Investigating the features that facilitate sexual parasitism in male Anglerfishes (Teleostei, Ceratioidei)

Abstract

Deep-sea anglerfishes (Ceratioidei) remain some of the most enigmatic fishes in the world. The sexual dimorphism seen in this group is the most extreme example amongst vertebrates. Male anglerfishes develop a specialized jaw called the denticular apparatus that is used to attach to females for reproduction. There are many questions regarding the biological mechanisms that facilitate this type of reproduction. The goals of the present study are to (1) describe the origin and structure of the denticular apparatus in male ceratioids with emphasis on the family Melanocetidae; (2) examine the ontogeny of male melanocetids to better define the metamorphic patterns; and (3) document similarities or differences in the denticular teeth and dermal spinules between taxa. Our results illustrate how dermal spinules and tooth-like structures of the denticular apparatus should be classified as odontodes, which represents a sixth radiation of odontodes in teleost fishes. Here we show that ceratioid anglerfishes develop odontodes that function as both body spines and as a secondary sexual trait, and we confirm that the denticular apparatus is a unique part of the cephalic skeleton not seen anywhere else in teleosts. Furthermore, we document male ontogeny within the family Melanocetidae to better understand the formative patterns of the denticular apparatus. The arrangement of male and female anatomies represents two different examples of the extreme phylogenetic economy of morphological parts, with females evolving lures from existing fin rays and males evolving secondary jaws from existing body spinules – both as apparent adaptions to life in the bathypelagic zone.