Understanding the mechanisms that control species genetic structure has always been a major objective in evolutionary studies. The association between genetic structure and species attributes has received special attention. As species attributes are highly taxonomically constrained, phylogenetically controlled methods are necessary to infer causal relationships. In plants, a previous study controlling for phylogenetic signal has demonstrated that Wright's FST, a measure of genetic differentiation among populations, is best predicted by the mating system (outcrossing, mixed-mating or selfing) and that plant traits such as perenniality and growth form have only an indirect influence on FST via their association with the mating system. The objective of this study is to further outline the determinants of plant genetic structure by distinguishing the effects of mating system on gene flow and on genetic drift. The association of biparental inbreeding and inbreeding depression with population genetic structure, mating system and plant traits are also investigated. Based on data from 263 plant species for which estimates of FST, inbreeding (FIS) and outcrossing rate (tm) are available, we confirm that mating system is the main influencing factor of FST. Moreover, using an alternative measure of FST unaffected by the impact of inbreeding on effective population size, we show that the influence of tm on FST is due to its impact on gene flow (reduced pollen flow under selfing) and on genetic drift (higher drift under selfing due to inbreeding). Plant traits, in particular perenniality, influence FST mostly via their effect on the mating system but also via their association with the magnitude of selection against inbred individuals: the mean inbreeding depression increases from short-lived herbaceous to long-lived herbaceous and then to woody species. The influence of perenniality on mating system does not seem to be related to differences in stature, as proposed earlier, but rather to differences in generation time. Plant traits correlated with generation time affect both inbreeding depression and mating system. These in turn modify genetic drift and gene flow and ultimately genetic structure.

/pdf/plant-traits-correlated-with-generation-time-directly-affect-2muug7ls66.pdf

Plant traits correlated with generation time directly affect inbreeding depression and mating system and indirectly genetic structure

 Premise of the study: The opuntias (nopales, prickly pears) are not only culturally, ecologically, economically, and medicinally important, but are renowned for their taxonomic diffi culty due to interspecifi c hybridization, polyploidy, and morphological variability. Evolutionary relationships in these stem succulents have been insuffi ciently studied; thus, delimitation of Opuntia s.s. and major subclades, as well as the biogeographic history of this enigmatic group, remain unresolved.  Methods: We sequenced the plastid intergenic spacers atpB-rbcL, ndhF-rpl32 , psbJ-petA , and trnL-trnF , the plastid genes matK and ycf1 , the nuclear gene ppc , and ITS to reconstruct the phylogeny of tribe Opuntieae, including Opuntia s.s. We used phylogenetic hypotheses to infer the biogeographic history, divergence times, and potential reticulate evolution of Opuntieae.  Key results: Within Opuntieae, a clade of Tacinga , Opuntia lilae , Brasiliopuntia , and O. schickendantzii is sister to a well-supported Opuntia s.s., which includes Nopalea . Opuntia s.s. originated in southwestern South America (SA) and then expanded to the Central Andean Valleys and the desert region of western North America (NA). Two major clades evolved in NA, which subsequently diversifi ed into eight subclades. These expanded north to Canada and south to Central America and the Caribbean, eventually returning back to SA primarily via allopolyploid taxa. Dating approaches suggest that most of the major subclades in Opuntia s.s. originated during the Pliocene.  Conclusions: Opuntia s.s. is a well-supported clade that includes Nopalea . The clade originated in southwestern SA, but the NA radiation was the most extensive, resulting in broad morphological diversity and frequent species formation through reticulate evolution and polyploidy.

https://bsapubs.onlinelibrary.wiley.com/doi/epdf/10.3732/ajb.1100375

Phylogeny of Opuntia s.s. (Cactaceae): Clade delineation, geographic origins, and reticulate evolution

