The logic begins with reproduction itself. Male and female plants fulfil fundamentally different functions: males invest heavily in flowers and pollen to maximize dispersal, while females channel resources into fewer flowers, seeds, and fruits to guarantee successful seed set. Because fruiting is so expensive, females carry a higher reproductive cost, and this biased partitioning of carbon, nitrogen, phosphorus, and water gives rise to differences in morphology, physiology, and life history that scientists call sexual dimorphism. Under optimal light and water conditions, these differences may barely register. But the moment stress appears, the sexes diverge sharply in photosynthetic efficiency, stress tolerance, and growth, and those divergences can determine whether a population survives.

Water is the clearest case study. Across species from dwarf willow to sea buckthorn, females cluster in mesic, nutrient-rich habitats while males dominate xeric, nutrient-poor sites, a pattern known as the spatial segregation of sexes that reflects niche specialization. In Salix glauca, both sexes grow more slowly at dry sites, but female growth rates fall significantly below those of males, suggesting that limited water diminishes nutrient uptake and photosynthesis especially in females, forcing a trade-off between vegetative growth and reproduction. In Pistacia lentiscus, females facing summer drought retain older leaves and reduce new leaf production compared with males, conserving resources for fruit formation in a water-limited environment. Yet the pattern is not universal: in box elder, drought favors females, whose deeper roots access groundwater and produce female-biased sex ratios, while in Populus cathayana females are more drought-sensitive than males. The direction of the response is species-specific.

Light tells an equally nuanced story. Because taller plants capture most of the light, scarcity triggers shade-avoidance responses driven by a lowered red-to-far-red ratio, and competition for light is asymmetrical in a way that water competition is not. In the annual herb Mercurialis annua, higher density reduced plant length, biomass, and reproductive allocation in both sexes, but the reduction hit females harder, reflecting a greater trade-off as they prioritize carbon acquisition and seed maturation. In Pistacia lentiscus, males show higher quantum yield and carbon assimilation than females only under low irradiance, while in Amaranthus palmeri the sexes are physiologically identical under ambient light but diverge under high intensity, where females possess lower chlorophyll content and flower earlier to maximize reproduction. Even the Mediterranean dwarf palm Chamaerops humilis shows sex-specific photoinhibition only during warm-dry summers, with females suffering higher photoinhibition and lower leaf water content while supporting their reproductive phase.

Aquatic plants add a surprising twist. In the dioecious macrophyte Vallisneria, photosynthesis actually increases with water depth, because shallow water causes light inhibition rather than scarcity. Females display more phenotypic plasticity than males across depths, adjusting leaf length, spathe number, and flowering ramets, while males maintain constant reproductive allocation. Both sexes invest equally in clonal propagation through tubers and stolons, but the trade-off with sexual reproduction is evident only in females, who reserve carbon for seed and fruit production. The review notes that this mirrors the differential plasticity documented in woody and herbaceous land plants, suggesting that female reproductive assurance strategies operate even underwater.

Nutrient currencies sharpen the picture. Carbon is generally considered the best currency for assessing allocation in limiting environments, and females rely heavily on carbon, nitrogen, and water for fruit and seed production, while males invest more nitrogen in pollen, making carbon less limiting for male reproduction. In Rubus chamaemorus, female flowers have lower dry mass and nutrient content than male flowers, yet the nitrogen and phosphorus content of fruit is many times that of male flowers. Salix glauca females show roughly four times higher phosphorus allocation than males, and female Amaranthus palmeri accumulate more nitrogen, phosphorus, potassium, and magnesium in stems than males. These patterns support the generalization that higher allocation in females demonstrates the higher cost of reproduction and a female-specific strategy for seed filling and fruit formation.

