The identity of Alfred Wallace’s mysterious butterfly taxon Lycaena nisa solved: Famegana nisa comb. nov., a senior synonym of F. alsulus (Lepidoptera, Lycaenidae, Polyommatinae)

Abstract Lycaena nisa Wallace, 1866 was described from Formosa (Taiwan) and is here recognized as a senior subjective synonym of Lycaena alsulus Herrich-Schäffer, 1869. It is resurrected to serve as the valid name, Famegana nisa (Wallace, 1866), comb nov. of the species commonly known as Famegana alsulus. The name Zizera taiwana Sonan, 1938 (syn. nov.), also described from Formosa, is recognized as a junior subjective synonym of L. nisa. Another name, Zizeeria alsulus eggletoni Corbet, 1941 (syn. nov.), described from Hong Kong is also considered a junior subjective synonym of L. nisa. Moreover, all former synonyms of alsulus automatically become new junior synonyms for nisa. This species occurs in the Oriental and Australian regions and western Pacific.


introduction
Anyone interested in natural history knows the name Alfred Russel Wallace, considered the father of zoogeography, who developed the idea of nature selection independently of Charles Darwin (Limolino et al. 2010;Beccaloni 2013). His achievements cover a variety of biological disciplines, including systematics. He described many plants and animals, mostly based on collections made by himself and his assistants. Nevertheless, he also worked on collections from other sources. A good example is a work on lepidopterous insects collected by Robert Swinhoe, an English biologist who worked as consul in Formosa (Taiwan) from 1860-1866. In collaboration with Frederic Moore, Wallace studied a collection made in Takaw [today's Kaohsiung]. The butterfly portion of the collection was investigated by Wallace, the moth portion by Moore, and a joint paper was subsequently published as Wallace and Moore (1866). This paper has been regarded as the starting point of lepidopteran research of Taiwan (Shirôzu, 1986). In this landmark work of the Lepidoptera of Taiwan, 46 diurnal species and 93 nocturnal species are mentioned. Wallace noted that most of the species in the collection were widespread species with distributions shared with India and Malay, but he recognized five species he considered distinctive and described them as new. These species were Pontia niobe Wallace, 1866 (Yata 1985;Hsu et al. 2018). Pieris formosana is generally considered as either a subspecies of Appias lyncida Cramer, 1777 (Pieridae) (e.g., Shirôzu 1960) or a junior synonym of A. lyncida eleonora Boisduval, 1836 (Pieridae) (e.g., Yata 1985;Hsu et al. 2018). Terias vagans is recognized as a junior synonym of Eurema laeta (Boisduval, 1836) (Pieridae) by Yata (1989). Euploea swinhoei is considered a subspecies of Euploea sylvester (Fabricius, 1793) (Nymphalidae) (Ackery and Vane-Wright 1984;Morishita 1985).
The status of Lycaena nisa, however, remains ambiguous and has not been re-examined (Shirôzu, 1986). Matsumura (1909) changed the generic assignment of L. nisa Wallace, 1866 to the genus Zizera but without giving any explanation. Lycaena nisa was excluded from a comprehensive checklist of Taiwan butterflies by Shirôzu (1960) and Shirôzu and Ueda (1992). During visits to the Natural History Museum, London (NHMUK) for a project on documenting information on the type specimens of Taiwan butterflies, the type material of L. nisa was retrieved from the Wallace collection. According to Wallace's (1866) original description, a pair of syntypes were available for L. nisa, but only a female specimen (Figs 1-3) was successfully located in the museum. The features of the specimen fully conform to the description given by Wallace (Wallace and Moore 1866: 360-361). Interestingly, it also agrees with a species commonly known as Famegana alsulus (Herrich-Schäffer, 1869) in all aspects, and these two taxa are shown to be conspecific.
As Lycaena nisa was published three years prior to Herrich-Schäffer's Lycaena alsulus, it takes the priority, and should be the valid name, invoking Article 23.1 of the ICZN (1999: 24). Although the name alsulus has been used for this lycaenid butterfly in the literature more than 25 times in the last 50 years, it would be inappropriate and insensitive to make efforts to suppress or abandon a name established by Wallace himself. Moreover, L. nisa was used as a valid name by Matsumura (1909) after 1899, thus the condition for reversal of precedence ruled by Article 23.9.1 (ICZN 1999: 27) is not met. In the present article, Lycaena nisa Wallace is resurrected as the valid name for this lycaenid, with a list of its synonyms.

Materials and methods
Type specimens relevant to the study were examined in the Natural History Museum, London (NHMUK) and the Taiwan Agricultural Research Institute, Taichung (TARI). Additional specimens were collected for comparison from Australia, Hong Kong and Hainan, with vouchers deposited in the Department of Life Science, National Taiwan Normal University, Taipei (NTNU).

