Predaceous diving beetles have an impressively diverse array of

morphological and behavioral attributes associated with sexual systems. These

include anatomical dimorphisms with males and females exhibiting many secondary

sexual features, behavioral dimorphisms in precopulatory and copulatory activities,

extensive variation in male and female genitalia, and sperm complexity that includes

sperm conjugation and heteromorphism. Many of these attributes appear to be

correlated, suggesting emphasis by certain clades on particular sexual systems.

For example, members of Dytiscinae appear to emphasize pre-insemination sexual

selection with female resistance behavior possibly associated with the male ability

to threaten suffocation of females during copulatory activities, which take place

over many hours of mate guarding. In this case, males have large adhesive discs

on their protarsi used to better subdue a resistant female, whereas females have

modified pronotal and elytral cuticle that interfere with male adhesive discs.

This group also has among the simplest male sperm and female reproductive tract 

 morphology, suggesting more limited post-insemination selection, but strong

pre-insemination sexual antagonism. In contrast, members of Hydroporinae

have no obvious pre- insemination mating behaviors and only short mating

durations. This group also has dramatically complex female reproductive tracts

and male sperm morphology including conjugation and heteromorphism suggesting

intensity in post- insemination sperm choice, sperm cooperation, and sperm competition.

Here, dytiscid sexual attributes are reviewed along with discussion of dytiscid

sexual system evolution.