Ecological uncertainty favours the diversification of host use in avian brood parasites

Abstract

Adaptive responses to ecological uncertainty may affect the dynamics of interspecific interactions and shape the course of evolution within symbioses. Obligate avian brood parasites provide a particularly tractable system for understanding how uncertainty, driven by environmental variability and symbiont phenology, influences the evolution of species interactions. Here, we use phylogenetically-informed analyses and a comprehensive dataset on the behaviour and geographic distribution of obligate avian brood parasites and their hosts to demonstrate that increasing uncertainty in thermoregulation and parental investment of parasitic young are positively associated with host richness and diversity. Our findings are consistent with the theoretical expectation that ecological risks and environmental unpredictability should favour the evolution of bet-hedging. Additionally, these highly consistent patterns highlight the important role that ecological uncertainty is likely to play in shaping the evolution of specialisation and generalism in complex interspecific relationships.

Host and brood parasite coevolutionary interactions covary with comparative patterns of the avian visual system

“…Eye size did not differ significantly for the phylogenetic regression model ( β = 0.002, p = 0.99), likely because brood parasitism has independently evolved only within a handful of avian families ( N = 7 origins, e.g. [ 2 ]). Hosts had significantly smaller eyes than non-hosts for both non-phylogenetic ( β = −0.11, p < 0.001) and phylogenetic models ( β = −0.02, p < 0.02).…”

“…We sourced host status, the identities of host-specific parasites, and egg rejection rates for hosts of obligate avian brood parasites also from previously published databases [ 2 , 12 , 26 ]. This information was then annotated regarding whether the respective parasite laid an avian-perceived mimetic or non-mimetic egg as modelled by the particular host's visual system [ 16 , 27 ] and indicated by the respective spectral and perceptual review literature (e.g.…”

“…We ran the analysis across 100 hypothesized trees from a previously published phylogeny [ 30 ] and extracted the median estimated marginal means of coefficients for inference using p -values calculated from pairwise contrasts corrected for multiple comparisons to assess significance [ 31 ]. We repeated the analysis using ordinary least-squares regression, because nest parasitism is conserved within few families [ 2 ], and high phylogenetic signal may obscure the ecological relationship between eye size and nest parasitism status.…”

“…A classic example is the relationship between avian obligate brood parasites and their hosts. In this case, host specialization by parasites may select for nesting behaviours that limit access of parasitic intruders into increasingly enclosed host nest structures [ 2 ]. Likewise, some hosts are better able to recognize and reject foreign eggs, even when the parasitic eggshells are highly mimetic in background coloration and maculation patterns [ 3 , 4 ].…”

A new approach to integrate phylogenetic structure and partner availability to study biotic specialization in ecological networks

“…Low heterogeneity in resources exchanged by partners can result in opportunistic interactions (Pinheiro et al, 2019). A recent study also showed that high ecological uncertainty can favor generalized host ranges in avian brood parasites (Antonson et al, 2020). How and when selection maintains the variation necessary for opportunistic interactions is not fully understood (Vamosi et al, 2014; but see Batstone et al, 2018), but it seems to be pervasive even in highly intimate symbioses such as lichens and corals (Fig.…”