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Evolutionary Hypotheses (evolutionary + hypothesis)
Selected AbstractsEVOLUTION OF MOUTHBROODING AND LIFE-HISTORY CORRELATES IN THE FIGHTING FISH GENUS BETTAEVOLUTION, Issue 4 2004Lukas Rüber Abstract The origin of and evolutionary transitions among the extraordinary diverse forms of parental care in teleost fish remain largely unknown. The "safe harbor" hypothesis predicts that the evolution from a "guarding" to a "brooding" form of care in teleost fish is associated with shifts in reproductive and life-history features such as reduced fecundity, and increased egg volume with higher parental investment. Robust phylogenetic hypotheses may help to identify evolutionary changes in key traits associated with differences in the form of parental care. Here, we used reconstruction of ancestral character states to study the evolution of the two forms of parental care, bubble nesting and mouthbrooding in the fighting fish genus Betta. We also applied a comparative analysis using the phylogenetic generalized least-squares method to test the "safe harbor" hypothesis by evaluating differences between the two forms of parental care in standard length, life-history traits, and three habitat variables. Evolutionary hypotheses were derived from the first molecular phylogeny (nuclear and mitochondrial DNA sequence data; 4448 bp) of this speciose group. Ancestral character state reconstructions of the evolution of the form of parental care in the genus Betta, using the methods of unweighted parsimony and maximum likelihood, are uncertain and further indicate a high rate of evolutionary transitions. Applying different weights for the suspected directionality of changes, based on the consistent phenotypic and behavioral differences found between bubble nesters and mouthbrooders, recurrent origin of mouthbrooding in the genus Betta is favored using parsimony. Our comparative analyses further demonstrate that bubble nesters and mouthbrooders do not have a consistent set of life-history correlates. The form of parental care in Betta is correlated only with offspring size, with mouthbrooders having significantly bigger offspring than bubble nesters, but is not correlated with egg volume, clutch size, and broodcare duration, nor with any of the three habitat variables tested. Our results thus challenge the general predictions of the "safe harbor" hypothesis for the evolution of alternative brood care forms in the fighting fish genus Betta. [source] The tropics: cradle, museum or casino?ECOLOGY LETTERS, Issue 7 2008A dynamic null model for latitudinal gradients of species diversity Abstract Several ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid-domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one- or two-dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients. [source] THE SHAPES OF NEUTRAL GENE GENEALOGIES IN TWO SPECIES: PROBABILITIES OF MONOPHYLY, PARAPHYLY, AND POLYPHYLY IN A COALESCENT MODELEVOLUTION, Issue 7 2003Noah A. Rosenberg Abstract., 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 , 1.300N generations after divergence, paraphyly becomes most likely, and reciprocal monophyly becomes most likely at ,1.665N generations. For a given species, the time at which 99% of its loci acquire monophyletic genealogies is ,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. [source] Pollen and sperm heteromorphism: convergence across kingdoms?JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2005I. Till-Bottraud Abstract Sperm competition theory predicts that males should produce many, similar sperm. However, in some species of animals and plants, males exhibit a heteromorphism that results in the production of at least two different types of sperm or pollen grains. In animals, sperm heteromorphism typically corresponds to the production of one fertile morph and one (or more) sterile morph(s), whereas in plants two or more pollen morphs (one of which can be either sterile or fertile) are produced in all flowers but sometimes in different anthers. Heteromorphism has arisen independently several times across phyla and at different phylogenetic levels. Here, we compare and contrast sperm and pollen heteromorphism and discuss the evolutionary hypotheses suggested to explain heteromorphism in these taxa. These hypotheses include facilitation, nutritive contribution, blocking, cheap filler, sperm flushing or killing for animals; outcrossing and precise cross-pollen transfer or bet-hedging strategy for plants; cryptic female choice for both. We conclude that heteromorphism in the two phyla is most likely linked to a general evolutionary response to sexual selection, either to increase one male's sperm or pollen success in competition with other males, or mediate male/female interactions. Therefore, although sperm and pollen are not homologous, we suggest that heteromorphism represents an example of convergence across kingdoms. [source] Patterns of carpal development among anuran amphibiansJOURNAL OF MORPHOLOGY, Issue 3 2001Marissa Fabrezi Abstract The unity and diversity of developmental processes in the vertebrate limb have singular importance in the interpretation of evolutionary hypotheses of tetrapod diversification. In anurans, the intraordinal diversity of forelimbs seems to be related to the fusion of distal carpals, whereas proximal carpals are invariable. However, there are different ontogenetic pathways involved in the differentiation of proximal carpals. This study presents a comparative analysis of early developmental features in one archeobatrachian and 23 neobatrachian species representing five families and explores the variability in the differentiation of carpal cartilages. We found new evidence supporting the presence of an embryonic intermedium that incorporates with the ulnare. Difference between the pipid Xenopus and the neobatrachians is interpreted as a change in the rate of differentiation of Distal Carpal 5 that does not affect the developmental pattern of digits. The developmental variability exhibited by the intermedium, radiale, and Element Y is combined in patterns that converge on the same adult carpal morphology among neobatrachians; these patterns appear to contain potentially useful phylogenetic information. J. Morphol. 