Showing papers in "Biological Journal of The Linnean Society in 2004"
TL;DR: It is reaffirmed that orchids are primarily pollination limited, the severity of which is affected by resource constraints and population structure, reproductive success and gene flow among populations suggest that in many situations genetic drift may be as important as selection in fostering genetic and morphological variation in this family.
Abstract: The great taxonomic diversity of the Orchidaceae is often attributed to adaptive radiation for specific pollinators driven by selection for outcrossing. However, when one looks beyond the product to the process, the evidence for selection is less than overwhelming. We explore this problem by discussing relevant aspects of orchid biology and asking which aspects of reproduction explain the intricate pollination mechanisms and diversification of this family. We reaffirm that orchids are primarily pollination limited, the severity of which is affected by resource constraints. Fruit set is higher in temperate than in tropical species, and in species which offer pollinator rewards than those that do not. Reproductive success is skewed towards few individuals in a population and effective population sizes are often small. Population structure, reproductive success and gene flow among populations suggest that in many situations genetic drift may be as important as selection in fostering genetic and morphological variation in this family. Although there is some evidence for a gradualist model of evolutionary change, we believe that the great diversity in this family is largely a consequence of sequential and rapid interplay between drift and natural selection. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 84, 1–54.
633 citations
TL;DR: The results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance and the nature of the evolutionary forces that may be driving DNA loss are discussed.
Abstract: All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database (http:// www.rbgkew.org.uk/cvavhomepage.html) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed.
594 citations
TL;DR: It is concluded that the evolutionary success of polyploids in the Arctic may be based on their fixed-heterozygous genomes, which buffer against inbreeding and genetic drift through periods of dramatic climate change.
Abstract: The Arctic is an excellent model system for the study of polyploidy It is one the Earth's most polyploid-rich areas, in particular of high-level and recently evolved polyploids Here we re-address previous hypotheses on arctic polyploidy based on a new analysis of the circumarctic flora, and review recent molecular, cytological and reproductive studies The frequency and level of polyploidy strongly increase northwards within the Arctic We found no clear-cut association between polyploidy and the degree of glaciation for the arctic flora as a whole, which contains many widespread species However, for ‘arctic specialist’ taxa with restricted distributions, the frequency of diploids is much higher in the Beringian area, which remained largely unglaciated during the last ice age, than in the heavily glaciated Atlantic area This result supports the hypothesis that polyploids are more successful than diploids in colonizing after deglaciation There is abundant molecular evidence for recurrent formation of arctic polyploids at different scales in time and space Examples are given of low-level polyploids formed after the last glaciation and of repeated and successively more high-level polyploidizations throughout the Quaternary Recurrent polyploid origins, followed by interbreeding within and across ploidal levels, provide a major explanation for the taxonomic complexity of the arctic flora In the well-studied, recently deglaciated archipelago of Svalbard, most species are mainly self-fertilizing or clonal All Svalbard polyploids examined so far are genetic allopolyploids with fixed heterozygosity at isozyme loci The level of heterozygosity in 65 taxa increases dramatically from diploids to high-level polyploids In the circumarctic area, there is evidence for numerous recently evolved sibling species within diploid taxonomic species Rapid evolution of crossing barriers at the diploid level promotes further diversification after expansion from different refugia, and may provide new raw materials for allopolyploid formation We conclude that the evolutionary success of polyploids in the Arctic may be based on their fixed-heterozygous genomes, which buffer against inbreeding and genetic drift through periods of dramatic climate change © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 521–536
527 citations
TL;DR: Morphological, morphological, allozyme and mitochondrial 16S rDNA sequence data have been jointly evaluated and gonad type proved to be a useful character for distinguishing the two species in north-west Europe.
Abstract: The importance and abundance of cryptic species among invertebrate taxa is well documented. Nowadays, taxonomic, phylogenetic and conservation biological studies frequently use molecular markers to delineate cryptic taxa. Such studies, however, often face the problem of the differential resolution of the molecular markers and techniques involved. This issue is explored in the present study of cryptic taxa within the terrestrial slug complex Arion subfuscus/fuscus in continental north-west Europe. To this end, morphological, allozyme and mitochondrial 16S rDNA sequence data have been jointly evaluated. Using allozyme data and gonad type, two distinct groups were consistently delineated, even under sympatric conditions. The 16S rDNA data strongly supported both those groups and even suggested the presence of three distinct taxa within one of them. However, in view of: (1) the allopatric distribution of three OTUs, (2) the lack of allozyme or morphological differentiation, and (3) the extremely high degree of intraspecific mtDNA variation reported in pulmonate gastropods, they are, for the time being, not regarded as valid species under the biological species concept. By means of 16S rDNA and allozyme data, the position of type and topotype material of A. subfuscus s.s. and A. fuscus relative to the newly defined OTUs was determined, thus clarifying the nomenclature of this species complex. Additionally, gonad type proved to be a useful character for distinguishing the two species in north-west Europe.
376 citations
TL;DR: It is shown that multiple origins of a polyploid species not only affect patterns of genetic variation in natural populations, but also contribute to differential patterns of gene expression and may therefore play a major role in the long-term evolution of polyploids.
