title: Outline-based morphometrics, an overlooked method in arthropod studies?
abstract: Modern methods allow a geometric representation of forms, separating size and shape. In entomology, as well as in many other fields involving arthropod studies, shape variation has proved useful for species identification and population characterization. In medical entomology, it has been applied to very specific questions such as population structure, reinfestation of insecticide-treated areas and cryptic species recognition. For shape comparisons, great importance is given to the quality of landmarks in terms of comparability. Two conceptually and statistically separate approaches are: (i) landmark-based morphometrics, based on the relative position of a few anatomical "true" or "traditional" landmarks, and (ii) outline-based morphometrics, which captures the contour of forms through a sequence of close "pseudo-landmarks". Most of the studies on insects of medical, veterinary or economic importance make use of the landmark approach. The present survey makes a case for the outline method, here based on elliptic Fourier analysis. The collection of pseudo-landmarks may require the manual digitization of many points and, for this reason, might appear less attractive. It, however, has the ability to compare homologous organs or structures having no landmarks at all. This strength offers the possibility to study a wider range of anatomical structures and thus, a larger range of arthropods. We present a few examples highlighting its interest for separating close or cryptic species, or characterizing conspecific geographic populations, in a series of different vector organisms. In this simple application, i.e. the recognition of close or cryptic forms, the outline approach provided similar scores as those obtained by the landmark-based approach.
authors.affiliation: IRD, UMR IRD-CIRAD INTERTRYP, Campus international de Baillarguet, Montpellier, France. Electronic address: dujardinbe@gmail.com.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Dujardin
authors.affiliation: Institut Pierre Richet, Bouake, Côte d'Ivoire.
authors.forename: D
authors.initials: D
authors.lastname: Kaba
authors.affiliation: IRD, UMR IRD-CIRAD INTERTRYP, CIRDES, Bobo-Dioulasso, Burkina Faso.
authors.forename: P
authors.initials: P
authors.lastname: Solano
authors.affiliation: MIVEGEC, UMR 5290 IRD-CNRS, Centre IRD, Montpellier, France.
authors.forename: M
authors.initials: M
authors.lastname: Dupraz
authors.affiliation: MIVEGEC, UMR 5290 IRD-CNRS, Centre IRD, Montpellier, France.
authors.forename: K D
authors.initials: KD
authors.lastname: McCoy
authors.affiliation: Instituto de Biologia, University of Antioquía, Medellin, Colombia.
authors.forename: N
authors.initials: N
authors.lastname: Jaramillo-O
mesh_terms: D000818:Animals; D001181:Arthropods / Q000033:anatomy & histology* / Q000145:classification*; D004772:Entomology / Q000379:methods*
keywords: Arthropods; Cryptic species; Landmarks; Modern morphometrics; Outlines; Population structure