When brood parasites exploit multiple host species, egg rejection by hosts may select for the evolution of host-specific races, where each race mimics a particular host’s egg type. However, some brood parasites that exploit multiple hosts with the ability to reject foreign eggs appear to have only a single egg type. In these cases, it is unclear how the parasite egg escapes detection by its hosts. Three possible explanations are: (i) host-specific races are present, but differences in egg morphology are difficult for the human eye to detect; (ii) the brood parasite evolves a single egg type that is intermediate in appearance between the eggs of its hosts; (iii) or the parasite evolves mimicry of one of its hosts, which subsequently allows it to exploit other species with similar egg morphology. Here we test these possibilities by quantifying parameters of egg appearance of the brood-parasitic Pacific Koel (Eudynamys orientalis) and seven of its hosts. Koel eggs laid in the nests of different hosts did not show significant differences in colour or pattern, suggesting that koels have not evolved host-specific races. Koel eggs were similar in colour, luminance and pattern to the majority of hosts, but were significantly more similar in colour and luminance to one of the major hosts than to two other major hosts, supporting hypothesis (iii). Our findings suggest that mimicry of one host can allow a brood parasite to exploit new hosts with similar egg morphologies, which could inhibit the evolution of host defences in naïve hosts.
Average egg pattern energies
Data in this file were used in the egg pattern discriminate function analysis to determine if the Pacific Koel exhibited host-specific egg mimicry in egg pattern. This data includes eggs from the CSIRO museum in Canberra, ACT, Australia and fresh from the field in Sydney, NSW and Canberra, ACT. Specific information about each clutch can be found in the appendix of the manuscript and details about this analysis can be found in the Methods section of the manuscript.
Egg size analyses data
This workbook contains three sheets all related to the egg size analyses. The first sheet contains average egg volume for all koel and host eggs used in an ANOVA analysis. The second sheet is data that was used in the first linear model mentioned in the manuscript, which was run to determine if koel egg volume was predicted by host species. The third sheet is data that was used in the second linear model, which was run to determine if koel egg volume was predicted by host egg volume. Eggs were from the CSIRO museum in Canberra, ACT, Australia and fresh from the field from Sydney, NSW and Canberra, ACT. For more information about each clutch, please see the supplemental material in the manuscript. For more information about the analyses, please see the Methods and Results sections in the manuscript.
Egg size Analyses_DRYAD.xlsx
CSIRO museum egg color data
This workbook contains data related to the museum egg color analyses and only includes data from the eggs at the CSIRO museum in Canbera, ACT, Australia or eggs from the field in Sydney, NSW and Canberra, ACT that were blown prior to measuring. The first sheet contains the average spectrophotometric data at each wavelength for each clutch and koel egg, which was used to determine the color catch cone values (second sheet). The second sheet contains the color catch cone values for all four avian color cones (VS, SWS, MWS, LWS) and the double cone for luminance. These color catch cone values were used in the discriminate function analysis to determine if koels exhibit host-specific races in color and the color catchcone values were also used to calculate Just Notcieable Differences (JNDs) to compare egg colors and luminances between species. For more information about each clutch, please see the supplemental material in the manuscript. For more information about the analyses, please see the Methods and Results section in the manuscript.
CSIRO_color data_DRYAD.xlsx
Field eggs color data
This workbook contains data related to the color data for eggs collected fresh from the field from Sydney, NSW, Australia and Canberra, ACT, Australia. Species measured include the Noisy Friarbird, Magpie-lark, Red Wattlebird, and Pacific Koel eggs from Red Wattlebird nests. Eggs were measured from 2013-2015. The first sheet contains the average spectrophotometric data for each wavelength from 300-700 nm, which was used to calculate the color catchcone values (second sheet). The second sheet contains the color catchcone values for the four avian color cones (VS, SWS, MWS, and LWS) and the double cone for luminance. Catchcone values were used to calculate Just Noticeable Differences to compare egg colors and luminance values between species. For more information about each clutch, please see the supplemental material in the manuscript. For more information about the analyses, please see the Methods and Results section in the manuscript.
Field eggs_color data_DRYAD.xlsx