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Testing the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

Clavijo-Baque S, Bozinovic F - PLoS ONE (2012)

Bottom Line: We found greater support for the thermogenic capacity model of the thermoregulatory model.In other words, greater thermogenic capacity is associated with increased fitness in rodent populations.To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile. sclavijo@bio.puc.cl

ABSTRACT
The origin of endothermy is a puzzling phenomenon in the evolution of vertebrates. To address this issue several explicative models have been proposed. The main models proposed for the origin of endothermy are the aerobic capacity, the thermoregulatory and the parental care models. Our main proposal is that to compare the alternative models, a critical aspect is to determine how strongly natural selection was influenced by body temperature, and basal and maximum metabolic rates during the evolution of endothermy. We evaluate these relationships in the context of three main hypotheses aimed at explaining the evolution of endothermy, namely the parental care hypothesis and two hypotheses related to the thermoregulatory model (thermogenic capacity and higher body temperature models). We used data on basal and maximum metabolic rates and body temperature from 17 rodent populations, and used intrinsic population growth rate (R(max)) as a global proxy of fitness. We found greater support for the thermogenic capacity model of the thermoregulatory model. In other words, greater thermogenic capacity is associated with increased fitness in rodent populations. To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

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Path diagrams of the evaluated causal models.The chart without shading shows all considered cause-effect relationships, colored arrows are relationships related to the tested models for endothermy while black arrows are unrelated relationships. Arrows have their corresponding number and variables. The shaded charts show the 12 models evaluated in this work, highlighting which endothermy models are represented and the involved variables. mb = body mass, BMR = basal metabolic rate, MMR = maximum metabolic rate, Rmax = intrinsic population growth rate; Tb = body temperature. Note that for testing Koteja’s parental care model, path b5 is a correlation (indicated by bidirectional arrows), because the relationship between both variables is mediated by parental care, as proposed by the model.
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pone-0037069-g001: Path diagrams of the evaluated causal models.The chart without shading shows all considered cause-effect relationships, colored arrows are relationships related to the tested models for endothermy while black arrows are unrelated relationships. Arrows have their corresponding number and variables. The shaded charts show the 12 models evaluated in this work, highlighting which endothermy models are represented and the involved variables. mb = body mass, BMR = basal metabolic rate, MMR = maximum metabolic rate, Rmax = intrinsic population growth rate; Tb = body temperature. Note that for testing Koteja’s parental care model, path b5 is a correlation (indicated by bidirectional arrows), because the relationship between both variables is mediated by parental care, as proposed by the model.

Mentions: All proposed models for the origin of endothermy, unfortunately, are verbal and there is no mathematical representation of them. This makes it difficult to test them rigorously (Angilleta, 2010). Hence, we translate the verbal models to mathematical ones (path models) including the assumptions and relationships which represent the proposed mechanism for the origin of endothermy (Figure 1, Table 1). First, the higher body temperature model posits that selection favoured a higher Tbs [25]. Therefore, an increase in this variable should be associated with an increase in Rmax. Thus, we expected to find that path b6 was significantly different from zero (Figure 1). The responsible mechanism to increase Tb is not clear; some authors suggest that Tb increases could be due to increase in BMR [2]. Therefore, we represented this relationship with path b8, from BMR to Tb (Figure 1, Table 1). However, experimental evidence suggests that significant increases in BMR do not increase Tb[7]; furthermore, increases in Tb may be because of changes in conductance [13]. In this case, path b8 could not be considered to test the higher body temperature model.


Testing the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

Clavijo-Baque S, Bozinovic F - PLoS ONE (2012)

Path diagrams of the evaluated causal models.The chart without shading shows all considered cause-effect relationships, colored arrows are relationships related to the tested models for endothermy while black arrows are unrelated relationships. Arrows have their corresponding number and variables. The shaded charts show the 12 models evaluated in this work, highlighting which endothermy models are represented and the involved variables. mb = body mass, BMR = basal metabolic rate, MMR = maximum metabolic rate, Rmax = intrinsic population growth rate; Tb = body temperature. Note that for testing Koteja’s parental care model, path b5 is a correlation (indicated by bidirectional arrows), because the relationship between both variables is mediated by parental care, as proposed by the model.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3351390&req=5

pone-0037069-g001: Path diagrams of the evaluated causal models.The chart without shading shows all considered cause-effect relationships, colored arrows are relationships related to the tested models for endothermy while black arrows are unrelated relationships. Arrows have their corresponding number and variables. The shaded charts show the 12 models evaluated in this work, highlighting which endothermy models are represented and the involved variables. mb = body mass, BMR = basal metabolic rate, MMR = maximum metabolic rate, Rmax = intrinsic population growth rate; Tb = body temperature. Note that for testing Koteja’s parental care model, path b5 is a correlation (indicated by bidirectional arrows), because the relationship between both variables is mediated by parental care, as proposed by the model.
Mentions: All proposed models for the origin of endothermy, unfortunately, are verbal and there is no mathematical representation of them. This makes it difficult to test them rigorously (Angilleta, 2010). Hence, we translate the verbal models to mathematical ones (path models) including the assumptions and relationships which represent the proposed mechanism for the origin of endothermy (Figure 1, Table 1). First, the higher body temperature model posits that selection favoured a higher Tbs [25]. Therefore, an increase in this variable should be associated with an increase in Rmax. Thus, we expected to find that path b6 was significantly different from zero (Figure 1). The responsible mechanism to increase Tb is not clear; some authors suggest that Tb increases could be due to increase in BMR [2]. Therefore, we represented this relationship with path b8, from BMR to Tb (Figure 1, Table 1). However, experimental evidence suggests that significant increases in BMR do not increase Tb[7]; furthermore, increases in Tb may be because of changes in conductance [13]. In this case, path b8 could not be considered to test the higher body temperature model.

Bottom Line: We found greater support for the thermogenic capacity model of the thermoregulatory model.In other words, greater thermogenic capacity is associated with increased fitness in rodent populations.To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile. sclavijo@bio.puc.cl

ABSTRACT
The origin of endothermy is a puzzling phenomenon in the evolution of vertebrates. To address this issue several explicative models have been proposed. The main models proposed for the origin of endothermy are the aerobic capacity, the thermoregulatory and the parental care models. Our main proposal is that to compare the alternative models, a critical aspect is to determine how strongly natural selection was influenced by body temperature, and basal and maximum metabolic rates during the evolution of endothermy. We evaluate these relationships in the context of three main hypotheses aimed at explaining the evolution of endothermy, namely the parental care hypothesis and two hypotheses related to the thermoregulatory model (thermogenic capacity and higher body temperature models). We used data on basal and maximum metabolic rates and body temperature from 17 rodent populations, and used intrinsic population growth rate (R(max)) as a global proxy of fitness. We found greater support for the thermogenic capacity model of the thermoregulatory model. In other words, greater thermogenic capacity is associated with increased fitness in rodent populations. To our knowledge, this is the first test of the fitness consequences of the thermoregulatory and parental care models for the origin of endothermy.

Show MeSH