Clade stability and the addition of data: A case study from erigonine spiders (Araneae: Linyphiidae, Erigoninae)

Abstract

This study presents a new phylogeny of erigonine spiders with emphasis on genera from the Neotropics. Thirty-nine exemplar taxa representing mostly Neotropical genera were added to a global sample of 31 erigonine and 12 outgroup exemplar taxa analyzed in a previous study. These 82 taxa were coded for 176 (172 informative) mostly morphological characters. Eighty-one characters were identical to or modified from the 73 (67 informative) characters included in a previous study; the remaining 95 characters are new. The complete data set includes 70 erigonine exemplars representing 65 genera, seven nonerigonine linyphiid exemplars, and five exemplars representing four araneoid families in the outgroup. Cladistic analysis resulted in a single most parsimonious tree (L ¼ 904, CI ¼ 0.23, RI ¼ 0.58; uninformative characters excluded: L ¼ 900, CI ¼ 0.23). This paper explores the implications of the new topology for the evolution of several characters of interest in erigonine evolution. The phylogeny implies that the desmitracheate condition is a synapomorphy of erigonines, with a reversal to the haplotracheate condition in one large clade within Erigoninae. We infer that the loss of the paracymbium in Neotropical erigonines occurred twice and may have progressed by different evolutionary pathways. Our phylogeny differs markedly from the previous cladistic hypothesis of erigonine relationships. We investigate how the addition of characters and taxa (alone and together) have altered the earlier hypothesis of erigonine phylogeny. We conclude that topological changes from the previous study to the current one are largely the result of adding and modifying characters, not adding taxa. Continuous Jackknife Function (CJF) analysis predicts that the inclusion of additional character data will continue to imply changes in the relationships among taxa in our analysis.

The female genitalic morphology of “micronetine” spiders (Araneae, Linyphiidae)

“…Furthermore, the illustrations of linyphiid vulvae provided by Millidge (1984Millidge ( , 1993 and those of Orsonwelles by Hormiga (2002) reveal that the basal part of the spermatheca is more or less spiraled with the copulatory and the fertilization ducts (grooves). Based on the strong support for the monophyly of Linyphiidae (Hormiga 1994(Hormiga , 2000Miller and Hormiga 2004;Arnedo et al 2009) Results of the present study suggest that in ''micronetines'' and erigonines the spermathecae, as the only connection between the copulatory and the fertilization grooves, may be partially derived from the groove itself (arrow indicates the proximal end of fertilization groove). CG copulatory groove, DP dorsal plate, FG fertilization groove, MP median plate, S spermatheca, S 1 upper chamber of spermatheca, S 2 lower chamber of spermatheca, SG special gland, VP ventral plate (Figs.…”

“…In ''micronetines'' the scape is a projection of the ventral wall (double layer) of the epigynal cavity and it is usually furnished with an apical pit which houses the suprategular apophysis of the male palp during copulation (Saaristo 1975(Saaristo , 1977van Helsdingen 1965). Ventral plate scapes seem to have evolved independently more than once in linyphiids (Arnedo et al 2009;Hormiga 2000;Miller and Hormiga 2004). In addition some linyphiids have a scape on the dorsal plate.…”

“…4g). Hormiga (2000) and Miller and Hormiga (2004) reported divided spermathecae (two pairs) in two other erigonine species, but coded it as absent in all other linyphiid groups in their character matrices. In light of the observations reported here, it is clear that their character coding/scoring should be corrected-e.g., the erigonine Tmeticus should be coded as having the same state than Tenuiphantes, that is, two chamber spermathecae.…”

“…Studies of genitalia have also provided a rich source of phylogenetic information for reconstructing evolutionary relationships (e.g., Á lvarez-Padilla 2007; Agnarsson 2004;Coddington 1986Coddington , 1990Coddington , 2005Coddington and Levi 1991;Hormiga 1994Hormiga , 2000Hormiga and Scharff 2005;Griswold et al 1998Griswold et al , 2005Kuntner et al 2008;Miller and Hormiga 2004). However, in contrast with male palpal morphology, which has played a critical role in phylogenetic studies and often dominates character data matrices, very limited detailed information on female genitalia is available.…”

“…By integrating data both from SEM and transmitted light microscopy we can interpret the morphology of the epigynum in ''micronetines''. We have assessed the phylogenetic implications of epigynal morphology in the ''micronetine-erigonine'' clade based on comparisons across the species examined here and those described and illustrated from other linyphiid groups by previous studies (Millidge 1984(Millidge , 1993Hormiga 2000;Miller and Hormiga 2004;Miller 2007).…”