Our findings demonstrate how viability-related thermal physiology evolves alongside sexual ornaments to balance the demands of survival and reproduction. We found that dragonfly species that produce dark, heat-absorbing wing coloration can also tolerate greater heat stress. In fact, the elevated CTmax of ornamented species is almost identical to the magnitude of heating caused by ornamentation (1-2°C).

Sexually selected structures often contain metabolically active tissue that can contribute significantly to whole-organism resting metabolic rate during adulthood, even when the trait is no longer growing. Our results suggest that sexually selected traits can account for a large proportion of resting metabolic rate in males, and that larger males pay a lower proportional energetic cost for maintaining these structures. Indeed, resting metabolic rate can account for 30–40% of daily energy expenditure in free living animals. Thus, the daily energy expenditure of maintaining sexual traits might impose a larger energetic burden on an organism than sexual contests and ultimately shape the evolution of sexually selected traits.

Larger bodies, ornaments, or weapons favoured by sexual selection can cause heat stress due to slow heat dissipation (i.e. increased thermal load). We develop hypotheses for how thermal ecology affects mating system dynamics and how the thermal consequences of mate competition favour the reciprocal co-adaptation of thermal biology and sexual traits.

"A trade-off occurs whereby the energetic demands from the development and maintenance of sexual ornaments of increasing size are countered by (1) the energetic demands associated with maintenance of body condition and survival, and (2) the energetic demands associated with development and maintenance of homeostatic mechanisms that enable organisms to cope with environmental stress." The paper discusses how stress and energetic limits can constrain the evolution of large sexual ornaments, implying that costs of ornamentation can oppose natural selection favoring survival under stress.

Environmentally induced changes in the costs and benefits of sexually selected traits. Alterations of the environment can change the costs and benefits of sexually selected traits at the individual level, which could have further consequences at the population level. The costs and benefits of sexually selected traits could also change indirectly during environmental change, if individuals adjust the costs and benefits of sexually selected traits to the new conditions through phenotypic plasticity. Increases in the fitness costs of sexually selected traits under changed environmental conditions could reduce the overall reproductive output of the population. If the decline is too fast for other selective forces to rescue the population, then this could, in the worst case, lead to extinction.

Our study thus exemplifies how environmental stress can influence the relative forces of natural and sexual selection. Using fourteen isofemale lines, we measured sex-specific reductions in fitness components, genotype-by-environment interactions and the strength of selection (variance in fitness) in the juvenile and adult stage. Variance in fitness increased with stress, was consistently greater in males than females for adult reproductive success (implying strong sexual selection), but was similar in the sexes in terms of juvenile survival across all levels of stress. Moreover, genotype-by-environment interactions for fitness were common but specific to the type of stress, sex and life stage, suggesting that new environments may change the relative alignment and strength of selection in males and females.

We find that sexual selection on males leads to a fertility debt that is revealed under heat stress. This debt was also apparent in females... Forecasts of species’ response to climate change that do not incorporate thermal fertility limits and sexual selection may therefore underestimate species’ vulnerability to increasing temperatures.

"Sexual selection promotes traits that enhance mating or fertilization success, but these traits can be very costly under harsh environmental conditions." The authors found that males from operating sex ratios (OSRs) with intense pre-copulatory sexual selection on body and wing size experienced greater size reduction under developmental heat stress. "Developing at high temperature generally reduced male body and trait size... limiting resource accumulation for sexually selected traits." They note that in populations under strong premating sexual selection, traits under such selection may be more affected by environmental stress, highlighting a trade-off between sexual selection and thermal stress effects on phenotype.

"Sexual selection can promote traits that are associated with considerable costs in the face of natural selection (Andersson, 1994; Zahavi, 1975). Harsh environments that impose strong natural selection are therefore predicted to limit the evolution of sexually selected traits in favor of allocation to maintenance and survival." The study shows that males evolving under strong postcopulatory sexual selection suffered increased temperature-induced sterility (TSF) under heat stress. "Our results suggest that trade-offs between fertility and traits increasing success in postcopulatory sexual selection can be revealed in harsh environments… populations that have evolved under a history of strong sexual selection are predicted to suffer a greater fertility loss following increased environmental stress."

