POTENTIAL PITFALLS OF RECONSTRUCTING DEEP TIME EVOLUTIONARY HISTORY WITH ONLY EXTANT DATA,A CASE STUDY USING THE CANIDAE (MAMMALIA,CARNIVORA)

Reconstructing evolutionary patterns and their underlying processes is a central goal in biology. Yet many analyses of deep evolutionary histories assume that data from the fossil record is too incomplete to include, and rely solely on databases of extant taxa. Excluding fossil taxa assumes that character state distributions across living taxa are faithful representations of a clade's entire evolutionary history. Many factors can make this assumption problematic. Fossil taxa do not simply lead‐up to extant taxa; they represent now‐extinct lineages that can substantially impact interpretations of character evolution for extant groups. Here, we analyze body mass data for extant and fossil canids (dogs, foxes, and relatives) for changes in mean and variance through time. AIC‐based model selection recovered distinct models for each of eight canid subgroups. We compared model fit of parameter estimates for (1) extant data alone and (2) extant and fossil data, demonstrating that the latter performs significantly better. Moreover, extant‐only analyses result in unrealistically low estimates of ancestral mass. Although fossil data are not always available, reconstructions of deep‐time organismal evolution in the absence of deep‐time data can be highly inaccurate, and we argue that every effort should be made to include fossil data in macroevolutionary studies.     

Morphological and molecular evidence converge upon a robust phylogeny of the megadiverse Holometabola

We present the largest morphological character set ever compiled for Holometabola. This was made possible through an optimized acquisition of data. Based on our analyses and recently published hypotheses based on molecular data, we discuss higher‐level phylogeny and evolutionary changes. We comment on the information content of different character systems and discuss the role of morphology in the age of phylogenomics. Microcomputer tomography in combination with other techniques proved highly efficient for acquiring and documenting morphological data. Detailed anatomical information (356 characters) is now available for 30 representatives of all holometabolan orders. A combination of traditional and novel techniques complemented each other and rapidly provided reliable data. In addition, our approach facilitates documenting the anatomy of model organisms. Our results show little congruence with studies based on rRNA, but confirm most clades retrieved in a recent study based on nuclear genes: Holometabola excluding Hymenoptera, Coleopterida (= Strepsiptera + Coleoptera), Neuropterida excl. Neuroptera, and Mecoptera. Mecopterida (= Antliophora + Amphiesmenoptera) was retrieved only in Bayesian analyses. All orders except Megaloptera are monophyletic. Problems in the analyses are caused by taxa with numerous autapomorphies and/or inapplicable character states due to the loss of major structures (such as wings). Different factors have contributed to the evolutionary success of various holometabolan lineages. It is likely that good flying performance, the ability to occupy different habitats as larvae and adults, parasitism, liquid feeding, and co‐evolution with flowering plants have played important roles. We argue that even in the “age of phylogenomics”, comparative morphology will still play a vital role. In addition, morphology is essential for reconstructing major evolutionary transformations at the phenotypic level, for testing evolutionary scenarios, and for placing fossil taxa.
© The Willi Hennig Society 2010.     

Median-joining networks for inferring intraspecific phylogenies.

Reconstructing phylogenies from intraspecific data (such as human mitochondrial DNA variation) is often a challenging task because of large sample sizes and small genetic distances between individuals. The resulting multitude of plausible trees is best expressed by a network which displays alternative potential evolutionary paths in the form of cycles. We present a method ("median joining" [MJ]) for constructing networks from recombination-free population data that combines features of Kruskal's algorithm for finding minimum spanning trees by favoring short connections, and Farris's maximum-parsimony (MP) heuristic algorithm, which sequentially adds new vertices called "median vectors", except that our MJ method does not resolve ties. The MJ method is hence closely related to the earlier approach of Foulds, Hendy, and Penny for estimating MP trees but can be adjusted to the level of homoplasy by setting a parameter epsilon. Unlike our earlier reduced median (RM) network method, MJ is applicable to multistate characters (e.g., amino acid sequences). An additional feature is the speed of the implemented algorithm: a sample of 800 worldwide mtDNA hypervariable segment I sequences requires less than 3 h on a Pentium 120 PC. The MJ method is demonstrated on a Tibetan mitochondrial DNA RFLP data set.     

