Environment-dependent metabolic investments in the mixotrophic chrysophyte Ochromonas.

Mixotrophic protists combine photosynthesis and phagotrophy to obtain energy and nutrients. Because mixotrophs can act as either primary producers or consumers, they have a complex role in marine food webs and biogeochemical cycles. Many mixotrophs are also phenotypically plastic and can adjust their metabolic investments in response to resource availability. Thus, a single species's ecological role may vary with environmental conditions. Here, we quantified how light and food availability impacted the growth rates, energy acquisition rates, and metabolic investment strategies of eight strains of the mixotrophic chrysophyte, Ochromonas. All eight Ochromonas strains photoacclimated by decreasing chlorophyll content as light intensity increased. Some strains were obligate phototrophs that required light for growth, while other strains showed stronger metabolic responses to prey availability. When prey availability was high, all eight strains exhibited accelerated growth rates and decreased their investments in both photosynthesis and phagotrophy. Photosynthesis and phagotrophy generally produced additive benefits: In low-prey environments, Ochromonas growth rates increased to maximum, light-saturated rates with increasing light but increased further with the addition of abundant bacterial prey. The additive benefits observed between photosynthesis and phagotrophy in Ochromonas suggest that the two metabolic modes provide nonsubstitutable resources, which may explain why a tradeoff between phagotrophic and phototrophic investments emerged in some but not all strains.

Captive rearing of orphaned African wild dogs (Lycaon pictus) in Namibia: A case study.

African wild dogs (AWDs; Lycaon pictus) are an endangered canid species facing drastic decline throughout their range due to habitat fragmentation and persecution by humans over livestock depredation, resulting in dens destroyed and adult members of packs and pups often being killed. Breeding of captive AWDs is challenging due to high juvenile mortality, only marginally improved from wild conditions, thus both in situ and ex situ conservation remains critical. As a result of human-wildlife conflict, between 2017 and 2018, the Namibian Ministry of Environment, Forestry and Tourism confiscated three litters of orphaned AWD pups from rural farmers who had destroyed the dens in Eastern Namibia and placed the pups with the Cheetah Conservation Fund. Seventeen of the 18 pups were successfully reared to yearlings with 15 individuals translocated for eventual soft release into a private game reserve. This case study provides information on the successful rearing of three litters of orphaned wild dog pups on behavior, housing, husbandry, diet, growth and medical issues as limited information is available for rearing orphaned pups from the age of 2.5 weeks old.