249:210,220, 2001. © 2001 Wiley-Liss, Inc. [source] Sexual segregation in western grey kangaroos: testing alternative evolutionary hypothesesJOURNAL OF ZOOLOGY, Issue 2 2007A. M. MacFarlane Abstract In sexually dimorphic ungulates, sexual segregation is hypothesized to have evolved because of sex-specific differences in body size and/or reproductive strategies. We tested these alternative hypotheses in kangaroos, which are ecological analogues of ungulates. Kangaroos exhibit a wide range of body sizes, particularly among mature males, and so the effects of body size and sex can be distinguished. We tested predictions derived from these hypotheses by comparing the distribution of three sex,sex size classes of western grey kangaroos Macropus fuliginosus, in different habitats, and the composition of groups of kangaroos, across seasons. In accordance with the predation risk-reproductive strategy hypothesis, during the non-breeding season, females, which were more susceptible to predation than larger males, and were accompanied by vulnerable young-at-foot, were over-represented in secure habitats. Large males, which were essentially immune to predation, occurred more often than expected in nutrient-rich habitat, and small males, which faced competing demands of predator avoidance and feeding, were intermediate between females and large males in their distribution across habitats. During the breeding season, females continued to be over-represented in secure habitats when their newly emerged pouch young were most vulnerable to predation. All males occupied these same habitats to maximize their chances of securing mates. Consistent with the social hypotheses, groups composed of individuals of the same sex, irrespective of body size, were over-represented in the population during the non-breeding season, while during the breeding season all males sought females so that mixed-sex groups predominated. These results indicate that body size and reproductive strategies are both important, yet independent, factors influencing segregation in western grey kangaroos. [source] DOES DIVING LIMIT BRAIN SIZE IN CETACEANS?MARINE MAMMAL SCIENCE, Issue 2 2006Lori Marino Abstract We 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. [source] Allochronic speciation, secondary contact, and reproductive character displacement in periodical cicadas (Hemiptera: Magicicada spp.): genetic, morphological, and behavioural evidenceMOLECULAR ECOLOGY, Issue 3 2001John R. Cooley Abstract Periodical cicadas have proven useful in testing a variety of ecological and evolutionary hypotheses because of their unusual life history, extraordinary abundance, and wide geographical range. Periodical cicadas provide the best examples of synchronous periodicity and predator satiation in the animal kingdom, and are excellent illustrations of habitat partitioning (by the three morphologically distinct species groups), incipient species (the year classes or broods), and cryptic species (a newly discovered 13-year species, Magicicada neotredecim). They are particularly useful for exploring questions regarding speciation via temporal isolation, or allochronic speciation. Recently, data were presented that provided strong support for an instance of allochronic speciation by life-cycle switching. This speciation event resulted in the formation of a new 13-year species from a 17-year species and led to secondary contact between two formerly separated lineages, one represented by the new 13-year cicadas (and their 17-year ancestors), and the other represented by the pre-existing 13-year cicadas. Allozyme frequency data, mitochondrial DNA (mtDNA), and abdominal colour were shown to be correlated genetic markers supporting the life-cycle switching/allochronic speciation hypothesis. In addition, a striking pattern of reproductive character displacement in male call pitch and female pitch preference between the two 13-year species was discovered. In this paper we report a strong association between calling song pitch and mtDNA haplotype for 101 individuals from a single locality within the M. tredecim/M. neotredecim contact zone and a strong association between abdomen colour and mtDNA haplotype. We conclude by reviewing proposed mechanisms for allochronic speciation and reproductive character displacement. [source] Brain size and the human cranial base: A prenatal perspectiveAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2002Nathan Jeffery Abstract Pivotally positioned as the interface between the neurocranium and the face, the cranial base has long been recognized as a key area to our understanding of the origins of modern human skull form. Compared with other primates, modern humans have more coronally orientated petrous bones and a