Abnormal spermatogenesis at low temperatures in the Japanese red-bellied newt,Cynops pyrrhogaster: possible biological significance of the cessation of spermatocytogenesis

In newt testis, spermatocytes never appear during winter, because secondary spermatogonia die by apoptosis just before meiosis. In the current study, we examined the effect of low temperatures on spermatogenesis. Incubation of newts at low temperatures (8, 12, 15 degrees C) induced defects in spermatogenesis in a temperature-dependent manner. At 8 degrees C, multinucleated giant cells (MGCs) were observed in spermatocytes and spermatogenesis never proceeded beyond meiosis. Although spermatocytes completed meiotic divisions at 12 degrees C, severe cell death was observed in the spermatids. At 15 degrees C both normal and abnormal spermiogenesis were observed. Under these conditions, impaired meiotic synapsis/recombination and down-regulation of the expression of the DMC1 protein, which play pivotal roles in meiotic pairing in eukaryotes, were also observed. Furthermore, to examine the quality of the sperm produced at low temperature for supporting development, artificial insemination was performed. The eggs inseminated with spermatozoa derived from newts kept at 15 degrees C demonstrated a restricted developmental capacity, even though these spermatozoa had an equal capacity for carrying out fertilization to those kept at 22 degrees C. These results suggest that meiosis at low temperatures cause the production of abnormal spermatozoa. Conservation and the significance of this phenomenon in poikilothermic vertebrates living in the temperate zones are also discussed.     

A comparative analysis of predator-induced plasticity in larval Triturus newts

Species that occupy similar habitats are expected to show convergent phenotypes. If habitats are defined by the presence of predators, then traits that modify vulnerability to predation, including predator-induced phenotypic plasticity, should be similar within habitats. We tested this idea using larvae of six syntopic newt species belonging to the two Triturus clades. Behavioural plasticity induced by odonate predators was strongly dissimilar between the two main clades but similar within them. Morphological plasticity was variable among species, even between one pair of closely related species. A predation experiment tested whether differences between clades could be caused by differences in body size. Size-specific vulnerability differed between newts in the small-bodied and large-bodied clades, indicating that similar predators may affect the two clades differently. The results showed both similarity and dissimilarity in predator-induced phenotypic plasticity in syntopic larval newts although theory suggests that divergence is unlikely in such ecologically similar species.     

Trunk elongation and ontogenetic changes in the axial skeleton of Triturus newts

Body elongation in vertebrates can be achieved by lengthening of the vertebrae or by an increase in their number. In salamanders, longer bodies are mostly associated with greater numbers of vertebrae in the trunk or tail region. However, studies on the relative contribution of the length of single vertebra to body elongation are lacking. In this study, we focus on evolutionary and ontogenetic changes in differentiation of the trunk vertebrae and the relative contribution of individual vertebrae to trunk lengthening in Triturus newts, a monophyletic group of salamanders that shows remarkable disparity in body shape. We compared juveniles and adults of the most elongated T. dobrogicus , which has 17 trunk vertebrae, with juveniles and adults of two closely related species (T. ivanbureschi and T. anatolicus belonging to the T. karelinii species complex) representing a stout and robust morphotype with thirteen trunk vertebrae. We show that trunk vertebrae are uniform in size at the juvenile stage of both analyzed morphotypes. In adults, the trunk vertebrae of the elongated T. dobrogicus are largely uniform, while in those of T. anatolicus , the first two vertebrae differ from the remaining trunk vertebrae. There was no difference in the relative contribution of individual vertebrae to body lengthening between species or stages. We conclude that body elongation in Triturus newts is achieved by increasing the number of vertebrae but not their length.     

