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Climate change is gripping our planet. News headlines proclaim warmer winters and hotter summers, and these changes are impacting Earth’s biodiversity. Have you ever wondered how climate change causes extinctions? This is an important, ongoing research question because understanding how heat impacts living organisms could help us predict how species will cope in a warmer world and give us the knowledge we need to help vulnerable organisms. Insects make honey, pollinate crops, control pests, and recycle waste into nutrients. Despite being numerous and often helpful to humans, insects, and the effects that climate change is having on them, are often overlooked. Due to climate change, heatwaves are becoming more common and intense. In this article, we explore the impact of simulated heatwaves on a beetle species in the laboratory. Keep reading to learn about how heatwaves could cause damage that lasts over generations, potentially leading to extinctions.

Why is polyandry such a common mating behaviour when it exposes females to a range of significant fitness costs? Here, we investigated whether polyandry protects females against reduced male fertility caused by thermal stress from heatwave conditions. Sperm production and function are vulnerable to heat, and heatwave conditions are forecast to increase as our climate warms, so we examined these effects on female reproduction and mating behaviour in the flour beetle, Tribolium castaneum, a promiscuous ectotherm model in which fertility is damaged by environmental warming. We tested whether polyandrous matings, or polyandrous sperm stores, protect females against reduced male fertility caused by heatwave conditions, and whether females flexibly adjust their remating behaviour to enable fertility rescue. We found that polyandry protected females against reduced male fertility: monogamous matings with males exposed to heatwave conditions halved female offspring production, but opportunities to mate with five of these males allowed normal female reproductive output. By contrast with this fertility improvement following polyandrous mating opportunities, there was no protective benefit for females already carrying sperm stores from multiple males, which suffered similar heatwave damage within the female tract as monogamous sperm stores. Importantly, female polyandry was flexible to male condition, with females showing greater motivation to remate with new males if their previous mate had been damaged by heatwave exposure, enabling a rapid reproductive rescue. Our results reveal that flexible polyandry enables females to rescue their fertility when male reproductive function is compromised by heatwave conditions, a phenomenon that may become more prevalent under climate change.

Adulthood-only downregulation of insulin/IGF-1 signaling (IIS), an evolutionarily conserved pathway regulating resource allocation between somatic maintenance and reproduction, increases life span without fecundity cost in the nematode, Caenorhabditis elegans. However, long-term multigenerational effects of reduced IIS remain unexplored and are proposed to carry costs for offspring quality. To test this hypothesis, we ran a mutation accumulation (MA) experiment and downregulated IIS in half of the 400 MA lines by silencing daf-2 gene expression using RNA interference (RNAi) across 40 generations. Contrary to the prediction, adulthood-only daf-2 RNAi reduced extinction of MA lines both under UV-induced and spontaneous MA. Fitness of the surviving UV-induced MA lines was higher under daf-2 RNAi. Reduced IIS increased intergenerational F1 offspring fitness under UV stress but had no quantifiable transgenerational effects. Functional hrde-1 was required for the benefits of multigenerational daf-2 RNAi. Overall, we found net benefit to fitness from multigenerational reduction of IIS and the benefits became more apparent under stress. Because reduced daf-2 expression during development carries fitness costs, we suggest that our findings are best explained by the developmental theory of ageing, which maintains that the decline in the force of selection with age results in poorly regulated gene expression in adulthood.

Dietary restriction (DR) increases lifespan in a broad variety of organisms and improves health in humans. However, long-term transgenerational consequences of dietary interventions are poorly understood. Here, we investigated the effect of DR by temporary fasting (TF) on mortality risk, age-specific reproduction and fitness across three generations of descendants in Caenorhabditis elegans . We show that while TF robustly reduces mortality risk and improves late-life reproduction of the individuals subject to TF (P 0 ), it has a wide range of both positive and negative effects on their descendants (F 1 –F 3 ). Remarkably, great-grandparental exposure to TF in early life reduces fitness and increases mortality risk of F 3 descendants to such an extent that TF no longer promotes a lifespan extension. These findings reveal that transgenerational trade-offs accompany the instant benefits of DR, underscoring the need to consider fitness of future generations in pursuit of healthy ageing.

