Empirical data indicate that sexual preferences are critical for maintaining species 4 boundaries 1-4 , yet theoretical work has suggested they can play only a minimal role 5 in maintaining biodiversity on their own 5-9 . This is because long-term coexistence 6 within overlapping ranges is thought to be unlikely in the absence of ecological 7 differentiation 9 . Here we challenge this widely held view by generalizing a standard 8 model of sexual selection to include two ubiquitous features of populations with 9 sexual selection: spatial variation in local carrying capacity and mate-search costs in 10 females. We show that, when these two features are combined, sexual preferences can 11 single-handedly maintain coexistence, even when spatial variation in local carrying 12 capacity is so slight that it might go unnoticed empirically. This is the first theoretical 13 study to demonstrate that sexual selection alone can promote the long-term 14 coexistence of ecologically equivalent species with overlapping ranges, and it thus 15 provides a novel explanation for the maintenance of species diversity. coexistence, and not speciation, we assume that the genetic variation at both loci is 57 already present, for example, due to recent migration from allopatric ranges. All else 58 being equal, females bearing a P (p) allele prefer [14][15][16] hasten the loss of diversity (compare Fig. 2a to 2b). Spatial variation in local carrying 82 capacity, on its own, also has little, if any, effect in stabilizing populations (compare 83 Fig. 2b to 2c). Sexual selection with mate-search costs slightly prolongs coexistence in a 84 spatially homogeneous environment by helping to prevent mixing of the mating 85 domains, but this effect is weak (Fig. 2d). However, in an environment with spatial 86 variation in local carrying capacity, sexual selection with mate-search costs dramatically 87 increases coexistence times (compare Fig. 2e to Fig. 2b and also Fig. 1a, c to Fig. 1b, d). In 88 this case, mate-search costs curb the neutral drift of preference alleles, thus preventing 89 the dilution of mating domains, while areas of high local carrying capacity provide 90 spatial "anchors", stabilizing the location and size of these domains (Fig. 1b, d). 91While neither spatial variation in local carrying capacity nor mate-search costs 92 suffice on their own to stabilize populations, surprisingly little of both can be enough to 93 ensure the long-term persistence of divergent mating types (Fig. 3) (Fig. S5d). Levels of variation in this range may be difficult to detect in nature, especially 101 if they are to be inferred from observing the stochastic spatial distribution of individuals. 102The stabilizing effect of spatial variation in local carrying capacity and mate-search 103 costs readily extends to more realistic and natural landscapes (Fig. 4) and also to multiple 104 5 genotypes ( Fig. 4c-d (Fig. S7). Our findings are also robust to changes in female-preference 108 strength, mate-search distance, movement distance, and competition dista...

9We analyze the joint evolution of an ecological character and of dispersal distance in asex-

Divergent adaptation to different environments can promote speciation, and it is thus important to consider spatial structure in models of speciation. Earlier theoretical work, however, has been limited to particularly simple types of spatial structure -linear environmental gradients and spatially discrete metapopulations -leaving unaddressed the effects of more realistic patterns of landscape heterogeneity, such as nonlinear gradients and spatially continuous patchiness. To elucidate the consequences of such complex landscapes, we adapt an established spatially explicit individual-based model of evolutionary branching. We show that branching is most probable at intermediate levels of various types of heterogeneity, and that different types of heterogeneity have, to some extent, additive effects in promoting branching. In contrast to such additivity, we find a novel refugium effect in which refugia in hostile environments provide opportunities for colonization, thus increasing the probability of branching in patchy landscapes.Effects of patchiness depend on the scale of patches relative to dispersal. Providing a needed connection to empirical research on biodiversity and conservation policy, we introduce empirically accessible spatial environmental metrics that quantitatively predict a landscape's branching propensity.3

Meiotic recombination is crucial for chromosomal segregation and facilitates the spread of beneficial and removal of deleterious mutations. Recombination rates frequently vary along chromosomes and Drosophila melanogaster exhibits a remarkable pattern. Recombination rates gradually decrease toward centromeres and telomeres, with a dramatic impact on levels of variation in natural populations. Two close sister species, Drosophila simulans and Drosophila mauritiana do not only have higher recombination rates but also exhibit a much more homogeneous recombination rate that only drops sharply very close to centromeres and telomeres. Because certain sequence motifs are associated with recombination rate variation in D. melanogaster , we tested whether the difference in recombination landscape between D. melanogaster and D. simulans can be explained by the genomic distribution of recombination rate–associated sequence motifs. We constructed the first high-resolution recombination map for D. simulans based on 189 haplotypes from a natural D. simulans population and searched for short sequence motifs linked with higher than average recombination in both sister species. We identified five consensus motifs significantly associated with higher than average chromosome-wide recombination rates in at least one species and present in both. Testing fine resolution associations between motif density and recombination, we found strong and positive associations genome-wide over a range of scales in D. melanogaster , while the results were equivocal in D. simulans . Despite the strong association in D. melanogaster , we did not find a decreasing density of these short-repeat motifs toward centromeres and telomeres. We conclude that the density of recombination-associated repeat motifs cannot explain the large-scale recombination landscape in D. melanogaster , nor the differences to D. simulans . The strong association seen for the sequence motifs in D. melanogaster likely reflects their impact influencing local differences in recombination rates along the genome.

Understanding the emergence and maintenance of biodiversity ranks among the most fundamental challenges in evolutionary ecology. While processes of community assembly have frequently been analyzed from an ecological perspective, their evolutionary dimensions have so far received less attention. To elucidate the eco-evolutionary processes underlying the long-term build-up and potential collapse of community diversity, here we develop and examine an individual-based model describing coevolutionary dynamics driven by trophic interactions and interference competition, of a pair of quantitative traits determining predator and prey niches. Our results demonstrate the (1) emergence of communities with multiple trophic levels, shown here for the first time for stochastic models with linear functional responses, and (2) intermittent and cyclic evolutionary transitions between two alternative community states. In particular, our results indicate that the interplay of ecological and evolutionary dynamics often results in extinction cascades that remove the entire trophic level of consumers from a community. Finally, we show the (3) robustness of our results under variations of model assumptions, underscoring that processes of consumer collapse and subsequent rebound could be important elements of understanding biodiversity dynamics in natural communities.