THE FUNCTION OF CALL ALTERNATION IN ANURAN AMPHIBIANS: A TEST OF THREE HYPOTHESES

Males of many species of anurans alternate calls with those of their neighbors in a chorus. This pattern of calling reduces signal interference and may: 1) facilitate intermale spacing because males can better gauge the intensity of neighbors' calls if these calls do not overlap with their own; 2) help preserve species-specific temporal information in calls required to attract females; and/or 3) make it easier for females to localize males in the chorus. I tested these hypotheses with three species that exhibit call alternation, Hyla crucifer, H. versicolor, and H. microcephala. Males of all three species gave more aggressive calls to high-intensity synthetic stimuli that alternated with their calls than to those that overlapped their calls. These results support the first hypothesis. Results of four-speaker female choice experiments using alternating and overlapping calls indicate that preservation of signal integrity also is important in H. versicolor and H. microcephala, species that have fine-scale temporal information in their calls. However, the third hypothesis was not supported; females failed to discriminate among alternating and overlapping calls if the problem of signal disruption was eliminated or irrelevant.     

LICHEN HERBIVORE PREFERENCE: A TEST OF TWO HYPOTHESES

Field data from a saxicolous lichen community in Shenandoah National Park, Virginia, suggested that the slug Pallifera varia grazed more frequently on certain lichen species than would be expected if it fed randomly. Two hypotheses might explain this grazing pattern. The preference hypothesis, that slugs select lichens of highest quality, was tested by measuring the concentration of essential elements in lichens eliciting high and low preference by slugs. Lichens with the highest element contents were assumed to be of the highest quality to herbivores. The avoidance hypothesis, that preference by slugs actually results from the rejection of unpalatable species, was tested by offering slugs choices of baited filter-paper disks impregnated with secondary products of the lichen species in question. Results suggested that preferred lichens had significantly lower concentrations of N, P, and Ca, and that avoided lichens produced secondary products that effectively inhibited Pallifera grazing activity. These results suggested that the avoidance hypothesis was the better explanation for nonrandom Pallifera grazing patterns. Furthermore, they suggested that lichens with the highest concentrations of essential elements are most likely to produce defense compounds, an observation that supports predictions to explain patterns of chemical defense in vascular plants.     

THE ORIGIN OF TETRAPODS-PAST AND PRESENT HYPOTHESES

HistoricalreviewoneshouldexpectthatanewtheorychangesorimprovestheunderstandingofPhylogeneticquestions.ThatdoesnotseemtobetrueoftheoriginoftetrapodsasRosenetal.(l98l)havealreadyshowninthecaseoftheapPearanceofDarwin's'ontheoriginofsPeciesinl859.Incontrast,thehistoryofthedevelopmentofhypothesesontheoriginoftetrapodsdemonstratesthatdiscoveryofnewextantorfos-silforms(Tab.l)shapesourunderstandingoftherelationshipoftetrapodstofishes.Thefrstextantlungfishwasdiscoveredinl836inSouthAmerica(Fitzinge…     

CLADISTIC TESTS OF HYPOTHESES CONCERNING EVOLUTION OF XEROPHYTES AND MESOPHYTES WITHIN TILLANDSIA SUBG. PHYTARRHIZA (BROMELIACEAE)

Tillandsia L. Subg. Phytarrhiza (Visiani) Baker (Bromeliaceae) is a distinctive group of about 35 epiphytic species. These exhibit a range of habits from xeric to mesic. The evolutionary relationships of the contrasting adaptations need to be established here as well as in the subfamily as a whole. Relations between the subgenus and other tillandsioids are problematical and phylogenetic reconstruction of its member-species would be facilitated by identification of Phytarrhiza's relative (sister taxon) sharing the same most recent common ancestor with Phytarrhiza. This paper examines the two most likely sister taxa, Subg. Pseudo-Catopsis Baker and Subg. Diaphoranthema (Beer) Baker. Diaphoranthema is rejected as sister taxon. The accepted evolutionary tree, rooted by Pseudo-Catopsis, indicates that most habital evolutionary changes in Phytarrhiza have been between mesic and semi-mesic forms and from mesic to xeric forms. Methods developed for testing specific evolutionary hypotheses are broadly applicable.     

MODELS OF CHARACTER DISPLACEMENT AND THE THEORETICAL ROBUSTNESS OF TAXON CYCLES

The appropriateness of the techniques used in modeling character displacement has been the focus of vigorous debate. In this paper, the three competing methods (the coevolutionarily stable community (CSC), the evolutionarily stable strategy (ESS), and quantitative genetic recursion (QGR)) are compared in models using a common ecological setting. Specific predictions of the CSC model have been used to understand features of character displacement among Cnemidophorous lizards on islands off Mexico, Anolis lizards in the Lesser Antilles and Galápagos finches. Nonetheless, the validity of the approach has been repeatedly questioned. Conceptually the three formalisms vary in the degree to which within species variability is allowed in the models. The predictions of the CSC are found not to be robust to even small violation of its fundamental assumption of absolute species monomorphy. We show by simulation and analytical observations that the CSC is not valid under frequency dependent selection, and that the ESS is the limiting case of QGR as intraspecific phenotypic variation goes to zero. Thus the ESS and the QGR models agree closely when the between-phenotype component (BPC) of the niche width is small. However, as the BPC increases, quantitative discrepancies between ESS and QGR predictions increase, although model behavior remains qualitatively similar. A fourth approach, termed “Quantitative Genetic Optimization” (QGO) analysis, is suggested, combining advantages of both the ESS and QGR. Although all approaches support the possibility of taxon cycles, the cycle patterns predicted are qualitatively different and strongly model dependent.     

