title: The nature of allometry in an exaggerated trait: The postocular flange in Platyneuromus Weele (Insecta: Megaloptera).
abstract: The origin and function of exaggerated traits exhibited by a great number of species with sexual dimorphism remain largely unexplored. The usual model considered as the evolutionary mechanism for the development of these structures is sexual selection. The nature of growth of the postocular flange (POF) in three species of the dobsonfly genus Platyneuromus (Megaloptera, Corydalidae, Corydalinae) is analyzed to explore sexual size dimorphism and allometric scaling. Results involve positive allometry of POF in males of two species, and negative allometry in males of one species, in general with a female-biased sexual dimorphism. We suggest an ancestral condition of dual incipient ornamentation in Platyneuromus, with a subsequent departure of size and shape of POF in males, triggered by sexual selection. Different sexual selection intensities may explain the parallel or divergent growth of POF within the scheme of dual ornamentation. Empirical behavioral data as well as a phylogenetic framework are necessary to clarify possible causes of phenotypic development, time of origin, and evolution of the POF.
authors.affiliation: Catedrático CONACYT, Laboratorio Regional de Biodiversidad y Cultivo de Tejidos Vegetales, Instituto de Biología, UNAM, Santa Cruz Tlaxcala, Tlaxcala, Mexico.
authors.forename: Andrés
authors.initials: A
authors.lastname: Ramírez-Ponce
authors.affiliation: Recent graduate, Licenciatura en Biología, Facultad de Ciencias, UNAM, Mexico City, Mexico.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Garfias-Lozano
authors.affiliation: Instituto de Biología, UNAM, Departamento de Zoología, Mexico City, Mexico.
authors.forename: Atilano
authors.initials: A
authors.lastname: Contreras-Ramos
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049628:Body Size; D005260:Female; D006257:Head / Q000033:anatomy & histology / Q000502:physiology; D007313:Insecta / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D025341:Principal Component Analysis; D012727:Sex Characteristics