Integration of conflict into integrative taxonomy: fitting hybridization in species delimitation of Mesocarabus (Coleoptera: Carabidae)

In species differentiation, characters may not diverge synchronously, and there are also processes that shuffle character states in lineages descendant from a common ancestor. Species are thus expected to show some degree of incongruence among characters; therefore, taxonomic delimitation can benefit from integrative approaches and objective strategies that account for character conflict. We illustrate the potential of exploiting conflict for species delimitation in a study case of ground beetles of the subgenus Carabus (Mesocarabus), where traditional taxonomy does not accurately delimit species. The molecular phylogenies of four mitochondrial and three nuclear genes, cladistic analysis of the aedeagus, ecological niche divergence and morphometry of pronotal shape in more than 500 specimens of Mesocarabus show that these characters are not fully congruent. For these data, a three‐step operational strategy is proposed for species delimitation by (i) delineating candidate species based on the integration of incongruence among conclusive lines of evidence, (ii) corroborating candidate species with inconclusive lines of evidence and (iii) refining a final species proposal based on an integrated characterization of candidate species based on the evolutionary analysis of incongruence. This procedure provided a general understanding of the reticulate process of hybridization and introgression acting on Mesocarabus and generated the hypothesis of seven Mesocarabus species, including two putative hybrid lineages. Our work emphasizes the importance of incorporating critical analyses of character and phylogenetic conflict to infer both the evolutionary history and species boundaries through an integrative taxonomic approach.     

How phenotypic convergence arises in experimental evolution

Evolutionary convergence is a core issue in the study of adaptive evolution, as well as a highly debated topic at present. Few studies have analyzed this issue using a “real‐time” or evolutionary trajectory approach. Do populations that are initially differentiated converge to a similar adaptive state when experiencing a common novel environment? Drosophila subobscura populations founded from different locations and years showed initial differences and variation in evolutionary rates in several traits during short‐term (～20 generations) laboratory adaptation. Here, we extend that analysis to 40 more generations to analyze (1) how differences in evolutionary dynamics among populations change between shorter and longer time spans, and (2) whether evolutionary convergence occurs after 60 generations of evolution in a common environment. We found substantial variation in longer term evolutionary trajectories and differences between short‐ and longer term evolutionary dynamics. Although we observed pervasive patterns of convergence toward the character values of long‐established populations, populations still remain differentiated for several traits at the final generations analyzed. This pattern might involve transient divergence, as we report in some cases, indicating that more generations should lead to final convergence. These findings highlight the importance of longer term studies for understanding convergent evolution.     

Evaluating character partitioning and molecular models in plastid phylogenomics at low taxonomic levels: A case study using Amphilophium (Bignonieae,Bignoniaceae)

The accurate analyses of massive amounts of data obtained through next‐generation sequencing depend on the selection of appropriate evolutionary models. Many plastid phylogenomic studies typically analyze plastome data as a single partition, or divided by a region, using a concatenate “supergene” approach. The effects of molecular evolutionary models and character partition strategies on plastome‐based phylogenies have generally been evaluated at higher taxonomic levels in green plants. Using plastome data from 32 species of Amphilophium, a genus of Neotropical lianas, we explored potential sources of topological incongruence with different plastid genome datasets and approaches. Specifically, we evaluated the effects of compositional heterogeneity, codon usage bias, positive selection, and incomplete lineage sorting as sources of systematic error (i.e., the recovery of well‐supported conflicting topologies). We compared different datasets (e.g., non‐coding regions, exons, and codon‐aligned and translated amino acids) using concatenated approaches under site‐heterogeneous and site‐homogeneous models, as well as multispecies coalescent (MSC) methods. We found incongruences in recovered phylogenetic relationships, which were mainly located in short internodes. The MSC and concatenated approaches recovered similar topologies. The analysis of GC content and codon usage bias indicated higher substitution rates and AT excess at the third codon positions, and we found evidence of positive selection in 3% of amino acid sites. There were no significant differences among species in site biochemical profiles. We argue that the selection of appropriate partition strategies and evolutionary models is important to increase accuracy in phylogenetic relationships, even when using plastome datasets, which is still the primarily used genome in plant phylogenetics.     

