Pregnancy is a physiological cost of reproduction for animals that rely on fleeing to avoid predators. Costs of reproduction are predicted to differ between alternative reproductive strategies or modes, such as egg-laying (oviparity) or live-bearing (viviparity). However, disentangling the factors that comprise this cost and how it differs for oviparous or viviparous females is challenging due to myriad environmental, biological, and evolutionary confounds. Here, we tested the hypothesis that costs of pregnancy differ between oviparous and viviparous common lizards (Zootoca vivipara). We predicted that the degree of locomotor impairment during pregnancy and therefore the cost of reproduction would be higher in viviparous females. We conducted our experiment in a hybrid zone containing oviparous and viviparous common lizards. Due to the common environment and inclusion of hybrid individuals, we could infer whether differences were inherent to parity mode. We found that the average and maximum running speed of pregnant females was slower than after they had given birth or laid eggs. Viviparous females experienced an additional pregnancy weight burden and for a longer time period, but were not slower at running than pregnant oviparous females. In addition, we found a parity mode-specific effect of reproductive investment; producing larger clutches was costlier for the locomotor performance of viviparous females for reasons other than the mass increase. Locomotor costs were found to be intermediate in hybrid females, indicating that they are specific to each reproductive mode. Our study shows that viviparous females experience an additional physical and physiological cost of pregnancy and reproductive investment. This two-fold cost implies that viviparous females modulate resource allocation decisions and/or adjust their behavioural responses that result from locomotor impairment.

Allocation of acquired resources to phenotypic traits is affected by resource availability and current selective context. While differential investment in traits is well documented, the mechanisms driving investment at lower levels of biological organization, which are not directly related to fitness, remain poorly understood. We supplemented adult male and female Anolis carolinensis lizards with an isotopically labelled essential amino acid (13C-leucine) to track routing in four tissues (muscle, liver, gonads, and spleen) under different combinations of resource availability (high and low-calorie diets) and exercise training (sprint training and endurance capacity). We predicted sprint training should drive routing to muscle, and endurance training to liver and spleen, and that investment in gonads should be of lower priority in each of the cases of energetic stress. We found complex interactions between training regime, diet, and tissue type in females, and between tissue type and training and tissue type and diet in males, suggesting that males and females adjust their 13C-leucine routing strategies differently in response to similar environmental challenges. Importantly, our data show evidence of increased 13C-leucine routing in training contexts not to muscle as we expected, but to the spleen, which turns over blood cells, and to the liver, which supports metabolism under differing energetic scenarios. Our results reveal the context-specific nature of long-term tradeoffs associated with increased chronic activity. They also illustrate the importance of considering the costs of locomotion in studies of life history strategies.

The mechanosensory lateral line (LL) system of salmonid fishes has been the focus of comparative morphological studies and behavioral and physiological analyses of flow sensing capabilities, but its morphology and development have not been studied in detail in any one species. Here, we describe the post-embryonic development of the cranial LL system in Brook Trout, Salvelinus fontinalis, using vital fluorescent staining (4-Di-2-ASP), scanning electron microscopy, µCT, and clearing and staining to visualize neuromasts and the process of cranial LL canal morphogenesis. We examined the relationship between the timing of LL development, the prolonged life history of salmonids, and potential ecological implications. The LL system is composed of seven canals containing canal neuromasts (CNs) and four lines of superficial neuromasts (SNs) on the skin. CNs and SNs increase in number and size during the alevin (larval) stage. CN number stabilizes as canal morphogenesis commences, but SN number increases well into the parr (juvenile) stage. CNs become larger and more elongated than SNs, but the relative area occupied by sensory hair cells decreases during ontogeny in both types of neuromasts. Neuromast-centered canal morphogenesis starts in alevins (yolk sac larvae), as they swim up into the water column from their gravel nests (~4 months post-fertilization), after which yolk sac absorption is completed and exogenous feeding begins. Canal morphogenesis proceeds asynchronously within and among canal series and is not complete until ~8 months post-fertilization (the parr stage). Three characters in the LL system and associated dermal bones were used to identify their homologs in other actinopterygians and to consider the evolution of LL canal reduction, thus demonstrating the value of salmonids for the study of LL evolution. The prolonged life history of Brook Trout and the onset of canal morphogenesis at swim-up are predicted to have implications for neuromast function at these critical behavioral and ecological transitions.

