Testing Evolutionary Hypotheses Research Articles

Hide and Go Seek: What Does Presence Mean in the Fossil Record

Our efforts to reconstruct accurate, complete records of events in vegetation history and in plant evolutionary history depend on accuracy in dating sediments, interpretation of structures preserved, reconstruction of whole organisms or communities from the preserved material, and interpretation of the interaction between past abundance and fossil presence. This contribution examines the interaction between past abundance of a target plant and the probability of retrieval of that species in the fossil record. By examining records of recolonization in volcanic areas, records of invasive species spread, succession in disturbed habitats, and historical migration patterns, we can provide estimates of the likelihood of appearance in the potential fossil record of newly evolved and reasonably successful species. The lag in discovery, recognition, and publication of a fossil as an important representative of a critical clade is also evaluated and is highlighted as a more important constraint on the use of fossils in testing evolutionary and ecological hypotheses than the recolonization rate. The lag between discovery and publication is particularly relevant in areas of the modern world where fossil plant–bearing deposits are either rare or inaccessible. Greater awareness of the density and reliability of the plant record should allow evolutionary biologists and paleoecologists to bracket not only time intervals but also geographic regions where the fossil record can be interpreted largely at face value. At the same time, more effort should be focused on intense collecting efforts and training in areas where fossil deposits are potentially present, but poorly collected and evaluated.

The dynamic evolutionary history of the bananaquit (Coereba flaveola) in the Caribbean revealed by a multigene analysis

BackgroundThe bananaquit (Coereba flaveola) is a small nectivorous and frugivorous emberizine bird (order Passeriformes) that is an abundant resident throughout the Caribbean region. We used multi-gene analyses to investigate the evolutionary history of this species throughout its distribution in the West Indies and in South and Middle America. We sequenced six mitochondrial genes (3744 base pairs) and three nuclear genes (2049 base pairs) for forty-four bananaquits and three outgroup species. We infer the ancestral area of the present-day bananaquit populations, report on the species' phylogenetic, biogeographic and evolutionary history, and propose scenarios for its diversification and range expansion.ResultsPhylogenetic concordance between mitochondrial and nuclear genes at the base of the bananaquit phylogeny supported a West Indian origin for continental populations. Multi-gene analysis showing genetic remnants of successive colonization events in the Lesser Antilles reinforced earlier research demonstrating that bananaquits alternate periods of invasiveness and colonization with biogeographic quiescence. Although nuclear genes provided insufficient information at the tips of the tree to further evaluate relationships of closely allied but strongly supported mitochondrial DNA clades, the discrepancy between mitochondrial and nuclear data in the population of Dominican Republic suggested that the mitochondrial genome was recently acquired by introgression from Jamaica.ConclusionThis study represents one of the most complete phylogeographic analyses of its kind and reveals three patterns that are not commonly appreciated in birds: (1) island to mainland colonization, (2) multiple expansion phases, and (3) mitochondrial genome replacement. The detail revealed by this analysis will guide evolutionary analyses of populations in archipelagos such as the West Indies, which include islands varying in size, age, and geological history. Our results suggest that multi-gene phylogenies will permit improved comparative analysis of the evolutionary histories of different lineages in the same geographical setting, which provide replicated "natural experiments" for testing evolutionary hypotheses.

Genome size and GC content evolution of Festuca: ancestral expansion and subsequent reduction.

Plant evolution is well known to be frequently associated with remarkable changes in genome size and composition; however, the knowledge of long-term evolutionary dynamics of these processes still remains very limited. Here a study is made of the fine dynamics of quantitative genome evolution in Festuca (fescue), the largest genus in Poaceae (grasses). Using flow cytometry (PI, DAPI), measurements were made of DNA content (2C-value), monoploid genome size (Cx-value), average chromosome size (C/n-value) and cytosine + guanine (GC) content of 101 Festuca taxa and 14 of their close relatives. The results were compared with the existing phylogeny based on ITS and trnL-F sequences. The divergence of the fescue lineage from related Poeae was predated by about a 2-fold monoploid genome and chromosome size enlargement, and apparent GC content enrichment. The backward reduction of these parameters, running parallel in both main evolutionary lineages of fine-leaved and broad-leaved fescues, appears to diverge among the existing species groups. The most dramatic reductions are associated with the most recently and rapidly evolving groups which, in combination with recent intraspecific genome size variability, indicate that the reduction process is probably ongoing and evolutionarily young. This dynamics may be a consequence of GC-rich retrotransposon proliferation and removal. Polyploids derived from parents with a large genome size and high GC content (mostly allopolyploids) had smaller Cx- and C/n-values and only slightly deviated from parental GC content, whereas polyploids derived from parents with small genome and low GC content (mostly autopolyploids) generally had a markedly increased GC content and slightly higher Cx- and C/n-values. The present study indicates the high potential of general quantitative characters of the genome for understanding the long-term processes of genome evolution, testing evolutionary hypotheses and their usefulness for large-scale genomic projects. Taken together, the results suggest that there is an evolutionary advantage for small genomes in Festuca.

