The production of haemoglobin by small pond Daphnia pulex: intraspecific variation and its relation to habitat

1. Haemoglobin production was measured for two populations of Daphnia putex, one from a temporary pond (GR Pond) and one from a permanent pond (Rash Pond). Surface water in Rash Pond remains high in oxygen, while by late summer very Uttle oxygen remains in GR Pond. Haemoglobin synthesis was induced in the laboratory by artificial oxygen deficiency. 2. Reproductive state influenced the level of haemoglobin in Daphnia. Females with parthenogenetic eggs had higher total body haemoglobin than ephippial females. Clutches laid by pale Daphnia immediately before exposure to low oxygen conditions were aborted. Offspring produced by haemoglobin-rich females later in the treatment survived. 3. Haemoglobin production was higher for Rash Pond Daphnia. Visual predators exist in GR Pond, but are absent in Rash Pond. Also, Daphnia are smaller in GR Pond. Visual predation may have selected against high levels of haemoglobin in the temporary pond. Thus oxygen availability in nature is not necessarily a good predictor of haemoglobin production by Daphnia. 4. Feeding behaviour was altered in low oxygen conditions. Browsing was dominant in low oxygen treatments while Daphnia in control treatments filtered algae normally. Browsing may increase access to sedimented iron necessary for haemoglobin synthesis.