Visual modeling shows that avian host parents use multiple visual cues in rejecting parasitic eggs

Abstract

One of the most striking outcomes of coevolution between species is egg mimicry by brood parasitic birds, resulting from rejection behavior by discriminating host parents. Yet, how exactly does a host detect a parasitic egg? Brood parasitism and egg rejection behavior provide a model system for exploring the relative importance of different visual cues used in a behavioral task. Although hosts are discriminating, we do not know exactly what cues they use, and to answer this it is crucial to account for the receiver's visual perception. Color, luminance ("perceived lightness") and pattern information have never been simultaneously quantified and experimentally tested through a bird's eye. The cuckoo finch Anomalospiza imberbis and its hosts show spectacular polymorphisms in egg appearance, providing a good opportunity for investigating visual discrimination owing to the large range of patterns and colors involved. Here we combine field experiments in Africa with modeling of avian color vision and pattern discrimination to identify the specific visual cues used by hosts in making rejection decisions. We found that disparity between host and foreign eggs in both color and several aspects of pattern (dispersion, principal marking size, and variability in marking size) were important predictors of rejection, especially color. These cues correspond exactly to the principal differences between host and parasitic eggs, showing that hosts use the most reliable available cues in making rejection decisions, and select for parasitic eggs that are increasingly mimetic in a range of visual attributes.brood parasitism | coevolution | egg color | egg pattern | vision

Hyperspectral imaging of cuttlefish camouflage indicates good color match in the eyes of fish predators

“…Previous investigations of camouflage using image analysis (including spatial filtering and edge detection) provided insights into the mechanisms of visual perception of predators (13,14), yet these studies suffer from the inability to assess the effectiveness of camouflage in the visual space of predators (15). Recent studies using digital photography in conjunction with color space modeling have examined body coloration in both spatial and spectral domains (16)(17)(18)(19)(20). In the present study, we exploit unique imaging technology [hyperspectral imaging (HSI)] (Fig.…”

Interspecific egg rejection as ecological collateral damage from selection driven by conspecific brood parasitism

“…If evolution has molded egg recognition and rejection responses to target the relatively similar eggs of conspecific parasites, selection should favor the use of features that most reliably allow birds to distinguish their own eggs from the foreign eggs (Spottiswoode & Stevens, 2010), in this case the eggs of conspecifics, and these features are unlikely to be the same ones that differ most between the host's eggs and those of the interspecific parasite's eggs. Thus, the more extreme differences in phenotype we see in the interspecific parasitic eggs would not necessarily lead to a more extreme rejection response, such as rejection of all parasitic eggs.…”

“…Given that hosts are capable of the very fine-scale discrimination required to accurately distinguish among eggs of conspecifics, shouldn't they always be able to recognize and reject the extremely different duck eggs (Figure 2)? This assumption is based both on theoretical considerations of recognition systems (Sherman, Reeve, & Pfennig, 1997), plus empirical evidence that egg rejection rates correlate with the degree of difference between host and parasite eggs in some brood-parasitic systems (de la Colina et al, 2012;Lotem et al, 1995;Rothstein, 1982;Spottiswoode and Stevens, 2010). Thus a key question, and one on which the rejection as incidental by-product hypothesis depends, is whether the evolution of egg rejection driven solely by conspecific brood parasitism could result in the intermediate rejection rates that we observed for the highly nonmimetic eggs of Heteronetta.…”

Hyperspectral Imaging of Cuttlefish Camouflage Indicates Good Color Match in the Eyes of Fish Predators

“…The potentially optimal solution for characterization of both spatial and spectral information in studying animal communication is the use of multispectral or hyperspectral imaging systems (but see a few exceptions in 16,[17][18][19][20]. In the last decade, this multiband imaging system, originally designed for remote sensing, has been applied largely in studying human color vision (41)(42)(43)(44)(45)(46) and animal color communication (47).…”

“…Previous investigations of camouflage using image analysis (including spatial filtering and edge detection) provided insights into the mechanisms of visual perception of predators (13,14), yet these studies suffer from the inability to assess the effectiveness of camouflage in the visual space of predators (15). Recent studies using digital photography in conjunction with color space modeling have examined body coloration in both spatial and spectral domains (16)(17)(18)(19)(20). In the present study, we exploit new imaging technology (HyperSpectral Imaging, HSI; Fig.…”