Abstract
Morphological differences associated with sex or stage, together with total lipids and carotenoids, were studied in Euphausia superba as possible indicators of physiological condition. E. superba displays sexual dimorphism during growth. A group of mature males, called Males II herein, has a greater abdominal length, suggesting that they are faster swimmers, a feature implying higher metabolic rates and a higher demand for protecting pigments like carotenoids. Mature Males II have proportionally lower lipids but higher total lipid-soluble carotenoids, a counterintuitive finding. Males II also have bigger eyes. Significant regressions with carotenoids were found for wet weight, abdominal length, and eye diameter. On a spatial analysis, population composition reflects reproductive activity. Males II would be in search of females for fecundation and, thus, are dominant in some areas. The PCA analysis of 10 allometric and biochemical variables show a distinct Males II group differing in morphology, carotenoids, and lipid contents. The carotenoid:lipid ratio was highest for Males II, supporting the hypothesis of the role of carotenoids in the activity of the species. Mature males may experience physiological stress during reproduction and probably die shortly afterwards. A relationship between activity, morphometrics, and carotenoid content seems evident, deserving further investigation.
Highlights
Morphological differences associated with sex or stage, together with total lipids and carotenoids, were studied in Euphausia superba as possible indicators of physiological condition
In order to determine the longevity of E. superba and T. macrura—the dominant and coexisting species during summer in the southern part of the Indian Ocean, a multivariate study including morphological information showed that total lipids and total carotenoids differ in quantity across development stages, assuming a 4-year life cycle based on morphometric, lipid, and carotenoid data, and a two-year life cycle for T. macrura
Carotenoid levels were highest in Males II, lowest in Juveniles, and intermediate in Males I, Mature Females, and Spent Females, in either per-individual or per-g (Table 2) basis
Summary
Morphological differences associated with sex or stage, together with total lipids and carotenoids, were studied in Euphausia superba as possible indicators of physiological condition. The allometric relationship of total length vs wet weight for Males II showed a steeper slope and a higher condition coefficient relative to the other sex or development stages; a spatial analysis revealed geographic differences beyond those related to sex or development stage[11]. We assumed a faster swimming capacity in mature Males II, which are expected to be more active in search of females for fecundation during the reproductive season in summer. The population sex ratio was found to be largely influenced by the swimming capacities of males and females, and may contribute to the segregation of different sexes or development stages within swarms of E. superba[13,15,16]; a faster growth rate was observed in males than in females during the Antarctic summer[17]. A reanalysis of body shrinkage during winter in E. superba in its natural habitat as compared to animals reared in aquaria[18] found that it occurred only in females, but not in m ales[19]
Sign-in/Register to view highlights & summary 
Published Version (
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