RESUMO
La valoración subjetiva de la calidad seminal ha dado paso al uso de las técnicas objetivas de valoración por medio de la tecnología CASA (computer-assisted semen analysis). Se pueden aplicar una serie de pruebas cinéticas, morfométricas, morfológicas o de integridad del ADN para caracterizar y entender la biología reproductiva del espermatozoide. En los últimos años, se ha dado un cambio significativo de paradigma conceptual respecto de qué es un eyaculado. Cabe decir que, hasta tiempos recientes, se consideró que una población representativa (miles de millones) de espermatozoides estaba formada por células "equivalentes" con un objetivo común: ser el que finalmente pudiese fecundar el ovocito. La comprobación de que el conjunto de espermatozoides se agrupa en subpoblaciones bien definidas de acuerdo con sus características cinéticas y/o morfométricas, ha abierto el camino hacia una visión más cooperativa. Además, se ha visto que la distribución subpoblacional es diferente entre individuos, lo que parece indicar diferentes estrategias que se pueden entender dentro de otro paradigma: el de la competencia espermática entre diferentes eyaculados. A pesar de que aún no se conoce el papel de las diferentes subpoblaciones, se deben continuar los trabajos en esa dirección. En esta revisión, se caracterizó la evaluación de la fertilidad con la tecnología CASA y se examinaron los principales métodos multivariados en la evaluación de subpoblaciones de espermatozoides analizados mediante un sistema CASA.
In recent years, there has been a substantive change in the conceptual paradigm regarding what an ejaculate is. Until recently, it was considered that a representative population (billions) of sperm was made up of "equivalent" cells with a common goal: to be the one that could finally fertilize the oocyte. New data suggesting that a set of spermatozoa is grouped in distinct subpopulations, according to their kinematic and morphometric characteristics, has opened the way towards a more cooperative vision. In addition, recently, it has been established that the subpopulation distribution is different among males, which seems to indicate that there are different strategies that can be understood within another paradigm: sperm competition between different ejaculates. These heterogeneous subpopulations of spermatozoa in the ejaculate, that show kinematics and morphometric patterns, has been widely known for a while, but the biological meaning of these different sperm subpopulations is still not clear. For this reason, the subjective evaluation of seminal quality is being displaced by objective assessment techniques using CASA technology (computer-assisted semen analysis). Also, the application of principal components (PC) and clustering methods to reveal subpopulations of spermatozoa are complementary tools used to characterize raw semen and processed cell suspensions. Despite the advances in such powerful tools, researchers are not well versed on such techniques and its advantages. For instance, PC analysis is a multivariate statistical method that reduces the number of variables used in subsequent calculations for describing the data. By integrating the original data into new complex mathematical variables, homogenous subpopulations of spermatozoa can define clearly. Furthermore, kinematic, morphometric, morphological or DNA integrity tests can be also applied to characterize and understand the reproductive biology of the spermatozoon. Although the role of the different subpopulations of spermatozoa remains unknown, the work should continue by implementing novel technologies and coordinated tools. In this review, we characterize the fertility evaluation with CASA technology and examine the main multivariate methods in the assessment of sperm subpopulations analyzed by CASA systems.