Temperature and salinity complicate matters further. Elevated temperature increases males in the herbaceous Valeriana edulis but females in the woody Populus cathayana, effects that are species-specific and even variable within a genus. In Populus tomentosa, females adapt better to high temperatures than males, while Populus trichocarpa shows no intersexual differences at all. Under combined salinity and water stress, female Populus tomentosa suffer greater reductions in leaves, stems, biomass, and total leaf area than males, and female Populus deltoides show lower reactive oxygen species scavenging ability. Yet in Salix linearistipularis the pattern reverses: female cuttings exhibit higher superoxide dismutase and peroxidase activities, higher photosynthetic capacity, lower hydrogen peroxide content, and lower sodium accumulation in leaves, making them more salt-tolerant than males. The review emphasizes that combined stresses may be far more pronounced than each acting independently, changing the magnitude of physiological specialization between sexes.

Perhaps the most provocative section asks whether stress is even necessary for physiological specialization to appear. In Amaranthus palmeri, Salix glauca, and Populus tomentosa, sex-specific responses in chlorophyll content, stomatal conductance, and photosynthetic nitrogen-use efficiency emerge only under drought, high light, or nutrient deficiency, suggesting that specialization is a stress-induced strategy rather than an intrinsic trait. But contrasting studies exist: in Pistacia lentiscus, females show higher water-use efficiency under stress despite lower photosynthetic rates, and in Clusia hilariana, a tree growing under extreme solar irradiance, wind, and heat in coastal Brazil, leaf parameters do not vary between sexes at all. Even Populus tremula shows no evidence of sexual dimorphism in non-reproductive traits. The review proposes that the stage of dioecy evolution may matter, with weak dimorphism reflecting early evolutionary stages, though this hypothesis remains untested.

Competition adds another layer. Although it is a biotic factor, competition interacts intimately with abiotic gradients, and the review shows that competitive ability is sex-specific and context-dependent. In Populus cathayana, females show higher growth rates and outcompete male seedlings under intersexual competition, accumulating more biomass and showing higher photosynthetic capacity. But in Osyris quadripartita, competition is asymmetrical and males are inhibited by neighboring females, while in Mercurialis annua both intra- and intersexual competition affect male aboveground growth but not female growth. Under light limitation and intersexual competition, females trade vegetative allocation for reproductive allocation, reiterating their attempts at successful reproduction. Warming even reverses intersexual interactions in mulberry, shifting from competition to facilitation in mixed-sex plantings.

The review’s conclusion is a caution against overgeneralization. Sexual dimorphism in plants manifests at multiple levels, from sex-specific physiological specialization to skewed sex ratios and clonality, yet its extent is so species-specific that broad generalizations are unsuitable. Generalizations made today may not hold tomorrow, because the plasticity responses exhibited by dioecious plants are themselves context-dependent and likely to shift under climate change. The author highlights crucial lacunae: underground structures such as roots, runners, and suckers remain understudied, anatomical and ultrastructural investigations have been largely neglected, and the genetic and molecular bases of resource allocation in relation to abiotic factors have not been examined in detail. For conservation strategies, agroforestry restoration, and weed management, the message is clear: the sexes of a dioecious species must be understood as distinct ecological entities, each with its own adaptive strategy, and any management plan that treats them as interchangeable risks misreading the very biology that keeps these species alive.

Subject of Research: Plant Biology

Article Title: Sexual dimorphism and pattern of resource allocation under variable abiotic factors

Article References: Mangla, Y. (2026). Sexual dimorphism and pattern of resource allocation under variable abiotic factors. Frontiers in Photobiology, 4, Article 1914724. https://doi.org/10.3389/fphbi.2026.1914724

Image Credits: AI Generated

DOI: 10.3389/fphbi.2026.1914724

Keywords: sexual dimorphism, dioecy, resource allocation, abiotic stress, drought, plant physiology, ecology, climate change, Sexual, dimorphism, pattern, resource

Radiolarians are planktic Rhizaria, a diverse group of marine organisms whose siliceous skeletons make them among the most important microfossils for understanding early ocean ecosystems. Molecular clock studies suggest that radiolarians lacking skeletons may have existed since the Late Neoproterozoic, but the fossil record of polycystine radiolarians — those bearing skeletons — is only confirmed from the Cambrian Series 2, Stage 4. The Cambrian and Ordovician periods are therefore of key significance for the early evolutionary history of these heterotrophic plankton, and the siliceous skeletons of early Palaeozoic radiolarians testify to significant diversifications and evolutionary changes during this interval.