Abstract: Tragopogon mirus Ownbey and T. miscellus Ownbey are allopolyploids that formed repeatedly during the past 80 years following the introduction of three diploids (T. dubius Scop., T. pratensis L. and T. porrifolius L.) from Europe to western North America. These polyploid species of known parentage are useful for studying the consequences of recent and recurrent polyploidization. We summarize recent analyses of the cytogenetic, genomic and genetic consequences of polyploidy in Tragopogon. Analyses of rDNA ITS (internal transcribed spacer) + ETS (external transcribed spacer) sequence data indicate that the parental diploids are phylogenetically well separated within Tragopogon (a genus of perhaps 150 species), in agreement with isozymic and cpDNA data. Using Southern blot and cloning experiments on tissue from early herbarium collections of T. mirus and T. miscellus (from 1949) to represent the rDNA repeat condition closer to the time of polyploidization than samples collected today, we have demonstrated concerted evolution of rDNA. Concerted evolution is ongoing, but has not proceeded to completion in any polyploid population examined; rDNA repeats of the diploid T. dubius are typically lost or converted in both allopolyploids, including populations of independent origin. Molecular cytogenetic studies employing rDNA probes, as well as centromeric and subtelomeric repeats isolated from Tragopogon, distinguished all chromosomes among the diploid progenitors (2n = 12). The diploid chromosome complements are additive in both allopolyploids (2n = 24); there is no evidence of major chromosomal rearrangements in populations of either T. mirus or T. miscellus. cDNA-AFLP display revealed differences in gene expression between T. miscellus and its diploid parents, as well as between populations of T. miscellus of reciprocal origin. Approximately 5% of the genes examined in the allopolyploid populations have been silenced, and an additional 4% exhibit novel gene expression relative to their diploid parents. Some of the differences in gene expression represent maternal or paternal effects. Multiple origins of a polyploid species not only affect patterns of genetic variation in natural populations, but also contribute to differential patterns of gene expression and may therefore play a major role in the long-term evolution of polyploids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 485–501.
340 citations
TL;DR: A chromosomal rearrangement of a genomic segment containing BnFLC3 was responsible for 29% of the phenotypic variation among the B. napus lines, and Expression of BnflC5 was silenced in all polyploids, although no changes in genome structure were detected.
Abstract: Novel phenotypes often arise in generations immediately following polyploidization. Previous studies have shown that separate lineages derived from a resynthesized Brassica napus allopolyploid rapidly evolved heritable differences in flowering time. These early-flowering and late-flowering polyploid lines were expected to be genetically identical because they were derived from a single, chromosome-doubled amphihaploid plant. In this study, we investigated the molecular genetic basis for these flowering time differences. We assessed the diploid B. rapa and B. oleracea parents and the early- and late-flowering B. napus lineages for changes in genome structure, and for changes in transcript levels of four sets of FLOWERING LOCUS C ( FLC ) genes. No such changes were observed for BnFLC1 , but we detected chromosomal rearrangements (e.g. de novo non-reciprocal transpositions) and changes in transcript level for BnFLC2 and BnFLC3 between the early- and late-flowering B. napus . A chromosomal rearrangement of a genomic segment containing BnFLC3 was responsible for 29% of the phenotypic variation among the B. napus lines. Expression of BnFLC5 was silenced in all polyploids, although no changes in genome structure were detected. An ongoing investigation of 50 identical B. napus allopolyploids may further reveal the dynamics of changes in phenotype, genome and transcriptome at the early stages in polyploid evolution. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 675‐688. ADDITIONAL KEYWORDS: Brassica napus ‐ chromosomal rearrangements ‐ de novo variation ‐ epigenetics ‐ evolution ‐ FLOWERING LOCUS C ‐ gene silencing ‐ life history traits ‐ polyploidy ‐ translocations.
289 citations
TL;DR: It is hypothesized that the functional and ecological diversity of labrids is due in part to a history of decoupled evolution of major components of the feeding system as well as among the muscular and skeletal elements of each component.
Abstract: The Labridae (including wrasses, the Odacidae and the Scaridae) is a species-rich group of perciform fishes whose members are prominent inhabitants of warm-temperate and tropical reefs worldwide. We analyse functionally relevant morphometrics for the feeding apparatus of 130 labrid species found on the Great Barrier Reef and use these data to explore the morphological and mechanical basis of trophic diversity found in this assemblage. Morphological measurements were made that characterize the functional and mechanical properties of the oral jaws that are used in prey capture and handling, the hyoid apparatus that is used in expanding the buccal cavity during suction feeding, and the pharyngeal jaw apparatus that is used in breaking through the defences of shelled prey, winnowing edible matter from sand and other debris, and pulverizing the algae, detritus and rock mixture eaten by scarids (parrotfishes). A Principal Components Analysis on the correlation matrix of a reduced set of ten variables revealed complete separation of scarids from wrasses on the basis of the former having a small mouth with limited jaw protrusion, high mechanical advantage in jaw closing, and a small sternohyoideus muscle and high kinematic transmission in the hyoid four-bar linkage. Some scarids also exhibit a novel four-bar linkage conformation in the oral jaw apparatus. Within wrasses a striking lack of strong associations was found among the mechanical elements of the feeding apparatus. These weak associations resulted in a highly diverse system in which functional properties occur in many different combinations and reflect variation in feeding ecology. Among putatively monophyletic groups of labrids, the cheilines showed the highest functional diversity and scarids were moderately diverse, in spite of their reputation for being trophically monomorphic and specialized. We hypothesize that the functional and ecological diversity of labrids is due in part to a history of decoupled evolution of major components of the feeding system (i.e. oral jaws, hyoid and pharyngeal jaw apparatus) as well as among the muscular and skeletal elements of each component.
251 citations
TL;DR: The effects of triploids on autotetraploid evolution is evaluated using computer simulations and by synthesizing research on the evolutionary dynamics of mixed-ploidy populations in Chamerion angustifolium (Onagraceae).
Abstract: Theory suggests that the evolution of autotetraploids within diploid populations will be opposed by a minority-cytotype mating disadvantage. The role of triploids in promoting autotetraploid establishment is rarely considered, yet triploids are often found in natural populations and are formed in experimental crosses. Here, I evaluate the effects of triploids on autotetraploid evolution using computer simulations and by synthesizing research on the evolutionary dynamics of mixed-ploidy populations in Chamerion angustifolium (Onagraceae). Simulations show that the fate of a tetraploid in a diploid population varies qualitatively depending on the relative fitness of triploids, the ploidy of their gametes and the fitness of diploids relative to tetraploids. In general, even partially fit triploids can increase the likelihood of diploid-tetraploid coexistence and, in some cases, facilitate tetraploid fixation. Within the diploid-tetraploid contact zone of C. angustifolium, mixed populations are common (43%), and often (39%) contain triploids. Greenhouse and field studies indicate that triploid fitness is low (9% of diploids) but variable. Furthermore, euploid gametes produced by triploids can be x, 2x or 3x and contribute the majority (62%) of new polyploids formed in each generation (2.3 x 10 -3 ). Although triploid bridge, alone, may not account for the evolution of autotetraploidy in C. angustifolium, it probably contributes to the prevalence of mixed-ploidy populations in this species. Therefore, in contrast to hybrids in homoploid species, triploids may actually facilitate rather than diminish the fixation of tetraploids by enhancing the rate of formation.
246 citations
TL;DR: The evidence for and against some of the traditional views on polyploidy is reviewed, with an attempt to synthesize factors promoting evolution through genome duplication in both groups.
Abstract: Although polyploidy has been involved in speciation in both animals and plants, the general perception is often that it is too rare to have been a significant factor in animal evolution and its role in plant diversification has been questioned. These views have resulted in a bias towards explanations for what deters polyploidy, rather than the somewhat more interesting question of the mechanisms by which polyploidy arises and becomes established in both plants and animals. The evidence for and against some of the traditional views on polyploidy is reviewed, with an attempt to synthesize factors promoting evolution through genome duplication in both groups. It is predicted that polyploidy should be more common in temperate than in tropical breeders because environmental fluctuations may promote unreduced gamete formation, it should be most common in organisms with sufficient numbers of gametes that random meiotic problems can be overcome, and it should be more frequent when mechanisms to promote assortative mating are a direct byproduct of genome duplication. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 453‐466.
245 citations
TL;DR: Transcriptional and post-transcriptional alterations of gene activity, including transcriptional activation of retro-elements, led to novel expression patterns that emphasize the plasticity of the genome with regard to both structure and gene expression, which might improve the adaptability of the newly formed allopolyploids and facilitate their rapid and successful establishment in nature.
Abstract: In the past few years we have analysed alterations in genome structure and expression that occur in wheat upon allopolyploidization. Our major findings in natural and synthetic allopolyploid wheat are reviewed here. It was found that allopolyploidization brings about rapid genome evolution through the instantaneous generation of a variety of cardinal genetic and epigenetic alterations comprising: (1) non-random elimination of coding and non-coding DNA sequences, (2) epigenetic changes such as DNA methylation of coding and non-coding DNA leading, among others, to gene silencing, and (3) activation of retroelements, which in turn alters the expression of adjacent genes. These changes were reproducible, occurring in the F1 hybrids or in the first generation(s) of a series of nascent allopolyploids corresponding to various interspecific and intergeneric combinations. Moreover, these changes were similar to those that occurred twice in nature: first, at the transition from diploid to tetraploid wheat (-0.5 Mya) and, second, at the transition from tetraploid to hexaploid wheat (-9500 years ago). Elimination of non-coding sequences augments the differentiation of homoeologous chromosomes at the polyploid level, thus increasing the physical divergence between homoeologues and contributing to the diploid-like meiotic behaviour of polyploid wheat. Transcriptional and post-transcriptional alterations of gene activity, including transcriptional activation of retro-elements, led to novel expression patterns. These phenomena emphasize the plasticity of the genome with regard to both structure and gene expression. This plasticity in turn might improve the adaptability of the newly formed allopolyploids and facilitate their rapid and successful establishment in nature.
244 citations
TL;DR: The hypothesis that Pleistocene land bridges enabled widespread movements in three rain-forest-restricted murine rodents of the Sunda shelf is tested and a deep history of vicariant evolution that may correspond with the Pliocene fragmentation of theSunda block is suggested.
