Systematics and Evolution of the Spider Family Mysmenidae
Open AccessThis thesis is the first comparative morphological study of mysmenid spiders and their close relatives. Hypotheses of primary homology are proposed, refined, and compiled into a morphological dataset of 65 taxa and almost 360 characters. DNA sequences from 81 taxa (49 mysmenids) are produced from six genes, gathering more than 5700 base pairs. The morphological and molecular datasets were combined, in a total-evidence generic-level comprehensive phylogenetic analysis that includes ca. 6100 characters scored for a total 109 taxa (74 mysmenids). Several hypotheses of primary homology, particularly at the level of male genitalia, are formulated. As circumscribed in this study, Mysmenidae is monophyletic, supported by more than 20 morphological and 440 molecular synapomorphies. Mysmenidae is also monophyletic under different analytical algorithms. Symphytognathoids is delimited to Anapidae, Mysmenidae, Symphytognathidae, Theridiosomatidae, Synaphridae and Micropholcommatinae. Four genera are removed from Mysmenidae. The composition of Mysmenidae is redelimited to eight genera and two subfamilies. Diagnostic features for symphytognathoid families are provided. The evolutionary implications of different behavioral and morphological aspects within symphytognathoids are discussed. The preferred phylogenetic hypothesis suggests a striking pattern of evolutionary changes in the anterior respiratory system, where anterior tracheae evolved from fully developed booklungs and, conversely, reduced booklungs have originated at least in two independent occasions from its homologous tracheal system. Furthermore, structurally similar booklungs might have originated from different processes of tracheal transformation. A tendency for the posterior tracheal system to become either highly complex or completely lost is suggested. No evident morphological or behavioral aspect seems to explain the remarkable diversity of respiratory arrays within symphytognathoids. In addition, no evident pattern of evolution is perceived regarding spinneret spigot conformation. The kleptoparasitic behavior appears to have a single origin within mysmenids. Also, this study supports an evolutionary scenario where the planar orbweb within symphytognathoids evolved independently two times from a three-dimensional web. Furthermore, the orbweb has been secondarily modified into a sheet or a cobweb three times. Objective diagnoses, deeper understanding of morphological and behavioral features, and natural classification of the family are based on its phylogenetic relationships, in the first attempt to redefine this so-called "waste disposal bucket" family.
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