Sexual selection may exaggerate traits beyond their optimum with respect to biomechanical or physiological function, thus imposing 'costs' of various types. These costs may be borne in terms of energetic expenditure, reduced locomotor performance, elevated predation risk, or impaired physiological homeostasis. Evaluating performance costs of sexually selected traits is therefore essential for understanding the trade-offs that shape the evolution of exaggerated ornaments and weapons.

Sexually selected traits (SSTs) evolve by sexual selection and include a wide range of behavioral, morphological, and physiological characters that increase mating success. Because these traits often impose survival costs, they can also have ecological consequences at the individual, population, and community levels. SSTs such as bright coloration, enlarged weapons, and energetically expensive courtship displays can alter predation risk, resource use, and energy budgets, thereby influencing how organisms interact with their environments.

Trade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Sexual selection may lead to the elaboration of (usually male) secondary sexual characters that improve mating success but handicap survival and/or impose energetic costs that reduce other fitness components. Moreover, trade-offs often occur only in populations that are experiencing harsh environmental conditions or energetic challenges at the extremes of phenotypic distributions.

When faced with increasing temperatures, strong sexual selection was associated with both increased fecundity and offspring survival compared with weak sexual selection, suggesting that sexual selection can facilitate adaptation to warming. However, sexual selection can also impose costs: in some scenarios, intense mate competition and the expression of costly sexual traits may reduce population growth or increase extinction risk if environmental change is too rapid for populations to adapt.

Sexual selection is a process that can interact with the thermal sensitivity of fertility and is strongest in males of polyandrous species, in which females mate multiply and sperm of multiple males compete for fertilization of female eggs. However, given finite resources, increased investment in sperm competition can come at an expense of other processes needed to maintain the integrity of the male germline, which when compromised can reduce fertility and offspring quality.

The authors test the "selection trade-off hypothesis" that sexual selection favors greater elaboration of male ornamentation whereas natural selection often favors dull, less conspicuous traits. "Environments with higher predator densities likely confer greater viability costs for bearing elaborated traits due to reduced locomotor ability or increased detectability." In Bahamas mosquitofish, bright orange dorsal-fin coloration is sexually attractive but decreases survivorship in high-risk environments. "Our results indicate that a trade-off between natural and sexual selection can indeed drive major patterns of signal diversity during an adaptive radiation."

We find that sexual selection on males leads to a fertility debt that is revealed under heat stress. This debt was also apparent in females, who themselves were not selected for increased reproductive investment. Thus, genes under sexual selection in males seem to have impaired fertility in both sexes under heat stress. Our results suggest that trade-offs between fertility and traits increasing success in postcopulatory sexual selection can be revealed in harsh environments. This can put polyandrous species under immediate risk during extreme heat waves expected under future climate change.

We investigated condition-dependent trade-offs between investment into male sexual trait expression, body mass, immune function and energy reserves in fluctuating asymmetry of the tail and badge size in blue tits. Consequently, the survival costs of a given level of sexual trait expression, as with most life history traits, will vary across habitats. Our results indicate that investment into sexual traits can trade off against body condition and immune function, especially under limited resources or environmental stress.

Trade-offs can occur between physiological traits expressed during the same or different times in the life cycle, and they can result from variation in genetic factors, environmental factors, or combinations of these two types of factors that give rise to negative interactions between traits. If the trade-off results from a negative genetic correlation, then short-term evolutionary change in one phenotype constrains evolutionary change in the other phenotype. In insects and mammals, allocation to maintenance or storage was found to take precedence over allocation to reproduction under nutrient-poor or stressful conditions, illustrating how environmental stress can shift investment away from costly reproductive traits.

A strong female choice for the expression alone, as opposed to the function, of a male ornament can oppose and undermine the forces of natural selection and result in the runaway sexual selection that leads to the further exaggeration of the ornament (as well as the preference) until the costs (incurred by natural selection) of the expression become greater than the benefit (bestowed by sexual selection).

