Physiological Entomology (2017) 42, 173–180 DOI: 10.1111/phen.12187 Assessing the morphological and physiological adaptations of the parasitoid wasp Echthrodesis lamorali for survival in an intertidal environment CANDICE A. OWEN1 , JULIE A. COETZEE2, SIMON VAN NOORT3,4 andANDREW D. AUSTIN5 1Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa, 2Department of Botany, Rhodes University, Grahamstown, South Africa, 3Department of Natural History, Iziko Museums of South Africa, Cape Town, South Africa, 4Department of Biological Sciences, University of Cape Town, Cape Town, South Africa and 5Department of Genetics and Evolution, School of Biological Sciences, Australian Centre for Evolutionary Biology and Biodiversity, The University of Adelaide, Adelaide, Australia Abstract. As a result of a variety of chemical, environmental, mechanical and physiological difficulties, insects that spend their entire life spans in the marine orinter- tidal region are relatively rare. The present study assesses whether morphological and physiological adaptations have evolved in a maritime parasitoid wasp species Echthrode- sis lamorali Masner, 1968 (Hymenoptera: Platygastridae, Scelioninae), in response to environmental pressures on its respiratory functioning. Scanning electron and light microscopy of whole and sectioned specimens show the presence of structure-retaining taenidia in the tracheal tubes, although there is an absence of other major adaptations associated with the trachea or spiracles. Histological sectioning reveals the presence of unusual sacs in the female metasoma whose role is unknown, although they are hypothesized to most likely be linked to ovipositor control. Respirometry experiments illustrate the formation of a plastron when submerged, with the longevity of the wasps being increased by quiescence. The critical thermal range of E. lamorali is shown to be large: from −1.1 ∘C ± 0.16 to 45.7 ∘C ± 0.26 (mean ± SE). Behavioural and physiolog- ical adaptations in E. lamorali appear to have evolved in response to exposure to the heterogeneous environmental conditions experienced within the intertidal zone. Key words. Desis formidabilis, hydrostatic ovipositor control, plastron, respiration, scanning electron microscopy, spiracle, taenidia, thermal physiology, trachea. Introduction despite a much wider host spider distribution from East London (Eastern Cape, South Africa), around the Peninsula to Namibia Echthrodesis lamorali Masner, 1968 (Hymenoptera: Platygastri- (Day, 1974; Dippenaar-Schoeman & Jocqué, 1997). The habi- dae, Scelioninae) is an endoparasitoid of the egg stage of the tat of this parasitoid sets the species apart as one of only three intertidal South African spider Desis formidabilis O.P. Cam- other such maritime wasps known worldwide (van Noort et al., bridge 1890 (Araneae: Desidae) (Lamoral, 1968; Masner, 1968; 2014). Females gain access to the multi-compartmentalized host Branch & Branch, 1981; van Noort, 2009; van Noort et al., spider egg sacs by chewing through their silken walls with strong 2014). This wasp displays high endemism, living and surviving mandibles, after which they oviposit in all eggs present (van only within the intertidal region along a small stretch of the Cape Peninsula (Western Cape, South Africa) (Owen et al., 2014), Noort, 2009; van Noort et al., 2014). Males eclose first and fight each other over access to their female kin, which emerge next Correspondence: Dr Candice A. Owen, Department of Zoology (van Noort et al., 2014). The mode of dispersal to other nests is and Entomology, Rhodes University, PO Box 94, Grahamstown, unknown, although it is hypothesized to occur post-copulation Eastern Cape, 6140, South Africa. Tel.: +27 84 716 4746; e-mail: through active searching at low tide by walking between rock [email protected] pools when the host nests are exposed (van Noort et al., 2014). © 2017 The Royal Entomological Society 173 174 C. A. Owen et al. Masner (1968) postulates that this species must exhibit a vari- et al., 2008) because its distribution and physiological adap- ety of unique adaptations for coping with salt water inundation tations are all influenced by its thermal tolerance (Terblanche that may occur during dispersal. Loss of the wings (aptery), et al., 2007; Hazell et al., 2008). which may otherwise weigh an insect down when immersed, In light of the extreme habitat in which E. lamorali persists, the is an obvious adaptation typical in maritime species (Cheng, present study aims to determine whether there are any external or 1976) and occurs in both sexes of E. lamorali (Masner, 1968; internal morphological structures associated with the spiracles van Noort, 2009; van Noort et al., 2014). Wing reduction or and trachea that allow it to withstand