Browsing by Author "Ros, Albert F. H."
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- Adjustment of brood size and androgen levels in a teleost species with exclusive male parental carePublication . Ros, Albert F. H.; Fagundes, Teresa; Oliveira, Rui FilipeIn maximizing reproductive success, individuals face a trade-off between parental care for their current offspring and investing in androgen-dependent sexual traits to produce further offspring. It has thus been proposed that parental effort would suppress androgen levels. Here, we studied parental effort by manipulating brood size in the peacock blenny, Salaria pavo, a littoral fish species in which males show long periods of paternal care.We focused on the effects of brood size on female spawning rate (measured as number of eggs received in the nest by focal males) and androgen levels. We found a positive linear relationship between brood size and the number of eggs received subsequently. Accordingly, spawning rate increased for males with experimentally enlarged broods while it decreased for males in which brood size was reduced. However, over a longer time interval, brood sizes of both treatments returned to the nonmanipulated brood size, suggesting an effect of additional factors such as male quality. Brood size did not show the expected negative relationship with levels of testosterone and 11-ketotestosterone. On the contrary, testosterone levels were positively correlated with brood size. However, in agreement with the prediction, changes in the level of parental care by manipulation of brood size showed an inverse relationship with testosterone levels. As with brood size, given time, testosterone levels tended to return to nonmanipulated levels. Such changes suggest that males adjust their brood size to an individual value through androgen modulation of courtship or other traits influencing female spawning rate.
- Aggressive behaviour and energy metabolism in a cichlid fish, Oreochromis mossambicusPublication . Ros, Albert F. H.; Becker, Klaus; Oliveira, Rui FilipeWe have investigated the effect of mirror-elicited agonistic behaviour on oxygen consumption in the Mozambique tilapia, Oreochromis mossambicus (Cichlidae). Males exposed to their mirror image showed higher frequencies of both lateral display and tail-beating and escalated aggression more frequently than males exposed to a transparent glass that was used as a control for the presence of a novel object in the tank. This aggressive response was correlated with an increase in oxygen consumption. Overt aggression was highly correlated with display behaviour and with locomotor activity. Bivariate analyses showed high correlation (explaining about 64% of variation) between overt aggression, locomotor activity and metabolic rates. Weakly positive bivariate correlations between displays and metabolic rates turned spurious after partialling out aggression. The data suggest that energetic costs only emerge late during the conflict, when animals escalate their aggressive behaviour.
- Alternative male reproductive tactics and the immunocompetence handicap in the azorean rock-pool blenny, Parablennius parvicornisPublication . Ros, Albert F. H.; Bouton, Niels; Santos, Ricardo Serrão; Oliveira, Rui FilipeIn the Azorean rock-pool blenny (Parablennius parvicornis) reproductively active males display alternative morphotypes, which differ in the expression of secondary sexual characters (SSC). Males expressing SSC, theMCmorphotype, have high androgen levels and compete for crevices that will be visited by females to spawn.MCmales holding nests court females and care for the eggs. Males with low expression of SSC, the MK morphotype, have low levels of androgens and reproduce by stealing fertilizations from the MC males. Based on the hypothesis that androgens are immunosuppressive, we expected these morphotypes to differ in immunocompetence. To test this hypothesis, we conducted a field study in which we collected repeated blood samples to monitor leukocyte populations (blood smears), and to measure the primary antibody response of males that were experimentally challenged with a foreign non-pathogenic antigen (sheep red blood cells). Circulating levels of 11-ketotestosterone and testosterone were higher in MC males than in MK males. Neither granulocyte nor thrombocyte counts did covariate with androgens or male tactic. In contrast, lymphocyte counts and humoral antibody response were negatively correlated with body size, and as expected, both were lower in MC than in MK males. Interestingly, in MC males androgen levels decreased after immunization, and this was less in nest-holder males than in MC males that were floating around in the pools. Within each morphotype we found no relationship between androgens and immunocompetence. The latter result is not supportive for androgen regulated immunosuppression in MC males. A possible alternative is enhancement of immunity in MK males. These males had relatively high levels of injuries in comparison withMCmales. High immunity might be a consequence of high infection rate because of such injuries.
