Time for change in Portuguese science

There is an almost perfect positive relationship between scientific output and gross domestic product (GDP) in Western Europe (Fig. 1). But two countries — Ireland and Portugal — spoil the relationship

Morphometric changes and sex steroid levels during the annual reproductive cycle of the Lusitanian toadfish, Halobatrachus didactylus

The Lusitanian toadfish has group synchronous oocytes, which grow from November until June–July when they are released probably as a single batch. Blood plasma levels of estradiol-17b (E2) and testosterone (T) increase during vitellogenesis and drop rapidly during final maturation and ovulation, when 17,20b, 21-trihydroxy-4-pregnen-3-one (17,20b,21-P) levels increase. The male reproductive apparatus is composed of paired testes and multichambered accessory glands, which secrete mucosubstances and are connected to the spermatic duct. Changes in the gonadosomatic index of males paralleled the females but started to drop slightly earlier. The swimbladder and accessory glands also underwent important seasonal changes in weight reaching a maximum at spawning. T, 11-ketotestosterone (11-KT) and 17,20a-dihydroxy-4-pregnen-3-one (17,20a-P) were generally low except for a sharp peak in June. 17,20b,21-P also peaked in June and then declined slowly. 17,20b-dihydroxy-4-pregnen-3-one (17,20a-P) was undetectable in males and females. As with other species of the family two types of males were identified: type I males with smaller testes (ca. 7-fold) and larger accessory glands (ca. 3-fold) and swimbladders than type II. Type I males also had significantly higher (ca. 6- fold) 11-KT levels than type II males. This suggests a role for 11-KT in the development of structures important for reproductive behaviour

Hormonal control of swimbladder sonic muscle dimorphism in the Lusitanian toadfish, Halobatrachus didactylus

The swimbladder and associated sonic muscle of the Lusitanian toadfish Halobatrachus didactylus increase in size throughout life and are, respectively, 25% and 30% larger in type I (nest-holder) males than females, which may generate sexual differences in sound production. Sexual dimorphism in swimbladder is also evident in the morphological features of sonic muscle fibers. During the breeding season, type I males have smaller myofibril contracting zones surrounded by larger sarcoplasm areas compared with females, possibly an adaptation to speed and fatigue resistance for the production of long mating calls. Type II (floater) males show characteristics that are intermediate, but statistically not significantly different, between type I males and females. Six weeks after castration and androgen (testosterone and 11- ketotestosterone) replacement in type I and type II males there were no alterations either in swimbladder mass or fiber morphology. However, 17b-estradiol induced a significant decrease in swimbladder mass and sarcoplasm area/myofibril area ratio. Six months after castration there was a clear reduction in the seasonal swimbladder hypertrophy in males and induction of sonic fiber morphological characteristics that resemble those occurring in females (low sarcoplasm area/myofibril area ratio). These results suggest that testicular factors are required to initiate sonic muscle hypertrophy and type I sonic fiber phenotype in H. didactylus, but a specific involvement of androgens has not been completely clarified

The swimbladder of the Lusitanian toadfish: sexual dimorphism and hormonal control

The members of the family Batrachoididae produce sounds associated with courtship and agonistic interactions. While long mating calls are only produced by nesting males, agonistic short duration grunts have been recorded from toadfishes and midshipmen in both males (nesting or not) and females. Sound production results from the contraction of paired sonic muscles attached to the walls of the swimbladder, which cause a rapid variation in swimbladder volume and internal pressure. Both sonic muscle growth and sonic fibre morphology have been shown to be androgen sensitive in batrachoidids

Follow your nose: chemical communication throughout the European eel (Anguilla anguilla, L.) life-cycle

European eels are important in both scientific and economic terms. Unfortunately, current populations are becoming increasingly endangered and urgentmanagement is needed. Several aspects of eel biology, together with their highly developed sense of smell, suggest that chemical communication could be involved at key stages of their life-history. Thus, advances in this area could generate novel tools for stock management

Olfactory sensitivity to changes in environmental [Ca2+] in the marine teleost Sparus aurata

Estuarine and/or migratory teleosts may experience large and rapid changes in external [Ca2+]. Previous studies have largely centred on the physiological mechanisms that maintain a constant plasma [Ca2+] in the face of such external fluctuations, but little work has been directed to examining how these changes may originally be detected. We present evidence that the olfactory system of the gilthead seabream (Sparus aurata) is highly sensitive to reductions in environmental [Ca2+] and suggest a possible mechanism by which this may be mediated. Multi-unit extracellular recordings were made from the olfactory nerve of Sparus aurata while the [Ca2+] of artificial sea water flowing over the olfactory epithelium was varied from 10 to 0mmoll-1. Reductions in [Ca2+] caused a large, nonaccommodating increase in the firing rate of the olfactory nerve (apparent IC50=1.67±0.26mmoll-1, apparent Hill coefficient=-1.22±0.14; means ± S.E.M., N=6). This response was not due to the concomitant reduction in osmolality and was specific for Ca2+. During continuous exposure of the olfactory epithelium to Ca2+-free sea water, the apparent IC50 and Hill coefficient in response to increases in [Ca2+] were 0.48±0.14mmoll-1 and -0.76±0.16 (means ± S.E.M., N=6), respectively, suggesting an adaptation of the Ca2+- sensing system to low-[Ca2+] environments. Ca2+ is intimately involved in signal transduction in the olfactory receptor neurones, but our data support a true olfactory response, rather than a non-specific effect to lowering of external [Ca2+]. The absence of Ca2+ from sea water only partially and temporarily blunted the olfactory response to the odorant L-serine; the response amplitude recovered to control levels within 20 min. This suggests that the olfactory system in general is able to adapt to low-[Ca2+] environments. We suggest that the Ca2+ sensitivity is mediated by an extracellular Ca2+-sensing receptor similar to the recently characterized mammalian Ca2+-sensing receptor

