Variation in the degree of sexual size dimorphism (SSD) among taxa is generally considered to arise from differences in the relative intensity of male-male competition and fecundity selection. One ...might predict, therefore, that SSD will vary systematically with (1) the intensity of sexual selection for increased male size, and (2) the intensity of fecundity selection for increased female size. To test these two fundamental hypotheses, we conducted a phylogenetic comparative analysis of SSD in fish. Specifically, using records of body length at first sexual maturity from FishBase, we quantified variation in the magnitude and direction of SSD in more than 600 diverse freshwater and marine fish species, from sticklebacks to sharks. Although female-biased SSD was common, and thought to be driven primarily by fecundity selection, variation in SSD was not dependent on either the allometric scaling of reproductive energy output or fecundity in female fish. Instead, systematic patterns based on habitat and life-history characteristics associated with varying degrees of male-male competition and paternal care strongly suggest that adaptive variation in SSD is driven by the intensity of sexual selection for increased male size.
Weapon performance drives weapon evolution Emberts, Zachary; Hwang, Wei Song; Wiens, John J
Proceedings of the Royal Society. B, Biological sciences,
01/2021, Letnik:
288, Številka:
1943
Journal Article
Recenzirano
Odprti dostop
Many sexually selected traits function as weapons, and these weapons can be incredibly diverse. However, the factors underlying weapon diversity among species remain poorly understood, and a ...fundamental hypothesis to explain this diversity remains untested. Although weapons can serve multiple functions, an undeniably important function is their role in fights. Thus, a crucial hypothesis is that weapon diversification is driven by the evolution of weapon modifications that provide an advantage in combat (e.g. causing more damage). Here, we test this fighting-advantage hypothesis using data from 17 species of coreid bugs. We utilize the fact that male-male combat in coreids often results in detectable damage, allowing us to link different weapon morphologies to different levels of damage among species. We find that certain weapon morphologies inflict much more damage than others, strongly supporting the fighting-advantage hypothesis. Moreover, very different weapon morphologies can inflict similarly severe amounts of damage, leading to a weapon performance landscape with multiple performance peaks. This multi-peak pattern could potentially drive different lineages towards divergent weapon forms, further increasing weapon diversity among species. Overall, our results may help explain how sexually selected weapons have evolved into the diversity of forms seen today.
Sexual selection is often thought to promote speciation. This expectation is largely driven by the fact that sexually selected traits can influence mating patterns and contribute to reproductive ...isolation. Indeed, some comparative studies have shown that clades with sexually selected traits have increased rates of speciation and diversification. However, these studies have almost exclusively focused on one mechanism of sexual selection: female choice. Another widespread mechanism is male-male competition. Few empirical studies (if any) have investigated the role of this alternative mechanism in driving diversification. Nevertheless, recent reviews have suggested that male-male competition can increase speciation rates. Here, we investigated whether traits associated with precopulatory male–male competition (i.e., sexually selected weapons) have promoted speciation and diversification in insects. We focused on three clades with both weapons and suitable phylogenies: leaf-footed and broad-headed bugs (Coreidae+Alydidae; ~2850 species), stick insects and relatives (Phasmatodea; ~3284 species), and scarab beetles (Scarabaeoidea; ~39,717 species). We found no evidence that weapon-bearing lineages in these clades have higher rates of speciation or diversification than their weaponless relatives. Thus, our results suggest that precopulatory male-male competition may not have strong, general effects on speciation and diversification in insects, a group encompassing ~60% of all described species.
Dietary restriction during development can affect adult body size and condition. In many species, larger (high-condition) males gain higher mating success through male-male competition and female ...choice, and female condition can affect the extent of both female mate choice and male investment in courtship or ejaculates. However, few studies have examined the joint effects and interplay of male and female condition during both the pre-and the postcopulatory phases of sexual selection. We therefore manipulated the larval diet of male and female Drosophila melanogaster to study how body size variation in both sexes biases competitive outcomes at different reproductive stages, from mating to paternity. We did not find a difference in mate preference or mating latency between females of different conditions, nor any interaction between male and female conditions. However, large males were more successful in gaining matings, but only when in direct competition, whereas mating latencies were shorter for low-condition males in noncompetitive settings. Small males also transferred more sperm to nonvirgin females, displaced a larger proportion of resident sperm, and achieved higher paternity shares per mating than large males. In agreement with existing theory, we suggest that small males might partially compensate for their low mating success by strategically investing in larger sperm numbers and potentially other, unmeasured ejaculate traits, when they do have a mating opportunity.
Competitive interactions shape the evolution of organisms. However, often it is not clear whether competition is the driving force behind the patterns observed. The recent use of experimental ...evolution in competitive environments can help establish such causality. Unfortunately, this literature is scattered, as competition for food, mates, and hosts are subject areas that belong to different research fields. Here, we group these bodies of literature, extract common processes and patterns concerning the role of competition in shaping evolutionary trajectories, and suggest perspectives stemming from an integrative view of competition across these research fields. This review reinstates the power of experimental evolution in addressing the evolutionary consequences of competition, but highlights potential pitfalls in the design of such experiments.
Organisms compete for several resource types, the most studied being food, mates, and hosts.
The study of each resource type belongs to different research fields, each with its own idiosyncrasies, including distinct vocabulary.
There are similarities in patterns and processes across diverse research fields that implicitly or explicitly study competition, as in all cases, individuals are competing for the use of a limiting resource.
