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Shell Characters (shell + character)

Distribution by Scientific Domains
Life Sciences100%
Distribution within Life Sciences
Animal Science & Zoology50%

Selected Abstracts

The cranial morphology of Kayentachelys, an Early Jurassic cryptodire, and the early history of turtles

ACTA ZOOLOGICA, Issue 3 2010
Eugene S. Gaffney
Abstract Gaffney, E.S. and Jenkins, F.A., Jr. 2010. The cranial morphology of Kayentachelys, an Early Jurassic cryptodire, and the early history of turtles. , Acta Zoologica (Stockholm) 91: 335,368 The skull morphology of Kayentachelys aprixGaffney et al., 1987, a turtle from the Early Jurassic Kayenta Fm of northern Arizona, demonstrates the presence of cryptodiran synapomorphies in agreement with Gaffney et al. (1987, 1991, 2007), and contrary to the conclusions of Sterli and Joyce (2007), Joyce (2007), Sterli (2008), and Anquetin et al. (2008). Specific characters found in Kayentachelys and diagnostic of cryptodires include the processus trochlearis oticum, the curved processus pterygoideus externus with a vertical plate, and the prefrontal,vomer contact, which are confirmed as absent in the outgroups, specifically the Late Triassic Proganochelys. The Joyce (2007) analysis suffers from the reduction of the signal from skull characters, with a consequently greater reliance on shell characters, resulting in pleurodires being resolved at various positions within the cryptodires. Kayentachelys reveals what a primitive cryptodire would be expected to look like: a combination of primitive and derived characters, with the fewer derived characters providing the best test of its relationships to other turtles. Although incompletely known, the Mid-Late Jurassic Condorchelys, Heckeremys, and Eileanchelys may be early cryptodires close to Kayentachelys. We confirm the Late Triassic Proterochersis as a pleurodire, dating the pleurodire,cryptodire split as Late Triassic or earlier. [source]

The genus Adriohydrobia (Hydrobiidae: Gastropoda): polytypic species or polymorphic populations?

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 4 2001
T. Wilke
In molluscs, the shell characters have historically played an important role in discrimination among species. However, because of the paucity, variability and degree of homoplasy of shell characters, their sole use for taxonomic and systematic studies is controversial in many groups. In the present paper the genus AdriohydrobiaRadoman, 1973 is used as a paradigm to test relationships of taxa that were considered to be species, mainly on the basis of the shell size variations. We tested whether the genus consists of several sympatric and polytypic species or a single species with polymorphic populations and whether the reported shell size differences, on which the description of three putative species is mainly based, are intrinsic or extrinsic. A fragment of the mitochondrial cytochrome oxidase I (COI) gene was used as an independent genetic marker. We found very little genetic variability in 40 specimens from four populations studied. The nucleotide-sequence diversity (,) within populations ranges from 0.0017 to 0.0056 and the nucleotide-sequence divergence (Dxy) between populations from 0.0018 to 0.0051. The phylogenetic network is very compact with two ,groups' of haplotypes that are separated by only two nucleotide positions. A plot of pairwise nucleotide differences against pairwise shell size differences did not reveal any distinct clusters and a Mantel test did not show any significant associations between the two matrices. Based on the very low genetic diversity, the lack of distinct clusters in the phylogenetic network and the lack of concordance between morphological and genetic differentiation it is concluded that only one species is involved, Adriohydrobia gagatinella. The previously reported morphogroups within Adriohydrobia are probably due to a discrete age structure in these population and/or due to the effect of trematode-induced gigantism. The observed genetic patterns in Adriohydrobia indicate a rapid population growth from an ancestral population of small evolutionary-effective size. The present study stresses the importance of testing species-level hypotheses based on shell characters using one or more independent markers. Die Gattung Adriohydrobia (Hydrobiidae: Gastropoda): polytypische Arten oder polymorphe Populationen? Schalenmerkmale spielen historisch eine wichtige Rolle bei der Bestimmung von Molluskenarten. Die alleinige Nutzung von Schalenmerkmalen für systematische und taxonomische Arbeiten ist jedoch in vielen Gruppen umstritten, da die relativ wenigen Schalenmerkmale oft sehr variabel und durch einen hohen Grad von Homoplasie gekennzeichnet sind. In der vorliegenden Arbeit wurde die Gattung AdriohydrobiaRadoman, 1973 als Fallbeispiel genutzt, um Beziehungen von Arten innerhalb einer Gattung zu untersuchen, die hauptsächlich anhand ihrer Schalengröße unterschieden werden. Es wurde getestet, ob die Gattung mehrere sympatrische und polytypische Arten oder nur eine Art mit polymorphen Populationen umfasst. Darüber hinaus wurde untersucht, ob die dokumentierten Unterschiede in der Schalenhöhe, auf welchen die Beschreibung der drei potentiellen Arten der Gattung hauptsächlich beruhte, intrinsisch oder extrinsisch sind. Als unabhängiger genetischer Marker wurde ein Fragment des mitochondrialen Gens für Cytochromoxidase I (COI) verwendet. Die untersuchten 40 Individuen von vier Populationen zeichneten sich durch eine nur sehr geringe genetische Variabilität aus. Die Nukleotidsequenz-Diversität (,) innerhalb der Populationen variiert zwischen 0.0017 und 0.0056; die Nukleotidsequenz-Divergenz (Dxy) zwischen den Populationen reicht von 0.0018 bi 0.0051. Das phylogenetische Netzwerk ist sehr kompakt und umfasst zwei ,Gruppen' von Haplotypen, welche durch nur zwei Nukleotidpositionen getrennt sind. Die graphische Darstellung von paarweisen Nukleotid-Differenzen gegen paarweise Gehäusegröße-Differenzen lässt keine diskreten Gruppen erkennen und ein Mantel-Test zeigt keine signifikanten Beziehungen zwischen den Matrices. Aufgrund der geringen genetischen Differenzierung, des Fehlens von diskreten Gruppen im phylogenetischen Netzwerk und des nicht-signifikanten Zusammenhanges von morphologischer and genetischer Differenzierung wird geschlussfolgert, dass nur eine Art involviert ist, Adriohydrobia gagatinella. Die in der Literatur dokumentierten Morpho-Gruppen beruhen vermutlich auf einer diskreten Altersstruktur in diesen Populationen und/oder auf den Auswirkungen von trematoden-induziertem Gigantismus. Die festgestellten genetischen Muster in Adriohydrobia lassen das schnelle Wachstum einer Stammpopulation von geringer evolutionär-effektiver Größe vermuten. Die vorliegende Studie ist ein Beispiel dafür, wie wichtig es sein kann, auf Schalenmerkmale beruhende Arthypothesen mit unabhängigen Markern zu verifizieren. [source]