The present paper reviews advances in the study of two major intercontinental disjunct biogeographic patterns: (i) between Eurasian and western North American deserts with the Mediterranean climate (the Madrean- Tethyan disjunctions); and (ii) between the temperate regions of North and South America (the amphitropical disjunctions). Both disjunct patterns have multiple times of origin. The amphitropical disjunctions have largely resulted from long-distance dispersal, primarily from the Miocene to the Holocene, with available data indicating that most lineages dispersed from North to South America. Results of recent studies on the Mediterranean disjuncts between the deserts of Eurasia and western North America support the multiple modes of origin and are mostly consistent with hypotheses of long-distance dispersal and the North Atlantic migration. Axelrod's Madrean-Tethyan hypothesis, which implies vicariance between the two regions in the early Tertiary, has been favored by a few studies. The Beringian migration corridor for semiarid taxa is also supported in some cases.

http://www.iab.uaf.edu/people/stefanie_bond/Publications_files/Wen_Ickert-Bond_Amphitrpical_JSE2009.pdf

Evolution of the Madrean–Tethyan disjunctions and the North and South American amphitropical disjunctions in plants

Aim Analytical methods are commonly used to identify historical processes of vicariance and dispersal in the evolution of taxa. Currently, dispersal-vicariance analysis implemented in the software ...

Use of dispersal–vicariance analysis in biogeography – a critique

The genus Prosopis is an important member of arid and semiarid environments around the world. To study Prosopis diversification and evolution, a combined approach including molecular phylogeny, molecular dating, and character optimization analysis was applied. Phylogenetic relationships were inferred from five different molecular markers (matK-trnK, trnL-trnF, trnS-psbC, G3pdh, NIA). Taxon sampling involved a total of 30 Prosopis species that represented all Sections and Series and the complete geographical range of the genus. The results suggest that Prosopis is not a natural group. Molecular dating analysis indicates that the divergence between Section Strombocarpa and Section Algarobia plus Section Monilicarpa occurred in the Oligocene, contrasting with a much recent diversification (Late Miocene) within each of these groups. The diversification of the group formed by species of Series Chilenses, Pallidae, and Ruscifoliae is inferred to have started in the Pliocene, showing a high diversification rate. The moment of diversification within the major lineages of American species of Prosopis is coincident with the spreading of arid areas in the Americas, suggesting a climatic control for diversification of the group. Optimization of habitat parameters suggests an ancient occupation of arid environments by Prosopis species. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 93, 621–640.

Molecular phylogeny and diversification history of Prosopis (Fabaceae: Mimosoideae)

Aim The genus Prosopis includes 44 species and has a pseudoamphitropical, disjunct distribution. We aimed to determine whether American Prosopis sections arose in North or South America, and to explain the current distribution of their species on the basis of their genetic relationships.



Location  South-western USA, Mexico, Caribbean Antilles, Peru–Ecuador, central and northern Argentina, south-western Argentina (Patagonia) and Cuyo, south-western Asia and northern Africa.



Methods  Internal transcribed spacer fragments from 21 species of Prosopis were sequenced and the data were used to analyse the phylogenetic relationships using Microlobius and Mimosa as outgroups. Genetic distances were calculated to estimate the degree of divergence. Dispersal–vicariance (DIVA) analysis was conducted to help understand the biogeographical history of the genus.



Main conclusions  The sections Strombocarpa and Algarobia are not monophyletic. Prosopis argentina (section Monilicarpa) and the species of Algarobia are included in single clade. The phylogeny, DIVA analysis, and the pattern of genetic distances indicate that the ancestral area for the American species was wide, from south-western USA to Central and northern Argentina. Successive vicariance events split this area, and long-distance dispersal episodes (perhaps mediated by birds) led to recolonizations from North to South America, and vice versa.

Genetic relationships among American species of the genus Prosopis (Mimosoideae, Leguminosae) inferred from ITS sequences: evidence for long-distance dispersal

J. C. Vilardi

Papers

Genetic relationships among American species of the genus Prosopis (Mimosoideae, Leguminosae) inferred from ITS sequences: evidence for long-distance dispersal