American Naturalist最新文献

AbstractThe biodiversity-ecosystem functioning (BEF) and the food web structure (FWS) theories are cornerstones of contemporary ecology. However, while several theoretical hypotheses predict a link between BEF and FWS, the integration of both frameworks has only recently been considered. In this study, we applied structural equation models to evaluate 73 sink food webs of predatory fish from the Paraná River, encompassing a wide gradient of community richness. Our analysis revealed a well-supported causal model where species richness drives food web structure, increasing link density, modularity, intermodular connections, and weak interactions while decreasing nestedness. Both link density and modularity were positively associated with standing biomass, suggesting that communities with multiple energy pathways and strong complementarity effects tend to support higher biomass. Surprisingly, while species richness had the largest overall effect on biomass, this effect was indirect, mediated through three positive pathways and one negative pathway. These findings highlight the complex associations between BEF and FWS, suggesting that anthropogenic impacts on modularity, such as community functional homogenization, could shift positive BEF effects to negative, with cascading consequences for entire ecosystems.

AbstractOrnamental traits signaling phenotypic and/or genetic quality play a central role in sexual selection and greatly determine the access to mating partners and thus fitness. Accordingly, they underlie strong directional selection. Ornament expression is often condition dependent and therefore supposed to be sensitive to inbreeding. Kin selection theory predicts that ornament expression may depend on the genetic relatedness of competitors. Here, we examined the dynamic color expression in male groups of the cichlid Pelvicachromis taeniatus during competition over breeding sites. Groups (trios) were either inbred or outbred, and each consisted of two unfamiliar brothers and an unfamiliar unrelated male. Males of P. taeniatus are territorial and develop a carotenoid-based yellow coloration at the ventral body region and the caudal fin. Intense body coloration signals dominance. Our study showed (i) that outbred males generally developed more intense yellow coloration (chromaticity) during the experiment compared with inbred males and (ii) that related males were more intensively colored at the caudal fin after the trials than the unrelated males. In conclusion, our study indicates environment-dependent inbreeding depression in a male ornament as well as positive kin-selected effects on ornament expression. Our study describes understudied sources of phenotypic variation in ornamental traits in animals.

AbstractWe used a "quasi-natural" selection experiment and subsequent reciprocal transplants to assess the means of divergence in mating signals early in a host shift. We worked with a member of the Enchenopa binotata complex of treehoppers (Hemiptera: Membracidae), where speciation results from host plant shifts and involves remarkable signal-preference codivergence. We shifted treehoppers from a natural population on one host plant to three different novel host species under conditions of allopatry and sympatry. After five generations, we conducted reciprocal transplants that manipulated oviposition and development hosts. We found tentative evidence of signal divergence fueled by standing genetic variation and strong evidence of signal divergence through overall plasticity and evolution in the form of plasticity, resulting in signal differences between treehoppers on novel and ancestral hosts. These results suggest that signal divergence (and consequently assortative mating) may arise early in a host shift from multiple means. Together with a prior analysis of the adaptive consequences of these experimental host shifts, our findings indicate that adaptation/specialization and divergence in sexual traits may originate independently and in parallel or with divergence in sexual traits leading. Thus, ecological specialization may be facilitated by sexual divergence rather than being the initiating factor.

AbstractMate choice is a critical decision, especially for females, that requires time and energy to assess potential partners' genetic quality. Consequently, in many species, females have evolved the ability to utilize social information by copying the mate choices of others, usually based on visual cues. However, many species, especially invertebrates, primarily rely on chemical not visual cues. Using chemical rather than visual cues provides several advantages, such as not requiring active observation of copulations. Despite that, empirical evidence for the existence of chemical mate choice copying is scarce. Using Drosophila melanogaster, we provide the first demonstration of chemical mate choice copying. Females exposed to a recently mated female select the same male genotype that the demonstrator female mated with at a higher frequency than expected by chance. Chemical mate choice copying requires sensing both male and female cues, which might indicate that other females have chosen that male genotype. Our work suggests that females, in the presence of mated females, increase choosiness at the virgin stage, elevating sexual selection on male traits. This study provides novel evidence that exploiting social information is more prevalent in flies than previously assumed.

AbstractA father's age at conception is predicted to affect not only his own fertility but also his offspring's fitness. Offspring born to old fathers are assumed to be less fit than those of young fathers. However, under low mating rates, paternal age might be confounded with the duration for which mature sperm are stored in fathers prior to ejaculation. Studies that disentangle the confounding paternal effects of sperm storage duration from those of age on offspring are lacking. We use Drosophila melanogaster to test the separate and interactive effects of paternal age and sexual rest on offspring fitness. As expected, old fathers produce fewer offspring than young fathers; however, paternal age does not influence the survival or age-dependent reproductive success of sons or daughters. Instead, a long duration of paternal sexual rest negatively impacts the reproductive success of the conceived sons. Furthermore, daughters of low reproductive quality selectively disappear with age, but sons do not, highlighting that demographic processes can further modulate paternal age effects. Overall, we highlight that paternal age effects might not be as pervasive as previously assumed and suggest that paternal sexual rest might be more important in influencing offspring phenotypes.

