No abstract

Altruism presents a challenge to evolutionary theory because selection should favor selfish over caring strategies. Greenbeard altruism resolves this paradox by allowing cooperators to identify individuals carrying similar alleles producing a form of genic selection. In sideblotched lizards, genetically similar but unrelated blue male morphs settle on adjacent territories and cooperate. Here we show that payoffs of cooperation depend on asymmetric costs of orange neighbors. One blue male experiences low fitness and buffers his unrelated partner from aggressive orange males despite the potential benefits of defection. We show that recognition behavior is highly heritable in nature, and we map genetic factors underlying color and self-recognition behavior of genetic similarity in both sexes. Recognition and cooperation arise from genome-wide factors based on our mapping study of the location of genes responsible for self-recognition behavior, recognition of blue color, and the color locus. Our results provide an example of greenbeard interactions in a vertebrate that are typified by cycles of greenbeard mutualism interspersed with phases of transient true altruism. Such cycles provide a mechanism encouraging the origin and stability of true altruism.alternative strategies ͉ linkage map ͉ frequency-dependent selection ͉ evolutionarily stable strategy ͉ cooperation T he evolutionary stability of cooperative and altruistic behaviors requires that interindividual benefits be protected from competition, cheating, and defection (1-4). Without such safeguards, selfish strategies will eliminate altruistic strategies (5, 6). Hamilton (5) theorized that true altruism might evolve if a supergene simultaneously affected a signal and recognition of the signal and that signal recognition elicited social acts costly to donors but beneficial to recipients. Dawkins (6) coined Hamilton's social supergene a greenbeard in a hypothetical example of altruists that sported a green beard distinct in color from other beards sported by nonaltruists. Despite studies consistent with greenbeard altruism (7-12), few provide definitive evidence for greenbeard altruism.The annual side-blotched lizard, Uta stansburiana, exhibits six color genotypes (13, 14) (oo, bo, yo, bb, by, and yy), which serve as markers for three male strategies (15). Orange males (oo, bo, and yo) usurp territory. Blue males (bb) mate-guard. Yellow males (by and yy) are sneakers. Male competition drives rock-paper-scissors (RPS) cycles of three strategies: sneakers beat usurpers, mate guarders defeat sneakers, and usurpers prevail over mate guarders (13,(15)(16)(17)(18)(19). Previously, we showed that males with b alleles prefer to settle near non-kin but genetically similar bb males and cooperate in territory defense (15). Hereafter, we refer to bb males with genetically similar neighbors (based on allele sharing at nine microsatellite loci) as ''dyadic bb pairs'' (15). We contrast dyadic bb males with ''loner bb males'' that may have bb neighbors, but none are genetically...

One of the common assumptions in the study of the evolution of parental care is that trade‐offs exist between parental investment and other fitness‐related traits. In general, this body of work follows the traditional definition that parental investment (in the current offspring) decreases that individual’s ability to invest in future reproduction (Trivers 1972). However, examination of the empirical evidence shows that assuming a trade‐off between parental and mating effort is not always appropriate. This overemphasis on a trade‐off between mating and parental effort has arisen in part because of an oversimplification of female reproductive strategies, a failure to consider interactions between the sexes, and a tendency to consider behaviours as unifunctional, thereby ignoring the more complex relationship between mating and parental effort in many species. Here, we first examine the empirical evidence for trade‐offs between mating and parental effort in males and females to ask when trade‐offs occur and what pattern they take. By highlighting a number of exemplar species, we then explore how the presence or absence of trade‐offs relates to mate choice and sexual selection in both sexes. Finally, we highlight the importance of considering individual variation, which has been particularly overlooked in examinations of female investment, and how preferences in one sex may influence the existence and our interpretation of apparent trade‐offs in the other sex.

In species with internal fertilization, females can favour certain males over others, not only before mating but also within the female's reproductive tract after mating. Here, we ask whether such directional post-mating (that is, cryptic) female mate choice can also occur in species with external fertilization. Using an in vitro sperm competition experiment, we demonstrate that female ovarian fluid (ovarian fluid) changes the outcome of sperm competition by decreasing the importance of sperm number thereby increasing the relative importance of sperm velocity. We further show that ovarian fluid does not differentially affect sperm from alternative male phenotypes, but generally enhances sperm velocity, motility, straightness and chemoattraction. Under natural conditions, female ovarian fluid likely increases the paternity of the preferred parental male phenotype, as these males release fewer but faster sperm. These results imply females have greater control over fertilization and potential to exert selection on males in species with external fertilization than previously thought possible.