1,720,964 research outputs found
Mating system and alternative male mating tactics in the grass goby Zosterisessor ophiocephalus (Teleostei: Gobiidae)
No full textPeculiar fertilization dynamics, with males releasing sperm in mucous trails lasting several hours, characterize some demersal spawning fish. The mating system was investigated in a natural population of one of these species: the grass goby Zosterisessor ophiocephalus (Pallas, 1814), a large coastal goby inhabiting seagrass meadows in shallow brackish water. Adult males ranged in size from 7.4 to 23 cm total length, but only larger ones were observed to dig and defend a burrow, where they performed parental care on eggs laid by one to several females. Field observations together with analyses of age, sperm production, trail sperm content and sperm competition tests indicated the occurrence of alternative male mating tactics, likely the expression of an ontogenetic gradient. Larger males are older than smaller ones, and while the former are territorial, the latter “sneak” territorial male spawns. The ejaculate characteristics indicate that grass goby males have functionally polymorphic spawns: in fact sperm trails of larger males last longer and release fewer sperm than those of smaller males. Sperm production over several days is more constant in larger than in smaller males, but the total number of sperm released is higher in the latter. The influence of seminal fluid in the functional intraspecific variability in sperm release in this species is discussed
Indivudual adjustment of sperm expendiiture accords with sperm competition theory
No full textSperm competition theory predicts that males should strategically
allocate their sperm reserves according to the level of sperm
competition, defined as the probability that the sperm of two
males compete for fertilizing a given set of ova. Substantial
evidence from numerous animal taxa suggests that, at the individual
level, sperm expenditure increases when the risk of sperm
competition is greater. In contrast, according to the ‘‘intensity
model’’ of sperm competition [Parker, G. A., Ball, M. A., Stockley,
P.&Gage, M. J. G. (1996) Proc. R. Soc. London Ser. B 263, 1291–1297],
when more than two ejaculates compete during a given mating
event, sperm expenditure should decrease as the number of
competing males increases. Empirical evidence supporting this
prediction, however, is still lacking. Here we measured sperm
expenditure in two gobiid fishes, the grass (Zosterisessor ophiocephalus)
and black goby (Gobius niger), in which up to six
sneakers can congregate around the nest of territorial males and
release their sperm when females spawn. We show that, in
accordance with theory, sneaker males of both species release
fewer sperm as the number of competitors increases
Social organization and sexual pattern in the mediterranean parrotfish Sparisoma cretense (Teleostei: Scaridae)
No full textWe examined the social organization and
reproductive pattern of a population of Sparisoma
cretense L. at Lampedusa Island (Italy). During the
breeding season (July to September) individuals occur
either in territorial or in non-territorial groups, which
quantitatively dier with respect to use of space, sex-
ratio and sexual activity. Territorial groups consist of
one male plus one to three females, whereas in non-
territorial groups as many as 54 ®sh share a common
area. Among non-territorial groups, variations, in both
sex-ratio and behavior, suggest they could represent
either feeding aggregations or reproductive aggrega-
tions. Spawning, always in pairs, occurs daily in a short
period of time before dusk and has been observed only
in territorial groups. Group spawning has never been
observed, but another alternative mating tactic,
streaking on pair spawning, was recorded. In the non-
breeding season ®sh do not aggregate in organized
social units. Histological examination of gonads
showed that adults are larger than 12 cm total length.
Females have an asynchronous ovary, typical of species
spawning several times during the breeding season.
