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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.05.004 Byline: Ralf Edler, Thomas W.P. Friedl Abstract: Two competing hypotheses are commonly used to explain matings with multiple males in female birds. The genetic benefit model sees extrapair copulations as a means to enhance offspring viability, while the fertility-insurance hypothesis states that females copulate with multiple males to guarantee fertilization of eggs. According to the genetic benefit hypothesis, extrapair young are expected to have a genetic advantage over their maternal half-sibs raised in the same brood. A quantifiable measure for offspring quality is the immunocompetence, the ability of an individual to cope with infections. In this study, we used the phytohaemagglutinin induced skin-swelling response technique to test whether the cell-mediated immune reaction differs between extrapair and within-pair nestlings from mixed-paternity broods in the polygynous red bishop, Euplectes orix. The strength of the nestlings' immune response was positively linked to general health status and immunological condition of their genetic fathers, indicating a heritable component of nestling immunocompetence. We found that extrapair young were actually significantly less immunocompetent than within-pair young from the same nest, a result that does not lend support to the genetic benefit hypothesis. We suggest that female red bishops mated to successful high-quality males engage in extrapair copulations to insure against temporary infertility in their social mates caused by sperm depletion because of frequent copulations with their multiple female partners. This result, however, was significant only in the hotter of 2 years, indicating that environmental factors can obscure variation in nestling fitness arising from female extrapair mating behaviour. Author Affiliation: AG Zoophysiologie & Verhalten, Institut fur Biologie und Umweltwissenschaften, Carl von Ossietzky Universitat Oldenburg, Germany Article History: Received 5 December 2006; Revised 26 January 2007; Accepted 4 May 2007 Article Note: (miscellaneous) MS. number: 9196R

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2005.01.017 Byline: Thomas W.P. Friedl, Georg M. Klump Abstract: Variation in male reproductive performance and success was studied over 2 years in a population of individually marked European treefrogs, Hyla arborea, a hylid frog with prolonged breeding season and a lek mating system. Reproductive success in males was not related to body size, age or growth rate, and there was no evidence for size- or age-assortative mating. Male mating success was significantly correlated with chorus attendance, that is, the number of nights spent calling at the breeding site. There were no significant differences with regard to body size, age or growth rate between males surviving to the next breeding season and those not surviving. However, surviving males showed a significantly higher chorus attendance than nonsurviving males, which is a novel finding for lekking anurans. Furthermore, males that survived from the previous breeding season spent significantly more nights calling at the breeding site than males that were observed for the first time. Since calling in frogs is costly, these results suggest that chorus attendance reflects male quality. The distribution of male mating success did not differ from a Poisson distribution, indicating a random mating pattern. Since male quality is related to chorus attendance, females that mate randomly are likely to mate with high-quality males and thereby gain indirect genetic benefits without incurring costs of extended mate searching and mate assessment. We suggest that a similar mating pattern is found in many lek-breeding hylid frogs in which male mating success is mainly determined by chorus attendance. Author Affiliation: Institut fur Biologie und Umweltwissenschaften, AG Zoophysiologie & Verhalten, Carl von Ossietzky Universitat Oldenburg, Germany Article History: Received 12 August 2004; Revised 15 October 2004; Accepted 15 February 2005 Article Note: (miscellaneous) MS. number: 8240

Although many studies have revealed differences in patterns of extrapair paternity between species and between populations of the same species, possible differences in female extrapair behavior within populations have received far less attention. Here, we propose and test the hypothesis that females of the highly polygynous Red Bishop (Euplectes orix) follow two different extrapair strategies, with benefits of extrapair copulations depending on the quality of their social mate ('conditional-extrapair-strategy hypothesis'). In particular, we propose that females mated to low-quality males enhance the genetic quality of their offspring by performing extrapair copulations with males of higher quality than their social mate (in accordance with the good-genes hypothesis), whereas females mated to high-quality males perform extrapair copulations as insurance against temporary infertility of their social mate caused by sperm depletion due to frequent copulations (in accordance with the fertility-insurance hypothesis). Several predictions derived from our hypothesis, regarding differences in frequency and distribution of both unhatched eggs and extrapair young between high-quality and low-quality males, are tested and shown to be supported. Most importantly, hatching failures occurred more often in territories of high-quality males than in those of low-quality males, and