Living in a fool’s paradise: The anatomy of doom

Few weeks back I returned home to the whimsical December chillness of South Bengal and was immediately absorbed into anxious addas centered around the recent surge in an unpredictable weather pattern and our role in it. It seemed that many of us have finally awakened to the present and clear danger of climate change, a phenomenon which in its original form has over the course of the history of life on Earth shaped its trajectory and diversity, but in its present form threatens to obliterate a huge fraction of life forms and possibly endanger existence of the human species as well. The human civilization, specifically in the past few centuries has directed an unprecedented onslaught on its surrounding environment, forcing the most drastic pattern of climate change. As a consequence, we are experiencing the sixth mass extinction in the history of life on Earth (Dirzo et al. 2014).

As we witness our environment crumbling under the sheer pressure of the human civilization, we are yet to fathom the rate and scale of the disaster which we brought upon life-forms. Few indirect references point towards the ominous signs of the link between urban civilization and endangerment or extinction of wildlife (McKinney 2002). For example, industrialization led to warmer climate which in turn rises temperatures in the poles causing the melting of ice sheets. Inhabitants of the polar regions like the polar bear and penguins, now face alarming levels of food scarcity (Hunter et al. 2010; Jenouvrier et al. 2014). Due to lack of arctic ice, polar bears often have to cover exceedingly long distances in search of prey. Similar is the fate of penguins who face heightened mortality due to exhaustion, fast depleting prey base and lack of suitable nesting sites. Wildfires rage in Australia, Europe and North America, fanned by historically high temperatures, and resulting in mass mortality of wildlife in heat waves as well as wildfires. Closer home, weather patterns are growing erratic, rising sea levels threatens the Sundarbans and warmer temperatures aid the spread of tropical diseases, further adding more gloom to our already miserable existence (Patz et al. 2005). For humans, in a nutshell, life is becoming harder and many of us are in the danger of becoming climate refugees in the near future. The financial burden of climate change is almost insurmountable, but a spectacular lack of public awareness and political will across the globe has ensured that we remain mostly illiterate when it comes to securing the future of our generation and that our progenies. The signs are so overwhelming that we can no longer sit back and sigh over a cup of piping hot tea because there may not be a tomorrow to save.

Climate change is here and we need to act fast and act now. However, any action grows upon informed decision making. Hence in this primer, I will elaborate a little about our scientific knowledge of effect of climate change in wildlife. I will expand this column further in future to add more dimensions of climate change and reveal how our survival in completely entwined with our environment.

The earth has experienced repeated episodes of climate cooling and warming over its history of billions of years. These earth-historic events of climate change remain one of the most critical factor that has shaped the trajectory of life in this planet (see Garg 2019 for a more nuanced understanding). While fossil records were the mainstay of scientific research to understand species extinction, high-throughput contemporary technologies of genome sequencing and exhaustive bioinformatic tools have provided some excellent discoveries that not only complements fossil data but also greatly advances our knowledge in ways that we could not know by traditional methods. The Genome of an individual is like the core database and the blueprint of our biological identity. In simple terms it represents the total DNA that is stored in each cell of our body. Genome sequencing technologies aim to sequence a genome to its entirety, and the resulting data requires hundreds of Gigabytes to Terabytes of computational space and specialized computers like servers and workstations for analyses. This fast-growing set of big data when analyzed by extensive bioinformatic and statistical protocols (each analysis often runs for several months), has already returned startling information about the biotic response to past episodes of climate change. For example, we now know that endangered mammals, specifically carnivores mostly fared badly in response to earth-historic climatic fluctuations in the Pleistocene epoch (~2.58 million years ago – ~12000 years ago), specifically during the period comprising of the last documented episodes of climate warming (Last Interglacial, around 110,000 to 130,000 years ago) and climatic cooling (resulting in the Last Glacial Maxima around 18,000 years ago) (Kim et al. 2016). Schematic of population fluctuation due to earth-historic climate change in few bat species Many species of birds, specifically endangered ones reacted strongly to climate change with their populations fluctuating in response to changes in global temperature and sea level (Nadachowska-Brzyska et al. 2015). However, the most extreme examples are possibly exemplified by the fate of bats, who regardless of being commonly occurring or endangered, seems to have been profoundly affected by the historical events of climate cooling and warming (Chattopadhyay et al. 2019a) (Figure 1). A recent collaborative study led by this author observed that most study species of bats entered the present epoch of warm climate that is the Holocene (~11,650 years ago) with a historically low effective population size (Chattopadhyay et al. 2019a) (Figure 1).

