Biology Letters最新文献

Historical sites preserved within cities often serve as refuges for local biodiversity. However, these sites are surrounded by buildings and roads, creating sharp contrasts in habitat suitability between them and the surrounding urban matrix. Under such conditions, reduced dispersal potential may be favoured if remaining within the site enhances fitness. We tested this hypothesis in the self-incompatible dandelion, Taraxacum platycarpum (Asteraceae). We compared the morphological traits affecting seed-dispersal potential between populations inhabiting historical sites (castles and shrines) in a major metropolitan area and those inhabiting open sites in rural areas. Pappus volume, which is positively associated with dispersal potential, was significantly smaller in historical-site than in open-site populations. In contrast, achene volume, which is less directly related to dispersal potential, did not differ between site types. Moreover, populations in historical sites tended to exhibit a lower genetic diversity than those in open sites did. These results suggest that seed dispersal traits in dandelions have diminished in urban historical sites, potentially leading to reduced genetic diversity as an evolutionary consequence. Together, our findings illustrate how extreme habitat isolation within cities can shape dispersal evolution and emphasize the importance of incorporating evolutionary processes into the conservation of plant populations in these environments.

Climate change is increasing the frequency of heatwaves with detrimental effects on reproduction. Sex differences in thermal sensitivity of fertility could impact population persistence under global warming, with some predictions indicating increased vulnerability in males. Yet, few studies have measured both male and female fertility simultaneously. Here, we investigated the independent and combined effect of temperature stress on male and female reproductive success and offspring fitness in the burying beetle Nicrophorus vespilloides. Despite the expectation of increased thermal sensitivity in males, we found a significant reduction in all reproductive success traits when females, but not males, were exposed to a heatwave. We also found evidence for additive combined effects of heat stress on male and female fertility, although this had no downstream consequences for offspring fitness. In sum, our findings suggest that the effects of climate change on female fertility may have been underestimated. This could have important implications for populations under increasing environmental threat, given that population growth tends to be determined by female fertility.

While satellite tracking is widely used to identify areas of conservation importance, whether there is a need to continue tag deployments across many years is unclear. We show that destinations of migrating animals from the same breeding population can differ significantly across years, and hence we highlight the value of multi-year tracking studies. Between 2012 and 2024, we used Fastloc-GPS Argos and Iridium tags to track 58 green turtles (Chelonia mydas) from their nesting sites in the Chagos Archipelago. If tracking had taken place in a single year, the number of countries used as foraging destinations could have been hugely underestimated (n = 1 country in 2024 versus n = 7 countries across years). Overall, 47% of tracked individuals foraged in the Seychelles, which likely hosts hundreds of thousands of foraging turtles across age classes. Further, the importance of foraging in areas beyond national jurisdiction (ABNJs) was only revealed by tracking over multiple years. Across years, 9% of tracked individuals foraged on the Saya de Malha Bank, a remote ABNJ, equating to likely >1000 adult females and >10 000 green turtles using this foraging area. This cumulative insight from multi-year tracking likely applies broadly to capital breeders where there is environmental variability across the foraging range.

Parasites can provide powerful insights into host evolution and biogeography. The bird Sapayoa aenigma, the only Neotropical member of the otherwise Old World clade Eurylaimides, has long puzzled ornithologists due to its phylogenetic placement and uncertain biogeographic origin. We investigated the evolutionary origin of a chewing louse in the genus Myrsidea found on Sapayoa. Using genome-wide data from 91 Myrsidea specimens from oscine, suboscine and non-passerine hosts, we reconstructed a global phylogeny to evaluate hypotheses about the origin of Sapayoa and its parasite. Phylogenomic, molecular dating and cophylogenetic analyses support a scenario in which the Myrsidea lineage on Sapayoa originated outside the Neotropics and was acquired via host-switching from an Old World oscine. The parasite's divergence time (24.4-17.9 Ma) postdates the split between Sapayoa and other Eurylaimides, ruling out strict codivergence. Ancestral host reconstruction supports an oscine origin and Old World acquisition, and biogeographic analysis also indicates Old World origins, though with uncertainty in the exact region. These findings support a co-dispersal scenario in which Sapayoa acquired its parasite in the Old World and brought it to the Neotropics. Our study highlights the value of parasites as complementary tools for disentangling complex evolutionary and biogeographic histories. A Spanish translation is available in the electronic supplementary material.

The Yanomami, an Indigenous group from the Amazon, confront multifaceted challenges endangering their health and cultural integrity. Of immediate concern is the humanitarian crisis caused by surges in malaria amid increasing illegal gold mining in their territory. Leveraging satellite imagery and panel regression analyses, we quantified the effect of land use changes on malaria incidence on their land (2016-2023). We observed an approximately 300% increase in malaria cases during this period, associated with increases in illegal gold mining. An increase of 1 s.d. in gold mining is associated with a 20-46% rise in malaria incidence 1-2 years later. We found that changes in forest areas significantly affect malaria rates: for every 1 s.d. increase in the perimeter of forest edges, malaria cases rise by 55%. Our findings highlight the major impact of illegal gold mining and the resulting fragmentation of forests on the high malaria burden experienced by the Yanomami.