Abstract: The Sunda region of south-east Asia comprises the Malay Peninsula and the islands of Java, Sumatra and Borneo, all of which lie on a shallow continental shelf projecting from Indochina. Pleistocene glacial cycles caused sea levels to drop repeatedly, exposing vast areas of the Sunda shelf and creating land bridges among the islands and mainland. These land bridges, the latest of which connected all three of the major Sunda islands to the Malay Peninsula as recently as 9500 years ago, may have enabled mammalian migrations across the Sunda shelf. Pleistocene land bridges on the Sunda shelf have been invoked to explain the current distributions of mammalian taxa occupying ranges corresponding with the Pleistocene limits of land and the appearance of new mammal species in the Pleistocene fossil record. The ability of mammals to move throughout the exposed shelf during periods of low sea level would, however, have been influenced by topographic and ecological features, which have been variously described as savanna-like or as moist tropical rain forest. Using a phylogeographical approach, we test the hypothesis that Pleistocene land bridges enabled widespread movements in three rain-forest-restricted murine rodents of the Sunda shelf: Maxomys surifer, Leopoldamys sabanus and Maxomys whiteheadi. Our results do not support the hypothesis of broad Pleistocene migrations in these taxa, but instead suggest a deep history of vicariant evolution that may correspond with the Pliocene fragmentation of the Sunda block. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 91–109.
TL;DR: Two new polyploid species of Senecio have originated in the British Isles in recent times following hybridization between native S. vulgaris and S. eboracensis, and what is known about when and how each species originated, and their reproductive isolation from parents due to high selfing rates is reviewed.
Abstract: Two new polyploid species of Senecio have originated in the British Isles in recent times following hybridization between native S. vulgaris (2n = 40) and introduced S. squalidus (2n = 20). One of these is the allohexaploid S. cambrensis (2n = 60), the other is the recombinant tetraploid S. eboracensis (2n = 40). We review what is known about when and how each species originated, and their reproductive isolation from parents due to high selfing rates. We also review evidence that suggests S. cambrensis may have undergone rapid genome evolution since its origin, and comment on the risks of extinction to each species due to chance factors operating during the early establishment phase. The discovery of both species soon after their origin provides an unparalleled opportunity to examine two different but related forms of speciation following hybridization between the same parent species. Further detailed study of the ecology and genomics of S. cambrensis and S. eboracensis will help improve our understanding of the process of polyploid speciation in plants.
TL;DR: This is the first phylogenetically controlled comparative study to report the evolution of parasite-defence grooming behaviours in response to selection pressures predicted by the programmed grooming hypothesis.
Abstract: Grooming repertoires are exhibited by all terrestrial mammals, and removal of ectoparasites is an important ances- tral and current function. Parasite-defence grooming is regulated both by a central control mechanism (programmed grooming model) and by cutaneous stimulation from bites (stimulus-driven model). To study the evolution of para- site-defence grooming in ungulates, we compared species-typical grooming behaviour with host morphology and hab- itat to test predictions of the programmed grooming model while taking into account phylogenetic relatedness. We observed grooming in 60 ungulate species at ectoparasite-free zoological parks in which the confound of differential tick exposure was controlled for and stimulus-driven grooming was ruled out. Concentrated-changes tests indicated that sexually dimorphic grooming (in which breeding males groom less than females) has coevolved with sexual body size dimorphism, suggesting that intrasexual selection has favoured reduced grooming that enhances vigilance of males for oestrous females and rival males. Concentrated-changes tests also revealed that the evolution of complex oral grooming (involving alternate use of both teeth and tongue) and adult allogrooming (whereby conspecifics oral groom body regions not accessible by self grooming) was concentrated in lineages inhabiting closed woodland or for- est habitat associated with increased tick exposure, with such advanced grooming being most concentrated in Cervidae. Regression analyses of independent contrasts indicated that both host body size and habitat play a role in the evolution of species-typical oral grooming rates, as previously reported. These results indicate that the observed grooming represents centrally driven grooming patterns favoured by natural selection in each lineage. This is the first phylogenetically controlled comparative study to report the evolution of parasite-defence grooming behaviours in response to selection pressures predicted by the programmed grooming hypothesis. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 17-37. ADDITIONAL KEYWORDS: body size - habitat - parasites - programmed grooming - sexual size dimorphism - ticks - vigilance.
TL;DR: Modifications of the methylation patterns in the genomes of S. x townsendii and S. anglica indicate that in this system, epigenetic changes have followed both hybridization and polyploidization.
Abstract: Spartina anglica arose during the end of the 19th century in England by hybridization between the indigenous Spartina maritima and the introduced East American Spartina alterniflora and following genome duplication of the hybrid (S. x townsendii). This system allows investigations of the early evolutionary changes that accompany stabilization of a new allopolyploid species in natural populations. Various molecular data indicate that S. anglica has resulted from a unique parental genotype. This young species contains two distinctly divergent homoeologous genomes that have not undergone extensive change since their reunion. No burst of retroelements has been encountered in the F 1 hybrid or in the allopolyploid, suggesting a 'structural genomic stasis' rather than 'rapid genomic changes'. However, modifications of the methylation patterns in the genomes of S. x townsendii and S. anglica indicate that in this system, epigenetic changes have followed both hybridization and polyploidization.