Their responses to earth-historic climate change seemed to be influenced not only by available habitat but also by their biological traits like body size and capability of long flight (Chattopadhyay et al. 2019a). In simple terms, effective population size represents the number of individuals who can reproduce and contribute to the diversity of the next generation. This number serves as a proxy of the genetic diversity and represents the overall fitness of a population or species. As a rule of thumb, higher the effective population size, higher is the genetic diversity and overall health of the population, allowing for a better chance of future survival. Hence, low historical population size of bats in the recent past makes them more vulnerable to extinction possibilities under further climatic upheavals (Chattopadhyay et al. 2019a). While the number of species in these panels of investigations were miniscule compared to the vast diversity of existing wildlife, all these studies were limited by the extent of availability of Genomes from diverse species groups on public databases. As more genomes from across all major living taxa will be sequenced and made freely available on public databases in the coming decade, this will radically revolutionize our understanding of the responses of life forms to climate change.

While studying species response to earth-historic climatic fluctuations, we also realized that we can leverage this information to understand the effect of a more proximal episode of climate change that occurred in response to the industrialization during the past few centuries, specifically during the past few decades which were characterized by ultra-rapid urbanization and is now also called the human dominated era of Anthropocene (post 1945, Corlett 2015). The Anthropocene has witnessed an almost unparalleled episode of destruction of natural habitats, sudden rise in global temperature and the sixth mass extinction in the history of life (Dirzo et al. 2014). This has effectively necessitated a knee-jerk reaction from scientists and governments to understand and mitigate damages to wildlife from this calamitous disaster. Again, armed with sophisticated genomic technologies, scientists are hoping to leverage species histories to also predict species responses and their survivability going into the future. In a nut-shell, if we can reconstruct the trajectory of a species or a population going back to regimes of past climate changes, then we may ultimately predict the survivability of the species/ population under the present climatic regimes and also into the future and tailor conservation management solutions specific to each endangered population. However, the first step in this process is to accurately reconstruct species trajectories in the recent past.

While technological advancements in DNA sequencing and analytical protocols have help us understand the past, it is still difficult to reconstruct more recent histories. However, museum collections over last few centuries when compared alongside contemporary populations, provide an avenue to understand evolutionary trajectories between these different time points (Chattopadhyay et al. 2019b). Unfortunately, DNA within these museum samples are heavily degraded due to storage as well as chemical damage from preservatives. Obtaining data from these samples using traditional methods is difficult as well as expensive. Yet, recent advances in genomic technologies has made possible to generate large-scale DNA sequencing data from such samples and coupled with sophisticated bioinformatic tools, we can now generate usable data sufficient for exhaustive evolutionary analyses. For example, comparing genomic data of woolly mammoth fossils from about 45,000 years, when population size was high to a sample from 4,300 years ago revealed detrimental effects of small population size and isolation, which must have preceded their extinction from one of their last strongholds in the Wrangel Island in the arctic ocean (Rogers and Slatkin 2017).

