Linda A. Whittingham

Relatedness, polyandry and extra-group paternity in the cooperatively-breeding white-browed scrubwren (Sericornis frontalis)

Abstract We used DNA fingerprinting to examine the genetic parentage and mating system of the cooperatively breeding white-browed scrubwren, Sericornis frontalis, in Canberra, Australia. Our analyses revealed a remarkable variety of mating tactics and social organization. Scrubwrens bred in pairs or multi-male groups that consisted of a female and two or more males. Females were always unrelated to the pair male or alpha (dominant) male. Among multi-male groups we found three different mating tactics. Firstly, when alpha and beta (subordinate) males were unrelated, they usually shared paternity in the brood. This resulted in both males gaining reproductive benefits directly. Secondly, when beta males were not related to the female but were related to the alpha males, beta males sired offspring in some broods. In this situation, beta males gained reproductive benefits both directly and potentially indirectly (through the related alpha male). Thirdly, when beta males were related to the female or both the female and alpha male, they remained on their natal territory and did not sire any offspring. Thus beta males gained only indirect reproductive benefits. Overall, when group members were related closely, the dominant male monopolized reproductive success, whereas when the members were not related closely the two males shared paternity equally. This positive association between monopolization of reproduction and relatedness is predicted by models of reproductive skew, but has not been reported previously within a single population of birds. Other cooperatively breeding birds with both closely related and unrelated helpers may show a similar variety of mating tactics. Finally, we found that extra-group paternity was more common in pairs (24% of young) than in multi-male groups (6%), and we discuss three possible reasons for this difference.

Sexual selection accelerates signal evolution during speciation in birds

Sexual selection is proposed to be an important driver of diversification in animal systems, yet previous tests of this hypothesis have produced mixed results and the mechanisms involved remain unclear. Here, we use a novel phylogenetic approach to assess the influence of sexual selection on patterns of evolutionary change during 84 recent speciation events across 23 passerine bird families. We show that elevated levels of sexual selection are associated with more rapid phenotypic divergence between related lineages, and that this effect is restricted to male plumage traits proposed to function in mate choice and species recognition. Conversely, we found no evidence that sexual selection promoted divergence in female plumage traits, or in male traits related to foraging and locomotion. These results provide strong evidence that female choice and male–male competition are dominant mechanisms driving divergence during speciation in birds, potentially linking sexual selection to the accelerated evolution of pre-mating reproductive isolation.

A test of the mismatch hypothesis: How is timing of reproduction related to food abundance in an aerial insectivore?

In seasonal environments, vertebrates are generally thought to time their reproduction so offspring are raised during the peak of food abundance. The mismatch hypothesis predicts that reproductive success is maximized when animals synchronize their reproduction with the food supply. Understanding the mechanisms influencing the timing of reproduction has taken on new urgency as climate change is altering environmental conditions during reproduction, and there is concern that species will not be able to synchronize their reproduction with changing food supplies. Using data from five sites over 24 years (37 site-years), we tested the assumptions of the mismatch hypothesis in the Tree Swallow (Tachycineta bicolor), a widespread aerial insectivore, whose timing of egg-laying has shifted earlier by nine days since the 1950s. Contrary to the mismatch hypothesis, the start of egg-laying was strongly related to food abundance (flying insect biomass) during the laying period and not to timing of the seasonal peak in food supply. In fact, food abundance generally continued to increase throughout the breeding season, and there was no evidence of selection based on the mistiming of laying with the seasonal peak of food abundance. In contrast, there was selection for laying earlier, because birds that lay earlier generally have larger clutches and fledge more young. Overall, initial reproductive decisions in this insectivore appear to be based on the food supply during egg formation and not the nestling period. Thus, the mismatch hypothesis may not apply in environments with relatively constant or abundant food throughout the breeding season. Although climate change is often associated with earlier reproduction, our results caution that it is not necessarily driven by selection for synchronized reproduction.

High paternal investment in unrelated young: extra.pair paternity and male parental care in house martins

The response of males to reduced paternity has important consequences for the evolution and maintenance of a mixed reproductive strategy. Paternity is predicted to affect directly the level of male parental care in some cases but not in others. The response of males to reduced paternity will be influenced by their ability to assess their paternity, the predictability of cuckoldry and the costs and benefits of parental care. Although male house martins (Delichon urbica) provide among the highest levels of male parental care known in passerines (incubation, brooding and feeding nestlings), there was no evidence that cuckolded males substantially reduced their level of parental care, and, as a result, all young fledged successfully. Thus, extra-pair fertilizations enhanced the reproductive success of some males because they were able to parasitize the parental care of cuckolded males. We discuss several conditions which may favor extensive male parental care even when the males paternity is very low.

Male parental effort and paternity in a variable mating system

Recent theoretical models suggest that males may respond to changes in paternity by adjusting their parental effort. Male response will depend on the availability of reliable paternity cues and the relative costs and benefits of parental effort to the male (i.e. its effect on the survival of young and alternative mating opportunities). Males breeding in pairs may be constrained because reductions in male parental effort are unlikely to be compensated for by the female and thus the survival of both related and unrelated young may decrease. In contrast, males breeding in cooperative groups (i.e. with helpers or co-breeders) may not have this constraint if other individuals in the group compensate for reductions in male parental effort. White-browed scrubwrens, Sericornis frontalis, breed in pairs and cooperative groups, typically with one female and two males (alpha and beta). We found that male parental effort was related positively to paternity for beta males, but not for alpha or pair males. Alpha males had paternity in all broods and always fed young. In contrast, beta males often had no paternity and sometimes did not feed young. Time spent near the fertile female was not an accurate predictor of the percentage of young sired in a brood, but it was a good predictor of having sired young in a brood. Our results are consistent with the idea that male parental effort is allocated according to whether or not the male copulated with the female. We suggest that the relationship between male parental effort and paternity may vary among cooperatively breeding species depending on the type and availability of cues to a males paternity. Copyright 1998 The Association for the Study of Animal Behaviour Copyright 1998 The Association for the Study of Animal Behaviour.

CHAPTER 10 – Phylogeny in Studies of Bird Ecology, Behavior, and Morphology

The chapter explores three fundamental issues: phylogenetic accuracy, adaptation, and phylogenetic constraint. These issues are central to historical ecology and cover a broad range of subjects in the field. The most important step to successful historical ecology is the collection of appropriate, accurate, ecological, and phylogenetic data. Although obvious, this assertion is remarkably underemphasized in ecophylogenetic studies. Emphasis is placed primarily on the quality of ecological data, which are viewed as dependent variables, instead of on the accuracy of phylogeny, which is generally viewed as an independent variable without error. However, phylogenetic estimates have error distributions, but these are commonly ignored because they are too complicated to quantify. Historical ecology is burgeoning because it provides structure to the study of ecological patterns and evolutionary processes. Emphasis on the use of accurate phylogenetic data is crucial because the interpretation of evolutionary patterns obviously changes as relationships among taxa change. Although progress may be limited without knowledge of the quantitative genetics of specific traits, initial hypothesis testing is possible with prudent use of the phylogenetic approach, provided that multiple examples of potential evolutionary phenomena are examined.