CONCEPTS AND TESTS OF HOMOLOGY IN THE CLADISTIC PARADIGM

Abstract— Logical equivalence between the notions of homology and synapomorphy is reviewed and supported. So-called transformational homology embodies two distinct logical components, one related to comparisons among different organisms and the other restricted to comparisons within the same organism. The former is essentially hierarchical in nature, thus being in fact a less obvious form of taxic homology. The latter is logically equivalent to so-called serial homology in a broad sense (including homonomy, mass homology or iterative homology). Of three tests of homology proposed to date (similarity, conjunction and congruence) only congruence serves as a test in the strict sense. Similarity stands at a basic level in homology propositions, being the source of the homology conjecture in the first place. Conjunction is unquestionably an indicator of non-homology, but it is not specific about the pairwise comparison where non-homology is present, and depends on a specific scheme of relationship in order to refute a hypothesis of homology. The congruence test has been previously seen as an application of compatibility analysis. However, congruence is more appropriately seen as an expression of strict parsimony analysis. A general theoretical solution is proposed to determine evolution of characters with ambiguous distributions, based on the notion of maximization of homology propositions. According to that notion, ambiguous character-state distributions should be resolved by an optimization that maximizes reversals relative to parallelisms. Notions of homology in morphology and molecular biology are essentially the same. The present tendency to adopt different terminologies for the two sources of data should be avoided, in order not to obscure the fundamental uniformity of the concept of homology in comparative biology. “A similar hierarchy is found both in ‘structures’ and in ‘functions’. In the last resort, structure (i.e. order of parts) and function (order of processes) may be the very same thing […].” L. von Bertalanlfy “[…] it is the fact that certain criteria enable us to match parts of things consistently which suggests that mechanisms of certain kinds must have been involved in their origin.” N. Jardine and C. Jardine     

EVOLUTIONARY ORIGIN OF THE CYCLORRHAPHA (DIPTERA): TEST OF ALTERNATIVE MORPHOLOGICAL HYPOTHESES

Abstract— The higher flies, infraorder Cyclorrhapha [=Muscomorpha (McAlpine, 1989)], have undergone enormous radiation since the Cretaceous (∼100 Myr). Rapid morphological evolution in cyclorrhaphans has made their phylogenetic placement with respect to more primitive clades a long-standing problem in dipteran systematics. Of the two most plausible hypotheses, one treats the Cyclorrhapha as sister group to the orthorrhaphous superfamily Empidoidea [=Empidiformia (Hennig, 1948), Orthogenya (Brauer, 1883)], while the other places them within the empidoids. The debate over cyclorrhaphan origin has heretofore focused on homology interpretations for a few character systems, particularly the male genitalia. We provide the first attempt to assemble and quantify all of the available morphological evidence. By cladistic analysis of these data under alternative codings of genitalic features reflecting opposing homology theories, and then excluding these features altogether, we sought to judge which genitalic theory is better supported by the evidence as a whole, and how much the debate matters to resolving cyclorrhaphan origins. Using the analog of a factorial design, we also measured the effect of alternative transformation series in several other controversial characters, of outgroup choice and of successive weighting. Under all manipulations, including both genitalic codings, the Cyclorrhapha originate within the Empidoidea, near the family Atelestidae. However, trees in which the Empidoidea are constrained to be monophyletic are only 1-6 steps longer (out of ∼150), a fit not significantly worse under a permutation test for monophyly. Adult morphological data may not suffice to settle either the placement of Cyclorrhapha or the debate over genitalic homology. Moreover, the issue of genitalic homology does not appear critical to that of cyclorrhaphan origin.     

THE NATURE OF CLADISTIC DATA

Abstract— Cladistic data are the characters of organisms. Character is defined as a feature that can be evaluated as a variable with two or more mutually exclusive and ordered states. Cladistic characters must be treated as multistate variables, and coded as sequential numbers or in additive binary fashion. Any other interpretation and handling of cladistic data will introduce error into analysis. Character states cannot be treated independently as present or absent, i.e., as nominal variables, because redundancy is introduced into the data and information content is sacrificed. Non-additive binary coding demonstrates that treating cladistic variables as nominal data will lead to multiple, equally parsimonious solutions. Defining characters found universally in a group of organisms, but unknown outside those organisms have no alternative state that can be designated as absent. Absence, however, is valid as a character state if it can be shown to be apomorphic. When two or more character states occur within a taxon, that taxon must be coded as having an unknown state for that character, or the taxon must be split in two or more taxa. Continuously varying quantitative data are not suitable for cladistic analysis because there is no justifiable basis for recognizing discrete states among them. Quantitative data are questionable even when they exhibit mutually exclusive states because the states can be interpreted only in reference to an archetype, i.e., as implied homologies not subject to test.     