However, until recently no study had documented in detail, the evolutionary responses of a species to the Anthropocene. In a study that is possibly one of the first of its kind, this author led a research venture addressing the effect of human-induced climate change on an urban population of a commonly occurring fruit bat (Cynopterus brachyotis) in the island population of Singapore to address this issue (Chattopadhyay et al. 2019b). We generated large tracts of genomic data from a contemporary population sampled during 2012 and compared it with museum samples collected in 1931, slightly preceding the advent of Anthropocene. Simple schematic representation of population crash in the Singaporean population of the Sunda fruit BatAfter painfully reconstructing the species history using this time-stamped data we observed signatures of drastic decline in the population size within this species in Singapore (Figure 2), coinciding with the advent of the Anthropocene that also witnessed rapid urbanization and massive loss of green cover in Singapore (Corlett 1992). When we compared the genetic diversity between these two time points, we observed large decay in diversity within the contemporary population compared to the pre-Anthropocene dataset, firmly establishing the ill-effect of human mediated habitat degradation during this period as a potential cause of endangerment.

These observations are particularly important for understanding human-induced climate change. On one hand, these results directly link the endangerment of wildlife to human urbanization, while on the other hand it calls for immediate alarm even a commonly occurring species was found to be greatly affected by human mediated habitat alterations and climate change. If a common species is so severely affected by urbanization, then the fate of endangered wildlife might be even more severe and catastrophic. Last but not the least, these fruit bats are important keystone species, performing critical role in pollination, germination and also regeneration of forest cover of the native flora and are essential for ecosystem functioning (Chattopadhyay 2018) and their decline can adversely affect in many unpredictable ways thereby affecting our survivability as well.

Unfortunately, we have just woken up to this climate emergency, and many more research studies are needed to clearly understand the extent of endangerment that Anthropocene has caused to both common species as well as endangered ones. Only then can we proceed to model future survivability of these species and design conservation management programs to save them from extinction.

 

Acknowledgment

BC thanks Dr. Kritika M Garg for helping in the manuscript preparation; and also Dr. Rajasri Ray and Dr. Avik Ray for their comments on an earlier version of the manuscript.

 

References:

  1. Chattopadhyay B. 2018. Tales of the night: Chapter I. CEiBa Newsletter 1(3):14–19. 10.13140/RG.2.2.17901.23526.
  2. Chattopadhyay B, Garg KM, Ray R, Rheindt FE. 2019a. Fluctuating fortunes: genomes and habitat reconstructions reveal global climate-mediated changes in bats’ genetic diversity. Proceedings of the Royal Society Biological Science 286:20190304.
  3. Chattopadhyay B, Garg KM, Mendenhall IH, Rheindt FE. 2019b. Historic reveals Anthropocene threat to a tropical urban fruit bat. Current Biology 29:R1299–300.
  4. Corlett RT. 1992. The ecological transformation of Singapore, 1819-1990. Journal of Biogeography 1:411–420.
  5. Corlett RT. 2015. The Anthropocene concept in ecology and conservation. Trends in Ecology and Evolution 30:36–41.
  6. Dirzo R, Young HS, Galetti M, Ceballos G, Isaac NJ, Collen B. 2014. Defaunation in the Anthropocene. Science 345:401–406.
  7. Garg KM. 2019. Last Ice Age: understanding Earth’s climatic history. CEiBa Newsletter 2(1):11–14. 10.13140/RG.2.2.11159.42409.
  8. Hunter CM, Caswell H, Runge MC, Regehr EV, Amstrup SC, Stirling I. 2010. Climate change threatens polar bear populations: a stochastic demographic analysis. Ecology 91:2883–2897.
  9. Jenouvrier S, Holland M, Stroeve J, Serreze M, Barbraud C, Weimerskirch H, Caswell H. 2014. Projected continent-wide declines of the emperor penguin under climate change. Nature Climate Change 4:715.
  10. Kim S, Cho YS, Kim HM, Chung O, Kim H, Jho S, Seomun H, Kim J, Bang WY, Kim C, An J. 2016. Comparison of carnivore, omnivore, and herbivore mammalian genomes with a new leopard assembly. Genome Biology 17:211.
  11. McKinney ML. 2002. Urbanization, Biodiversity, and Conservation: The impacts of urbanization on native species are poorly studied, but educating a highly urbanized human population about these impacts can greatly improve species conservation in all ecosystems. Bioscience 52:883–890.
  12. Nadachowska-Brzyska K, Li C, Smeds L, Zhang G, Ellegren H. 2015. Temporal dynamics of avian populations during Pleistocene revealed by whole-genome sequences. Current Biology 25:1375–1380.
  13. Patz JA, Campbell-Lendrum D, Holloway T, Foley JA. 2005. Impact of regional climate change on human health. Nature 438:310.
  14. Rogers RL, Slatkin M. 2017. Excess of genomic defects in a woolly mammoth on Wrangel island. PLoS Genetics 13:e1006601.

