The effects of orchidectomy and gonadotropins on steroidogenesis and oogenesis in Bidder's organs of the toad Bufo woodhousii.

In the family Bufonidae, male toads possess rudimentary ovaries, called Bidder's organs, which are attached to the testes. The mechanisms involved in the inhibition of oogenesis in these structures were investigated in male Bufo woodhousii. Orchidectomized and sham-operated animals were injected with gonadotropins (pregnant mare serum gonadotropin [PMSG] + human chorionic gonadotropin [hCG]) for 26 days and the effects of these hormones on oogenesis and steroidogenic activity (3 beta-hydroxysteroid dehydrogenase [3 beta-HSD] and 17 beta-HSD) in the Bidder's organ were quantified. Bilateral orchidectomy alone resulted in the growth of bidderian oocytes and a shift towards later stages of oogenesis. Gonadotropins enhanced this effect and stimulated the proliferation of new germ cells. In the presence of testes, however, bidderian oogenesis remained inhibited despite high levels of circulating gonadotropins. In both ooplasm and follicular layers of the bidderian oocytes of all toads, 3 beta-HSD and 17 beta-HSD activities were detected by histochemistry. Follicular enzymatic activity increased in orchidectomized toads treated with PMSG + hCG but decreased in sham-operated toads treated with gonadotropins. Testis weights, rudimentary oviduct weights, and plasma steroid levels increased in intact toads injected with hCG + PMSG. Gonadotropins had no effect on plasma steroid levels in orchidectomized toads, however. These results suggest that the testes play a major role in the inhibition of oogenesis in Bidder's organs of B. woodhousii and are a major source of androgens. High circulating levels of gonadotropins do not overcome the inhibitory effects of the testes.     

Dynamics of Oogenesis in a Lower Vertebrate,the Toad Bufo bufo

The patterns of production and growth of oocytes were studied in female toads brought into the laboratory after hibernation and kept at 20°C. The oogenic state of the ovaries was determined from the number and size frequency distribution of the oocytes, and change in oogenic state was followed by comparing ovarian biopsies with the ovaries at autopsy one month later. New oocytes grew within one month to sizes up to 0.16 mm or more in diameter, and were integrated in the existing pool of small oocytes. Production of new oocytes continued for more than one month, perhaps 2–3 months, to increase the pool of oocytes by about 50%. An episode of oogenesis sensu stricto is followed by a resting period, probably lasting for about 1–2 years. Oogenesis was not coordinated with ovulation or recruitment of oocytes to vitellogenic growth and it occurred also in the ovaries of sexually immature toads. Exogenous gonadotropin (hCG) and/or fasting for one month of toads in a good nutritional condition did not affect oogenesis, but no oogenic episodes were observed in the ovaries of starving toads that were depleted of energy reserves. It is concluded that oogenesis and growth of oocytes constitute a dynamic system that is only inadequately described by the widely accepted linear, sequential model of production of eggs in amphibians and teleosts.     

The ecological impact of commercial beehives on invasive cane toads (<Emphasis Type="Italic">Rhinella marina</Emphasis>) in eastern Australia

Understanding the factors that affect an invasive species’ viability and distribution has vital implications for biocontrol. In Australia, invasive cane toads (Rhinella marina) are anecdotally reported to utilise commercial beehives as a prey resource, but that interaction has never been studied in detail. We investigated the impact of apiaries on cane toads in northern New South Wales via mark-recapture surveys, dissections, and camera-trap observations. Cane toads were the most frequent visitors to apiaries, followed by bandicoots and corvid birds. Cane toads at apiaries were more abundant and in better body condition (i.e., larger mass relative to snout-urostyle length) than were toads at nearby control sites. Toads at beehives contained more prey items per stomach (mostly bees, which were never recorded in the stomachs of toads from other sites), and adult female toads at beehives had larger livers and ovaries relative to body size. We conclude that commercial apiaries attract cane toads, influence their diets, and increase their feeding rates and reproductive capacity. Like other habitat modifications wrought by agricultural activities, honey bee colonies provide resources that facilitate the spread of cane toads through an otherwise harsh landscape matrix. Minor modifications to beehives could exclude toads, thereby eliminating their positive impact on the invader.     