Recodon: coalescent simulation of coding DNA sequences with recombination, migration and demography.

BackgroundCoalescent simulations have proven very useful in many population genetics studies. In order to arrive to meaningful conclusions, it is important that these simulations resemble the process of molecular evolution as much as possible. To date, no single coalescent program is able to simulate codon sequences sampled from populations with recombination, migration and growth.ResultsWe introduce a new coalescent program, called Recodon, which is able to simulate samples of coding DNA sequences under complex scenarios in which several evolutionary forces can interact simultaneously (namely, recombination, migration and demography). The basic codon model implemented is an extension to the general time-reversible model of nucleotide substitution with a proportion of invariable sites and among-site rate variation. In addition, the program implements non-reversible processes and mixtures of different codon models.ConclusionRecodon is a flexible tool for the simulation of coding DNA sequences under realistic evolutionary models. These simulations can be used to build parameter distributions for testing evolutionary hypotheses using experimental data. Recodon is written in C, can run in parallel, and is freely available from .

Parasite variation and the evolution of virulence in a Daphnia-microparasite system

Understanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. This study therefore examined variation between parasite isolates (the bacterium Pasteuria ramosa) from the crustacean Daphnia magna. From a single wild-caught infected host we obtained 2 P. ramosa isolates that differed substantially in the mortality they caused. Surprisingly, the isolate causing higher early mortality was, on average, less successful at establishing infections and had a slower growth rate within hosts. The observation that within-host replication rate was negatively correlated with mortality could violate a central assumption of the trade-off hypothesis for the evolution of virulence, but we discuss a number of caveats which caution against premature rejection of the trade-off hypothesis. We sought to test if the characteristics of these parasite isolates were constant across host genotypes in a second experiment that included 2 Daphnia host clones. The relative growth rates of the two parasite isolates did indeed depend on the host genotype (although the rank order did not change). We suggest that testing evolutionary hypotheses for virulence may require substantial sampling of both host and parasite genetic variation, and discuss how selection for virulence may change with the epidemiological state of natural populations and how this can promote genetic variation for virulence.

Counting labeled transitions in continuous-time Markov models of evolution

Counting processes that keep track of labeled changes to discrete evolutionary traits play critical roles in evolutionary hypothesis testing. If we assume that trait evolution can be described by a continuous-time Markov chain, then it suffices to study the process that counts labeled transitions of the chain. For a binary trait, we demonstrate that it is possible to obtain closed-form analytic solutions for the probability mass and probability generating functions of this evolutionary counting process. In the general, multi-state case we show how to compute moments of the counting process using an eigen decomposition of the infinitesimal generator, provided the latter is a diagonalizable matrix. We conclude with two examples that demonstrate the utility of our results.

MEGA4: Molecular Evolutionary Genetics Analysis (MEGA) Software Version 4.0

We announce the release of the fourth version of MEGA software, which expands on the existing facilities for editing DNA sequence data from autosequencers, mining Web-databases, performing automatic and manual sequence alignment, analyzing sequence alignments to estimate evolutionary distances, inferring phylogenetic trees, and testing evolutionary hypotheses. Version 4 includes a unique facility to generate captions, written in figure legend format, in order to provide natural language descriptions of the models and methods used in the analyses. This facility aims to promote a better understanding of the underlying assumptions used in analyses, and of the results generated. Another new feature is the Maximum Composite Likelihood (MCL) method for estimating evolutionary distances between all pairs of sequences simultaneously, with and without incorporating rate variation among sites and substitution pattern heterogeneities among lineages. This MCL method also can be used to estimate transition/transversion bias and nucleotide substitution pattern without knowledge of the phylogenetic tree. This new version is a native 32-bit Windows application with multi-threading and multi-user supports, and it is also available to run in a Linux desktop environment (via the Wine compatibility layer) and on Intel-based Macintosh computers under the Parallels program. The current version of MEGA is available free of charge at (http://www.megasoftware.net).