Adulthood-only downregulation of insulin/IGF-1 signalling (IIS), an evolutionarily conserved pathway regulating resource allocation between somatic maintenance and reproduction, increases lifespan without fecundity cost in the nematode, Caenorhabditis elegans. However, long-term multigenerational effects of reduced IIS remain unexplored and are proposed to carry costs for offspring quality. To test this hypothesis, we ran a mutation accumulation (MA) experiment and downregulated IIS in half of the 400 MA lines by silencing daf-2 gene expression using RNA interference (RNAi) across 40 generations. Contrary to the prediction, adulthood-only daf-2 RNAi reduced extinction of MA lines both under UV-induced and spontaneous mutation accumulation. Fitness of the surviving UV-induced MA lines was higher under daf-2 RNAi. Reduced IIS increased intergenerational F1 offspring fitness under UV stress but had no quantifiable transgenerational effects. Functional hrde-1 was required for the benefits of multigenerational daf-2 RNAi. Overall, we found net benefit to fitness from multigenerational reduction of IIS and the benefits became more apparent under stress. Because reduced daf-2 expression during development carries fitness costs, we suggest that our findings are best explained by the developmental theory of ageing, which maintains that the decline in the force of selection with age results in poorly regulated gene expression in adulthood.

Rising and more variable global temperatures pose a challenge for biodiversity, with reproduction and fertility being especially sensitive to heat. Here, we assessed the potential for thermal adaptation in sperm and egg function using Tribolium flour beetles, a warm-temperate-tropical insect model. Following temperature increases through adult development, we found opposing gamete responses, with males producing shorter sperm and females laying larger eggs. Importantly, this gamete phenotypic plasticity was adaptive: thermal translocation experiments showed that both sperm and eggs produced in warmer conditions had superior reproductive performance in warmer environments, and vice versa for cooler production conditions and reproductive environments. In warmer environments, gamete plasticity enabled males to double their reproductive success, and females could increase offspring production by one-third. Our results reveal exciting potential for sensitive but vital traits within reproduction to handle increasing and more variable thermal regimes in the natural environment.

Climate change is affecting biodiversity, but proximate drivers remain poorly understood. Here, we examine how experimental heatwaves impact on reproduction in an insect system. Male sensitivity to heat is recognised in endotherms, but ectotherms have received limited attention, despite comprising most of biodiversity and being more influenced by temperature variation. Using a flour beetle model system, we find that heatwave conditions (5 to 7 °C above optimum for 5 days) damaged male, but not female, reproduction. Heatwaves reduce male fertility and sperm competitiveness, and successive heatwaves almost sterilise males. Heatwaves reduce sperm production, viability, and migration through the female. Inseminated sperm in female storage are also damaged by heatwaves. Finally, we discover transgenerational impacts, with reduced reproductive potential and lifespan of offspring when fathered by males, or sperm, that had experienced heatwaves. This male reproductive damage under heatwave conditions provides one potential driver behind biodiversity declines and contractions through global warming., Animal physiology, including reproduction, could respond to climate change in complex ways. Here, the authors use experiments with an insect model system to show that simulated heatwaves harm male reproductive potential by reducing sperm number and viability, an effect which persisted into the next generation