EVOLUTIONARY CHARACTER ANALYSIS: TRACING CHARACTER CHANGE ON A CLADOGRAM

Abstract— There has been little formal discussion concerning character analysis in cladistics, even though characters and their character state trees are central to phylogenetic analyses. We refer to this field as Evolutionary Character Analysis. This paper defines the components of evolutionary character analysis: character state trees, transmodal characters, cladogram characters, attribute and character phylogenies; and the use of these components in phylogenetic inference and evolutionary studies. Character state trees and their effect on cladogram construction are discussed. A new method for numerically coding complex character state trees is described that further reduces the number of variables required to describe them. This method, ordinal coding, reduces the size of data matrices, and facilitates retrieval of state codes. This paper advocates the use of both biological evidence and evidence internal to the cladogram itself to construct character state trees (CSTs). We discuss general models of character evolution (morphocline analysis, Fitch minimum mutation model, etc.) and their role in forming CSTs. Character state trees formed with theories of character evolution are referred to as transmodal characters. These transmodal characters are contrasted with cladogram characters (Mickevich, 1982), and the place of each in a phylogenetic analysis is discussed. The method for determining cladogram characters is detailed with more complicated examples than found in previous publications. We advocate testing transmodal characters by comparing them with the resultant cladogram characters. This comparison involves transformation series analysis (TSA; Mickevich, 1982) which is viewed as an extension of reciprocal illumination. The TSA procedure and its place in hypothesis testing are reviewed. Tracing the evolution of characters interests both systematists and non-systematists alike. When character state trees (transmodal characters) are optimized on pre-existing phylogenies, character phylogenies and attribute phylogenies result. Attributes are defined as a feature that may or may not be homologous (i.e., ecological categories, plant hosts, etc.). We provide two illustrations of this approach, one involving the evolution of the anuran ear and another involving the coevolution of the butterfly Heliconius and its hostplants. Finally, the components of phylogenetic character analysis can be used to test more general evolutionary theories such as the biogenetic law and vicariance biogeography.     

Inferring the mode of origin of polyploid species from next‐generation sequence data

Many eukaryote organisms are polyploid. However, despite their importance, evolutionary inference of polyploid origins and modes of inheritance has been limited by a need for analyses of allele segregation at multiple loci using crosses. The increasing availability of sequence data for nonmodel species now allows the application of established approaches for the analysis of genomic data in polyploids. Here, we ask whether approximate Bayesian computation (ABC), applied to realistic traditional and next‐generation sequence data, allows correct inference of the evolutionary and demographic history of polyploids. Using simulations, we evaluate the robustness of evolutionary inference by ABC for tetraploid species as a function of the number of individuals and loci sampled, and the presence or absence of an outgroup. We find that ABC adequately retrieves the recent evolutionary history of polyploid species on the basis of both old and new sequencing technologies. The application of ABC to sequence data from diploid and polyploid species of the plant genus Capsella confirms its utility. Our analysis strongly supports an allopolyploid origin of C. bursa‐pastoris about 80 000 years ago. This conclusion runs contrary to previous findings based on the same data set but using an alternative approach and is in agreement with recent findings based on whole‐genome sequencing. Our results indicate that ABC is a promising and powerful method for revealing the evolution of polyploid species, without the need to attribute alleles to a homeologous chromosome pair. The approach can readily be extended to more complex scenarios involving higher ploidy levels.     

