Novel seminal fluid proteins in the seed beetle Callosobruchus maculatus identified by a proteomic and transcriptomic approach

Abstract

The seed beetle Callosobruchus maculatus is a significant agricultural pest and increasingly studied model of sexual conflict. Males possess genital spines that increase the transfer of seminal fluid proteins (SFPs) into the female body. As SFPs alter female behaviour and physiology, they are likely to modulate reproduction and sexual conflict in this species. Here, we identified SFPs using proteomics combined with a de novo transcriptome. A prior 2D-sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis identified male accessory gland protein spots that were probably transferred to the female at mating. Proteomic analysis of these spots identified 98 proteins, a majority of which were also present within ejaculates collected from females. Standard annotation workflows revealed common functional groups for SFPs, including proteases and metabolic proteins. Transcriptomic analysis found 84 transcripts differentially expressed between the sexes. Notably, genes encoding 15 proteins were highly expressed in male abdomens and only negligibly expressed within females. Most of these sequences corresponded to 'unknown' proteins (nine of 15) and may represent rapidly evolving SFPs novel to seed beetles. Our combined analyses highlight 44 proteins for which there is strong evidence that they are SFPs. These results can inform further investigation, to better understand the molecular mechanisms of sexual conflict in seed beetles.

Superior stimulation of female fecundity by subordinate males provides a mechanism for telegony

“…Since there is no courtship behaviour in burying beetles, nor the presentation of any nuptial gifts, nor any pheromonal displays when beetles are in close proximity, we suggest these effects could be due to differences in ejaculate composition. Detailed analyses of Drosophila and Tribolium ejaculates, for example, have found that they contain a multitude of proteins which alter female physiology in diverse ways (Sirot et al 2011;Yamane et al 2015;Bayram et al 2017;Wigby et al 2016). Furthermore, smaller Drosophila allocate more proteins from their accessory gland to their ejaculate than do larger males (Wigby et al 2016) and a mechanism like this could account for the differences we found between Small and Large burying beetles.…”

Postmating sexual selection and the enigmatic jawed genitalia ofCallosobruchus subinnotatus

“…Our results suggest that the genital jaws of C. subinnotatus may also affect female uptake of male seminal fluid, although this may then be manifested as elevated female egg production in this species. We note that that male seminal fluid in seed beetles contains a very large number of proteins, some of which affect male fertilization success and others that affect female egg production (Goenaga et al, 2015; Yamane et al, 2015; Bayram et al, 2017). Needless to say, given everything else equal, male postmating reproductive success is elevated by an increase in female egg production (Arnqvist and Rowe, 2005).…”

Postmating sexual selection and the enigmatic jawed genitalia of Callosobruchus subinnotatus

“…Our results suggest that the genital jaws of C. subinnotatus may also affect female uptake of male seminal fluid, although this may then be manifested as elevated female egg production in this species. We note that that male seminal fluid in seed beetles contains a very large number of proteins, some of which affect male fertilization success and others that affect female egg production ( Goenaga et al, 2015 ; Yamane et al, 2015 ; Bayram et al, 2017 ). Needless to say, given everything else equal, male postmating reproductive success is elevated by an increase in female egg production ( Arnqvist and Rowe, 2005 ).…”