Evolutionary History of Vegetative Reproduction in Porpidia s.l. (Lichen-Forming Ascomycota)

The evolutionary history of gains and losses of vegetative reproductive propagules (soredia) in Porpidia s.l., a group of lichen-forming ascomycetes, was clarified using Bayesian Markov chain Monte Carlo (MCMC) approaches to monophyly tests and a combined MCMC and maximum likelihood approach to ancestral character state reconstructions. The MCMC framework provided confidence estimates for the reconstructions of relationships and ancestral character states, which formed the basis for tests of evolutionary hypotheses. Monophyly tests rejected all hypotheses that predicted any clustering of reproductive modes in extant taxa. In addition, a nearest-neighbor statistic could not reject the hypothesis that the vegetative reproductive mode is randomly distributed throughout the group. These results show that transitions between presence and absence of the vegetative reproductive mode within Porpidia s.l. occurred several times and independently of each other. Likelihood reconstructions of ancestral character states at selected nodes suggest that--contrary to previous thought--the ancestor to Porpidia s.l. already possessed the vegetative reproductive mode. Furthermore, transition rates are reconstructed asymmetrically with the vegetative reproductive mode being gained at a much lower rate than it is lost. A cautious note has to be added, because a simulation study showed that the ancestral character state reconstructions were highly dependent on taxon sampling. However, our central conclusions, particularly the higher rate of change from vegetative reproductive mode present to absent than vice versa within Porpidia s.l., were found to be broadly independent of taxon sampling.

DOES DIVING LIMIT BRAIN SIZE IN CETACEANS?

AbstractWe test the longstanding hypothesis, known as the dive constraint hypothesis, that the oxygenation demands of diving pose a constraint on aquatic mammal brain size.Using a sample of 23 cetacean species we examine the relationship among six different measures of relative brain size, body size, and maximum diving duration. Unlike previous tests we include body size as a covariate and perform independent contrast analyses to control for phylogeny. We show that diving does not limit brain size in cetaceans and therefore provide no support for the dive constraint hypothesis. Instead, body size is the main predictor of maximum diving duration in cetaceans. Furthermore, our findings show that it is important to conduct robust tests of evolutionary hypotheses by employing a variety of measures of the dependent variable, in this case, relative brain size.

The inheritance of organelle genes and genomes: patterns and mechanisms

Unlike nuclear genes and genomes, the inheritance of organelle genes and genomes does not follow Mendel's laws. In this mini-review, I summarize recent research progress on the patterns and mechanisms of the inheritance of organelle genes and genomes. While most sexual eukaryotes show uniparental inheritance of organelle genes and genomes in some progeny at least part of the time, increasing evidence indicates that strictly uniparental inheritance is rare and that organelle inheritance patterns are very diverse and complex. In contrast with the predominance of uniparental inheritance in multicellular organisms, organelle genes in eukaryotic microorganisms, such as protists, algae, and fungi, typically show a greater diversity of inheritance patterns, with sex-determining loci playing significant roles. The diverse patterns of inheritance are matched by the rich variety of potential mechanisms. Indeed, many factors, both deterministic and stochastic, can influence observed patterns of organelle inheritance. Interestingly, in multicellular organisms, progeny from interspecific crosses seem to exhibit more frequent paternal leakage and biparental organelle genome inheritance than those from intraspecific crosses. The recent observation of a sex-determining gene in the basidiomycete yeast Cryptococcus neoformans, which controls mitochondrial DNA inheritance, has opened up potentially exciting research opportunities for identifying specific molecular genetic pathways that control organelle inheritance, as well as for testing evolutionary hypotheses regarding the prevalence of uniparental inheritance of organelle genes and genomes.

