Statistical approaches to assess intraspecific variations of morphological continuous characters: the case study of the family Phytoseiidae (Acari: Mesostigmata)

Abstract

Statistical methods for delimiting species with morphological data remain woefully understudied. The present study presents statistical approaches to study the intraspecific variations of continuous characters used in species diagnosis. For this, the data set comprised 14 species of the mite family Phytoseiidae (Acari: Mesostigmata) and 23 continuous characters (seta lengths). The statistical approaches aim to determine (i) how intraspecific variations differ depending on the characters and species considered, and (ii) how to choose the number of specimens to be considered for characterizing intraspecific boundaries. The means of the related confident limits at 95% (rCL95) of the 14 species and the 23 setae are around 20%, suggesting that 95% of the specimens of a same species are included in the interval mu +/- 0.2 mu. No relationship was found between seta variations and the number of specimens considered for each species, nor for seta variations and their position on the mite body. However, a correlation between seta lengths and rCL95 means was observed. An abacus was proposed to determine the coefficient that must be applied to mean seta length to calculate the lower and upper limits of the interval that will include 95% of the specimens of a same species. The higher the precision around the mean, the higher the number of specimens considered. Furthermore, this number varies considerably depending on the characters and species considered for high precisions. However, for a priori error around the mean of 15%, the number of specimens needed to characterize the intraspecific variation is quite homogeneous and ten specimens would be required. I discuss the utility of such results to resolve some persistent problems in the alpha-taxonomy of the family Phytoseiidae but also of other taxa. (c) The Willi Hennig Society 2012

New Phytoseiid mites of the FrenchWest Indies, with description of a new species, and new records (Acari: Mesostigmata)

“…The measurements of the single specimen collected fit rather well the measurements given by Denmark and Muma (1989). All the setae are however slightly longer, but at maximum less than 10 % of variation, which is less than the threshold of 20 % around the mean defined by Tixier (2012) to characterize intraspecific variations.…”

“…The measurements of five (4 ♀ and 1 ♂) of the nine specimens collected fit rather well the measurements given by Denmark et al (1999). All setae are however slightly shorter, between 1 and 5 for the greater, which represent less than 10 % of variation, which is less than the intraspecific of 20 % around the mean defined by Tixier (2012). The measurements of the single adult male presently found are as follow: dorsal shield sclerotized and reticulated, dorsal shield length 245, width 162, 2 solenostome (gd 1, 2, 6, 8 and 9), j1 15, j3 25, j4 7, j5 7, j6 9, J2 10, J5 8, z2 10, z4 12, z5 7, Z1 9, Z4 38, Z5 58, s4 32, S2 14, S4 12, S5 9, r3 13, R1 8, all setae smooth except Z4 and Z5, st1-st1 49, st2-st2 55, st1-st3 59, st1-st5 103.…”

“…The measurements of the single specimen collected fit rather well the measurements given by De Leon (1967) and by Denmark et al (1999). All setae are however slightly shorter, between 1 and 5 µm, which represent less than 10 % of variation, which is less than the intraspecific variation of 20 % around the mean defined by Tixier (2012). In addition, Denmark et al (1999) mentioned that T. amilus is a species submitted to variation in lengths of setae.…”

Phytophagous and predatory mites on olive trees in Tunisia. Catalogue, description of one new species and key for identification (Acari, Eriophyidae, Tetranychidae, Tenuipalpidae and Phytoseiidae)

“…Euseius gallicus also feeds on pollen and on spider mites, tarsonemid mites and eggs of various insect pests (Pijnakker 2014 Note -As most species of the genus Euseius, this species also develops on pollen. It was collected on a wide range of plants, generally on deciduous plants (Tixier et al 2013). Note -this species has a wide distribution in Africa and around the Mediterranean Sea on a great variety of plants (McMurtry 1977;Papaioannou et al 1994;Swirski and Amitai 1997;Grissa-Lebdi 2003;Sahraoui et al 2012).…”

“…Note -This species has been reported on a wide range of plants, essentially on herbaceous plants. It is reared and sold by several bio-factories in the world (Tixier et al 2013). It is a very efficient natural enemy of T. urticae especially in greenhouses (Van Lenteren and Woets 1988).…”