Outline-Based Morphometrics, an Overlooked Method in Arthropod Studies? Infect
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MEEGID 2043 No. of Pages 10, Model 5G 12 August 2014 Infection, Genetics and Evolution xxx (2014) xxx–xxx 1 Contents lists available at ScienceDirect Infection, Genetics and Evolution journal homepage: www.elsevier.com/locate/meegid 5 6 3 Outline-based morphometrics, an overlooked method in arthropod 4 studies? a,⇑ b c d d e 7 Q1 Jean-Pierre Dujardin , D. Kaba , P. Solano , M. Dupraz , K.D. McCoy , N. Jaramillo-O 8 a IRD, UMR IRD–CIRAD INTERTRYP, Campus international de Baillarguet, Montpellier, France 9 b Institut Pierre Richet, Bouake, Côte d’Ivoire 10 c IRD, UMR IRD–CIRAD INTERTRYP, CIRDES, Bobo-Dioulasso, Burkina Faso 11 d MIVEGEC, UMR 5290 IRD-CNRS, Centre IRD, Montpellier, France 12 e Instituto de Biologia, University of Antioquía, Medellin, Colombia 13 14 article info abstract 1630 17 Article history: Modern methods allow a geometric representation of forms, separating size and shape. In entomology, as 31 18 Received 9 April 2014 well as in many other fields involving arthropod studies, shape variation has proved useful for species 32 19 Received in revised form 25 July 2014 identification and population characterization. In medical entomology, it has been applied to very specific 33 20 Accepted 31 July 2014 questions such as population structure, reinfestation of insecticide-treated areas and cryptic species 34 21 Available online xxxx recognition. For shape comparisons, great importance is given to the quality of landmarks in terms of 35 comparability. Two conceptually and statistically separate approaches are: (i) landmark-based 36 22 Keywords: morphometrics, based on the relative position of a few anatomical ‘‘true’’ or ‘‘traditional’’ landmarks, 37 23 Modern morphometrics and (ii) outline-based morphometrics, which captures the contour of forms through a sequence of close 38 24 Landmarks 25 Outlines ‘‘pseudo-landmarks’’. 39 26 Arthropods Most of the studies on insects of medical, veterinary or economic importance make use of the landmark 40 27 Cryptic species approach. The present survey makes a case for the outline method, here based on elliptic Fourier analysis. 41 28 Population structure The collection of pseudo-landmarks may require the manual digitization of many points and, for this rea- 42 29 son, might appear less attractive. It, however, has the ability to compare homologous organs or structures 43 having no landmarks at all. This strength offers the possibility to study a wider range of anatomical struc- 44 tures and thus, a larger range of arthropods. 45 We present a few examples highlighting its interest for separating close or cryptic species, or charac- 46 terizing conspecific geographic populations, in a series of different vector organisms. In this simple appli- 47 cation, i.e. the recognition of close or cryptic forms, the outline approach provided similar scores as those 48 obtained by the landmark-based approach. 49 Ó 2014 Published by Elsevier B.V. 50 51 52 53 54 1. Introduction (or ‘‘anatomical’’, or ‘‘traditional’’) landmarks. True landmarks are 66 considered homologous. Homology here refers to the positional 67 55 Contrary to classical morphology, the main objective of mor- equivalence of a small biological structure, as small as a point at 68 56 phometrics is not to describe organisms, but to compare them. the requisite scale. The level of homology of a landmark is gov- 69 57 Because of the geometric constraints of modern morphometrics, erned by the precision with which it can be localized from one 70 58 data are generally collected on a non-articulated part, often a sin- organism to another. Thus, true, anatomical landmarks are homol- 71 59 gle organ (but see David et al. (1996) and Adams (1999)). A few ogous in the sense that they are relocatable points, and according 72 60 characters are enough, provided that they are homologous. to this criterion various levels of homology have been recognized 73 61 Insect species studies generally made use of the wings because (see type I, II and III landmarks, Bookstein (1991)). A special devel- 74 62 these structures are almost bidimensional and relatively rigid, opment of type III landmarks, called ‘‘semi-landmarks’’ (also ‘‘slid- 75 63 reducing digitizing error; also, importantly, because the wings of ing semi-landmarks’’) allows the description of curved lines 76 64 many groups of insects provide a large number of landmarks. between two classical landmarks (Bookstein, 1997). 77 65 Not only are they many, they also are of good quality, called ‘‘true’’ Anatomical, true landmarks are opposed to ‘‘pseudo-land- 78 marks’’ used in the outline-based approach. Pseudo-landmarks 79 ⇑ Corresponding author. describing contours or boundary outlines do not depend on the 80 Q1 E-mail address: [email protected] (J.