Role of population traits and local social interactions in sex-change plasticity of the protandric marine gastropod Crepidula coquimbensis

Abstract

Theoretical and experimental work suggests that time to sex change in sequential hermaphrodites may be strongly linked to local population traits and the social environment of the individuals. We evaluated social control and temporal and spatial plasticity in the sex-change response of the protandric marine gastropod Crepidula coquimbensis, which inhabits the empty shells of other gastropods and reproduces via direct development. Over 2 yr, 2 populations with significant genetic distance were sampled, and the abundance, population sex ratio, and sex ratio within hosting shells was measured. Reproductive responses, minimum female size, and the size at which 50% of the males changed sex to female (L 50 ) were calculated for each location and sampling date. The sex ratio was male-biased in all cases. High temporal and spatial variability in the abundance, sex ratio, and body size at sex change was observed. However, negative and significant correlations were found between minimum female size and number of males in the aggregation and between population sex ratio and L 50 . Although earlier studies have suggested that sexchange strategy of gastropod species with direct development is less plastic and responsive to conspecifics, the present work indicates that the protandric marine gastropod C. coquimbensis may adjust its sexual strategy to local social conditions. KEY WORDS: Sequential hermaphroditism · Life-history strategy · Size advantage · Population genetics · Sex ratio Resale or republication not permitted without written consent of the publisher

The relationship between sex change and reproductive success in a protandric marine gastropod

“…None of the individuals bypassed the male stage. Minimum shell length recorded for males was 4 mm and for females was 8 mm; this is in concordance with body sizes recorded in the field by Brante et al 24 at the same site.…”

“…Nevertheless, the aggregations of these two species differ in terms of their social structure. Specifically, it is common to observe more than two females and many males in C. fornicata aggregations while more than 85% of host shells in C. coquimbensis aggregations are occupied by only one female and two to four males 24 . From these observations, a conundrum arises considering the evolution of reproduction in C. coquimbensis .…”

“…The juveniles were fed twice a day with aliquots of cultured phytoplankton Isochrysis galbana . The sexual stage of the individuals was recorded weekly; the individuals were sexed according to the presence of sexual organs 24 37 . Males and females were classified by the presence or absence of a penis and female genital papilla ( Fig.…”

“…Males and females were classified by the presence or absence of a penis and female genital papilla ( Fig. 1a ); transitional individuals (changing from male to female) had both a penis and female genital papilla or were >8 mm and lacked a penis or female genital papilla 24 ( Fig. 1b ).…”

“…Studying two populations of C . coquimbensis , Brante and collaborators 24 found that the timing of sex change may depend on local population conditions; body size at sex change was negatively correlated with the number of males in the aggregation and the aggregation sex ratio 24 . In another study, paternity analyses using microsatellite markers indicated that most of the males in the aggregation participated in the brood but with different percentages of contribution 25 .…”