Characterization of proteins in breeding females vs. non-breeding females vs. third-instar larvae

Abstract

Burying beetles (genus Nicrophorus) are known for breeding on small vertebrate carcasses and providing extensive parental care. Parents produce oral and anal secretions that aid in the preservation of the carcass and help protect the developing offspring. In this study of Nicrophorus orbicollis, we used proteomic analysis to characterize protein profiles of these secretions in non-breeding females and in reproductive females across three reproductive stages (carcass preparation, first instar, and larval dispersal). In addition, we characterized hemolymph protein profiles of breeding females, non-breeding females and dispersing larvae. Proteins from anal and oral secretions and hemolymph were classified into immune/defense, structural/developmental, metabolic, sensory/signaling, and antioxidant/stress-response groups. General protein shifts were observed, especially during early reproductive stages (carcass preparation and first instar stages) compared with the larval dispersal stage and non-breeding females. Breeding females showed the highest number of immune proteins in anal secretions, followed by oral secretions during early stages. These proteins, including AMPs, lysozymes, and the serine protease inhibitor family, reflect the enrichment of social immunity. Immune proteins in breeding females' hemolymph were significantly higher than in non-breeding and third-instar larvae. Noticeable reduction in protein diversity in anal secretion samples of breeding females during the larval dispersal stage suggests shifts toward a non-breeding state. The intensity of all proteins in oral secretion samples from breeding females was higher than in non-breeding females, suggesting greater investment in maternal care.