The existence of widespread male same-sex sexual behaviour (SSB) is puzzling: why does evolution allow costly homosexual activity to exist, when reproductive fitness is primarily achieved through heterosexual matings? Here, we used experimental evolution to understand why SSB occurs in the flour beetle Tribolium castaneum. By varying the adult operational sex ratio across 82–106 generations, we created divergent evolutionary regimes that selected for or against SSB depending upon its function. Male-biased (90:10 M:F) regimes generated strong selection on males from intrasexual competition, and demanded improved ability to locate and identify female mates. By contrast, Female-biased regimes (10:90 M:F) generated weak male–male competition, and relaxed selection on mate-searching abilities in males. If male SSB functions through sexually selected male–male competition, it should be more evident within Male-biased regimes, where reproductive competition is nine times greater, than in the Female-biased regimes. By contrast, if SSB exists due to inaccurate mate choice, it should be reduced in Male-biased regimes, where males experience stronger selection for improved mate finding and discrimination abilities than in the Female-biased regime, where most potential mating targets are female. Following these divergent evolutionary regimes, we measured male engagement in SSB through choice experiments simultaneously presenting female and male mating targets. Males from both regimes showed similar overall levels of mating activity. However, there were significant differences in levels of SSB between the two regimes: males that evolved through male-biased operational sex ratios located, mounted and mated more frequently with the female targets. By contrast, males from female-biased selection histories mated less frequently with females, exhibiting almost random choice between male and female targets in their first mating attempt. Following experimental evolution, we therefore conclude that SSB does not function through sexually selected male–male competition, but instead occurs because males fail to perfectly discriminate females as mates., Animal Behaviour, 139, ISSN:0003-3472, ISSN:1095-8282

Triploidy could prevent escaped farm salmon breeding in the wild, while also improving nutrient quality within farmed fillets. Despite these potential advantages, triploid Atlantic salmon have not been widely used in aquaculture, and their reproductive function has yet to be fully evaluated. Here, we compare reproductive function and fillet composition between triploid and diploid farm salmon under standard aquaculture rearing conditions. We show that female triploids are sterile and do not develop gonads. By contrast, males produce large numbers of motile spermatozoa capable of fertilizing wild salmon eggs. However, compared with diploids, reproductive development and survival rates of eggs fertilized by triploid males were significantly reduced, with less than 1% of eggs sired by triploid males reaching late-eyed stages of development. Analyses of fillets showed that total lipid and fatty acid quantities were significantly lower in triploid than in diploid Atlantic salmon fillets. However, when fatty acids were normalized to total lipid content, triploid fillets had significantly higher relative levels of important omega-3 longchain polyunsaturated fatty acids. Our results show that: (i) escaped triploid farm salmon are very unlikely to reproduce in the wild and (ii) if able to match diploid fillet lipid content, triploid farm salmon could achieve better fillet quality in terms of essential fatty acids. aquaculture, nutrition, polyploidy, sustainability, sterility, sperm

The niches of epiphytes are widely studied and have been shown to be complex involving interspecific competition, succession and predation. This study is unique in that it applies the niche concept to moss and lichen distributions within Killarney National Park, Kerry, Ireland. We studied 75 trees between three pristine ancient woodlands and measured a range of physical and biological factors to ascertain influences on epiphyte cover. The species of tree was found as the principal determinant in community structure as it bioengineers conditions such as light, temperature and humidity that the epiphytes are reliant upon. Furthermore, the bark character and trunk circumference were important. Zonation of the epiphytes was apparent with both aspect and height on the trunk. Typically, moss dominated over lichen within a niche that was relatively sheltered. Lichen tolerated drier and lighter niches often being further up the trunk on sun facing aspects. Ultimately, there was succession up the tree mediated through competition. This study highlights the complexity and interrelatedness between biotic and abiotic factors in a relatively unstudied geographical and biological area. Understanding agents behind a population's distribution enables manipulation for conservation or sustainable exploitation.

The theory that ageing evolves because of competitive resource allocation between the soma and the germline has been challenged by studies showing that somatic maintenance can be improved without impairing reproduction. However, it has been suggested that cost-free improvement in somatic maintenance is possible only under a narrow range of benign conditions. Here, we show that experimental downregulation of insulin/IGF-1 signaling (IIS) in C. elegans nematodes, a robustly reproducible life span- and health span-extending treatment, reduces fitness in a complex variable environment when initiated during development but does not reduce fitness when initiated in adulthood. Thus, our results show that the costs and benefits of reduced IIS can be uncoupled when organisms inhabit variable environments, and, therefore, do not provide support for the resource allocation theory. Our findings support the theory that the force of natural selection on gene expression in evolutionarily conserved signaling pathways that shape life-history traits declines after the onset of reproduction resulting in organismal senescence.