Rates of male rivalry and mate choice vary with density and determine whether size-assortative mating is absent, positive, or negative in the clown weevil, Eudiagogus pulcher

AbstractAt four sites in Texas, the density of the clown weevil, Eudiagogus pulcher, in stands of rattlebox, Sesbania drummondii, increased with proximity to water. Size-assortative mating (SAM) was negative at high density, positive at intermediate density, and absent at low density. Only at intermediate density were relatively small potential mates frequently rejected. Females rejected males via resistance to attempts to mount while males rejected females by abandoning them soon after mounting. A laboratory experiment showed that mate rejection is more likely when individuals experience intermediate densities, but not low or high densities, prior to courtship. In the field, rival males displaced mounting males that were small relative to either the female or rival. Rates of rivalry increased with density. At high density, low rates of mate rejection and high rates of rivalry resulted in the formation of displacement-resistant pairs consisting of large males and small females. This left small males to vie for large females and resulted in negative SAM. At intermediate density, low rates of rivalry coupled with rejection of small individuals favored the formation of pairs consisting of similarly sized males and females, causing positive SAM. At low density, low rates of both mate rejection and rivalry resulted in random mating by size and the absence of SAM.Key Words: clown weevilsize-assortative matingmutual choicepopulation densityrivalry ACKNOWLEDGMENTSWe thank the residents of Lake Irene and Lake Bedias in Bedias, Texas for providing access to rattlebox stands on their property. We thank the referees for suggestions that simplified and improved the manuscript.DISCLOSURE STATEMENTNo potential conflict of interest was reported by the authors.ETHICAL STANDARDThe study was done in full compliance with the guidelines of the Institutional Animal Care and Use Committee to ensure the ethical treatment of study animals.AUTHOR CONTRIBUTIONBoth authors contributed to the study conception, experimental design, analysis of results, and manuscript preparation.DATA ACCESSIBILITYAll data analyzed in and supporting conclusions of this manuscript are accessible at http://digitalcommons.georgiasouthern.edu/data/8/ (https://doi.org/10.20429/data.2022.02).