Adaptive divergence in seed color camouflage in contrasting soil environments (original) (raw)
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Aob Plants, 2017
Whether close evolutionary relatives can coexist is expected to depend on evolutionary divergence in niches relative to divergence in competitive abilities. We investigated how plant species' responses to soil texture might affect coexistence by analysing distributions, seedling emergence and performance, and competitive abilities of the winter annuals Clarkia speciosa ssp. polyantha and C. xantiana ssp. xantiana. A landscape survey showed that the species have distinct associations with soil texture, C. speciosa presence correlating with fine soil and C. xantiana correlating with coarse soil. At the scale of population presences, the species co-occur less often than would be expected at random. On small scales within sites where they do co-occur, each species was negatively associated with the other. Clarkia xantiana presence and/or density also correlated positively with coarse soil texture and steep, poleward slopes, suggesting limitation by water availability. Lab experiments that varied substrate texture and imposed drought revealed contrasting species' fundamental niches at the seed and seedling stages. In coarse substrates, C. xantiana seedlings emerged at several-fold higher rates than C. speciosa, and, unlike C. speciosa, emerged when seeds were buried 0.5 cm. Clarkia speciosa seedlings had superior drought tolerance, independent of substrate. Competition coefficients estimated in a response surface experiment in artificial substrates predicted competitive exclusion of C. speciosa by C. xantiana in coarse substrate, with possible founder control of competitive outcome in fine substrate. Species' differences in responses to soil texture generate spatial segregation that likely facilitates coexistence, despite competitive ability differences that oppose it.
POPULATION DIFFERENTIATION IN AN ANNUAL LEGUME: LOCAL ADAPTATION
Evolution, 2000
Studies of many plants species have demonstrated adaptive genetic differentiation to local environmental conditions. Typically these studies are conducted to evaluate adaptation to contrasting environments. As a consequence, although local adaptation has been frequently demonstrated, we have little information as to the spatial scale of adaptive evolution. We evaluated adaptive differentiation between populations of the annual legume Chamaecrista fasciculata using a replicated common-garden design. Study sites were established in three field locations that are home to native populations of C. fasciculata. Each location was planted for two years with seed from the population native to the study site (home population) and populations located six distances (0.1-2000 km) from each site (transplanted populations). Seeds were planted into the study sites with minimum disturbance to determine the scale of local adaptation, as measured by a home-site fitness advantage, for five fitness components: germination, survival, vegetative biomass, fruit production, and the number of fruit produced per seed planted (an estimate of cumulative fitness). For all characters there was little evidence for local adaptation, except at the furthest spatial scales. Patterns of adaptive differentiation were fairly consistent in two of the three sites, but varied between years. Little genetic variation was expressed at the third site. These results, combined with previous estimates of limited gene flow, suggest that metapopulation processes and temporal environmental variation act together to reduce local adaptation, except over long distances.
Plant domestication versus crop evolution: a conceptual framework for cereals and grain legumes
Domestication syndrome' (DS) denotes differences between domesticated plants and their wild progenitors. Crop plants are dynamic entities; hence, not all parameters distinguishing wild progenitors from cultigens resulted from domestication. In this opinion article, we refine the DS concept using agronomic, genetic, and archaeobotanical considerations by distinguishing crucial domestication traits from traits that probably evolved post-domestication in Near Eastern grain crops. We propose that only traits showing a clear domesticated-wild dimorphism represent the pristine domestication episode, whereas traits showing a phenotypic continuum between wild and domesticated gene pools mostly reflect post-domestication diversification. We propose that our approach may apply to other crop types and examine its implications for discussing the timeframe of plant domestication and for modern plant science and breeding.
