Coevolution is linked with phenotypic diversification but not speciation in avian brood parasites

Abstract

Coevolution is often invoked as an engine of biological diversity. Avian brood parasites and their hosts provide one of the best-known examples of coevolution. Brood parasites lay their eggs in the nests of other species, selecting for host defences and reciprocal counteradaptations in parasites. In theory, this arms race should promote increased rates of speciation and phenotypic evolution. Here, we use recently developed methods to test whether the three largest avian brood parasitic lineages show changes in rates of phenotypic diversity and speciation relative to non-parasitic lineages. Our results challenge the accepted paradigm, and show that there is little consistent evidence that lineages of brood parasites have higher speciation or extinction rates than non-parasitic species. However, we provide the first evidence that the evolution of brood parasitic behaviour may affect rates of evolution in morphological traits associated with parasitism. Specifically, egg size and the colour and pattern of plumage have evolved up to nine times faster in parasitic than in non-parasitic cuckoos. Moreover, cuckoo clades of parasitic species that are sympatric (and share similar host genera) exhibit higher rates of phenotypic evolution. This supports the idea that competition for hosts may be linked to the high phenotypic diversity found in parasitic cuckoos.

Comparing vocal structures of the parasitic and nonparasitic groups in Cuculinae

“…S1). The choice of trees may not change the results qualitatively as shown in other studies (e.g., Medina and Langmore 2015). Statistical significance of the difference in the mean of the contrast values from zero was tested using a one-sample t test.…”

“…The evolutionary arms race between avian brood parasites and their hosts to maximize their respective fitness has been a model system for co-evolutionary studies for over a century (Davies 2000;Erritzøe et al 2012). From these studies, we know that such a co-evolutionary relationship results in profound effects, directly or indirectly, on various aspects of the biological evolution of brood parasites, for example, egg mimicry, reduced female body size and accelerated phenotypic diversification (Sorenson et al 2003;Stoddard and Stevens 2011;Medina and Langmore 2015). However, little is known about how this behavior is associated with the vocal evolution of brood parasites.…”

“…Avian Research (Medina and Langmore 2015) and increased breeding home range size (Krüger and Davies 2002), may also be associated directly or indirectly with vocal evolution. In this study, we analysed male calls produced by species belonging to the subfamily Cuculinae to explore the evolutionary patterns of vocalization between the lineage of parasitic and nonparasitic species, which may have implications for understanding the vocal evolution of non-oscine birds.…”

The evolution of host specialisation in avian brood parasites

“…Another scenario that could lead to young, specialised species is one where specialised clades have higher speciation rates than generalist species. However, there is no evidence for differences in speciation rates across brood parasites (Medina & Langmore ). Alternatively, extinction rates may be higher in specialist species, leading to a pattern where older species tend to be generalists because old specialist species go extinct, but there is no current evidence supporting differences in extinction rates or extinction risk between specialist or generalist species of brood parasites (Ducatez ; Medina & Langmore ).…”

Evolutionary change: facultative virulence by brood parasites and tolerance and plastic resistance by hosts

“…A particular type of parasitism is that in which individuals exploit the parental care of nonrelatives, thereby reducing the costs of parenting (parental-care parasitism; Rold an & Soler, 2011). Obligate avian brood parasitism is an extreme form of parental-care parasitism, and an appropriate study system to test predictions related to a variety of coevolutionary scenarios and outcomes (Medina & Langmore, 2016b), including the influence of coevolution in promoting species richness (Krüger, Sorenson, & Davies, 2009) or the evolutionary rate of change of morphological traits of brood parasites (Medina & Langmore, 2015). Here we suggest that virulence of the parasite and defensive strategies of the hosts, together with phenotypic plasticity in host defences and parasite counter-defences, would affect rates of specialization and speciation by brood parasites (see Fig.…”