A change in competitive context reverses sexual selection on male size

In studies of sexual selection, larger size is often argued to increase male fitness, and relatively smaller males are explained by genetic and/or environmental variation. We demonstrate that a size–development life‐history trade‐off could underlie the maintenance of a broad, unimodal distribution of size in male redback spiders (Latrodectus hasselti). Larger males are superior in direct competition, but redback males mature rapidly at small size in the presence of females. In field enclosures, we simulated two competitive contexts favouring development of divergent male sizes. Relatively smaller males lost when competing directly, but had 10 times higher fitness than relatively larger males when given the temporal advantage of rapid development. Linear selection gradients confirmed the reversal of selection on size, showing that it is critical to consider life‐history decisions underlying the development of traits related to fitness.     

Sonic hedgehog antagonists reduce size and alter patterning of the frog inner ear

Sonic hedgehog (Shh) signaling plays a major role in vertebrate development, from regulation of proliferation to the patterning of various organs. In amniotes, Shh affects dorsoventral patterning in the inner ear but affects anteroposterior patterning in teleost ears. It remains unknown how altered function of Shh relates to morphogenetic changes that coincide with the evolution of limbs and novel auditory organs in the ear. In this study, we used the tetrapod, Xenopus laevis , to test how increasing concentrations of the Shh signal pathway antagonist, Vismodegib, affects ear development. Vismodegib treatment dose dependently alters the development of the ear, hypaxial muscle, and indirectly the Mauthner cell through its interaction with the inner ear afferents. Together, these phenotypes have an effect on escape response. The altered Mauthner cell likely contributes to the increased time to respond to a stimulus. In addition, the increased hypaxial muscle in the trunk likely contributes to the subtle change in animal C‐start flexion angle. In the ear, Vismodegib treatment results in decreasing segregation between the gravistatic sensory epithelia as the concentration of Vismodegib increases. Furthermore, at higher doses, there is a loss of the horizontal canal but no enantiomorphic transformation, as in bony fish lacking Shh. Like in amniotes, Shh signaling in frogs affects dorsoventral patterning in the ear, suggesting that auditory sensory evolution in sarcopterygians/tetrapods evolved with a shift of Shh function in axis specification. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1385–1400, 2017     

Forelimb regeneration in thyroidectomized adult newts following organ culture and autografting of the thyroid glands

Summary Thyroidectomy and organ culture of adult newt thyroid glands three days prior to forelimb amputation was followed by autografting the glands subcutaneously into the animal's lower jaw region 9, 18 or 25 days postamputation (GC^{9, 18, 25} day series). This was an attempt, utilizing 515 animals, to elucidate further the role of the thyroids in regeneration. Amputated limbs of the thyroidectomized (Thx) and autografted muscle explant (MC = sham) cases underwent stumping or were significantly delayed in their regeneration rate and displayed abnormal morphogenesis compared with control regenerates. In the GC⁹ series newts, regenerates were identical to controls 45 days postamputation. However, regenerates of the GC¹⁸ series cases exhibited delayed and abnormal development at 45 days; but they were not as delayed and had fewer abnormalities than those cases in the Thx and MC groups. Results of the GC²⁵ series newts were similar to those of the Thx group. Within 5 days of autografting the thyroids, epidermal moulting resumed and long-term survival ensued. We conclude that normal limb regeneration in the adult newt is thyroid hormone(s) dependent, specifically the later stages of growth, differentiation and morphogenesis.Supported by grant A-1208 from the Natural Sciences and Engineering Research Council of Canada to R.A.L.     

Sexual size dimorphism and male contest in wild Siamese fighting fish

Larger males of the wild Siamese fighting fish Betta splendens were more successful in male contests. There were no differences in fighting duration among treatments. Comparing agonistic behaviour between large and small males in ±1 and ±2 S.D treatments, larger males attacked, chased and performed total agonistic behaviour more than smaller males. There were no differences between larger and smaller males concerning other agonistic behaviour during fighting. Females presented with two potential mates of different sizes did not prefer larger males.     

