Abstract
The family Hydrophilidae is the largest group of the superfamily Hydrophiloidea to which the largest aquatic Polyphaga are allocated. Phylogenetic studies based on morphological characters suggest that in Hydrophilidae, specifically in Hydrophilini, the body size is related to the group evolution. Despite these morphological analyses, cytogenetic studies of this family are scarce, and there is not a correlation of morphologic and cytogenetic data outlined for this group. In this paper, we analyzed seventeen specimens of Tropisternus mutatus sapucay Fernández & Bachman from rivers from two localities in Southern Brazil. Chromosome analyses showed 2n=18 with a sex chromosome system of the Xyp type (2n=18=16+Xyp). All the autosomes, including the Xp chromosome, were metacentric. The basal number and the possible divergence among the different Hydrophilidae species analyzed to date, as well as the phylogeny proposed for Hydrophilini, are discussed.
