Xiang-Yi Li Richter

Biodiversity loss driven by climate change and human activities poses a critical global challenge. Population restoration and reintroduction programs are essential for mitigating this threat to endangered species, yet their outcomes often remain unpredictable due to poorly understood success factors, such as the inevitable inbreeding during bottleneck events. The conservation programme of the crested ibis (Nipponia nippon) marks a successful example where the population rose from just seven individuals to over 9000 in the past four decades. By developing an individual-based model that simulates the restoration process and incorporates species-specific demography and inbreeding data, we conclude that this successful restoration is largely deterministic, as our results closely mirror empirical recovery time and population-level inbreeding coefficients. To establish general guidelines for reintroduction programs, we compare how inbreeding depression influences the recovery success of two reintroduction strategies involving small founder populations. Our simulations reveal that the ‘firework’ approach (one-source translocations) outperforms the ‘sequential’ (serial translocations) approach in restoration effectiveness. Furthermore, by expanding analyses over a broad demographic space, we demonstrate that the net effect of inbreeding varies with species-specific demography and highlight the importance of considering their interaction when interpreting conservation outcomes and designing future reintroduction programs.

Body size is a fundamental organismal trait, affecting a wide variety of physiological and ecological functions. Such relationships are often interactive and nonlinear, forming complex feedbacks. In terrestrial mammals, larger bodies are associated with higher mobility in trade-off with larger absolute resource demand. Here we propose a hypothesis, with support from empirical patterns and a mathematical model, that this trade-off interacts with diet specialization to drive diverging selection on body size because specialists are more efficient resource users and have lower mortality risks at extreme sizes. Our analysis of a global terrestrial mammal species dataset found significantly lower proportions of specialists at intermediate sizes, but higher proportions towards extreme sizes; this pattern also applies to species assemblages in zoographic realms. Our mathematical model of coexistence between equal-sized specialists and generalists shows that specialists of extreme sizes have higher equilibrium frequencies and likelihood of coexistence with generalists at quasi-stability. The combined results support dietary specialization as a key factor for shaping body size diversity. Our work highlights the value of connecting ecology and evolution in understanding the diversity of key traits like body size, and calls for further investigations on the related history of resource distribution and lineage diversification.

Traits that affect organismal fitness are often highly genetically variable. This genetic variation is vital for populations to adapt to their environments, but it is also surprising given that nature – after all – ‘selects’ the best genotypes at the expense of those that fall short. Explaining the extensive genetic variation of fitness‐related traits is thus a longstanding puzzle in evolutionary biology, with cascading implications for ecology, conservation, and human health. Balancing selection – an umbrella term for scenarios in which natural selection maintains genetic variation – is a century‐old explanation to resolve this puzzle that has gained recent momentum from genome‐scale methods for detecting it. Yet evaluating whether balancing selection can, in fact, resolve the puzzle is challenging, given the logistical constraints of distinguishing balancing selection from alternative hypotheses and the daunting collection of theoretical models that formally underpin this debate. Here, we track the development of balancing selection theory over the last century and provide an accessible review of this rich collection of models. We first outline the range of biological scenarios that can generate balancing selection. We then examine how fundamental features of genetic systems – non‐random mating between individuals, ploidy levels, genetic drift, linkage, and genetic architectures of traits – have been progressively incorporated into the theory. We end by linking these theoretical predictions to ongoing empirical efforts to understand the evolutionary processes that explain genetic variation.

Microplastics (MPs), small plastic particles under 5 mm, are increasingly recognized for their environmental persistence and ubiquity across ecosystems. While research has long focused on MPs’ toxicity, their influence on the dispersal of small organisms, including fungal, bacterial, and viral pathogens and their vector species such as insects, is gaining attention. This perspective examines how MPs could act as carriers for microorganism dispersal via the formation of unique biofilms, termed as ‘plastisphere,’ which hosts diverse microbial communities and facilitates horizontal gene exchange, including antibiotic-resistant genes. We also explore indirect impacts, as MPs influence the physiology and life history traits of organisms, which can alter dispersal dynamics. Despite increasing interest, significant research gaps remain, particularly concerning MPs in terrestrial ecosystems and the effects of biofouled versus pristine MPs in natural settings. Additionally, inconsistent methodologies, such as the use of unrealistically high MP concentrations and the lack of control materials or systematic experimental design challenge current research, limiting a comprehensive risk assessment. Addressing these limitations is essential to accurately evaluate MPs’ role in the dispersal of small organisms and to inform potential policy measures.

Sex differences in ageing and lifespan are widespread across taxa, yet their evolutionary causes remain debated. A leading hypothesis suggests these differences are adaptive and driven by sex-specific life-history trade-offs, but formal theoretical support is lacking. To address this, we developed a mathematical model to investigate how such trade-offs shape lifespan evolution in a monogamous mating system. In the model, individuals evolve to optimise a trade-off between reproduction and survival – mediated by mating opportunities in males and offspring production in females. By systematically varying trade-off strengths, we show that either sex can evolve greater longevity, but male-biased longevity evolves under a broader set of conditions – consistent with patterns in monogamous species. This asymmetry arises because female longevity is more constrained: the trade-off between offspring production and survival directly affects the fertility of both sexes. In contrast, the male trade-off for mating opportunities has a weaker indirect effect on female fertility, allowing selection to more readily favour longer male lifespans. We also show that extrinsic density-dependent mortality can disproportionately affect the intrinsically longer-living sex, and obscure the magnitude of this evolved difference. Together, our results provide new theoretical insights into the adaptive bases of sex-biased longevity and highlight the importance of life-history trade-offs in shaping lifespan evolution.

Traits that affect organismal fitness are often very genetically variable. This genetic variation is vital for populations to adapt to their environments, but it is also surprising given that nature (after all) “selects” the best genotypes at the expense of those that fall short. Explaining the extensive genetic variation of fitness-related traits is thus a longstanding puzzle in evolutionary biology, with cascading implications for ecology, conservation, and human health. Balancing selection—an umbrella term for scenarios of natural selection that maintain genetic variation— is a century-old explanation to resolve this paradox that has gained recent momentum from genome-scale methods for detecting it. Yet evaluating whether balancing selection can, in fact, resolve the paradox is challenging, given the logistical constraints of distinguishing balancing selection from alternative hypotheses and the daunting collection of theoretical models that formally underpin this debate. Here, we track the development of balancing selection theory over the last century and provide an accessible review of this rich collection of models. We first outline the range of biological scenarios that can generate balancing selection. We then examine how fundamental features of genetic systems—including non-random mating between individuals, differences in ploidy, genetic drift, and different genetic architectures of traits— have been progressively incorporated into the theory. We end by linking these theoretical predictions to ongoing empirical efforts to understand the evolutionary processes that explain genetic variation.