Sexual selection is a specific form of natural selection that acts on an organism's ability to obtain or successfully reproduce with a mate. While sexual selection can sometimes work in concert with natural selection (traits that attract mates can also confer survival advantages), it often opposes natural selection. For example, the peacock’s elaborate tail, while attractive to females, can make it more vulnerable to predators. This conflict can lead to evolutionary trade-offs where the benefits of increased reproductive success outweigh the costs to survival, and natural selection can limit sexually selected traits if their costs become too great, especially under challenging environmental conditions.

The Darwin Correspondence Project explains Darwin’s concept: "Darwin proposed that these characteristics were the result of a secondary mechanism operating alongside natural selection – a mechanism he called 'sexual selection'." It emphasizes that sexually selected traits such as ornamentation, weapons, and displays evolve due to advantages in mating, even when they may be detrimental under ordinary survival-focused natural selection.

In harsh or changing environments, sexually selected traits may either bolster population resilience by favouring high-quality alleles or exacerbate extinction risk by imposing additional costs on survival and reproduction. When environmental stress is high, the energetic and physiological costs associated with maintaining exaggerated ornaments or displays can reduce tolerance to stressors such as heat, desiccation or food scarcity, potentially shifting the balance between sexual and natural selection.

Here, we review the empirical evidence that female mate preferences, like male ornaments, are condition dependent.

The Wikipedia article summarizes sexual selection in humans and notes that sexually selected traits are often costly: "Traits that evolve during contest competition, such as large body size and physical aggression, are often costly to produce and maintain." It adds that such traits "may therefore be indicators of male genetic quality" despite their energetic or viability costs. The article also describes female sexual ornamentation and body fat distribution as potentially sexually selected traits that can affect survival or reproductive outcomes, implying trade-offs between sexual attractiveness and other fitness components.

Animals will often put their lives on the line for reproduction, even if it comes at the cost of being the wrong temperature. Because this risky strategy can sometimes pay off and lead to greater offspring production over the long run, the researchers found widespread evidence that animals have also evolved mechanisms that allow them to tolerate the perilous temperatures they only encounter during mating. If increased heat tolerances have evolved in some populations to accommodate the heat absorbed or retained by a trait used for mating, those populations may have advantages that give them a leg up on adaptation to warming temperatures. In some cases, sexual traits are even directly beneficial for dissipating heat, like antelope horns and fiddler crab claws.

In this lecture on sexual selection, the speaker explains that some traits decrease an individual's chances of surviving, yet substantially increase mating success. As a result, the genes underlying such traits can spread in the population even if the trait carries a survival cost. Evolution is described as being shaped by trade-offs between surviving long enough to reproduce and reproducing successfully, with sexual selection favouring traits that do not improve survival and might even reduce it, especially when environmental conditions make survival more challenging.

Natural selection in the context you're using it favors traits that promote survival, while sexual selection favors traits that promote mating. Sexual selection is a subset of natural selection, but it emphasizes traits that increase mating success even when they impose survival costs. This creates a tension where sexually selected traits like large ornaments or elaborate displays can be maintained despite physiological or ecological handicaps, and these costs may be intensified under environmental stress.

Ornament quality is weakly negatively correlated with parasite load overall, but the relationship is more strongly negative among ornaments that are dynamic or condition-dependent. Exaggerated sexual ornaments have long been proposed to signal health or parasite resistance, implying that producing and maintaining them can be costly and linked to viability.

The video explains that sexual selection leads to adaptations for gathering mates and breeding, which can differ from traits favored by classic natural selection for survival and resource acquisition. It notes that gene interactions can enable development of "fancy traits" only if high-quality genes are present, but such ornaments can be costly and do not necessarily improve survival, illustrating a conceptual trade-off between sexually selected traits and viability.

In this discussion thread, biologists debate whether sexual ornaments confer survival benefits beyond reproductive success. Several contributors note that many sexual ornaments, such as peacock tails, impose energetic and predation costs and are often considered viability handicaps, especially under environmental stress, aligning with handicap and trade-off theories of sexual selection versus natural selection.

In principle, sexually selected traits can arise and persist without providing a direct fitness advantage. When an ornament carries a fitness cost, it can remove the lowest-rung individuals from the selective pool altogether. This shows that survivors of such selection possess higher quality genetics than one would expect, aside from the costly trait itself.