Euremini Grote, 1898

Zhang, Jing, Cong, Qian, Shen, Jinhui, Song, Leina & Grishin, Nick V., 2023, Butterfly classification and species discovery using genomics, The Taxonomic Report of the International Lepidoptera Survey 11 (3), pp. 1-94 : 9-10

Classification of the tribe Euremini Grote, 1898

The phylogenetic tree of the tribe Euremini Grote, 1898 (type genus Eurema Hübner, [1819] ) inferred from protein-coding regions in the nuclear genome (autosomes only) reveals strong statistical support (100% for most branches) and noticeable tree levels (resulting from coinciding diversifications in different clades at about the same distance from the root) to aid its higher classification ( Fig. 2). The level closest to the origin of the tribe consists of three prominent clades that we treat as subtribes: Nathalina Bálint, 2022 , stat. nov. (type genus Nathalis Boisduval, 1836 ), Kricogonina Bálint, 2022 , stat. nov. (type genus Kricogonia Reakirt, 1864 ) and the nominotypical, Euremina . The former two were originally proposed as tribes, but the early split of the subfamily Coliadinae Swainson, 1821 (type genus Colias [Fabricius], 1807) into two prominent clades argues for treating these clades as tribes ( Euremini and Coliadini ) rather than dividing them further. Therefore, further divisions would correspond to the subtribal level. The monotypic genus Prestonia Schaus, 1920 (type species Prestonia clarki Schaus, 1920 ) placed in Euremini by Zhang et al. (2021) is sister to Kricogonia and diverged from it approximately 27 million years ago (Mya), as estimated in Kawahara et al. (2023), which is close to the split of the subtribe Euremina into two clades (25 Mya). Due to this similar level of genetic differentiation between Kricogonia and Prestonia and between the two first clades of Euremina , Prestonia is placed in the subtribe Kricogonina rather than in a subtribe of its own. Such classification emphasizes the sister relationship of the two genera ( Kricogonia and Prestonia ) rather than the distinction between them.

While there is little doubt that the five known species in Nathalina and Kricogonina are best classified into the three genera corresponding to the most prominent clades in the tree ( Fig. 2), the taxonomy of the subtribe Euremina is more complex. Traditionally, the entire subtribe has been treated as a single genus Eurema Hübner, [1819] (type species Papilio delia Cramer, 1780 , a junior homonym, valid name for this species is Pieris daira Godart, 1819 ) ( Klots 1933). However, early DNA work suggested strong genetic differentiation within the subtribe ( Pollock et al. 1998), formalized by Opler and Warren (2002), who partitioned the US species into three genera: Eurema , Pyrisitia A. Butler, 1870 (type species Papilio proterpia Fabricius, 1775 ), and Abaeis Hübner, [1819] (type species Papilio nicippe Cramer, 1779 ). This split has been largely followed ( Lamas 2004; Pelham 2008), although some species have been reassigned between these genera (Zhang et al. 2019b). Our work (Zhang et al. 2019c; Zhang et al. 2019b) and more recent publications (Kawahara et al. 2023) support the notion of strong genetic differentiation within Euremina and date its diversification to approximately 25 Mya ( Fig. 2). This level of differentiation and age are too large for placing all Euremina in the single genus Eurema .

The subtribe Euremina splits into two prominent clades at approximately 25 Mya, as estimated by Kawahara et al. (2023). These two clades can be taken to represent genera, and the subtribe can be divided into two genera: Eurema and Abaeis . However, even this level of genetic differentiation and age would be larger than for most genera of butterflies ( Talavera et al. 2012; Li et al. 2019; Zhang et al. 2019a, c), and the ages between 15 and 20 Mya would be more consistent with the genus level. Even if absolute values of age estimates are not particularly accurate due to various errors, their relative values validity of such comparisons of estimated ages between nodes. For these reasons, we regard the two clades of Euremina as “sections”: the Eurema section and the Abaeis section, and take the next level in the tree to define genera.

The next tree level, dating to approximately 20 Mya, consists of five clades, one of which is entirely from the Old Word, the only Old Word group in the entire tribe Euremina ( Fig. 2 marked with red asterisk). We propose that these five clades represent genera in Euremina : Terias W. Swainson, 1821 (type species Papilio hecabe Linnaeus, 1758 ) and Eurema with its sister Pyrisitia A. Butler, 1870 (type species Papilio proterpia Fabricius, 1775 ) belong to the Eurema section, and Abaeis with Teriocolias Röber, 1909 (type species Terias atinas Hewitson, 1874 , a junior subjective synonym of Terias zelia Lucas, 1852 ) belong to the Abaeis section. This partitioning into genera is biogeographically significant because it reflects the invasion of the only Euremini lineage from the New World, where the tribe likely originated, into the Old World, giving rise to the genus Terias , followed by its extensive diversification. Genera of Euremina defined this way are analogous to Codatractus Lindsey, 1921 vs. Lobocla Moore, 1884 , Heliopetes Billberg, 1820 vs. Pyrgus Hübner, [1819] , and Oarisma Scudder, 1872 vs. Thymelicus Hübner, [1819] (in the latter two, pairs some species from the Old World genus returned to the New World at a later time) and correspond to similar geological time-frame of the mid-Miocene climatic optimum characterized by elevated biotic movement from America to Asia ( Jiang et al. 2019).

The phylogenetic tree ( Fig. 2) guides the assignment of species to genera, and we restore the monophyly by proposing new genus-species combinations: Pyrisitia amelia (Poey, [1852]) , comb. nov., Pyrisitia lirina (H. Bates, 1861) , comb. nov., Abaeis paulina (H. Bates, 1861) , comb. nov., Abaeis xantochlora (Kollar, 1850) , comb. nov., Abaeis fabiola (C. Felder & R. Felder, 1861) , comb. nov., Abaeis tupuntenem (Lichy, 1976) , comb. nov., Abaeis adamsi (Lathy, 1898) , comb. nov., Abaeis brephos (Hübner, [1809]) , comb. nov., and Abaeis elvina (Godart, 1819) , comb. nov. The latter two combinations reflect our treatment of Leucidia E. Doubleday, 1847 , stat. nov. (type species Pieris elvina Godart, 1819 ) as a subgenus of Abaeis despite its unique phenotype. Such treatment results in a more internally consistent classification because an Abaeis that includes Leucidia corresponds to a more prominent clade in the tree, and the Leucidia clade has split from the rest of Abaeis at the tree level corresponding to subgenera ( Fig. 2). This level allows us to define five subgenera in Euremina in addition to the five genera ( Fig. 2 and listed below). Finally, we note that Teriocolias doris (Röber, 1909) , stat. rest. (type locality in Bolivia), currently regarded as a subspecies of Teriocolias deva (E. Doubleday, 1847) (type locality in French Guiana), is genetically very distant from it: e.g., COI barcodes differ by 7.6% (50 bp) and is a distinct species.

Below is a proposed classification of the tribe Euremini . Only available genus-group names are listed; subspecies names are not given and can be found on the Butterflies of America website ( Warren et al. 2023), and the Old Word species are not provided (all belong to the genus Terias , which consists only of Old World species). Type genus (for family-group names) or type species (for genus-group names) names are given in parenthesis; synonyms are preceded by = and all but subjective synonyms also by ‡ with a valid name of this species following the colon. New taxa and status changes are shown in red font.