Journal of Evolutionary Biology最新文献

Foraging ecology and visual ability are often strongly related across animal lineages, as many organisms identify food sources by sight. Birds particularly rely upon vision to seek out prey or other food items, leading to the correlated evolution of eye size and foraging behaviour. Here, we focus on a specialized foraging tactic termed "disturbance foraging," whereby a responding species exploits prey items flushed by a disturbing species. Using global databases of disturbance-responder species and eye size measurements from museum specimens, we tested the prediction that relative eye size accounting for body mass allometry (a proxy for visual acuity and sensitivity) would be larger in disturbance foragers that require enhanced visual performance to locate escaping prey (N = 463) compared to other species (N = 2,840). As predicted, disturbance foragers possessed larger relative eye sizes. Residual eye size was correlated with a gradient in avian foraging behaviour, such that species with the smallest and largest relative eye sizes were near-sighted and far-sighted non-disturbance foragers, respectively, while disturbance foragers had intermediate eye sizes. Birds appeared to invest similarly in acuity and sensitivity in relation to foraging behaviour as measured by their respective anatomical proxies (residual axial length [AL] and cornea diameter [CD]), although there was partial evidence that some species groups invested more in acuity based upon the eye shape ratio (CD/AL). These patterns imply that even highly specialized behavioural tactics may evolve in concert with their respectively linked neurological and sensory systems.

Programmed cell death (PCD), the genetically controlled active cellular suicide mechanism in multicellular organisms, also exists in unicellular organisms. However, explaining the evolution of PCD by natural selection in these organisms remains a challenge. PCD likely emerged during early endosymbiotic events as an initial antagonistic adaptation, enabling unicellular parasitic proto-endosymbionts to exploit their hosts, for example, by triggering host death in response to nutrient depletion or releasing offspring. Over time, during endosymbiont domestication and, as proposed, through horizontal gene transfer from endosymbionts to the host, PCD evolved in the host, providing benefits to both the host and the endosymbionts. However, the underlying assumption of this hypothesis, that PCD benefits and non-PCD (necrosis) harms the endosymbionts and/or the host, remains untested. Here, we investigated the fitness consequences of heat-shock-induced PCD in the endosymbiotic chlorophyte Chlorella variabilis and its facultative symbiotic ciliate host Paramecium bursaria, the non-symbiotic C. sorokiniana, and the predatory host P. duboscqui. Heat shock triggered PCD in C. variabilis and the two ciliate species, causing significant fitness consequences. The supernatant from C. variabilis PCD enhanced the growth of its own clones and endosymbiotic host while inhibiting the growth of the predatory host. The supernatants from necrotic C. variabilis reduced growth of both Chlorella and Paramecium. Similarly, PCD in the symbiotic Paramecium host benefited Chlorella, whereas PCD and necrosis in the predatory Paramecium host were detrimental. These results expand the understanding of unicellular PCD, highlighting its dual role in benefiting clonal populations and their specific endosymbiotic partners, thereby affecting endosymbiosis evolution.

Sensory system evolution plays a crucial role in shaping species' interactions with their environment, yet the extent to which olfactory system diversity reflects ecological and evolutionary pressures at a macroevolutionary scale remains unclear. Here, we investigate the evolution of the olfactory system across the Heliconiini butterfly tribe, an ecologically diverse but closely related group. Using a comparative approach, we examined variation in antennal lobe morphology and its constituent structures, the glomeruli and antennal lobe hub, as well as odourant receptor repertoires across species. We found that antennal lobe size variation is driven by independent shifts in glomerular and antennal lobe hub volumes, with species-specific differences occurring against a backdrop of broader phylogenetic stability. While no direct associations with ecological traits were observed, certain species showed large expansions in total glomerular volume and odourant receptor numbers, warranting further investigation into unmeasured ecological or behavioural factors. Additionally, comparisons between wild-caught and insectary-reared individuals revealed a surprising pattern of developmental plasticity, with antennal lobe hub volumes increasing and glomeruli volumes decreasing in captivity, highlighting the influence of environmental conditions on neural development. These findings suggest that olfactory evolution in Heliconiini is shaped by both evolutionary divergence and developmental plasticity, emphasizing the need to integrate phylogenetic, ecological, and developmental perspectives to fully understand sensory system adaptation.

