The dragonflies and damselflies of the Galapagos Islands, Ecuador (Insecta: Odonata).
Psyche 99(4):309-321, 1992.
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THE DRAGONFLIES AND DAMSELFLIES OF THE
GALAPAGOS ISLANDS, ECUADOR (INSECTA: ODONATA)~ Department of Biology, Carleton University, Ottawa K1S 5B6, Canada
The Galapagos Islands of Ecuador are famous as "living labora- tories of evolution." Much has been written about the biota of the islands, especially the vascular plants, vertebrates, and marine invertebrates (Berry, 1984, Bowman et al. 1983, James 1991, Perry 1984). The insect fauna of the islands was summarized by Linsley and Usinger (1966) and Linsley (1977) and found to contain about 900 species. I have undertaken a program of field studies and am attempting to summarize the taxonomic composition, ecological characteristics, and evolutionary dynamics of the insect fauna of the Galapagos Islands (e.g., Klimaszewski et al., Peck and Kukalova-Peck 1990). As a partial result, the islands are now known to have at least 1600 species of insects (Peck 1991; unpub- lished). This paper summarizes published and new data on the Odonata, based on 12 months of field work in 1985, 1989, 1991, and 1992, and provides a key for the identification of adults. Adult Odonata in the Galapagos Islands often fly about fresh water in the highlands of the islands or around coastal brackish mangrove and open saline lagoons. Their predatory larvae have been found in pools in temporary streams near the Media Luna cin- der cone, Santa Cruz Island, and in submerged grasses or sedges at the edges of apparently fresh water coastal lagoons (or fresh water lenses on salt water) near Villamil, Isabela Island. Most odonate larvae cannot tolerate saline conditions (Needham and Westfall 1955) so few would be expected to live in saline coastal waters, but some can apparently live in brackish water. Since long distance migrations of many Odonata have been found far at sea (Corbet 1962), their presence on the islands should not be surprising. The 'contribution 476 of the Charles Darwin Research Foundation Manuscript received 28 December 1992.
Pu&f 99:30SI-321 t 1992). http:llpsyche cnlclub oreflim-W html
depauperate Galapagos fauna is probably a reflection of the limited amount of permanent fresh water available for larval development. The only permanent fresh water is in the highlands of San Cristo- bal Island at El Junco and La Toma. Mineral-laden lakes exist in active or dormant volcanic craters on other islands. Biological data on most of the species in places other than the Galapagos can be found in Needham and Westfall (1955) and Dunkle (1989, 1990). Corbet (1962, 1980) provides general reviews of Odonata biology. SYSTEMATIC, DISTRIBUTIONAL, AND BIONOMIC SUMMARY Linsley (1977) and Linsley and Usinger (1966) catalogue early literature on the Galapagos entornofauna. For each species, I give a statement on general distribution of the species; whether it is endemic to the islands or a native (occurring naturally both else- where and in the Galapagos); and a summary of the islands where the species is known. The island summary uses the accepted Ecuadorian names for the islands (Fig. 1). If earlier reports have used the English names, they have been changed here. Detailed label data on specimens is not given, although this information is available from the author and primary literature. Turner (1967) provides label data for important collections of four species made between 193 1 and 1964. Included is an account which summarizes habitat associations of the adults and elevational occurrences. The vegetational-habitat zonation of the Galapagos is discussed in many general natural history works on the islands (or see Peck and Kukalova-Peck 1990) and is not repeated here. Finally, a statement gives the months in which adults have been captured or observed. Little attempt was made to document the presence or absence of larvae in various water-bodies. No detailed or quantative ecologi- cal studies exist for Galapagos Odonata. Larvae have been seen in the volcanic crater lake at the summit of the active volcano on Fer- nandina Island (Eibl-Eibesfeldt 196 1 : 102) and so could also occur in the summit crater-lake on the active volcano of Cerro Azul, Isabela Island, or in lakes in other active volcanic craters. During and following the unusually rainy conditions of the El Nifio of Jan- uary-May 1992, I found hawking dragonflies to be exceptionally abundant along the coasts of many islands. Voucher material is in the collection of the author, the Canadian Museum of Nature, and the Charles Darwin Research Station (CDRS).
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6 A (3 GENOVESA
Figure 1. Outline map of Galapagos Archipelago, Ecuador, with names of princi- pal islands.
