| 1. |
|
|
| 2. |
- Kim, Jae-Young, et al.
(author)
-
Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
- 2020
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 640
-
Journal article (peer-reviewed)abstract
- 3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3mm (230 GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array, at an angular resolution of ∼20 μas (at a redshift of z = 0:536 this corresponds to ∼0:13 pc ∼ 1700 Schwarzschild radii with a black hole mass MBH = 8 × 108 M⊙). Imaging and model-fitting techniques were applied to the data to parameterize the fine-scale source structure and its variation.We find a multicomponent inner jet morphology with the northernmost component elongated perpendicular to the direction of the jet, as imaged at longer wavelengths. The elongated nuclear structure is consistent on all four observing days and across diffierent imaging methods and model-fitting techniques, and therefore appears robust. Owing to its compactness and brightness, we associate the northern nuclear structure as the VLBI "core". This morphology can be interpreted as either a broad resolved jet base or a spatially bent jet.We also find significant day-to-day variations in the closure phases, which appear most pronounced on the triangles with the longest baselines. Our analysis shows that this variation is related to a systematic change of the source structure. Two inner jet components move non-radially at apparent speeds of ∼15 c and ∼20 c (∼1:3 and ∼1:7 μas day-1, respectively), which more strongly supports the scenario of traveling shocks or instabilities in a bent, possibly rotating jet. The observed apparent speeds are also coincident with the 3C 279 large-scale jet kinematics observed at longer (cm) wavelengths, suggesting no significant jet acceleration between the 1.3mm core and the outer jet. The intrinsic brightness temperature of the jet components are ≤1010 K, a magnitude or more lower than typical values seen at ≥7mm wavelengths. The low brightness temperature and morphological complexity suggest that the core region of 3C 279 becomes optically thin at short (mm) wavelengths.
|
|
| 3. |
- Akiyama, Kazunori, et al.
(author)
-
The persistent shadow of the supermassive black hole of M 87: I. Observations, calibration, imaging, and analysis*
- 2024
-
In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 681
-
Journal article (peer-reviewed)abstract
- In April 2019, the Event Horizon Telescope (EHT) Collaboration reported the first-ever event-horizon-scale images of a black hole, resolving the central compact radio source in the giant elliptical galaxy M 87. These images reveal a ring with a southerly brightness distribution and a diameter of ∼42 μas, consistent with the predicted size and shape of a shadow produced by the gravitationally lensed emission around a supermassive black hole. These results were obtained as part of the April 2017 EHT observation campaign, using a global very long baseline interferometric radio array operating at a wavelength of 1.3 mm. Here, we present results based on the second EHT observing campaign, taking place in April 2018 with an improved array, wider frequency coverage, and increased bandwidth. In particular, the additional baselines provided by the Greenland telescope improved the coverage of the array. Multiyear EHT observations provide independent snapshots of the horizon-scale emission, allowing us to confirm the persistence, size, and shape of the black hole shadow, and constrain the intrinsic structural variability of the accretion flow. We have confirmed the presence of an asymmetric ring structure, brighter in the southwest, with a median diameter of 43.3-3.1+1.5 μas. The diameter of the 2018 ring is remarkably consistent with the diameter obtained from the previous 2017 observations. On the other hand, the position angle of the brightness asymmetry in 2018 is shifted by about 30 relative to 2017. The perennial persistence of the ring and its diameter robustly support the interpretation that the ring is formed by lensed emission surrounding a Kerr black hole with a mass ∼6.5× 109M. The significant change in the ring brightness asymmetry implies a spin axis that is more consistent with the position angle of the large-scale jet.
|
|
| 4. |
- Li, Li-Chun, et al.
(author)
-
Changes in Red Color Sensitivity over the Spawning Cycle of Female Three-spined Stickleback (Gasterosteus aculeatus)
- 2022
-
In: Zoological Studies. - 1021-5506 .- 1810-522X. ; 61
-
Journal article (peer-reviewed)abstract
- Male red nuptial coloration is a primary mating signal for three-spined sticklebacks (Gasterosteus aculeatus), and the retinae of both sexes are especially sensitive to red during the breeding season. Red sensitivity is an important aspect of female mate choice in this species, but only when they are ready to spawn and not over the entire breeding period. Here, we aimed to determine if the red sensitivity of female sticklebacks change over their repeat spawning cycle. To this end, we assessed retinal opsin mRNA levels and behavioral red sensitivity in females over this cycle. Both methods indicated that females were more sensitive to red during spawning than in the inter-spawning intervals. Relative expression levels of red color opsin genes (lws) and optical motor sensitivity were high during spawning, decreased after the spawning period, and then increased again 72–96 h later when they were ready to spawn again. Thus, female sticklebacks altered their color sensitivity according to need, but the underlying mechanism remains unclear.
|
|
| 5. |
- Roufidou, Chrysoula, et al.
