The paper states that thermal biology and reproductive ecology can evolve together as organisms adapt to their thermal environment. It specifically proposes that thermal consequences of mate competition can favor reciprocal co-adaptation of thermal biology and sexual traits, showing that thermal selection and sexual selection can interact in linked but potentially conflicting ways.

This study reports that males from different sexual-selection regimes showed different heat-stress responses. Males from some populations were larger but showed greater reduction in body size under developmental heat stress, while males from strongly male-biased populations showed a more pronounced decline in sperm competitiveness after heat stress, highlighting a trade-off between sexual selection and heat tolerance.

The review explains that temperature can modulate sexual selection through direct effects on secondary sexual traits and preferences, and through indirect effects on mating parameters, sex-specific reproductive costs and benefits, and trade-offs. It reports a clear association between temperature and sexual selection measures in both sexes.

The article reports that selection for divergent male morphologies and behaviors can drive divergence in metabolic pathways underlying the plastic response to temperature. It also notes that selection acting on males can affect female physiology and genes associated with metabolism, potentially affecting female fitness at different temperatures.

We found males from even and slightly male-biased OSRs to be larger and display greater reduction in body size under developmental heat stress, suggesting pre-mating sexual selection on body size and condition-dependent thermal sensitivity. Conversely, males from strongly male-biased OSR populations experienced more pronounced decline in sperm competitiveness following exposure to developmental or adult heat stress. These results highlight how environmental stressors differentially impact populations, shaped by varying strengths of pre- and post-mating sexual selection.

Strong sexual selection frequently leads to sexual conflict and ensuing male harm, whereby males increase their reproductive success at the expense of harming females… This phenomenon, termed sexual conflict, favors traits in one sex that might be costly for the other, and can thus lead to antagonistic female-male coevolution… Our work shows that pre- and post-copulatory processes of sexual conflict, and sexual selection at large, exhibit marked phenotypic plasticity in response to normal temperature fluctuations… warm temperatures may buffer sexual conflict in itself by aligning male and female reproductive interests.

The paper finds that natural and sexual selection can favor opposite outcomes in thermal reaction norms. In one species, natural and sexual selection on reaction norm slopes and intercepts had opposite signs consistent with a trade-off, with longevity decreasing as slopes and intercepts increased, while mating success increased.

Even though we found phenotypic variation along climatic gradients to be strongest in naturally selected traits, some sexually selected traits also showed systematic gradual divergence.[9] Generally, males and females diverged in response to different components of climatic gradients (latitudinal or longitudinal variation) and in different trait suites.[9] We discuss that not only temperature regimes, but also indirect effects of increased resource and mate competition (as a function of different extrinsic overwinter mortality rates) alter the selective landscape along climatic gradients.[9]

Our results show that population structure can exacerbate the impact of a warming climate, potentially leading to declines in population viability, but that sexual selection can buffer the negative influence of population subdivision on adaptation to warm temperatures… We found that individuals from subdivided populations had lower lifetime reproductive success at hot temperatures, but only in lines evolving under relaxed sexual selection… These results reveal a complex interaction between sexual selection, population structure, and thermal environmental stress on fitness and adaptive plasticity.

Populations showed evidence of thermal adaptation under precopulatory sexual selection, but this effect was not detected in the postcopulatory sexual selection and the no choice mating regime.[11] We further demonstrate that sexual dimorphism decreased when flies evolved under increasing temperatures, consistent with recent theory predicting more sexually concordant selection under environmental stress.[11] These suggests a role of postcopulatory sexual selection acting as a buffer, limiting the negative effects of high temperatures and facilitating population recovery more than promoting local adaptation.[11]

The study found that polygamy magnifies detrimental effects of heat stress in males but relaxes negative effects in females. The authors conclude that sexual selection can reverse sex differences in thermal sensitivity and alter sex-specific selection on alleles associated with heat tolerance.

When faced with increasing temperatures, strong sexual selection was associated with both increased fecundity and offspring survival compared with populations experiencing weak sexual selection, suggesting sexual selection acts to drive adaptive evolution by favouring beneficial alleles. Strong sexual selection did not, however, delay extinction when the temperature became excessively high. These results indicate that sexual selection can provide a buffer against climate change and increase adaptation rates within a continuously changing environment, although these positive effects may be too small to protect populations and delay extinction when environmental changes are relatively rapid.

Sexual selection often leads to trait elaboration and energetically demanding behavioral displays that can drive organisms to expand into different thermal environments.[7] Multiple lines of evidence suggest that sexual selection may play an underappreciated role in the diversification of thermal niches.[7] The enlarged bodies, ornaments, and weapons often favored by mate choice and/or competition confer greater “thermal inertia,” resulting in slower heating and cooling rates.[7]

The general finding is that plasticity, compared with neither party showing plasticity, always reduces the conflict load of the non-plastic party, but that of the other party can either increase or decrease… However, mismatch hinges on negative frequency-dependent selection, and many adaptations are frequency-independent (e.g. temperature tolerance)… If selection on a trait is frequency-independent, we suggest that it will usually be true that, following an environmental change, adaptive phenotypic plasticity and selection on mean trait values will shape phenotypes to evolve in the same direction.

This preprint states that strong sexual selection can enhance adaptation and reduce mutational load while simultaneously reducing survival or causing sexual conflict that reduces fitness for one or both sexes. It frames sexual selection as a force that can interact with heatwaves in ways that may not align with survival selection.