- Androgens and immune function in male alternative reproductive morphotypes of the peacock blenny Salaria pavoPublication . Ros, Albert F. H.; Oliveira, Rui FilipeSpecies with alternative reproductive tactics offer the opportunity to analyse how behavioural and morphological traits are tuned to produce successfully competing phenotypes within one sex. In the teleost fish Salaria pavo, alternative reproductive tactics are sequential. The older ornamented males compete for access to females by guarding a cavity to which they attract females to spawn. Ornamented males that are found without a nest are called ‘floaters’. Younger mature males which are too small to compete with nest-holders attempt to ‘sneak’ as female mimics into successful nests and release their sperm to fertilize freshly spawned eggs. The alternative tactics in S. pavo are associated with different levels of the androgens testosterone and 11-ketotestosterone, which have been found to suppress immune function in several teleost fish. A field study was carried out to analyse the relationship between these reproductive tactics, androgens and blood levels of lymphocytes as a monitoring method of immune function. We expected highest investment in the immune system in sneakers because these have the lowest androgen levels and functionally because investing in self-maintenance increases their future prospect to switch tactic and to reproduce as a nest-holder. Indeed, the relative count of lymphocytes correlated negatively with body size and thus was highest in sneakers and lowest in nest-holders. In concordance, 11-ketotestosterone and testosterone levels were found to be higher in floaters and nest-holders than in sneakers. However, no correlation was found between individual levels of testosterone or 11-ketotestosterone and lymphocytes. Thus, a trade-off between reproductive traits associated with high androgen levels and immunocompetence might exist at the level of alternative tactics but this might not be explained by acute immunosuppressive effects of circulating androgens.
- Birth date predicts alternative life-history pathways in a fish with sequential reproductive tacticsPublication . Fagundes, Teresa; Simões, Mariana G.; Saraiva, João Luis Vargas de Almeida; Ros, Albert F. H.; Gonçalves, David; Oliveira, Rui Filipe1. In species with plastic expression of alternative reproductive tactics (ARTs), individuals of the same sex, usually males, can adopt different reproductive tactics depending on factors such as body size. 2. The ‘birth date hypothesis’ proposes that condition-dependent expression of ARTs may ultimately depend on birth date, because individuals born at different times of the year may achieve different sizes and express different reproductive tactics accordingly. However, this has rarely been tested. 3. Here, we tested this hypothesis in a fish with ARTs, the peacock blenny (Salaria pavo). A long-term (6 years) mark–recapture study demonstrated that ARTs in the peacock blenny were sequential and that males may follow at least two alternative life-history pathways: a nestholder pathway, in which males express the nest-holder tactic from their first breeding season onwards, and a parasitic pathway, where males reproduce on their first breeding season as sneaker males and subsequently as nest-holders. 4. We have found evidence of a birth date effect on the expression of ARTs in the peacock blenny. Males following the nest-holder pathway are born earlier and are larger at the first breeding season than males following the parasitic pathway, but they have similar growth curves. 5. The mechanisms underlying a birth date effect are far from clear and might be diverse. We have not found support for a mechanism of body size threshold triggering sexual maturation and subsequent ARTs. A mechanism of tactic determination that is strictly based on timing of first maturation is also unlikely. 6. A proxy of lifetime reproductive success shows crossing (body size associated) fitness curves for the two main life-history pathways.
- Dear enemies elicit lower androgen responses to territorial challenges than unfamiliar intruders in a cichlid fishPublication . Aires, Rui F.; Oliveira, Gonçalo A.; Oliveira, Tânia Sofia Ferreira de; Ros, Albert F. H.; Oliveira, Rui FilipeIn many territorial species androgen hormones are known to increase in response to territorial intrusions as a way to adjust the expression of androgen-dependent behaviour to social challenges. The dear enemy effect has also been described in territorial species and posits that resident individuals show a more aggressive response to intrusions by strangers than by other territorial neighbours. Therefore, we hypothesized that the dear enemy effect may also modulate the androgen response to a territorial intrusion. Here we tested this hypothesis in male cichlid fish (Mozambique tilapia, Oreochromis mossambicus) using a paradigm of four repeated territorial intrusions, either by the same neighbour or by four different unfamiliar intruders. Neighbour intruders elicited lower aggression and a weaker androgen response than strangers on the first intrusion of the experiment. With repeated intrusions, the agonistic behaviour of the resident males against familiar intruders was similar to that displayed towards strangers. By the fourth intrusion the androgen response was significantly reduced and there was no longer a difference between the responses to the two types of intruders. These results suggest that the dear enemy effect modulates the androgen response to territorial intrusions and that repeated intrusions lead to a habituation of the androgen response.
- Does access to the bluestreak cleaner wrasse Labroides dimidiatus affect indicators of stress and health in resident reef fishes in the Red Sea?Publication . Ros, Albert F. H.; Lusa, Jeanne; Meyer, Meghann; Soares, Marta C.; Oliveira, Rui Filipe; Brossard, Michel; Bshary, RedouanInteractions between the bluestreak cleaner wrasse Labroides dimidiatus and its client reef fish are a textbook example of interspecific mutualism. The fact that clients actively visit cleaners and invite inspection, together with evidence that cleaners eat many client ectoparasites per day, indeed strongly suggests a mutualistic relationship. What remains unknown is how parasite removal affects the physiology of clients and thereby their body condition, health, and immune function. Here we addressed these issues in a field study in Ras Mohammed National Park, Egypt. In our study area, small reef patches are inter-spaced with areas of sandy substrate, thereby preventing many species (i.e., residents, including cleaner wrasses) from travelling between the reef patches. This habitat structure leads to a mosaic of resident clients with and without access to bluestreak cleaner wrasses, further referred to as “cleaner access”, on which we focused our study. We found that residents with cleaner access had higher body condition than residents without cleaner access. However, indicators of stress like variation in cortisol levels corrected for handling time and various immune parameters were apparently unaffected by cleaner access. In fact antibody responses were significantly higher in fishes without cleaner access. This suggests that cleaner access decreases the need for active immunity and that this releases resources that might be allocated to other functions such as somatic growth and reproduction.
