Browsing by Author "Silva, K."
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- Can the limited marsupium space be a limiting factor for Syngnathus abaster with size-assortative matingPublication . Silva, K.; Vieira, Maria Natividade; Almada, Vítor Carvalho; Monteiro, Nuno Miguel1. Some syngnathid species show varying degrees of sex role reversal aside from male pregnancy, with females competing for access to mates and sometimes presenting conspicuous secondary sexual characters. Among other variables, brooding space constraints are usually considered a key element in female reproductive success, contributing strongly to the observed morphological and behavioural sexual differences. Nevertheless, a close relationship between sex role reversal and male brooding space limitation has not yet been accurately demonstrated in field studies. 2. The present work, conducted over two consecutive breeding seasons in a wild population of the sex role-reversed pipefish Syngnathus abaster , simultaneously analysed egg number and occupied space, as well as the free area in the male’s marsupium. The number of eggs that would fit in the observed unoccupied space was estimated. 3. Contrary to what would be expected, given the marked sexual dimorphism observed in the population studied, where females were larger and more colourful, male brooding space did not appear to limit female reproduction as neither large nor small individuals presented a fully occupied pouch. Interestingly, the largest unoccupied areas of marsupium were found in the larger individuals, although they received more and larger eggs. Laboratory data also showed that larger females lay larger eggs. 4. Together, these results suggest the existence of assortative mating, which may result from: (i) the reluctance of larger males (which tend not to receive small eggs usually laid by small females) to mate with lower quality females, even at the expense of a smaller number of offspring; or (ii) female– female competition, which might strongly reduce the hypothesis of a small female mating with a large male. The potential impact of temperature on reproduction and population dynamics is also discussed in the light of ongoing climatic changes.
- Development and early life history behaviour of aquarium reared Syngnathus acus (Pisces: Syngnathidae)Publication . Silva, K.; Monteiro, Nuno Miguel; Almada, Vítor Carvalho; Vieira, Maria NatividadeSome notes on development and early life history behaviour of aquarium-reared Syngnathus acus are presented and compared with other syngnathid species, namely S. abaster. Implications in population dynamics and connectivity are discussed.
- Diet preference reflects the ontogenetic shift in microhabitat use in Lipophrys pholisPublication . Monteiro, Nuno Miguel; Quinteira, S. M.; Silva, K.; Vieira, Maria Natividade; Almada, Vítor CarvalhoBased on the heterogenous nature of Lipophrys pholis diet, the stage of the species’ ontogenetic development when major niche shifts occurred was identified, and the causes that force this blennid to change its feeding behaviour, vertical distribution and shelter occupation were considered. The diet analysis of the different size classes consistently showed two clusters, grouping individuals < or >8 cm total length. This shift occurred simultaneously with the onset of reproduction; it seemed to be independent of inter- and intraspecific competition and reflected a quantitative and qualitative alteration of the dietary constituents. The analysis of the diet of other sympatric intertidal blennids, Lipophrys trigloides and Coryphoblennius galerita, showed that, apart from the first developmental stages, there seemed to be no important dietary overlap. The inevitability of this niche alteration could be explained by the combination of at least two different factors: the development of the scraping capability that enabled the fish to feed on large benthic prey, together with the limited number of suitable shelters that were available in rock pools.
- Early life history of Syngnathus abasterPublication . Silva, K.; Monteiro, Nuno Miguel; Almada, Vítor Carvalho; Vieira, Maria NatividadeThe embryonic and larval development of the pipefish Syngnathus abaster is described, based on ex situ observations. The full development sequence lasted 24–32 days (at 18–19 C), which was shortened to 21 days at higher temperatures (21–22 C). Newborn juveniles, with a uniform dark brown colouration, immediately assumed a benthic spatial distribution. This vertical distribution pattern remained unchanged at least during the first 4 weeks, after the release from the marsupium. The apparent absence of a pelagic life phase might have important repercussions in terms of population connectivity given increasing fragmentation and degradation of the eelgrass habitat in the species’ range.
