Insects-Bats Arms Race

Bats has become an important and main predator of nocturnal insects, and known as the most important biological pest control. As a well-known predator–prey model system have long fascinated scientists and are interesting to study, where adaptations in one species lead to counter adaptations in the other (Dawkins and Krebs, 1979; Dielt and Kelly, 2002).

How to escape from this flying creature?! – Mr Insects

Source: Josch13

Bats have place a strong natural selection pressure on insects to evolve from being eaten, thus they developed two kinds of defenses. Their primary defense is, to avoid detection at the first place, and secondary defense mechanism, will be used to escape once they are detected by bats. Most insects with non-auditory organ, are vulnerable to bats, hence, are restricted to using only the primary defense. They will either adapt physically where being too small or too big sizes (Houston et al., 2014), and having cryptic shapes or texture to avoid bats (Conner, 2014), having large eyes to detect the bats (Soutar and Fullard, 2004), or adapt behaviorally, by being diurnal (Fullard and Napoleone, 2001).

Occasionally, insects will stay motionless and silent in vegetation to make themselves less detectable to bats, as this will increase the masking effects of background clutter, where non-smooth surfaces may create echoes (Claire and Holderied, 2015) thus making it impossible for bats to discriminate between both. Insects also exploited a situation where their density are higher over ripples water since bats avoided that kind of area, turbulent water may interfere with their echolocation abilities (Rydell et al., 1999).

Secondary defense mechanism come in handy, where insects can improve their chances of survival, and mainly using acoustic, where they exploit bat’s echolocation (Staudinger et al., 2012). To counter measure the predator, insects have evolved ultrasound sensitive tympanal organ that can hear ultrasonic bat calls (Conner and Corcoran, 2012). This allows them, once detected, to  maneuver evasively with increasing speed out of the bats sonar beam (Miller and Surlykke, 2001), making a rapid and tight turn that will be difficult for the predator to follow. Sometimes insects display acoustic startle response (ASR) when encounter bats ultrasound by closing the wings, resulting a free fall to the ground (Fullard et al., 2008; Jacobs et al., 2008). Even some moth species can emit ultrasonic clicks of their own which will startle the bats and jam the bio sonar, forcing a bat to break off its attack (Dunning and Roeder, 1965; Corcoran et al., 2011; Conner and Corcoran, 2012), or presented themselves as unpalatable to bats by giving an aposematic warning (Dunning and Krüger, 1996).

We will try our best to hunt you. -Bats Family 

Source: Brian Zwiebel

Bats need to keep up with these defense mechanism, so bats too, need to improve their tactics, to make them less detectable by insects. Where insects thought it will be an advantage to camouflage around vegetation, but it can be a counter-advantage for bats, if they stay on a smooth leaf surface (Siemers et al, 2005) where such surfaces will reflect higher echo amplitude of a target on it, and bats could gain more information from these specific angles ensonification due to an acoustic mirror effect making the detection of insects much more easier. Smaller bats will use high frequencies and some fast flying bats will use lower frequencies, outside moth’s hearing range to make them less audible to most moth (Miller and Surlykke, 2001; Rydell and Arlettaz, 1994).

As a counter-strategy against the sensitive ears of insects, some bats like Barbastelle bats adapted to lower their call intensity by 20-40 dB as to avoid prey detection (Goerlitz et al, 2010). Even until the last pursuit phase, some bats will broaden their echolocation beam to keep the insect within their “sonar view” despite the evasive maneuvers (Jakobsen and Surlykke, 2010). Species like horseshoe bats emit calls continuously and shorten pulse intervals to detect and attack fluttering insects (Siemers and Ivanova, 2004).

Another interesting and sophisticated way is by eavesdropping where gleaning bats that have large pinnae may find insects just by listening passively to rustling noise (Faure and Barclay, 1994; Jones et al, 2011) or to wings fluttering (Siemers and Ivanova, 2004). When the insects advertise their sexual calls, bats seem to exploit to this and can determine their location like Myotis septentrionalis that attacks katydids on grass tips, calling for mates (ter Hofstede et al, 2008). Apparently, passive listening is a strategy for bats to overcome the masking effects that arise from the overlap between clutter and target echoes (Jacobs and Bastian, 2017).

Until when?

Because of the extraordinary global diversity of bats and insects, different species of predator and prey are likely to employ specialized pursuit and escape strategies. These findings has suggests an interesting adaptations in both bats and insects, where insects were pressured to respond appropriately to bats attacks, and bats’ counter-adaptations to prey defenses. But, until when this arm-race will be, it is remain unknown.