saltwater inundation, loss also aids individuals in remaining in one area during the as well as to establish whether the insect forms a plastron strong wind activity typical of this habitat (Cheng, 1976; van in a similar manner to its host D. formidabilis. Furthermore, Noort, 2009) and, in the case of E. lamorali and other scelionine the study also aims to determine the critical thermal range of spider-egg parasitoids, a streamlined body eases physical issues E. lamorali to better understand how the species persists within associated with gaining access through the wall of the spider the intertidal zone. host’s silken egg sac (Austin, 1988; Austin et al., 2005; Stevens & Austin, 2007; van Noort et al., 2014). In maritime species, aptery is often not displayed in isolation, with other morpholog- Materials and methods ical adaptations also having evolved to cope with the extreme environment (Cheng, 1976; Foster & Treherne, 1976; Hinton, Specimen collection 1976). Therefore, it follows that E. lamorali is likely to exhibit additional adaptations for survival within the intertidal zone. All E. lamorali specimens used for morphological and thermal Lamoral (1968) illustrates how the wasp’s host, physiological examinations were collected in early 2012 within D. formidabilis, possesses dense, short, chitinous setae spaced the intertidal region on the stretch of rocky shore at ‘The Island’ at regular intervals on the edges of the openings to the book (Kommetjie, Cape Peninsula, South Africa; 34∘8′22.7034′′S, lungs. These are hypothesized to avert water entering and 18∘19′17.5794′′E) through active searching for spider nests preventing the ‘leaves’ of the book lungs from closing as a containing egg sacs. Egg sacs were placed in a mesh-lidded result of pressure when underwater, allowing for continued container in the laboratory and covered in paper towel moistened respiration (Lamoral, 1968). It is unknown whether E. lamorali with seawater every day to allow for emergence of the wasps. possesses similar structures in its trachea. Furthermore, the host spider develops a plastron when submerged (Lamoral, 1968; Masner, 1968; Branch & Branch, 1981). This mechanism is Specimen examination dependent on the presence of setae covering the spider’s body, which trap a film of air that is capable of exchanging gasses Both the external and internal features of the eclosed wasps with the surrounding environment without collapsing (Lamoral, were examined using scanning electron microscopy of entire 1968; Masner, 1968; Hinton, 1976; Branch & Branch, 1981). specimens and light microscopy of thin-sectioned individuals Evolving independently several times (Hebets & Chapman, mounted on glass slides. Independent dissections of E. lamorali 2000), a variety of insect species are demonstrated to pos- by O. Popovici (pers. comm.) revealed that the species lacks the sess this adaptation (Cheng, 1976; Foster & Treherne, 1976; posterior metasomal spiracles common in other Hymenoptera. Neumann & Woermann, 2009; Seymour & Matthews, 2013), By default, the mesosomal spiracles were the focus of investiga- which may take the form of either a compressible (termed a tion in the present study. ‘physical gill’) or an incompressible (termed a ‘plastron’) gill To examine the external spiracular structure, five wasps (Balmert et al., 2011; Seymour & Matthews, 2013). Physical were sputter-coated with gold as per standard methods, and gills are those that form as an unsupported layer of air over the images captured using a Vega LMU Scanning Electron Micro- insect’s body, whereas plastrons require some form of support, scope (Tescan, Kohoutovice, Czech Republic) (20 kV current; such as setae and microtrichia (Balmert et al., 2011; Seymour analysis photocapture and measurement software, Olympus & Matthews, 2013). Echthrodesis lamorali exhibits a densely Soft Imaging Solutions GmbH, Germany) housed in the Rhodes pilose body surface (Masner, 1968; van Noort, 2009; van Noort University Electron Microscopy Unit (Cross & Pinchuck, et al., 2014), suggesting the formation of an incompressible gill 1987). Captured images were visually assessed for the presence during submersion similar to that of its host spider. of any structures or adaptations that may assist with submerged In addition to likely morphological adaptations, the intertidal survival. zone often exhibits huge daily temperature fluctuations, and so For internal tracheal structure, specimens were prepared for species living in this environment need to have large critical ther- resin-immersion and subsequent sectioning by placing 10 live mal limits to maintain normal bodily functionality (Huey et al., insects into 2.5% glutaraldehyde [CH2(CH2CHO)2] in 0.1 m 1992; Hazell et al., 2008). Subsequent