Clutch size and the rejection of parasitic eggs: a comparative test of the maternal investment hypothesis

Host learning selects for the coevolution of greater egg mimicry and narrower antiparasitic egg-rejection thresholds

“…At the level of individual hosts, Weber’s law predicts that smaller, rather than larger, clutch sizes should yield more discriminating host responses ( Akre & Johnsen, 2014 ; Dixit et al, 2021 ). There is empirical evidence for this pattern both intraspecifically (e.g., Abolins-Abols & Hauber, 2020b ) and comparatively ( Hauber et al, 2022 ), but these single time-point patterns cannot be equated with the course of coevolutionary interactions as the cowbird eggs also evolve across time. In turn, regarding the role of a greater parasitism rate in increasing the accuracy of parasite–egg detection through lowering hosts’ rejection thresholds, the modeled pattern is intuitive in the sense that more selection by greater parasitism rate should result in more discriminating hosts (order of the lines, Figure 3 , bottom).…”

“…During a nesting season, each host female lays a single clutch of eggs (see Table 1 for the biological meaning of key symbols). We varied the host clutch size ( ) in our model as it has been known to impact egg rejection rates both comparatively and intraspecifically through Weber’s law ( Akre & Johnsen, 2014 ; Dixit et al, 2021 ; Hauber et al, 2022 ). Following Servedio and Lande, (2003) , and for simplicity of exposition, we use the term “‘size’” as a proxy for the appearance of the egg (size is also an important cue used by hosts for egg recognition, Samas et al, 2021 ).…”