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Results for “Mate Selection”

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At least 325 records · Page 18Linked to original sources
PubMed1972

Experimentally determined, two locus fitnesses of Drosophila melanogaster males.

A pilot demonstration of experimental fitness estimation utilizing pedigree data from D. melanogaster was described. Fitnesses were obtained for the male segregants of the two "complex loci," spineless-spineless aristapedia and radius incompletus-inturned. A good fit between selection model and data was obtained, perhaps because the experimental design largely eliminated concerns of frequency or density-dependent selection and assortative mating. The selection model assumed that net fitness was divided into two components: an "early" component operative from conception to the time of observation in the generation interval, and a late component operative from the time of observation to the time of gamete pool formation. These fitness components were roughly descriptive of the physiological components viability and reproductive ability. No simple systematic relationship between the fitness of two-locus genotypes and the marginal one-locus fitness emerged. These conclusions were based on relatively precise (by current standards) fitness estimates. It was argued that pedigree data is highly desirable for fitness estimation.

Age Factors↗
PubMed2002

Sexual selection and alternative mating behaviours generate demographic stochasticity in small populations.

Recent theory predicts that environmental variation and small population size facilitate the coexistence of alternative phenotypes despite unequal mean fitness. However, traditional studies of reproductive strategies often assume that the stability of alternative mating behaviours relies on equal male fitness. We present results from field observations and experimental manipulations of thermal resources on territories demonstrating the coexistence of alternative reproductive behaviours with unequal fitness. The side-blotched lizard Uta stansburiana exhibits two alternative strategies for territoriality: "usurp" and "defend". Paternity analysis revealed significantly greater mean fitness for "usurpers" than "defenders" in our study of natural variation. Moreover, variance in fitness was significantly higher for usurpers on both experimental and natural plots, implying that "usurp" is a risky strategy with potentially large pay-offs or none at all. We show theoretically that significantly higher variance in usurper fitness can allow for coexistence with defenders despite higher mean fitness of usurpers. This coexistence is facilitated by small population size. Our results have general implications for the evolution of alternative strategies and the maintenance of genetic diversity in small populations.

Animals↗
PubMed2003

Melanin-based plumage coloration and flight displays in plovers and allies.

Plovers and their allies exhibit an impressive diversity of melanin-based plumage patterns ranging from non-melanized to completely melanized species. We use phylogenetic comparative methods to test whether melanization has evolved in relation to sexual selection for attracting mates, to selection for signalling territory defence, or to natural selection for camouflage. First, according to sexual-selection theory, melanized plumage has evolved to amplify the courtship displays of males. As predicted by this hypothesis, we found that males with aerial displays had more melanized plumage than males of ground-displaying species. In addition, sexual dimorphism in melanization was greater in species with display flights than in species with ground displays. Second, melanization may have evolved through social interactions to signal competitive ability in territory defence. We did not find evidence for this hypothesis, since breeding density was unrelated to the melanization of either sex. Finally, melanized plumage may camouflage the incubating parent. The latter hypothesis was not supported, since melanization was unrelated either to the darkness of nest substrate or the extent of vegetation cover. Taken together, our results are most consistent with the sexual-selection hypothesis, and suggest that melanized plumage has evolved to enhance the aerial displays of male plovers.

Animal Communication↗
PubMed2005

Cytonuclear models of epistatic mating with backcrossing and selection.

We develop hybrid zone models that explore the combined effects of mating system and either backcrossing or viability selection on the disequilibria between nuclear and cytoplasmic genes. In the epistatic mating plus backcrossing model, we find patterns of permanent cytonuclear disequilibria like those found when epistatic mating is the only factor, as well as a novel combination of significant cytonuclear disequilibria sign patterns. The second group of models evaluates the potential of epistatic mating and postzygotic viability selection to maintain cytonuclear disequilibria. Simulations are used to evaluate nine patterns of selection, each of which represent differing forms of selection against hybrids, and show that while all disequilibria usually decay to zero, under certain circumstances a number of different patterns of significant cytonuclear disequilibria are possible at equilibrium. The results from these models are compared to the observed cytonuclear disequilibria previously found in a hybrid population of Hyla treefrogs.

Animals↗
PubMed2003

Sexual selection and the risk of extinction in birds.

The relationship between sexual selection and extinction risk has rarely been investigated. This is unfortunate because extinction plays a key role in determining the patterns of species richness seen in extant clades, which form the basis of comparative studies into the role that sexual selection may play in promoting speciation. We investigate the extent to which the perceived risk of extinction relates to four different estimates of sexual selection in 1030 species of birds. We find no evidence that the number of threatened species is distributed unevenly according to a social mating system, and neither of our two measures of pre-mating sexual selection (sexual dimorphism and dichromatism) was related to extinction risk, after controlling for phylogenetic inertia. However, threatened species apparently experience more intense post-mating sexual selection, measured as testis size, than non-threatened species. These results persisted after including body size as a covariate in the analysis, and became even stronger after controlling for clutch size (two known correlates of extinction risk). Sexual selection may therefore be a double-edged process-promoting speciation on one hand but promoting extinction on the other. Furthermore, we suggest that it is post-mating sexual selection, in particular, that is responsible for the negative effect of sexual selection on clade size. Why this might be is unclear, but the mean population fitness of species with high intensities of post-mating sexual selection may be especially low if costs associated with multiple mating are high or if the selection load imposed by post-mating selection is higher relative to that of pre-mating sexual selection.