higher degree of basicranial flexion, resulting in a deeper and wider posterior cranial fossa. It has been argued that this derived condition results from a phylogenetic increase in the size of the brain and its subcomponents (infra- and supratentorial volumes) relative to corresponding lengths of the cranial base (posterior and anterior, respectively). The purpose of this study was to test such evolutionary hypotheses in a prenatal ontogenetic context. We measured the degree of basicranial flexion, petrous reorientation, base lengths, and endocranial volumes from high-resolution magnetic resonance images (hrMRI) of 46 human fetuses ranging from 10,29 weeks of gestation. Bivariate comparisons with age revealed a number of temporal trends during the period investigated, most notable of which were coronal rotation of the petrous bones and basicranial retroflexion (flattening). Importantly, the results reveal significant increases of relative endocranial sizes across the sample, and the hypotheses therefore predict correlated variations of cranial base flexion and petrous orientation in accordance with these increases. Statistical analyses did not yield results as predicted by the hypotheses. Thus, the propositions that base flexion and petrous reorientation are due to increases of relative endocranial sizes were not corroborated by the findings of this study, at least for the period investigated. Am J Phys Anthropol 118:324,340, 2002. © 2002 Wiley-Liss, Inc. [source] Resprouting responses of trees in a fire-prone tropical savanna following severe tornado damageAUSTRAL ECOLOGY, Issue 6 2010DONALD C. FRANKLIN Abstract Fire and windstorms can cause severe disturbance, but their consequences for trees may differ. Resprouting enables persistence through frequent and severe disturbance. To explore responses to an abnormal disturbance and evolutionary hypotheses about resprouting as an adaptation, we analysed patterns of resprouting in four taxa following a tornado in a tropical savanna (Kakadu National Park, northern Australia) that is frequently burnt but is rarely subject to severe windthrow. Resprouting (i.e. survival) rates varied markedly among taxa and damage types, from 35% in uprooted Acacia spp. (Mimosaceae) to over 90% in eucalypts (Myrtaceae) and Erythrophleum chlorostachys (Caesalpiniaceae) with persistent tertiary branches. Most resprouting was from the epicormic strand-bank on the stem or branches. Across all taxa, greater architectural damage reduced resprouting rates. Damage was magnified by proximity to the centre of the tornado path, suggesting an additional effect of internal damage. Smaller trees, trees whose trunks were snapped below 2 m, and those closer to the tornado path were more likely to resprout basally or from the roots rather than epicormically, although in Acacia spp. these resprouting modes were positively correlated. We hypothesize that trees of fire-prone savannas have evolved to grow rapidly out of the flame zone; this was supported by more detailed analyses of Eucalyptus tetrodonta suggesting that resprouts emerging nearer the ground grow faster. Resprouting at ground level may be a bet-hedging strategy to spread the risk of mortality among multiple stems when elevated sprouting was not possible. We conclude that the adaptation of eucalypts to frequent fire does not jeopardize their survival (by comparison with the more generalist Acacia spp.) following severe windthrow, providing an example of ,exaptation' rather than trade-off in fitness under contrasting stressors. [source] Male genes: X-pelled or X-cluded?BIOESSAYS, Issue 8 2003David W. Rogers Two recent studies by Parisi et al.1 and Ranz et al.,2 catalogue sex differences in gene expression across the whole genome of the fruit fly Drosophila melanogaster. Both report striking associations of sex-biased gene expression with the X chromosome. Genes with male-biased expression are depauperate on the X chromosome, whereas genes with female-biased expression show weaker evidence of being in excess. A number of evolutionary hypotheses for the expulsion or exclusion of male-biased genes from the X chromosome have been suggested. None is entirely consistent with the available evidence. BioEssays 25:739,741, 2003. © 2003 Wiley Periodicals, Inc. [source] Evolutionary morphology of the circulatory system in Peracarida (Malacostraca; Crustacea)CLADISTICS, Issue 2 2010Christian S. Wirkner 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. [source] Evolution of advertisement signals in North American hylid frogs: vocalizations as end-products of calling behaviorCLADISTICS, Issue 6 2006Tony Robillard We studied the advertisement signals in two clades of North American hylid frogs in order to characterize the relationships between signal acoustic structure and underlying behavior. A mismatch was found between the acoustic structure and the mechanism of sound production. Two separate sets of phylogenetic characters were coded following acoustic versus mechanistic criteria, and exploratory treatments were made to compare their respective phylogenetic content in comparison with the molecular phylogeny (Faivovich et al., 2005). We discuss the consequences of the acoustic/mechanistic mismatch in terms of significance of acoustic characters for phylogenetic and comparative studies; and the evolution of vocalizations in North American treefrogs. Considering only the acoustic structure of frog vocalizations can lead to misleading results in terms of both phylogenetic signal and