Rapid evolution and the convergence of ecological and evolutionary time

Recent studies have documented rates of evolution of ecologically important phenotypes sufficiently fast that they have the potential to impact the outcome of ecological interactions while they are underway. Observations of this type go against accepted wisdom that ecological and evolutionary dynamics occur at very different time scales. While some authors have evaluated the rapidity of a measured evolutionary rate by comparing it to the overall distribution of measured evolutionary rates, we believe that ecologists are mainly interested in rapid evolution because of its potential to impinge on ecological processes. We therefore propose that rapid evolution be defined as a genetic change occurring rapidly enough to have a measurable impact on simultaneous ecological change. Using this definition we propose a framework for decomposing rates of ecological change into components driven by simultaneous evolutionary change and by change in a non‐evolutionary factor (e.g. density dependent population dynamics, abiotic environmental change). Evolution is judged to be rapid in this ecological context if its contribution to ecological change is large relative to the contribution of other factors. We provide a worked example of this approach based on a theoretical predator–prey interaction [ Abrams, P. & Matsuda, H. (1997) . Evolution, 51, 1740], and find that in this system the impact of prey evolution on predator per capita growth rate is 63% that of internal ecological dynamics. We then propose analytical methods for measuring these contributions in field situations, and apply them to two long‐term data sets for which suitable ecological and evolutionary data exist. For both data sets relatively high rates of evolutionary change have been found when measured as character change in standard deviations per generation (haldanes). For Darwin's finches evolving in response to fluctuating rainfall [ Grant, P.R. & Grant, B.R. (2002) . Science, 296, 707], we estimate that evolutionary change has been more rapid than ecological change by a factor of 2.2. For a population of freshwater copepods whose life history evolves in response to fluctuating fish predation [ Hairston, N.G. Jr & Dillon, T.A. (1990) . Evolution, 44, 1796], we find that evolutionary change has been about one quarter the rate of ecological change – less than in the finch example, but nevertheless substantial. These analyses support the view that in order to understand temporal dynamics in ecological processes it is critical to consider the extent to which the attributes of the system under investigation are simultaneously changing as a result of rapid evolution.     

Some ‘ant’swers: Application of a layered barcode approach to problems in ant taxonomy

DNA barcoding has emerged as a routine tool in modern taxonomy. Although straightforward, this approach faces new challenges, when applied to difficult situation such as defining cryptic biodiversity. Ants are prime examples for high degrees of cryptic biodiversity due to complex population differentiation, hybridization and speciation processes. Here, we test the DNA barcoding region, cytochrome c oxidase 1 and two supplementary markers, 28S ribosomal DNA and long‐wavelength rhodopsin, commonly used in ant taxonomy, for their potential in a layered, character‐based barcoding approach across different taxonomic levels. Furthermore, we assess performance of the character‐based barcoding approach to determine cryptic species diversity in ants. We found (i) that the barcode potential of a specific genetic marker varied widely among taxonomic levels in ants; (ii) that application of a layered, character‐based barcode for identification of specimens can be a solution to taxonomical challenging groups; (iii) that the character‐based barcoding approach allows us to differentiate specimens even within locations based on pure characters. In summary, (layered) character‐based barcoding offers a reliable alternative for problematic species identification in ants and can be used as a fast and cost‐efficient approach to estimate presence, absence or frequency of cryptic species.     

