A Critique of "Bromeliales, Related Monocots, and Resolution of Relationships among Bromeliaceae Subfamilies" Source: Systematic Botany, Vol. 13, No. 4 (Oct. - Dec., 1988), pp. 610-619 Published by: American Society of Plant Taxonomists Stable URL: http://www.jstor.org/stable/2419205 Accessed: 06-04-2016 16:20 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. American Society of Plant Taxonomists is collaborating with JSTOR to digitize, preserve and extend access to Systematic Botany This content downloaded from 130.191.17.38 on Wed, 06 Apr 2016 16:20:32 UTC All use subject to http://about.jstor.org/terms Systematic Botany (1988), 13(4): pp. 610-619 ? Copyright 1988 by the American Society of Plant Taxonomists Commentaries A Critique of "Bromeliales, Related Monocots, and (length = 23) and has the highest consistency index Resolution of Relationships among Bromeliaceae (C.I. = 0.957) is that seen in figure lb, in which out- Subfamilies." In a recent article by Gilmartin and group X is analyzed alone with the ingroup. In con- Brown (1987), the interrelationships of the three de- trast, the trees of figure lc and ld are both longer and fined subfamilies of the Bromeliaceae were studied have lower consistency indices. Thus, according to using both phenetic and cladistic analyses. It is their the reasoning of Gilmartin and Brown, because the cladistic analysis that I wish to address. As noted by cladogram of figure lb is shortest and has the highest the authors, one of the major difficulties with cladistic C.I., then the most likely sister group to the ingroup studies is determination of the evolutionary direction is taxon X and the best supported ingroup resolution (polarity) of character state transformations. The out- is (F(D,E)). However, the global analysis, including group method, which is generally accepted as that all outgroups, indicated both a different ingroup to- most valid for determining character polarity, is often pology and a different sister group (closest outgroup) problematic in that the closest outgroups of the in- to the ingroup. From an inspection of the cladogram group are usually not known with any degree of cer- at figure le, the cause of this apparent inconsistency tainty. Gilmartin and Brown do utilize outgroups in can be seen. First, an erroneous designation of the their cladistic analysis both for assessing the inter- sister group can occur if the "true" sister group (from relationships of the subfamilies of the Bromeliaceae the global analysis) shows a certain degree of con- and for determining the sister group to that family. vergence with a member of the ingroup. Because of However, I do not believe their specific methodology these convergent state changes (characters 14-18 in is valid. fig. 1), a cladistic analysis treating only that sister group Gilmartin and Brown selected ten families of mono- with the ingroup may show a greater length and low- cotyledons as the possible outgroups. This was wise er consistency index (cf. fig. ld) than one treating because the interfamilial relationships in this com- only an earlier diverging outgroup (showing less con- plex have not been definitively established (e.g., com- vergence) with the ingroup (cf. fig. lb). Thus, the pare the cladograms/phylograms of Dahlgren and occurrence of a short length and high consistency Rasmussen 1983, and Dahlgren and Bremer 1985, with index indicates only that the outgroup under consid- that of Walker 1986). The three bromeliad subfamilies eration shows little or no character convergence with were treated as separate O.T.U.'s, and a "hypothetical the ingroup; this outgroup may or may not be closely monocot ancestor" (curiously undefined in their char- related to the ingroup. Second, even when the in- acter/taxon matrix) was used to root trees. The au- group is clearly monophyletic, differing ingroup to- thors performed cladistic analyses using PAUP, ver- pologies can occur between a global analysis versus sion 2.4 (Swofford 1983) with assignment of states of one treating a single outgroup if one or more derived all twenty characters as unordered. The major meth- states are shared between the true sister group and odological error of this study is that each of the ten some (but not all) members of the ingroup. For ex- hypothetical outgroup families was treated