searchable PDF - Association for Mexican Cave Studies

elated species IS probably best interpreted as aparallelism.28) Stylar apophysis (SA) ongm. The SA ofmost species originates laterally on the stylus (Figs.77, 84, 88, 96, 107, 116, 120, 136, 164). In thespinoperea infragroup (except T. homi, Fig. 201)the SA is clearly in a more ventral position (Figs.169, 177, 180, 187), which is considered derived.29) Ventral plate setae number. The lowestnumber of < 15 setae per prong is found in Banksulaand the species of the bifureata and kokoweefgroups (Figs. 5, 6, 15, 27, 41, 42-47); the highest(> 25), apparently derived, in the brevidenta andspinoperea infragroups (Figs. 160-164, 169, 177,181, 188,200).The character transformations were studied withthe help of MacClade (Maddison and Maddison,1987). The preferred tree (Table 1) has a length of96 steps and a character index of 0.50.Some ambiguities exist within the mulaiki speciesgroup. The relationships within the mulaiki subgroupare uncertain as two characters, 23 (PSLshape) and 24 (palpal megaspines), cluster the mulaikiand longistyla infragroups whereas a third (22,S shape) clusters the mulaiki and bilobata infragroups.This problem may be resolved as additionaland fresh material of T. bilobata becomes availableto permit more detailed examination of that unusualspecies. The relationships of the three species in themulaiki infragroup are likewise unresolved. However,the form of the SA varies among the threespecies (see discussion under the infragroup) and themost strongly developed SA tooth in T. mulaikimay be plesiomorphic. Finally, the spinop'erea infragroup,with the exception of the synapomorphiesfor T. fendi and homi (10, reduced TrIV spur; 15,absence of POP; 22, tubular S; 23, attenuated PSL)is unresolved. However, the high number (11) andbiserial arrangement (12) of the AT in T. diplospinasuggests plesiomorphy.BIOGEOGRAPHYThe species of Texella are strongly allopatric intheir distribution and closely resemble the westernNearctic phalangodid genera recently studied. Thebifureata and kokoweef groups are Californian andoccur at the extreme parts of the state, both spatiallyand ecologically (Map 1). Markedly disjunct is themulaiki group (Maps 2, 5) which occurs in SE NewMexico and adjacent Texas (longistyla infragroup)and central Texas (all remaining species). With oneexception, all species are geographically isolated, asare all higher level clusters, from infragroup tospecies group. This high degree of disjunction immediatelysuggests a vicariant model of speciation.The presumed barriers, and their relative appearance,are immediately evident (Map 3). Given ourphylogenetic interpretation, the initial barrierswould have been in what is now California: the firstbarrier separating Texella from Banksula (currentlyrestricted to caves of the central Sierran foothills;see map in Briggs and Ubick, 1981); the secondseparating T. bifureata from the kokoweef group; thethird separating the Californian species from the mulaikigroup. All subsequent barriers would havebeen in Texas, the fourth isolating the brevistylasubgroup and the fifth separating the mulaiki andreddelli subgroups.Of some interest, but of uncertain significance, isthe fact that the relatively plesiomorphic elements(Banksula and T. bifureata) occur on presumed exoticterranes, whereas the relatively apomorphicelements (all remaining Texella) occur on the NorthAmerican Plate (Silberling et aI., 1984).However, some dispersal is nonetheless requiredto arrive at the present distribution, as indicated bythe single instance of sympatry: that of T. mulaikiwith diplospina and renkesae. Interestingly, theformer species is the most troglomorphic, whereasthe others (especially T. diplospina) are the leasttroglomorphic of all cavernicolous Texella. Giventhe presumably lower dispersal potential of troglobites,the simplest hypothesis requires the dispersalof the two species of the spinoperea infragroup intothe range of T. mulaiki.TROGLOMORPHYOver two thirds of the species of Texella occur incaves and, as expected, show at least some morphologicalmodification to that environment. The severaltroglomorphic characters identified in Texella(most of which are given in Table 2) appear torepresent four basic types:1) Appendage elongation. The most apparenttroglomorphy is leg elongation. To remove the effectsof body size on leg length the ratio of leg IIlength (the longest leg) to the scute length (whichexhibits less intraspecific variation than the totalbody length) was used. The lowest LII/SL valuesare found in epigean species (2.3-3.1, except for 3.4in T. desertieola); the longest in the mulaiki infragroup(LII/SL = 9.9-15.3), T. reyesi (4.3-8.7), andT. welbourni (4.6), the species here consideredtroglobites. Intermediate leg lengths occur in allremaining (cavernicolous) species (3.2-4.3) exceptfor T. brevistyla and diplospina which have shorter165