Bridging the cytogenetic gap in Trichoptera (Insecta): first karyotypic data on Neotropical species and insights into chromosomal evolution in caddisflies

Abstract

Trichoptera are a diverse group of insects with aerial adults and aquatic immature stages. Despite their importance in freshwater environments, fundamental aspects of their biology are unknown, and no chromosomal studies have been performed in Neotropical species. The aim of this study was to provide the first cytogenetic analysis of four Trichoptera species from the Neotropics. We analysed the meiotic development and chromosome behaviour in Smicridea (Rhyacophylax) pampeana Flint (Annulipalpia: Hydropsychidae), Marilia flexuosa Ulmer (Integripalpia: Odontoceridae), Triplectides misionensis Holzenthal (Integripalpia: Leptoceridae), and Grumicha grumicha (Vallot) (Integripalpia: Sericostomatidae) by conventional cytogenetic procedures. The chromosome numbers are 2n = 31/32 (female/male) in S. (R.) pampeana, 2n = 57 (female) in M. flexuosa, 2n = 47 (female) in T. misionensis, and 2n = 35 (female) in G. grumicha. All four species have a simple sex chromosome system Z/ZZ (female/male). Females are the heterogametic sex, and their meiosis is achiasmatic. Our results together with available cytogenetic data provide more information on the karyology of Trichoptera and contribute to the current scientific knowledge of the possible mechanisms involved in chromosomal evolution. Based on all the evidence, we propose the existence of possible positive relationships between biological traits, ecological strategies, and cytogenetic features in Trichoptera.