Suborder Zygoptera (Damselflies)
Ischnura (Anomalagrion) hastata (Say)
The Citrine Forktail
Galapagos references. Currie ls901 : 382; Calvert 1906: 130; Gloger 1964: 3; Turner 1967: 285, 290; all these references use the name Anomalagrion hastatum (Say).
Distribution. United States, West Indies, Central and northern South America; native to Galapagos. Found on Isabela (abundant near Villamil), San Cristobal (abundant around El Junco), Santi- ago, Santa Cruz (abundant near Media Luna). Bionomics. Littoral saline meadows to pampa zones, around permanent wet spots and pools; found in January-May, December.
312 Psyche [vo~. 99
This can be a very abundant species in the Galapagos. It is known elsewhere to frequent salt meadows (Needham and Heywood 1929: 358; Dunkle 1990), as well as ponds, swamps, ditches, and seep- ages. Nymphs have been collected in brackish lagoons at Villamil, Isla Isabela. The wide distribution results from being carried by winds.
Suborder Anisoptera (Dragonflies)
Key to Galapagos Anisoptera
la. Triangles (t) in front and hind wing similar in shape and about equidistant from arculus (ar) (Fig. 2); brace vein below proxi- mal end of stigma; hind wing without foot-shaped anal loop (al), "toe" absent (Aeshnidae) ................................................. 2 lb. Triangles (t) in front and hind wing not similar in shape and not equidistant from arculus (ar) (Fig. 3); no brace vein below proximal end of stigma; hind wing with foot-shaped anal loop (al), with well developed "toe" (Libellulidae) ......................... 3 2a. Sector veins (sv) arising from arculus vein (ar) near its middle (Fig. 2); thorax multicolored; male with anal border of hind wing angulate; auricles on male 2nd abdominal segment .......... ............................................................. Aeshna galapagoensis 2b. Sector veins arising from arculus vein on its upper half; thorax green; anal border of hind wing rounded in both sexes; auri- cles (lateral earlike projections) absent on male 2nd abdominal ................................................................ segment Anax amazili
3a. Wing vein M2 waved or undulating (Fig. 3) (Pantala) ............ 5 3b. Wing vein M2 smoothly curved .............................................. 4 4a. Hind wing with 2 paranal cells (pc) (behind anal vein) before the start of the anal loop (al) (Fig. 4); no brown band at hind wing base ................................................. Brachymesia herbida 4b. Hind wing with 3 paranal cells (pc) before start of anal loop (al) (Fig. 5); brown band at hind wing base (Tramea) ............. 6 5a. Hind wing with large brown spot at base near broadly rounded .................................................... anal angle. Pantala hymenaea
5b. Hind wing with no spot near base or anal angle ........................ .................................................................. Pantala flavescens
Figures 2-7. Figure 2. Wing base of Aeshna galapagoensis, showing similar tri- angles (t) of Aeshnidae; sv, sector veins; ar, arculus; al, anal loop. Figure 3. Wings of Pantala hymenaea; M-,, undulating M., vein. Figure 4. Hind wing of Brachymesia herbida, showing two paranal cells before start of anal loop. Figure 5. Hind wing of Tramea cophysa showing three paranal cells (pc) before start of anal loop (al). Figure 6. Male abdominal tip of T. calverti. Figure 7. Male abdominal tip of T. cophysa. Figs 6 and 7 from De Marmels and Racenis 1982. 6a. Underside of abdomen black; abdominal segment 8 all black (Fig. 7); hindwing clear with sharply edged dark basal band; male at maturity with frons all violet, male face black .............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tramea cophysa 6b. Underside of abdomen brown to red; abdominal segment 8 with a semicircular pale basal-lateral spot (Fig. 6); hindwing tinged brown with an amber-edged basal band; male with only broad band on top of frons violet; female band on frons top narrower, lower frons and face otherwise pale; male at matu- rity with lower frons and face red ..................... Tramea calverti
Aeshna galapagoensis Currie
The Galapagos Darner
Galapagos references. Currie 1901 : 382; Needham 1902: 695 Calvert 1952: 258 as Neureclipta; 1956: 137; Asahina 1961: 1 Gloger 1964: 4; Turner 1967: 288, 290.