Pure gonadal dysgenesis. Case report with unusual anatomical and endocrine findings

The syndrome of pure gonadal dysgenesis (PGD) cannot always easily be distinguished from other disorders of gonadal development. Relations are evident with Turner's syndrome, females with hypoplastic ovaries, male pseudohermaphroditism, mixed gonadal dysgenesis and the vanishing testes syndrome. The case is reported of a 40 year old female with primary amenorrhea, alopecia, eunuchoid features, XY karyotype with normal breast development and sexual hair after estrogen therapy. On laparotomy streak ovaries were found at ovarian site. Pathohistological examination revealed on the left side wolffian duct remnants such as ductuli deferentes and epididymis besides sparse Leydig-(hilus-)cells and on the right side only a rudimentary fallopian tube with subendothelial accumulation of hyperplastic Leydig-(hilus-)cells. Serum-testosterone elevation above the normal female range (630 ng/dl) persisted following gonadectomy (151 ng/dl). Ectopic Leydig-(hilus-)cells were regarded responsible for the continuing testosterone production. The present case lies on borderline between PGD and mixed gonadal dysgenesis because remnants of wolffian duct derivatives suggest unilateral fetal testicular activity; classification as PGD however was justified in purely female body features and lacking evidence of testicular tissue.     

Differential proteomics in dequeened honeybee colonies reveals lower viral load in hemolymph of fertile worker bees

The eusocial societies of honeybees, where the queen is the only fertile female among tens of thousands sterile worker bees, have intrigued scientists for centuries. The proximate factors, which cause the inhibition of worker bee ovaries, remain largely unknown; as are the factors which cause the activation of worker ovaries upon the loss of queen and brood in the colony. In an attempt to reveal key players in the regulatory network, we made a proteomic comparison of hemolymph profiles of workers with completely activated ovaries vs. rudimentary ovaries. An unexpected finding of this study is the correlation between age matched worker sterility and the enrichment of Picorna-like virus proteins. Fertile workers, on the other hand, show the upregulation of potential components of the immune system. It remains to be investigated whether viral infections contribute to worker sterility directly or are the result of a weaker immune system of sterile workers.     

Wild Cane Toads (Rhinella marina) Expel Foreign Matter from the Coelom via the Urinary Bladder in Response to Internal Injury,Endoparasites and Disease

Dissections of >1,200 wild-caught cane toads (Rhinella marina) in tropical Australia confirm a laboratory report that anurans can expel foreign objects from the coelom by incorporating them into the urinary bladder. The foreign objects that we found inside bladders included a diverse array of items (e.g., grass seeds, twigs, insect prey, parasites), many of which may have entered the coelom via rupture of the gut wall. In some cases, the urinary bladder was fused to other organs including liver, fat bodies, ovaries, Bidder’s organs, lungs, mesentery, stomach wall, gall bladder, and the abdominal wall. Acanthocephalan parasites (of a range of developmental stages) were identified from the walls of the urinary bladders of three cane toads. This organ may play a significant role in destroying or excreting metazoan parasites, as well as inanimate objects.     

Observations on myiasis by the calliphorid,Bufolucilia silvarum,in the eastern American toad (Bufo americanus americanus) from southeastern Wisconsin

Larvae of certain species of blowflies (Calliphoridae) cause myiasis in amphibians which may result in significant mortality, yet there are few reports from North America. In this study, we observed primary myiasis in a population of juvenile eastern American toads (Bufo americanus americanus) collected during May-July 1998 from southeastern Wisconsin (USA). Nine (6%) of 140 toads were infected by the green blow fly (Bufolucilia silvarum) with a mean intensity of 10.5 +/- 7.2 (range = 1-24). Weekly parasite prevalence and mean intensity remained low, ranging from 0-20% and 2 +/- 1.4 to 14 +/- 6, respectively. We found: 1) flies lay eggs on healthy toads, 2) eggs hatch with first instar maggots penetrating under the skin, 3) maggots develop to mature third instars within 5-7 days, 4) maggots leave the host and form pupa within 8-11 days of hatching, and 5) maggots pupate within 7-9 days at room temperature. All infected toads died within 1-2 wk as a result of the infection. The low prevalence observed in this study and other reports of this species from mammalian and bird carcasses indicated that B. silvarum is probably a facultative parasite of toads and other amphibians in the United States. This is the first report of B. silvarum causing myiasis in Wisconsin amphibians and the first report in eastern American toads in the United States.     