About Author :

Balaji Chattopadhyay

e-mail: balaji.chattopadhyay@gmail.com

Tales of the night: Chapter I

It is a spectacle to experience the sight of hundreds of bats emerging from the shadow of caves in a perfectly choreographed flight maneuver, before eventually disappearing into the vanishing tinge of the dusky sky. Bats, the only volant mammals form the second largest mammalian order Chiroptera (chiro= hand, pteron= wing) comprising of more than 1300 species (Fenton and Simmons 2014). An Indian flying fox (Pteropus giganteus) colony near Bangalore.They show extraordinary specializations in their ecology, anatomy and physiology and a diverse dietary habit feeding on anything from nectar, pollens, leaves and fruits, to insects, small mammals and vertebrates, other bats, fishes as well as blood (Kunz et al. 2005).  Most bats can echolocate emitting ultrasonic sounds for spatial orientation, social contact as well as for foraging (locating and hunting prey), others have strong sense of smell and are well adapted for herbivory. And a small group of bats (the vampire bats of central and south America) possess thermal sensors to choose prey and feeds on blood of wild mammals as well as livestock and less frequently humans (Kunz et al. 2005; Fenton and Simmons 2014). In this article, I will share some contributions of bats to our ecosystem that ultimately benefits us in many ways. I will also share some concerns regarding their continuous decline due to human mediated alteration of our environment as well as continuous persecution resulting from superstition and ignorance (Figure 1). We will save the discussion of their unique capabilities of time keeping and other idiosyncrasies for another chapter of ‘Tales of the night’. 

Bats as bioindicators

Bats occupy an amazing array of habitats are found widely across the globe inhabiting major ecosystems. The endangered Mauritius fruit bat (Pteropus niger) endemic to MauritiusThey are keystone species contributing towards the sustenance of eco-systems they inhabit and performs many important ecosystem services (Kunz et al. 2005). However, bats are also extremely sensitive to disturbances to their habitats, ecology and climate. Over the past few decades, volumes of research studies have revealed that bat communities can be specifically tracked to obtain important estimates of biodiversity, level of pollution and effect of climate change (Jones et al. 2009). For example, frugivores and insectivores can be tracked to understand changes in plant and insect communities (Jones et al. 2009). Similarly, mass mortalities in flying foxes due to sudden warming in parts of Australia (Welbergen et al. 2008) indicated adverse impact of climate change over the population. Many island bats like the Dark flying fox of the Reunion and Mauritius islands, the Guam flying fox endemic to Guam, the Christmas Island pipistrelle found native to the Christmas Island have already gone extinct and many other species face imminent risk of extinction (IUCN) (Figure 2). Even, more commonly occurring species experience drastic loss in population size and risk extinction locally as well as globally.

Ecosystem services: agrodiversity, forest regeneration and pest control

Contribution of bats to the ecosystem benefits humanity in many ways. Fruit bats are pollinator for many plant species which are economically important (banana, mango guava, durian, coconut, ficus, cocoa etc.) as well as species critical for eco-system functioning (agave, various cacti species, baobab tree etc.). Flowers of such species employ multitude of tactics to attract and recruit fruit bats, they open in the night, emit strong odor, and are often large and white in color to ensure that they are located easily in the darkness. Agave plants are primarily pollinated by the nectar feeding long-nosed bats, who in turn are heavily dependent of the nectar and pollen of agave mainly to meet their energetic requirement (Arita and Wilson 1987). Compared to many other biotic pollinators, bats are often efficient long-distance pollinator (Fleming et al. 2009). Over 500 species of flowering plants are pollinated by bats (Fleming et al. 2009) (Figure 3).