African elephants (Loxodonta africana) can rely on olfactory cues to guide foraging decisions. While odour can play a key role in indicating food quality, the potential for elephants to use odour to discriminate between food quantities from distance is unknown. Using a giant Y-maze, we examined the extent to which four captive elephants could use odour cues to discriminate between patches containing between 100 and 1000 g of food from 9.5 m away. As food quantities in the two patches became similar (proportional difference declined, ratios increased), the elephants' ability to discriminate between them declined. In line with Weber's Law, the elephants were only able to select the greater food amount when the absolute (>600 g) and proportional (>0.86) differences (i.e. discrepancy) were large, and the ratios were small. Previous research suggests that 600 g corresponds to approximately 6-10 trunk loads of grass or 16-29 trunk loads of woody vegetation leaves. Our findings suggest that African elephants could use olfactory cues to facilitate between-patch foraging decisions based on relatively fine-scale differences in food availability. Understanding this and linking it to patch selection may provide broader insight into elephant impacts on plant communities.

Current environmental changes are often considered as negatively impacting the affective state of animals. Yet, the interplay between environmental conditions and affective state should rather be viewed as a reciprocal and dynamic relationship, as variation in affective state likely determines how animals decide to respond to environmental changes. Here, I illustrate how affective states may contribute to determining how animals respond to environmental changes through phenotypic plasticity, environmental modification or dispersal. A condition for future studies to examine this hypothesis will be to consider the response of animals in parallel with valid indicators of affective state reflecting different affective dimensions (valence, arousal) over different timescales. Moreover, considering affective state as a central component of the response of animals to environmental changes implies that a condition to realistically investigate this response is to provide animals with the freedom to decide between options associated with different affective values.

Protein evolution is influenced by historical contingencies and functional constraints, but their combined impact on rapidly diversifying pathogen virulence effectors remains poorly understood. Here, we combined ancestral state reconstructions and functional assays to recapitulate the evolution of the MAX-fold effector protein APikL2 of the plant pathogenic blast fungus Magnaporthe (syn. Pyricularia) oryzae, focusing on the ancestral and functionally critical amino acid residue D66 (Asp, codon: GAT). 'Rewinding the tape' experiments based on ancestral sequence resurrection revealed that, out of the seven potential amino acid substitutions derived from single nucleotide polymorphisms, only the naturally occurring D66N (Asp to Asn, GAT to AAT) expanded the binding spectrum to host plant proteins of the heavy metal associated (HMA) family. In contrast, three of the non-synonymous substitutions were deleterious resulting in loss of binding to HMA proteins. Additionally, we identified three cases of homoplasy in the APikL effector family, involving HMA-binding interfaces, indicating recurrent convergent evolution. Our findings suggest an experimental framework for predicting evolutionary outcomes of pathogen effector-host target interactions with implications for plant disease resistance breeding.

The metabolic theory of ecology links the effects of temperature on metabolic rates at the cellular scale to larger-scale ecological processes, providing a framework for predicting how individuals, populations and communities will respond to climate change. Metabolic theory predicts that carrying capacity will have a unimodal (hump-shaped) response to temperature, and that this relationship could be altered by resource availability. However, few studies have empirically tested these predictions, despite the fundamental role that carrying capacity plays in governing population and community dynamics. To test the effect of temperature on carrying capacity and to determine whether this is mediated by resource quality, we conducted a fully crossed experiment in which we grew populations of the model organism Tribolium castaneum for 22 weeks at all 12 treatment combinations of four temperatures (27.5, 30, 32.5, 35°C) and three resource qualities (flour mixtures). Our results support the prediction that carrying capacity has a unimodal relationship with temperature, however resource quality did not alter this relationship. These findings support emerging theory describing temperature's effect on carrying capacity, and contribute to our understanding of how population dynamics will shift under climate change.

Nutritional status is a key determinant of disease outcomes in animals, yet its effects are complex. While abundant food supplies support host immunity, they may also fuel pathogen proliferation, whereas food limitation can restrict resources for both host and parasite. The balance between these opposing processes and the physiological limits to fasting as a protective strategy remain poorly understood. Here we tested how the duration of food deprivation affects infection outcome, using the Pacific oyster (Magallana gigas) and its lethal pathogen Ostreid herpesvirus 1 as a model system. We found that moderate fasting markedly improved survival, with the lowest mortality observed after 14-28 days without food. However, beyond this range, survival declined sharply, revealing a tipping point where prolonged starvation reversed its protective effect. Biochemical analyses of oysters from Sequence 1 at the onset of infection provided mechanistic insight: carbohydrate reserves were depleted rapidly, lipid reserves fell by approximately 90% after 28 days of starvation and protein catabolism occurred only after extended fasting, coinciding with the decline in survival. Our results demonstrate that fasting can transiently enhance resistance to viral infection but is constrained by finite energy reserves. By identifying a physiological threshold beyond which starvation compromises survival, we uncover a novel mechanism linking host energetics to disease outcomes.