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

SUMMARY.

• 1 Hemoglobin production was measured for two populations of Daphnia pulex, 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 little oxygen remains in GR Pond. Hemoglobin synthesis was induced in the laboratory by artificial oxygen deficiency.
• 2 Reproductive state influenced the level of hemoglobin in Daphnia. Females with parthenogenesis eggs had higher total body hemoglobin than ephippial females. Clutches laid by pale Daphnia immediately before exposure to low oxygen conditions were aborted. Offspring produced by hemoglobin-rich females later in the treatment survived.
• 3 Hemoglobin 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 hemoglobin in the temporary pond. Thus oxygen availability in nature is not necessarily a good predictor of hemoglobin production by Daphnia.
• 4 Feeding behavior 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 hemoglobin synthesis.