Natural variation in the limb skeletal pattern of the crested newt,Triturus carnifex (amphibia: Salamandridae)

The forelimb skeletal patterns of two geographically isolated populations of Triturus carnifex, one from northern Italy (Rosate, Milano) and one from central Italy (Bagnaia, Perugia) were studied. A total of 1,018 limbs were examined. Limb skeletal variants, generally consisting either of a reduced number of carpals and/or of an alternate phalangeal formula, were commonly observed, as has been reported for other amphibian species. The population from northern Italy showed a greater variability than that from central Italy. Skeletal variants were present in 34% and 12% of the limbs, respectively (i.e., in 48% and 20% of the newts). In the Rosate population, the majority of variants consisted of fusions of radiale and prepollicis and of the phalangeal formula 1-2-3-2. Severe skeletal defects were also found in 3% of the limbs of the newts from Rosate and in 1% of the limbs of those from Bagnaia. At present, no conclusion can be drawn about the evolutionary significance of the limb skeletal variation observed in the two populations, because of the paucity of data on intra- and interpopulation variations in other species of the genus Triturus. © 1992 Wiley-Liss, Inc.     

Breeding dynamics of Triturus carnifex at a pond in northwestern Italy (Amphibia, Urodela, Salamandridae)

A population of the Italian crested newt ( Triturus carnifex ) was studied in 1984 at a pond near Druento (Turin, Piedmont, northwestern Italy). Animals entering and leaving the pond fell into paired pit-fall traps during both spring and autumn migrations. A positive correlation found between rainfall and migration, a shortening of migration periods and summer inactivity suggest that, in the Mediterranean region, air moisture may be a limiting factor for newt activity. During their aquatic period adults showed strong individual differences in weight changes that cannot be explained on the basis of initial body weight or length. High variability in crested newt life history traits may be the result of repeated bottlenecks caused by environmental stress and high population isolation.     

Endocrine-disrupting effects of nonylphenol in the newt, Triturus carnifex (Amphibia, Urodela)

The aim of our study was to verify whether environmental concentrations of nonylphenol influenced the adrenal gland of Triturus carnifex. Newts were exposed to 19 μg/L nominal concentration of nonylphenol throughout the periods of December-January and March-April, corresponding to different stages of the chromaffin cell functional cycle. The morphological features of the steroidogenic and chromaffin tissues, and the serum levels of ACTH, aldosterone, corticosterone, norepinephrine and epinephrine were evaluated. Nonylphenol did not influence ACTH serum levels. During the two periods examined, the steroidogenic tissue had the same reaction: the quantity of cytoplasmic lipids, and the corticosteroid serum levels, decreased, suggesting the inhibition of synthesis and release of corticosteroids. During the two periods examined, the chromaffin tissue reacted differently to nonylphenol. During December-January, the numeric ratio of norepinephrine granules to epinephrine granules, and the epinephrine serum levels, increased, suggesting the stimulation of epinephrine release. During March-April, the numeric ratio of norepinephrine granules to epinephrine granules did not change, and the norepinephrine serum levels decreased, suggesting the inhibition of norepinephrine release. Our results show that nonylphenol influences the activity of the newt adrenal gland; considering the physiological role of this gland, our results suggest that nonylphenol may contribute to amphibian decline.     

The Sexual Behaviour of the Great Crested Newt,Triturus cristatus (Amphibia: Salamandridae)

The sexual behaviour of Triturus cristatus is described. The first stage of sexual behaviour consists of an orientation phase in which the male approaches the female, sniffs her and moves in front of and perpendicular to her. The second stage is a prolonged period of static display with two different tail movements, called Fan and Lash, in 13.8 ± 1.3 bouts (x? ± SE) with intervals of 10.5 ± 0.3 s between bouts. Each bout contains 6.7 ± 0.3 regular Fan beats at a frequency of 0.5–0.8 Hz. This Fanning provides olfactory and mechanical stimulation to the female. 15% of bouts also contain a violent Lash, in which the male rapidly slaps the female's flank. Some Lashes are used to stop the female when she tries to move away. In the third stage of the sexual sequence, the male turns away, Creeps for 6.7 ± 0.3 s (x? ± SE) and then Quivers his tail. A receptive female follows and touches his tail, and the male deposits a spermatophore and then turns to one side with his tail folded along his flank in a position called Brake. The female now approaches again and the male steps away sideways in a movement called Rebrake. After several Rebrakes the male stops, the female touches his tail and the spermatophore may now be picked up in her cloaca. This sequence can be repeated several times during one encounter. This behaviour is discussed in relation to previous studies of courtship in this genus.     

