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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 re

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.

Animals vary in thermal tolerance, which set the limits at which survival and reproduction can occur. Thermal tolerance defines species distributions on earth and indicates vulnerability to climate change. Thermal plasticity, or the ability to respond to temperature exposure via phenotypic changes, can alter thermal limits, allowing animals to tolerate more extreme temperatures. In this thesis, I investigate the response of insects – significant as ecosystem service providers, vectors of disease, and crop pests – to warming temperatures using a multi-faceted approach, by means of comparative meta-analyses across over 100 insect species, and detailed experimental work on tsetse flies (Glossina spp.), vectors of human and animal African trypanosomiasis. I find that plasticity of insect thermal tolerance is generally weak, especially upper thermal limits, indicating physiological and evolutionary limits at high temperatures. Weak plasticity of upper thermal limits was mirrored in tsetse, which show limited or non-existent adult and between-generation thermal plasticity. I found considerable variation in the level of thermal plasticity among insects generally, and among tsetse species, but trends in tolerance remained obscure. I find that, thermal fertility limits, the temperature at which reproduction is prevented, occur at lower temperatures than those which kill tsetse, but, in contrast to studies on other insect species, female fertility as temperature sensitive as male fertility. These differences indicate that a diversity of species should be examined to ensure generalisations are relevant across insect species. Finally, I found that body size was important in shaping thermal tolerance limits, with high developmental temperature leading to small adult body size and, in consequence, reduced upper thermal tolerance and survival. These data support predictions of range contractions in tsetse species in response to climate change. More broadly, my findings highlight g

Dung-colonising beetles, commonly known as dung beetles, provide several ecosystem services for farmland pasture systems. However, dung beetles are in decline in northern temperate regions, in part due to widespread endectocide use for control of pests and parasites of cattle. Endectocide residues are excreted in the dung of cattle, at concentrations that are still toxic to insects. The overall aim of this study was to examine the effects of endectocide exposure on the reproductive output of dung-colonising beetles. To achieve this, the first objective was an examination of the short-term sublethal effects of ivermectin, a macrocyclic lactone, on two common northern temperate species, Onthophagus similis (Scriba) and Aphodius prodromus (Brahm). Constant exposure of field-collected adult beetles, over a period of 3 weeks, resulted in smaller oocytes of O. similis at 1 ppm (wet weight). Beetles also had smaller fat bodies and motility was reduced. The study of A. prodromus was inconclusive due to extensive mortality in all treatments. The second objective was an examination of different long-term endectocide treatment regimes (macrocyclic lactones, synthetic pyrethroids, or no treatment) on 24 beef cattle farms, using pitfall trapped beetle samples. Four species of dung beetle were considered: Aphodius rufipes (L.), Aphodius fossor (L.), Onthophagus coenobita (Herbst) and O. similis. Endectocide use was associated with a lower proportion of gravid O. similis females. A more variable size of O. similis and a smaller size of A. fossor was seen on farms using macrocyclic lactones. On the other hand, A. rufipes was larger on farms using endectocides, possibly through reduced competition with other species. The reproduction of A. fossor or O. coenobita did not appear to differ between regimes. The study suggests that beetle reproductive output is affected by endectocide use and in the long-term, such effects may be as ecologically damaging as lethal effects.