(author)
-
Hormonal changes over the spawning cycle in the female three-spined stickleback, Gasterosteus aculeatus
- 2018
-
In: General and Comparative Endocrinology. - : Elsevier BV. - 0016-6480 .- 1095-6840. ; 257:SI, s. 97-105
-
Journal article (peer-reviewed)abstract
- Female three-spined sticklebacks are batch spawners laying eggs in a nest built by the male. We sampled female sticklebacks at different time points, when they were ready to spawn and 6, 24, 48 and 72 hours post-spawning (hps) with a male. Following spawning, almost all females (15 out of 19) had ovulated eggs again at Day 3 post-spawning (72hps). At sampling, plasma, brain and pituitaries were collected, and the ovary and liver were weighed. Testosterone (T) and estradiol (E2) were measured by radioimmunoassay. Moreover, the mRNA levels of follicle-stimulating hormone (fsh-β) and luteinizing hormone (lh-β) in the pituitary, and of the gonadotropin-releasing hormones (GnRHs: gnrh2, gnrh3) and kisspeptin (kiss2) and its G protein-coupled receptor (gpr54) in the brain were measured by real-time qPCR. Ovarian weights peaked in “ready to spawn” females, dropped after spawning, before again progressively increasing from 6 to 72hps. Plasma T levels showed peaks at 24 and 48hps and decreased at 72hps, while E2 levels increased already at 6hps and remained at high levels up to 48hps. There was a strong positive correlation between T and E2 levels over the spawning cycle. Pituitary lh-β mRNA levels showed a peak at 48hps, while fsh-β did not change. The neuropeptides and gpr54 did not show any changes. The changes in T and E2 over the stickleback spawning cycle were largely consistent with those found in other multiple-spawning fishes whereas the marked correlation between T and E2 does not support T having other major roles over the cycle than being a precursor for E2.
|
|
| 6. |
- Roufidou, Chrysoula, et al.
(author)
-
Overripening of eggs and changes in reproductive hormones in the threespine stickleback, Gasterosteus aculeatus
- 2016
-
In: Evolutionary Ecology Research. - 1522-0613 .- 1937-3791. ; 17:3, s. 583-601
-
Journal article (peer-reviewed)abstract
- Background: Female threespine sticklebacks, Gasterosteus aculeatus, are batch spawners. As in most teleosts, the ovulated eggs are kept in the ovarian cavity until spawning. If spawning or spontaneous release of the eggs does not take place, they can become overripe and harden, and in most cases remain in the ovary. The overripe eggs are lost for reproduction and also block further spawnings. Reproductive hormones regulate egg production and may be involved in the mechanism of overripening. Question: What are the reproductive endocrinological parameters characterizing overripening of ovulated eggs in the threespine stickleback? Organism: Wild-caught adult threespine sticklebacks from the southern Baltic at Skare in southern Sweden and the island of Asko in northwestern Baltic Proper in Sweden. Experiments: We collected blood samples for hormone measurements, as well as pituitaries and brains for measurement of mRNA from both sexually mature non-overripe (non-ovulated and/or ovulated) and overripe (egg-bound) females. For the Skare fish, sexual maturation was induced under laboratory conditions by exposure to a long photoperiod and we compared the non-overripe (including non-ovulated, with oocytes in different maturing or ripening stages, and ovulated females) with the overripe females. The Asko fish were sampled directly from nature, during the natural summer breeding season and we compared the non-overripe (including non-ovulated, with oocytes in different maturing or ripening stages, and ovulated females) with the overripe females. Methods: In the fish collected from Skare, we used radioimmunoassay to measure the plasma levels of four steroids: testosterone, estradiol, 17,20 beta-dihydroxypregn-4-en-3-one (17,20 beta-P), and 17,20 beta, 21-trihydroxypregn-4-en-3-one (17,20 beta,21-P). We also measured the mRNA levels of gonadotropins [GTHs: follicle-stimulating hormone (fsh-beta) and luteinizing hormone (lh-beta)] in the pituitary, and of gonadotropin-releasing hormones (GnRHs: gnrh2, gnrh3) and kisspeptin (kiss2) and its G protein-coupled receptor (gpr54) in the brain by real-time quantitative PCR. In the fish collected from Asko, we measured only progestogens (17,20 beta-P and 17,20 beta,21-P). Results: In the fish from Skare, overripe female sticklebacks had significantly lower levels of circulating plasma steroid hormones (testosterone, estradiol, 17,20 beta-P), as well as of pituitary lh-beta and brain kiss2 and gpr54 mRNA than the non-overripe females. In the fish caught from Asko, overripe females had lower 17,20 beta-P levels than the non-overripe non-ovulated females, but there was no difference between the non-overripe ovulated and the overripe females. The 17,20 beta,21-P plasma levels were under the limit of detection in all groups.
