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Most theoretical treatments of the evolutionary ecology of offspring size assume a simple and direct effect of investment per offspring on offspring fitness. In this paper I experimentally determine the relationship between seed mass and several main fitness components of the oak Quercus ilex, to estimate phenotypic selection acting on seed mass during the early life cycle and to discover any potential selective conflicts occurring between different stages from dispersal to establishment. I found a positive effect of acorn size on most fitness components related to seedling establishment. Large size increased germination rate and seedling survival, accelerated germination timing, and enhanced seedling growth. Nevertheless, there was also a direct negative effect of acorn size on survival to predation, because large acorns were highly preferred by the main postdispersal seed predators at the study site, wild boars and wood mice. Because of the low probability of escape from predation, the fitness of large acorns estimated on this component was significantly lower than the fitness of smaller acorns. Therefore, seed size affected fitness in two different ways, yielding opposing and conflicting selective forces. These findings suggest that the general assumption that offspring fitness is a fixed positive function of seed size needs to be reconsidered for some systems. The existence of conflicting selection might explain the occurrence of an optimal seed size in some plant species without invoking a seed number‐size trade‐off.

The evolution of the seed represents a remarkable life-history transition for photosynthetic organisms. Here, we review the recent literature and historical understanding of how and why seeds evolved. Answering the ' how' question involves a detailed understanding of the developmental morphology and anatomy of seeds, as well as the genetic programs that determine seed size. We complement this with a special emphasis on the evolution of dormancy, the characteristic of seeds that allows for long ' distance' time travel. Answering the ' why' question involves proposed hypotheses of how natural selection has operated to favor the seed life-history phenomenon. The recent flurry of research describing the comparative biology of seeds is discussed. The review will be divided into sections dealing with: (1) the development and anatomy of seeds; (2) the endosperm; (3) dormancy; (4) early seed-like structures and the transition to seeds; and (5) the evolution of seed size (mass). In many cases, a special distinction is made between angiosperm and gymnosperm seeds. Finally, we make some recommendations for future research in seed biology.

This article is a Commentary on Meade et al. (2021), 229: 1782–1794.

Premise of the Study Conifers are an important living seed plant lineage with an extensive fossil record spanning more than 300 million years. The group therefore provides an excellent opportunity to explore congruence and conflict between dated molecular phylogenies and the fossil record. Methods We surveyed the current state of knowledge in conifer phylogenetics to present a new time‐calibrated molecular tree that samples ~90% of extant species diversity. We compared phylogenetic relationships and estimated divergence ages in this new phylogeny with the paleobotanical record, focusing on clades that are species‐rich and well known from fossils. Key Results Molecular topologies and estimated divergence ages largely agree with the fossil record in Cupressaceae, conflict with it in Araucariaceae, and are ambiguous in Pinaceae and Podocarpaceae. Molecular phylogenies provide insights into some fundamental questions in conifer evolution, such as the origin of their seed cones, but using them to reconstruct the evolutionary history of specific traits can be challenging. Conclusions Molecular phylogenies are useful for answering deep questions in conifer evolution if they depend on understanding relationships among extant lineages. Because of extinction, however, molecular datasets poorly sample diversity from periods much earlier than the Late Cretaceous. This fundamentally limits their utility for understanding deep patterns of character evolution and resolving the overall pattern of conifer phylogeny.

Premise of research. Toadflaxes (LinariaMill., ∼150 spp. from the Palearctic region) constitute the largest genus of the snapdragon lineage (tribe Antirrhineae). Here we provide the first extensive phylogenetic testing of systematic and evolutionary hypotheses about toadflaxes. Methodology. Internal transcribed spacer (ITS) sequences were obtained for 94 species representing all sections ofLinariarecognized by recent taxonomic treatments, as well as three species of the morphologically related American genusNuttallanthus. In addition, 71 sequences representing the remaining 26 genera of Antirrhineae were gathered to test the monophyly of toadflaxes. Phylogenetic analyses were conducted using Bayesian inference and maximum likelihood. Evaluation of alternative topologies was assessed by means of Bayes factor analyses. Pivotal results. LinariaandNuttallanthusconstituted a monophyletic group within the Antirrhineae.Linariawas recovered as a paraphyletic group withNuttallanthusnested within it. Six major clades were recognized within theLinaria-Nuttallanthusclade. The seed wing, a structure that has been extensively used in systematic treatments, appears to be a homoplasious character inLinaria. Conclusions. The circumscription ofNuttallanthuswithinLinariais suggested to preserve the monophyly of the latter genus. Three sections ofLinaria(Macrocentrum,Pelisserianae, andVersicolores) that are well defined by distinct morphological traits are also supported as natural groups, while monophyly of the remaining sections (Supinae,Linaria,Speciosae, andDiffusae) is unsupported by our results. Habit, inflorescence, and flower morphology, coupled with seed morphology, are revealed as the key characters in the evolution of toadflaxes.

Flavonoid metabolism innovation is critical for seed plants' terrestrial adaptation. Three key 2-oxoglutarate-dependent dioxygenase (2ODD) families-F3H, ANS, FLS-underpin flavonoid biosynthesis, but their evolutionary diversification mechanisms remain unclear. Comprehensive analyses were performed across 238 seed plant genomes, including phylogenetic/collinearity analyses, conserved motif detection, duplication-type classification, selection pressure assessment, and Brassica napus promoter/expression profiling. These families originated from a common ancestral gene (ancestor X) and diversified via multiple duplications (TRD/WGD as primary drivers). Their evolution aligns with the EAC model, with subfunctionalization resolving ancestral multifunctionality. Structural conservation and lineage-specific motif variations support functional differentiation, and purifying selection predominates. Our findings clarify the molecular evolutionary mechanisms of flavonoid pathway diversification, providing novel insights into the origin of flavonol and anthocyanin biosynthesis in seed plants.

Background and Aims Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda, the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade. Methods Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms. Key Results Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth. Conclusions Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.

Most theoretical treatments of the evolutionary ecology of offspring size assume a simple and direct effect of investment per offspring on offspring fitness. In this paper I experimentally determine the relationship between seed mass and several main fitness components of the oak Quercus ilex, to estimate phenotypic selection acting on seed mass during the early life cycle and to discover any potential selective conflicts occurring between different stages from dispersal to establishment. I found a positive effect of acorn size on most fitness components related to seedling establishment. Large size increased germination rate and seedling survival, accelerated germination timing, and enhanced seedling growth. Nevertheless, there was also a direct negative effect of acorn size on survival to predation, because large acorns were highly preferred by the main postdispersal seed predators at the study site, wild boars and wood mice. Because of the low probability of escape from predation, the fitness of large acorns estimated on this component was significantly lower than the fitness of smaller acorns. Therefore, seed size affected fitness in two different ways, yielding opposing and conflicting selective forces. These findings suggest that the general assumption that offspring fitness is a fixed positive function of seed size needs to be reconsidered for some systems. The existence of conflicting selection might explain the occurrence of an optimal seed size in some plant species without invoking a seed number-size trade-off.

Fil: Lopez Fernandez, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina

A critical analysis of different criteria used in investigating seed diversity was made. It is concluded that the most promising way to understand the evolution of seeds is to study not only their morphological features, as used by most workers in the field, but also the physiological diversity of seeds in connection with the taxonomic system of plants, together with their ecological and geographical peculiarities.