- Female reproductive tactics in a sex-role reversed pipefish: scanning for male quality and numberPublication . Silva, K.; Almada, Vítor Carvalho; Vieira, Maria Natividade; Monteiro, Nuno MiguelTheoretical studies predict that females should invest in current reproduction according to both the expected payoffs from mating with different-quality males and their future mating prospects. The Syngnathidae family, with its male pregnancy together with the occurrence of varying degrees of sex-role reversal, constitutes an exceptional model to study female allocation strategies. The present work tests for the influence of male availability and quality (translated into body size) on the egg allocation pattern of different-sized females of the sex role–reversed pipefish Syngnathus abaster. Besides revealing a multiple mating strategy and showing that females do not produce enough eggs to fully occupy a male’s brood pouch during the extent of a pregnancy, results reveal a complex pattern with different-sized females adopting different investment tactics. In contrast to small, less attractive females, who show a much more constant reproductive effort through the tested mating contexts, large females seem able to monitor the number and quality of available males responding accordingly by 1) laying more eggs in the presence of several large males or saving efforts for future breeding and 2) laying larger eggs in larger males while depositing smaller ones in lower quality individuals as a consequence of a serial mating process (large males first, small males later).
- Reproductive behaviour of the black-striped pipefish Syngnathus abaster (Pisces; Syngnathidae)Publication . Silva, K.; Monteiro, Nuno Miguel; Vieira, Maria Natividade; Almada, Vítor CarvalhoThe reproductive behaviour of Syngnathus abaster is described and compared with those of other syngnathids. The need for standardized behavioural data is discussed in light of the actual theories of evolution of mating patterns and sex-role reversal within this family.
- Reversing sex role reversal: compete only when you mustPublication . Silva, K.; Vieira, Maria Natividade; Almada, Vítor Carvalho; Monteiro, Nuno MiguelThe operational sex ratio (OSR) is thought to be a major factor influencing the intensity of mating competition and sexual selection. Even though many studies on species with conventional sex roles have shown that alterations in the OSR can either intensify male–male competition or promote female–female competitive interactions, sometimes resulting in a reversal of sex roles, it is not known how, and how quickly, individuals with reversed sex roles respond to fluctuations in this ratio. We tested for a direct influence of adult sex ratios (as a direct estimation of the OSR) on the reproductive behaviour of the sex role-reversed black striped pipefish, Syngnathus abaster. Although imbalances in the OSR effectively modulated the expression of sex roles, with males and females varying in the degree of choosiness and competitive displays, alterations in the sex ratios did not promote a similar response pattern in both sexes. A surplus of males resulted in a reversion to conventional sex roles observed when both sexes coexist in similar numbers, with males competing intensely and exhibiting a conspicuous ornament towards other males. An excess of females, in contrast, did not result in an overall increase in female competitive interactions. Only small, less attractive, females were more prone to compete as the proportion of males decreased. Large females, however, seemed to rely on their greater mating prospects, thereby avoiding the hypothetical costs of intrasexual competition.
- The effect of temperature on mate preferences and female-female interactions in Syngnathus abasterPublication . Silva, K.; Vieira, Maria Natividade; Almada, Vítor Carvalho; Monteiro, Nuno MiguelDespite much effort to ascertain the consequences of temperature variation for a wide range of animal performance traits, the effect of temperature on interactions among organisms is still poorly understood. The present work tests for a direct influence of water temperature on sexual recognition, mate preferences and femaleefemale interactions in the pipefish, Syngnathus abaster. Three experiments were conducted by monitoring time spent in the vicinity of conspecifics at three water temperatures intended to reflect sea water temperatures before the onset of reproduction (15 ºC) and during the early (18º C) and late breeding season (24 ºC). Four major results emerged: (1) S. abaster can visually discriminate potential mates from fish of the same sex; (2) males and females responded differently with the former diverting their attention towards the opposite sex at intermediate (18º C) and high temperatures (24º C), while the latter only showed a significant interest in potential mates at 24 ºC, devoting an equal amount of interest towards both males and females at 18º C; (3) at breeding season water temperatures, both sexes discriminated against smaller partners, preferring larger ones; (4) different-sized females adopted distinct temperature-modulated behavioural responses, possibly because large dominant females, which engage in competition at 18º C, constrained the reproduction of smaller ones, which seem to compete only at 24º C. These results highlight the importance of temperature as an effective agent in the modulation of S. abaster reproductive behaviour. Considerations on the ecological significance of the observed behavioural patterns are also discussed.