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Body size is an important component of burying beetle (genus ) life history, affecting competitive interactions and resource use. Currently, there is no comprehensive analysis of what drives these differences in size and how body size is distributed within the genus and across its geographic range. We used a large dataset of body size measurements and geographical data to evaluate the relative importance of phylogeny, biogeography, and ecology in explaining body size variation in burying beetles. Mean body size distribution among species is broad (4.15-10.97 mm pronotal width) and skewed, with more small and medium-bodied species than large species. We found evidence of phylogenetic signal in the evolution of body size across the genus, although only one instance of sister species both being giants and no instances of sister species being both small. However, the phylogenetic analysis does not explain the evolution of extremes in body size. Areas with higher species richness have a greater spread between the largest and smallest species, and body size is divergent between most sister species and more strongly so between sympatric sister species, even after correcting for phylogeny. We found evidence of rapid initial divergence in body size following speciation, which increased over time in sympatric species, but stabilized in non-sympatric species. Smallest body sizes and highest species richness are concentrated in northern hemisphere temperate latitudes. Taken together, these results suggest character displacement by body size may be a significant factor allowing coexistence of burying beetle species; however, other mechanisms of niche partitioning are likely important contributors to coexistence. High species richness in temperate, mesic areas of the northern hemisphere may be driven by habitat and climatic suitability. We encourage further experimentation to test our proposed mechanisms of body size divergence and geographic distribution in .

An increased divergence in characters between species in secondary contact can be shaped by selection against competition for a common resource (ecological character displacement, ECD) or against maladapted hybridization (reproductive character displacement, RCD). These selective pressures can act between incipient species (reinforcement) or well-separated species that already completed the speciation process, but that can still hybridize and produce maladapted hybrids. Here, we investigated two well-separated sexually deceptive orchid species that, unusually, share their specific pollinator. Sympatric individuals of these species are more divergent than allopatric ones in floral characters involved in a mechanical isolating barrier, a pattern suggestive of RCD. To experimentally test this scenario, we built an artificial sympatric population with allopatric individuals. We measured flower characters, genotyped the offspring in natural and artificial sympatry and estimated fertility of hybrids. Different from naturally sympatric individuals, allopatric individuals in artificial sympatry hybridized widely. Hybrids showed lower pollination success and seed viability than parentals. Character displacement did not affect plant pollination success. These findings suggest that RCD evolved between these species to avoid hybridization and that selection on reinforcement may be very strong even in plants with highly specialized pollination.

Sex differences in selection arise for at least two possible reasons: (1) differences originating from anisogamy—the Darwin‐Bateman paradigm—and (2) competition‐driven ecological character displacement (ECD), agnostic of anisogamy. Despite mounting evidence of ECD and increasing focus on the ecological causes and consequences of sexual dimorphism, progress in understanding the evolution of ecological sex differences has likely been hindered because ecological dimorphisms are not exclusive to ECD. I argue that embracing nonexclusivity of causal models of sexual dimorphism itself may provide insight into evolution of sex differences. This integrated view of the evolution of sexual dimorphism leads to four predictions for how sex‐specific selection and phenotypic divergence between the sexes change over the course of the evolution of sexual dimorphism. First, dimorphism resulting directly from anisogamy likely precedes evolution of ecological dimorphism driven by ECD. Second, ecological sexual dimorphism driven by ECD may (initially) evolve in directions in trait space favored by other sources of sex‐specific selection. Third, we may expect correlated evolution of ecological dimorphism and other forms of sexual dimorphism. Finally, ecological optima may be sex specific even when competition plays a role in reaching them. Rather than simply a less‐parsimonious alternative explanation for ecological sex differences, ECD should be seen as one likely contributor to sex‐specific selection that could act at predictable times during the evolution of ecological sexual dimorphisms.

Reproductive character displacement is the adaptive evolution of traits that minimize deleterious reproductive interactions between species. When arising from selection to avoid hybridization, this process is referred to as reinforcement. Reproductive character displacement generates divergence not only between interacting species, but also between conspecific populations that are sympatric with heterospecifics versus those that are allopatric. Consequently, such conspecific populations can become reproductively isolated. We compared female mate preferences in, and evaluated gene flow between, neighbouring populations of spadefoot toads that did and did not occur with heterospecifics (mixed- and pure-species populations, respectively). We found that in mixed-species populations females significantly preferred conspecifics. Such females also tended to prefer a conspecific call character that was dissimilar from heterospecifics. By contrast, females from pure-species populations did not discriminate conspecific from heterospecific calls. They also preferred a more exaggerated conspecific call character that resembles heterospecific males. Moreover, gene flow was significantly reduced between mixed- and pure-species population types. Thus, character displacement (and, more specifically, reinforcement) may initiate reproductive isolation between conspecific populations that differ in interactions with heterospecifics.

The evidence for character displacement as a widespread response to competition is now building. This progress is largely the result of the establishment of rigorous criteria for demonstrating character displacement in the animal literature. There are, however, relatively few well‐supported examples of character displacement in plants. This review explores the potential for character displacement in plants by addressing the following questions: (1) Why aren't examples of character displacement in plants more common? (2) What are the requirements for character displacement to occur and how do plant populations meet those requirements? (3) What are the criteria for testing the pattern and process of character displacement and what methods can and have been used to address these criteria in the plant literature? (4) What are some additional approaches for studying character displacement in plants? While more research is needed, the few plant systems in which character displacement hypotheses have been rigorously tested suggest that character displacement may play a role in shaping plant communities. Plants are especially amenable to character displacement studies because of the experimental ease with which they can be used in common gardens, selection analyses, and breeding designs. A deeper investigation of character displacement in plants is critical for a more complete understanding of the ecological and evolutionary processes that permit the coexistence of plant species. While the case for character displacement continues to build in the animal literature, we still have relatively few examples of character displacement in plants. This review explores whether character displacement is likely to occur in plant communities and offers some guidelines for rigorous experimental testing of this process. A deeper investigation of character displacement in plants is critical for a more complete understanding of the ecological and evolutionary forces that shape plant communities.