TL;DR: Overall, only in tobacco is there any evidence that NCI may have influenced genome evolution, and here further data are required to verify chromosome identity.
Abstract: The nuclear cytoplasmic interaction (NCI) hypothesis of genome evolution and speciation in plants states that newly formed allopolyploids pass through a bottleneck of sterility and the fertile plants that emerge are fixed for species-specific chromosome translocations. These translocations restore fertility and reduce negative effects of the maternal cytoplasm on an alien paternal genome. Using fluorescent in situ hybridization and genomic in situ hybridization and by reviewing published data, we test the NCI hypothesis using three natural Nicotiana allotetraploids (all 2n = 4x = 48, N. arentsii, N. rustica and several genotypes, including a feral plant and cultivars, of N. tabacum (tobacco)). We compare these data with three synthetic tobacco plants (Th37) that are F3 descendent progeny of an allotetraploid formed from ♀N. sylvestris (2n = 24) ×♂N. tomentosiformis (2n = 24). No intergenomic translocations were observed in N. arentsii and N. rustica. An analysis of subtelomeric tandem repeats in these allotetraploids and their putative parents shows minimal genetic changes; those that do occur may reflect evolution in the diploids or the polyploids subsequent to allopolyploidy. All natural N. tabacum genotypes have intergenomic translocations. This may reflect a large ‘genomic-shock’ generated by allopolyploidy involving widely diverged parental species. Two of three synthetic tobacco plants had a translocation similar to that found in all cultivars of tobacco. This translocation may be significant in tobacco fertility and may have been fixed early in tobacco's evolution. But it is lacking in the feral tobacco, which might indicate a polyphyletic origin or early divergence from all cultivars examined. Overall, only in tobacco is there any evidence that NCI may have influenced genome evolution, and here further data are required to verify chromosome identity. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 599–606.
TL;DR: The Nicotiana allotetraploids show evidence of concerted evolution, including both intralocus and interlocus gene conversion, and factors that may control the occurrence and extent of rDNA homogenization are discussed for allopolyploids inNicotiana and other taxa.
Abstract: We review and extend data showing concerted evolution of parental 18-5.8-26S nuclear ribosomal DNA (18-26S rDNA) gene families in three natural Nicotiana allotetraploids (N. tabacum, N. rustica and N. arentsii, each 2n = 4x = 48) and one synthetic N. tabacum line (Th37, ♀ N. sylvestris (2n = 24) x ♂ N. tomentosiformis (2n = 24)). The origin of the gene families was analysed by sequence polymorphisms in the intergenic spacer (IGS) region and the number of chromosomal loci by fluorescence in situ hybridization (FISH). FISH revealed that the number and locations of 18-26S rDNA in the natural allopolyploids was the sum of those found in the diploid progenitors. However, the rDNA restriction patterns showed polymorphisms in the IGS that were not additive, suggesting that parental rDNA clusters were partially (N. tabacum, N rustica) or completely (N. arentsii) overwritten by hybrid-specific units. Thus the Nicotiana allotetraploids show evidence of concerted evolution, including both intralocus and interlocus gene conversion. A feral N. tabacum collected in Bolivia had a higher proportion of unconverted parental rDNA units than cultivated tobacco varieties, suggesting either that rDNA homogenization is accelerated by inbreeding or multiple origins of tobacco. There is no evidence for the elimination of N. sylvestris-derived rDNA units in the synthetic Th37 tobacco line as occurred in natural tobacco, although several novel rDNA unit variants were found in most but not all the hybrid plants. Factors that may control the occurrence and extent of rDNA homogenization are discussed for allopolyploids in Nicotiana and other taxa.
TL;DR: Overall nest survivorship rates were comparable to those for diurnal relatives, but rates of cell parasitism for Megalopta (< < 5%) were substantially lower than they are for day-flying relatives, offering some support for the hypothesis that the evolution of nocturnal behaviour enables escape from natural enemies.
Abstract: Evolutionary transitions to dim-light foraging (predawn matinal, crepuscular, nocturnal) have occurred repeatedly in bees, and may be associated with an escape from enemies or competitors To date, however, little information has been available to test these hypotheses Here we provide the first detailed information on the nesting behaviour of two species of Neotropical, nocturnal sweat bees, Megalopta genalis and M ecuadoria (Hymenoptera: Halictidae) Females are facultatively social or solitary, and construct nests in dead wood Nocturnal foraging behaviour is bimodal Bees began foraging after sunset (∼18:30 h) and ceased foraging approximately 1 h later even though nocturnal flowers with pollen were still abundant; a second foraging bout occurred in the predawn morning, which began at ∼04:45 h and ended around sunrise (∼06:15 h) when diurnal-blooming flowers were abundant Bees are capable of controlled flight in full light They utilized pollen from both canopy and understory plant species, which have diurnal or nocturnal pollen anthesis Megalopta nests are attacked by generalist predators such as ants, as well as the endoparasitic fly Melaloncha sp nov (Phoridae), the beetle Macrosaigon gracilis (Rhipophoridae), the parasitic wasp Lophostigma cincta (Mutillidae), and the brood parasite Megalopta byroni (Halictidae) Overall nest survivorship rates were comparable to those for diurnal relatives, but rates of cell parasitism for Megalopta (< < 5%) were substantially lower than they are for day-flying relatives, offering some support for the hypothesis that the evolution of nocturnal behaviour enables escape from natural enemies © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 377–387
TL;DR: It is concluded that polyploidy may have been of considerable importance in the evolution of fishes, and that fishes, with their diverse life histories, represent a useful model system with which to test theories relating to the origin and consequences of polyploids that have been derived from work on plants.
