Ontogenetic Age Research Articles

Interleukin-1β-immunoreactive neurons in the hippocampus and paraventricular nucleus of the hypothalamus after stress stimulation in aged versus adult rats.

It is believed that the impact of stress on interleukin-1β (IL-1β) depends on the ontogenetic age. This study examines the influence of acute or chronic exposure to forced-swim (FS) stress or high-light open-field (HL-OF) stimulation on the expression of IL-1β. Double immunofluorescence staining was used to reveal the density of IL-1β/NeuN (NeuN is a neuronal nuclear marker)-immunoreactive (-ir) cells in the hippocampal subfields CA1 and CA3, dentate gyrus (DG), and paraventricular nucleus (PVN) of the hypothalamus. Adult postnatal day 90 (P90) and aged (P720) rats were used in this experiment. The data showed a significant increase in the density of IL-1β/NeuN-ir cells in the CA1, CA3, DG, and PVN in P720 nonstressed rats in relation to P90 control animals. Neither FS nor HL-OF acute stimulation caused alteration in the density of IL-1β-ir neurons in any of the investigated structures in P90 and P720 rats in comparison with control groups. However, chronic FS caused a significant increase in CA3 and DG of P720 rats, and chronic HL-OF led to a significant increase in the density of IL-1β-ir neurons in the PVN of P90 rats and in all hippocampal subfields of P720 animals. These results indicate that chronic HL-OF stimulation is a factor that induces changes in the number of IL-1β-ir neurons in the PVN of adult rats, whereas both chronic FS and HL-OF are aggravating factors for the hippocampus of aged (P720) animals.

Maturation and related aspects in clonal forestry—part II: reinvigoration, rejuvenation and juvenility maintenance

Several techniques have been developed for reinvigorating, rejuvenating or maintaining the juvenility of plants. None of these techniques is as effective as natural rejuvenation whereby the most mature plant parts, the reproductive organs, produce the most juvenile plant parts, the embryos, through gametogenesis and sexual reproduction. The most common criteria for identifying reinvigoration or rejuvenation are based on morphology, morphogenic capacity and the ability to produce cones or flowers. Doubts remain over whether true rejuvenation (reduced ontogenetic age) can be achieved by artificial methods such as serial vegetative propagation, or whether these methods merely provide reinvigoration (reduced physiological age) by temporarily removing environmental and physiological constraints to growth. Rejuvenation and reinvigoration are difficult to distinguish from each other but there is some evidence that artificial methods provide at least partial rejuvenation of plants. This review examines methods for delaying the maturation of juvenile plants and for reducing the ontogenetic or physiological age of more-mature plants. The review discusses theoretical and practical aspects of juvenility, rejuvenation and reinvigoration in clonal forestry, and identifies research areas in maturation that could lead to more-effective methods for establishing high-productivity plantations.

Influence of ontogenetic age on the role of dentate granule neurons

New neurons are continuously produced in the adult dentate gyrus of the hippocampus, a key structure in learning and memory. It has been shown that adult neurogenesis is crucial for normal memory processing. However, it is not known whether neurons born during the developmental period and during adulthood support the same functions. Here, we demonstrate that neurons born in neonates (first postnatal week) are activated in different memory processes when they are mature compared to neurons born in adults. By imaging the activation of these two different neuron generations in the same rat and using the IEG Zif268 and Fos, we show that these neurons are involved in discriminating dissimilar contexts and spatial problem solving, respectively. These findings demonstrate that the ontogenetic stage during which neurons are generated is crucial for their function within the memory network.

Remodelling of skeletal tissues bone and structural specialisations in an elasmosaurid (Sauropterygia: Plesiosauroidea) from the Upper Cretaceous of Patagonia, Argentina