- Effects of putative stressors in public aquaria on locomotor activity, metabolic rate and cortisol levels in the Mozambique tilapia Oreochromis mossambicusPublication . Leong, H.; Ros, Albert F. H.; Oliveira, Rui FilipeMozambique tilapia Oreochromis mossambicus were housed individually during 7 days in a continuous flow-trough respirometry system and daily exposed to one of three treatments: (1) a series of knocks on the side of the aquarium, (2) a series of photo-flashes and (3) control group. Exposure to photo-flashes did not change locomotor activity but decreased both nighttime and daytime oxygen consumption throughout the experiment. Knocking induced a shortlived increase in locomotor activity and tended to increase oxygen consumption, but this latter effect was not significant. Night-time oxygen consumption was not affected by knocking exposure. Cortisol levels assayed from fish-holding water collected at the end of the experiment were significantly lower in subjects exposed to photo-flashes than in subjects exposed to knocks or controls. Males did not respond differently than females to the treatments in any of the measurements taken. In summary, the data reported here suggest that exposure to repetitive photo-flashes, but not knocking, suppressed normal energy metabolism and cortisol levels. These effects were present hours to a half day after exposure to the flashes.
- Endocrine correlates of intra-specific variation in the mating system of the St. Peter’s fish (Sarotherodon galilaeus)Publication . Ros, Albert F. H.; Canário, Adelino V. M.; Couto, Elsa; Zeilstra, IIja; Oliveira, Rui FilipeThe Challenge Hypothesis postulates that androgen levels are a function of the social environment in which the individual is living. Thus, it is predicted that in polygynous males that engage in social interactions, androgen levels should be higher than in monogamous animals that engage in parental care. In this study, we tested this hypothesis at the intra-specific level using a teleost species, Sarotherodon galilaeus, which exhibits a wide variation in its mating system. Experimental groups of individually marked fish were formed in large ponds with different operational sex-ratios (OSR) to study the effects of partner availability on blood plasma levels of sex steroids [11-ketotestosterone (11-KT), testosterone (T), and 17,20B-dihydroxy-4-pregnen-3-one (17,20B-P)] and gonadosomatic index (GSI). Polygyny mostly occurred in the female biased OSR groups. 17,20B-P and gonadosomatic index did not differ among OSR groups. However, 11-KT was high in male biased OSR and positively correlated with aggressive challenges, thereby supporting the central postulate of the Challenge Hypothesis. The results of T were the inverse of those of 11-KT, probably because 11-KT is metabolized from T. 11-KT levels of polygynous males did not differ neither from those of monogamous males, nor from those of males that participated in parental care. These results do not support the expected relationships between polygyny, parental care, and androgen levels. The differences from expectations for 11-KT may be related to the fact that in S. galilaeus, the mating and the parenting phase are not clearly separated and thus, males may still fight and court while they are brooding.
- Immune activation suppresses plasma testosterone level: a meta-analysisPublication . Boonekamp, Jelle J.; Ros, Albert F. H.; Verhulst, SimonFemales often select mates on the basis of sexual signals, which can be reliable indicators of male quality when the costliness of these signals prevents cheating. The immunocompetence handicap hypothesis (ICHH) provides a mechanistic explanation of these costs, by proposing a trade-off between immune function and sexual displays. This trade-off arises because testosterone enhances sexual signals, but suppresses immune function. Many studies have investigated the ICHH by administrating testosterone, and a recent meta-analysis found little evidence that testosterone suppressed immune function. However, another component of the ICHH, which has received less empirical interest, suggests that there may also be an interaction in the other direction, with immune activation suppressing testosterone levels. We present a meta-analysis to test for this effect. Overall, there was a strong suppressive effect of experimental immune activation on testosterone levels (rZL0.52), regardless of whether live pathogens or non-pathogenic antigens were used to challenge the immune system. The latter is important because it shows that immune activation per se suppresses testosterone levels. Thus, a trade-off between immunocompetence and sexual displays may primarily be generated by the effect of immune activation on testosterone, rather than the opposite effect that has received most attention.