Transgenerational phenotypic modification can alter organismal fitness, population demographics, and community interactions. For ectotherms, both dietary composition and temperature have important effects on organismal fitness, but they are rarely investigated together. Mormon crickets Anabrus simplex are capable of diapausing as eggs in the soil for multiple years with duration largely dependent on cumulative heat units or degree days. Because Mormon crickets can be abundant in the landscape in one year and disappear suddenly the next, I asked: does parental nutrition affect the duration of egg diapause? Beginning in the ultimate nymphal instar, Mormon crickets were fed a diet high in protein, one equal in protein to carbohydrate, or a diet high in carbohydrates and the time for eggs to develop after they were laid was measured. If parental nutrition affects temperature-sensitive egg diapause, then that change in sensitivity to temperature might also alter the relationship between embryonic development rate and temperature. I asked: does parental nutrition affect embryonic development rate as a function of temperature? To this end, I manipulated densities of Mormon cricket nymphs and protein-rich prey (grasshoppers) in field cages, collected eggs from the adult Mormon crickets, and measured the optimal temperature, maximum development rate, and thermal breadth for embryonic development of the offspring. I found that Mormon crickets fed a high protein diet laid eggs with shorter diapause. Consistent with this long-term result, those housed with the most grasshoppers to eat laid eggs that had the fastest maximum development rate, whereas those without grasshoppers laid eggs with slower maximum developmental rates but the broadest thermal breadth. Eggs from Mormon crickets housed with intermediate levels of grasshopper densities had a decline in peak development rate with an increase in density. In addition, Mormon crickets housed with more conspecifics laid eggs with faster development rates, whereas thermal breadth and the temperature optima were not affected by cricket density. As predicted, Mormon cricket diets significantly affected egg diapause and development rates. Contrary to expectations based on observed changes in diet preferences during a Mormon cricket outbreak, Mormon crickets fed high protein diets laid eggs with significantly shorter egg diapause and significantly faster egg development rates. Interestingly, doubling of Mormon cricket density caused eggs to develop in nearly half the time. This latter result indicates that Mormon cricket aggregations promote rapid development of progeny. Moreover, the tight, linear structure of migratory bands in which females intermittently stop to lay eggs assures that the progeny hatch and develop in dense cohorts. In this manner, the banding behavior might carry-over into subsequent generations as long as cohorts are dense and protein is available. With band thinning or protein restriction, females spread their bet-hedging and progeny remain longer as eggs in the soil.

Ballan wrasse Labrus bergylta is the largest species of wrasse inhabiting European waters and one of the longest-living species within the family Labridae. A large specimen was caught off the coast of Skjerjehamn, western Norway (total length = 410 mm; weight = 1274 g). The age of the specimen was determined to be 34 years old based on the analysis of its opercula bones. This specimen establishes a new maximum age for ballan wrasse, 5 years older than the previously observed maximum age.

By analyzing otolith microchemistry, we examined the use of freshwater and marine environments by brown trout Salmo trutta L. that spawn in the Swedish River Emån and migrate to the Baltic Sea. We estimated the time juveniles spent in freshwater and the number of times the fish returned to freshwater, presumably to spawn. Twenty-six percent of the fish migrated to sea by 1 year of age. However, 13% spent less than one year in the river. Most brown trout (48%) migrated to the sea between 1 and 2 years of age. On average, brown trout, which averaged 4.4 years in age (range 3-6 years), returned to freshwater 2.3 times, and there was an inverse relationship between time spent in freshwater after hatching and the number of visits to freshwater. Our results do not support the classical life history pattern, where brown trout spend one or more years in freshwater before migrating to the sea. Here, we found evidence that part of the population leaves freshwater during their first year. While the cause for precocial migration in the River Emån is not known, our results from this permanently flowing river do not support the idea proposed for other Baltic Sea populations, where the risk of drought has been suggested to be the cause.