Elasmosauridae were cosmopolitan Late Cretaceous plesiosaurs with conspicuous morphological diversity. Within this group, vertebral morphology is a criterion for estimating relative age in plesiosaur. On the other hand, the microstructure of plesiosaur bone is considered as indicative of ontogenetic stage. However, knowledge about ontogenetic tissue transformation in different elements of the skeleton is poorly known. Resorption and remodelling of skeletal tissues are required for development and growth, mechanical adaptation, repair and mineral homeostasis of the vertebrate skeleton. This contribution analyses different postcranial elements of a Late Cretaceous elasmosaurid from Patagonia. Characterisation of bone microstructure indicates the presence of compact bone inner organisation in an adult derived plesiosaur from the Cretaceous and that the distribution of bone specialisations depicts conspicuous variations within a single skeleton depending on the skeletal element considered. Bone compactness or degree of remodelling in elasmosaurids is not necessarily correlated with the ontogenetic age of the animal or to costal versus pelagic lifestyles. The available data are still scarce, but we propose a topic of discussion: perhaps the degree of remodelling and compactness also may be related to the activity level and increased mechanical load in different skeletal elements.

A juvenile turtle (Testudines, Eucryptodira) from the Upper Jurassic of Langenberg Quarry, Oker, Northern Germany

AbstractTurtles are frequently found in fluviatile to lagoonal and shallow marine sediments in the Upper Jurassic of Western Europe. These turtles usually show a mixture of basal and derived characters, but phylogenetic relationships are still largely unresolved. This is mainly due to the incompleteness of fossils and the lack of taxonomically unambiguous characters and is also related to the presence of different ontogenetic stages, which are not easy to compare. The morphological description of a new turtle from the Upper Jurassic of Langenberg Quarry (Oker, Lower Saxony, Germany) gives further insights into the ontogeny of basal eucryptodire turtles as well as into aquatic adaptation of Upper Jurassic turtles. The specimen is herein left in open nomenclature, due to the fact that it represents a juvenile individual. Several characters define the specimen as juvenile: its small size (7.28 cm carapace length); lateral carapacial fontanelles; enlarged vertebral scutes; a radial striation pattern covering the entire carapace; and the grade of ossification of preserved skull and limb elements. A clear aquatic adaptation of the individual is the elongated manus, a feature that is independent of ontogenetic age. The elongated manus may indicate a marine lifestyle and the individual possibly inhabited nearshore to offshore areas around the former Jurassic islands, which today form the Saxony Basin. The ossification pattern of the carapace of this eucryptodire turtle resembles that of known Jurassic paracryptodires and thus provides new insights to the ontogeny of Jurassic turtles.

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

A few dinosaurs are inferred to have undergone an ontogenetic shift from quadrupedal-to-bipedal posture, or vice versa, based on skeletal allometry. The basal ceratopsian Psittacosaurus lujiatunensis is considered to have been mainly bipedal as an adult. Here we infer a postural shift in this species based on a novel combination of limb measurements and histological data. The forelimb is strongly negatively allometric relative to the hindlimb, and patterns of vascular canal orientation provide evidence that growth of the hindlimb was particularly rapid during the middle part of ontogeny. Histology also makes it possible to determine the ontogenetic ages of individual specimens, showing that the forelimb-to-hindlimb ratio changed rapidly during the first or second year of life and thereafter decreased gradually. Occurrence of an ontogenetic shift from quadrupedality to bipedality was evidently widespread in dinosaurs, and may even represent the ancestral condition for the entire group.

Eurhomalea exalbida (Bivalvia): A reliable recorder of climate in southern South America?

Due to the lack of suitable high-resolution archives, regional and continental-scale climate dynamics of southern South America are not well understood. Shells of the long-lived, shallow-marine bivalve mollusk, Eurhomalea exalbida (Dillwyn), are likely to contain information on the past water temperatures. As yet, however, no rigorous calibration study has been presented so that growth history traits and the reliability of shell oxygen isotope-based temperature estimates remain unknown. Shell growth patterns and oxygen isotope ratios of four young specimens of E. exalbida from the Falkland Islands (Southwest Atlantic) were analyzed and cross-calibrated with environmental parameters. Results indicate that E. exalbida likely captured the full seasonal temperature amplitude in its shell. Annual growth line formation occurred between fall and early winter. The most remarkable finding, however, was that E. exalbida formed its shell with an offset of −0.48 to −1.91‰ from expected oxygen isotopic equilibrium with the ambient water. If this remained unnoticed, paleotemperature estimates would overestimate actual water temperatures by 2.1–8.3°C. With increasing ontogenetic age, the discrepancy between measured and reconstructed temperatures increases exponentially, irrespective of the seasonally varying shell growth rates. We attribute this finding to a pH increase in the extrapallial fluid during ontogeny favoring a dominance of the (isotopically lighter) carbonate ions over (isotopically heavier) bicarbonate ions. When this disequilibrium fractionation effect is taken into account, E. exalbida can serve as a high-resolution paleoclimate archive for mid to high latitudes of southern South America providing quantifiable temperature estimates, even from single fossil specimens.

