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排序方式: 共有190条查询结果,搜索用时 15 毫秒
121.
Rui F. Oliveira Vitor C. Almada 《Ethology : formerly Zeitschrift fur Tierpsychologie》1998,104(10):841-858
We present data on the relationship between social status and male secondary sex traits, both morphological and ethological, in Oreochromis mossambicus at the onset of sexual maturation. There is a differential expression of morphological (dorsal fin height, anal fin height, mandible width and premaxilla length) and behavioural (nuptial coloration, per cent time defending a territory, spawning pit volume, pit hovering and courtship rate) traits according to social status, with dominants presenting the highest expression of these dimorphic traits. Social status also affects the development of the genital papillae, which is considered to be a good predictor of androgen levels in cichlid fishes. The results support a causal model in which social status modulate androgen levels that in turn modulate the expression of behavioural and morphological male traits. 相似文献
122.
Although it is now apparent that the intracellular pH may rise considerably above neutrality under physiological conditions, information on the effect of alkaline pH on microtubule assembly and disassembly is still quite fragmentay. We have studied the assembly/disassembly of bovine brain microtubule protein at alkaline pH in vitro. When microtubules are assembled to a new steady state at pH less than 7 and pH is then made more alkaline, they undergo a rapid disassembly to a new steady state. This disassembly is reversed by acidification. The degree of disassembly is determined largely by the pH- dependence of the critical concentration, which increases five to eight times, from pH 7 to 8. A fraction of assembly-incompetent tubulin is identified that increases with pH, but its incompetency is largely reversed with acidification. Measurements of microtubule lengths are used to indicate that disassembly occurs by uniform shortening of microtubules. A comparison of shortening by alkalinization with dilution suggests that the intrinsic rate of disassembly is accelerated by increasing pH. The capacity for initiating assembly is progressively lost with incubation at alkaline pH (although some protection is afforded by sulfhydryl-reducing agents). However, direct assembly from depolymerized mixtures is possible at least up to pH 8.3, and the steady state achieved at these alkaline pH values is stable. Such preparations are readily disassembled by cold and podophyllotoxin (PLN). Disassembly induced by PLN is also markedly enhanced at alkaline pH, suggesting a corresponding enhancement of “treadmilling.” The implications of physiological events leading to alkaline shifts of pH for microtubule assembly/disassembly are discussed, particularly in the light of recent hypotheses regarding treadmilling and its role in controlling the distribution of microtubules in vivo. 相似文献
123.
Data on the juvenile recruitment, growth and size at maturation of Lipophrys pholis in Portuguese waters are compared with the information available on the biology of this species at higher latitudes. In Portugal, recruitment extends for a much longer period, young fish grow faster and sexual maturation is earlier than at higher latitudes. There is a delay of 2–3 months between the appearance of the first eggs on the shore and the recruitment of the first juveniles to the pools. 相似文献
124.
Vitor C. Almada Emanuel J. Gonçlalves Antóio J. Santos Céu Baptista 《Journal of fish biology》1994,45(5):819-830
In this paper we present data on the breeding ecology and patterns of nest aggregation in a population of Salaria pavo (Pisces: Blenniidae), in an area where hard substrates are very scarce. The study site was at Ria Formosa, an extensive littoral lagoon on the south coast of Portugal. The only hard materials available are bricks, tiles, stones and debris that clam culturists use to delimit their fields. The males of S. pavo establish nests intertidally in the holes of the bricks where they guard the eggs. Data were collected at low tide inspections of these artificial ridges and underwater behavioural observations during high tide. The main results are: (i) the same male can establish sequentially more than one nest in the same breeding season; the number of males that stay within the bricks increases before the start of the breeding season and declines towards its end; (ii) there is a large excess of mature males that do not establish nests and they are significantly smaller than the nesting males, suggesting very strong competition for nest sites; (iii) the nests of several males occur in adjacent holes of the same brick, sometimes being entirely surrounded by other nests. Thus, in this population, there is virtually no defended territory around the nest, a situation not known for other blenniid species. This pattern of nest aggregation implies both strong competition among males and reduction of aggression between neighbour parental fishes. This can be explained by the extreme scarcity and spatial distribution of available nest sites. 相似文献
125.
