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- Cheraghchi, M., et al.
(författare)
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Approximating linear threshold predicates
- 2012
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Ingår i: ACM Transactions on Computation Theory. - : Association for Computing Machinery (ACM). - 1942-3454 .- 1942-3462. ; 4:1
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Tidskriftsartikel (refereegranskat)abstract
- We study constraint satisfaction problems on the domain {-1, 1}, where the given constraints are homogeneous linear threshold predicates, that is, predicates of the form sgn(w 1 x 1 + · · · + w n x n ) for some positive integer weights w 1 , . . . , w n . Despite their simplicity, current techniques fall short of providing a classification of these predicates in terms of approximability. In fact, it is not easy to guess whether there exists a homogeneous linear threshold predicate that is approximation resistant or not. The focus of this article is to identify and study the approximation curve of a class of threshold predicates that allow for nontrivial approximation. Arguably the simplest such predicate is the majority predicate sgn(x 1 + · · · + x n ), for which we obtain an almost complete understanding of the asymptotic approximation curve, assuming the Unique Games Conjecture. Our techniques extend to a more general class of "majority-like" predicates and we obtain parallel results for them. In order to classify these predicates, we introduce the notion of Chow-robustness that might be of independent interest.
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- Järvi-Laturi, Maria, et al.
(författare)
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Sand goby males trade off between defence against egg predators and sneak intrusions
- 2011
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Ingår i: Journal of Zoology. - : Wiley. - 0952-8369 .- 1469-7998. ; 283:4, s. 269-275
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Tidskriftsartikel (refereegranskat)abstract
- According to life-history theory, a care-taking parent should balance investment in current and future reproduction in such a way that it maximizes lifetime reproductive success. In the sand goby Pomatoschistus minutus, a small marine fish with paternal care, nest-guarding males may lose current reproductive success to both parasitically fertilizing males and egg predators. Here, we observed sand gobies at a marine and a brackish site, two geographically distant and ecologically different habitats. In a field experiment, we found that sand gobies at the marine site suffered from severe egg predation by netted dogwhelks Nassarius nitidus, which are lacking at the brackish site. Because egg laying takes hours and several females often lay eggs sequentially in one nest, the risk of parasitic spawnings and egg predation overlaps in time during breeding activities. Hypothesizing that egg predators might influence the success of parasitic spawnings, we then simulated these natural conditions in a laboratory experiment with the presence or absence of egg predators, combined with the presence of sneaker males. As expected, in the egg predator treatment, egg-guarding males had to compromise between defence behaviours and thus had less time to devote to defence against sneaker males. Sneaker males took advantage of the situation and approached the nests more actively than in the predator-free treatment. However, the increase in approaches did not result in more successful parasitic fertilizations by sneaker males, as determined using microsatellite DNA. Nevertheless, in nature the adjustment of time budgets by the egg-guarding male are likely to have serious fitness consequences, both if the male fails to defend his paternity and if he fails to defend his offspring.
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- Kvarnemo, Charlotta, 1963, et al.
(författare)
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Investment in testes, sperm-duct glands and lipid reserves differs between male morphs but not between early and late breeding season in Pomatoschistus minutus
- 2010
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Ingår i: Journal of Fish Biology. - : Wiley. - 0022-1112 .- 1095-8649. ; 76:7, s. 1609-1625
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Tidskriftsartikel (refereegranskat)abstract
- This study of the sand goby Pomatoschistus minutus, a nest-holding fish with paternal care, focused on gonadal investment among males of different sizes collected early and late in the breeding season. All males caught at the nest had breeding colour, whereas trawl-caught fish consisted of males both with and without colour. The absence or presence of breeding colour was a good predictor of testes investment. Compared to males with breeding colour, males without colour were smaller in body size but had extraordinarily large testes. In absolute terms, testes mass of males without breeding colour was on average 3.4 times greater than those of males with breeding colour. Since small colourless males are known to reproduce as sneaker males, this heavy investment in testes probably reflects that they are forced to spawn under sperm competition. Contrary to testes size, sperm-duct glands were largest among males with breeding colour. These glands produce mucins used for making sperm-containing mucous trails that males place in the nest before and during spawning. Since both sneakers and nest-holders potentially could benefit from having large glands, this result is intriguing. Yet, high mucus production may be more important for nest-holders, because it also protects developing embryos from infections. There was no significant effect of season on body size, testes or sperm-duct glands size, but colourless males tended to be less common late in the season. Possibly this may indicate that individual small colourless males develop into their more colourful counterparts within the breeding season.
