Evolution最新文献

Models of optimal offspring size and bacterial aging share the same underlying mathematical problem: how should a parent optimally distribute limited resources among its offspring? Optimal offspring size theory has long explored the trade-off between offspring number and size in higher organisms. Meanwhile, the emerging field of bacterial aging examines whether and under what conditions cells evolve unequal sharing of old cellular components. Despite addressing similar problems, these models remain constrained by field-specific assumptions. We unify them in a generalized resource-distribution framework that yields insights and predictions unreachable by either field alone. Our central finding is that the convexity of the function relating resources to offspring survivorship determines whether equal or unequal distribution of resources is the optimal strategy. We show that these optimal strategies evolve, characterize their robustness to fluctuating environments, and uncover the conditions that select for producing a "runt of the litter."

Mammals exhibit remarkable diversity in brain size and morphology, resulting from numerous ecological radiations throughout the Cenozoic. Although previous studies have demonstrated the influence of phylogeny, allometry, and various ecological variables on endocranial morphology in certain mammalian lineages, the extent to which locomotor habitat influences brain shape evolution remains unclear. The suborder Caniformia, or "dog-like" carnivorans, is an ecologically diverse clade, containing terrestrial, arboreal, fossorial, and semiaquatic species, each facing a unique set of sensory and motor challenges. Here, we evaluate the impact of phylogeny, allometry, and locomotor habitat on brain shape evolution in caniforms. We examine endocranial morphology in 73 species using high-density 3D geometric morphometrics, principal component analysis and phylogenetic comparative methods. Our findings indicate that the land-to-water transition has a significant impact on endocranial shape across caniforms. This effect is more pronounced in pinnipeds than in other semiaquatic fissipeds, such as mustelids and ursids, likely due to their more derived ecology and greater commitment to aquatic life. Aquatic caniforms tend to exhibit expanded cerebra alongside reduced paleocortices and olfactory bulbs. These morphological changes likely reflect selection pressures acting on both the brain and the surrounding cranial architecture in aquatic environments.

Hominoidea are a diverse superfamily, with potential selection on the postcranium from divergent locomotor patterns. The scarcity of postcranial primate fossil remains, however, means that selection on the appendicular skeleton has been difficult to study directly. Here, we use complementary methods from evolutionary quantitative genetics to assess selection versus drift within hominoids and an outgroup of cercopithecoid monkeys. While most branches were characterized by drift or stabilizing selection, directional selection was indicated on the branch leading to Homo sapiens and potentially on the branch to Hylobates lar. Directional selection gradients were then assessed for each trait on these two lineages. Strong selection was detected on limb length and traits of the os coxa in both lineages. Our results are consistent with prior studies of evolution in the hominoid postcranium and indicate that these methods may be useful in studying multiple elements in conjunction for a holistic assessment of evolution in the primate skeleton in the absence of extensive fossil data.

Evolutionary transitions to diurnality are often associated with specialized ocular morphology, such as pits (foveae) in the retina. Foveae are required for high visual acuity and are found primarily in diurnal vertebrate taxa, including lizards. Geckos have undergone repeated evolutionary transitions between nocturnality and diurnality. Aristelliger is a nocturnal lineage embedded within a largely diurnal clade and represents a putative reversal to nocturnality. We investigated eye development and morphology of Aristelliger geckos. Despite sharing a most recent common ancestor with its diurnal sister lineage over 60 million years ago, Aristelliger exhibit a fovea. Fovea development is coordinated by dynamic changes in eye shape-such as ocular elongation and retraction-during embryonic development. In Aristelliger embryos, these elongation and retraction phases occur in the same region where the fovea forms, closely resembling the pattern seen in Anolis, a diurnal lizard with two foveae. Given the retention of a fovea in Aristelliger, we hypothesize that the transition to nocturnality is relatively recent. Incorporating these results into comparative phylogenetic methods results in a hypothesized diurnal ancestral temporal niche for sphaerodactylid geckos. We illustrate, similar to some nocturnal primates, that developmental data and robust morphological investigation can provide unique insights into macroevolutionary studies.

Viruses typically have high decay rates (mortality rates outside hosts), and applications of phage viruses for combating harmful bacterial in clinical and agricultural contexts would favor slow-decaying phage materials. There is evidence for a trade-off between viral survival and growth rate, which may constrain the evolution of reduced decay rate. Temperature is likely to affect the optimal balance of this trade-off; for example, faster growth may be more beneficial at warmer temperatures where phages spend less time outside of hosts in waiting for encountering a new host individual. We tested this hypothesis by experimentally evolving a lytic phage that infects the bacterium Pseudomonas fluorescens. Phages evolved at two temperatures for 20 cycles of dilution and propagation, with the ancestral bacteria being supplied every cycle. Phage populations from different temperatures showed different modes of adaptation in growth and decay traits. In particular, phages that evolved at the colder temperature showed a reduction in decay rate, regardless of assay conditions. Our results suggest phage training programs and resource collecting efforts to focus on cold environments for slow-decaying phage materials.

