Revisiting Adaptations of Neotropical Katydids (Orthoptera: Tettigoniidae) to Gleaning Bat Predation
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Erschienen in: Neotropical Biodiversity ; 3 (2017), 1. - S. 41-49 https://dx.doi.org/10.1080/23766808.2016.1272314 Neotropical Biodiversity, 2017 Vol. 3, No. 1, 41–49, http://dx.doi.org/10.1080/23766808.2016.1272314 Revisiting adaptations of neotropical katydids (Orthoptera: Tettigoniidae) to gleaning bat predation Hannah ter Hofstedea*, Silke Voigt-Heuckeb, Alexander Langc, Heinrich Römerc, Rachel Paged , Paul Fauree and Dina Dechmannf aDepartment of Biological Sciences, Dartmouth College, Hanover, NH, USA; bDepartment of Biology, Chemistry, and Pharmacy, Freie Universität Berlin, Berlin, Germany; cZoology Institute, University of Graz, Graz, Austria; dSmithsonian Tropical Research Institute, Ancon, Panama; eDepartment of Psychology, Neuroscience & Behaviour, McMaster University, Hamilton, Canada; fDepartment of Biology, Universitat Konstanz, Konstanz, Germany (Received 22 February 2016; accepted 12 December 2016) All animals have defenses against predators, but assessing the effectiveness of such traits is challenging. Neotropical katydids (Orthoptera: Tettigoniidae) are an abundant, ubiquitous, and diverse group of large insects eaten by a variety of predators, including substrate-gleaning bats. Gleaning bats capture food from surfaces and usually use prey-generated sounds to detect and locate prey. A number of Neotropical katydid signaling traits, such as the emission of ultrasonic fre- quencies, substrate vibration communication, infrequent calling, and ultrasound-evoked song cessation are thought to have evolved as defenses against substrate-gleaning bats. We collected insect remains from hairy big-eared bat (Micronycteris hirsuta) roosts in Panama. We identified insect remains to order, species, or genus and quantified the pro- portion of prey with defenses against predatory bats based on defenses described in the literature. Most remains were from katydids and half of those were from species with documented defenses against substrate-gleaning bats. Many culled remains were from insects that do not emit mate-calling songs (e.g. beetles, dragonflies, cockroaches, and female katydids), indicating that eavesdropping on prey signals is not the only prey-finding strategy used by this bat. Our results show that substrate-gleaning bats can occasionally overcome katydid defenses. Keywords: anti-predator defenses; Chiroptera; eavesdropping; Panama; predator-prey arms race Introduction spines on their legs or thorax (e.g. Steirodon spp., Predation is one of the strongest agents of natural selec- Figure 1) and a strong bite owing to their large tion [1], and in response, prey has evolved a spectacular mandibles (e.g. Copiphora spp.). Behavioral defenses diversity of anti-predator defenses [2]; however, the effi- include well-hidden daytime roosts [3,5], reduced activ- cacy of prey defenses is difficult to quantify in nature. In ity during bright phases of the moon [7], singing from the Neotropics, katydids (Orthoptera: Tettigoniidae) are protected perches [8], and changes in acoustic behavior an abundant, ubiquitous, and diverse group of large [4]. Male katydids use their wings to produce calling insects that are eaten by a variety of predators including songs that attract females, and have acoustic defenses bats, monkeys, rodents, birds, lizards, and amphibians such as song cessation at the approach of a potential [3,4]. Katydids exhibit an assortment of morphological predator and the production of loud sounds when and behavioral traits considered to be anti-predator touched that might startle a predator [4]; however, the fi defenses [5]. ef cacy of these defenses in the wild remains unknown. Katydid morphological defenses include crypsis, In the Neotropics, substrate-gleaning bats capture mimicry, chemical defenses, spines, and a strong bite. prey from surfaces and are known to exert top-down Many katydids are visually cryptic, having broad green control on insect populations [9,10]. In addition, many fi wings to blend in with vegetation, or other forms of col- gleaning bats are signi cant predators of katydids specif- – oration to blend in with bark or lichen. Likewise, there ically [8,11 15, this study]. Many substrate-gleaning bats are a number of spectacular forms of mimicry found in listen to the mate-calling songs of male katydids to katydids, such as wasp (Scaphura spp. and Aganacris detect and locate them as prey [8,16,17]. Thus, some spp.) and leaf (Mimetica spp., Aegimia spp., Pycnopalpa acoustic characteristics of Neotropical katydid songs are fi bicordata) mimics [6]. Some species have