Parasymmela, Pacheco & Monné & Vaz-de-Mello & Ahrens, 2022

Pacheco, Thaynara L., Monné, Marcela L., Vaz-de-Mello, Fernando Z. & Ahrens, Dirk, 2022, First non-feeding Sericini beetles (Coleoptera, Scarabaeidae): new genus from Amazonia and phylogenetic position, Organisms Diversity & Evolution (New York, N. Y.) 22 (3), pp. 733-748 : 745-746

Nonfeeding in Parasymmela , other Scarabaeoidea , and evolutionary implications

Compared to the known number of species of scarabs, reported cases of non-feeding are rather rare ( Table 1). A short discussion of non-feeding in scarabs appear to be worthwhile in order to highlight the importance of the record of these two non-feeding Sericini species in the Amazon region. Among scarabs, we may distinguish between facultative non-feeding and obligatory non-feeding. While the first have fully developed mouth parts, the latter show a number of reductions as a consequence of the omission of feeding.

Most of the records of the facultative non-feeding scarabs are from the postglacially reoccupied areas such as central Europe, and a few others, for the biodiverse areas of the world (the few registered cases for the latter, could be due to the difficult detection of non-feeding since species biology is not well known). While there seem to be no recognizable patterns for facultative non-feeding scarabs, obligatory non-feeding can be observed commonly in relict, even ancient, lineages that often contain only a very few species (e.g., Diphyllostoma , Pleocoma , Pachypus , see also Table 1). Often such relics are found in areas with temperate climate but stable climatic conditions (such as the southern part of the continents (southern South America and South Africa, Australia), or Mediterranean islands ( Pachypus ; Crovetti, 1969; Eberle et al., 2019b). Non-feeding is also often associated with loss of capacity of flight in at least one sex (female).

We assume that many of such non-feeding cases have not yet been recorded as such (due to lack of knowledge of species biology and of examination of mouthparts) and neither their phylogenetic position is likely being addressed appropriately in order to recognize them as isolated or relic lineages ( Eberle et al., 2019a). However, according to our present knowledge (which we suppose is very fragmentary), the case of a non-feeding Amazon species would not necessarily fit into that pattern of preferred occurrence of such non-feeding scarab species. Furthermore, since type series were composed only of males in both new species, we hypothesize that females are strongly restricted in their mobility.

One very interesting fact about this genus is that all specimens of the type species, Parasymmela amazonica sp. n., were found in feces of the cervid species Mazama gouazoubira (Fischer von Waldheim, 1814) which is, in contrast to the newly discovered Parasymmela , widely distributed in South America. Given the strong Latin American dung beetle scientific and collector community, it is very unlikely that the species is really associated with dung, but rather geographically restricted and only occasionally associated with feces. Mouth parts strictly exclude a feeding of adults on dung. One other case among supposedly dung-feeding melolonthines is Sparrmannia flava Arrow, 1917 , where the saprophagous larvae (!) (but not the adults) feed on antelope dung in desert habitats ( Scholtz, 1988). This could be also the case for the larvae of Parasymmela , but without further data in both cases, we can only speculate.

Morphology of mouth parts of Parasymmela clearly suggests that both species are non-feeding: galea without teeth or soft-skinned lobes for particle filtering; all setae on ventral side of labrum reduced; mandibles reduced in size and with small molar lobe.

The new genus apparently is closely related to Symmela , which would suggest a rather young age compared to all other South American Sericini genera (i.e., Astaenina ). On the other hand, the number of autapomorphies of Parasymmela is considerable (some not included in this data set for phylogenetic analysis, see above), which makes a more basal position among Astaenina more likely. However, to resolve this question, a detailed molecular phylogeny including all genera must be completed.