Consequences of being unfaithful : costs and benefits of extra pair copulations in birds

Die bedeutendste Entdeckung der letzten 30 Jahre in Bezug auf das Fortpflanzungsverhalten von Vögeln war die Erkenntnis, dass es bei mehr als 80% aller sozial monogamen Singvogelarten regelmäßig zu Kopulationen außerhalb des Paarbundes kommt („extra-pair copulations“; EPCs). In der Folge setzte sich eine beeindruckende Zahl von Untersuchungen mit verschiedenen Aspekten dieses Verhaltens auseinander. Neben Studien, die sich mit Unterschieden in der Häufigkeit des Auftretens von „Fremdvaterschaften” bei verschiedenen Vogelarten beschäftigten, wurden vor allem Untersuchungen zum Kosten und Nutzen von EPCs für Männchen und Weibchen durchgeführt. Auf der Basis eigener Untersuchungen, die dazu dienten, das genetische Paarungssystem von sozial monogamen Kohl- und Tannenmeisen (Parus major and P. ater) zu ergründen, werden hier einige Resultate dieser Bemühungen und auch die ihnen zugrundeliegenden Überlegungen dargestellt. Kosten von EPCs beinhalten für Weibchen möglicherweise eine Reduktion in der Brutfürsorge durch die Männchen, weil die Anzahl eigener Nachkommen und damit der Fortpflanzungswert einer Brut für „betrogene“ Männchen abnimmt. In Übereinstimmung mit dieser Hypothese fanden wir, dass sich die Brutverteidigung männlicher Kohlmeisen nach der Anzahl eigener Nachkommen und nicht nach der Brutgröße richtet. Außerdem fütterten „betrogene“ Männchen ihre Bruten weniger als nicht „betrogene“ Männchen. Wenn EPCs den Weibchen Kosten verursachen, so muss auf der anderen Seite ein entsprechender Nutzen vorhanden sein, da Selektion sonst zum Verschwinden dieses Verhaltens führen sollte. Während männliche Kohl- und Tannenmeisen ihren Fortpflanzungserfolg durch EPCs direkt erhöhen können, ist ein Nutzen für die Weibchen nicht derart offensichtlich. Bei der Analyse einer großen Zahl von Tannenmeisenbruten konnten wir keinerlei Hinweis dafür finden, dass die vieldiskutierten „Gute Gene”-Modelle den Nutzen von EPCs für Weibchen erklären. Würden Weibchen durch EPCs „bessere“ oder „kompatiblere“ väterliche Gene für die betreffenden Nachkommen erhalten, wäre zu erwarten, dass EPY ihren Halbgeschwistern in irgendeiner Form überlegen sind. Zwischen den beiden Halbgeschwistergruppen fand sich jedoch weder in Bezug auf die Überlebenswahrscheinlichkeit noch in Bezug auf den Fortpflanzungserfolg im ersten Brutjahr ein Unterschied. Aus diesen und anderen Befunden wird geschlossen, dass „Gute Gene”-Modelle das weit verbreitete Auftreten von EPCs bei Vögeln alleine kaum erklären können und dass wahrscheinlich mehr als ein einzelner Selektionsfaktor die Evolution dieses Verhaltens bei Vögeln beeinflusst hat.The most important discovery with respect to avian mating systems in the last three decades was the finding that extra-pair paternity occurs regularly in over 80% of all passerine bird species that were cursorily classified as monogamous in the past. Not surprisingly, this insight entailed an impressive body of research focussing on different aspects of this behavioural pattern. Besides analyses of the variation in the frequency of extra-pair paternity, particularly potential costs and benefits of xtra-pair copulations for (individual) males and females had been analysed. Some results of this effort and the rationales behind it are exemplified here, by detailing own work that was performed to investigate the genetic mating systems of socially monogamous great and coal tits (Parus major and P. ater). Costs of extra-pair copulations for females potentially involve a decrease in paternal care, since the number of own offspring and therefore the reproductive value of a brood decreases for cuckolded males. In agreement with this hypothesis we found, that nest defence of male great tits was related to the number of offspring fathered by themselves, but not to brood size per se. Furthermore, cuckolded males fed their broods less frequently than non-cuckolded males. Since extra-pair matings seem to be costly to females, also some benefits of extra-pair copulations have to be postulated, as otherwise selection should act against its occurrence. While male great and coal tits benefit through extra-pair paternity by directly increasing their reproductive success, the benefits for females are far less clear. By studying a large number of coal tit broods, we were unable to provide evidence that “good genes” models can explain the benefits resulting from extra-pair copulations for females. Neither survival probability nor first year reproductive performance of extra-pair young and their maternal half-siblings differed, indicating that females cannot increase their reproductive success by obtaining “higher quality” or “more compatible” paternal genes through extra-pair matings. Based on these and other results it is argued, that “good genes” models alone can hardly explain the occurrence and maintenance of extra-pair paternity in birds in general and that presumably more than a single selective pressure has shaped the evolution of female multiple mating in birds

