Figure 1.
Mating behavior and morphology in leiobunine harvestmen.
(A) Precopulatory behavior in Leiobunum vittatum. Male on left, female on right. Photograph courtesy of Joe Warfel (Eighth-Eye Photography). (B) Major phases in mating in Leiobunum verrucosum (semi-diagrammatic, legs not included for clarity).
Figure 2.
Female genital morphology in leiobunine harvestmen.
(A) Ventral surface of generalized female showing relative positions of the feeding apparatus and pregenital opening. (B) As in A, but with genital operculum removed and flipped to show the inner structures of a simple (primitive) operculum and sternum, not modified into a pregenital barrier. (C) Ventral surface of Hadrobunus maculosus from same perspective as B, showing pregenital barrier (see also Fig. 3). The large sclerotized sternum engages the opercular sclerite anteriorly and apodemal processes posteriorly. (D) Ventral surface of Leiobunum hoffmani from same perspective as B and C, showing pregenital barrier (see also Fig. 3). The anterior median notch in the sclerotized sternum engages a sclerotized median septum on the genital operculum; the posterior margin of the sternum abuts the anterior margin of the levator apodeme (based on [54]). In both C and D, a barrier is formed by a sclerotized sternum wedged between anterior and posterior elements of the genital operculum.
Figure 3.
Structures from representative sacculate and non-sacculate species of leiobunine harvestmen.
Penes are depicted from a dorsal view. The genital opercula are shown from the inner (dorsal) perspective (compare with Figs. 2B-D). All penes and opercula (right box) are drawn to the same scale; bar = 1 mm. The pedipalps are from male Leiobunum euserratipalpe and L.calcar [54]. Simple male pedipalps are roughly similar in shape and relative size to those of females. The enhanced male pedipalps (left box) depicted have femoral apophyses which are used in concert with the base of the tibia to clamp the trochanter of the female's first pair of legs during mating. See Fig. 1A for a different form of enhanced male pedipalp, in which the overall length of the pedipalps is sexually dimorphic (longer in males relative to females).
Figure 4.
Phylogenetic hypotheses and distribution of reproductive characters.
The maximum clade credibility Bayesian tree (left) was assembled using the TreeAnnotator program [31], visualized with FigTree v1.3.1 [73], and depicts relationships recovered in BEAST v1.7.1 [31] for trees that passed the backbone constraint tree (right). Values above branches indicate the posterior probabilities per node for filtered trees (n = 431). Values below braches are the posterior probabilities of the maximum clade credibility tree for a subset of 1000 random trees resampled from the original posterior probability distribution. Scale is in substitutions per site for the filtered subset maximum clade credibility tree. The most parsimonious distribution of reproductive characters (assuming no parallel gains in penile sacs) is mapped to the maximum clade credibility tree. Geographic codes are given for undescribed species: IL = Illinois, MO = Missouri, NE = Nebraska, TN = Tennessee. The backbone constraint tree (right) depicts relationships that were well supported (>95% posterior probability) in the [26] tree and that were used to generate sets of trees for the present study.
Figure 5.
Transition models used to test hypotheses for the evolution of reproductive characters with Bayesian analysis.
(A) No-precedence model of male morphological evolution versus (B) Penis precedence model, where male morphological transitions are limited to sacculate (S+) to nonsacculate (S−) penis and simple pedipalps (P−) to enhanced pedipalps (P+). The root of A was treated as fixed to S+P− (Table 1, row 3) or determined empirically (Table 1, row 1). (C) Independent and (D) dependent models of discrete male and female reproductive morphology. Here, the female pregenital barrier is coded as present (B+) or absent (B−). Both models allow for all possible character transitions. (E) No precedence model was compared to dependent model (F), where character precedence is possible. In this model, penile sac loss (S+B− →S−B−) and barrier acquisition (S+B− →S+B+) are constrained to have equal rates of evolution.
Table 1.
Model Bayes factors.