Insect Seed Predators as Novel Agents of Selectionon Fruit Color
Ecology, 2004
The ecological and evolutionary dynamics of fruit color polymorphisms remain poorly known because patterns and agents of selection have rarely been identified. Here, we examine Acacia ligulata, a shrub of the Australian arid zone characterized by a red/yellow/orange aril color polymorphism. Seed production patterns over four populations and three years suggested that spatially variable selection may be acting to maintain the polymorphism: red and yellow aril color morphs each had the highest seed production in alternate sites. Seed production differences between morphs were a function of both intrinsic plant characters (fruit production) and predispersal seed predation, which affects the number of viable seeds matured per ovule. Fruit production differences are hypothesized to result from a genotype-by-environment interaction, perhaps related to plant vigor. In contrast, morph differences in the numbers of viable seeds per ovule are produced via differential seed predation by heteropteran insects, as demonstrated by exclusion experiments. Because these predators feed when aril color is not visible, differential predation is evidently a response to pleiotropic effects of fruit color alleles. We suggest that such pleiotropic effects may be a common feature of fruit color polymorphisms, and that the most obvious selective agents (that is, seed dispersers) may not always be the most important.
Frontiers in plant science, 2018
It has been widely suggested that invasion success along broad environmental gradients may be partially due to phenotypic plasticity, but rapid evolution could also be a relevant factor for invasions. Seed and fruit traits can be relevant for plant invasiveness since they are related to dispersal, germination, and fitness. Some seed traits vary along environmental gradients and can be heritable, with the potential to evolve by means of natural selection. Utilizing cross-latitude and reciprocal-transplant experiments, we evaluated the adaptive value of seed thickness as assessed by survival and biomass accumulation inplants. In addition, thickness of a seed and Endosperm to Seed Coat Proportion (ESCP) in a second generation () was measured to evaluate the heritability of this seed trait. On the other hand, we characterized the genetic variability of the sampled individuals with amplified fragment length polymorphism (AFLP) markers, analyzing its spatial distribution and population st...
Environmental context influences the outcome of a plant?seed predator interaction
Oikos, 2007
Linking trait selection to environmental context is necessary to move beyond the simple recognition that selection is spatially variable and to understand what ultimately drives this variation. Natural selection acts through differences among individuals in lifetime fitness and information about effects on fitness components is therefore often not sufficient to gain such an understanding. We investigated how environmental context influenced intensity of seed predation, flower abortion and selection on floral display traits in 44-52 populations of the perennial herb Primula veris over 2 years. Phenotypic selection on both inflorescence height and flower number varied among populations and was mediated partly by pre-dispersal seed predation and flower abortion in one of the years. Among-population variation in selection on inflorescence height, but not flower number, was linked to variation in canopy cover via its effects on seed predation. Lifetime fitness was less sensitive to seed predator damage in shaded environments but estimates of selection based on lifetime fitness agreed qualitatively with those based on seed output. Our results demonstrate that seed predators constitute an important link between environmental conditions and trait evolution in plants, and that selection on plant traits by seed predators can depend on environmental context.
Bimodal colour pattern of individual Pinus halepensis Mill. seeds: a new type of crypsis
Variation in seed traits is a well-known phenomenon affecting plant ecology and evolution. Here we describe, for the first time, a bimodal colour pattern of individual seeds, proposing an adaptive explanation, using Pinus halepensis as a model. Pinus halepensis disperses its seeds either by wind on hot dry days, from regular cones, or after fires, mainly from serotinous cones. Post-dispersal seeds are exposed to strong predation by passerine birds, making crypsis important for seed survival. Individual seeds from non-serotinous cones have a bimodal colour pattern: one side is light brown and the other black, exposing only one colour when lying on the ground. Serotinous cones from most trees have seeds with similar bimodal colour patterns, whereas seeds from serotinous cones of some trees are light brown on both sides. The dark side provides the seed with better crypsis on dark soils, whereas the light-brown side is better adapted to light-coloured soils, and mainly to light-grey ash-covered soil, which is the natural post-fire regeneration niche of P. halepensis. The relative reflection curves of the black and brown seed colours differ, and their calculated relative chromatic distance is 5: meaning that seed-predating passerine birds see them differently, and probably prefer seeds that present a higher contrast against the soil background. We propose that such a bimodal colour pattern of individual seeds is probably an overlooked general phenomenon mainly linked to seed dispersal in post-fire and other heterogeneous environments.