Lectotype of Lycaena nisa
Female (Figs 1, 2). Forewing length 10.9 mm. Head hairy, brown, with medial white band on frons. Antennae dark brown, segmented with white. Proboscis brown. Labial palpus hairy, porrect; third segment slender, pointed at distal end, white but brown dorsally. Compound eyes smooth. Thorax and abdomen dark brown dorsally, white ventrally. Forewing broad, somewhat elongate, termen slightly convex. Hindwing rounded. Wing uppersides uniformly brown. Wing undersides ground color white tinged with gray, spotless except for presence of submarginal bands consisted of faint narrow bands proximally and a series of faint brown spots distally along termen of both wings; dot in cell CuA 1 prominent, black. Fringe white.

Holotype of Lycaena taiwana
Male (Figs 4, 5). Forewing length 10.9 mm. Morphology conformed to those of L. nisa, except metallic purple patches present on uppersides of both wings proximally and those on hindwings.
Holotype of Zizeeria alsulus eggletoni Male (Figs 7, 8). Forewing length 11.4 mm. Morphology conformed to those of L. nisa, except metallic purple patches present on uppersides of both wings proximally, and those on hindwings; submarginal bands on wing undersides slightly paler than those of L. nisa and L. taiwana.
Distribution. This species occurs in the Oriental and Australian regions, and western Pacific, including southern China, Taiwan, the Philippines, Thailand, Sulawesi, Australia, the Torres Strait islands, Vanuatu, Fiji, Samoa, and Tonga (Eliot 1973;Braby 2000;Vane Wright and de Jong 2003;Ek-Amnuay 2012).  (Bascombe et al. 1999;Braby 2000Braby , 2016. Life histories are illustrated and described in Bascombe et al. (1999). Eggs are laid near flowers, upon which the larvae feed. Facultative mymecophily does occur.

Discussion
Famegana nisa dwells on open, grassy habitats, as suggested by its common names 'Grass Blue' (e.g., Kimura et al. 2014), 'Small Grass Blue' (e.g., Bascombe et al. 1999) or 'Black-spotted Grass Blue ' (e.g., Braby 2000;Orr and Kitching 2010). This habitat is shared with members of several Polyommatinae, such as Zizeeria, Zizula or Zizina, but Famegana can easily be distinguished by its uniformly grayish white undersides of wings, with a single prominent black spot in the cell CuA 1 of hindwing, and obscure submarginal bands (Common and Waterhouse 1981;Bascombe et al. 1999;Braby 2000;Orr and Kitching 2010). Its male genitalia are also peculiar (Common and Waterhouse 1981), leading Eliot (1973) to establish a monospecific genus for it, stating "unlike those of any other species known to me, the principal peculiarity being the very stout brachia which are hinged wholly to the lateral processes of the tegumen and are capable of only limited movement". The male genitalia of the species have been illustrated in the literature, including Shirôzu (1960), Eliot (1973), and Bascombe et al. (1999) and are unique in the family Lycaenidae. Although up to four subspecies have been recognized, this species is poorly marked and seasonably variable in wing pattern, and subspecific delimitation is perhaps unnecessary for this species. Specimens in dry season have a reduced black spot, darker ground color on wing undersides, and more distinct submarginal bands on the hindwing undersides (Figs 14-17) when compared to those in wet season (Figs 10-13) according to Bascombe et al. (1999) and Braby (2000).
In addition to the name Lycaena nisa of Wallace, another name from Taiwan is available for the species, Zizera taiwana Sonan, 1938. Shirôzu (1944 pointed out that Z. taiwana is conspecific with Z. alsulus based on examination of the male genitalia, but retained taiwana as a subspecies of Z. alsulus. However, as mentioned above, there is no doubt that Z. taiwana represents a junior subjective synonym of L. nisa. Moreover, the population from southern China has been assigned to ssp. eggletoni Corbet, 1941, originally described from Hong Kong (Bascombe et al. 1999). As already pointed out by Shirôzu (1944), the specimens from Hong Kong (Figs 14-17), however, are indistinguishable from those from Taiwan (Figs 1-6). Consequently, eggletoni Corbet, 1941 should also be regarded as a junior subjective synonym of L. nisa Wallace, 1866.

Acknowledgments
This study was financially supported by grants of Taiwan Forestry Bureau, COA, Taipei, Taiwan, 101-FM-2.1-C-12 and 107-FD-8.2-C-16(1). The author thanks George Beccaloni and Blanca Huertas (NHMUK) for locating type specimens in the Wallace collection under their care, and for permission to use the photographs of the types. Chi-Feng Lee (TARI) helped locating type specimens in the Sonan collection. Michael Braby (The Australian National University, Acton) and Philip Lo (Kadoorie Farm, Hong Kong) kindly assisted in field work. Jia-Yuan Liang (NTNU) prepared the plates. I also express my cordial thanks to Rienk de Jong (Naturalis Biodiversity Center, Leiden), Toshiya Hirowatari (Osaka Prefecture University, Osaka), and Erik J Van Nieukerken (Naturalis Biodiversity Center, Leiden) for giving many useful comments.