Rapids clubtail (Gomphus quadricolor) COSEWIC assessment and status report: chapter 6

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Biology

Little information is available about many aspects of Gomphus quadricolor biology. Much of the information in this section was derived from descriptions of other riverine gomphids in Walker (1958), supplemented with information on behaviour and ecology from Corbet (1999).

Life cycle and reproduction

The dragonfly life cycle consists of an aquatic larval stage and terrestrial adult stage. Adult Gomphus quadricolor fly between early June and early July in Ontario and from early May to late July in the U.S. midwest (Walker 1958, Cuthrell 2000). Adults live about three to four weeks, while the larvae probably live two to four years. Generally, adult gomphids are active in daytime, and inactive at dusk and on dull days (Walker 1958).

Adult males typically perch on rocks in midstream, making short forays over the riffles to forage, find mates and drive away competitors. Females inhabit the forest adjacent to the river, perching in trees and shrubs and basking in grassy clearings and bare sandy spots up to 800 m inland from the river (Walker 1958, Larry Rosche pers. comm. 2007). They move to the river only when ready to breed. As a consequence of their more cryptic behavior, adult females are far less frequently collected than males (Walker 1958).

Before copulation, the male transfers sperm from the end of the abdomen to the secondary genitalia beneath the second abdominal segment. The male patrols over the rapids until encountering a female. The courtship flight, if any, is undescribed. After grasping the female by the thorax with his legs, the male clasps the female at the base of her head with his abdominal claspers. The pair flies in tandem while the female bends her abdomen forward so that her ovipositor contacts the male’s secondary genitalia, where she picks up the sperm. The pair separate shortly thereafter. Unlike some dragonfly species, the females ofGomphus quadricolor oviposit unattended by males, typically flying low over rapids and depositing eggs at irregular intervals on the water surface (Walker 1958). On average, female dragonflies deposit 200 to 300 eggs, but over 5000 were produced by a female Gomphus externus (Plains Clubtail - Walker 1953).

Eggs probably require at least five days and perhaps up to a month or more to hatch (Walker 1953, Corbet 1999). Eggs or recently emerged larvae are carried downstream to pools. Larvae spend most of their time buried just below the surface of the sediment in the bottom of the pool, breathing through the tip of the abdomen raised above the sediments.

The duration of the larval stage of Gomphus quadricolor is unknown, but the presence of two or more size classes of larvae in Wisconsin streams suggests that the larval stage lasts two or more years (William Smith pers. comm. 2007). Larval sizes suggest a two-year life cycle farther south in Tennessee and Alabama (Ken Tennessen pers. comm. 2007). Species of Gomphus and Ophiogomphus at temperate latitudes in Europe require at least three to four years to reach adulthood (Walker 1953, Corbet et al. 1960). Duration of the larval stage may be shorter where food is abundant.

Before the final moult, larvae crawl onto vegetation on the edge of the stream. Newly emerged adults (tenerals) disperse inland to avoid predation until the exoskeleton hardens and they are able to fly strongly. After a period of feeding (generally lasting a week or more in other dragonfly species), adult males return to the stream to establish territories (Walker 1953).

Adults are generalist opportunist predators, feeding on flying small insects, especially Trichoptera, Emphemeroptera, small Lepidoptera, and Diptera (Walker 1953). Males feed on prey species emerging from streams, while females perch on the ground in patches of sunlight in forest making short flights to capture aerial insects. Larvae ambush prey from the sediments using their prehensile labium. Early instars feed on very small prey (e.g. ciliates and rotifers) and the size of the prey increases as the larvae grow. Larger larvae feed on macroinvertebrates, small fish, and tadpoles.

Predation

Predators on adult dragonflies include birds (especially small raptors such as American kestrel, merlin, and sharp-shinned hawk), frogs, larger dragonflies, and spiders (Walker 1953).