DO CONSTANT ENVIRONMENTS PROMOTE COMPLEXITY OF FORM?: THE DISTRIBUTION OF BRYOZOAN POLYMORPHISM AS A TEST OF HYPOTHESES

The distribution of cheilostome bryozoans on the Caribbean reefs of Panama was surveyed to test the hypothesis that physically constant environments favor increased morphologic complexity, expressed as the number of zooid types within a colony. The proportion of species within defined grades of complexity did not vary significantly with locality, depth, or substratum. Some differences were found in grade-specific ecological success, measured by colony abundance and spatial cover, but these were not consistently related to habitat type. There was no inverse correlation between morphologic complexity and range of distribution: morphologically specialized cheilostomes were not more stenotopic than generalized forms. Patterns of distribution and total space occupation indicate a sensitivity to local habitat conditions, but relative success of species was not correlated with level of polymorphism. In a bryozoan fauna from Florida, the frequency of polymorphic species was weakly associated with constancy of habitat. In estuaries, polymorphic cheilostomes are almost absent at salinities below 18‰, but this pattern is strongly confounded taxonomically. All species tolerant of low salinities are encrusting anascans; within this group, polymorphism does not decrease significantly with declining salinity. Bryozoan faunas from different biogeographic zones may vary in frequency of avicularian polymorphism, but not along a simple latitudinal cline. These large-scale comparisons may be strongly biased historically and taxonomically. The distribution of cheilostome polymorphism on a local and geographic scale provides no evidence for a causal relationship between habitat constancy and morphologic specialization at the zooidal level. This is in striking contrast to the strong habitat dependence of colony form, which suggests that selective processes may operate differently at the zooidal and colonial levels.     

CLADISTIC AND BIOGEOGRAPHIC ANALYSIS OF THE "BLUE ASH' EUCALYPTS

Abstract— A cladistic analysis of the "blue ash" eucalypts ( Eucalyptus , Myrtaceae) is presented. Five equally parsimonious trees were found, and a strict consensus tree constructed. A revised informal classification, recognizing five series ( Planchonianinae, Sphaerocarpinae, Piperitinae, Fraxininae and Haemastominae , informal subgenus Monocalyptus ) is based on the consensus cladogram. A biogeographic analysis applies a new implementation of Assumptions 0 and 1, coding data in the form of three-area statements and using parsimony analysis. These results are used to evaluate hand resolution of Assumption 2. In comparison, Brooks parsimony analysis did not produce area cladograms that best fit the data. Series and subseries were analysed separately for area relationships, which showed a repeated pattern across the blue ash clade; combining all the data in one analysis was seen as equivalent to confounding paralogy and orthology in molecular studies. A resolved area cladogram is presented for southeastern Australia.     

EVOLUTION OF PELVIC REDUCTION IN THREESPINE STICKLEBACK FISH: A TEST OF COMPETING HYPOTHESES

Reimchen hypothesized that pelvic reduction in threespine stickleback is favored by an absence of piscivorous fishes and the resulting increase in predation by insects, but Giles hypothesized that the predation regime is unimportant and that a low dissolved calcium concentration favors evolution of pelvic reduction. Substantial pelvic reduction in threespine stickleback sampled from 179 lakes around Cook Inlet, Alaska is strongly associated both with an absence of predatory fishes and a low calcium concentration. However, the association of pelvic reduction with low calcium concentration appears to be contingent on the absence of predatory fishes. These results emphasize the importance of interactions between seemingly unrelated environmental variables for selection of a single trait. However, these results also conflict with some observations elsewhere and do not rule out the possibility that other environmental factors are important for selection for pelvic reduction in threespine stickleback.     

THE PLEURASTROPHYCEAE AND MICROMONADOPHYCEAE: A CLADISTIC ANALYSIS OF NUCLEAR rRNA SEQUENCE DATA1

Partial sequences from the nuclear-encoded 18S and 26S ribosomal RNA molecules from representatives of the five classes of Chlorophyta sensu Mattox and Stewart (1984) were analyzed cladistically in a study of the phylogenetic relationships among the Micromonadophyceae, Pleurastrophyceae, and other green algae. The sequence data indicate that the Micromonadophyceae (= Prasinophyceae) is not monophyletic but comprises at least three lineages occupying a basal position among the green algae. Though the Pleurastrophyceae and the Ulvophyceae both possess counter-clockwise basal body orientations, the sequence data indicate that the Pleurastrophyceae is the sister group to the Chlorophyceae. The molecular data alone do not resolve the monophyly of the Pleurastrophyceae or the Ulvophyceae; however, a combined data set of molecular and non-molecular characters support a monophyletic Pleurastrophyceae. Analyses with user-defined tree topologies and the bootstrap method of character resampling indicate that the relationships shown in the most parasimonious cladograms are well supported by the character data.