Abstract: Fishes are the most speciose group of vertebrates, with more than 24 000 species. They are characterized by great diversity in ecology, morphology, life history, behaviour and physiology. Here, the phylogenetic patterns of orders in which polyploidy has been recorded are considered, with special reference to patterns of species richness and hybridization: these orders include such phylogenetically diverse taxa as the Lepidosireniformes (lungfish) and the Perciformes (perch). Examples, predominantly drawn from the Cyprinidae and Salmonidae, are used to illustrate attributes of polyploidy in fishes. It is concluded (i) that polyploidy may have been of considerable importance in the evolution of fishes, and (ii) that fishes, with their diverse life histories, represent a useful model system with which to test theories relating to the origin and consequences of polyploidy that have been derived from work on plants.
TL;DR: The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements, which differs from many temperate taxa that were subjected to climate change.
Abstract: The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to ...
TL;DR: The hypothesis that the early cladogenesis of the Gekkota was associated with the split of Eastern Gondwanaland from Western GondWanaland is supported.
Abstract: A phylogeny of gekkotan lizards was derived from C-mos nuclear DNA sequence data. Forty-one currently recognized genera, representing all major gekkotan lineages, were included in the study. A total of 378 bp of partial C-mos gene sequences was obtained and aligned. Maximum parsimony (MP) and maximum likelihood (ML) trees were generated based on unweighted analysis using PAUP*; similar tree topologies were recovered by both methods. The Eublepharidae were monophyletic and its relationship to other major clades was poorly resolved. The Pygopodidae of Kluge (1987) was monophyletic, but relationships within this group differed from those retrieved by previous analyses. The Diplodactylini + padded carphodactylines were the sister group of pygopods + padless carphodactylines. The Gekkonidae were monophyletic, but we found no evidence in support of the Teratoscincinae, as Teratoscincus was embedded well within the gekkonids. Both MP and ML analyses supported the basal position of Sphaerodactylus within the gekkonids, in contrast to morphologically based hypotheses. We propose a new higher order classification of the Gekkota that reflect these results. Five gekkotan families: Eublepharidae, Gekkonidae, Pygopodidae, Diplodactylidae, and Carphodactylidae are recognized. The higher order status of the sphaerodactyls will require more intensive sampling of this group. Our results support the hypothesis that the early cladogenesis of the Gekkota was associated with the split of Eastern Gondwanaland from Western Gondwanaland. Divergences among living genera in the Eublepharidae and the Eastern Gondwanan lineages (Diplodactylidae, Pygopodidae and Carphodactylidae) may be older than those in the Gekkonidae. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 353–368.
TL;DR: An increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions, and dispersers moving down in elevation may be more successful than those moving up.
Abstract: Variation in the degree of insect wing melanin affects thermoregulation, and is expected to be adapted to local environmental conditions, for example over an elevational gradient. The effects of melanization on flight activity and egg maturation rate were assessed in the closely related butterflies Colias philodice eriphyle and C. eurytheme using experimental manipulation of wing darkness and transplant experiments between high and low elevation sites. Experimental manipulation of wing darkness in C. p. eriphyle demonstrated that light males had reduced flight activity at high elevations, and darkened males had reduced flight activity at low elevations. In contrast, the transplant experiments revealed asymmetrical adaptation for male C. p. eriphyle. At high elevations darker, high-elevation males had higher flight activity than lighter, low-elevation males, but there was no difference between the two groups at low elevation. For females, melanization had no effect on flight activity. However, an increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions. Therefore, dispersers moving down in elevation may be more successful than those moving up. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 79–87.
TL;DR: Analysis of patterns of correlation between skull length and geographical latitude in 44 species of carnivores indicates that the occurrence of Bergmann's rule in the Carnivora is less frequent than earlier published data suggest.
Abstract: Studies of Bergmann's rule may encompass a non-random subsample of extant homeotherms. We examined patterns of correlation between skull length and geographical latitude in 44 species of carnivores in order to test the validity of Bergmann's rule in the Carnivora. Results were then compared to those of other studies. Significant positive cor- relation between skull length and latitude was found in 50% of carnivore species, while significant negative corre- lation was found in only 11% of species. These results indicate that the occurrence of Bergmann's rule in the Carnivora is less frequent than earlier published data suggest. Publication bias is not detected in published data. Therefore, previous studies of geographical size variation might be biased in favour of species known to follow Berg- mann's rule. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 579-588.
TL;DR: Because a large number of plant lineages include polyploid species, the evolution ofPolyploidy may have had major effects on the interaction structure of terrestrial communities.
