Eine Studie zu dem väterlichen Investment nach Schönheit des Weibchens:
Introduction
The differential allocation hypothesis (DAH) predicts that individuals should adjust their parental investment to their current mate’s quality. Although in principle the DAH holds for both sexes, male adjustment of parental investment has only been tested in a few experimental studies, revealing contradictory results. We conducted a field experiment to test whether male blue tits (Cyanistes caeruleus) allocate their parental effort in relation to female ornamentation (ultraviolet colouration of the crown), as predicted by the DAH.
Results
We reduced the UV reflectance in a sample of females and compared parental care by their mates with that of males paired to sham-manipulated control females. As predicted by the DAH our results demonstrate that males paired with UV-reduced females invested less in feeding effort but did not defend the chicks less than males paired with control females.
Conclusions
To our knowledge, this is one of the first studies providing support for male differential allocation in response to female ornamentation.
Quelle: Female attractiveness affects paternal investment: experimental evidence for male differential allocation in blue tits (PDF)
Hier aus der Studie zu den Ergebnissen:
According to the basic idea that individuals choose mates on the basis of ornaments that reflect quality, males paired with females in poor condition might face the problem of producing offspring with low reproductive success. In other words, because of reduced female quality the reproductive value of the offspring will be reduced, also from the male’s perspective. The difference in male feeding investment in response to the female treatment is therefore consistent with the prediction that DA is strongly related to reproductive lifehistory. Our results on paternal care investment complement other studies, which demonstrated the female’s differential allocation of parental care in blue tits in response to the manipulation of male UV coloration of the crown [28,29]. Both studies indicate that male UV coloration is under selection pressure, created by the female allocation of parental care. Based on our results and other studies [32,33], which likewise showed assortative mating in response to UV reflectance, we suggest that male differential allocation may affect selection on female UV coloration.
Demnach würden die Spatzen also bei schönen Weibchen mehr investieren als bei nicht so schönen, wobei „schön“ letztendlich anhand bestimmter Attraktivitätsmerkmale für gepflegtes Federkleid festgemacht wird, ein klassisches Signal, weil es üblicherweise auch für eine gewisse Parasitenfreiheit etc spricht.
Aus einer Darstellung des Artikel:
Die UV-Reflexion des Gefieders der Weibchen wirke sich unmittelbar auf das Verhalten ihrer männlichen Partner aus, hiess es. Bei der Studie handelt es sich um eine seltene Untersuchung männlicher Reaktionen auf weibliche Schönheit in der Tierwelt. Die Ergebnisse zeigen, dass weibliche Blaumeisen viel Zeit damit verbringen müssen, ihr Gefieder zu putzen, um für die Männchen attraktiv zu bleiben.
Das Pflegen des Haares ist ja auch menschlichen Weibchen nicht fremd, eben weil dieses ebenfalls ein gutes Signal sind.
Hier noch einmal eine Darstellung der zugrundeliegenden Theorie, die für Männchen und Weibchen gilt, aber häufiger in Bezug auf die Weibchen als diejenigen, die ihre Investition variieren vorzufinden ist:
Females frequently choose males on the basis of traits [1] that may signal individual quality [2]. As a consequence they gain direct benefits, e.g. through high-quality territories and paternal investment, or indirect benefits, because attractive mates may provide genes for passing viability and attractiveness to the offspring [2]. On the other hand little is known about why females of several species also possess elaborate traits [3,4]. For a long time the presence of female ornaments was interpreted as being the consequence of genetic correlation with male ornamentation [3,5]. However, recent studies have suggested that female ornaments play a role in female – female competition (intrasexual selection) [6-10] or are sexually selected by males (intersexual selection) [11-17]. In species with biparental care males may gain benefits from choosing “high quality females” and adjust their parental investment to female quality. This may happen if there is much variance in female quality, if the latter affects offspring survival and if the males parental provide some parental investment and/or remating opportunities are low [2]. The idea of adjusting parental effort in response to the aesthetic traits of partners, when they represent honest signals of quality, is known as the Differential Allocation Hypothesis (DAH). Differential allocation is expected whenever individuals face a trade-off between current and future reproduction and the reproductive value of the offspring is connected to the attractiveness of the mate [18,19]. Since its original formulation, the DAH has been tested and supported in a number of taxa possessing different attractiveness traits and levels of parental care [20] but such studies have almost exclusively related female breeding investment to male attractiveness [21]. Given that female traits can indicate quality [9,11,14,22,23], males may differentially allocate parental investment in response to female attractiveness [24,25]. Some studies have explored the importance of female ornaments in male mate choice and as possible signals of female quality but very few have considered how they influence male parental investment [9,21,24,25].
Es leuchtet aus meiner Sicht unmittelbar ein, dass man mehr in besonders hochwertigen Nachwuchs investiert und weniger in weniger hochwertigen. Dies gilt aber nur dann, wenn die Nachwuchsfolgen hinreichend hoch sind, dass man eine solche Differenzierung treffen kann. Bei schnell brütenden Vögeln geht das schneller als bei menschlichen Kindern, die lange betreut werden müssen.
Eine männliche Anpassung der Investition kann es zudem nur geben, wenn überhaupt investiert wird. Bei Tierarten, bei denen die Mütter Betreuung und Versorgung übernehmen ist eine solche Anpassung nicht zu erwarten.
Es ist aber interessant, dass solche Berechnungen auf der Tierebene tatsächlich stattfinden. Vielleicht spiegeln sie sich beim Menschen in Anpassungen der väterlichen Investition nach Vaterschaftswahrscheinlichkeit. Um so wahrscheinlicher eine Vaterschaft ist um so eher lohnt sich eine Förderung des Kindes.
Alles Evolution 