Males show secondary testes, indicating that their go-
nads develop ovaries as juveniles, which are later re-
dierentiated into functional testes. Histological and
demographic data seem to indicate that, as in other
species of this genus, prematurational sex-change oc-
curs. The sexual pattern appears to be essentially go-
nochoristic, but the potential for sex-change is not
excluded
Changes along the male reproductive axis in response to social context in a gonochoristic gobiid, Zosterisessor ophiocephalus (Teleostei, Gobiidae), with alternative mating tactics
No full textSexual selection has given rise, in several taxa, to intrasexual variation in male phenotype. While evolutionary studies have provided
explanations of the adaptive function of this dramatic male phenotypic diversity, the proximate control of its expression has still to be
completely understood. Several observations, primarily from sex-changing species, indicated a major role of social interactions in
reproductive axis regulation and consequently in the expression of alternative male phenotypes. Here we documented changes along the male
reproductive axis in response to social context in a gonochoristic species, the grass goby Zosterisessor ophiocephalus, where fully functional
alternative male mating tactics appear to be expressed as an ontogenetic gradient. In the grass goby, larger and older males dig a nest and
perform parental care, while smaller males sneak fertilization during territorial male spawning. Territorial males are characterized by a higher
number of gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area, smaller testes, larger seminal vesicles, and viscous
ejaculates that last longer and contain fewer sperm than those of sneakers. To experimentally investigate the role of social factors in inducing
changes along the male reproductive axis, sneakers were tested in two different situations: nesting alone or with ripe females. Sneakers that
mated and performed parental care showed dramatic changes in brain, reproductive apparatus morphology, and ejaculate traits. GnRHimmunoreactive
cells in forebrain preoptic area increased in number, reaching values typical of wild-caught parental males. Testes size
decreased while seminal vesicle size increased and ejaculates showed lower sperm densities. These results were discussed within the
framework of the social transduction hypothesis, which predicts that social experience should mediate, through a cascade of internal
processes, shifts between morphs throughout life
Sperm competition and the mode of fertilization in the grass goby Zosterisessor ophiocephalus (Teleostei: Gobiidae)
No full textAccessory structures to the male reproductive system are known in several families
of teleost, but their role in sperm production patterns and fertilization dynamics is still unclear.
The intraspecific variability in seminal vesicles, shown by the grass goby Zosterisessor
ophiocephalus, presents an opportunity to examine both its possible correlation to alternative
male mating tactics and the function of these accessory structures. In this species, males are
known to release sperm in the form of sperm trails, bands of mucosubstances in which sperm are
embedded.
Surgical removal of seminal vesicles and histochemistry demonstrate that mucins, involved in
the production of sperm trails, are secreted by the seminal vesicles. Gametes show a high longevity;
sperm motility lasts on average 80 minutes. Eggs can be fertilized for several hours and do not
need to be laid over trails because sperm are able to reach them via the surrounding water.
Gonosomatic and seminal vesicle somatic indices, histology and histochemistry of gonads and
seminal vesicles, sperm counts, and sperm trail longevity, suggest the presence of alternative
male mating tactics in this species. Larger males have smaller testes and larger seminal vesicles
compared to those of smaller males. The major role of seminal vesicles is mucin secretion in
larger males, sperm storage in smaller ones. Trails of larger males last longer and release
sperm more constantly over time than those of smaller males. Overall differences between
males support the presence of differences in the intensity of sperm competition, with larger
males performing nesting behaviour while smaller ones sneak spawning
Variability of GnRH secretion in two goby species with socially controlled alternative male mating tactics
No full textMale reproductive phenotypic plasticity related to environmental–social conditions is common among teleost fish. In several species, males
adopt different mating tactics depending on their size, monopolizing mates when larger, while parasitizing dominant male spawns when smaller.
Males performing alternative mating tactics are often characterized by a strong dimorphism in both primary and secondary reproductive traits.
According to studies on sex-changing species and on species where only one male morph is reproductively active, male alternative phenotypes are
expected to vary also in gonadotropin-releasing hormone (GnRH) neurons in forebrain preoptic area (POA). Here, we compared the intra- and
inter-sexual variations in number and size of GnRH neurons, along with gonads and male accessory structure investment, in two goby species, the
grass goby, Zosterisessor ophiocephalus, and the black goby, Gobius niger, characterized by male alternative mating phenotypes. In both species,
older and larger males defend nests, court and perform parental care, while younger and smaller ones try to sneak territorial male spawning. We
found that grass goby and black goby have different patterns of GnRH expression. Grass goby presents a clear intra-sexual dimorphism in GnRH
expression, related to the occurrence of alternative mating tactics, while in the black goby, only inter-sexual differences are observed. The interand
intra-specific variability in the GnRH neurons in these two goby species is discussed in light of the differences in migratory behavior, nest
type, and mating system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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