The rostrum shows a large variation across caridean shrimps; however, our knowledge about the biological significance of this morphological structure is very limited, and information on its genetic control is completely absent. The present study concentrates on an unusual rostral dimorphism in a population of small Mediterranean caridean shrimp and combines laboratory and field observations. Analysis of lab‐reared offspring supports the hypothesis that the post‐larval elongation of the rostrum is controlled by a single genetic locus, with the long dentate rostrum representing the recessive state and the short larval‐like rostrum representing the completely dominant state. The short rostrum is a sparsely distributed character; our results obtained from field studies suggest that it reduces the viability and probability of egg‐bearing among large females but, unexpectedly, the specimens with a short rostrum show consistently more rapid sex differentiation and a significantly higher propensity to become males. Therefore, it has to be concluded that, under certain conditions, a single emergent character could influence the species evolution in a rather complex manner, thus affecting the life history, population structure and dynamics and mortality in certain subgroups. In turn, the genetic factors responsible for the different phenotypes would tend to be segregated through different subpopulations and size classes, thus partially escaping the negative selective pressure.
The complete series of larval staging of Hippolyte sapphica d’Udekem d’Acoz, 1993 forma A and B from Louros estuary was studied in the laboratory and described in detail for the first time. The reared larvae of H. sapphica passed through six zoeal stages and one megalopal stage. The larval monitoring completed when the individuals could be assigned clearly to form A and B via rostra formation. Under the experimental conditions, the average durations of the larval stages were as follows: three days for 1 st and 2 nd stages, three to four days for 3 rd , 4 th , 5 th and 6 th stages, four days for the megalopal stage and 19 to 30 days for immature form A and B individuals. Comparison of the larval morphological characters among the described material and the bibliographic data of closely related species was made and discussed. The offspring of females of the forma A includes forma A and B and the same can be said of the offspring of the forma B. This confirms that the formae A and B are indeed conspecific.
The life history characteristics of AristotleÕs catfish, Silurus aristotelis (Agassiz 1856) were studied in Lake Pamvotis (northwestern Greece). Samples were collected on a monthly basis using gillnets, trammel-nets and traps. Total lengths ranged from 11.1 to 36.7 cm. Sex ratio was biased toward females (F : M = 1.8 : 1) and was statistically different from unity (v 2 = 46.94, P < 0.001). Spawning is from April to June. The relationship between total length and total weight showed positive allometric growth for males (TW = 0.0035 · TL 3.21 , r 2 = 0.93, n = 198, P < 0.001) and females (TW = 0.0066 · TL 3.02 , r 2 = 0.95, n = 363, P < 0.001). Age was determined on the annual growth marks formed on the spine of the pectoral fin. Based on cross-section readings of the spine, lifespan of the AristotleÕs catfish was 5 years. Age classes 1 and 2 dominated the catches (39.1 and 40.0% of the total sample, respectively). Back-calculated lengths at age showed a rapid increase in fish size during the first year of life, reaching 61.1% of maximum attainable length, and a declining growth rate thereafter. Growth parameters were calculated as L ¥ = 36.12 cm, K = 0.37 year )1 , t 0 = )0.76 year based on the observed lengths at age and as L ¥ = 28.19 cm, K = 0.53 year )1 , t 0 = )0.62 year based on the back-calculated lengths at age. It seems that some of the life history traits (longevity, growth pattern, reproductive period) are influenced significantly by adverse effects of pollution and eutrophication on the lacustrine ecosystem.
The shrimp Hippolyte sapphica has a unique and sharp rostral dimorphism: morphotype A with a well-developed dentate rostrum, and morphotype B with a short, juvenile-like toothless rostrum. Previous research has shown that both morphotypes/forms belong to the same species and co-occur in the same habitat. Both forms occur in both sexes; however, form B individuals have a higher tendency to become males. Moreover, form A females are characterized by prolonged viability. The present comparative morphometric study concentrates on the changes induced by the rostral dimorphism and interprets them in terms of eco-morphological adaptations. Results showed that (i) the rostral length was the most isometric among the studied morphometric variables; (ii) males of A and B forms were not significantly different morphometrically; (iii) unexpectedly, form A non-ovigerous females had more developed carapace, abdominal somites and appendages in comparison with form B and, finally (iv), form B ovigerous females had higher tail and scaphocerite lengths, suggesting that they overcome higher turbulent force during the rapid backward movements and that the long rostrum improves hydrodynamic streamlining and stability. In conclusion, the previous finding that form B individuals tend to become males receives an adaptational explanation. The gene(s) responsible for the short rostrum accumulate in males, where their micro-evolutionary disadvantage is minimal or even absent.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.