The ontogenetic origins of skull shape disparity in the Triturus cristatus group.

Comparative studies of ontogenies of closely related species provide insights into the mechanisms responsible for morphological diversification. Using geometric morphometrics, we investigated the ontogenetic dynamics of postlarval skull shape and disparity in three closely related crested newt species. The skull shapes of juveniles just after metamorphosis (hereafter metamorphs) and adult individuals were sampled by landmark configurations that describe the shape of the dorsal and ventral side of the newt skull, and analyzed separately. The three species differ in skull size and shape in metamorphs and adults. The ontogenies of dorsal and ventral skull differ in the orientation but not lengths of the ontogenetic trajectories. The disparity of dorsal skull shape increases over ontogeny, but that of ventral skull shape does not. Thus, modifications of ontogenetic trajectories can, but need not, increase the disparity of shape. In species with biphasic life-cycles, when ontogenetic trajectories for one stage can be decoupled from those of another, increases and decreases in disparity are feasible, but our results show that they need not occur.

Morphing of the phylogeographic lineages of the Balkan alpine newts (Ichthyosaura alpestris, Caudata, Salamandridae): in situ morphological diversification.

Numerous alpine newt (Ichthyosaura alpestris) populations from the Balkans, representing all the previously established phylogeographic lineages, were studied for variations in various morphological characteristics (body size and shape, skull qualitative traits and number of trunk vertebrae). Here, we present a decoupling of morphological and mtDNA phylogeographic substructuring in the alpine newt on the Balkan Peninsula. In sharp contrast to other European newts (Triturus spp., Lissotriton spp.), the vast majority of morphological variation in the alpine newt is concentrated at the population level indicating an in situ morphological diversification. We found that the rate of morphological change is similar to the rate of mtDNA change. We hypothesize that the alpine newts are characterized by non-adaptive morphological evolution.

Morphological integration and ontogenetic niche shift: a study of crested newt limbs.

This study deals with the ontogenetic and evolutionary aspects of integration patterns in the limbs of crested newt species, which, like most amphibians, have a biphasic life history with two morphologically distinct stages (larval vs. juvenile and adult) that occupy different environments (aquatic vs. terrestrial). We analyzed the structure and pattern of correlation between limb skeletal elements at three ontogenetic stages (larval, juvenile, and adult) of four closely related species that differ in their preferences of aquatic habitats (more terrestrial and more aquatic). We found dynamic changes in the pattern of morphological integration between successive ontogenetic stages, as well as changes over the course of crested newt phylogeny. Generally, equivalent ontogenetic stages of different species of crested newts show higher concordance in the correlation pattern than successive ontogenetic stages within species. Among species, two opposing correlation patterns were observed: in more terrestrial species, homologous limb elements are less correlated and within-limb elements are more correlated; in aquatic species, the reverse pattern occurs. These results indicate that the function seems to be the covariance-generating factor, which has shaped the patterns of morphological integration of crested newt limbs.

Testing the hypothesis of morphological integration on a skull of a vertebrate with a biphasic life cycle: a case study of the alpine newt.

In this article, we explore the possible influences of the developmental and functional relationships between skeletal elements on the pattern of morphological integration in the adult skull of the alpine newt. Like many tailed amphibians, the alpine newt has a biphasic life cycle, which implies the possibility that two distinct sets of constraints on development and function of the cranial skeleton may act at different times. We study how trait covariation, resulting from processes early in development, affects patterns of covariation at the adult stage. We test whether the observed patterns of integration are consistent with those predicted from three a priori hypothesized sources of integration: developmental timing, hormonally mediated growth/remodeling during metamorphosis, and developmental and functional relationships. The analyses of the covariation among the landmarks in the dorsal and ventral alpine newt craniums yield somewhat contrasting results. Our results do not indicate a clear correspondence between the observed variations in the skull shape and any of the three proposed hypotheses. No traceable reflection of hypothesized developmental relationships in the pattern of morphological integration/modularity in the adult skull indicate that covariation structure is continually restructured by overlaying variation introduced through developmental and environmental factors at different stages of development. This finding supports the recently elaborated palimpsest view of morphological integration. Also, our results indicate that the allometry-free shape data have an even higher level of morphological integration than the data that contain the allometric component of the shape variation.

Sexual size dimorphism in the evolutionary context of facultative paedomorphosis: insights from European newts.