Preliminary evaluation of potential stable isotope and trace element productivity proxies in the oyster Crassostrea gigas

As most bivalve mollusks are filter feeders or deposit feeders—predatory septibranchs (Poromyacea) being the notable exception—they are closely linked with the activity of primary producers. Perhaps this is nowhere more evident than in shallow water habitats influenced by seasonal phytoplankton blooms. In these systems, photoautotrophs are capable of changing the physical and chemical properties of the water column. In turn, clams, ingest large quantities of phytoplankton and precipitate their shells in these chemically altered waters. Thus, clam shells likely archive valuable information about phytoplankton dynamics in shallow water habitats. To better understand this relationship, we investigated geochemical records from two potential productivity proxy systems archived in shells of the oyster Crassostrea gigas that live in the San Francisco Bay estuary, California, USA. Here we present multi-year records of shell carbon isotope (δ13Ccarb) and barium/calcium (Ba/Cacarb) variation. These archives are compared with records of environmental variation using oxygen isotopes (δ18Ocarb) as a temporal marker. We also present high-resolution δ13Ccarb, δ18Ocarb and Ba/Ca profiles associated with the 2003 spring phytoplankton bloom. Our results suggest that the prominent positive δ13Ccarb excursion, present in shell material deposited in the spring of 2003, most likely reflects photosynthetic enrichment of the dissolved inorganic carbon pool. Calibration of stable isotopes with calculated chlorophyll a concentrations, measured during the bloom, suggests that our δ13Ccarb sample variation reflects phytoplankton abundance with 3 to 4day resolution. These findings highlight the potential utility of stable isotope records as tools for reconstructing patterns of primary productivity. Elevated Ba/Ca values are recorded each year in the spring. Thus, like stable isotope profiles, Ba/Ca profiles from these specimens demarcate individual years of shell growth and establish ontogenetic age. Low- and high-resolution Ba/Ca profiles do not, however, correlate with the 2003 spring phytoplankton bloom, casting doubt on the relationship between Ba/Ca ratios and phytoplankton blooms. Although the Ba/Ca peak timing loosely correlates with freshwater discharge events, peak amplitude does not, leaving the environmental cause/trigger of these peaks unknown. Nevertheless, the San Francisco Bay estuary seems like an ideal environment in which to further investigate the relationship between skeletal geochemical variation and patterns of primary productivity.

Incremental growth and mineralogy of Pannonian (Late Miocene) sciaenid otoliths: paleoecological implications

Incremental growth and mineralogy of Pannonian (Late Miocene) sciaenid otoliths: paleoecological implicationsOntogenetic age and body dimensions were studied on three extremely well-preserved sciaenid fish otoliths from sublittoral marls of Lake Pannon from Doba, Bakony Mts, Hungary. Macroscopic and microscopic observations offered clear evidence for the preservation of the genuine structural characteristics, for instance the bipartite incremental features. Ontogenetic ages were assigned for the three specimens as 16, 7 and 6 years by counting the annuli of the sagittae. Analytical results prove that the original aragonitic mineralogy has been preserved making them, and probably other Late Miocene teleost fossils, suitable for future microchemical analysis to reconstruct the past physicochemical environment.

Production of phytohormones, siderophores and population fluctuation of two root-promoting rhizobacteria in Eucalyptus globulus cuttings