Water calcium concentration modifies whole-body calcium uptake in sea bream larvae during short-term adaptation to altered salinities

Whole-body calcium uptake was studied in gilthead sea bream larvae (9–83·mg) in response to changing environmental salinity and [Ca2+]. Calcium uptake increased with increased fish size and salinity. Fish exposed to calcium-enriched, diluted seawater showed increased calcium uptake compared with fish in diluted seawater alone. Calcium uptake was unchanged in Na+- enriched, diluted seawater. Overall, [Ca2+], and not salinity/osmolarity per se, appears to be the main factor contributing to calcium uptake. By contrast, drinking was reduced by a decrease in salinity/osmolarity but was little affected by external [Ca2+]. Calculations of the maximum contribution from drinking-associated calcium uptake showed that it became almost insignificant (less than 10%) through a strong decrease in drinking rate at low salinities (0–8‰). Diluted seawater enriched in calcium to the concentration present in full-strength seawater (i.e. constant calcium, decreasing salinity) restored intestinal calcium uptake to normal. Extra-intestinal calcium uptake also benefited from calcium addition but to a lesser extent

Social modulation of sex steroid concentrations in the urine of male cichlid fish Oreochromis mossambicus

The relationship between urinary concentrations (free + sulfates + glucuronides) of the steroids testosterone (T), 11-ketotestosterone (11KT), 17α, 20ß-dihydroxy-4-preg- nen-3-one (17,20ß-P) and 17a,20a-dihydroxy-4-preg- nen-3-one (17,20α-P), and the social behavior of males of the cichlid fish Oreochromis mossambicus was inves- tigated. After 8 days of isolation none of the steroids were good predictors of social dominance developed after subsequent formation of all-male groups. One day after group formation dominance indexes were good predictors of the urine concentrations of all sex steroids. Dominance indexes and androgen concentrations mea- sured after all-male group formation were positively cor- related with territoriality, courtship rate, and nest size. Similar relationships were found for progestins with the exception that they were not correlated with courtship rate. All-male group formation was also accompanied by an increase in urinary sex steroid concentrations in fish that became territorial and a decrease in non-territorial fish with the exception of T, which increased in both groups. Addition of ovulating females caused steroid concentrations to return to levels near isolation, except for 17,20α-P in territorials, which underwent a large in- crease. Thus, social interactions may have an important modulatory effect on sex steroid concentrations in O. mossambicus

Analysis of the goldfish Carassius auratus olfactory epithelium transcriptome reveals the presence of numerous non-olfactory GPCR and putative receptors for progestin pheromones

The goldfish (Carassius auratus) uses steroids and prostaglandins as pheromone cues at different stages of the reproductive cycle to facilitate spawning synchronization. Steroid progestin pheromone binding has been detected in goldfish olfactory membranes but the receptors responsible for this specific binding remain unknown. In order to shed some light on the olfactory epithelium transcriptome and search for possible receptor candidates a large set of EST from this tissue were analysed and compared to and combined with a similar zebrafish (Danio rerio) resource

Adaptation to reduced salinity affects the olfactory sensitivity of Senegalese sole (Solea senegalensis Kaup 1858) to Ca2+ and Na+ but not amino acids

The Senegalese sole is a marine flatfish, which often penetrates into estuarine waters to feed. It cannot, however, survive in full freshwater. The current study investigated the effect of adaptation to low salinity (10‰) on olfactory responses to changes in environmental [Ca2+] and [Na+] and amino acids by the electro-encephalogram (EEG) recorded from the olfactory bulb. The sole showed olfactory responses to increases in environmental [Na+] and decreases in environmental [Ca2+]; sensitivity to Na+ was greater at 10‰ whereas sensitivity to Ca2+ was greater at 35‰. Decreased environmental [Na+] increased sensitivity to changes in [Ca2+] whereas increased environmental [Ca2+] decreased bulbar responses to changes in [Na+]. Sensitivity to amino acids was unaffected by external salinity. However, the absence of external Na+ strongly decreased bulbar responses to amino acids in fish adapted to 35‰ seawater but not in those at 10‰. The absence of external Ca2+ had no such effect at either salinity. This suggests that odorant-receptor binding and/or olfactory transduction is reliant on external Na+ (but not Ca2+) at higher salinities but the olfactory system is able to adapt to lower environmental [Na+]. Taken together, these results suggest that reductions of external salinity modulate olfactory sensitivity to environmental Ca2+ and Na+ but not amino acids. However, at low salinities, olfactory sensitivity to amino acids is maintained by decreasing reliance on external Na+