individ- ample, in figure 1 the ingroup topology from the ually with the three bromeliad subfamilies in separate global analysis (fig. le) differs from that of figure lb, parsimony analyses. The premise of the authors was which has the shortest length and highest C.I., be- that the most likely resolution of the ingroup and of cause characters 19-20 are synapomorphic for taxa Z the sister group to the ingroup is that indicated by and D-F in figure le (with a reversal in the clade to the most parsimonious tree which is both shortest in taxon F) but, with the elimination of outgroup Z, they number of state changes and has a high (but not nec- are synapomorphic for only D and E in figure lb. essarily highest) consistency index. The flaw of this Because the possibilities both of convergence be- premise is demonstrated in the following example. tween the sister group and an ingroup member and Consider the data matrix of figure la, which lists of reversal within an ingroup clade are very possible three outgroups (X-Z), the ingroup (comprised of the (and likely to be encountered) in cladistic analyses, sub-taxa D-F), and a hypothetical ancestor (ANC). If the reasoning of Gilmartin and Brown appears faulty. a cladistic analysis is conducted in which all three The hypothetical example of figure 1 was con- putative outgroups are included, then the most par- structed to "force" the monophyly of the ingroup (D- simonious cladogram for all taxa is that of figure le. F) in all most parsimonious trees. Figure 2 shows an This cladogram indicates that outgroup Z is the sister example in which the monophyly of the ingroup is group to the ingroup and that the most parsimonious in doubt. From the data matrix of figure 2a, the most topology for the ingroup is (D(E,F)). If, however, each parsimonious cladogram in a global analysis, includ- of the outgroups is individually analyzed with the in- ing all outgroups (X-Z), is that of figure 2e. This tree group and ancestor (as done by Gilmartin and Brown), splits the pre-designated ingroup such that taxon E the resultant most parsimonious cladograms are il- is most closely related to outgroup Z and taxon D is lustrated in figures lb-d. The tree that is both shortest most closely related to outgroup Y. If each of the 610 This content downloaded from 130.191.17.38 on Wed, 06 Apr 2016 16:20:32 UTC All use subject to http://about.jstor.org/terms 1988] COMMENTARIES 611 X D E F CH AR ACTERS TAXA 1 2 3 4-13 14-18 19-20 21 22 \ C X 1 00 0 0 0 0 0 Y 1 10 0 0 0 0 1 9-20 Z 1 1 1 0 1 1 0 0 D 1 1 1 1 0 1 0 0 -13 E 1 1 1 1 0 F 1 1 1 1 0 0 1 1 C.l. = .957 ANC 0 00 0 0 0 0 0 b LENGTH =23 a ANC Z D E F Y D E F 14-18 - 3 LENGTH A29 C.I. =.917 2 ANC ANC X Y Z D E F \ \ \14-18 C\ f14518 \ \ + 19~~~-20 y ~~~~~C. I. = .733 e~~~~Z LENGTH = 30 ANC FIG. 1. a. Hypothetical data set for outgroups X-Z, ingroup taxa D-F, and ancestor ANC. b-d. Most parsimonious cladograms including ingroup, ancestor, and only outgroup X, Y, or Z. Note that figure lb has the highest consistency index (C.I.) and the smallest length. e. Most parsimonious cladograms including ingroup, ancestor, and all outgroups. Note different topologies of ingroup as compared to figure lb. C = convergence; R = reversal. (The change for character #21 in fig. lb and lc and that for character #22 in fig. lc can be explained with equal parsimony by a single apomorphic event followed by a subsequent reversal.) outgroups is treated individually with the ingroup, be accepted over the others as showing the most likely however, the resultant most parsimonious clado- interrelationships of the ingroup. Thus, in this ex- grams are those of figure 2b-d. The cladogram of ample, they would argue both that the ingroup is figure 2b is shortest and has the highest consistency monophyletic and that taxon X is the sister group to index and would, by the logic of Gilmartin and Brown, the ingroup; however, the most parsimonious global This content downloaded from 130.191.17.38 on Wed, 06 Apr 2016 16:20:32 UTC All use subject to http://about.jstor.org/terms 612 SYSTEMATIC BOTANY [Volume 13 X D E F CHARACTERS TAXA 1 2 3-7 8-12 13 14 15-16 15- 1 3 X 1 0 0 0 0 0 0 Y 1 1 0 1 1 0 \ 8-10 37 Z 1 1 1 0 0 1 1 D 1 0 1 0 0 1 E 1 1 0 1 0 F 1 1 1 0 1 0 0 ANC 0 0 0 0 0 0 0 b LENGTH =16 a ANC Y D E F D E Z F C~~~~~~~~~~~~~~~~~~~~~~~51 \/ ~~~C.1.