Date of Award

August 2020

Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant and Environmental Science

Committee Member

Michael S Caterino

Committee Member

Peter Adler

Committee Member

Juan Antonio Baeza

Committee Member

Joseph Parker


Secondary sexual characters (SSC) are traits present only in one sex, commonly on males, and different from the reproductive organs. These characters have evolved mainly through the action of Sexual Selection, the differential mating success of organisms of the same species. Males use SSC to challenge other males for access to females, while females use these traits as signals to choose mates with overall good. SSC can manifest as horns, tusks, enlarged appendages, spines, coloration, and body size. Sexually dimorphic traits are present in all major groups of animals, including Insects. Sexual selection and secondary sexual traits have been proposed to be drivers for speciation on hypothetical bases, but empirical evidence has proven to be inconclusive.

To explore this hypothesis in species rich lineages, such as insects, it is necessary to identify the diversity and frequency of SSC within particular lineages. Pselaphinae beetles (Coleoptera: Staphylinidae) are a great example of high species richness and broad morphological variation in sexual traits. This group contains more than 10,470 described species distributed worldwide. They are predators of small invertebrates, and their large number of species contrasts with their small size, between 0.6 and 3.0 mm. The diversity and frequency of SSC in Pselaphinae was obtained from species descriptions, fauna catalogues, and databases. A total of 40 dimorphic body structures were identified in 218 species from 34 tribes. The SSC present in the largest number of species were modification of abdominal sternites, eyes, and mesotibiae. Differences on the quality and quantity of SSC were found among different tribes. To look at the evolution of SSC at the genus scale, in the genus Batrisodes were documented on a phylogenetic context. The basal process on antennomere XI showed most convergence among species of Nearctic and Palearctic regions. The ventral fovea on antennomere X, was the most constant across the genus. This research is an initial step towards the recollection of SSC in Pselaphinae, that can be used to study character evolution, character correlations with microhabitats, and character correlation with other characters.



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