The evolutionary dynamics of endogenous retroviruses

Endogenous retroviruses (ERVs) are vertically transmitted intragenomic elements derived from integrated retroviruses. ERVs can proliferate within the genome of their host until they either acquire inactivating mutations or are lost by recombinational deletion. We present a model that unifies current knowledge of ERV biology into a single evolutionary framework. The model predicts the possible long-term outcomes of retroviral germline infection and can account for the variable patterns of observed ERV genetic diversity. We hope the model will provide a useful framework for understanding ERV evolution, enabling the testing of evolutionary hypotheses and the estimation of parameters governing ERV proliferation.

Conceptual issues in local adaptation

AbstractStudies of local adaptation provide important insights into the power of natural selection relative to gene flow and other evolutionary forces. They are a paradigm for testing evolutionary hypotheses about traits favoured by particular environmental factors. This paper is an attempt to summarize the conceptual framework for local adaptation studies. We first review theoretical work relevant for local adaptation. Then we discuss reciprocal transplant and common garden experiments designed to detect local adaptation in the pattern of deme × habitat interaction for fitness. Finally, we review research questions and approaches to studying the processes of local adaptation – divergent natural selection, dispersal and gene flow, and other processes affecting adaptive differentiation of local demes. We advocate multifaceted approaches to the study of local adaptation, and stress the need for experiments explicitly addressing hypotheses about the role of particular ecological and genetic factors that promote or hinder local adaptation. Experimental evolution of replicated populations in controlled spatially heterogeneous environments allow direct tests of such hypotheses, and thus would be a valuable way to complement research on natural populations.

MEGA3: Integrated software for Molecular Evolutionary Genetics Analysis and sequence alignment.

With its theoretical basis firmly established in molecular evolutionary and population genetics, the comparative DNA and protein sequence analysis plays a central role in reconstructing the evolutionary histories of species and multigene families, estimating rates of molecular evolution, and inferring the nature and extent of selective forces shaping the evolution of genes and genomes. The scope of these investigations has now expanded greatly owing to the development of high-throughput sequencing techniques and novel statistical and computational methods. These methods require easy-to-use computer programs. One such effort has been to produce Molecular Evolutionary Genetics Analysis (MEGA) software, with its focus on facilitating the exploration and analysis of the DNA and protein sequence variation from an evolutionary perspective. Currently in its third major release, MEGA3 contains facilities for automatic and manual sequence alignment, web-based mining of databases, inference of the phylogenetic trees, estimation of evolutionary distances and testing evolutionary hypotheses. This paper provides an overview of the statistical methods, computational tools, and visual exploration modules for data input and the results obtainable in MEGA.

Molecular clocks and explosive radiations.

Molecular data are ideal for exploring evolutionary history because of its universality, stochasticity, and abundance. These features provide a means of exploring the evolutionary history of all organisms (including those that do not tend to leave fossils), potentially within a statistical framework that allows testing of evolutionary hypotheses. However, the discrepancy between molecular and paleontological dates for three key "explosive" radiations inferred from the fossil record--the Cambrian explosion of animal phyla and the post-KT radiations of modern orders of mammals and birds--have led to a reexamination of the assumptions on which molecular dates are based. Could variation in the rate of molecular evolution, perhaps associated with "explosive" radiations, cause overestimation of diversification dates? Here I examine four hypothetical causes of fast molecular rates in explosive radiations--body size, morphological rate, speciation rate, and ecological diversification--using available empirical evidence on patterns of variation in rate of molecular evolution.

The shapes of neutral gene genealogies in two species: probabilities of monophyly, paraphyly, and polyphyly in a coalescent model.

The genealogies of samples of orthologous regions from multiple species can be classified by their shapes. Using a neutral coalescent model of two species, I give exact probabilities of each of four possible genealogical shapes: reciprocal monophyly, two types of paraphyly, and polyphyly. After the divergence that forms two species, each of which has population size N, polyphyly is the most likely genealogical shape for the lineages of the two species. At approximately 1.300N generations after divergence, paraphyly becomes most likely, and reciprocal monophyly becomes most likely at approximately 1.665N generations. For a given species, the time at which 99% of its loci acquire monophyletic genealogies is approximately 5.298N generations, assuming all loci in its sister species are monophyletic. The probability that all lineages of two species are reciprocally monophyletic given that a sample from the two species has a reciprocally monophyletic genealogy increases rapidly with sample size, as does the probability that the most recent common ancestor (MRCA) for a sample is also the MRCA for all lineages from the two species. The results have potential applications for the testing of evolutionary hypotheses.

