Outcomes of Brood Parasite–Host Interactions Mediated by Egg Matching: Common Cuckoos Cuculus canorus versus Fringilla Finches

Antagonistic species often interact via matching of phenotypes, and interactions between brood parasitic common cuckoos (Cuculus canorus) and their hosts constitute classic examples. The outcome of a parasitic event is often determined by the match between host and cuckoo eggs, giving rise to potentially strong associations between fitness and egg phenotype. Yet, empirical efforts aiming to document and understand the resulting evolutionary outcomes are in short supply.We used avian color space models to analyze patterns of egg color variation within and between the cuckoo and two closely related hosts, the nomadic brambling (Fringilla montifringilla) and the site fidelic chaffinch (F. coelebs). We found that there is pronounced opportunity for disruptive selection on brambling egg coloration. The corresponding cuckoo host race has evolved egg colors that maximize fitness in both sympatric and allopatric brambling populations. By contrast, the chaffinch has a more bimodal egg color distribution consistent with the evolutionary direction predicted for the brambling. Whereas the brambling and its cuckoo host race show little geographical variation in their egg color distributions, the chaffinch's distribution becomes increasingly dissimilar to the brambling's distribution towards the core area of the brambling cuckoo host race.High rates of brambling gene flow is likely to cool down coevolutionary hot spots by cancelling out the selection imposed by a patchily distributed cuckoo host race, thereby promoting a matching equilibrium. By contrast, the site fidelic chaffinch is more likely to respond to selection from adapting cuckoos, resulting in a markedly more bimodal egg color distribution. The geographic variation in the chaffinch's egg color distribution could reflect a historical gradient in parasitism pressure. Finally, marked cuckoo egg polymorphisms are unlikely to evolve in these systems unless the hosts evolve even more exquisite egg recognition capabilities than currently possessed

The critically endangered forest owlet <i>Heteroglaux blewitti</i> is nested within the currently recognized <i>Athene</i> clade: A century-old debate addressed

<div><p>Range-restricted species generally have specific niche requirements and may often have unique evolutionary histories. Unfortunately, many of these species severely lack basic research, resulting in poor conservation strategies. The phylogenetic relationship of the Critically Endangered Forest Owlet <i>Heteroglaux blewitti</i> has been the subject of a century-old debate. The current classifications based on non-phylogenetic comparisons of morphology place the small owls of Asia into three genera, namely, <i>Athene</i>, <i>Glaucidium</i>, and <i>Heteroglaux</i>. Based on morphological and anatomical data, <i>H</i>. <i>blewitti</i> has been alternatively hypothesized to belong within <i>Athene</i>, <i>Glaucidium</i>, or its own monotypic genus <i>Heteroglaux</i>. To test these competing hypotheses, we sequenced six loci (~4300 bp data) and performed phylogenetic analyses of owlets. Mitochondrial and nuclear trees were not congruent in their placement of <i>H</i>. <i>blewitti</i>. However, both mitochondrial and nuclear combined datasets showed strong statistical support with high maximum likelihood bootstrap (>/ = 90) and Bayesian posterior probability values (>/ = 0.98) for <i>H</i>. <i>blewitti</i> being nested in the currently recognized <i>Athene</i> group, but not sister to Indian <i>A</i>. <i>brama</i>. The divergence of <i>H</i>. <i>blewitti</i> from its sister taxa was between 4.3 and 5.7 Ma coinciding with a period of drastic climatic changes in the Indian subcontinent. This study presented the first genetic analysis of <i>H</i>. <i>blewitti</i>, a Critically Endangered species, and addressed the long debate on the relationships of the <i>Athene</i>-<i>Heteroglaux</i>-<i>Glaucidium</i> complex. We recommend further studies with more data and complete taxon sampling to understand the biogeography of Indian <i>Athene</i> species.</p></div