1,720,977 research outputs found
Male mating tactics and secondary sexual traits: insights from the Mediterranean killifish, Aphanius fasciatus
Full text linkContext. Sexual selection results from male competition and female choice linked by complex interactions that drive the population’s life history, often leading to the development of specific secondary sexual traits with an increased reproductive success. Aims. To investigate the male mating tactics and the role of a secondary sexual trait (‘black band’ on the caudal fin) along the male ontogenetic development in the Mediterranean killifish, Aphanius fasciatus (Valenciennes, 1821). Methods. Male–male competition was investigated through a combination of an extensive field collection and behavioural analysis under controlled conditions, comparing four groups differing in the presence or absence of the black band and body size. Key results. Banded males courted more and tended to monopolise the female, but the overall spawning performance did not differ significantly among the analysed groups. Conclusion. (1) The black band on the caudal fin depends on ontogeny; (2) all mature males express the entire courtship and competitive repertory; (3) sexual maturity occurs in fish of at least 20 mm; (4) large size and presence of the black band seem to contribute to male dominance. Implications. This study has highlighted the role of Aphanius fasciatus as an excellent model for studying polygynandrous mating systems, on the basis of intense male–male competition
Comparing the reproductive success of three Palaemonid species in a Mediterranean coastal lagoon: native and invasive responses to salinity changes
No full textSalinity changes in transitional water
ecosystems are a natural feature, but anthropogenic
direct or indirect impacts are drastically altering their
equilibrium and, therefore, their biological communities.
Females of three species of Palaemonidae
shrimps (the invasive Palaemon macrodactylus and
the native P. adspersus and P. elegans) were collected
in nature and kept in laboratory at salinities 20 and 30.
For each species, the reproductive strategy (investment
devoted to reproduction) and the reproductive
performance (larval output and hatching success) were
determined. Significant differences were observed
comparing the three species, highlighting an opportunistic
r-strategy in P. macrodactylus and P. elegans,
while P. adspersus resulted to produce fewer and
larger eggs. Palaemon elegans showed a lower
hatching success than the other two species, and the
size-adjusted larval output appeared to be highly
sensitive to salinity variations, with a strong increase
under euhaline conditions (salinity 30), while this
increase was limited in the other two species. The
selected species were used as model organisms to
understand which could be the shift in biological
communities due to salinity variations. Data suggest
that a shift towards euhaline conditions will favor the
native populations, while a shift towards mesohaline
waters could determine an increase of the invasive
shrimps
Interspecific aggression and food competition between the global invader Palaemon macrodactylus and the native Palaemon elegans
Full text linkThe impact of invasive alien species on native communities can act at different levels both
by affecting the ecosystem’s structure (i.e., mainly in the case of vegetation) and through direct
interactions (i.e., competition for food or space). Behavioral studies under controlled conditions can
provide relevant information on both the invasive potential of alien species and the potential impact
of the invaders on the local native species. In the laboratory, the competition for food resources
between the invasive oriental shrimp Palaemon macrodactylus, Rathbun, 1902, and the Mediterranean
native shrimp Palaemon elegans, Rathke, 1836, was analyzed. These species are typical residents of
coastal transitional and estuarine waters, so the experiments were carried out using two salinity
conditions that characterize the coastal lagoon of Venice. Although at both salinity treatments the
alien species tended to be more aggressive than the native one, significant differences between the
two species were mainly observed at a salinity of 30. In particular, at a salinity of 30, P. macrodactylus
spent more time attending to the food source than the native species. The results are discussed in
light of the potential inter-specific competition between the two species within the conditions of the
Venice lagoon
Trophic adaptability shapes isotopic niche of the resident fish Aphanius fasciatus across lagoon habitats
No full textCoastal lagoons are characterized by high habitat heterogeneity where natural habitats coexist with artificial ones, historically set up to support human activities. Increasing anthropogenic pressure may lead to progressive degradation of the most vulnerable lagoonal habitats and the associated biological communities. One of the strictly estuarine-dependent fish species that may be affected by the degradation of lagoon habitats is the South European toothcarp Aphanius fasciatus, archetype of Mediterranean lagoon residents. Carbon and nitrogen stable isotopes were used to disentangle the influence of habitat types (natural vs artificial) and fish community (multi-trophic context) on the trophic niche features of A. fasciatus. Fish communities and organic matter sources were sampled in two Mediterranean lagoons located at the northernmost (Lagoon of Venice) and at the mid-latitude (Stagnone di Marsala, Trapani) of A. fasciatus distribution. Results showed evidence of high trophic adaptability of A. fasciatus, whose omnivorous feeding habit resulted in seasonal changes in isotopic niche width and niche partitioning with co-occurring species, constituting an advantage in habitats characterized by high seasonal variation of resources availability. Furthermore, while macrophytes drove the main trophic pathways leading to A. fasciatus in natural habitats, artificial habitats were mainly based on sedimentary organic matter routes. These outcomes broaden our knowledge on how natural and artificial habitats trophically support A. fasciatus populations and results are discussed in light of the ecological implications for environmental management of coastal lagoons
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
Vulnerability of the Small-Scale Fishery to Climate Changes in the Northern-Central Adriatic Sea (Mediterranean Sea)
No full textClimate change is altering the functioning of ecosystems and species distribution worldwide, with negative impacts on human activities, including fisheries. The Adriatic Sea is an extremely productive area for fisheries, due to the strong outflow of nutrients from rivers and the periodic mixing of nutrients from the Mediterranean. However, the Adriatic Sea is also a semi-closed basin, where species do not have the ability to move to higher latitudes to avoid warming of the waters. Climate change acts on biodiversity in a variety of ways, such as causing changes in the trophic network-favoring the intake of thermophilic alien species, often in competition with local species-and altering the biological cycles of acclimatized marine species to temperate-cold climates. These problems become critical factors for the survival of species and for fisheries relying on these resources. Within this context, to have estimates of possible modifications of the nektonic community in the near future could be quite useful for preparing adaptation plans. In this paper, using Maximum Entropy models under RCP 4.5 and 8.5 scenarios, we estimated the future habitat suitability for a set of marine nektonic species of different thermal affinity (e.g., cold, temperate and warm species) within GSA17 (Northern and Central Adriatic Sea), among the most productive-and most exploited-areas of the Mediterranean Sea. This study shows how, at the current pace, climate change could modify marine ecosystems to the extent that future habitat suitability will decrease for nearly half of the species considered, with a decrease in landings from 13.5 to 86.9%, depending on the scenario. Only for the blue crab Callinectes sapidus has an increase in habitat suitability been observed. For most of the species considered, temperature was the most important variable to explain the probability of relative presence within the GSA17. On the other hand, GSA17 climatic conditions in the near future under the tested scenarios could become a suitable environment for tropical species, which could find here a suitable habitat, at least in terms of thermal features. Results of the present study can help the management of fishery resources and local markets in the near future, providing information to predict changes in the composition of the aquatic community and draw up management plans that take into account the effects of climate change
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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