YIJC [H2] ETB Impact of Climate Change (N) Part 2 (Vetted)

9744 H2 BIOLOGY LECTURE NOTES | JC 2 Impact of Climate Change on Animals & Plants 30 Extension Topic B Impact of Climate Change on Animals and Plants Part 2 Learning Outcomes (e) Explain how temperature changes impact insects, including increased temperature leading to increased metabolism and the narrow temperature tolerance of insects. (f) Outline the life cycle of Aedes aegypti as an example of a typical mosquito vector. (g) Outline the development of viral dengue disease in humans, including host -pathogen interactions, human susceptibility to the virus, pathogen virulence, transmission, and drug resistance. (h) Explain how global warming affects the spread of mosquito -borne infectious diseases, including malaria and dengue, beyond the tropics. (i) Discuss the effects of increased environmental stress (including increased temperatures and more extreme weather conditions) as a result of global climate change, on habitats, organisms, food chains and niche occupation. (j) Discuss how climate change affects the rich biodiversity of the tropics including the potential loss of this rich reservoir for biomedicines and genetic diversity for food. Lecture Outline 1) Impact of Temperature Change on Insects 1.1 Effect on Insects Growth, Development & Activity 2) Life cycle of a Mosquito Vector 2.1 The Aedes aegypti mosquito 2.2 Life cycle of Aedes aegypti 3) Viral Dengue Disease 3.1 Transmission 3.2 Pathogenesis 3.3 Treatment 3.4 Prevention 4) Effect of Global Warming on Mosquito-borne Diseases 4.1 Effect on Insect Distribution 4.2 Spread of Mosquito-borne Diseases 5) Effects of Environmental Stress 5.1 Impact on Distribution of Animals and Plants 5.2 Impact on Breeding Success of Animals and Plants 6) Effect on Biodiversity 6.1 Loss of Biomedicines 6.2 Loss of Genetic Diversity of Foods

31 Learning Outcome (e): Explain how temperature changes impact insects, including increased temperature leading to increased metabolism and the narrow temperature tolerance of insects. 1 IMPACT OF TEMPERATURE CHANGE ON INSECTS 1.1 Effect on Insect Growth, Development & Activity The body temperature of ectotherms1 fluctuates with environmental temperatures, and basic physiological functions such as locomotion, growth and reproduction are strongly influenced by environmental temperature. Growth and development are fuelled by metabolism. Metabolic rate is the result of many different biological reactions which are catalysed by enzymes. Thus, temperature controls metabolism through its effect on the rates of these enzyme-catalysed biochemical reactions. Fig. 1.1 Global changes in temperature and corresponding changes in metabolic rates of ectotherms In ectotherms, rates of both somatic growth and ontogenic development 2 increase with increasing temperature. A 10°C temperature increase results in approximately 2.5 -fold increase in developmental rate. Therefore, the time to maturity is shorter at higher temperatures. For insects, faster development of egg, larva and pupa stages implies a shorter time of exposure to adverse environmental conditions (e.g. low temperature, too low or too high humidity, attack by predators), hence resulting in higher reproductive success. 1 Organisms whose regulation of blood temperature depends on external sources, such as sunlight/ a heated rock surface. Examples of organisms are fishes, reptiles, amphibians, invertebrates (such as insects). 2 Development of organism from the time of fertilization of the egg to the organism’s mature form.

32 However, insects have a narrow temperature tolerance for development, meaning that they can only develop within a limited range of temperatures. The difference between an organism’s thermal optimum and its current climate is called the thermal safety margin. For insects, thermal safety margins increase sharply with latitude. Insects in tropic environments: • Species living in tropic environments that are already close to their physiological optimum have small thermal safety margins . Thus, tropical insects are more sensitive to climate changes, and even small amounts of warming will likely decrease performance since they will approach near-lethal temperatures much faster. • Many species also have small dispersal ranges which increases their risk of extinction in the case of habitat or environmental changes. Insects in temperate environments: • Species living in temperate environments have large thermal safety margins . Their environments are on average cooler than their physiological optimal, and thus have broader thermal tolerance. • Warming may thus enhance the fitness of insects in temperate environments. For example, with warmer winters, the insects will not all die out like they used to. In addition, since spring starts earlier, these insects also emerge earlier. With summer lasting longer, the insects also persist in the environment for a longer duration. Fig. 1.2 Relative fitness curves of temperate (A) and a tropical (B) species of ectotherms (Tmin and Tmax represent the minimum and maximum temperature at which organisms can perform, and Topt is the optimal temperature for performance. The grey curve beneath the thermal performance curve is the temperature that the organism is exposed to during an average year and the average is depicted as Thab. ΔT is the distance between Thab and Topt, which represents the organisms’ thermal safety margin.)

33 Insects’ physiological responses to warming temperatures can produce large and rapid effects causing significant changes to ecological landscapes and patterns of infectious disease , especially those caused by pathogens which require insects as vectors for transmission. Learning Outcome (f): Outline the life cycle of Aedes aegypti as an example of a typical mosquito vector. 2 LIFE CYCLE OF A MOSQUITO VECTOR 2.1 The Aedes aegypti mosquito Aedes aegypti is a vector of viral diseases such as dengue fever, chikungunya, yellow fever and Zika fever. It is a small, dark mosquito with white lyre shaped markings and banded legs. It primarily bite humans. Fig. 2.1.1 Body features of Aedes aegypti Aedes aegypti dwell in tropical and subtropical regions (warmer climates) all around the world, where the winter temperature is no colder than 10C, and at altitudes below 1000m. The adult life span can range from two weeks to a month depending on environmental conditions. Fig. 2.1.2 Global distribution of Aedes aegypti

34 2.2 Life Cycle of Aedes aegypti The life cycle of Aedes aegypti can be completed within one-and-a-half to three weeks depending on environmental conditions. There is an aquatic phase (larvae, pupae) and a terrestrial phase (eggs, adults) in the life cycle of the A. aegypti mosquito. Fig. 2.2.1 Life cycle of Aedes aegypti (i) Egg ▪ After a blood meal, adult female mosquitoes lay about 100 – 200 eggs on the inner, wet walls of containers with water. ▪ Eggs are very hardy and can survive drying out for up to 8 months and over very cold periods. In warm climates eggs may develop in as little as 2 days, whereas in cooler temperate climates, development can take up to a week. (ii) Larva ▪ Larvae hatch from eggs and feed on organic matter in the water, such as algae and microscopic organisms. The larvae breathe oxygen through a posteriorly located siphon which is held above the water surface. ▪ The larvae will shed their skins three times to be able to grow from first to fourth instars. An instar refers to the developmental stage of an arthropod between moults until sexual maturity is reached. ▪ Larval development is temperature dependent. If temperatures are cool, Aedes aegypti can remain in the larval stage for months so long as the water supply is sufficient. ▪ When the larvae has acquire