Muscle fibers, swimming and metabolic performance of landlocked and diadromous populations of the native fish, Galaxias maculatus, in southernmost Patagonia. First preliminary results

ROJO, J.H.; BOY, C.C.; LEFRANCOIS, C.; TERNON, Q.; RUBEL, M.D.

Ciudad Autónoma de Buenos Aires

Congreso; X Jornadas Nacionales de Ciencias del Mar; 2018

Facultad de Ciencias Exactas y Naturales. UBA

Understanding the mechanisms involved in theadaptation of the organisms to their environment is a challenging question inecology and evolutionary biology. The first preliminary results of a broadstudy regarding functional and energetic consequences of morphometricdifferences are presented. The native fish Galaxiasmaculatus shows two populations: Arroyo Negro (AN, diadromous population)and Laguna Negra (LN, landlocked) both in the Parque Nacional Tierra del Fuego.Individuals from AN and LN are characterized by a thinner/elongated and a robust/shortercaudal peduncle respectively, phenotype being involved in locomotor propulsion.The fast/slow muscle fibers ratio and swimming/metabolic performances were investigatedin these two populations. Histological sections (8 µm) of caudal peduncle weremade and stained with Hematoxilin-Eosin (n=20 individuals/population), totallength: AN 60.39±1.44 mm; LN 61.92±1.85 mm; age: 1.5-2.5 years. The fast/slowfibers areas were measured, and ratio between them was calculated. Challengingswimming experiments (step protocol) coupled to oxygen consumption measurementswere carried out in swimming respirometers (275 ml) on 20 individuals from eachpopulation (total length AN: 60.44±1.94 mm; LN: 61.95±1.02 mm). The experimentswere conducted under summer experimental conditions (10°C, 17 h daylight). Ahigher ratio of fast/slow fibers was found for AN than LN (ANOVA, p=2.84x10-9)with mean values of 6.29±1.07x 10-2 and 3.97±0.662x10-2respectively. The active metabolic rate (AMR) was significantly higher (ANOVA,p=0.0414) in AN (0.61±0.1516 mgO2/h/g) than in LN (0.521±0.1128 mgO2/h/g.On the other side the critical swimming speed (Ucrit, 2.66±0.36 totallength/sec) didn?t differ between populations (ANOVA, p=0.1050). Otherdifferences may reside on other aspects such us tail beat frequency and/oramplitude, season. More experiments are being conducted to elucidate this and toexplore the links between environmental pressure, driving evolutionary changes,phenotypic and functional consequences on thesetwo populations at thesouthernmost extreme of the species? distribution.