Molecular genetic evidence for mixed maternity in broods of the Coal Tit Parus ater

Mittels molekulargenetischer Elternschaftsanalyse wurde eine niedrige Rate gemischter Mutterschaften in Bruten der sozial monogamen Tannenmeise nachgewiesen, einer Art, die sich durch hohe Fremdvaterschaftsraten auszeichnet. Gemischte Mutterschaften wurden in vier (= 0,8 %) von 483 Bruten entdeckt und nur für zehn (= 0,3 %) von 3563 erfolgreich genotypisierten Nachkommen wurde die Putativmutter von der genetischen Mutterschaft ausgeschlossen. In Anbetracht dieser sehr niedrigen Rate kann in evolutionsbiologischen Studien der soziale Fortpflanzungserfolg mit dem genetischen Fortpflanzungserfolg für Weibchen der Tannenmeise ohne weiteres gleichgesetzt werden. Die Putativväter wurden ebenfalls in allen Fällen von der genetischen Elternschaft ausgeschlossen, was Quasiparasitismus als Erklärung für gemischte Mutterschaften ausschließt. In einem Fall konnten die Partner eines Brutpaares, das zeitgleich in der Nähe eine eigene Brut aufzog, zweifelsfrei als die genetischen Eltern eines einzelnen Nachkommen identifiziert werden. Mögliche Ursachen für das Auftreten gemischter Mutterschaften bei der Tannenmeise schließen die Übernahme von Nistkästen samt begonnenen Gelegen nach dem Tod oder Abwandern der Vorbesitzer und innerartlichen Brutparasitismus ein.Molecular genetic analysis of parentage revealed a low frequency of mixed maternity in broods of the Coal Tit, a socially monogamous passerine with a high frequency of extra-pair paternity. Mixed maternity was detected in four (= 0.8 %) out of 483 analysed broods. For ten (= 0.3 %) out of 3563 successfully genotyped offspring the attending putative (social) mother was excluded from genetic parentage. Given the very low frequency of mixed maternity, social reproductive success can conveniently be equated with genetic reproductive success for female Coal Tits in evolutionary studies. Attending putative fathers were excluded from genetic parentage in all cases, too, ruling out quasi-parasitism as a mechanistic explanation for mixed maternity. In one case, the pair members from an adjacent territory were unequivocally identified as the genetic parents of a single offspring (they were simultaneously attending their own brood). Possible mechanisms leading to mixed maternity broods in the Coal Tit may include nest/clutch take-over and intraspecific brood parasitism and their respective relevance is briefly discussed

Are low-frequency songs sexually selected, and do they lose their potency in male–female interactions under noisy conditions?

ABSTRACT: We agree with Halfwerk et al. on the importance of including the receivers when studying the impact of anthropogenic noise. However, we find the conclusion that the use of lowfrequency song is sexually selected in great tits and that noisy conditions affect male–female communication premature for several reasons

Ornamental non-carotenoid red feathers of wild burrowing parrots

Bird plumage colors have the potential to indicate individual quality, condition, health, immunocompetence, or the extend of parental care. Color intensity of feathers has been found to correlate with parameters of individual quality, condition, parental care and breeding success. Psittaciformes are well known for their colorful plumage but the significance of parrot coloration is still poorly understood. Red colors are very common in many parrot species. They are produced by at least four non-carotenoid-based pigments (linear polyenal structure). In the present study, we investigated a collection of red abdominal feathers of a marked population of wild Burrowing Parrots Cyanoliseus patagonus in Patagonia, Argentina. The aims of this study were to investigate the ecological significance of the recently described non-carotenoid-based red pigments of Psittaciformes, and the relationships between objectively assessed plumage color and body size, body condition, breeding success and nestling growth in wild Psittaciformes. We found that sexes differed in plumage coloration (sexual dichromatism), that plumage color was a good predictor of female body condition and male size, and we identified the red coloration of the abdominal patch as a signal of individual quality and parental investment.Facultad de Ciencias Naturales y Muse

Dicromatismo sexual oculto en el loro barranquero (Cyanoliseus patagonus) revelado por medio de análisis espectrométricos