Sequel for bat pollination

Growing body of evidence proves that fruit bats are excellent agents of fruit and seed dispersal and germination and greatly accelerates regeneration of forest cover over degraded patches. Fruit bats like the flying foxes inhabiting the Old World biomes can aid in dispersal across tens to hundreds of kilometers and often across isolated islands where many times they are the sole pollinators (Jones et al. 2009). In the New World Tropics, dispersal of seeds of pioneer plant species by fruit bats is essential for regeneration of forest cover (Kelm et al. 2008). Research suggests that seeds ingested by bats influences germination, for example, bat-consumed seeds with their pulp removed show better germination in the neotropical tree species, Calophyllum brasiliense (Marques and Fischer 2009). In addition to their role in pollination, dispersal and germination, bats significantly contribute towards the increase of genetic diversity within their host species by mixing gene pools from different and many times faraway populations. Such act helps maximizing agrodiversity among cultivated plant species as well as forest diversity. In the face of the ongoing episode of human mediated habitat fragmentation, long distance pollination by bats are often responsible for maintaining gene flow and connectivity of plant populations (Fleming et al. 2009). Successful management of fruit bats can effectively aid in the regenerating forest cover thereby forming the base of effective conservation and management of native biodiversity.

Majority of bats however are insectivore, either obligatory or facultative and in many cases act as effective biological control agents of arthropod pest management. Studies have shown that insect bats can eliminate tons of insects per night from farm lands. A colony of 20 million Mexican tree-tailed bats can consume 13000 tonnes of insect over one summer (Altringham 1996). Research from North America suggests that bats contribute around 23 billion annually (by consuming pests and reducing pesticide application) to the agricultural industry in US alone. In the absence of bats, agricultural industry would require to spend additional 4–53 billion USD annually on pesticides alone. But these estimates only include the benefits of pest management and do not include other indirect effects to the environment due to reduce use of pesticides (Boyles et al. 2011), which adds more economic value to their services. Additionally, excrements of insect bats, called guano are rich in nitrogenous compounds are acts as effective fertilizer and are regularly mined in countries like providing livelihood for many. Some insect bats are carnivorous, like the false vampire bats commonly found in the subcontinent. These bats prey upon small mammals like rodents and act as biological control for mammalian pest.

Persecution: superstition and ignorance

While contribution of bats is etched in oriental cultures as positive associations, western cultures nurture largely negative stereotypic myths. Within a large collective mindset across the globe, bats rule the realm of the dark and are usually associated with everything evil. Regardless, many communities not only hunt them and harvest every part of their body in the belief that these could cure almost every possible disease but also consume bats as bushmeat (a source of cheap protein), Endangered Rodrigues fruit bat (Pteropus rodricensis)leading to mass annihilation of colonies often comprising thousands of animals. Such activities act as important stressor for bat communities and significantly contribute towards their decline.

Bats are very gregarious in nature, most species can utilize diverse types of natural formations (also manmade structures), and some like the short-nosed fruit bats from south and southeast Asia can even modify plant-parts to construct simple tents wherein they spend their day (Kunz et al. 2005). Males of the commonly occurring short-nosed fruit in south Asia regularly uses foliage roosts. They chew and modify the underside of leaves of the plant (e.g Palmyra palm) creating a semi-permanent tent-like structure that lasts for years.

Bats often cohabit with humans and livestock. Human contacts are unavoidable due to anthropogenic loss of natural habitats, forcing bats to live in close proximity with humans. However, this association has proven particularly costly for the species as they face merciless persecution and are not only hunted for meat and medicine but also exterminated for their possible role in spreading deadly viruses among humans. Added to this are human mediated destruction of natural habitats and the vagaries of climate change, factors which have collectively resulted in an accelerated loss in their number, diversity, distribution as well as local extinctions in many cases (Figure 4).

