characteristics, and low dispersal ability. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 914–930.