Vegetative propagation by stem cuttings and mini-cuttings has been used worldwide for growing Eucalyptus plants. However, clones and hybrids of this plant present a great variability in their rooting capacity, apart from a gradual decrease in the rooting potential due to the ontogenetic age of the mother plant. Several studies have demonstrated that some bacteria promote plant growth and rooting through the action of direct and indirect mechanisms that are not still completely clear. Considering this, the objective of this study was to assess the production of auxins, abscisic acid and siderophores in Bacillus subtilis and Stenotrophomona maltophilia, which in previous studies increased rooting of E. globulus cuttings. Additionally, the population of these bacteria in the rhizosphere, superficial tissues of the stem-base and callus of the mini-cuttings was identified, and quantified by real-time PCR. Only S. maltophilia produced IAA in the presence of tryptophan; none of the bacterial strains produced ABA, but both produced siderophores. A comparative analysis of the separation profiles showed that there is a diverse microbial community in the rhizosphere, and only S. maltophilia was capable of keeping its population at a density of 2.03 × 10(7) cells/mg in different tissues of the mini-cuttings. The results would indicate that the rooting stimulus in E. globulus could be related to the action of one or several mechanisms such as the production of auxins and siderophores, and it could also be associated with the ability of bacteria to stay in the rhizosphere or in plant callus tissues.

Are Low Birth Weight Infants at Risk for Mineral Disturbance in Early Neonatal Period?

Bacground and Aims: The physiological levels of calcium and magnesium are very unstable in the first few days after birth, due to abrupt interruption of placental supply, low level of PTH and high levels of calcitonin, physiological acidosis. Infants with intrauterine growth retardation and preterm birth are at risk for hypocalcemia or hypomagnesemia. Often asymptomatic they can be undiscovered and untreated. There are a lot of controversies in regards with the physiological low limit of calcium and magnesium; are their values, smaller than those which are biostatistic classified, without any clinical and electrocardiographic aspects, physiological or not for ontogenetic age? The aim of these paper is to establish the incidence of early hypocalcemia and hypomagnesemia in low birth weight infants and the risk factors that impose the cases in a screening program. Methods: Calcium and magnesium were determined in 120 newborns (50 term SGA newborns, 50 prematures and 20 AGA newborns), 48 hours after birth. Results: Hypocalcemia was detected in 16% of term SGA with Rohrer index below 1.8 and 16% of prematures with gestational age under 32 weeks and birth weight below 1500g. Hypomagnesemia was detected in 4% of term SGA and 16% of SGA prematures. 4 term SGA have had hypocalcemia and hypomagnesemia. Onely 5 cases of term SGA with hypocalcemia were simptomatic. Conclusions: Low birth weight infants and severe intrauterine growth retardation are high risk factors for mineral disturbance. Screening is usefull in SGA new bornes with low Rohrer index and prematures under 1500g.

First evidence of Macaca sylvanus (Primates, Cercopithecidae) from the Late Pleistocene of Lezetxiki II cave (Basque Country, Spain)

In this article, we describe an almost complete macaque mandible from the Middle Pleistocene locality Marathousa 1 in the Megalopolis Basin of southern Greece. The mandible belonged to a male individual of advanced ontogenetic age and of estimated body mass ∼13 kg. Comparative metric analysis of its teeth permits its attribution to the Barbary macaque Macaca sylvanus, a species that was geographically widely distributed in Western Eurasia during the Plio-Pleistocene. The dental dimensions of the Marathousa 1 macaque fit better within the variation of the Early Pleistocene M. s. florentina and the Middle to Late Pleistocene M. s. pliocena rather than with the extant representative M. s. sylvanus. Moreover, principal component analysis reveals a better match with M. s. pliocena. However, because no clear-cut diagnostic criteria have been defined to differentiate these European fossil subspecies, we attribute the Marathousa 1 specimen to M. s. cf. pliocena, in agreement with the chronology of the locality. Previously known only from the Early Pleistocene of Greece by some isolated teeth, this is the first record of Macaca in the Middle Pleistocene of the country and one of very few in the eastern sector of the peri-Mediterranean region. We discuss the presence of macaques in the paleolake environment of Marathousa 1, as well as their predation risks from both carnivores and hominins present at the locality.