Fish are probably the most significant predators on stream-dwelling dragonfly larvae (Corbet 1999). Waterbirds, including pied-billed grebe, mallard, American black duck, and wood duck, all consume large numbers of odonate larvae (Walker 1953). Blackbirds, swallows and particularly purple martins take newly emerged adult dragonflies, and these birds often occur in higher numbers in residential areas. Wading birds, especially herons, also feed on larvae. Insect predators include larvae of larger dragonflies, aquatic hemiptera, and aquatic beetles. Turtles and amphibians (including frogs and mudpuppies) also eat larvae.

Several introduced species of fishes inhabiting the Humber and Credit rivers are potential predators on Gomphus quadricolor larvae and could limit their populations or impede their restoration. The most significant of these may be brown trout, rainbow trout, species of pacific salmon, common carp, and round goby. Common carp and round goby also inhabit the Thames River. Degrading water quality could cause further shifts in fish species composition with unknown impacts on odonate populations.

Odonates have few known host-specific parasites (Corbet 1999). Parasitic mites attack adults of some odonate species and egg parasites (Hymenoptera; Chalcidoidea) have also been documented (Walker 1953).

Physiology

Physiological requirements of Gomphus quadricolor are not documented. The preferred habitat of the species is generally considered to be cool, clear streams (E.G. Cuthrell 2000, NHESP 2003).The Humber River site is fairly turbid and possibly warmer than usual but would still be considered cool by stream biologists. Biological oxygen demand (BOD) greater than 10 mg/l cannot be tolerated by most odonate larvae (Corbet 1999).

Larvae are probably sensitive to pesticides, especially organochlorides and organophosphates (Corbet 1999). Metals, chloride, and lampricides may also affect larvae in southern Ontario rivers. Effects of pollutants on odonate larvae include slow growth, developmental deformities, and behavioural abnormalities (Corbet 1999). Biological accumulation of persistent chemicals may be significant given their predatory diet and relatively long life cycle.

Dispersal/migration 

Adults are capable of strong flight. The average distance travelled between reproductive and roosting or foraging sites is generally < 200 m in dragonflies (Corbet 1999). Maiden flights of up to 800 m into surrounding forest have been recorded for Gomphus quadricolor (Larry Rosche pers. comm. 2007). No migratory behaviour has been observedfor this or any other North American gomphid.

Other stream-dwelling odonates tend to remain close to their breeding sites, moving short distances upstream and downstream and very short distances inland (Corbet et al. 1960). Unlike odonates inhabiting ephemeral pools or other seasonal habitats, Gomphus quadricolor lives in relatively stable habitats where the requirement for dispersal is lower and the likelihood of finding unoccupied suitable habitat is small. Their flight behaviour of remaining close to the river surface or in forest cover makes them less vulnerable to passive disperal by winds than odonates that habitually swarm above the canopy. Downstream dispersal of eggs or young larvae by river currents could result in establishment of new populations where suitable unoccupied habitat exists.

All known current and historical Canadian sites are separated by 40 to 300 km from the nearest population in Canada or the U.S. and probably constitute separate populations.

Interspecific interactions

Gomphus quadricolor has no known symbiotic relationships. Both adults and larvae are probably generalist predators, feeding on a wide range of prey species within the suitable size range. 

Gomphus quadricolor typically coexists with other riverine species of odonates, especially Calopteryx maculata and Ophiogomphus rupinsulensis, which are known at both extant Ontario sites. Larvae of these species may compete for prey with Gomphus quadricolor but adults may minimize competition by foraging more widely and having somewhat different emergent periods. These other odonate species may also reduce predation on Gomphus quadricolor by distracting predators from that species.

Adaptability

The disappearance of Gomphus quadricolor from two Canadian sites and some U.S. sites (Table 2) suggests that it is unable to adapt to the pressures of broad landscape changes. No artificial rearing has been attempted, but late instar larvae have been raised to adulthood in the laboratory (Walker 1932).