Parental Care Model

1. Parental Care Model Koteja, P. 2000. Energy assimilation, parental care and the evolution of endothermy. Proc. R. Soc. Lond. B 267:479-484. Farmer, C.G. 2000. Parental care: the key to understanding endothermy and other convergent features in birds and mammals. Am. Nat. 155:326-334. Farmer, C.G. 2003. Reproduction: the adaptive significance of endothermy. Am. Nat. 162:826-840. Angilletta, M.J., Jr. and M.W. Sears. 2003. Is parental care the key to understanding endothermy in birds and mammals? Am. Nat. 162:821-825.

2. Selective Factor for Parental Care Model Posits that endothermy evolved to promote intensive parental care that increased survival of young, thereby increasing fitness. Farmer (2000, 2003) hypothesis ? Selective factor = high and stable body temperature for incubation and brooding of young (special case of Thermoregulatory Model) . Koteja (2000) hypothesis ? Selective factor = high MR allows high levels of parental care activities for provisioning young (special case of Aerobic Capacity Model) .

4. Selective Factor for Parental Care Model Posits that endothermy evolved to promote intensive parental care that increased survival of young, thereby increasing fitness. Farmer (2000, 2003) hypothesis ? Selective factor = high and stable body temperature for incubation and brooding of young (special case of Thermoregulatory Model) . Koteja (2000) hypothesis ? Selective factor = high MR allows high levels of parental care activities for provisioning young (special case of Aerobic Capacity Model) .

6. Incubation Model (Farmer 2000) Parental Care responsible for many convergent features of birds and mammals: Endothermy Insulative covering High sustained activity High energetic costs of living High investment in relatively few offspring

7. Incubation Model (Farmer 2000) Distinction from Thermoregulatory and Aerobic Capacity Models: Selective Factor = control of incubation temp Mechanism = ? BMR from higher and continuous thyroid hormone secretion (dual role in reproduction and MR) Sustained exercise capacity evolved independently for provisioning of young Provides unifying theme for convergence between birds and mammals

8. Incubation Model (Farmer 2000) Why Thermoregulation for Reproduction? Vertebrate embryos adversely affected by small changes in temperature (poor survival outside of restricted temperature range) Incubation at extremes of viable temperature range ? developmental defects Thermal environmental during development affects duration of development Incubation temp can influence many characters under hypothalamic control Constant incubation temp improves fitness

9. Incubation Model (Farmer 2000) Many adaptations exist among ectotherms to control temperature during incubation This includes thermogenesis in pythons and insects Shivering in pythons elevates egg temps above Ta and temp differential increases in cold temps

12. Incubation Model: Evolutionary Scenario Hormone secretion during reproduction (thyroid hormones and others) could ? RMR Continued elevation of thyroid hormone levels after reproduction could lead to permanent increase in RMR Continuation of this trend could eventually lead to endothermy ? BMR and ? aerobic capacity evolve independently to support parental care

13. Problems with Incubation Model Suffers from same problems as thermoregulatory model Small ? in BMR with little impact on thermoregulation Selection for high RMR only in incubating parent Little evidence that mean incubation temp has a strong influence on hatching success under natural conditions (Angilletta and Sears 2003) Why not facultative endothermy during breeding season? Does fitness of parents increase with endothermy and increased parental care?

14. Selective Factor for Parental Care Model Posits that endothermy evolved to promote intensive parental care that increased survival of young, thereby increasing fitness. Farmer (2000, 2003) hypothesis ? Selective factor = high and stable body temperature for incubation and brooding of young (special case of Thermoregulatory Model) . Koteja (2000) hypothesis ? Selective factor = high MR allows high levels of parental care activities for provisioning young (special case of Aerobic Capacity Model) .

15. Provisioning Model (Koteja 2000) Focus on daily energy expenditure (DEE) so long-term sustained MR More active organisms with ? DEE and ? rates of food consumption and energy assimilation ? energy processing requires ? digestive capacity (and other visceral organs) ? size and activity of visceral organs should ? BMR Similar to Aerobic Capacity Model in that selection is on levels of sustained activity

16. Provisioning Model (Koteja 2000) Differences from Aerobic Capacity Model Focus on DEE (and energy budgets), rather than on shorter-term levels of sustained activity Aerobic Capacity can ? without DEE ? if time resting is adjusted accordingly DEE can ? by spending more time in moderate activity, without approaching ceiling for aerobic capacity Model doesn’t really consider that endurance at submaximal levels of activity is strongly positively correlated with aerobic capacity

17. Provisioning Model (Koteja 2000) Koteja argues that highest DEE during annual cycle for both mammals and birds is during periods of intense parental care Thus, selection for highest levels of long-term sustained activity should be during this time period Caveat: Field MR for small birds wintering in cold climates (doubly-labeled water or time-energy budgets) is usually higher in winter than during nesting.

18. Evolutionary Scenario ? in parental care behavior, such as guarding hatchlings, then providing food (acts to? offspring mortality without ? in MR) Selection for maximal growth rates of young ? in parental locomotor activity to provision young (? DEE ? ? BMR) When level of routine activity approaches aerobic capacity, then selection for ? aerobic capacity should occur ? ? BMR

21. Provisioning Model Predictions Endothermy should evolve in carnivorous lineages where food is difficult to capture and more widely spaced (? provisioning costs) Consistent with fossil record BMR should be correlated with sustained MR (DEE, or longer periods) Both BMR and DEE should be correlated with capacity of visceral organs Caveat: Similar predictions would also hold for aerobic capacity model

25. Problems with Provisioning Model Visceral capacity generally positively correlated with susMR, less consistent for BMR Daily energy expenditures are correlated with BMR in mammals, but less consistent correlation in birds Selection for high RMR only in parents that provision young Why not facultative endothermy during breeding season? Does increased parental care (and concomitant ? in # of offspring) really ? fitness of parents?

26. Future Research Questions:Parental Care Model Does correlation between BMR and susMR (or MMR) extend to individual organisms? Is correlation between BMR and susMR (or MMR) genetically based or just a result of phenotypic flexibility? How does life-history optimization fit into the framework of the evolution of endothermy?