Heterochrony in fringeheads (Neoclinus) and amplification of an extraordinary aggressive display in the Sarcastic Fringehead (Teleostei: Blenniiformes)

Abstract

The Sarcastic Fringehead (Neoclinus blanchardi, Teleostei) exhibits an extreme version of a common aggressive display, the "gaping display," in which an open mouth is presented toward an opponent. Males of this species have extremely long jaws that extend posteriorly well past the posterior margin of the head and are flared laterally during the gaping display. In this study, we explored morphological traits related to this extraordinary display in this and related species of blennies. Morphological modifications include enlargement of the buccopalatal membrane, elongation of the maxilla via an uncalcified posterior extension, and evolution of a novel hinge between the anterior maxilla and lacrimal bones permitting lateral movement of the upper jaw. Geometric morphometry using the truss network system, thin-plate spline, and PCA of three closely related species of Neoclinus indicate that the elongate maxilla of N. blanchardi most likely evolved via acceleration (faster growth compared to outgroups) and hypermorphosis (continued growth to a larger body size), both forms of peramorphic heterochrony. Coloration and fluorescence of the buccopalatal membrane may also serve to amplify the extraordinary gaping display of the Sarcastic Fringehead.

Function of an extraordinary display in sarcastic fringeheads (Neoclinusblanchardi) with comments on its evolution

“…In particular, this species has elongated maxillary bones with an unossified portion, extending well past the head in adult males. This trait, in combination with modified lacrimal bones that permit the upper jaw to be rotated laterally, enables the sarcastic fringehead to have a considerably wider gape than other related fishes that also perform a gaping display (Hongjamrassilp et al, 2018). In addition, the margin of the maxilla is yellow, and the buccopalatal membrane reflects ultaviolet light and is fluorescent.…”

“…These features are hypothesized to further enhance the display. Even though Hongjamrassilp et al (2018) described the special features related to the gaping display in sarcastic fringeheads and hypothesized the possible function of this display as a part of agonistic behavior, the real functions of this extraordinary gaping display have never been accurately quantified.…”

“…From a developmental perspective, the elongate jaws of the sarcastic fringeheads evolved via two forms of peramorphosis (Hongjamrassilp et al, 2018): acceleration, in which the growth of jaws of males is positively allometric compared to those of females (and males of other species of Neoclinus ), and hypermorphosis, in which the jaws grow relatively longer in this, the largest species in the genus. The underlying selection for large body size in this species is unknown.…”

“…Gaping displays that function in territorial defense are known in other species of Neoclinus (Murase & Sunobe, 2011), in other chaenopsids (e.g., Robins et al, 1959; P. A. Hastings, personal observation), and in other blenniiforms (e.g., Sazima et al, 2002). The uniquely exaggerated display in the sarcastic fringehead also serves this defense function (Hongjamrassilp et al, 2018), but epigamic selection (or intersexual selection) may have also played a role in elaborating this display, especially given the flexible, unossified posterior extension of the maxilla F I G U R E 1 (a) A sarcastic fringehead (Neoclinus blanchardi) guards its shelter, a wavy turban snail shell, which is important for its survival and reproduction. (b) A sarcastic fringehead signals to the conspecific intruder by gaping its mouth displaying a colorful membrane and teeth to the intruder.…”

Anatomy and ontogenetic changes of the facial and gular musculature of the tetra Astyanax brucutu: A remarkable case of adaptation to durophagy

“…Curiously, the opposite heterochronic event, paedomorphosis, has been more widely documented in the family and thought to have occurred multiple times during the characid radiation (Weitzman & Malabarba, 1998;Menezes & Weitzman, 2009;Pastana et al, 2020). Peramorphic events have been described in several other actinopterygian orders (e.g., Findeis, 1997;Gunter et al, 2014;Ivanyisky III & Albert, 2014;Hongjamrassilp et al, 2018;Webb, 1990;Bird & Webb 2014) but rarely involving myological features.…”