Despite the importance of bats towards maintaining an ecological balance, scientific studies of bats are not a prominent component of the peer-reviewed literature. Lack of enough scientific research means that in many cases we are losing precious biodiversity even before they get discovered, a situation particularly acute in South and Southeast Asia (Kunz et al. 2005; Fenton and Simmons 2014). For the little fraction that we are aware of, bats seem to be an enigma gradually enfolding a bewildering array of behavior so intertwined with nature that their demise can certainly spell doom to many natural ecosystems. This has also prompted in many scientific studies addressing their biology, ecology as well as evolution. Among these studies, researches dealing with association of bats with deadly disease outbreaks have become particularly illuminating for humanity in general. Bats carry numerous viruses like SARS, Ebola, Nipah and Rabies virus, but rarely show signs of infection. However, such viruses, if transmitted to livestock or humans causes high mortality, and widespread epidemics (Han et al. 2015; Plowright et al. 2015).  We now know that, direct spread of virus from bats to humans is rare and most infection find their way into humans through livestock. Some studies have also pointed out that bats shed more viruses when under stress. Many documented bat borne disease outbreaks can be linked to close proximity of bats with humans wherein, human settlements have encroached into forest lands and bats are forced to stay close to human settlements, in many cases roosting (nesting) close to livestock. As they shed viruses though excrements, or saliva, the viruses are picked up by livestock and gradually transmitted to humans. Scientists, on a regular basis are discovering novel mechanisms by which bats make themselves immune to viral diseases and believe that bats can form an effective model system to study immunity to virus infections ultimately helping us to devise better technology to combat viral infections and outbreaks.

There is a lesson for us to learn from bats and that is, there are other organisms in this world who are different from us, but nonetheless intelligent and with unique capabilities. The web of life binds us all intricately into a matrix of coexistence that has lasted for over millions of years. It is for us to decide if we still want to cohabit with our neighbors, or consider this diversity as alien, remove them from our surroundings and keep curating the earth as our kitchen garden, to our own peril.

 

References

1) Altringham JD (1996) Bats: Biology and Behaviour. Oxford University Press, New York.

2) Arita HT & Wilson DE (1987) Long-nosed bats and agaves: the tequila connection. Bats 5:3-5.

3) Boyles JG, Cryan PM, McCracken GF & Kunz TH (2011) Economic importance of bats in agriculture. Science 332:41-42.

4) Fenton MB & Simmons NB (2015) Bats: a world of science and mystery. University of Chicago Press, Chicago.

5) Fleming TH, Geiselman C & Kress WJ (2009) The evolution of bat pollination: a phylogenetic perspective. Ann Bot 104:1017-1043.

6) Han HJ, Wen HL, Zhou CM, Chen FF, Luo LM, Liu JW & Yu XJ (2015) Bats as reservoirs of severe emerging infectious diseases. Virus Res 205:1-6.

7) Jones G, Jacobs DS, Kunz TH, Willig MR & Racey PA (2009) Carpe noctem: the importance of bats as bioindicators. Endangered Species Res 8:93-115.

8) Kelm DH, Wiesner KR & Helversen OV (2008) Effects of artificial roosts for frugivorous bats on seed dispersal in a Neotropical forest pasture mosaic. Conserv Biol 22:733-741.

9) Kunz TH & Fenton MB (2005) Bat ecology. University of Chicago Press, Chicago.

10) Marques MC & Fischer E (2009) Effect of bats on seed distribution and germination of Calophyllum brasiliense (Clusiaceae). Ecotropica 15:1-6.

11) Plowright RK, Eby P, Hudson PJ et al (2015) Ecological dynamics of emerging bat virus spillover. Proc R Soc B 282:20142124.

12) Welbergen JA, Klose SM, Markus N & Eby P (2008) Climate change and the effects of temperature extremes on Australian flying-foxes. Proc R Soc B 275:419-425.

About Author: 

Balaji Chattopadhyay, National University of Singapore, Singapore

email: balaji@nus.edu.sg