Eubrianax edwardsii (LeConte, 1874), the water penny beetle (Coleoptera: Psephenidae), is commonly found in a wide variety of aquatic habitats in California, such as snowmelt-dominated mountain streams, groundwater-fed isolated pools in intermittent streams, and high elevation lakes. Little is known about the basic biology and ecology of this species, however. The objectives of this study were to (1) redescribe the morphological characteristics of the larva, pupa, and adults, and compare the larval morphology among instars and populations; (2) determine the life cycle and timing of development; and (3) investigate the landscape genetics of populations in California. To do this, we collected larval water pennies from ~12 locations throughout central and northern California, performed regular sampling of one population (Mt. Tamalpais, Marin County), reared individuals from two populations in the laboratory, and sequenced the DNA Barcoding gene (mtDNA COI) from individuals from each population.
Results/Conclusions
We found that E. edwardsii has five larval instars, and growth rates roughly correspond with Dyar’s rule. The patterning or number of spots on the larval exoskeleton increase in later instars. All larval instars are present throughout the year in the Mt. Tamalpais population, suggesting an asynchronous development pattern. Adults have only been collected during the summer in the field; however, adults emergence in the lab occurred during the late fall and winter. The adults exhibit extreme sexual dimorphism, including distinctive differences in coloration, size, and antennae morphology. We also found a highly level of genetic variation between populations in California, including large differences between populations on either side of Central Valley, which evidently serves as a barrier to gene flow in this species. Given the wide variety of aquatic habitats that this species inhabits, it seems clear that local populations may exhibit unique evolutionary adaptations. Our next steps include examining possible differences in physiological responses to water temperature variation among populations.