RESUMEN
The medfly, Ceratitis capitata, is an invasive species in which polyandry, associated with sperm precedence, is a common behaviour in the wild. In this species, characterized by internal fertilization, we disclose how the sperm from two males are stored in the female storage organs and how they are used in terms of paternity outcome. The experiments were designed to furnish comparable and unbiased estimates of sperm numbers and progeny in twice-mated females. Results are incorporated in a model through which it is possible to relate the amount of stored sperm with the progeny of twice-mated females. The results show that polyandrous medfly females conserve equal amounts of sperm from the two males to fertilize their eggs. However, we observed a clear advantage of the second male's sperm in siring progeny, which interestingly decreases in favor of the first male as ovipositions progress. The results enable us to exclude differential sperm mortality and suggest that it is the mechanics governing the storage organs which causes the initial, but decreasing second male sperm precedence during the female reproductive life. These outcomes allow us to correlate sperm use in polyandrous females with the mating strategies and invasiveness of this fly.
Asunto(s)
Ceratitis capitata/fisiología , Conducta Sexual Animal/fisiología , Espermatozoides/fisiología , Animales , Ceratitis capitata/genética , Femenino , Genitales Femeninos/fisiología , Masculino , Repeticiones de Microsatélite , ReproducciónRESUMEN
We consider a model of frequency-dependent selection, which we refer to as the Wildcard Model. A variety of more specific models, representing quite diverse biological situations, are covered by the Wildcard Model as particular cases. Two very different particular models that are subsumed by the Wildcard Model are the game theoretically motivated two-phenotype model of Lessard [Lessard, S.,1984. Evolutionary dynamics in frequency-dependent two-phenotype models, Theor. Popul. Biol. 25, 210-234], and the model of selection on a continuous trait due to intraspecific competition of Bürger [Bürger, R., 2005. A multilocus analysis of intraspecific competition and stabilizing selection on a quantitative trait. J. Math. Biol. 50 (4), 355-396] and Schneider [Schneider, K.A., 2006. A multilocus-multiallele analysis of frequency-dependent selection induced by intraspecific competition. J. Math. Biol. 52 (4), 483-523]. Both these models have been shown in the past to have a global Lyapunov function (LF) under appropriate genetic assumptions. We show that (i) the Wildcard Model in continuous time for a single multiallelic locus, or for multiple multiallelic loci in linkage equilibrium, has a global LF, of which the Lessard and Bürger-Scheneider LF are special cases in spite of their widely different biological interpretations; (ii) the LF of the Wildcard Model can be derived from an LF previously identified for a model of density- and frequency-dependent selection due to Lotka-Volterra competition, with one locus, multiple alleles, multiple species and continuous-time dynamics [Matessi, C., Jayakar, S.D., 1981. Coevolution of species in competition: A theoretical study. Proc. Natl. Acad. Sci. USA, 78 (2, part2), 1081-1084]. We extend the LF with density and frequency dependence to the multilocus case with linkage-equilibrium dynamics. As a possible application of our results, the optimization principle we established can be used as a tool in the study of long-term evolution of various models subsumed by the Wildcard Model based on explicit short-term dynamics.
Asunto(s)
Frecuencia de los Genes , Variación Genética , Modelos Genéticos , Selección Genética , Evolución Biológica , Genética de Población , Impresión Genómica , Polimorfismo GenéticoRESUMEN
We have investigated, numerically and analytically, long-term evolution under frequency-dependent disruptive selection of a continuous trait varying in a finite range and controlled by one diploid mendelian locus. We found that evolution converges towards a unique long-term equilibrium where only two extreme phenotypes are present with frequencies identical to those of the mixed strategy that would be the unique ESS of the game defined by the basic fitness function of the model. As long as this precise phenotypic composition is preserved, any genetic configuration of the polymorphism is equally acceptable (selectively neutral) at the equilibrium. Thus the number of alleles and their dominance pattern may vary considerably among different equilibrium populations. If genetic expression of the trait is variable but the amount of variability is genetically modifiable, disruptive selection, acting on such modifiers, produces a steady increase of expression variability before the equilibrium is attained. In this case a population at the long-term equilibrium might even be genetically monomorphic, with the phenotypic dimorphism resulting from purely random individual variation.
Asunto(s)
Frecuencia de los Genes , Genética de Población , Herencia Multifactorial , Polimorfismo Genético , Caracteres Sexuales , Alelos , Recolección de Datos , Variación Genética , Genotipo , Humanos , Modelos Genéticos , Modelos Teóricos , Fenotipo , Carácter Cuantitativo Heredable , Selección Genética , Factores de TiempoRESUMEN
In certain cases, predicted by evolutionary theory of sex-allocation and confirmed by empirical evidence, animals adaptively change their progeny sex-ratio according to individual circumstances. Here we argue that a similar response of offspring sex-ratio must exist in relation to genetic variation of mothers' mitochondria, as a consequence of maternal inheritance of these organelles and of their influence on fitness resulting from their crucial role in metabolism. In fact, a mathematical analysis of evolutionary dynamics of sex-allocation mutants demonstrates that natural selection promotes an evolutionarily stable allocation policy where mothers with defective mitochondria generate only sons, while those with optimal mitochondria have female biased progenies.