Extra-pair mating in a socially monogamous and paternal mouth-brooding cardinalfish

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Marine Biology

Background:

• Social monogamy is prevalent in vertebrates, including coral reef fishes.
• Genetic studies increasingly challenge assumptions of reproductive exclusivity within pair bonds.
• Paternal care, like mouth-brooding, is often linked to high paternity confidence.

Purpose of the Study:

• To investigate the extent of monogamy and extra-pair reproduction in the cardinalfish Sphaeramia nematoptera.
• To determine the parentage of embryos using genetic tools in a species with paternal mouth-brooding.

Main Methods:

• Conducted two years of long-term behavioral observations of Sphaeramia nematoptera.
• Employed genetic parentage analysis on 105 broods from 64 males to identify offspring.
• Examined embryo parentage to confirm pair-bond fidelity and detect extra-pair fertilization.

Main Results:

• Confirmed long-term pair bonding in S. nematoptera within social groups.
• Genetic analysis revealed significant extra-pair mating: 30.1% of broods had non-partner mothers, and 11.5% involved multiple females.
• Extra-pair fertilization occurred in 7.6% of broods, despite paternal mouth-brooding, suggesting opportunistic mating.

Conclusions:

• Social pair formation in S. nematoptera enhances group cohesion but does not guarantee reproductive exclusivity.
• Both males and females engage in extra-pair mating, likely to maximize lifetime reproductive success.
• Opportunistic extra-pair mating is a significant reproductive strategy, even in species with high paternal investment.