Interspecific Density Influences the Adaptive Significance of Provisioning Coordination Between Breeding Partners

Chloe Burdick,Lynn Siefferman

doi:10.3389/fevo.2020.00029

Abstract

Cooperation between parents in species with biparental care can reduce sexual conflict and increase reproductive success. If parents cooperate in a conditional way- that is, alternate feeding visits to offspring- this should equalize parental investment and may improve nestling growth. Environmental variation, including competition for limited resources, may influence the need for, and benefits of, parental cooperation. We measured the benefits of partner coordination in offspring provisioning behavior among eastern bluebird partners (Sialia sialis) in which the strength of interspecific density varied spatially. Tree swallows (Tachycineta bicolor) are a recent (<40 years) arrival in our study area, are aggressive nestbox competitors with eastern bluebirds, and their density varies across the field site. Nesting among higher densities of tree swallows led to reduced parental feeding rates and reproductive success of bluebirds. Partner alternation, however, did not vary with tree swallow density. Additionally, alternation level and provisioning rate only influenced nestling growth in areas of high swallow density. It may be that the benefits of parental coordination may only be apparent when environmental conditions are poor. This study provides an important new perspective on the resolution of negotiations between breeding partners; environmental variation could influence the benefits of parental cooperation in a wide variety of animals.

Highlights

Biparental care involves the cooperation of two unrelated individuals that share fitness benefits in the current breeding attempt but, because each individual pays the costs of reproduction, should have conflicting interests in parental investment. Trivers (1972) argued that, in biparental care systems, each parent should save energy for future reproductive attempts by decreasing their current parental effort
We focus on parental coordination of eastern bluebirds (Sialia sialis), a species that experiences high competition for nesting sites with tree swallows (Tachycineta bicolor)
Average provisioning rate positively predicted mass (Effect size ± 1 SE = 0.52 ± 0.17, F = 9.43, df = 1, 75.4, n = 47 nestlings, p = 0.003), whereas we found no evidence that provisioning rates influenced nestling mass amongst partners breeding in low-density areas (Effect size ± 1 SE = 0.11 ± 0.08, F = 1.33, df = 1, 101, n = 83 nestlings, p = 0.25, Figure 2)

Summary

Introduction

Biparental care involves the cooperation of two unrelated individuals that share fitness benefits in the current breeding attempt but, because each individual pays the costs of reproduction, should have conflicting interests in parental investment (reviewed in Westneat and Sargent, 1996). Trivers (1972) argued that, in biparental care systems, each parent should save energy for future reproductive attempts by decreasing their current parental effort. Biparental care involves the cooperation of two unrelated individuals that share fitness benefits in the current breeding attempt but, because each individual pays the costs of reproduction, should have conflicting interests in parental investment (reviewed in Westneat and Sargent, 1996). Trivers (1972) argued that, in biparental care systems, each parent should save energy for future reproductive attempts by decreasing their current parental effort. Because individuals benefit when their offspring are fed at high rates, the perception of a partner withholding energy in the current breeding attempt should lead to conflict between mated partners (Stearns, 1989) when partners are unlikely to breed together in the future (Griffith, 2019; Johnstone and Savage, 2019).

Objectives

Methods

Results

Conclusion