Physiological energetics may contribute to competitive exclusion in African killifish (Aphyosemion spp.).

Abstract

In the equatorial watersheds of Cameroon, two monophyletic groups of killifish species (genus Aphyosemion) have a parapatric distribution based on altitude, one occupying altitudes to 400m (low altitude, LA) and the other altitudes above this (high altitude, HA). These groups are mutually exclusive although LA species occupy high altitudes in watersheds where HA species are absent. The basis for this apparent altitude-related competitive exclusion is unknown. This study investigated the hypothesis that LA and HA groups differ for the effects of temperature on their physiological energetics. Two species from each group (mass ~ 400 mg) were acclimated to 19°, 25° and 31 °C, and their appetite, metabolic rate (MR) and specific dynamic action response (SDA) compared. Appetite was assessed by feeding ad-libitum with live Artemia, MR and SDA by measuring patterns of instantaneous oxygen uptake. At 19 °C, there were no significant differences in appetite (~ 20% body mass after 72 h fast), or in routine MR (3.36 ± 0.47 vs 3.05 ± 0.38 mol O2 g -1 h-1 in HA vs LA, respectively, n = 12). When fed 5% of their body mass as Artemia, however, the HA species completed the SDA response faster than the LA (7.4 ± 1.1 vs 13.8 ± 0.8 h, respectively), with lower overall metabolic cost of the SDA (9.15 ± 1.88 vs 14.31 ± 1.92 kJ g-1, respectively). This is consistent with an energetic advantage to HA fish at 19°C. We are currently investigating effects at the other temperatures. Email Address for correspondence: david.mckenzie@univ-montp2.fr Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology Volume 153, Issue 2, Supplement 1, June 2009, Page S150 Abstracts of the Annual Main Meeting of the Society of Experimental Biology, 28th June 1st July, Glasgow, UK