Adipose fin development and its relation to the evolutionary origins of median fins

Abstract

The dorsal, anal and caudal fins of vertebrates are proposed to have originated by the partitioning and transformation of the continuous median fin fold that is plesiomorphic to chordates. Evaluating this hypothesis has been challenging, because it is unclear how the median fin fold relates to the adult median fins of vertebrates. To understand how new median fins originate, here we study the development and diversity of adipose fins. Phylogenetic mapping shows that in all lineages except Characoidei (Characiformes) adipose fins develop from a domain of the larval median fin fold. To inform how the larva’s median fin fold contributes to the adipose fin, we study Corydoras aeneus (Siluriformes). As the fin fold reduces around the prospective site of the adipose fin, a fin spine develops in the fold, growing both proximally and distally, and sensory innervation, which appears to originate from the recurrent ramus of the facial nerve and from dorsal rami of the spinal cord, develops in the adipose fin membrane. Collectively, these data show how a plesiomorphic median fin fold can serve as scaffolding for the evolution and development of novel, individuated median fins, consistent with the median fin fold hypothesis.

A critical appraisal of appendage disparity and homology in fishes

“…In support of this hypothesis, although the developmental pattern for the anterior dorsal fin of most teleosteans is either bidirectional or directed anteroposteriorly for both radials and finrays, it has recently been shown that a third developmental pattern exists, exclusive to the spinous dorsal fin of Atheriniformes, whereby the pterygiophores sequentially develop in a posterior to anterior direction while the fin-rays develop in the opposite direction (Richter & Moritz, 2017). Finally, the adipose fin has also been proposed as a novel fin module that, as previously mentioned, might have evolved more than once (Stewart, 2015;Stewart et al, 2019Stewart et al, , 2014.…”

“…For the median fins ( Figure 2), a dorsal and anal fin module has been proposed based on the observations that these fins share a symmetrical position along the anteroposterior body axis in basal teleosteans and that they show similarities in developmental patterns (Mabee et al, 2002). Finally, the adipose fin has also been proposed as a novel fin module that, as previously mentioned, might have evolved more than once (Stewart, 2015;Stewart et al, 2019Stewart et al, , 2014. The anterior dorsal fin has been interpreted as a novel fin module in both chondrichthyans (Maisey, 2009) and actinopterygians (Mabee et al, 2002).…”

“…Indeed, median fins have been found to develop from a continuous fin-fold in lampreys (Freitas, Zhang, & Cohn, 2006), chondrichthyans (Ballard, Mellinger, & Lechenault, 1993) and actinopterygians (Abe, Ide, & Tamura, 2007;Bemis & Grande, 1999;van Eeden et al, 1996;Richter & Moritz, 2017). However, this may not always be the case as Stewart, Bonilla, Ho, and Hale (2019) have found that adipose fins in Characoidei develop from fin-buds that appear after the reduction of the median larval fin-fold. As for palaeontological evidence, the most basal vertebrates from the fossil record are described as having elongated median fins that extend over most of the dorsal and ventral aspects of the fish (Shu et al, 1999;Hou et al, 2002;Zhang & Hou, 2004).…”

Genome Sequencing of the Japanese Eel (Anguilla japonica) for Comparative Genomic Studies on tbx4 and a tbx4 Gene Cluster in Teleost Fishes

“…In fact, Acanthopterygii is named for the representative sharp and bony rays in their dorsal fins, anal fins or pelvic fins. Members of Siluriformes are armed with spines in the anal, dorsal, caudal, adipose, and paired fins [31,32,33]. Additionally, fin spines are characterized in some members of the Characiformes [34].…”

Development of the dorsal and anal fin in Kneria stappersii (Otomorpha: Gonorynchiformes)

“…Most non‐acanthomorph actinopterygians are characterised by the presence of one dorsal and one anal fin (Nelson et al, 2016). Exceptions are the Polypteriformes, which have a series of finlets, and some teleost taxa, such as Characiformes, Siluriformes, or Salmoniformes, that additionally have an adipose fin (Bender & Moritz, 2013; Stewart et al, 2014, 2019). While in Acipenseriformes each pterygiophore supports multiple fin rays, there is a one‐to‐one relation of pterygiophores and fin rays within Neopterygii (Grande, 2010; Grande & Bemis, 1998).…”