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Fisher's general principle for sex allocation holds that population sex ratios are typically balanced because parents producing the rare sex are benefited and the rare sex alternates over time. In species that have temperature-dependent sex determination (TSD), thermal reaction norms need to be adjusted at the population level to avoid extremely biased sex ratios and extinction. Extant species with TSD experienced drastic climatic changes in the geological past and must necessarily have mechanisms of adaptation. I propose here a conceptual framework to explain how TSD curves could be adjusted by means of natural selection, based on Fisher's equilibrium sex-ratio principle. Through a process that alternatively favors mothers that tend to produce the rare sex under new temperatures, sex ratios eventually return toward a theoretical equilibrium. Prerequisites for this model are variability among mothers in the tendency to produce a particular sex at a given temperature (i.e., variability in the thermal reaction norm), inheritance of this trend, and higher fitness of the rare sex. This straightforward mechanism could facilitate thermal adaptation in species with TSD over multiple generations., (© 2024 John Wiley & Sons Ltd.)

Terrestrial ectotherms are vulnerable to climate change since their biological rates depend on the ambient temperature. As temperature may interact with toxicant exposure, climate change may cause unpredictable responses to toxic stress. A population's thermal adaptation will impact its response to temperature change, but also to interactive effects from temperature and toxicants, but these effects are still not fully understood. Here, we assessed the combined effects of exposure to the insecticide imidacloprid across the temperatures 10-25 °C of two populations of the Collembola Hypogastrura viatica (Tullberg, 1872), by determining their responses in multiple life history traits. The con-specific populations differ considerably in thermal adaptations; one (arctic) is a temperature generalist, while the other (temperate) is a warm-adapted specialist. For both populations, the sub-lethal concentrations of imidacloprid became lethal with increasing temperature. Although the thermal maximum is higher for the warm-adapted population, the reduction in survival was stronger. Growth was reduced by imidacloprid in a temperature-dependent manner, but only at the adult life stage. The decrease in adult body size combined with the absence of an effect on the age at first reproduction suggests a selection on the timing of maturation. Egg production was reduced by imidacloprid in both populations, but the negative effect was only dependent on temperature in the warm-adapted population, with no effect at 10 °C, and decreases of 41 % at 15 °C, and 74 % at 20 °C. For several key traits, the population best adapted to utilize high temperatures was also the most sensitive to toxic stress at higher temperatures. It could be that by allocating more energy to faster growth, development, and reproduction at higher temperatures, the population had less energy for maintenance, making it more sensitive to toxic stress. Our findings demonstrate the need to take into account a population's thermal adaptation when assessing the interactive effects between temperature and other stressors., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Temperature drives adaptation in life-history traits through direct effects on physiological processes. However, multiple life-history traits co-evolve as a life-history strategy. Therefore, physiological limitations constraining the evolution of trait means and phenotypic plasticity can be larger for some traits than the others. Comparisons of thermal responses across life-history traits can improve our understanding of the mechanisms determining the life-history strategies. In the present study, we focused on a soil microarthropod species abundant across the Northern Hemisphere, Folsomia quadrioculata (Collembola), with previously known effects of macroclimate. We selected an arctic and a temperate population from areas with highly contrasting climates - the arctic tundra and a coniferous forest floor, respectively - and compared them for thermal plasticity and thermal efficiency in growth, development, fecundity, and survival across four temperatures for a major part of their life cycle. We intended to understand the mechanisms by which temperature drives the evolution of life-history strategies. We found that the temperate population maximized performance at 10-15 °C, whereas the arctic population maintained its thermal efficiency across a wider temperature range (10-20 °C). Thermal plasticity varied in a trait-specific manner, and when considered together with differences in thermal efficiency, indicated that stochasticity in temperature conditions may be important in shaping the life-history strategies. Our study suggests that adopting a whole-organism approach and including physiological time considerations while analysing thermal adaptation will markedly improve our understanding of plausible links between thermal adaptation and responses to global climate change., Competing Interests: Declaration of Competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Mixotrophs, organisms that combine photosynthesis and heterotrophy to gain energy, play an important role in global biogeochemical cycles. Metabolic theory predicts that mixotrophs will become more heterotrophic with rising temperatures, potentially creating a positive feedback loop that accelerates carbon dioxide accumulation in the atmosphere. Studies testing this theory have focused on phenotypically plastic (short‐term, non‐evolutionary) thermal responses of mixotrophs. However, as small organisms with short generation times and large population sizes, mixotrophs may rapidly evolve in response to climate change. Here, we present data from a 3‐year experiment quantifying the evolutionary response of two mixotrophic nanoflagellates to temperature. We found evidence for adaptive evolution (increased growth rates in evolved relative to acclimated lineages) in the obligately phototrophic strain, but not in the facultative phototroph. All lineages showed trends of increased carbon use efficiency, flattening of thermal reaction norms, and a return to homeostatic gene expression. Generally, mixotrophs evolved reduced photosynthesis and higher grazing with increased temperatures, suggesting that evolution may act to exacerbate mixotrophs' effects on global carbon cycling. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity of insect thermal reaction norms (TRNs) (the lower thermal threshold, coefficient of thermal sensitivity, and sum of degree-days) ensures precise adjustment of the seasonal cycle to local environments by changing the pattern of temperature-dependence of developmental rate. In different geographic populations the plasticity of TRNs can be manifested in different ways. We investigated the photoperiodic and diet-induced plasticity of TRNs, body mass and structural size (hind femur length) of the multicolored Asian ladybird, Harmonia axyridis, from native (Irkutsk) and invasive (Sochi) laboratory populations. Each population was tested in 16 experimental treatments that represented combinations of 4 temperatures (17, 20, 24, and 28°C), 2 photoperiods (10 and 16 h of light per day), and 2 larval diets (frozen eggs of the grain moth Sitotroga cerealella and larvae and adults of the green peach aphid Myzus persicae). The lady beetle eggs developed at a temperature of 20°C; first instar larvae were distributed among experimental treatments. We have demonstrated that under both photoperiodic regimes larval feeding on a low-quality diet (grain moth eggs) resulted in a disproportional (more strongly manifested at a low temperature) retardation of preimaginal development of individuals from both populations. The lower temperature thresholds for preimaginal development were also greater on the inferior diet. When fed on grain moth eggs, larvae from the Irkutsk population showed weaker temperature-sensitivity of development, whereas in the Sochi population the slope of the TRN did not differ between the two diets. In contrast, H. axyridis from Irkutsk showed practically no photoperiodic plasticity of TRN, whereas those from Sochi were sensitive to photoperiod on both diets. Under short-day conditions, the lower temperature threshold in the latter population was smaller and temperature-sensitivity was weaker so that at the temperatures of 17 and 20°C, development under short-day conditions was faster than that under long-day conditions, whereas at 28°C, on the contrary, it was slightly slower. In both studied populations the thermal plasticity of adult body mass and hind femur length was manifested in different ways and to varying degrees, depending on the larval photoperiodic conditions and diet. Adult body mass could decrease or increase with larval developmental temperature or show no change. Despite being maintained in the laboratory for many generations, the H. axyridis populations from Sochi and Irkutsk have retained differences in physiological responses to photoperiodic conditions and larval diet. [ABSTRACT FROM AUTHOR]

The influence of photoperiod on the thermal requirements for development was discovered for the first time in insects during experiments on the linden-bug, Pyrrhocoris apterus. The effect of photoperiod on the duration of linden-bug development at five constant temperatures (20, 22, 24, 26 and 28°C) was measured and the thermal requirements for development at three photoperiods (14, 17 and 20 h light per day) were calculated. Bugs from four geographic populations were used in these experiments: Pyatigorsk (44°02´N, 43°04´E), Borisovka (50°36´N, 36°01´E), Mikhailov (54°15´N, 39°0´E) and Ryazan (54°36´N, 39°42´E). From the values of individual development times at different temperatures the coefficient of linear regression of development rate (the inverse of the duration) on temperature and the thermal threshold for development were calculated. Both these parameters were found to decrease significantly with decrease in day-length for all four populations studied. It means that at shorter day-lengths nymphal development is less dependent on temperature compared to the development at longer day-lengths. These effects seem to be adaptive. The development times of nymphs at relatively high temperatures (above 24-25°C) are shorter under long-days than under short days which should be advantageous at the height of summer when the days are long and the weather is warm. In the contrast, at relatively low temperatures (below 24-25°C) the nymphs develop significantly faster under short-days than under long days, which is advantageous at the end of summer as it allows the nymphs to reach the adult stage, the only stage capable of overwintering. The influence of photoperiod on the thermal reaction norm appeared to be more or less gradual, i.e. the shorter the day-length the shallower the slope of the regression line of development rate on temperature and the lower the thermal threshold for development. An analysis of the literature shows that this effect of photoperiod on the thermal requirements for development is widespread among insects but has been overlooked by previous authors. The authors conclude that the variation in the development time observed in insects at different seasons, photoperiods or food regimes, or from different populations, etc., are generally due to some modification of the thermal reaction norms and more specifically to differences in the thermal requirements for development.