Microhabitat use by larvae of the endangered dragonfly Sympetrum pedemontanum elatum (Selys) in Japan

Abstract

Sympetrum pedemontanum (Müller in Allioni) (Odonata: Libellulidae), which is distributed widely in the Eurasian continent and its neighboring islands, is listed as a Least Concern species in the International Union for Conservation of Nature Red List (2015). In Japan, however, the population of its subspecies S. pedemontanum elatum (Selys) has been rapidly decreasing since the 1970s. In order to conserve this subspecies, it is important to understand the seasonal microhabitat use by its larvae. However, this has been a difficult task because larvae of S. pedemontanum elatum often coexist with those of a common congener, S. eroticum (Selys), and cannot be morphologically distinguished from the latter. Thus, in this study, we first established a molecular technique based on the polymerase chain reaction to accurately identify each species. In the subsequent field survey in 2015 with its application in the Sakasegawa River, Hyogo Prefecture, we found that S. pedemontanum elatum larvae hatch in stagnant water and subsequently advance into weakly flowing water. Our results indicated a change in the microhabitats during the larval developmental process, reflecting the need for a continuous spectrum of stagnant, transitional, and flowing water. Such aquatic environments with a spectrum of water conditions are disappearing in Satoyama, a rural farming area in Japan. This has endangered species such as S. pedemontanum elatum and Oryzias latipes (Beloniformes: Adrianichthyidae) by depriving them of their favorable habitats. For their conservation, it is necessary to develop methods to recover the traditional aquatic environments in Satoyama.

Short and flat grass preferred by adults of the endangered dragonfly Sympetrum pedemontanum elatum (Odonata: Libellulidae)

“…Adults of Sympetrum pedemontanum (Müller in Allioni), an attractive darter widely distributed across the Eurasian continent and its neighboring islands, often inhabit semi-natural grasslands and rice paddy fields in rural agricultural landscapes (Higashikawa et al 2016;Lockwood 2007;Taguchi and Watanabe 1985). Although it is categorized as a Least Concern (LC) species in the IUCN Red List, this species is now threatened in some European countries and Japan (Higashikawa et al 2016;IUCN 2015).…”

“…Notably, the subspecies S. p. elatum (Selys) is exposed to an even higher extinction risk, especially in Japan (Higashikawa et al 2016). Until the 1970s, this subspecies was one of the most common dragonflies, along with some other Sympetrum species, found in the traditional agricultural landscapes called ''satoyama'' in Japan (Aoki 2013;Ishida et al 1988;Kadoya et al 2009).…”

“…However, it has been rapidly decreasing in population in both rural and suburban areas and is now listed as Extinct (EX) in Chiba Prefecture, Critically Endangered (CR) in Nagasaki Prefecture, Vulnerable (VU) in Tokyo Metropolis, and Near Threatened (NT) in other eight prefectures (Association of Wildlife Research and EnVision 2013). Loss of larval habitat is likely one of the most critical factors in its recent decline in Japan (Higashikawa et al 2016), but little is known about the importance of adult habitat use for the conservation of this species.…”

“…Larvae of S. p. elatum are typically found in either weakly flowing or shallow and stagnant water, especially in sunny, seepage-fed, terraced paddy fields, or slowly running ditches and channels in open fields in hilly areas (Aoki 1998(Aoki , 2013Higashikawa et al 2016;Ishida et al 1988;IUCN 2015;Kawachino 2015;Kondo et al 2005;Maeto et al 2003;Muraki 2010;Yagi et al 2006). Adults usually emerge in early summer (most in early July), and weakly fly or perch on short grass near the water from which they emerged, until they mature in mid-summer (late July to August) in Honshu (Aoki 1998(Aoki , 2013Higashikawa et al 2016;Ishida et al 1988;Ozono et al 2013). Such habitat preference of the adult S. p. elatum at the immature stage is different from that of many other Sympetrum species in Japan (e.g., S.…”

“…After copulation, the tandem pairs or independent females lay eggs at the edge of the water, dipping their abdomen into the sediment with the males performing guarding flights. The eggs tend to be laid in shallow, stagnant, or slightly flowing water (Aoki 2013;Higashikawa et al 2016). The adults typically disappear by the end of November (Ishida et al 1988;Yagi et al 2006).…”