The world fauna of Synchroidae Lacordaire , 1859 ( Coleoptera , Tenebrionoidea , Synchroidae )

Synchroidae Lacordaire, 1859 is a taxonomically and biologically poorly known group. In the present paper, diagnostic characters used to separate genera are analysed and the phylogenetic relationships within this family are preliminarily investigated. Results suggest that the characteristic Synchroa pangu Hsiao, Li, Liu & Pang, 2016 can be removed to establish a new genus, Thescelosynchroa gen. nov. The new combination, T. pangu (Hsiao, Li, Liu & Pang) gen. et comb. nov., is proposed. The definitions of Synchroa Newman, 1838 and Synchroina Fairmaire, 1898 are revised. Moreover, morphological analysis and character comparison also suggest that the familial placement of Mallodrya subaenea Horn, 1888 is questionable. Six species are re-examined and rediagnosed: Synchroa chinensis Nikitsky, 1999, S. elongatula Nikitsky, 1999, S. formosana Hsiao, 2015, S. melanotoides Lewis, 1895, S. punctata Newman, 1838 and Synchroina tenuipennis Fairmaire, 1898. The male of S. chinensis and the female of S. formosana are described for the first time. Synchroa elongatula and Synchroina tenuipennis are newly recorded from Laos and Indonesia, respectively. We also hypothesize that the Eastern Asian-North American disjunction of Synchroa could be connected to a Mid-Late Tertiary migration of plants via the Bering Land Bridge.


Introduction
Synchroidae Lacordaire, 1859 is a small family, including only nine extant species subdivided amongst three genera (Nikitsky 1999;Hsiao 2015;Hsiao et al. 2016); the fossil record includes only one species from the Eocene Florissant Formation of Colorado (Wickham 1911).Comparative morphological studies of larval characters suggest that synchroids may be more closely related to Zopheridae and Stenotrachelidae than Melandryidae, although adult synchroids and melandryids are extremely similar in overall appearance (Böving & Craighead 1931;Crowson 1966).Synchroidae was recovered as sister to a clade including Pterogeniidae, Tetratomidae, Mycetophagidae, Archeocrypticidae, Chalcodryidae, Promecheilidae and Ulodidae (McKenna et al. 2015) although the results are not exhaustive due to the low number of species included in the analyses.
Synchroids are generally poorly known and notoriously difficult to collect, except Synchroa punctata Newman, 1838 and S. melanotoides Lewis, 1895.Furthermore, the majority of the species were described based on a single or few specimens, including females, and diagnostic characters and intraspecific variation have been scarcely considered.During our study more specimens of previously described species were examined.This paper aims to provide precise information on the morphology of Synchroidae, with major emphasis on the diagnostic characters.Synchroa chinensis Nikitsky, 1999, S. melanotoides Lewis, 1895, S. punctata Newman, 1838 and Synchroina tenuipennis Fairmaire, 1898 are redescribed, and the male of S. chinensis and female of S. formosana Hsiao, 2015 are described for the first time.Synchroa elongatula Nikitsky, 1999 and Synchroina tenuipennis are newly reported from Laos and Indonesia, respectively.The previously established key for the identification of Synchroidae (Nikitsky 1999;Hsiao 2015;Hsiao et al. 2016) is modified.In addition, a morphologybased phylogenetic analysis including all described taxa of Synchroidae is performed.The results reveal that Synchroa pangu Hsiao, Li, Liu & Pang, 2016 cannot be assigned to any previously described genus.Together with the morphological comparison, we herein separate this species to establish a new genus, Thescelosynchroa gen.nov., with a new combination proposed: T. pangu (Hsiao, Li, Liu & Pang, 2016) gen.et comb.nov.Furthermore, a preliminary and brief discussion of familial placement of Mallodrya subaenea Horn, 1888 and the biogeography of the family are provided.

Material and methods
All specimens examined in this paper are deposited in the following institutions and private collections: Terminology for morphology used in the paper follows Ślipiński & Lawrence (2010) and Hsiao (2015).
Abdomens detached from the body were kept in 20% KOH for 1-2 hours before observation.Elytra were detached and placed in 75% alcohol to make the elytral striae clearer to examine.Photographs and measurements were produced following Hsiao (2015) and Hsiao et al. (2016).The distribution map was prepared using the SimpleMappr program (Shorthouse 2010).
In the resultant trees, the unsupported nodes were hard collapsed and only the best trees were kept in WinClada.The characters and character states on the tree were optimized using unambiguous character changes in WinClada.

