Andrea Marconato

Bio: Andrea Marconato is an academic researcher from University of Padua. The author has contributed to research in topics: Spawn (biology) & Sperm. The author has an hindex of 13, co-authored 15 publications receiving 1230 citations.

Sperm Economy in a Coral Reef Fish, Thalassoma Bifasciatum

Abstract: In many coral reef fishes, males face the evolutionary problems of how to allocate sperm among frequent, daily mating in order to maximize the number of eggs they fertilize. A method is developed and tested for collecting and counting the number of sperm and eggs released during separate spawns of the coral reef fish Thalassoma bifasciatum. The method was used to examine the pattern of sperm allocation for pair— and group—spawning males. The number of sperm released by pair—spawning males varied positively with the number of eggs released by their female mates and with female body size. The data suggest that males economize on sperm release by providing the minimum amount of sperm needed to fertilize the egg clutch of the female partner. Fertilization efficiency (the number of eggs fertilized by a given number of sperm) was higher with large females than it was with small females. Males differed significantly among themselves in sperm output per spawn, with some males consistently releasing more sperm than other males with same—sized females. Male—male differences were not due to differences in male body size, quality of the spawning site, or the apparent degree of water movement. The number of sperm released per spawn did not decline throughout the daily spawning period, a pattern that disproved one but not all possible patterns of sperm depletion. In group spawns, the total number of sperm released and the number released per male were respectively 50 and 6 times the number released in pair spawns, on average. Both of these measures increased significantly with the clutch size of the spawning female. Overall, sperm production is probably sufficiently costly that males have been selected to allocate sperm carefully among their frequent daily spawns.

Endocrinology of teleost reproduction: A testicular steroid pheromone in the black goby, Gobius jozo L.

Abstract: The male black goby, Gobius jozo, is known to possess a large mesorchial gland which synthesizes large amounts of 5β-reduced androgens conjugates, especially etiocholanolone glucuronide. When gravid females releasing eggs on stripping were exposed singly to this steroid in a tank monitored through a closed television circuit, most of them manifested appetitive behaviour with negative kinesis towards the steroid source and were stimulated to lay their eggs. The steroid stimulus was effective in low concentration (below 2μM), in still water, and in the absence of sensorial reinforcements by a male partner. Females were little or not responsive outside in the interval between ovulation and oviposition. The pheromonal system of the black goby resembles that of the pig where the smell of the testicular 16-androstenes in the boar's breath induces the mating stance in the estrous sow. Both species are characterized by overdevelopment of the Leydighian compartment, chemical divergence between hormonal an...

The effects of fishing on marine ecosystems

Abstract: We review the effects of fishing on benthic fauna, habitat, diversity, community structure and trophic interactions in tropical, temperate and polar marine environments and consider whether it is possible to predict or manage fishing-induced changes in marine ecosystems Such considerations are timely given the disillusionment with some fishery management strategies and that policy makers need a scientific basis for deciding whether they should respond to social, economic and political demands for instituting or preventing ecosystem-based management Fishing has significant direct and indirect effects on habitat, and on the diversity, structure and productivity of benthic communities These effects are most readily identified and last longest in those areas that experience infrequent natural disturbance The initiation of fishing in an unfished system leads to dramatic changes in fish community structure As fishing intensity increases the additional effects are more difficult to detect Fishing has accelerated and magnified natural declines in the abundance of many forage fishes and this has lead to reduced reproductive success and abundance in birds and marine mammals However, such donor-controlled dynamics are less apparent in food webs where fishes are the top predators since their feeding strategies are rather more plastic than those of most birds and mammals Fishers tend to target species in sequence as a fishery develops and this leads to changes in the composition of the fished communities with time The dramatic and apparently compensatory shifts in the biomass of different species in many fished ecosystems have often been driven by environmental change rather than the indirect effects of fishing Indeed, in most pelagic systems, species replacements would have occurred, albeit less rapidly, in the absence of fishing pressure In those cases when predator or prey species fill a key role, fishing can have dramatic indirect effects on community structure Thus fishing has shifted some coral reef ecosystems to alternate stable states because there is tight predator–prey coupling between invertebrate feeding fishes and sea urchins Fishing has reduced, and locally extirpated, populations of predatory fishes These reductions do not have a consistent effect on the abundance and diversity of their prey: environmental processes control prey populations in some systems, whereas top-down processes are more important in others By-catch which is discarded during fishing activities may sustain populations of scavenging species, particularly seabirds We conclude by identifying the circumstances in which new research is needed to guide managers and stress the importance of unfished control sites for studies of fishing effects We discuss the advantages and disadvantages of closed area management (marine reserves) and the conditions under which such management is likely to provide benefits for the fishery or ecosystem

Sperm competition, male prudence and sperm-limited females

Abstract: Sperm are produced in astronomical numbers compared with eggs, and there is good evidence that sperm competition is the force behind the evolution of many tiny sperm. However, sperm production inevitably has costs. Recent research shows that male ejaculate expenditure is dynamic in both time and space, and that males are sensitive to risks of sperm competition and can vary ejaculate size accordingly. We focus on studies showing that males assess mating status and relative fecundity of females, and reveal that modulation of ejaculate investment by males can sometimes result in sperm limitation for females.

Armaments and ornaments: an evolutionary explanation of traits of dual utility

Abstract: Secondary sexual characters in many species function both in male-male competition and as cues for female choice. Based on a literature compilation of existing knowledge of traits with this dual fu ...

Directional patterns of female mate choice and the role of sensory biases

Abstract: A review of the literature reveals that, if females prefer traits that deviate from the population mean, they usually prefer traits of greater quantity. In cases in which the sensory bases of these preferences are identified, females prefer traits of greater quantity because these traits elicit greater sensory stimulation. However, two caveats apply. First, the studies surveyed might not represent an unbiased sample of mate choice, because researchers usually study systems characterized by exaggerated traits. Second, a preference for traits of greater quantity does not suggest that preference for average traits is unimportant; it might be more usual than preference for exaggerated traits. Phylogenetic comparisons sometimes allow one to distinguish among competing hypotheses for the evolution of female mating preferences. Two hypotheses, Fisher's theory of "runaway" sexual selection and the "good genes" hypothesis, predict that traits and preferences coevolve, whereas the "sensory exploitation" hypothesis ...

Sneakers, Satellites, and Helpers: Parasitic and Cooperative Behavior in Fish Reproduction

Abstract: Organisms compete for various resources in the course of sexual reproduction. First, there is intrasexual competition for obtaining mates. Then, there is the need to exclude reproductive competitors who might displace or affect the individual's own gametes (e.g., sperm competition, egg dumping). There is competition for sites that are used to raise progeny andtor that will optimally support them, and it may be highly advantageous to monopolize the resources that are essential for offspring survival and development. In this chapter I review our current knowledge of the ways in which fish compete at these different levels. I further describe how competition for resources may lead to cooperative behavior, even between the competitors themselves. Finally, I draw attention to the model character of fish social systems and suggest crucial directions for future research.