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Pennak-454

Physiology

The physiology of D. lumholtzi is relatively well studied for a Daphnid, this most likely being because it is an invasive species. Nevertheless, information on the physiology of D. lumholtzi is still rather limited compared to more charismatic species.

Respiration

D. lumholtzi individuals prefer areas with high levels of dissolved oxygen saturation and avoid areas where oxygen saturation is low. Population surveys have found robust D. lumholtzi populations in water with saturation ranging from 65-163% and no populations in water with saturation ranging from 7-50% (Davidson).

The mechanism D. lumholtzi uses for respiration is very similar to that used by other species of Daphnia, with gas exchange occurring through gills that are fed oxygenated water by appendages on the thorax (Pennak).

Solute Exchange

As with most other members of the order Cladocera, D. lumholtzi lives in freshwater and is hyperosmotic to its environment (Hebert). D. lumholtzi is generally not found in habitats with a salinity greater than zero, but can stand slightly saline water, up to 1.5 grams per liter, for short amounts of time (Devries). This ability to survive short bouts of salinity has likely contributed to D. lumholtzi’s ability to invade North America (Devries).

Temperature maintenance

The most unique characteristic of D. lumholtzi compared to most North American Daphnid species is its ability to tolerate and thrive in relatively high temperatures. While most species of Daphnia begin to see higher rates of mortality at temperatures greater than 25°C (Lennon), D. lumholtzi individuals have been found able to survive and reproduce at temperatures up to 30°C (Engel) (Lennon) (Havel), with a thermal optimum occurring at 29°C (Engel). This ability to survive at higher temperatures in comparison to other Daphnids seems to be a result of genetic changes in D. lumholtzi that resulted in enzymes that are better able to function at higher temperatures (Yurista).

The lower temperature range of D. lumholtzi extends to 5°C, where some individuals are able to survive (Engel) (Lennon) (Havel), with survival increasing significantly at 10°C (Lennon) (Havel) and reproduction beginning to occur at 15°C (Lennon) (Havel). This significantly broad temperature range in which D. lumholtzi can survive has led to it being labeled a eurythermal species (Yurista).

Ephippia

It should be noted that D. lumholtzi, as with most Daphnid species, produce eggs called ephippia when exposed to high environmental stress (Dzialowski). These ephippia are able to resist temperature, oxygen, and salinity levels significantly lower and higher than those hospitable to adult D. lumholtzi (Dzialowski). Therefore the ephippia stage is an example of diapause, a state of suspended animation an organism can enter in order to survive a harsh environment (Wilmer).           

Cherifi O, Chifaa A, and Tifnouti A. 1994. “Etude de regime alimentaire de cinq especes de Cladoceres dans la retenue Lalla Takerkoust”. International Journal of Limnology 30: 285-296.

Davidson NL and Kelso WE. 1997. “The exotic daphnid, Daphnia lumholtzi, in a Louisiana river-swamp”. Journal of Freshwater Ecology 12: 431-435.

Devries DR, Devries TS, and Wright RA. 2006. “Daphnia lumholtzi in the mobile river drainage, USA: invasion of a habitat that experiences salinity”. Journal of Freshwater Ecology 21: 527-530.

Engel K and Tollrian R. 2012. “Competitive ability, thermal tolerance and invasion success in exotic Daphnia lumholtzi”. Journal of Plankton Research 34: 92-97.

Havel JE and Lampert W. 2006. “Habitat partitioning of native and exotic Daphnia in gradients of temperature and food: mesocosm experiments”. Freshwater Biology 51: 487-498.

Lennon JT, Smith VH, and Williams K. 2001. “Influence of temperature on exotic Daphnia lumholtzi and implication for invasion success”. Journal of Plankton Research 23: 425-434.

Yurista PM. 2004. “Bioenergetic of a semi-tropical Cladoceran, Daphnia lumholtzi”. Journal of Freshwater Ecology 19: 681-694.