Abstract
Among calyptraeid gastropods, males become females as they get older, and egg capsules containing developing embryos are maintained beneath the mother’s shell until the encapsulated embryos hatch. Crepipatella dilatata is an interesting biological model considering that is an estuarine species and thus periodically exposed to elevated environment-physiological pressures. Presently, there is not much information about the reproductive biology and brooding parameters of this gastropod. This paper describes field and laboratory observations monitoring sex changes, brooding frequencies, sizes of brooding females, egg mass characteristics, and embryonic hatching conditions. Our findings indicate that C. dilatata is a direct-developing protandric hermaphrodite, changing from male to female when individuals were between 18 and 20 mm in shell length. At our study site in Quempillén estuary, females were found to be brooding almost continuously throughout the year, having an average maximum of 85% of simultaneous brooding, with a short rest from April through June. No relationship was found between the number of capsules per egg mass and the size of the brooding female. However, capsule size and the number of embryos and nurse eggs were strongly related to female size. The offspring hatched with an average shell length > 1 mm. About 25% of the hatched capsules were found to contain both metamorphosed (juveniles) and non-metamorphosed (veliger) individuals. The sizes of the latter were < 1000 μm. The length of hatching juveniles was inversely related to the number of individuals per capsule, which seems related to differences in the availability of nurse eggs per embryo. Although fecundity per reproductive event of this species is relatively low (maximum approx. 800 offspring per egg mass) compared with those of calyptraeid species showing mixed development, the overall reproductive potential of C. dilatata seems to be high considering that females can reproduce up to 5 times per year, protecting their encapsulated embryos from physical stresses until well-developed juveniles are released into the population, avoiding a dangerous pelagic period prior to metamorphosis.
Highlights
Benthic marine invertebrates present a wide variety of reproductive patterns in their life histories [1,2]
We considered only those individuals with a shell length that was at least as large as that of the smallest brooding female found during each sampling period ( 18 mm shell length)
The analyses indicate that there were no significant differences between the total number of eggs deposited inside an egg mass (ANCOVA, F(3,61) = 2.401, p = 0.076) and inside an individual egg capsule (ANCOVA, F(3,61) = 1.383, p = 0.256), depending on the different seasons of the year
Summary
Benthic marine invertebrates present a wide variety of reproductive patterns in their life histories [1,2]. Through the release of gametes into the water column, where a free-swimming larva is generated, continuing its development until settlement and metamorphosis take place [3,4]. In these cases, there is no maternal care of their offspring. Females produce egg capsules and leave them alone, others brood their fertilized eggs until the embryos hatch, generating a close physical relationship between the mother and her offspring [5,6]. Through incubation, the capsules are physically protected by the mother [7,8,9], their multi-layered walls provide some extra levels of protection to the initial stages of development [2,10,11,12,13]
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