Character analysis
Diagnostic characters of Synchroidae and intergeneric/intraspecific variation are listed and discussed as follows: 01 Body size.Synchroa species are mostly 10.0-13.0mm although a few exceptional specimens are ca 8.0-9.0 mm.The length varies from 7.0-9.0mm in Synchroina and from 6.0-8.5 mm in Mallodrya according to the original description (Horn 1888).02 Body form.Mallodrya is characterized by its elongate, oblong and somewhat convex body, which is widened posteriorly.It is similar to melandryid genera such as Melandrya (Melandrya) Fabricius, 1801 and M. (Emmesa) Newman, 1838 (Horn 1888).Synchroa (excl.S. elongatula Nikitsky, 1999 andS. pangu Hsiao, Li, Liu &Pang, 2016) and Synchroina are similar in overall appearance, with the length ca 3.4-3.6times as long as maximum width and flat body.S. elongatula and S. pangu are more slender, with the length ca 3.8-4.0times as long as maximum width.
05 Eyes.Eyes are lateral, oval, and emarginate in front of antennal insertions in synchroids, with long interfacetal setae (excl.Mallodrya).The eyes are large in Synchroa (excl.S. pangu), with ratio of eye diameter to interocular space ca 1.2-1.7 and small in Synchroa pangu and species of Synchroina, with ratio of eye diameter to interocular space ca 1.8-2.2.The eyes of Mallodrya subaenea are similar to other synchroids, but very small, lacking long interfacetal setae, with a ratio of eye diameter to interocular space ca 3.0.European Journal of Taxonomy 407: 1-33 (2018) 06 Shape of pronotum.In Synchroa (excl.S. pangu), the lateral sides of the pronotum are strongly narrowed anteriorly; anterior edge is ca 0.50-0.60 times as long as posterior edge; the posterior edge is unmargined; pronotum is as wide as elytra at humeri (Fig. 2A).Synchroa pangu can be distinguished from its congeners on the basis of the following character combination: feebly arcuate lateral sides; anterior edge ca 0.65 times as long as posterior edge; unmargined posterior edge; pronotum narrower than elytra at humeri (Fig. 2B).The lateral sides of the pronotum of Synchroina are somewhat rounded; anterior edge is ca 0.60-0.70times as long as posterior edge; posterior edge is unmargined; pronotum is as wide as elytra at humeri (Fig. 2C).Although the shape of pronotum  07 Elytral striae (Fig. 2I).Nikitsky (1999) used elytral striae as a diagnostic character, followed by Hsiao (2015) and Hsiao et al. (2016).However, elytral striae of synchroids are dark brown and faint, difficult to observe in dried specimens and possibly leading to erroneous observations.To solve this problem, a new examination method has been developed (see Material and methods for details).Furthermore, we confirm that the intraspecific variation of elytral striae is notable after examining more specimens, which varies from obviously present to extremely indistinct (see the detail in description).It suggests that the variations of this character among specimens should not be overestimated for species delimitation in future works.
08 Prosternal process and procoxae.The prosternal process is laminate in Mallodrya, ending just before the posterior edges of procoxae, which is slightly projecting below prosternum and nearly contiguous.In Synchroa and Synchroina, the prosternal process is broad, markedly extending beyond procoxae, which is not projecting below prosternum and separated.The prosternal process is narrowed apically, with rounded apex in Synchroa (excl.S. melanotoides, S. pangu and S. punctata) and Synchroina (Fig. 2E).S. melanotoides, S. pangu and S. punctata have prosternal process with long oval apex (Fig. 2F).
09 Mesoventral cavity and mesometaventral junction.A mesoventral cavity and mesometaventral junction are absent in Mallodrya, but the former is moderately large, shallow and the latter usually a complex fitting in Synchroa and Synchroina.In Synchroa, the mesoventral cavity is distinctly punctate (Fig. 2G) while Synchroina species have smoother mesoventral cavity (Fig. 2H).
10 Pretarsal claws.The pretarsal claws of Synchroa and Mallodrya are simple and serrate in Synchroina.
11 Aedeagus (Fig. 2J).The shape of fused parameres and median lobe are diagnostic for species identification, although Synchroa punctata appears to be similar to S. melanotoides in aedeagus, and intraspecific variation is present in some species (see details in descriptions and figures).The median lobe of Synchroa (excl.S. pangu) is tapered apically, not exceeding from the apex of parameres in natural condition; on the other side S. pangu has a slender, elongate and clavate median lobe with an apex, extending over the apex of parameres.In Synchroina, the median lobe is elongate, clavate and slightly narrowed apically, not exceeding the apex of parameres.