Morphological evolution reflects a balance between the emergence of novel traits and the reduction or loss of existing traits, and both of these processes shape the diversity of life. Trait simplification, which involves the reduction or loss of structures, is a common phenomenon that provides adaptive advantages in novel ecological contexts. In this study, we examined the evolutionary dynamics and morphological outcomes of the reduction and simplification of the stinging apparatus in ants to elucidate the effect of these changes on broader evolutionary trajectories. Using a phylogenetically informed sampling of 98 ant genera, we explored how stinger morphology evolved in conjunction with behavioural and ecological changes, employing linear morphometrics and phylogenetic comparative methods. Our results revealed that transitions from piercing to nonpiercing stingers were substantially associated with dietary diversification and shifts in foraging strategies, thus reflecting the evolutionary compromises between defense, predation, and ecological specialization. Piercing stingers promoted predatory efficiency and ecological specialization, while nonpiercing stingers imparted behavioural and dietary versatility, such as herbivory and cooperative foraging. These findings highlight that morphological simplification is a key adaptive mechanism in driving ecological transitions and diversification and promoting evolutionary innovation.

Carpenter ants (Family Formicidae; Genus Camponotus) are a globally distributed, arboreal clade. They harbor an intracellular obligate bacterial endosymbiont known as "Candidatus Blochmanniella spp." (hereafter Blochmanniella). The host ant species, C. vicinus, is geographically dispersed across the western United States of America and western Canada. To investigate how Blochmanniella have differentially evolved from related host-endosymbiont lineages, we sampled a C. vicinus population from California's Sierra Nevada mountains, California, U.S.A., at an elevation of 2,300 m. Using morphological characters and Cytochrome Oxidase I markers, we determined that this population is genetically distinct from geographically distributed lineages of C. vicinus from Central California and Western North America (Arizona, U.S.A. to British Columbia, Canada). Thus, we sequenced the genome of the Blochmanniella endosymbiont from this host to understand how closely related symbiont lineages evolve. While our newly sequenced lineage is syntenic with other Blochmanniella, it has lost genes involved in membrane maintenance, bacterial cell information, and nutrition synthesis. Protein-coding genes across its genome are highly divergent as well (average sequence similarity = 93.6%). Therefore, we refer to our novel lineage as the B. vicinus Sequoia lineage (BSEQ). BSEQ can provide 7 of the 10 essential amino acids required by its insect host. It can also help break down toxic urea and repair UV radiation-induced DNA damage. Tests of selection reveal that most protein-coding genes BSEQ and related lineages are under strong or relaxed purifying selection. Taken together, our results demonstrate that while BSEQ and related Blochmanniella lineages have highly conserved content, there is considerable evolutionary diversity between them.

Many who have obtained PhDs in evolutionary biology will ultimately pursue careers that fall outside a narrow definition of an academic career. At the same time, PhD students and supervisors of PhD students are often ill-informed about career options outside of academia. Here, we report on a survey of evolutionary biologists who have pursued non-academic careers, to understand what careers they pursue, how they transitioned into those careers, how well prepared they were, and how satisfied they are with their current work. Overall, the message from this survey is positive-evolutionary biologists are readily employable outside of academia, generally well-prepared for those jobs, and report high levels of satisfaction in their non-academic careers. We also highlight areas where preparation for non-academic careers could be improved, which might be addressed by individual mentors or PhD training programmes.

Offspring size and number, key fitness components, are expected to evolve under a trade-off between them. In mammals, the evolution of larger offspring size may be promoted in aquatic environments, where the selective advantages of large body size are more pronounced than in terrestrial environments. A transition from a fully terrestrial to an aquatic lifestyle has occurred within the family Mustelidae (Mammalia: Carnivora). Sea otters (Enhydra lutris) are unique in this family for giving birth in water, with offspring living almost exclusively in the aquatic environment. Controlling for phylogeny and adult body mass, we identified a trade-off between neonate mass and litter size (i.e., offspring number per litter) across species in the Mustelidae. Using models of trait evolution on the phylogeny of this family, we revealed lineage-specific directional selection in sea otters favoring larger neonate mass and smaller litter size relative to adult mass. These results support the unique evolution of larger offspring size in sea otters, resulting in a decreased litter size through the trade-off. Furthermore, we revealed lineage-specific directional selection in sea otters favoring larger total litter mass relative to adult mass, as well as larger neonate mass after excluding the effect of the trade-off against litter size. Lineage-specific directional selection in sea otters favoring larger neonate mass and litter mass cannot be solely attributed to the prolonged gestation period. This study suggests that sea otters have undergone distinctive evolutionary changes, investing more resources in offspring size than can be allocated merely by reducing offspring number.