Understanding how divergent selection generates adaptive phenotypic and population diversification provides a mechanistic explanation of speciation in recently separated species pairs. Towards this goal, we sought ecological gradients of divergence between the cryptic malaria vectors Anopheles coluzzii and An. gambiae and then looked for a physiological trait that may underlie such divergence. Using a large set of occurrence records and eco‐geographic information, we built a distribution model to predict the predominance of the two species across their range of sympatry. Our model predicts two novel gradients along which the species segregate: distance from the coastline and altitude. Anopheles coluzzii showed a ‘bimodal’ distribution, predominating in xeric West African savannas and along the western coastal fringe of Africa. To test whether differences in salinity tolerance underlie this habitat segregation, we assessed the acute dose–mortality response to salinity of thirty‐two larval populations from Central Africa. In agreement with its coastal predominance, Anopheles coluzzii was overall more tolerant than An. gambiae. Salinity tolerance of both species, however, converged in urban localities, presumably reflecting an adaptive response to osmotic stress from anthropogenic pollutants. When comparing degree of tolerance in conjunction with levels of syntopy, we found evidence of character displacement in this trait.

The relative importance of male and female mating preferences in causing sexual isolation between species remains a major unresolved question in speciation. Despite previous work showing that male courtship bias and/or female copulation bias for conspecifics occur in many taxa, the present study is one of the first large-scale works to study their relative divergence. To achieve this, we used data from the literature and present experiments across 66 Drosophila species pairs. Our results revealed that male and female mate preferences are both ubiquitous in Drosophila but evolved largely independently, suggesting different underlying evolutionary and genetic mechanisms. Moreover, their relative divergence strongly depends on the geographical relationship of species. Between allopatric species, male courtship and female copulation preferences diverged at very similar rates, evolving approximately linearly with time of divergence. In sharp contrast, between sympatric species pairs, female preferences diverged much more rapidly than male preferences and were the only drivers of enhanced sexual isolation in sympatry and Reproductive Character Displacement (RCD). Not only does this result suggest that females are primarily responsible for such processes as reinforcement, but it also implies that evolved female preferences may reduce selection for further divergence of male courtship preferences in sympatry.

Character displacement can reduce costly interspecific interactions between young species. We investigated the mechanisms behind divergence in three key traits—breeding habitat choice, timing of breeding, and plumage coloration—in Ficedula flycatchers. We found that male pied flycatchers became expelled from the preferred deciduous habitat into mixed forest as the superior competitor, collared flycatchers, increased in numbers. The peak in food abundance differs between habitats, and the spatial segregation was paralleled by an increased divergence in timing of breeding between the two species. Male pied flycatchers vary from brown to black with brown coloration being more frequent in sympatry with collared flycatchers, a pattern often proposed to result from selection against hybridization, that is, reinforcement. In contrast to this view, we show that brown male pied flycatchers more often hybridize than black males. Male pied flycatcher plumage coloration influenced the territory obtained in areas of co-occurrence with collared flycatchers, and brown male pied flycatchers experienced higher relative fitness than black males when faced with heterospecific competition. We suggest that allopatric divergence in resource defense ability causes a feedback loop at secondary contact where male pied flycatchers with the most divergent strategy compared to collared flycatchers are favored by selection.

Classic evolutionary theory suggests that sexual dimorphism evolves primarily via sexual and fecundity selection. However, theory and evidence are beginning to accumulate suggesting that resource competition can drive the evolution of sexual dimorphism, via ecological character displacement between sexes. A key prediction of this hypothesis is that the extent of ecological divergence between sexes will be associated with the extent of sexual dimorphism. As the stable isotope ratios of animal tissues provide a quantitative measure of various aspects of ecology, we carried out a meta‐analysis examining associations between the extent of isotopic divergence between sexes and the extent of body size dimorphism. Our models demonstrate that large amounts of between‐study variation in isotopic (ecological) divergence between sexes is nonrandom and may be associated with the traits of study subjects. We, therefore, completed meta‐regressions to examine whether the extent of isotopic divergence between sexes is associated with the extent of sexual size dimorphism. We found modest but significantly positive associations across species between size dimorphism and ecological differences between sexes, that increased in strength when the ecological opportunity for dietary divergence between sexes was greatest. Our results, therefore, provide further evidence that ecologically mediated selection, not directly related to reproduction, can contribute to the evolution of sexual dimorphism. Theoretical and empirical work suggests that between‐sex competition for resources plays a role in the evolution of sexual dimorphism. We investigated this concept by analyzing cross‐species relationships between the extent of sexual dimorphism and published sex differences in tissue stable isotope values, which are a proxy of dietary differences. We found that sexual dimorphism is related to sex differences in trophic level, in directions and contexts consistent with those expected if resource competition is involved in the evolution of sexual dimorphism.

Fil: Peretti, Alfredo Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina