Limited differentiation of fundamental thermal niches within the killifish assemblage from shallow temporary waters

The coexistence of ectothermic species is enabled among other factors by the differentiation of their thermal niches. While this phenomenon is well described from deep temperate lakes, it is unclear whether the same pattern applies to temporary pools. In this study, we examined fundamental thermal niches in three coexisting annual killifish species Nothobranchius furzeri, N. orthonotus and N. pienaari from temporary pools in southern Mozambique. We hypothesized that the disparate thermal requirements of the three congeneric species are a candidate niche component that facilitates their local coexistence. We estimated species' thermal requirements as preferred body temperatures (T_pref) in a horizontal thermal gradient. Under thermal gradient conditions, sympatric killifish maintained their body temperatures within similar T_pref ranges despite some variation in mean T_pref. The daily variation in water temperature in their native habitats enables killifish to thermoregulate at least for part of the diurnal cycle. We conclude that the coexistence of African annual killifish species is possible without the differentiation of their fundamental thermal niches.