Redescription
COlOur.Body and legs completely blackish-brown.Antennae brown in some specimens.
PrONOtuM.Truncate anteriorly, anterior edge slightly concave, bisinuate posteriorly, with obtuse median lobe, width ca 1.4-1.5 times as long as length, ca 1.6-1.7 times as wide as head.Lateral sides rounded and strongly narrowed in anterior two-thirds toward head, subparallel in posterior one-third, completely or almost completely margined.Anterior angle rounded; posterior angle rectangular and obtuse.Disc slightly flattened medially, surface lustrous, densely and coarsely punctate; spaces between punctures smaller than puncture diameter.Scutellum width ca 1.50-1.70times length.
PrONOtuM.Ca 1.5 times wider than length, ca 1.7 times as wide as head.
elytrA.Slightly wider than in male, as wide as pronotal width at humeri, length ca 2.5-2.6 times width.

Notes
This species is fairly common in eastern North America, found on tree bark or attracted to light.It can also be collected using Malaise or Lindgren funnel traps.Larvae develop in the moist environment beneath the bark of decaying woods (Payne 1931;Young 1991Young , 2002;;Majka & Pollock 2006;Ślipiński & Lawrence 2010).

Distribution
Eastern North America: USA, Canada.

Diagnosis
This species resembles Synchroa elongatula Nikitsky, 1999 in pronotal configuration with lateral sides of the pronotum margined in posterior one-third to one-fourth, but it can be also separated by its reddishbrown antennae and legs; stout elytra; prosternal process with long oval apex; aedeagus: paramere more slender, with lateral sides gradually narrowed apically.It resembles S. punctata in the shape of the aedeagus, but can be separated in the body being closely covered with yellowish simple setae; eyes larger; pronotum margined in posterior one-third to one-fourth of lateral sides; prosternal process thinner; dorsal groove of aedeagus narrower basally.

Material examined
JAPAN

Redescription
COlOur.Body completely blackish-brown.Antennae and legs somewhat reddish-brown.
PrONOtuM.Truncate anteriorly, anterior edge slightly concave, bisinuate posteriorly, with obtuse median lobe, width ca 1.4-1.5 times length, ca 1.5-1.6 times as wide as head.Lateral sides rounded and strongly HSIAO Y. et al., The world fauna of Synchroidae narrowed in anterior two-thirds toward head, subparallel in posterior one-third, margined in posterior one-third to one-fourth.Anterior angle rounded; posterior angle rectangular and obtuse.Disc slightly flattened medially, surface lustrous, densely and coarsely punctate; spaces between punctures smaller than puncture diameter.Scutellum width ca 1.4-1.6 times length.
PrONOtuM.Ca 1.5 times wider than length, ca 1.5-1.6 times as wide as head.
elytrA.Slightly wider than in male, as wide as pronotal width at humeri, length ca 2.5 times width.

Notes
This is a common species in Japan, which can be captured at light (S.Makita, personal communication).Larvae can be collected under the bark of decaying oak wood (Hayashi 1975) and walnut trees, Juglans mandshurica var.sachalinensis.Nikitsky (1999) mentioned that antennomere XI of this species is ca 2.5-2.8 times as long as the width, whose data were followed by Hsiao (2015) and Hsiao et al. (2016).However, our examination shows that this species has a wider variation in the length of antennomere XI than previously documented.

Diagnosis
This species resembles Synchroa formosana Hsiao, 2015 by the unmargined lateral sides of pronotum, but can be distinguished by the following combination of characters: blackish-brown body and reddishbrown to dark brown antennae, apical maxillary palpomere and tarsi; aedeagus: more slender paramere and narrower basal part of median lobe.

HSIAO Y. et al., The world fauna of Synchroidae
PrONOtuM.Truncate anteriorly, bisinuate posteriorly, with obtuse median lobe, width ca 1.5 times length, ca 1.6-1.7 times as wide as head.Lateral sides slightly rounded and strongly narrowed in anterior twothirds toward head, subparallel in posterior one-third, unmargined.Anterior angle rounded; posterior angle rectangular and obtuse.Disc slightly flattened medially, surface lustrous, densely and coarsely punctate; spaces between punctures smaller than puncture diameter.Scutellum with width ca 1.6-1.7 times length.

