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Ontogenetic Variation (ontogenetic + variation)
Selected AbstractsOntogenetic Variation in Ammonia Excretion during the Early Life Stages of the Amazon River Prawn, Macrobrachium amazonicumJOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2010Liliam De Arruda Hayd Dry mass (DM) and total ammonia-N (TAN) excretion were determined in embryos, larvae (ZI,ZIX, Z = zoea ), and postlarvae (PL) at 1, 7, and 14 d after metamorphosis (PL1, PL7, and PL14) of Macrobrachium amazonicum. Animals in postmolt,intermolt (A,C) stages were sorted according to their developmental stages, and placed into incubation chambers (, 30 mL) for 2 h to quantify TAN excretion. After this period, analyses were carried out using Koroleff's method for TAN determination. Individual TAN excretion generally increased throughout ontogenetic development and varied from 0.0090 ± 0.0039 µg TAN/individual/h in embryo to 1.041 ± 0.249 µg TAN/individual/h in PL14. There was no significant difference between embryo,ZIV and ZV,ZIX (P > 0.05), whereas PL1, PL7, and PL14 differed (P < 0.05) from each other. Higher increments in individual ammonia-N excretion were observed between ZIV,ZV, PL1,PL7, and PL7,PL14. Mass-specific excretion rates presented two groups, embryo,ZII (P > 0.05) and ZIII,PL14 (P > 0.05). The lowest value was found in embryo (0.17 ± 0.07 µg TAN/mg DM/h) and the maximum values in ZV and PL1 (0.65 ± 0.25 and 0.64 ± 0.27 µg TAN/mg DM/h, respectively). Results indicate that metabolic rate is proportional to the body mass in M. amazonicum, during early life stages. Variations in ammonia excretion during this phase may be associated mainly with body size. Data obtained in the present study may be useful in developing and optimizing rearing techniques of M. amazonicum, such as the proportions between biofilter and rearing tank size, and stocking density in culture tanks or in transport bags. [source] The ontogeny of cross-sex genetic correlations: an analysis of patternsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 12 2009J. POISSANT Abstract The independent evolution of males and females is typically constrained by shared genetic variance. Despite substantial research, we still know little about the evolution of cross-sex genetic covariance and its standardized measure, the cross-sex genetic correlation (rMF). In particular, it is unclear if rMF tend to vary with age. We compiled 28 traits for which ontogenetic trends in rMF were documented. Decreases in rMF with age were observed significantly more often than increases and the mean effect size for the relationship between rMF and age was large and negative. This suggests that sexual dimorphism (SD) may typically evolve more readily for phenotypes expressed later in ontogeny and that evolutionary inferences related to the evolution of SD should be limited to the ontogenetic stage at which rMF was estimated. Knowledge about ontogenetic variation in rMF should help improving our understanding of evolutionary patterns related to SD and the resolution of intralocus sexual conflicts. [source] Skull shape and feeding strategy in Sphenodon and other Rhynchocephalia (Diapsida: Lepidosauria),JOURNAL OF MORPHOLOGY, Issue 8 2008Marc E.H. Jones Abstract The Rhynchocephalia are a group of small diapsid reptiles that were globally distributed during the early Mesozoic. By contrast, the only extant representatives, Sphenodon punctatus and S. guntheri (Tuatara), are restricted to New Zealand off-shore islands. The Rhynchocephalia are widely considered to be morphologically uniform but research over the past 30 years has revealed unexpected phenotypic and taxonomic diversity. Phylogenetically "basal taxa" generally possess relatively simple conical or columnar teeth whereas more derived taxa possessed stouter flanged teeth and sophisticated shearing mechanisms: orthal in some (e.g., Clevosaurus hudsoni) and propalinal in others (e.g., S. punctatus). This variation in feeding apparatus suggests a wide range of feeding niches were exploited by rhynchocephalians. The relationship of skull shape to skull length, phylogenetic grouping, habit, and characters relating to the feeding apparatus are explored here with geometric morphometric analysis on two-dimensional landmarks. Principle components analysis demonstrates that there are significant differences between phylogenetic groups. In particular, Sphenodon differs significantly from all well known fossil taxa including the most phylogenetically basal forms. Therefore, it is not justifiable to use Sphenodon as a solitary outgroup when studying skull shape and feeding strategy in squamates; rhynchocephalian fossil taxa also need to be considered. There are also significant differences between the skull shapes of aquatic taxa and those of terrestrial taxa. Of the observed variation in skull shape, most variation is subsumed by variation in dentary tooth base shape, the type of jaw movement employed (e.g., orthal vs. propalinal) and the number of palatal tooth rows. By comparison, the presence or absence of flanges, dentary tooth number and palatal tooth row orientation