Search

We determined whether supernumerary B chromosomes were nonrandomly distributed among major angiosperm lineages and among lineages within families, as well as the identity of lineages with unusually high B-chromosome frequencies (hot spots). The incidence of B chromosomes for each taxon was gathered from databases showing species with and without these chromosomes (among species with known chromosome numbers). Heterogeneity was found at all ranks above the species level. About 8% of monocots had B chromosomes versus 3% for eudicots; they were rare in nonmonocot basal angiosperms. Significant heterogeneity in B-chromosome frequency occurred among related orders, families within orders, and major taxa within families. There were many B-chromosome hot spots, including Liliales and Commelinales at the order level. At the family level, there was a trend suggesting that B-chromosome frequencies are positively correlated with genome size. [ABSTRACT FROM AUTHOR]

Although homoploid hybrid speciation is increasingly recognized as an important phenomenon in plant evolution, its role in adaptive radiations is poorly documented. We studied a clade of seven extant species of Scaevola that are endemic to the Hawaiian Islands and show substantial ecological and morphological diversity. We estimated the genealogies for alleles isolated from multiple accessions of each species at four nuclear loci: the ITS region, and the introns of three nuclear genes, LEAFY (LFY), NITRATE REDUCTASE (NIA), and GLYCERALDEHYDE 3-PHOSPHATE DEHYDROGENASE (G3PDH). For five of the seven species, there was complete concordance among the genealogies estimated from the four loci and, when all four regions were combined, the relationships among these five species were fully resolved. Inclusion of alleles from the remaining two species, S. procera and S. kilaueae, resulted in incongruence among loci, which appears to reflect a history of hybridization. Based on the distribution of alleles, we infer that S. procera is the result of a homoploid hybrid speciation event between S. gaudichaudii and S. mollis and that S. kilaueae is probably the result of hybrid speciation between S. coriacea and S. chamissoniana. In each case the inferred hybridization is consistent with morphological, ecological, and geographic information. We conclude that homoploid hybrid speciation may be more common than is perceived and may play a role in generating novel combinations of adaptive traits that arise during island radiations. [ABSTRACT FROM AUTHOR]

The biota of Hawaiian Islands is derived entirely from long distance dispersal, often followed by in situ speciation. Species descended from each colonist constitute monophyletic lineages that have diverged to varying degrees under similar spatial and temporal constraints. We partitioned the Hawaiian angiosperm flora into lineages and assessed morphological, ecological, and biogeographic characteristics to examine their relationships to variation in species number (S). Lineages with external bird dispersal (through adhesion) were significantly more species-rich than those with abiotic dispersal, but only weakly more species-rich than lineages with internal bird dispersal (involving fleshy fruits). Pollination mode and growth form (woody vs. herbaceous) had no significant effect on S, in contrast to studies of angiosperm families. S relates positively to the geographic and ecological range size of whole lineages, but negatively to local abundance and mean range sizes of constituent species. Species-rich lineages represent a large proportion of major adaptive shifts, although this appears to be an artifact of having more species. Examination of 52 sister species pairs in numerous lineages provides evidence for allopatric (including peripheral isolates) and parapatric (ecological) modes, with 15 cases of each. Although postspeciational dispersal may obscure these modes in many of the remaining cases, instances of sympatric and hybrid speciation are also discussed. Because speciation is both a consequence and a cause of ecological and biogeographic traits, speciation mode may be integral to relationships between traits. We discuss the role of speciation in shaping the regional species pool. [ABSTRACT FROM AUTHOR]

Genome size has been suggested to be a fundamental biological attribute in determining life-history traits in many groups of organisms. We examined the relationships between pine genome sizes and pine phylogeny, environmental factors (latitude, elevation, annual rainfall), and biological traits (latitudinal and elevational ranges, seed mass, minimum generation time, interval between large seed crops, seed dispersal mode, relative growth rate, measures of potential and actual invasiveness, and level of rarity). Genome sizes were determined for 60 pine taxa and then combined with published values to make a dataset encompassing 85 species, or 70% of species in the genus. Supertrees were constructed using 20 published source phylogenies. Ancestral genome size was estimated as 32 pg. Genome size has apparently remained stable or increased over evolutionary time in subgenus Strobus. while it has decreased in most subsections in subgenus Pinus. We analyzed relationships between genome size and life-history variables using cross-species correlations and phylogenetically independent contrasts derived from supertree constructions. The generally assumed positive relation between genome size and minimum generation time could not be confirmed in phylogenetically controlled analyses. We found that the strongest correlation was between genome size and seed mass. Because the growth quantities specific leaf area and leaf area ratio (and to a lesser extent relative growth rate) are strongly negatively related to seed mass, they were also negatively correlated with genome size. Northern latitudinal limit was negatively correlated with genome size. Invasiveness, particularly of wind-dispersed species, was negatively associated with both genome size and seed mass. Seed mass and its relationships with seed number, dispersal mode. and growth rate contribute greatly to the differences in life-history strategies of pines. Many life-history patterns are... [ABSTRACT FROM AUTHOR]