The establishment and eradication of an extra-limital population of invasive cane toads

Biological invasions expand not only as a continuous front, but also via translocation of small numbers of individuals to sites far from the main distribution. Detecting and eradicating such satellite populations is critical to curtailing the invasion. Cane toads (Rhinella marina) have been spreading through Australia since 1935, and in 2010 were reported in suburban Sydney, 500 km from the main invasion. The amphibians arrived as stowaways in trucks, and bred successfully in at least 3 years. Local residents noted the toads’ presence long before management authorities. As soon as they recognised the population’s establishment, however, the authorities surveyed locations of toads, assessed toad demography, and culled toads. Radio-tracking revealed the locations of spawning sites, which were then fenced to exclude access. As a result of reproduction, growth, and sex-specific culling (due to sex differences in distribution and catchability), successive years saw major changes in toad abundance, body-size distributions and sex ratios. Rates of infection of toads by parasites (lungworms) increased through time also. Adult male toads were collected primarily from the initial introduction site, whereas adult females were collected from a broader area. A total of > 900 post-metamorphic cane toads and > 5000 earlier life stages were collected, and those efforts (plus predation by rats and birds) exterminated the population (no sightings for the past 3 years). Cane toads will continue to be translocated to sites far outside their main invaded range, but the successful eradication effort suggests that well-integrated programs, with close collaboration among stakeholders, can prevent such populations from establishing.     

On the fringe of the invasion: the ecology of cane toads in marginally-suitable habitats

Understanding how invasive species flourish under climatic conditions outside those found within their native range can inform management. In southeastern Australia, cane toads (Rhinella marina) are spreading into montane areas cooler than have been predicted to be suitable. We monitored the presence of active toads in two high-elevation sites (750–1010 m above sea level [asl]) and two adjacent low-elevation sites (150–210 m asl) in northeastern New South Wales over spring and summer. We radio-tracked 28 field-collected adult toads (n = 5–9 toads per site) and quantified their thermoregulatory opportunities and body temperatures. Toads were active at low-elevation sites in spring, but were not seen in high-elevation sites until late summer. At low elevations, toads had access to a wide range of temperatures and selected cool diurnal refugia. In montane sites, toads had less control over their temperatures, because thermal differentials between exposed and sheltered microhabitats were smaller. Overall though, body temperatures of toads at high-elevation sites in summer were not different to those of conspecifics at lower elevations in spring. As a result, toads at high elevations moved as far (mean daily displacement around 50 m) as did low-elevation conspecifics. Toads in high elevations spent the day in superficial shelter, often partly exposed. Thus, although toads only appear in high-elevation sites seasonally, their behaviour at those sites (spending the day exposed; moving extensively at night) likely exacerbates their ecological impact by bringing them to the attention of vulnerable native predators.     

Altitudinal distribution and blood values in the toad, Bufo spinulosus Wiegmann

1. Red blood cell (RBC) count, RBC size, hematocrit, cell and blood hemoglobin concentrations and plasma total solid concentration were measured in 16 lowland (from near sea level up to 2700 m) and 18 highland (3200 up to close to 4500 m) adult toads (Bufo spinulosus). 2. Lowland toads showed higher hematocrit values than highland toads, but their blood hemoglobin concentration and plasma solid concentration were not significantly different. 3. Highland toads had smaller RBC size, higher corpuscular hemoglobin concentration, a trend toward larger RBC count and a considerably smaller body size. These features may contribute to their successful life at high altitude.     

Aposematism and Bioluminescence: Experimental evidence from Glow-worm Larvae(Coleoptera: Lampyridae)

Bioluminescence most likely evolved under selection from the visually guided behaviours of co-occurring organisms, in particular that of predators. Many possible functions of light signals have been proposed and some are supported, but whatever their function may be, they make an easy target of the emitter unless it is defended. Therefore, we want to emphasise that in many cases bioluminescence can only have evolved through a defensive function. If this were the case, one would expect multimodal adaptiveness of luminescence with at least some evidence for a defensive function. Light signals could be used in many ways to reduce predation, but for spontaneous glowing species in particular, aposematism seems the only functional strategy. In a preliminary experiment with glowing and non-glowing dummy prey, we found that wild-caught toads discriminated against glowing prey. They showed significantly lower attack responses and higher latencies towards glowing prey dummies. However, some of the toads were less reluctant because they did not distinguish initially between prey with or without the light stimulus. Since the toads were collected in areas abundant with lampyrid glow-worms, which is the only luminous organism at this locality, and our results concur with the general evidence that they may have had previous experiences with this prey, we attribute the result to luminescent aposematism. From the literature, and from our own experiments, we know that toads and many other potential predators experience lampyrids as disagreeable prey. In future experiments we will test whether glow-worms are defended by luminescent aposematism or not. This revised version was published online in July 2006 with corrections to the Cover Date.     