Wolbachia is a widespread maternally-transmitted endosymbiotic bacteria with diverse phenotypic effects on its insect hosts, ranging from parasitic to mutualistic. Wolbachia commonly infects social insects, where it faces unique challenges associated with its hosts\' caste-based reproductive division of labor and colony living. Here we dissect the benefits and costs of Wolbachia infection on life-history traits of the invasive pharaoh ant, Monomorium pharaonis, which are relatively short-lived and show natural variation in Wolbachia infection status between colonies. We quantified effects of Wolbachia infection on the lifespan of queen and worker castes, the egg-laying rate of queens across queen lifespan, and the metabolic rates of whole colonies and colony members. Infected queens laid more eggs than uninfected queens but had similar metabolic rates and lifespans. Interestingly, infected workers outlived uninfected workers. At the colony level, infected colonies were more productive due to increased queen egg-laying rates and worker longevity, and infected colonies had higher metabolic rates during peak colony productivity. While some effects of infection, such as elevated colony-level metabolic rates may be detrimental in more stressful natural conditions, we did not find any costs of infection under relatively benign laboratory conditions. Overall, our study emphasizes that Wolbachia infection can have beneficial effects on ant colony growth and worker survival in at least some environments.

An understanding of biological fitness is central to theory and practice in ecology and evolution, yet fitness remains an elusive concept to define and challenging to measure accurately. Fitness reflects an individual\'s ability to pass its alleles on to subsequent generations. Researchers often quantify proxies for fitness, such as survival, growth or reproductive success. However, it can be difficult to determine lifetime fitness, especially for species with long lifespans. The abiotic and biotic environment strongly affects the expression of fitness, which means that fitness components can vary through both space and time. This spatial and temporal heterogeneity results in the impressive range of adaptations that we see in nature. Here, we review definitions of fitness and approaches to measuring fitness at the level of genes, individuals, genotypes, and populations and highlight that fitness is a key concept linking ecological and evolutionary thought.

Insects play a crucial role in all ecosystems, and are increasingly exposed to higher in temperature extremes under climate change, which can have substantial effects on their abundances. However, the effects of temperature on changes in abundances or population fitness are filtered through differential responses of life-history components, such as survival, reproduction, and development, to their environment. Such differential responses, or trade-offs, have been widely studied in birds and mammals, but comparative studies on insects are largely lacking, limiting our understanding of key mechanisms that may buffer or exacerbate climate-change effects across insect species. Here, we performed a systematic literature review of the ecological studies of lacewings (Neuroptera), predatory insects that play a crucial role in ecosystem pest regulation, to investigate the impact of temperature on life cycle dynamics across species. We found quantitative information, linking stage-specific survival, development, and reproduction to temperature variation, for 62 species from 39 locations. We then performed a metanalysis calculating sensitives to temperature across life-history processes for all publications. We found that developmental times consistently decreased with temperature for all species. Survival and reproduction however showed a weaker response to temperature, and temperature sensitivities varied substantially among species. After controlling for the effect of temperature on life-history processes, the latter covaried consistently across two main axes of variation related to instar and pupae development, suggesting the presence of life-history trade-offs. Our work provides new information that can help generalize life-history responses of insects to temperature, which can then expand comparative demographic and climate-change research. We also discuss important remaining knowledge gaps, such as a better assessment of adult survival and diapause.

Phenotypic plasticity, which involves phenotypic transformation in the absence of genetic change, may serve as a strategy for organisms to survive in complex and highly fluctuating environments. However, its reaction norm, molecular basis, and evolution remain unclear in most organisms, especially microbial eukaryotes. In this study, we explored these questions by investigating the reaction norm, regulation, and evolution of phenotypic plasticity in the cosmopolitan marine free-living ciliates Glauconema spp., which undergo significant phenotypic changes in response to food shortages. This study led to the de novo assembly of macronuclear genomes using long-read sequencing, identified hundreds of differentially expressed genes associated with phenotypic plasticity in different life stages, validated the function of two of these genes, and revealed that the reaction norm of body shape in response to food density follows a power-law distribution. Purifying selection may be the dominant evolutionary force acting on the genes associated with phenotypic plasticity, and the overall data support the hypothesis that phenotypic plasticity is a trait maintained by natural selection. This study provides novel insight into the developmental genetics of phenotypic plasticity in non-model unicellular eukaryotes and sheds light on the complexity and long evolutionary history of this important survival strategy.