Daily rhythmic changes of cell size and shape in the first optic neuropil in Drosophila melanogaster

Daily rhythms of changes in axon size and shape are seen in two types of monopolar cell—L1 and L2—that are unique cells within each of the modules or cartridges of the first optic neuropil or lamina in the fly's optic lobe. In the fruit fly Drosophila, L1 and L2's axons swell at the beginning of both day and night, with larger size increases occurring at the beginning of night. Later, they shrink during the day and night, respectively. Simultaneously, they change shape from an inverted conical form during the day to a cylindrical one at night. This is because the axonal cross section of L1 increases during the night, especially at proximal depths of the lamina, closest to the brain, whereas the axon of L2 increases in size at distal lamina depths. The cross‐sectional areas of the L1 cell and of an individual cartridge both change under constant darkness (DD), indicating the circadian origin of changes observed under day/night (LD) conditions. We sought to see whether such changes impart a net change to the entire lamina's volume or shape that is visible by light microscopy, but oscillations in the volume or the curvature of the whole lamina neuropil are found neither in LD nor in DD. These size changes are discussed in relation to previous findings in the housefly Musca, with respect to differences in L1 and L2 between the two species, and to differences in the time course of their circadian changes. © 1999 John Wiley & Sons, Inc. J Neurobiol 40: 77–88, 1999     

Application of induced pluripotent stem cell and embryonic stem cell technology to the study of male infertility

Stem cells (SCs) are classes of undifferentiated biological cells existing only at the embryonic, fetal, and adult stages that can divide to produce specialized cell types during fetal development and remain in our bodies throughout life. The progression of regenerative and reproductive medicine owes the advancement of respective in vitro and in vivo biological science on the stem cell nature under appropriate conditions. The SCs are promising therapeutic tools to treat currently of infertility because of wide sources and high potency to differentiate. Nevertheless, no effective remedies are available to deal with severe infertility due to congenital or gonadotoxic stem cell deficiency in prepubertal childhood. Some recent solutions have been developed to address the severe fertility problems, including in vitro formation of germ cells from stem cells, induction of pluripotency from somatic cells, and production of patient‐specific pluripotent stem cells. There is a possibility of fertility restoration using the in vitro formation of germ cells from somatic cells. Accordingly, the present review aimed at studying the literature published on the medical application of stem cells in reproductive concerns.     

NARROW AND ROLLED LEAF 2 regulates leaf shape,male fertility,and seed size in rice

Grain yield in rice(Oryza sativa L.) is closely related to leaf and flower development. Coordinative regulation of leaf, pollen, and seed development in rice as a critical biological and agricultural question should be addressed. Here we identified two allelic rice mutants with narrow and semirolled leaves, named narrow and rolled leaf 2-1(nrl2-1) and nrl2-2. Map-based molecular cloning revealed that NRL2 encodes a novel protein with unknown biochemical function. The mutation of NRL2 caused pleiotropic effects, including a reduction in the number of longitudinal veins, defective abaxial sclerenchymatous cell differentiation, abnormal tapetum degeneration and microspore development, and the formation of more slender seeds compared with the wild type(WT). The NRL2 protein interacted with Rolling-leaf(RL14),causing the leaves of the nrl2 mutants to have a highercellulose content and lower lignin content than the WT, which may have been related to sclerenchymatous cell differentiation and tapetum degeneration. Thus, this gene is an essential developmental regulator controlling fundamental cellular and developmental processes, serving as a potential breeding target for high-yielding rice cultivars.     