Ontogenetic variation and craniometric sexual dimorphism in the social giant mole-rat, Fukomys mechowii (Rodentia: Bathyergidae), from Zambia

The degree of maxillary molar tooth-row eruption and wear were used to assign samples of the social giant mole-rat, Fukomys mechowii, from Zambia, into nine relative age classes in order to assess ontogenetic (age) variation and craniometric sexual dimorphism, with reference to body mass. Univariate and multivariate statistical analyses showed craniometric differences between age classes 1–3 and age classes 5–9, with age class 4 being intermediate between these two age class groupings. This suggests that age class 4 lies at a point on a hypothetical growth curve where growth begins to stabilize. The intermediate placement of age class 4 in multivariate space broadly coincided with body mass categorizations into juveniles (age classes 1–3; <100 g), subadults (age class 4; c. 100–150 g), and adults (age classes 5–9; >150 g). The analyses also revealed the absence of sexual dimorphism in the relatively younger age classes 1–4 but its presence in the relatively older age classes 5–9, and these results are supported by data on body mass. These results may have implications in our understanding of the population and social structures, and reproductive strategies in this little-studied giant mole-rat.

Cranial ontogenetic variability, sex ratio and age structure of the Red fox

Abstract Describing the sex ratio, age structure of the population and ontogenetic variability of Red fox, Vulpes vulpes (Canidae, Carnivora) skull parameters, this study is based on 416 male and 289 female skulls collected in the Czech Republic. The skulls analysed came from feral individuals, that were shot by hunters. The male to female ratio was 1:0.69 regarding the whole population. Individuals younger than one year prevailed in the population (54% males, 48% females were in their first year of life). Four growth patterns of skull dimensions were described. The first group included mainly skull length dimensions (e.g. condylobasal length). They grew rapidly until the sixth month of life, becoming stabilised afterwards. The second group comprised parameters that were stable throughout the life (e.g. cheek tooth rows). Measurements representing the third growth pattern showed continual growth (mainly width dimensions, e.g. zygomatic breadth). Conversely, smaller dimensions of postorbital breadth were observed after the sixth month of life. Postorbital breadth represented the fourth growth pattern. It was concluded, that male and female Red foxes had similar ontogenetic skull development, even though there were some differences, e.g. in jugular breadth, which increased after the age of six months in males unlike in females.

Vertebral and rib anatomy in Caperea marginata: Implications for evolutionary patterning of the mammalian vertebral column

AbstractThe pygmy right whale, Caperea marginata, is a rare mysticete cetacean with an unusual suite of axial skeletal characters. Distally expanded first ribs, a long thorax with broadly overlapping vertebral transverse processes, plate‐like posterior ribs, and a short tail contrast with other cetaceans and suggest unique developmental patterning. Twenty‐four individuals of diverse ontogenetic age were available for analysis. Multiple, variable examples of incomplete rib fusion in dependent calves indicate that the first rib of adults is an ontogenetic fusion product of ribs 1 and 2. The composite rib articulates by way of its anterior (Rib1) component to the sternum and by way of its posterior (Rib2) component with thoracic vertebra 2. Thoracic vertebra 1 lacks rib articulations. When rib fusion is taken into account, the most frequent column formulas are C7T18L1Cd16–17 = 42–43 and C7T17L1Cd16–18 = 41–43. Thoracic and lumbar series are not reciprocal in count, arguing against their developmental linkage. Instead, parallel reduction in both lumbar and caudal counts supports the existence of neocete patterning in Caperea, as in all other living cetaceans. Ontogenetic vertebral column elongation is most marked in the posterior thorax, lumbos, and anterior tail. Vertebrae in these column regions are excellent predictors of total body length.

Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells ( Arctica islandica) and their function as paleotemperature proxies

The Sr/Ca and Mg/Ca ratios of many biogenic skeletons provide useful paleotemperature estimates. As yet however, it has remained largely impossible to obtain such information from bivalve shells. In the present study, metal-to-calcium values in the hinge plate (aragonite, outer shell layer) of four ontogenetically old (85 to 374 year-old) specimens of the long-lived bivalve, Arctica islandica, were measured on a LA–ICP–MS. The shells were collected alive in 1868, 1986 and 2003 from three different localities around Iceland. With increasing ontogenetic age and decreasing growth rate, a distinct trend toward increasing Sr/Ca (max. 5.17 mmol/mol) and Mg/Ca values (max. 0.89 mmol/mol) and greater variance were observed. Three potential explanations for these trends include a reduced capacity for element selection due to cell ageing, changing metabolism and/or a relative increase in the number of organic-rich (= Mg-rich) and organic-poor (= Sr-rich) shell portions through ontogeny. Partition coefficients however, remained far below 1, indicating that physiology exerted a strong control over the element partitioning between the shells and the ambient water. After mathematical elimination of these vital effects, residuals exhibited a highly significant negative correlation (e.g., age-detrended Sr/Ca data: R = − 0.64, R 2 = 0.41, p < 0.0001, growth rate-detrended Mg/Ca data: R = − 0.52, R 2 = 0.27, p < 0.0001) with sea surface temperature. These results are in good agreement with results obtained from the precipitation of abiogenic aragonite. The results of the present study can help to develop new techniques to extract environmental signals from the metal-to-calcium ratios of bivalve shells.