the proportion of unhatched eggs within the territory was positively correlated to breeding synchrony for high-quality males only. Those results suggest that sperm depletion is a risk for females mated to high-quality males with many mating opportunities. The fact that broods of high-quality males without unhatched eggs had a significantly higher proportion of extrapair young than broods of high-quality males with unhatched eggs is consistent with the hypothesis that females mated to high-quality males were successful in performing EPCs as insurance against temporary infertility of their social mates. Furthermore, genetic fathers of extrapair young hatched in territories of low-quality males were found to be of higher quality than the corresponding social fathers, whereas no difference in quality was found between genetic and social fathers of extrapair young hatched in territories of high-quality males. Although we cannot exclude the possibility that the observed pattern was a result of females mating randomly from within the available pool of extrapair males, it is in accordance with our prediction that females mated to low-quality males perform extrapair copulations with males of higher quality than their social mate to enhance offspring fitness. Overall, the data presented here suggest that females within our study colony adjusted their extrapair behavior to the quality of their social mate, even if we cannot entirely rule out alternative explanations for some of the results obtained. Thus, the study provides support for the conditional-extrapair-strategy hypothesis, which states that within populations, females may follow different extrapair strategies to gain different benefits. Received 14 July 2003, accepted 24 June 2004. Key words: conditional-extrapair-strategy hypothesis, Euplectes orix, extrapair paternity, female behavior, fertility insurance, good genes, male quality, Red Bishops, sexual selection, weaverbirds. Aunque muchos estudios han indicado que existen diferencias en los patrones de paternidad extra-pareja entre especies y entre poblaciones de la misma especie, las posibles diferencias en el comportamiento extra-pareja de las hembras dentro de una poblacion han recibido mucha menos atencion. En este trabajo proponemos y ponemos a prueba la hipotesis de que las hembras de la especie altamente poliginica Euplectes orix siguen dos estrategias extra-pareja diferentes, en las que los beneficios de las copulas extra-pareja dependen de la calidad de su pareja social ('hipotesis condicional de estrategia extra-pareja'). En particular, proponemos que las hembras apareadas con machos de baja calidad mejoran la calidad genetica de sus crias realizando copulas extrapareja con machos de mayor calidad que su pareja (de acuerdo a la hipotesis de genes buenos), mientras que las hembras apareadas con machos de alta calidad realizan copulas extra-pareja como un seguro contra la infertilidad temporal de su pareja social causada por agotamiento del esperma debido a copulas frecuentes (de acuerdo a la hipotesis de fertilidad asegurada). Varias predicciones derivadas de nuestra hipotesis en cuanto a diferencias en la frecuencia y distribucion de huevos no eclosionados y pichones extrapareja entre machos de alta y baja calidad, son puestas a prueba y resultan cumplirse. Lo mas importante es que los fracasos de eclosion sucedieron mas frecuentemente en los territorios de machos de alta calidad que en los de machos de baja calidad, y la proporcion de huevos no eclosionados dentro del territorio estuvo correlacionada positivamente con la sincronia de la reproduccion solo para los machos de alta calidad. Estos resultados sugieren que el agotamiento de esperma es un riesgo para las hembras que se aparean con machos de alta calidad que tienen muchas oportunidades para aparearse. El hecho de que las nidadas de los machos de alta calidad sin huevos no eclosionados tuvieron una proporcion de pichones extra-pareja significativamente mayor que la de las nidadas de machos del mismo tipo con huevos no eclosionados es consistente con la hipotesis de que las hembras apareadas con machos de alta calidad incrementaron su exito reproductivo al realizar copulas extra-pareja como un seguro contra la infertilidad temporal de sus parejas sociales. Mas aun, los padres geneticos de los pichones extra-pareja que eclosionaron en los territorios de machos de baja calidad fueron de mayor calidad que los padres sociales correspondientes, mientras que no existio diferencia en la calidad de los padres geneticos y sociales de los pichones extrapareja que eclosionaron en los territorios de machos de alta calidad. Aunque no podemos excluir la posibilidad de que el patron observado sea el resultado de que las hembras se aparean aleatoriamente con los machos extra-pareja disponibles, este patron esta de acuerdo con nuestra prediccion de que las hembras apareadas con machos de baja calidad realizan copulas extra-pareja con machos de mayor calidad que su pareja social para incrementar la adecuacion de sus crias. En general, los datos aqui presentados sugieren que las hembras de nuestra colonia de estudio ajustaron su comportamiento extra-pareja a la calidad de su pareja social, aun si no podemos descartar completamente explicaciones alternativas para algunos de los resultados obtenidos. Asi, este estudio respalda la hipotesis condicional de estrategia extrapareja, que propone que al interior de una poblacion las hembras pueden seguir estrategias extra-pareja diferentes para obtener distintos beneficios.