Abstract
Digitaria digitaria, a small astartid usually less than 10 mm in length, has a non-brooding behaviour in spite of its limited space for gonad development. This species lives in highly unstable environments with strong currents, which represent a challenge for fertilization and larval settlement. The studied population of D. digitaria from the Strait of Gibraltar area was dioecious, with significant predominance of females and sexual dimorphism, where females are larger than males. The reproductive cycle is asynchronous throughout the year, without a resting period, but with successive partial spawning events. The presence of stored sperm in the suprabranchial chamber and inside the gonad of some females, together with the release of eggs along the dorsal axis of both gills, points to internal oocyte fertilization. Bacteriocytes were found in the female and male follicle walls, but no bacteria were observed inside any of the gametes. Digitaria digitaria could represent a “missing link” between spermcast mating bivalves with brooded offspring and bivalves with broadcast release of eggs and sperm. The small size, limiting the oocyte production, together with the unstable environment could represent evolutionary pressures towards sperm uptake in D. digitaria.
Highlights
Digitaria digitaria, a small astartid usually less than 10 mm in length, has a non-brooding behaviour in spite of its limited space for gonad development
Some additional specimens were collected in bioclastic and sandy bottoms between 15 and 25 m depth in the Mediterranean littoral of Mijas (Málaga province) (36°29′6′′N-04°41′30′′W). These specimens were used for performing dissections and additional Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) analyses
It was possible to identify the sex of 2,147 specimens, of which 1,031 (48.02%) were male and 1,116 (51.98%) female
Summary
A small astartid usually less than 10 mm in length, has a non-brooding behaviour in spite of its limited space for gonad development This species lives in highly unstable environments with strong currents, which represent a challenge for fertilization and larval settlement. The species with internal fertilization that require several hours of courtship to coordinate the transfer of gametes represent the other extreme[6] Between both reproductive behaviours there is a wide range of different types of sexual b ehaviour[7]. Females of spermcast species are selected to produce fewer but larger eggs that ensure a greater proportion of fertilized e ggs[14] Another hypothesis for the prevalence of brooding in small organisms is the oxygenation of the o ffspring[11]. Environmental factors may make brooding advantageous e.g. for polychaetes living in vent environments, the high acidification of seawater seems to be behind parental care or lecithotrophic development of the dominant s pecies[20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