long, sharp believed to be speci c adaptations against gleaning bat Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-0-397240 *Corresponding author. Email: [email protected] © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unre- stricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 42 H. ter Hofstede et al. when they emerged from the roost at night. We filmed the inside of one roost to confirm that the bats inside were responsible for dropping arthropod remains at night. This also demonstrated that bats frequently returned to the same roost to consume insects throughout the foraging period. To collect culled arthropod parts, a plastic sheet was suspended off the ground inside the hollow tree roost to keep the prey remains dry and prevent them from being washed away by rainwater. From roost 1, collections were made 2–14 times/month covering all seasons except Figure 1. Lateral view of Steirodon stalii showing thoracic April and May (63 collections). Remains were also col- spines as thick protuberances. lected from two other M. hirsuta roosts (roost 2 collec- tion dates: 27 September 2002, 21 November 2002 and 5 December 2002; roost 3 collection date: 29 November predation [3]. For example, sporadic/infrequent calling 2002). Cockroaches and ants were observed removing [8,18,19], the emission of high ultrasonic frequencies bat feces and, more rarely, insect remains, thus our sam- [20], and substrate vibration communication [8,20,21] ples likely underestimate the total number of prey items have all been proposed as defensive forms of communi- brought back to bat roosts. However, the purely chiti- cation to evade detection by eavesdropping bats. Katy- nous remains that are important items for taxonomic dids have ultrasound-sensitive ears and some will cease classification, such as arthropod wings, legs, and oviposi- singing in response to ultrasonic pulses and bat echolo- tors, were seldom removed. cation calls [22–25]. Cessation of singing can effectively Most insect parts were identified to order, and in case thwart the gleaning attacks of temperate northern long- of katydids to the level of family, subfamily, genus, and eared bats, Myotis septentrionalis [26], but the efficacy species whenever possible using keys and information of such an acoustic defense has not been tested against from [4,30–32]. For all insect remains, we report the Neotropical gleaning bats. For example, the Neotropical total number of body parts found as a measure of the common big-eared bat Micronycteris microtis, a con- maximum number of individuals that were captured for gener of our study species, uses biosonar to locate silent, each taxonomic group. For katydids, we additionally motionless arthropods resting on leaf surfaces [27], sug- examined forewings to classify them as male (having gesting that song cessation alone will not always prevent characteristic sound producing structures) or female the predatory attacks of substrate-gleaning bats. (lacking these structures). Some wings could not be clas- The goal of this study was to identify the katydid sified in this way because they were missing the area of species eaten by the hairy big-eared bat M. hirsuta,a the wing with sound-producing structures and these were major gleaning bat predator, and to assess the proportion included as individuals of unknown sex in the count. We of katydid species with described anti-bat defenses in the also identified each forewing as a left or right wing. By diet. Previous studies have shown that M. hirsuta eats matching the left and right wings of the same sex, we many katydids ([11]: 25% by number, [28]: 41% by were able to calculate the minimum number of individual number, 61.5% by weight); however, the relative number katydids at each roost. and sex of all katydid prey have never been reported. We conducted a literature search to document Detailed data about the dietary composition of bat preda- defenses of Neotropical katydids believed to be effective tors can help address hypotheses about the efficacy of against predatory bats. These defenses were noted for presumed katydid defenses. all species of katydid from Panama and are reported here for those species found as remains in bat roosts (Table 1). A number of defenses are common to all Methods Neotropical katydids and are not listed in Table 1: The study was conducted at the Smithsonian Tropical regurgitation of crop fluid (thought to be distasteful to Research Institute (STRI) field station on Barro Colorado predators; [3,5]), holding tightly to a substrate when Island (BCI) in Panama (9°10′ N, 79°51′ W). The 15.6 grabbed [3], kicking [5], and autotomy of the hind legs km2 island is covered with moist, semi-deciduous