Correlation of seasonal changes in sperm output with endocrinological changes in the adult male bonnet monkey,Macaca radiata

We have examined the monthly variations in sperm output and attempted to correlate the profiles of endocrine hormones secreted with the sperm counts throughout the year in the adult male bonnet monkey. As previously reported, there was a distinct spurt in sperm output beginning September through December months. A concomitant increase in serum testosterone and prolactin concentrations were also noted during September through November (mid and post-monsoon season). Although there was a marked increase in gonadotropin releasing hormone stimulated testosterone secretion, the peak testosterone concentrations post gonadotropin releasing hormone injection did not vary significantly (P > 0.05) throughout the year. Basal serum follicle stimulating hormone concentrations did not vary significantly (P > 0.05) during April to June months compared to September-November months. Serum inhibin concentration remained unaltered throughout the year, except in the month of March. The results of this study provide evidence for annual rhythms in prolactin and testosterone secretion and a distinct seasonality in the sperm output of the adult male bonnet monkey, but the pituitary responsiveness to exogenous gonadotropin releasing hormone remains unaltered throughout the year. Because of the existence of seasonality as noted in the present study, future studies which utilize the adult male bonnet monkey as an experimental model need to take into consideration the seasonal effects on reproductive function in this species.     

Plastic and evolutionary responses of cell size and number to larval malnutrition in Drosophila melanogaster

Both development and evolution under chronic malnutrition lead to reduced adult size in Drosophila. We studied the contribution of changes in size vs. number of epidermal cells to plastic and evolutionary reduction of wing size in response to poor larval food. We used flies from six populations selected for tolerance to larval malnutrition and from six unselected control populations, raised either under standard conditions or under larval malnutrition. In the control populations, phenotypic plasticity of wing size was mediated by both cell size and cell number. In contrast, evolutionary change in wing size, which was only observed as a correlated response expressed on standard food, was mediated entirely by reduction in cell number. Plasticity of cell number had been lost in the selected populations, and cell number did not differ between the sexes despite males having smaller wings. Results of this and other experimental evolution studies are consistent with the hypothesis that alleles which increase body size through prolonged growth affect wing size mostly via cell number, whereas alleles which increase size through higher growth rate do so via cell size.     

Effects of carcass size and male presence on clutch size in Nicrophorus quadripunctatus (Coleoptera: Silphidae)

The effects of carcass size and male presence on clutch size in Nicrophorus quadripunctatus were examined. Male presence increased clutch size and improved the female's ability to produce replacement clutches. Clutch size was also related to carcass size. There was a negative correlation between number of clutches and clutch size for most carcass sizes. We conclude that N. quadripunctatus is potentially iteroparous and hypothesize that reproductive energy is reserved for brood failure.     

Germ cell loss in the XXY male mouse: Altered X-chromosome dosage affects prenatal development

Male mammals with two X chromosomes are sterile due to the demise of virtually all germ cells; however, the underlying reasons for the germ cell loss remain unclear. The use of a breeding scheme for the production of XXY male mice has allowed us to experimentally address the question of when and why germ cells die in the XXY testis and whether the defect is due to the presence of an additional X chromosome in the soma, the germ cells themselves, or both. Our studies demonstrate that altered X-chromosome dosage acts to impair germ cell development in the testis at a much earlier stage than suggested by previous studies of XX sex-reversed males or XX/XY chimeras. Specifically, we noted significantly reduced germ cell numbers in the XXY testis during the period of germ cell proliferation in the early stages of testis differentiation. Although the somatic development of the XXY testis is morphologically and temporally normal, our studies indicate that germ cell demise reflects a defect in somatic/germ cell communication, since, in an in vitro system, the proliferative potential of fetal germ cells from XXY males is indistinguishable from that of normal males. Mol. Reprod. Dev. 49:101–111, 1998. © 1998 Wiley-Liss, Inc.     

