Temperature sensitivity of gamogenesis in littoral cladocerans and its ecological implications

Temperature sensitivity of chydorid (Cladocera, Chydoridae) gamogenesis in southern Finland was examined. Chydorid sweep net samples and littoral surface water temperature measurements of seven lakes were taken weekly. Percentage abundances of gamogenetic females were used to estimate the temperature optima and tolerances for gamogenesis of individual chydorid species. The estimations were carried out using a weighted averaging (WA) technique. The results indicated that the optimum temperature of gamogenesis ranged between 7.0 and 9.7 °C and the total tolerances were between 2.0 and 4.7 °C suggesting a species-specific response for gamogenesis. Alonella nana and Chydorus sphaericus s.l. had the lowest optima, which was possibly due to their ubiquitous ecological preference and wide geographical distribution. Camptocercus rectirostris, Alonella excisa and Grabtoleberis testudinaria had high optima for their gamogenesis. These estimations provide first numerical autecological data on gamogenesis of natural and contemporary chydorid populations. Furthermore, the results provide species-specific estimations of the effect of the present climate warming on chydorid reproduction patterns. This information can be useful background data in global change assessments regarding freshwater lakes.