References:
1. Clare EL, Holderied MW. 2015. Acoustic shadows help gleaning bats find prey but may be defeated by prey acoustic camouflage on rough surfaces. eLife, 4:e07404.
2. Conner WE. 2014. Adaptive sounds and silences: acoustic anti-predator strategies in insects. In Hedwig B (ed) Insect hearing and acoustic communication, vol 1. Animal signals and communication, Springer, Berlin. pp 65–79.
3. Conner WE, Corcoran AJ. 2012. Sound strategies: the 65-million-year-old battle between bats and insects. Annual Review of Entomology 57: 21–39.
4. Corcoran AJ, Barber JR, Hristov NI, Conner WE. 2011. How do tiger moths jam bat sonar? Journal of Experimental Biology 214(14): 2416–2425.
5. Dawkins R, Krebs JR. 1979. Arms races between and within species. Proceedings of the Royal Society London B: Biological Sciences 205(1161): 489-511.
6. Dielt GP, Kelly PH. 2002. The fossil record of predator-prey arms races: coevolution and escalation hypotheses. The Paleontological Society Papers 8: 353–374.
7. Dunning DC, Krüger M. 1996. Predation upon moths by free-foraging Hipposideros caffer. Journal of Mammalogy 77: 708–715.
8. Dunning DC, Roeder KD. 1965. Moth sounds and insect-catching behavior of bats. Science 147 (3654): 173–174.
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11. Goerlitz HR, Geberl C, Wiegrebe L. 2010. Sonar detection of jittering real targets in a free-flying bat. The Journal of the Acoustical Society of America 128(3): 1467–1475.
12. ter Hofstede HM, Ratcliffe JM, Fullard JH. 2008. The effectiveness of katydid (Neoconocephalus ensiger) song cessation as antipredator defence against the gleaning bat Myotis septentrionalis. Behavioral Ecology and Sociobiology 63(2): 217–226.
13. Houston RD, Boonman AM, Jones G. 2004. Do echolocation signal parameters restrict bats’ choice of prey? Echolocation in bats and dolphins. University of Chicago Press, Chicago. pp 339–345.
14. Jacobs DS, Bastian A. 2016. Predator–prey interactions: Co-evolution between bats and their prey. Cham, Switzerland: Springer.
15. Jacobs DS, Ratcliffe JM, Fullard JH. 2008. Beware of bats, beware of birds: the auditory responses of eared moths to bat and bird predation. Behavioral Ecology 19(6): 1333–1342.
16. Jakobsen L, Surlykke A. 2010. Vespertilionid bats control the width of their biosonar sound beam dynamically during prey pursuit. Proceedings of the National Academy of Sciences of the United States of America 107: 13930-13935.
17. Jones PL, Page RA, Hartbauer M, Siemers BM. 2011. Behavioral evidence for eavesdropping on prey song in two palearctic sibling bat species. Behavioral Ecology and Sociobiology 65(2): 333–340.
18. Miller LA, Surlykke A. 2001. How Some Insects Detect and Avoid Being Eaten by Bats: Tactics and Countertactics of Prey and Predator. BioScience 51(7): 57-581.
19. Rydell J, Arlettaz R. 1994. Low-frequency echolocation enables the bat Tadarida teniotis to feed on tympanate insects. Proceedings of the Royal Society of London B: Biological Sciences 257: 175–178.
20. Rydell J, Miller LA, Jensen ME. 1999. Echolocation constraints of Daubenton’s Bat foraging over water. Functional Ecology 13: 247–255.
21. Siemers BM, Bauer E, Schnitzler HU. 2005. Acoustic mirror effect increases prey detection distance in trawling bats. Die Naturwissenschaften 92: 272–276.
22. Siemers BM, Ivanova T. 2004. Ground gleaning in horseshoe bats: comparative evidence from Rhinolophus blasii, R. euryale and R. mehelyi. Behavioral Ecology and Sociobiology 56: 464–471.
23. Soutar AR, Fullard JH. 2004. Nocturnal anti-predator adaptations in eared and earless Nearctic Lepidoptera. Behavioral Ecology 15(6): 1016–1022.
24. Staudinger MD, Hanlon RT, Juanes F. 2011. Primary and secondary defences of squid to cruising and ambush fish predators: variable tactics and their survival value. Animal Behavior 81: 585–594.

 

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