Excluding access to invasion hubs can contain the spread of an invasive vertebrate

Many biological invasions do not occur as a gradual expansion along a continuous front, but result from the expansion of satellite populations that become established at 'invasion hubs'. Although theoretical studies indicate that targeting control efforts at invasion hubs can effectively contain the spread of invasions, few studies have demonstrated this in practice. In arid landscapes worldwide, humans have increased the availability of surface water by creating artificial water points (AWPs) such as troughs and dams for livestock. By experimentally excluding invasive cane toads (Bufo marinus) from AWP, we show that AWP provide a resource subsidy for non-arid-adapted toads and serve as dry season refuges and thus invasion hubs for cane toads in arid Australia. Using data on the distribution of permanent water in arid Australia and the dispersal potential of toads, we predict that systematically excluding toads from AWP would reduce the area of arid Australia across which toads are predicted to disperse and colonize under average climatic conditions by 38 per cent from 2,242,000 to 1,385,000 km(2). Our study shows how human modification of hydrological regimes can create a network of invasion hubs that facilitates a biological invasion, and confirms that targeted control at invasion hubs can reduce landscape connectivity to contain the spread of an invasive vertebrate.     

Osmoregulation of the cane toad, Bufo marinus, in salt water

Adult cane toads, B. marinus, survived in salinities up to 40% sea-water (SW). Pre-exposure to 30, then 40% SW, increased the survival time of toads in 50% SW. Plasma from toads acclimated to salt water is hyperosmotic to the environment--a result of increased plasma sodium, chloride and urea concentrations. When toads were placed in tap-water and 20% SW, all significant changes to plasma sodium, chloride, urea and osmotic pressure occurred within the first 2 days of exposure. When toads were placed in 30 and 40% SW environments, the increases in plasma sodium and chloride concentrations occurred within the first 2 days of exposure while urea and total osmotic pressure continued to rise until some time between 2 and 7 days exposure.     

In vitro Transformation of Ovules into Rudimentary Pistils in Nicotiana tabacum L.

In our experiments with in vitro cultured young ovaries of Nicotianatabacum, var. havanensis we observed greening and extensivegrowth of the ovular primordia. Four to 6 weeks after inoculationa mass of rudimentary pistils bearing secondary ovules was tobe seen on the protruding placenta. Histological investigationproved these pistilloids not to be adventive organs arisingfrom callusing tissue, but the result of altered growth of theoriginal ovu1ar prirnordia. Though comparatively rare, reportson spontaneous ovular pistillody, including two Nicotiana species,exist in the teratological literature. However, whereas thesespon taneous ovular transformations are described as carpel-likestructures with marginally inserted secondary ovules, the invitro proliferating ovules develop into rudimentary pistilswith an early differentiating and very prominent central placenta.An interpretation of these differences is proposed.     

Ultrastructural Observations on the Origin and Differentiation of Somatic Cells during Gonadal Development in the Frog Rana nigromaculata

The process of gonad development in the frog Rana nigromaculata was observed using the electron microscope. The gonadal medulla was formed by the proliferation and displacement of the epithelial cells within the primordial gonad, and a distinct continuity was observed between the cortical and medullary cells. Sex differentiation of the gonad occurred directly from the sexually indifferent primordial gonads. In the rudimentary testes, the continuity between the cortical and medullary regions increased closer, and the intermingling of cortical and medullary cells was evident. The inner region of the cortex developed into a cord-like structure and subsequently differentiated into rudimentary seminiferous tubules. The medulla differentiated into the testicular rete and efferent duct. In the rudimentary ovaries, the cortex and medulla were separated and the ovarian cavity was formed in the medullary region. In the cortex, the cortical cells surrounding oocytes which had reached the diplotene stage, differentiated into follicular cells. The intrusion of mesenchymal or blastemal cells derived from extragonadal regions into the cortex or medulla was never observed. These findings do not support Witschi's cortico-medullary antagonistic theory of sex differentiation.     

