Morphological Evolution of the Cave-, Spring-, and Swampfishes of the Amblyopsidae (Percopsiformes)
The Amblyopsidae is a small family of fishes from North America in which most of the species occur in caves. Despite considerable interest and study by biologists, a comprehensive morphological phylogenetic analysis of the family has not been conducted to date. We examined the skeletal morphology of all six genera and recognized species, which included 66 characters. The resulting phylogeny was compared to morphological- and molecular-based phylogenies of previous studies. Results showed a progression of cave adaptation that was significantly different from previous phylogenetic studies. Amblyopsidae was supported by 34 synapomorphies of the skeleton, but relationships within the Amblyopsidae were comparatively weak. The relationships of amblyopsids are likely influenced by morphological convergence as well as changes in the timing of development of some characters. Heterochrony is most visible in the unfused bones of the dorsal portion of the skull. The sister group to Amblyopsidae is Aphredoderidae (pirate perches), and the main character that supports this relationship is the presence of a unique set of upper jaw bones termed here lateromaxillae. This relationship is also supported by an anterior position of the vent, which is used for expelling gametes in Aphredoderus and for moving eggs to the gill chamber in Amblyopsis. It is more likely that Amblyopsis is the only branchial brooding amblyopsid and all other species likely exhibit transbranchioral spawning.
Lateral views of (A) epigean Chologaster cornuta (by David Neely), (B) stygophilic Forbesichthys agassizii (by Dante B. Fenolio), and (C) stygobiotic Typhlichthys subterraneus (by Jonathan W. Armbruster).
Previous phylogenies of the Amblyopsidae. (A) Woods and Inger (1957) morphological, pre-cladistic phylogeny, Speoplatyrhinus placed based on listed character states, (B) implied phylogeny of Poulson (1963) based on relative amounts of cave adaptation indicating the amount of time spent in caves, (C) Swofford (1982) phylogeny based on allozymes, dotted lines show the uncertain placement of Troglichthys as either sister to Amblyopsis or the trichotomy of Chologaster, Forbesichthys, and Typhlichthys, (D) Dillman et al. (2011) molecular phylogeny, (E) Niemiller et al. (2013a) molecular phylogeny, and (F) Grande et al. (2013) molecular phylogeny. Taxa colored according to habitat.
Important skeletal characters. (A–C) Basihyal and basibranchials, dorsal view. (D–E) Autogenous tooth bones along ceratobranchials, dorsal view. (F–G) Preopercles, lateral view. (A) Percopsis omiscomaycus, INHS 88030. (B, G) Amblyopsis hoosieri, INHS 42424. (C, D) Typhlichthys subterraneus, AUM 16045. (E) Forbesichthys agassizii, INHS 37654. (F) Aphredoderus sayanus, AUM 26377. Abbreviations: autogenous tooth bones (ATB), basibranchial 4 (BB4), basihyal (BH), preopercular serrae (POPS).
Ventrolateral view of right mandible. (A) Percopsis omiscomaycus, AUM 23034. (B) Typhlichthys subterraneus, AUM 16045. Abbreviations: angulo-articular (AA), dentary (D), medial lamina of dentary (MLD), medial process of angulo-articular (MPAA), orbital process of angulo-articular (OAA), retroarticular (RA). Teeth are approximated. Scale = 1 mm.
Dorsolateral view of right premaxilla (PM) and lateromaxillae (LM) of Forbesichthys agassizii, INHS 37654.
Lateral view of right hyomandibula. (A) Aphredoderus sayanus, AUM 31430. (B) Typhlichthys subterraneus, AUM 16045. Abbreviation: anterior process of hyomandibula (APH). Gray areas are cartilage, and black area is a foramen. Scale = 1 mm.
Lateral view of right opercle. (A) Percopsis omiscomaycus, AUM 23034. (B) Aphredoderus sayanus, AUM 31430. (C) Typhlichthys subterraneus, AUM 16045. Abbreviations: dorsal process of opercle (DPO), posterior process of opercle (PPO). Scale = 1 mm.
Dorsolateral view of left posttemporal. (A) Aphredoderus sayanus, AUM 31430. (B) Typhlichthys subterraneus, AUM 16045. Abbreviations: posttemporal (PT), ligament of the ventral arm of the posttemporal (PTL). Scale = 1 mm.
Single most parsimonious tree (L = 76 steps, CI = 0.895, RI = 0.881). Numbers above the branches are the number of unambiguous changes along the branch. Numbers below the branches are Bremer Decay Index Values/Bootstrap Values. Taxa colored according to habitat.
Dorsal view of the skull of Typhlichthys subterraneus, AUM 16045, showing the crenulate, overlapping borders of the frontals (F) as well as the junctions of the frontals, pterotics (P), and supraoccipital (SO). Other indicated bones are the infraorbitals (IO), lateral ethmoid (LE), and mesethmoid (ME). Photo by Pamela B. Hart and Charles D. R. Stephen.
Contributor Notes
Associate Editor: T. Grande.