subsume much less. Skull length was also found to be a poor descriptor of overall skull shape. Compared to basal rhynchocephalians members of more derived terrestrial radiations possess an enlarged postorbital area, a high parietal, and a jaw joint positioned ventral to the tooth row. Modification of these features is closely associated with increased biting performance and thus access to novel food items. Some of these same trends are apparent during Sphenodon ontogeny where skull growth is allometric and there is evidence for ontogenetic variation in diet. J. Morphol., 2008. © 2008 Wiley-Liss, Inc. [source] Cranial osteology of the sauropterygian Plesiosaurus brachypterygius from the Lower Toarcian of GermanyPALAEONTOLOGY, Issue 1 2000Michael W. Maisch An osteological re-study of the holotype skull of Plesiosaurus brachypterygius leads to a correction of several inaccuracies and misidentifications of the original description by von Huene and reveals additional facts on the cranial anatomy of this plesiosaur. Comparison with the type species, Plesiosaurus dolichodeirus, from the Lower Lias of England shows considerable differences in many parts of the cranial skeleton, even though the two species are generally so similar that their inclusion in the same genus proposed by von Huene, and agreed with by all subsequent authors, can be supported. Plesiosaurus brachypterygius is provisionally considered as a valid species distinguishable from the contemporaneous Plesiosaurus guilelmiimperatoris by its much shorter limbs, a difference that cannot be explained by ontogenetic variation as proposed by Storrs. Plesiosaurus brachypterygius was probably an ichthyophagous form that occurred rarely in the Posidonienschiefer fauna. [source] Historical DNA from museum type specimens clarifies diversity of Asian leaf turtles (Cyclemys)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2008BRYAN L. STUART Species boundaries in Asian leaf turtles of the genus Cyclemys are difficult to define on the basis of morphology, primarily because many populations exhibit considerable ontogenetic variation in shell and head coloration. Two recent molecular phylogenetic hypotheses of Cyclemys species relationships, based largely on market and pet-trade samples of uncertain provenance, were highly incongruent. We used historical DNA methods to sequence fragments of the mitochondrial cytochrome b gene from eight type specimens of Cyclemys (including one collected by Alfred Russel Wallace), and phylogenetically placed these type sequences into the context of published cytochrome b variation. Our phylogenetic hypothesis supports the recognition of four named species (Cyclemys atripons, Cyclemys dentata, Cyclemys oldhamii, and C. pulchristriata), as well as a fifth species of unknown geographical provenance obtained from the Hong Kong pet trade. The type sequences show that previous molecular phylogenetic studies were hampered by misidentifications, supporting the notion that Cyclemys of unknown provenance are not reliably identified to species solely on the basis of morphology. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 131,141. [source] Trophodynamic modeling of walleye pollock (Theragra chalcogramma) in the Doto area, northern Japan: model description and baseline simulationsFISHERIES OCEANOGRAPHY, Issue 2004ORIO YAMAMURA Abstract An age-structured trophodynamic model was constructed to quantitatively analyze factors affecting post-settlement mortality and growth of walleye pollock (Theragra chalcogramma) in the Doto area, the main nursery ground of the Japan Pacific population. The model included (i) multiple age classes of pollock, (ii) a generic predator, (iii) fisheries, and (iv) major prey of pollock. Major processes considered were (i) recruitment, (ii) bottom-up control of somatic growth, (iii) mortality because of predation, cannibalism and fishing, (iv) size-selective prey selection, (v) temperature-dependent bioenergetics such as conversion efficiency and daily consumption rate, and (vi) production and advective supply of prey. By assuming that pollock select prey based upon both relative abundance and predator,prey size relationships, the model accurately simulated seasonal and ontogenetic variations in the diet. However considering ontogenetic segregation, the model showed that, due to cannibalism, newly recruited fish would be totally consumed within 6 months after settlement. By considering segregation (10% overlap during spring and 0.1% during other seasons), an agreement of diet between the simulation and empirical data averaged 82.7% for the different seasons and fish sizes. Euphausiids, the most important prey of pollock, suffered the highest predation impact (22.2 ± 5.3 WWg m,2 yr,1) exceeding annual production in the model domain (17.2 ± 0.1 WWg m,2 yr,1), indicating that an advective supply of prey is necessary to support the pollock population. The daily ration of pollock during spring and summer averaged at 1.2 and 0.6% BW day,1 for small (,200 mm) and large (>200 mm) pollock, respectively; this daily ration was reduced by half during autumn and winter. [source] | |||||||||||||