Sousa-Santos C Collares-Pereira MJ Almada V 《Journal of experimental zoology. Part A, Ecological genetics and physiology》2007,307(4):220-225
The endemic Iberian minnow Squalius alburnoides is a complex of fishes of hybrid origin including both males and females with distinct ploidy levels and varying proportions of the parental genomes. In this paper we demonstrated that in contrast to many vertebrate hybrid lineages the sperm of triploid hybrid males of S. alburnoides is viable and fully functional. Flow cytometry and analysis of sequences of a fragment of the beta-actin nuclear gene applied to progenitors and offspring evidenced that these males produced their sperm clonally, as already described for diploid hybrids. The presence of different types of fertile males (nonhybrid diploids with normal meiosis and both diploid and triploid hybrids) coupled with hybridogenetic meiosis in females endows this vertebrate complex with a high level of independence from other species and contributes to maintain its genetic variability. 相似文献
126.
In this paper, we analysed the phylogeography of the Critically Endangered fish Chondrostoma lusitanicum (Cyprinidae) endemic to Portugal. A fragment of the mitochondrial cyt b gene and one from the nuclear beta-actin gene were sequenced. The results support recognition of 3 ESU's distributed as follows:
1) Sado River, 2) the Tagus River basin and 3 independent nearby coastal rivers (collectively named "West") and 3) Lagoa de
Albufeira, a small coastal lagoon between Tagus and Sado basins. 相似文献
127.
S Stefanni R Castilho M Sala-Bozano J I Robalo S M Francisco R S Santos N Marques A Brito V C Almada S Mariani 《Heredity》2015,115(6):527-537
The processes and timescales associated with ocean-wide changes in the distribution
of marine species have intrigued biologists since Darwin''s earliest insights
into biogeography. The Azores, a mid-Atlantic volcanic archipelago located
>1000 km off the European continental shelf, offers ideal opportunities to
investigate phylogeographic colonisation scenarios. The benthopelagic sparid fish
known as the common two-banded seabream (Diplodus vulgaris) is now
relatively common along the coastline of the Azores archipelago, but was virtually
absent before the 1990s. We employed a multiple genetic marker approach to test
whether the successful establishment of the Azorean population derives from a recent
colonisation from western continental/island populations or from the demographic
explosion of an ancient relict population. Results from nuclear and mtDNA sequences
show that all Atlantic and Mediterranean populations belong to the same phylogroup,
though microsatellite data indicate significant genetic divergence between the
Azorean sample and all other locations, as well as among Macaronesian, western
Iberian and Mediterranean regions. The results from Approximate Bayesian Computation
indicate that D. vulgaris has likely inhabited the Azores for ∼40
(95% confidence interval (CI): 5.5–83.6) to 52 (95% CI:
6.32–89.0) generations, corresponding to roughly 80–150 years, suggesting
near-contemporary colonisation, followed by a more recent demographic expansion that
could have been facilitated by changing climate conditions. Moreover, the lack of
previous records of this species over the past century, together with the absence of
lineage separation and the presence of relatively few private alleles, do not exclude
the possibility of an even more recent colonisation event. 相似文献
128.
Winter segregation of migrant European robins Erithacus rubecula in relation to sex, age and size 总被引:2,自引:0,他引:2
Birds often show some form of social segregation during winter, both at large geographical scales (a consequence of differential migration) and at the regional or local level, when comparing different habitats or micro-habitats. However, our understanding of the mechanisms underlying such patterns is still poor. These issues have been rarely investigated in migratory Old-World passerines, particularly with respect to differences between the sexes. In this study, we show that female European robins Erithacus rubecula (sexed by molecular techniques) greatly outnumber males in southern Iberia, which confirms that this species is a differential migrant with a strong latitudinal segregation of the sexes. Furthermore, sex, age and body size influence the habitat distribution of robins in winter. Subordinate birds (females, juveniles and small individuals) were generally more common in habitats with a greater shrub development, and comparatively scarce in woodlands with relatively little undergrowth. Birds wintering in woodlands were in better condition (assessed by breast-muscle scoring) than birds wintering in shrubland. These results are consistent with the hypothesis that proposes that social dominance, mediated by differences in size and experience, is important in determining the habitat segregation of sex and age classes. The alternative hypothesis (habitat specialization), although not specifically supported by our findings, cannot be ruled out on the basis of the available evidence. 相似文献
129.
Reproductive behaviour of the black-striped pipefish Syngnathus abaster (Pisces; Syngnathidae) 总被引:1,自引:0,他引:1
K. Silva †‡ N. M. Monteiro †§ M. N. Vieira † V. C. Almada 《Journal of fish biology》2006,69(6):1860-1869
The 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. 相似文献
130.