The use of experimental evolution as methodology allows for a complete understanding of the reciprocal effects of competition on evolution.
Experimental evolution can be transversally applied to studies of competition across diverse research fields, in view of establishing a common integrative framework.
An integrative view of competitive interactions creates new predictions and clarifies patterns observed.
Women and female great apes both continue giving birth into their forties, but not beyond. However humans live much longer than other apes do. Even in hunting and gathering societies, where the ...mortality rate is high, adult life spans average twice those of chimpanzees, which become decrepit during their fertile years and rarely survive them. Since women usually remain healthy through and beyond childbearing age, human communities include substantial proportions of economically productive postmenopausal women. A grandmother hypothesis8–12 may explain why greater longevity evolved in our lineage while female fertility still ends at ancestral ages. This hypothesis has implications for the evolution of a wide array of human features. Here we review some history of the hypothesis, recent findings, and questions for ongoing research.
Hybridisation is increasingly recognised as an important cause of diversification and adaptation. Here, we show how divergence in male secondary sexual characters between two lineages of the common ...wall lizard (Podarcis muralis) gives rise to strong asymmetries in male competitive ability and mating success, resulting in asymmetric hybridisation upon secondary contact. Combined with no negative effects of hybridisation on survival or reproductive characters in F1‐hybrids, these results suggest that introgression should be asymmetric, resulting in the displacement of sexual characters of the sub‐dominant lineage. This prediction was confirmed in two types of secondary contact, across a natural contact zone and in two introduced populations. Our study illustrates how divergence in sexually selected traits via male competition can determine the direction and extent of introgression, contributing to geographic patterns of genetic and phenotypic diversity.
Emitting conspicuous signals into the environment to attract mates comes with the increased risk of interception by eavesdropping enemies. As a defence, a commonly described strategy is for ...signallers to group together in leks, diluting each individual's risk. Lekking systems are often highly social settings in which competing males dynamically alter their signalling behaviour to attract mates. Thus, signalling at the lek requires navigating fluctuations in risk, competition and reproductive opportunities. Here, we investigate how behavioural defence strategies directed at an eavesdropping enemy have cascading effects across the communication network. We investigated these behaviours in the túngara frog (
), examining how a calling male's swatting defence directed at frog-biting midges indirectly affects the calling behaviour of his rival. We found that the rival responds to swat-induced water ripples by increasing his call rate and complexity. Then, performing phonotaxis experiments, we found that eavesdropping fringe-lipped bats (
) do not exhibit a preference for a swatting male compared to his rival, but females strongly prefer the rival male. Defences to minimize attacks from eavesdroppers thus shift the mate competition landscape in favour of rival males. By modulating the attractiveness of signalling prey to female receivers, we posit that eavesdropping micropredators likely have an unappreciated impact on the ecology and evolution of sexual communication systems.
Why Sexually Selected Weapons Are Not Ornaments McCullough, Erin L.; Miller, Christine W.; Emlen, Douglas J.
Trends in ecology & evolution (Amsterdam),
October 2016, 2016-10-00, 20161001, Letnik:
31, Številka:
10
Journal Article
Recenzirano
The elaboration and diversification of sexually selected weapons remain poorly understood. We argue that progress in this topic has been hindered by a strong bias in sexual selection research, and a ...tendency for weapons to be conflated with ornaments used in mate choice. Here, we outline how male–male competition and female choice are distinct mechanisms of sexual selection, and why weapons and ornaments are fundamentally different types of traits. We call for research on the factors contributing to weapon divergence, the potential for male–male competition to drive speciation, and the specific use of weapons in the context of direct fights versus displays. Given that weapons are first and foremost fighting structures, biomechanical approaches are an especially promising direction for understanding weapon design.
The potential for male–male competition to drive the elaboration and diversification of weapon morphologies remains one of the most understudied topics in the field of sexual selection.
Progress in our understanding of weapon evolution has been hampered by a strong bias in sexual selection research, and imprecise terminology that erroneously equates all sexually selected structures with ornaments used in mate choice.
We outline how the processes and outcomes of female choice and male–male competition are distinct, and why weapons and ornaments are fundamentally different types of traits.
We encourage an integration of engineering techniques into studies of weapon function and performance, and highlight examples of how this biomechanical approach promises to improve our understanding of the evolution of weapon design.
Studies of socially mediated phenotypic plasticity have demonstrated adaptive male responses to the 'competitive' environment. Despite this, whether variation in the paternal social environment also ...influences offspring reproductive potential in an intergenerational context has not yet been examined. Here, we studied the descendants of wild-caught house mice, a destructive pest species worldwide, to address this knowledge gap. We analysed traits that define a 'competitive' phenotype in the sons of males (sires) that had been exposed to either a high-male density (competitive) or high-female density (non-competitive) environment. We report disparate reproductive strategies among the sires: high-male density led to a phenotype geared for competition, while high-female density led to a phenotype that would facilitate elevated mating frequency. Moreover, we found that the competitive responses of sires persisted in the subsequent generation, with the sons of males reared under competition having elevated sperm quality. As all sons were reared under common-garden conditions, variation in their reproductive phenotypes could only have arisen via nongenetic inheritance. We discuss our results in relation to the adaptive advantage of preparing sons for sperm competition and suggest that intergenerational plasticity is a previously unconsidered aspect in invasive mammal fertility control.
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