evolution of vocalizations. In contrast, interpreting the acoustic signals with regard to the mechanism of sound production results in consistent phylogenetic information. The mechanistic coding also provides strong homologies for use in comparative studies of frog vocalizations, and to derive and test evolutionary hypotheses. © The Willi Hennig Society 2005. [source] CALORIE RESTRICTION AND AGING: A LIFE-HISTORY ANALYSISEVOLUTION, Issue 3 2000Daryl P. Shanley Abstract., The disposable soma theory suggests that aging occurs because natural selection favors a strategy in which fewer resources are invested in somatic maintenance than are necessary for indefinite survival. However, laboratory rodents on calorie-restricted diets have extended life spans and retarded aging. One hypothesis is that this is an adaptive response involving a shift of resources during short periods of famine away from reproduction and toward increased somatic maintenance. The potential benefit is that the animal gains an increased chance of survival with a reduced intrinsic rate of senescence, thereby permitting reproductive value to be preserved for when the famine is over. We describe a mathematical life-history model of dynamic resource allocation that tests this idea. Senescence is modeled as a change in state that depends on the resources allocated to maintenance. Individuals are assumed to allocate the available resources to maximize the total number of descendants. The model shows that the evolutionary hypothesis is plausible and identifies two factors, both likely to exist, that favor this conclusion. These factors are that survival of juveniles is reduced during periods of famine and that the organism needs to pay an energetic "overhead" before any litter of offspring can be produced. If neither of these conditions holds, there is no evolutionary advantage to be gained from switching extra resources to maintenance. The model provides a basis to evaluate whether the life-extending effects of calorie-restriction might apply in other species, including humans. [source] Phylogenetic reconstruction of carnivore social organizationsJOURNAL OF ZOOLOGY, Issue 1 2007F. Dalerum Abstract It is generally assumed that carnivore social organizations evolved directionally from a solitary ancestor into progressively more advanced forms of group living. Although alternative explanations exist, this evolutionary hypothesis has never been tested. Here, I used literature data and maximum likelihood reconstruction on a complete carnivore phylogeny to test this hypothesis against two others: one assuming directional evolution from a non-solitary ancestor, and one assuming parallel evolutions from a socially flexible ancestor, that is, an ancestor with abilities to live in a variety of social organizations. The phylogenetic reconstructions did not support any of the three hypotheses of social evolution at the root of Carnivora. At the family level, however, there was support for a non-solitary and socially flexible ancestor to Canidae, a socially flexible or solitary ancestor to Mustelidae, a solitary or socially flexible ancestor to Mephitidae, a solitary or group living ancestor to Phocidae, a group living ancestor to Otariidae and a solitary ancestor to Ursidae, Felidae, Herpestidae and Viverridae. There was equivocal support for the ancestral state of Procyonidae and Hyaenidae. It is unclear whether the common occurrence of a solitary ancestry at the family level was caused by a solitary ancestor at the root of Carnivora or by multiple transitions into a solitary state. The failure to support a solitary ancestor to Carnivora calls for caution when using this hypothesis in an evolutionary framework, and I suggest continued investigations of the pathways of the evolution of carnivore social organizations. [source] Parent,Daughter Transmission of the Androgen Receptor Gene as an Explanation of the Effect of Father Absence on Age of MenarcheCHILD DEVELOPMENT, Issue 4 2002David E. Comings Based on an evolutionary theory of socialization, Belsky and colleagues proposed that girls exposed to a stressful environment, especially when due to father absence in the first 7 years of life, showed an early onset of puberty, precocious sexuality, and unstable relationships as adults. The authors of this article examined an alternative explanation that a variant X,linked androgen receptor (AR) gene, predisposing the father to behaviors that include family abandonment, may be passed to their daughters causing early puberty, precocious sexuality, and behavior problems. The results of a study of 121 White males and 164 White females showed a significant association of the short alleles of the GGC repeat polymorphism of the AR gene with a range of measures of aggression and impulsivity, increased number of sexual partners, sexual compulsivity, and lifetime number of sex partners in males; and paternal divorce, father absence, and early age of menarche in females. These findings support a genetic explanation of the Belsky psychosocial evolutionary hypothesis regarding the association of fathers' absence and parental stress with early age of onset of menarche and early sexual activity in their daughters. A genetic explanation of the father absence effect is proposed in which fathers carrying the AR alleles are more likely to abandon a marriage (father absence) and pass those alleles to their daughters in whom they produce an earlier age of menarche and behavioral problems. [source] | ||||||||||||||||||||||