Using Stable Isotopic Data to Resolve Rate and Duration of Growth throughout Ontogeny: An Example from the Surf Clam, Spisula solidissima

Other| April 01, 2003 Using Stable Isotopic Data to Resolve Rate and Duration of Growth throughout Ontogeny: An Example from the Surf Clam, Spisula solidissima LINDA C. IVANY; LINDA C. IVANY 1Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, lcivany@syr.edu Search for other works by this author on: GSW Google Scholar BRUCE H. WILKINSON; BRUCE H. WILKINSON 2Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48130 Search for other works by this author on: GSW Google Scholar DOUGLAS S. JONES DOUGLAS S. JONES 3Florida Museum of Natural History, University of Florida, Gainesville, FL 32611 Search for other works by this author on: GSW Google Scholar Author and Article Information LINDA C. IVANY 1Department of Earth Sciences, Syracuse University, Syracuse, NY 13244, lcivany@syr.edu BRUCE H. WILKINSON 2Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48130 DOUGLAS S. JONES 3Florida Museum of Natural History, University of Florida, Gainesville, FL 32611 Publisher: SEPM Society for Sedimentary Geology Accepted: 31 Jul 2002 First Online: 03 Mar 2017 Online ISSN: 1938-5323 Print ISSN: 0883-1351 Society for Sedimentary Geology PALAIOS (2003) 18 (2): 126–137. https://doi.org/10.1669/0883-1351(2003)18<126:USIDTR>2.0.CO;2 Article history Accepted: 31 Jul 2002 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation LINDA C. IVANY, BRUCE H. WILKINSON, DOUGLAS S. JONES; Using Stable Isotopic Data to Resolve Rate and Duration of Growth throughout Ontogeny: An Example from the Surf Clam, Spisula solidissima. PALAIOS 2003;; 18 (2): 126–137. doi: https://doi.org/10.1669/0883-1351(2003)18<126:USIDTR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Abstract Examination of ontogenetic variation in the stable isotopic composition of accretionary biogenic hard parts is becoming a commonplace technique for gaining insights into organism age, changes in growth rate through ontogeny, and environmental conditions under which organisms lived. However, the application of isotopic data to life-history studies often is impeded by the noisy nature of environmental signals, as well as by seasonal cessation of hardpart accretion. A computational approach is presented that quantitatively resolves secular (seasonal) change in environmental parameters such as temperature and salinity with spatial (hard part) variation in isotopic composition. Output consists of determinations of mean annual isotopic composition, seasonal range in isotopic composition, and variation in hard-part growth rate for any interval of data in an accretionary transect. Quantitative estimates of absolute growth rates, as well as the proportion of each season represented by hard-part accretion, are derived for every season of the organism's life recorded in their hard parts.This methodology is applied to δ18O data from a valve of the surf clam, Spisula solidissima, collected live from the New Jersey shelf. Based on the saw-toothed pattern of δ18O variation in this clam, and on the fact that observed amplitudes of δ18O variation are only a fraction of those anticipated from measurements of ambient water salinity and temperature, it is apparent that growth cessation occurred during each of the dozen summers and dozen winters of ontogeny. Determination of best-fit sinusoids for each season of growth reveals that: (1) rate of growth decreased exponentially during the ontogeny of this individual; (2) net spring season accretion was initially twice that in the fall; and (3) ontogenetic decrease in net accretion was accomplished in part by reduction in rate of accretion, and in part by reduction in the number of spring and fall days during which growth occurred. Isotope thermometry suggests that all growth intervals span an optimum temperature; shorter (or longer) durations of seasonal shell accretion occur over narrower (or wider) temperature ranges centered on about 11°C.Beyond the obvious paleoenvironmental applications, the advantage of this method for biologists and paleontologists is that rate and duration of growth can be approximated at seasonal to subseasonal levels of resolution for any living or fossil organism. Such information from a suite of individuals can reveal how growth within a species is affected by changes in latitude, depth, productivity, anthropogenic influence, and other environmental gradients. In addition, because changes in rate and timing of growth within a lineage are the mainstay of heterochrony studies, quantitative methods for assessing such variables through time in fossil specimens will allow more rigorous testing of evolutionary hypotheses. 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What can DNA Tell us About the Cambrian Explosion?