Histochemical and quantitative study of the cloacal glands of Triturus marmoratus marmoratus (Amphibia: Salamandridae)

The cloacal glands of the male marbled newt Triturus marmoratus marmoratus were studied during winter and summer by histochemical and quantitative histologic methods. Four types of glands were distinguished: pelvic, dorsal, ventral, and Kingsbury's glands. The pelvic and dorsal glands have an eosinophilic epithelium and secrete neutral mucins. The ventral and Kingsbury's glands have a basophilic epithelium and secrete acid mucins. The lectin-histochemical characterization of the carbohydrates secreted by the four gland types revealed that the secretion of both the pelvic and Kingsbury's glands contain β-GalNAc in the peripheral region of the oligosaccharide, and that the dorsal glands secrete a glycoprotein with α-GalNAc. The ventral gland sections did not react to any of the lectins used here. The quantitative study revealed that the cloaca undergoes seasonal variations in volume, being significantly larger in winter than in summer. The total volume occupied by both the pelvic and ventral glands, as well as their tubular diameter, are also significantly greater in winter, while these parameters do not vary in dorsal and Kingsbury's glands. No seasonal differences were observed in the height of the epithelium in any gland     

Field observations of the sexual behaviour of the smooth newt, Triturus vulgaris vulgaris (Amphibia: Salamandridae)

This study reports observations of smooth newts, Triturus vulgaris vulgaris , breeding in a pond in southern England. Efforts were made to collect data on the timing of oviposition and on sexual behaviour during the breeding seasons of 1985 and 1986. Despite some between-year differences in the timing of certain events, the qualitative pattern of reproduction was similar in both years. Courtship interactions were seen most frequently during a relatively short period of time before females began laying their eggs, which occurred in a highly synchronized manner. It seems likely that the probability of any one courtship encounter resulting in spermatophore transfer was low. Males competed for mates by chasing females and by interfering with one another's courtships, but no overt aggression was seen. Females appeared to find such male-male interactions 'aversive'. Scramble competition between males was most intense when the majority of females in the population were laying their eggs and were unresponsive to courtship. The mating system of the smooth newt most closely resembles a lek in which the intensity of sexual selection among males varies as a function of female availability.     

Brain-capillary architecture of the newt,Triturus cristatus carnifex (Caudata: Salamandridae): Scanning electron-microscopical study of vascular corrosion casts

The brain-microvascular architecture of the newt (Triturus cristatus carnifex) was studied by scanning electron-microscopical examination of microvascular corrosion casts. It is characterized at the leptomeningeal level by a superficial network of single vessels that leave the meningeal sheath to form hairpin-shaped capillary loops. These loops penetrate the nervous parenchyma to varying depths and are variously bent, inclined, and twisted. Each hairpin-like loop consists of descending and ascending limbs connected by a distal U-shaped segment. The limbs are of equal diameter and lack physical differentiation. Some loops branch in a secondary loop, but there are no intraparenchymal connections with analogous surrounding structures. On vascular casts we observed detailed imprints of endothelial cell nuclei. This microvascular architecture is present in the whole brain except in leptomeninx and choroidal plexuses. The vascular pattern of T. cristatus carnifex resembles that of apodans. However, it differs from the anuran condition, which is characterized by a three-dimensional parenchymal network and from that of Ambystoma mexicanum which displays an intermediate condition between a single-capillary network and a capillary-loop model. At the level of paired capillaries, a counter-current exchange system may occur between the two limbs of the same loop, an arrangement that could promote uniformity of extracellular fluid composition in parenchyma.     

Sexual Interference and Sexual Defense in the Smooth Newt,Triturus vulgaris (Amphibia,Urodela, Salamandridae)

• 1 When a male smooth newt encounters a ♀ who is already engaged in courtship, he may mimic her behaviour during the spermatophore deposition and transfer stages of the courtship. He thereby usurps the courting ♂ and may inseminate the ♀ himself. Such sexual interference depresses the short-term, and perhaps long-term, mating success of the courting ♂.
• 2 In the presence of a potential rival, the courting ♂ alters certain aspects of his sexual behaviour. He displays more intensely to the ♀ and attempts to draw her away from the rival by increasing the duration of his display. He may also “check” that it is the ♀, and not the rival, who will elicit the deposition of a spermatophore from him. These changes in the behaviour of the courting ♂ are interpreted as defense against sexual interference.
• 3 Female smooth newts may be multiply inseminated as a consequence of sexual interference; this may result in sperm competition. However, ♀♀ seem to find competitive interactions between ♂ ♂ “aversive”.
• 4 Sexual interference by ♀-mimicry and associated defensive behaviour patterns are common in the urodele amphibians. Interference can be thought of as a “side-payment” conditional mating strategy.