Animals↗
PubMed2004

Nonlinear effects of female mate choice in wild threespine sticklebacks.

Sexual selection by mate choice represents a very important selective pressure in many animal species and might have evolutionary impacts beyond exaggeration of secondary sexual traits. Describing the shape and strength of the relationships linking mating success and nonsexual traits in natural conditions represents a challenging step in our understanding of adaptive evolution. We studied the effect of behavioral (nest site choice), immunological (trematode level of infection), genetic diversity (measured by mean d2) and morphological (standard length and pectoral fin size) traits on male mating success in a natural population of threespine sticklebacks Gasterosteaus aculeatus. Male mating success was measured by microsatellite genotyping of embryos used to infer female genotypes. First, we analyzed all territorial males (full analysis) but also considered independently only males with a nonzero mating success (reduced analysis) because some of the males with no eggs could have been part of a later breeding cycle. Multiple linear regressions identified a significant negative effect of parasite load in the full analysis, whereas no linear effect was found in the reduced analysis. The quadratic analyses revealed that nest location and parasite load were significantly related to mating success by positive (concave selection) and negative (convex selection) quadratic coefficients respectively, resulting in a saddle-shaped fitness surface. Moreover, there were significant interactions between nest location, mean d2 and parasite load in the reduced analysis. The subsequent canonical rotation of the matrix of quadratic and cross-product terms identified two major axes of the response surface: a vector representing mostly nest site choice and a vector representing parasite load. These results imply that there exists more than one way for a male threespine stickleback to maximize its mating success and that such nonlinear relationships between male mating success induced by female mate choice and male characteristics might have been overlooked in many studies.

Animals↗
PubMed2006

Assortative mating through a mechanism of sexual selection.

We propose that assortative mating can arise through a mechanism of sexual selection by active female choice of partners based on a 'self-seeking like' decision rule. Using a mathematical model, we show that a gene can be selected that make females to choose mates that are similar to themselves with respect to an arbitrary tag, even if two independent and unlinked genes determine the preference and the tag. The necessary requisite for this process to apply is an asymmetry between partners, such that the female can choose the male but this one must always accept to mate. The fitness advantage is due to linkage disequilibrium built up between both genes. Simulations have been run to check the algebraic results and to analyse the influence of several factors on the evolution of the system. Any factor that favors linkage disequilibrium also favors the evolution of the preference allele. Moreover, in a large population subdivided in small subpopulations connected by migration, the assortative mating homogenizes the population genotypic structure for the tags in contrast to random mating that maintains most of the variation.

Animals↗
PubMedDate not supplied

Mating systems and sexual selection in male-pregnant pipefishes and seahorses: insights from microsatellite-based studies of maternity.

In pipefishes and seahorses (family Syngnathidae), the males provide all postzygotic care of offspring by brooding embryos on their ventral surfaces. In some species, this phenomenon of male "pregnancy" results in a reversal of the usual direction of sexual selection, such that females compete more than males for access to mates, and secondary sexual characteristics evolve in females. Thus the syngnathids can provide critical tests of theories related to the evolution of sex differences and sexual selection. Microsatellite-based studies of the genetic mating systems of several species of pipefishes and seahorses have provided insights into important aspects of the natural history and evolution of these fishes. First, males of species with completely enclosed pouches have complete confidence of paternity, as might be predicted from parental investment theory for species in which males invest so heavily in offspring. Second, a wide range of genetic mating systems have been documented in nature, including genetic monogamy in a seahorse, polygynandry in two species of pipefish, and polyandry in a third pipefish species. The genetic mating systems appear to be causally related to the intensity of sexual selection, with secondary sex characters evolving most often in females of the more polyandrous species. Third, genetic studies of captive-breeding pipefish suggest that the sexual selection gradient (or Bateman gradient) may be a substantially better method for characterizing the mating system than previously available techniques. Finally, these genetic studies of syngnathid mating systems have led to some general insights into the occurrence of clustered mutations at microsatellite loci, the utility of linked loci in studies of parentage, and the use of parentage data for direct estimation of adult population size.

Animals↗
PubMed2006

Monogamy in the maternally mouthbrooding Lake Tanganyika cichlid fish Tropheus moorii.

Supported by evidence for assortative mating and polygynandry, sexual selection through mate choice was suggested as the main force driving the evolution of colour diversity of haplochromine cichlids in Lakes Malawi and Victoria. The phylogenetically closely related tribe Tropheini of Lake Tanganyika includes the genus Tropheus, which comprises over 100 colour variants currently classified into six morphologically similar, polyphyletic species. To assess the potential for sexual selection in this sexually monochromatic maternal mouthbrooder, we used microsatellite-based paternity inference to investigate the mating system of Tropheus moorii. In contrast to haplochromines in Lake Malawi, multiple paternity is rare or even absent in broods of T. moorii. Eighteen of the 19 analysed families were consistent with genetic monogamy, while either a mutation or more than one sire explained the genotype of one offspring in another brood. We discuss the differences in breeding behaviour between T. moorii and the Lake Malawi haplochromines, and evaluate additional factors or alternatives to sexual selection as promoters of colour diversification. A preliminary survey of other Tropheini species suggested that multiple paternity is infrequent in the entire tribe.

Alleles↗