Catching the phylogenic history through the ontogenic hourglass: a phylogenomic analysis of Drosophila body segmentation genes

SUMMARY The phylogenetic information content of different developmental stages is a long‐standing issue in the study of development and evolution. We performed phylogenetic analyses of 51 body segmentation genes in 12 species of Drosophila in order to investigate the impact of the mode of evolution of development on phylogeny inference. Previous studies of these genes in Drosophila using pairwise phenetic comparisons at the species group level revealed the presence of an “hourglass model” (HG), wherein mid‐embryonic stages are the most evolutionarily constrained. We utilized two character‐based approaches: taxonomic congruence using the relative consensus fork index (RCFI), in which phylogenies are inferred from each gene separately and compared with a total evidence tree (TET), and partitioned simultaneous analysis using several indices such as branch support (BS) and localized incongruence length difference (LILD) test. We also proposed a new index, the recapitulatory index (R), which divides the number of synapomorphies on the total number of informative characters in a data set. Polynomial adjustment of both BS and R indices showed strong support for the hourglass model regardless of the taxonomic level (species subgroup vs. subgenera), showing less phylogenetic information content for mid‐developmental stages (mainly the zygotic segment polarity stage). Significant LILD scores were randomly distributed among developmental stages revealing the absence of differential selective constraints, but were significantly related to chromosomal location showing physical (linkage) impact on phylogenetic incongruence. RCFI was the most sensitive measure to taxonomic level, having a convex parabola at the species subgroup level in support of the hourglass model and a concave parabola at the subgeneric level in support of the adaptive penetrance model. This time‐dependent discrepancy of best fit developmental model parallels previous conflicting results from the vertebrates. Because of the quasi‐phenetic nature of this index, we argue that the discrepancy is due to the evolutionary rate heterogeneity of developmental genes rather than to fundamental differences among organisms. We suggest that simultaneous character‐based analyses give better macroevolutionary support to the hourglass model of the developmental constraints on genome evolution than pairwise phenetic comparisons.     

Design of character‐based DNA barcode motif for species identification: A computational approach and its validation in fishes

The DNA barcodes are generally interpreted using distance‐based and character‐based methods. The former uses clustering of comparable groups, based on the relative genetic distance, while the latter is based on the presence or absence of discrete nucleotide substitutions. The distance‐based approach has a limitation in defining a universal species boundary across the taxa as the rate of mtDNA evolution is not constant throughout the taxa. However, character‐based approach more accurately defines this using a unique set of nucleotide characters. The character‐based analysis of full‐length barcode has some inherent limitations, like sequencing of the full‐length barcode, use of a sparse‐data matrix and lack of a uniform diagnostic position for each group. A short continuous stretch of a fragment can be used to resolve the limitations. Here, we observe that a 154‐bp fragment, from the transversion‐rich domain of 1367 COI barcode sequences can successfully delimit species in the three most diverse orders of freshwater fishes. This fragment is used to design species‐specific barcode motifs for 109 species by the character‐based method, which successfully identifies the correct species using a pattern‐matching program. The motifs also correctly identify geographically isolated population of the Cypriniformes species. Further, this region is validated as a species‐specific mini‐barcode for freshwater fishes by successful PCR amplification and sequencing of the motif (154 bp) using the designed primers. We anticipate that use of such motifs will enhance the diagnostic power of DNA barcode, and the mini‐barcode approach will greatly benefit the field‐based system of rapid species identification.     

A phylogeny of anisopterous dragonflies (Insecta,Odonata) using mtRNA genes and mixed nucleotide/doublet models

