ABSTRACT
Variation is the basis for evolution, and understanding how variation can evolve is a central question in biology. In complex phenotypes, covariation plays an even more important role, as genetic associations between traits can bias and alter evolutionary change. Covariation can be shaped by complex interactions between loci, and this genetic architecture can also change during evolution. In this article, we analyzed mouse lines experimentally selected for changes in size to address the question of how multivariate covariation changes under directional selection, as well as to identify the consequences of these changes to evolution. Selected lines showed a clear restructuring of covariation in their cranium and, instead of depleting their size variation, these lines increased their magnitude of integration and the proportion of variation associated with the direction of selection. This result is compatible with recent theoretical works on the evolution of covariation that take the complexities of genetic architecture into account. This result also contradicts the traditional view of the effects of selection on available covariation and suggests a much more complex view of how populations respond to selection.
Subject(s)
Evolution, Molecular , Genetic Variation , Phenotype , Selection, Genetic , Animals , Body Size/genetics , Female , Male , Mice , Skull/anatomy & histologySubject(s)
Body Weight/genetics , Animals , Breeding , Genetic Loci , Genetic Markers , Genetic Variation , Mice, Inbred Strains , Microsatellite RepeatsABSTRACT
La capacidad reproductiva femenina se modificó como consecuencia de la selección de peso realizada en un par de líneas de selección divergente durante 50 generaciones (s: bajo peso; s': alto peso), originadas a partir de una población testigo (t) de ratones CF1 y criadas en la Facultad de Ciencias Veterinarias (UNR). Se probó la existencia de diferencias reproductivas atribuibles al genotipo paterno observadas en el tamaño de camada al nacimiento y en los días transcurridos desde el ingreso a servicio hasta la parición. Con el propósito de explicar las diferencias se comparó la estructura testicular - peso testicular (PTEST), diámetro del túbulo seminífero (DTS), altura de su epitelio (AES) - y la calidad seminal - número de espermatozoides (NE), porcentaje de células anormales (AN), motilidad y desplazamiento de las células espermáticas (Parámetros CASA) -, en machos adultos de 10 a 14 semanas de edad. Se estimó el promedio del DTS y AES en 100 túbulos seminíferos por individuo. El semen se obtuvo de la porción caudal de los epidídimos y de los conductos deferentes. El recuento de espermatozoides se realizó en cámara de Neubauer hemocitométrica y el porcentaje de células anormales se calculó sobre 100 espermatozoides por extendido. Los parámetros de motilidad se determinaron con analizador computarizado de semen Ceros 12.1. La selección por peso diferenció significativamente a las líneas en el mismo sentido de la selección practicada para PTEST, AES y NE. Los machos de la línea más pesada (s') presentaron PTEST y AES mayores y tuvieron un mayor número de espermatozoides al compararlos con los de las líneas s y t (p<0,05). La calidad del semen, bajo las condiciones del setup utilizado, fue similar para los machos de las tres líneas. Por lo tanto, la calidad del semen no aportó a la explicación de las diferencias de fertilidad masculina entre las líneas.
Reproductive female capacity was affected by the genetic selection performed in a pair of lines of two-way selection of body weight for 50 generations (s: downward selection; s': upward selection). These lines were originated from a control CF1 mice population (t) at the Faculty of Veterinary Sciences (UNR). The existence of reproductive differences attributed to the male genotype in the litter size and in the interval from the service beginning to first parturition was proven. With the aim of explaining them, the testicular structure - testicular weight (PTEST), vas deferens diameter (DTS), epithelium height (AES) - and the semen quality - spermatozoa number (NE), abnormal cell percentage (AN), motility and movement of spermatic cells (CASA parameters) were compared, in adult males between 10 and 14 weeks of age. The means of the DTS and AES were estimated for 100 seminiferous tubules per individual. Semen was obtained from the caudal portion of the epididymides and vasa deferentia. Sperm count was performed in Neubauer hemocytometer and abnormal cell percentage was estimated over 100 spermatozoa per sample. Motility parameters were determined with a Ceros 12.1 semen computerized analyzer. Body weight selection occasioned significant differences between lines in the same way of the selection performed for PTEST, AES and NE. Males of the heaviest line (s') show heavier testicles, higher seminiferous epithelium and, consequently, a higher number of spermatozoa when compared with s and t males (p<0,05). Semen quality under the employed setup conditions was similar for males of the three lines. Therefore, semen quality does not contribute to the explanation of the fertility differences between lines.