Divergence history of the Carpathian and smooth newts modelled in space and time

Information about demographic history is essential for the understanding of the processes of divergence and speciation. Patterns of genetic variation within and between closely related species provide insights into the history of their interactions. Here, we investigated historical demography and genetic exchange between the Carpathian (Lissotriton montandoni, Lm) and smooth (L. vulgaris, Lv) newts. We combine an extensive geographical sampling and multilocus nuclear sequence data with the approximate Bayesian computation framework to test alternative scenarios of divergence and reconstruct the temporal and spatial pattern of gene flow between species. A model of recent (last glacial period) interspecific gene flow was favoured over alternative models. Thus, despite the relatively old divergence (4–6 mya) and presumably long periods of isolation, the species have retained the ability to exchange genes. Nevertheless, the low migration rates (ca. 10^?6 per gene copy per generation) are consistent with strong reproductive isolation between the species. Models allowing demographic changes were favoured, suggesting that the effective population sizes of both species at least doubled as divergence reaching the current ca. 0.2 million in Lm and 1 million in Lv. We found asymmetry in rates of interspecific gene flow between Lm and one evolutionary lineage of Lv. We suggest that intraspecific polymorphism for hybrid incompatibilities segregating within Lv could explain this pattern and propose further tests to distinguish between alternative explanations. Our study highlights the importance of incorporating intraspecific genetic structure into the models investigating the history of divergence.     

Proximate determination of male horn dimorphism in the beetle Onthophagus taurus (Coleoptera: Scarabaeidae)

The existence of discrete phenotypic variation within one sex poses interesting questions regarding how such intrasexual polymorphisms are produced and modified during the course of evolution. Approaching these kinds of questions requires insights into the genetic architecture underlying a polymorphism and an understanding of the proximate mechanisms determining phenotype expression. Here we explore the genetic underpinnings and proximate factors influencing the expression of beetle horns – a dramatic sexually selected trait exhibiting intramale dimorphism in many species. Two relatively discrete male morphs are present in natural populations of the dung beetle Onthophagus taurus (Scarabaeidae, Onthophagini). Males exceeding a critical body size develop a pair of long, curved horns on their heads, while those smaller than this critical body size remain essentially hornless. We present results from laboratory breeding experiments designed to assess the relative importance of inherited and environmental factors as determinants of male morphology. Using father–son regressions, our findings demonstrate that horn length and body size of male progeny are not predicted from paternal morphology. Instead, natural variation in an environmental factor, the amount of food available to larvae, determined both the body sizes exhibited by males as adults and the presence or absence of horns. The nonlinear scaling relationship between the body size and horn length of males bred in the laboratory did not differ from the pattern of variation present in natural populations, suggesting that nutritional conditions account for variation in male morphology in natural populations as well. We discuss our results by extending ideas proposed to explain the evolution of conditional expression of alternative phenotypes in physically heterogeneous environments toward incorporating facultative expression of secondary sexual traits. We use this synthesis to begin characterizing the potential origin and subsequent evolution of facultative horn expression in onthophagine beetles.     

The relationship between male head size and harem size in the sexually dimorphic mountain stone weta Hemideina maori

Abstract 1. Tree weta are a group of large, flightless orthopterans with pronounced sexual dimorphism. Males have enlarged heads that are used in fighting for possession of cavities in trees or under rocks where females shelter during the day.
2. The fieldwork reported here examined the relationship between male head size and mating success in Hemideina maori , an alpine tree weta that shelters under rock slabs that have broken off isolated outcrops or tors.
3. The relationship between male head size and harem size in H. maori is not as clear-cut as thought previously. First, overall body size is a better predictor of male mating success than head size per se . Second, both body size and head size explained a relatively low percentage (19.8%) of the overall variation in mating success. Third, despite the intensity of directional selection being estimated to move the frequency distribution of head size and femur size 0.49 and 0.54 standard deviations from the mean, male heads and femurs were ≈ 2 mm smaller at the main study site than at a second site 100 m higher in elevation. A similar pattern was found for adult females. Additional surveys have indicated that body size in H. maori decreases with decreasing altitude, which is correlated with increasing night-time temperature.
4. Although there are reasons why natural selection might favour weta maturing earlier and at smaller body sizes in warmer environments, relatively large males would still have a mating advantage over smaller males under such conditions. This sexually dimorphic alpine insect might be a good example of the trade-offs and conflicting demands that sexual selection versus natural selection can place on organisms.