The application of mixed nucleotide/doublet substitution models has recently received attention in RNA‐based phylogenetics. Within a Bayesian approach, it was shown that mixed models outperformed analyses relying on simple nucleotide models. We analysed an mt RNA data set of dragonflies representing all major lineages of Anisoptera plus outgroups, using a mixed model in a Bayesian and parsimony (MP) approach. We used a published mt 16S rRNA secondary consensus structure model and inferred consensus models for the mt 12S rRNA and tRNA valine. Secondary structure information was used to set data partitions for paired and unpaired sites on which doublet or nucleotide models were applied, respectively. Several different doublet models are currently available of which we chose the most appropriate one by a Bayes factor test. The MP reconstructions relied on recoded data for paired sites in order to account for character covariance and an application of the ratchet strategy to find most parsimonious trees. Bayesian and parsimony reconstructions are partly differently resolved, indicating sensitivity of the reconstructions to model specification. Our analyses depict a tree in which the damselfly family Lestidae is sister group to a monophyletic clade Epiophlebia + Anisoptera, contradicting recent morphological and molecular work. In Bayesian analyses, we found a deep split between Libelluloidea and a clade ‘Aeshnoidea’ within Anisoptera largely congruent with Tillyard’s early ideas of anisopteran evolution, which had been based on evidently plesiomorphic character states. However, parsimony analysis did not support a clade ‘Aeshnoidea’, but instead, placed Gomphidae as sister taxon to Libelluloidea. Monophyly of Libelluloidea is only modestly supported, and many inter‐family relationships within Libelluloidea do not receive substantial support in Bayesian and parsimony analyses. We checked whether high Bayesian node support was inflated owing to either: (i) wrong secondary consensus structures; (ii) under‐sampling of the MCMC process, thereby missing other local maxima; or (iii) unrealistic prior assumptions on topologies or branch lengths. We found that different consensus structure models exert strong influence on the reconstruction, which demonstrates the importance of taxon‐specific realistic secondary structure models in RNA phylogenetics.     

Mapping characters on a tree with or without the outgroups

A character of special interest in evolutionary studies is usually optimized on a phylogenetic tree, with or without the outgroups employed in that analysis. Both practices are never justified and look like arbitrary choices. Focusing on one example, we draw the conclusion that authors retain or remove outgroups depending on the way these outgroups sample the diversity of states of the character(s) of special interest. The topology without outgroups is often used by authors when different outgroup taxa non‐exhaustively sample the different states of the character of interest outside of the ingroup. This can make the analysis incoherent, because its different steps are not based on the same data matrix (outgroups are removed in the last step). It can provide several incoherent and possibly different patterns for a same character of interest, one issuing from the first step of phylogeny construction and the other resulting from the a posteriori optimization on the truncated topology. Phylogenetic analyses should be designed to minimize this problem, selecting outgroup and ingroup taxa whose diversity of character states is needed for reconstructing the evolutionary history of the character of interest. © The Willi Hennig Society 2004.     

A method for constraining the age of origination of derived characters

Fossils are the physical records of the history of morphological character evolution on Earth and can provide valuable information concerning the sequence and timing of origination of derived characters. Knowledge of the timing of origination of synapomorphies makes it possible to estimate when unobserved character changes occurred in the geological past. Here we present a method for estimating the temporal interval during which synapomorphies evolved. The method requires either direct inclusion of fossil taxa (with or without extant taxa) in cladistic analyses based on morphological or combined data, or indirectly using the “molecular scaffold approach.” Second, characters of interest are mapped on a most parsimonious tree and “minimum age node mapping” is used to place minimum ages on the nodes of the tree. Finally, characters of interest are evaluated for younger and/or older temporal constraints on the time of their origination; application of the older bound assumes ancestry of fossil terminals included in the tree. A key is provided herein describing the method. Among other applications, this approach has the potential to provide a powerful test of purported evolutionary cause–effect relationships. For example, the method has the ability to discover that derived characters of suggested adaptational significance may considerably pre‐date the cause(s) that are hypothesized to have favored their establishment. © The Willi Hennig Society 2007.     

Investigating Devonian trees as geo‐engineers of past climates: linking palaeosols to palaeobotany and experimental geobiology