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- Pedroso, S. S., et al.
(författare)
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Courtship Sounds Advertise Species Identity and Male Quality in Sympatric Pomatoschistus spp. Gobies
- 2013
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 8:6
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Tidskriftsartikel (refereegranskat)abstract
- Acoustic signals can encode crucial information about species identity and individual quality. We recorded and compared male courtship drum sounds of the sand goby Pomatoschistus minutus and the painted goby P. pictus and examined if they can function in species recognition within sympatric populations. We also examined which acoustic features are related to male quality and the factors that affect female courtship in the sand goby, to determine whether vocalisations potentially play a role in mate assessment. Drums produced by the painted goby showed significantly higher dominant frequencies, higher sound pulse repetition rates and longer intervals between sounds than those of the sand goby. In the sand goby, male quality was predicted by visual and acoustic courtship signals. Regression analyses showed that sound amplitude was a good predictor of male length, whereas the duration of nest behaviour and active calling rate (i.e. excluding silent periods) were good predictors of male condition factor and fat reserves respectively. In addition, the level of female courtship was predicted by male nest behaviour. The results suggest that the frequency and temporal patterns of sounds can encode species identity, whereas sound amplitude and calling activity reflects male size and fat reserves. Visual courtship duration (nest-related behaviour) also seems relevant to mate choice, since it reflects male condition and is related to female courtship. Our work suggests that acoustic communication can contribute to mate choice in the sand goby group, and invites further study.
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- Svensson, Ola, 1971, et al.
(författare)
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Offspring recognition and the influence of clutch size on nest fostering among male sand gobies, Pomatoschistus minutus
- 2010
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Ingår i: Behavioral Ecology and Sociobiology. - Heidelberg : Springer. - 0340-5443 .- 1432-0762. ; 64:8, s. 1325-1331
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Tidskriftsartikel (refereegranskat)abstract
- When parental care is costly, parents should avoid caring for unrelated young. Therefore, it is an advantage to discriminate between related and unrelated offspring so that parents can make informed decisions about parental care. In the present study, we test the hypothesis that male sand gobies (Pomatoschistus minutus) recognize and differentially care for their own offspring when given a choice between a nest with sired eggs and a second nest with eggs sired by an unrelated male. The sand goby is a species with exclusive and costly paternal care. Male parasitic spawnings (e.g., sneaking) as well as nest takeovers by other males are common. Our results show that nests containing sired eggs were preferred and received significantly more care, as measured by nest building and nest occupancy, than nests with foreign eggs even when males cared for both nests. These findings suggest that males respond to paternity cues and recognize their own clutches. Relative clutch size also had a significant effect on male parental care. When sired clutches were larger than foreign clutches, males preferred to care for their own nest. In the few cases where males chose to take care of foreign nests, the foreign clutch was larger than their own clutch. Taken together, our results provide evidence that both paternity cues and clutch size influence parenting decisions among male sand gobies.
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| 9. |
- Svensson, Ola, 1971, et al.
(författare)
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Segregation of species-specific male attractiveness in F2 hybrid Lake Malawi cichlid fish
- 2011
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Ingår i: International Journal of Evolutionary Biology. - : Hindawi Limited. - 2090-052X. ; 2011
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Tidskriftsartikel (refereegranskat)abstract
- Among the huge radiations of haplochromine cichlid fish in Lakes Malawi and Victoria, closely related species are often reproductively isolated via female mate choice although viable fertile hybrids can be produced when females are confined only with heterospecific males. We generated F2 hybrid males from a cross between a pair of closely related sympatric cichlid fish from Lake Malawi. Laboratory mate choice experiments using microsatellite paternity analysis demonstrated that F2 hybrid males differed significantly in their attractiveness to females of the two parental species, indicating heritable variation in traits involved in mate choice that may contribute to reproductive isolation between these species. We found no significant correlation between male mating success and any measurement of male colour pattern. A simple quantitative genetic model of reproductive isolation suggests that there may be as few as two chromosomal regions controlling species-specific attractiveness. We propose that adaptive radiation of Lake Malawi cichlids could be facilitated by the presence of genes with major effects on mate choice and reproductive isolation.
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