TY  - JOUR
A1  - Lukas, Marcus
A1  - Wacker, Alexander
T1  - Constraints by oxygen and food quality on carbon pathway regulation: a co-limitation study with an aquatic key herbivore
JF  - Ecology : a publication of the Ecological Society of America
N2  - In food webs, herbivores are often constrained by low food quality in terms of mineral and biochemical limitations, which in aquatic ecosystems can co-occur with limited oxygen conditions. As low food quality implies that carbon (C) is available in excess, and therefore a regulation to get rid of excess C is crucial for the performance of consumers, we examined the C pathways (ingestion, feces release, excretion, and respiration) of a planktonic key herbivore (Daphnia magna). We tested whether consumer C pathways increase due to mineral (phosphorus, P) or biochemical (cholesterol and fatty acid) limitations and how these regulations vary when in addition oxygen is low. Under such conditions, at least the capability of the upregulation of respiration may be restricted. Furthermore, we discussed the potential role of the oxygen-transporting protein hemoglobin (Hb) in the regulation of C budgets. Different food quality constraints led to certain C regulation patterns to increase the removal of excess dietary C: P-limited D. magna increased excretion and respiration, while cholesterol-limited Daphnia in addition upregulated the release of feces. In contrast, the regulative effort was low and only feces release increased when D. magna was limited by a long-chain polyunsaturated fatty acid (eicosapentaenoic acid, EPA). Co-limiting oxygen did not always impact the discharge of excess C. We found the food-quality-induced upregulation of respiration was still present at low oxygen. In contrast, higher excretion of excess C was diminished at low oxygen supply. Besides the effect that the Hb concentration increased under low oxygen, our results indicate a low food-quality-induced increase in the Hb content of the animals. Overall, C budgeting is phenotypically plastic towards different (co-) limiting scenarios. These trigger specific regulation responses that could be the result of evolutionary adaptations.
KW  - carbon budget
KW  - carbon stoichiometry
KW  - cholesterol
KW  - co-limitation
KW  - Daphnia
KW  - EPA
KW  - hemoglobin
KW  - oxygen
KW  - phosphorus
KW  - polyunsaturated fatty acid
KW  - zooplankton
Y1  - 2014
SN  - 0012-9658
SN  - 1939-9170
VL  - 95
IS  - 11
SP  - 3068
EP  - 3079
PB  - Wiley
CY  - Washington
ER  - 
TY  - JOUR
A1  - Signore, Anthony V.
A1  - Paijmans, Johanna L. A.
A1  - Hofreiter, Michael
A1  - Fago, Angela
A1  - Weber, Roy E.
A1  - Springer, Mark S.
A1  - Campbell, Kevin L.
T1  - Emergence of a chimeric globin pseudogene and increased Hemoglobin Oxygen Affinity Underlie the evolution of aquatic specializations in Sirenia
JF  - Molecular biology and evolution
N2  - As limits on O2 availability during submergence impose severe constraints on aerobic respiration, the oxygen binding globin proteins of marine mammals are expected to have evolved under strong evolutionary pressures during their land-to-sea transition. Here, we address this question for the order Sirenia by retrieving, annotating, and performing detailed selection analyses on the globin repertoire of the extinct Steller’s sea cow (Hydrodamalis gigas), dugong (Dugong dugon), and Florida manatee (Trichechus manatus latirostris) in relation to their closest living terrestrial relatives (elephants and hyraxes). These analyses indicate most loci experienced elevated nucleotide substitution rates during their transition to a fully aquatic lifestyle. While most of these genes evolved under neutrality or strong purifying selection, the rate of nonsynonymous/synonymous replacements increased in two genes (Hbz-T1 and Hba-T1) that encode the α-type chains of hemoglobin (Hb) during each stage of life. Notably, the relaxed evolution of Hba-T1 is temporally coupled with the emergence of a chimeric pseudogene (Hba-T2/Hbq-ps) that contributed to the tandemly linked Hba-T1 of stem sirenians via interparalog gene conversion. Functional tests on recombinant Hb proteins from extant and ancestral sirenians further revealed that the molecular remodeling of Hba-T1 coincided with increased Hb–O2 affinity in early sirenians. Available evidence suggests that this trait evolved to maximize O2 extraction from finite lung stores and suppress tissue O2 offloading, thereby facilitating the low metabolic intensities of extant sirenians. In contrast, the derived reduction in Hb–O2 affinity in (sub)Arctic Steller’s sea cows is consistent with fueling increased thermogenesis by these once colossal marine herbivores.
KW  - ancient DNA
KW  - aquatic adaptation
KW  - gene conversion
KW  - hemoglobin
KW  - oxygen affinity
KW  - molecular evolution
KW  - myoglobin
KW  - neuroglobin
KW  - cytoglobin
KW  - pseudogene
Y1  - 2019
U6  - https://doi.org/10.1093/molbev/msz044
SN  - 0737-4038
SN  - 1537-1719
VL  - 36
IS  - 6
SP  - 1134
EP  - 1147
PB  - Oxford Univ. Press
CY  - Oxford
ER  -