We present the rationale for a cross‐disciplinary investigation addressing the ‘Devonian plant hypothesis’ which proposes that the evolutionary appearance of trees with deep, complex rooting systems represents one of the major biotic feedbacks on geochemical carbon cycling during the Phanerozoic. According to this hypothesis, trees have dramatically enhanced mineral weathering driving an increased flux of Ca²⁺ to the oceans and, ultimately, a 90% decline in atmospheric CO₂ levels through the Palaeozoic. Furthermore, experimental studies indicate a key role for arbuscular mycorrhizal fungi in soil–plant processes and especially in unlocking the limiting nutrient phosphorus in soil via Ca‐phosphate dissolution mineral weathering. This suggests co‐evolution of roots and symbiotic fungi since the Early Devonian could well have triggered positive feedbacks on weathering rates whereby root–fungal P release supports higher biomass forested ecosystems. Long‐standing areas of uncertainty in this paradigm include the following: (1) limited fossil record documenting the origin and timeline of the evolution of tree‐sized plants through the Devonian; and (2) the effects of the evolutionary advance of trees and their in situ rooting structures on palaeosol geochemistry. We are addressing these issues by integrating palaeobotanical studies with geochemical and mineralogical analyses of palaeosol sequences at selected sites across eastern North America with a particular focus on drill cores from Middle Devonian forests in Greene County, New York State.     

Jasminum polyanthum Franch. as a natural source of (−)‐methyl jasmonate: an alternative to the use of the synthetic standard

Introduction – Methyl jasmonate (MJ) contains two chiral centres at C‐3 and C‐7 in its chemical structure, which implies that it can exist in four possible stereoisomeric forms, namely (+)‐MJ, (?)‐MJ, (+)‐epiMJ and (?)‐epiMJ. The absolute configuration of the two side chains of MJ affects the biological activity associated with this compound. Objective – To isolate pure (?)‐MJ from a natural source, Jasminum polyanthum Franch., with the intention of increasing the knowledge about its biological properties, including its effect on the biosynthesis of plant metabolites. Methodology – The method used was based on steam distillation extraction (SDE) as an extraction technique followed by high‐performance liquid chromatography (HPLC) as a purification procedure. The HPLC flow‐rate as well as the number of fractions accumulated were optimised to achieve the concentration and purity required. Results – The employment of 0.3 mL/min as HPLC flow‐rate and the accumulation of three HPLC fractions allowed the required enantiomeric purity (95%) and concentration (0.36 mg/L in each HPLC fraction) to efficiently obtain (?)‐methyl jasmonate from Jasminum polyanthum Franch. to be achieved. Conclusion – The approach proposed may enable the properties and effect of pure (?)‐MJ on plant responses to be studied. The use of a natural source to obtain (?)‐MJ is presented as an alternative to the enantioselective synthesis and enantiomeric resolution from the standard racaemic mixture. Copyright © 2009 John Wiley & Sons, Ltd.     

Evolutionary morphology of the circulatory system in Peracarida (Malacostraca; Crustacea)

We demonstrate that by formulating guidelines for evolutionary morphology the transparency, reproducibility, and intersubject testability of evolutionary hypotheses based on morphological data can be enhanced. The five main steps in our concept of evolutionary morphology are (i) taxon sampling, (ii) structural analysis, (iii) character conceptualization, (iv) phylogenetic analysis, and (v) evolutionary interpretation. We illustrate this concept on the example of the morphology of the circulatory organs in peracarid Malacostraca. The analysis is based on recently published accounts in which detailed structural analyses were carried out, and on the older literature. Detailed conceptualizations of 22 characters of the circulatory system are given for 28 terminals. In a further step these characters are included in a recently revised matrix, resulting in 110 characters. The resulting parsimony analysis yielded a single most parsimonious tree with a length of 309 steps. The most significant results are that Peracarida is monophyletic, Amphipoda is the sister taxon to the Mancoida sensu stricto, the relict cave‐dwelling taxa Thermosbaenacea, Spelaeogriphacea, and Mictocarididae form a monophylum and Tanaidacea is the sister group to a monophylum comprising Cumacea and Isopoda. The evolutionary analysis shows that the ground pattern features of the circulatory organs in Peracarida are a tubular heart extending through the whole thorax, a posterior aorta with lateral arteries, and a ventral vessel system. Important features within the Peracarida are the backward shift of the anterior border of the heart, the reduction of the ventral vessel system, and two patterns of cardiac arteries, one common to the amphipod and tanaidacean terminals, and one to the cumacean and isopod terminals. © The Willi Hennig Society 2009.