For the past 35 years, progress in understanding the taxonomy and biostratigraphy of early Palaeozoic radiolarians has relied largely on the discovery of well-preserved faunas and their description using two-dimensional imaging techniques such as scanning electron microscopy. While SEM has been invaluable, it cannot capture the full three-dimensional complexity of a radiolarian skeleton, particularly its most internal parts, which carry the greatest taxonomic significance. The recent application of micro-computed tomography to radiolarians has changed this, allowing researchers to observe the most internal architectures of these fossils in a non-destructive way and opening new avenues for understanding their internal organisation.

The species at the centre of the new study was first introduced by Kozur, Mostler and Repetski in 1996, based on Tremadocian (Lower Ordovician) material from Nevada. It was described as the type species of the newly-defined genus Protoentactinia and type-genus of the family Protoentactiniidae. The original description characterised it as bearing a spicular system initiated from a bar-centred entactinarian spicule with three terminal rays at each end, with the subglobular skeleton formed of a repeatedly branching pattern of spicules that accommodated a nearly spherical inner empty space. The species was later reported from upper Cambrian and lowermost Ordovician strata of western Newfoundland.

The single specimen analysed in the new study came from a basal Tremadocian radiolarian assemblage extracted by Lauren Pouille of the University of Lille during her PhD work, after hydrochloric acid leaching from a limestone sample of the Green Point section of the Cow Head Group in western Newfoundland, Canada. Protoentactinia gracilispinosa is abundant in this assemblage, representing approximately 15 percent of over 2,000 identified specimens, and has been well documented by Pouille and colleagues. Skeleton analysis was conducted at Ghent University’s Centre of X-ray Tomography in Belgium using a custom-built Nanowood micro-CT scanner operating at 70 kV and 4 W, with a voxel size of 900 nanometres. A total of 2,322 projections were acquired at an exposure time of 1,000 milliseconds per projection, resulting in a total scan time of around 40 minutes. The projections were reconstructed using Octopus Reconstruction software, during which ring filtering and beam hardening corrections were applied.

Stacks of two-dimensional images were then processed using the open-source 3D Slicer software, which is commonly used to extract structural models from images primarily in clinical and biomedical applications. Image segmentation delineates regions within an image — in this case, structures of the siliceous skeleton — and is essential for visualising and quantifying them. The segmentation was performed semi-automatically: by manually scanning all the slices in three dimensions and using the segmentation tools provided by 3D Slicer, the researchers delineated areas of interest by selecting corresponding grey levels. Each part or segment could then be coloured, facilitating the interpretation of each branch within the three-dimensional volume. Remarkably, although the physical specimen was inadvertently lost during transport after all imaging had been completed, the description presented in the study is based on the comprehensive microscopic documentation acquired prior to its loss.

The colouring dissection allowed the researchers to recognise eight successive stages of spicular branching that result in the formation of a subspherical spicular test displaying a practically empty inner space. The first stage is represented by the initial bar-centred entactinarian spicule, which displays two terminal trifurcating branchings developed at the two extremities of the median bar. The vast majority of branchings throughout the skeleton’s development are of the trifurcating type, though rare single-rayed, bifurcating, quadrifurcating, pentafurcating and hexafurcating branchings were also observed, with only one single case of a heptafurcating branching recorded.

The numbers tell a striking story of growth dynamics. The total number of new branchings and rays increases rapidly up to stage 5, after which both decrease. Stage 2 produced 6 new branchings and 18 new rays; stage 3 generated 17 branchings and 50 rays; stage 4 yielded 35 branchings and 108 rays; and stage 5 recorded the maximum, with 36 branchings and 109 rays. However, after stage 2, only a fraction of existing rays leads to the development of new branchings. Out of the 18 new rays developed at stage 2, only 17 produce new branchings at stage 3. Out of the 50 new rays formed during stage 3, only 35 produce new branchings during stage 4. More remarkably, only a third of the rays newly formed during stage 4 branch out during stage 5. Therefore, the dynamic of skeletal growth decreases after stage 4, even though stage 5 records the maximum number of rays ever produced for this specimen.

