Dataset Information

Referential alarm calling elicits future vigilance in a host of an avian brood parasite.

ABSTRACT: Yellow warblers (Setophaga petechia) use referential 'seet' calls to warn mates of brood parasitic brown-headed cowbirds (Molothrus ater). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by seet calls on one day, extend their anti-parasitic responses into the future by engaging in vigilance at sunrise on the next day, when parasitism may occur. As predicted, daytime seet call playbacks caused female warblers to leave their nests less often on the following morning, relative to playbacks of both their generic anti-predator calls and silent controls. Thus, referential calls do not only convey the identity or the type of threat at present but also elicit vigilance in the future to provide protection from threats during periods of heightened vulnerability.

SUBMITTER: Lawson SL

PROVIDER: S-EPMC8440030 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Referential alarm calling elicits future vigilance in a host of an avian brood parasite.

Lawson Shelby L SL Enos Janice K JK Wolf Caroline S CS Stenstrom Katharine K Winnicki Sarah K SK Benson Thomas J TJ Hauber Mark E ME Gill Sharon A SA

Biology letters 20210915 9

Yellow warblers (<i>Setophaga petechia</i>) use referential 'seet' calls to warn mates of brood parasitic brown-headed cowbirds (<i>Molothrus ater</i>). In response to seet calls during the day, female warblers swiftly move to sit tightly on their nests, which may prevent parasitism by physically blocking female cowbirds from inspecting and laying in the nest. However, cowbirds lay their eggs just prior to sunrise, not during daytime. We experimentally tested whether female warblers, warned by s ...[more]

PMID: 34520683

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Project description:Abstract One of the most effective defenses of avian hosts against obligate brood parasites is the ejection of parasitic eggs from the nests. Despite the clear fitness benefits of this behavior, individuals within so‐called “egg‐rejecter” host species still show substantial variation in their propensity to eliminate foreign eggs from the nest. We argue that this variation can be further understood by studying the physiological mechanisms of host responses to brood parasitic egg stimuli: independent lines of research increasingly support the hypothesis that stress‐related physiological response to parasitic eggs may trigger egg rejection. The “stress‐mediated egg rejection” hypothesis requires that hosts activate the stress‐response when responding to parasitic egg stimuli. We tested this prediction by asking whether hosts showed differential stress response when exposed to host‐like (mimetic) or parasite‐like (non‐mimetic) eggs. We experimentally parasitized incubating American robins Turdus migratorius, a robust egg‐rejecter host to obligate brood parasitic brown‐headed cowbirds Molothrus ater, with mimetic or non‐mimetic model eggs. To assess the stress response, we measured the heart rate in incubating females immediately after experimental parasitism. We also measured plasma corticosterone and, in a subset of birds, used RNA‐sequencing to analyze the expression of proopiomelanocortin (POMC), a precursor of adrenocorticotropic hormone, 2 h after experimental parasitism. We found that egg type had no effect on heart rate. Two hours following experimental parasitism, plasma corticosterone did not differ between the differently‐colored model egg treatments or between rejecter and accepter females within the non‐mimetic treatment. However, females exposed to non‐mimetic eggs showed an upregulation of POMC gene expression (before FDR correction) in the pituitary compared with females treated with mimetic eggs. Our findings suggest that in an egg‐rejecter host species, non‐mimetic parasitic eggs may increase the activity of the stress‐related hypothalamic–pituitary–adrenal axis compared with mimetic eggs, although the temporal dynamics of this response are not yet understood. Stress‐related signaling has been shown to mediate anti‐parasitic behaviors in avian brood parasite hosts. Here we tested if brood parasite‐like model eggs activated the hypothalamic–pituitary–adrenal (HPA) axis and autonomic nervous system compared with host‐like model eggs. We show that, compared with experimental parasitism with mimetic eggs, parasitism with nonmimetic eggs does not affect blood corticosterone or heart rate, but that exposure to parasitic eggs may increase the expression of POMC gene, a precursor to ACTH, a central hormone in the HPA axis.

Dataset Information

Referential alarm calling elicits future vigilance in a host of an avian brood parasite.

Publications

Referential alarm calling elicits future vigilance in a host of an avian brood parasite.

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