     

The Cloaca and Spermatheca of the Female Smooth Newt, Triturus vulgaris L. (Amphibia: Urodela: Salamandridae)

The anatomy and histology of the cloaca and spermatheca of 13 female smooth newts ( Triturus vulgaris ) were studied by light microscopy. The cloaca consists of a short, anterior tube (which receives the oviducts), which opens into a larger, more posterior chamber. The spermatheca, which is the only gland in the cloaca, consists of a mass of exocrine, acinar tubules which empty individually and dorsolaterally into the posterior part of the cloacal tube and all but the most posterior part of the cloacal chamber. Stored sperm are most abundant in the spermathecal tubules during the peak of the breeding season (in May and June); during their period of storage, the sperm do not appear to make intimate contact with the epithelial cells lining the spermathecal tubules. Longterm storage of viable sperm from one breeding season to the next is probably absent in the smooth newt. Sperm storage by and multiple insemination of females both occur in this species and are necessary preconditions for competition between the sperm of different males for the fertilization of eggs. However, sperm competition has not been demonstrated in the smooth newt.     

Experimental hybridization within the genus Triturus (Urodela: Salamandridae)

The spermatogenesis of 9 F₁ hybrids of Triturus cristatus carnifex × T. vulgaris meridionalis was studied in squash preparations of testicular fragments, treated by the C-staining method. The chromosome number of these hybrids was examined in spermatogonial metaphases and found to be diploid. The two parental sets were always recognized, which means that a regular, although heterospecific, amphimixis occurred (2n=n+n). Meiotic prophase I is greatly altered owing to a failure of typical chromosome pairing and chiasma formation. At metaphase I and/or meta-anaphase I, the effects of the hybrid combination of the 2 specific parental sets are clearly visible. Most primary spermatocytes contain only univalents. A few show chromosome associations (bivalents, trivalents and, more rarely, quadrivalent chains) besides univalents. Such associations are of 2 types: (a) intragenomal associations = associations of 2 chromosomes by a terminal (a¹) or subterminal chiasma (a²); (b) intergenomal associations = associations of 2 chromosomes by a terminal (b¹) or subterminal chiasma (b²). Univalents segregate at random while the associations often lag on the equatorial plane or migrate entire to a spindle pole. Primary spermatocytes with chromosome multivalents can encounter greater difficulties in accomplishing the first cytokinesis. Secondary spermatocytes are numerically and qualitatively unbalanced; however, some of them undergo spermiogenesis and can give rise to a small number of sperms, generally abnormal and never united in bundles. — Problems related to the occurrence of anomalous chiasmata and of intra- and inter-genomal homologies are discussed.     

Experimental hybridization within the genus Triturus (Urodela: Salamandridae)

Spermatogenesis in the F₁ hybrid (2n=24=12 +12 ) between the closely related newt species T. cristatus carnifex and T. marmoratus was apparently normal up to pachytene. Many unpaired chromosomes were present at diplotene and a typical diakinesis was lacking. Primary spermatocytes at meta-and meta-anaphase contained up to 12 regular intergenomal bivalents and a corresponding number of univalents when less then 12 II. Most chiasmata were terminal or subterminal, some intercalary. Chiasmata between corresponding heterospecific chromosomes can be reported as true: real crossing over has taken place, proving the presence of primary chromosomal homologies between the 2 sets of the parental species. Evidence for recombination is based on the segregation of particular markers (i.e., subterminal C-bands and NORs) observed in certain chromosomes at metaphase II. One chromatid of single chromosomes can show the T. cristatus phenotype and the other the T. marmoratus phenotype. A few primary spermatocytes contain a certain number of irregular associations (intragenomal or intrahaploid bivalents, irregular intergenomal bivalents, chromosome multivalents) joined by chiasmata which can be defined as anomalous. Other abnormalities concern the occurrence of interlocked bivalents which occasionally show an anomalous exchange between heterologous chromatids. — Cytogenetic criteria useful to evaluate the taxonomic relationships between different species have been discussed as well as some possible trends in chromosome evolution and speciation within the genus Triturus.     