Nonreciprocal gonadal dysgenesis in Chironomus thummi hybrids: temperature sensitivity of female sterility

In nonreciprocal hybrids of Chironomus thummi an environmental factor has been detected which, along with genetic factors, determines gonadal dysgenesis. Female hybrids of the cross Ch' thummi thummi female female x Ch. thummi piger male male show various degrees of rudimentary developed ovaries and sterility. The extent of these abnormalities is dependent on the developmental temperature of the hybrids. At a temperature of 21 degrees C approximately 90% of the females are completely sterile and at 16 degrees C only 30%. The curative effect of a temperature of 16 degrees C on sterility occurs, however, only in those hybrid females which hatch from a specific type of egg mass (class A). Females of another type of egg mass (class B) show nearly as many dysgenic ovaries as do those developed at 21 degrees C. At a developmental temperature of 21 degrees C no such differentiation between the A and B class of egg masses is possible. Ovarian dysgenesis and sterility is induced during a temperature-sensitive period which extends from the beginning of embryonic development through the first two-thirds of the first larva instar stage. The abnormalities observed must be due to a failure in the early development of the germ line and are probably initiated by an inhibition of primordial germ cell divisions.     

Shrinking before our isles: the rapid expression of insular dwarfism in two invasive populations of guttural toad (Sclerophrys gutturalis)

Island ecosystems have traditionally been hailed as natural laboratories for examining phenotypic change, including dramatic shifts in body size. Similarly, biological invasions can drive rapid localized adaptations within modern timeframes. Here, we compare the morphology of two invasive guttural toad (Sclerophrys gutturalis) populations in Mauritius and Réunion with their source population from South Africa. We found that female toads on both islands were significantly smaller than mainland counterparts (33.9% and 25.9% reduction, respectively), as were males in Mauritius (22.4%). We also discovered a significant reduction in the relative hindlimb length of both sexes, on both islands, compared with mainland toads (ranging from 3.4 to 9.0%). If our findings are a result of natural selection, then this would suggest that the dramatic reshaping of an amphibian''s morphology—leading to insular dwarfism—can result in less than 100 years; however, further research is required to elucidate the mechanism driving this change (e.g. heritable adaptation, phenotypic plasticity, or an interaction between them).     

Stress and immunity at the invasion front: a comparison across cane toad (Rhinella marina) populations

At an invasion front, energetic and physiological trade‐offs may differ from those at the range‐core as a result of selection for enhanced dispersal, combined with a low density of conspecifics (which reduces pathogen transmission and competition for food). We measured traits related to energy stores and immunity in wild cane toads (Rhinella marina) across a 750‐km transect from their invasion front in tropical Australia, back into sites colonized 21 years earlier. Several traits were found to vary with population age; some linearly and others in a curvilinear manner. The relative size of spleens and fat bodies was highest in the oldest and newest populations, where rates of lungworm infection were lowest. Toads from older populations produced more corticosterone in response to a standardized stressor, and had higher lymphocyte counts (but lower basophil counts). The amount of skin swelling elicited by phytohaemagglutinin injection did not vary geographically, although recruitment of leukocytes to the injected tissue was higher in toads from long‐colonized areas. Because this was a field‐based study, we cannot differentiate the effects of population age, toad density or pathogen pressure on our measures of stress and immune responses, nor can we distinguish whether the causation involves hard‐wired adaptive processes or phenotypically plastic responses. Nonetheless, our data demonstrate substantial variation in immune systems among toads at varying distances from an invasion front, showing that a biological invasion imposes strong pressures on physiological systems of the invader.     

Abnormal ovarian morphogenesis in Drosophila melanogaster after injection of embryos with conditioned media from the Daudi cell line

Summary Drosophila melanogaster embryos were injected before the blastoderm stage with conditioned media from several male Burkitt's lymphoma human cell lines and the Daudi cell line. Such injections do not have any effect on the male genital apparatus or on the female tract. The Daudi conditioned medium modifies the ovarian morphogenesis of the flies and the rudimentary ovaries obtained look like nymphal gonads. Moreover, they have a drastically reduced number of germ cells. The ovaries that looked functional contain numerous necrotic germ cells and the mean number of ovarioles per fly is significantly smaller than that of the controls. The abnormalities observed resemble the results of experimental and genetic lack of germ cells. They disappear at very high dilution (1×10^–6).