Abstract: Until recently almost nothing was known about the effects of plant polyploidy on interactions with herbivores and pollinators. Studies of the saxifrage Heuchera grossulariifolia throughout its geographical range in the US northern Rockies have shown that autopolyploidy has probably arisen multiple times within this species since the end of the Pleistocene. Tetraploids from those different origins experience higher levels of attack by the moth Greya politella (Prodoxidae) than sympatric or parapatric diploids. In addition, within one intensively studied region, the plants are also attacked by two other lepidopteran species: G. piperella, which preferentially attack diploids, and Eupithecia misturata (Geometridae), which preferentially attacks tetraploids. Sympatric diploid and tetraploid plants also differ in the overall suites of pollinators they attract. Hence, the evolution of polyploid populations has the potential to change significantly the evolutionary ecology of interactions with herbivores and pollinators. Because a large number of plant lineages include polyploid species, the evolution of plant polyploidy may have had major effects on the interaction structure of terrestrial communities.
TL;DR: Phylogeographical analyses of AFLP data revealed four groups of populations of high alpine Ranunculus glacialis, which suggest longer isolation and/or lower levels of gene flow in the two western groups, whereas the two eastern Alpine groups were genetically more similar to each other.
Abstract: There is considerable controversy concerning the fate of Alpine plants during Pleistocene glaciations. While some studies have found evidence for nunatak survival, others have explained the present genetic patterns by survival only in peripheral refugia. We investigated 75 populations of high alpine Ranunculus glacialis from its entire Alpine distribution. Phylogeographical analyses of AFLP data revealed four groups of populations. Two of them, located in the western Alps, were genetically isolated from each other and from the eastern groups, whereas the two eastern Alpine groups were genetically more similar to each other. This suggests longer isolation and/or lower levels of gene flow in the two western groups. As all groups are close to, or overlap with, presumed glacial refugia, invoking glacial survival on nunataks is unnecessary to explain the present genetic pattern. Similar to the phylogeographical patterns of R. glacialis, the previously investigated alpine Phyteuma globulariifolium and Androsace alpina, which are also confined to siliceous bedrock, showed strong geographical affinities to peripheral refugial areas and there were large-scale congruencies in the location of these refugia for all three species. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 183–195.
TL;DR: It is concluded that phenotypic plasticity has played a significant role in the evolution of this trophic polymorphism, but that the evolutionary process has progressed to the point that the gene pool is now segregated.
Abstract: Recent models suggest that the existence of environmentally induced polymorphisms within a single population (especially those related to foraging) facilitates the process of evolutionary divergence within a single gene pool by generating distinct phenotypic modes that are exposed to differential selection. In order to test a prediction of the phenotypic plasticity model of divergence, we used a well-documented polymorphism to disentangle the relative effects of morph and rearing environment in generating phenotypic variance. We reared first-generation offspring of two sympatric morphs of Arctic charr Salvelinus alpinus in the laboratory and compared their head morphology with that of their wild parents. Morphological characters with a known functional role in foraging were highly plastic. Rearing environment accounted for the largest component of the variation in expressed phenotype, but this environmental effect overlaid a clear (but small) genetic effect. We conclude that phenotypic plasticity has played a significant role in the evolution of this trophic polymorphism, but that the evolutionary process has progressed to the point that the gene pool is now segregated. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 81, 611–618.
TL;DR: It is shown that novel phenotypic variation within the base Brassicas can be achieved by replication of a single gene, BrFLC, that acts additively to influence flowering time and within the derived allopolyploids, intergenomic heterozygosity is associated with higher seed yields.
Abstract: The crop species within the genus Brassica have highly replicated genomes. Three base ‘diploid’ species, Brassica oleracea , B. nigra and B. rapa , are likely ancient polyploids, and three derived allopolyploid species, B. carinata , B. juncea and B. napus , are created from the interspecific hybridization of these base genomes. The base Brassica genome is thought to have hexaploid ancestry, and both recent and ancient polyploidization events have been proposed to generate a large number of genome rearrangements and novel genetic variation for important traits. Here, we revisit and refine these hypotheses. We have examined the B. oleracea linkage map using the Arabidopsis thaliana genome sequence as a template and suggest that there is strong evidence for genome replication and rearrangement within the base Brassicas, but less evidence for genome triplication. We show that novel phenotypic variation within the base Brassicas can be achieved by replication of a single gene, BrFLC , that acts additively to influence flowering time. Within the derived allopolyploids, intergenomic heterozygosity is associated with higher seed yields. Some studies have reported that de novo genomic variation occurs within derived polyploid genomes, whereas other studies have not detected these changes. We discuss reasons for these different findings. Large translocations and tetrasomic inheritance can explain some but not all genomic changes within the polyploids. Transpositions and other small-scale sequence changes probably also have contributed to genomic novelty. Our results have shown that the Brassica genomes are remarkably plastic, and that polyploidy generates novel genetic variation through gene duplication, intergenomic heterozygosity and perhaps epigenetic change. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 665‐674.
TL;DR: New knowledge about polyploidy will be most useful only when it reliably predicts which crops can be usefully improved as stable autopolyploids and which genomes combined to create successful new allopolyloids.