AbstractUnderstanding how the functional role of species within seed dispersal networks varies across geographical and climatic gradients can reveal the drivers of network organization. Because bird-plant interactions differ depending on where these occur, species' centrality (a measurement of species importance in the networks) is expected to vary across species' geographic distributions. Using a global dataset of bird-plant seed dispersal networks, we applied a cross-random mixed effects model to evaluate the variation of 239 bird species' centrality within local networks across their occupied climatic conditions and in response to coexisting bird and plant diversities in those networks. Our model indicated that centrality did not vary significantly with the distance to the climatic niche centroid but increased with increasing bird diversity. However, by examining species' individual responses we found that centrality did vary with the distance to the climatic niche centroid: 43% of the evaluated species (102) showed a negative relationship (higher centrality closer to the climatic niche centroid), whereas 51% of species (122) showed a positive relationship (higher centrality farther from the climatic niche centroid). The effect of bird diversity on individual species' centrality covaried positively with that of plant diversity more than having opposite effects, regardless of the network's position within the climatic niche. Taken together, the variation in individual species' centrality within the occupied climatic conditions suggests the existence of areas where species achieve high centrality, which might form the substrate for evolutionary and ecological dynamics.

AbstractPrenatal environmental cues can affect embryonic development to produce suitable phenotypes to match the expected conditions after birth. In gulls, parental alarm calls during incubation affect postnatal antipredator behavior, but how chicks integrate reliable prenatal and postnatal information and how this influences their development and viability remain unclear. In this study, we performed a match-mismatch experiment in which we manipulated acoustic cues of predator presence during embryonic development (adult alarm calls vs. colony noise) and the nestling period (simulated intrusions of a mink decoy triggering adult alarm calls vs. a rabbit decoy) in yellow-legged gulls. Our results show that embryonic exposure to predator cues alters the antipredator responses of chicks in early postnatal life, as indicated by increased tonic immobility. Chicks exposed to prenatal adult alarm calls also displayed faster crouching behavior but, unexpectedly, only in the absence of predators during the postnatal period. Chicks exposed to postnatal predator presence begged less during a standardized begging behavior test. The chicks experiencing mismatched prenatal and postnatal cues of predator presence showed smaller skeletal size and greater genomic damage at fledging compared with those developed in matched environments. Our results highlight the importance of the late embryonic stage in shaping phenotypic outcomes, depending on alignment with the postnatal environment.

AbstractUncovering the patterns and structure in species interactions is central to understanding community assembly and dynamics. Species interact via their phenotypes, but identifying and quantifying the traits that structure species-specific interactions (links) can be challenging. Where these traits show phylogenetic signal, link properties (such as which species interact and how often) may be predictable using models that incorporate phylogenies in place of trait data. However, quantification of phylogenetic patterns in link properties is conceptually and methodologically challenging because it requires coestimation of multiple phylogenetic and nonphylogenetic pattern types in interaction data for multiple sites while controlling for confounding effects and making biologically plausible assumptions about which species can interact. Here we show how this can be done in a Bayesian mixed modeling framework, using data for trophic interactions between oak cynipid galls and parasitoid natural enemies. We find strong signatures of cophylogeny (i.e., related parasitoids attack related host galls) in both link incidence (presence/absence) and link frequency data, alongside patterns in link incidence/richness and identity across sites that are independent of either parasitoid or gall wasp phylogeny. Our results are robust to substantially reduced sample completeness and are consistent with structuring of trophic interactions by a combination of phylogenetically conserved and phylogenetically labile traits in both trophic levels. We show that incorporation of phylogenetic relationships into analyses of species interactions has substantial explanatory power even in the absence of trait data, with potential applied use in prediction of natural enemies of invading pests and nontarget hosts of biocontrol agents.

AbstractMolt is a critical event in the annual cycle of birds. Although we know an increasing amount about the impacts of climate change on the timing of other avian events, there has been relatively limited work conducted on changes in molt phenology over time. In this study, we utilized a 13-year bird-banding dataset from southeastern Utah to examine long-term trends in the molt timing of body and flight feathers during both the spring and the fall migratory seasons, accounting for temporal trends in nonmolting birds and how trends may vary between different sexes and ages of birds. We found that there were no significant temporal trends in molt timing in the spring but there were significant trends in the fall, such that birds were advancing the timing of their body and flight feather molt over time. Finally, we highlight the significant influence of climate on molt phenology: El Niño/Southern Oscillation and maximum temperature were both associated with advances in spring body molt, maximum temperature was associated with delays in fall flight feather molt timing, and precipitation was associated with advances in both fall body and flight feather molt timing. This study provides the first examination of long-term trends in the molt phenology of North American birds, showing that over the past decade, birds in the western United States have advanced their feather molt timing in the fall at a rate of roughly one day/year.

AbstractDisentangling the relative importance of biotic versus abiotic factors at a macroevolutionary scale is key to our understanding of the processes of diversification. Mutualistic Müllerian mimicry is a compelling example of an ecological interaction that affects population and species ecology and evolution. Here, we test how Müllerian mimicry shapes macroevolutionary patterns of diversification in the Ithomiini butterflies. We show that the age of color patterns is the most important predictor of species richness within mimicry rings but does not predict phylogenetic diversity of mimicry rings. We find pervasive phylogenetic signal in mimicry rings and in color patterns associated within polymorphic species. Only a small set of mimicry rings show high phylogenetic diversity. We identify patterns of saturation in the accumulation of new mimicry rings and in the number of evolutionary convergences toward the most species-rich mimicry rings. We discuss how the time-dependent effects detected in our study illustrate how neutral processes and ecological interactions interact and shape species and phenotypic diversification. Our results show that selection driven by mimetic interaction has not erased the effect of time and phylogenetic signal on the formation of mimicry rings but ecological saturation linked to mimetic interactions affected the dynamics of color pattern evolution and species diversification.