Molecular data is ideal for exploring deep evolutionary history because of its universality, stochasticity and abundance. These features provide a means of exploring the evolutionary history of all organisms (including those that do not tend to leave fossils), independently of morphological evolution, and within a statistical framework that allows testing of evolutionary hypotheses. In particular, molecular data have an important role to play in examining hypotheses concerning the tempo and mode of evolution of animal body plans. Examples are given where molecular phylogenies have led to a re-examination of some fundamental assumptions in metazoan evolution, such as the immutability of early developmental characters, and the evolvability of bauplan characters. Molecular data is also providing a new and controversial timescale for the evolution of animal phyla, pushing the major divisions of the animal kingdom deep into the Precambrian. There have been many reasons to question the accuracy and precision of molecular date estimates, such as the failure to account for lineage-specific rate variation and unreliable estimation of rates of molecular evolution. While these criticisms have been largely countered by recent studies, one problem has remained a challenge: could temporal variation in the rate of molecular evolution, perhaps associated with "explosive" adaptive radiations, cause overestimation of diversification dates? Empirical evidence for an effect of speciation rate, morphological evolution or ecological diversification on rates of molecular evolution is examined, and the potential for rate-variable methods for molecular dating are discussed.

Experimental evolution and the Krogh principle: generating biological novelty for functional and genetic analyses.

August Krogh counseled the careful selection of the best subject organism on which to undertake mechanistic physiological research. But what if an organism with the desired properties does not exist? It is now within our power to engineer organisms genetically to achieve novel combinations of traits. I propose that it is a logical extension of the Krogh principle that we use biological methodologies to create novel organisms ideally suited for particular physiological studies. Transgenics may first come to mind as the method for such transformations, but here I suggest that an alternative and complementary technique for generating biological novelty is experimental evolution. The latter has several advantages, including modification of multiple characters in one experiment, the production of advantageous traits, the testing of evolutionary hypotheses, and the identification of previously unsuspected factors involved in adaptation. Three experiments are reviewed, each of which examined the evolution of different physiological characters in different environments and organisms: locomotor performance in mice, desiccation tolerance in fruit flies, and high temperature adaptation in bacteria. While diverse in experimental type and subject, all resulted in the successful production of new variants with enhanced function in their new environments. Each experiment successfully tested hypotheses concerning physiological evolution, and in each case, unanticipated results emerged, which suggests previously unsuspected adaptive pathways and mechanisms. In addition, replicate populations in each experiment adjusted to their common environments by several different means, which indicates that physiological evolution may follow diverse stochastic pathways during adaptation. Experimental evolution can be a valuable method to produce and investigate new physiological variants and traits. The choice of experimental subjects, according to the Krogh principle, is no longer limited to currently existing organisms but is open to our imaginations and our ingenuity.

Integrating historical and mechanistic biology enhances the study of adaptation.

Adding a causal, mechanistic dimension to the study of character evolution will increase the strength of inferences regarding the evolutionary history of characters and their adaptive consequences. This approach has the advantage of illuminating mechanism and testing evolutionary hypotheses rigorously. We consider the advantages of combining mechanistic and historical biology in the study of behavior, physiology, and development. We present six examples to illustrate the advantages: (1) preexisting biases in sound perception in frogs; (2) preexisting biases in visual cues in swordtailfishes; (3) exploitation of prey location behavior for attraction of mates in water mites; (4) heterospecific mating in asexual molly fishes; (5) developmental foundation of morphological diversification in amphibian digits; and (6) locomotor performance at low temperature and the evolution of nocturnality in geckos. In each of these examples, the dominant role of history, combined with organismal integration, makes ignoring history a risky proposition.

Testing evolutionary hypotheses in the classroom with MacClade software

MacClade is a Macintosh-based software package that uses the techniques of cladistic analysis to explore evolutionary patterns. Although designed for the Macintosh platform, MacClade delivers excellent results onPCs when used with MacOs emulators. This paper describes a novel and effective exercise that allows under-graduate biology majors to test a hypothesis about behavioural evolution in insects. The exercise is derived from a real data set in the literature and provides students with the opportunity to learn firsthand how scientists evaluate hypotheses about patterns of adaptive change. The exercise can be modified to fit the needs of particular classes. In general, MacClade offers the life science teacher a wide variety of instructional possibilities.