Frontline interactions between avian interspecific brood parasites and their hosts
Date
2014
Authors
Feeney, William Edgar
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Abstract
Studying interactions within and between species provides opportunities to observe consequences of natural selection. My thesis examines some aspects of the ecology and evolution of the interactions between avian brood parasites and their hosts. Evidence of coevolution, reciprocal evolution, between avian interspecific brood parasites and hosts is evident at all stages of the host nesting cycle. The first chapter of this thesis presents a broad literature review of these interactions. Following this, the thesis focuses on those that occur prior to the parasite laying its egg in the host nest: the 'frontline' of the arms race. While abundant research of frontline interactions between brood parasites and hosts has been conducted, their relative importance compared to interactions at other stages of the nesting cycle was, until recently, relatively ambiguous. Chapter 2 is a more specific literature review of the diversity of frontline interactions between brood parasites and hosts. Chapters 3-5 use the cooperatively breeding superb fairy-wren, Malurus cyaneus, one of the primary hosts of the Horsfield's bronze-cuckoo, Chalcites basalis, as a model species to investigate frontline defences in hosts. I show that recognition of adult brood parasites by cuckoo naive superb fairy-wrens can be achieved by social learning (chapter 3), they vary their nest vigilance according to their perceived risk of brood parasitism (chapter 4), and that they recognize cuckoos distinctly from other nest threats, produce a referential call that induces group attacking (mobbing) of the parasite and that larger breeding groups are more aggressive towards parasites than smaller groups (chapter 5). With collaborators, I then show that larger groups are parasitized less than smaller groups, despite benefits to cuckoos that successfully parasitize larger groups, indicating that cooperative breeding facilitates defence against brood parasites. We further show that the evolutionary association between brood parasitism and cooperative breeding in birds is globally generalizable (also chapter 5). My final chapter (6) focuses on a putative offensive frontline adaptation by a brood parasite. The cuckoo finch, Anomalospiza imberbis, is the primary brood parasite of the tawny-flanked prinia, Prinia subflava, in southern Zambia and is a suspected mimic of harmless and abundant Euplectes weavers. I show that: 1) the plumage colour and pattern of female cuckoo finches more closely resembles that of sympatric Euplectes weavers than sympatric Vidua finches, their closest relatives, 2) prinias are equally aggressive to female cuckoo finches and female Euplectes weavers, and more aggressive to both than to their dissimilar-looking male counterparts, and 3) that prinias decrease their egg rejection threshold after seeing a female cuckoo finch or Euplectes weaver, but not after seeing a dissimilar-looking male Euplectes weaver. I combine these data with pre-existing data in the literature to provide quantitative evidence of aggressive mimicry by this species. Collectively, these findings describe some mechanisms that facilitate frontline defences and their effectiveness as defences against brood parasitism. In doing so, these results highlight how coevolution can affect trait evolution in brood parasites and their hosts, and how interactions between species can affect global patterns of trait evolution.
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