Dark eyes in female sand gobies indicate readiness to spawn.

Ola Svensson,Karin H Olsson,Charlotta Kvarnemo,Helen Nilsson Sköld,Eva-Lotta Blom,Kai Lindström,John A Craft,Sandra Johansson

doi:10.1371/journal.pone.0177714

Ola Svensson, Karin H Olsson + Show 6 more

Open Access

https://doi.org/10.1371/journal.pone.0177714

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Journal: PloS one	Publication Date: Jun 7, 2017
Citations: 7	License type: CC BY 4.0

Affiliation: University of Gothenburg, Åbo Akademi University

Abstract

In animals, colorful and conspicuous ornaments enhance individual attractiveness to potential mates, but are typically tempered by natural selection for crypsis and predator protection. In species where males compete for females, this can lead to highly ornamented males competing for mating opportunities with choosy females, and vice versa. However, even where males compete for mating opportunities, females may exhibit conspicuous displays. These female displays are often poorly understood and it may be unclear whether they declare mating intent, signal intrasexual aggression or form a target for male mate preference. We examined the function of the conspicuous dark eyes that female sand gobies temporarily display during courtship by experimentally testing if males preferred to associate with females with artificially darkened eyes and if dark eyes are displayed during female aggression. By observing interactions between a male and two females freely associating in an aquarium we also investigated in which context females naturally displayed dark eyes. We found that dark eyes were more likely to be displayed by more gravid females than less gravid females and possibly ahead of spawning, but that males did not respond behaviorally to dark eyes or prefer dark-eyed females. Females behaving aggressively did not display dark eyes. We suggest that dark eyes are not a signal per se but may be an aspect of female mate choice, possibly related to vision.

Highlights

Ornaments, whether in the form of colors, long feathers, fins, or combs, are often shown predominantly by one of the sexes, and often only during the reproductive season
2) If dark eyes are used in intra-sexual competition, we predict that round females interacting aggressively, will display them
3) If dark eyes correspond to a pre-existing male preference, we predict that males will prefer to associate with dark-eyed females

Summary

Introduction

Whether in the form of colors, long feathers, fins, or combs, are often shown predominantly by one of the sexes, and often only during the reproductive season. A fourth explanation for female ornamentation is that it has evolved as a result of male preferences for such a trait [5,14,15] This phenomenon has been primarily studied in species where the operational sex ratio is female-biased [11,16]. The function of the dark eye markings in females is unknown, but its complete absence in males makes the explanations of correlated gene expression, camouflage and generally improved vision in shallow waters unlikely. We formulated the following hypotheses: 1) If dark eyes declare an intention to spawn, we predict that the ornament will be more frequently displayed by rounder females, which are more gravid and closer to spawning, and primarily in conjunction with male courtship. We formulated the following hypotheses: 1) If dark eyes declare an intention to spawn, we predict that the ornament will be more frequently displayed by rounder females, which are more gravid and closer to spawning, and primarily in conjunction with male courtship. 2) If dark eyes are used in intra-sexual competition, we predict that round females interacting aggressively, will display them. 3) If dark eyes correspond to a pre-existing male preference, we predict that males will prefer to associate with dark-eyed females

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