Climate change exposes populations to more frequent periods of extreme temperatures and faster temperature fluctuations. Theoretical models suggest that different types of adaptations should occur in constant versus fluctuating environments of varying frequency. Furthermore, it has been hypothesized that the number and severity of fitness trade-offs evolving in fluctuating environments depend on population size. To evaluate whether specific types of adaptations evolve at fluctuating temperatures and how population size might affect the evolution of trade-offs, we performed an evolution experiment with fission yeast (Schizosaccharomyces pombe). Small and large populations were evolved for 500 generations at constant and fluctuating temperatures, after which the evolved strains were competed against ancestral strains in their respective selection environments, and in alternative environments to detect fitness trade-offs. We observed significant adaptation and maladaptation only to constant heat, but not to fluctuating temperatures. Moreover, population size did not have significant effect on capacity of adaptation or trade-offs in alternative environments. Our results suggest that constant extreme temperatures may act as stronger selective pressures than temperature variations, and that fitness trade-offs are unlikely to constrain adaptation to fluctuating temperatures. Future experiments in fluctuating temperatures should consider that the number of generations required for populations to adapt may be longer than for constant environments.

Flight is a crucial activity for winged insects, involving diverse behaviours, and wing morphology has often been proposed as a key factor influencing flight capacity. Traits such as wing loading, wing:ratio, and wing aspect ratio have been suggested as targets of natural selection, exhibiting environmental and genetic variability. Here, we evaluate the relationship between morphological traits and two aspects of flight performance: flight duration (PTF) and its robustness (CVPTF) in Drosophila melanogaster. Additionally, we investigate the genetic basis of PTF and CVPTF. Our findings highlight two main insights. First, while genetic variation was detected in both morphological and flight traits, variability was considerably lower in the first case compared to the second one. This likely explains the absence of a strong relationship between these traits. Furthermore, among 107 candidate genes detected for flight traits, only a few were associated with wing morphology, reinforcing the weak link between morphology and performance. Second, we observed a negative relationship between PTF and CVPTF across sexes. However, CVPTF was associated with more polymorphisms and candidate genes than PTF, and only three genes (if, fru, and nAChRα5) were associated with both traits. These results suggest that both flight traits present distinct genetic bases.In conclusion, our results challenge the hypotheses that emphasize that wing morphology is determinant for flight performance. We also provide a first approximation to the genetic basis underlying two flight estimators, advancing our understanding of this behavioural trait in Drosophila.

Sexual communication allows individuals to find and choose a mate, but also to avoid hybridization with individuals from different species. Sexual signals can thus play an important role in speciation. However, many sexual signals come with potential trade-offs with other life history traits, which may only be revealed under stressful conditions. To determine if intraspecific variation in sexual signals is affected by limited resource intake during the larval stage, we studied variation in the sex pheromone of the noctuid moth Heliothis subflexa when larvae were reared on limited resources. Females of this species produce acetate esters in their sex pheromone blend that attract males from the same species while repelling a sympatrically occurring species, Heliothis virescens. As H. subflexa females produce high amounts of acetates when the interfering species is present but low amounts in its absence, we hypothesized that high-acetate sex pheromone signals trade off with female fitness. To identify potential trade-offs between high acetate levels and female fitness, we manipulated the quantity of resources available at the larval stage. We showed that under larval food stress, females with high ratios of acetates in their sex pheromone had longer developmental times and lower fertility compared to females producing less acetates. These results thus support our hypothesis that a balance between costly acetates and the benefit of deterring heterospecific mates may at least partly explain the intraspecific variation in the H. subflexa female sex pheromone blend.