|
|
| 7. |
- Shao, Yi Ta, et al.
(author)
-
Androgen feedback effects on LH and FSH, and photoperiodic control of reproduction in male three-spined sticklebacks, Gasterosteus aculeatus
- 2013
-
In: General and Comparative Endocrinology. - : Elsevier BV. - 0016-6480 .- 1095-6840. ; 182, s. 16-23
-
Journal article (peer-reviewed)abstract
- Sexual maturation in the stickleback is controlled by photoperiod. The aim of this study was to find out whether changes in feedback effects exerted by sex steroids could mediate the photoperiodic effect, which is regarded to be of an all-or-nothing character. To that end, males were castrated and treated with different doses of testosterone (T) and in one experiment also with the aromatase inhibitor fadrozole (AI) and kept under different photoperiods. In control fish, long day (LD 16:8) stimulated maturation, associated with more hypertrophied kidneys (a secondary sexual character) and higher levels of pituitary lhb and fshb mRNA than under short day conditions (LD 8:16). Under LD 8:16, low doses of T suppressed both lhb and fshb mRNA levels. However, with the use of high doses of T and/or longer photoperiods the inhibitory effects on lhb and fshb mRNA levels became less clear or instead positive effects were observed. Under intermediate photoperiod conditions, the negative feedback effect of a low dose of T on fshb was more prominent with shorter photoperiods, whereas no such shift was observed for lhb mRNA. The inhibitory effect of the low dose of T on lhb mRNA levels under LD 8:16 was abolished by AI, whereas the stimulatory effect of the high dose of T was not. The negative feedback effects were more marked under short days than under long days, whereas positive feedback effects were more marked under long days. The suppression of both fshb and lhb mRNA levels by low androgen levels, especially under short days, may inhibit maturation completely unless a rise of androgens above threshold levels would allow complete maturation.
|
|
| 8. |
- Shao, Yi Ta, et al.
(author)
-
Androgens Increase Iws Opsin Expression and Red Sensitivity in Male Three-Spined Sticklebacks
- 2014
-
In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:6, s. e100330-
-
Journal article (peer-reviewed)abstract
- Optomotor studies have shown that three-spined sticklebacks (Gasterosteus aculeatus) are more sensitive to red during summer than winter, which may be related to the need to detect the red breeding colour of males. This study aimed to determine whether this change of red light sensitivity is specifically related to reproductive physiology. The mRNA levels of opsin genes were examined in the retinae of sexually mature and immature fish, as well as in sham-operated males, castrated control males, or castrated males implanted with androgen 11-ketoandrostenedione (11 KA), maintained under stimulatory (L16:D8) or inhibitory (L8:D16) photoperiods. In both sexes, red-sensitive opsin gene (Iws) mRNA levels were higher in sexually mature than in immature fish. Under L16:D8, lws mRNA levels were higher in intact than in castrated males, and were up-regulated by 11 KA treatment in castrated males. Moreover, electroretinogram data confirmed that sexual maturation resulted in higher relative red spectral sensitivity. Mature males under L16:D8 were more sensitive to red light than males under L8:D16. Red light sensitivity under L16:D8 was diminished by castration, but increased by 11 KA treatment. Thus, in sexually mature male sticklebacks, androgen is a key factor in enhancing sensitivity to red light via regulation of opsin gene expression. This is the first study to demonstrate that sex hormones can regulate spectral vision sensitivity.
|
|
| 9. |
- Shao, Yi Ta, et al.
