Syst. Biol. 51(1) 2002

Buckley et al.

Abstract.—We have applied Bayesian and maximum likelihood methods of phylogenetic estimation to data from four mitochondrial genes (COI, COII, 12S, and 16S) and a single nuclear gene (EF1f) from several genera of New Zealand, Australian, and New Caledonian cicada taxa. We specifically focused on the heterogeneity of phylogenetic signal among the different data partitions and the biogeographic origins of the New Zealand cicada fauna. The Bayesian analyses circumvent many of the problems associated with other statistical tests for comparing data partitions. We took an information-theoretic approach to model selection based on the Akaike Information Criterion (AIC). This approach indicated that there was considerable uncertainty in identifying the best-fit model for some of the partitions. Additionally, a large amount of uncertainty was associated with many parameter estimates from the substitution model. However, a sensitivity analysis on the combined dataset indicated that the model selection uncertainty had little effect on estimates of topology because these estimates were largely insensitive to changes in the assumed model. This outcome suggests strong signal in our data. Our analyses support a New Caledonian affiliation of the New Zealand cicada genera Maoricicada, Kikihia, and Rhodopsalta and Australian affinities for the genera Amphipsalta and Notopsalta. This result was surprising, given that previous cicada biologists suspected a close relationship between Amphipsalta, Notopsalta, and Rhodopsalta based on genitalic characters. Relationships among the closely related genera Maoricicada, Kikihia, and Rhodopsalta were poorly resolved, the mitochondrial data and the EF1f data favoring different arrangements within this clade.

Dowton and Austin

Abstract.—Comprehensive phylogenetic analyses utilize data from distinct sources, including nuclear, mitochondrial, and plastid molecular sequences and morphology. Such heterogeneous datasets are likely to require distinct models of analysis, given the different histories of mutational biases operating on these characters. The incongruence length difference (ILD) test is increasingly being used to arbitrate between competing models of phylogenetic analysis in cases where multiple data partitions have been collected. Our work suggests that the ILD test is unlikely to be an effective measure of congruence when two datasets differ markedly in size. We show that models that increase the contribution of one data partition over another are likely to increase congruence, as measured by this test. More alarmingly, for many bipartition comparisons, character congruence increases bimodally - either increasing or decreasing the contribution of one data partition will increase congruence - making it impossible to arrive at a single optimally congruent model of analysis.

Hahn

Abstract.— Notoriously slow rates of molecular evolution and convergent evolution among some morphological characters have limited phylogenetic resolution for the palm family (Arecaceae). This study adds nuclear DNA (18S SSU rRNA) and chloroplast DNA (cpDNA; atpB and rbcL) sequence data for 65 genera of palms and characterizes molecular variation for each molecule. Phylogenetic relationships were estimated with maximum likelihood and maximum parsimony techniques for the new data and for previously published molecular data for 45 palm genera. Maximum parsimony analysis was also used to compare molecular and morphological data for 33 palm genera. Incongruence among datasets was detected between cpDNA and 18S data and between molecular and morphological data. Most conflict between nuclear and cpDNA data was associated with the genus Nypa. Several taxa showed relatively long branches with 18S data, but phylogenetic resolution of these taxa was essentially the same for 18S and cpDNA data. Base composition bias for 18S that contributed to erroneous phylogenetic resolution in other taxa did not seem to be present in Palmae. Morphological data were incongruent with all molecular data due to apparent morphological homoplasy for Caryoteae, Ceroxyloideae, Iriarteae, and Thrinacinae. Both cpDNA and nuclear 18S data firmly resolved Caryoteae with Borasseae of Coryphoideae, suggesting that at least some morphological characters used to place Caryoteae in Arecoideae are homoplastic. In this study, increased character sampling seems to be more important than increased taxon sampling; a comparison of the full (65-taxon) and reduced (45- and 33-taxon) datasets suggests little difference in core topology but considerably more nodal support with the increased character sample sizes. These results indicate a general trend toward a stable estimate of phylogenetic relationships for the Palmae. Although the 33-taxon topologies are even better resolved, they lack several critical taxa and are affected by incongruence between molecular and morphological data. As such, a comparison of results from the 45- and 33-taxon trees offers the best available reference for phylogenetic inference on palms.

Huelsenbeck et al.

Abstract.—Phylogenetic trees can be rooted by a number of criteria. Here, we introduce a Bayesian method for inferring the root of a phylogenetic tree by using one of several criteria: the outgroup, molecular clock, and nonreversible model of DNA substitution. We perform simulation analyses to examine the relative ability of these three criteria to correctly identify the root of the tree. The outgroup and molecular clock criteria were best able to identify the root of the tree, whereas the nonreversible model was able to identify the root only when the substitution process was highly nonreversible. We also examined the performance of the criteria for a tree of four species for which the topology and root position are well supported. Results of the analyses of these data are consistent with the simulation results.

