Bioecology of large Branchiopods in Central District, Botswana

Abstract

The bioecology of large branchiopods in Central District, Botswana, was analysed to determine if genetic relatedness or environment of origin determined the thermal physiology of large branchiopods. Two temporary wetland types (Rock-pools and Pans) were identified and their thermal conditions characterised. Temperatures experienced in each wetlands type were measured for synchronised periods spanning both dry phases and hydroperiods of the temporary wetlands. Anostraca and Spinicaudata specialists from each temporary wetland were then identified and their thermal physiology assessed. Physiological thermal fitness of large branchiopods were measured using critical thermal limits and thermal preferences. Finally, the effect of light and temperature on dormant cysts of a dominant large branchiopod were assessed. Streptocephalus cafer dormant cyst hatching success was analysed using variable temperatures and light durations. The thermal properties of rock-pools and pans were grouped according to wetland type, highlighting the thermal differences between these different temporary wetland types. Rock-pools experienced high temperatures compared to pans in general. However, thermal physiologies of large branchiopods differed according to taxonomic orders in thermal limits. Spinicaudatans were tolerant to higher temperatures than anostracans. The results for thermal limits and thermal preference differed across species. The hatching success of S. cafer was optimal at 27 °C in 12hrs:12hrs light:dark regime. In conclusion, the thermal physiologies of large branchiopods appear to primarily determined by genetic relatedness with the environment of origin being secondary. While not part of the thesis itself, the opportunity to describe the complete mitochondrial DNA of the studied 2 species was also taken, to aid in resolving phylogenies for these understudied taxa. These results are presented as supplementary material (See files S1-3).