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In the animal kingdom there are countless strategies via which males optimize their reproductive success when faced with male-male competition. These male strategies typically fall into two main categories: pre- and post-copulatory competition. Within these 2 categories, a set of behaviors, referred to as reproductive suppression, is known to cause inhibition of reproductive physiology and/or reproductive behavior in an otherwise fertile individual. What becomes evident when considering examples of reproductive suppression is that these strategies conventionally encompass reproductive interference strategies that occur between members of a hierarchical social group. However, mechanisms aimed at impairing a competitor's reproductive output are also present in non-social animals. Yet, current thinking emphasizes the importance of sociality as the primary driving force of reproductive suppression. Therefore, the question arises as to whether there is an actual difference between reproductive suppression strategies in social animals and equivalent pre-copulatory competition strategies in non-social animals. In this perspective paper we explore a broad taxonomic range of species whose individuals do not repeatedly interact with the same individuals in networks and yet, depress the fitness of rivals. Examples like alteration of male reproductive physiology, female mimicry, rival spermatophore destruction, and cementing the rival's genital region in non-social animals, highlight that male pre-copulatory reproductive suppression and male pre-copulatory competition overlap. Finally, we highlight that a distinction between male reproductive interference in animals with and without a social hierarchy might obscure important similarities and does not help to elucidate why different proximate mechanisms evolved. We therefore emphasize that male reproductive suppression need not be restricted to social animals. [ABSTRACT FROM AUTHOR]

Background: A little more than a decade ago a review entitled 'Biological basis for human capacitation' was published. A primary conclusion of the review was that with all the technological advances that have been made since the first experiments demonstrated the in vivo requirement of capacitation for fertilization, very little progress had since been made, most significantly for human.Objective and Rationale: The present review was carried out to provide an update on the biological basis for human capacitation. It briefly revisits the original schema, presents a review of the literature that urged research interest in human sperm capacitation and puts under the spotlight the original definition of capacitation balanced against the limitations of experiments in vitro to characterize a complex process that necessarily mandates a female component, and very recent findings in the mouse. It also includes proposed considerations for new thinking regarding capacitation, and progress toward understanding the biology of human capacitation.Search Methods: The PubMed, Google Scholar and Scopus literature databases were reviewed extensively using inclusive, broad and multispecies search terms without publication date limitation.Outcomes: Comprehensive screening of the literature database showed that no papers regarding human sperm capacitation in vivo have been published in the past 20 years. Recent experiments in the mouse have provided compelling and unanticipated data regarding capacitation and in vivo fertilization. Questions were posed and addressed regarding: stimuli for initiation of capacitation, capacitation relative to the cumulus-oocyte complex, comparison between in vivo and in vitro capacitation, and potential species-specific differences in location and timing of capacitation.Wider Implications: There has been no progress on the in vivo biology of human sperm capacitation since before the turn of the century. Human IVF and its technologies may likely have inhibited, and continue to hold back, any future in vivo experiments that would address one or more questions regarding acquisition of fertilizing capacity in human. The limiting factor for progress in the area is access to funding and human subjects. [ABSTRACT FROM AUTHOR]