In terms of spatial development, nearly half of the final subspherical spicular test is formed by the end of stage 3. Starting with stage 4, shell growth becomes clearly unidirectionally and asymmetrically orientated, away from the initial spicule, establishing a clear heteropolarity in the skeleton growth and structural organisation while simultaneously forming a more complete subspherical test. The distally orientated development of the shell is more obvious during stage 5. Most of the branches developed during stage 6 are generated on the opposite side of the initial spicule and in such a way as to form a subspherical shell. The few new branchings and rays generated during stages 7 and 8 are also developed so as to increase the subspherical aspect of the test.

The discovery of heteropolar development is particularly significant. Until now, heteropolar development of a polycystine radiolarian skeleton had been recognised only for radiolarians of the order Nassellaria. The new study documents for the first time the heteropolar growth of the test in a primitive entactinarian species. The skeleton growth of Protoentactinia gracilispinosa recalls the heteropolar and unidirectional skeleton development described in Nassellaria, but without the axial symmetry characteristic of nassellarians, as the end product is a subspherical form. During the first two stages of skeletal growth, the type of branchings is always trifurcating, and since this type represents the vast majority of total branchings formed during skeleton formation, it may very well be that the trifurcating type is the standard, with all other types of branching representing possible malformations or simply part of the infraspecific variability of the species. However, additional material needs to be analysed in the future to assess this, as three specimens of the species illustrated recently in a PhD thesis remain pending analysis.

Few studies provide insights into the function of polycystine radiolarian skeletal morphology. The researchers suggest that the siliceous skeleton might have served as an anchoring structure for a better function of the axoflagellates and cytoplasmic extensions. They also speculate that Protoentactinia gracilispinosa had a cell structure similar to the periaxoplastitid-type, described from cellular observations of living radiolarians from the western Mediterranean. If such was indeed the case, the axoplast of the organism was likely positioned close to the initial spicule, and axoflagellates were all orientated antapically, away from the axoplast. Such an axoflagellate organisation would be consistent with the unidirectional and heteropolar skeletal growth observed, in spite of the final subspherical form.

The analysis confirms the initial description provided by Kozur and colleagues in 1996: the subglobular spongy test of this entactinarian species is formed by repeated branchings of rays starting from the two trifurcating branchings of the initial spicule formed out of each termination of the median bar. The skeleton is formed subsequently through seven additional stages of reiterated branchings, but the subglobular form of the test is essentially developed during stages 3, 4 and 5. The maximum number of branchings is manifested in stage 5, and the total number of new rays also reaches its maximum at stage 5, after which it decreases during stages 6, 7 and 8. Unidirectional and heteropolar skeletal growth, similar to that observed in nassellarians, is established here for the first time using micro-CT analysis. Heteropolarity is expressed by the directional asymmetry in the skeleton growth and architecture, starting with the very eccentric position of the initial spicule at the edge of an empty spherical space. The study highlights how modern imaging techniques can extract detailed biological information from microscopic fossils, even when the physical specimen itself is no longer available, and underscores the value of micro-CT for the taxonomic analysis of early Palaeozoic radiolarians.

Subject of Research: X-ray tomography reveals the skeletal growth pattern of the early radiolarian Protoentactinia gracilispinosa

Article Title: Skeletal growth pattern of Protoentactinia gracilispinosa Kozur, Mostler & Repetski, 1996, a late Cambrian – Early Ordovician radiolarian species, revealed by X-ray tomography

Article References: Harutyunyan, L., Habert, R., Schröer, L., Cnudde, V., & Danelian, T. (2026). Skeletal growth pattern of Protoentactinia gracilispinosa Kozur, Mostler & Repetski, 1996, a late Cambrian – Early Ordovician radiolarian species, revealed by X-ray tomography. Fossil Record, 29(2), 759-764. https://doi.org/10.3897/fr.29.200748

Image Credits: AI Generated

DOI: 10.3897/fr.29.200748

Keywords: radiolaria, micro-CT, palaeontology, Cambrian, Ordovician, entactinarian, skeletal growth, Newfoundland, Skeletal, growth, pattern, Protoentactinia