Sperm competition, sexual selection and the diverse reproductive biology of Osteoglossiformes

Abstract

Osteoglossiformes are an order of “bony tongue” fish considered the most primitive living order of teleosts. This review seeks to consolidate known hypotheses and identify gaps in the literature regarding the adaptive significance of diverse reproductive traits and behaviour of osteoglossiforms within the context of sperm competition and the wider lens of sexual selection. Many of the unusual traits observed in osteoglossiforms indicate low levels of sperm competition; most species have unpaired gonads, and mormyroids are the only known vertebrate species with aflagellate sperm. Several osteoglossiform families have reproductive anatomy associated with internal fertilization but perform external fertilization, which may be representative of the evolutionary transition from external to internal fertilization and putative trade‐offs between sperm competition and the environment. They also employ every type of parental care seen in vertebrates. Geographically widespread and basally situated within teleosts, osteoglossiforms present an effective study system for understanding how sperm competition and sexual selection have shaped the evolution of teleost reproductive behaviour, sperm and gonad morphology, fertilization strategies, courtship and paternal care, and sexual conflict. The authors suggest that the patterns seen in osteoglossiform reproduction are a microcosm of teleost reproductive diversity, potentially signifying the genetic plasticity that contributed to the adaptive radiation of teleost fishes.

Feasibility of In Vivo Semen Collection and Description of the Morphology and Ultrastructure of the Spermatozoa of Arapaima gigas (Schinz, 1822)

“…So far, a great variety of sperm types have been described within Osteoglossiformes, such as monoflagellated sperm in Pantodontidae and Notopteridae, biflagellate in Osteoglossidae and aflagellate in Mormyrydae and Gymnarchidae [6]. Our findings for A. gigas support the biflagellate character previously assigned to Osteoglossidae based on H. niloticus [7].…”

“…With the vast, divergent gross morphology of sperm structure, Mattei [4] found it difficult to correlate sperm morphology with taxonomic models in Teleostei. Within Osteoglossiformes, tremendous variability has been reported with families having either monoflagellate (Pantodontidae and Notopteridae), biflagellate (Osteoglossidae) or even aflagellate (Mormyridae and Gymnarchidae) spermatozoon types [6,7]. Although bearing aflagellate spermatozoa suggests internal fertilization, species such as Mormyridae and Gymnarchidae have external fertilization with low sperm competition [8,9].…”

“…Although bearing aflagellate spermatozoa suggests internal fertilization, species such as Mormyridae and Gymnarchidae have external fertilization with low sperm competition [8,9]. Monoflagellate spermatozoa are the most frequently found type among teleosts, described for species with internal fertilization and external fertilization [6,10]. The presence of biflagellate spermatozoa is widespread in the animal kingdom from flatworms to mammals [5,11]; however, in fishes, the biflagellate condition seems to be less frequent and has only been described for over 16 families from seven orders [10].…”

A review of the reproductive biology of mormyroid fishes: An emerging model for biomedical research

“…Despite this, mormyroid GSI, similar to other Osteoglossiformes (Adite et al, 2006; Hussain et al, 2015), is generally considered low, especially male GSI. However, as Koenig and Gallant (2021) state, it is unclear how these low GSI values compare to other teleost species because, again, many authors do not report the phase of the reproductive cycle and, unlike many other teleosts, Osteoglossiformes have singular rather than paired gonads.…”

The Alimentary Tract of African Bony-Tongue, Heterotis niloticus (Cuvier, 1829): Morphology Study

“…It has also been found in swamps and floodplains, which proves its capability to survive in deoxygenated waters [ 3 , 6 , 7 ]. It belongs to the family Arapaimidae and represents the only species of the genus Heterotis [ 8 ]. Its basal position in the general fish phylogeny as Osteoglossiforms put it in an important taxon of interest for evolutionary processes studies [ 9 ].…”