SummaryCoastal dunes form valuable ecosystems that provide flood protection, drinking water, and high biodiversity worldwide. Although their functioning hinges on habitat zonation along >km-scale sea-to-land gradients, infrastructure development progressively squeezes natural dune ecosystems into a narrow strip. Yet it remains unknown how much undisturbed coastal width is required to support the diverse suites of habitats and species assemblages found in natural dune systems. Here, we investigate plant and habitat diversity in 614 plots along 47 sea-to-land transects in the southeastern USA and the Netherlands. We discover a linear relation between habitat diversity and species richness, indicating that species-rich dunes require diverse habitat assemblages. Moreover, we find that both plant and habitat diversity nonlinearly depend on coastal width, with cumulative plant diversity reaching ∼75% of its potential at 800 and 1,800 m widths in the southeastern USA and the Netherlands, respectively. Alarmingly, dune areas are narrower than these widths along 79% and 66% of southeastern USA and Dutch coastlines, highlighting that lack of space compromises biodiversity along the majority of coastlines. Finally, analyses of management measures along the transects reveal that strategic interventions can, at least in part, mitigate biodiversity losses from infrastructure encroachment. As coastal squeeze—i.e., combined losses from infrastructure and sea level rise—is a global phenomenon, our results suggest that it threatens biodiversity in dune ecosystems worldwide. We argue that the establishment or expansion of nature reserves may be vital for conserving wide dune systems and that targeted management measures can help maintain biodiversity where squeeze cannot be alleviated.

<h2>Summary</h2> The Earth BioGenome Project, which aims to decode the genomes of all named eukaryotes, is preparing to enter phase II. Thanks to continuing improvements in technologies, it has so far managed to exceed expectations while staying on budget. A key target of the next phase is to build capacity in the Global South, where most of Earth's biodiversity is found. <b>Michael Gross</b> reports.

SummaryThe plastids of photosynthetic organisms on land are predominantly “primary plastids,” derived from an ancient endosymbiosis of a cyanobacterium. Conversely, the plastids of marine photosynthetic organisms were mostly gained through subsequent endosymbioses of photosynthetic eukaryotes generating so-called “complex plastids.” The plastids of the major eukaryotic lineages—cryptophytes, haptophytes, ochrophytes, dinoflagellates, and apicomplexans—were posited to derive from a single secondary endosymbiosis of a red alga in the “chromalveloate” hypothesis. Subsequent phylogenetic resolution of eukaryotes has shown that separate events of plastid acquisition must have occurred to account for this distribution of plastids. However, the number of such events and the donor organisms for the new plastid endosymbioses are still not resolved. A perceived bottleneck of endosymbiotic plastid gain is the development of protein targeting from the hosts into the new plastids, and this supposition has often driven hypotheses toward minimizing the number of plastid-gain events to explain plastid distribution in eukaryotes. But how plastid-protein-targeting is established for new endosymbionts is often unclear, which makes it difficult to assess the likelihood of plastid transfers between lineages. Here, we show that Kareniaceae dinoflagellates, which possess complex plastids known to be derived from haptophytes, acquired all the necessary protein import machinery from these haptophytes. Furthermore, cryo-electron tomography revealed that no additional membranes were added to the Kareniaceae complex plastid during serial endosymbiosis, suggesting that the haptophyte-derived import processes were sufficient. Our analyses suggest that complex red plastids are pre-adapted for horizontal transmission, potentially explaining their widespread distribution in algal diversity.

The causes of heterogeneity in evolutionary rates are a key question in macroevolution. Origination and extinction rates are closely related to abiotic factors, such as climate1,2 and geography,3,4 as well as biotic factors such as taxonomic richness5,6 and morphology,7 which are influenced by phylogeny.8,9 Studies on the relationship between morphology and macroevolution have focused on morphological traits, including body size,6,7,9 shape,10 color,11,12 and complexity,13,14,15 and have proposed biological laws, such as the zero-force evolutionary law16 and Cope's rule.17 However, the relationship between morphological complexity and turnover rates remains poorly defined because of the lack of suitable measures for various subjects.18,19 Here, we establish a quantitative method, the two-dimensional ornamentation index (2D-OI), which allows the description of the ornamental complexity of ammonoids. Ammonoids are one of the most abundant and well-studied fossil groups, with complex conch structures.20 Ammonoids display some similarities with trilobites and mammals21,22 in terms of their high evolutionary rates; however, the underlying mechanisms remain elusive. Moreover, ammonoids exhibit marked heterogeneity in turnover rates across spatiotemporal scales23 and clades,23,24 making them key clades for investigating the relationship between turnover rates and morphological complexity. The results show that morphologically complex genera and species often have higher origination and extinction rates than morphologically simple taxa. Diversity fluctuations of taxa with complex ornamentation generally overimprint and control the overall net diversification rates of ammonoids. This double-edged sword of rapid evolution and increased extinction risk driven by complex morphologies has significant implications for our understanding of how species survive over geological timescales.