Here, we outline the main pathways through which temperature can affect the intensity and form (i.e. mechanisms) of sexual selection, via: (i) direct effects on secondary sexual traits and preferences... and (ii) indirect effects on key mating parameters, sex-specific reproductive costs/benefits, trade-offs, demography and correlated abiotic factors.[1] Our results show a clear association between temperature and sexual selection measures in both sexes.[1] We show that sexual selection is modulated by temperature, but the overall directional mean effect on variance in all cases did not differ from zero, indicating no clear directional impact of temperature on sexual selection.[5]

Sexual conflict arises from differences in the fitness interests of males and females… A trait that is beneficial for the reproductive success of one sex reduces the fitness of the other sex, resulting in opposing selection pressures on the two sexes… This can cause sexually antagonistic selection, where the same phenotype is subject to opposite selection in males and females, leading to a tug of war over trait values and potentially constraining adaptation to other ecological pressures.

Our results show that inbreeding and developmental temperature independently influence some sexually selected male traits, suggesting that climate change and habitat fragmentation might alter evolution under sexual selection. First, while most of the sexual traits under precopulatory sexual selection that we measured were unaffected by inbreeding or a higher developmental temperature, both factors caused a decline in male attractiveness. Rising temperatures and increased rates of inbreeding are therefore likely to have stronger effects on precopulatory than postcopulatory sexual selection.

Thermal adaptation did not differ between the monogamous and polyandrous populations.[4] However, sexual selection did not affect the rate of adaptation. Therefore, adaptive female selection for thermal tolerance either was insignificant or negated by other aspects of sexual selection, for example, male-induced female harm.[4] Yet, the hypothesized positive association between sexual selection and adaptation was not found. This result, combined with recent theory and experiments, implies that sexual selection need not be driven by adaptive choice for mates with superior nonsexual fitness.[4]

Morphological phenotypes, gene expression can be viewed in the same phenotype framework, where opposing selection acting on male and female gene regulation creates sexual conflict and distinct sex-specific fitness optima… Sexual selection and sexual conflict can shape phenotypes in ways that are not necessarily aligned with viability selection, because traits that increase mating success may decrease survival or other components of fitness… This generates trade-offs and can lead to phenotypes that are intermediate compromises between opposing selective pressures.

The article reports that individuals from subdivided populations had lower lifetime reproductive success at hot temperatures, but only in lines evolving under relaxed sexual selection. It also notes that sexual selection can buffer some negative consequences of population subdivision under environmental stress, while not buffering the negative effects of increased temperature on focal pair fitness.

Species could have temperature‐dependent sex determination if temperature affects fitness differentially for males and females either directly or through a factor highly correlated with temperature. If fitness differentials between males and females vary with temperature, then selection can favour a correlation between sex and incubation temperature. Under such conditions, thermal selection acting on fitness and sex-specific life histories can shape sex-determining mechanisms.

The overall aim of the project was to improve the general understanding of how sexual conflict unfolds in nature and how ecological factors such as temperature may affect evolutionary processes (i.e. sexual selection/conflict) that impact a much wider range of phenotypic traits than those directly shaped by temperature… This enabled us to shed light on the underlying genomic basis of thermally selected sexual traits, with a special emphasis on sexual conflict… Our findings highlight that ecological context, including temperature variation, can modulate the strength and direction of sexual conflict, thereby influencing how sexual selection and thermal selection jointly shape phenotypes in the wild.

The paper states that a longstanding hypothesis in evolutionary biology is that trade-offs between natural and sexual selection often underlie diversification of sexual signals in the wild. It presents the selection trade-off hypothesis, in which elaborate ornamentation can evolve under sexual selection even when it is costly under natural selection.

In contrast, we found no evidence that condition-dependence in a suite of male sexually selected traits evolved in response to the strength of sexual selection, manipulated via the sex ratio. Our results suggest that the evolution of condition dependence in sexually selected traits may be constrained, and not simply driven by variation in sexual selection intensity. This implies that environmental stressors, such as thermal stress, could affect sexually selected traits without leading to rapid evolutionary changes in their condition dependence.

Natural selection favors genes that enhance an individual's chances of survival, while sexual selection pertains to genes that improve mating success.[14] This distinction is why "sexual selection" is a separate concept from "natural selection."[14] Because these two components of selection act on different aspects of fitness (survival vs. mating success), they can sometimes favor different phenotypic traits or directions of trait change.[14]

Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic development determine the sex of the offspring. The Charnov–Bull model predicted that selection should favour TSD over chromosome-based systems when "the developmental environment differentially influences male versus female fitness"; this model was later empirically validated. This framework highlights how thermal selection that acts differently on male and female fitness can drive the evolution of sex-specific phenotypes and sex-determining mechanisms.

Thermal selection refers to natural selection imposed by temperature and thermal conditions, shaping traits such as thermal tolerance, thermal preference, and body temperature regulation. Sexual selection is selection arising from differences in mating success, favoring traits that increase attractiveness or competitive ability. Because thermal selection acts primarily on survival and performance across temperatures, while sexual selection acts on mating success, these two forms of selection can in some cases favor opposite changes in the same trait, generating trade-offs between thermal adaptation and sexually selected phenotypes.[2][4]

First, maladaptive environmental variation, including temperature, can directly affect sexual selection… Strong sexual selection frequently leads to sexual conflict, where male and female evolutionary interests do not coincide… Spatio-temporal variation in temperature can modulate intralocus sexual conflict by changing the degree to which male and female interests overlap, implying that thermal ecology can alter the balance between sexually antagonistic selection and other selective forces on shared phenotypes.