Molecular characterization of firefly nuptial gifts: a multi-omics approach sheds light on postcopulatory sexual selection

Abstract

Postcopulatory sexual selection is recognized as a key driver of reproductive trait evolution, including the machinery required to produce endogenous nuptial gifts. Despite the importance of such gifts, the molecular composition of the non-gametic components of male ejaculates and their interactions with female reproductive tracts remain poorly understood. During mating, male Photinus fireflies transfer to females a spermatophore gift manufactured by multiple reproductive glands. Here we combined transcriptomics of both male and female reproductive glands with proteomics and metabolomics to better understand the synthesis, composition and fate of the spermatophore in the common Eastern firefly, Photinus pyralis. Our transcriptome of male glands revealed up-regulation of proteases that may enhance male fertilization success and activate female immune response. Using bottom-up proteomics we identified 208 functionally annotated proteins that males transfer to the female in their spermatophore. Targeted metabolomic analysis also provided the first evidence that Photinus nuptial gifts contain lucibufagin, a firefly defensive toxin. The reproductive tracts of female fireflies showed increased gene expression for several proteases that may be involved in egg production. This study offers new insights into the molecular composition of male spermatophores, and extends our understanding of how nuptial gifts may mediate postcopulatory interactions between the sexes.

Structural complexity and molecular heterogeneity of a butterfly ejaculate reflect a complex history of selection

“…In summary, we urge more careful consideration of the structural and biochemical complexity of male ejaculates. Such work is likely to uncover insights into reproductive interactions between the sexes and highlight previously unconsidered axes of reproductive adaptation (64,65). How males and females collaborate and quarrel over ejaculate processing in both space and time may lead us to better understand the control of reproductive tissues and by extension, the origin of reproductive dysfunctions that play critical roles in infertility, individual fitness, and reproductive isolation during speciation.…”

Firefly genomes illuminate parallel origins of bioluminescence in beetles

“…Both sexes are capable of mating several times during their adult lives. During mating, males transfer to females a fitness-enhancing nuptial gift consisting of a spermatophore manufactured by multiple accessory glands (5); the molecular composition of this nuptial gift has recently been elucidated for P. pyralis (6). In other Photinus species, male gift size decreases across sequential matings (7), and multiple matings are associated with increased female fecundity (8).…”

“…The library was sequenced at the Whitehead Institute Genome Technology Core (Cambridge, MA) on two lanes of an Illumina HiSeq 2500 using rapid mode 100x100 bp PE. This library was multiplexed with the P. pyralis RNA-Seq libraries of Al-Wathiqui and colleagues (6), and thus, P. pyralis reads arising from index misassignment were present in this library which necessitated downstream filtering to avoid misinterpretation.…”

“…1A; Video S1) has been long studied for its role in mate recognition (1)(2)(3), while non-adult bioluminescence is likely a warning signal of their unpalatable chemical defenses (4), such as the cardiotoxic lucibufagins of Photinus fireflies (5). The biochemical understanding of firefly luminescence: an ATP, Mg 2+ , and O 2 -dependent luciferase-mediated oxidation of the substrate luciferin (6), along with the cloning of the luciferase gene (7,8), led to its widespread use of luciferase as a reporter with unique applications in biomedical research and industry (9). With >2000 species globally, fireflies are undoubtedly the most culturally-appreciated bioluminescent group, yet there are at least three other beetle families with bioluminescent species: click beetles (Elateridae), American railroad worms (Phengodidae) and Asian starworms (Rhagophthalmidae) (10).…”

“…With >2000 species globally, fireflies are undoubtedly the most culturally-appreciated bioluminescent group, yet there are at least three other beetle families with bioluminescent species: click beetles (Elateridae), American railroad worms (Phengodidae) and Asian starworms (Rhagophthalmidae) (10). These four closely related families (superfamily Elateroidea) have homologous luciferases and structurally identical luciferins (6), implying a single origin of beetle bioluminescence.…”