(author)
-
Changes in kisspeptin, GnRH, and gonadotropin mRNA levels in male threespine stickleback (Gasterosteus aculeatus) during photoperiod-induced sexual maturation
- 2019
-
In: Evolutionary Ecology Research. - 1522-0613 .- 1937-3791. ; 20:3, s. 317-329
-
Journal article (peer-reviewed)abstract
- Background: Both gonadotropin-releasing hormone (GnRH) and kisspeptin have a critical role in the photoperiodic control of sexual maturation in mammals. Question: What are the roles of GnRH and kisspeptin in the photoperiodic control of sexual maturation in the threespine stickleback, Gasterosteus aculeatus? Method: If kisspeptin and GnRH trigger the photoperiodic induction of maturation in fishes, they would be expected to be activated prior to, or at least no later than, the gonadotropins. The mRNA levels of brain gnrh2, gnrh3, kiss2 and its receptor, gpr54, as well as of pituitary lh-beta and fsh-beta, were measured in males under standard laboratory conditions [16 hours light/8 hours dark (L16/D8) or 8 hours light/16 hours dark (L8/D16)] after 3, 10, 19, and 29 days at 20 degrees C. Results: From day 19, males in the long-day photoperiod (L16/D8) condition were visibly mature with bright breeding coloration. Compared with short-day photoperiod (L8/D16) fish, L16/D8 fish had higher lh-beta mRNA levels at days 10, 19, and 29, and higher fsh-beta mRNA levels at day 10 only. Furthermore, L16/D8 fish had higher gnrh3 mRNA levels at days 10 and 29, and higher gnrh2 mRNA levels at day 29, than L8/D16 fish. Finally, kiss2 and gpr54 mRNA levels of L16/D8 fish were significantly higher than those of L8/D16 fish at days 19 and 29, respectively. Conclusions: At the onset of sexual maturation, the levels of lh-beta, fsh-beta, and gnrh3 rose earlier than those of kiss2 and gpr54. These results are consistent with GnRH3 having a role in the early phases of maturation, but do not support a role for kisspeptin in photoperiodic initiation of maturation in male stickleback.
|
|
| 10. |
- Shao, Yi Ta, et al.
(author)
-
GnRH mRNA levels in male three-spined sticklebacks, Gasterosteus aculeatus, under different reproductive conditions
- 2015
-
In: Comparative Biochemistry and Physiology A. - : Elsevier BV. - 1095-6433 .- 1531-4332. ; 180, s. 6-17
-
Journal article (peer-reviewed)abstract
- In vertebrates, reproduction is regulated by the brain-pituitary-gonad (BPG) axis, where the gonadotropin-releasing hormone (GnRH) is one of the key components. However, very little is known about the possible role of GnRH in the environmental and feedback control of fish reproduction. To investigate this, full-length gnrh2 (chicken GnRH II) and gnrh3 (salmon GnRH) sequences of male three-spined sticklebacks (Gasterosteus aculeatus), which are clustered with the taxa of the same GnRH type as other Euteleostei, were cloned and annotated. gnrh1 is absent in this species. The mRNA levels of gnrh2 and gnrh3 in the sticklebacks' brain were measured under breeding and post-breeding conditions as well as in castrated and sham-operated breeding fish and castrated/sham-operated fish kept under long-day (LD 16:8) and short-day (LD 8:16) conditions. Fully breeding males had considerably higher mRNA levels of gnrh2 and gnrh3 in the thalamus (Th) and in the telencephalon and preoptic area (T + POA), respectively, than post-breeding males. Sham-operated breeding males have higher gnrh3 mRNA levels than the corresponding castrated males. Moreover, higher gnrh2 mRNA levels in the Th and higher gnrh3 mRNA levels in the T + POA and hypothalamus (HypTh) were also found in long-day sham-operated males than in sham-operated fish kept under an inhibitory short day photoperiod. Nevertheless, gnrh2 and gnrh3 mRNA levels were not up-regulated in castrated males kept under long-day photoperiod, which suggests that positive feedbacks on the brain-pituitary-gonad axis are necessary for this response.
|
|