Annually resolved δ13C shell chronologies of long-lived bivalve mollusks ( Arctica islandica) reveal oceanic carbon dynamics in the temperate North Atlantic during recent centuries

The ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change. However, relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long-term, high-resolution dissolved inorganic carbon isotope ( δ 13C DIC) data, especially for the temperate North Atlantic, which is the major oceanic sink for anthropogenic CO 2. Here, we report shell carbon isotope values ( δ 13C shell), a potential proxy for δ 13C DIC, of old-grown specimens of the long-lived bivalve mollusk, Arctica islandica. This paper presents the first absolutely dated, annually resolved δ 13C shell record from surface waters of the North Atlantic (Iceland, Gulf of Maine) covering the time interval between 1753 and 2003. According to our results, the δ 13C shell data were unaffected by trends related to ontogenetic age. However, the shell carbonate was precipitated with a constant offset from expected equilibrium by − 1.54 to − 2.7 ± 0.2‰ corresponding to a 6.2 to 10.8 ± 0.8% contribution of respiratory CO 2 (− 25‰). The offset did not appear to vary through the lifetime of individual specimens and among specimens. Therefore, the δ 13C shell data of this species can very likely be used as a measure of δ 13C DIC. Furthermore, shell stable carbon isotope chronologies exhibited habitat-specific differences and a significant inter-annual and decadal variability related to the natural carbon cycle. In addition, a distinct negative δ 13C shell shift was found reflecting the oceanic Suess effect, i.e. the admixture of anthropogenic CO 2. However, this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic Polar Front in the Nordic Seas and a large-scale reorganization of atmospheric and oceanic currents in the North Atlantic. This likely resulted in a reduced admixture of cold Polar water onto the North Icelandic shelf (through the East Iceland Current) and the Gulf of Maine (through the Labrador Current) with an increased volume of warmer, isotopically well-equilibrated Atlantic waters. Our shell-based δ 13C DIC proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the North Atlantic.

Manganese speciation inDiplodon chilensis patagonicusshells: a XANES study

X-ray absorption near-edge spectroscopy (XANES) at the Mn K-edge was used to investigate the environment of Mn in situ within the growth increments of the long-lived freshwater bivalve species Diplodon chilensis patagonicus. Single XANES spectra and Mn Kalpha fluorescence distributions were acquired at submillimetre resolution (up to 100 microm x 50 microm), at Mn concentrations below the weight percent range (100-1000 microg g(-1)) in a high Ca matrix. The position and intensity of the pre-edge feature in the shell spectrum resembles best that of the Mn(II)-bearing reference compounds, suggesting that this is the oxidation state of Mn in the bivalve shells. By comparison with the XANES spectra of selected standard compounds, hypotheses about Mn speciation in the shell are also reported. In particular, different factors, such as provenance, ontogenetic age, variable Mn-concentrations or seasonal shell deposition seem not to influence the speciation of the metal in this bivalve species.

The Perinate Skull of Byronosaurus (Troodontidae) with Observations on the Cranial Ontogeny of Paravian Theropods