Distribution. Endemic species. Found on Isabela, San Cristoba (La Toma), Santa Cruz.
Relationships. Schmidt (1938) states that this species is near A. cornigera and A. californica (both of California). Bionomics. Arid to pampa zones; January, March-May, Decem- ber. A nymph has been taken in a brackish pool at the bottom of Grieta Iguana (a cave) at CDRS.
Anax amazili (Burmeister)
The Ringed Darner
Galapagos references. Asahina 1961 : 1; Gloger 1964: 4; Turner 1967: 288,290
Distribution. Southern USA (vagrant), Mexico and West Indies, S. to Argentina; native to Galapagos. Found on Bartolomk, Flore- ana, San Cristobal, Santa Cruz, Santiago. Bionomics. Arid to pampa zone; January, March-May; it breeds in weedy ponds and ditches, and can breed in brackish water (Dun- kle 1989). Nymphs have been collected in brackish lagoons at Vil- lamil, Isla Isabela.
Brachymesia herbida (Gundlach)
The Tawny Pennant
Galapagos references. Kirby 1889: 341 as Cannacria batesii; Currie 1901: 387; Calvert 1906: 326; Turner 1967: 290 as Can- nacria fumipennis.
Distribution. Texas to West Indies, south to Argentina; Native to Galapagos. Found on Isabela, Santa Cruz. Bionomics. Arid and littoral zones; January-March; it breeds in ponds, ditches, and marshes, and nymphs can live in brackish water (Dunkle 1989). Although there have been no new literature
19921 Peck 315
records of the species since 1901 it was the most abundant species during my 1989 field work.
Pantala flavescens (Fabricius)
The Wandering Glider
Galapagos references. Currie 1901 : 385; Calvert 1906: 307; 1947: 227; Turner 1967: 289
Distribution. Cosmopolitan (including Hawaii) (but not breed- ing in Europe); Native to Galapagos. Found on Baltra, Floreana, Isabela, San Cristobal (La Toma), Santa Cruz, Santiago. Bionomics. Littoral and arid to pampa zones; March-May. It is often taken on vessels far at sea. The species breeds in open tem- porary ponds, including brackish waters. It drifts with the wind and feeds on aerial plankton (Dunkle 1989). Pantala hymenaea (Say)
The Spot-winged Glider
Galapagos references. McLachlan 1877: 84; Currie 1901 : 385; Calvert 1906: 309; Gloger 1964: 5; Turner 1967: 289 Distribution. North, Central, and South America, and the West Indies; Native to Galapagos. Found on Espafiola, Floreana, Isabela. Bionomics. March, April, June-October. Breeds in open tempo- rary pools, including brackish waters. Nymphs have been collected in temporary ponds on Isla Santa Cruz. Larval development may be as quick as five weeks (Dunkle 1989). Tramea calverti Muttkowski, 1910
The Striped Glider
Galapagos references. Dunkle (1989: 115, no specific islands mentioned).
Distribution. A vagrant in Florida, USA, and resident in south- ern Texas, Mexico, the West Indies, Central and South America to Argentina; native to Galapagos. Found on Floreana, Isabela, Santa Cruz, Santiago.
Bionomics. Littoral and arid to pampa zones; January-June, August, December. Breeds in temporary or permanent pools and quiet waters, and probably in brackish water (Dunkle 1989).
316 Psyche [VOI. 99
Nymphs have been collected in brackish lagoons at Villamil, Isla Isabela, and temporary ponds on Isla Santa Cruz. Tramea cophysa Hagen 1867
Tramea darwini Kirby, 1889: 3 15 "Galapagos Islands"; Currie 1901: 386.
Tramea cophysa, Calvert, 1906: 301; De Marmels & Racenis 1982: 112.
Tramea (Trapezostigma) cophysa darwini Calvert 1947: 227; Asahina 1961 : 2; Turner 1967: 288.
