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Exposure to extreme temperatures can negatively affect animal reproduction, by disrupting the ability of individuals to produce any offspring (fertility), or the number of offspring produced by fertile individuals (fecundity). This has important ecological consequences, because reproduction is the ultimate measure of population fitness: a reduction in reproductive output lowers the population growth rate and increases the extinction risk. Despite this importance, there have been no large-scale summaries of the evidence for effect of temperature on reproduction. We provide a systematic map of studies testing the relationship between temperature and animal reproduction. We systematically searched for published studies that statistically test for a direct link between temperature and animal reproduction, in terms of fertility, fecundity or indirect measures of reproductive potential (gamete and gonad traits). Overall, we collated a large and rich evidence base, with 1654 papers that met our inclusion criteria, encompassing 1191 species. The map revealed several important research gaps. Insects made up almost half of the dataset, but reptiles and amphibians were uncommon, as were non-arthropod invertebrates. Fecundity was the most common reproductive trait examined, and relatively few studies measured fertility. It was uncommon for experimental studies to test exposure of different life stages, exposure to short-term heat or cold shock, exposure to temperature fluctuations, or to independently assess male and female effects. Studies were most often published in journals focusing on entomology and pest control, ecology and evolution, aquaculture and fisheries science, and marine biology. Finally, while individuals were sampled from every continent, there was a strong sampling bias towards mid-latitudes in the Northern Hemisphere, such that the tropics and polar regions are less well sampled. This map reveals a rich literature of studies testing the relationship between t

Critical thermal limits (CTLs) gauge the physiological impact of temperature on survival or critical biological function, aiding predictions of species range shifts and climatic resilience. Two recent Drosophila species studies, using similar approaches to determine temperatures that induce sterility (thermal fertility limits [TFLs]), reveal that TFLs are often lower than CTLs and that TFLs better predict both current species distributions and extinction probability. Moreover, many studies show fertility is more sensitive at less extreme temperatures than survival (thermal sensitivity of fertility [TSF]). These results present a more pessimistic outlook on the consequences of climate change. However, unlike CTLs, TFL data are limited to Drosophila, and variability in TSF methods poses challenges in predicting species responses to increasing temperature. To address these data and methodological gaps, we propose 3 standardized approaches for assessing thermal impacts on fertility. We focus on adult obligate sexual terrestrial invertebrates but also provide modifications for other animal groups and life-history stages. We first outline a gold-standard protocol for determining TFLs, focussing on the effects of short-term heat shocks and simulating more frequent extreme heat events predicted by climate models. As this approach may be difficult to apply to some organisms, we then provide a standardized TSF protocol. Finally, we provide a framework to quantify fertility loss in response to extreme heat events in nature, given the limitations in laboratory approaches. Applying these standardized approaches across many taxa, similar to CTLs, will allow robust tests of the impact of fertility loss on species responses to increasing temperatures. Graphical AbstractOverview of the systematic methods (A, C, and D) to simultaneously assay lethal limits and thermal fertility limits or (B and E) thermal sensitivity of fertility. These are most easily applied to laboratory settings

RNA sequencing (RNAseq) methodology has experienced a burst of technological developments in the last decade, which has opened up opportunities for studying the mechanisms of adaptation to environmental factors at both the organismal and cellular level. Selecting the most suitable experimental approach for specific research questions and model systems can, however, be a challenge and researchers in ecology and evolution are commonly faced with the choice of whether to study gene expression variation in whole bodies, specific tissues, and/or single cells. A wide range of sometimes polarised opinions exists over which approach is best. Here, we highlight the advantages and disadvantages of each of these approaches to provide a guide to help researchers make informed decisions and maximise the power of their study. Using illustrative examples of various ecological and evolutionary research questions, we guide the readers through the different RNAseq approaches and help them identify the most suitable design for their own projects.

The outcomes of interspecific and intraspecific ecological interactions can be considered to fall along continua from cooperative (mutually beneficial) to antagonistic (detrimental to one or both parties). Furthermore, the position of an interaction outcome along the continuum, for example whether a symbiont provides net costs or benefits to its host, or whether two conspecifics cooperatively forage or compete for food, is often not fixed but can change over time or across contexts. In this systematic review, we investigate the role of intraspecific trait variation (‘ITV') in one or both interacting parties in determining the cooperative-antagonistic outcome of inter- and intraspecific ecological interactions. Based on a literature collection of 96 empirical and theoretical publications meeting our inclusion criteria, we give an overview of the types of interaction continua involved; traits related to outcome variance; and mechanisms as well as constraints on shifts in interactions outcomes. We propose that ITV can lead to shifts in interaction outcomes via two interrelated mechanisms. First, trait frequency effects occur when there are changes in a population's composition of traits linked to cooperation or antagonism (e.g. aggressive personality types, cheater phenotypes etc.), leading to net shifts in interaction outcomes. Second, systemic variance effects occur where the level of ITV in a trait in a population (as opposed to the mean value) is the factor that influences the cooperative-antagonistic outcome. Heritable trait differences and phenotypic plasticity are sources of phenotypic variation among individuals, and both the degree of heritability and plasticity of the trait involved may determine whether shifts between cooperation and antagonism are likely to be short-term (i.e. context-dependent) or lead to more persistent shifts (e.g. mutualism breakdown). To guide future research, we describe knowledge gaps and divergences between empirical a

Sperm function is pivotal to successful sexual reproduction. The phenotype of sperm is defined by the male’s genotype and by the environment sperm encounter during their travel to the oocyte. During their functional lifespan, sperm encounter a variety of environments: After manufacture in the testis, they are stored in males before they are ejaculated along with seminal fluids and transferred to and stored in females for hours up to years before getting a chance to fertilise an egg. The sperm environment in male and female reproductive tract will be determined by male and female genotype, but also by environmental factors that affect sperm directly or indirectly by altering male and female condition. Like somatic cells, sperm age and decline in function over time due to the accumulation of cellular damage. Reactive oxygen species (ROS) that emerge as a by-product of aerobic metabolism and environmental stress are believed to be the main cause of cell senescence. Spermatozoa are in particular susceptible to ROSinduced damage because they have only limited defence and repair mechanism. As it contains many polyunsaturated fatty acids, the sperm membrane is especially prone to peroxidation by ROS and can consequently become leaky. The condition of the sperm membrane can hence be used to assess sperm age. Sperm quality has frequently been measured as sperm viability even though this approach has several biological and technical pitfalls. I developed an osmotic sperm stress test to assess sperm quality and predict future sperm performance that circumvents several of these pitfalls. Further, using osmotic stress to challenge the sperm membrane and observing sperm viability in a longitudinal approach is probably more meaningful in predicting future sperm performance than sperm viability per se. An essential abiotic factor that affects sperm directly and indirectly during storage in males and females is temperature. Ectotherms that inhabit different climates like D. melanoga