The skulls of two perinate paravians from Ukhaa Tolgod, Djadoktha Formation, Mongolia, are described here. The skulls are nearly unique in their combination of ontogenetic age and preservational quality and provide us with the first look at the morphology of such important anatomical regions as the rostrum, palate, and braincase at or near the onset of postnatal development in a nonavian paravian coelurosaur. Based on a number of derived characters, the skulls are allocated to a derived position within Troodontidae that is outside the clade consisting of Saurornithoides mongoliensis, Saurornithoides junior, Troodon formosus, and probably Sinornithoides youngi. A single synapomorphy, presence of a lateral maxillary groove, supports the Ukhaa perinates as Byronosaurus. The comparative morphology of the Ukhaa perinates with adult troodontids indicates a number of significant postnatal transformations (e.g., elongation and flattening of the rostrum, increase in the number of maxillary and dentary teeth, restructuring of the occipital plate and paroccipital process). These comparisons demonstrate that many characters historically considered important for phylogenetic and taxonomic assessments of adult maniraptorans are present at a relatively early stage of ontogeny. Differences in the developmental timing of various cranial characters have important implications for interpreting the fossil record as well as for understanding the role heterochrony has played in the evolution of derived coleurosaurs, including birds. The ontogenetic information provided by the Ukhaa perinates also allow us to comment on the enigmatic paravian Archaeornithoides deinosauriscus, which has been considered both the sister taxon to Avialae and a juvenile specimen of the troodontids Saurornithoides mongoliensis and Byronosaurus jaffei. We found no unique characters that support a priviledged relationship of Archaeornithoides deinosauriscus with avialans and only weak character support for this taxon as a basal troodontid—there is no known character evidence supporting it as a juvenile of either Saurornithoides or Byronosaurus.

Vergleichende Untersuchungen an drei Subspecies von Xiphophorus helleri Heckel (Pisces): (Morphologische Merkmale, geschlechtliche Differenzierung, Wachstum und Geschlechtsverhältnisse)

Summary Xiphophorw, helleri has four subspecies living in different water systems of Central America. We have no idea how long they have been geographically isolated, because there could have been temporary communications between the single water systems in the past, even as they may occur today. The four subspecies can easily be distinguished by colour patterns and body shape. Four breeding stocks representing two subspecies and two populations of another subspecies were examined concerning morphology, development of gonads, growth rate, and maturity. ♀♀ and ♂♂ were always treated separately. For investigations of genotypical differences between the four breeding stocks it was necessary to carry out the experiments under constant environmental conditions. Among numerous morphological characteristics only three showed differences which were guaranteed by statistical calculations: 1. number of dorsal fin rays, 2. relation between total length and maximal body depth, 3. relation between total length and depth of peduncule. For all three characteristics a cline from north to south was obvious. Great differences concerning early development of gonads in either male or female direction were not observed between the stocks of X. helleri. Only in X. helleri strigatus the formation of gonoduct was slightly retarded in comparison with the other subspecies. This fact is related to late maturity in X. helleri strigatus. The connection between age, size, and maturity when genetically determined is the following: Late maturity is correlated to high ontogenetic age (= size); however, body size does not increase as fast as absolute age, meaning that growth rate is reduced. For other species some authors partly state the contrary. The possibility is established that different species exhibit different connections between maturity, size, and age. The modificability of growth rate and sexual maturity was studied by changing the conditions of space and food. The deterioration of environmental conditions leads to poorer growth rate and later size at maturity. These results correspond to Svardsons conception; however, Svardsons curve of modification includes, as well, an extremely favourable environment. The ♂♂ are always divided into two groups: those that show sexual differentiation at a young stage (Fruhmannchen, ♂♂F) are tiny, slender ♂♂ which reach maturity and break off growth very early. On the other hand there are those which have a clumpsy, femalelike figure and whose maturity is retarded (Spatmannchen, ♂♂s). The curve of growth rate of these animals is similar to that of ♀♀. ♂♂s and ♀♀ do not stop their growth rate after maturity immediately but reduce their growth rate slowly. The different growth rate of ♂♂F on one hand and ♀♀ and ♂♂s on the other may be explained by different production and different effect of sexual hormones. ♀♀ inseminated by ♂♂F produce an offspring with a higher percentage of ♂♂ than ♀♀ inseminated by ♂♂S. Inasmuch aspolygenic sex determination can be taken for granted, ♂♂F and ♂♂S can be interpreted as sexually strong and weak individuals. In contradiction to frequently occurring statements in literature sexual inversion within X. helleri never could be observed in spite of long-dated investigations. It has become evident that ♀♀-likeness of ♂♂S before maturity, arrhenoidie- and seneacence-phenomena of ♀♀ have given rise to descriptions of sexual inversion. Aus dem Zoologischen Staatsinstitut und Zoologischen Museum Hamburg