Abstract: It is timely to re-examine the phenomenon of polyploidy in plants. Indeed, the power of modern molecular technology to provide new insights, and the impetus of genomics, make polyploidy a fit, fashionable and futuristic topic for review. Some historical perspective is essential to understand the meaning of the terms, to recognize what is already known and what is dogma, and to frame incisive questions for future research. Polyploidy is important because life on earth is predominantly a polyploid phenomenon. Moreover, civilization is mainly powered by polyploid food – notably cereal endosperm. Ongoing uncertainty about the origin of triploid endosperm epitomizes our ignorance about somatic polyploidy. New molecular information makes it timely to reconsider how to identity polyploids and what is a polyploid state. A functional definition in terms of a minimal genome may be helpful. Genes are known that can raise or lower ploidy level. Molecular studies can test if, contrary to dogma, the relationship between diploids and polyploids is a dynamic two-way system. We still need to understand the mechanisms and roles of key genes controlling ploidy level and disomic inheritance. New evidence for genome duplications should be compared with old ideas about cryptopolyploidy, and new views of meiosis should not ignore premeiotic genome separation. In practice, new knowledge about polyploidy will be most useful only when it reliably predicts which crops can be usefully improved as stable autopolyploids and which genomes combined to create successful new allopolyloids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 411–423.
TL;DR: South America was invaded by members of one clade, Eladinea, which is infer to have dispersed to South America prior to closure of the Panamanian Portal, and the existence of large genetic diversity within morphologically homogeneous taxa is uncovered.
Abstract: The largest genus of salamanders, Bolitoglossa (Plethodontidae), is widespread in tropical America, where it occurs in diverse habitats and elevations, from high elevation grasslands to lowland rain forest. It has the most extensive geographical range of any salamander genus. While most species occur in Middle America, it ranges throughout most of tropical South America as well. Phylogenetic analysis of 1196 bp of two mitochondrial genes (cytochrome b, 16S RNA) from 55 species offers strong support for the monophyly of the genus and sorts the species into a number of clades. Taking into account morphology, distribution, general ecology, and prior systematic and taxonomic studies, we recognize seven subgenera, four of them new: Bolitoglossa Dumeril, Bibron et Dumeril, 1854, Eladinea Miranda Ribeiro, 1937, Magnadigita Taylor, 1944, Mayamandra, Nanotriton, Oaxakia and Pachymandra. All South American and some lower Middle American species are included in a single well supported clade, Eladinea. At the species level our analyses uncover the existence of large genetic diversity within morphologically homogeneous taxa. We propose the new combination: B. (Eladinea) paraensis (Unterstein, 1930) stat. nov., for Brazilian salamanders previously included under B. altamazonica. We evaluate evidence for the multiple colonization of the tropical lowlands by morphologically derived species groups. South America was invaded by members of one clade, Eladinea, which we infer to have dispersed to South America prior to closure of the Panamanian Portal. Despite the relatively long history of salamanders in South America, that continent now accounts for a relatively small proportion of the lineages and species of neotropical salamanders. (C) 2004 The Linnean Society of London,
TL;DR: Allopolyploids differ from one another in such ways as number of origins, amount of allelic diversity harboured at different loci, bidirectional vs. unidirectional origins, retention of ribosomal gene homoeologues, success as measured by geographical range and abundance, and patterns of gene expression.
Abstract: Glycine subgenus Glycine, the sister group to the cultivated soybean and its progenitor, have received considerable study over several decades. The combination of biosystematic data and an extensive germplasm collection has provided a strong foundation for molecular systematic studies in the group, including those on allopolyploids. These studies have shown that the various polyploid taxa known from the subgenus are all part of a single large allopolyploid complex, linked by shared diploid genomes. Many elements of the complex have arisen recently, and most show evidence of recurrent origins. However, there are also many dissimilarities among even closely related polyploids. Polyploids differ from one another in such ways as number of origins, amount of allelic diversity harboured at different loci, bidirectional vs. unidirectional origins, retention of ribosomal gene homoeologues, success as measured by geographical range and abundance, and patterns of gene expression.
TL;DR: The empirical evidence for several potentially important genetic and ecological interactions between ploidy and the sexual system in plants is reviewed and particular emphasis is placed on work in the laboratory on the European annual plant Mercurialis annua, which offers promising scope for detailed investigations.
Abstract: The evolutionary success of polyploidy most directly requires the ability of polyploid individuals to reproduce and transmit their genes to subsequent generations. As a result, the sexual system (i.e. the mating system and the sex allocation of a species) will necessarily play a key role in determining the fate of a new polyploid lineage. The effects of the sexual system on the evolution of polyploidy are complex and interactive. They include both aspects of the genetic system, the genetic load maintained in a population and the ecological context in which selection takes place. Here, we explore these complexities and review the empirical evidence for several potentially important genetic and ecological interactions between ploidy and the sexual system in plants. We place particular emphasis on work in our laboratory on the European annual plant Mercurialis annua, which offers promising scope for detailed investigations on this topic. M. annua forms a polyploid complex that varies in its sexual system from dioecy (separate sexes) through androdioecy (males and hermaphrodites) to functional hermaphroditism.