Distribution. In South America from Venezuela through Ecuador to Argentina. Native to Galapagos. Reported from Espafiola, Floreana, Isabela, San Cristobal, Notes. This species may have been confused with T. calverti, and its literature records may refer to T. cophysa. De Marmels and Racenis (1982) clarify the characters and distributions of T. calverti and T. cophysa, and list only T. cophysa from the Galapa- gos. The key in De Marmels and Racenis (1982) should be con- sulted. Dunkle (1989, and pers. comm.) has seen material of T. calverti but not T. cophysa from the Galapagos. My material con- tains only specimens of T. calverti. I have examined Galapagos specimens in USNM and CAS collections and found specimens of T. calverti which had been labeled as T. cophysa. If T. cophysa was actually once present and is now absent in the Galapagos it represents a case of natural extripation of island populations. Although there is a very rich odonate fauna in mainland South America, that of the Galapagos is impoverished. For instance, Venezuela is known to have 449 species, 116 genera, and 14 fami- lies of Odonata (De Marmels 1990). No such list has been prepared for adjacent mainland areas such as Ecuador. In the Galapagos, only seven native and one endemic species are known. The native species all have very large New World distributions, and the fauna is clearly derived from continental tropical America (Schmidt 1938). The 1000 km separating the islands and the mainland is not likely to be much of an effective barrier for wandering or migra- tory Odonata species. Rather, it is the seasonal and harsh aridity of
the islands which must limit colonization. The highlands of most of the large islands may have seasonal streams or pools for repro- duction but these can completely vanish in a dry season. Larvae of some species may pass the dry season by burrowing into the mud. If an island population does not survive a dry season, the recolo- nization of the island is necessary. Permanent fresh water occurs only on Isabela Island at El Junco Lake, its outlet stream, and the reservoir and stream at La Toma.
The low level of endemism (one species) in the archipelagos' fauna may be explained by the relative youth of the islands (about 3 million years at most), and sufficient nearness to the mainland to permit continued gene-flow and recolonization from the continent, and between islands. With this in mind, the "endemic" status of Aeshna galapagoensis might bear re-evaluation. There appears to be no recent general discussion in the literature about the odonate fauna of oceanic islands. Schmidt (1938) sum- marizes data from over 50 years ago. I present some additional data (Table 1). It seems that comparatively few odonate species can reach and establish themselves on distant, semi-arid, oceanic islands. Schmidt (1938) tabulated only 162 species and subspecies in all of Oceania. His listing indicates that the dragonflies (Anisoptera) are the better or more frequent dispersers and colo- nizers than The Zygoptera, and they show comparatively lower (44%) endemism in Oceania. The damselflies (Zygoptera) are weaker fliers and would thus be expected to be poorer dispersers, but they do have some long-distance dispersal potential. They were able to reach Hawaii, but the 29 endemic species of Megalagrion which occur in Hawaii are descended from only a single ancestral colonist. The fact that there is a higher proportion of endemic species of island damselflies (86%, Schmidt 1938) shows that they are more likely to become isolated populations after the initial and infrequent colonization event. Within the Hawaiian Island chain, the older more northwestern islands have more endemic species which are limited to a single island (Kennedy 1930). The Odonata fauna of the Galapagos Islands consists of three families, six genera, and eight species (one of which is endemic). A key for identification is given to the seven Anisoptera species.
3 18 Psyche [vo~. 99
Table 1. Data on Odonata fauna of some island regions compared with peninsular Florida, giving number of species and subspecies (endemics in parentheses), and references. Other data are in Schmidt (1938). Area or Island Odonata Zygoptera Anisoptera Reference -- - - - -
Dunkle (1989, 1990)
Dunkle (1989, 1990)
Dunkle (1989, 1990)
Zimmerman ( 1948)
Howarth ( 1990),
Species distribution and habitats are summarized for each species. Seven of the species are widely distributed in North, Central, and South America, and are able to tolerate the seasonally arid condi- tions or brackish waters of the islands. It is a pleasure to offer this paper as a contribution to this issue of Psyche in honor of Professor F. M. Carpenter and in recognition of his many contributions to entomology, including his support of my desire to work on island insects when I was his graduate stu- dent. Field work in the Galapagos was permitted by the authorities of the Galapagos National Park Service (A. Izurieta, Superinten- dat), Department of Forestry, Ministry of Agriculture, Republic of Ecuador. Field work was facilitated by the Charles Darwin Research Station, Santa Cruz Island (C. Blanton, Director), and partly supported by research grants from the Natural Sciences and Engineering Research Council of Canada. Nancy House helped determine specimens of nymphs. Nancy House and Sid Dunkle provided many helpful suggestions on an earlier draft of the manuscript.
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