Bird colour perception differs fundamentally from that of humans. Birds have more cone types in the retina, including UV or violet cones, which enable them to perceive a wider spectral range. Thus, human colour perception can be deceiving when assessing functional aspects of bird plumage coloration, such as the intensity of sexual selection. In this study we measured reflectance spectra of different plumage regions of male and female Burrowing Parrot (Cyanoliseus patagonus) individuals. Although not obvious to human eyes, spectrometry revealed that adults are sexually dichromatic. Plumage regions with structure-based (blue) and structure-psittacofulvin pigment-based (green) coloration differed in achromatic brightness. In contrast, the psittacofulvin-based (red) region differed in spectral shape between the sexes. Thus, Burrowing Parrot is among the growing number of bird species which were formerly classed as sexually monochromatic based on human vision, but which are actually sexually dichromatic.La percepción del color por parte de las aves difiere esencialmente de la de los humanos. Las aves tienen más conos en su retina, incluyendo conos sensibles al ultravioleta y violeta, los que les permite percibir un rango espectral más amplio. Por lo tanto, la percepción humana de los colores puede engañar a la hora de evaluar aspectos funcionales del color del plumaje de las aves, tales como la intensidad de la selección sexual. En este trabajo se midieron los espectros de reflectancia de diferentes regiones del plumaje de machos y hembras de Loro Barranquero (Cyanoliseus patagonus). Si bien no resulta obvio a los ojos humanos, las mediciones espectrométricas revelaron que los adultos son sexualmente dicromáticos. Regiones del plumaje con coloración basada en la estructura (azul) o con color basado en una mezcla de estructura y psittacofulvinas (verde) difirieron en el brillo acromático. En cambio, la coloración basada en psittacofulvinas (rojo) difirió en la forma del espectro entre los sexos. Por lo tanto, el Loro Barranquero es una más de un creciente número de aves que, de acuerdo a la visión humana, fueron previamente clasificadas como sexualmente monocromáticas pero que, en realidad, son sexualmente dicromáticas

Ornamental non-carotenoid red feathers of wild burrowing parrots

Bird plumage colors have the potential to indicate individual quality, condition, health, immunocompetence, or the extend of parental care. Color intensity of feathers has been found to correlate with parameters of individual quality, condition, parental care and breeding success. Psittaciformes are well known for their colorful plumage but the significance of parrot coloration is still poorly understood. Red colors are very common in many parrot species. They are produced by at least four non-carotenoid-based pigments (linear polyenal structure). In the present study, we investigated a collection of red abdominal feathers of a marked population of wild Burrowing Parrots Cyanoliseus patagonus in Patagonia, Argentina. The aims of this study were to investigate the ecological significance of the recently described non-carotenoid-based red pigments of Psittaciformes, and the relationships between objectively assessed plumage color and body size, body condition, breeding success and nestling growth in wild Psittaciformes. We found that sexes differed in plumage coloration (sexual dichromatism), that plumage color was a good predictor of female body condition and male size, and we identified the red coloration of the abdominal patch as a signal of individual quality and parental investment.Facultad de Ciencias Naturales y Muse

Immune Activation Reduces Sperm Quality in the Great Tit

Mounting an immune response against pathogens incurs costs to organisms by its effects on important life-history traits, such as reproductive investment and survival. As shown recently, immune activation produces large amounts of reactive species and is suggested to induce oxidative stress. Sperm are highly susceptible to oxidative stress, which can negatively impact sperm function and ultimately male fertilizing efficiency. Here we address the question as to whether mounting an immune response affects sperm quality through the damaging effects of oxidative stress. It has been demonstrated recently in birds that carotenoid-based ornaments can be reliable signals of a male's ability to protect sperm from oxidative damage. In a full-factorial design, we immune-challenged great tit males while simultaneously increasing their vitamin E availability, and assessed the effect on sperm quality and oxidative damage. We conducted this experiment in a natural population and tested the males' response to the experimental treatment in relation to their carotenoid-based breast coloration, a condition-dependent trait. Immune activation induced a steeper decline in sperm swimming velocity, thus highlighting the potential costs of an induced immune response on sperm competitive ability and fertilizing efficiency. We found sperm oxidative damage to be negatively correlated with sperm swimming velocity. However, blood resistance to a free-radical attack (a measure of somatic antioxidant capacity) as well as plasma and sperm levels of oxidative damage (lipid peroxidation) remained unaffected, thus suggesting that the observed effect did not arise through oxidative stress. Towards the end of their breeding cycle, swimming velocity of sperm of more intensely colored males was higher, which has important implications for the evolution of mate choice and multiple mating in females because females may accrue both direct and indirect benefits by mating with males having better quality sperm

Speeding Up Microevolution: The Effects of Increasing Temperature on Selection and Genetic Variance in a Wild Bird Population

The authors show that environmental variation may lead to a positive association between the annual strength of selection and expression of genetic variance in a wild bird population, which can speed up microevolution and have important consequences for how fast natural populations adapt to environmental changes