Convergent evolution of the lateral line system in Apogonidae (Teleostei: Percomorpha) determined from innervation

Abstract

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.

The paedomorphic lateral line system in Pseudamiops and Gymnapogon (Percomorpha, Apogonidae), with morphological and molecular‐based phylogenetic considerations

“… Pseudamia gelatinosa , canal and superficial neuromasts (stained with 4‐Di‐2‐ASP) in increasing sizes: (a) 17.3 mm SL (BSKU 127152); (b) 20.2 mm SL (BSKU127151); (c) 30.5 mm SL (BSKU1271510); (d) 61.0 mm SL (BSKU123521; from Sato et al, 2019). Scale bar = 10 mm.…”

“… Pseudamia gelatinosa , lateral line canals and neuromasts on the head in increasing sizes: (a) 17.3 mm SL (BSKU 127152); (b) 20.2 mm SL (BSKU127151); (c) 30.5 (BSKU1271510); (d) 61.0 mm SL (BSKU123521; from Sato et al, 2019). Gray – Canals; dark gray – Pore openings; large dark blue dots – Canal neuromasts or presumptive canal neuromasts; small dots – Superficial neuromasts (yellow dots – dh [= dorsal head] group; dark green dots – no [= nostril] group; orange dots – ch [= cheek] group; blue dots – pr [= preopercular] group; red dots – md [= mandibular] group; bright gray dots – gu [= gular] group; bright green dots – op [= opercular] group; black dots – pd [= predorsal] group and snl [= longitudinal row] subgroup of trunk lateral line system).…”

“… Pseudamia gelatinosa , lateral line system on the trunk, and dorsal, anal and caudal fins in increasing sizes: (a) 17.3 mm SL specimen (BSKU 127152); (b) 20.2 mm SL (BSKU127151); (c) 30.5 mm SL (BSKU1271510); (d) 61.0 mm SL (BSKU123521; from Sato et al, 2019). Large dark blue dots – Canal neuromasts or presumptive canal neuromasts; small dots – Superficial neuromasts (dark green dots – pd [= predorsal] group; orange dots – snt [= transverse row] subgroup; blue dots – snl [= longitudinal row] subgroup; red dots– df [= dorsal fin] group; light green dots– af [= anal fin] group; pink dots – cf [= caudal fin] group).…”

“…Apogonidae is a large percomorph family, including more than 370 species (Fricke et al, 2019), which inhabit mainly shallow coral reefs, sandy bottoms, or seaweed beds, although some groups occupy the deep sea or riverine habitats. The family is characterized by having many rows of SNs, the distribution pattern of SN rows being highly variable among taxa (Bergman, 2004; Sato et al, 2019). Mabuchi et al (2014) recognized four apogonid subfamilies, based on a molecular phylogenetic analysis: Apogoninae (14 tribes with 35 genera), Pseudamiinae ( Pseudamia ), Amioidinae ( Amioides and Holapogon ), and Paxtoninae ( Paxton ; molecular data unavailable).…”

“…Based on osteology, Pseudamiops had been considered phylogenetically close to Pseudamia (Fraser, 1972), while the latter genus was believed to be unique in having a double series of lateral line scales (plus a short series on the caudal fin base; Smith, 1954; Randall et al, 1985; Sato et al, 2019). However, Pseudamiops species have generally been referred to as having “no lateral line” (meaning no trunk canal) in most taxonomic descriptions (e.g., Gon et al, 2013; Mabuchi et al, 2014; Randall, 1998, 2001; Randall et al, 1990; Smith, 1954), the exception being Randall et al (1985), who noted that P. gracilicauda (Lachner, 1953) and two undescribed congeners had two series of inconspicuous lateral line scales, as in Pseudamia .…”