Leaché and Reeder

Abstract.— Phylogenetic analysis of large datasets using complex nucleotide substitution models under a maximum likelihood framework can be computationally infeasible, especially when attempting to infer confidence values by way of nonparametric bootstrapping. Recent developments in phylogenetics suggest the computational burden can be reduced by using Bayesian methods of phylogenetic inference. However, few empirical phylogenetic studies exist that explore the efficiency of Bayesian analysis of large datasets. To this end, we conducted an extensive phylogenetic analysis of the wide-ranging and geographically variable Eastern Fence Lizard (Sceloporus undulatus). Maximum parsimony, maximum likelihood, and Bayesian phylogenetic analyses were performed on a combined mitochondrial DNA dataset (12S and 16S rRNA, ND1 protein-coding gene, and associated tRNA; 3,688 bp total) for 56 populations of S. undulatus (78 total terminals including other S. undulatus group species and outgroups). Maximum parsimony analysis resulted in numerous equally parsimonious trees (82,646 from equally weighted parsimony and 335 from weighted parsimony). The majority rule consensus tree derived from the Bayesian analysis was topologically identical to the single best phylogeny inferred from the maximum likelihood analysis, but required ~80% less computational time. The mtDNA data provide strong support for the monophyly of the S. undulatus group and the paraphyly of "S. undulatus" with respect to S. belli, S. cautus, and S. woodi. Parallel evolution of ecomorphs within "S. undulatus" has masked the actual number of species within this group. This evidence, along with convincing patterns of phylogeographic differentiation suggests "S. undulatus" represents at least four lineages that should be recognized as evolutionary species.

Salamin et al.

Abstract. Large and comprehensive phylogenetic trees are desirable for studying macroevolutionary processes and for classification purposes. Such trees can be obtained in two different ways. Either the widest possible range of taxa can be sampled and used in a phylogenetic analysis to produce a "big tree," or preexisting topologies can be used to create a supertree. Although large multigene analyses are often favored, combinable data are not always available, and supertrees offer a suitable solution. The most commonly used method of supertree reconstruction, matrix representation with parsimony (MRP), is presented here. We used a combined data set for the Poaceae to (1) assess the differences between an approach that uses combined data and one that uses different MRP modifications based on the character partitions and (2) investigate the advantages and disadvantages of these modifications. Baum and Ragan and Purvis modifications gave similar results. Incorporating bootstrap support associated with pre-existing topologies improved Baum and Ragan modification and its similarity with a combined analysis. Finally, we used the supertree reconstruction approach on 55 published phylogenies to build one of most comprehensive phylogenetic trees published for the grass family including 403 taxa and discuss its strengths and weaknesses in relation to other published hypotheses.

Salzburger et al.

Abstract.—Lake Tanganyika, the oldest of the East African Great Lakes, harbors the ecologically, morphologically, and behaviorally most complex of all assemblages of cichlid fishes, consisting of about 200 described species. The evolutionary old age of the cichlid assemblage, its extreme degree of morphological differentiation, the lack of species with intermediate morphologies, and the rapidity of lineage formation have made evolutionary reconstruction difficult. The number and origin of seeding lineages, particularly the possible contribution of riverine haplochromine cichlids to endemic lacustrine lineages, remains unclear. Our phylogenetic analyses, based on mitochondrial DNA sequences of three gene segments of 49 species (25% of all described species, up to 2,400 bp each), yield robust phylogenies that provide new insights into the Lake Tanganyika adaptive radiation as well as into the origin of the Central- and East-African haplochromine faunas. Our data suggest that eight ancient African lineages may have seeded the Tanganyikan cichlid radiation. One of these seeding lineages, probably comprising substrate spawning Lamprologus-like species, diversified into six lineages that evolved mouthbrooding during the initial stage of the radiation. All analyzed haplochromines from surrounding rivers and lakes seem to have evolved within the radiating Tanganyikan lineages. Thus, our findings contradict the current hypothesis that ancestral riverine haplochromines colonized Lake Tanganyika to give rise to at least part of its spectacular endemic cichlid species assemblage. Instead, the early phases of the Tanganyikan radiation affected Central and East African rivers and lakes. The haplochromines may have evolved in the Tanganyikan basin before the lake became a hydrologically and ecologically closed system and then secondarily colonized surrounding rivers. Apparently, therefore, the current diversity of Central and East African haplochromines represents a relatively young and polyphyletic fauna that evolved from or in parallel to lineages now endemic to Lake Tanganyika.

Wiens and Penkrot

Abstract. Haplotype phylogenies based on DNA sequence data are increasingly being used to test traditional species-level taxonomies based on morphology. However, few studies have critically compared species limits based on morphological and DNA data, and the methods used to delimit species using either type of data are only rarely explained. In this paper, we review three approaches for species delimitation (tree-based with DNA data and tree-based and character-based with morphological data) and propose explicit protocols for each. We then compare species limits inferred from these approaches, using morphological and mtDNA data for the Yarrow's spiny lizard (Sceloporus jarrovii), a traditionally polytypic species from the southwestern United States and Mexico. All three approaches support division of S. jarrovii into five species, but only two species are the same among the three approaches. We find the greatest support for the five species that are delimited based on mtDNA data, and we argue that mtDNA data may have important (and previously unappreciated) advantages for species delimitation. Because different data and approaches can disagree so extensively, our results demonstrate that the methodology of species delimitation is a critical issue in systematics.