1. Comparative studies have demonstrated extensive variation in age trajectories of mortality and fecundity, both within and among species, with many taxa exhibiting a general pattern of age-related demographic decline referred to as senescence. Whereas a considerable body of theory is devoted to explaining the origin and persistence of senescence, the evolutionary forces underlying variation in demographic trajectories more generally remain poorly understood.2. Studying variation in demographic trajectories is complicated by the fact that different species (or even different populations of a given species) may live and reproduce on different time-scales, which, for comparative purposes, can make it challenging to disentangle patterns of age-related demographic change (the shape of demographic age trajectories) from the time-scale on which those changes happen (the pace of demographic age trajectories).3. Here, we examine variation in the pace and shape of demographic trajectories among strains of the aquatic plant Lemna turionifera Landolt from 24 sites across Alberta, Canada. Our main objectives were to describe the shape of demographic trajectories in L. turionifera, and test for among-strain variation in pace and shape.We also tested whether potential variation in pace and shape is (1) constrained by trade-offs with other life-history traits, and (2) consistent with local adaptation to environmental characteristics at the sites of strain origin.4. The strains we examined were overwhelmingly subject to age-related increases in mortality and declines in fecundity, with increases in mortality tending to decelerate and plateau at advanced ages. Despite substantial among-strain variation in cumulative fecundity and plant size, measures of pace and shape did not in themselves vary significantly among strains. Both within and among strains, we observed a negative relationship between plant size and the shape of fecundity trajectories, but we found no other evidence for life-history trade-offs involving pace or shape, nor for local adaptation. Synthesis. Angiosperms display remarkable demographic variation. Our resultssuggest that the pace and shape of demographic trajectories are highly conserved within one particular angiosperm species (Lemna turionifera), despite substantial among-strain variation in other life-history traits. K E Y W O R D Sageing, biodemography, lemnoideae, life-history tradeoff, pace-shape, senescence | 2133Journal of Ecology BARKS et Al.

No abstract

Background: The biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range. Results: We found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three genetic clusters, of which one was O. cooperi. Cluster 1 contained most individuals in COI clade X and some from clade B and cluster 2 was predominantly made up of individuals from COI clades B and B′ and a few from clade X. ITS2 alleles were shared in a narrow contact zone between two COI clades, suggestive of hybridization between the two. Conclusions: A sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.

No abstract

Background: The biodiversity and distributions of terrestrial snails at local and regional scales are influenced by their low vagility and microhabitat specificity. The accessibility of large-bodied species and their characteristically high levels of genetic polymorphism make them excellent ecological and evolutionary models for studies on the phylogeography, phylogenetics, and conservation of organisms in fragmented populations. This study aims to elucidate the biodiversity, systematics, and distributions of genetic lineages within the genus Oreohelix at the northern and western periphery of their range. Results: We found four mitochondrial clades, three of which are putative subspecies of Oreohelix subrudis. One clade was geographically widespread, occurring within numerous sites in Cypress Hills and in the Rocky Mountains, a second was geographically restricted to the Rocky Mountains in Alberta, and a third was restricted to the Cypress Hills region. A fourth clade was the small-bodied species, O. cooperi. ITS2 sequence and screening data revealed three haplotype clusters, of which one was O. cooperi. Cluster 1 was typical of the first clade and cluster 2 was typical of the second and third clades. ITS2 alleles were shared in a narrow contact zone between the first and second clades, suggestive of hybridization between the two. Conclusions: A sky island known as Cypress Hills, in southeastern Alberta, Canada, is a biodiversity hotspot for terrestrial land snails in the genus Oreohelix. The observed phylogeographic patterns likely reflect reproductive isolation during the Last Glacial Maximum, followed by secondary contact due to passive, long-range dispersal resulting from low vagility, local adaptation, and complex glacial history.