Human follicle-stimulating hormone modulation of adrenal gland activity in the Italian crested newt, Triturus carnifex (Amphibia, Urodela)

The aim of the present study was to verify if human FSH influences the adrenal gland of the newt, Triturus carnifex. Newts were given intraperitoneal injections of human FSH throughout the periods of February-March, and December-January; periods in which newt FSH levels are normally very low. The effects of human FSH on adrenal gland activity were observed in the morphological features of the steroidogenic and chromaffin adrenal cells, and in the serum levels of aldosterone, corticosterone, norepinephrine and epinephrine. The effect of human FSH on the steroidogenic cells was significant during the February-March period; the quantity of cytoplasmic lipids decreased, and the corticosteroid serum levels increased. During the December-January period, the human FSH effects were negligible. The effect of human FSH on the chromaffin cells was significant during both the February-March, and the December-January periods. During February-March, the human FSH increased the numeric ratio of norepinephrine granules to epinephrine granules, and increased the epinephrine serum levels. During December-January, the human FSH decreased the numeric ratio of norepinephrine granules to epinephrine granules, and increased the norepinephrine serum levels. The results of the present study show that human follicle-stimulating hormone influences the activity of the newt adrenal gland, thus indicating a relationship between the annual sexual cycle and the annual adrenal cycle of the newt.     

Intermediate heterochromatic zones in Triturus (Amphibia: Caudata)

Employment of the C-banding procedure disclosed the presence of slightly stained bands in some chromosome regions of several Triturus species. These regions have been previously described in other organisms as 'grey C-bands'. Possible explanations for the presence of these bands in Triturus karyotypes are discussed.     

Chromosome differentiation in the Triturus alpestris complex (Amphibia: Caudata)

Several individuals from distinct populations of 7 subspecies included in the Triturus alpestris complex have been analysed to obtain characteristic C-banding patterns.The differences found among the populations as regards the amount, complexity and distribution of heterochromatin bands have been employed to test a pattern of chromosome evolution.Relevant similarities and dissimilarities of these populations are discussed in the light of the tentative evolutionary history inferred from a rooted tree.     

Heterochromatic DNA in Triturus (Amphibia,Urodela)

The MspI family of highly repeated sequences is a centromeric satellite DNA representing about 1% of the genome of the Italian smooth newt, Triturus vulgaris meridionalis. We have studied the structure, genomic organization, chromosomal localization and conservation across species of this family. MspI sequences are around 197 bp long, as shown by sequencing of three cloned units. The family is organized in large clusters of tandemly arrayed units, present at almost all the centromeres of T.v. meridionalis, and is well conserved in the T.v. vulgaris subspecies. Conserved MspI sequences are also present in the related species T. helveticus, where they appear to be clustered at the centromeres of only a few chromosomes. MspI sequences are not found in other Triturus species analysed. The correlation of these sequences with the overall distribution pattern of heterochromatin and the extent of their conservation within the genus Triturus, are discussed.     

First Evidence of an Altitudinal Variation in the Brain Size of Triturus alpestris alpestris (Laur.) (Amphibia,Caudata, Salamandridae)

This study deals with geographical variations in brain-body weight relationships in the alpine newt, Triturus alpestris alpestris. According to the canonical axis, C.A., the mean allometry in this species is 0.473±0.03; an allometry value of 0.5 is considered to be characteristic of Caudata. No significant difference was observed between the four reduced major axes (R.M.A.) of lowland animal samples (mean value of the pooled samples, C.A. = 0.469±0.210). In contrast, between the mountain samples a significant difference exists, the R.M.A. in the sample from l'Alpe d'Huez (Isère, France) being 0.331±0.57 as compared to 0.72±0.18 in the sample from Durmitor (Montenegro, Yugoslavia). In spite of this difference, their encephalisation index (Ie) did not differ significantly, having on average a value of 118.18±8.5, against īe = 93.8±8.0 for lowland samples. A significant difference in encephalisation index between mountain and lowland alpine newts thus exists. This is probably the first observation in vertebrates of an encephalisation index increase with altitude. A biological hypothesis is proposed to explain this peculiar observation.     

Sexual isolation between two newt species, Triturus vulgaris and T. montandoni (Amphibia, Urodela, Salamandridae)

In the present study we investigated sexual isolation between Triturus vulgaris and 77 montandoni in mating experiments run under semi-natural conditions. The two newt species offer a suitable model for studying evolution of reproductive isolation and mating preferences because they arc genetically the most similar species within the genus and readily hybridize in nature. Separate experiments were conducted in which groups of virgin females were placed together (in artificial pools) with groups of homospecific, heterospecific or both types of males. The estimates of reproductive isolation and mating propensity were based on the numbers of females producing hybrids and/or non-hybrid progeny. The levels of reproductive isolation, isolation asymmetry (IA) and propensity asymmetry (PA) were significant only for experiments in which females were given a choice between conspecific and heterospecific males. This implies that mating experiments with no interspecific choice may reduce discrimination and affect patterns of IA and PA. Asymmetry in reproductive isolation was also significant when the analysis was confined to just inseminated females. Differences in habitat preferences and condition of females possibly contributed to the relatively high values of PA.