Remarks
In the original description, Nikitsky (1999) provided as diagnostic character the presence of faint striae only in apical part and illustrated it.This character together with the posteriorly narrowed elytra has been used in Hsiao (2015) and Hsiao et al. (2016) as comparative information to distinguish S. formosana.
European Journal of Taxonomy 407: 1-33 (2018) However, in the course of this study we discovered that the elytral striae are variable, noticeable on the entire elytron or even indistinct in some specimens.Elytral striae of synchroids are vague and difficult to observe accurately if the specimen is dry and not dissected, consequently it is possible that the elytral striae of the holotype have not been not observed correctly.After examining a large number of specimens, the shape of the elytra appears proved to be variable as well (length ca 2.4-2.7 times width).Therefore, we eliminate both inappropriate characters from the diagnosis and re-diagnose the differences between the species (see the detail in diagnosis and key).

Notes
This species was described based on a single female from Qingchengshan in Sichuan Province.On the basis of new available specimens S. chinensis is confirmed as a valid species, distributed in Shaanxi and Gansu province.

Notes
Although this species was described as having elytral striae in the basal half of the elytron, we discovered that the elytral striae are noticeable on the entire elytron (Fig. 4D) or indistinct in some specimens.Besides, elytral striae on each elytron vary from 4-7 traces in this species.On the other hand, we examined one specimen having narrower apical half of paramere than the holotype (Fig. 6L).After examination of the external morphological characters and the median lobe of the aedeagus, and in consideration of the intraspecific variation of other synchroids, we herein conclude that it is conspecific with S. formosana.

Diagnosis
This species resembles Synchroa melanotoides in pronotal structure, with lateral sides margined in posterior one-third to one-fourth, but it can be distinguished by its blackish brown antennae and legs; elongate and slender elytra; prosternal process narrowed apically; aedeagus: paramere wider, with lateral sides subparallel or sinuate.It is also similar to S. formosana, but differs in partially margined pronotum; aedeagus: basal part of median lobe narrower.Supplementary description of male from Laos (Fig. 3I)
PrONOtuM.Ca 1.5 times wider than length, ca 1.7 times as wide as head.
Parameres narrowly separated apically and with a groove in dorsal median part, lateral sides distinctly widened in middle, length ca 3.2 times maximum width.Median lobe elongate, tapered, strongly narrowed apically in apical half.

Notes
In the original description, this species was mentioned as having striae only in the apical part of the elytral suture.However, we discovered extremely indistinct elytral striae on this specimen.Together with our analysis of this character, it is possible that the elytral striae of the type series are too faint to observe or this character varies from absent to indistinct within this species.On the other hand, although most of the characters are in accordance with the original description, the parameres of this specimen are different from the illustration given in Nikitsky (1999)
PrONOtuM.Truncate anteriorly, bisinuate posteriorly, with obtuse median lobe, width ca 1.5 times length, ca 1.4-1.5 times as wide as head.Lateral sides slightly rounded and moderately narrowed in anterior two-thirds toward head, subparallel in posterior one-third, shortly margined basally.Anterior angle rounded; posterior angle rectangular and obtuse.Disc slightly flattened medially, surface lustrous, densely and coarsely punctate; spaces between punctures smaller than puncture diameter.Scutellum width ca 1.5-1.9times length.
elytrA.Elongate, narrowed posteriorly, apex rounded, as wide as pronotal width at humeri, length ca 2.6 times width, surface lustrous.Disc covered with oval punctures, denser in lateral and basal part; interspaces narrower as long as or slightly wider than puncture diameter.4-8 faint traces of striae in each elytron from dorsal view, stria I fused with II (Fig. 4F), gradually shortened outwards, elytral striae indistinct in some specimens.Prosternum before procoxae about as long as shortest diameter of procoxae.Prosternal process long, margined laterally, rounded and narrowed apically; length behind procoxae longer than width between procoxae.Width between procoxae ca 0.4 times transverse coxa diameter.Mesoventrite with shallow, oval mesoventral cavity, smooth.Abdominal ventrite V truncated apically, with terminal margin serrate and slightly concave, serrations at both sides larger than in middle, lateral sides nearly straight (Fig. 4L); sternite VIII concave in middle of apical edge, forming two hornshaped lobes curved inwards on both sides, densely pubescent apically (Fig. 5L); sternite IX without spiculum gastrale on apical edge (Fig. 5R); tergite VIII without median strut on apical edge, subtruncated apically, emarginate in middle, densely pubescent apically (Fig. 5K); tergite IX and X completely fused, rounded apically, densely pubescent on apical edge (Fig. 5R).
PrONOtuM.Ca 1.5 times wider than length, ca 1.5 times as wide as head.
elytrA.Slightly wider than in male, as wide as pronotal width at humeri, length ca 2.5-2.6 times width.
PrONOtuM.Truncate anteriorly, bisinuate posteriorly, with obtuse median lobe.Lateral sides rounded and narrowed in anterior two-thirds toward head, subparallel in posterior one-third.Anterior angle rounded; posterior angle rectangular and obtuse.
AedeAgus.Lanceloate.Parameres fused together forming apicale, narrowly separated apically and with a groove in dorsal median part.Median lobe long, slender and clavate, extending from the tegmen in natural condition.

