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Sexual selection is responsible for a great diversity of elaborate male traits. A general female preference for males that have exaggerated traits drives this process, but the reasons females exhibit this preference are often unclear. Recent advances in understanding signal evolution have emerged from studies of receiver psychology that focus on how receivers perceive and process communication signals. I apply the perspective of receiver psychology to understand female preference for elaborate signals in túngara frogs (Physalaemus pustulosus). Male túngara frogs produce advertisement calls of variable complexity. Females exhibit a strong preference for complex to simple calls, but previous studies have not found consistent patterns of preference between calls of variable complexity. In my doctoral research, I investigate the function of variable complexity in túngara frogs. Specifically, I address the following questions: 1) Are calls of variable complexity especially relevant to females in certain contexts? Do males respond to female behavior by increasing their production of complex calls? 2) Does male to female proximity influence female response to call complexity? 3) Are females constrained by their perceptual biology in discriminating differences in call complexity? 4) Can females remember attractive males over silences between bouts of advertising? Is working memory for attractive males dependent upon signal complexity? And 5) Does signal memorability increase with signal complexity in a linear relationship? These studies provide several new perspectives to an understanding of female preference for elaborate signals. Phonotaxis experiments demonstrate that females use elicitation behaviors to influence male production of complex calls, that proximity influences female response to signal elaboration, that females are constrained by their perceptual biology in discriminating between complex calls, that memory can influence the evolution of signal complexity, and that memorability and signal complexity share a non-linear relationship. / text

Das menschliche Gehirn ist ein komplexes System, dessen Komplexität von großer funktioneller Bedeutung. Das APOE ɛ4 Allel ist ein gut untersuchter genetischer Risiko-Faktor für die Ausbildung der Alzheimer’schen Demenz. Das wesentliche Ziel dieser Dissertation ist die Untersuchung der Verbindungen zwischen der Komplexität von Hirn-Signalen, APOE-Genotyp und kognitiver Leistung bei jungen gesunden Erwachsenen unter dem Gesichtspunkt individueller Unterschiede. Nachdem ich in der ersten Studie die Reliabilität der Residual Iteration Decomposition (RIDE), einer Methode zur Analyse von Gehirnsignalen, validiert hatte, im der zweiten Studie untersuchte ich, wie APOE-Genotypen mit der Komplexität des Gehirnsignals assoziiert sind, gemessen mit Multiscale Entropy (MSE) und kognitiven Fähigkeiten. Die zweite Studie zeigte, dass APOE ɛ4 mit einer höheren Entropie im Skala 1 bis 4 und einer niedrigeren Entropie im Skala 5 und darüber assoziiert ist; Darüber hinaus gibt es bei ε4-Trägern einen stärkeren Abfall der MSE von geschlossenen zu offenen Augen als bei Nicht-Trägern. Die ε4-Assoziation mit der kognitiven Leistung war komplex, aber im Grunde scheint ε4 mit einer schlechteren kognitiven Leistung bei Menschen mit niedrigerem Bildungsstand verbunden zu sein, während bei Hochschulabsolventen keine solche Assoziation auftrat. Anschließend verband die dritte Studie MSE mit einer anderen kognitiven Domäne - Gesichts- und Objekterkennungsfähigkeiten. Wir haben gezeigt, dass 1) eine erhöhte MSE bei geschlossenen Augen auf allen Skalen mit einer besseren kognitiven Leistung verbunden ist. 2) Eine erhöhte MSE in höheren Skalen war mit einer engeren Kopplung zwischen der RIDE-extrahierten Geschwindigkeit der Bewertung des Stimulus für einen einzelnen Versuch und der Reaktionszeit verbunden. Zusammenfassend, die Ergebnisse verbanden die Komplexität des Gehirnsignals, den APOE-Genotyp und das kognitive Verhalten bieten ein tieferes Verständnis der Gehirn-Verhaltens-Beziehungen. / Human brain is a complex dynamical system, whose complexity could be highly functional and characterize cognitive abilities or mental disorders. The APOE ɛ4 allele is a well-known genetic risk factor for the development of Alzheimer’s Disease and cognitive decline in later human life. The main goal of this study is to investigate the bridges between brain signal complexity, APOE genotype and cognitive performance among young adults under the framework of individual difference. After validating the reliability of Residue Iteration decomposition (RIDE), a method for analysis brain signals in the first study, I investigated in the second study how individual differences in APOE genotypes are associated with brain signal complexity measured with Multiscale Entropy (MSE) and cognitive ability. The second study demonstrated that APOE ε4 is associated with higher entropy at scale 1-4 and lower entropy at scale 5 and above, especially at frontal scalp regions and in an eyes open condition; in addition, there’s a stronger drop in MSE from closed to open eyes condition among ε4 carriers than non-carriers. The ε4 association with cognitive performance was complex, but basically ε4 seems to be associated with worse cognitive performance among lower educated people, whereas no such association appeared among the higher educated. Afterwards, the third study connected MSE with a different cognitive domain – face and object cognition abilities. We showed that 1) increased MSE for a closed eyes condition at all scales is associated with better cognitive performance. 2) Increased MSE at higher scales (7 or 8) was associated with tighter coupling between RIDE-extracted single trial stimulus evaluation speed at the neural level and reaction time at the behavior level. To summarize, the results of my doctoral study connected brain signal complexity, APOE genotype and cognitive behavior among young healthy adults, providing a deeper understanding of brain-behavior relationships and – potentially – for early AD diagnosis when cognitive decline is not yet evident.