BACKGROUND: Sexual size dimorphism (SSD) is a key evolutionary feature that has been studied in many organisms. In a wide range of species, this pattern is more complex because of polymorphism within each sex. However, it is not known whether the magnitude and direction of SSD could be affected by alternative developmental trajectories within sexes. Our aim was to test whether an intrasexual polymorphism, facultative paedomorphosis (a process in which the development of somatic and gonadal tissues differs in alternative morphs), could affect SSD variation patterns in European newts. RESULTS: We report here the first evidence that SSD varies depending on the paedomorphic or metamorphic ontogenetic pathway. In species with a consistent female-biased SSD, paedomorphosis decreased the SSD level, but did not affect its direction. In species with moderate female-biased SSD or variable SSD patterns, paedomorphosis changed the magnitude, or both the magnitude and the direction, of SSD. CONCLUSION: Our study highlights the importance of developmental processes for shaping SSD patterns in populations in which contrasting life-history pathways evolved. European newts express different SSD patterns depending on their developmental pathway (i.e., metamorphosis versus paedomorphosis), as well as their species and population. These findings emphasize the importance of studying alternative morphotypes, which are found in a wide range of animal groups, to understand the evolution of SSD.

SRYand architectural gene regulation: the kinetic stability of a bent protein-DNA complex can regulate its transcriptional potency.

Protein-directed DNA bending is proposed to regulate assembly of higher-order DNA-multiprotein complexes (enhanceosomes and repressosomes). Because transcriptional initiation is a nonequilibrium process, gene expression may be modulated by the lifetime of such complexes. The human testis-determining factor SRY contains a specific DNA-bending motif, the high-mobility group (HMG) box, and is thus proposed to function as an architectural factor. Here, we test the hypothesis that the kinetic stability of a bent HMG box-DNA complex can in itself modulate transcriptional potency. Our studies employ a cotransfection assay in a mammalian gonadal cell line as a model for SRY-dependent transcriptional activation. Whereas sex-reversal mutations impair SRY-dependent gene expression, an activating substitution is identified that enhances SRY's potency by 4-fold. The substitution (I13F in the HMG box; fortuitously occurring in chimpanzees) affects the motif's cantilever side chain, which inserts between base pairs to disrupt base pairing. An aromatic F13 cantilever prolongs the lifetime of the DNA complex to an extent similar to its enhanced function. By contrast, equilibrium properties (specific DNA affinity, specificity, and bending; thermodynamic stability and cellular expression) are essentially unchanged. This correlation between potency and lifetime suggests a mechanism of kinetic control. We propose that a locked DNA bend enables multiple additional rounds of transcriptional initiation per promoter. This model predicts the occurrence of a novel class of clinical variants: bent but unlocked HMG box-DNA complexes with native affinity and decreased lifetime. Aromatic DNA-intercalating agents exhibit analogous kinetic control of transcriptional elongation whereby chemotherapeutic potencies correlate with drug-DNA dissociation rates.

Effect of engineering Hsp70 copy number on Hsp70 expression and tolerance of ecologically relevant heat shock in larvae and pupae of Drosophila melanogaster.

To determine how the accumulation of the major Drosophila melanogaster heat-shock protein, Hsp70, affects inducible thermotolerance in larvae and pupae, we have compared two sister strains generated by site-specific homologus recombination. One strain carried 12 extra copies of the Hsp70 gene at a single insertion site (extra-copy strain) and the other carried remnants of the transgene construct but lacked the extra copies of Hsp70 (excision strain). Hsp70 levels in whole-body lysates of larvae and pupae were measured by ELISA with an Hsp70-specific antibody. In both extra-copy and excision strains, Hsp70 was undetectable prior to heat shock. Hsp70 concentrations were higher in the extra-copy strain than in the excision strain at most time points during and after heat shock. Pretreatment (i.e. exposure to 36 degrees C before heat shock) significantly improved thermotolerance, and this improvement was greater and more rapid in larvae and pupae of the extra-copy strain than in those of the excision strain. The experimental conditions resemble thermal regimes actually experienced by Drosophila in the field. Thus, these findings represent the best evidence to date that the amount of a heat-shock protein affects the fitness of a complex animal in the wild.

[Value of thyroid function tests after long term hormone therapy]. / Vrijednost testova funkcije stitne zlijezde nakon dugotrajne hormonske terapije.

Estrogens are known to change the level of specific circulating proteinthyroid binding globulin (TBG). In view of this, a study was conducted of the effect of some hormonal oral contraceptives on the thyroid function by using routine procedures: thyroid scintigraphy, protein bound iodine (PBI), determination of thyroid hormones thyroxine and triiodothyronine. No statistically significant difference was found between the experimental (N = 84) and the control (N = 34) group.