Morphological and physiological traits of Mediterranean sticklebacks living in the Camargue wetland (Rhone river delta)

Abstract

Three-spined sticklebacks (Gasterosteus aculeatus L.) living at the southern limit of the species distribution range could possess specific morphological and physiological traits that enable these fish to live at the threshold of their physiological capacities. Morphological analysis was carried out on samples of sticklebacks living in different saline habitats of the Camargue area (Rhone delta, northern Mediterranean coast) obtained from 1993 to 2017. Salinity acclimation capacities were also investigated using individuals from freshwater-low salinity drainage canals and from mesohalineeuryhaline lagoons. Fish were maintained in laboratory conditions at salinity values close to those of their respective habitats: low salinity (LS, 5‰) or seawater (SW, 30‰). Fish obtained from a mesohaline brackish water lagoon (BW, 15‰) were acclimated to SW or LS. Oxygen consumption rates and branchial Na + /K +-ATPase (NKA) activity (indicator of fish osmoregulatory capacity) were measured in these LS or SW control fish and in individuals subjected to abrupt SW or LS transfers. At all the studied locations, only the low-plated "leiurus" morphotype showed no spatial or temporal variations in their body morphology. Gill rakers were only longer and denser in fish sampled from the LS-freshwater (FW) drainage canals. All fish presented similar physiological capacities. Oxygen consumption rates were not influenced by salinity challenge except in SW fish transferred to LS immediately and 1 h after transfer. However, and as expected, gill NKA activity was salinity dependent. Sticklebacks of the Camargue area sampled from habitats with contrasted saline conditions are homogenously euryhaline, have low oxygen consumption rates and do not appear to experience significantly greater metabolic costs when challenged with salinity. However, an observed difference in gill raker length and density is most probably related to the nutritional condition of their habitat, indicating that individuals can rapidly acclimatize to different diets.

Diversity and sexual dimorphism in the head lateral line system in North Sea populations of threespine sticklebacks, Gasterosteus aculeatus (Teleostei: Gasterosteidae)

“…As the freshwater ecotype evolved from the anadromous type (Schluter and Conte 2009), the marine type is ancestral to the anadromous ecotype (Dodson et al 2009). Despite longlasting research on threespine stickleback radiation (Raeymaekers et al 2005;Spoljaric and Reimchen 2011;Leinonen et al 2011;Aguirre and Bell 2012;Svanbäck and Schluter 2012;Wund et al 2012;Vila et al 2017) virtually nothing is known about the behavior and the habitat of the marine type (Demchuk et al 2015;Ivanova et al 2016;Ahnelt 2018;Lajus et al 2019;Rind et al 2020). However, knowledge of the ancestral form, its intraspecific variability and polymorphism, provides insight into radiation patterns, and thus might help explaining why the same phenotypes have evolved repeatedly under similar environmental constraints (Schluter 1996;Walker and Bell 2000;Pfennig et al 2010).…”