-P. Dujardin). presence of true anatomical landmarks, they can exist with no 81 http://dx.doi.org/10.1016/j.meegid.2014.07.035 1567-1348/Ó 2014 Published by Elsevier B.V. Q1 Please cite this article in press as: Dujardin, J.-P., et al. Outline-based morphometrics, an overlooked method in arthropod studies? Infect. Genet. Evol. (2014), http://dx.doi.org/10.1016/j.meegid.2014.07.035 MEEGID 2043 No. of Pages 10, Model 5G 12 August 2014 Q1 2 J.-P. Dujardin et al. / Infection, Genetics and Evolution xxx (2014) xxx–xxx 82 anatomical landmark at all, or can include one or more of them. the field, there is frequently some size overlap, so specimens col- 144 83 Obviously, pseudo-landmarks are of another nature than true land- lected from trees are assumed to be R. robustus, and those collected 145 84 marks: comparability is not expected from them separately, but from houses are assumed to be R. prolixus. Our material contains 146 85 from the structure they describe. Thus, if carefully chosen, like three groups previously identified by molecular tools (Monteiro 147 86 the mandible of a beetle, the genital paramere of a sandfly or an et al., 2003): one is R. prolixus from houses in the Pampanito village 148 87 internal cell of the wing, a contour represents an homologous (State of Trujillo, Venezuela), the second one is R. prolixus from 149 88 structure allowing interindividual and/or intergroup comparisons. palm trees collected in another locality, San José Tiznados (State 150 89 It is quite possible to develop both approaches on the same of Guárico, Venezuela), and the last one is R. robustus from two 151 90 organ (Baylac and Frieß, 2005). One can see the wings of an insect localities of Venezuela: Pampanito and Candelaria (State of 152 91 as a configuration of anatomical landmarks, but the wing can be Trujillo). 153 92 seen also as an assemblage of closed contours, i.e. the internal cells We performed analyzes both combining the two R. prolixus hab- 154 93 designated by the intersecting veins (Francoy et al., 2012). More- itats, as well as the two R. robustus origins, into single samples and 155 94 over, other anatomical parts, because they are generally deficient considering them as separated groups. A total of 7 landmarks could 156 95 in true landmarks, are only amenable to an outline analysis. For be used, thus excluding the eighth used in Feliciangeli et al. (2007) 157 96 instance, many insect species, including very close species, are sep- because of the inconsistency of the clavum position on the pic- 158 97 arated by the shape of some genital pieces. Such parts often lack tures. The outline submitted to the elliptical Fourier analysis 159 98 anatomical landmarks, like the paramere of sandflies, the prono- (EFA, see Section 2.2.2) contained 5 of them, as well as the external 160 99 tum of Coleoptera (Faille et al., 2007), the genital leaflet of Culex boundary of the membranous part of the wing (Fig. 1). 161 100 neavei (Boussès et al., 2013; Garros and Dujardin, 2013) or the 101 mandible parts of beetles (Tatsuta et al., 2009). Eggs and juvenile 2.1.2. Glossina palpalis palpalis and Glossina palpalis gambiensis 162 102 instars which also provide important taxonomic characters gener- G. p. palpalis (Robineau-Desvoidy), 1830 and G. p. gambiensis 163 103 ally lack acceptable configurations of true landmarks: they can be Vanderplank 1949 (Diptera: Glossinidae) are important vectors of 164 104 considered through outline analyzes. Also good or natural candi- sleeping sickness in West Africa. Both species hybridize readily in 165 105 dates for the outline approach are the many wingless forms of the laboratory but hybridized females produce fewer offspring 166 106 insects, as for instance fleas, lice, ants, many of them of great vet- and hybrid males are sterile (Gooding, 1988). These two subspecies 167 107 erinary, medical or agronomic importance. Finally, arthropods are difficult to separate on morphological ground. Although males 168 108 other than insects may present poorly defined landmarks but a show consistent differences in the terminal dilatation of inferior 169 109 particular anatomy which can be submitted to outline analyzes, claspers of their genitalia (Machado, 1954), morphological differ- 170 110 as for instance the rounded body of ticks. In sum, the outline entiation of female flies is not conclusive. The material we used 171 111 approach offers the possibility to study a wider range of organs, here is from Ivory Coast and was collected in 2007. Male and 172 112 along with a wider range of arthropods. female specimens of G. p. palpalis were collected in Aniassue, South 173 113 The question is not limited however to technical considerations of Ivory Coast. The G. p. gambiensis specimens came from Ganse, 174 114 about presence or absence of landmarks (Rohlf, 1986), it also con- North of Ivory Coast. The subspecies identity of all the female 175 115 cerns the biological relevance of outlines.