A central challenge in comparative biology is linking present-day trait variation across species with unobserved evolutionary processes that occurred in the past. In this endeavor, phylogenetic comparative methods are invaluable for fitting, comparing, and selecting evolutionary models of varying complexity and biological meaning. Traditionally, evolutionary studies have relied on conventional statistical approaches to assess model fit and identify the one that best explains variation in a given trait. Here we explore an alternative strategy by applying supervised learning to predict evolutionary models via discriminant analysis. We formally introduce Evolutionary Discriminant Analysis (EvoDA) as an addition to the biologist's toolkit, offering a suite of new methods for studying trait evolution. We evaluate the performance of EvoDA alongside conventional model selection through a series of fungal phylogeny case studies, each targeting increasingly challenging analytical tasks. These results showcase the strengths of EvoDA, with substantial improvements over conventional approaches when studying traits subject to measurement error, which likely reflect realistic conditions in empirical datasets. To complement our simulation-based benchmarking, we explore the application of EvoDA for tackling a notoriously difficult task: predicting the mode and tempo of gene expression evolution. This empirical analysis suggests that stabilizing selection acts on a majority of genes, with bursts of expression evolution in a handful of genes related to stress, cellular transportation, and transcription regulation. Collectively, our findings illustrate the promise of EvoDA for predicting trait models across a range of evolutionary and experimental contexts, establishing a new methodological framework for the next era of comparative research.

The inhibitory cascade model (ICM) of morphogenesis is an effort to link development to the production of variation, which can influence evolutionary trajectories. The ICM proposes that serially developing features, such as molar teeth, are governed by the relative magnitudes of one activating and one inhibiting developmental process. The statistical expectations of the ICM are typically expressed and analyzed on a first-element standardized scale and seem to be a good predictor of molar proportions. However, the ICM has been applied to traits that occur in series but do not develop in sequence and still recovers as good a fit as when applied to serially developing traits. Such an undiscriminating result raises questions about whether the fit of the ICM is an artifact of standardization. The mathematical rendition of the ICM does not correspond with the verbal descriptions of the developmental argument. Applying our novel re-articulation of the ICM to biological, non-biological, and simulated data, we demonstrate that the apparent goodness of fit of the ICM to many biological systems is an artifact of scaling correlated values with a common denominator. There is no evidence supporting the ICM at the developmental, variational, or evolutionary levels.

There is great variation across species in how many individuals participate in territorial defense. Here, we test the hypotheses that joint territorial defense by pairs or family groups is more common in songbird species that (1) nest in tropical latitudes, (2) exhibit weak sexual selection, (3) maintain long-term social bonds, (4) defend year-round territories, (5) nest cooperatively, and (6) are sedentary. We conducted the first broad-scale test of these hypotheses by performing 3177 playback experiments across the Americas to measure territorial defense behaviors for 264 species. We found support for three of our six predictions: tropical species, cooperative nesters, and species with long-term social bonds are indeed more likely to jointly defend territories, but other variables were unrelated to joint territorial defense. Latitudinal zone was the strongest predictor, suggesting that tropical environments select for joint territory defense above and beyond the life history traits we included in our analysis. The remaining traits that predicted territorial defense describe aspects of communal living, though the association with long-term social bonds was marginal. Overall, we document a strong latitudinal gradient wherein joint territorial defense is consistently more common in the tropics even when accounting for different life history traits of tropical birds.

Sexual selection has strong effects on gonad size, which has been proposed to shift energetic allocations, resulting in concomitant decreases in brain size. However, mixed findings leave it unclear whether negative correlations reflect direct energetic trade-offs or selection on trait combinations broadly. We tested whether male reproductive tactics impose energetic trade-offs by comparing brain and gonad sizes in Poecilia parae, a fish with discrete alternative male morphs specializing in three reproductive strategies: coercion, display, and sneaking. The obligate sneaker morph had substantially larger gonads and smaller brains than the other morphs, consistent with an energetic trade-off. However, examining individuals within morphs revealed a positive relationship, contradicting the energetic trade-off hypothesis. To resolve which morphs reflect the ancestral tissue state, we also compared gonad and brain sizes of the morphs to two closely related species whose males utilize more flexible reproductive strategies, Poecilia picta and Poecilia reticulata. Again, the Poecilia parae obligate sneaker morph had the largest gonads and the smallest brains. Neuron-to-glia ratio (a proxy for energetic demands) showed no link to gonad size. Our results suggest that reproductive strategies shape brain evolution through correlational selection rather than direct energetic trade-offs, challenging assumptions that sexually selected traits impose constraints through direct resource allocation.

There have been many recent discussions of the Fundamental Theorem of Natural Selection, with an emphasis on its mathematical accuracy. It is argued here that, despite the mathematical problems that have been uncovered, it still has utility for biologists. In particular, it predicts an absence of additive genetic variance for fitness for populations at equilibrium under selection alone, a result that is valid under very general conditions. This raises the question as to why there are such high levels of additive variance in fitness and fitness components, but little evidence for non-additive variance.