A phylogenetic analysis for the South-east Asian mite harvestman family Stylocellidae (Opiliones : Cyphophthalmi) – a combined analysis using morphometric and molecular data

Abstract

In an effort to place type specimens lacking molecular data into a phylogenetic framework ahead of a taxonomic revision, we used morphometric data, both alone and in combination with a molecular dataset, to generate phylogenetic hypotheses under the parsimony criterion for 107 members of the South-east Asian mite harvestman family Stylocellidae (Arachnida: Opiliones: Cyphophthalmi). For the morphometric analyses, we used undiscretised characters, analysed for independence and collapsed by principal components analysis (PCA) when dependent. Two challenges not previously encountered in the use of this method were (a) handling terminals with missing data, necessitated by the inclusion of old and damaged type specimens, and (b) controlling for extreme variation in size. Custom scripts for independence analysis were modified to accommodate missing data whereby placeholder numbers were used during PCA for missing measurements. Size was controlled in four ways: choosing characters that avoided misleading size information and were easily scaled; using only locally scaled measurements; adjusting ratios by y-intercepts; and collapsing dependent characters into one. These steps removed enough size information that miniaturised and large species, suspected from molecular and discrete morphological studies to be closely related, were closely placed using morphometric data alone. Both morphometric and combined analyses generated relationships that positioned type specimens in agreement with taxonomic expectations and our knowledge of the family from prior studies. The hypotheses generated here provide new direction in linking molecular analyses with established taxonomy in this large group of South-east Asian arachnids.