Description
See details in Hsiao et al. (2016).

Notes
Two errata were present in the original description and are corrected as follows: (1) the ventral view of aedeagus was misplaced as dorsal view in figures 6-8; (2) transverse coxal diameter is 4.38 times width between fore coxae, rather than the width between fore coxae 4.38 times transverse coxa diameter.

China (Sichuan).
European Journal of Taxonomy 407: 1-33 (2018) diversification in Asia and dispersal of a branch to America is comparable in some cases of butterflies (Mullen 2006;Vila et al. 2011).The previous studies on the EA-NA disjunction primarily utilized plants as model organisms and the timing of most disjunctions could be dated to less than 30 Ma (Mid-Late Tertiary), which suggests vicariance over the Bering Land Bridge (Wen 1999;Sanmartin et al. 2001;Donoghue & Smith 2004;Ren et al. 2013).The studies of insects distributed in EA and NA, such as swallowtail butterflies of the Papilio elwesi species-group, support a dispersal route of the ancestor to Eurasia via the Bering Land Bridge (BLB) (Wu et al. 2015), and the cases of aphids and leaf beetles reveal a consistent biogeographic pattern with their host plants, highlighting the significance of host distribution for diversification (von Dohlen et al. 2002;Sota et al. 2008;Ren et al. 2013).Apart from its diversification in Eastern Asia, no species have been recorded in the western Palaearctic region.Given the wood-feeding on cambium of decaying deciduous trees during the immature stage (Payne 1931;Young 1991;Majka & Pollock 2006) and the fossil record from the Late Eocene Florissant Formation of Colorado (34.07 ± 0.10 Ma, Evanoff et al. 2001), which corresponds to closure of the BLB, it is likely that the EA-NA disjunction of Synchroa could also be related to plant migration through BLB during Tertiairy climate change, although synchroids are not specialized phytophagous insects such as aphids and the classification of the Eocene S. quiescens Wickham, 1911 may require reevaluation.
On the other hand, the endemic genus Synchroina of West Malesia (i.e., the area west of Wallace's line), possibly originated from the route through the Indo-Chinese peninsula, as is the case for most plants and animals distributed in this area (Turner et al. 2001).
However, due to a lack of recognized synapomorphies in the phylogenetic analysis, the relationships among the members of this family are not well resolved, which results in difficulties proposing a biogeographic scenario to explain their distribution pattern and evolution.A molecular approach could solve the problem of insufficient characters to give a higher resolution to the relationships and date the timing of Synchroa disjunction.Further studies of phylogeny and historical biogeography are badly needed and will give insight into the evolutionary history of Synchroidae.

1 Table 1 .
Data matrix.HSIAO Y. et al.,The world fauna of Synchroidae in Mallodrya is similar to that in Synchroina, it can be easily separated from other synchroids by distinctly margined posterior edge of pronotum.
basis of the following characters: body slender and elongate; pronotum narrower than elytra; anterior edge of the pronotum slightly concave in dorsal view; lateral margins of the pronotum feebly arcuate and unmargined; apex of prosternal process long oval.The character combination suggests that the species should not be placed into any previously established genus and assigned to a new one.
by its distinctly widened lateral sides and narrower dorsal groove, which implies that it could belong to another taxon new to science.Considering the insufficient material, intraspecific variation within other species and geographic distribution, we herein regard this specimen as representing a variation of S. elongatula instead of giving it a new taxonomic status.Synchroa and Thescelosynchroa gen.nov.; the differential diagnosis is given in Table2.