SEMINAL FLUID PROTEINS AND SPERMATOGENESIS

Using RNAseq in collaboration with Erica Larson, we found that many seminal fluid proteins (SFPs) are upregulated in testes of males producing long sperm. SFPs are secreted in the male accessory glands (AGs) and transferred to females in seminal fluid. There, they induce changes in many aspects of female behavior and physiology, including sexual receptivity, ovulation, feeding, and sleep. SFPs are usually expressed in testis at high levels (though lower than in AG), but there is no known role for SFPs in spermatogenesis.  

In knockouts of two well-studied SFPs in our dataset, Sex Peptide (SP) and ovulin, we found slightly but significantly shorter sperm. However, disruption of AG function does not affect sperm length, suggesting that SFP-mediated effects on spermatogenesis are limited to expression in testis rather than AG. We also found that males from two DSPR RILs with long sperm were able to delay female remating relative to two short sperm RILs (above), suggesting that long sperm males also transfer more AG-secreted SFPs. Long sperm males are in yellow, short sperm males are in blue. Lines are replicate DSPR RILs with known sperm lengths. The x-axis is Days to Remate, y-axis is cumulative percentage of females that remated.

These results point to sophisticated coordination of gene expression and pleiotropy across tissues, with a double benefit for male reproductive success in both sperm competition and delayed female remating.

The discovery of a novel role for AG-specific genes in testis provides opportunities for understanding the evolutionary trajectory of tissue-specific expression and pleiotropy for de novo genes, evolutionary constraints and modularity of reproductive traits, and how pleiotropy impacts male reproductive fitness within species and patterns of molecular evolution across species. Our future goals are to characterize the roles of SFPs in spermatogenesis and AG using RNAi and immunohistochemistry and investigate mechanisms of regulatory coordination between SFP expression in testis and accessory gland.