Camouflaged invasion of Lake Malawi by an Oriental gastropod

MOLECULAR ECOLOGY, Issue 8 2004
MARTIN J. GENNER
Abstract In this study we report the first animal invasion, to our knowledge, into Lake Malawi. The colonizer is a non-native morph of the gastropod Melanoides tuberculata that differs substantially in external shell characters from co-occurring indigenous forms. However, because the species possesses extensive within-Africa geographical variation in shell morphology, it was unclear whether the invasion was range expansion of a native African morph, or a colonization from elsewhere. Mitochondrial DNA sequences indicate a southeast Asian origin for the invader, suggesting that shell variation found among indigenous allopatric populations camouflaged an intercontinental invasion. [source]

A land snail's view of a fragmented landscape

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2009
HEIKE KAPPES
Habitat fragmentation may influence the genetic structure of populations, especially of species with low mobility. So far, these effects have been mainly studied by surveying neutral markers, and much less by looking at ecologically relevant characters. Therefore, we aimed to explore eventual patterns of covariation between population structuring in neutral markers and variation in shell morphometrics in the forest-associated snail Discus rotundatus in relation to habitat fragment characteristics. To this end, we screened shell morphometric variability and sequence variation in a fragment of the mitochondrial 16S rDNA gene in D. rotundatus from the fragmented landscape of the Lower Rhine Embayment, Germany. The 16S rDNA of D. rotundatus was highly variable, with a total of 118 haplotypes (384 individuals) forming four clades and one unresolved group. There was a geographic pattern in the distribution of the clades with the river Rhine apparently separating two groups. Yet, at the geographic scale considered, there was no obvious effect of fragmentation on shell morphometrics and 16S rDNA variation because GST often was as high within, as between forests. Instead, the age of the habitat and (re-)afforestation events appeared to affect shell shape and 16S rDNA in terms of the number of clades per site. The ecologically relevant characters thus supported the presumably neutral mitochondrial DNA markers by indicating that populations of not strictly stenecious species may be (relatively) stable in fragments. However, afforestation after large clearcuts and habitat gain after the amendment of deforestation are accompanied by several, seemingly persistent peculiarities, such as altered genetic composition and shell characters (e.g. aperture size). © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 839,850. [source]