Larval biomass and chemical composition at hatching in two geographically isolated clades of the shrimpMacrobrachium amazonicum: intra- or interspecific variation?

Abstract

The shrimp Macrobrachium amazonicum (Heller 1862) has an extremely large geographic range (44000 km across) in northern and central South America, comprising estuarine and fully limnic inland populations, which are hydrologically isolated from each other. Significant variations in ecology, physiology, reproduction, and larval development suggest an at least incipient allopatric speciation due to limited genetic exchange. In a comparative experimental investigation with shrimps from the Pantanal (upper Paraguay River basin) and the Amazon delta, respectively, we measured larval body size, dry weight (W), biochemical (total protein; lipid; fatty acids, FA), and elemental composition (carbon, hydrogen, nitrogen; collectively CHN) at hatching. All these early larval traits are relevant for the degree of developmental dependence on planktonic food sources. Various consistent differences were observed between the two populations: Newly hatched larvae produced by shrimps from the Amazon delta were significantly smaller and showed lower values of W, CHN, protein, and unsaturated FA compared to those from the Pantanal. On the other hand, they contained significantly higher quantities of total lipid and saturated FA and, in consequence, higher ratios of lipid:protein, C:N, and saturated:unsaturated FA. All these differences in biomass and chemical composition suggest that the larvae of the Amazon population are energetically better adapted to planktonic food limitation, which likely occurs during riverine downstream transport toward coastal marine waters, also explaining previous observations of much stronger initial starvation tolerance in larvae from the Amazon versus those from the Pantanal. The latter develop in highly productive lentic inland waters, where large body size, an early onset of feeding, and a strong musculature (indicated by a high protein content) should facilitate their role as planktonic predators and allow for fast growth. An initial independence from food (lecithotrophy in the zoea I stage) as well as a preference for oligohaline rather than fully limnic conditions observed in the Pantanal larvae are interpreted as traits that have persisted from an ancestral coastal marine clade. Altogether, consistent ontogenetic differences between shrimps from the Pantanal and the Amazon estuary support the hypothesis that the taxon M. amazonicum comprises a complex of closely related but separate species.

Effect of salinity on the metabolism and osmoregulation of selected ontogenetic stages of an amazon population of Macrobrachium amazonicum shrimp (Decapoda, Palaemonidae)

“…This wide geographical distribution has as consequence the existence of distinct physiological, reproductive, behavioral, and ecological patterns among many populations. In relation to reproduction, Urzúa and Anger (2011) verified differences in biomass and chemical composition of larvae of M. amazonicum populations from Pantanal (state of Mato Grosso, Brazil) and Belém (state of Pará, Brazil). In relation to physiology, it is observed, among the different M. amazonicum populations, a curious pattern of brackish water dependence, in which there are either populations that complete their life cycle in fresh water (Zanders and Rodriguez, 1992;Charmantier and Anger, 2011) and those in which larvae die when kept in this salinity (Augusto et al, 2007a).…”

“…Charmantier and Anger (2011) compared two M. amazonicum populations hydrologically and genetically separated and verified distinct osmoregulation and tolerance to salinity patterns among them. Urzúa and Anger (2011) suggested that the existing biological diversity among M. amazonicum populations may happen due to the limited genetic exchange among them, a case of allopatric speciation. Although the studies about the genetics of different populations are still incipient, Vergamini et al (2011) verified that the genetic variability of coast and countryside M. amazonicum populations happen at an intraespecific level.…”

Growth, elemental and proximate biochemical composition of larval Amazon River prawn, Macrobrachium amazonicum, reared under different salinity conditions

“…For each sample, parallel determinations of dry weight (W) and contents of carbon (C), nitrogen (N), total lipid, and protein were carried out with standard techniques (Urzúa & Anger, 2011;Urzúa et al, 2012), considering these constituents as proxies of organic matter. Moreover, carapace length (CL) was microscopically measured in first-stage juveniles, indicating the increment in body size achieved during the period of total larval development.…”

Seasonal variations in larval biomass and biochemical composition of brown shrimp, Crangon crangon (Decapoda, Caridea), at hatching

“…Total length (TL), dry weight (W), elemental composition (CHN) and proximate biochemical composition (total protein and lipid) of newly hatched larvae Newly hatched larvae were taken in regular intervals (approximately monthly) for parallel determinations of total length (TL), dry weight (W), elemental composition (contents of carbon, hydrogen and nitrogen; collectively CHN) and proximate biochemical composition (total protein and lipid), which were measured with standard techniques (for recent description of details, see Urzúa and Anger 2011;Urzúa et al 2012). The energy content was estimated from biochemical data (Winberg 1971), because conversions from CHN data (Salonen et al 1976) tend to underestimate the energy content more strongly than conversions from biochemical composition (Anger 2001;Urzúa et al 2012).…”